7.9: Does the Militarization of Police Contribute to Use of Force Issues? One Study Finds Yes
On June 19, 2018, a rookie police officer in suburban Pittsburgh, Pennsylvania, stopped a silver Chevy Cruz that matched the description of a vehicle involved in an earlier crime. While the driver exited the car and got on the ground, 17-year-old Antwan Rose and another passenger ran. The officer fired three shots at Rose, striking him with all three. He died in hospital.
The basic storyline of this incident is all too familiar now: a police officer (or several) confronts a civilian with suspicion of some wrongdoing. The civilian fails to comply, actively resists, or simply moves too quickly and is killed. In the case of the 2016 shooting death of Philando Castile in Minnesota, a police officer—again during a traffic stop, this time for a broken brake light—drew his weapon and fired six times as Castile reached for his driver’s license. Similar to Antwan Rose, on March 18th in California, Stephon Clark fled police on foot, but eventually surrendered. A police officer shot him after mistaking his phone—which was in his hand, raised above his head—for a gun.
Why do some police officers resort to lethal force so quickly? Why do police kill, even in situations where their lives—or the lives of others—do not seem to be in danger? The militarization of American law enforcement has become the topic of much discussion—among scholars, in the media, and in the general public—over the last several years, and has become the target of those who desire reforms to reduce the number of civilian deaths. However, most of the scholarship on militarization is limited, either focusing on certain specific behaviors that result from militarization, on the existence of police Special Response Teams (also known as Special Weapons and Tactics or SWAT teams) as a way to capture the spread of militarization, or on county-level, but geographically narrow and theoretically limited, use of federal programs that allow police departments to acquire surplus military equipment.
In new research, I argue that militarization is a psychological process that affects individual officers as well as departments. This process involves the adoption of a more militaristic world view, where militarism is the emphasis on the use of force as an acceptable—or even desirable—option to address problems. Militarization may affect the behavior of individual officers in one, or both, or two ways.
To learn more about differences and similarities in police and military functionality, watch this video: why the police look and act like the military .
*If you are accessing a print version of this book, type the following short url into your browser to visit this source: bit.ly/3xJzYZ1
Imagine that, when a police officer encounters a civilian or suspect, every possible action that officer may take is on a continuum from least to most violent. Of course, not every possible action is legally or morally acceptable, so on that continuum, there is a window of options the officer believes to be acceptable choices for initiating the encounter. From that window, the officer picks an initial action. If the civilian complies, the process ends. If the civilian resists, the officer escalates, moving more to the violent end of the continuum with each action until reaching a resolution. Militarization either moves the window of acceptable options toward the most violent side, moves the officer’s initial choice of action within that window toward the more violent side, or both. The result is that officers reach lethal force more quickly.
Militarized police departments see themselves not as public servants upholding the law, but as an army fighting a war against a dangerous and invisible enemy and occupying territory that is hostile to them. To carry out these actions, the leaders of those departments desire military equipment—vehicles, weapons, body armor, and so forth—because it provides better protection from the enemy and promotes both more efficient use of force and more fear among the public. And, when departments are more militarized, their officers should kill more people.
My statistical analysis supports this argument, controlling for other possible drivers of police killings such as the racial composition of the area, the total population, the level of poverty, and the rate of violent crime, using cross-national data that includes law enforcement agencies from over 40 states quarterly from the last quarter of 2014 to the last quarter of 2016. I find that, as a police department’s militarization increases, so does the number of civilians killed.
Figure 1 displays the expected number of police killings at varying levels of militarization, which I measure using police department acquisitions through the federal ‘1033’ program. This is a program that allows law enforcement agencies to obtain surplus military equipment from the federal government, paying only the cost of transport. Think of it as a backward Amazon Prime: the item is free, but they pay for shipping. I obtained data on the number of civilians killed by police for this period from Fatal Encounters, a project collecting information about victims of police violence since 2000.


2.2.19: Walt Whitman (1819-1892)
Song of Myself Crossing Brooklyn Ferry Out of the Cradle, Endlessly Rocking O Captain, My Captain Walt Whitman was born on Long Island, New York. His family moved to Brooklyn in 1823, when young Whitman was four. He attended public school, but left when he was 12 to learn the printing trade. At this time, he also worked as a reporter for the Long Island Patriot . Due to a fire in the printing district of New York, Whitman was forced to seek employment as a rural school teacher. While he was like by students, he often clashed with those in charge of educational system. He returned to New York in 1841. By 1846, he became the editor of the Brooklyn Daily Eagle , an important newspaper. However, Brooklyn Daily Eagle fired Whitman two years later, due to his growing political activism and support of abolishing slavery. Afterwards, he worked in New Orleans as the editor the Crescent City newspaper for a brief period of time. His trip there cemented his support for abolishing slavery. Upon his return to New York, Whitman attended lectures by prominent thinkers, such as Ralph Waldo Emerson. Emerson's work was particularly inspirational for Whitman, who embraced Emerson's idea of Transcendentalism in his work "Song of Myself" from Leaves of Grass (1855-1892) . During the Civil War started, Whitman served as a nurse. After the war, Whitman enjoyed some success for his work on Abraham Lincoln and from his published poetry. However, his writing was experimental in nature, and often contained erotic elements that garnered him harsh criticism. His most influential collection is Leaves of Grass , which he continued to revise and republish until his death. From that work, "Song of Myself" is seen as the hallmark piece. In this poem, Whitman introduced his free verse style that would transform American poetry. He experiments with repetition and catalogues to communicate his ideas. "Out of the Cradle, Endlessly Rocking" appeared in the 1860 collection of Leaves of Grass. The poem uses nature imagery to document the speaker's transformation into a poet. Whitman focuses on nature and brotherhood in "Crossing Brooklyn Ferry," which appeared in the 1856 edition of Leaves of Grass . The poem expresses Whitman's concept of his feeling of oneness with the world that transcends time. One of his more traditional works in terms of meter and form is "O Captain, My Captain," which first appeared in the 1865 edition of Leaves of Grass . Easily Whitman's most popular poem in his lifetime, this elegy conceptualizes President Abraham Lincoln as the captain of ship. Whitman's continued process of refining and reinventing his poems cemented his reputation as an influential literary and cultural figure in America. Consider while reading:
- How does Whitman use prosody to underscore the meaning in his poems?
- What is the significance of Whitman's use of nature?
- Whitman was influenced by Emerson's ideas of the enlightened poet. How and where does he use this idea in "Song of Myself"?
- What is effect of Whitman using lists in his poetry?
Written by Laura Ng


3.5.2: Primate Skeletal Anatomy
-
- Last updated
- Save as PDF
The study of bones is called osteology . It is necessary to have a basic understanding of the skeletal anatomy since the data used in the study of primate and human evolution is based on fossilized bones. The information presented here focuses on the human skeleton. Human beings have an endoskeleton , which means that the skeletal structure is on the inside of the body. The endoskeleton grows along with the rest of the body. Endoskeletons are lighter than exoskeletons (skeletal system on the outside of the body), which allowed for the evolution of large vertebrate animals. The endoskeleton is comprised of bone. Bone has three structural parts:
- Compact bone (periosteum): dense outer layer
- Spongy bone: light, softer inner layer
- Marrow: fills the inside core and makes red and white blood cells.
For the skeletal system to work properly it must have ligaments that connect the bone at the joints, muscles connected to the bones with tendons that allow for movement of the bone, and cartilage that fills the spaces between the bones, preventing them from scraping against one another.
Human infants have 270 bones, several of which fuse together during growth so that adult humans have 206 bones. The skeleton is divided into two categories: the axial skeleton and the appendicular skeleton. The axial skeleton is comprised of the vertebral column, ribs, sternum, and skull.
Figure \(\PageIndex{1}\) - Axial Skeleton
The human skull has a number of bones. These bones were seperate at birth and then fuse together as an individual ages.
Figure \(\PageIndex{2}\) - Human skull bones (simplified)
Figure \(\PageIndex{3}\) - Human skull front bones (simplified)
The appendicular skeleton is composed of the shoulder girdle, upper limbs, pelvic girdle, and the lower limbs.
