<IP_ADDRESS>: Architecture
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In case you hadn't noticed, the previous section established a pretty substantial set of requirements for network design—a computer network must provide general, cost-effective, fair, and robust connectivity among a large number of computers. As if this weren't enough, networks do not remain fixed at any single point in time but must evolve to accommodate changes in both the underlying technologies upon which they are based as well as changes in the demands placed on them by application programs. Furthermore, networks must be manageable by humans of varying levels of skill. Designing a network to meet these requirements is no small task.
To help deal with this complexity, network designers have developed general blueprints—usually called network architectures —that guide the design and implementation of networks. This section defines more carefully what we mean by a network architecture by introducing the central ideas that are common to all network architectures. It also introduces two of the most widely referenced architectures—the OSI (or 7-layer) architecture and the Internet architecture.
Layering and Protocols
Abstraction—the hiding of details behind a well-defined interface—is the fundamental tool used by system designers to manage complexity. The idea of an abstraction is to define a model that can capture some important aspect of the system, encapsulate this model in an object that provides an interface that can be manipulated by other components of the system, and hide the details of how the object is implemented from the users of the object. The challenge is to identify abstractions that simultaneously provide a service that proves useful in a large number of situations and that can be efficiently implemented in the underlying system. This is exactly what we were doing when we introduced the idea of a channel in the previous section: we were providing an abstraction for applications that hides the complexity of the network from application writers.
Abstractions naturally lead to layering, especially in network systems. The general idea is that you start with the services offered by the underlying hardware and then add a sequence of layers, each providing a higher (more abstract) level of service. The services provided at the high layers are implemented in terms of the services provided by the low layers. Drawing on the discussion of requirements given in the previous section, for example, we might imagine a simple network as having two layers of abstraction sandwiched between the application program and the underlying hardware, as illustrated in Figure 1 . The layer immediately above the hardware in this case might provide host-to-host connectivity, abstracting away the fact that there may be an arbitrarily complex network topology between any two hosts. The next layer up builds on the available host-to-host communication service and provides support for process-to-process channels, abstracting away the fact that the network occasionally loses messages, for example.
Layering provides two nice features. First, it decomposes the problem of building a network into more manageable components. Rather than implementing a monolithic piece of software that does everything you will ever want, you can implement several layers, each of which solves one part of the problem. Second, it provides a more modular design. If you decide that you want to add some new service, you may only need to modify the functionality at one layer, reusing the functions provided at all the other layers.
Thinking of a system as a linear sequence of layers is an oversimplification, however. Many times there are multiple abstractions provided at any given level of the system, each providing a different service to the higher layers but building on the same low-level abstractions. To see this, consider the two types of channels discussed in the previous section. One provides a request/reply service and one supports a message stream service. These two channels might be alternative offerings at some level of a multilevel networking system, as illustrated in Figure 2 .
Using this discussion of layering as a foundation, we are now ready to discuss the architecture of a network more precisely. For starters, the abstract objects that make up the layers of a network system are called protocols . That is, a protocol provides a communication service that higher-level objects (such as application processes, or perhaps higher-level protocols) use to exchange messages. For example, we could imagine a network that supports a request/reply protocol and a message stream protocol, corresponding to the request/reply and message stream channels discussed above.
Each protocol defines two different interfaces. First, it defines a service interface to the other objects on the same computer that want to use its communication services. This service interface defines the operations that local objects can perform on the protocol. For example, a request/reply protocol would support operations by which an application can send and receive messages. An implementation of the HTTP protocol could support an operation to fetch a page of hypertext from a remote server. An application such as a web browser would invoke such an operation whenever the browser needs to obtain a new page (e.g., when the user clicks on a link in the currently displayed page).
Second, a protocol defines a peer interface to its counterpart (peer) on another machine. This second interface defines the form and meaning of messages exchanged between protocol peers to implement the communication service. This would determine the way in which a request/reply protocol on one machine communicates with its peer on another machine. In the case of HTTP, for example, the protocol specification defines in detail how a GET command is formatted, what arguments can be used with the command, and how a web server should respond when it receives such a command.
To summarize, a protocol defines a communication service that it exports locally (the service interface), along with a set of rules governing the messages that the protocol exchanges with its peer(s) to implement this service (the peer interface). This situation is illustrated in Figure 3 .
Except at the hardware level, where peers directly communicate with each other over a physical medium, peer-to-peer communication is indirect—each protocol communicates with its peer by passing messages to some lower-level protocol, which in turn delivers the message to its peer. In addition, there are potentially more than one protocol at any given level, each providing a different communication service. We therefore represent the suite of protocols that make up a network system with a protocol graph . The nodes of the graph correspond to protocols, and the edges represent a depends on relation. For example, Figure 4 illustrates a protocol graph for the hypothetical layered system we have been discussing—protocols RRP (Request/Reply Protocol) and MSP (Message Stream Protocol) implement two different types of process-to-process channels, and both depend on the Host-to-Host Protocol (HHP) which provides a host-to-host connectivity service.
In this example, suppose that the file access program on host 1 wants to send a message to its peer on host 2 using the communication service offered by RRP. In this case, the file application asks RRP to send the message on its behalf. To communicate with its peer, RRP invokes the services of HHP, which in turn transmits the message to its peer on the other machine. Once the message has arrived at the instance of HHP on host 2, HHP passes the message up to RRP, which in turn delivers the message to the file application. In this particular case, the application is said to employ the services of the protocol stack RRP/HHP.
Note that the term protocol is used in two different ways. Sometimes it refers to the abstract interfaces—that is, the operations defined by the service interface and the form and meaning of messages exchanged between peers, and sometimes it refers to the module that actually implements these two interfaces. To distinguish between the interfaces and the module that implements these interfaces, we generally refer to the former as a protocol specification . Specifications are generally expressed using a combination of prose, pseudocode, state transition diagrams, pictures of packet formats, and other abstract notations. It should be the case that a given protocol can be implemented in different ways by different programmers, as long as each adheres to the specification. The challenge is ensuring that two different implementations of the same specification can successfully exchange messages. Two or more protocol modules that do accurately implement a protocol specification are said to interoperate with each other.
We can imagine many different protocols and protocol graphs that satisfy the communication requirements of a collection of applications. Fortunately, there exist standardization bodies, such as the Internet Engineering Task Force (IETF) and the International Standards Organization (ISO), that establish policies for a particular protocol graph. We call the set of rules governing the form and content of a protocol graph a network architecture . Although beyond the scope of this book, standardization bodies have established well-defined procedures for introducing, validating, and finally approving protocols in their respective architectures. We briefly describe the architectures defined by the IETF and ISO shortly, but first there are two additional things we need to explain about the mechanics of protocol layering.
Encapsulation
Consider what happens in when one of the application programs sends a message to its peer by passing the message to RRP. From RRP's perspective, the message it is given by the application is an uninterpreted string of bytes. RRP does not care that these bytes represent an array of integers, an email message, a digital image, or whatever; it is simply charged with sending them to its peer. However, RRP must communicate control information to its peer, instructing it how to handle the message when it is received. RRP does this by attaching a header to the message. Generally speaking, a header is a small data structure—from a few bytes to a few dozen bytes—that is used among peers to communicate with each other. As the name suggests, headers are usually attached to the front of a message. In some cases, however, this peer-to-peer control information is sent at the end of the message, in which case it is called a trailer . The exact format for the header attached by RRP is defined by its protocol specification. The rest of the message—that is, the data being transmitted on behalf of the application—is called the message's body or payload . We say that the application's data is encapsulated in the new message created by RRP.
This process of encapsulation is then repeated at each level of the protocol graph; for example, HHP encapsulates RRP's message by attaching a header of its own. If we now assume that HHP sends the message to its peer over some network, then when the message arrives at the destination host, it is processed in the opposite order: HHP first interprets the HHP header at the front of the message (i.e., takes whatever action is appropriate given the contents of the header) and passes the body of the message (but not the HHP header) up to RRP, which takes whatever action is indicated by the RRP header that its peer attached and passes the body of the message (but not the RRP header) up to the application program. The message passed up from RRP to the application on host 2 is exactly the same message as the application passed down to RRP on host 1; the application does not see any of the headers that have been attached to it to implement the lower-level communication services. This whole process is illustrated in Figure 5 . Note that in this example, nodes in the network (e.g., switches and routers) may inspect the HHP header at the front of the message.
Note that when we say a low-level protocol does not interpret the message it is given by some high-level protocol, we mean that it does not know how to extract any meaning from the data contained in the message. It is sometimes the case, however, that the low-level protocol applies some simple transformation to the data it is given, such as to compress or encrypt it. In this case, the protocol is transforming the entire body of the message, including both the original application's data and all the headers attached to that data by higher-level protocols.
Multiplexing and Demultiplexing
Recall from that a fundamental idea of packet switching is to multiplex multiple flows of data over a single physical link. This same idea applies up and down the protocol graph, not just to switching nodes. In Figure 4 , for example, we can think of RRP as implementing a logical communication channel, with messages from two different applications multiplexed over this channel at the source host and then demultiplexed back to the appropriate application at the destination host.
Practically speaking, this simply means that the header that RRP attaches to its messages contains an identifier that records the application to which the message belongs. We call this identifier RRP's demultiplexing key , or demux key for short. At the source host, RRP includes the appropriate demux key in its header. When the message is delivered to RRP on the destination host, it strips its header, examines the demux key, and demultiplexes the message to the correct application.
