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Search Results: 1 - 10 of 315523 matches for " G. F. Cao "
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Flavour symmetry breaking in the polarized nucleon sea
F. -G. Cao,A. I. Signal
Physics , 2001,
Abstract: After a brief review on flavour symmetry breaking (FSB) in the unpolarized nucleon sea, we discuss theoretical predications for FSB in the polarized nucleon sea from meson cloud and `Pauli blocking'.
The spin dependent structure functions of the nucleon
F. Bissey,F. G. Cao,A. I. Signal
Physics , 2005, DOI: 10.1103/PhysRevD.73.094008
Abstract: We calculate the spin dependent structure functions g_{1}(x) and g_{2}(x) of the proton and neutron. Our calculation uses the meson cloud model of nucleon structure, which has previously given a good description of the HERMES data on polarized sea quark distributions, and includes all the leading contributions to spin dependent effects in this model. We find good agreement between our calculations and the current experimental data for the structure functions. We include in our calculations kinematic terms, which mix transverse and longitudinal spin components, for hadrons of spin 1/2, 1 and 3/2, and which can give considerable contributions to the g_{2} structure functions. We also consider the possible interference terms between baryons or mesons in different final states with the same quantum numbers, and show that most of these terms do not give leading contributions to the spin dependent structure functions.
Quantum slow-roll and quantum fast-roll inflationary initial conditions: CMB quadrupole suppression and further effects on the low CMB multipoles
Cao, F. J.;de Vega, H. J.;Sanchez, N. G.
High Energy Physics - Phenomenology , 2008, DOI: 10.1103/PhysRevD.78.083508
Abstract: Quantum fast-roll initial conditions for the inflaton which are different from the classical fast-roll conditions and from the quantum slow-roll conditions can lead to inflation that last long enough. These quantum fast-roll initial conditions for the inflaton allow for kinetic energies of the same order of the potential energies and nonperturbative inflaton modes with nonzero wavenumbers. Their evolution starts with a transitory epoch where the redshift due to the expansion succeeds to assemble the quantum excited modes of the inflaton in a homogeneous (zero mode) condensate, and the large value of the Hubble parameter succeeds to overdamp the fast-roll of the redshifted inflaton modes. After this transitory stage the effective classical slow-roll epoch is reached. Most of the efolds are produced during the slow-roll epoch and we recover the classical slow-roll results for the scalar and tensor metric perturbations plus corrections. These corrections are important, both for scalar and for tensor perturbations, if scales which are horizon-size today exited the horizon by the end of the transitory stage and as a consequence the lower CMB multipoles get suppressed (fast-roll) or enhanced (precondensate). These two types of corrections can compete and combine in a scale dependent manner. They arise as natural consequences of the quantum nonperturbative inflaton dynamics, and provide a consistent and contrastable model for the origin of the suppression of the quadrupole and for other departures of the low CMB multipoles from the slow-roll inflation-LambdaCMB model which are to be contrasted to the TE and EE multipoles and to the forthcoming and future CMB data.
Strange sea distributions of the nucleon
H. Chen,F. -G. Cao,A. I. Signal
Physics , 2009, DOI: 10.1088/0954-3899/37/10/105006
Abstract: The strange and antistrange quark distributions of the nucleon are less constrained by experimental data than the non-strange quark sea. The combination of light quark sea distributions, $\Delta(x)=\dbar(x)+\ubar(x)-s(x)-\sbar(x)$, originates mainly from non-perturbative processes and can be calculated using non-perturbative models of the nucleon. We have calculated $\Delta(x)$ using the meson cloud model, which, when combined with the relatively well known non-strange light antiquark distributions obtained from global analysis of available experimental data, enables us to make new estimates of the total strange sea distributions of the nucleon and the strange sea suppression factor.
