**4. Discussion**

Air storage systems have been shown to be particularly useful to allow excess energy storage from renewable energies, with air storage in tanks or caverns (in periods of extra energy production) and a successive expansion of the pressurized air in a turbine (in periods of more consistent energy need). Among the different CAES configurations, including diabatic, adiabatic and isothermal mode, isothermal operations appear to be favorable to increase the overall performances, in terms of system efficiency [24]. The developed model for compressed air storage in WWTPs is highly flexible and can be specifically designed for target WWTPs, specifying plant potentiality and wastewater characteristics, both in terms of influent characterization, energy consumption of the biological phase and operating conditions of the activated sludge basin (such as air diffusers efficiency, HRT, SRT, X). It should be remembered that steady-state conditions, such as the ones considered in the present study, are not typically encountered in daily operations in WWTPs. However, this study was aimed at preliminarily evaluating the feasibility of the proposed solution to reduce operating costs for plant managing authorities. Furthermore, data scarcity has been recently recognized as a limiting factor to allow a widespread utilization of mathematical modelling, considering the complicated usage of online sensors and the huge workload required for sampling campaigns [38].

AD has been largely recognized as a significant source of renewable energy from different organic sources, able to provide fully renewable biogas, that has a high potential energy value [36]. Traditionally, AD was known to be beneficial in large-scale WWTPs, where a sufficient amount of sludge is available to continuously feed the digester, avoiding discontinuous operations throughout the year [39]. However, recently, by analyzing a large range (25,000–1,000,000 PE) of WWTP potentialities, it was proved that AD implementation is convenient also in small-scale plants when assessing environmental and economic benefits, particularly if agro-waste addition can be provided to the digester [40]. This can lead to an enhanced biogas generation, due to an augmented organic load, and a consequently favorable energy balance [40]. Regarding the second proposed scenario, further advances could include the co-digestion of sewage sludge with other locally available organic substrates to increase the obtainable methane yield from AD [31] or the application of sludge pre-treatments to increase its biodegradability [41]. Finally, the possibility to upgrade biogas to high-value biomethane, with technical characteristics totally comparable to fossil-derived natural gas, should be considered [41].

A following phase of the work is forecast, where the available commercial items for air storage will be investigated, to allow for an easier implementation of the proposed optimization system in existing plants. An in-depth process analysis of the aerobic (for example, considering the ASM1 model) and anaerobic (such as Anaerobic Digestion Model Number 1, ADM1 [42]) sections of the plant could be performed, better evaluating the performances of the proposed air storage system in dynamic conditions.

The detailed energy consumption data resulting from WWTP modelling through commercially available software's (such as GPSX ®, WEST ® or Biowin ®) could be integrated in the proposed economic saving approach, with further insights in achievable energy saving.

When considering the oxygen requirement of the biological treatment in WWTPs, it is known that the energy consumption for aeration strongly depends on a pool of di fferent parameters (often di fficult to monitor), such as oxygen transfer e fficiency, di ffuser fouling phenomenon, and di ffuser selection [43]. The proposed empirical approach for air supply calculation is extremely simplified and needs to be sustained by an in-depth experimental or modelling campaign. Novel techniques that were recently proposed to save energy in biological wastewater treatment include smart aeration control, consisting of variable frequency drive (VFD), dissolved oxygen (DO) sensors and programmable logic controller (PLC) [44]. When applying the proposed approach to target WWTPs, the experimental data obtained from these novel smart aeration systems could be used to update the input datasets for the proposed economic optimization.


**3. Conclusion**

Considering both theoretical and experimental research and applications, this book will provide a broad perspective on developments in ion beam technology and the future of ion technology. Therefore, the book focuses on expanding and improving the application areas of ion beam technology.

*Ion Beam Technology and Applications*


**6. Numerical Implementation and Test Problems**

The model is implemented similarly to the conventional LB *D*2*Q*9 model [3]. Firstly, we perform the collision step, then post-collision distribution functions are streamed at appropriate directions. It is well-known from the LB theory that the discretization of space–time affects the viscosity. The DV Boltzmann model discretized in a similar form as LB model reads as

$$f\_i(t + \delta t, \mathbf{r} + \mathbf{c}\_i \delta t) - f\_i(t, \mathbf{r}) = I\_i[f\_1, \dots, f\_N](t, \mathbf{r})\delta t,\tag{42}$$

by applying the Taylor expansion this equation can be rewritten as

$$\left(\frac{\partial}{\partial t} + \mathbf{c}\_{\dot{t}} \frac{\partial}{\partial \mathbf{r}}\right) f\_{\mathbf{i}}(t, \mathbf{r}) \delta t + \frac{1}{2} \left(\frac{\partial}{\partial t} + \mathbf{c}\_{\dot{t}} \frac{\partial}{\partial \mathbf{r}}\right)^2 f\_{\mathbf{i}}(t, \mathbf{r}) \delta t^2 + O(\delta t^3) = l\_{\mathbf{i}}[f\_1, \dots, f\_N](t, \mathbf{r}) \delta t, \mathbf{r}$$

then

$$I\_i\left(\frac{\partial}{\partial t} + \mathbf{c}\_i \frac{\partial}{\partial r}\right) f\_i(t, r) = I\_i[f\_1, \dots, f\_N](t, r) - \frac{1}{2} \left(\frac{\partial}{\partial t} + \mathbf{c}\_i \frac{\partial}{\partial r}\right)^2 f\_i(t, r) \delta t + O(\delta t^2), \quad i = 1, 2$$

therefore, we can conclude that the scheme (42) led to the hydrodynamic equations in which the contributions from −1 2 *∂ ∂t* + *ci ∂ ∂r* 2 *fi*(*t*,*r*)*δt* + *O*(*δt* 2) = −*δt* 2 *d*2 *dt*2 *fi* + *O*(*δt* 2) are present. The additional terms for the Navier–Stokes equations can be obtained with the application of the Chapman–Enskog expansion [3]. Note that the terms *O*(*δt* 2) do not affect the Navier–Stokes equations, since they contain third order derivatives, which, in the Chapman–Enskog multiple-scale expansion, enter the equations for the moments at the Burnett level. For the Navier–Stokes equation, the additional viscosity terms result from −*δt* 2 *d*2 *dt*2 *f eq i* , its contribution to *∂ ∂r* · *P*(1) is *δt* 2 ∑*i cici* · *d dr d dt f eq i* , remembering that *d dt f eq i* can be expressed by (40), we eventually obtain *δt* 6 ( *∂*2 *∂x*2 + *∂*2 *∂y*2 )*u*.

Then, for the DV *D*2*Q*9 Boltzmann model in the form (42), the viscosity is given by

$$\nu = \frac{3}{4a} - \frac{\delta t}{6}.$$

In the simulations, the parameters are taken as follows

$$\alpha = \frac{3}{4\left(\nu + \frac{\delta t}{6}\right)'}, \quad \beta = 0.25a, \quad \gamma = 4a - 4\beta = 3a, \quad \lambda = 0,\tag{43}$$

i.e., we have six different collisions.

To validate the second-order convergence of the presented scheme, we estimate the simulation error defined as

$$error = \frac{\sqrt{\sum\_{z} (u\_m(z) - u\_{bmch}(z))^2}}{\sqrt{\sum\_{z} u\_{bmch}(z)^2}},\tag{44}$$

where *z* denotes the spatial variable, *um*, *ubench* are the modeled variable (velocity) and the benchmark solution, respectively. The convergence rate is evaluated by fitting the values of log(*error*) for the various log(*h*) = log( 1 *N* ) (*N* is the number of the lattice nodes, *h* is proportional to the lattice spacing) using the linear regression, the second-order convergence is achieved if the regression slope coefficient is close to 2.

Compared to LB *D*2*Q*9 model, the scheme (29)–(37) differs only in the collision term and the expression for the viscosity. This means that the computation time for (29)–(37) implemented in the form (42) is approximately the same as for LB *D*2*Q*9 model.


**8.1 Exercise testing versus physical activity recalls**

Actual measurement of aerobic fitness, as opposed to estimating it in some fashion, is usually preferable. There are a variety of reference books available detailing exercise protocols for various health and fitness statuses. The researcher who wants to include

cycling set that progressed in intensity with each event presentation could be incorporated (Carter and Sheih, 2010). Obviously, much pilot work would need to be done to determine the

If actual physical exercise testing is not possible, there is still one other avenue to determine cerebral activation during an exercise task: mental imagery. For example, a sport psychology study investigated motor imagery of the golf swing to determine brain region activation. Using the sensori-motor homunculus map as a guide, Ross et al. (2003) compared the amount of fMRI BOLD response in brain regions related to the golf swing between novice versus expert golfers. It was determined that the greater the golf handicap, the greater the region of activation (greater than 2%) in specific somatatropic regions of interest relevant to golf. The powerpoint presentation can be downloaded from the internet with a search engine.  Their imagined walking (speed = 2.3 ± 0.4 m/s) was associated with activation in the right dorsolateral prefrontal cortex, posterior parietal lobule, and the left cerebellar hemisphere. Therefore, it might be interesting to conduct an imagery intervention study to determine the acute response to an imagined exercise stress test as well as an imagined chronic response to a

long-term exercise intervention. Studies of this nature have not yet been reported.

with both the science and the targeted subject population in mind.

