480 research outputs found
|\epsilon|-Near-Zero materials in the near-infrared
We consider a mixture of metal coated quantum dots dispersed in a polymer
matrix and, using a modified version of the standard Maxwell-Garnett mixing
rule, we prove that the mixture parameters (particles radius, quantum dots
gain, etc.) can be chosen so that the effective medium permittivity has an
absolute value very close to zero in the near-infrared, i.e. |Re(epsilon)|<<1
and |Im (epsilon)|<<1 at the same near-infrared wavelength. Resorting to
full-wave simulations, we investigate the accuracy of the effective medium
predictions and we relate their discrepancy with rigorous numerical results to
the fact that |epsilon|<<1 is a critical requirement. We show that a simple
method for reducing this discrepancy, and hence for achieving a prescribed
value of |\epsilon|, consists in a subsequent fine-tuning of the nanoparticles
volume filling fraction.Comment: 3 pages, 3 figure
Geometric Entanglement of Symmetric States and the Majorana Representation
Permutation-symmetric quantum states appear in a variety of physical
situations, and they have been proposed for quantum information tasks. This
article builds upon the results of [New J. Phys. 12, 073025 (2010)], where the
maximally entangled symmetric states of up to twelve qubits were explored, and
their amount of geometric entanglement determined by numeric and analytic
means. For this the Majorana representation, a generalization of the Bloch
sphere representation, can be employed to represent symmetric n qubit states by
n points on the surface of a unit sphere. Symmetries of this point distribution
simplify the determination of the entanglement, and enable the study of quantum
states in novel ways. Here it is shown that the duality relationship of
Platonic solids has a counterpart in the Majorana representation, and that in
general maximally entangled symmetric states neither correspond to anticoherent
spin states nor to spherical designs. The usability of symmetric states as
resources for measurement-based quantum computing is also discussed.Comment: 10 pages, 8 figures; submitted to Lecture Notes in Computer Science
(LNCS
To wet or not to wet: that is the question
Wetting transitions have been predicted and observed to occur for various
combinations of fluids and surfaces. This paper describes the origin of such
transitions, for liquid films on solid surfaces, in terms of the gas-surface
interaction potentials V(r), which depend on the specific adsorption system.
The transitions of light inert gases and H2 molecules on alkali metal surfaces
have been explored extensively and are relatively well understood in terms of
the least attractive adsorption interactions in nature. Much less thoroughly
investigated are wetting transitions of Hg, water, heavy inert gases and other
molecular films. The basic idea is that nonwetting occurs, for energetic
reasons, if the adsorption potential's well-depth D is smaller than, or
comparable to, the well-depth of the adsorbate-adsorbate mutual interaction. At
the wetting temperature, Tw, the transition to wetting occurs, for entropic
reasons, when the liquid's surface tension is sufficiently small that the free
energy cost in forming a thick film is sufficiently compensated by the fluid-
surface interaction energy. Guidelines useful for exploring wetting transitions
of other systems are analyzed, in terms of generic criteria involving the
"simple model", which yields results in terms of gas-surface interaction
parameters and thermodynamic properties of the bulk adsorbate.Comment: Article accepted for publication in J. Low Temp. Phy
Influence of Humidity on Microtribology of Vertically Aligned Carbon Nanotube Film
The aim of this study is to probe the influence of water vapor environment on
the microtribological properties of a forestlike vertically aligned carbon
nanotube (VACNT) film, deposited on a silicon (001) substrate by chemical vapor
deposition. Tribological experiments were performed using a gold tip under
relative humidity varying from 0 to 100%. Very low adhesion forces and high
friction coefficients of 0.6 to 1.3 resulted. The adhesion and friction forces
were independent of humidity, due probably to the high hydrophobicity of VACNT.
These tribological characteristics were compared to those of a diamond like
carbon (DLC) sample
Direct and inverse pumping in flows with homogeneous and non-homogeneous swirl
The conditions in which meridional recirculations appear in swirling flows
above a fixed wall are analysed. In the classical Bodew\"adt problem, where the
swirl tends towards an aysmptotic value away from the wall, the well-known
"tea-cup effect" drives a flow away from the plate at the centre of the vortex.
