24,603 research outputs found
The attainable superconducting Tc in a model of phase coherence by percolation
The onset of macroscopic phase coherence in superconducting cuprates is
considered to be determined by random percolation between mesoscopic
Jahn-Teller pairs, stripes or clusters. The model is found to predict the onset
of superconductivity near 6% doping, maximum Tc near 15% doping and Tc= T* at
optimum doping, and accounts for the destruction of superconductivity by Zn
doping near 7%. The model also predicts a relation between the pairing
(pseudogap) energy and Tc in terms of experimentally measurable quantities.Comment: 3 pages + 3 postscript figure
Nucleon Form Factors from Generalized Parton Distributions
We discuss the links between Generalized Parton Distributions (GPDs) and
elastic nucleon form factors. These links, in the form of sum rules, represent
powerful constraints on parametrizations of GPDs. A Regge parametrization for
GPDs at small momentum transfer, is extended to the large momentum transfer
region and it is found to describe the basic features of proton and neutron
electromagnetic form factor data. This parametrization is used to estimate the
quark contribution to the nucleon spin.Comment: 18 pages, 5 figures, replaced with published versio
Deciphering Deconfinement in Correlations of Conserved Charges
Diagonal and off-diagonal flavor and conserved charge susceptibilities reveal
the prevalent degrees of freedom of heated strongly interacting matter. Results
obtained from lattice simulations are compared with various model estimates in
an effort to weed down various possible pictures of a quark gluon plasma. We
argue that the vanishing of the off-diagonal quark flavor susceptibilities and
its derivatives with respect to chemical potential, at temperatures above
1.5Tc, can only be understood in a picture of a gas or liquid composed of
quasi-particles which carry the same quantum numbers as quarks and antiquarks.
A potential new observable, blind to neutral and non-strange particles, is
introduced and related via isospin symmetry to the ratio of susceptibilities of
baryonic strangeness to strangeness generated in the excited matter created at
RHIC.Comment: 5 pages, 3 figures, LATEX, To appear in the proceedings of the
International Conference on Strangeness in Quark Matter, Los Angeles, CA, Mar
26-31, 200
Aharanov-Bohm excitons at elevated temperatures in type-II ZnTe/ZnSe quantum dots
Optical emission from type-II ZnTe/ZnSe quantum dots demonstrates large and
persistent oscillations in both the peak energy and intensity indicating the
formation of coherently rotating states. Furthermore, the Aharanov-Bohm (AB)
effect is shown to be remarkably robust and persists until 180K. This is at
least one order of magnitude greater than the typical temperatures in
lithographically defined rings. To our knowledge this is the highest
temperature at which the AB effect has been observed in semiconductor
structures
Temperature dependence of trapped magnetic field in MgB2 bulk superconductor
Based on DC magnetization measurements, the temperature dependencies of the
trapped magnetic field have been calculated for two MgB2 samples prepared by
two different techniques: the high-pressure sintering and the hot pressing.
Experimentally measured trapped field values for the first sample coincide
remarkably well with calculated ones in the whole temperature range. This
proves, from one side, the validity of the introduced calculation approach, and
demonstrates, from another side, the great prospects of the hot pressing
technology for large scale superconducting applications of the MgB2.Comment: 3 pages, 3 figures, submitted to AP
Solving the m-mixing problem for the three-dimensional time-dependent Schr\"{o}dinger equation by rotations: application to strong-field ionization of H2+
We present a very efficient technique for solving the three-dimensional
time-dependent Schrodinger equation. Our method is applicable to a wide range
of problems where a fullly three-dimensional solution is required, i.e., to
cases where no symmetries exist that reduce the dimensionally of the problem.