RRP is not unique in its support for multiplexing; nearly every protocol implements this mechanism. For example, HHP has its own demux key to determine which messages to pass up to RRP and which to pass up to MSP. However, there is no uniform agreement among protocols—even those within a single network architecture—on exactly what constitutes a demux key. Some protocols use an 8-bit field (meaning they can support only 256 high-level protocols), and others use 16- or 32-bit fields. Also, some protocols have a single demultiplexing field in their header, while others have a pair of demultiplexing fields. In the former case, the same demux key is used on both sides of the communication, while in the latter case each side uses a different key to identify the high-level protocol (or application program) to which the message is to be delivered.
7-Layer OSI Model
The ISO was one of the first organizations to formally define a common way to connect computers. Their architecture, called the Open Systems Interconnection (OSI) architecture and illustrated in Figure 6 , defines a partitioning of network functionality into seven layers, where one or more protocols implement the functionality assigned to a given layer. In this sense, the schematic given in is not a protocol graph, per se , but rather a reference model for a protocol graph. It is often referred to as the 7-layer model.
Starting at the bottom and working up, the physical layer handles the transmission of raw bits over a communications link. The data link layer then collects a stream of bits into a larger aggregate called a frame . Network adaptors, along with device drivers running in the node's operating system, typically implement the data link level. This means that frames, not raw bits, are actually delivered to hosts. The network layer handles routing among nodes within a packet-switched network. At this layer, the unit of data exchanged among nodes is typically called a packet rather than a frame, although they are fundamentally the same thing. The lower three layers are implemented on all network nodes, including switches within the network and hosts connected to the exterior of the network. The transport layer then implements what we have up to this point been calling a process-to-process channel . Here, the unit of data exchanged is commonly called a message rather than a packet or a frame. The transport layer and higher layers typically run only on the end hosts and not on the intermediate switches or routers.
There is less agreement about the definition of the top three layers, in part because they are not always all present, as we will see below. Skipping ahead to the top (seventh) layer, we find the application layer. Application layer protocols include things like the Hypertext Transfer Protocol (HTTP), which is the basis of the World Wide Web and is what enables web browsers to request pages from web servers. Below that, the presentation layer is concerned with the format of data exchanged between peers—for example, whether an integer is 16, 32, or 64 bits long, whether the most significant byte is transmitted first or last, or how a video stream is formatted. Finally, the session layer provides a name space that is used to tie together the potentially different transport streams that are part of a single application. For example, it might manage an audio stream and a video stream that are being combined in a teleconferencing application.
Internet Architecture
The Internet architecture, which is also sometimes called the TCP/IP architecture after its two main protocols, is depicted in Figure 7 . An alternative representation is given in Figure 8 . The Internet architecture evolved out of experiences with an earlier packet-switched network called the ARPANET. Both the Internet and the ARPANET were funded by the Advanced Research Projects Agency (ARPA), one of the research and development funding agencies of the U.S. Department of Defense. The Internet and ARPANET were around before the OSI architecture, and the experience gained from building them was a major influence on the OSI reference model.
While the 7-layer OSI model can, with some imagination, be applied to the Internet, a 4-layer model is often used instead. At the lowest level is a wide variety of network protocols, denoted NET 1 , NET 2 , and so on. In practice, these protocols are implemented by a combination of hardware (e.g., a network adaptor) and software (e.g., a network device driver). For example, you might find Ethernet or wireless protocols (such as the 802.11 Wi-Fi standards) at this layer. (These protocols in turn may actually involve several sublayers, but the Internet architecture does not presume anything about them.) The second layer consists of a single protocol—the Internet Protocol (IP). This is the protocol that supports the interconnection of multiple networking technologies into a single, logical internetwork. The third layer contains two main protocols—the Transmission Control Protocol (TCP) and the User Datagram Protocol (UDP). TCP and UDP provide alternative logical channels to application programs: TCP provides a reliable byte-stream channel, and UDP provides an unreliable datagram delivery channel ( datagram may be thought of as a synonym for message). In the language of the Internet, TCP and UDP are sometimes called end-to-end protocols, although it is equally correct to refer to them as transport protocols.
Running above the transport layer is a range of application protocols, such as HTTP, FTP, Telnet (remote login), and the Simple Mail Transfer Protocol (SMTP), that enable the interoperation of popular applications. To understand the difference between an application layer protocol and an application, think of all the different World Wide Web browsers that are or have been available (e.g., Firefox, Chrome, Safari, Netscape, Mosaic, Internet Explorer). There is a similarly large number of different implementations of web servers. The reason that you can use any one of these application programs to access a particular site on the Web is that they all conform to the same application layer protocol: HTTP. Confusingly, the same term sometimes applies to both an application and the application layer protocol that it uses (e.g., FTP is often used as the name of an application that implements the FTP protocol).
Most people who work actively in the networking field are familiar with both the Internet architecture and the 7-layer OSI architecture, and there is general agreement on how the layers map between architectures. The Internet's application layer is considered to be at layer 7, its transport layer is layer 4, the IP (internetworking or just network) layer is layer 3, and the link or subnet layer below IP is layer 2.
The Internet architecture has three features that are worth highlighting. First, as best illustrated by Figure 8 , the Internet architecture does not imply strict layering. The application is free to bypass the defined transport layers and to directly use IP or one of the underlying networks. In fact, programmers are free to define new channel abstractions or applications that run on top of any of the existing protocols.
Second, if you look closely at the protocol graph in Figure 7 , you will notice an hourglass shape—wide at the top, narrow in the middle, and wide at the bottom. This shape actually reflects the central philosophy of the architecture. That is, IP serves as the focal point for the architecture—it defines a common method for exchanging packets among a wide collection of networks. Above IP there can be arbitrarily many transport protocols, each offering a different channel abstraction to application programs. Thus, the issue of delivering messages from host to host is completely separated from the issue of providing a useful process-to-process communication service. Below IP, the architecture allows for arbitrarily many different network technologies, ranging from Ethernet to wireless to single point-to-point links.
A final attribute of the Internet architecture (or more accurately, of the IETF culture) is that in order for a new protocol to be officially included in the architecture, there must be both a protocol specification and at least one (and preferably two) representative implementations of the specification. The existence of working implementations is required for standards to be adopted by the IETF. This cultural assumption of the design community helps to ensure that the architecture's protocols can be efficiently implemented. Perhaps the value the Internet culture places on working software is best exemplified by a quote on T-shirts commonly worn at IETF meetings:
We reject kings, presidents, and voting. We believe in rough consensus and running code. (David Clark)
Key Takeaway
Of these three attributes of the Internet architecture, the hourglass design philosophy is important enough to bear repeating. The hourglass's narrow waist represents a minimal and carefully chosen set of global capabilities that allows both higher-level applications and lower-level communication technologies to coexist, share capabilities, and evolve rapidly. The narrow-waisted model is critical to the Internet's ability to adapt rapidly to new user demands and changing technologies.


11.7: Inscribed Stone Vessels and Stelae
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Constructing, Deconstructing and Curating Personal Identity
Inscription on stone is sometimes characterised as intending permanency and immutability (e.g. Hiebert et al. 2000: 8; Kreamer et al. 2007: 110), yet many examples from ancient Egypt exhibit evidence for adjustment, addendum, palimpsest and erasure. Attested throughout the Pharaonic period (e.g. Der Manuelian 1999; Gozzoli 2000; Yoyotte 1951), erasure can be understood as an act of damnatio memoriae or the result of other changes in social status and relationships between individuals or between people and inscribed things, such as ‘ownership’. Evidence of similar changing relationships is also evidenced on Early Dynastic stone objects including vessels.
Over half of all known early inscribed objects (more than 4500) are inscribed on vessels, the majority being made of hard stone, although most survive as fragments (Regulski 2010: 6, 26; see also El-Khouli 1978). Among these are a variety of rock and mineral types (e.g. basalt, diorite, granite, yellow limestone, quartz crystal, etc., see Aston 1994: 11–73), shaped into a range of forms (Aston 1994: 106–128). They are typically found in high status funerary contexts (e.g. Petrie 1901: pl. 46–53), and to a lesser extent ceremonial contexts (e.g. Quibell 1989 [1900]: pls 31 (2), 36). Vessel imagery contrasts somewhat with that of the labels. The former floats and clusters together with few narratival relationships between images in a compositional field with undefined boundaries beyond the surface area provided by the vessel. On the labels, narrative scenes are attested more often, particularly in the first-half of the 1 st Dynasty, and compositional space is organised by register and column lines as well as the rectangular shape of the plaque itself (Piquette 2007). It therefore seems evident that images on the vessels, while depictive, are intended to serve a more scriptorial than pictorial function. The use of image categories such as ‘sign’, ‘writing’ or ‘inscription’ seems appropriate for the stone vessel imagery, but assumptions concerning a communicative function and a relationships to spoken language, such as the pronunciation of ‘readings’ from this early period, should be considered provisional (Trigger et al. 2001 [1983]: 56; see also Engel 1997: 434–435)
A survey of vessel inscriptions shows that they were made by removing surface material through incisions and less commonly, low relief carving. Many incisions are infilled with pigment/paste, as also attested on the inscribed labels (above). This would have aided visibility but colour also could also serve a symbolic purpose (Griffith in Petrie 1901: 51). Incised inscription usually occurs on the exterior of the vessel. Red or black colour applied directly to the vessel surface, attested more commonly during the 2 nd Dynasty, was often located on the interior vessel surface (Regulski 2004: 955). Among the vessels and vessel fragments at least four types of scribal practice can be distinguished:
- inscription
- inscription > inscription
- inscription > partial erasure / complete erasure
- inscription > erasure > re-inscription
Subsequent to initial inscription (1), at least a dozen vessels bear inscriptions of type (2). These consist of a series of PIs laid out horizontally and understood as ‘royal’ titles (conventionally rendered nsw.t-bi.t and nbty ) associated with Den, Adjib, Semerkhet and Qa’a (see Helck 1987: 101; see also Raffaele 2001 / 2002). It is suggested that after initial inscription, presumably commencing during the reign of the first ruler’s PI in the list, the successor appropriated or otherwise acquired a vessel. The PI of the successor was then inscribed beside the predecessor’s PI (see Kahl 2006: 96–99 for ideological influences on sequence for cylinder seals). Such examples highlight another way in which time is bound up in mark-making. In comparison with the use of different techniques on different faces of a label and implications for the passage of time (above), here a temporal aspect that spans lifetimes is foregrounded in the sequence of graphical expressions of individual identity and social position.
