48670 research outputs found
Sort by
Low Energy Order-To-Disorder Transition Pathways In Phase-Change Nanowires
No full textPhase change memory (PCM) can reversibly transform between the amorphous and crystalline phase within nanoseconds, making it a promising candidate for non-volatile memory (NVM) applications. The conventional method to realize the crystal−amorphous transformation in PCM is to heat the material above its melting point by an electrical pulse, after which it is quenched by sudden removal of the pulse. However, such a method requires very large current densities, which results in massive parasitic heat losses and also accelerated failure of the device. On the other hand, it has been recently shown that resistance switching in PCM systems such as superlattices and nanowires can occur at much lower current densities, where the temperature of the material always stays below its melting point. In-situ transmission electron microscopy (TEM) studies on nanowires, with a growth direction aligned with the dislocation slip system, have shown that the resistance change occurs by a dislocation-templated amorphization process. However, the resistance switching mechanism in superlattices, which consist of periodically alternating layers of two different PCM materials, has been much debated with many studies claiming it to be an order-to-order transition.In this study, we attempt to further lower the current density for the crystal-amorphous transformation by multiple strategies: pre-inducing defects in the nanowire by a size-mismatched dopant, synthesizing self-assembled compositionally modulated superlattice nanowires, and lastly by utilizing an unconventional flat phonon mode based amorphization mechanism in In2Se3 nanowires. Furthermore, we utilize TEM extensively to correlate the structural and electrical resistance changes in these nanowires, which reveal several interesting characteristics. The resistance switching mechanism in the superlattice nanowires is found to be an order-disorder transition, contrary to what is proposed in literature. Ab-initio simulations indicate that such an amorphization occurs with the aid of large concentration of vacancies in this material. On the other hand, In2Se3 PCM are found to undergo a collapse of long-range order by a d.c. voltage, but at intermediate voltage range, nucleation of topological dislocation occurs suggesting a possible charge density wave in this material. Overall, in this work, synthesis of novel nanowires is combined with ex-situ TEM experiments to uncover the structure-property correlations in the PCM materials, which is otherwise difficult to perform in thin-film PCM devices
Additively Fabricated Laminated Inductors For Miniaturized Switching Power Converters
No full textThis thesis work proposed an innovative idea to solve the problem of building a small integrated inductor, a bottleneck of realizing power supply-on chip (PwrSoC): utilization of material that has intermediate electrical conductivity as an interlamination material for a magnetic core
We theoretically analyzed that the electrical conductivity of 0.1 S/m - 1 S/m is a desirable range for an interlamination material that enables sequential electrodeposition (CMOS-compatible process) yet suppression of eddy-current loss. Polypyrrole (PPy) was selected as such interlamination material to validate our idea. We empirically demonstrated sequential stacking of PPy and metallic magnetic alloy, NiFe via continuous and additive electrodeposition process. We also experimentally showed that PPy interlamination effectively suppresses eddy-current loss by building and testing inductors. A laminated 10-layer NiFe inductor showed higher inductance retention (88% vs. 21%), and lower AC resistance (1.68 ohm vs. 12.7 ohm) at 8 MHz compared to a single layer NiFe inductor having comparable total NiFe thickness; both higher inductance retention and lower AC resistance are signs of suppressed eddy current loss.
