2,065 research outputs found
Chapter 1: A Time For Change
The proposed Title I sets forth a goal of educational excellence and equity for all students. It sets high standards, something that has not been done in the past
Repeat optical satellite images reveal widespread and long term decrease in land-terminating glacier speeds
By matching of repeat optical satellite images it is now possible to investigate glacier dynamics within large regions of the world and also between regions to improve knowledge about glacier dynamics in space and time. In this study we investigate whether the negative glacier mass balance seen over large parts of the world has caused the glaciers to change their speeds. The studied regions are Pamir, Caucasus, Penny Ice Cap, Alaska Range and Patagonia. In addition we derive speed changes for Karakoram, a region assumed to have positive mass balance and that contains many surge-type glaciers. We find that the mapped glaciers in the five regions with negative mass balance have over the last decades decreased their velocity at an average rate per decade of: 43 % in the Pamir, 8 % in the Caucasus, 25 % on Penny Ice Cap, 11 % in the Alaska Range and 20 % in Patagonia. Glaciers in Karakoram have generally increased their speeds, but surging glaciers and glaciers with flow instabilities are most prominent in this area. Therefore the calculated average speed change is not representative for this area
Staggered Pairing Phenomenology for UPd_2Al_3 and UNi_2Al_3
We apply the staggered-pairing Ginzburg-Landau phenomenology to describe
superconductivity in UPd_2Al_3 and UNi_2Al_3. The phenomenology was applied
successfully to UPt_3 so it explains why these materials have qualitatively
different superconducting phase diagrams although they have the same
point-group symmetry. UPd_2Al_3 and UNi_2Al_3 have a two-component
superconducting order parameter transforming as an H-point irreducible
representation of the space group. Staggered superconductivity can induce
charge-density waves characterized by new Bragg peaks suggesting experimental
tests of the phenomenology.Comment: 4 pages, REVTeX, 2 Postscript figure
Eliashberg theory with ab-initio Coulomb interactions: a minimal numerical scheme applied to layered superconductors
We present a minimal approach to include static Coulomb interactions in Eliashberg theory of superconductivity from first principles. The method can be easily implemented in any existing Eliashberg code (isotropic or anisotropic) to avoid the standard use of the semiempirical parameter μ*, which adds unnecessary uncertainty to Tc predictions. We evaluate the prediction accuracy of the method by simulating the superconducting properties of a set of layered superconductors, which feature unconventional Coulomb effects: CaC6, MgB2, Li-doped β-ZrNCl and YNi2B2C. We find that the estimated critical temperatures are consistent with those from ab-initio density functional theory for superconductors, and in close agreement with the experimental values
Security of coherent state quantum cryptography in the presence of Gaussian noise
We investigate the security against collective attacks of a continuous
variable quantum key distribution scheme in the asymptotic key limit for a
realistic setting. The quantum channel connecting the two honest parties is
assumed to be lossy and imposes Gaussian noise on the observed quadrature
distributions. Secret key rates are given for direct and reverse reconciliation
schemes including postselection in the collective attack scenario. The effect
of a non-ideal error correction and two-way communication in the classical
post-processing step is also taken into account.Comment: 12 pages, 5 figures updated version including two-way communication;
changed the definition of the excess noise to match the definition given
earlier (Phys. Rev. Lett. 92, 117901); submitted to PRA; presented at the 8th
International Conference on Quantum Communication, Measurement and Computing,
Tsukub
Witnessing effective entanglement in a continuous variable prepare&measure setup and application to a QKD scheme using postselection
We report an experimental demonstration of effective entanglement in a
prepare&measure type of quantum key distribution protocol. Coherent
polarization states and heterodyne measurement to characterize the transmitted
quantum states are used, thus enabling us to reconstruct directly their
Q-function. By evaluating the excess noise of the states, we experimentally
demonstrate that they fulfill a non-separability criterion previously presented
by Rigas et al. [J. Rigas, O. G\"uhne, N. L\"utkenhaus, Phys. Rev. A 73, 012341
(2006)]. For a restricted eavesdropping scenario we predict key rates using
postselection of the heterodyne measurement results.Comment: 12 pages, 12 figures, 2 table
Proximity Eliashberg theory of electrostatic field-effect-doping in superconducting films
We calculate the effect of a static electric field on the critical
temperature of a s-wave one band superconductor in the framework of proximity
effect Eliashberg theory. In the weak electrostatic field limit the theory has
no free parameters while, in general, the only free parameter is the thickness
of the surface layer where the electric field acts. We conclude that the best
situation for increasing the critical temperature is to have a very thin film
of a superconducting material with a strong increase of electron-phonon (boson)
constant upon charging.Comment: 9 pages, 5 figure
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