Super Landau Models on Odd Cosets

We construct d=1 sigma models of the Wess-Zumino type on the SU(n|1)/U(n) fermionic cosets. Such models can be regarded as a particular supersymmetric extension (with a target space supersymmetry) of the classical Landau model, when a charged particle possesses only fermionic coordinates. We consider both classical and quantum models, and prove the unitarity of the quantum model by introducing the metric operator on the Hilbert space of the quantum states, such that all their norms become positive-definite. It is remarkable that the quantum n=2 model exhibits hidden SU(2|2) symmetry. We also discuss the planar limit of these models. The Hilbert space in the planar n=2 case is shown to carry SU(2|2) symmetry which is different from that of the SU(2|1)/U(1) model.Comment: 1 + 33 pages, some typos correcte

Strings and AdS/CFT at finite density

This thesis is devoted to applications of string theoretic methods of holography to strongly coupled phases of quantum field theories. In chapter 2 we consider a finite-density system of quarks, realized holographically by a probe brane in Anti-de Sitter space, with a non-trivial gauge field background on its world-volume. We reproduce the holographic zero-sound in the longitudinal channel of the current-current correlation function. We generalize this result to the case of a non-vanishing background magnetic field. This field leads to a gap in the zero-sound mode, which scales proportionally to the magnitude of the field when it is small. In chapter 3 we study the classical dynamics of the tachyon field in an AdS background described by the tachyon-Dirac-Born-Infeld action. By considering a black hole in AdS space and switching on a non-vanishing background gauge field we obtained a holographic model of conformal symmetry breaking in a strongly coupled system at finite temperature and charge density. In chapter 4 we provide the exact string theoretic description of a quantum field theory at finite temperature and charge densityTheoretical Physic

Retrieval of Parameters for Layered non-Smooth Interface Media: Theory and Experiment.

Many naturally occurring or manmade objects can be modeled as three layer media with non-smooth interfaces. Most of the existing forward and inverse scattering models that can be applied to such media are either too inefficient or have limited regions of validity. In this dissertation an efficient forward scattering model based on the Extended Boundary Condition Method is developed for a three layer medium. The boundary between the first and the second layers is periodic while the boundary between the second and third layers is rough. The model is then extended by including an arbitrarily shaped cylinder placed into the third layer. Both TM and TE polarizations and PEC and Dielectric cylinder cases are considered. The Method of Moments (MOM) is used to obtain an impedance matrix, which is then transformed into a T-matrix. The T-matrix is transformed into a scattering matrix and cascaded with scattering matrices for the periodic and rough interfaces to obtain a generalized scattering matrix for the total system. A solution to the inverse problem for a three-layer medium is developed using simulated radar data. The retrieval of the layered- medium parameters is accomplished by sequential nonlinear optimizaxiii tion starting from the top layer and progressively characterizing the layers below. The optimization process is achieved by an efficient iterative technique built around the solution of the forward scattering problem. To be efficiently utilized in the inverse problem, the forward scattering model is simulated over a wide range of unknowns to obtain a complete set of subspace-based equivalent closed-form models that relate radar backscattering coefficients to the sought-for parameters, including the dielectric constants of each layer and the thickness of the middle layer. The inversion algorithm is implemented as a modified conjugate-gradient-based nonlinear optimization. It is shown that this technique results in accurate retrieval of surface and subsurface parameters, even in the presence of noise. To validate forward and inverse scattering models, a compact tower-based radar system is built. The data collected with the instrument is used to demonstrate sensitivity of radar measurements to changes in soil moisture and the potential for estimating surface and subsurface parameters.Ph.D.Electrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/89647/1/yuriy_1.pd

Prognostic Value of E/E′ Ratio in Patients With Unoperated Severe Aortic Stenosis