Figure \(\PageIndex{4}\) - Appendicular Skeleton
Function of Bone
Bones function to:
- give structural support to the body
- protect vital organs
- provide an environment for the production of red blood cells
- store minerals like calcium
- aid in movement of the body
Bone Types
There are four types of bones based on shape.
- Long bones: long central shaft (diaphysis) and two knobby ends (epiphysis); e.g., femur
- Short bones: about as long as wide; e.g., patella
- Flat bones: characterized by being relatively thin and flat, e.g., sternum
- Irregular bones: odd-shaped bones; e.g., vertebrae
Bones can also be classified based on their origin and texture, but for the purposes of this class you need only be familiar with the types based on shape.
You should spend some time on the website eSkeletons in order to familiarize yourself with the look of the various bones listed above in the different primates.
Types of Bone Cells
- Osteoblast: forms new bone tissue
- Osteoclast: absorbs and removes unwanted tissue
- Osteocyte: maintains bone as living tissue
- Hematopoietic: produces red blood cells
References
- Carnagie J, Bruno LC, editors. 2001. Skeletal system. Detroit (MI): UXL. p. 538-542. (UXL Complete Life Science Resource; vol. 3).
- Martin EL. Skeletal system. In: Lerner KL , Lerner BW, editors. The Gale Encyclopedia of Science, 5th edition, Vol. 7. Farmington Hills (MI): Gale; 2014. p. 3975-3981.
- University of Chicago Medicine. c2015. Anatomy of the bone. The University of Chicago Medical Center [Internet] [cited 2015 Aug 2]. Available from: www.uchospitals.edu/online-library/content=P00109
Study Guide
Figure \(\PageIndex{5}\) - Human skeleton diagram
Print this blank image to make your own study guide of the human skeleton


4.2A: Characteristics of Epithelial Tissue
The human body consists of four types of tissue: epithelial, connective, muscular, and nervous. Epithelial tissue covers the body, lines all cavities, and composes the glands.
- Describe the primary functions and characteristics of epithelial tissue
Key Points
- Epithelial tissue is composed of cells laid together in sheets with the cells tightly connected to one another. Epithelial layers are avascular, but innervated.
- Epithelial cells have two surfaces that differ in both structure and function.
- Glands, such as exocrine and endocrine, are composed of epithelial tissue and classified based on how their secretions are released.
Key Terms
- epithelium : A membranous tissue composed of one or more layers of cells that form the covering of most internal and external surfaces of the body and its organs.
- avascular : Lacking blood vessels.
- vascular : Containing blood vessels.
Functions of the Epithelium
Epithelia tissue forms boundaries between different environments, and nearly all substances must pass through the epithelium. In its role as an interface tissue, epithelium accomplishes many functions, including:
- Protection for the underlying tissues from radiation, desiccation, toxins, and physical trauma.
- Absorption of substances in the digestive tract lining with distinct modifications.
- Regulation and excretion of chemicals between the underlying tissues and the body cavity.
- The secretion of hormones into the blood vascular system. The secretion of sweat, mucus, enzymes, and other products that are delivered by ducts come from the glandular epithelium.
- The detection of sensation.
Characteristics of Epithelial Layers
Epithelial tissue is composed of cells laid out in sheets with strong cell-to-cell attachments. These protein connections hold the cells together to form a tightly connected layer that is avascular but innervated in nature.
The epithelial cells are nourished by substances diffusing from blood vessels in the underlying connective tissue. One side of the epithelial cell is oriented towards the surface of the tissue, body cavity, or external environment and the other surface is joined to a basement membrane. The basement layer is non-cellular in nature and helps to cement the epithelial tissue to the underlying structures.
Types of Epithelial Tissue
Epithelial tissues are identified by both the number of layers and the shape of the cells in the upper layers. There are eight basic types of epithelium: six of them are identified based on both the number of cells and their shape; two of them are named by the type of cell (squamous) found in them. Epithelial tissue is classified based on the number of cells, the shape of those cells, and the types of those cells.
| Epithelial Tissue Cells | ||
|---|---|---|
| Cells | Locations | Function |
|
Simple squamous epithelium
|
Air sacs of the lungs and the lining of the heart, blood vessels and lymphatic vessels | Allows materials to pass through by diffusion and filtration, and secretes lubricating substances |
|
Simple cuboidal epithelium
|
In ducts and secretory portions of small glands and in kidney tubules | Secretes and absorbs |
|
Simple columnar epithelium
|
Ciliated tissues including the bronchi, uterine tubes, and uterus; smooth (nonciliated tissues) are in the digestive tract bladder | Absorbs; it also secretes mucous and enzymes. |
|
Pseudostratified columnar epithelium
|
Ciliated tissue lines the trachea and much of the upper respiratory tract | Secrete mucous; ciliated tissue moves mucous |
|
Stratified squamous epithelium
|
Lines the esophagus, mouth, and vagina | Protects against abrasion |
|
Stratified cuboidal epithelium
|
Sweat glands, salivary glands, and mammary glands | Protective tissue |
|
Stratified columnar epithelium
|
The male urethra and the ducts of some glands. | Secretes and protects |
|
Transitional epithelium
|
Lines the bladder, urethra and ureters | Allows the urinary organs to expand and stretch |


2.1: Overview of Transcription
Learning Objectives
- Identify the key steps of transcription, the function of the promoter and the function of RNA polymerase.
- Distinguish between coding (RNA-like) and non-coding (template) strands of DNA. Understand that within a single piece of DNA, either strand can be used as the template for different genes, but the RNA will still be produced from 5’ → 3’.
- Draw a line diagram showing a segment of DNA from a gene and its RNA transcript, indicating which DNA strand is the template, the direction of transcription and the polarities of all DNA and RNA strands.
- Give examples of non-coding RNA molecules.
What is transcription?
Consider that all of the cells in a multicellular organism have arisen by division from a single fertilized egg and therefore, all have the same DNA. Division of that original fertilized egg produces, in the case of humans, over a trillion cells, by the time a baby is produced from that egg (that's a lot of DNA replication!). Yet, we also know that a baby is not a giant ball of a trillion identical cells, but has the many different kinds of cells that make up tissues like skin and muscle and bone and nerves. How did cells that have identical DNA turn out so different?
The answer lies in gene expression, which is the process by which the information in DNA is used. Although all the cells in a baby have the same DNA, each different cell type uses a different subset of the genes in that DNA to direct the synthesis of a distinctive set of RNAs and proteins. The first step in gene expression is transcription, the process of copying information from DNA sequences into RNA sequences. This process is also known as DNA-dependent RNA synthesis. When a sequence of DNA is transcribed, only one of the two DNA strands is copied into RNA, when this RNA encodes a protein is it known as messenger RNA (mRNA).
Important features of transcription
- All RNA, mRNA as well as tRNA, rRNA, microRNA and more, is produced by transcription.
- Only one strand of DNA is used as a template by enzymes called RNA polymerases
- RNA is synthesized from 5' to 3'.
- RNA polymerases do not need primers to begin transcription.
- The four ribonucleotide triphosphates (rNTPs) are ATP, GTP, UTP, and CTP.
- RNA polymerases begin transcription at DNA sequences called promoters.
- RNA polymerases end transcription at sequences called terminators.
In transcription, an RNA polymerase uses only one strand of DNA, called the template strand, of a gene to catalyze synthesis of a complementary, antiparallel RNA strand. RNA polymerases use ribose nucleotide triphosphate (NTP) precursors, in contrast to DNA polymerases, which use deoxyribose nucleotide (dNTP) precursors (compared on page 1.1: The Structure of DNA ). In addition, RNAs incorporate uracil (U) nucleotides into RNA strands instead of the thymine (T) nucleotides used in DNA. RNA polymerases differ from DNA polymerases in that they do not require primers. With the help of transcription initiation factors, RNA polymerase locates the transcription start site of a gene and begins synthesis of a new RNA strand from scratch by joining the two ribonucleotides that are complementary to the first two bases of the template strand.