One of the earliest occurrences of sign erasure (3) on stone vessels derives from Abydos tomb complex X attributed to Adjib. These had apparently been inscribed during the previous reigns of Merneith and Den based on traces of their PIs. Excavation of Abydos tomb complex U ascribed to Semerkhet also yielded a number of stone vessels bearing erasures (Petrie 1900: 19–20). Just visible beneath two examples are the faint remains of signs identified by Flinders Petrie as the name of Adjib, Semerkhet’s predecessor ( Figure 11 ), while others bore erasures of the PI of Merneith (Petrie 1900: 19, pl. 5, no. 5, see also 20, pl. 7, no. 6). This practice of erasing (though not completely enough to prevent the PI from being reconstructed) continued into the Old Kingdom. In the Valley Temple complex of Menkaure, a 4 th Dynasty ruler, a cache of Early Dynastic vessels contained examples bearing both erasures and reincision. These included an erased and reinscribed vessel with the PI of Hetepsekhemwy and the erased PI of his successor, Nebra, on another (Reisner 1931).
These various episodes of scribal unmaking and remaking provide the modern investigator with valuable evidence for charting succession and lengths of reign (e.g. Kahl 2006). They also raise the question of whether these activities should be understood as damnatio memoriae , theft or usurpation, or seen as economically motivated. The notion of ‘heirlooms’ (see Jeffreys 2003) and seeing these activities as maintenance or curation may be more appropriate for some vessels, particularly those which bear accumulations of PI inscriptions rather than erasure. The proposal that an inscription was carved by an individual who was not fully literate and made an error in the copying process thus leading to erasure (Dusinberre 2005: 52), is probably not relevant here. Unlike the majority of labels for which making, use and deposition appear to be relatively restricted in time-space (e.g. spanning one, two or three reigns at most), the inscribed stone vessels exhibit more diverse and extended life histories. This may have involved greater opportunities for changes in function and meaning over the generations, as the vessels took on different kinds of significance for those who engaged with and experienced them — presumably rulers, scribes/artisans and individuals working in the funerary domain, if not the great beyond.
A potentially important link might be observed in the relationship between inscribed vessels and changes in high status funerary practices. During the 1 st Dynasty, inscribed stone vessels turned up in close association with the burial chamber and the ruler’s body. By the mid-Old Kingdom, inscribed vessels were still deployed within the funerary domain, but deposited some distance from the pyramid (where the body was presumably entombed), within the Valley Temple where the cult of the ruler was perpetuated. Further study of burial chamber deposition versus placement elsewhere may elucidate the nature and significance of vessel curation where inscriptions undergo replacement versus accumulation.
Partially Incomplete, Partially Complete
The final inscribed find type briefly treated in this chapter is a funerary stele. The vast majority of early stelae derive from the large mudbrick tomb complexes built for many Early Dynastic rulers at Abydos. The entrance to the main structure, the burial chamber and series of side chambers (Reisner 1936), was probably flanked by two large ‘royal’ stone stelae each adorned with the ruler’s PI (e.g. Amélineau 1899: pls 34–37; 1904: pl. 18; Petrie 1900: pl. 1). Surrounding the burial chamber and magazines were rows of male and female human (and some faunal) subsidiary graves. Based on general archaeological association it seems that more than 300 graves were marked with small ‘private’ limestone stelae (e.g. Martin 2011: 2–3; Petrie 1900: pl. 33; see also Martin 2003 on ‘royal: private’ distinction). Small numbers of signs and often a seated or standing human figure were painted, carved, hammered, pecked or scratched onto/into the upper part of often roughly shaped slabs.
A small number of stelae show evidence for multiple or incomplete graphical episodes (e.g. Martin 2011: Stelae 96, 122, 131, 132, 142, 193, 201). A relatively large and exceptionally elaborate example of the so-called private stelae (No. 48) was found in a small chamber (unlikely its original context) to the west of the burial chamber of Qa’a ( Figure 12 ; Petrie 1900: 26–27, 44–45, pls 30–31, 36). Based on Petrie’s (1900: 26–27) written description and Geoffrey Thorndike Martin’s (2011: 44) more recent study, this medium-sized rectangular limestone slab is smoothly dressed on the front from the top to the bottom of the panel. Below this the surface is roughly dressed and the back carefully worked. The edges were rounded off rather than squared. The inscription was sketched onto the surface in a red-brown pigment and finalised in black. Work was then begun to roughly hammer the matrix from around the drafted images, but intriguingly, the task was never completed. This is particularly apparent on the right in the second row where the height of the surface around the sign has not been reduced completely.
If we assume a right to left ‘reading’ direction (into the faces of the images), it is interesting to note that the process of surface transformation appears to have been undertaken in a different sequence from reading, leaving the right-most images in the second and third rows incompletely defined, including the upright staff held by the stele-owner. From the perspective of the presumed right-left reading direction and importance of this object as a vehicle for expressing the owner’s identity, it seems unusual that the image of the owner, and the beginning of the row just above, were not prioritized in the production process. Perhaps the act of inscription in certain media may have been undertaken according to the combined intentions and technological requirements of the scribe and/or other craftsperson(s) involved.
This evidence for the process of drafting, redrafting and partial carving, as well as erasure, raises a whole host of questions about why objects were not completed prior to being brought to the cemetery. It may be the case that in some circumstances aspects of production took place at or near the graveside (see also Martin 2011: 1). Alternatively, rather than seeing this stele as ‘unfinished’, perhaps its status within its past context of practice was constructed in a more contingent way. As long as a sufficient proportion of the imagery was present and / or discernible by the viewer (where intended), then perhaps the stele was considered to be sufficiently complete to serve its intended purpose. For this and the numerous other smaller stelae found in the same cemetery, the focus of material-graphical action appears to have been marking the personal identity of the deceased. In addition to the inscription, this function may have also been accomplished via the spatial location of the stel(a)e adjacent to (or inside?) the tomb or grave of the individual concerned. If meaning was situated in and constructed through a network of spatial and material, as well as iconographic and semantic relationships, perhaps that an element was not ‘fully’ expressed would not have been perceived as problematic.


6.8: The Kinsey Scale
For generations, people have attempted to understand sexuality as something a person is born with, with the belief that a person’s sexual preference can be changed through religion, therapy, torture, or other measures.  For example, those wishing to “pray away the gay” with types of “Conversion therapies” do irreparable harm to LBTQIA+ individuals. In Chapter 4, you were introduced to Alfred Kinsey’s groundbreaking work, making him one of the classic theorists in the study of human sexuality. In 1949, he along with his colleagues published, Sexual Behavior in the Human Male (1949) .  In 1949, this was seen as revolutionary. The Kinsey Scale, as it was later named, proved that not all people are inherently heterosexual or homosexual; in fact, sexuality exists on a wide spectrum. The Kinsey Scale set a standard for measuring sexuality as existing along a spectrum, rather than what was once thought of as bipolar (heterosexual or homosexual).
Dr. Kinsey’s research uncovered that most people aren’t absolutely straight or gay/lesbian. Instead of just asking “Do you prefer men or women?” he asked people to report their fantasies, dreams, thoughts, emotional investments in others, and frequency of sexual contact.  Ultimately, a person’s sexuality cannot be fully measured through testing, and can only be defined by an individual's own expression.
The Kinsey Reports do not include all types of sexualities but have helped build a framework for other scales to dive deeper into the spectrum of sexuality. Two noted examples are the Klein Grid | Bi.org and the Storms Sexuality Axis . Over time, people have made adaptations to the Kinsey Scale by developing their own graphics, illustrations, and charts that showcase the fidelity of sexuality.
Decades of research has supported this idea that sexual orientation ranges along a continuum, from exclusive attraction to the opposite sex/gender to exclusive attraction to the same sex/gender (Carroll, 2016).
 A closer examination illustrates this:


9.1: Abstract
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The practice of cutting clay tablets is evident in both Minoan Linear A and Mycenaean Linear B administration. Tablets were most probably cut after having been inscribed, when the residue of clay with no text was removed, either to be reused for producing further tablets, or to minimise space needed for their storage. This habit is especially apparent in the earliest deposit of Linear B tablets — the Room of the Chariot Tablets — where nearly 20% of all tablets were cut. It is precisely these tablets that will be discussed in this chapter. Most of the cut tablets from the Room of the Chariot Tablets are of elongated shape. Some were cut on the sides immediately before the first sign or immediately after the last one. This may reflect the practice of saving clay whenever possible. The tablets generally give an impression of economy: their entire surface is usually inscribed without leaving any unused space; when a tablet was larger than needed, the unneeded parts seem to have been excised and reused. Another explanation has been proposed for the cutting of these tablets: the practice of dividing a set of information into separate records. Although cut and separated in the past, scholars recently joined some of these tablets proving that these small documents initially belonged to one larger tablet. The name introduced to describe this kind of a document is a simili-join. As for the purpose of simili-joins, it has been previously suggested that larger tablets were divided into smaller units for the purpose of rearranging the information, and this is a possibility that is further explored in this paper. Apart from the actual cutting, another feature may be an indication of the practice of similijoins. A certain number of elongated tablets from the Room of the Chariot tablets have vertical lines incised across them. It seems that their function was to divide certain sections of a tablet. Perhaps these lines were incised to indicate where to cut the tablet, as suggested by Jan Driessen. By following this line of thought, it will be proposed that records of this type were probably written with the anticipated need for rearranging of the data, meaning that the simili-joins may have been planned in advance — hence the practice of marking tablets with vertical lines for cutting. These lines must have been incised when the tablet was still moist, i.e. either while inscribing the text, or not much longer afterwards. If so, the question is: why did such tablets remain undivided?
