18,890 research outputs found
Suppression of core polarization in halo nuclei
We present a microscopic study of halo nuclei, starting from the Paris and
Bonn potentials and employing a two-frequency shell model approach. It is found
that the core-polarization effect is dramatically suppressed in such nuclei.
Consequently the effective interaction for halo nucleons is almost entirely
given by the bare G-matrix alone, which presently can be evaluated with a high
degree of accuracy. The experimental pairing energies between the two halo
neutrons in He and Li nuclei are satisfactorily reproduced by our
calculation. It is suggested that the fundamental nucleon-nucleon interaction
can be probed in a clearer and more direct way in halo nuclei than in ordinary
nuclei.Comment: 11 pages, RevTex, 2 postscript figures; major revisions, matches
version to appear in Phys. Rev. Letter
On testing effectiveness of metamorphic relations: A case study
One fundamental challenge for software testing is the oracle problem which means that either there does not exist a mechanism (called oracle) to verify the test output given any possible program input or it is very expensive if not impossible to apply the oracle. Metamorphic testing is an innovative approach to oracle problem. In metamorphic testing metamorphic relations are derived from the innate characteristics of the software under test. These relations can help to generate test data and verify the correctness of the test result without the need of oracle. The effectiveness of metamorphic relations can play a significant role in the testing process. It has been argued that the metamorphic relations that cause different software execution behaviors should have high fault detection ability. In this paper we conduct a case study to analyze the relationship between the execution behavior and the fault-detection effectiveness of metamorphic relations. Some code coverage criteria are used to reflect the execution behavior. It is shown that there is a certain degree of correlation between the code coverage achieved by a metamorphic relation and its fault-detection effectiveness
Low momentum nucleon-nucleon potential and shell model effective interactions
A low momentum nucleon-nucleon (NN) potential V-low-k is derived from meson
exhange potentials by integrating out the model dependent high momentum modes
of V_NN. The smooth and approximately unique V-low-k is used as input for shell
model calculations instead of the usual Brueckner G matrix. Such an approach
eliminates the nuclear mass dependence of the input interaction one finds in
the G matrix approach, allowing the same input interaction to be used in
different nuclear regions. Shell model calculations of 18O, 134Te and 135I
using the same input V-low-k have been performed. For cut-off momentum Lambda
in the vicinity of 2 fm-1, our calculated low-lying spectra for these nuclei
are in good agreement with experiments, and are weakly dependent on Lambda.Comment: 5 pages, 5 figure
Development of the ALMA-North America Sideband-Separating SIS Mixers
As the Atacama Large Millimeter/submillimeter Array (ALMA) nears completion,
73 dual-polarization receivers have been delivered for each of Bands 3 (84-116
GHz) and 6 (211-275 GHz). The receivers use sideband-separating superconducting
Nb/Al-AlOx/Nb tunnel-junction (SIS) mixers, developed for ALMA to suppress
atmospheric noise in the image band. The mixers were designed taking into
account dynamic range, input return loss, and signal-to-image conversion (which
can be significant in SIS mixers). Typical SSB receiver noise temperatures in
Bands 3 and 6 are 30 K and 60 K, resp., and the image rejection is typically 15
dB.Comment: Submitted to IEEE Trans. Microwave Theory Tech., June 2013. 10 pages,
21 figure
Temperature dependence of the excitation spectrum in the charge-density-wave ErTe and HoTe systems
We provide optical reflectivity data collected over a broad spectral range
and as a function of temperature on the ErTe and HoTe materials, which
undergo two consecutive charge-density-wave (CDW) phase transitions at
= 265 and 288 K and at = 157 and 110 K, respectively. We
observe the temperature dependence of both the Drude component, due to the
itinerant charge carriers, and the single-particle peak, ascribed to the
charge-density-wave gap excitation. The CDW gap progressively opens while the
metallic component gets narrow with decreasing temperature. An important
fraction of the whole Fermi surface seems to be affected by the CDW phase
transitions. It turns out that the temperature and the previously investigated
pressure dependence of the most relevant CDW parameters share several common
features and behaviors. Particularly, the order parameter of the CDW state is
in general agreement with the predictions of the BCS theory
Proton-Neutron Interaction near Closed Shells
Odd-odd nuclei around double shell closures are a direct source of
information on the proton-neutron interaction between valence nucleons. We have
performed shell-model calculations for doubly odd nuclei close to Pb,
Sn and Sn using realistic effective interactions derived from
the CD-Bonn nucleon-nucleon potential. The calculated results are compared with
the available experimental data, attention being focused on particle-hole and
particle-particle multiplets. While a good agreement is obtained for all the
nuclei considered, a detailed analysis of the matrix elements of the effective
interaction shows that a stronger core-polarization contribution seems to be
needed in the particle-particle case.Comment: 8 pages, 6 figures, Proccedings of the International Conference
"Nuclear Structure and Related Topics", Dubna, Russia, September 2-6, 2003,
to be published in Yadernaia Fizika (Physics of Atomic Nuclei
Realistic shell-model calculations for proton particle-neutron hole nuclei around 132Sn
We have performed shell-model calculations for nuclei with proton particles
and neutron holes around 132Sn using a realistic effective interaction derived
from the CD-Bonn nucleon-nucleon potential. For the proton-neutron channel this
is explicitly done in the particle-hole formalism. The calculated results are
compared with the available experimental data, particular attention being
focused on the proton particle-neutron hole multiplets. A very good agreement
is obtained for all the four nuclei considered, 132Sb, 130Sb, 133Te and 131Sb.
We predict many low-energy states which have no experimental counterpart. This
may stimulate, and be helpful to, future experiments.Comment: 8 pages, 6 figures, to be published on Physical Review
Glueball matrix elements on anisotropic lattices
We describe a lattice calculation of the matrix elements relevant for
glueball production in radiative decays. The techniques for such a
calculation on anisotropic lattices with an improved action are outlined. We
present preliminary results showing the efficacy of the computational method.Comment: 3 pages (LaTeX), 3 figures (PostScript), Presented at Lattice '9
Modeling interfacial liquid layers on environmental ices
Interfacial layers on ice significantly influence air-ice chemical interactions. In solute-containing aqueous systems, a liquid brine may form upon freezing due to the exclusion of impurities from the ice crystal lattice coupled with freezing point depression in the concentrated brine. The brine may be segregated to the air-ice interface where it creates a surface layer, in micropockets, or at grain boundaries or triple junctions. <br><br> We present a model for brines and their associated liquid layers in environmental ice systems that is valid over a wide range of temperatures and solute concentrations. The model is derived from fundamental equlibrium thermodynamics and takes into account nonideal solution behavior in the brine, partitioning of the solute into the ice matrix, and equilibration between the brine and the gas phase for volatile solutes. We find that these phenomena are important to consider when modeling brines in environmental ices, especially at low temperatures. We demonstrate its application for environmentally important volatile and nonvolatile solutes including NaCl, HCl, and HNO<sub>3</sub>. The model is compared to existing models and experimental data from literature where available. We also identify environmentally relevant regimes where brine is not predicted to exist, but the QLL may significantly impact air-ice chemical interactions. This model can be used to improve the representation of air-ice chemical interactions in polar atmospheric chemistry models
- âŠ