Overview of the Stages of Transcription
The basic steps of transcription are initiation, elongation, and termination. Here we can identify several of the DNA sequences that characterize a gene. The promoter is the binding site for RNA polymerase. It usually lies 5’ to, or upstream of the transcription start site. Binding of the RNA polymerase positions the enzyme to near the transcription start site, where it will start unwinding the double helix and begin synthesizing new RNA. The transcribed grey DNA region in each of the three panels are the transcription unit of the gene. Termination sites are typically 3’ to, or downstream from the transcribed region of the gene. By convention, upstream refers to DNA 5’ to a given reference point on the DNA (e.g., the transcription start-site of a gene). Downstream then, refers to DNA 3’ to a given reference point on the DNA.
RNA polymerase
Building an RNA strand is very similar to building a DNA strand. This is not surprising, knowing that DNA and RNA are very similar molecules. What enzyme carries out transcription? Transcription is catalyzed by the enzyme RNA Polymerase. "RNA polymerase" is a general term for an enzyme that makes RNA. There are many different RNA polymerases.
Like DNA polymerases, RNA polymerases synthesize new strands only in the 5' to 3' direction, but because they are making RNA, they use ribonucleotides (i.e., RNA nucleotides) rather than deoxyribonucleotides. Ribonucleotides are joined in exactly the same way as deoxyribonucleotides, which is to say that the 3'OH of the last nucleotide on the growing chain is joined to the 5' phosphate on the incoming nucleotide.
One important difference between DNA polymerases and RNA polymerases is that the latter do not require a primer to start making RNA. Once RNA polymerases are in the right place to start copying DNA, they just begin making RNA by stringing together RNA nucleotides complementary to the DNA template.
This, of course, brings us to an obvious question- how do RNA polymerases "know" where to start copying on the DNA. Unlike the situation in replication, where every nucleotide of the parental DNA must eventually be copied, transcription, as we have already noted, only copies selected genes into RNA at any given time.What indicates to an RNA polymerase where to start copying DNA to make a transcript? Signals in DNA indicate to RNA polymerase where it should start (and end) transcription. These signals are special sequences in DNA that are recognized by the RNA polymerase or by proteins that help RNA polymerase determine where it should bind the DNA to start transcription. A DNA sequence at which the RNA polymerase binds to start transcription is called a promoter.
A promoter is generally situated upstream of the gene that it controls. What this means is that on the DNA strand that the gene is on, the promoter sequence is "before" the gene. Remember that, by convention, DNA sequences are read from 5' to 3'. So the promoter lies 5' to the start point of transcription.
Also notice that the promoter is said to "control" the gene it is associated with. This is because expression of the gene is dependent on the binding of RNA polymerase to the promoter sequence to begin transcription. If the RNA polymerase and its helper proteins do not bind the promoter, the gene cannot be transcribed and it will therefore, not be expressed.
What is special about a promoter sequence? In an effort to answer this question, scientists looked at many genes and their surrounding sequences. It makes sense that because the same RNA polymerase has to bind to many different promoters, the promoters should have some similarities in their sequences. Sure enough, common sequence patterns were seen to be present in many promoters. We will first take a look at prokaryotic promoters. When prokaryotic genes were examined, the following features commonly emerged:
- A transcription start site (this the base in the DNA across from which the first RNA nucleotide is paired).
- A -10 sequence: this is a 6 bp region centered about 10 bp upstream of the start site. The consensus sequence at this position is TATAAT. In other words, if you count back from the transcription start site, which by convention, is called the +1, the sequence found at -10 in the majority of promoters studied is TATAAT).
- A -35 sequence: this is a sequence at about 35 basepairs upstream from the start of transcription. The consensus sequence at this position is TTGACA.
What is the significance of these sequences? It turns out that the sequences at -10 and -35 are recognized and bound by a subunit of prokaryotic RNA polymerase before transcription can begin.
The RNA polymerase of E. coli, for example, has a subunit called the sigma (σ) subunit (or sigma factor) in addition to the core polymerase, which is the part of the enzyme that actually makes RNA. Together, the sigma subunit and core polymerase make up what is termed the RNA polymerase holoenzyme . The sigma subunit of the polymerase can recognize and bind to the -10 and -35 sequences in the promoter, thus positioning the RNA polymerase at the right place to initiate transcription. Once transcription begins, the core polymerase and the sigma subunit separate, with the core polymerase continuing RNA synthesis and the sigma subunit wandering off to escort another core polymerase molecule to a promoter. The sigma subunit can be thought of as a sort of usher that leads the polymerase to its "seat" on the promoter.
As already mentioned, an RNA chain, complementary to the DNA template, is built by the RNA polymerase by the joining of the 5' phosphate of an incoming ribonucleotide to the 3'OH on the last nucleotide of the growing RNA strand. How does the polymerase know where to stop? A sequence of nucleotides called the terminator is the signal to the RNA polymerase to stop transcription and dissociate from the template.
Although the process of RNA synthesis is the same in eukaryotes as in prokaryotes, there are some additional issues to keep in mind in eukaryotes. One is that in eukaryotes, the DNA template exists as chromatin, where the DNA is tightly associated with histones and other proteins. The "packaging" of the DNA must therefore be opened up to allow the RNA polymerase access to the template in the region to be transcribed.
A second difference is that eukaryotes have multiple RNA polymerases, not one as in bacterial cells. The different polymerases transcribe different genes. For example, RNA polymerase I transcribes the ribosomal RNA genes, while RNA polymerase III copies tRNA genes. The RNA polymerase we will focus on most is RNA polymerase II, which transcribes protein-coding genes to make mRNAs.
All three eukaryotic RNA polymerases need additional proteins to help them get transcription started. In prokaryotes, RNA polymerase by itself can initiate transcription (remember that the sigma subunit is a subunit of the prokaryotic RNA polymerase). The additional proteins needed by eukaryotic RNA polymerases are referred to as transcription factors.
Finally, in eukaryotic cells, transcription is separated in space and time from translation. Transcription happens in the nucleus, and the mRNAs produced are processed further before they are sent into the cytoplasm. Protein synthesis (translation) happens in the cytoplasm. In prokaryotic cells, mRNAs can be translated as they are coming off the DNA template, and because there is no nucleus, transcription and protein synthesis occur in a single cellular compartment.
Like genes in prokaryotes, eukaryotic genes also have promoters. Eukaryotic promoters commonly have a TATA box, a sequence about 25 base pairs upstream of the start of transcription that is recognized and bound by proteins that help the RNA polymerase to position itself correctly to begin transcription. (Some eukaryotic promoters lack TATA boxes, and have, instead, other recognition sequences to help the RNA polymerase find the spot on the DNA where it spot on the DNA where it binds and initiates transcription.)
We noted earlier that eukaryotic RNA polymerases need additional proteins to bind promoters and start transcription. What are these additional proteins that are needed to start transcription? General transcription factors are proteins that help eukaryotic RNA polymerases find transcription start sites and initiate RNA synthesis. We will focus on the transcription factors that assist RNA polymerase II. These transcription factors are named TFIIA, TFIIB and so on (TF= transcription factor, II=RNA polymerase II, and the letters distinguish individual transcription factors).
Transcription in eukaryotes requires the general transcription factors and the RNA polymerase to form a complex at the TATA box called the basal transcription complex or transcription initiation complex. This is the minimum requirement for any gene to be transcribed. The first step in the formation of this complex is the binding of the TATA box by a transcription factor called the TATA Binding Protein or TBP. Binding of the TBP causes the DNA to bend at this spot and take on a structure that is suitable for the binding of additional transcription factors and RNA polymerase. As shown in the figure at left, a number of different general transcription factors, together with RNA polymerase (Pol II) form a complex at the TATA box.
The final step in the assembly of the basal transcription complex is the binding of a general transcription factor called TFIIH. TFIIH is a multifunctional protein that has helicase activity (i.e., it is capable of opening up a DNA double helix) as well as kinase activity. The kinase activity of TFIIH adds a phosphate onto the C-terminal domain (CTD) of the RNA polymerase. This phosphorylation appears to be the signal that releases the RNA polymerase from the basal transcription complex and allows it to move forward and begin transcription.
Either DNA strand can be a template
The promoter is the sequence of DNA that encodes the information about where to begin transcription for each gene. Depending on the promoter, either strand of DNA can be used as the template strand.
Watch this video to see how either strand of DNA can be used as a template for different genes on the same chromosome.
template vs. non-template strands summary
- The template strand is the one that RNA polymerase uses as the basis to build the RNA. This strand is also called the non-coding strand or the antisense strand.
