1,029 research outputs found
Uniqueness in Discrete Tomography of Delone Sets with Long-Range Order
We address the problem of determining finite subsets of Delone sets
with long-range order by -rays in prescribed
-directions, i.e., directions parallel to non-zero interpoint
vectors of . Here, an -ray in direction of a finite set
gives the number of points in the set on each line parallel to . For our
main result, we introduce the notion of algebraic Delone sets
and derive a sufficient condition for the determination
of the convex subsets of these sets by -rays in four prescribed
-directions.Comment: 15 pages, 2 figures; condensed and revised versio
Superconducting d-wave junctions: The disappearance of the odd ac components
We study voltage-biased superconducting planar d-wave junctions for arbitrary
transmission and arbitrary orientation of the order parameters of the
superconductors. For a certain orientation of the superconductors the odd ac
components disappear, resulting in a doubling of the Josephson frequency. We
study the sensitivity of this disappearance to orientation and compare with
experiments on grain boundary junctions. We also discuss the possibility of a
current flow parallel to the junction.Comment: 5 pages, 3 figure
-decay half-life of Kr: a bridge nuclide for the rp-process beyond A = 70
The -decay half-life of Kr has been measured for the first time at the ISOLDE PSB Facility at CERN. Mass separated Kr ions were produced by 1 GeV proton induced spallation reactions in a Nb foil. The measured half-life is 57(21) ms. This value is consistent with the half-life calculated assuming a pure Fermi decay, but is clearly lower than the value used in a recent rp-process reaction flow calculation. The result shows that the reaction flow via two-proton-capture of Se is 2.5 times faster than previously calculated assuming an astrophysical temperature of 1.5 GK and a density of 10g/cm
- decay of the proton-rich T nucleus, Kr
- decay of the T = - 1/2 nuclide Kr has been studied at the ISOLDE PSB Facility at CERN. Kr ions were produced in spallation reactions in a Nb foil using the 1 GeV proton beam and studied by means of -delayed proton, - and -ray spectroscopy. The half-life and the -decay energy of Kr were determined using the decay of protons and positrons. These results: T = 100 ± 3 ms and = 10 ± 0.32 MeV and the first observation of the b-branch to the 207 keV level in Br makes the extension of the systematics of Gamow-Teller matrix elements of mirror nuclei up to A = 71 possible. Gamow-Teller strength of the same magnitude as that of the -shell mirror nuclei is observed for the ground state transition
Keldysh action for disordered superconductors
Keldysh representation of the functional integral for the interacting
electron system with disorder is used to derive microscopically an effective
action for dirty superconductors. In the most general case this action is a
functional of the 8 x 8 matrix Q(t,t') which depends on two time variables, and
on the fluctuating order parameter field and electric potential. We show that
this approach reproduces, without the use of the replica trick, the well-known
result for the Coulomb-induced renormalization of the electron-electron
coupling constant in the Cooper channel. Turning to the new results, we
calculate the effects of the Coulomb interaction upon: i) the subgap Andreev
conductance between superconductor and 2D dirty normal metal, and ii) the
Josephson proximity coupling between superconductive islands via such a metal.
These quantities are shown to be strongly suppressed by the Coulomb interaction
at sufficiently low temperatures due to both zero-bias anomaly in the density
of states and disorder-enhanced repulsion in the Cooper channel.Comment: RevTeX; 39 pages + 10 EPS figure
ac Josephson effect in superconducting d-wave junctions
We study theoretically the ac Josephson effect in superconducting planar
d-wave junctions. The insulating barrier assumed to be present between the two
superconductors may have arbitrary strength. Many properties of this system
depend on the orientation of the d-wave superconductor: we calculate the ac
components of the Josephson current. In some arrangements there is substantial
negative differential conductance due to the presence of mid-gap states. We
study how robust these features are to finite temperature and also comment on
how the calculated current-voltage curves compare with experiments. For some
other configurations (for small barrier strength) we find zero-bias conductance
peaks due to multiple Andreev reflections through midgap states. Moreover, the
odd ac components are strongly suppressed and even absent in some arrangements.
This absence will lead to a doubling of the Josephson frequency. All these
features are due to the d-wave order parameter changing sign when rotated
. Recently, there have been several theoretical reports on parallel
current in the d-wave case for both the stationary Josephson junction and for
the normal metal-superconductor junction. Also in our case there may appear
current density parallel to the junction, and we present a few examples when
this takes place. Finally, we give a fairly complete account of the method used
and also discuss how numerical calculations should be performed in order to
produce current-voltage curves
Broadband Dielectric Spectroscopy on Glass-Forming Propylene Carbonate
Dielectric spectroscopy covering more than 18 decades of frequency has been
performed on propylene carbonate in its liquid and supercooled-liquid state.
Using quasi-optic submillimeter and far-infrared spectroscopy the dielectric
response was investigated up to frequencies well into the microscopic regime.
We discuss the alpha-process whose characteristic timescale is observed over 14
decades of frequency and the excess wing showing up at frequencies some three
decades above the peak frequency. Special attention is given to the
high-frequency response of the dielectric loss in the crossover regime between
alpha-peak and boson-peak. Similar to our previous results in other glass
forming materials we find evidence for additional processes in the crossover
regime. However, significant differences concerning the spectral form at high
frequencies are found. We compare our results to the susceptibilities obtained
from light scattering and to the predictions of various models of the glass
transition.Comment: 13 pages, 9 figures, submitted to Phys. Rev.
Trust, Salience and Deterrence: Evidence from an Antitrust Experiment
We present results from a laboratory experiment identifying the main channels through which different law enforcement strategies deter organized economic crime. The absolute level of a fine has a strong deterrence effect, even when the exogenous probability of apprehension is zero. This effect appears to be driven by distrust or fear of betrayal, as it increases significantly when the incentives to betray partners are strengthened by policies offering amnesty to “turncoat whistleblowers”. We also document a strong deterrence effect of the sum of fines paid in the past, which suggests a significant role for salience or availability heuristic in law enforcement
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