2,250 research outputs found
Angular distributions of γ rays from the 7Li(p,γ) reaction at low energies
Angular distributions of the 14–17 MeV γ rays from the 7Li(p,γ) reaction at Ep=450, 402, and 80 keV were measured at 0°≤θlab≤135°, using a BGO detector and a 28-μg/cm2 LiF target. The angular distributions at Ep=450 and 402 keV agree with the previous results by Mainsbridge; at Ep=80 keV the ground-state transition is anisotropic on the order of 20%, confirming recent results by Chasteler et al
The structure of borders in a small world
Geographic borders are not only essential for the effective functioning of
government, the distribution of administrative responsibilities and the
allocation of public resources, they also influence the interregional flow of
information, cross-border trade operations, the diffusion of innovation and
technology, and the spatial spread of infectious diseases. However, as growing
interactions and mobility across long distances, cultural, and political
borders continue to amplify the small world effect and effectively decrease the
relative importance of local interactions, it is difficult to assess the
location and structure of effective borders that may play the most significant
role in mobility-driven processes. The paradigm of spatially coherent
communities may no longer be a plausible one, and it is unclear what structures
emerge from the interplay of interactions and activities across spatial scales.
Here we analyse a multi-scale proxy network for human mobility that
incorporates travel across a few to a few thousand kilometres. We determine an
effective system of geographically continuous borders implicitly encoded in
multi-scale mobility patterns. We find that effective large scale boundaries
define spatially coherent subdivisions and only partially coincide with
administrative borders. We find that spatial coherence is partially lost if
only long range traffic is taken into account and show that prevalent models
for multi-scale mobility networks cannot account for the observed patterns.
These results will allow for new types of quantitative, comparative analyses of
multi-scale interaction networks in general and may provide insight into a
multitude of spatiotemporal phenomena generated by human activity.Comment: 9 page
Total cross section for p-d breakup below 30 MeV
The total cross section for p-d breakup is studied in terms of the elastic S-matrix through the unitary condition. Calculations using the complex Kohn variational method along with the Pair Correlated Hyperspherical Harmonic basis are presented. The results have been restricted to energies below Ep=30 MeV where Coulomb effects are expected to be sizable and are compared to the existing data. Two different measurements have been found in the literature: 40 years ago, Gibbons and Macklin (1959); and 26 years ago, Carlosn et al. (1973). The calculations are found to be in reasonable agreement with these old data, though a discrepancy is observed near the deuteron breakup threshold. Moreover, a detailed analysis of the contributions to the observable from different partial waves has been presented. Unexpectedly, the main contribution for a wide range of energies has been detected in the J=3/2- state
The Three-Nucleon System Near the N-d Threshold
The three-nucleon system is studied at energies a few hundred keV above the
N-d threshold. Measurements of the tensor analyzing powers and
for p-d elastic scattering at keV are presented
together with the corresponding theoretical predictions. The calculations are
extended to very low energies since they are useful for extracting the p-d
scattering lengths from the experimental data. The interaction considered here
is the Argonne V18 potential plus the Urbana three-nucleon potential. The
calculation of the asymptotic D- to S-state ratio for H and He, for
which recent experimental results are available, is also presented.Comment: Latex, 11 pages, 2 figures, to be published in Phy.Lett.
Realization of a superconducting atom chip
We have trapped rubidium atoms in the magnetic field produced by a
superconducting atom chip operated at liquid Helium temperatures. Up to
atoms are held in a Ioffe-Pritchard trap at a distance of 440
m from the chip surface, with a temperature of 40 K. The trap
lifetime reaches 115 s at low atomic densities. These results open the way to
the exploration of atom--surface interactions and coherent atomic transport in
a superconducting environment, whose properties are radically different from
normal metals at room temperature.Comment: Submitted to Phys. Rev. Let
High-resolution spatial mapping of a superconducting NbN wire using single-electron detection
Superconducting NbN wires have recently received attention as detectors for
visible and infrared photons. We present experiments in which we use a NbN wire
for high-efficiency (40 %) detection of single electrons with keV energy. We
use the beam of a scanning electron microscope as a focussed, stable, and
calibrated electron source. Scanning the beam over the surface of the wire
provides a map of the detection efficiency. This map shows features as small as
150 nm, revealing wire inhomogeneities. The intrinsic resolution of this
mapping method, superior to optical methods, provides the basis of a
characterization tool relevant for photon detectors.Comment: 2009 IEEE Toronto International Conference, Science and Technology
for Humanity (TIC-STH
An Alternative Parameterization of R-matrix Theory
An alternative parameterization of R-matrix theory is presented which is
mathematically equivalent to the standard approach, but possesses features
which simplify the fitting of experimental data. In particular there are no
level shifts and no boundary-condition constants which allows the positions and
partial widths of an arbitrary number levels to be easily fixed in an analysis.
These alternative parameters can be converted to standard R-matrix parameters
by a straightforward matrix diagonalization procedure. In addition it is
possible to express the collision matrix directly in terms of the alternative
parameters.Comment: 8 pages; accepted for publication in Phys. Rev. C; expanded Sec. IV,
added Sec. VI, added Appendix, corrected typo
Microwave probes Dipole Blockade and van der Waals Forces in a Cold Rydberg Gas
We show that microwave spectroscopy of a dense Rydberg gas trapped on a
superconducting atom chip in the dipole blockade regime reveals directly the
dipole-dipole many-body interaction energy spectrum. We use this method to
investigate the expansion of the Rydberg cloud under the effect of repulsive
van der Waals forces and the breakdown of the frozen gas approximation. This
study opens a promising route for quantum simulation of many-body systems and
quantum information transport in chains of strongly interacting Rydberg atoms.Comment: PACS: 03.67.-a, 32.80.Ee, 32.30.-
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