Examples include arbitrarily oriented molecules in external fields and atoms
interacting with elliptically polarized light. We demonstrate that even in such
cases, the three-dimensional problem can be decomposed exactly into two
two-dimensional problems at the cost of introducing a trivial rotation
transformation. We supplement the theoretical framework with numerical results
on strong-field ionization of arbitrarily oriented H2+ molecules.Comment: 5 pages, 4 figure
The Zeeman effect in the G band
We investigate the possibility of measuring magnetic field strength in G-band
bright points through the analysis of Zeeman polarization in molecular CH
lines. To this end we solve the equations of polarized radiative transfer in
the G band through a standard plane-parallel model of the solar atmosphere with
an imposed magnetic field, and through a more realistic snapshot from a
simulation of solar magneto-convection. This region of the spectrum is crowded
with many atomic and molecular lines. Nevertheless, we find several instances
of isolated groups of CH lines that are predicted to produce a measurable
Stokes V signal in the presence of magnetic fields. In part this is possible
because the effective Land\'{e} factors of lines in the stronger main branch of
the CH A--X transition tend to zero rather quickly for
increasing total angular momentum , resulting in a Stokes spectrum of
the G band that is less crowded than the corresponding Stokes spectrum. We
indicate that, by contrast, the effective Land\'{e} factors of the and
satellite sub-branches of this transition tend to for increasing .
However, these lines are in general considerably weaker, and do not contribute
significantly to the polarization signal. In one wavelength location near 430.4
nm the overlap of several magnetically sensitive and non-sensitive CH lines is
predicted to result in a single-lobed Stokes profile, raising the
possibility of high spatial-resolution narrow-band polarimetric imaging. In the
magneto-convection snapshot we find circular polarization signals of the order
of 1% prompting us to conclude that measuring magnetic field strength in
small-scale elements through the Zeeman effect in CH lines is a realistic
prospect.Comment: 22 pages, 6 figures. To be published in the Astrophysical Journa
Ultrasound mapping of lymph node and subcutaneous metastases in patients with cutaneous melanoma: Results of a prospective multicenter study
Background: Ultrasound (sonography, B-mode sonography, ultrasonography) examination improves the sensitivity in more than 25% compared to the clinical palpation, especially after surgery on the regional lymph node area. Objective: To evaluate the distribution of metastases during follow-up in the draining lymph node areas from the scar of primary to regional lymph nodes ( head and neck, supraclavicular, axilla, infraclavicular, groin) in patients with cutaneous melanoma with or without sentinel lymph node biopsy (SLNB) or former elective or consecutive complete lymph node dissection in case of positive sentinel lymph node (CLND). Methods: Prospective multicenter study of the Departments of Dermatology of the Universities of Homburg/Saar, Tubingen and Munich (Germany) in which the distribution of lymph node and subcutaneous metastases were mapped from the scar of primary to the lymphatic drainage region in 53 melanoma patients ( 23 women, 30 men; median age: 64 years; median tumor thickness: 1.99 mm) with known primary, visible lymph nodes or subcutaneous metastases proven by ultrasound and histopathology during the follow-up. Results: Especially in the axilla, infraclavicular region and groin the metastases were not limited to the anatomic lymph node regions. In 5 patients (9.4%) ( 4 of them were in stage IV) lymph node metastases were not located in the corresponding lymph node area. 32 patients without former SLNB had a time range between melanoma excision and lymph node metastases of 31 months ( median), 21 patients with SLNB had 18 months ( p < 0.005). In 11 patients with positive SLNB the time range was 17 months, in 10 patients with negative SLNB 21 months ( p < 0.005); in 32 patients with CLND the time range was 31 m< 0.005). In thinner melanomas lymph node metastases occurred later ( p < 0.05). Conclusions: After surgery of cutaneous melanoma, SLNB and CLND the lymphatic drainage can show significant changes which should be considered in clinical and ultrasound follow-up examinations. Especially for high-risk melanoma patients follow-up examinations should be performed at intervals of 3 months in the first years. Patients at stage IV should be examined in all regional lymph node areas clinically and by ultrasound. Copyright (c) 2006 S. Karger AG, Basel
Quantum Phase Transition in Pr2CuO4 to Collinear Spin State in Inclined Magnetic Field: A Neutron Diffraction Observation
In the external field slightly inclined to the - or y-axis of the
frustrated tetragonal atiferromagnet Pr2CuO4, a transition is discovered from
the phase with orthogonal antiferromagnetic spin subsystems along [1,0,0] and
[0,1,0] to the phase with the collinear spins. This phase is shown to be due to
the pseudodipolar interaction, and transforms into the spin-flop phase S perp H
asymptotically at very high field. The discovered phase transition holds at T=0
and is a quantum one, with the transition field being the critical point and
the angle between two subsystems being the order parameter
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