561 research outputs found
VLA Survey of Dense Gas in Extended Green Objects: Prevalence of 25 GHz Methanol Masers
We present resolution Very Large Array (VLA) observations of four
CHOH - 25~GHz transitions (=3, 5, 8, 10) along with 1.3~cm
continuum toward 20 regions of active massive star formation containing
Extended Green Objects (EGOs), 14 of which we have previously studied with the
VLA in the Class~I 44~GHz and Class~II 6.7~GHz maser lines (Cyganowski et al.
2009). Sixteen regions are detected in at least one 25~GHz line (=5), with
13 of 16 exhibiting maser emission. In total, we report 34 new sites of
CHOH maser emission and ten new sites of thermal CHOH emission,
significantly increasing the number of 25~GHz Class I CHOH masers observed
at high angular resolution. We identify probable or likely maser counterparts
at 44~GHz for all 15 of the 25~GHz masers for which we have complementary data,
providing further evidence that these masers trace similar physical conditions
despite uncorrelated flux densities. The sites of thermal and maser emission of
CHOH are both predominantly associated with the 4.5 m emission from
the EGO, and the presence of thermal CHOH emission is accompanied by 1.3~cm
continuum emission in 9 out of 10 cases. Of the 19 regions that exhibit 1.3~cm
continuum emission, it is associated with the EGO in 16 cases (out of a total
of 20 sites), 13 of which are new detections at 1.3~cm. Twelve of the 1.3~cm
continuum sources are associated with 6.7~GHz maser emission and likely trace
deeply-embedded massive protostars
Nuclear Structure Calculations and Modern Nucleon-Nucleon Potentials
We study ground-state properties of the doubly magic nuclei 4He, 16O, and
40Ca employing the Goldstone expansion and using as input four different
high-quality nucleon-nucleon (NN) potentials. The short-range repulsion of
these potentials is renormalized by constructing a smooth low-momentum
potential V-low-k. This is used directly in a Hartree-Fock approach and
corrections up to third order in the Goldstone expansion are evaluated.
Comparison of the results shows that they are only slightly dependent on the
choice of the NN potential.Comment: 5 pages, submitted to Physical Review
Effective Interactions for the Three-Body Problem
The three-body energy-dependent effective interaction given by the
Bloch-Horowitz (BH) equation is evaluated for various shell-model oscillator
spaces. The results are applied to the test case of the three-body problem
(triton and He3), where it is shown that the interaction reproduces the exact
binding energy, regardless of the parameterization (number of oscillator quanta
or value of the oscillator parameter b) of the low-energy included space. We
demonstrate a non-perturbative technique for summing the excluded-space
three-body ladder diagrams, but also show that accurate results can be obtained
perturbatively by iterating the two-body ladders. We examine the evolution of
the effective two-body and induced three-body terms as b and the size of the
included space Lambda are varied, including the case of a single included
shell, Lambda hw=0 hw. For typical ranges of b, the induced effective
three-body interaction, essential for giving the exact three-body binding, is
found to contribute ~10% to the binding energy.Comment: 19 pages, 9 figures, submitted to PR
Renormalization of the weak hadronic current in the nuclear medium
The renormalization of the weak charge-changing hadronic current as a
function of the reaction energy release is studied at the nucleonic level. We
have calculated the average quenching factors for each type of current (vector,
axial vector and induced pseudoscalar). The obtained quenching in the axial
vector part is, at zero momentum transfer, 19% for the sd shell and 23% in the
fp shell. We have extended the calculations also to heavier systems such as
Ni and Sn, where we obtain stronger quenchings, 44% and 59%,
respectively. Gamow--Teller type transitions are discussed, along with the
higher order matrix elements. The quenching factors are constant up to roughly
60 MeV momentum transfer. Therefore the use of energy-independent quenching
factors in beta decay is justified. We also found that going beyond the zeroth
and first order operators (in inverse nucleon mass) does not give any
substantial contribution. The extracted renormalization to the ratio
at q=100 MeV is -3.5%, -7.1$%, -28.6%, and +8.7% for mass 16, 40, 56, and 100,
respectively.Comment: 28 pages, 6 figure
Scalable background-limited polarization-sensitive detectors for mm-wave applications
We report on the status and development of polarization-sensitive detectors
for millimeter-wave applications. The detectors are fabricated on
single-crystal silicon, which functions as a low-loss dielectric substrate for
the microwave circuitry as well as the supporting membrane for the
Transition-Edge Sensor (TES) bolometers. The orthomode transducer (OMT) is
realized as a symmetric structure and on-chip filters are employed to define
the detection bandwidth. A hybridized integrated enclosure reduces the
high-frequency THz mode set that can couple to the TES bolometers. An
implementation of the detector architecture at Q-band achieves 90% efficiency
in each polarization. The design is scalable in both frequency coverage, 30-300
GHz, and in number of detectors with uniform characteristics. Hence, the
detectors are desirable for ground-based or space-borne instruments that
require large arrays of efficient background-limited cryogenic detectors.Comment: 7 pages, 3 figures, Presented at SPIE Astronomical Telescopes and
Instrumentation 2014: Millimeter, Submillimeter, and Far-Infrared Detectors
and Instrumentation for Astronomy VII. To be published in Proceedings of SPIE
Volume 915
A Microscopic T-Violating Optical Potential: Implications for Neutron-Transmission Experiments
We derive a T-violating P-conserving optical potential for neutron-nucleus
scattering, starting from a uniquely determined two-body -exchange
interaction with the same symmetry. We then obtain limits on the T-violating
-nucleon coupling from neutron-transmission
experiments in Ho. The limits may soon compete with those from
measurements of atomic electric-dipole moments.Comment: 8 pages, 2 uuencoded figures in separate files (replaces version sent
earlier in the day with figures attached), in RevTeX 3, submitted to PR
Gamow-Teller Strength in the Region of Sn
New calculations are presented for Gamow-Teller beta decay of nuclei near
Sn. Essentially all of the Sn Gamow-Teller decay strength is
predicted to go to a single state at an excitation energy of 1.8 MeV in
In. The first calculations are presented for the decays of neighboring
odd-even and odd-odd nuclei which show, in contrast to Sn, surprisingly
complex and broad Gamow-Teller strength distributions. The results are compared
to existing experimental data and the resulting hindrance factors are
discussed.Comment: 12 pages (latex) and 2 figures available on reques
Delta Excitations in Neutrino-Nucleus Scattering
We derive the contribution of -h excitations to quasielastic
charged-current neutrino-nucleus scattering in the framework of relativistic
mean-field theory. We discuss the effect of production on the
determination of the axial mass in neutrino scattering experiments.Comment: 14 pages, revtex, 3 postscript figures (available upon request
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