3,972 research outputs found
Algebraic time-decay for the bipolar quantum hydrodynamic model
The initial value problem is considered in the present paper for bipolar
quantum hydrodynamic model for semiconductors (QHD) in . We prove
that the unique strong solution exists globally in time and tends to the
asymptotical state with an algebraic rate as . And, we show that
the global solution of linearized bipolar QHD system decays in time at an
algebraic decay rate from both above and below. This means in general, we can
not get exponential time-decay rate for bipolar QHD system, which is different
from the case of unipolar QHD model (where global solutions tend to the
equilibrium state at an exponential time-decay rate) and is mainly caused by
the nonlinear coupling and cancelation between two carriers. Moreover, it is
also shown that the nonlinear dispersion does not affect the long time
asymptotic behavior, which by product gives rise to the algebraic time-decay
rate of the solution of the bipolar hydrodynamical model in the semiclassical
limit.Comment: 23 page
Exchange effects on electron scattering through a quantum dot embedded in a two-dimensional semiconductor structure
We have developed a theoretical method to study scattering processes of an
incident electron through an N-electron quantum dot (QD) embedded in a
two-dimensional (2D) semiconductor. The generalized Lippmann-Schwinger
equations including the electron-electron exchange interaction in this system
are solved for the continuum electron by using the method of continued
fractions (MCF) combined with 2D partial-wave expansion technique. The method
is applied to a one-electron QD case. Cross-sections are obtained for both the
singlet and triplet couplings between the incident electron and the QD electron
during the scattering. The total elastic cross-sections as well as the
spin-flip scattering cross-sections resulting from the exchange potential are
presented. Furthermore, inelastic scattering processes are also studied using a
multichannel formalism of the MCF.Comment: 11 pages, 4 figure
Determination of the superconducting gap in near optimally doped Bi_2Sr_{2-x}La_xCuO_{6+\delta} (x ~ 0.4) from low-temperature specific heat
Low-temperature specific heat of the monolayer high-Tc superconductor
Bi_2Sr_{2-x}La_xCuO_{6+\delta} has been measured close to the optimal doping
point (x ~ 0.4) in different magnetic fields. The identification of both a T^2
term in zero field and a \sqrt{H} dependence of the specific heat in fields is
shown to follow the theoretical prediction for d-wave pairing, which enables us
to extract the slope of the superconducting gap in the vicinity of the nodes
(v_{\Delta}, which is proportional to the superconducting gap \Delta_0 at the
antinodes according to the standard d_{x^2-y^2} gap function). The v_{\Delta}
or \Delta_0 (~ 12 meV) determined from this bulk measurement shows close
agreement with that obtained from spectroscopy or tunneling measurements, which
confirms the simple d-wave form of the superconducting gap.Comment: 5 pages, 4 figures, 1 tabl
The Nature of Optical Features in the Inner Region of the 3C48 Host Galaxy
The well-known quasar 3C48 is the most powerful compact steep-spectrum
radio-loud QSO at low redshifts. It also has two unusual optical features
within the radius of the radio jet (~1"): (1) an anomalous, high-velocity
narrow-line component, having several times as much flux as does the
narrow-line component coinciding with the broad-line redshift; and (2) a bright
continuum peak (3C48A) ~1" northeast of the quasar. Both of these optical
features have been conjectured to be related to the radio jet. Here we explore
these suggestions. We have obtained Gemini North GMOS integral-field-unit (IFU)
spectroscopy of the central region around 3C48. We use the unique features of
the IFU data to remove unresolved emission at the position of the quasar. The
resolved emission at the wavelength of the high-velocity component is peaked
<~0.25" north of the quasar, at virtually the same position angle as the base
of the radio jet. These observations appear to confirm that this high-velocity
gas is connected with the radio jet. However, most of the emission comes from a
region where the jet is still well collimated, rather than from the regions
where the radio maps indicate strong interaction with an external medium. We
also present the results of HST STIS spectroscopy of 3C48A. We show that 3C48A
is dominated by stars with a luminosity-weighted age of ~1.4 X 10^8 years,
substantially older than any reasonable estimate for the age of the radio
source. Our IFU data indicate a similar age. Thus, 3C48A almost certainly
cannot be attributed to jet-induced star formation. The host galaxy of 3C48 is
clearly the result of a merger, and 3C48A seems much more likely to be the
distorted nucleus of the merging partner, in which star formation was induced
during the previous close passage.Comment: 10 pages, accepted by The Astrophysical Journa
Two body non-leptonic decays in quark model with factorization ansatz
The two body non-leptonic decays are analyzed in factorization
approximation, using quark model, as a free parameter. It is
shown that the experimental branching ratio for restricts and this ratio can be understood for a value
of which lies in the range suggested by two body
B meson decays. The branching ratios for are predicted to be larger than the previous estimates. Finally it
is pointed that CKM-Wolfenstein parameter , where is CP
phase, can be determined from the ratio of widths of and or that of
and
independent of the parameter .Comment: 18 pages, latex, 1 figure available on request, please send any
questions or comments to [email protected]
Two types of generalized integrable decompositions and new solitary-wave solutions for the modified Kadomtsev-Petviashvili equation with symbolic computation
The modified Kadomtsev-Petviashvili (mKP) equation is shown in this paper to
be decomposable into the first two soliton equations of the 2N-coupled
Chen-Lee-Liu and Kaup-Newell hierarchies by respectively nonlinearizing two
sets of symmetry Lax pairs. In these two cases, the decomposed
(1+1)-dimensional nonlinear systems both have a couple of different Lax
representations, which means that there are two linear systems associated with
the mKP equation under the same constraint between the potential and
eigenfunctions. For each Lax representation of the decomposed (1+1)-dimensional
nonlinear systems, the corresponding Darboux transformation is further
constructed such that a series of explicit solutions of the mKP equation can be
recursively generated with the assistance of symbolic computation. In
illustration, four new families of solitary-wave solutions are presented and
the relevant stability is analyzed.Comment: 23 page
Non-deterministic Gates for Photonic Single Rail Quantum Logic
We discuss techniques for producing, manipulating and measureing qubits
encoded optically as vacuum and single photon states. We show that a universal
set of non-deterministic gates can be constructed using linear optics and
photon counting. We investigate the efficacy of a test gate given realistic
detector efficiencies.Comment: 8 pages, 6 figure
An SO(10) GUT Model with Flavor Symmetry
We present a supersymmetric grand unification model based on SO(10) group
with flavor symmetry. In this model, the fermion masses are from Yukawa
couplings involving and Higgs multiplets and the
flavor structures of mass matrices of both quarks and leptons are determined by
spontaneously broken . This model fits all of the masses and mixing angles
of the quarks and leptons. For the most general CP-violation scenario, this
model gives a wide range of values from zero to the current
bound with the most probable values . With certain assumptions where
leptonic phases have same CP-violation source as CKM phase, one gets a narrower
range for with the most probable values
. This model gives leptonic Dirac CP phase the most probable values
2-4 radians in the general CP-violation case.Comment: 14 pages,2 figures. Version published in Physical Review
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