We then investigated the practicality of our findings. A thick core having 45 NiFe layers was fabricated to show the developed technology can achieve tens of microns in thickness which is necessary for watt scale power converters. The air gap was introduced to increase saturation current up to 500 mA which was then implemented in a buck converter. Our toroid inductor and commercial inductor showed comparable power efficiency of ~75% in a buck converter that steps down 2.7V to 1.2 V at 20 MHz switching frequency. Although our inductor was larger than the commercial inductors, utilization of higher saturation flux density material like CoNiFe and optimization of inductor design expects to reduce inductor size
On The Ethics Of Neuroenhancements And The Use Of Race Theory In Biomedical Ethics
Get PDFDrawing from normative ethics and analytic philosophy of race, this dissertation focuses on the ethical, legal, and social implications (ELSI) of emerging biotechnologies and novel clinical practices in relation to potentially vulnerable populations. The first two chapters challenge presumptive duties in favor of moral bioenhancements (MBs). Here, MBs are understood as medical interventions that alter human moral cognition – e.g., the use of non-invasive brain stimulation to mitigate aggressive behavior. In Chapter 1, I argue that there is no universal moral obligation to utilize MBs, because the mass utilization of MBs may undermine the moral dispositions they seek to promote through unwarranted differential treatment between enhanced individuals and unenhanced individuals. Chapter 2 zooms in to focus on the obligations owed to and by individuals with psychiatric disorders. I argue that when an individual with a psychiatric disorder can act autonomously and make informed decisions, and when there are viable alternatives to MBs for the prevention of harm, the person with a psychiatric disorder is not obligated to utilize MBs. The second pair of chapters demonstrate how race theory from the analytic philosophy tradition can and should inform discourse in medical ethics and public health policy. In Chapter 3, I use a virtue theoretic framework to construct a decision tree to determine when, if ever, it is morally permissible to use a biological racial classification in medicine. In Chapter 4, I offer a modified version of Jorge L.A. Garcia’s volitional account of racism (VAR) and argue that my modified account is a superior alternative to competing theories of racism when considered in a healthcare context because of its accuracy and comprehensiveness. Though seemingly disparate topics, each chapter aims to promote the just and benevolent treatment of all humans contending with life, death, and health – so, everyone
Counting Extreme Points From Poisson Processes On A Half Line
Get PDFRun a Poisson process to generate points on the positive vertical axis, so that the counting process looks like an increasing arc with random jagged edges (see Figure 1.2). The outermost Poisson points---the extreme points---are those that sit on the boundary of the counting process\u27 convex hull. How many extreme points are there? This thesis examines numerous approaches to this question with different styles of answers. Originally, the inspiration for this problem and the purpose of an answer was to guess a growth exponent for the extreme primes studied by McNew (2018), Tutaj (2018), and Pomerance (1979); from estimates here, one might guess 1/3. Upon exploration, the Poisson problem, certain results, and certain techniques herein have unmistakable ties to work by Groeneboom (2011) on a closely related problem about empirical distributions. In fact, the approach by Groeneboom (2011) would likely yield these 1/3 answers for our problem, as well (perhaps even with greater precision than we can provide), though we cannot say with complete certainty, since not all the details were laid out. Moreover, certain techniques here share features with the work by Groeneboom (2011), though the approach here begins from a slightly different point-by-point perspective. We also comment on these similarities and make use of this relationship. Aside from Poisson processes leading to growth exponent 1/3, we study other examples that have growth exponent 1 instead
Marriage And Family In India
Get PDFThis dissertation studies two important dimensions of family life in contemporary India, marriage partner selection and female seclusion, using three different data sources: 48 interviews with the middle-class in New Delhi, panel survey data from the India Human Development Survey, and survey data from the Center for the Advanced Study of India Delhi National Capital Region Survey. The first half of this dissertation sheds light on attitudes towards and the processes involved in arranged marriage among the urban middle class. The young people interviewed approach marriage decision-making with marital pragmatism, framing their choices in terms of risks, uncertainties, and costs. Most describe arranged marriage as the safer option due to the support that these relationships receive from parents. Despite a strong preference for arranged marriage, interviews revealed significant hybridization between arranged and self-choice or “love” marriage. Couples in arranged marriages often engaged in courtship during their engagement. Furthermore, new survey data suggests that many families are willing to call off a wedding if the betrothed find themselves to be incompatible during their engagement, revealing the family’s prioritization of choice and compatibility for the couple. The second half of this dissertation examines patterns of female seclusion