40 research outputs found
Created-by-current states in long Josephson junctions
Critical curves "critical current - external magnetic field" of long
Josephson junctions with inhomogeneity and variable width are studied. We
demonstrate the existence of the regions of magnetic field where some fluxon
states are stable only, if the external current through the junction is
different from zero. Position and size of such regions depend on length of the
junction, its geometry, parameters of inhomogeneity and form of the junction.
The noncentral (left and right) pure fluxon states are appeared in the
inhomogeneous Josephson junction with increase in the junction length. We
demonstrate new bifurcation points with change in width of the inhomogeneity
and amplitude of the Josephson current through the inhomogeneity.Comment: 7 pages, 8 figure
Vortex structure in exponentially shaped Josephson junctions
We report the numerical calculations of the static vortex structure and
critical curves in exponentially shaped long Josephson junctions for in-line
and overlap geometries. Each solution of the corresponding boundary value
problem is associated with the Sturm-Liouville problem whose minimal eigenvalue
allows to make a conclusion about the stability of the vortex. The change in
width of the junction leads to the renormalization of the magnetic flux in
comparison to the case of a linear one-dimensional model. We study the
influence of the model's parameters and, particularly, the shape parameter on
the stability of the states of the magnetic flux. We compare the vortex
structure and critical curves for the in-line and overlap geometries. Our
numerically constructed critical curve of the Josephson junction matches well
with the experimental one.Comment: 8 pages, 10 figures, NATO Advanced Research Workshop on "Vortex
dynamics in superconductors and other complex systems" Yalta, Crimea,
Ukraine, 13-17 September 200
Exact analytical solution of the problem of current-carrying states of the Josephson junction in external magnetic fields
The classical problem of the Josephson junction of arbitrary length W in the
presence of externally applied magnetic fields (H) and transport currents (J)
is reconsidered from the point of view of stability theory. In particular, we
derive the complete infinite set of exact analytical solutions for the phase
difference that describe the current-carrying states of the junction with
arbitrary W and an arbitrary mode of the injection of J. These solutions are
parameterized by two natural parameters: the constants of integration. The
boundaries of their stability regions in the parametric plane are determined by
a corresponding infinite set of exact functional equations. Being mapped to the
physical plane (H,J), these boundaries yield the dependence of the critical
transport current Jc on H. Contrary to a wide-spread belief, the exact
analytical dependence Jc=Jc(H) proves to be multivalued even for arbitrarily
small W. What is more, the exact solution reveals the existence of unquantized
Josephson vortices carrying fractional flux and located near one of the
junction edges, provided that J is sufficiently close to Jc for certain finite
values of H. This conclusion (as well as other exact analytical results) is
illustrated by a graphical analysis of typical cases.Comment: 21 pages, 9 figures, to be published in Phys. Rev.
Static Solitons of the Sine-Gordon Equation and Equilibrium Vortex Structure in Josephson Junctions
The problem of vortex structure in a single Josephson junction in an external
magnetic field, in the absence of transport currents, is reconsidered from a
new mathematical point of view. In particular, we derive a complete set of
exact analytical solutions representing all the stationary points (minima and
saddle-points) of the relevant Gibbs free-energy functional. The type of these
solutions is determined by explicit evaluation of the second variation of the
Gibbs free-energy functional. The stable (physical) solutions minimizing the
Gibbs free-energy functional form an infinite set and are labelled by a
topological number Nv=0,1,2,... Mathematically, they can be interpreted as
nontrivial ''vacuum'' (Nv=0) and static topological solitons (Nv=1,2,...) of
the sine-Gordon equation for the phase difference in a finite spatial interval:
solutions of this kind were not considered in previous literature. Physically,
they represent the Meissner state (Nv=0) and Josephson vortices (Nv=1,2,...).
