9,393 research outputs found
Phase transition of the nucleon-antinucleon plasma at different ratios
We investigate phase transitions for the Walecka model at very high
temperatures. As is well known, depending on the parametrization of this model
and for the particular case of a zero chemical potential (), a first
order phase transition is possible \cite{theis}. We investigate this model for
the case in which . It turns out that, in this situation, phases
with different values of antinucleon-nucleon ratios and net baryon densities
may coexist. We present the temperature versus antinucleon-nucleon ratio as
well as the temperature versus the net baryon density for the coexistence
region. The temperature versus chemical potential phase diagram is also
presented.Comment: 5 pages, 8 figure
Direct Observation of Condon Domains in Silver by Hall Probes
Using a set of micro Hall probes for the detection of the local induction,
the inhomogeneous Condon domain structure has been directly observed at the
surface of a pure silver single crystal under strong Landau quantization in
magnetic fields up to 10 T. The inhomogeneous induction occurs in the
theoretically predicted part of the H-T Condon domain phase diagram.
Information about size, shape and orientation of the domains is obtained by
analyzing Hall probes placed along and across the long sample axis and by
tilting the sample. On a beryllium surface the induction inhomogeneity is
almost absent although the expected induction splitting here is at least ten
times higher than in silver.Comment: 4 pages, 6 figures, submitted to PR
Hysteresis in the de Haas-van Alphen Effect
A hysteresis loop is observed for the first time in the de Haas-van Alphen
(dHvA) effect of beryllium at low temperatures and quantizing magnetic field
applied parallel to the hexagonal axis of the single crystal. The irreversible
behavior of the magnetization occurs at the paramagnetic part of the dHvA
period in conditions of Condon domain formation arising by strong enough dHvA
amplitude. The resulting extremely nonlinear response to a very small
modulation field offers the possibility to find in a simple way the Condon
domain phase diagram. From a harmonic analysis, the shape and size of the
hysteresis loop is constructed.Comment: 4 pages, 5 figures, submitted to PR
新収作品 : ジョルジュ・ド・ラ・トゥール《聖トマス》
We present a tomographic technique making use of a gigaelectronvolt electron beam for the determination of the material budget distribution of centimeter-sized objects by means of simulations and measurements. In both cases, the trajectory of electrons traversing a sample under test is reconstructed using a pixel beam-telescope. The width of the deflection angle distribution of electrons undergoing multiple Coulomb scattering at the sample is estimated. Basing the sinogram on position-resolved estimators enables the reconstruction of the original sample using an inverse radon transform. We exemplify the feasibility of this tomographic technique via simulations of two structured cubes—made of aluminium and lead—and via an in-beam measured coaxial adapter. The simulations yield images with FWHM edge resolutions of (177 ± 13) μm and a contrast-to-noise ratio of 5.6 ± 0.2 (7.8 ± 0.3) for aluminium (lead) compared to air. The tomographic reconstruction of a coaxial adapter serves as experimental evidence of the technique and yields a contrast-to-noise ratio of 15.3 ± 1.0 and a FWHM edge resolution of (117 ± 4) μm
Condon Domain Phase Diagram for Silver
We present the Condon domain phase diagram for a silver single crystal
measured in magnetic fields up to 28 T and temperatures down to 1.3 K. A
standard ac method with a pickup coil system is used at low frequency for the
measurements of the de Haas-van Alphen effect (dHvA). The transition point from
the state of homogeneous magnetization to the inhomogeneous Condon domain state
(CDS) is found as the point where a small irreversibility in the dHvA
magnetization arises, as manifested by an extremely nonlinear response in the
pickup voltage showing threshold character. The third harmonic content in the
ac response is used to determine with high precision the CDS phase boundary.
The experimentally determined Condon domain phase diagram is in good agreement
with the theoretical prediction calculated by the standard Lifshitz-Kosevich
(LK) formula
Two-Dimensional Spectroscopy of Extended Molecular Systems: Applications to Energy Transport and Relaxation in an α-Helix
A simulation study of the coupled dynamics of amide I and amide II vibrations in an α-helix dissolved in water shows that two-dimensional (2D) infrared spectroscopy may be used to disentangle the energy transport along the helix through each of these modes from the energy relaxation between them. Time scales for both types of processes are obtained. Using polarization-dependent 2D spectroscopy is an important ingredient in the method we propose. The method may also be applied to other two-band systems, both in the infrared (collective vibrations) and the visible (excitons) parts of the spectrum.
Quantum Transport with Spin Dephasing: A Nonequilibrium Green's Function Approach
A quantum transport model incorporating spin scattering processes is
presented using the non-equilibrium Green's function (NEGF) formalism within
the self-consistent Born approximation. This model offers a unified approach by
capturing the spin-flip scattering and the quantum effects simultaneously. A
numerical implementation of the model is illustrated for magnetic tunnel
junction devices with embedded magnetic impurity layers. The results are
compared with experimental data, revealing the underlying physics of the
coherent and incoherent transport regimes. It is shown that small variations in
magnetic impurity spin-states/concentrations could cause large deviations in
junction magnetoresistances.Comment: NEGF Formalism, Spin Dephasing, Magnetic Tunnel Junctions,
Magnetoresistanc
Novel features of diffraction at the LHC
Interest and problems in the studies of diffraction at LHC are highlighted.
Predictions for the global characteristics of proton-proton interactions at the
LHC energy are given. Potential discoveries of the antishadow scattering mode
and diffractive scattering conjugated with high-- jets are discussed.Comment: 10 pages, 7 figures, journal version, 1 figure added, extended
introductio
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