**8.1 Exercise testing versus physical activity recalls**

Neuroimaging studies are expensive. Exercise testing and training are expensive. Recruitment drop-outs are expensive. And botched tests are expensive. They are expensive in terms of time, money and patience. Neuroimaging and exercise testing aged individuals bring a unique set of challenges to intervention research. There are the standard safety issues to consider when using a neuroimaging technique or conducting a physical exercise test; but the less obvious issues of comfort and trust sometimes slip by unasked, until it is too late and the subject has dropped out of the study. Therefore, when screening an older individual for an imaging and/or an exercise study, the following question must be asked: can the volunteer complete the testing protocol accurately and in relative comfort? The researcher must ascertain that the older volunteer can hear, see, follow directions, and adhere to the instructions. Volunteers must be able to complete enough of the exercise protocol to get valid physiological baseline data and/or remain motionless and pain free in the MRI scanner anywhere from 15 to 120 minutes. The brief breaks afforded between imaging sequences when a subject is free to move slightly may be insufficient. Arthritis, nasal-sinus drainage, and circulatory issues have thwarted many research MRI scans. For a first-time MRI scan, volunteers may back out at the last minute due to unanticipated fright (hence a simulator is an invaluable resource) or the irrational worry that the MRI will read their minds (thanks to outlandish media stories). Thus, the researcher must design protocols

Actual measurement of aerobic fitness, as opposed to estimating it in some fashion, is usually preferable. There are a variety of reference books available detailing exercise protocols for various health and fitness statuses. The researcher who wants to include

exact power outputs required to elicit measureable BOLD signals.

**7.2 Exercise mental imagery**

**8. Testing pearls and pitfalls**

exercise in the research design should obtain the ACSM Guidelines for Exercise Testing and Training (2009). A good textbook is Nieman's (2010) exercise prescription textbook used for training undergraduates in exercise science. However, there are times when it is inconvenient, illogical, or cost-prohibitive to conduct a fitness test. For those times when actual exercise testing is ruled out, there is a rather good non-exercise aerobic fitness estimation equation that is quite easy to use, providing one is trained in obtaining a valid physical activity recall. While it can be difficult to get accurate physical activity recalls beyond a few weeks, a seasoned investigator in physical activity recall questionnaires can elicit excellent responses, even recalls spanning several years.

One physical activity recall formula for estimating aerobic fitness has been in the literature since 1990. It was gathering dust until recently when we used it for a retrospective analysis exploring the role aerobic fitness might have on cerebral white matter integrity on both younger and older adults (Marks et al., 2007). Ever since that publication, we have been getting inquiries about the formula and how to use it. The formula was developed and tested at the Cooper Aerobic Institute in Texas on over 2,000 U.S. Air Force personnel ranging in age from 18 to 70 years. The subject population included males and females, fit and unfit, healthy and unhealthy. The estimated aerobic fitness value (VO2) has a standard error of about 5 ml/kg/min. This formula is very good for cross-sectional, population-based studies when the purpose is to simply categorize one's fitness level. However, the error range is a bit too high and the fitness categorizing a bit too vague for pre-post research designs where VO2 change is a critical factor. For that, VO2 does need to actually be measured. Although the formula tends to underestimate the highly fit and over-estimate the very low fit, all subjects are still able to be categorized accurately into a fitness level (e.g., low fit, average fit, high fit). The estimation formula and its accompanying physical activity rating scale (PARS) are contained in *Table 2* and T*able 3* below:

```
VO2 max ≈ 56.363 – (0.381 * age) + (1.951 * PARS) – (0.754 * BMI) + (gender * 10.987)
 where: Gender: 0 = women; 1 = men
 BMI = body mass index = weight (kg) / (height in meters2)
 PARS = physical activity rating scale from 0 to 7 (see Table 3)
```
Table 2. Estimated Aerobic Fitness (VO2 max) (Jackson et al., 1990).


Mechanism of Sedimentary Basin Formation

Multidisciplinary Approach on Active Plate Margins

*Edited by Yasuto Itoh*

#### **Mechanism of Sedimentary Basin Formation - Multidisciplinary Approach on Active Plate Margins**

http://dx.doi.org/10.5772/50016 Edited by Yasuto Itoh

#### **Contributors**

Shigekazu Kusumoto, Yasuto Itoh, Osamu Takano, Machiko Tamaki, Atsushi Noda, Takeshi Nakajima, Kosuke Egawa, Gentaro Kawakami, Akira Takeuchi, Tetsuya Sakai, Mototaka Saneyoshi, Yoshihiro Sawada, Masato Nakatsukasa, Yutaka Kunimatsu, Emma Mbua, Keiji Takemura

#### **© The Editor(s) and the Author(s) 2013**

The moral rights of the and the author(s) have been asserted.

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#### **Notice**

Statements and opinions expressed in the chapters are these of the individual contributors and not necessarily those of the editors or publisher. No responsibility is accepted for the accuracy of information contained in the published chapters. The publisher assumes no responsibility for any damage or injury to persons or property arising out of the use of any materials, instructions, methods or ideas contained in the book.

First published in Croatia, 2013 by INTECH d.o.o. eBook (PDF) Published by IN TECH d.o.o. Place and year of publication of eBook (PDF): Rijeka, 2019. IntechOpen is the global imprint of IN TECH d.o.o. Printed in Croatia

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*3.1. Landscape Character Types and Areas at the Regional Scale*

At the regional scale, five variables for 45 landscape indicators were divided into 30,591 grid cells. Eleven landscape character types were classified by the scatter plots and spatial distribution of clusters (Figure 3). Type 3 covered a maximum area of 4363 km2, type 11 covered a minimum area of 549 km2, and the other clusters covered more than 1000 km2 (Figure 4a). The ratios of the landscape indicators to the landscape character types were expressed by coding as detailed in the materials and methods section. Figures 3 and 4b show that "L3L4, V1V5V8V10, S5, H7 G4" accounted for more than 60% and were prominent characteristics of the types; "{L3L4}, {V4V5V7V8}, {S5S14}, {G1G3G8G12G15G16}" accounted for 30–60% and were typical characteristics; and "(L2L3L4), (V1V3V6V8V7V10V11), (S4S5S6S7S8S11), (G1G4G5G7G9G11G13G14G15G16 G17)" accounted for 10–30% and were

general characteristics. The ratios of the landscape indicators to the landscape character types indicated the common feature of the railway that landform was prominent in or features typical of a plateau lake basin subregion or karst middle mountain platform subregion. The vegetation included various types of needleleaf forests in the subtropical zone, as well as grasslands and steppes in both the subtropical and tropical zones. The hydrology was characterized by plateau lakes and natural rivers where the soil was dominated by red earths, while the geology included various typologies of the Triassic system, Cambrian system, Devonian system, Nanhua system, Mesoproterozoic system, Quaternary system, and Jurassic system.

**Figure 3.** Landscape character types at the regional scale.

**Figure 4.** (**a**) Areas of landscape character types at the regional scale; (**b**) the ratios of landscape indicators to landscape character types at the regional scale.

The MRS tool was used to divide the landscape character areas. To ensure the segmentation effect, the scale, shape, and compactness parameters were set to 200, 0.4, and 0.1, respectively. A total of 98 landscape character areas were divided in eCognition (Figure 5A). Then, 80 landscape character areas were divided after manual adjustment (Figure 5B). The distribution of the landscape character areas in Kunming City and Yuxi City was relatively compact, while the distribution of the areas in Honghe Hani and Yi Autonomous Prefecture and Wenshan Zhuang and Miao Autonomous Prefecture was relatively sparse. The landscape character areas gradually decreased in number from north to south. The landscape character areas were more distributed when closer to an urban area and vice versa. In order to further identify the landscape character of the Yunnan–Vietnam Railway (Yunnan Section), 26 landscape character areas along the railway were selected to be named and described according to the prominent or typical features of the landscape character types and field survey (Appendix A) (Table 3). All of the 26 landscape character areas contained red earths, which was a highly representative landscape character along the railway. According to the landform statistics, seventeen landscape character areas contained plateau lake basin, three landscape character areas contained karst middle mountain platform, and six landscape character areas contained both plateau lake basin and karst middle mountain platform. According to the geology statistics, nine landscape character areas included the Triassic system, six landscape character areas included the Devonian system, three landscape character areas included the Cambrian system, and the others included mixed landscape indicators. In addition, there were several special areas. For instance, the landscape character areas for B5, B51, B54, and B71 were characterized as having urban and lake features, and B27, B73, B74, and B76 were characterized as having karst middle mountain platform and tropical rain forest, grassland, and shrub features.

**Figure 5.** Landscape character areas at the regional scale: (**A**) delineation in eCognition; (**B**) delineation by manual adjustment.

