443 research outputs found
Green’s function method to the ground state properties of a two-component Bose–Einstein condensate
The elementary excitation spectrum of a two-component Bose–Einstein condensate is obtained by Green’s function method. It is found to have two branches. In the long-wave limit, the two branches of the excitation spectrum are reduced to one phonon excitation and one single-particle excitation. With the obtained excitation spectrum and the Green’s functions, the depletion of the condensate and the ground state energy have also been calculated in this paper
Quantum impurity solvers using a slave rotor representation
We introduce a representation of electron operators as a product of a
spin-carry ing fermion and of a phase variable dual to the total charge (slave
quantum rotor). Based on this representation, a new method is proposed for
solving multi-orbital Anderson quantum impurity models at finite interaction
strength U. It consists in a set of coupled integral equations for the
auxiliary field Green's functions, which can be derived from a controlled
saddle-point in the limit of a large number of field components. In contrast to
some finite-U extensions of the non-crossing approximation, the new method
provides a smooth interpolation between the atomic limit and the weak-coupling
limit, and does not display violation of causality at low-frequency. We
demonstrate that this impurity solver can be applied in the context of
Dynamical Mean-Field Theory, at or close to half-filling. Good agreement with
established results on the Mott transition is found, and large values of the
orbital degeneracy can be investigated at low computational cost.Comment: 18 pages, 15 figure
New occurence of the Cambrian (Stage 4, Series 2) Guanshan Biota in Huize, Yunnan, South China
Magnetic Fields in the Milky Way
This chapter presents a review of observational studies to determine the
magnetic field in the Milky Way, both in the disk and in the halo, focused on
recent developments and on magnetic fields in the diffuse interstellar medium.
I discuss some terminology which is confusingly or inconsistently used and try
to summarize current status of our knowledge on magnetic field configurations
and strengths in the Milky Way. Although many open questions still exist, more
and more conclusions can be drawn on the large-scale and small-scale components
of the Galactic magnetic field. The chapter is concluded with a brief outlook
to observational projects in the near future.Comment: 22 pages, 5 figures, to appear in "Magnetic Fields in Diffuse Media",
eds. E.M. de Gouveia Dal Pino and A. Lazaria
Effects of oxygen adsorption on carbon nanotube field emitters
Effects of oxygen adsorption on the field emission of carbon nanotubes are studied through first-principles calculations. Calculated emission currents are significantly enhanced when oxygen is adsorbed at the tip and the underlying physics is explained in terms of the change in the electronic structure by oxidation and the local field increase at the adsorption site. The issue of the current degradation accompanied by the oxidative etching is also addressed. The field-emission-microscopy images on the phosphor screen are simulated, displaying various patterns characteristic of each adsorption configuration.open546
Environment-friendly surface acoustic wave humidity sensor with sodium alginate sensing layer
A low-cost and environment-friendly surface acoustic wave (SAW) humidity sensor was fabricated on a quartz substrate using sol-gel/spin-coated sodium alginate (SA) sensing layer. The sensing mechanism is based on the frequency shift of the SAW sensor caused by both mass loading and electrical loading, with the former being the dominant factor. The SA film prepared in this study is an environment-friendly material with a large number of hydroxyl and carboxylate groups, which easily adsorb and react with H2O molecules to form hydrogen bonds. These adsorbed H2O molecules lead to significantly enhanced mass loading and signal responses of the SAW sensor. Electrical loading effect is also generated due to the transfer of hydrogen ions in the H2O molecules, which alters the electrical resistance and results in changes of resonant frequencies of the SAW device. When the relative humidity (RH) is increased from 35% to 85%, the responses of the SAW sensor with 1 wt% SA are significantly decreased. Whereas in a low humidity environment (e.g., RH <35%), the responses of the sensor show a linear relationship with the change of humidity. The developed humidity sensor shows good short-term/long-term stabilities and a low temperature coefficient of frequency
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
A Measurement of Psi(2S) Resonance Parameters
Cross sections for e+e- to hadons, pi+pi- J/Psi, and mu+mu- have been
measured in the vicinity of the Psi(2S) resonance using the BESII detector
operated at the BEPC. The Psi(2S) total width; partial widths to hadrons,
pi+pi- J/Psi, muons; and corresponding branching fractions have been determined
to be Gamma(total)= (264+-27) keV; Gamma(hadron)= (258+-26) keV, Gamma(mu)=
(2.44+-0.21) keV, and Gamma(pi+pi- J/Psi)= (85+-8.7) keV; and Br(hadron)=
(97.79+-0.15)%, Br(pi+pi- J/Psi)= (32+-1.4)%, Br(mu)= (0.93+-0.08)%,
respectively.Comment: 8 pages, 6 figure
Measurements of the Mass and Full-Width of the Meson
In a sample of 58 million events collected with the BES II detector,
the process J/ is observed in five different decay
channels: , , (with ), (with
) and . From a combined fit of all five
channels, we determine the mass and full-width of to be
MeV/ and
MeV/.Comment: 9 pages, 2 figures and 4 table. Submitted to Phys. Lett.
- …