Major properties of the new physical solutions are thoroughly discussed. An
exact, closed-form analytical expression for the Gibbs free energy is derived
and analyzed numerically. Unstable (saddle-point) solutions are also classified
and discussed.Comment: 17 pages, 4 Postscript figure
Unfavourable birth outcomes of the Roma women in the Czech Republic and the potential explanations: a population-based study
BACKGROUND: Data on the health status of the Roma people in Central and Eastern Europe are sparse and the reasons for their poor health are not clear. The objective of this study was to quantify the differences in birth outcomes between Roma and non-Roma mothers in the Czech Republic and to investigate the potential causes of such differences. METHOD: A population-based study recruited 8938 non-Roma and 1388 Roma hospitalised singleton births that occurred in two Czech districts (Teplice and Prachatice) between 1995 and 2004. During their stay in hospital, mothers completed a questionnaire on their demographic and socioeconomic characteristics and maternal smoking and alcohol consumption. Data on maternal height and weight and on infants' birth weight and gestational age were taken from hospital records. RESULTS: Birth weight and gestational age of Roma infants was 373 (SE 15) g and 0.92 (0.05) weeks, respectively, lower than in non-Roma infants. Controlling for demographic, socioeconomic and behavioural factors reduced these differences to 133 (18) g and 0.57 (0.06) weeks, respectively (all p-values < 0.001). In terms of binary outcomes, the Roma vs. non-Roma odds ratios were 4.5 (95% CI 3.7–5.4) for low birth weight (< 2500 g), 2.8 (2.2–3.4) for preterm birth (< 37 weeks of gestation), and 2.9 (2.5–3.4) for intrauterine grown retardation (<10(th )percentile of birth weight for gestational age); controlling for all covariates reduced these odds ratios to 1.7 (1.3–2.2), 1.5 (1.1–2.0) and 1.3 (1.0–1.6), respectively. Maternal education made the largest contribution to the ethnic differences; the role of health behaviours was relatively modest. CONCLUSION: There are striking differences in birth outcomes between Roma and non-Roma mothers. The causes of these differences are complex but largely socioeconomic
Disruption of the Syp/VAMP2 complex.
<p>(<b>a</b>) Immunoprecipitation of VAMP2 from hippocampal extracts assayed by western blotting for VAMP2 and Syp. A band of 19 kDa corresponding to VAMP2 and a band of 38 kDa, corresponding to Syp were detected in all conditions. A reduction in immunoprecipitated Syp was induced by Aβ42 (lane 3) compared to control (scrambled Aβ, lane 4). (<b>b</b>) The intensity ratio between Syp and VAMP2 is reduced in the presence of Aβ42 (n = 3, student t-test p = 0.0026). (<b>c</b>) co-labelling for Syp and VAMP2 in untreated hippocampal neurons, in neurons treated either with Aβ42 and allowed to recover for 15 min (<b>d</b>) or with scrambled peptide (<b>f</b>) display a significant degree of co-localisation. (<b>e</b>) Aβ42 treated neurons allowed to recover for 2 hrs display stretches of VAMP2 immunoreactivity (indicated by arrows). (<b>g</b>) Quantification of the extent of co-localisation between Syp and VAMP2. Aβ42 treated neurons left to recover for 2 hrs showed decreased level of co-localisation (M = 0.85±0.09, n = 24) compared to control (M = 0.961±0.03, n = 24, student t-test ** = 0.0003), whereas neurons left to recover for 15 min (M = 0.99±0.02, n = 24) or incubated with the scrambled peptide (M = 0.99±0.01, n = 18) did not display differences compared to control. Scale bar = 10 µm.</p
Neurotrasmitter release is affected by Aβ.
<p>(<b>a</b>) Induction of CA1- LTP after HFS in control hippocampal slices (Two-way ANOVA p = 0.0006 n = 5). (<b>b</b>) Induction of CA1-LTP after HFS is blocked in hippocampal slices after a 45 min bath application of Aβ42. (<b>c</b>) fEPSPs recorded in the CA1 in response to a 50 V stimulus of the Schaffer collateral commissural pathway showed a concentration dependent effect of Aβ in fEPSPs. Only mid-range concentrations of 0.3 nM and 1 nM were able to increase the fEPSP slope (p = 0.028 and p = 0.048 respectively with student t-test, n = 5 for each concentration tested). (<b>d</b>) Treatment with Aβ42 (45 min) increases the stimulation response compared to control, untreated slices over a range of stimuli. Results are presented as the percentage of the maximum fEPSP from control recordings (n≥5 each). Inlet in shows a trace of EPSP slopes between a control slice and a slice treated with Aβ42 stimulated at 50 V. (<b>e</b>) Chelation of Aβ42 using 6E10, a specific antibody for the peptide, abrogates the enhancement at all input values (n = 5). (<b>f</b>) Scrambled Aβ did not induce increased responses compared to controls.</p