183 research outputs found
Properties of the SR Ca-ATPase in an Open Microsomal Membrane Preparation
SR vesicles isolated from rabbit muscle were treated by a SDS incubation and subsequent dialysis to obtain open membrane fragments that allow a direct access to the luminal membrane surface and especially to the ion-binding sites in the P-E2 conformation of the Ca-ATPase. The open membrane fragments showed about 80% of the enzyme activity in the untreated membranes. Pump function was investigated by using electrochromic styryl dyes. The kinetic properties of cytoplasmic ion binding showed no significant differences between the Ca-ATPases in SR vesicles and in membrane fragments. From pH-dependent Ca2+ binding it could be deduced that due to the SDS treatment the density of negatively charged lipid was increased by one elementary charge per 12 lipid molecules. Major differences between Ca-ATPase from SR vesicles and membrane fragments were the respective fluorescence amplitudes. This effect is, however, produced by dye-lipid interaction and not by pump function. It was demonstrated that time-resolved kinetics may be study by the use of caged compounds such as caged ATP or caged calcium also in the case of the membrane fragments
Statistics and Characteristics of Spatio-Temporally Rare Intense Events in Complex Ginzburg-Landau Models
We study the statistics and characteristics of rare intense events in two
types of two dimensional Complex Ginzburg-Landau (CGL) equation based models.
Our numerical simulations show finite amplitude collapse-like solutions which
approach the infinite amplitude solutions of the nonlinear Schr\"{o}dinger
(NLS) equation in an appropriate parameter regime. We also determine the
probability distribution function (PDF) of the amplitude of the CGL solutions,
which is found to be approximately described by a stretched exponential
distribution, , where . This
non-Gaussian PDF is explained by the nonlinear characteristics of individual
bursts combined with the statistics of bursts. Our results suggest a general
picture in which an incoherent background of weakly interacting waves,
occasionally, `by chance', initiates intense, coherent, self-reinforcing,
highly nonlinear events.Comment: 7 pages, 9 figure
Finite-Band-width Effects on the Transition Temperature and NMR Relaxation Rate of Impure Superconductors
We study the thermodynamic properties of impure superconductors by explicitly
taking into consideration the finiteness of electronic bandwidths within the
phonon-mediated Eliashberg formalism. For a finite electronic bandwidth, the
superconducting transition temperature, , is suppressed by nonmagnetic
impurity scatterings. This is a consequence of a reduction in the effective
electron-phonon coupling, . The reduced is
reflected in the observation that the coherence peak in , where
is the nuclear spin-lattice relaxation time and is the temperature,
is enhanced by impurity scatterings for a finite bandwidth. Calculations are
presented for and as bandwidths and impurity scattering rates
are varied. Implications for doped C superconductors are discussed in
connection with and measurements.Comment: 10 pages. REVTeX. 5 postscript figures. Scheduled to be published in
Physical Review B, March 1. The previous submission is revised and two
figures are adde
Qualitative and quantitative analysis of stability and instability dynamics of positive lattice solitons
We present a unified approach for qualitative and quantitative analysis of
stability and instability dynamics of positive bright solitons in
multi-dimensional focusing nonlinear media with a potential (lattice), which
can be periodic, periodic with defects, quasiperiodic, single waveguide, etc.
We show that when the soliton is unstable, the type of instability dynamic that
develops depends on which of two stability conditions is violated.
Specifically, violation of the slope condition leads to an amplitude
instability, whereas violation of the spectral condition leads to a drift
instability. We also present a quantitative approach that allows to predict the
stability and instability strength
Stability of narrow beams in bulk Kerr-type nonlinear media
We consider (2+1)-dimensional beams, whose transverse size may be comparable
to or smaller than the carrier wavelength, on the basis of an extended version
of the nonlinear Schr\"{o}dinger equation derived from the Maxwell`s equations.
As this equation is very cumbersome, we also study, in parallel to it, its
simplified version which keeps the most essential term: the term which accounts
for the {\it nonlinear diffraction}. The full equation additionally includes
terms generated by a deviation from the paraxial approximation and by a
longitudinal electric-field component in the beam. Solitary-wave stationary
solutions to both the full and simplified equations are found, treating the
terms which modify the nonlinear Schr\"{o}dinger equation as perturbations.
