Slowdown and splitting of gap solitons in apodized Bragg gratings

We study the motion of gap solitons in two models of apodized nonlinear fiber Bragg gratings (BGs), with the local reflectivity (LR) varying along the fiber. A single step of LR, and a periodic array of alternating steps with opposite signs (a "Bragg superstructure") are considered. A challenging possibility is to slow down and eventually halt the soliton by passing it through the step of increasing reflectivity, thus capturing a pulse of standing light. First, we develop an analytical approach, assuming adiabatic evolution of the soliton, and making use of the energy conservation and balance equation for the momentum. Comparison with simulations shows that the analytical approximation is quite accurate (unless the inhomogeneity is too steep): the soliton is either transmitted across the step or bounces back. If the step is narrow, systematic simulations demontrate that the soliton splits into transmitted and reflected pulses (splitting of a BG soliton which hits a chirped grating was observed in experiments). Moving through the periodic "superstructure", the soliton accummulates distortion and suffers radiation loss if the structure is composed of narrow steps. The soliton moves without any loss or irreversible deformation through the array of sufficiently broad steps.Comment: to appear in a special issue on Wave-Optical Engineering, Journal of Modern Optic

Biomarkers in acute coronary syndromes and their role in diabetic patients

Diabetic patients with acute coronary syndromes are at high risk for cardiovascular complications but risk stratification in these patients remains challenging. Regularly, diabetic patients have a less typical clinical presentation, which could lead to delayed diagnosis and subsequent delayed initiation of treatment. Since diabetic patients derive particular benefit from aggressive anti-platelet therapy, early diagnostic and therapeutic risk stratification of these patients is of critical importance to improve their adverse outcome. Although the electrocardiogram remains a pivotal diagnostic tool in the evaluation of patients suspected of having an acute coronary syndrome, only significant STsegment changes provide reasonable prognostic information. Therefore, repeated assessment of circulating protein biomarkers represents a valuable diagnostic tool for improving efficacy and safety of decision-making in these patients. The combined use of biomarkers reflecting distinct pathophysiological aspects, such as myocardial necrosis, vascular inflammation, oxidative stress and neurohumoral activation, may significantly improve triage of patients with chest pain. These tools may identify those patients that are at particularly high risk for short-term and/or long-term cardiovascular events. Eventually, tailored medical and interventional treatment of diabetic patients should help to prevent these cardiac events in a cost-effective manner

Multilevel blocking approach to the fermion sign problem in path-integral Monte Carlo simulations

A general algorithm toward the solution of the fermion sign problem in finite-temperature quantum Monte Carlo simulations has been formulated for discretized fermion path integrals with nearest-neighbor interactions in the Trotter direction. This multilevel approach systematically implements a simple blocking strategy in a recursive manner to synthesize the sign cancellations among different fermionic paths throughout the whole configuration space. The practical usefulness of the method is demonstrated for interacting electrons in a quantum dot.Comment: 4 pages RevTeX, incl. two figure

Causal Bulk Viscous Dissipative Isotropic Cosmologies with Variable Gravitational and Cosmological Constants

We consider the evolution of a flat Friedmann-Robertson-Walker Universe, filled with a causal bulk viscous cosmological fluid, in the presence of variable gravitational and cosmological constants. The basic equation for the Hubble parameter, generalizing the evolution equation in the case of constant gravitational coupling and cosmological term, is derived, under the supplementary assumption that the total energy of the Universe is conserved. By assuming that the cosmological constant is proportional to the square of the Hubble parameter and a power law dependence of the bulk viscosity coefficient, temperature and relaxation time on the energy density of the cosmological fluid, two classes of exact solutions of the field equations are obtained. In the first class of solutions the Universe ends in an inflationary era, while in the second class of solutions the expansion of the Universe is non-inflationary for all times. In both models the cosmological "constant" is a decreasing function of time, while the gravitational "constant" increases in the early period of evolution of the Universe, tending in the large time limit to a constant value.Comment: 14 pages, 15 figure

