22,845 research outputs found
Hard thermal effective action in QCD through the thermal operator
Through the application of the thermal operator to the zero temperature
retarded Green's functions, we derive in a simple way the well known hard
thermal effective action in QCD. By relating these functions to forward
scattering amplitudes for on-shell particles, this derivation also clarifies
the origin of important properties of the hard thermal effective action, such
as the manifest Lorentz and gauge invariance of its integrand.Comment: 6 pages, contribution of the quarks to the effective action included
and one reference added, version to be published in Phys. Rev.
Influence of Domain Wall on Magnetocaloric Effect in GdPt
The resistivity, magnetoresistance and in-field heat capacity measurements
were performed on GdPt intermetallic compound. The magnetocaloric
parameters and were derived from the in-field heat
capacity data. Comparison has been made between the magnetocaloric effect
and difference in resistivity
as a function of temperature. There is distinct difference in the temperature
dependence of and below the ferromagnetic transition
temperature. However after removing the domain wall contribution from , the nature of and dependence as a function of
temperature are similar. Our observation indicates that the domain wall
contribution in magnetocaloric effect is negligible in spite of the fact that
it has significant contribution in magnetotransport.Comment: RevTex 4 pages, 6 figure
Factorization of finite temperature graphs in thermal QED
We extend our previous analysis of gauge and Dirac fields in the presence of
a chemical potential. We consider an alternate thermal operator which relates
in a simple way the Feynman graphs in QED at finite temperature and charge
density to those at zero temperature but non-zero chemical potential. Several
interesting features of such a factorization are discussed in the context of
the thermal photon and fermion self-energies.Comment: 4 page
Spin Accumulation in the Extrinsic Spin Hall Effect
The drift-diffusion formalism for spin-polarized carrier transport in
semiconductors is generalized to include spin-orbit coupling. The theory is
applied to treat the extrinsic spin Hall effect using realistic boundary
conditions. It is shown that carrier and spin diffusion lengths are modified by
the presence of spin-orbit coupling and that spin accumulation due to the
extrinsic spin Hall effect is strongly and qualitatively influenced by boundary
conditions. Analytical formulas for the spin-dependent carrier recombination
rates and inhomogeneous spin densities and currents are presented.Comment: 5 pages, 3 figure
Spin transport in inhomogeneous magnetic fields: a proposal for Stern-Gerlach-like experiments with conduction electrons
Spin dynamics in spatially inhomogeneous magnetic fields is studied within
the framework of Boltzmann theory. Stern-Gerlach-like separation of spin up and
spin down electrons occurs in ballistic and diffusive regimes, before spin
relaxation sets in. Transient dynamics and spectral response to time-dependent
inhomogeneous magnetic fields are investigated, and possible experimental
observations of our findings are discussed.Comment: 7 pages, 4 figures; revised and extended version, to appear in PR
Thermal Operator and Cutting Rules at Finite Temperature and Chemical Potential
In the context of scalar field theories, both real and complex, we derive the
cutting description at finite temperature (with zero/finite chemical potential)
from the cutting rules at zero temperature through the action of a simple
thermal operator. We give an alternative algebraic proof of the largest time
equation which brings out the underlying physics of such a relation. As an
application of the cutting description, we calculate the imaginary part of the
one loop retarded self-energy at zero/finite temperature and finite chemical
potential and show how this description can be used to calculate the dispersion
relation as well as the full physical self-energy of thermal particles.Comment: 17 pages, 13 figures. Added references, version to appear in Physical
Review
Aeroacoustics of a porous plug supersonic jet noise suppressor
The aeroacoustics of a porous plug supersonic jet noise suppressor was investigated. The needed modifications of the existing multistream coaxial jet rig; the compressed air facility and pressure controls; the design, the fabrication, and the installation of the plenum chamber for the plug nozzle, and the design and the machining of the first contoured plug nozzle were completed. The optical and the aeroacoustic data of the contoured plug nozzles and of the conical convergent nozzle alone were discussed
Spin Injection and Detection via the Anomalous Spin Hall Effect in a Ferromagnetic Metal
We report a novel spin injection and detection mechanism via the anomalous
Hall effect in a ferromagnetic metal. The anomalous spin Hall effect (ASHE)
refers to the transverse spin current generated within the ferromagnet. We
utilize the ASHE and its reciprocal effect to electrically inject and detect
magnons in a magnetic insulator in a non-local geometry. Our experiments reveal
that permalloy can have a higher spin injection and detection efficiency to
that of platinum, owing to the ASHE. We also demonstrate the tunability of the
ASHE via the orientation of the permalloy magnetization, thus creating new
possibilities for spintronic applications
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