12,197 research outputs found
Coarsening Dynamics of an Antiferromagnetic XY model on the Kagome Lattice: Breakdown of the Critical Dynamic Scaling
We find a breakdown of the critical dynamic scaling in the coarsening
dynamics of an antiferromagnetic {\em XY} model on the kagome lattice when the
system is quenched from disordered states into the Kosterlitz-Thouless ({\em
KT}) phases at low temperatures. There exist multiple growing length scales:
the length scales of the average separation between fractional vortices are
found to be {\em not} proportional to the length scales of the quasi-ordered
domains. They are instead related through a nontrivial power-law relation. The
length scale of the quasi-ordered domains (as determined from optimal collapse
of the correlation functions for the order parameter )
does not follow a simple power law growth but exhibits an anomalous growth with
time-dependent effective growth exponent. The breakdown of the critical dynamic
scaling is accompanied by unusual relaxation dynamics in the decay of
fractional () vortices, where the decay of the vortex numbers is
characterized by an exponential function of logarithmic powers in time.Comment: 13 pages, 26 figure
Microstructure and superconducting properties of hot isostatically pressed MgB2
Bulk samples of MgB2 have been formed by hot isostatic pressing (HIPping) of
commercial powder at 100MPa and 950=B0C. The resulting material is 100% dense
with a sharp superconducting transition at 37.5K. Microstructural studies have
indicated the presence of small amounts of second phases within the material,
namely MgO and B rich compositions, probably MgB4. Magnetisation measurements
performed at 20K have revealed values of Jc=1.3 x 106A/cm2 at zero field, and
9.3 x 105A/cm2 at 1T. Magneto optical (MO) studies have shown direct evidence
for the superconducting homogeneity and strong intergranular current flow in
the material.Comment: 3 pages, 6 figures, text updated, new references included and
discussed. Submitted to Superconductor Science and Technolog
Johnson-Kendall-Roberts theory applied to living cells
Johnson-Kendall-Roberts (JKR) theory is an accurate model for strong adhesion
energies of soft slightly deformable material. Little is known about the
validity of this theory on complex systems such as living cells. We have
addressed this problem using a depletion controlled cell adhesion and measured
the force necessary to separate the cells with a micropipette technique. We
show that the cytoskeleton can provide the cells with a 3D structure that is
sufficiently elastic and has a sufficiently low deformability for JKR theory to
be valid. When the cytoskeleton is disrupted, JKR theory is no longer
applicable
Terahertz Security Image Quality Assessment by No-reference Model Observers
To provide the possibility of developing objective image quality assessment
(IQA) algorithms for THz security images, we constructed the THz security image
database (THSID) including a total of 181 THz security images with the
resolution of 127*380. The main distortion types in THz security images were
first analyzed for the design of subjective evaluation criteria to acquire the
mean opinion scores. Subsequently, the existing no-reference IQA algorithms,
which were 5 opinion-aware approaches viz., NFERM, GMLF, DIIVINE, BRISQUE and
BLIINDS2, and 8 opinion-unaware approaches viz., QAC, SISBLIM, NIQE, FISBLIM,
CPBD, S3 and Fish_bb, were executed for the evaluation of the THz security
image quality. The statistical results demonstrated the superiority of Fish_bb
over the other testing IQA approaches for assessing the THz image quality with
PLCC (SROCC) values of 0.8925 (-0.8706), and with RMSE value of 0.3993. The
linear regression analysis and Bland-Altman plot further verified that the
Fish__bb could substitute for the subjective IQA. Nonetheless, for the
classification of THz security images, we tended to use S3 as a criterion for
ranking THz security image grades because of the relatively low false positive
rate in classifying bad THz image quality into acceptable category (24.69%).
Interestingly, due to the specific property of THz image, the average pixel
intensity gave the best performance than the above complicated IQA algorithms,
with the PLCC, SROCC and RMSE of 0.9001, -0.8800 and 0.3857, respectively. This
study will help the users such as researchers or security staffs to obtain the
THz security images of good quality. Currently, our research group is
attempting to make this research more comprehensive.Comment: 13 pages, 8 figures, 4 table
Fragmented and Single Condensate Ground States of Spin-1 Bose Gas
We show that the ground state of a spin-1 Bose gas with an antiferro-
magnetic interaction is a fragmented condensate in uniform magnetic fields. The
number fluctuations in each spin component change rapidly from being enormous
(order ) to exceedingly small (order 1) as the magnetization of the system
increases. A fragmented condensate can be turned into a single condensate state
by magnetic field gradients. The conditions for existence and the method of
detecting fragmented states are presented.Comment: 4 pages, no figure
Coarsening Kinetics of a Two Dimensional O(2) Ginzburg-Landau Model: Effect of Reversible Mode Coupling
We investigate, via numerical simulations, the phase ordering kinetics of a
two- dimensional soft-spin O(2) Ginzburg-Landau model when a reversible mode
cou- pling is included via the conserved conjugate momentum of the spin order
parameter (the model E). Coarsening of the system, when quenched from a dis-
ordered state to zero temperature, is observed to be enhanced by the existence
of the mode coupling terms. The growth of the characteristic length scale L(t)
exhibits an effective super-diffusive growth exponent that can be interpreted
as a positive logarithmic-like correction to a diffusive growth, i.e., L(t) ~
(t ln t)^{1/2}. In order to understand this behavior, we introduced a simple
phenomenological model of coarsening based on the annihilation dynamics of a
vortex-antivortex pair, incorporating the effect of vortex inertia and
logarithmically divergent mobility of the vortex. With a suitable choice of the
parameters, numerical solutions of the simple model can fit the full simulation
results very adequately. The effective growth exponent in the early time stage
is larger due to the effect of the vortex inertia, which crosses over into late
time stage characterized by positive logarithmic correction to a diffusive
growth. We also investigated the non-equilibrium autocorrelation function from
which the so called {\lambda} exponent can be extracted. We get {\lambda} =
1.99(2) which is distinctively larger than the value of {\lambda} = 1.17 for
the purely dissipative model-A dynamics of non-conserved O(2) models.Comment: 19 pages, 8 figure
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