Growth of Zn-polar BeMgZnO/ZnO heterostructure with two dimensional electron gas (2DEG) and fabrication of silver Schottky diode on BeMgZnO/ZnO heterostructure.

Title of dissertation: GROWTH OF Zn POLAR BeMgZnO/ZnO HETEROSTRUCTURE WITH TWO DIMENSIONAL ELECTRON GAS (2DEG) AND FABRICATION OF SILVER SCHOTTKY DIODE ON BeMgZnO/ZnO HETEROSTRUCTURE By Md Barkat Ullah, Ph.D A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Electrical and Computer Engineering at Virginia Commonwealth University. Virginia Commonwealth University,2017 Major Director: Dr. Hadis Morkoç, Professor, Electrical and Computer Engineering This thesis focuses on growth of Zn polar BeMgZnO/ZnO heterostructure on GaN/sapphire template with two dimensional electron gas (2DEG) for the application of UV photodetector/emitter and high speed electronics. The motivation of using BeMgZnO as a barrier layer originates from the need to reach plasmon-LO phonon resonance in order to obtain minimum longitudinal optical (LO) phonon lifetime. Presence of 2DEG was realized in BeMgZnO/ZnO heterostructure only when the Zn polarity was achieved during the nucleation growth of ZnO on GaN/sapphire template. It was found that, polarity of ZnO on (0001) GaN/sapphire template can be controlled by the oxygen to Zn ratio used during the nucleation growth. To obtain high structural and optical quality of BeMgZnO quaternary alloy, growth kinetics of BeMgZnO layer has been studied at the temperature range from 450°C-500°C. We have achieved the growth of single crystal Be.03Mg00.15ZnO alloy at 500 °C, more than 100°C higher compared to what reported in literature, on the (0001) GaN/sapphire template through the control of Zn/(Be+Mg) flux ratio. We have also observed a thermodynamic limitation of Mg incorporation into the wurtzite BeMgZnO alloy where the excess Mg adatom accumulated in the growing surface as a MgO rich cluster. Two dimensional electron gas with high (1.2×1013cm-2) sheet carrier density was achieved at the Be0.03Mg0.41ZnO/ZnO interface through strain engineering by incorporating Be into MgZnO ternary alloy. To obtain the similar sheet carrier density it would require above 60% of Mg in MgZnO/ZnO heterostructure with reduced structural quality. A systematic comparison of sheet carrier density has been made with the already reported results from Zn polar MgZnO/ZnO heterostructure as well as with the theoretical calculation. Silver Schottky diode on Be0.02Mg0.26ZnO/ZnO heterostructure with barrier height 1.07 eV and ideality factor 1.22 was obtained with 8 order of rectification ratio. The temperature-dependent electrical characteristics were studied by using temperature dependent current-voltage (I-V) measurements. Richardson constant value of 34.8 Acm-2K-2 was found experimentally which was close to the theoretical value of 36 Acm-2K-2 known for Be0.02Mg0.26ZnO alloy

Financing patterns in transition economies: Privatized former SOEs versus ab initio private firms

We employ 19,521 unique firms in 30 transition economies to investigate the relation between the origins of private firms and their financing patterns. In our sample, the private firms are either privatized former state-owned enterprises (SOEs) or ab initio (from the beginning) private firms. Our results show that privatized former SOEs finance a higher proportion of their fixed assets from bank finance and supplier credit, while ab initio private firms rely more on informal finance. We argue that privatized former SOEs continue to benefit from the political and financial connections established during their SOE era. We further document that financial institution development affects the financing patterns of these two groups differently. In our sample countries, financial institution advancement benefits privatized SOEs more than it benefits ab initio private firms

Experimental study on hydrodynamic characteristics of underwater glider

1091-1097The enhancement of the hydrodynamic characteristics of autonomous underwater gliders (AUGs) is an important factor because of their weak inner propulsion system and altitude control. Moreover, resistance forces acting on the glider limit its operational range and increase energy utilisation. In this paper, towing tanks experiments were conducted to investigate the hydrodynamic characteristic of a newly developed underwater glider with fixed wings and a tail rudder. Specifically, this work presents the hydrodynamic performance of a newly developed AUG in a horizontal plane towed tank environment. This hydrodynamic study investigates the glider performance at a wide range of speed (0.3-0.7 m/sec) and drift angles (0-18o). The resistance forces were measured by internal strain gauges, mounted on the towing carriage. The experimental results were used to analyse the resistance with variation in Froude’s number and drift angles, using Reynold’s Average Navier Stoke equation in Ansys FLUENT. Both experimental and simulation are well corroborated and show that resistance force is a strong function of the drift angle. The results are useful for the potential development of AUGs and their control surfaces

Ransomware 2.0: An emerging threat to national security

The global Covid-19 pandemic has seen the rapid evolution of our traditional working environment; more people are working from home and the number of online meetings has increased. This trend has also affected the security sector. Consequently, the evolution of ransomware to what is now being described as ‘Ransomware 2.0’ has governments, businesses and individuals alike rushing to secure their data

The dark side of transparency in developing countries: The link between financial reporting practices and corruption

This paper examines the impact of financial reporting practices on corruption obstacles for about 150,000 firms across 143 mostly developing countries from 2006 to 2019. We document a strong positive relationship between the production of audited financial statements (AFS) and corruption obstacles (CO) faced by the firm. We argue that in a corrupt business environment, rent-seeking bureaucrats use the credible financial information to optimize their bribe demands. Our baseline results remain robust after addressing endogeneity concerns. We further show that country-level institutional quality has a moderating effect on the AFS-CO relation. The evidence from surveying entrepreneurs also provides qualitative support for our empirical findings. Our study sheds light on a previously under-explored adverse consequence of transparency - exposure to corrupt bureaucrats where institutions are weak