How to cite this book chapter:
Tomas, H. 2013. Saving on Clay: The Linear B practice of cutting tablets. In: Piquette, K. E. and Whitehouse, R. D. (eds.)
Writing as Material Practice: Substance, surface and medium.
Pp. 175-191. London: Ubiquity Press. DOI:
http://dx.doi.org/10.5334/bai.i


2.5: Electron Affinities
- To master the concept of electron affinity as a measure of the energy released by adding an electron to an atom or ion.
- To recognize the inverse relationship of ionization energies and electron affinities
The electron affinity (\(EA\)) of an element \(X\) is defined as the energy released that occurs when an electron is added to a gaseous atom or ion:
\[ X(g)+e^- \rightarrow X^-(g) \;\;\; EA = E(X) - E(X^-) \label{7.5.1} \]
where \(E(X)\) is the energy of the gaseous atom \(X\) and \(E(X^-)\) is the energy of the gaseous anion \(X^-\). The positive electron affinities (EA>0) imply that the energy is released when an electron is added, which is an exothermic process. The negative EA imply that the energy must be added to the system to produce an anion. A more positive EA indicates a stronger attraction for an additional electron. (Figure \(\PageIndex{1}\)).
The chlorine atom has the most positive electron affinity of any element, which means that more energy is released when an electron is added to a gaseous chlorine atom than to an atom of any other element:
\[ \ce{ Cl(g) + e^- \rightarrow Cl^- (g)} \;\;\; EA \; = \; +348.6 \; kJ/mol \label{7.5.2} \]
In contrast, beryllium does not form a stable anion, so its effective electron affinity is
\[ \ce{ Be(g) + e^- \rightarrow Be^- (g)} \;\;\; EA \le 0 \label{7.5.3} \]
Nitrogen is unique in that it has an electron affinity of approximately zero. Adding an electron neither releases nor requires a significant amount of energy:
\[ \ce{ N(g) + e^- \rightarrow N^- (g)} \;\;\; EA \approx 0 \label{7.5.4} \]
Generally, electron affinities become more positive across a row of the periodic table.
In general, electron affinities of the main-group elements become less positive as we proceed down a column. This is because as n increases, the extra electrons enter orbitals that are increasingly far from the nucleus.
Atoms with the largest radii, which have the lowest ionization energies (affinity for their own valence electrons), also have the lowest affinity for an added electron. There are, however, two major exceptions to this trend:
- The electron affinities of elements B through F in the second row of the periodic table are less positive than those of the elements immediately below them in the third row. Apparently, the increased electron–electron repulsions experienced by electrons confined to the relatively small 2 p orbitals overcome the increased electron–nucleus attraction at short nuclear distances. Fluorine, therefore, has a lower affinity for an added electron than does chlorine. Consequently, the elements of the third row ( n = 3) have the most positive electron affinities. Farther down a column, the attraction for an added electron decreases because the electron is entering an orbital more distant from the nucleus. Electron–electron repulsions also decrease because the valence electrons occupy a greater volume of space. These effects tend to cancel one another, so the changes in electron affinity within a family are much smaller than the changes in ionization energy.
- The electron affinities of the alkaline earth metals become more positive from Be to Ba. The energy separation between the filled ns 2 and the empty np subshells decreases with increasing n , so that formation of an anion from the heavier elements becomes energetically more favorable.
The equations for second and higher electron affinities are analogous to those for second and higher ionization energies:
\[X(g) + e^- \rightarrow X^-(g) \;\;\; EA_1 = E(X) - E(X^-) \label{7.5.5} \]
\[X^- (g) + e^- \rightarrow X^{2-} (g) \;\;\; EA_2 = E(X^-) - E(X^{2-}) \label{7.5.6} \]
As we have seen, the first electron affinity can be greater than or equal to zero or negative, depending on the electron configuration of the atom. In contrast, the second electron affinity is always positive because the increased electron–electron repulsions in a dianion are far greater than the attraction of the nucleus for the extra electrons. For example, the first electron affinity of oxygen is +141 kJ/mol, but the second electron affinity is −744 kJ/mol:
\[O(g) + e^- \rightarrow O^- (g) \;\;\; EA_1=+141 \;kJ/mol \label{7.5.7} \]
\[O^- (g) + e^- \rightarrow O^{2-} (g) \;\;\; EA_2=-744 \;kJ/mol \label{7.5.8} \]
Thus the formation of a gaseous oxide (\(O^{2−}\)) ion is energetically quite unfavorable (estimated by adding both steps):
\[O (g) + 2e^- \rightarrow O^{2-} (g) \;\;\; EA=-603 \;kJ/mol \label{7.5.9} \]
Similarly, the formation of all common dianions (such as \(S^{2−}\)) or trianions (such as \(P^{3−}\)) is energetically unfavorable in the gas phase.
While first electron affinities can be positive, negative, or zero, second electron affinities are always negative.
If energy is required to form both positively charged cations and monatomic polyanions, why do ionic compounds such as \(MgO\), \(Na_2S\), and \(Na_3P\) form at all? The key factor in the formation of stable ionic compounds is the favorable electrostatic interactions between the cations and the anions in the crystalline salt .
Based on their positions in the periodic table, which of Sb, Se, or Te would you predict to have the most positive electron affinity?
Given: three elements
Asked for: element with most positive electron affinity
Strategy:
- Locate the elements in the periodic table. Use the trends in electron affinities going down a column for elements in the same group. Similarly, use the trends in electron affinities from left to right for elements in the same row.
- Place the elements in order, listing the element with the most positive electron affinity first.
Solution:
A We know that electron affinities become less positive going down a column (except for the anomalously low electron affinities of the elements of the second row), so we can predict that the electron affinity of Se is more positive than that of Te. We also know that electron affinities become more positive from left to right across a row, and that the group 15 elements tend to have values that are less positive than expected. Because Sb is located to the left of Te and belongs to group 15, we predict that the electron affinity of Te is more positive than that of Sb. The overall order is Se > Te > Sb, so Se has the most positive electron affinity among the three elements.
Based on their positions in the periodic table, which of Rb, Sr, or Xe would you predict to most likely form a gaseous anion?
- Answer
-
Rb
Summary
The electron affinity ( EA ) of an element is the energy released that occurs when an electron is added to a gaseous atom to give an anion. In general, elements with the most positive electron affinities (the highest affinity for an added electron) are those with the smallest size and highest ionization energies and are located in the upper right corner of the periodic table.


7.2: Overharvesting
People have always hunted, collected, trapped, or otherwise harvested the food and other natural resources they need to survive. When human populations were small, at least relative to the abundance of their resources, and collection methods were relatively unsophisticated, people could sustainably harvest and hunt wildlife in their local environments. However, as human populations have increased, and roads have provided access to previously remote areas, our impact on the environment has escalated. At the same time, our methods of harvesting have become dramatically more efficient. Guns are now used instead of blowpipes, spears, or arrows, while networks of wire snares indiscriminately catch animals of all types, even young and pregnant females. Populations of species that mature and reproduce rapidly can often recover quickly after harvests and can thus be exploited sustainably; however, species that are slow-maturing and slow-reproducing cannot sustain current harvest levels. Consequently, many species are threatened due to overharvesting, the unsustainable collection of natural resources (Maxwell et al., 2016). Overharvesting may take on many forms, including hunting, fishing, logging, and gathering of plants and animals for medicine, captive collections, subsistence, commerce, or recreation purposes (Figure 7.8).
The Bushmeat Crisis
Bushmeat harvesting is one of Africa’s most prominent overharvesting concerns (see Box 4.1). Bushmeat—wild sources of protein obtained on land by hunting and collecting birds, mammals, snails, and caterpillars—provides much of the protein in people’s diets in large parts of Africa. For example, in Nigeria and Cameroon, 12,000 tonnes of bushmeat—two tonnes obtained from bay duiker (Cephalophus dorsalis, NT) alone—are sold at markets in the Cross-Sanaga rivers region each year (Fa et al., 2006). Similarly, more than 9,000 primates are killed annually for a single market in Côte d’Ivoire (Covey and McGraw, 2014); people from Central Africa harvest an astonishing 5.3 million tonnes of mammalian bushmeat annually (Fa et al., 2002). Usually seen as a conservation challenge in Africa’s tropical forests, the bushmeat crisis also impacts savannah regions (reviewed in Lindsey et al., 2013). For example, bushmeat hunters, numbering between 1.500 and 2,000, remove over 600,000 kg of herbivore biomass from Botswana’s Okavango Delta each year, despite the region’s protected status and importance for ecotourism sectors (Rogan et al., 2017).
The massive wildlife declines caused by the bushmeat crisis are also threatening ecosystem services, food security and people’s livelihoods.
Outside influences play a prominent role in the harvesting pressure associated with the bushmeat crisis. In Section 5.2, we discussed neocolonialism, where jobs associated with land-grabbing industries are frequently reserved for migrant labourers. Poorly paid and with limited rights, migrant labourers are often forced to turn to local natural resources to fulfil their basic needs (Thibault and Blaney, 2003). The impact of these migrant labourers on the local environment is massive compared to traditional (and many other local) peoples that prioritise sustainability. For example, immigrants working at logging concessions in the northern parts of the Republic of the Congo hunt 72% of all bushmeat harvested in the region (Poulsen et al., 2009). The increased commercialisation of bushmeat also poses challenges (Lindsey et al., 2013); for example, in the broader Congo Basin, commercial hunters are exploiting bushmeat at scales 27 times that of the area’s traditional peoples (Fa et al., 2016). In addition to hunting for local markets, illegal exports also play an important role. For example, more than 50 tonnes of wild fish and bushmeat enters France from Africa each week (Chaber et al., 2010); similar amounts were also estimated for airports in Switzerland (Wood et al., 2014).