Human P450 CYP17A1: Control of Substrate Preference by Asparagine 202

CYP17A1 is a key steroidogenic enzyme known to conduct several distinct chemical transformations on multiple substrates. In its hydroxylase activity, this enzyme adds a hydroxyl group at the 17α position of both pregnenolone and progesterone at approximately equal rates. However, the subsequent 17,20 carbon–carbon scission reaction displays variable substrate specificity in the numerous CYP17A1 isozymes operating in vertebrates, manifesting as different Kd and kcat values when presented with 17α-hydroxypregnenlone (OHPREG) versus 17α-hydroxyprogesterone (OHPROG). Here we show that the identity of the residue at position 202 in human CYP17A1, thought to form a hydrogen bond with the A-ring alcohol substituent on the pregnene- nucleus, is a key driver of this enzyme’s native preference for OHPREG. Replacement of asparagine 202 with serine completely reverses the preference of CYP17A1, more than doubling the rate of turnover of the OHPROG to androstenedione reaction and substantially decreasing the rate of formation of dehydroepiandrosterone from OHPREG. In a series of resonance Raman experiments, it was observed that, in contrast with the case for the wild-type protein, in the mutant the 17α alcohol of OHPROG tends to form a H-bond with the proximal rather than terminal oxygen of the oxy–ferrous complex. When OHPREG was a substrate, the mutant enzyme was found to have a H-bonding interaction with the proximal oxygen that is substantially weaker than that of the wild type. These results demonstrate that a single-point mutation in the active site pocket of CYP17A1, even when far from the heme, has profound effects on steroidogenic selectivity in androgen biosynthesis

Cost-sharing in directed networks: experimental study of equilibrium choice and system dynamics

This study reports the results of an experiment on directed networks with positive externalities induced by cost-sharing. Subjects participated in a network game in which they had to choose between private and public transportations. If a player chose public transportation, then she shared the travel cost equally with other players making the same choice, whereas if she chose private transportation, then her travel cost was fixed. Travel costs on the private route were manipulated across the two experimental conditions. In one condition, these costs were homogeneous among players; in the other condition, they were heterogeneous among players and only privately known. We found that half (none) of the player groups in the homogeneous (heterogeneous) condition converged toward the efficient equilibrium. Examination of the system dynamics shows that convergence toward efficiency was facilitated by: (1) the existence of an intermediate equilibrium choice; and (2) strategic teaching by which a farsighted player chooses strategies with poor short-term payoff in order to shift group decisions to the efficient equilibrium and thereby increase her own long-term benefit.This research was supported by NSF Grant SES-1418923 awarded to the University of Nevada, Las Vegas

Dynamical simulation of transport in one-dimensional quantum wires

Transport of single-channel spinless interacting fermions (Luttinger liquid) through a barrier has been studied by numerically exact quantum Monte Carlo methods. A novel stochastic integration over the real-time paths allows for direct computation of nonequilibrium conductance and noise properties. We have examined the low-temperature scaling of the conductance in the crossover region between a very weak and an almost insulating barrier.Comment: REVTex, 4 pages, 2 uuencoded figures (submitted to Phys. Rev. Lett.

The Influence of Gamma-rays on the Injury and Chromosomal Aberrations of Long Bean (Vigna sesquipedalis, Fruw.)

The effects of gamma-rays on three varieties of long bean (Vigna sesquipedalis, Fruw), namely Melaka, Local Black and Local Long were studied using Jive doses ranging from 10 to 50 kR. Both Chromosomal aberrations and characteristics related to physiological damage were used to study radiation sensitivity of the varieties. In general, gamma radiation did not affect % seed germination but caused a significant reduction in characteristics related to survival, growth and fertility. Percentage chromosomal aberrations also increased with increasing dose. As the measurement of seedling height is simple, quick and highly correlated with most characteristics studied, it could be a useful parameter in the study of radiation effects on long bean. Using a critenrion of approximately 30% reduction in seedling height or 50% lethality, it is suggested that doses ranging from 30 to 50 kR would be suitable for mutation induction in long bean

Effect of next-nearest neighbor coupling on the optical spectra in bilayer graphene

We investigate the dependence of the optical conductivity of bilayer graphene (BLG) on the intra- and inter-layer interactions using the most complete model to date. We show that the next nearest-neighbor intralayer coupling introduces new features in the low-energy spectrum that are highly sensitive to sample doping, changing significantly the ``universal'' conductance. Further, its interplay with interlayer couplings leads to an anisotropy in conductance in the ultraviolet range. We propose that experimental measurement of the optical conductivity of intrinsic and doped BLG will provide a good benchmark for the relative importance of intra- and inter-layer couplings at different doping levels.Comment: 5 pages, 5 figure