- The non-template strand has the identical sequence of the RNA (except for the substituion of U for T). This strand is also called the coding strand or sense strand .
Major Types of Cellular RNA
Cells make several different kinds of RNA:
- mRNAs that code for proteins
- rRNAS that form part of ribosomes
- tRNAs that serve as adaptors between mRNA and amino acids during translation
- MicroRNAs that regulate gene expression
- Other small RNAs that have a variety of functions.


23.3: Cytotoxic T Cells and Superantigens
-
- Last updated
- Save as PDF
- Ying Liu
- City College of San Francisco
Learning Objectives
- Compare and contrast the activation of helper T cells and cytotoxic T cells (CTLs)
- Describe the mechanism of CTL-mediated destruction of infected cells
- Define superantigens and give some examples
Activation and Differentiation of Cytotoxic T Cells
Cytotoxic T cells (also referred to as cytotoxic T lymphocytes, or CTLs ) are activated by APCs in a three-step process similar to that of helper T cells. The key difference is that the activation of cytotoxic T cells involves recognition of an antigen presented with MHC I (as opposed to MHC II) and interaction of CD8 (as opposed to CD4) with the receptor complex. After the successful co-recognition of foreign epitope and self-antigen, the production of cytokines by the APC and the cytotoxic T cell activate clonal proliferation and differentiation. Activated cytotoxic T cells can differentiate into effector cytotoxic T cells that target pathogens for destruction or memory cells that are ready to respond to subsequent exposures.
As noted, proliferation and differentiation of cytotoxic T cells is also stimulated by cytokines secreted from T H 1 cells activated by the same foreign epitope. The co-stimulation that comes from these T H 1 cells is provided by secreted cytokines. Although it is possible for activation of cytotoxic T cells to occur without stimulation from T H 1 cells, the activation is not as effective or long-lasting.
Once activated, cytotoxic T cells serve as the effector cells of cellular immunity, recognizing and kill cells infected with intracellular pathogens through a mechanism very similar to that of NK cells. However, whereas NK cells recognize nonspecific signals of cell stress or abnormality, cytotoxic T cells recognize infected cells through antigen presentation of pathogen-specific epitopes associated with MHC I. Once an infected cell is recognized, the TCR of the cytotoxic T cell binds to the epitope and releases perforin and granzymes that destroy the infected cell (Figure \(\PageIndex{6}\)). Perforin is a protein that creates pores in the target cell, and granzymes are proteases that enter the pores and induce apoptosis. This mechanism of programmed cell death is a controlled and efficient means of destroying and removing infected cells without releasing the pathogens inside to infect neighboring cells, as might occur if the infected cells were simply lysed.
Query \(\PageIndex{1}\)
Superantigens and Unregulated Activation of T Cells
When T cell activation is controlled and regulated, the result is a protective response that is effective in combating infections. However, if T cell activation is unregulated and excessive, the result can be a life-threatening. Certain bacterial and viral pathogens produce toxins known as superantigens (see Virulence Factors of Bacterial and Viral Pathogens ) that can trigger such an unregulated response. Known bacterial superantigens include toxic shock syndrome toxin (TSST), staphylococcal enterotoxins, streptococcal pyrogenic toxins, streptococcal superantigen, and the streptococcal mitogenic exotoxin. Viruses known to produce superantigens include Epstein-Barr virus (human herpesvirus 4), cytomegalovirus (human herpesvirus 5), and others.
The mechanism of T cell activation by superantigens involves their simultaneous binding to MHC II molecules of APCs and the variable region of the TCR β chain. This binding occurs outside of the antigen-binding cleft of MHC II, so the superantigen will bridge together and activate MHC II and TCR without specific foreign epitope recognition (Figure \(\PageIndex{7}\)). The result is an excessive, uncontrolled release of cytokines, often called a cytokine storm, which stimulates an excessive inflammatory response. This can lead to a dangerous decrease in blood pressure, shock, multi-organ failure, and potentially, death.
Query \(\PageIndex{1}\)
Case in Point: Superantigens
Melissa, an otherwise healthy 22-year-old woman, is brought to the emergency room by her concerned boyfriend. She complains of a sudden onset of high fever, vomiting, diarrhea, and muscle aches. In her initial interview, she tells the attending physician that she is on hormonal birth control and also is two days into the menstruation portion of her cycle. She is on no other medications and is not abusing any drugs or alcohol. She is not a smoker. She is not diabetic and does not currently have an infection of any kind to her knowledge.
While waiting in the emergency room, Melissa’s blood pressure begins to drop dramatically and her mental state deteriorates to general confusion. The physician believes she is likely suffering from toxic shock syndrome (TSS). TSS is caused by the toxin TSST-1, a superantigen associated with Staphylococcus aureus , and improper tampon use is a common cause of infections leading to TSS. The superantigen inappropriately stimulates widespread T cell activation and excessive cytokine release, resulting in a massive and systemic inflammatory response that can be fatal.
Vaginal or cervical swabs may be taken to confirm the presence of the microbe, but these tests are not critical to perform based on Melissa’s symptoms and medical history. The physician prescribes rehydration, supportive therapy, and antibiotics to stem the bacterial infection. She also prescribes drugs to increase Melissa’s blood pressure. Melissa spends three days in the hospital undergoing treatment; in addition, her kidney function is monitored because of the high risk of kidney failure associated with TSS. After 72 hours, Melissa is well enough to be discharged to continue her recovery at home.
Exercise \(\PageIndex{6}\)
In what way would antibiotic therapy help to combat a superantigen?
Key Concepts and Summary
- Once activated, cytotoxic T cells target and kill cells infected with intracellular pathogens. Killing requires recognition of specific pathogen epitopes presented on the cell surface using MHC I molecules. Killing is mediated by perforin and granzymes that induce apoptosis.
- Superantigens are bacterial or viral proteins that cause a nonspecific activation of helper T cells, leading to an excessive release of cytokines ( cytokine storm ) and a systemic, potentially fatal inflammatory response.


20.3D: Lymphocytes
A lymphocyte is a type of white blood cell in the vertebrate immune system.
- Describe the role of lymphocytes
Key Points
- The main types of T cells are helper T cells, cytotoxic T cells, memory T cells, and regulatory T cells.
- The main types of B cells are plasma cells, plasmablasts, memory B cells, and regulatory B cells.
- T cells are involved in cell-mediated immunity, whereas B cells are primarily responsible for humoral ( antibody -related) immunity.
- If an antigen is detected again after the initial adaptive immune response, memory T cells create new helper and cytotoxic T cells, while memory B cells create new antibodies.
- Regulatory T and B cells suppress immune responses at the end of an infection and suppress T and B cells involved in autoimmunity.
Key Terms
- Memory T cells : A type of T cell that rapidly differentiates into helper and cytotoxic T cells if its associated antigen is detected.
- Plasma Cell : A type of B cell that produces most of the antibodies during development of adaptive immune response.
A lymphocyte is a type of white blood cell in the immune system, including both the B and T cells of the adaptive immune system and natural killer (NK) cells of the innate immune system.
B and T cells and their various subdivisions perform many adaptive immune functions.
T Cells
T cells mature in the thymus and contain T cell receptors (TCRs) that allow them to bind to antigens on MHC complexes. T cells are a major component in cell-mediated adaptive immunity because they provide a pathway for the direct killing of pathogens. There are two main types of T cells that express either CD4 or CD8 depending on signals that occur during T cell maturation, as well as less common types:
- Helper T cells (CD4s) facilitate the organization of immune responses, and can bind to MHC class II. Subtype 2 helper T cells present antigens to B cells. Subtype 1 helper T cells produce cytokines that guide cytotoxic T cells to pathogens and activate macrophages.
-
Cytotoxic T cells (CD8s) destroy pathogens associated with an
antigen. They function similarly to NK cells by binding to
MHC class I and releasing perforin, granzymes, and proteases to induce apoptosis in a pathogen. They are different from NK cells because they only bind to
cells that express their specific antigen, and are not large or granular like NK cells. - Suppressor T cells (T-reg cells) retain some of their ability to bind to self-cells. They have an immunosuppressive effect that inhibits cell-mediated immunity at the end of a response and destroys autoimmune T cells that aren’t filtered out by negative selection in the thymus.
