451 research outputs found
Influence of Fermi surface topology on the quasiparticle spectrum in the vortex state
We study the influence of Fermi surface topology on the quasiparticle density
of states in the vortex state of type II superconductors. We observe that the
field dependence and the shape of the momentum and spatially averaged density
of states is affected significantly by the topology of the Fermi surface. We
show that this behavior can be understood in terms of characteristic Fermi
surface functions and that an important role is played by the number of points
on the Fermi surface at which the Fermi velocity is directed parallel to the
magnetic field. A critical comparison is made with a broadened BCS type density
of states, that has been used frequently in analysis of tunneling data. We
suggest a new formula as a replacement for the broadened BCS model for the
special case of a cylindrical Fermi surface. We apply our results to the two
gap superconductor MgB and show that in this particular case the field
dependence of the partial densities of states of the two gaps behaves very
differently due to the different topologies of the corresponding Fermi
surfaces, in qualitative agreement with recent tunneling experiments.Comment: 12 pages 12 figure
Raman spectroscopy study of NaxCoO2 and superconducting NaxCoO2.yH2O
The Raman spectra of the parent compound NaxCoO2 (x=0.75) and the
superconducting oxyhydrates NaxCoO2.yH2O with different superconducting
temperatures (Tc) have been measured. Five Raman active phonons around 195 cm-1
(E1g), 482 cm-1, 522 cm-1, 616 cm-1 (3E2g), 663 cm-1 (A1g) appear in all
spectra. These spectra change systematically along with the intercalation of
H2O and superconducting properties. In particular, the Raman active phonons
(A1g and E1g) involving the oxygen motions within the Co-O layers show up
monotonous decrease in frequency along with superconducting temperature Tc. The
fundamental properties and alternations of other active Raman phonons in the
superconducting materials have also been discussed.Comment: 16 pages, 4 figures, 2 table
Magnetically recoverable Ni@C composites: The synthesis by carbonization and adsorption for Fe3+
Carbon-encapsulated nickel particles (Ni@C composites) for removing Fe3+ in wastewater have been prepared by the carbonization of phenolic resin mixing with nickel particles. XRD results reveal that the Ni@C composites are consisted of C, Ni, and Ni3S2. The TG-DTG curves of Ni@C composites are almost same as that of phenolic resin. The morphology investigation shows that Ni is distributed randomly on carbon. Based on analysis of N2 adsorption-desorption isotherm, the surface area and pore volume of Ni@C composites are 187.47 m2 g−1 and 0.06900 cm3 g−1 nm−1, respectively. The saturation magnetization values for Ni@C composites are 68.99 emu·g−1 determined by the Vibrating Sample Magnetometer. Ni@C composites exhibit a high adsorption capacity for Fe3+. The adsorption behavior follows the pseudo-second-order kinetic and Langmuir model between the adsorbents and Fe3+. Furthermore, the adsorption capacity of Ni@C composites derives from the attractive force between the adsorbed anion and the surface positive charge of Ni@C composites, as well as the bond between the adsorbed cation and the COO− groups. From the above results Ni@C composites can be widely applied in wastewater treatment as a new efficiency and excellent recoverable adsorbent
Improved Eavesdropping Detection Strategy in Quantum Direct Communication Protocol Based on Four-particle GHZ State
In order to improve the eavesdropping detection efficiency in two-step
quantum direct communication protocol, an improved eavesdropping detection
strategy using four-particle GHZ state is proposed, in which four-particle GHZ
state is used to detect eavesdroppers. During the security analysis, the method
of the entropy theory is introduced, and two detection strategies are compared
quantitatively by using the constraint between the information which
eavesdropper can obtain and the interference introduced. If the eavesdroppers
intend to obtain all information, the eavesdropping detection rate of the
original two-step quantum direct communication protocol by using EPR pair block
as detection particles is 50%; while the proposed strategy's detection rate is
88%. In the end, the security of the proposed protocol is discussed. The
analysis results show that the eavesdropping detection strategy presented is
more secure.Comment: 14 pages, 3 figures. arXiv admin note: substantial text overlap with
arXiv:quant-ph/0308173 by different author
Early carboniferous brachiopod faunas from the Baoshan block, west Yunnan, southwest China
38 brachiopod species in 27 genera and subgenera are described from the Yudong Formation in the Shidian-Baoshan area, west Yunnan, southwest China. New taxa include two new subgenera: Unispirifer (Septimispirifer) and Brachythyrina (Longathyrina), and seven new species: Eomarginifera yunnanensis, Marginatia cylindrica, Unispirifer (Unispirifer) xiangshanensis, Unispirifer (Septimispirifer) wafangjieensis, Brachythyrina (Brachythyrina) transversa, Brachythyrina (Longathyrina) baoshanensis, and Girtyella wafangjieensis. Based on the described material and constraints from associated coral and conodont faunas, the age of the brachiopod fauna from the Yudon Formation is considered late Tournaisian (Early Carboniferous), with a possibility extending into earlyViseacutean.<br /
Electron Backscatter Diffraction Study on Microstructure, Texture, and Strain Evolution in Armco Iron Severely Deformed by the Differential Speed Rolling Method
Partial Wave Analysis of
BES data on are presented. The
contribution peaks strongly near threshold. It is fitted with a
broad resonance with mass MeV, width MeV. A broad resonance peaking at 2020 MeV is also required
with width MeV. There is further evidence for a component
peaking at 2.55 GeV. The non- contribution is close to phase
space; it peaks at 2.6 GeV and is very different from .Comment: 15 pages, 6 figures, 1 table, Submitted to PL
Longitudinal double-spin asymmetry and cross section for inclusive neutral pion production at midrapidity in polarized proton collisions at sqrt(s) = 200 GeV
We report a measurement of the longitudinal double-spin asymmetry A_LL and
the differential cross section for inclusive Pi0 production at midrapidity in
polarized proton collisions at sqrt(s) = 200 GeV. The cross section was
measured over a transverse momentum range of 1 < p_T < 17 GeV/c and found to be
in good agreement with a next-to-leading order perturbative QCD calculation.
The longitudinal double-spin asymmetry was measured in the range of 3.7 < p_T <
11 GeV/c and excludes a maximal positive gluon polarization in the proton. The
mean transverse momentum fraction of Pi0's in their parent jets was found to be
around 0.7 for electromagnetically triggered events.Comment: 6 pages, 3 figures, submitted to Phys. Rev. D (RC
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