1,326 research outputs found
Closed expression of the interaction kernel in the Bethe-Salpeter equation for quark-antiquark bound states
The interaction kernel in the Bethe-Salpeter equation for quark-antiquark
bound states is derived from the Bethe-Salpeter equations satisfied by the
quark-antiquark four-point Green's function. The latter equations are
established based on the equations of motion obeyed by the quark and antiquark
propagators, the four-point Green's function and some other kinds of Green's
functions which follow directly from the QCD generating functional. The B-S
kernel derived is given an exact and explicit expression which contains only a
few types of Green's functions. This expression is not only convenient for
perturbative calculations, but also suitable for nonperturbative
investigations.Comment: 27 pages,no figure
Glueball spectrum based on a rigorous three-dimensional relativistic equation for two-gluon bound states II: calculation of the glueball spectrum
In the preceding paper, a rigorous three-dimensional relativistic equation
for two-gluon bound states was derived from the QCD with massive gluons and
represented in the angular momentum representation. In order to apply this
equation to calculate the glueball spectrum, in this paper, the equation is
recast in an equivalent three-dimensional relativistic equation satisfied by
the two-gluon positive energy state amplitude. The interaction Hamiltonian in
the equation is exactly derived and expressed as a perturbative series. The
first term in the series describes the one-gluon exchange interaction which
includes fully the retardation effect in it. This term plus the linear
confining potential are chosen to be the interaction Hamiltonian and employed
in the practical calculation. With the integrals containing three and four
spherical Bessel functions in the QCD vertices being analytically calculated,
the interaction Hamiltonian is given an explicit expression in the angular
momentum representation. Numerically solving the relativistic equation with
taking the contributions arising from the retardation effect and the
longitudinal mode of gluon fields into account, a set of masses for the
and glueball states are
obtained and are in fairly good agreement with the predictions given by the
lattice simulatio
Development Of A Cathode Designing Method To Avoid Electrodes’ Interference During Blisk Electrochemical Machining
Electrochemical machining plays a prominent role in blisk (bladed integrated disk) construction process. Since blisk channel is narrow and twisted, interference between electrodes may happen during electrochemical machining. Therefore, this paper develops a cathode designing method to avoid interference. Firstly, according to theory of electrochemical machining, machined channel is predicted by calculation. Second, with this channel, interference analysis is carried out and a cathode is designed. Finally, the cathode is employed in experiment and no interference appears
Glueball spectrum based on a rigorous three-dimensional relativistic equation for two-gluon bound states I: Derivation of the relativistic equation
A rigorous three-dimensional relativistic equation satisfied by two-gluon
bound states is derived from the QCD with massive gluons. With the gluon fields
and the quark fields being expanded in terms of the gluon multipole fields and
the spherical Dirac spinors respectively, the equation is well established in
the angular momentum representation and hence is much convenient for solving
the problem of two-gluon glueball spectra. In particular, the interaction
kernel in the equation is exactly derived and given a closed expression which
includes all the interactions taking place in the two-gluon glueballs. The
kernel contains only a few types of Green's functions and commutators.
Therefore, it is not only easily calculated by the perturbation method, but
also provides a suitable basis for nonperturbative investigations
Symmetry Properties on Magnetization in the Hubbard Model at Finite Temperatures
By making use of some symmetry properties of the relevant Hamiltonian, two
fundamental relations between the ferromagnetic magnetization and a spin
correlation function are derived for the -dimensional Hubbard model
at finite temperatures. These can be viewed as a kind of Ward-Takahashi
identities. The properties of the magnetization as a function of the applied
field are discussed. The results thus obtained hold true for both repulsive and
attractive on-site Coulomb interactions, and for arbitrary electron fillings.Comment: Latex file, no figur
A novel route to phase formation of cobalt oxyhydrates using KMnO4 as an oxidizing agent
We have first succeefully synthesized the sodium cobalt oxyhydrate
superconductors using KMnO4 as a de-intercalating and oxidizing agent. It is a
novel route to form the superconductive phase of NaxCoO2.yH2O without resorting
to the commonly used Br2/CH3CN solution. The role of the KMnO4 is to
de-intercalate the Na+ from the parent compound Na0.7CoO2 and oxidize the Co
ion as a result. The higher molar ratio of KMnO4 relative to the sodium content
tends to remove more Na+ from the parent compound and results in a slight
expansion of the c-axis in the unit cell. The superconducting transition
temperature is 4.6-3.8 K for samples treated by the aqueous KMnO4 solution with
the molar ratio of KMnO4 relative to the sodium content in the range of 0.3 and
