87,733 research outputs found
Ultracold molecules: new probes on the variation of fundamental constants
Ultracold molecules offer brand new opportunities to probe the variation of
fundamental constants with unprecedented sensitivity. This paper summarizes
theoretical background and current constraints on the variation of fine
structure constant and electron-to-proton mass ratio, as well as proposals and
experimental efforts to measure the variations based on ultracold molecules. In
particular, we describe two novel spectroscopic schemes on ultracold molecules
which have greatly enhanced sensitivity to fundamental constants: resonant
scattering near Feshbach resonances and spectroscopy on close-lying energy
levels of ultracold molecules
Physical modelling of amorphous thermoplastic polymer and numerical simulation of micro hot embossing process
Micro hot embossing process is considered as one of the most promising micro replication processes for manufacturing of polymeric components, especially for the high aspect ratio components and large surface structural components. A large number of hot embossing experimental results have been published, the material modelling and processes simulation to improve the quality of micro replication by hot embossing process are still lacking. This paper consists to 3D modelling of micro hot embossing process with amorphous thermoplastic polymers, including the mechanical characterisation of polymers properties, identification of the viscoelastic behaviour law of the polymers, numerical simulation and experimental investigation of micro hot embossing process. Static compression creep tests have been carried out to investigate the selected polymers’ viscoelastic properties. The Generalized Maxwell model has been proposed to describe the relaxation modulus of the polymers and good agreement has been observed. The numerical simulation of the hot embossing process in 3D has been achieved by taking into account the viscoelastic behaviour of the polymers. The microfluidic devices with the thickness of 2 mm have been elaborated by hot embossing process. The hot embossing process has been carried out using horizontal injection/compression moulding equipment, especially developed for this study. A complete compression mould tool, equipped with the heating system, the cooling system, the ejection system and the vacuum system, has been designed and elaborated in our research. Polymer-based microfluidic devices have been successfully replicated by the hot embossing process using the compression system developed. Proper agreement between the numerical simulation and the experimental elaboration has been observed. It shows strong possibility for the development of the 3D numerical model to optimize the micro hot embossing process in the future
Hadronic B Decays to Charmed Baryons
We study exclusive B decays to final states containing a charmed baryon
within the pole model framework. Since the strong coupling for is larger than that for , the two-body charmful decay
has a rate larger than
as the former proceeds via the pole while the latter via the
pole. By the same token, the three-body decay receives less baryon-pole contribution than
. However, because the important charmed-meson
pole diagrams contribute constructively to the former and destructively to the
latter, has a rate slightly larger than
. It is found that one quarter of the rate comes from the resonant contributions. We discuss
the decays and
and stress that they are not color suppressed even though they can only proceed
via an internal W emission.Comment: 25 pages, 6 figure
Determination of Freeze-out Conditions from Lattice QCD Calculations
Freeze-out conditions in Heavy Ion Collisions are generally determined by
comparing experimental results for ratios of particle yields with theoretical
predictions based on applications of the Hadron Resonance Gas model. We discuss
here how this model dependent determination of freeze-out parameters may
eventually be replaced by theoretical predictions based on equilibrium QCD
thermodynamics.Comment: presented at the International Conference "Critical Point and Onset
of Deconfinement - CPOD 2011", Wuhan, November 7-11, 201
Local Density of States and Angle-Resolved Photoemission Spectral Function of an Inhomogeneous D-wave Superconductor
Nanoscale inhomogeneity seems to be a central feature of the d-wave
superconductivity in the cuprates. Such a feature can strongly affect the local
density of states (LDOS) and the spectral weight functions. Within the
Bogoliubov-de Gennes formalism we examine various inhomogeneous configurations
of the superconducting order parameter to see which ones better agree with the
experimental data. Nanoscale large amplitude oscillations in the order
parameter seem to fit the LDOS data for the underdoped cuprates. The
one-particle spectral function for a general inhomogeneous configuration
exhibits a coherent peak in the nodal direction. In contrast, the spectral
function in the antinodal region is easily rendered incoherent by the
inhomogeneity. This throws new light on the dichotomy between the nodal and
antinodal quasiparticles in the underdoped cuprates.Comment: 5 pages, 9 pictures. Phys. Rev. B (in press
On the Casimir effect for parallel plates in the spacetime with one extra compactified dimension
In this paper, the Casimir effect for parallel plates in the presence of one
compactified universal extra dimension is reexamined in detail. Having
regularized the expressions of Casimir force, we show that the nature of
Casimir force is repulsive if the distance between the plates is large enough,
which is disagree with the experimental phenomena.Comment: 7 pages, 3 figure
Radiative Kaon Decays and Direct CP Violation
It is stressed that a measurement of the electric dipole amplitude for direct
photon emission in \kpm decays through its interference with inner
bremsstrahlung is important for differentiating among various models. Effects
of amplitude CP violation in the radiative decays of the charged kaon are
analyzed in the Standard Model in conjunction with the large approach. We
point out that gluon and electromagnetic penguin contributions to the
CP-violating asymmetry between the Dalitz plots of \kpm are of equal weight.
The magnitude of CP asymmetry ranges from to when the photon energy in the kaon rest frame varies from 50 MeV to
170 MeV.Comment: Latex, 11 pages, ITP-SB-93-36, IP-ASTP-22-9
Is GRO J1744-28 a Strange Star?
The unusal hard x-ray burster GRO J1744-28 recently discovered by the Compton
Gamma-ray Observatory (GRO) can be modeled as a strange star with a dipolar
magnetic field Gauss. When the accreted mass of the star exceeds
some critical mass, its crust may break, resulting in conversion of the
accreted matter into strange matter and release of energy. Subsequently, a
fireball may form and expand relativistically outward. The expanding fireball
may interact with the surrounding interstellar medium, causing its kinetic
energy to be radiated in shock waves, producing a burst of x-ray radiation. The
burst energy, duration, interval and spectrum derived from such a model are
consistent with the observations of GRO J1744-28.Comment: Latex, has been published in SCIENCE, Vol. 280, 40
Boundary effect on CDW: Friedel oscillations, STM image
We study the effect of open boundary condition on charge density waves (CDW).
The electron density oscillates rapidly close to the boundary, and additional
non-oscillating terms (~ln(r)) appear. The Friedel oscillations survive beyond
the CDW coherence length (v_F/Delta), but their amplitude gets heavily
suppressed. The scanning tunneling microscopy image (STM) of CDW shows clear
features of the boundary. The local tunneling conductance becomes asymmetric
with respect to the Fermi energy, and considerable amount of spectral weight is
transferred to the lower gap edge. Also it exhibits additional zeros reflecting
the influence of the boundary.Comment: 7 pages, 6 figure
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