Hopping Conduction and Metallic behavior in 2D Silicon Surface States induced by an Ionic Liquid

University of Minnesota Ph.D. dissertation. June 2015. Major: Physics. Advisor: Allen Goldman. 1 computer file (PDF); ix, 95 pages.Ionic liquids (ILs) are essentially molten salts with a melting point below room temperature. When used as the gate dielectric of a transistor, carrier densities on the order of $10^{15}\text{ cm}^{-2}$ can be achieved. These record high carrier densities are significantly higher than the maximum carrier density achievable with oxide dielectrics. The physical mechanism for inducing carriers to such a high carrier density is not well understood. Some groups have reported that the induced carriers are a result of electrostatic and electrochemical processes. Other groups have suggested that carriers induced with an IL may be entirely due to electrochemical reactions. Here we report on IL gated Si at carrier densities from $10^{11}\text{ cm}^{-2}$ to $10^{13}\text{ cm}^{-2}$. The experiment was designed to preferentially induce electrostatic carriers over electrochemical reactions. At low carrier densities, sample surface conductivity follows nearest neighbor hopping conduction. This form of conduction has also been observed in experiments where surface conductivity was induced by implanting $\text{Na}^{+}$ near the oxide surface interface. A surprising result of this work was that in some samples a 2D metallic state could be created on the surface of Si. The transition to metallic behavior occurred just below $10^{13}\text{ cm}^{-2}$. High quality Si transistors with oxide dielectric materials observe critical carrier densities around $10^{11}\text{ cm}^{-2}$. The critical carrier density observed in IL gated Si is the highest density reported to date. At carrier densities higher than $10^{13}\text{ cm}^{-2}$ it was observed that the sample conductivity decreased with increasing carrier density. The behavior was unexpected and not fully understood. Both metallic and non metallic samples show a similar reduction in conductivity that is not thought to be due to sample degradation by the IL. The reduction in the sample conductivity at high carrier densities is thought to be due to surface roughness scattering. Similar behavior has been observed in other IL gated experiments on different materials

Mechanisms and points of control in the spread of inflammation: a mathematical investigation

Understanding the mechanisms that control the body’s response to inflammation is of key importance, due to its involvement in myriad medical conditions, including cancer, arthritis, Alzheimer’s disease and asthma. While resolving inflammation has historically been considered a passive process, since the turn of the century the hunt for novel therapeutic interventions has begun to focus upon active manipulation of constituent mechanisms, particularly involving the roles of apoptosing neutrophils, phagocytosing macrophages and anti-inflammatory mediators. Moreover, there is growing interest in how inflammatory damage can spread spatially due to the motility of inflammatory mediators and immune cells. For example, impaired neutrophil chemotaxis is implicated in causing chronic inflammation under trauma and in ageing, while neutrophil migration is an attractive therapeutic target in ailments such as chronic obstructive pulmonary disease. We extend an existing homogeneous model that captures interactions between inflammatory mediators, neutrophils and macrophages to incorporate spatial behaviour. Through bifurcation analysis and numerical simulation, we show that spatially inhomogeneous outcomes can present close to the switch from bistability to guaranteed resolution in the corresponding homogeneous model. Finally, we show how aberrant spatial mechanisms can play a role in the failure of inflammation to resolve and discuss our results within the broader context of seeking novel inflammatory treatments

The Conformal Sector of F-theory GUTs

D3-brane probes of exceptional Yukawa points in F-theory GUTs are natural hidden sectors for particle phenomenology. We find that coupling the probe to the MSSM yields a new class of N = 1 conformal fixed points with computable infrared R-charges. Quite surprisingly, we find that the MSSM only weakly mixes with the strongly coupled sector in the sense that the MSSM fields pick up small exactly computable anomalous dimensions. Additionally, we find that although the states of the probe sector transform as complete GUT multiplets, their coupling to Standard Model fields leads to a calculable threshold correction to the running of the visible sector gauge couplings which improves precision unification. We also briefly consider scenarios in which SUSY is broken in the hidden sector. This leads to a gauge mediated spectrum for the gauginos and first two superpartner generations, with additional contributions to the third generation superpartners and Higgs sector.Comment: v2: 51 pages, 2 figures, remark added, typos correcte

