Theory of Extreme Optical Concentration in All-Dielectric Waveguides

Dielectric waveguides are the solution to the ultra-fast optical communication. In all-dielectric waveguide systems, the boundary condition of Maxwell’s electromagnetic equation can be exploited. Crucially dielectric materials have very low optical losses compared to metal hence the plasmonic structures. Due to very high losses, plasmonic structures are not suitable for practical usage. Achieving small mode dimensions has become an important factor in modern devices since smaller mode dimensions fosters high device density, efficiency, and or performance in a wide array of photonic systems. Keeping these criteria in focus, a transversely structured all-dielectric waveguide has been introduced in this thesis which exploits the vectorial nature of light to achieve extreme sub-wavelength confinement in high index dielectrics, enabling characteristic mode dimensions below λ_0^2/1,000 without metals or plasmonics. A new metric of performance measurement for waveguide structures has been introduced – “optical concentration”. This metric of optical concentration has been derived and illustrated for its convenient usage in characterizing enhanced linear and nonlinear interactions at the nanoscale. This work expands the toolbox of nanophotonics and opens the door to new types of ultra-efficient and record performing linear and nonlinear devices with broad applications spanning classical and quantum optics

Response of asphalt matrix under multi-axial stress state

textThe pavement system is subjected to complex stress states under vehicular loading. A combination of axial and shear stress has been identified as a potential cause of top down cracking (or more precisely near surface cracking) in asphalt surface. Therefore, in terms of modeling the material response a pertinent question is whether the typical one-dimensional viscoelastic properties of the material are affected by a multi-axial stress state. Such changes are referred to as interaction non-linearity. The objective of this study was to evaluate whether or not asphalt composites are susceptible to such interaction effects. The study was conducted using fine aggregate matrix (FAM), which comprises graded sand and asphalt binder. To provide multi-modal loading, the rectangular prismatic FAM specimens were used with the Arcan apparatus. This apparatus ensures low bending stress and offers adjustments in the setup to provide different proportions of axial and shear stress. Finite element modeling was done to evaluate the stress state for different orientations of the sample in the Arcan apparatus. For measurement of strain, the study used digital image correlation (DIC), which is an optical, non-contact measurement technology. The strain thus measured was used to compute shear compliance. Fitting parameters of the shear compliances were estimated for power-law and Prony series for different loading orientations. When compared, the measured shear compliances do not show perceivable variation with respect to different proportion of axial stress applied in conjunction. However, further testing with different temperatures and other magnitudes of shear stress is necessary. This study is the first step to allow modeling of stress and crack propagation behavior near the pavement surface where complex stress state is present.Civil, Architectural, and Environmental Engineerin

Conformity Level of AAOIFI Accounting Standards by Six Islamic Banks of Bangladesh

In response to this global rise in Islamic financial organism and banking, the need for setting up a common standard for the accounting function in Islamic Banks, became an unuttered need. Addressing this need, in the year 1991, the global institute for setting accounting standards for Islamic financial institutes, Accounting and Auditing Organization for Islamic Financial Institutions (AAOIFI) has been established in Bahrain. This study tries to find out the conformity level of the Islamic Banks in Bangladesh with these standards. This study analyses the annual reports of six Islamic banks from Bangladesh of the year 2012. The Reports are collected from the Banks’ website sources. It is found that these six banks conform with the AAOIFI standards by 53.79% on average in financial statements. A 2.79 standard deviation in case of total conformity refers to the low level of difference among these banks in case of disclosure. This study suggests that it is highly of importance for the banks to increase the level of conformity of the AAOIFI standards to ensure the stakeholders about their sincerity and determination to comply with Islamic Shari’ah. Analysis of AAOFI standard compliance is relatively new in Bangladesh. This research study may provide some new insights into the existing Islamic literature. Keywords: Islamic Banking, Islamic Finance, AAOIFI Standards

Hardware Accelerator for Star Centroiding

Since the dawn of civilization mankind has gazed upon the night sky and looked for directions. In this modern age, the stars have proved to be a reliable reference point for navigation in space. From small-satellites for gathering weather data to inter-planetary missions like Cassini Orbiter, figuring out the location of a spacecraft has been done successfully by taking images of star filed visible from the spacecraft, processing and analyzing the image to find the stars and then finding out from a star catalog which part of the sky the patterns of the visible stars best matches. But a lot of calculation is involved in this process which means it takes up huge amount of power and time to complete. In this research work a hardware will be developed that will reduce the power and increase the speed of this process. The accuracy of this design will be tested under different environmental conditions, modeling the actual region of operation of this design which is the space

Determination of Natural and Artificial Radionuclides in Soil Samples of Habigonj District, Bangladesh

The specific activities of natural and artificial radionuclides in 22 soil samples collected from Habiganj district in Bangladesh, have been Studied and evaluated. Experimental results were obtained by using a High Purity Germanium (HPGe) Detector and the radioactive standard sources supplied by IAEA were used to determine the efficiency. The measuring time of all samples is 5000 seconds. It was found that, the soil specific activity ranges from 5.27733 ± 0.01534 - 18.8277 ± 0.0155 Bq/kg for Radium-226 (226Ra), 7.1355 ± 0.00248 - 38.1423 ± 0.00338 Bq/kg for Thorium-232 (232Th) and 93.140877±0.006196 - 392.62765±0.007421 Bq/kg for Potassium-40 (40K), with mean values of 11.09224 ± 0.01090 Bq/kg, 21.98392 ±0.00293 Bq/kg and 227.96598± 0.00676 Bq/kg respectively. It was also found that there is no artificial radionuclide (137Cs) in any kind of samples of Habiganj district. In order to evaluate the radiological hazard of the natural and artificial radioactivity, Radium equivalent activity (Raeq), gamma absorbed dose rate, The external hazard index (Hex), annual effective dose rate for different soil samples were calculated 58.513 Bq/Kg, 27.99008 nGy/h, 0.162327, 33.17704 µSv respectively. Keywords: Habiganj, HPGe detector; soil, Natural Radionuclides, Artificial Radionuclides, 40K, 137Cs, 226Ra, 232Th.

