University of Maryland, Baltimore County
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A Discrete, Three-Dimensional, Force-Based Mathematical Model of Collective Cell Migration
No full textWe present a novel mathematical approach to modeling the collective cell migration process that occurs during stages eight to ten of Drosophila oogenesis. This new approach uses the forces of adhesion, repulsion, migration and stochastic fluctuation to simulate the movement of discrete cells. At the start of oogenesis, the motile and non-motile cells of this system lie in the anterior follicular epithelium. These cells form a cluster and translocate as a collective to the posterior of the egg chamber, in the direction of the developing egg chamber. Our model captures the dynamics of these cells, as well as the epithelium that encloses the egg chamber, and the nurse cells that comprise the space that the cluster migrates through. We implement this using Identical Math Cells, or IMCs. These IMCs may each represent one biological cell of the system, or can be aggregated to model the dynamics of larger biological cells. They each can be assigned unique biophysical properties, which can be used to model a heterogeneous cell population. This also increases the diversity and biological accuracy of the cell-to-cell interactions that may potentially be modeled. Using this mathematical construct we have successfully simulated the migration of this cluster of cells. We have also used this model to investigate how altering the number of motile cells in the system affects the behavior of the migrating cluster. We show that decreasing the number of motile cells results in increased migration time, which has not been shown directly, but is believed to cause the loss of viability in vivo. We also show that the forces utilized in this model are sufficient to produce rotation of the cluster. Similar rotation has been observed in vivo and this result suggests that a more complex biophysical mechanism is not necessary to produce rotation of a migrating cluster. This model was developed to capture a heterogeneous cell population and was implemented with the flexibility to allow for diverse, but precise, initial position specification over a three-dimensional domain. Therefore, we believe that this model will be useful for not only examining aspects of Drosophila oogenesis, but also for modeling other two or three-dimensional systems that have multiple cell types and where investigating the forces between these cells is of interest
A Membraneless Single Compartment Abiotic Glucose Fuel Cell
No full textA rapid growth in technology and a sheer dependence on fossil fuels and disposable power supplies has produced an energy crisis in dire need of assistance. As a result, energy harvesting techniques have recently received a significant amount of attention in order to find environmentally friendly, renewable alternatives to provide power to everyday conveniences. Focus has been placed on using biological fluids as a potential source of energy for implantable sensors and life-saving medical devices. An abiotically catalyzed fuel cell has been successfully fabricated, based on a glucose oxidizing aluminum and gold electrode, coated with zinc oxide nanoparticles and combined with an oxygen reducing, platinum cathode. The fuel cell was able to achieve a peak power density of 16.2 �W cm^-2 and a short circuit current density of 93.33 �A cm^-2. Additionally, the cell was able to light an LED using two different electronic circuits, further supporting potential microelectronic applications
THE HISTORY OF KINDERGARTEN IN BALTIMORE CITY, MARYLAND
No full textABSTRACT Title of Document: THE HISTORY OF KINDERGARTEN IN BALTIMORE CITY, MARYLAND Nancy Watts, M.A. Historical Studies, 2014 Directed By: Dr. Anne Rubin, Ph.D. Department Chair, History Department. Kindergarten was originally designed in 1837 to create social interaction and learning through play, became a sculpting tool for political issues at the turn of the twentieth century. This thesis explores how the changing racial and ethnic demographic of students in Baltimore affected policies related to kindergarten in the city. It shows kindergarten as a tool for social activism under the guise of teaching American patriotism. This thesis uses government legislation and secondary sources to show how education was influenced by increased immigration and segregation in Baltimore City during the mid-twentieth century. The significance of this thesis lies in its exposure of class, ethnic, and racial stratification in education at its most basic level; class in this regard refers to socioeconomic status influenced by ethnicity and race. Kindergarten, while being promoted as a way to blend cultures in a changing society, actually reinforced the disparity among classes by allowing elites to capitalize on their fears related to these differing cultures
THE POTENTIAL FOR GENETIC INFORMATION IN THE SOCIAL SECURITY DISABILITY PROCESS
No full textThis research effort examined the level of understanding and practices among disability claims examiners and medical and psychological consultants regarding the use of genetic information in disability determinations to help inform Social Security Administration (SSA) policy in the field of genetics. As the number of genetic tests increases, it is expected that public perception of the role of genetic information in disability determinations has evolved and the prevalence of genetic information included as part of a claimant's medical evidence has become more common-place. While SSA has specific criteria related to a limited number of medical conditions with known genetic origin, the agency does not have regulatory guidance, policies, or procedures related to the general use of genetic information in making a medical determination. In the absence of comprehensive and clear direction, SSA disability examiners and medical and psychological consultants are left to their own discretion. It is unclear what impact this discretion has, and what is needed to ensure an accurate, consistent, and timely disability determinations. The SSA disability program is a large federal program with significant expenditures and impact on individuals; therefore, changes in policies and procedures requires significant time and planning--and in many cases, involves regulatory and statutory changes. As such, it is essential that SSA anticipate the possibilities for the use of genetic information and plan accordingly. Plausible practices and beliefs among members of the public, SSA disability examiners, and SSA medical and psychological consultants in regards to use of genetic information in SSA disability determinations are discussed in this research effort. Further, insight into possible policy opportunities, knowledge gaps, and training needs are provided, as well as recommendations for future research studies