Quantum slow-roll and quantum fast-roll inflationary initial conditions: CMB quadrupole suppression and further effects on the low CMB multipoles
F. J. Cao,H. J. de Vega,N. G. Sanchez
Physics , 2008, DOI: 10.1103/PhysRevD.78.083508
Abstract: Quantum fast-roll initial conditions for the inflaton which are different from the classical fast-roll conditions and from the quantum slow-roll conditions can lead to inflation that last long enough. These quantum fast-roll initial conditions for the inflaton allow for kinetic energies of the same order of the potential energies and nonperturbative inflaton modes with nonzero wavenumbers. Their evolution starts with a transitory epoch where the redshift due to the expansion succeeds to assemble the quantum excited modes of the inflaton in a homogeneous (zero mode) condensate, and the large value of the Hubble parameter succeeds to overdamp the fast-roll of the redshifted inflaton modes. After this transitory stage the effective classical slow-roll epoch is reached. Most of the efolds are produced during the slow-roll epoch and we recover the classical slow-roll results for the scalar and tensor metric perturbations plus corrections. These corrections are important, both for scalar and for tensor perturbations, if scales which are horizon-size today exited the horizon by the end of the transitory stage and as a consequence the lower CMB multipoles get suppressed (fast-roll) or enhanced (precondensate). These two types of corrections can compete and combine in a scale dependent manner. They arise as natural consequences of the quantum nonperturbative inflaton dynamics, and provide a consistent and contrastable model for the origin of the suppression of the quadrupole and for other departures of the low CMB multipoles from the slow-roll inflation-LambdaCMB model which are to be contrasted to the TE and EE multipoles and to the forthcoming and future CMB data.
The quantum inflaton, primordial perturbations and CMB fluctuations
F. J. Cao,H. J. de Vega,N. G. Sanchez
Physics , 2004, DOI: 10.1103/PhysRevD.70.083528
Abstract: We compute the primordial scalar, vector and tensor metric perturbations arising from quantum field inflation. Quantum field inflation takes into account the nonperturbative quantum dynamics of the inflaton consistently coupled to the dynamics of the (classical) cosmological metric. For chaotic inflation, the quantum treatment avoids the unnatural requirements of an initial state with all the energy in the zero mode. For new inflation it allows a consistent treatment of the explosive particle production due to spinodal instabilities. Quantum field inflation (under conditions that are the quantum analog of slow roll) leads, upon evolution, to the formation of a condensate starting a regime of effective classical inflation. We compute the primordial perturbations taking the dominant quantum effects into account. The results for the scalar, vector and tensor primordial perturbations are expressed in terms of the classical inflation results. For a N-component field in a O(N) symmetric model, adiabatic fluctuations dominate while isocurvature or entropy fluctuations are negligible. The results agree with the current WMAP observations and predict corrections to the power spectrum in classical inflation.Such corrections are estimated to be of the order of m^2/[N H^2] where m is the inflaton mass and H the Hubble constant at horizon crossing. This turns to be about 4% for the cosmologically relevant scales. This quantum field treatment of inflation provides the foundations to the classical inflation and permits to compute quantum corrections to it.
RELATIONSHIP BETWEEN J-INTEGRAL AND FRACTURE SURFACE AVERAGE PROFILE
YG Cao,SF Xue,and K Tanaka,
Y.G.
,Cao,S.F.,Xue,K.,Tanaka

金属学报(英文版) , 2007,
Abstract: To investigate the causes that led to the formation of cracks in materials, a novel method that only considered the fracture surfaces for determining the fracture toughness parameters of J-integral for plain strain was proposed. The principle of the fracture-surface topography analysis (FRASTA) was used. In FRASTA, the fracture surfaces were scanned by laser microscope and the elevation data was recorded for analysis. The relationship between J-integral and fracture surface average profile for plain strain was deduced. It was also verified that the J-integral determined by the novel method and by the compliance method matches each other well.
Understanding the Mechanisms of Proteinuria: Therapeutic Implications
Jorge E. Toblli,P. Bevione,F. Di Gennaro,L. Madalena,G. Cao,M. Angerosa
International Journal of Nephrology , 2012, DOI: 10.1155/2012/546039
Abstract: A large body of evidence indicates that proteinuria is a strong predictor of morbidity, a cause of inflammation, oxidative stress and progression of chronic kidney disease, and development of cardiovascular disease. The processes that lead to proteinuria are complex and involve factors such as glomerular hemodynamic, tubular absorption, and diffusion gradients. Alterations in various different molecular pathways and interactions may lead to the identical clinical end points of proteinuria and chronic kidney disease. Glomerular diseases include a wide range of immune and nonimmune insults that may target and thus damage some components of the glomerular filtration barrier. In many of these conditions, the renal visceral epithelial cell (podocyte) responds to injury along defined pathways, which may explain the resultant clinical and histological changes. The recent discovery of the molecular components of the slit diaphragm, specialized structure of podocyte-podocyte interaction, has been a major breakthrough in understanding the crucial role of the epithelial layer of the glomerular barrier and the pathogenesis of proteinuria. Thispaper provides an overview and update on the structure and function of the glomerular filtration barrier and the pathogenesis of proteinuria, highlighting the role of the podocyte in this setting. In addition, current antiproteinuric therapeutic approaches are briefly commented. 