**Table 3.** Descriptions of landscape character areas at the regional scale.

*3.2. Landscape Character Types and Areas at the Corridor Scale*

At the corridor scale, five variables of the 24 landscape indicators were divided into 35,554 grid cells. Combined with the scatter plots and the spatial distribution of clusters, 12 landscape character types were identified (Figure 6A). Type 6 covered a maximum area of 1224.4 km2 and type 7 covered a minimum area of 17.75 km2 (Figure 7a). Figures 6A and 7b showed that "α4, β1β2β3, γ4γ5, θ2θ4, ε1ε2" were the prominent landscape characteristics of the types, "{α3α4}, {β1β2β3β4}, {γ2γ3γ4γ5}, {θ1θ2}" were typical characteristics, and "(α2α3), (β1β2β3β4), (γ1γ2γ3γ4γ5), (θ1θ2θ3θ5), (ε3)" were the general characteristics (Figure 3). The ratios of the landscape indicators to the landscape character types showed a common feature of the railway, namely, that altitude was prominent in or typical of a middle-high altitude and a high altitude. The slope and aspect were diverse, encompassing flat slope, gentle slope, sunny slope, shady slope, etc. The land use included various types of arable land, built area, and forest land, while the heritage density was characterized by low and medium densities, with zero to four heritage points per square kilometer.

An effective segmentation was received when the parameters for scale, shape, and compactness were set to 100, 0.1, and 0.5, respectively. A total of 63 landscape character areas were divided in eCognition (Figure 6B). Then, 58 landscape character areas were divided after manual adjustment (Figure 6C). The landscape character areas were more distributed when they were closer to an urban area and vice versa. The landscape character areas were named and described by the landscape character types and the field survey (see Appendix B), as shown in Table 4. All of the 58 landscape character areas contained middle–high altitude and high altitude characteristics, which were highly representative landscape characters. Land use was the key variable for dividing the landscape character areas. The five areas containing water landscape characters were located in Dianchi, Fuxian, Yangzonghai, Yilong, and Datunhai Lake; 23 were characterized by forest land, 13 were characterized by arable land and built area types, and the others included mixed types of arable land, forest land, and built area. The landscape character areas for C6, C27, and C45 were characterized by medium- and low-heritage densities, which primarily covered the urban areas of Kunming City and the Kaiyuan and Mengzi County Cities.

**Figure 6.** Landscape character types and areas at the corridor scale: (**A**) landscape character types; (**B**) delineation areas in eCognition; (**C**) delineation by manual adjustments.

**Figure 7.** (**a**) Areas of landscape character types at the corridor scale; (**b**) the ratios of landscape indicators to landscape character types at the corridor scale.

**Table 4.** Descriptions of landscape character areas at the corridor scale.


*1.1.1. History of ovariohysterectomy*

If taken from another person, the bitch may have been sterilized, which a new owner may overlook. Presence of a tattoo in the inguinal region and palpation or inspection of a scar from operation in the ventral wall of the abdomen may be indicators of ovariohysterectomy. However, it should be kept in mind that such a scar may be present if any intra-abdominal operation has been performed, so it may be premature to conclude that the scar resulted from ovariohysterectomy. Serum LH level measurement may be used to identify bitches that have undergone ovariohysterectomy, as serum LH is continuously high in such bitches as a result of the absence of negative feedback on LH (because the ovaries have been removed). Although elevation in serum LH provides information about ovariohysterectomy, note that this indicator may also be seen in ovarian dysfunction or during the preovulatory period (i.e., the preovulatory LH peak). Therefore, repeated measurements are required to confirm and experimental laparotomy may also be performed for a definitive diagnosis [8]. Whether ovariohysterectomy has been performed may also be detected by measuring the serum estrogen level before and 60–90 min after intravenous administration of 0.02–0.03 μg/kg buserelin. If ovariohysterectomy has been performed, estrogen levels will be found above 15–20 pg/mL.

  Silent heat (subestrus)*

Silent heat is defined as the maintenance of ovarian functions without the presence of vulvar edema, serosanguinous vaginal discharge, and charm for male dogs. Silent heat may be observed for several cycles before first estrus in younger bitches of smaller breeds. These animals may be evaluated as "anestrus" because the pet owner may not find the external signs of estrus, or they may be identified as healthy male dogs although ovarian functions continue normally.

If silent heat is suspected, serum progesterone level should be measured once monthly in order to verify that the ovaries are functioning. A serum progesterone level above 2 ng/mL indicates functional luteal tissue. Observation of increasing superficial epithelial cells in regular vaginal cytological examinations is an indicator of functional ovaries [5].


**2. The teaching and learning experience in the 21st century**

The 21st century is demanding profound changes in veterinary education. Scientific knowledge grew at a dizzying speed, so even for researchers, it is difficult to keep up with the literature. The world is completely different and never the expression "times are changing" heard in the transition from our parents' generation to ours, was applied with as true sense as now. As in all sectors of society, Education systems are also changing. Big transformations occurred following the Bologna treaty that changed the educational paradigm, advocating greater student autonomy and selflearning. These changes must now be optimized considering technological evolution, that have begun to change how students acquire information [15]. It is imperative to occupy the fast fingers of students on smartphones in favor of teaching and science. This is a challenge for today's teachers, according to the idea that "The more complex the world becomes, the more creative we need to be to meet its challenges" [15, 16]. Another issue is the curricula reforms, that resulted in a reduction of teaching hours. In some core disciplines such as physiology, this reduction has resulted in serious reviews of the way it is taught [15].

#### **2.1 Who are the 21st century students?**

Current higher education students are generally in their late teens and early adulthood (although naturally some are older and a small number may be younger), and belong to the so-called Generation Z, born between 1995 and 2009. Generation Z follows members of Generation Y, more commonly known as Millennials, who were born between 1975 and 1995. Most of them do not remember life without the internet, and have had technology like smartphones, iPads, smartboards and other devices available throughout most of their schooling years [17, 18]. They grew up around gaming and have great affinity with not just technology platforms, but also with game-like settings

that provide, among other components such as continuous challenges, captivating storylines, immediate rewards and feedback, and sometimes fun [19].

Students from the so-called Generation Alpha, born between 2010 and 2025, future students in the higher education system, are younger than smartphones, the iPad, 3D television, Instagram, and music streaming apps like Spotify. This will be the first generation to be born entirely within the 21st century and likely to live in the 22nd century in large numbers. They are also the first generation to experience a pandemic situation in their early childhood: the SARS-CoV-19 pandemic (**Figure 2**) [17, 18].

Interestingly, Generation Alpha started at the same year that Apple launched its iPad, Instagram made its debut and the American Dialect Society crowned "app" as its word of the year. Surrounded by technology, this generation does not live without it, as an extension of itself. Digital tools are omnipresent in their lives, being the "most materially endowed and technologically literate generation to ever grace the planet!" [18].

This generation has grown up like no other, surrounded by technology from childhood, making it, certainly, the fittest generation in terms of digital skills. They are immersed in technology, almost as an extension of their way of being. It is widely accepted that technology can bring countless benefits. Let's think about the SARS-CoV-19 pandemic. Although too early to know exactly the pandemic impact, in early 2020, the coronavirus pandemic forced schools and most employers to operate remotely, and technology was the one who came to the rescue. This crisis has driven unpredictable direct and indirect effects on the entire educational system. Although technology can be extremely useful, when it is overkill, it can create some drawbacks, such as shorter attention spans and delayed social development [17, 18]. The impact of all this crisis is yet to be determined for years and years to come.

At this point we all understand that the entire educational system (including higher education), must undergo a phenomenal adaptation to keep up with this distinct new generation of students [18]. Past/traditional methods of teaching and learning may already make little sense to today's students who learn and think differently, and to their future workplace, where change is a constant, and where making use of information is now far more valuable than simply knowing things. Schools are probably failing to teach students to respond to rapid changes and how to handle new information because they are clinging to obsolete methods, namely memorize facts for a test when all the information will be fully available at a click [17]. To avoid demotivation, the learning process has been advocating new strategies, including activities

**Figure 2.** *The 21st century students in higher education system in 2021.*

#### *Virtual Physiology: A Tool for the 21st Century DOI: http://dx.doi.org/10.5772/intechopen.99671*

student-centred, to achieve the expected learning outcomes and at the same time, to maintain student's engagement [20, 21]. In order to increase students' knowledge, understanding, and at same time enhancing their motivation and engagement, teachers must create a joy, an excitement, and a love for learning, while inspiring students. It is imperative for teachers to demonstrate how to learn, rather than dictating what they know [22]. New strategies will lead to success, reducing the frustration of a lonely, passive study, reducing despair, depression and poor quality of life.


*3.2.3 Genetically engineered models*

The above-mentioned models have been in use for more than 30 years and allow for a deeper understanding of the pathogenic mechanisms involved in chronic liver

#### *Models of Hepatotoxicity for the Study of Chronic Liver Disease DOI: http://dx.doi.org/10.5772/intechopen.106219*

disease and malignant transformation. The better known genetically engineered models include HBV-transgenic, HCV-transgenic, *c-myc*-transgenic, *c-myc*-/ TGF-α transgenic, E2F-1 transgenic, *c-myc*-/E2F-1 transgenic, *Apc* knockout mice, β-catenin/H-ras mutant, and cMyc+shp53 mice. Transgenic technology was initiated by inserting exogenous viral DNA into mice to induce the expression of different components of the viral particle [57]. Afterward, several important protein-coding genes and transcriptional enhancers associated with cancer were micro-injected into single-cell embryos of specific mice strains. Most transgenic mice show micro- and macro-fat vacuoles (at 6 and 11 months of age). Although inflammation is not commonly observed between 6 and 15 months of age, most mice develop preneoplastic hepatic lesions and adenomas at 6 and 11 months [100]. Those changes are accompanied by alterations in glycolysis and lipogenesis, which play a key role in the early (preneoplastic) stages of hepatocarcinogenesis. A high incidence of adenomas and carcinomas appears between 40 and 136 weeks. The advantage of these models is that they are highly reproducible and resemble human disease.

