10,100 research outputs found
Thermal modeling of terahertz quantum-cascade lasers: comparison of optical waveguides
We compare a set of experimental lattice temperature profiles measured in a surface-emitting terahertz (THz) quantum-cascade laser (QCL) with the results of a 2-D anisotropic heat diffusion model. We evaluate the temperature dependence of the cross-plane thermal conductivity (kappaperp) of the active region which is known to be strongly anisotropic due to its superlattice-like nature. Knowledge of kappaperp and its temperature dependence is crucial in order to improve the temperature performance of THz QCLs and this has been used to investigate the longitudinal lattice temperature distribution of the active region and to compare the thermal properties of metal-metal and semi-insulating surface-plasmon THz optical waveguides using a 3-D anisotropic heat diffusion model
Van der Waals Interactions in a Magneto-Dielectric Medium
The van der Waals interaction between two ground-state atoms is calculated
for two electrically or magnetically polarizable particles embedded in a
dispersive magneto-dielectric medium. Unlike previous calculations which infer
the atom-atom interaction from the dilute-medium limit of the macroscopic,
many-body van der Waals interaction, the interaction is calculated directly for
the system of two atoms in a magneto-dielectric medium. Two approaches are
presented, the first based on the quantized electromagnetic field in a
dispersive medium without absorption and the second on Green functions that
allow for absorption. We show that the correct van der Waals interactions are
obtained regardless of whether absorption in the host medium is taken into
account.Comment: 9 pages, 1 figur
Post-Mortem Immunohistochemical Evidence of β2-Adrenergic Receptor Expression in the Adrenal Gland
The evidence from post-mortem biochemical studies conducted on cortisol and catecholamines suggest that analysis of the adrenal gland could provide useful information about its role in human pathophysiology and the stress response. Authors designed an immunohistochemical study on the expression of the adrenal β2-adrenergic receptor (β2-AR), a receptor with high-affinity for catecholamines, with the aim to show which zones it is expressed in and how its expression differs in relation to the cause of death. The immunohistochemical study was performed on adrenal glands obtained from 48 forensic autopsies of subjects that died as a result of different pathogenic mechanisms using a mouse monoclonal β2-AR antibody. The results show that immunoreactivity for β2-AR was observed in all adrenal zones. Furthermore, immunoreactivity for β2-AR has shown variation in the localization and intensity of different patterns in relation to the original cause of death. To the best of our knowledge, this is the first study that demonstrates β2-AR expression in the human cortex and provides suggestions on the possible involvement of β2-AR in human cortex hormonal stimulation. In conclusion, the authors provide a possible explanation for the observed differences in expression in relation to the cause of death
Noise effects in polymer dynamics
The study of the noise induced effects on the dynamics of a chain molecule
crossing a potential barrier, in the presence of a metastable state, is
presented. A two-dimensional stochastic version of the Rouse model for a
flexible polymer has been adopted to mimic the molecular dynamics and to take
into account the interactions between adjacent monomers. We obtain a
nonmonotonic behavior of the mean first passage time and its standard
deviation, of the polymer centre of inertia, with the noise intensity. These
findings reveal a noise induced effect on the mean crossing time. The role of
the polymer length is also investigated.Comment: 6 pages, 5 figures, to appear in Intern. Journ. of Bifurcation and
Chaos, 200
Temperature dependence of the magnetic Casimir-Polder interaction
We analyze the magnetic dipole contribution to atom-surface dispersion
forces. Unlike its electrical counterpart, it involves small transition
frequencies that are comparable to thermal energy scales. A significant
temperature dependence is found near surfaces with a nonzero DC conductivity,
leading to a strong suppression of the dispersion force at T > 0. We use
thermal response theory for the surface material and discuss both normal metals
and superconductors. The asymptotes of the free energy of interaction and of
the entropy are calculated analytically over a large range of distances. Near a
superconductor, the onset of dissipation at the phase transition strongly
changes the interaction, including a discontinuous entropy. We discuss the
similarities with the Casimir interaction beween two surfaces and suggest that
precision measurements of the atom-surface interaction may shed new light upon
open questions around the temperature dependence of dispersion forces between
lossy media.Comment: 11 figure
Noise delayed decay of unstable states: theory versus numerical simulations
We study the noise delayed decay of unstable nonequilibrium states in
nonlinear dynamical systems within the framework of the overdamped Brownian
motion model. We give the exact expressions for the decay times of unstable
states for polynomial potential profiles and obtain nonmonotonic behavior of
the decay times as a function of the noise intensity for the unstable
nonequilibrium states. The analytical results are compared with numerical
simulations.Comment: 9 pages, 6 figures, in press in J. Phys.
