2,260 research outputs found
What can break the Wandzura--Wilczek relation?
We analyze the breaking of the Wandzura-Wilczek relation for the g_2
structure function, emphasizing its connection with transverse momentum
dependent parton distribution functions. We find that the relation is broken by
two distinct twist-3 terms, and clarify how these can be separated in
measurements of double-spin asymmetries in semi-inclusive deep inelastic
scattering. Through a quantitative analysis of available g_2 data we also show
that the breaking of the Wandzura-Wilczek relation can be as large as 15-30% of
the size of g_2.Comment: 12 page
Modulated Amplitude Waves in Bose-Einstein Condensates
We analyze spatio-temporal structures in the Gross-Pitaevskii equation to
study the dynamics of quasi-one-dimensional Bose-Einstein condensates (BECs)
with mean-field interactions. A coherent structure ansatz yields a
parametrically forced nonlinear oscillator, to which we apply Lindstedt's
method and multiple-scale perturbation theory to determine the dependence of
the intensity of periodic orbits (``modulated amplitude waves'') on their wave
number. We explore BEC band structure in detail using Hamiltonian perturbation
theory and supporting numerical simulations.Comment: 5 pages, 4 figs, revtex, final form of paper, to appear in PRE
(forgot to include \bibliography command in last update, so this is a
correction of that; the bibliography is hence present again
An Automatic Invisible Axion In The SUSY Preon Model
It is shown that the recently proposed preon model which provides a unified
origin of the diverse mass scale and an explanation of family replication as
well as of inter-family mass-hierarchy, possesses a Peccei-Quinn symmetry whose
spontaneous breaking leads to an automatic invisible axion. Existence of the
PQ-symmetry is simply a consequence of supersymmetry and requirement of
minimality in the field-content and interactions, which propose that the
lagrangian should possess only those terms which are dictated by the gauge
principle and no others. In addition to the axion, the model also generates two
superlight Goldstone bosons and their superpartners which are cosmologically
safe.Comment: (TeX file) 16 Page
Ultrafast carrier relaxation in GaN, In_(0.05)Ga_(0.95)N and an In_(0.05)Ga_(0.95)/In_(0.15)Ga_(0.85)N Multiple Quantum Well
Room temperature, wavelength non-degenerate ultrafast pump/probe measurements
were performed on GaN and InGaN epilayers and an InGaN multiple quantum well
structure. Carrier relaxation dynamics were investigated as a function of
excitation wavelength and intensity. Spectrally-resolved sub-picosecond
relaxation due to carrier redistribution and QW capture was found to depend
sensitively on the wavelength of pump excitation. Moreover, for pump
intensities above a threshold of 100 microJ/cm2, all samples demonstrated an
additional emission feature arising from stimulated emission (SE). SE is
evidenced as accelerated relaxation (< 10 ps) in the pump-probe data,
fundamentally altering the re-distribution of carriers. Once SE and carrier
redistribution is completed, a slower relaxation of up to 1 ns for GaN and
InGaN epilayers, and 660 ps for the MQW sample, indicates carrier recombination
through spontaneous emission.Comment: submitted to Phys. Rev.
CONTROL OF COLUMNAR-TO-EQUIAXED TRANSITION IN CONTINUOUS CASTING OF 16% Cr STAINLESS STEEL
In continuous casting of 16%Cr ferritic stainless steel, columnar grains undesirably forming among equiaxedgrains make non-uniform microstructure and degrade ridging property. Since this phenomenon results fromthe change of solidification condition during continuous casting, we focused on Cellular-to-Equiaxed Transition(CET) in continuous casting of 16%Cr ferritic stainless steel to control the microstructure of as-cast slab.In order to find the CET condition, we carried out the one dimensional heat transfer analysis of the melt, andpredicted the CET condition by Hunt’s model. It was revealed that the secondary columnar grains usually formedat 0.5~0.8 solid fractions, and the formation of them resulted from a steep increase of G/V1/2 value as themelt was getting out of EMS field; however the increase of G/V1/2 was readily controlled by changing EMSpattern and the secondary cooling intensity. In result, secondary columnar grains were eliminated by optimizingthe upper and lower EMS intensity, and increasing secondary cooling intensity. We also investigatedthe effect of solidification parameters including superheat and casting speed as CET condition in continuouscasting process, and the results were also discussed by the terms of thermal condition of melt
Magnetic Field Dependent Behavior of the CDW ground state in Per2M(mnt)2 (M = Au, Pt)
The Per2M(mnt)2 class of organic conductors exhibit a charge density wave
(CDW) ground state below about 12 K, which may be suppressed in magnetic fields
of order 20 to 30 T. However, for both cases of counter ion M(mnt)2 species
studied (M = Au (zero spin) and M = Pt (spin 1/2)), new high field ground
states evolve for further increases in magnetic field. We report recent
investigations where thermopower, Hall effect, high pressure and additional
transport measurements have been carried out to explore these new high field
phases.Comment: 6 pages, 10 figures, 27 reference
Theory of nonlinear Landau-Zener tunneling
A nonlinear Landau-Zener model was proposed recently to describe, among a
number of applications, the nonadiabatic transition of a Bose-Einstein
condensate between Bloch bands. Numerical analysis revealed a striking
phenomenon that tunneling occurs even in the adiabatic limit as the nonlinear
parameter is above a critical value equal to the gap of avoided
crossing of the two levels. In this paper, we present analytical results that
give quantitative account of the breakdown of adiabaticity by mapping this
quantum nonlinear model into a classical Josephson Hamiltonian. In the critical
region, we find a power-law scaling of the nonadiabatic transition probability
as a function of and , the crossing rate of the energy levels.
In the subcritical regime, the transition probability still follows an
exponential law but with the exponent changed by the nonlinear effect. For
, we find a near unit probability for the transition between the
adiabatic levels for all values of the crossing rate.Comment: 9 figure
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