### *3.2.4 Humanized mouse model*

Humanized mouse models are widely used to mimic the human immune system in mice [101]. This mouse model is based on transplanted human cells and tissues that have been uniquely engineered to produce combinations of human cytokines in immunocompromised mice and avoid rejection of implanted cells. This kind of model results in a more physiologically relevant model system for evaluating new cancer therapies, immuno-oncology, and effective treatments targeting the tumor microenvironment. Proteomics studies of humanized models have shown that there is an increase in proteins related to apoptosis at 12 months, the defense of fatty acid metabolism against oxidative stress [102]. Other studies have shown that, in combination with DEN, there can be an increase in the size of neoplastic nodules [103]. The mouse is the most widely used animal model in biomedical research because it is versatile, inexpensive, and genetically very similar to humans. However, success depends on animal age, sex, and strain.


**7. International status**

RT-qPCR assays were already known, but development can lead to better results. Thus, one study was done by targeting two monoplex assays recommended by WHO that was targeted on the envelope gene (E-Sarbeco) and RNA-Dependant RNA Polymerase coding genes (RdRp-IP4). This was combined and test named as 'Duo SARS-CoV-2 RT-qPCR assay'. As already lots of duo assays are commercially available, but this study was done to combine in-house assays. Can be used to reduce the chances of false negative results as it is dual assay [60]. As dual target assays are commercially available, developed specifically to

target multiple sites in the viral genome, but mutation rates in virus found to be moderate which can cause problem with respect to results. Some of the tests were done by using 'cobas SARS-CoV-2 E gene qRT-PCR' but some failures were seen due to change in nucleotide at position 26340 of the SARS-CoV-2 gene. So the study was done to identify single nucleotide polymorphism in E gene of the virus. This includes the importance of study regarding mutations in the virus and thus to prevent false negative results [61]. The protocol provided by WHO mention the three assay that is to be performed: First line screening assay - E gene assay, Confirmatory assay - RdRp gene assay, and Additional confirmatory assay - N gene assay [24]. 'Multiplex Real Time PCR' was also use to find its efficacy for SARS-CoV-2 detection. Found to be rapid and accurate method for viral detection [62]. 'Aus Diagnostics respiratory MT-PCR assay' was also found to be reliable and sensitive [63]. Two 'Single-tube nested (STN) real-time RT-PCR assays' specifically targets RdRp/Hel and N genes, found to be 100% specific for detection of SARS-CoV-2 [64]. Even high cost assays were given preference during a pandemic situation like TaqMan-based real-time RT-qPCR which was not even accessible to lots of laboratories. So it was performed by using 2 methods that are SYBR green RT-qPCR and conventional PCR basically standardisation was done of this 2 methods which is cost effective methods and found to give equal results as that of TaqMan-based real-time RT-qPCR [65].

COVID-19 diagnosis now done by one step RT-qPCR by using primers and probes which were developed at different institutes like China CDC, Charite (Germany), The University of Hong Kong, National Institute of Infectious Diseases in Japan (Japan NIID), National Institute of Health in Thailand (Thailand NIH) and US CDC which was announced by WHO [2, 24]. One study performed the analysis of primer-probe sets specifically targeting the N region and RdRp/Orf1 of SARS-CoV-2 by N-assay and RdRp/Orf1 Assays. Primer probe set for N-assay was N (China CDC), HKU-N (HKU), NIID\_2019-nCOV\_N (Japan NIID), WH-NIC N (Thailand NIH), and 2019-nCoV\_N1, -N2, and -N3 (US CDC) and for RdRp/Orf1 Assay RdRp\_SARSr (Charite), HKU-ORF1b-nsp14 (HKU), and ORF1ab (China CDC) primer probe set was studied. Results says that NIID\_2019-nCOV\_N" from the Japan NIID and "ORF1ab" from China CDC gave a good performance for RT-qPCR analysis without any cross-reactivity and nonspecific amplifications. This can be used for further diagnosis [66]. Sensitivity of PCR also depends on primer concentration, degeneration and multi target detection. Initial concentration of primer was 300-900 nM but as its concentration rises sensitivity also improves [67]. One study found that concentration upto 400 nM rise the sensitivity [68]. Degenerate primers plays an important role with respect to diversity of SARS-CoV-2. While screening assays with a single target area are more prone to sequence differences than dual or triple-target assays for multi-target identification [67]. Other than this primer length, melting temperature, GC content and annealing temperature also affects the sensitivity of PCR assay [67]. One study attempted to deduce the specific patterns among SARS-CoV-2 isolates and accordingly primers were design targeted to nsp2 gene and further use for diagnosis of probe free real-time RT-PCR. Sensitive and rapid SARS-CoV-2-specific real-time RT-PCR assay COVID-19-nsp2 has therefore been developed [69]. In one research, the efficiency of three novel real-time reverse transcription-PCR (RT-PCR) assays targeting RNA-dependent RNA polymerase (RdRp)/helicase (Hel), spike (S) and nucleocapsid (N) SARS-CoV-2 genes was developed and compared. RNA polymerase (RdRp)/(Hel) assay found to be effective with no cross reactivity with other viruses among samples [27]. Some of the RT-PCR kits manufactured at International level along with sample requirement has been shown in **Table 5**.

#### *Development of RT-PCR Based Diagnosis of SARS-CoV-2 DOI: http://dx.doi.org/10.5772/intechopen.96823*

**Table 5.**

*RT-PCR kits developed by International companies and sample requirement.*


**Author details** Retracted

Pınar Kirezli Uludağ Department of Physics, Namık Kemal University, Tekirdağ, Turkey

\*Address all correspondence to<EMAIL_ADDRESS>
© 2020 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

*Brans-Dicke Solutions of Stationary, Axially Symmetric Spacetimes DOI: http://dx.doi.org/10.5772/intechopen.89906*

#### **References**

**4. GR limit of the solutions**

*Advances on Tensor Analysis and Their Applications*

the corresponding GR ones.

equations should be provided.

limit of these solutions.

**Author details**

**44**

Pınar Kirezli Uludağ

**5. Conclusion**

According to the common belief, since BD parameter *ω* ! ∞, the BD solutions reduce to corresponding GR ones. Contrary to this belief, several counter examples were presented in the literature [20–24]. In our study, the GR limit of the BD solutions is out of complexity. When *k* ! 1, BD transformation equations of (44)– (46) reduce to seed GR metric functions for any finite *ω* since scalar field *ϕ* becomes constant. It is obvious from the given examples that, as *k* ! 1, BD metrics reduce

In this section, we have studied to obtain corresponding BD or BD-Maxwell solution from any known solution of the Einstein or the Einstein-Maxwell theory for stationary, axially symmetric spacetimes in Jordan frame. First we present that, although several field equations of BD are not included by Ernst equations, BD field equations can be written in the form of Ernst Eqs. BD solutions can be obtained by selecting the appropriate physical potentials or by integrating Ernst equations, but it should be remembered that the equations which are not included in the Ernst

In order to obtain BD solutions, we have constructed two parameter solutiongenerating techniques. It was seen that, in previous works, it was studied with one parameter. From any given seed GR solution of Eqs. (6) or (20), the corresponding BD solution can be obtained by the two parameter solution-generating techniques. In order to show how this method works, we have constructed several known solutions and also some new solutions for BD theory. We have also discussed the GR

Department of Physics, Namık Kemal University, Tekirdağ, Turkey

© 2020 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

\*Address all correspondence to<EMAIL_ADDRESS>
provided the original work is properly cited.

