421 research outputs found
The theoretical reflectance of X-rays from optical surfaces
The theoretical reflectance of X-rays from various materials and evaporated films is presented. A computer program was written that computes the reflected intensity as a function of the angle of the incident radiation. The quantities necessary to generate the efficiency and their effect on the data are demonstrated. Five materials were chosen for evaluation: (1) fused silica, (2) chromium, (3) beryllium, (4) gold, and (5) a thin layer contaminant. Fused silica is a versatile and common material; chromium has high reflection efficiency at X-ray wavelengths and is in the middle of the atomic number range; beryllium contains a single atomic shell and has a low range atomic number; gold contains multiple atomic shells and has a high atomic number; the contaminant is treated as a thin film in the calculations and results are given as a function of thickness for selected wavelengths. The theoretical results are compared to experimental data at lambda = 8.34 A
Does the quark-gluon plasma contain stable hadronic bubbles?
We calculate the thermodynamic potential of bubbles of hadrons embedded in
quark-gluon plasma, and of droplets of quark-gluon plasma embedded in hadron
phase. This is a generalization of our previous results to the case of non-zero
chemical potentials. As in the zero chemical potential case, we find that a
quark-gluon plasma in thermodynamic equilibrium may contain stable bubbles of
hadrons of radius fm. The calculations are performed within the
MIT Bag model, using an improved multiple reflection expansion. The results are
of relevance for neutron star phenomenology and for ultrarelativistic heavy ion
collisions.Comment: 12 pages including 8 figures. To appear in Phys. Rev.
All-optical generation of states for "Encoding a qubit in an oscillator"
Both discrete and continuous systems can be used to encode quantum
information. Most quantum computation schemes propose encoding qubits in
two-level systems, such as a two-level atom or an electron spin. Others exploit
the use of an infinite-dimensional system, such as a harmonic oscillator. In
"Encoding a qubit in an oscillator" [Phys. Rev. A 64 012310 (2001)], Gottesman,
Kitaev, and Preskill (GKP) combined these approaches when they proposed a
fault-tolerant quantum computation scheme in which a qubit is encoded in the
continuous position and momentum degrees of freedom of an oscillator. One
advantage of this scheme is that it can be performed by use of relatively
simple linear optical devices, squeezing, and homodyne detection. However, we
lack a practical method to prepare the initial GKP states. Here we propose the
generation of an approximate GKP state by using superpositions of optical
coherent states (sometimes called "Schr\"odinger cat states"), squeezing,
linear optical devices, and homodyne detection.Comment: 4 pages, 3 figures. Submitted to Optics Letter
Chiral phase properties of finite size quark droplets in the Nambu--Jona-Lasinio model
Chiral phase properties of finite size hadronic systems are investigated
within the Nambu--Jona-Lasinio model. Finite size effects are taken into
account by making use of the multiple reflection expansion. We find that, for
droplets with relatively small baryon numbers, chiral symmetry restoration is
enhanced by the finite size effects. However the radius of the stable droplet
does not change much, as compared to that without the multiple reflection
expansion.Comment: RevTex4, 9 pages, 6 figures, to be published in Phys. Rev.
Qualitative description – the poor cousin of health research?
<p>Abstract</p> <p>Background</p> <p>The knowledge and use of qualitative description as a qualitative research approach in health services research is limited.</p> <p>The aim of this article is to discuss the potential benefits of a qualitative descriptive approach, to identify its strengths and weaknesses and to provide examples of use.</p> <p>Discussion</p> <p>Qualitative description is a useful qualitative method in much medical research if you keep the limitations of the approach in mind. It is especially relevant in mixed method research, in questionnaire development and in research projects aiming to gain firsthand knowledge of patients', relatives' or professionals' experiences with a particular topic. Another great advantage of the method is that it is suitable if time or resources are limited.</p> <p>Summary</p> <p>As a consequence of the growth in qualitative research in the health sciences, researchers sometimes feel obliged to designate their work as phenomenology, grounded theory, ethnography or a narrative study when in fact it is not. Qualitative description might be a useful alternative approach to consider.</p
Universality class of the restricted solid-on-solid model with hopping
We study the restricted solid-on-solid (RSOS) model with finite hopping
distance , using both analytical and numerical methods. Analytically, we
use the hard-core bosonic field theory developed by the authors [Phys. Rev. E
{\bf 62}, 7642 (2000)] and derive the Villain-Lai-Das Sarma (VLD) equation for
the case which corresponds to the conserved RSOS (CRSOS) model
and the Kardar-Parisi-Zhang (KPZ) equation for all finite values of .