The spike train statistics for consonant and dissonant musical accords
The simple system composed of three neural-like noisy elements is considered.
Two of them (sensory neurons or sensors) are stimulated by noise and periodic
signals with different ratio of frequencies, and the third one (interneuron)
receives the output of these two sensors and noise. We propose the analytical
approach to analysis of Interspike Intervals (ISI) statistics of the spike
train generated by the interneuron. The ISI distributions of the sensory
neurons are considered to be known. The frequencies of the input sinusoidal
signals are in ratios, which are usual for music. We show that in the case of
small integer ratios (musical consonance) the input pair of sinusoids results
in the ISI distribution appropriate for more regular output spike train than in
a case of large integer ratios (musical dissonance) of input frequencies. These
effects are explained from the viewpoint of the proposed theory.Comment: 22 pages, 6 figure
Dynamics of a Quantum Particle in Asymmetric Bistable Potential with Environmental Noise
In this work we analyze the dynamics of a quantum particle subject to an asymmetric bistable potential and interacting with a thermal reservoir. We obtain the time evolution of the population distributions in both energy and position eigenstates of the particle, for different values of the coupling strength with the thermal bath. The calculation is carried out using the Feynman-
Vernon functional under the discrete variable representation
Prioritization of high-cost new drugs for HCV: making sustainability ethical
Hepatitis C virus (HCV) infection is a major health problem worldwide. Chronic HCV infection may in the long run cause cirrhosis, hepatic decompensation and hepatocellular carcinoma, with an ultimate disease burden of at least 350,000 deaths per year worldwide. The new generation of highly effective direct acting antivirals (DAA) to treat HCV infection brings major promises to infected patients in terms of exceedingly high rates of sustained virological response (SVR) but also of tolerability, allowing even the sickest patients to be treated. Even in the face of the excellent safety and efficacy and wide theoretical applicability of these regimens, their introduction is currently facing cost and access issues denying their use to many patients in need. Health systems in all countries are facing a huge problem of distributive justice, since while they should guarantee individual rights, among which the right to health in its broader sense, therefore not limited to healing, but extended to quality of life, they must also grant equal access to the healthcare resources and keep the distribution system sustainable. In the face of a disease with a relatively unpredictable course, where many but not of all chronically infected will eventually die of liver disease, selective allocation of this costly resource is debatable. In most countries the favorite solution has been a stratification of patients for prioritization of treatment, which means allowing Interferon-free DAA treatment only in patients with advanced fibrosis or cirrhosis, while keeping on hold persons with lesser stages of liver disease.
In this report, we will perform an ethical assessment addressing the issues linked to access to new therapies, prioritization and eligibility criteria, analyzing the meaning of the term “distributive justice” and the different approaches that can guide us (individualistic libertarianism, social utilitarianism and egalitarianism) on this specific matter. Even if over time the price of new DAA will be reduced through competition and eventual patent expiration, the phenomenon of high drug costs will go on in the next decades and we need adequate tools to face the problems of distributive justice that come with it
Volatility Effects on the Escape Time in Financial Market Models
We shortly review the statistical properties of the escape times, or hitting
times, for stock price returns by using different models which describe the
stock market evolution. We compare the probability function (PF) of these
escape times with that obtained from real market data. Afterwards we analyze in
detail the effect both of noise and different initial conditions on the escape
time in a market model with stochastic volatility and a cubic nonlinearity. For
this model we compare the PF of the stock price returns, the PF of the
volatility and the return correlation with the same statistical characteristics
obtained from real market data.Comment: 12 pages, 9 figures, to appear in Int. J. of Bifurcation and Chaos,
200
- …