273 research outputs found
Practical free-space quantum key distribution over 1 km
A working free-space quantum key distribution (QKD) system has been developed
and tested over an outdoor optical path of ~1 km at Los Alamos National
Laboratory under nighttime conditions. Results show that QKD can provide secure
real-time key distribution between parties who have a need to communicate
secretly. Finally, we examine the feasibility of surface to satellite QKD.Comment: 5 pages, 2 figures, 2 tables. Submitted to Physics Review Letters,
May 199
LSPR properties of metal nanoparticles adsorbed at a liquid–liquid interface
Unlike the solid–air and solid–liquid interfaces, the optical properties of metal nanoparticles adsorbed at the liquid–liquid interface have not been theoretically exploited to date. In this work, the three dimensional finite difference time domain (3D-FDTD) method is employed to clarify the localized surface plasmon resonance (LSPR) based optical properties of gold nanoparticles (NPs) adsorbed at the water–oil interface, including near field distribution, far field absorption and their relevance. The LSPR spectra of NPs located at a liquid–liquid interface are shown to differ significantly from those in a uniform liquid environment or at the other interfaces. The absorption spectra exhibit two distinct LSPR peaks, the positions and relative strengths of which are sensitive to the dielectric properties of each liquid and the exact positions of the NPs with respect to the interface. Precise control of the particles’ position and selection of the appropriate wavelength of the excitation laser facilitates the rational design and selective excitation of localized plasmon modes for interfacial NPs, a necessary advance for the exploration of liquid–liquid interfaces via surface enhanced Raman spectroscopy (SERS). According to our calculations, the SERS enhancement factor for Au nanosphere dimers at the water–oil interface can be as high as 107–109, implying significant promise for future investigations of interfacial structure and applications of liquid–liquid interfaces towards chemical analysis
The Small Conductance Calcium Activated Potassium Current Modulates the Ventricular Escape Rhythm in Normal Rabbit Hearts
Background
The apamin-sensitive small-conductance calcium-activated K (SK) current (IKAS) modulates automaticity of the sinus node; IKAS blockade by apamin causes sinus bradycardia.
Objective
To test the hypothesis that IKAS modulates ventricular automaticity.
Methods
We tested the effects of apamin (100 nM) on ventricular escape rhythms in Langendorff perfused rabbit ventricles with atrioventricular (AV) block (Protocol 1) and on recorded transmembrane action potential (TMP) of pseudotendons of superfused right ventricular (RV) endocardial preparations (Protocol 2).
Results
All preparations exhibited spontaneous ventricular escape rhythms. In Protocol 1, apamin decreased the atrial rate from 186.2±18.0 bpm to 163.8±18.7 bpm (N=6, p=0.006) but accelerated the ventricular escape rate from 51.5±10.7 to 98.2±25.4 bpm (p=0.031). Three preparations exhibited bursts of nonsustained ventricular tachycardia (NSVT) and pauses, resulting in repeated burst-termination pattern. In Protocol 2, apamin increased the ventricular escape rate from 70.2±13.1 to 110.1±2.2 bpm (p=0.035). Spontaneous phase 4 depolarization was recorded from the pseudotendons in 6 of 10 preparations at baseline and in 3 in the presence of apamin. There were no changes of phase 4 slope (18.37±3.55 vs. 18.93±3.26 mV/s, p=0.231, N=3), but the threshold of phase 0 activation (mV) reduced from -67.97±1.53 to -75.26±0.28 (p=0.034). Addition of JTV-519, a ryanodine receptor 2 (RyR2) stabilizer, in 5 preparations reduced escape rate back to baseline.
Conclusions
Contrary to its bradycardic effect in the sinus node, IKAS blockade by apamin accelerates ventricular automaticity and causes repeated NSVT in normal ventricles. RyR2 blockade reversed the apamin effects on ventricular automaticity
Stochastic processes with finite correlation time: modeling and application to the generalized Langevin equation
The kangaroo process (KP) is characterized by various forms of the covariance
and can serve as a useful model of random noises. We discuss properties of that
process for the exponential, stretched exponential and algebraic (power-law)
covariances. Then we apply the KP as a model of noise in the generalized
Langevin equation and simulate solutions by a Monte Carlo method. Some results
appear to be incompatible with requirements of the fluctuation-dissipation
theorem because probability distributions change when the process is inserted
into the equation. We demonstrate how one can construct a model of noise free
of that difficulty. This form of the KP is especially suitable for physical
applications.Comment: 22 pages (RevTeX) and 4 figure
Existence theorems in the geometrically non-linear 6-parametric theory of elastic plates
In this paper we show the existence of global minimizers for the
geometrically exact, non-linear equations of elastic plates, in the framework
of the general 6-parametric shell theory. A characteristic feature of this
model for shells is the appearance of two independent kinematic fields: the
translation vector field and the rotation tensor field (representing in total 6
independent scalar kinematic variables). For isotropic plates, we prove the
existence theorem by applying the direct methods of the calculus of variations.