Consequently, we find that the CRSOS model belongs to the VLD universality
class and the RSOS models with any finite hopping distance belong to the KPZ
universality class. There is no phase transition at a certain finite hopping
distance contrary to the previous result. We confirm the analytic results using
the Monte Carlo simulations for several values of the finite hopping distance.Comment: 13 pages, 3 figure
Facet ridge end points in crystal shapes
Equilibrium crystal shapes (ECS) near facet ridge end points (FRE) are
generically complex. We study the body-centered solid-on-solid model on a
square lattice with an enhanced uniaxial interaction range to test the
stability of the so-called stochastic FRE point where the model maps exactly
onto one dimensional Kardar-Parisi-Zhang type growth and the local ECS is
simple. The latter is unstable. The generic ECS contains first-order ridges
extending into the rounded part of the ECS, where two rough orientations
coexist and first-order faceted to rough boundaries terminating in
Pokrovsky-Talapov type end points.Comment: Contains 4 pages, 5 eps figures. Uses RevTe
Coronary artery disease-associated genetic variants and biomarkers of inflammation
Introduction: Genetic constitution and inflammation both contribute to development of coronary artery disease (CAD). Several CAD-associated single-nucleotide polymorphisms (SNPs) have recently been identified, but their functions are largely unknown. We investigated the associations between CAD-associated SNPs and five CAD-related inflammatory biomarkers. Methods: We genotyped 45 CAD-associated SNPs in 701 stable CAD patients in whom levels of high-sensitivity C-reactive protein (hsRCP), interleukin-6, calprotectin, fibrinogen and complement component 3 levels had previously been measured. A genetic risk score was calculated to assess the combined risk associated with all the genetic variants. A multiple linear regression model was used to assess associations between the genetic risk score, single SNPs, and the five inflammatory biomarkers. Results: The minor allele (G) (CAD risk allele) of rs2075650 (TOMM40/APOE) was associated with lower levels of high-sensitivity C-reactive protein (effect per risk allele: -0.37 mg/l [95%CI -0.56 to -0.18 mg/l]). The inflammatory markers tested showed no association with the remaining 44 SNPs or with the genetic risk score. Conclusions: In stable CAD patients, the risk allele of a common CAD-associated marker at the TOMM40/APOE locus was associated with lower hsCRP levels. No other genetic variants or the combined effect of all variants were associated with the five inflammatory biomarkers
Breakdown of the classical description of a local system
We provide a straightforward demonstration of a fundamental difference
between classical and quantum mechanics for a single local system; namely the
absence of a joint probability distribution of the position and momentum
. Elaborating on a recently reported criterion by Bednorz and Belzig [Phys.
Rev. A {\bf 83}, 52113] we derive a simple criterion that must be fulfilled for
any joint probability distribution in classical physics. We demonstrate the
violation of this criterion using homodyne measurement of a single photon
state, thus proving a straightforward signature of the breakdown of a classical
description of the underlying state. Most importantly, the criterion used does
not rely on quantum mechanics and can thus be used to demonstrate
non-classicality of systems not immediately apparent to exhibit quantum
behavior. The criterion is directly applicable any system described by the
continuous canonical variables x and p, such as a mechanical or an electrical
oscillator and a collective spin of a large ensemble.Comment: 5 pages, 2 figure
Derivation of continuum stochastic equations for discrete growth models
We present a formalism to derive the stochastic differential equations (SDEs)
for several solid-on-solid growth models. Our formalism begins with a mapping
of the microscopic dynamics of growth models onto the particle systems with
reactions and diffusion. We then write the master equations for these
corresponding particle systems and find the SDEs for the particle densities.
Finally, by connecting the particle densities with the growth heights, we
derive the SDEs for the height variables. Applying this formalism to discrete
growth models, we find the Edwards-Wilkinson equation for the symmetric
body-centered solid-on-solid (BCSOS) model, the Kardar-Parisi-Zhang equation
for the asymmetric BCSOS model and the generalized restricted solid-on-solid
(RSOS) model, and the Villain--Lai--Das Sarma equation for the conserved RSOS
model. In addition to the consistent forms of equations for growth models, we
also obtain the coefficients associated with the SDEs.Comment: 5 pages, no figur
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