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[2] Perlmutter S et al. Measurements of Ω and Λ from 42 high redshift supernovae. The Astrophysical Journal. 1999;**517**:565-586

[3] Perlmutter S, Turner MS, White M. Constraining dark energy with SNe Ia and large scale structure. Physical Review Letters. 1999;**83**:670-673

[4] Riess AG et al. Type Ia supernova discoveries at *z* > 1 from the hubble space telescope: Evidence for past deceleration and constraints on dark energy evolution. The Astrophysical Journal. 2004;**607**:665-687

[5] Weyl H. A new extension of relativity theory. Annalen der Physik. 1919;**59**:101-103

[6] Eddeington AS. The Mathematical Theory of Relativity. Cambridge: Cambridge University Press; 1923

[7] Brans C, Dicke R. Mach's principle and a relativistic theory of gravitation. Physics Review. 1961;**124**:925-935

[8] McHugh MP. The Brans-Dicke theory and its experimental tests. Fundamental Theories of Physics. 2016; **183**:163

[9] Banerjee N, Pavon D. Cosmic acceleration without quintessence. Physical Review D. 2001;**63**:043504

[10] Sen AA, Sen S, Sethi S. Dissipative fluid in Brans-Dicke theory and late time acceleration. Physical Review D. 2001;**63**:107501

[11] Lima NA, Ferreira PG. On the phenomenology of extended Brans-Dicke gravity. JCAP. 2016;**1601**:010. DOI: 10.1088/1475-7516/2016/01/010 [arXiv:1506.07771 [astro-ph.CO]]

[12] Chatterjee S, Banerji S. Acta Physica Polonica B. 1980;**11**:493

[13] Tsuchida T, Watanabe K. Comment on the exterior solutions and their geometry in scalar-tensor theories of gravity. Progress in Theoretical Physics. 1999;**101**:73-90 Retracted

[14] Astorino M. Embedding hairy black holes in a magnetic universe. Physical Review D. 2013;**87**:084029

[15] Nayak BK, Tiwari RN. Class of the Brans-Dicke Maxwell fields. Physical Review D. 1976;**14**:2502-2504

[16] Singh T, Rai LN. Stationary axially symmetric Brans-Dicke-Maxwell fields. General Relativity and Gravitation. 1979;**11**:37-43

[17] Kirezli P, Delice O. Stationary axially symmetric solutions in Brans-Dicke theory. Physics Review. 2015; **D92**:104045

[18] Park DH. Rotating black hole solutions in the Brans-Dicke theory. Journal of the Korean Physical Society. 2007;**51**:258-262

[19] Gibbons GW, Mujtaba AH, Pope CN.  Classical and Quantum Gravity. 2013;**30** Retracted

> [20] Baykal A, Delice O. Cylindrically symmetric Brans-Dicke-Maxwell solutions. General Relativity and Gravitation. 2009;**41**:267-285

[21] Romero C, Barros A. Does Brans-Dicke theory of gravity go over to the general relativity when omega ––– > infinity? Physics Letters A. 1993; **173**:243-246

[22] Banerjee N, Sen S. Does Brans-Dicke theory always yield general relativity in the infinite omega limit? Physical Review D. 1997;**56**:1334-1337

[23] Bhadra A, Nandi KK. Omega dependence of the scalar field in Brans-Dicke theory. Physical Review D. 2001; **64**:087501

[24] Faraoni V, Côté J. Two new approaches to the anomalous limit of Brans-Dicke theory to Einstein gravity. Physical Review D. 2019;**99**(6):064013 Retracted


*2.2.1 Challenges and trends*

*Quantum Cryptography in Advanced Networks*

*2.1.1 Challenges and trends*

**2.2 Optical detector**

to remember that the optical sources described have to be suitable for FSO links where a complete QKD system is implemented, that is, the restriction of singlephoton is crucial for support the secure aspect inherent in QKD systems, however, the FSO links imposes trade-off that have to be analyzed. For this reason, the faint pulse is the common technique for FSO applications. Until now, the single-photon source information presented has been analyzed based on certain particular characteristics. However, an important aspect is the quantum state of the single photon generated by the optical source, that is, a photon can be generated with a particular quantum state (related to a quasi-probabilistic density functions) such as coherent, Fock, entanglement, among others. In fact, an ideal single-photon deterministic source should be generating a single photon with Fock distribution. On the other hand, an entanglement "single-photon" (probabilistic way) can be used in some short-distance-FSO-QKD systems and laboratory considering a high efficiency channel and finally, a single-photon source with coherent state (faint laser) is the most useful source and distribution used for long distance free space links.

In general, the challenges in the actual optical sources are regarding the band telecommunication of the device, inherent bandwidth, emission efficiency and output spatial mode. Therefore, the important advance imposes a clear trend based on efficient optical sources at common telecom wavelengths (i.e. C-band) [5]. Although sources at O-band are available [6]. Basically, the improved performance of the optical sources is based on the use of novel materials, structures and quan-

An ideal single-photon detector is useful in QKD systems in order to detect and resolve (determinate) an amount of photons per observation time (related to bit), that is, the detector is enabled to detect a single-photon and determine the exact quantity of a single-photon. However, this definition is based on the assumption of an ideal single-photon source. Obviously, ideal single-photon source and detector permits directly assure specific security levels based on the detection of an Eve system that disturbs the amount of photons transmitted by Alice. However, due to physical characteristics of the materials used on the manufacturing, there are deviations between the idealistic and realistic performance parameters. Thus, many realistic single-photon detectors have the ability of distinguish between zero photons per bit and more than zero photons, but they do not resolve the amount of photon. Based on

photon-number-resolving detectors, that is, they have the ability of detecting photon but do not resolving the exact amount of photons. However, there are different modes of operation based on multiple detectors that allow improving the resolving process. Some examples about single-photon detector proposals are: (a) the Photo-Multiplier Tube (PMT) which is a classical single-photon detector that operates from the visible region to the infrared. However, the detection efficiency is considerably reduced, for example, at 500 nm the efficiency is 0.4, while for 1550 nm is 0.02; meaning a major problem for its application in some real optical networks; (b) Single-Photon Avalanche Photodiode (SPAP) category has a wide variety of technical options for detection process, having minimum and maximum efficiencies from 0.40 to 0.74 for 450–780 nm band, respectively (based on Silice). In both cases (i.e. a and b options), the wavelength range is not completely suitable for FSO communications systems, although some beacon systems can use these detectors with previous analysis.

tum devices that permits the near-ideal quantum state generation [7].

the above, the most common used single-photon detectors are the non-

**28**

The principal challenges are related to minimizing the electronic noise and maximizing the gain of the detector maintaining high transmission rates [8, 9]. To do the aforementioned, novel materials and electrical designs are required. In particular, reducing the Noise Equivalent Power (NEP) parameter permits the detection of low optical power with different electrical bandwidth [10]. However, although novel optical detectors have been developed, coherent detection techniques have been helps at Bob side, relaxing the detector selection due to inherent amplification and spectrum filtering of the coherent technique.

### **2.3 Digital processing systems**

The DP&Comm subsystem implemented in conventional QKD systems performs particular basic tasks such as: driver for different devices (e.g. phase and amplitude modulators, true random number generator (TRNG), etc.), quantum key data base, perform the algorithm need to distillation, reconciliation and privacy amplification processes between Alice and Bob. In particular, this algorithm requires access to both quantum and classical channels. Therefore, the DP&Comm requires some important technical specifications so as not to degrade the secure level and secrete key rate of the QKD systems. In particular, Field Programmable Gate Arrays (FPGA) have been used in a real-time QKD systems reaching secret key rate at 17 kb/s in an optical fiber link of 20 Km [11]. It is clear that, the FPGA specifications impact the performance of a QKD systems, therefore, improved synchronization and jitter methods based on high speed and precision devices can reduce the Quantum Bit Error Rate (QBER) and increase the final secret key rate [12].

In addition, the secret key rate has an important relation with the performance of the TRNG subsystems, thus, FPGAs have been used for generation and acquisition of true random digital sequences reaching 1.25 Gb/s [13]. An important issue in DP&Comm subsystems is the ability to adapt and generate countermeasures to maintain or improve the specific performance against external dynamic factors such as atmospheric turbulence in FSO links, resizing and adaptive parameters based on an optimization process [14, 15]. In addition, some QKD systems use a Graphics Processing Unit (GPU) as a DP&Comm (although some considerations have to be analyzed to complete all the task of the DP&Comm) because it provides some important technical features such as parallel computing and processing floatingpoint information allowing rates of 1.35 Gb/s [16]. The novel standalone modules for particular stages of the protocol used (e.g. sifting, error correction, and privacy amplification modules) also support the performance of QKD systems, which are based on high-end electronic design. These particular technical innovations in specific modules permits reaching secret key rate of ≈13.72 Mb/s [17].

### *2.3.1 Challenges and trends*

Thus, the DP&Comm subsystem depends on the electronic development regarding the high performance related to speed processing and the novel design of Printed Circuit Board (PCB) used in different subsystems within DP&Comm. Among the devices that need to be improved are high-end converters (Digital-to-Analog-Converter and Analog-to-Digital-Converter), fast output/input ports (e.g. analog and digital) and fast memories. On the other hand, an optimized QKD protocol have to be programmed in DP&Comm subsystems, which includes different algorithms needed in different protocol stages, that is, detecting-correcting errors codes, performing some Hash functions among other used. Therefore, no matter the high-end devices used in the DP&Comm subsystem, the designer should try to reduce the trade-off based on optimized programming.

In addition, Commercial Off-The-Shelf (COTS) devices have been used for QKD-FSO systems using an optimized protocol to not degrade the security level and secret key rate [18]. **Figures 2** and 3 show the Alice and Bob set-up, respectively. Both systems use COTS devices in a Local Area Network (LNA). In particular, Alice set up (**Figure 2**) consists of an optical source in order to generate a LO and a data signal (the way to divide the optical signal is not graphically clear expressed, but 1X2 fiber splitters were used), the LO signal will be sent to Bob separately in order to perform a self-homodyne detection. In addition, a minimum optical signal is used for the TRNG to generate two random digital sequences (RSA1 and RSA2). These sequences are used by a COTS device that uses a DB-RN in order to drive the PM and perform the quantum protocol using both classical and quantum channels. The PC and PBS are used in order to maintain and ensure a vertical SOP in the incoming PM signal because in order to avoid a residual amplitude modulation. Since the optical source is non-polarized and it has an optical fiber output, a PC is used as the first element for polarization controlling, but because Alice and Bob have to be implemented in free space, a PBS was added in order to ensure the SOP. However, the PC can be deleted if an optical source with free space coupling and linear vertical polarization is used. Thus, residual amplitude modulation can affect the overall performance of the QKD systems. Next, phase modulation is used to encrypt the information and a half-wave plate to produce a linear SOP at 45 degrees needed for Bob set-up. Because the optical source generates a coherent state, an attenuator is used to produce a weak coherent state emulating a long distance free-space link. Before the optical signal is transmitted through the free space channel, a BS and PD are used for monitoring the optical power corresponding to the weak coherent state.