and attitudes towards women’s careers. Analysis of panel data shows that women from households which became wealthier reported increased restrictions on their physical mobility and greater odds of practicing head-covering or purdah. These findings suggest that the upwardly mobile may be using female seclusion as a way to signal household status. Dual earner professional couples in India challenge male breadwinner norms through their division of labor. Men who married working women mostly report that they were actively searching for an employed wife on the marriage market because of the financial security that a second income could provide. In addition, to some respondents, dual earning was believed to help facilitate a companionate marriage. This dissertation highlights the role of family, economic precarity, risk, and social norms in shaping marriage and family life in India
Penn Library\u27s LJS 410 - al-Mulakhkhaṣ fī al-hayʼah. = الملخص في الهيئة. (Video Orientation)
No full texthttps://repository.upenn.edu/sims_video/1163/thumbnail.jp
A Practitioner Perspective on Implementing Guided Pathways at California Community Colleges
No full textThe U.S. college-going population has diversified significantly in the past five decades. That fact, combined with a large community college capacity, an increased need for highly skilled workers, and the knowledge that higher education means social and economic mobility, makes improving student success at community colleges essential. All 116 California community colleges and several hundred more around the United States have begun implementation of Guided Pathways, a framework that may facilitate the necessary meaningful change. This is a qualitative multi-case study of four California community colleges that have been highly successful at implementing Guided Pathways. Using the conceptual framework of street-level bureaucracy and informed by implementation theory, the sources of evidence include semi-structured interviews of staff, faculty, and administrators directly involved in implementation and select campus documents. The findings revealed that having a vision for change, an open and collaborative campus culture, and good relationships throughout all levels of the organization are essential. Successful practitioners were inclusive, used data and small working groups to accomplish the tasks, included the student voice, and adapted the Guided Pathways framework to their culture to achieve the desired results. The people doing the work were the most important factor in success, but because Guided Pathways touches all aspects of the campus, focusing efforts on benefitting students and aligning the process with campus culture was also important
How Institutional Change, Including Cultural Change, Unfolded at Two Liberal Arts Colleges through Enacted Dei Initiatives
No full textHigher education diversity, equity, and inclusion (DEI) initiatives have become an imperative for institutional change in an ever-changing pluralistic society. The impact of diversity on college campuses has come a long way since the Civil Rights Act of 1964 (Chang, 2005), but there is still needed work. Higher education institutions continue to grapple with ways to build institutional capacity, meaning “how diversity is embedded in every core function including research, hiring, competencies required, and serving the ‘public good’” (Smith, 2020). Research on DEI in higher education has spanned the literature to include topics on racial climate, student access and success, curriculum impact, intergroup relations, and the professoriate, but few studies have focused on the process of DEI agendas’ implementation and cultural change. In the context of the current societal shifts toward anti-racism, inclusive excellence, and equity mindedness, this study investigated how change unfolded and the role of leadership in diversity initiatives at two liberal arts colleges. This dissertation examines the process of implementing a diversity agenda to improve the campus racial climate and create inclusive environments for the campus community, utilizing qualitative methods and a cross-case study approach to explore how these peer institutions approached DEI initiatives. Semi-structured interviews with 31 participants and triangulated data across multiple sources, including institutional documents and reports, websites, news outlets, and social media, helped contextualize information and analyze data to understand how change unfolded at these institutions. The institutions in this study represent different phases of DEI implementation. Schein’s (1980) three levels of culture and Kotter’s (2012) framework for organizational change provided conceptual frameworks to analyze and frame a deep examination of these campuses\u27 diversity agenda implementation process. Key findings illustrate DEI change processes in decentralized liberal arts institutions, the role of the president and governance structures in the change process, and the role of loud and persistent student voices to inform the leadership of the lived experiences of its student body
Experiences of Underrepresentation in Corporate America: Chinese American Stories of Tackling the Bamboo Ceiling