- Memory T cells are created after an adaptive immune response subsides, retaining the presented antigen. They rapidly proliferate and differentiate into helper and cytotoxic T cells that are specific to that antigen should it be detected in the body again.
While these are the main categories of T lymphocytes, there are other subtypes within these categories as well as additional categories that are not fully understood.
B Cells
Lymphocyte : A scanning electron microscope (SEM) image of a single human lymphocyte.
B cells are involved in humoral adaptive immunity, producing the antibodies that circulate through the plasma. They are produced and mature in bone marrow tissues and contain B cell receptors (BCRs) that bind to antigens. While in the bone marrow, B cells are sorted through positive and negative selection in a manner somewhat similiar to T cell maturation in the thymus, with the same process of killing B cells that are nonreactive to antigens or reactive to self-antigens.  Mature B cells leave the thymus and travel to secondary lymphoid tissue such as the lymph nodes.
During antigen presentation, antigen-presenting cells first present antigens to T cells. Then mature helper T cells bind their antigen to naive B cells through BCRs. After antigen presentation, the naive B cells migrate together to germinal centers within the lymphoid tissue, where they undergo extensive proliferation and differentiation into different types of mature B cells. Some of the major categories of B cells that arise include:
- Plasma cell and long-lived B cells that are the main source of antibodies. They do not have the ability to proliferate and are considered terminally-differentiated.
- Plasmablasts are short-lived B cells produced early in an infection. Their antibodies have a weaker binding affinity than those of plasma cells.
- Regulatory B cells (B reg cells) are immunosuppresive B cells that secrete anti-inflammatory cytokines (such as IL-10) to inhibit autoimmune lymphocytes.
- Memory B cells are dormant B cells with the same BCR as the B cell from which they differentiated. They are specific to the antigen presented to that BCR and rapidly secrete large amounts of antigen-specific antibodies to prevent reinfection if that antigen is detected again.
Besides antibody production, B cells may also function in antigen presentation, though not to the degree of macrophages or dendritic cells. B cells are important to adaptive immune function but can cause problems as well. Autoreactive B cells may cause autoimmune disease that involves antibody-induced damage and inflammation. Certain B cells may undergo malignant tranformation into cancer cells such as lymphoma, in which they continually divide and form solid tumors.


29.6: What Is the Universe Really Made Of?
By the end of this section, you will be able to:
- Specify what fraction of the density of the universe is contributed by stars and galaxies and how much ordinary matter (such as hydrogen, helium, and other elements we are familiar with here on Earth) makes up the overall density
- Describe how ideas about the contents of the universe have changed over the last 50 years
- Explain why it is so difficult to determine what dark matter really is
- Explain why dark matter helped galaxies form quickly in the early universe
- Summarize the evolution of the universe from the time the CMB was emitted to the present day
The model of the universe we described in the previous section is the simplest model that explains the observations. It assumes that general relativity is the correct theory of gravity throughout the universe. With this assumption, the model then accounts for the existence and structure of the CMB; the abundances of the light elements deuterium, helium, and lithium; and the acceleration of the expansion of the universe. All of the observations to date support the validity of the model, which is referred to as the standard (or concordance) model of cosmology.
Figure 29.21 and Table 29.2 summarize the current best estimates of the contents of the universe. Luminous matter in stars and galaxies and neutrinos contributes about 1% of the mass required to reach critical density. Another 4% is mainly in the form of hydrogen and helium in the space between stars and in intergalactic space. Dark matter accounts for about an additional 27% of the critical density. The mass equivalent of dark energy (according to E = mc 2 ) then supplies the remaining 68% of the critical density.
| Object | Density as a Percent of Critical Density |
|---|---|
| Luminous matter (stars, etc.) | <1 |
| Hydrogen and helium in interstellar and intergalactic space | 4 |
| Dark matter | 27 |
| Equivalent mass density of the dark energy | 68 |
This table should shock you. What we are saying is that 95% of the stuff of the universe is either dark matter or dark energy—neither of which has ever been detected in a laboratory here on Earth. This whole textbook, which has focused on objects that emit electromagnetic radiation, has generally been ignoring 95% of what is out there. Who says there aren’t big mysteries yet to solve in science!
Figure 29.22 shows how our ideas of the composition of the universe have changed over just the past three decades. The fraction of the universe that we think is made of the same particles as astronomy students has been decreasing steadily.
What Is Dark Matter?
Many astronomers find the situation we have described very satisfying. Several independent experiments now agree on the type of universe we live in and on the inventory of what it contains. We seem to be very close to having a cosmological model that explains nearly everything. Others are not yet ready to jump on the bandwagon. They say, “show me the 96% of the universe we can’t detect directly—for example, find me some dark matter!”
At first, astronomers thought that dark matter might be hidden in objects that appear dark because they emit no light (e.g., black holes) or that are too faint to be observed at large distances (e.g., planets or white dwarfs). However, these objects would be made of ordinary matter, and the deuterium abundance tells us that no more than 5% of the critical density consists of ordinary matter.
Another possible form that dark matter can take is some type of elementary particle that we have not yet detected here on Earth—a particle that has mass and exists in sufficient abundance to contribute 23% of the critical density. Some physics theories predict the existence of such particles. One class of these particles has been given the name WIMPs, which stands for weakly interacting massive particles . Since these particles do not participate in nuclear reactions leading to the production of deuterium, the deuterium abundance puts no limits on how many WIMPs might be in the universe. (A number of other exotic particles have also been suggested as prime constituents of dark matter, but we will confine our discussion to WIMPs as a useful example.)
If large numbers of WIMPs do exist, then some of them should be passing through our physics laboratories right now. The trick is to catch them. Since by definition they interact only weakly (infrequently) with other matter, the chances that they will have a measurable effect are small. We don’t know the mass of these particles, but various theories suggest that it might be a few to a few hundred times the mass of a proton. If WIMPs are 60 times the mass of a proton, there would be about 10 million of them passing through your outstretched hand every second—with absolutely no effect on you. If that seems too mind-boggling, bear in mind that neutrinos interact weakly with ordinary matter, and yet we were able to “catch” them eventually.
Despite the challenges, more than 30 experiments designed to detect WIMPS are in operation or in the planning stages. Predictions of how many times WIMPs might actually collide with the nucleus of an atom in the instrument designed to detect them are in the range of 1 event per year to 1 event per 1000 years per kilogram of detector. The detector must therefore be large. It must be shielded from radioactivity or other types of particles, such as neutrons, passing through it, and hence these detectors are placed in deep mines. The energy imparted to an atomic nucleus in the detector by collision with a WIMP will be small, and so the detector must be cooled to a very low temperature.
The WIMP detectors are made out of crystals of germanium, silicon, or xenon. The detectors are cooled to a few thousandths of a degree—very close to absolute zero. That means that the atoms in the detector are so cold that they are scarcely vibrating at all. If a dark matter particle collides with one of the atoms, it will cause the whole crystal to vibrate and the temperature therefore to increase ever so slightly. Some other interactions may generate a detectable flash of light.
A different kind of search for WIMPs is being conducted at the Large Hadron Collider (LHC) at CERN, Europe’s particle physics lab near Geneva, Switzerland. In this experiment, protons collide with enough energy potentially to produce WIMPs. The LHC detectors cannot detect the WIMPs directly, but if WIMPs are produced, they will pass through the detectors, carrying energy away with them. Experimenters will then add up all the energy that they detect as a result of the collisions of protons to determine if any energy is missing.
So far, none of these experiments has detected WIMPs. Will the newer experiments pay off? Or will scientists have to search for some other explanation for dark matter? Only time will tell (Figure 29.23).
Dark Matter and the Formation of Galaxies
As elusive as dark matter may be in the current-day universe, galaxies could not have formed quickly without it. Galaxies grew from density fluctuations in the early universe, and some had already formed only about 400–500 million years after the Big Bang. The observations with WMAP, Planck, and other experiments give us information on the size of those density fluctuations.  In the hot, early universe, energetic photons collided with hydrogen and helium, and kept them moving so rapidly that gravity was still not strong enough to cause the atoms to come together to form galaxies. How can we reconcile this with the fact that galaxies did form and are all around us?