2.29.Comment: 10 pages, 3 figure
Time-Dependent Spintronic Transport and Current-Induced Spin Transfer Torque in Magnetic Tunnel Junctions
The responses of the electrical current and the current-induced spin transfer
torque (CISTT) to an ac bias in addition to a dc bias in a magnetic tunnel
junction are investigated by means of the time-dependent nonquilibrium Green
function technique. The time-averaged current (time-averaged CISTT) is
formulated in the form of a summation of dc current (dc CISTT) multiplied by
products of Bessel functions with the energy levels shifted by . The tunneling current can be viewed as to happen between the photonic
sidebands of the two ferromagnets. The electrons can pass through the barrier
easily under high frequencies but difficultly under low frequencies. The tunnel
magnetoresistance almost does not vary with an ac field. It is found that the
spin transfer torque, still being proportional to the electrical current under
an ac bias, can be changed by varying frequency. Low frequencies could yield a
rapid decrease of the spin transfer torque, while a large ac signal leads to
both decrease of the electrical current and the spin torque. If only an ac bias
is present, the spin transfer torque is sharply enhanced at the particular
amplitude and frequency of the ac bias. A nearly linear relation between such
an amplitude and frequency is observed.Comment: 13 pages,8 figure
Modeling water waves beyond perturbations
In this chapter, we illustrate the advantage of variational principles for
modeling water waves from an elementary practical viewpoint. The method is
based on a `relaxed' variational principle, i.e., on a Lagrangian involving as
many variables as possible, and imposing some suitable subordinate constraints.
This approach allows the construction of approximations without necessarily
relying on a small parameter. This is illustrated via simple examples, namely
the Serre equations in shallow water, a generalization of the Klein-Gordon
equation in deep water and how to unify these equations in arbitrary depth. The
chapter ends with a discussion and caution on how this approach should be used
in practice.Comment: 15 pages, 1 figure, 39 references. This document is a contributed
chapter to an upcoming volume to be published by Springer in Lecture Notes in
Physics Series. Other author's papers can be downloaded at
http://www.denys-dutykh.com
Technical Note: Calibration and validation of geophysical observation models
We present a method to calibrate and validate observational models that interrelate remotely sensed energy fluxes to geophysical variables of land and water surfaces. Coincident sets of remote sensing observation of visible and microwave radiations and geophysical data are assembled and subdivided into calibration (Cal) and validation (Val) data sets. Each Cal/Val pair is used to derive the coefficients (from the Cal set) and the accuracy (from the Val set) of the observation model. Combining the results from all Cal/Val pairs provides probability distributions of the model coefficients and model errors. The method is generic and demonstrated using comprehensive matchup sets from two very different disciplines: soil moisture and water quality. The results demonstrate that the method provides robust model coefficients and quantitative measure of the model uncertainty. This approach can be adopted for the calibration/validation of satellite products of land and water surfaces, and the resulting uncertainty can be used as input to data assimilation schemes
Vitamin D deficiency in traumatic brain injury and its relationship with severity of injury and quality of life: a prospective, observational study
This single-centre prospective observational study aims to describe the prevalence of vitamin D deficiency (VDD) in the traumatic brain injury (TBI) population and identify any relationship between vitamin D and severity of head injury or quality of life.
124 TBI patients had serum vitamin D (25-OHD) levels measured at the local post-TBI endocrine screening clinic over 20 months. Quality of Life after Brain Injury (QOLIBRI) questionnaires were completed by the patient concurrently. A multivariate regressional analysis was performed, controlling for age, season, ethnicity, time since injury, TBI severity and gender.
34% (n=42) of the cohort were vitamin D deficient (25-OHD <25nmol/L) with a further 23% (n=29) having insufficient levels (25-OHD 25-50nmol/L). Vitamin D was significantly lower in severe TBI compared to mild TBI (n=95, p=0.03, CI 95% -23.60 to -1.21, mean effect size 12.40 nmol/L). There was a trend for self-reported quality of life to be better in patients with optimum vitamin D levels compared to patients with deficient vitamin D levels, controlling for severity of injury (n=81, p=0.05, CI 95% -0.07 to 21.27).
This is the first study to identify a significant relationship between vitamin D levels and severity of head injury. Clinicians should actively screen for and treat VDD in head injured patients to reduce the risk of further morbidity such as osteomalacia and cardiovascular disease. Future research should establish the natural history of vitamin D levels following TBI to identify at which stage VDD develops and whether vitamin D replacement could have a beneficial effect on recovery and quality of life
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