Advances in microchannel heating and cooling based on fine scale heterogeneity of thermal conductivity; Theory, Optimization, and Experimental Validation
No full textA major advance in microchannel heating and cooling technology is described and has the potential to change the way thermal processing of microscale fluidic samples is achieved. The microchannel is one of the key building blocks of micro total analysis systems (�TAS), which are already being released to market in the form of disposable test kits for biometrics and disease identification. However, significant cost reductions and other advances in microchannel heating and cooling technology are still needed and can be expected to improve the accuracy with which quantitative analysis can be performed. In part, this is because the fidelity of many existing and potential microfluidic applications is critically dependent on precise temperature control. The scientific objective of the study was to understand and then manipulate the physics of thermal transport within fine scale composite materials containing an embedded microchannel. In essence, it was necessary that the composition of the composite materials be manipulated in a precise way that established a particular nonlinear pattern of temperature along the length of the microchannel. In practice, this required the development of a systematic inverse solution process that could identify an acceptable composition to exactly match the desired pattern of temperature variation. As a demonstration of capability, fully operational prototypes comprised of patterned copper laminated within polyimide and acrylic polymers were designed, fabricated, and tested. In terms of conceptual advances, this is the first time that composite materials of this type have been used for microchannel heating AND cooling. From an analytical perspective, the critical advance was the development of a robust simulation framework consisting of an outer optimization loop and an inner finite element analysis (FEA) loop, which was used to iteratively identify the optimal copper pattern for each of several applications. In terms of experimental advances, the key fabrication steps included UV laser micromachining, acid etching, microchannel formation, and hot vacuum lamination. To avoid any ambiguity or artifact, microchannel temperatures were painstakingly measured at each of several flow rates using fine thermocouples embedded in the microchannel wall. For the most part, the measured temperatures were within 1 �C of the expected values based on simulation, with spatial temperature gradients of up to +/-94 �C/mm (or equivalently +/-188 �C/s at 2 l/min flow rate) within the range of 16 �C to 92 �C, using a resistively heated source at 100 �C and a thermoelectrically cooled sink at 2 �C. The temperature profiles studied here included two highly nonlinear cyclical profiles applicable to 1) continuous-flow polymerase chain reaction (PCR) and 2) thermally mediated counter-flow separation in conjunction with electrophoresis
The role of sexual selection in darter speciation
No full textSexual selection results from the competition over mating opportunities in natural populations. Just as natural selection favors traits that increase survival and fecundity, sexual selection favors traits that increase mating opportunities and fertilization success. These two processes cause changes within populations but are also important in driving divergence between populations. Speciation by divergent natural selection, also called ecological speciation, is now a widely accepted driver of diversity; however the role of sexual selection is less concrete. Speciation by sexual selection is thought to occur via divergence in female mating preferences between populations followed by coevolution of male mating traits. These differences eventually lead to behavioral reproductive isolation as female preferences in one population no longer correspond to male traits in another. Although verbal and quantitative models demonstrate the plausibility of speciation by sexual selection, empirical examples are relatively few and evidence often comes from comparative datasets that rely on proxy measures of divergent sexual selection. Additionally, natural and sexual selection often interact making it difficult to distinguish speciation by sexual selection alone. Here, I address the potential for speciation by natural selection, by sexual selection, or by a combination of the two in a group of freshwater fishes commonly called darters (Etheostoma). My results suggest a primary role for sexual selection in early darter divergence. Interestingly, however, trait divergence and the evolution of behavioral isolation in darters appear to involve divergence in male aggressive responses and male mate preferences, respectively. Further, differences in the sexual environment predict total reproductive isolation between species while differences in the ecological environment do not. The influence of male behavior was unexpected given the overwhelming focus on divergence in female mate preferences in speciation by sexual selection models. Additionally, the potential for divergence in sexual selection to promote reproductive barriers outside behavioral isolation is surprising. Taken together, my results suggest that early darter divergence is driven by sexual selection and imply that the definition of speciation by sexual selection should be expanded to encompass the multiple mechanisms of sexual selection and how they might contribute to all reproductive barriers
Parallel Regularized Maximum Likelihood Estimation For Proportional Odds Models