At the Bob side (**Figure 3**), a free space optical hybrid (π-hybrid) based on BS, PBS and BHDs is used in order to measure simultaneously both quadrature components of the weak coherent stated received. Mirrors and attenuators are used in order to calibrate the optical power received in each photodetector (implemented in each BHDs) due to the different optical paths. In particular, a quarter-wave plate

### **Figure 2.**

*Alice set-up. PBS, polarized beam splitter; TRNG, true random number generator; PM, phase modulator; DB-RN, database-random number; BS, beam splitter; ATT, attenuator; PD, photodetector; RSA, random sequence in Alice; PC, polarization controller; λ/2, half-wave plate; LO, local oscillator. Own figure and presented in [18].*

**31**

*Free-Space-Optical Quantum Key Distribution Systems: Challenges and Trends*

is used to change the SOP of the LO, that is, the LO needs a circular SOP in order to allow simultaneous measurements. Therefore, the complete Bob scheme is based on coherent detection technique, where an opto-electronic Costal loop permits the improvement of the complete performance reducing the phase noise due to different optical paths. Particularly, a COTS device and TRNG (it generates other random digital sequence, RSB1) are used in a similar way as Alice in order to perform the quantum protocol. The quantum transmitter-receiver shows an experimental average Quantum Bit Error Rate (QBER) of 30% using auto-homodyne detection with 0.25 photons per bit in locking phase mode. The final secret key rate measurements were 20 and 40 Kbps for minimum and maximum throughput in the LAN. Finally, although common elements (i.e. passive and active optical elements) are used in **Figures 2** and **3**, the important aspect is the uses of COTS devices in QKD systems that allow relaxing some design parameters maintain adequate performance param-

*Bob set-up. M, mirror; BHD, balanced homodyne detector; λ/4, quarter-wave plate; RSB, random sequence in*

The research on the protocols used for the distribution of the cryptographic key based on the principles of quantum mechanics had a great boom in the last 10 years. In general, the QKD protocols describe the particular tasks or steps (i.e. algorithm) needed in order to generate a final quantum secret key rate. Although the QKD protocols are programmed in a DP&Comm subsystem, they require all the subsystems. In particular, the protocols and their performance depend on the statistical information (discrete and continuous variables, DV and CV, respectively) regarding

The BB84 protocol is the first protocol proposed to guarantee unconditional security (because it is based on orthogonal states) when transmitting the cryptographic key that gives access to the information of a message. It has been considered as the ideal protocol, at least in theory, since it is based on the transmission of the quantum state of a single photon to represent a bit of information and provide immediate information through the characteristics of the received signal, about a possible attack by a spy [19]. In addition, if we add that the key is used in a single occasion (One Time Pad) it provides better protection in case that at some point an intruder manages to obtain the key. Next, B92 protocol was proposed based on BB84 protocol.

eters as mentioned (e.g. QBER, final secret key rate).

**3. QKD protocols: challenges and trends**

the quantum state used.

**Figure 3.**

*bob. Own figure and presented in [18].*

*DOI: http://dx.doi.org/10.5772/intechopen.81032*

*Free-Space-Optical Quantum Key Distribution Systems: Challenges and Trends DOI: http://dx.doi.org/10.5772/intechopen.81032*

### **Figure 3.**

*Quantum Cryptography in Advanced Networks*

reduce the trade-off based on optimized programming.

of Printed Circuit Board (PCB) used in different subsystems within DP&Comm. Among the devices that need to be improved are high-end converters (Digital-to-Analog-Converter and Analog-to-Digital-Converter), fast output/input ports (e.g. analog and digital) and fast memories. On the other hand, an optimized QKD protocol have to be programmed in DP&Comm subsystems, which includes different algorithms needed in different protocol stages, that is, detecting-correcting errors codes, performing some Hash functions among other used. Therefore, no matter the high-end devices used in the DP&Comm subsystem, the designer should try to

In addition, Commercial Off-The-Shelf (COTS) devices have been used for QKD-FSO systems using an optimized protocol to not degrade the security level and secret key rate [18]. **Figures 2** and 3 show the Alice and Bob set-up, respectively. Both systems use COTS devices in a Local Area Network (LNA). In particular, Alice set up (**Figure 2**) consists of an optical source in order to generate a LO and a data signal (the way to divide the optical signal is not graphically clear expressed, but 1X2 fiber splitters were used), the LO signal will be sent to Bob separately in order to perform a self-homodyne detection. In addition, a minimum optical signal is used for the TRNG to generate two random digital sequences (RSA1 and RSA2). These sequences are used by a COTS device that uses a DB-RN in order to drive the PM and perform the quantum protocol using both classical and quantum channels. The PC and PBS are used in order to maintain and ensure a vertical SOP in the incoming PM signal because in order to avoid a residual amplitude modulation. Since the optical source is non-polarized and it has an optical fiber output, a PC is used as the first element for polarization controlling, but because Alice and Bob have to be implemented in free space, a PBS was added in order to ensure the SOP. However, the PC can be deleted if an optical source with free space coupling and linear vertical polarization is used. Thus, residual amplitude modulation can affect the overall performance of the QKD systems. Next, phase modulation is used to encrypt the information and a half-wave plate to produce a linear SOP at 45 degrees needed for Bob set-up. Because the optical source generates a coherent state, an attenuator is used to produce a weak coherent state emulating a long distance free-space link. Before the optical signal is transmitted through the free space channel, a BS and PD are used for monitoring the optical power corresponding to the weak coherent state. At the Bob side (**Figure 3**), a free space optical hybrid (π-hybrid) based on BS, PBS and BHDs is used in order to measure simultaneously both quadrature components of the weak coherent stated received. Mirrors and attenuators are used in order to calibrate the optical power received in each photodetector (implemented in each BHDs) due to the different optical paths. In particular, a quarter-wave plate

*Alice set-up. PBS, polarized beam splitter; TRNG, true random number generator; PM, phase modulator; DB-RN, database-random number; BS, beam splitter; ATT, attenuator; PD, photodetector; RSA, random sequence in Alice; PC, polarization controller; λ/2, half-wave plate; LO, local oscillator. Own figure and*

**30**

**Figure 2.**

*presented in [18].*

*Bob set-up. M, mirror; BHD, balanced homodyne detector; λ/4, quarter-wave plate; RSB, random sequence in bob. Own figure and presented in [18].*

is used to change the SOP of the LO, that is, the LO needs a circular SOP in order to allow simultaneous measurements. Therefore, the complete Bob scheme is based on coherent detection technique, where an opto-electronic Costal loop permits the improvement of the complete performance reducing the phase noise due to different optical paths. Particularly, a COTS device and TRNG (it generates other random digital sequence, RSB1) are used in a similar way as Alice in order to perform the quantum protocol. The quantum transmitter-receiver shows an experimental average Quantum Bit Error Rate (QBER) of 30% using auto-homodyne detection with 0.25 photons per bit in locking phase mode. The final secret key rate measurements were 20 and 40 Kbps for minimum and maximum throughput in the LAN. Finally, although common elements (i.e. passive and active optical elements) are used in **Figures 2** and **3**, the important aspect is the uses of COTS devices in QKD systems that allow relaxing some design parameters maintain adequate performance parameters as mentioned (e.g. QBER, final secret key rate).

### **3. QKD protocols: challenges and trends**

The research on the protocols used for the distribution of the cryptographic key based on the principles of quantum mechanics had a great boom in the last 10 years. In general, the QKD protocols describe the particular tasks or steps (i.e. algorithm) needed in order to generate a final quantum secret key rate. Although the QKD protocols are programmed in a DP&Comm subsystem, they require all the subsystems. In particular, the protocols and their performance depend on the statistical information (discrete and continuous variables, DV and CV, respectively) regarding the quantum state used.