Very few animal populations can withstand such high extraction rates. Consequently, regions dependent on bushmeat have already seen substantially wildlife declines (Lindsey et al., 2013). West Africa, where forest mammal populations are down an estimated 80%, have been hot particularly hard (Benítez-López et al., 2019). These wildlife declines also lead to reduced harvests—some hunters have seen their harvests reduced by over 80%, with impacts to wildlife notable as far as 40 km from hunters’ access points along roads from their villages (Benítez-López et al., 2017). At current exploitation rates, supplies are expected to decrease by an additional 80% within the next 50 years (Fa et al., 2003). Unless more sustainable, alternative sources of protein are found, people dependent upon bushmeat will see increased malnutrition and compromised livelihoods as bushmeat species are pushed to extinction. When that happens, families relying on bushmeat will face even worse food insecurity than that which is driving the current bushmeat crisis.
Exacerbating the risk of food insecurity, people in the affected regions will also suffer from compromised ecosystem services as populations of predators, seed dispersers, and pollinators are reduced (Rosin and Poulsen, 2016). For example, reduced mammal populations have been linked to reduced abundance of fruits and other useful plant products available for human consumption (Vanthomme et al., 2010). Some areas are already suffering from “empty forest syndrome”—a condition where a forest appears to be green and healthy, but is practically devoid of animals, and in which ecological processes have been irreversibly altered such that the forest’s species composition will change over subsequent decades (Nasi et al., 2011; Benítez-López et al., 2019). The bushmeat crisis is thus a major concern to people concerned about biodiversity and/or human well-being.
Overfishing
Pressure on biodiversity in aquatic environments is also increasing as people continue to harvest fish, sea turtles, dolphins, shellfish, and manatees for meat at increasing rates. Modernised fishing methods play a major role. For example, a motorised fishing fleet that faces few restrictions has caused a 75% decline in fish populations at Ethiopia’s Lake Tana in recent years (de Graaf et al., 2004). Also, in the marine environment, motorised fleets and enormous factory ships can now spend months at sea where they catch fish to sell at local and global markets (Ramos and Grémillet, 2013; Pauly et al., 2014). Some estimates suggest that wild-caught seafood could be virtually absent by 2050 if current exploitation levels persist (Worm et al., 2006).
For many aquatic organisms, the indirect impacts of modern commercial fishing methods outweigh direct exploitation (Figure 7.9). One example is ghost fishing, which causes thousands of animals to die each year after becoming entangled in dumped, abandoned, and lost fishing gear. Similarly, approximately 25% of fish harvests are considered bycatch—animals that are accidentally caught, injured, or killed during fishing operations. Recent declines in skates, rays, turtles, sharks, dolphins, and seabirds have all been linked to incidental deaths as bycatch (Cox et al., 2007; Carruthers et al., 2009). Seabird biologists from South Africa have been at the forefront of solving bycatch problems in recent years (Box 7.1).
Ross Wanless
DST-NRF Centre of Excellence at the FitzPatrick Institute of African Ornithology,
University of Cape Town, South Africa.
The global problem of seabird bycatch in fisheries—the accidental death of seabirds during fishing—is one of the biggest threats to pelagic seabirds (Croxall et al., 2012). Ironically, it is both one of the easiest and one of the most challenging problems to solve. How so? Simple technical fixes to stop birds from getting snagged on fishing gear and drowning can work amazingly well, but fishermen must be convinced to use them.
Techniques for preventing bycatch break down into two basic approaches. The first approach is to prevent access to the danger point (the baited hook or the cables that birds strike). Fishing only at night eliminates up to 80% of the problem, but still jeopardises nocturnal foragers and diurnal species during a full moon. Another option is bird-scaring lines (Figure 7.A) consisting of a mainline flown from the stern of a boat with hanging streamers that scare birds away from danger areas behind the vessel. The second approach, primarily used in longline fishing, is to remove the risky gear (baited hooks) as quickly as possible; essentially this involves adding weights to lines to sink them faster. It has reduced seabird bycatch on some fisheries by 90–95%.
Despite clear harm to seabirds caused by fisheries and the simple, effective fixes at hand, implementing these mitigation measures has been patchy at best in most fisheries where seabird bycatch occurs. There are some exceptions, and it is useful to examine what elements led certain fisheries to fix the problem. A good case study is in South Africa, where BirdLife South Africa’s Albatross Task Force (ATF) demonstrated in 2006 that trawl fishing for hake (Merluccius spp.) was killing around 18,000 seabirds each year (Watkins et al., 2008). The fishery involved had Marine Stewardship Council (MSC) certification, which gives a fishery access to premium European markets on the condition that it meets environmentally friendly and sustainable metrics, including no significant bycatch impacts. This provided a powerful incentive for fleet-wide implementation of a bycatch mitigation measure; failure to do so would have resulted in a loss of certification, with catastrophic financial implications.
Despite this strong incentive, it required another five years of work from the ATF to assess bird scaring lines and refine the design, overcome resistance to their use, and close loopholes in regulations. In 2014, the ATF published an assessment of the effectiveness of their bird scaring lines—a single measure to prevent the accidental and avoidable deaths of around 10,000 albatrosses and large numbers of other species. When used correctly, the system eliminated 90–95% of seabird bycatch (Maree et al., 2014). Why did it take so long for the fleet to adopt this measure, despite it costing almost nothing, requiring no skill or time to use, and posing no meaningful operational problems? And why have identical fishing industries in many other countries failed to follow suite?
The answer is complex. ATF teams are present in South Africa (and now also in Namibia), providing sustained pressure and constant presence. South Africa had standing legislation, yet compliance from the South African fleet was initially minimal (and remains less than perfect today). MSC certification certainly created an enabling environment (Wanless and Maree, 2014) and incentive to drive change, yet it took more than that to change the entire fleet. Constant lobbying from BirdLife and regular dialogue from deck to boardroom were also critical ingredients. A legislative framework that provides some hope of censure against non-compliant vessels meant that there was internal pressure within the industry to “tow the line”—pun intended. Ultimately, widespread change became possible when there was a credible, independent observer program to verify deck practice and give teeth to agencies when addressing non-compliance.
The impact of traditional medicine
Africa has a long history of sustainable use of traditional medicines. Unfortunately, as the number of people living in Africa has increased, so has the demand for traditional medicine. Today, harvesting for traditional medicine is putting unsustainable pressure on species exploited for this purpose (Williams et al., 2014). One prominent example is vultures: the demand of vulture body parts, believed to bestow clairvoyant abilities, is driving massive vulture population declines across Africa (see Box 4.4). The growth in traditional medicine markets in East Asian countries such as China, Thailand, Cambodia, and Vietnam exacerbates these problems. For example, as tigers (Panthera tigris, EN) and rhinoceros have become scarce in Asia, Asian traditional healers are increasingly targeting African predators and rhinoceros to satisfy their market demands. Another group of species threatened by the Asian traditional medicine trade is sea horses (Hippocampus spp.). Due to population declines from overharvesting, sea horse exports from Kenya and Tanzania to East Asia have halved over recent years; yet, more than 600 kg of dried sea horses (over 254,000 individuals) continue to be exported annually (McPherson and Vincent, 2004). Exploitation for Asian traditional medicine markets has already pushed the western black rhinoceros (Diceros bicornis longipes, EX) to extinction. In a similarly perilous position is the northern white rhinoceros (Ceratotherium simum cottoni, CR); with only two non-reproductive females left in the world, this species is now considered committed to extinction (see Section 8.3; Box 11.4). A group of species sought after by both African and Asian traditional medicine markets is pangolins, thought to be the most heavily poached animals on Earth. For example, between 2012 and 2016, more than 20 tonnes of African pangolin scales (involving up to 30,000 animals) were seized during law enforcement operations across the region (Andersen, 2016). The problem is also getting worse: authorities intercepted 13 tonnes of scales in Singapore in 2019, all from a single shipment believed to travel from Nigeria to Vietnam (Geddie, 2019). With such a large active operational scale, it comes as no surprise that all four African pangolin species are now threatened with extinction (IUCN, 2019).
The impact of live animal trade
Millions of non-domesticated animals are sold as pets around the world each year (Table 7.1). Given that many of these pets were originally collected in the wild, it is no surprise that the most popular species tend to be at a high risk of extinction (Bush et al., 2014). These huge numbers are magnified by the extra millions of animals needed to compensate for deaths during collection and shipping. Collection of wild animals for pets and other purposes has a massive impact of biodiversity in Africa, the world’s largest pet trade exporter (Bush et al. 2014).