No full textOrdinal categorical random variables are random variables which take on values from a finite ordered set of possible values. They often result from qualitative assessments, such as rating a movie from one to five stars. Unlike continuous variables whose values are also ordered, ordinal categories are qualitative, so the distance between them may not be well-defined. This work focuses on computational aspects of predicting ordinal categorical random variables. We employ multinomial logistic models as the workhorse of our methodology. Beginning with the proportional odds version of the cumulative logit model, usually called the Proportional Odds Model (POM), we develop a regularized variant of that model. In particular, we study a special case of the generalized L1 regularized POM which we call the Fused Proportional Odds Model (FPOM) because it can result in coefficients whose values are equal, they can be fused together. FPOM incorporates a penalty term composed of a positive combination of terms: the absolute value of each coefficient, the absolute differences of coefficients, and the absolute differences of consecutive intercepts. This penalty makes sense when there is a notion of adjacency among coefficients, as occurs in signal processing, and when reduction of degrees of freedom is desired, e.g., in the context of high dimensional predictors. The geometry of this optimization, convex with edges and points, can aid finding a sparse solution, which is desirable in some contexts. As an illustration, we apply FPOM to a wine quality assessment dataset. We show, using various measures of prediction accuracy, that our model is competitive with other methods that have been applied to this data. Using a simulation, we show that FPOM can be used for variable selection. For many modern problems, especially those involving automated data collection, large quantities of data can be produced. Analyzing this data in a reasonable amount of time can be of practical importance. Accordingly, we study the use of parallel computation to speed up FPOM parameter estimation. Using computational nodes with two multi-core processors, we show that enabling parallel computation can result in an order of magnitude speedup on a single computational node
Surface Reactions During the Atomic Layer Deposition of High-κ Dielectrics on III-V Semiconductor Surfaces
No full textThe quality of the dielectric/semiconductor interface is one of the most critical parameters for the fabrication of high-speed and low-power-consumption III-V semiconductor based metal-oxide-semiconductor field effect transistors (MOSFETs), as it determines the device performance. This dissertation contains investigations of the deposition and interface of binary oxide films on GaAs(100) and InAs(100) surfaces aiming at understanding the removal of the surface native oxides during certain atomic layer deposition (ALD) processes. To accomplish that, two complementary experimental approaches have been used. Initially, films were deposited in a conventional ALD reactor and characterized ex situ using spectroscopic ellipsometry (SE), X-ray photoelectron spectroscopy (XPS), high-resolution transmission electron microscopy (HRTEM), and atomic force microscopy (AFM). The systems examined were Ta2O5 on GaAs(100) surfaces from pentakis(dimethylamino) tantalum (Ta(N(CH3)2)5, PDMAT) and TiO2 on GaAs(100) and InAs(100) surfaces from tetrakis(dimethylamino) titanium (Ti(N(CH3)2)4, TDMAT). For these systems, deposition at the optimal ALD temperature resulted in practically sharp interfaces. Indium oxides were found to diffuse through ~ 6 nm of TiO2 film and accumulate on the topmost film layer. For the ALD of Ta2O5 on GaAs(100) surfaces, native oxide removal was enhanced at deposition temperatures above the ALD window; for ALD of TiO2 on both GaAs(100) and InAs(100) surfaces, native oxide removal was enhanced as the deposition temperatures increased up to 250 °C, while oxidation of the interface was observed for deposition above 300 °C due to the formation of noncontinuous films. To elucidate the surface reactions occurring during the deposition, an in situ attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy apparatus was constructed and used to investigate the surface reactions during the ALD of TiO2 and HfO2 on GaAs(100) surfaces. The existence of a ligand exchange mechanism was verified for both processes. Additionally, the formation of methylmethyleneimine (CH3N=CH2, MMI) was observed, indicating the existence of a beta hydride reaction pathway. Additionally, at 275 °C continuous removal of arsenic oxides was observed during the first 20 process cycles, an observation that challenges the prevailing understanding of the native oxide removal and indicates a much more complex surface chemistry
Analysis of a Specimen of Visual Basic Malware
No full textVisual Basic platform is increasingly becoming popular amongst malware authors. This is due to the fact, Visual Basic malwares are more complicated to analyze and it can be used to avoid precise detection by most antiviruses. Conventional tools like IDA Pro and OllyDbg do not provide much help when it comes to analyzing Visual Basic binaries. Along with this, a malware author can add self-defined algorithms for obfuscation and encryption. This combination allows the malware authors to create a malware that would be difficult to discover and analyze. This study mainly focuses on the growing impact of Visual Basic binaries in the world of malware. Our major malware for discussion would be Vobfus, which is a VB-obfuscated sample that connects to a server to download other malware to the victim's machine. The analysis of Vobfus would be accompanied with analysis of a few other Visual Basic malware samples. In the end, a critique of the conventional malware analysis tools while analyzing Visual Basic malwares would be presented
Big Data Analytics Performance for Large Out-of-Core Matrix Solvers on Advanced Hybrid Architectures
No full textThis thesis examines the performance of large Out-Of-Core matrices to assess the optimal Big Data system performance of evolving computer architectures, based on the performance evaluation of a large Lower-Upper Matrix Decomposition (LUD) employing a highly tuned, I/O managed, slab based LUD software package developed by the Lockheed Martin Corporation. We present extensive benchmark studies conducted with this package on UMBC's Bluegrit and Bluewave clusters, and NASA-GFSC's Discover cluster systems. Our results show speedup for a single node achieved by Phi Coprocessors relative to the host CPU SandyBridge processors is about a 1.5X improvement, which compares with the studies published by F.Masci (2013) where he obtains a 2-2.5x performance. The performances across 20 CPU nodes of SandyBridge obtains a uniform speedup of 0.5X over Westmere for problem sizes of 10K, 20K and 40K unknowns. With an Infiniband DDR, the performance of Nehalem processors is comparable to Westmere without the interconnect