3,114 research outputs found
Pion Generalized Parton Distributions within a fully covariant constituent quark model
We extend the investigation of the Generalized Parton Distribution for a
charged pion within a fully covariant constituent quark model, in two respects:
(i) calculating the tensor distribution and (ii) adding the treatment of the
evolution, needed for achieving a meaningful comparison with both the
experimental parton distribution and the lattice evaluation of the so-called
generalized form factors. Distinct features of our phenomenological covariant
quark model are: (i) a 4D Ansatz for the pion Bethe-Salpeter amplitude, to be
used in the Mandelstam formula for matrix elements of the relevant current
operators, and (ii) only two parameters, namely a quark mass assumed to hold
MeV and a free parameter fixed through the value of the pion decay
constant. The possibility of increasing the dynamical content of our covariant
constituent quark model is briefly discussed in the context of the Nakanishi
integral representation of the Bethe-Salpeter amplitude.Comment: Pages 20, figure 11 and table 8. Minor changes. To be published in
EPJ
Direct Measurement of Competing Quantum Effects on the Kinetic Energy of Heavy Water upon Melting
Even at room temperature, quantum mechanics plays a major role in determining
the quantitative behaviour of light nuclei, changing significantly the values
of physical properties such as the heat capacity. However, other observables
appear to be only weakly affected by nuclear quantum effects (NQEs): for
instance, the melting temperatures of light and heavy water differ by less than
4 K. Recent theoretical work has attributed this to a competition between intra
and inter molecular NQEs, which can be separated by computing the anisotropy of
the quantum kinetic energy tensor. The principal values of this tensor change
in opposite directions when ice melts, leading to a very small net quantum
mechanical effect on the melting point. This paper presents the first direct
experimental observation of this phenomenon, achieved by measuring the
deuterium momentum distributions n(p) in heavy water and ice using Deep
Inelastic Neutron Scattering (DINS), and resolving their anisotropy. Results
from the experiments, supplemented by a theoretical analysis, show that the
anisotropy of the quantum kinetic energy tensor can also be captured for
heavier atoms such as oxygen
Four wave mixing oscillation in a semiconductor microcavity: Generation of two correlated polariton populations
We demonstrate a novel kind of polariton four wave mixing oscillation. Two
pump polaritons scatter towards final states that emit two beams of equal
intensity, separated both spatially and in polarization with respect to the
pumps. The measurement of the intensity fluctuations of the emitted light
demonstrates that the final states are strongly correlated.Comment: 5 pages, 5 figures In this strongly revised version several new
experimental data are adde
The sentiment analysis of tweets as a new tool to measure public perception of male erectile and ejaculatory dysfunctions
Twitter is a social network based on "tweets," short messages of up to 280 characters. Social media has been investigated in health care research to ascertain positive or negative feelings associated with several conditions but never in sexual medicin
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Computational and experimental investigation of mixing in microchannels
This paper was presented at the 2nd Micro and Nano Flows Conference (MNF2009), which was held at Brunel University, West London, UK. The conference was organised by Brunel University and supported by the Institution of Mechanical Engineers, IPEM, the Italian Union of Thermofluid dynamics, the Process Intensification Network, HEXAG - the Heat Exchange Action Group and the Institute of Mathematics and its Applications.Mixing is a key process for the successful of all chemical or biochemical reactions, so effective micromixers represent essential components for micro total analysis systems (ÎĽTAS) or lab-on-a-chip. In the present study a combined computational and experimental approach was adopted to evaluate how the efficiency of a Y-mixer can be enhanced by modifying its downstream geometry. Three different geometries were studied and compared: Y-straight channel, Y-sine channel and Y-wrinkled wall channel. For each of them the influence of perfusing flow rates and channel cross section aspect ratio was investigated. Physical prototypes were built using a simple technique based on a xerographic process, and their mixing
performance was experimentally evaluated. Computational models of the designed micromixers were generated: the Navier-Stokes equations for an incompressible Newtonian fluid and the advection-diffusion
equation were solved with an uncoupled approach by means of the finite volume method. The computational and experimental results were critically compared, revealing Y-wrinkled wall mixer as the best performer
among those considered and suggesting criteria of possible improvements and optimization
Quantum Mechanical Search and Harmonic Perturbation
Perturbation theory in quantum mechanics studies how quantum systems interact
with their environmental perturbations. Harmonic perturbation is a rare special
case of time-dependent perturbations in which exact analysis exists. Some
important technology advances, such as masers, lasers, nuclear magnetic
resonance, etc., originated from it. Here we add quantum computation to this
list with a theoretical demonstration. Based on harmonic perturbation, a
quantum mechanical algorithm is devised to search the ground state of a given
Hamiltonian. The intrinsic complexity of the algorithm is continuous and
parametric in both time T and energy E. More precisely, the probability of
locating a search target of a Hamiltonian in N-dimensional vector space is
shown to be 1/(1+ c N E^{-2} T^{-2}) for some constant c. This result is
optimal. As harmonic perturbation provides a different computation mechanism,
the algorithm may suggest new directions in realizing quantum computers.Comment: 6 pages, 4 figures, revtex
Cardiovascular Diseases (CVDs) Patients with Hypertrophic Epicardial Adipose Tissue (EAT) Has a Microbiome Core Associated to Innate Immunity Activation
Dual HDAC/BRD4 Inhibitors Relieves Neuropathic Pain by Attenuating Inflammatory Response in Microglia After Spared Nerve Injury
Hypertension in adult Fabry's disease: is cardiotrophin-1 a diagnostic biomarker?
Background: Cardiotrophin-1 (CT-1), a cytokine produced by cardiomyocytes and non-cardiomyocytes in conditions of stress, can be used as a biomarker of left ventricular hypertrophy and dysfunction in hypertensive patients. Hypertension is one of the main adverse events in the third and last phase of Fabry's disease (FD). We measured CT-1 in order to examine its correlation with the vascular and cardiac alterations at different ages and assess its potential for use as a biomarker of hypertension in FD.
Findings: The level of CT-1 was clearly higher in hypertensive adults than in adult FD patients. FD patients show a small, non-significant decrease in plasma CT-1 with age, while in hypertensive patients CT-1 in plasma rises strongly and highly significantly with age.
Conclusions: CT-1 can be considered a good biomarker of the progression of hypertension with age, but particular care is needed when following hypertension in FD patients, since CT-1 does not correlate the same way with this disease
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