Simple dimensional arguments applied to a single vortex show that if the
intensity of the swirl decreases away from the wall, the sense of the
recirculation can be inverted, and that the associated flow rate scales with
the swirl gradient. Only if the flow is quasi-2D, does the classical tea-cup
effect take place. This basic theory is confirmed by numerical simulations of a
square array of steady, electrically driven vortices. Experiments in the
turbulent regimes of the same configuration reveal that these mechanisms are
active in the average flow and in its fluctuating part. The mechanisms singled
out in this letter provide an explanation for previously observed phenomena in
electrolyte flows. They also put forward a possible mechanism for the
generation of helicity in flows close to two-dimensionality, which plays a key
role in the transition between 2D and 3D turbulence
Precise Measurements of Beam Spin Asymmetries in Semi-Inclusive production
We present studies of single-spin asymmetries for neutral pion
electroproduction in semi-inclusive deep-inelastic scattering of 5.776 GeV
polarized electrons from an unpolarized hydrogen target, using the CEBAF Large
Acceptance Spectrometer (CLAS) at the Thomas Jefferson National Accelerator
Facility. A substantial amplitude has been measured in the
distribution of the cross section asymmetry as a function of the azimuthal
angle of the produced neutral pion. The dependence of this amplitude
on Bjorken and on the pion transverse momentum is extracted with
significantly higher precision than previous data and is compared to model
calculations.Comment: to be submitted PL
Measurement of the Bottom-Strange Meson Mixing Phase in the Full CDF Data Set
We report a measurement of the bottom-strange meson mixing phase \beta_s
using the time evolution of B0_s -> J/\psi (->\mu+\mu-) \phi (-> K+ K-) decays
in which the quark-flavor content of the bottom-strange meson is identified at
production. This measurement uses the full data set of proton-antiproton
collisions at sqrt(s)= 1.96 TeV collected by the Collider Detector experiment
at the Fermilab Tevatron, corresponding to 9.6 fb-1 of integrated luminosity.
We report confidence regions in the two-dimensional space of \beta_s and the
B0_s decay-width difference \Delta\Gamma_s, and measure \beta_s in [-\pi/2,
-1.51] U [-0.06, 0.30] U [1.26, \pi/2] at the 68% confidence level, in
agreement with the standard model expectation. Assuming the standard model
value of \beta_s, we also determine \Delta\Gamma_s = 0.068 +- 0.026 (stat) +-
0.009 (syst) ps-1 and the mean B0_s lifetime, \tau_s = 1.528 +- 0.019 (stat) +-
0.009 (syst) ps, which are consistent and competitive with determinations by
other experiments.Comment: 8 pages, 2 figures, Phys. Rev. Lett 109, 171802 (2012
Characterization of large area APDs for the EXO-200 detector
EXO-200 uses 468 large area avalanche photodiodes (LAAPDs) for detection of
scintillation light in an ultra-low-background liquid xenon (LXe) detector. We
describe initial measurements of dark noise, gain and response to xenon
scintillation light of LAAPDs at temperatures from room temperature to 169K -
the temperature of liquid xenon. We also describe the individual
characterization of more than 800 LAAPDs for selective installation in the
EXO-200 detector.Comment: 10 pages, 17 figure
Methane Clumped Isotopes: Progress and Potential for a New Isotopic Tracer
The isotopic composition of methane is of longstanding geochemical interest, with important implications for understanding petroleum systems, atmospheric greenhouse gas concentrations, the global carbon cycle, and life in extreme environments. Recent analytical developments focusing on multiply substituted isotopologues (‘clumped isotopes’) are opening a valuable new window into methane geochemistry. When methane forms in internal isotopic equilibrium, clumped isotopes can provide a direct record of formation temperature, making this property particularly valuable for identifying different methane origins. However, it has also become clear that in certain settings methane clumped isotope measurements record kinetic rather than equilibrium isotope effects. Here we present a substantially expanded dataset of methane clumped isotope analyses, and provide a synthesis of the current interpretive framework for this parameter. In general, clumped isotope measurements indicate plausible formation temperatures for abiotic, thermogenic, and microbial methane in many geological environments, which is encouraging for the further development of this measurement as a geothermometer, and as a tracer for the source of natural gas reservoirs and emissions. We also highlight, however, instances where clumped isotope derived temperatures are higher than expected, and discuss possible factors that could distort equilibrium formation temperature signals. In microbial methane from freshwater ecosystems, in particular, clumped isotope values appear to be controlled by kinetic effects, and may ultimately be useful to study methanogen metabolism
Extent and Causes of Chesapeake Bay Warming
Coastal environments such as the Chesapeake Bay have long been impacted by eutrophication stressors resulting from human activities, and these impacts are now being compounded by global warming trends. However, there are few studies documenting long-term estuarine temperature change and the relative contributions of rivers, the atmosphere, and the ocean. In this study, Chesapeake Bay warming, since 1985, is quantified using a combination of cruise observations and model outputs, and the relative contributions to that warming are estimated via numerical sensitivity experiments with a watershed–estuarine modeling system. Throughout the Bay’s main stem, similar warming rates are found at the surface and bottom between the late 1980s and late 2010s (0.02 +/- 0.02C/year, mean +/- 1 standard error), with elevated summer rates (0.04 +/- 0.01C/year) and lower rates of winter warming (0.01 +/- 0.01C/year). Most (~85%) of this estuarine warming is driven by atmospheric effects. The secondary influence of ocean warming increases with proximity to the Bay mouth, where it accounts for more than half of summer warming in bottom waters. Sea level rise has slightly reduced summer warming, and the influence of riverine warming has been limited to the heads of tidal tributaries. Future rates of warming in Chesapeake Bay will depend not only on global atmospheric trends, but also on regional circulation patterns in mid-Atlantic waters, which are currently warming faster than the atmosphere.
Supporting model data available at: https://doi.org/10.25773/c774-a36
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