40,287 research outputs found
c-Axis longitudinal magnetoresistance of the electron-doped superconductor Pr1.85Ce0.15CuO4
We report c-axis resistivity and longitudinal magnetoresistance measurements
of superconducting Pr1.85Ce0.15CuO4 single crystals. In the temperature range
13K<T<32K, a negative magnetoresistance is observed at fields just above Hc2.
Our studies suggest that this negative magnetoresistance is caused by
superconducting fluctuations. At lower temperatures (T<13K), a different
magnetoresistance behavior and a resistivity upturn are observed, whose origin
is still unknown.Comment: Accepted for publication in Phys. Rev.
Vacuum induced Berry phases in single-mode Jaynes-Cummings models
Motivated by the work [Phys. Rev. Lett. 89, 220404 (2002)] for detecting the
vacuum-induced Berry phases with two-mode Jaynes-Cummings models (JCMs), we
show here that, for a parameter-dependent single-mode JCM, certain atom-field
states also acquire the photon-number-dependent Berry phases after the
parameter slowly changed and eventually returned to its initial value. This
geometric effect related to the field quantization still exists, even the filed
is kept in its vacuum state. Specifically, a feasible Ramsey interference
experiment with cavity quantum electrodynamics (QED) system is designed to
detect the vacuum-induced Berry phase.Comment: 10 pages, 4 figures
Orthorhombic Phase of Crystalline Polyethylene: A Monte Carlo Study
In this paper we present a classical Monte Carlo simulation of the
orthorhombic phase of crystalline polyethylene, using an explicit atom force
field with unconstrained bond lengths and angles and periodic boundary
conditions. We used a recently developed algorithm which apart from standard
Metropolis local moves employs also global moves consisting of displacements of
the center of mass of the whole chains in all three spatial directions as well
as rotations of the chains around an axis parallel to the crystallographic
c-direction. Our simulations are performed in the NpT ensemble, at zero
pressure, and extend over the whole range of temperatures in which the
orthorhombic phase is experimentally known to be stable (10 - 450 K). In order
to investigate the finite-size effects in this extremely anisotropic crystal,
we used different system sizes and different chain lengths, ranging from C_12
to C_96 chains, the total number of atoms in the super-cell being between 432
and 3456. We show here the results for structural parameters, such as the
orthorhombic cell parameters a,b,c, and the setting angle of the chains, as
well as internal parameters of the chains, such as the bond lengths and angles.
Among thermodynamic quantities, we present results for thermal expansion
coefficients, elastic constants and specific heat. We discuss the temperature
dependence of the measured quantities as well as the related finite-size
effects. In case of lattice parameters and thermal expansion coefficients, we
compare our results to those obtained from other theoretical approaches as well
as to some available experimental data. We also suggest some possible ways of
extending this study.Comment: 27 pages, RevTex, 24 figures, submitted to Journal of Chemical
Physic
Acute Stroke Multimodal Imaging: Present and Potential Applications toward Advancing Care.
In the past few decades, the field of acute ischemic stroke (AIS) has experienced significant advances in clinical practice. A core driver of this success has been the utilization of acute stroke imaging with an increasing focus on advanced methods including multimodal imaging. Such imaging techniques not only provide a richer understanding of AIS in vivo, but also, in doing so, provide better informed clinical assessments in management and treatment toward achieving best outcomes. As a result, advanced stroke imaging methods are now a mainstay of routine AIS practice that reflect best practice delivery of care. Furthermore, these imaging methods hold great potential to continue to advance the understanding of AIS and its care in the future. Copyright © 2017 by Thieme Medical Publishers, Inc
Spin Polarisability of the Nucleon in the Heavy Baryon Effective Field Theory
We have constructed a heavy baryon effective field theory with photon as an
external field in accordance with the symmetry requirements similar to the
heavy quark effective field theory. By treating the heavy baryon and
anti-baryon equally on the same footing in the effective field theory, we have
calculated the spin polarisabilities of the nucleon at
third order and at fourth-order of the spin-dependent Compton scattering. At
leading order (LO), our results agree with the corresponding results of the
heavy baryon chiral perturbation theory, at the next-to-leading order(NLO) the
results show a large correction to the ones in the heavy baryon chiral
perturbation theory due to baryon-antibaryon coupling terms. The low energy
theorem is satisfied both at LO and at NLO. The contributions arising from the
heavy baryon-antibaryon vertex were found to be significant and the results of
the polarisabilities obtained from our theory is much closer to the
experimental data.Comment: 21pages, title changed, minimal correction
Searching for Dark Matter Signals in the Left-Right Symmetric Gauge Model with CP Symmetry
We investigate singlet scalar dark matter (DM) candidate in a left-right
symmetric gauge model with two Higgs bidoublets (2HBDM) in which the
stabilization of the DM particle is induced by the discrete symmetries P and
CP. According to the observed DM abundance, we predict the DM direct and
indirect detection cross sections for the DM mass range from 10 GeV to 500 GeV.
We show that the DM indirect detection cross section is not sensitive to the
light Higgs mixing and Yukawa couplings except the resonance regions. The
predicted spin-independent DM-nucleon elastic scattering cross section is found
to be significantly dependent on the above two factors. Our results show that
the future DM direct search experiments can cover the most parts of the allowed
parameter space. The PAMELA antiproton data can only exclude two very narrow
regions in the 2HBDM. It is very difficult to detect the DM direct or indirect
signals in the resonance regions due to the Breit-Wigner resonance effect.Comment: 24 pages, 8 figures. minor changes and a reference added, published
in Phys. Rev.
Local tunneling spectroscopy of the electron-doped cuprate Sm1.85Ce0.15CuO4
We present local tunneling spectroscopy in the optimally electron-doped
cuprate Sm2-xCexCuO4 x=0.15. A clear signature of the superconducting gap is
observed with an amplitude ranging from place to place and from sample to
sample (Delta~3.5-6meV). Another spectroscopic feature is simultaneously
observed at high energy above \pm 50meV. Its energy scale and temperature
evolution is found to be compatible with previous photoemission and optical
experiments. If interpreted as the signature of antiferromagnetic order in the
samples, these results could suggest the coexistence on the local scale of
antiferromagnetism and superconductivity on the electron-doped side of cuprate
superconductors
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