Our instruments that measure the CMB give us information about density fluctuations only for ordinary matter , which interacts with radiation. Dark matter, as its name indicates, does not interact with photons at all. Dark matter could have had much greater variations in density and been able to come together to form gravitational “traps” that could then have begun to attract ordinary matter immediately after the universe became transparent. As ordinary matter became increasingly concentrated, it could have turned into galaxies quickly thanks to these dark matter traps.
For an analogy, imagine a boulevard with traffic lights every half mile or so. Suppose you are part of a motorcade of cars accompanied by police who lead you past each light, even if it is red. So, too, when the early universe was opaque, radiation interacted with ordinary matter, imparting energy to it and carrying it along, sweeping past the concentrations of dark matter. Now suppose the police leave the motorcade, which then encounters some red lights. The lights act as traffic traps; approaching cars now have to stop, and so they bunch up. Likewise, after the early universe became transparent, ordinary matter interacted with radiation only occasionally and so could fall into the dark matter traps.
The Universe in a Nutshell
In the previous sections of this chapter, we traced the evolution of the universe progressively further back in time. Astronomical discovery has followed this path historically, as new instruments and new techniques have allowed us to probe ever closer to the beginning of time. The rate of expansion of the universe was determined from measurements of nearby galaxies. Determinations of the abundances of deuterium, helium, and lithium based on nearby stars and galaxies were used to put limits on how much ordinary matter is in the universe. The motions of stars in galaxies and of galaxies within clusters of galaxies could only be explained if there were large quantities of dark matter. Measurements of supernovae that exploded when the universe was about half as old as it is now indicated that the rate of expansion of the universe has sped up since those explosions occurred. Observations of extremely faint galaxies show that galaxies had begun to form when the universe was only 400–500 million years old. And observations of the CMB confirmed early theories that the universe was initially very hot.
But all this moving further and further backward in time might have left you a bit dizzy. So now let’s instead show how the universe evolves as time moves forward.
Figure 29.24 summarizes the entire history of the observable universe from the beginning in a single diagram. The universe was very hot when it began to expand. We have fossil remnants of the very early universe in the form of neutrons, protons, electrons, and neutrinos, and the atomic nuclei that formed when the universe was 3–4 minutes old: deuterium, helium, and a small amount of lithium. Dark matter also remains, but we do not yet know what form it is in.
The universe gradually cooled; when it was about 380,000 years old, and at a temperature of about 3000 K, electrons combined with protons to form hydrogen atoms. At this point, as we saw, the universe became transparent to light, and astronomers have detected the CMB emitted at this time. The universe still contained no stars or galaxies, and so it entered what astronomers call “the dark ages” (since stars were not lighting up the darkness). During the next several hundred million years, small fluctuations in the density of the dark matter grew, forming gravitational traps that concentrated the ordinary matter, which began to form galaxies about 400–500 million years after the Big Bang.
By the time the universe was about a billion years old, it had entered its own renaissance: it was again blazing with radiation, but this time from newly formed stars, star clusters, and small galaxies. Over the next several billion years, small galaxies merged to form the giants we see today. Clusters and superclusters of galaxies began to grow, and the universe eventually began to resemble what we see nearby.
During the next 20 years, astronomers plan to build giant new telescopes both in space and on the ground to explore even further back in time. In 2021, the James Webb Space Telescope, a 6.5-meter telescope that is the successor to the Hubble Space Telescope, will be launched and assembled in space. The predictions are that with this powerful instrument (see Figure 29.1) we should be able to look back far enough to analyze in detail the formation of the first galaxies.


3.2: Transformations of Common Graphs
The transformation of graphs, using common functions, will be a skill that will bring insight to graphing functions quickly and painlessly. Anticipating how a graph of a function will look, and transforming old graphs to new graphs, is a skill we will explore in this section. Mastering this skill will give you a leg up on understanding analytic geometry, a key component to calculus.
Here are nine common functions and their graphs. Each of these functions will be referred to as “the parent function” for its family of transformed functions.
| \(f(x) = mx + b\) | \(f(x) = x^2\) | \(f(x) = |x|\) |
| \(f(x) = \sqrt{x}\) | \(f(x) = x^3\) | \(f(x) = \ln x\) |
| \(f(x) = \dfrac{1}{x}\) | \(f(x) = b^x\) where \(b>1\) | \(f(x) = b^x\) where \(0 < b< 1\) |
Using the transformations described in Section \(3.1\), the nine graphs shown on the previous page can be shifted, reflected, stretched, and compressed. The take-away for this section is to recognize the parent function from function notation and apply the appropriate transformations to quickly sketch a graph or visualize the graph in your head. No technology is necessary! It’s enough to have an understanding for functions and their shifting graphs.
Name the parent function of the given function. Then describe in words the transformation(s) on the parent function.
- \(y = |5x| − 6\)
- \(y = 8 − (x + 9)^3\)
- \(y = \dfrac{2}{x−10}\)
Solution
- The parent function is \(y = |x|\):
- The parent function is \(y = x^3\):
- The parent function is \(y = \dfrac{1}{x}\):
Use the parent function and its transformation(s) to sketch the graph of the given function. It is much more important to create a rough but accurate sketch without technology than a detailed sketch with technology.
- \(y = 2^x − 3\)
- \(y = \ln(x + 2)\)
Solution
- The parent function is \(y = b^x\) where \(b = 2 > 1\). Shift this graph, including its horizontal asymptote, down \(3\) units.
- The parent function is \(y = \ln x\). Shift this graph, including its vertical asymptote, left \(2\) units.
Try It! (Exercises)
For exercises #1-18, use the parent functions (see graphs within this section), along with appropriate transformations, to create a sketch of the graph of the given function. Do not use graphing technology.
- \(y = \dfrac{1}{x+5}\)
- \(y = e^{x−4}\)
- \(y = |x| − 6\)
- \(y = −(x + 2)^3\)
- \(y = 4 + x^2\)
- \(y = \sqrt{x − 4}\)
- \(y = \left( \dfrac{1}{2} \right)^x + 3\)
- \(y = 1 − \sqrt{x}\)
- \(y = |x − 5| + 2\)
- \(y = 1 + (x − 6)^2\)
- \(y = 4 − \dfrac{1}{x}\)
- \(y = 3 + \ln (−x)\)
- \(y = 2\sqrt{x} − 4\)
- \(y = −2(x − 5)^2\)
- \(y = 1 + x^3\)
- \(y = −3|x − 7|\)
- \(y = 5 + \sqrt{-x}\)
- \(y= 3^{x+2} + 4\)
- Use the graph of \(y = |x|\) and transformations to discuss why the graph of the transformed function \(y = |-x|\) is the same graph.
- Use the graph of \(y = x^2\) and transformations to discuss why the graph of the transformed function \(y = (-x)^2\) is the same graph.
- Using \(f(x) = x^2\) as the parent function, write the function that would correspond to the transformations on \(f\). No need to graph.
a. Reflected through the \(x\)-axis and shifted down \(12\) units.
b. Shifted \(10\) units left and \(25\) units up.
- Discuss two different approaches to transform the parent function \(y = \dfrac{1}{x}\) to graph \(y = \dfrac{1}{2x}\). What are the transformations? Discuss how and why each approach will produce the same graph for the new function \(y = \dfrac{1}{2x}\).


1.6: Staff, Clefs, Ledger Lines, Steps, and Accidentals
Staff
In Western musical notation, the staff is a set of five horizontal lines and four spaces that each represent a different musical pitch—or, in the case of a percussion staff, different percussion instruments. Appropriate music symbols, depending upon the intended effect, are placed on the staff according to their corresponding pitch or function. Musical notes are placed by pitch, percussion notes are placed by instrument, and rests and other symbols are placed by convention.
The absolute pitch of each line of a non-percussive staff is indicated by the placement of a clef symbol at the appropriate vertical position on the left-hand side of the staff (possibly modified by conventions for specific instruments). For example, the treble clef, also known as the G clef, is placed upon the second line (counting upwards), fixing that line as the pitch first G above “middle C.”
The lines and spaces are numbered from bottom to top; the bottom line is the first line and the top line is the fifth line .