The BB84 protocol is the first protocol proposed to guarantee unconditional security (because it is based on orthogonal states) when transmitting the cryptographic key that gives access to the information of a message. It has been considered as the ideal protocol, at least in theory, since it is based on the transmission of the quantum state of a single photon to represent a bit of information and provide immediate information through the characteristics of the received signal, about a possible attack by a spy [19]. In addition, if we add that the key is used in a single occasion (One Time Pad) it provides better protection in case that at some point an intruder manages to obtain the key. Next, B92 protocol was proposed based on BB84 protocol. While BB84 protocol uses 4 orthogonal states, B92 only uses 2 non-orthogonal states. Therefore, the different quantum states (i.e. orthogonal and non-orthogonal) used in BB84 and B92 protocols impose a trade-off regarding the final secret key rate generated by Alice, Bob and the attacks performed by Eve [20]. Since the BB84 protocol is extremely vulnerable to Photon Number Splitting attacks, the SARG04 protocol was proposed, which uses 4 non-orthogonal quantum states; however, the final secret key rate is also affected [21]. Additionally, there exists the E91 protocol based on Einstein, Podolsky and Rosen (EPR) paradox that uses entangled quantum states generated either by Alice, Bob or a trusted third party [22]. Later, the BBM92 protocol was proposed which implies EPR pairs, that is, entangled photon pairs. This protocol can be described as the BB84-EPR protocol [23]. Until now, the protocols mentioned are based on State of Polarization (SOP), DV framework and general stages such as: raw key exchange, key sifting and privacy amplification, that is, all the protocols have the same stages in order to generate the final quantum key. On the other hand, QKD protocols based on CV variables are also suitable, such as COW protocol (Coherent One-Way), which is based on an amplitude encoded sequence of weak coherent pulse with the same phase for each particular time slot. In particular, different time slots have several optical pulses (related to an optical power average) and, occasionally, decoy sequences are sent in order to hinder the eavesdropped process [24]. Due to the different quantum states and encoding scheme used, this protocol is so-called distributed-phase-reference (DPR), in fact, there are many protocols in the same category such as the differential-phase-shift (DPS), which uses different phases but the amplitude remains constant. Therefore, interferometric techniques are required in the receiver [25]. All the DPR protocols perform joint measurements on subsequent signals. Actually, GG02 protocol is present in many commercial equipment. In general, this protocol is based on random distributions of coherent or squeezed states and modulates either the phase or amplitude of a quantum state and uses coherent detection in Bob's side [26]. Finally, each protocol mentioned has a particular security principle, be it the Heisenberg uncertainty or quantum entanglement. Although there exist novel protocols that change the security principle in order to improve the performance of particular QKD systems.

### **3.1 Challenges and trends**

The challenges present in the QKD protocols are related with the performance parameters of the QKD systems. In particular, although each protocol uses different security principle and quantum states, the important issues are increasing the security level, secret key rate and distance link between Alice and Bob in presence of Eve system. In fact, while a particular protocol presents a high security level and particular secret key rate for short distance links, other protocol presents the same security level and secret key rate for long distance links. However, as was mentioned, a QKD protocol requires the other subsystems, thus, a hypothetically complicated protocol imposes a strict and detailed design, that is, the experimental set-up is not simple. Therefore, the tendency of the protocols refers to proposing novel QKD protocols that allow to easily implement them in optical commercial networks, while the performance parameters remain constant or improved. In addition, a high dimension protocol is proposed in order to increase the photon information capacity when the photon rate is restrained. This protocol is based on entangled photon pairs that allow information to be transmitted using an extremely large alphabet [27].

Now, each QKD protocol has been theoretically described, however, free space and atmospheric channels impose important trade-off that determines the suitable protocol. In particular, BB84 protocol has been optimized for FSO links affected by atmospheric turbulence improving the secret key rate up to over 20% [28].

**33**

**4.1 Challenges and trends**

*Free-Space-Optical Quantum Key Distribution Systems: Challenges and Trends*

**4. Techniques and structure in QKD: challenges and trends**

to each protocol have been proposed for QKD systems implemented in FSO. For example, the atmospheric turbulence is an important problem for QKD systems based on FSO links. In order to mitigate the degraded performance of the secret key rate for QKD systems based on BB84 protocol, an optimization technique was proposed based on an adaptive optical power transmission considering the random irradiance fluctuation [28]. In the same context, a novel encoder technique was proposed for the classical channel in QKD-FSO systems based on adaptively encoder gain according to atmospheric turbulence levels [29], The results show that the secret key rate remains constant for a region of turbulence levels and imposes the need of a high-end DP&Comm subsystem in order to extend the operating region. In addition, many structures and techniques used in conventional classical optical communication systems have been adapted to QKD-FSO systems. In particular, Multi-Input-Multi-Output (MIMO) and Wavelength Division Multiplexing (WDM) are suitable options used in order to increase the capacity of free space channel based on Orthogonal Angular Momentum (OAM) modulation [30]. Among the structures and techniques necessary to implement a QKD-FSO system are the subsystems used in order to pointing, acquisition and tracking the two parties (Alice and Bob, represented by satellites and ground stations). In this case, pointing systems used in

satellites have reached from 0.6 μrad to 3 μrad pointing capability [31, 32].

In general, the structures and techniques allow to improve the performance of a QKD-FSO system. Therefore, the design of techniques and high-end structures allows to support in a better way the actual QKD system proposals. In fact, the principal challenges are related with the optimization and improving of the secondary subsystems of a QKD-FSO systems (i.e. secondary subsystems are not mentioned in detail in this chapter, such as telescope, mechanical structures, access multiplexing techniques, among others). Finally, the QKD-FSO system trends related with the structures and techniques are: maximize the channel capacity, increase the distance link and secret key rate, increase the power consumption efficiency in order to support long-time missions, improve the thermal control and isolation, among others. In addition, novel encoding technique for classical channel has been proposed in order to increase the secret key rate at QKD-FSO links. **Figure 4** shows a diagram proposed based on an adaptive LDPC (Low-Density Parity-Check Codes) encoder in order to countermeasure the effect caused by the dynamical atmospheric turbulence [29].

demonstrate their performance under particular conditions.

However, BB84 protocol remains unchanged while other subsystems are modified. In fact, many QKD protocols have been implemented in FSO links in order to

The techniques and structures used in QKD context involve the different set-ups, operation rules and devices that perform a particular protocol. Therefore, the first step is choosing the quantum protocol and next, the general structure can be proposed and implemented. In particular, the structure consists of optical source, optical detector, digital processing unit (the challenges and trends that have already been mentioned) among other specific devices connected together in order to perform a complete QKD system. On the other hand, the techniques are the novel operational rules in order to enhance the complete performance of the QKD system. Each protocol mentioned was proofed, first, using a particular technique and structure, these can be can be found and analyzed in the references listed. However, many improves

*DOI: http://dx.doi.org/10.5772/intechopen.81032*

However, BB84 protocol remains unchanged while other subsystems are modified. In fact, many QKD protocols have been implemented in FSO links in order to demonstrate their performance under particular conditions.


**5. Conclusions**

We conclude that diet plays an important role in the composition of the intestinal microbiota in MS patients and controls. In addition, intestinal dysbiosis, detected in RRMS patients receiving DMTs, could be involved in increased intestinal permeability and affect clinical response, future relapses, and disease progression in MS patients. Additional studies in patients with different forms of MS, using DMTs, in different populations are needed, and the future goal is to predict therapeutic responses based on individual microbiome analyses (personalized medicine) and propose dietary interventions and the use of probiotics or other microbiota modulators as adjuvant therapy to enhance the therapeutic efficacy of DMTs.

**Author Contributions:** Conceptualization, G.L.V.d.O.; data curation, F.P.P., A.Z.L., N.d.C.R., M.J.U., M.I.G., N.N.C.T., V.S.M., W.P.O., D.G.P., and G.L.V.d.O.; formal analysis, F.P.P., A.Z.L., V.S.M. and G.L.V.d.O.; funding acquisition, N.d.C.R., E.M.J. and G.L.V.d.O.; investigation, F.P.P., A.Z.L., N.d.C.R., M.J.U., M.I.G., V.S.M., and G.L.V.d.O.; methodology, F.P.P., A.Z.L., N.d.C.R., M.I.G., N.N.C.T., V.S.M., W.P.O.; D.G.P., and V.S.M.; project administration, E.G. and G.L.V.d.O.; resources, E.G. and G.L.V.d.O.; supervision, D.G.P., E.M.J., E.G. and G.L.V.d.O.; validation, D.G.P., E.G., G.L.V.d.O.; visualization, G.L.V.d.O.; writing—original draft, F.P.P., A.Z.L., and G.L.V.d.O.; writing—review and editing, E.G. and G.L.V.d.O. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by the Brazilian governmental agency, Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP), grant numbers #2016/50204-0, #2016/05062-2, #2017/04508-0, #2021/03866-5.

**Institutional Review Board Statement:** The study was conducted according to the guidelines of the Declaration of Helsinki, and approved by the Ethics Committee on Human Research from the Barretos Educational Foundation (protocol code 1522.762/2016; 29 April 2016).

**Informed Consent Statement:** Informed consent was obtained from all subjects involved in the study.

**Conflicts of Interest:** The authors declare no conflict of interest.


*3.2. Risk-Adjusted Performances*

The MAP results show that the MA timing strategy outperforms the buy-and-hold strategy. However, we observe that generally, portfolios with higher returns have higher standard deviations, which suggests that their risk (or total risk) levels are di fferent. Therefore, a natural research question is whether the return di fferences are due to exposure to risks. In this sub-section, we concentrate on the risk-adjusted profitability of MAP and TLS using three asset pricing models: the CAPM, FF3F, and LIQ4F models. We use MAP and *TLSMAP*,*t*,*L* as dependent variables and run time-series regressions against the risk factors. The results are presented in Table 2.

If the portfolio average return, *MAPj*,*t*,*L* is not fully explained by the risk factors, we expect α*j*,*L* to be significantly di fferent from zero. Otherwise, it suggests that the positive additional return found in the MA strategy is artificial after taking exposure to well-documented risk factors into consideration.