Religious perspectives on the use of psychopharmaceuticals as an enhancement technology

The use of psychopharmaceuticals as an enhancement technology has been the focus of attention in the bioethics literature. However, there has been little examination of the challenges that this practice creates for religious traditions that place importance on questions of being, authenticity and identity. We asked expert commentators from six major world religions to consider the issues raised by psychopharmaceuticals as an enhancement technology. These commentaries reveal that in assessing the appropriate place of medical therapies, religious traditions, like secular perspectives, rely upon ideas about health and disease and about normal human behavior. But unlike secular perspectives, faith traditions explicitly concern themselves with ways in which medicine should or should not be used to live a ‘good life’. KEYWORDS: Enhancement; bioethics, psychopharmacology, religio

The Architectural Design Rules of Solar Systems based on the New Perspective

On the basis of the Lunar Laser Ranging Data released by NASA on the Silver Jubilee Celebration of Man Landing on Moon on 21st July 1969-1994, theoretical formulation of Earth-Moon tidal interaction was carried out and Planetary Satellite Dynamics was established. It was found that this mathematical analysis could as well be applied to Star and Planets system and since every star could potentially contain an extra-solar system, hence we have a large ensemble of exoplanets to test our new perspective on the birth and evolution of solar systems. Till date 403 exoplanets have been discovered in 390 extra-solar systems. I have taken 12 single planet systems, 4 Brown Dwarf - Star systems and 2 Brown Dwarf pairs. Following architectural design rules are corroborated through this study of exoplanets. All planets are born at inner Clarke Orbit what we refer to as inner geo-synchronous orbit in case of Earth-Moon System. By any perturbative force such as cosmic particles or radiation pressure, the planet gets tipped long of aG1 or short of aG1. Here aG1 is inner Clarke Orbit. The exoplanet can either be launched on death spiral as CLOSE HOT JUPITERS or can be launched on an expanding spiral path as the planets in our Solar System are. It was also found that if the exo-planet are significant fraction of the host star then those exo-planets rapidly migrate from aG1 to aG2 and have very short Time Constant of Evolution as Brown Dwarfs have. This vindicates our basic premise that planets are always born at inner Clarke Orbit. This study vindicates the design rules which had been postulated at 35th COSPAR Scientific Assembly in 2004 at Paris, France, under the title ,New Perspective on the Birth & Evolution of Solar Systems.Comment: This paper has been reported to Earth,Moon and Planets Journal as MOON-S-09-0007

Synchrony in directed connectomes

Synchronisation plays a fundamental role in a variety of physiological functions, such as visual perception, cognitive function, sleep and arousal. The precise role of the interplay between local dynamics and directed cortical topology on the propensity for cortical structures to synchronise, however, remains poorly understood. Here, we study the impact that directed network topology has on the synchronisation properties of the brain by considering a range of species and parcellations, including the cortex of the cat and the Macaque monkey, as well as the nervous system of the C. elegans round worm. We deploy a Kuramoto phase model to simulate neural dynamics on the aforementioned connectomes, and investigate the extent to which network directionality influences distributed patterns of neural synchrony. In particular, we find that network directionality induces both slower synchronisation speeds and more robust phase locking in the presence of network delays. Moreover, in contrast to large-scale connectomes, we find that recently observed relations between resting state directionality patterns and network structure appear to break down for invertebrate networks such as the C. elegans connectome, thus suggesting that observed variations in directed network topology at different scales can significantly impact patterns of neural synchrony. Our results suggest that directionality plays a key role in shaping network dynamics and moreover that its exclusion risks simplifying neural activation dynamics in a potentially significant way