No full textAsian Americans have been and continue to be subjected to significant discrimination, projection, and bias in the United States across context, place, and sector, which includes education and corporate contexts. The model minority stereotype fosters the belief that Asian Americans are collectively smart and successful. However, whereas Asian Americans are seen as successful in academics, there is limited scholarly attention paid to the bamboo ceiling, identity-based trauma, and biases that accompany discriminatory processes and norms in professional contexts. Asian Americans encounter multiple barriers to obtaining high-level leadership roles despite superb education and training qualifications. This qualitative study explored the experiences of Chinese American leaders to understand their professional experiences and trajectories in the context of identity-based obstacles to corporate advancement. Critical Race Theory (CRT) and implicit and explicit bias theory served as the study’s theoretical framework. This study was based on one-on-one interviews with a pilot sample of 20 C-suite occupants and high-potential employees (HiPos) and should be followed by a more focused study involving 100 participants. The study found that even though all Chinese Americans are underrepresented, first-generation Chinese Americans are the most disadvantaged. The respondents revealed awareness of microaggressions and indirect discrimination, but most brushed them off or accepted them as the norm. They attributed most blame for Chinese Americans’ lack of leadership positions on a failure to speak up, be assertive, or develop soft skills and recommended Chinese Americans to address these through strategic posturing, networking, mentorship, assertiveness, and carefully choosing their employers
Machine Learning on Large-Scale Graphs
No full textGraph neural networks (GNNs) are successful at learning representations from most types of network data but suffer from limitations in the case of large graphs. Challenges arise in the very design of the learning architecture, as most GNNs are parametrized by some matrix representation of the graph (e.g., the adjacency matrix) which can be hard to acquire when the network is large. Moreover, in many GNN architectures graph operations are defined through convolutional operations in the spectral domain. In this case, another obstacle is the obtention of the graph spectrum, which requires a costly matrix eigendecomposition. Yet, large graphs can often be identified as being similar to each other in the sense that they share structural properties. We can thus expect that processing data supported on such graphs should yield similar results, which would mitigate the challenge of large size since we could then design GNNs for small graphs and transfer them to larger ones. In this thesis, I formalize this intuition and show that this graph transferability is possible when the graphs belong to the same family , where each family is identified by a different graphon. A graphon is a function W:(x,y) that describes a class of stochastic graphs with similar shape. One can think of the arguments (x,y) as the labels of a pair of nodes and of the graphon value W(x,y) as the probability of an edge between x and y. This yields a notion of a graph sampled from a graphon or, equivalently, a notion of a limit as the number of nodes in the sampled graph grows. Graphs sampled from a graphon almost surely share properties in the limit such as homomorphism densities which, in practice, implies that graphons identify families of networks that are similar in the sense that the density of certain motifs is preserved. This motivates the study of information processing on graphons as a way to enable information processing on large graphs. The central component of a signal processing theory is a notion of shift that induces a class of linear filters with a spectral representation characterized by a Fourier transform (FT). In this thesis, we show that graphons induce a linear operator which can be used to define a shift and therefore graphon filters and the graphon FT. Building on the convergence properties of sequences of graphs and associated graph signals, it is then possible to show that for these sequences the graph FT converges to the graphon FT and that graph filter outputs converge to the outputs of the graphon filter with same coefficients. These theorems imply that for graphs that belong to certain families, graph Fourier analysis and graph filter design have well defined limits. In turn, these facts enable graph information processing on graphs with large number of nodes, since information processing pipelines designed for limit graphons can be applied to finite graphs. We further define graphon neural networks (WNNs) by composing graphon filters banks with pointwise nonlinearities. WNNs are idealized limits which do not exist in practice, but they are a useful tool to understand the fundamental properties of GNNs. In particular, the sampling and convergence results derived for graphon filters can be readily extended to WNNs, allowing to show that GNNs converge to WNNs as graphs converge to graphons. If two GNNs can be made arbitrarily close to the same WNN, then by a simple triangle inequality argument they can also be made arbitrarily close to one other. This result formalizes our intuition that GNNs are transferable between similar graphs. A GNN can be trained on a moderate-scale graph and executed on a large-scale graph with a transferability error dominated by the inverse of the size of the smallest graph. Interestingly, this error increases with the variability of the spectral response of the convolutional filters, revealing a trade-off between transferability and spectral discriminability that is inherited from graph filters. In practice, this trade-off is less present in GNNs due to nonlinearities, which are able to scatter spectral components of the data to different parts of the eigenvalue spectrum where they can be discriminated. This explains why GNNs are more transferable than graph filters