1,106 research outputs found
Nonlinear Schr\"odinger Equation with Spatio-Temporal Perturbations
We investigate the dynamics of solitons of the cubic Nonlinear Schr\"odinger
Equation (NLSE) with the following perturbations: non-parametric
spatio-temporal driving of the form , damping, and a
linear term which serves to stabilize the driven soliton. Using the time
evolution of norm, momentum and energy, or, alternatively, a Lagrangian
approach, we develop a Collective-Coordinate-Theory which yields a set of ODEs
for our four collective coordinates. These ODEs are solved analytically and
numerically for the case of a constant, spatially periodic force . The
soliton position exhibits oscillations around a mean trajectory with constant
velocity. This means that the soliton performs, on the average, a
unidirectional motion although the spatial average of the force vanishes. The
amplitude of the oscillations is much smaller than the period of . In
order to find out for which regions the above solutions are stable, we
calculate the time evolution of the soliton momentum and soliton
velocity : This is a parameter representation of a curve which is
visited by the soliton while time evolves. Our conjecture is that the soliton
becomes unstable, if this curve has a branch with negative slope. This
conjecture is fully confirmed by our simulations for the perturbed NLSE.
Moreover, this curve also yields a good estimate for the soliton lifetime: the
soliton lives longer, the shorter the branch with negative slope is.Comment: 21 figure
Coherent Error Suppression in Multi-Qubit Entangling Gates
We demonstrate a simple pulse shaping technique designed to improve the
fidelity of spin-dependent force operations commonly used to implement
entangling gates in trapped-ion systems. This extension of the
M{\o}lmer-S{\o}rensen gate can theoretically suppress the effects of certain
frequency and timing errors to any desired order and is demonstrated through
Walsh modulation of a two-qubit entangling gate on trapped atomic ions. The
technique is applicable to any system of qubits coupled through collective
harmonic oscillator modes
Instruments of RT-2 Experiment onboard CORONAS-PHOTON and their test and evaluation II: RT-2/CZT payload
Cadmium Zinc Telluride (CZT) detectors are high sensitivity and high
resolution devices for hard X-ray imaging and spectroscopic studies. The new
series of CZT detector modules (OMS40G256) manufactured by Orbotech Medical
Solutions (OMS), Israel, are used in the RT-2/CZT payload onboard the
CORONAS-PHOTON satellite. The CZT detectors, sensitive in the energy range of
20 keV to 150 keV, are used to image solar flares in hard X-rays. Since these
modules are essentially manufactured for commercial applications, we have
carried out a series of comprehensive tests on these modules so that they can
be confidently used in space-borne systems. These tests lead us to select the
best three pieces of the 'Gold' modules for the RT-2/CZT payload. This paper
presents the characterization of CZT modules and the criteria followed for
selecting the ones for the RT-2/CZT payload. The RT-2/CZT payload carries,
along with three CZT modules, a high spatial resolution CMOS detector for high
resolution imaging of transient X-ray events. Therefore, we discuss the
characterization of the CMOS detector as well.Comment: 26 pages, 19 figures, Accepted for publication in Experimental
Astronomy (in press
Cosmological Models with Variable Gravitational and Cosmological constants in Gravity
We consider the evolution of a flat Friedmann-Roberstson-Walker Universe in a
higher derivative theories, including terms to the
Einstein-Hilbert action in the presence of a variable gravitational and
cosmological constants. We study here the evolution of the gravitational and
cosmological constants in the presence of radiation and matter domination era
of the universe. We present here new cosmological solutions which are
physically interesting for model building.Comment: 14 pages, no figure. to be published in Int. J. Mod. Phys.
Galerkin FEM for fractional order parabolic equations with initial data in
We investigate semi-discrete numerical schemes based on the standard Galerkin
and lumped mass Galerkin finite element methods for an initial-boundary value
problem for homogeneous fractional diffusion problems with non-smooth initial
data. We assume that , is a convex
polygonal (polyhedral) domain. We theoretically justify optimal order error
estimates in - and -norms for initial data in . We confirm our theoretical findings with a number of numerical tests
that include initial data being a Dirac -function supported on a
-dimensional manifold.Comment: 13 pages, 3 figure
A New Variable Modified Chaplygin Gas Model Interacting with Scalar Field
In this letter we present a new form of the well known Chaplygin gas model by
introducing inhomogeneity in the EOS. This model explains crossing.
Also we have given a graphical representation of the model using
parameters. We have also considered an interaction of this model with the
scalar field by introducing a phenomenological coupling function and have shown
that the potential decays with time.Comment: 7 pages, 3 figure
Structure of the Bacterial Cellulose Ribbon and Its Assembly-Guiding Cytoskeleton by Electron Cryotomography
Cellulose is a widespread component of bacterial biofilms, where its properties of exceptional water retention, high tensile strength, and stiffness prevent dehydration and mechanical disruption of the biofilm. Bacteria in the genus Gluconacetobacter secrete crystalline cellulose, with a structure very similar to that found in plant cell walls. How this higher-order structure is produced is poorly understood. We used cryo-electron tomography and focused-ion-beam milling of native bacterial biofilms to image cellulose-synthesizing Gluconacetobacter hansenii and Gluconacetobacter xylinus bacteria in a frozen-hydrated, near-native state. We confirm previous results suggesting that cellulose crystallization occurs serially following its secretion along one side of the cell, leading to a cellulose ribbon that can reach several micrometers in length and combine with ribbons from other cells to form a robust biofilm matrix. We were able to take direct measurements in a near-native state of the cellulose sheets. Our results also reveal a novel cytoskeletal structure, which we have named the cortical belt, adjacent to the inner membrane and underlying the sites where cellulose is seen emerging from the cell. We found that this structure is not present in other cellulose-synthesizing bacterial species, Agrobacterium tumefaciens and Escherichia coli 1094, which do not produce organized cellulose ribbons. We therefore propose that the cortical belt holds the cellulose synthase complexes in a line to form higher-order cellulose structures, such as sheets and ribbons
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