ObjectivesThe aim of this study was to evaluate the value of clinical and echo-Doppler parameters for the prognosis of unoperated severe aortic stenosis (AS).BackgroundApproximately one-third of severe, symptomatic AS patients are denied surgery. Risk stratification of unoperated AS is important to determine eligibility for percutaneous aortic valve replacement, an evolving treatment option for AS patients deemed suboptimal for surgical aortic valve replacement.MethodsWe retrospectively compared clinical and echo-Doppler parameters between survivors and nonsurvivors of 125 patients with unoperated severe AS.ResultsThe 1-year survival rate was 62.4%. In univariate analysis, survivors compared with nonsurvivors were younger (80.0 ± 10.9 years vs. 84.9 ± 11.1 years, p = 0.02), had a greater left ventricular ejection fraction (LVEF) (55 ± 15% vs. 50 ± 16%, p = 0.042), a higher left ventricular stroke volume (63 ± 19 ml vs. 56 ± 13 ml, p = 0.015), a lower E/E′ ratio (12.19 ± 5.7 vs. 16.87 ± 7.43, p < 0.001), and a lower prevalence of E/E′ >15 (20% vs. 55%, p < 0.001). Symptomatic status was nonsignificantly different between survivors and nonsurvivors. In patients with an LVEF ≥50%, the subgroup with E/E′ ≤15 and with E/E′ >15 had a 73.8% and 47.8% 1-year survival rate, respectively (p = 0.027). In the patients with an LVEF <50%, the patients with E/E′ ≤15 and those with E/E′ >15 demonstrated a 70.6% and 22.3% 1-year survival rate, respectively (p = 0.003). In multivariate analysis, significant predictors of mortality were E/E′ >15 and a combination of E/E′ >15 and B-type natriuretic peptide >300 ng/ml: adjusted mortality risk 2.34 (95% confidence interval (CI) 1.27 to 4.33, p = 0.0072) and 2.59 (95% CI 1.21 to 5.55, p = 0.014), respectively.ConclusionsThe E/E′ ratio is the single most predictive clinical and echo-Doppler parameter in the assessment of overall prognosis in patients with unoperated severe AS. LVEF was a significant predictor of survival only in the univariate analysis. B-type natriuretic peptide alone was not a predictor of prognosis in the study population. However, the combination of E/E′ and B-type natriuretic peptide is even more predictive of the 1-year prognosis

On-Chip Integrated, Silicon-Graphene Plasmonic Schottky Photodetector with High Responsivity and Avalanche Photogain.

We report an on-chip integrated metal graphene-silicon plasmonic Schottky photodetector with 85 mA/W responsivity at 1.55 μm and 7% internal quantum efficiency. This is one order of magnitude higher than metal-silicon Schottky photodetectors operated in the same conditions. At a reverse bias of 3 V, we achieve avalanche multiplication, with 0.37A/W responsivity and avalanche photogain ∼2. This paves the way to graphene integrated silicon photonics.We acknowledge funding from EU Graphene Flagship (No. 604391), ERC Grant Hetero2D, and EPSRC Grant Nos. EP/ K01711X/1, EP/K017144/1, EP/N010345/1, EP/M507799/ 1, and EP/L016087/1.This is the final version of the article. It first appeared from the American Chemical Society via https://doi.org/10.1021/acs.nanolett.5b0521

Development of neural network models for the analysis of infocommunication traffic

This article discusses the problems of today’s infocommunication networks, the basis of which are multiservice networks serving all types of traffic, presented as a set of IP packets. The characteristic features of this traffic are analyzed, each of which is oriented to a certain class of services. The knowledge gained as a result of ongoing traffic research is an essential factor for increasing the effectiveness of decisions made in various fields of the telecommunications industry. The need for knowledge of the nature of traffic circulating in the network and the laws of its behavior is revealed and substantiated. Without this, it is impossible to effectively manage networks, develop solutions for their development, ensure network security and maintain the required level of quality. Despite the large number of works about building multi - service networks, a number of issues require further study. Analysis of traffic studies of modern converged, multiservice networks showed the lack of knowledge about its nature and laws of behavior, given the high variability of its characteristics. Thus, it can be argued that the parameters of the studied traffic are statistical, probabilistic in nature, can vary randomly over time and, accordingly, based on the study, the author proposes a study using statistical analysis methods. To study traffic, you should use the tools of probability theory and mathematical statistics

Excitonic Emission of Monolayer Semiconductors Near-Field Coupled to High-Q Microresonators.

We present quantum yield measurements of single layer WSe2 (1L-WSe2) integrated with high-Q ( Q > 106) optical microdisk cavities, using an efficient (η > 90%) near-field coupling scheme based on a tapered optical fiber. Coupling of the excitonic emission is achieved by placing 1L-WSe2 in the evanescent cavity field. This preserves the microresonator high intrinsic quality factor ( Q > 106) below the bandgap of 1L-WSe2. The cavity quantum yield is QYc ≈ 10-3, consistent with operation in the broad emitter regime (i.e., the emission lifetime of 1L-WSe2 is significantly shorter than the bare cavity decay time). This scheme can serve as a precise measurement tool for the excitonic emission of layered materials into cavity modes, for both in plane and out of plane excitation