1. Introduction Proteinuria is considered a major healthcare problem that affects several hundred million people worldwide. In addition, proteinuria is a sensitive marker for progressive renal dysfunction and it is considered an independent risk factor for cardiovascular (CV) morbidity and mortality [1]. Furthermore, it is widely accepted that microalbuminuria (albumin urinary excretion of 30?mg–300?mg/day) is the earliest clue about the renal involvement of diabetes, obesity, and the metabolic syndrome. Interestingly, while microalbuminuria is more predictive of reaching CV end points than kidney end points, macroalbuminuria (total protein urinary excretion >500?mg/day) has been demonstrated to be more associated with reaching kidney end points [2]. However, microalbuminuria can often progress to overt proteinuria leading 10–50% of the patients to end-stage kidney disease development, ultimately requiring dialysis or transplantation. Of similar importance is the observation that even levels of albumin under the microalbuminuria threshold (so-called ‘‘high normal’’) are associated with an increased risk for CV outcomes [3]. Therefore, a reduction or
Effect of isoprene emissions from major forests on ozone formation in the city of Shanghai, China
F. Geng, X. Tie, A. Guenther, G. Li, J. Cao,P. Harley
Atmospheric Chemistry and Physics (ACP) & Discussions (ACPD) , 2011,
Abstract: Ambient surface level concentrations of isoprene (C5H8) were measured in the major forest regions located south of Shanghai, China. Because there is a large coverage of broad-leaved trees in this region, high concentrations of isoprene were measured, ranging from 1 to 6 ppbv. A regional dynamical/chemical model (WRF-Chem) is applied for studying the effect of such high concentrations of isoprene on the ozone production in the city of Shanghai. The evaluation of the model shows that the calculated isoprene concentrations agree with the measured concentrations when the measured isoprene concentrations are lower than 3 ppb, but underestimate the measurements when the measured values are higher than 3 ppb. Isoprene was underestimated only at sampling sites near large bamboo plantations, a high isoprene source, indicating the need to include geospatially resolved bamboo distributions in the biogenic emission model. The assessment of the impact of isoprene on ozone formation suggests that the concentrations of peroxy radicals (RO2) are significantly enhanced due to the oxidation of isoprene, with a maximum of 30 ppt. However, the enhancement of RO2 is confined to the forested regions. Because the concentrations of NOx were low in the forest regions, the ozone production due to the oxidation of isoprene (C5H8 + OH → → RO2 + NO → → O3) is low (less than 2–3 ppb h 1). The calculation further suggests that the oxidation of isoprene leads to the enhancement of carbonyls (such as formaldehyde and acetaldehyde) in the regions downwind of the forests, due to continuous oxidation of isoprene in the forest air. As a result, the concentrations of HO2 radical are enhanced, resulting from the photo-disassociation of formaldehyde and acetaldehyde. Because the enhancement of HO2 radical occurs in regions downwind of the forests, the enhancement of ozone production (6–8 ppb h 1) is higher than in the forest region, causing by higher anthropogenic emissions of NOx. This study suggests that the biogenic emissions in the major forests to the south of Shanghai have important impacts on the levels of ozone in the city, mainly due to the carbonyls produced by the continuous oxidation of isoprene in the forest air.
Magnetic and Orbital Orders Coupled to Negative Thermal Expansion in Mott Insulators, Ca2Ru1-xMxO4 (M = Mn and Fe)
T. F. Qi,O. B. Korneta,S. Parkin,Jiangping Hu,G. Cao
Physics , 2011, DOI: 10.1103/PhysRevB.85.165143
Abstract: Ca2RuO4 is a structurally-driven Mott insulator with a metal-insulator transition at TMI = 357K, followed by a well-separated antiferromagnetic order at TN = 110 K. Slightly substituting Ru with a 3d transition metal ion M effectively shifts TMI by weakening the orthorhombic distortion and induces either metamagnetism or magnetization reversal below TN. Moreover, M doping for Ru produces negative thermal expansion in Ca2Ru1-xMxO4 (M = Cr, Mn, Fe or Cu); the lattice volume expands on cooling with a total volume expansion ratio, {\Delta}V/V, reaching as high as 1%. The onset of the negative thermal expansion closely tracks TMI and TN, sharply contrasting classic negative thermal expansion that shows no relevance to electronic properties. In addition, the observed negative thermal expansion occurs near room temperature and extends over a wide temperature interval up to 300 K. These findings underscores new physics driven by a complex interplay between orbital, spin and lattice degrees of freedom.
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