Among the most popular groups of wildlife traded are Africa’s parrots (Figure 7.10). For example, 32,000 wild-sourced African grey parrots (Psittacus erithacus, EN) were imported into the European Union in 2005 (UNEP-WCMC, 2007). Combined with habitat loss, the wild bird trade has already caused extirpations of this species in some areas of West Africa (Annorbah et al., 2015). Similarly, 82 of the 291 species of African freshwater fish known to occur in the pet trade are considered threatened with extinction (UNEP-WCMC, 2008). While it is true that collecting wild animals for the pet trade sustains many people’s livelihoods, research on harvesting of ornamental fish in Cameroon has shown that this practice is not sustainable in the long term (Brummet et al., 2010). It is therefore critical to find ways to make these practices more sustainable, for the sake of the pet collectors and biodiversity.
|
Group |
Number traded each year |
Notes |
|---|---|---|
|
Orchids |
250 million |
Mainly cultivated, but about 10% sourced from the wild. Illegal trade—and mislabelling to avoid regulation—a major problem. |
|
Succulent plants |
35 million |
Mainly cultivated, but about 15% sourced from the wild. Illegal trade remains a major problem. |
|
Corals |
13 million |
Collected using destructive methods; used for aquarium decor and jewellery. |
|
Reptiles |
7.2 million |
Mainly sourced from the wild for zoos and pet trade, but increasingly from farms. Does not include large skin trade. |
|
Birds |
2.3 million |
Mostly perching birds destined for zoos and pet trade. Also includes legal and illegal trade of parrots. |
|
Ornamental fish |
2 million |
Most originate from wild reefs, caught by illegal methods that damage the surrounding coral reef and other wildlife. |
|
Primates |
148,000 |
Used for biomedical research, while many also destined for pets, circuses, zoos, and private collections. |
Sources: http://cites-dashboards.unep-wcmc.org , data presented as live specimens exported from 2011–2015. Data generally do not include illegal traded specimens, which are usually not reported to CITES.
Overharvesting of plant products
Overharvesting is not restricted to animals and animal products. While legal and illegal timber and firewood extraction is a major source of deforestation throughout Africa, it is also an important extinction driver. In fact, logging and other forms of wood harvesting have already contributed to the extinction of at least six plant species in Sub-Saharan Africa, with an additional 116 species considered Critically Endangered in part due to these threats (IUCN, 2019). Other plant species face extinction due to exploitation for medicines, spices, fragrances, and ornaments. For example, White’s ginger (Mondia whitei)—reputed to have aphrodisiac and antidepressant properties—has been harvested to extirpation in parts of central Kenya and South Africa (Aremu et al., 2011). Similarly, harvesting rates of African blackwood (Dalbergia melanoxylon, NT)—popular for making musical instruments and fine furniture—are currently unsustainable because the tree is slow-growing, has low germination rates, and extractions are seldom offset with planting of new seeds or seedlings (Amri et al., 2009).
Challenges in managing overharvesting
One of the biggest challenges in combatting overharvesting is the non-enforcement and/or outright absence of legal controls to protect exploited species. But even where strong regulatory frameworks exist, the sheer scale of the problem poses practical challenges for effective enforcement (discussed in Chapter 12), as billions of dollars flow among participants in illegal wildlife trade, which include local people trying to make a living, professional poachers, corrupt government officials, unethical dealers, and wealthy buyers who are not concerned about how the wildlife products they use were obtained. The illegal wildlife trade has hit Africa’s megafauna particularly hard. For example, even though there has been an international ban on the ivory trade since 1989, thousands of African elephants continue to be illegally killed on an annual basis (Box 7.2). Similarly, despite a ban on rhinoceros horn trade since 1977, an increasing number of rhinoceros succumb to poaching every year (Figure 7.11). Worse yet, the illegal wildlife trade shares many characteristics and practices with the illegal trade in drugs and weapons; in some cases, the same syndicates run these various criminal enterprises (Christy and Stirton, 2015). Apprehending these criminal networks is generally very dangerous, requiring vast resources.
David H.M. Cumming 1,2
1 FitzPatrick Institute of African Ornithology, University of Cape Town,
Cape Town, South Africa.
2 Tropical Resource Ecology Programme, University of Zimbabwe,
Harare, Zimbabwe.
As our increasingly human-dominated planet enters a new geological era, will there still be room for Earth’s largest land mammals? Or will there be, as happened to mammoths, sabre-toothed cats, and giant sloths during the Pleistocene (see Box 8.1), another hominid-induced extinction of large mammals? Our new human-dominated era has become known as the Anthropocene (Waters et al., 2015), and the animals are, of course, Africa’s elephants.
Elephants encapsulate the dilemmas of conserving large charismatic mammals. They are dominant ecosystem engineers that, depending on their densities, can facilitate or adversely impact species diversity and ecosystem processes (Section 4.2.1). They are also economically important to ecotourism industries and revered by many; ivory ornaments and carvings have been valued highly by many cultures past and present. But elephants are also regarded as dangerous pests by expanding small-scale farming communities, responsible for destroying crops and killing people. While retaliatory killings and habitat loss (primarily through agricultural expansion) certainly contribute to the endangerment of elephants, poaching to supply Asian markets (see Figure 12.1) is the primary cause behind massive population reductions we are currently witnessing (Wittemyer et al., 2014).
Africa’s elephants have, in the past, been greatly exploited, first for their meat and later also for their ivory. In 1887, about 1,000 tonnes of ivory were being exported from Africa (Spinage, 1973) and, by 1900, elephant populations in many African countries had all but collapsed. In Southern Africa, for example, it was feared that they might soon go extinct. However, with effective protection, elephant populations increased twentyfold, to more than 200,000, south of the Zambezi River by the 1970s. Elsewhere, elephant numbers also recovered, and, in the mid-1970s, the continental elephant population was estimated to be more than 1 million (Table 7.B). But a rapid escalation of the illegal killing of elephants for ivory and meat soon followed, accompanied by a steep rise in the price of ivory. In response, African elephants were placed on CITES Appendix II in 1976 to control the international trade in ivory. Elephants in some Southern African countries were well protected, so numbers continued to grow. However, elsewhere poaching and illegal trade in ivory continued and, in 1989, the African elephant was placed on CITES Appendix I, which banned all international trade in elephants and elephant products. The result was a decline in the price of ivory, and recovery of many populations.
Conservationists, and the world at large, traditionally regarded the African elephant as a single species. Recent morphometric and genetic evidence has revealed that forest and savannah elephants represent two distinct species, with forest elephants (Loxodonta cyclotis) occupying the West and Central African forests, and the larger savannah elephants (Loxodonta africana) being widespread in non-forested regions of Sub-Saharan Africa (Roca et al., 2015). The distinction has important implications for their conservation, as each of these elephant species now viewed on its own is even more sensitive to population declines (CBD, 2015).
Since about 2006, poaching of elephants again began to escalate, in part a response to an increase in the price of ivory, poorly funded wildlife agencies, and corruption (Hauenstein et al., 2019). The scale of these killings is extraordinary. For example, an estimated 30,000 elephants were killed in 2013 alone. Forest elephants declined by about 60% (Maisel et al., 2013). While population trends for savannah elephants vary across the region, they too face increased poaching pressure (Chase et al., 2016). Due to these large-scale killings, combined with the impact of habitat loss from agricultural expansion, West Africa’s elephants are today confined to small isolated protected areas with a total population of about 17,000 (Maisel et al., 2013). Elephant population trends in East Africa vary: numbers are increasing in Uganda and Kenya, but Tanzania has lost some 60,000 elephants in the last few years. In Southern Africa, Botswana has the largest elephant population, estimated in 2014 to number at least 130,000. Neighbouring Zimbabwe has a population of 83,000 elephants, much the same number as it had in 2001. However, two of Zimbabwe’s four regional populations declined significantly between 2006 and 2014 with a loss of at least 20,000 elephants (Figure 7.C).
Global and national efforts to curb elephant poaching are currently focused on improving law enforcement on the ground, intercepting ivory shipments to Asia, closing ivory markets in Africa and Asia, and leading campaigns to reduce demand for ivory in major consuming countries in Asia, particularly in China. Importantly, while these initiatives are relieving poaching pressure on African elephant populations, they fail to address core issues relating to the interactions between people and elephants in the rural areas of Africa. A high proportion of elephant ranges lie outside protected areas where they overlap with people. Relieving continued pressures on elephants, outside as well as inside protected areas, would only happen if people who are harmed by elephants derive enough benefits from elephants and other wildlife to outweigh the direct and indirect costs of sharing land with them. Community-based natural resource management (CBNRM) projects, such as those in Namibia (Section 14.3) show that this can be achieved. Establishing secure and sustainable funding streams through payments for ecosystem services (Section 15.3), or payments for co-existing with large dangerous mammals such as elephants (Section 14.4), could extend these promising initiatives even further.
Now, consider a hypothetical conservationist concerned about the bushmeat crisis’ impact on biodiversity. This person may very well think that effective enforcement of a hunting ban would be the best solution to prevent further overharvesting. Unfortunately, solving complex challenges with simplistic steps runs a high risk of being counterproductive. For example, local bushmeat markets provide important contributions to food and financial security in many rural parts of Africa (van der Merwe et al., 2015). Replacing bushmeat with livestock and crops production—two primary drivers of habitat loss (Chapter 5)—also carries risks. For example, an estimated 250,000 km 2 of forest will need to be converted to pastureland to replace the bushmeat trade just for the Congo Basin (Nasi et al., 2011). Clearly, there is a need for the bushmeat trade, albeit in a sustainable manner to ensure long-term viability of the local biodiversity, as well as the prosperity of the people who inhabit these areas. We delve deeper into solutions for these kinds of complex challenges from Chapter 9 onwards.


25.1E: Structural Adaptations for Land in Seedless Plants
- Discuss the primary structural adaptations made by plants to living on land
Land Plant Adaptations
As plants adapted to dry land and became independent from the constant presence of water in damp habitats, new organs and structures made their appearance. Early land plants did not grow more than a few inches off the ground, competing for light on these low mats. By developing a shoot and growing taller, individual plants captured more light. Because air offers substantially less support than water, land plants incorporated more rigid molecules in their stems (and later, tree trunks).