Spectrally-Accurate Algorithm for Flows in 3-Dimensional Rough Channels

In this work a spectrally accurate algorithm has been developed for the simulation of three-dimensional flows bounded by rough walls. The algorithm is based on the velocity-vorticity formulation and uses the concept of Immersed Boundary Conditions (IBC) for the enforcement of the boundary conditions. The flow domain is immersed inside a fixed computational domain. The geometry of the boundaries is expressed in terms of double Fourier expansions and boundary conditions enter the algorithm in the form of constraints. The spatial discretization uses Fourier expansions in the stream-wise and span-wise directions and Chebyshev expansions in the wall-normal direction. The algorithm can use either the fixed flow rate constraint or the fixed pressure gradient constraint; a direct implementation of the former constraint is described. An efficient solver which takes advantage of the structure of the coefficient matrix has been developed. Taking the advantage of the reality conditions enhances the efficiency of the solver both in terms of memory and computational speed. It is demonstrated that the applicability of the algorithm can be extended to more extreme geometries using the over-determined formulation. Various tests confirm the spectral accuracy of the algorithm

How YouTube Health Vloggers Influence Viewer Compliance: The Interplay between Vlogger Characteristics, Parasocial Interaction, and Viewer Characteristics

Drawing on the notion of parasocial interaction (PSI) theory (Horton and Wohl, 1956), this dissertation provides a framework to demonstrate how YouTube health vloggers can influence viewer compliance intention toward a prescribed health behavior (i.e., weight-loss diet to lose weight). Initially, drawing on the discounting principles of attribution theory (Kelly, 1973), physical attractiveness stereotype (Eagly et al., 1991), and the black sheep effect (Marques and Yzerbyt, 1988), the interaction effects of three vlogger characteristics on viewer PSI experience were conceptualized and examined (Study 1). Then by using a scenario-based experiment, viewer PSI experience with the vlogger was manipulated (high vs. low) and drawing on social comparison theory (Festinger, 1954), PSI’s effect on the core dependent variable of this research, compliance intention was tested. In the process, this research also accounted for the mediating role of viewer readiness (role clarity, ability, and motivation), the moderating and the mediated moderating role of viewer health consciousness through viewer readiness in the PSI—compliance intention relationship. Overall, results indicated the dominance of vloggers’ credibility over the other two vlogger characteristics—physical attractiveness and ethnic similarity in engendering PSI experience with the viewers. While no main or interaction effects of vloggers’ physical attractiveness and ethnic similarity were found in generating viewers’ PSI experience with vloggers. The positive influence of PSI on compliance intention was found both as a direct effect and also through the mediating role of viewer readiness. While viewer health consciousness is found to have no moderating influence in the PSI—compliance relationship both in the direct effect and also in the indirect effect mediated through viewer readiness. The findings and their implications are discussed

Determination of Natural and Artificial Radionuclides in Water Samples of Habigonj District, Bangladesh

The specific activities of natural and artificial radionuclides in 8 Water samples collected from Habiganj district in Bangladesh, have been Studied and evaluated. Experimental results were obtained by using a High Purity Germanium (HPGe) Detector and the radioactive standard sources supplied by IAEA were used to determine the efficiency. The measuring time of all samples is 5000 seconds. It was found that, the water specific activity ranges from 1.4470 ± 0.00281 - 13.0836 ± 0.00335 Bq/kg for Radium-226 (226Ra), 0.0 - 14.0196 ± 0.00265 Bq/kg for Thorium-232 (232Th) and 0.0 - 73.4632 ± 0.006899 Bq/kg for Potassium-40 (40K), with mean values of 5.6947 ± 0.00278 Bq/kg, 6.2259 ± 0.00177 Bq/kg and 24.6966 ± 0.00426 Bq/kg respectively. It was also found that there is no artificial radionuclide (137Cs) in any kind of samples of Habiganj district. In order to evaluate the radiological hazard of the natural and artificial radioactivity, Radium equivalent activity (Raeq), gamma absorbed dose rate, the external hazard index (Hex), annual effective dose rate for different water samples were calculated 16.25248 Bq/Kg, 7.397393 nGy/h, 0.044364, 9.072163 µSv respectively. Keywords: Habiganj, HPGe detector; Water, Natural Radionuclides, Artificial Radionuclides, 40K, 137Cs, 226Ra, 232Th

Effects of incorporating renewable energy sources into the electricity grid

With the increasing demand for energy throughout the world, the environment around us is getting severely affected. The conventional energy sources (coal, oil and gas) are unfortunately the biggest polluters of the environment. The aforementioned energy sources emit greenhouse gases like carbon dioxide and methane, which are responsible for global warming and ozone layer depletion. The only feasible answer to this problem is to reduce the use of the conventional energy sources and focus more on other energy sources. The renewable energy sources (solar, wind and hydro) have been present in nature, but the technology to harvest these energies have always been relatively expensive until recently. The biggest advantage of using renewable energy sources is the fact that these energy sources will never run out and they also do not pollute the environment as their more conventional counterparts. With more research being conducted into better ways of storing the power trapped from the renewable energy sources and the relative difficulty of obtaining the ever-depleting conventional energy sources, the future for renewable energy sources definitely looks better than at any time in the pastM.S