Then, we generalize our existence result to the case of anisotropic plates. We
also present a detailed comparison with a previously established Cosserat plate
model.Comment: 19 pages, 1 figur
Experimental observation of topological Fermi arcs in type-II Weyl semimetal MoTe2
Weyl semimetal is a new quantum state of matter [1-12] hosting the condensed
matter physics counterpart of relativisticWeyl fermion [13] originally
introduced in high energy physics. The Weyl semimetal realized in the TaAs
class features multiple Fermi arcs arising from topological surface states [10,
11, 14-16] and exhibits novel quantum phenomena, e.g., chiral anomaly induced
negative mag-netoresistance [17-19] and possibly emergent supersymmetry [20].
Recently it was proposed theoretically that a new type (type-II) of Weyl
fermion [21], which does not have counterpart in high energy physics due to the
breaking of Lorentz invariance, can emerge as topologically-protected touching
between electron and hole pockets. Here, we report direct spectroscopic
evidence of topological Fermi arcs in the predicted type-II Weyl semimetal
MoTe2 [22-24]. The topological surface states are confirmed by directly
observing the surface states using bulk-and surface-sensitive angle-resolved
photoemission spectroscopy (ARPES), and the quasi-particle interference (QPI)
pattern between the two putative Fermi arcs in scanning tunneling microscopy
(STM). Our work establishes MoTe2 as the first experimental realization of
type-II Weyl semimetal, and opens up new opportunities for probing novel
phenomena such as exotic magneto-transport [21] in type-II Weyl semimetals.Comment: submitted on 01/29/2016. Nature Physics, in press. Spectroscopic
evidence of the Fermi arcs from two complementary surface sensitive probes -
ARPES and STS. A comparison of the calculated band structure for T_d and 1T'
phase to identify the topological Fermi arcs in the T_d phase is also
included in the supplementary informatio
Effect of noise on coupled chaotic systems
Effect of noise in inducing order on various chaotically evolving systems is
reviewed, with special emphasis on systems consisting of coupled chaotic
elements. In many situations it is observed that the uncoupled elements when
driven by identical noise, show synchronization phenomena where chaotic
trajectories exponentially converge towards a single noisy trajectory,
independent of the initial conditions. In a random neural network, with
infinite range coupling, chaos is suppressed due to noise and the system
evolves towards a fixed point. Spatiotemporal stochastic resonance phenomenon
has been observed in a square array of coupled threshold devices where a
temporal characteristic of the system resonates at a given noise strength. In a
chaotically evolving coupled map lattice with logistic map as local dynamics
and driven by identical noise at each site, we report that the number of
structures (a structure is a group of neighbouring lattice sites for whom
values of the variable follow certain predefined pattern) follow a power-law
decay with the length of the structure. An interesting phenomenon, which we
call stochastic coherence, is also reported in which the abundance and
lifetimes of these structures show characteristic peaks at some intermediate
noise strength.Comment: 21 page LaTeX file for text, 5 Postscript files for figure
Neuroimaging at 7 Tesla: a pictorial narrative review
Neuroimaging using the 7-Tesla (7T) human magnetic resonance (MR) system is rapidly gaining popularity after being approved for clinical use in the European Union and the USA. This trend is the same for functional MR imaging (MRI). The primary advantages of 7T over lower magnetic fields are its higher signal-to-noise and contrast-to-noise ratios, which provide high-resolution acquisitions and better contrast, making it easier to detect lesions and structural changes in brain disorders. Another advantage is the capability to measure a greater number of neurochemicals by virtue of the increased spectral resolution. Many structural and functional studies using 7T have been conducted to visualize details in the white matter and layers of the cortex and hippocampus, the subnucleus or regions of the putamen, the globus pallidus, thalamus and substantia nigra, and in small structures, such as the subthalamic nucleus, habenula, perforating arteries, and the perivascular space, that are difficult to observe at lower magnetic field strengths. The target disorders for 7T neuroimaging range from tumoral diseases to vascular, neurodegenerative, and psychiatric disorders, including Alzheimer’s disease, Parkinson’s disease, multiple sclerosis, epilepsy, major depressive disorder, and schizophrenia. MR spectroscopy has also been used for research because of its increased chemical shift that separates overlapping peaks and resolves neurochemicals more effectively at 7T than a lower magnetic field. This paper presents a narrative review of these topics and an illustrative presentation of images obtained at 7T. We expect 7T neuroimaging to provide a new imaging biomarker of various brain disorders
Isospin-tracing: A probe of non-equilibrium in central heavy-ion collisions
Four different combinations of Ru and Zr nuclei, both
as projectile and target, were investigated at the same bombarding energy of
400 MeV using a detector. The degree of isospin mixing between
projectile and target nucleons is mapped across a large portion of the phase
space using two different isospin-tracer observables, the number of measured
protons and the yield ratio. The experimental results
show that the global equilibrium is not reached even in the most central
collisions. Quantitative measures of stopping and mixing are extracted from the
data. They are found to exhibit a quite strong sensitivity to the in-medium
(n,n) cross section used in microscopic transport calculations.Comment: 4 pages RevTeX, 3 figures (ps files), submitted to Phys. Rev. Let
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