The musical staff is analogous to a mathematical graph of pitch with respect to time. Pitches of notes are given by their vertical position on the staff and notes to the left are played before notes to the right. Unlike a graph, however, the number of semitones represented by a vertical step from a line to an adjacent space depends on the key, and the exact timing of the beginning of each note is not directly proportional to its horizontal position; rather, exact timing is encoded by the musical symbol chosen for each note in addition to the tempo.
A time signature to the right of the clef indicates the relationship between timing counts and note symbols, while bar lines group notes on the staff into measures.
Clef
A clef (from French: clef “key”) is a musical symbol used to indicate the pitch of written notes.Placed on one of the lines at the beginning of the stave, it indicates the name and pitch of the notes on that line. This line serves as a reference point by which the names of the notes on any other line or space of the stave may be determined. Only one clef that references a note in a space rather than on a line has ever been used.
There are three types of clef used in modern music notation: F , C , and G . Each type of clef assigns a different reference note to the line (and in rare cases, the space) on which it is placed.
| Clef | Name | Note | Line |
|---|---|---|---|
| G-clef | G4 | passes through the curl of the clef. | |
| C-clef | Middle C(C4) | passes through the center of the clef. | |
| F-clef | F3 | passes between the two dots of the clef. |
Ledger Lines
A ledger line or ledger line is used in Western musical notation to notate pitches above or below the lines and spaces of the regular musical staff. A line slightly longer than the note head is drawn parallel to the staff, above or below, spaced at the same distance as the lines within the staff.
Accidentals
In music, an accidental is a note whose pitch (or pitch class) is not a member of the scale or mode indicated by the most recently applied key signature. In musical notation, the sharp ( ♯ ), flat ( ♭ ), and natural ( ♮ ) symbols, among others, are used to mark such notes, and those symbols may themselves be called accidentals. In the measure (bar) in which it appears, an accidental sign raises or lowers the immediately following note (and any repetition of it in the bar) from its normal pitch, overriding sharps or flats (or their absence) in the key signature. A note is usually raised or lowered by a semitone, although microtonal music may use “fractional” accidental signs. One occasionally sees double sharps or flats, which raise or lower the indicated note by a whole tone. Accidentals apply within the measure and octave in which they appear, unless canceled by another accidental sign, or tied into a following measure. If a note has an accidental and the note is repeated in a different octave within the same measure, the accidental does not apply to the same note of the different octave.
Theory Lesson
Click on the link Music Basics and review the following lessons in the Basics Section:
- The Staff, Clefs, and Ledger Lines
- Steps and Accidentals
Contributors and Attributions
- Clef. Provided by : Wikipedia. Located at : https://en.Wikipedia.org/wiki/Clef . License : CC BY-SA: Attribution-ShareAlike
- Staff (Music). Provided by : Wikipedia. Located at : https://en.Wikipedia.org/wiki/Staff_(music) . License : CC BY-SA: Attribution-ShareAlike
- Accidentals. Provided by : Wikipedia. Located at : https://en.Wikipedia.org/wiki/Accidental_(music) . License : CC BY-SA: Attribution-ShareAlike
- Staves. Authored by : Marek52. License : CC BY-NC: Attribution-NonCommercial


1.1: Watermain Installation
Student Learning Outcomes
After reading this chapter, you should be able to:
- Understand the basic practices of water main installation
- Evaluate the processes of backfilling and main testing
- List the steps of installing a water main and placing into service
- Analyze the use of maps and various types of drawings
In a previous chapter, we discussed the importance and purpose of selecting specific water mains. In some instances, plastic pipe might be a better selection and other times ductile iron pipe might be useful. There are different uses for different types of pipe too. Regardless of the type of pipe selected, all pipe needs to be installed appropriately. The installation process will be discussed in this chapter.
Pipe Shipment
Water utilities need to order pipe from various manufacturers and sometimes the pipe needs to be shipped larger distances. The cost of shipping pipe is typically dependent on the distance the pipe is being transported, the size of the pipe, the weight of the pipe, and the quantity of the pipe being purchased. These variables will also dictate the method the pipe will be transported and will also contribute to the shipping costs. Ultimately, pipes are usually delivered to the water utility by truck. However, depending on the origin of the manufacturing of the pipe it may be transported by train or barge.
Pipe Handling
Once the pipe is delivered to a water utility, it should be properly inspected before it is unloaded from the truck. Even though manufacturers typically have a final inspection process prior to leaving their plant, damage can occur during transport. In addition, the wrong material or size may have been delivered by mistake. Therefore, it is important to inspect the following things prior to the pipe being unloaded:
- Size of pipe and fittings
- Class of pipe and fittings
- Quantity of pipe and fittings
- Condition of pipe and fittings
Any problems observed during unloading should be noted in writing. The driver, shipping company, and manufacturer should all be notified. The unloading process is usually accomplished using some type of equipment. Often times with smaller shipments, the pipe will be strapped to wooden pallets and they can be unloaded from the truck using a forklift. However, with larger shipments or larger size pipe, heavy equipment might be needed. It is important that the pipe not dropped or placed down roughly, Pipes should not be allowed to strike other pipes, the ground or other items. Some pipes are shipped with special coatings and it is important these coatings are in good condition and not damaged. Padded forks on forklifts, rubber hooks, or slings are ways to prevent such damage.
Pipe Storing
Once the pipe has been unloaded from the delivery truck, it must be properly stored to prevent damage and contamination. If pipe is stored at job sites or remote locations, protection from vandalism should also be considered. Stockpiles of pipe should be built on a flat base to prevent rolling. If possible, the pipe should be stored off the ground and grouped by size and class. If all different sizes and classes are stored together, it will make it more difficult to transport the pipe to the job site when it is time for construction. It is helpful to lay the pipe by alternating the bell and spigot ends. This allows the pipe to be stored evenly.
Polyvinyl chloride pipe should be stored out of direct sunlight as ultraviolet radiation can damage it. Any pipe that can crack or become damaged by hitting the ground, the height of the stacks of pipe should be limited to no more than three high. It is also prudent to cover the ends of the pipe during storage to prevent rodents or other animals from entering the pipe. Covering the ends also protects against contamination from dirt or other foreign objects. Sometimes covering the ends is not feasible and not critical since part of the installation process includes proper flushing and disinfecting of the pipe before being placed in service.
Preparing the Pipe for Installation
Pipeline projects can be small jobs requiring only a few sticks of pipe. Or, they can be extensive jobs covering several miles or more. Regardless of the size of the job, it is important to properly plan. Preparing the pipe at the job site is an important aspect of job preparation.
The pipe should be placed as close to the trench as possible. This makes it easier for the pipe to be accessed and placed into the trench. String the pipe on the opposite side of the trench as the dirt (spoils) that is being excavated and should be located away from traffic and heavy equipment. The bells should be located in the direction of installation and only enough pipe should be laid out for a days work. It is also important that the pipe is protected from rolling into the trench or away from the job site.
Excavation
Trench excavation is the most expensive process of pipeline installation. It is important to know the location, depth, and width required for pipeline installation. A nonprofit organization called “Underground Service Alert” provides a means for anyone digging underground the opportunity to identify any other utilities or conflicts, which may exist. A toll-free number (811) should be called at least forty-eight (48) hours before any digging occurs. By calling this number, any utility in the area receives a notification that trenching will be occurring and they are then responsible to mark their utilities on the ground with an appropriately colored paint. Each different utility has a specific color as standardized by the American Public Works Association (APWA).
|
White |
Propose Excavation |
|
Red |
Electric Power Lines |
|
Orange |
Cable, Communication |
|
Purple |
Irrigation |
|
Pink |
Temporary Survey Marking |
|
Yellow |
Gas, Oil, Steam, Chemical |
|
Green |
Sewer, Storm Drain |
|
Blue |
Potable Water |
The local soil conditions should also be considered before trenching begins. Is there local groundwater, which can fill the trench? Is there frost or freeze issues? Is the native soil in good condition or will “fill” material need to be brought in for backfilling? Sometimes in cold climates where adequate depths are not possible, special insulation might be needed to prevent the water in the pipes from freezing. In some areas (especially in warmer climates), minimum ground cover depths are required. Some common depths are thirty-six (36) inches for water mains and eighteen (18) inches for service laterals.