Apical Meristems
Shoots and roots of plants increase in length through rapid cell division in a tissue called the apical meristem, which is a small zone of cells found at the shoot tip or root tip. The apical meristem is made of undifferentiated cells that continue to proliferate throughout the life of the plant. Meristematic cells give rise to all the specialized tissues of the organism. Elongation of the shoots and roots allows a plant to access additional space and resources: light, in the case of the shoot, and water and minerals, in the case of roots. A separate meristem, called the lateral meristem, produces cells that increase the diameter of tree trunks.
Vascular structures
In small plants such as single-celled algae, simple diffusion suffices to distribute water and nutrients throughout the organism. However, for plants to develop larger forms, the evolution of vascular tissue for the distribution of water and solutes was a prerequisite. The vascular system contains xylem and phloem tissues. Xylem conducts water and minerals absorbed from the soil up to the shoot, while phloem transports food derived from photosynthesis throughout the entire plant. A root system evolved to take up water and minerals from the soil, while anchoring the increasingly taller shoot in the soil.
Additional land plant adaptations
In land plants, a waxy, waterproof cover called a cuticle protects the leaves and stems from desiccation. However, the cuticle also prevents intake of carbon dioxide needed for the synthesis of carbohydrates through photosynthesis. To overcome this, stomata, or pores, that open and close to regulate traffic of gases and water vapor, appeared in plants as they moved away from moist environments into drier habitats.
Water filters ultraviolet-B (UVB) light, which is harmful to all organisms, especially those that must absorb light to survive. This filtering does not occur for land plants. This presented an additional challenge to land colonization, which was met by the evolution of biosynthetic pathways for the synthesis of protective flavonoids and other compounds: pigments that absorb UV wavelengths of light and protect the aerial parts of plants from photodynamic damage.
Plants cannot avoid being eaten by animals.  These toxic compounds can also cause severe diseases and even death, thus discouraging predation. Humans have used many of these compounds for centuries as drugs, medications, or spices. In contrast, as plants co-evolved with animals, the development of sweet and nutritious metabolites lured animals into providing valuable assistance in dispersing pollen grains, fruit, or seeds. Plants have been enlisting animals to be their helpers in this way for hundreds of millions of years.
Key Points
- Many plants developed a vascular system: to distribute water from the roots (via the xylem ) and sugars from the shoots (via the phloem ) throughout the entire plant.
- An apical meristem enables elongation of the shoots and roots, allowing a plant to access additional space and resources.
- Because of the waxy cuticle covering leaves to prevent water loss, plants evolved stomata, or pores on the leaves, which open and close to regulate traffic of gases and water vapor.
- Plants evolved pathways for the synthesis of complex organic molecules, called secondary metabolites, for protection from both UV lights and predators.
Key Terms
- phloem : a vascular tissue in land plants primarily responsible for the distribution of sugars and nutrients manufactured in the shoot
- stoma : a pore found in the leaf and stem epidermis used for gaseous exchange
- xylem : a vascular tissue in land plants primarily responsible for the distribution of water and minerals taken up by the roots; also the primary component of wood
- meristem : the plant tissue composed of totipotent cells that allows plant growth


7.2: One-Dimensional Noncontinuous Motion
In continuous motion, we used a single mathematical function each to describe the position, velocity, or acceleration over time. If we cannot describe the motion with a single mathematical function over the entire time period, that motion is considered noncontinuous motion. In cases such as this, we will use different equations for different sections of the overall time period.
For an example of noncontinuous motion, imagine a car that accelerates for a few seconds, then holds a steady speed for a few seconds, then puts on the brakes and comes to a stop over the final few seconds. There is no one mathematical function we can use to describe the motion for the full time period, but if we break the motion into three pieces, then we can come up with an equation for each section of the motion.
Analyzing the first time period will be exactly the same as analyzing a continuous function. We will initially need to identify the mathematical function to describe position, or velocity, or acceleration for that first time period. Next we take derivatives to move from position to velocity to acceleration or take integrals to move from acceleration to velocity to position. Whenever we take an integral, we need to remember to include the constant of integration which will represent the initial velocity or the initial position (in the velocity and position equations, respectively).
For the second, third, and any other following sections, we will do much the same process. We will start by identifying an equation for the position, or velocity, or acceleration for that time period. From there we again take derivatives or integrals as appropriate, but now the constants of integration will be a little more complicated. Those constants still represent initial velocities and and positions in a sense, but they will be the velocity and position when \(t=0\), not the velocity and position at the start of that section.
To find the constants of integration, we are instead going to have to use the transition point, which is the point in time where we are moving from one set of equations to the next. Even though the equations are changing, we cannot have an instantaneous jump in either the position or velocity. An instantaneous jump in either position or velocity would require infinite acceleration, which is physically impossible.
To find the velocity equations for the second time frame (or third, fourth, etc.), we start by integrating the acceleration equation for that same time period. This will lead to an equation with an unknown constant of integration. To solve for that constant, we look back to the velocity equation for the previous time frame and solve for the velocity at the very end of this prior time period. Since it can't jump instantaneously, this is also the velocity at the start of the current time period. Using this velocity, along with the time \(t\) at the transition point, we can solve for the last unknown in the current velocity equation (the constant of integration).
To find the position equation for the second time frame (or third, fourth, etc.), we start by integrating the velocity equation for the same time period (you will need to solve for the unknowns in the velocity equation first, as discussed above). After integration, we should have one new constant of integration in the position equation. Just as we did with the velocity equations, we will use the position equation from the prior time frame to solve for the position at the transition point, then use that value along with the known time \(t\) to solve for the unknown constant in the current position equation.
A car accelerates from rest at a rate of 10 m/s 2 for 10 seconds. The car then immediately begins decelerating at a rate of 4 m/s 2 for another 25 seconds before coming to a stop. Find the equations for the acceleration, velocity, and position functions over the full 35-second time period, and plot these functions.
- Solution
A plane with an initial speed of 95 m/s touches down on a runway. For the first second the plane rolls without decelerating. For the next 5 seconds reverse thrust is applied, decelerating the plane at a rate of 4 m/s 2 . Finally, the brakes are applied with reverse thrust increasing the rate of deceleration to 8 m/s 2 . How long does it take for the plane to come to a complete stop? How far does the plane travel before coming to a complete stop?
- Solution
A satellite's motion is described by the velocity function shown below over a sixty-second time period. For that same time period, determine the satellite's acceleration and position functions and draw these functions on a plot.
- Solution


10.17: Introduction to Material Variances
What you’ll learn to do: Discuss different types of material variances
As the production manager at Z-Corp, a manufacturer of computer circuit boards, you are reviewing your direct material costs and notice a variance in the amount spent this year compared to the budgeted amount. Your manager is concerned about this increase and has asked you to analyze it to find out what has happened. You check in with your purchasing department to get some information, and find that not only did you purchase a higher quantity of one particular component for your boards, but strangely, the price for this component was lower than you had budgeted. How could this happen? Your purchasing department purchased at a lower price, but ended up needing to order a larger quantity?
Let’s look at some scenarios and examples of how these types of variances might occur, and what we can do to fix the problem.


6.2: Anti-Vaccination Movement
Vaccines are one of the greatest achievements in the history of medicine and continue to save millions of lives every year. But a persistent group of voices – the anti-vaccination movement – is undermining those public health successes by spreading fear and misinformation . In recent years, cases of vaccine-preventable diseases, such as measles, have started to surge in Canada and some developing countries, due in large part to vaccine hesitancy, which the World Health Organization (WHO) has declared a top global health threat.
To understand the risks posed by anti-vaccination activists and how public health professionals can combat the rising tide of misinformation, it is important to examine how this movement evolved and why the methods of anti-vaccination activists are often effective.
The Roots of Anti-Vaccine Activism
The anti-vaccination movement has been around since the invention of vaccines in the late 1700s when the first successful vaccine was developed for smallpox, an infectious disease that killed three out of every ten infected. Throughout the 19th century, anti-vaccination groups formed and held rallies, protests, and even riots to bring attention to false beliefs about vaccines.
Those early anti-vaccine activists argued the vaccine was unsafe and that focusing on better sanitation and hygiene were the real keys to combatting smallpox. The anti-vaccination advocates were well-organized and gained significant public support, as well as favourable coverage in the media, which hampered the rollout and delivery of vaccination programs.
Points of Consideration
In Canada, the smallpox vaccine was discontinued as a routine immunization in 1972 since vaccination campaigns successfully led to the elimination of endemic smallpox in Canada by 1946. The final laboratory-confirmed case of smallpox in Canada was in 1962 (Government of Canada, 2014). Through worldwide vaccination efforts, naturally occurring smallpox disease was globally eradicated by 1977 (Government of Canada, 2014). When infectious diseases are eradicated worldwide because of vaccines, the vaccination programs can be stopped.
An interactive or media element has been excluded from this version of the text. You can view it online here:
https://ecampusontario.pressbooks.pub/immunizations/?p=186


7.4: Barriers to Listening
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Barriers to effective listening are present at every stage of the listening process (Hargie, 2011). In this section, we will explore how environmental and physical factors, cognitive and personal factors, prejudices, and bad listening practices present barriers to effective listening.
Environmental and Physical Barriers to Listening
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Image: © Joe Decie/ joedecie.com , printed with permission for use in I.C.A.T.)
Environmental factors linked to the physical context, such as lighting, temperature, and furniture, affect our ability to listen. A room that is too dark can make us sleepy, just as a room that is too warm or cool can raise awareness of our physical discomfort to a point that it is distracting. Some seating arrangements facilitate listening, while others separate people. In general, listening is easier when listeners can make direct eye contact with and are in close physical proximity to a speaker. The ability to effectively see and hear a person increases people’s confidence in their abilities to receive and process information. Eye contact and physical proximity can still be affected by noise. Environmental noises such as a whirring air conditioner, barking dogs, or a ringing fire alarm can obviously interfere with listening despite direct lines of sight and well-placed furniture.