Within the framework of the perturbative approach, a conserved power of the
beam is obtained in an explicit form. It is found that the nonlinear
diffraction affects stationary beams much stronger than nonparaxiality and
longitudinal field. Stability of the beams is directly tested by simulating the
simplified equation, with initial configurations taken as predicted by the
perturbation theory. The numerically generated solitary beams are always stable
and never start to collapse, although they display periodic internal
vibrations, whose amplitude decreases with the increase of the beam power.Comment: 7 pages, 6 figures Accepted for publication in PR
Three Dimensional Simulation of Jet Formation in Collapsing Condensates
We numerically study the behavior of collapsing and exploding condensates
using the parameters of the experiments by E.A. Donley et al. [Nature,
412, 295, (2001)]. Our studies are based on a full three-dimensional
numerical solution of the Gross-Pitaevskii equation (GPE) including three body
loss. We determine the three body loss rate from the number of remnant
condensate atoms and collapse times and obtain only one possible value which
fits with the experimental results. We then study the formation of jet atoms by
interrupting the collapse and find very good agreement with the experiment.
Furthermore we investigate the sensitivity of the jets to the initial
conditions. According to our analysis the dynamics of the burst atoms is not
described by the GPE with three body loss incorporated.Comment: 9 pages, 10 figure
Two and three-dimensional oscillons in nonlinear Faraday resonance
We study 2D and 3D localised oscillating patterns in a simple model system
exhibiting nonlinear Faraday resonance. The corresponding amplitude equation is
shown to have exact soliton solutions which are found to be always unstable in
3D. On the contrary, the 2D solitons are shown to be stable in a certain
parameter range; hence the damping and parametric driving are capable of
suppressing the nonlinear blowup and dispersive decay of solitons in two
dimensions. The negative feedback loop occurs via the enslaving of the
soliton's phase, coupled to the driver, to its amplitude and width.Comment: 4 pages; 1 figur
Stability and symmetry-breaking bifurcation for the ground states of a NLS with a interaction
We determine and study the ground states of a focusing Schr\"odinger equation
in dimension one with a power nonlinearity and a strong
inhomogeneity represented by a singular point perturbation, the so-called
(attractive) interaction, located at the origin. The
time-dependent problem turns out to be globally well posed in the subcritical
regime, and locally well posed in the supercritical and critical regime in the
appropriate energy space. The set of the (nonlinear) ground states is
completely determined. For any value of the nonlinearity power, it exhibits a
symmetry breaking bifurcation structure as a function of the frequency (i.e.,
the nonlinear eigenvalue) . More precisely, there exists a critical
value \om^* of the nonlinear eigenvalue \om, such that: if \om_0 < \om <
\om^*, then there is a single ground state and it is an odd function; if \om
> \om^* then there exist two non-symmetric ground states. We prove that before
bifurcation (i.e., for \om < \om^*) and for any subcritical power, every
ground state is orbitally stable. After bifurcation (\om =\om^*+0), ground
states are stable if does not exceed a value that lies
between 2 and 2.5, and become unstable for . Finally, for and \om \gg \om^*, all ground states are unstable. The branch of odd
ground states for \om \om^*,
obtaining a family of orbitally unstable stationary states. Existence of ground
states is proved by variational techniques, and the stability properties of
stationary states are investigated by means of the Grillakis-Shatah-Strauss
framework, where some non standard techniques have to be used to establish the
needed properties of linearization operators.Comment: 46 pages, 5 figure
Quasiparticle Inelastic Lifetime from Paramagnons in Disordered Superconductors
The paramagnon contribution to the quasiparticle inelastic scattering rate in
disordered superconductors is presented. Using Anderson's exact eigenstate
formalism, it is shown that the scattering rate is Stoner enhanced and is
further enhanced by the disorder relative to the clean case in a manner similar
to the disorder enhancement of the long-range Coulomb contribution. The results
are discussed in connection with the possibility of conventional or
unconventional superconductivity in the borocarbides. The results are compared
to recent tunneling experiments on LuNiBC.Comment: 5 pages, no figure
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