565 research outputs found
Universal transport in 2D granular superconductors
The transport properties of quench condensed granular superconductors are
presented and analyzed. These systems exhibit transitions from insulating to
superconducting behavior as a function of inter-grain spacing.
Superconductivity is characterized by broad transitions in which the resistance
drops exponentially with reducing temperature. The slope of the log R versus T
curves turns out to be universaly dependent on the normal state film resistance
for all measured granular systems. It does not depend on the material, critical
temperature, geometry, or experimental set-up. We discuss possible physical
scenarios to explain these findings.Comment: 4 pages, 3 figure
Specific Heat Signature of the Berezinskii-Kosterlitz-Thouless Transition in Ultrathin Superconducting Films
The Berezinskii-Kosterlitz-Thouless (BKT) transition is expected to have a
clear signature on the specific heat. The singularity at the transition
temperature is predicted to be immeasurable, and a broad
non-universal peak is expected at . Up to date this has not been
observed in two-dimensional superconductors. We use a unique highly sensitive
technique to measure the specific heat of ultrathin Pb films. We find that
thick films exhibit a specific heat jump at that is consistent with BCS
theory. As the film thickness is reduced below the superconducting coherence
length and the systems enters the 2D limit the specific heat reveals BKT-like
behavior. We discuss these observations in the framework of the continuous
BCS-BKT crossover as a function of film thickness.Comment: 5 pages, 4 figure
Proximity effect in ultrathin Pb/Ag multilayers within the Cooper limit
We report on transport and tunneling measurements performed on ultra-thin
Pb/Ag (strong coupled superconductor/normal metal) multilayers evaporated by
quench condensation. The critical temperature and energy gap of the
heterostructures oscillate with addition of each layer, demonstrating the
validity of the Cooper limit model in the case of multilayers. We observe
excellent agreement with a simple theory for samples with layer thickness
larger than 30\AA . Samples with single layers thinner than 30\AA deviate from
the Cooper limit theory. We suggest that this is due to the "inverse proximity
effect" where the normal metal electrons improve screening in the
superconducting ultrathin layer and thus enhance the critical temperature.Comment: 4 pages, 4 figure
Note on Unaccompanied Children Fleeing from Ukraine
It is evident that the scale and pace, and potentially long lasting nature, of the situation leads to huge difficulties in organising comprehensive responses from a legal, policy and practical perspective. Clearly, lack of shared information, and lack of connection between the different actors, could cause additional problems and place already vulnerable children at further risk.This joint report, by Child Circle and KIND, aims to serve the efforts of the many stakeholders who are working together under a common EU framework of measures, by providing an overview of key issues to consider in particular from the perspective of procedural safeguards and access to protection and safety
Establishing spin-network topologies by repeated projective measurements
It has been recently shown that in quantum systems, the complex time
evolution typical of many-bodied coupled networks can be transformed into a
simple, relaxation-like dynamics, by relying on periodic dephasings of the
off-diagonal density matrix elements. This represents a case of "quantum Zeno
effects", where unitary evolutions are inhibited by projective measurements. We
present here a novel exploitation of these effects, by showing that a
relaxation-like behaviour is endowed to the polarization transfers occurring
within a N-spin coupled network. Experimental implementations and coupling
constant determinations for complex spin-coupling topologies, are thus
demonstrated within the field of liquid-state nuclear magnetic resonance (NMR).Comment: 4+ pages, 3 figure
Privatization and State Capacity in Postcommunist Society
Economists have used cross-national regression analysis to argue that postcommunist economic failure is the result of inadequate adherence liberal economic policies. Sociologists have relied on case study data to show that postcommunist economic failure is the outcome of too close adherence to liberal policy recommendations, which has led to an erosion of state effectiveness, and thus produced poor economic performance. The present paper advances a version of this statist theory based on a quantitative analysis of mass privatization programs in the postcommunist world. We argue that rapid large-scale privatization creates severe supply and demand shocks for enterprises, thereby inducing firm failure. The resulting erosion of tax revenues leads to a fiscal crisis for the state, and severely weakens its capacity and bureaucratic character. This, in turn, reacts back on the enterprise sector, as the state can no longer support the institutions necessary for the effective functioning of a modern economy, thus resulting in deindustrialization. Using cross-national regression techniques we find that the implementation of mass privatization programs negatively impacts measures of economic growth, state capacity and the security of property rights.http://deepblue.lib.umich.edu/bitstream/2027.42/40192/3/wp806.pd
Maximum Likelihood Estimator for Hidden Markov Models in continuous time
The paper studies large sample asymptotic properties of the Maximum
Likelihood Estimator (MLE) for the parameter of a continuous time Markov chain,
observed in white noise. Using the method of weak convergence of likelihoods
due to I.Ibragimov and R.Khasminskii, consistency, asymptotic normality and
convergence of moments are established for MLE under certain strong ergodicity
conditions of the chain.Comment: Warning: due to a flaw in the publishing process, some of the
references in the published version of the article are confuse
Effect of an extract of Centella asiatica on the biodistribution of sodium pertechnetate (Na<sup>99m</sup>TcO<sub>4</sub>) and on the fixation of radioactivity on blood constituents
This study evaluates the effects of an acute treatment with a Centella asiatica (CA) extract on the biodistribution of the radiopharmaceutical Na99mTcO4 and on the fixation of technetium-99m on blood constituents. Wistar rats were treated with CA extract and, 1 hour after, Na99mTcO4 was administered; organs/tissues were withdrawn and weighted. The radioactivity was counted to calculate the percentage of activity per gram (%ATI/g). Also, blood samples were withdrawn, plasma (P), blood cells (BC), insoluble fraction (IF) and soluble fractions of P and BC were isolated and the radioactivity was counted to calculate the percentage of activity (%ATI). Data indicated that the acute treatment with CA extract changed significantly (p99mTcO4 and the fixation of the technetium-99m on blood constituents in an acute treatment
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