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71.
We construct a new exact solution to the vacuum Einstein field equations. This solution possesses a naked physical singularity. The norm of the Riemann curvature tensor of the solution takes infinity at some points and the solution does not have any event horizon around the singularity. A detailed analysis of this new singularity is also presented. 相似文献
72.
C. Merino C. Pajares Yu. M. Shabelski 《The European Physical Journal C - Particles and Fields》2009,59(3):691-703
In the framework of the quark–gluon string model we calculate the inclusive spectra of secondaries produced in d+Au collisions at intermediate (CERN SPS) and at much higher (RHIC) energies. The results of numerical calculations at intermediate
energies are in reasonable agreement with the data. At RHIC energies numerically large inelastic screening corrections (percolation
effects) should be accounted for in the calculations. We extract these effects from the existing experimental data of RHIC
on minimum-bias and central d+Au collisions. The predictions for p+Au interactions at LHC energy are also given. 相似文献
73.
Xin Dong 《The European Physical Journal C - Particles and Fields》2009,61(4):659-664
I report the most recent measurements on open heavy flavor production at RHIC on behalf of the STAR collaboration. The total
charm production cross section in midrapidity at RHIC energy is found to approximately scale by number of binary collisions
in d + Au, Cu + Cu and Au + Au collisions. The nuclear modification factor of non-photonic electrons is strongly suppressed in
central Au + Au collisions, suggesting substantial heavy quark energy loss at RHIC. The bottom decay contribution to non-photonic
electrons was studied via the e–h and e–D
0 azimuthal angular correlations. The bottom contribution is found to be important at p
T
>5 GeV/c, and is consistent with the FONLL calculation within uncertainties. Charm production through gluon jet splitting was measured
by studying the D
*± contents in the fully reconstructed jets in p+p collisions. This rate is consistent with pQCD evaluation of gluon splitting into a pair of charm quarks and subsequent hadronization. 相似文献
74.
We study the evolution of heavy quarkonium states with temperature in a Quark-Gluon Plasma (QGP) by evaluating an in-medium
Qˉ T-matrix within a reduced Bethe-Salpeter equation in S- and P-wave channels. The interaction kernel is extracted from finite-temperature QCD lattice calculations of the singlet free energy
of a Qˉ pair. Quarkonium bound states are found to gradually move across the Qˉ threshold after which they rapidly dissolve in the hot system. We calculate Euclidean-time correlation functions and compare
to results from lattice QCD. We also study finite-width effects in the heavy-quark propagators. 相似文献
75.
We report on the fabrication and characterization of phototransistors based on AIGaN/GaN heterostructure grown over 6H-SiC substrates. The device has two functions: as a high electron mobility transistor (HEMT) and an ultraviolet photodetector at the same time. As an HEMT, its maximum transconductance is 170mS/ram, while the minimum cutoff frequency fT and the maximum oscillation frequency fm are 19 and 35 GHz, respectively. As a photodetector, the device is visible blind, with an ultraviolet/green contrast of three orders of magnitude, and a responsivity as high as 1700 A/W at the wavelength of 362nm. 相似文献
76.
High precision approximate analytic expressions of the ground state energies and wave functions for the arbitrary physical potentials are found by first casting the Schrödinger equation into the nonlinear Riccati form and then solving that nonlinear equation analytically in the first iteration of the quasilinearization method (QLM). In the QLM the nonlinear differential equation is treated by approximating the nonlinear terms by a sequence of linear expressions. The QLM is iterative but not perturbative and gives stable solutions to nonlinear problems without depending on the existence of a smallness parameter. The choice of zero iteration is based on general features of exact solutions near the boundaries. The approach is illustrated on the examples of the Yukawa, Woods-Saxon and funnel potentials. For the latter potential, solutions describing charmonium, bottonium and topponium are analyzed. Comparison of our approximate analytic expressions for binding energies and wave functions with the exact numerical solutions demonstrates their high accuracy in the wide range of physical parameters. The accuracy ranging between 10−4 and 10−8 for the energies and, correspondingly, 10−2 and 10−4 for the wave functions is reached. The derived formulas enable one to make accurate analytical estimates of how variation of different interactions parameters affects correspondent physical systems. 相似文献
77.
We study the π± spectra obtained in 2, 4, 6 and 8A GeV Au - Au collisions within the thermal model. We find that the main features of the data can be well described after we
include the pions from the decay of the Δ -resonance with medium mass modification. 相似文献
78.
A. Blatter M. Faller M. von Allmen W. Bührer 《Applied Physics A: Materials Science & Processing》1992,54(1):26-30
The configurations involved in the spontaneous vitrification of quenched Cr-Ti -phase alloys were investigated by X-ray diffraction and elastic neutron scattering. The two methods yield complementary information: X-rays are sensitive to the topology whereas neutrons emphasize the chemical fluctuations. The results show the presence of two simultaneous but opposing processes, the formation of CsCl-type chemical short range order on one hand and progressive structural disordering on the other. The latter ultimately leads to amorphization. The probable reason for this behavior is that at the temperature in question only the chromium atoms are mobile. 相似文献
79.
‘Spontaneous’ noncolinear frequency doubling (SNCFD) is a type of optical second-harmonic generation (SHG) that uses scattered
light to provide additional fundamental beams in order to accomplish noncolinear phase matching. Based on a novel algorithm for the automated evaluation of the resulting ring patterns, we present an easy-to-apply,
sensitive, and non-destructive method for the characterization of photorefractive materials, yielding two-dimensional spatial
resolution. As applications of the technique, examples for the characterization of lithium niobate crystals are presented.
Received: 30 October 1998 / Revised version: 17 December 1998 / Published online: 7 April 1999 相似文献
80.
A. Sibirtsev K. Tsushima A.W. Thomas 《The European Physical Journal A - Hadrons and Nuclei》1999,6(3):351-359
We examine the production of open charm in antiproton annihilation on finite nuclei. The enhancement of the subthreshold
production cross section, even in a nucleus as light as carbon, should provide a clean signature of the reduction in the masses
of these mesons in-medium. We also show that a careful analysis of the D+ and D− spectra can yield important information on the cross section for D±N scattering.
Received: 10 June 1999 / Revised version: 13 August 1999 相似文献