Whenever a pipe needs to be installed in an existing street, special consideration needs to be addressed to minimize inconveniences to the public. For example, some local cities may limit the times of construction activities. If the road is a main thoroughfare, construction may not be allowed during commute times in the mornings and evenings. Special permits for excavation may also be required. It is also very important to understand the existing and future road conditions, because these will dictate the road surface restoration requirements.
Once these and other considerations are reviewed, it is important to set an excavation plan. The construction crew should review the work zone. What heavy equipment will be needed, where will the spoils and materials be placed, where will traffic control be required, and where might there be public exposure to the work zone are just a few areas crews will need to understand prior to beginning work.
Since the excavation process is the most expensive part of pipeline installation, it is important to understand how much dirt is required to be removed. This is important because you don’t want to remove more dirt than is needed. Typically, the trench width should be one (1) to (2) feet greater than the outside diameter of the pipe.
Trenches can be very dangerous for workers from the potential of cave-ins. There are four (4) common danger signs workers should look for to help prevent trench wall failure. These are:
- Tension cracks in the ground surface parallel to the trench
- Material crumbling off the walls of the trench
- Settling or slumping of the ground surrounding the trench
- Sudden changes in soil color, which indicates previous excavations
In addition to these warning signs, certain precautions need to be in place to protect crews working in trenches. There are four (4) basic methods of preventing trench wall cave-ins.
-
Sloping
—If there is enough room in the construction work zone, sloping the trench walls is an adequate means of preventing cave-ins. This process involves excavating the walls at an angle. The angle of repose prevents the downward forces of the soil from exceeding the soils cohesive strength. Sloping a trench is dependent on the type of soil being excavated, the amount of moisture in the soil, the surrounding conditions, and the potential of soil vibration from heavy equipment. Various angles of repose are used depending on the type of soil. Below are some common examples.
- Compacted crushed rock—for every foot of depth, the trench is cut one half of a foot wide
- Average soils—for every foot of depth, the trench is cut one foot wide
- Compacted sharp sand—for every foot of depth, the trench is cut one and one half foot wide
- Well-rounded loose sand—for every foot of depth, the trench is cut two feet wide
- Shielding —This form of trench wall protection involves the use of a steel box, which is placed into the trench. It is open at the top, bottom, and on the ends, so workers can work inside of it. The protective box is pushed or towed along the trench to provide constant shield against cave-ins. It is important that the shield extends above the ground level in order to provide complete protection. These shielding boxes are also referred to as trench shields.
-
Shoring
—Shoring is a general term used when referring to trench wall projection. It is a framework system of wood, metal, or a combination of both. This support system maintains pressure against both trench walls preventing cave-ins. It is important to install shoring from the top of the trench to the bottom of the trench. Removal of the shoring should be done in the opposite manner. This will minimize worker’s exposure of unprotected trench walls. There are three (3) main components of a shoring system.
- Uprights—These are the vertical boards placed in direct contact with the face of the trench wall. The spacing of the uprights is dependent upon the soil stability. If the soil is sandy, then the uprights would be placed tightly together.
- Stringers—These are the horizontal members of the shoring system to which the braces are attached. The stringers are commonly referred to as whalers.
- Braces—The braces are the horizontal members, which run across the excavation to keep the uprights separated
The trench bottom should be level so the pipe has support along the entire length. Sometimes a leveling board is needed to ensure the bedding is level. After the pipe is placed in the trench, the backfill material should be compacted beneath the pipe curvature. This process is known as “ haunching .” It is important to make sure the pipe has proper support on all sides underground. The pipe should be set on flat firm ground. This proper bedding provides support and strength under the pipe. Bedding up to fifty (50) percent of the pipe diameter increases supporting strength by thirty-six (36) percent and proper bedding up to sixty (60) percent of the pipe diameter increases supporting strength by seventy-three (73) percent. By providing bedding over one hundred (100) percent of the pipe diameter and good compaction along the sides of the pipe increases the supporting strength by one hundred fifty (150) percent.
It is also important to protect potable water mains from non-potable pipes such as sewer and storm drain. Ideally, water mains should be installed above any non-potable pipes and a one (1) foot vertical distance is commonly required. In addition, a ten (10) foot horizontal separation from sewer pipes and four (4) foot from storm drains is common. Instances where these minimum offsets cannot be achieved, special provisions and health department regulatory approval might be required. Placing water mains in a larger diameter “sleeve” and concrete encasement are some alternative solutions.
Push-On Joint Installation Procedure
-
Prepare the pipe:
- Thoroughly clean the bell socket and plain end
- Inspect the gasket for any damage
- Follow the manufacturer’s recommendation on whether the socket should be lubricated
- Insert the gasket into the socket
- In cold weather, it may be necessary to warm the gasket to facilitate insertion
- Apply lubricant to the gasket and plain end
- Protect the lubricant from contamination
-
Connect the pipe:
- Be sure the plain end is properly beveled. Sharp edges can damage the gasket.
- Keep pipes in line when making up the joint. Deflection should take place only after the joint is assembled.
- Push the plain end into the socket
- When pushing pipe with a backhoe or jack, use a timber header across the end of the pipe to protect it
Mechanical Joint Installation Procedure
-
Prepare the pipe:
- Clean the socket and plain the end
- Lubricate the gasket and plain end with soapy water of an approved lubricant
- Install the gland and rubber gasket
-
Connect the pipe:
- Keep the pipes in line during joint assembly
- Insert the plain end into the socket
- Press the gasket evenly into the bell
-
Prepare the mechanical connection:
- Push the gland toward the socket
- Insert the bolts and hand tighten the nuts
-
Tighten the bolts:
- Alternately tighten the nuts on opposite sides to maintain the same distance between the gland and the flange
- Tighten the nuts to the correct torque
Sample Questions
-
What is the most common cause of joint failure?
- Having the joint too clean
- Using unapproved soap or lubricant
- Not having the joint completely clean
- None of the above
-
What types of things in the recesses of the bells of pipe can cause joints to leak?
- Sand
- Gravel
- Dust
- All of the above
-
What is the piece of pipe that is cut out during tapping called?
- Slug
- Coupon
- Cookie
- Only 1 and 2
- All of the above
-
Large-diameter pipe should be unloaded ___________.
- By hand
- With heavy equipment
- By rolling it off the truck
- Any of the above
-
What is the most expensive part of pipeline installation?
- The material
- The planning
- The excavation
- All of the above
-
What is a “story pole”?
- A pole which is used to track the progress of the days work
- A pole designed to improve efficiency during pipe installation
- A pole that marks how many feet of pipe are installed each day
- A pole with a string used to check the depth and grade of a trench


Chapter 5: Criminological Theory
Learning Objectives
After reading this section, students will be able to:
- Distinguish between classical, biological, psychological, and sociological explanations of criminal behavior.
- Understand the links between crime control policy and theories of criminal behavior.
- Demonstrate effective application of criminological theories to behavior.
This section introduces the importance of theory and theory creation. It also briefly describes some of the major paradigms of criminal explanations.
Critical Thinking Questions
- How do we know what theories explain crime better than other theories?
- How did the classical theory of crime influence the American criminal justice system?
- Why is it difficult to study biological theories of crime without thinking about the social environment?
- Which theory do you think explains criminal behavior the best? Why?
- Why do you think there have been so many different explanations to describe the origins of criminal behavior?
-
- 5.6: Positivist Criminology
- Positivism is the use of empirical evidence through scientific inquiry to improve society. Ultimately, positivist criminology sought to identify other causes of criminal behavior beyond choice. The basic premises of positivism are measurement, objectivity, and causality. Early positivist theories speculated that there were criminals and non-criminals. Thus, we have to identify what causes criminals.
-
- 5.9: Strain Theories
- Strain theories assume people will commit crime because of strain, stress, or pressure. Depending on the version of strain theory, strain can come from a variety of origins. Strain theories also assume that human beings are naturally good; bad things happen, which “push” people into criminal activity.
-
- 5.10: Learning Theories
- In the previous sections, strain theories focused on social structural conditions that contribute to people experiencing strain, stress, or pressure. Strain theories explain how people can respond to these structures. Learning theories compliment strain theories because learning theories focus on the content and process of learning.