An empirical demonstration of the effect of study design on density estimations

Funding was provided by the Snow Leopard Trust and Global Environmental Facility through Pakistan Snow Leopard and Ecosystem Protection Program (PSLEP). The publication of this article was funded by Qatar National Library.The simultaneous development of technology (e.g. camera traps) and statistical methods, particularly spatially capture-recapture (SCR), has improved monitoring of large mammals in recent years. SCR estimates are known to be sensitive to sampling design, yet existing recommendations about trap spacing and coverage are often not achieved, particularly for sampling wide-ranging and rare species in landscapes that allow for limited accessibility. Consequently, most camera trap studies on large wide-ranging carnivores relies on convenience or judgmental sampling, and often yields compromised results. This study attempts to highlight the importance of carefully considered sampling design for large carnivores that, because of low densities and elusive behavior, are challenging to monitor. As a motivating example, we use two years of snow leopard camera trapping data from the same areas in the high mountains of Pakistan but with vastly different camera configurations, to demonstrate that estimates of density and space use are indeed sensitive to the trapping array. A compact design, one in which cameras were placed much closer together than generally recommended and therefore have lower spatial coverage, resulted in fewer individuals observed, but more recaptures, and estimates of density and space use were inconsistent with expectations for the region. In contrast, a diffuse design, one with larger spacing and spatial coverage and more consistent with general recommendations, detected more individuals, had fewer recaptures, but generated estimates of density and space use that were in line with expectations. Researchers often opt for compact camera configurations while monitoring wide-ranging and rare species, in an attempt to maximize the encounter probabilities. We empirically demonstrate the potential for biases when sampling a small area approximately the size of a single home range-this arises from exposing fewer individuals than deemed sufficient for estimation. The smaller trapping array may also underestimate density by significantly inflating [Formula: see text]. On the other hand, larger trapping array with fewer detectors and poor design induces uncertainties in the estimates. We conclude that existing design recommendations have limited utility on practical grounds for devising feasible sampling designs for large ranging species, and more research on SCR designs is required that allows for integrating biological and habitat traits of large carnivores in sampling framework. We also suggest that caution should be exercised when there is a reliance on convenience sampling.Publisher PDFPeer reviewe

Effect of water current on underwater glider velocity and range

An autonomous underwater glider speed and range is influenced by water currents. This is compounded by a weak actuation system for controlling its movement. In this work, the effects of water currents on the speed and range of an underwater glider at steady state glide conditions are investigated. Extensive numerical simulations have been performed to determine the speed and range of a glider with and without water current at different net buoyancies. The results show that the effect of water current on the glider speed and range depends on the current relative motion and direction. In the presence of water current, for a given glide angle, glide speed can be increased by increasing the net buoyancy of the glider

Experimental study to optimize cold working, aging temperature, and time on the properties of AA6061 tubes: analysis using design of experiment

The purpose of this study is to examine the impact of various process parameters, such as cold work, aging temperature, and aging time, on the yield strength, ultimate tensile strength (UTS), and elongation of AA6061 tubes. The experimental plan is carried out, and the data is analyzed using Design Expert software. Main effects plots and interaction plots are generated to visually examine the effects of individual factors and the interaction between two factors on the output response variables. ANOVA analysis is conducted to assess the statistical significance of the model and individual model coefficients. The results reveal that all input factors had a significant impact on yield, whereas cold work and temperature and their interaction are significant for UTS. However, the model is not significant for elongation. The most notable finding is that the aging temperature’s effect is significant than the other two factors. These study findings can inform future experiments or process optimization efforts by considering the combined impact of these factors and their interactions. The study also found that the optimal temperature range is between 155°C to 170°C, along with a recommended cold work percentage of 10% or more and preferred time of above 10 h up to overage time. The model achieved an overall accuracy rate of over 90%, indicating its ability to predict the response variable with a high degree of precision

A home calendar and recall method of last menstrual period for estimating gestational age in rural Bangladesh: a validation study

Background: The best method of gestational age assessment is by ultrasound in the first trimester; however, this method is impractical in large field trials in rural areas. Our objective was to assess the validity of gestational age estimated from prospectively collected date of last menstrual period (LMP) using crown-rump length (CRL) measured in early pregnancy by ultrasound. Methods: As part of a large, cluster-randomized, controlled trial in rural Bangladesh, we collected dates of LMP by recall and as marked on a calendar every 5 weeks in women likely to become pregnant. Among those with a urinetest confirmed pregnancy, a subset with gestational age of <15 weeks (n = 353) were enrolled for ultrasound follow-up to measure CRL. We compared interview-assessed LMP with CRL gestational age estimates and classification of preterm, term, and post-term births. Results: LMP-based gestational age was higher than CRL by a mean (SD) of 2.8 (10.7) days; differences varied by maternal education and preterm birth (P < 0.05). Lin\u2019s concordance correlation coefficient was good at ultrasound [0.63 (95 % CI 0.56, 0.69)] and at birth [0.77 (95 % CI 0.73, 0.81)]. Validity of classifying preterm birth was high but post-term was lower, with specificity of 96 and 89 % and sensitivity of 86 and 67 %, respectively. Results were similar by parity. Conclusions: Prospectively collected LMP provided a valid estimate of gestational age and preterm birth in a rural, low-income setting and may be a suitable alternative to ultrasound in programmatic settings and large field trials. Trial registration: ClinicalTrials.gov NCT0086047