**Table 2.** Time-series regressions with the CAPM and LIQ4F models.

The sample stocks are sorted in ascending order by their BM ratios and assigned into decile portfolios each year. The equally-weighted portfolio daily returns are then obtained. MAP is the difference between the MA(20) strategy and the buy-and-hold strategy. The regression models are *MAPj*,*t*,*L* = α*j*.*L* + β*j*,*L*,*MKTRMKT*,*t* + ε*j*,*t*,*L* and *MAPj*,*t*,*L* = α*j*.*L* + β*j*,*L*,*MKTRMKT*,*t* + β*j*,*L*,*SMBRSMB*,*t* + β*j*,*L*,*HMLRHML*,*t* + β*j*,*L*,*LIQRLIQ*,*t* + ε*j*,*t*,*L*, where *RMKT*,*t* is market excess returns; *RSMB*,*t* is the size factor; *RHML*,*t* is the book-to-market factor; *RLIQ*,*t*. is the liquidity risk factor proxied by turnover ratio; ε*j*,*t*,*L* is an error term assumed to have a zero mean and to be uncorrelated with all other explanatory variables; and the factor sensitivities or loadings, β*j*,*L*,*MKT*, β*j*,*L*,*SMB*, β*j*,*L*,*HML*, and β*j*,*L*,*LIQ*, are the slope coefficients for the factors, respectively. α*j*.*L* is the intercept of the regression. *t*-test statistics are presented in the parentheses.

Table 2 provides the results of the equally-weighted portfolios on the CAPM and LIQ4F models. Because the results of FF3F are similar to those from the LIQ4F model, we do not report them to save space. All of the alphas of the 10 portfolios in the two models are significantly different from zero at the 5% level, which suggests that the profits generated from the timing strategy are not fully captured by these well-known risk factors. The alphas of the CAPM model range from 4.65 to 8.18 points, while the alphas of the LIQ4F model range from 6.57 to 9.08 points.

The betas of the market excess return and size factors are all negative and highly significant, which can partially explain why the alpha becomes larger than the unadjusted return of the MAPs. Half of the coefficients of the HML factor are positive and half are negative. The coefficients of the LIQ factor are all significantly positive.

The alphas of the *TSLMAP* in the CAPM and LIQ4F models are 13.24 and 15.14 points, respectively, which are larger than the unadjusted *TSLMAP* (11.23 points). Interestingly, while the adjusted R2 for most of the deciles in the two models are larger than 40%, the adjusted R2 for the *TSLMAP* is extremely low. Overall, the low R2 and significant alphas indicate that the CAPM and LIQ4F models cannot explain the excess profit from the new BM strategy.

### *3.3. Components of Strategies*

We now establish that the moving average technical analysis can help us obtain better returns than the buy-and-hold strategy. We are curious about how exactly the excess returns are created. To answer this question, we consider the operation of the MA timing strategy. We know that we hold the underlying portfolio when the signal *Pj*,*t*−1 > *Aj*,*t*−1,*L* appears and hold the risk-free asset otherwise. Comparing this with the buy-and-hold strategy, a difference appears only when *Pj*,*t*−1 < *Aj*,*t*−1,*L*. This difference is between the return generated from the underlying portfolio and the risk-free asset. Therefore, we can express the MAP return in another way:

$$MAP\_{j,t,L} = \begin{cases} 0, & \text{if } P\_{j,t-1} > A\_{j,t-1,L}, \\ R\_{f,t} - R\_{j,t}, & \text{otherwise}, \end{cases} \tag{9}$$

To examine the difference, we separate the sample into two parts: when *Pj*,*t*−1 > *Aj*,*t*−1,*L* (buy signal) and when *Pj*,*t*−1 ≤ *Aj*,*t*−1,*L* (sell signal). We calculate the proportion of days when *Rj* is higher (or lower) than *Rf* for the buying and selling signal states. The results are shown in Table 3.

**Table 3.** Components of strategies.

We separate the MA(20) portfolio sample into two parts. One is when *Pj*,*t*−1 > *Aj*,*t*−1,*L* which indicates a buy signal and the other is when *Pj*,*t*−1 ≤ *Aj*,*t*−1,*L* which suggests a sell signal. We then compare the return of the BM portfolio and the risk-free rate. We calculate the proportion of each situation for buying and selling signal states.

We find that the proportions of the state in which *Rj*,*t* > *Rf*,*t* are all bigger than 50%, ranging from 56.71% to 60.15%, when *Pj*,*t*−1 > *Aj*,*t*−1,*L*. However, this does not affect the MAP. In addition, the proportions of the state in which *Rj*,*t* < *Rf*,*t* are also all bigger than 50% when *Pj*,*t*−1 ≤ *Aj*,*t*−1,*L*. The highest is 53.97% in decile 6 and the lowest is 50.18% in decile 10. Although the successful rates are not very high (mostly between 50% and 60%), all of them are bigger than 50%, which leads to better performance by MA strategy when a selling signal emerges. These results show that the MA signal is useful in generating positive excess returns and help explain why the moving average can outperform the buy-and-hold strategy.

## *3.4. Alternative Lag Lengths*

In this sub-section, we investigate how the returns of the MAP and TLS change with the lag lengths. We conduct the moving average timing strategy with 5-day, 10-day, 20-day, 50-day, 100-day, and 200-day timing signals. The results are illustrated in Figure 1.

**Figure 1.** (**a**) For each BM portfolio, the moving average timing strategy is imposed with 5-day, 10-day, 20-day, 50-day, 100-day, and 200-day timing signals. The MAP returns for the decile portfolios are then averaged cross-sectionally. The raw returns of the average MAP, risk-adjusted alphas of CAPM and LIQ4F models are plotted; (**b**) The proposed technical analysis enhanced BM strategy is imposed with 5-day, 10-day, 20-day, 50-day, 100-day, and 200-day timing signals. The raw returns of the average TLS strategy, risk-adjusted alphas of CAPM and LIQ4F models are plotted.

Figure 1a plots the average return of MAPs across the decile portfolios with different lag lengths. The 20-day average MAP return is the highest (in fact, although it is not plotted, the 20-day MAP is the highest for each decile portfolio). The 5-day MAP and 10-day MAP are also significantly positive but are slightly smaller than that of the 20-day signals. The returns with signals that are longer than 20 days start to decline and become progressively smaller, and the results of the 100-day lag even become negative. The CAPM and LIQ4F model-adjusted MAP alphas present similar patterns to that of the unadjusted returns.

The returns of the proposed trading strategy, TLS, are plotted in Figure 1b. Again, the 20-day lag strategy generates the highest raw and risk-adjusted profits. The MA(5) and MA(10) strategies also perform well, as their returns are close to that of MA(20). However, when lags longer than 50 days are used, the strategy return drops sharply, almost reaching zero. We conjecture that this is because the Chinese stock market is highly volatile. A shorter moving average signal can capture the fluctuations in information more accurately than a longer moving average signal. The signals with long lag length may miss important information changes, and so the abnormal return produced by these signals becomes flat and small.

The results seem to suggest that a shorter moving average of up to 50 days can produce significant and meaningful positive returns. However, the 20-day lag signal provides the best result by capturing the most information regarding past prices. To sum up, lag length can influence the performance of the moving average timing strategy, and we need to choose the best one for China's stock market.


Fundamentals of Boundary Layer Theory

**125**

**Chapter 6**

**Abstract**

physical simulation

**1. Introduction**

simulations are performed.

Applications

Physical Models of Atmospheric

Experimental studies on wind engineering require the use of different types of physical models of boundary layer flows. Small-scale models obtained in a wind tunnel, for example, attempt to reproduce real atmosphere phenomena like wind loads on structures and pollutant dispersion by the mean flow and turbulent mixing. The quality of the scale model depends on the similarity between the laboratory-generated flow and the atmospheric flow. Different types of neutral atmospheric boundary layer (ABL) including full-depth and part-depth simulations are experimentally evaluated. The Prof. Jacek Gorecki wind tunnel of the UNNE, Argentina, and the Prof. Joaquim Blessmann closed-return wind tunnel of the UFRGS, Brazil, were used to obtain the experimental data. Finally, some recent wind engineering applications of this type of physical wind models are shown.

**Keywords:** wind tunnel, turbulence, aerodynamic loads, atmospheric dispersion,

Wind tunnels are designed to realize similarity in model studies, with the confidence that actual operational conditions will be reproduced. The first step is the evaluation of the flow characteristics with the empty wind tunnel, and then, different flow characteristics are achieved or reproduced at the test section to be applied in the experimental tests. To perform aerodynamic studies of structural models, the distribution of the incident flow must be such that the atmospheric boundary layer (ABL) at the actual location of the structure is reproduced. This is obtained by surface roughness elements and vortex generators, so that natural wind

The atmospheric boundary layer (ABL) is the lowest part of the atmosphere where the effects of the surface roughness, temperature, and others properties are transmitted by turbulent flows. Turbulent exchanges are very weak when there are conditions of weak winds and very stable stratification [1]. On the other hand, the atmospheric boundary layer over nonhomogeneous terrain is not well defined, and

Boundary Layer Flows: Some

Developments and Recent

*Adrián R. Wittwer, Acir M. Loredo-Souza,*

*Mario E. De Bortoli and Jorge O. Marighetti*