Cognitive and Personal Barriers to Listening
Physiological noise linked to the individual context, can also interfere with our ability to process incoming information. This is considered a physical barrier to effective listening because it emanates from our physical body. Physiological noise is noise stemming from a physical illness or injury.
Another type of noise that is part of the individual context, psychological noise, bridges physical and cognitive barriers to effective listening. Psychological noise, or noise stemming from our psychological states including moods and level of arousal, can facilitate or impede listening. Any mood or state of arousal, positive or negative, that is too far above or below our regular baseline creates a barrier to message reception and processing. The generally positive emotional state of being in love can be just as much of a barrier as feeling hatred.
Cognitive limits and personal concerns can interfere with our ability to listen. Whether you call it multitasking, daydreaming, glazing over, or drifting off, we all cognitively process other things while receiving messages. If you think of your listening mind as a wall of ten televisions, you may notice that in some situations five of the ten televisions are tuned into one channel. If that one channel is a lecture being given by your professor, then you are exerting about half of your cognitive processing abilities on one message. In another situation, all ten televisions may be on different channels.
Personal concerns are often the focus of competing thoughts that can take us away from listening and challenge our ability to concentrate on others’ messages. Two common barriers to concentration are self-centeredness and lack of motivation (Brownell, 1993). For example, when our self-consciousness is raised, we may be too busy thinking about how we look, how we’re sitting, or what others think of us to be attentive to an incoming message. Additionally, we are often challenged when presented with messages that we do not find personally relevant. In general, we employ selective attention, which refers to our tendency to pay attention to the messages that benefit us in some way and filter others out.
Bad Messages and/or Speakers
Bad messages also present a barrier to effective listening. Sometimes our trouble listening originates in the sender. In terms of message construction, poorly structured messages or messages that are too vague, too jargon filled, or too simple can present listening difficulties. In terms of speakers’ delivery, verbal fillers, monotone voices, distracting movements, or a disheveled appearance can inhibit our ability to cognitively process a message (Hargie, 2011). Listening also becomes difficult when a speaker tries to present too much information.
Prejudice
Unfortunately, some of our default ways of processing information and perceiving others lead us to rigid ways of thinking. When we engage in prejudiced listening, we are usually trying to preserve our ways of thinking and avoid being convinced of something different. This type of prejudice is a barrier to effective listening, because when we prejudge a person based on their identity or ideas, we usually stop listening in an active and/or ethical way. We exhibit prejudice in our listening in several ways, some of which are more obvious than others. For example, we may claim to be in a hurry and only selectively address the parts of a message that we agree with or that aren’t controversial. We can also operate from a state of denial where we avoid a subject or person altogether so that our views are not challenged. Prejudices that are based on a person’s identity, such as race, age, occupation, or appearance, may lead us to assume that we know what they will say, essentially closing down the listening process.
Bad Listening Practices
(Image: © Cathy Thorne/ www.everydaypeoplecartoons.com ;printed with permission for use in I.C.A.T.)
The previously discussed barriers to effective listening may be difficult to overcome because they are at least partially beyond our control. Physical barriers, cognitive limitations, and perceptual biases exist within all of us, and it is more realistic to believe that we can become more conscious of and lessen them than it is to believe that we can eliminate them altogether. Other “bad listening” practices may be habitual, but they are easier to address with some concerted effort. These bad listening practices include interrupting, distorted listening, and pseudo-listening.
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Interrupting:
Conversations unfold as a series of turns and turn taking is negotiated through a complex set of verbal and nonverbal signals that are consciously and subconsciously received. In this sense, conversational turn taking has been likened to a dance where communicators try to avoid stepping on each other’s toes. One of the most frequent glitches in the turn-taking process is interruption, but not all interruptions are considered “bad listening.” Sometimes interruptions are more like overlapping statements that show support (e.g., “I think so, too.”) or excitement about the conversation (e.g., “That’s so cool!”). Back-channel cues like “uh-huh” also overlap with a speaker’s message. We may also interrupt out of necessity if we’re engaged in a task with the other person and need to offer directions (e.g., “Turn left here.”), instructions (e.g., “Will you whisk the eggs?”), or warnings (e.g., “Look out behind you!”). All these interruptions are not typically thought of as evidence of bad listening unless they become distracting for the speaker or are unnecessary. -
Distorted Listening:
Distorted listening occurs in many ways. Sometimes we just get the order of information wrong, which can have relatively little negative effects if we are casually recounting a story, annoying effects if we forget the order of turns (left, right, left or right, left, right?) in our driving directions, or very negative effects if we recount the events of a crime out of order, which leads to faulty testimony at a criminal trial. Rationalization is another form of distorted listening through which we adapt, edit, or skew incoming information to fit our existing schemata. We may, for example, reattribute the cause of something to better suit our own beliefs. If a professor is explaining to a student why he earned a “D” on his final paper, the student could reattribute the cause from “I didn’t follow the paper guidelines” to “this professor is an unfair grader.” Sometimes we actually change the words we hear to make them better fit what we are thinking. This can easily happen if we join a conversation late, overhear part of a conversation, or are being a lazy listener and miss important setup and context. -
Response Preparation:
Response preparation refers to our tendency to rehearse what we are going to say next while a speaker is still talking. Rehearsal of what we will say once a speaker’s turn is over is an important part of the listening process that takes place between the recalling and evaluation and/or the evaluation and responding stage. Rehearsal becomes problematic when response preparation begins as someone is receiving a message and hasn’t had time to engage in interpretation or recall. In this sense, we are listening with the goal of responding instead of with the goal of understanding, which can lead us to miss important information that could influence our response.
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Pseudo-listening:
Pseudo-listening is behaving as if you’re paying attention to a speaker when you’re actually not (McCornack, 2007). Outwardly visible signals of attentiveness are an important part of the listening process, but when they are just an “act,” the pseudo-listener is engaging in bad listening behaviors. They are not actually going through the stages of the listening process and will likely not be able to recall the speaker’s message or offer a competent and relevant response. Although it is a bad listening practice, we all understandably engage in pseudo-listening from time to time. If a friend needs to talk but you’re really tired or experiencing some other barrier to effective listening, it may be worth engaging in pseudo-listening as a relational maintenance strategy, especially if the friend just needs a sounding board and isn’t expecting advice or guidance. We may also pseudo-listen to a romantic partner or grandfather’s story for the fifteenth time to prevent hurting their feelings.


27.7.9: Practice- Arrays and Lists
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Review Questions
True / False
- The array data type is one of the standard data types in C++.
- Arrays can have more than one dimension.
- For loops are often used to display the members of an array.
- When defining an array, it is preferable to specify how many members are in the array.
- Arrays are rarely used to represent data.
- Linear searches require complex algorithms.
- Functions are often created for searching for the max and min values in an array.
- The bubble sort is an easy way to arrange data an array.
- There is only one method of bubble sorting.
- Sorting an array is frequently done.
Answers:
- false
- true
- true
- false
- false
- false
- true
- true
- false
- true
Short Answer
- Briefly explain what an array is and list the two common operators used with arrays.
- Give a short explanation of bubble sorting.
Activities
Complete the following activities using pseudocode, a flowcharting tool, or your selected programming language. Use separate functions for input, each type of processing, and output. Avoid global variables by passing parameters and returning results. Create test data to validate the accuracy of each program. Add comments at the top of the program and include references to any resources used.
- Review MathsIsFun: Definition of Average . Create a program that asks the user to enter grade scores. Start by asking the user how many scores they would like to enter. Then use a loop to request each score and add it to a static (fixed-size) array. After the scores are entered, calculate and display the high, low, and average for the entered scores.
- Review MathsIsFun: Leap Years . Create a program that asks the user for a year, and then calculate whether or not the given year is a leap year. Build an array where each entry is the number of days in the corresponding month (January = 31, February = 28 or 29 depending on year, March = 31, etc.). Build a parallel string array with the names of each month. Then ask the user to enter a month number, and look up the corresponding month name and number of days and display the information. Continue accepting input and displaying results until the user enters a number less than 1 or greater than 12.
- Review Wikipedia: Zeller’s congruence. Create a program that asks the user for their birthday (year, month, and day) and then calculates and displays the day of the week on which they were born. Use an array lookup to convert the numeric day of the week to the correct string representation (Monday, Tuesday, Wednesday, etc.).
- Review Khan Academy: A guessing game . Write a program that allows the user to think of a number between 0 and 100, inclusive. Then have the program try to guess their number. Start at the midpoint (50) and ask the user if their number is (h)igher, (l)ower, or (e)qual to the guess. If they indicate lower, guess the new midpoint (25). If they indicate higher, guess the new midpoint (75). Record each guess in an an array and continue efficiently guessing higher or lower until they indicate equal, then display the list of guesses required to guess their number and end the program.
- Review Wikipedia: Monty Hall problem. Create a program that uses an array to simulate the three doors. Use 0 (zero) to indicate goats and 1 (one) to indicate the car. Clear each “door” and then use a random number function to put the number 1 in one of the array elements. Then use the random number function to randomly select one of the three elements. Run the simulation in a loop 100 times to confirm a 1/3 chance of winning. Then run the simulation again, this time switching the selection after a 0 (goat) is removed from the remaining choices. Run the simulation in a loop 100 times to confirm a 2/3 chance of winning by switching.
- If your programming language supports it, use a built-in sort function to sort the grade scores from the activity above and display the array in order from highest score to lowest score.
- If your programming language supports it, update one or more of the programs above to replace the static array with a dynamic array, and extend the array as each item is added to the array. Continue accepting scores until the user enters no value (empty input).
References
- cnx.org: Programming Fundamentals – A Modular Structured Approach using C++
- Wikiversity: Computer Programming