1,216,223 research outputs found
On the discrepancies in the low energy neutron-deuteron breakup
In view of recent neutron-deuteron (nd) breakup data for neutron-neutron (nn)
and neutron-proton (np) quasi-free-scattering (QFS) arrangements and the large
discrepancy found between theoretical predictions and measured nn QFS cross
sections, we analyze the sensitivity of the QFS cross sections to different
partial wave components of the nucleon-nucleon (NN) interaction. We found that
the QFS cross section is strongly dominated by the 1S0 and 3S1-3D1
contributions. Because the standard three-nucleon force (3NF) only weakly
influence the QFS region, we conjecture, that it must be the nn 1S0 force
component which is responsible for the discrepancy in the nn QFS peak. A
stronger 1S0 nn force is required to bring theory and data into agreement. Such
an increased strength of the nn interaction will, however, not help to explain
the nd breakup symmetric-space-star (SST) discrepancy. Further experimental
cross-checkings are required.Comment: 17 pages, 10 figure
Two-stage coaxial gas compressor
Compressor raises pressure of gases from low ambient supply during space experiments by a system of low weight, size, and power input. Dc rotary-torque motor and ball-screw drive shaft activate first and second stage of compressor, utilizing inertia forces to operate check valves
Unified models of the cosmological dark sector
We model the cosmological substratum by a viscous fluid that is supposed to
provide a unified description of the dark sector and pressureless baryonic
matter. In the homogeneous and isotropic background the \textit{total} energy
density of this mixture behaves as a generalized Chaplygin gas. The
perturbations of this energy density are intrinsically non-adiabatic and source
relative entropy perturbations. The resulting baryonic matter power spectrum is
shown to be compatible with the 2dFGRS and SDSS (DR7) data. A joint statistical
analysis, using also Hubble-function and supernovae Ia data, shows that,
different from other studies, there exists a maximum in the probability
distribution for a negative present value of the
deceleration parameter. Moreover, different from other approaches, the unified
model presented here favors a matter content that is of the order of the
baryonic matter abundance suggested by big-bang nucleosynthesis.Comment: 4 pages, 1 figure, submitted to the Proceedings of the Spanish
Relativity Meeting - ERE 2010, Granada, September 6 - September 10, 201
Gas chromatograph sample-transfer valve
Slide-type gate valve incorporates sampling volume and transfer passageway for guiding a metered quantity of gas from pressurized test cell to gas chromatograph. Gate is moved by pneumatic bellows-type actuator
Miniature high pressure regulator
Metal bellows, capable of suppling required spring rate and operational stability, replaced diaphragms, sliding seals, and springs in design of small gas regulator
Spectrum of low-lying configurations with negative parity
Spectrum of low-lying five-quark configurations with strangeness quantum
number and negative parity is studied in three kinds of constituent
quark models, namely the one gluon exchange, Goldstone Boson exchange, and
instanton-induced hyperfine interaction models, respectively. Our numerical
results show that the lowest energy states in all the three employed models are
lying at 1800 MeV, about 200 MeV lower than predictions of various
quenched three-quark models. In addition, it is very interesting that the state
with the lowest energy in one gluon exchange model is with spin 3/2, but 1/2 in
the other two models.Comment: Version published in Phys. Rev.
Collisional Semiclassical Aproximations in Phase-Space Representation
The Gaussian Wave-Packet phase-space representation is used to show that the
expansion in powers of of the quantum Liouville propagator leads, in
the zeroth order term, to results close to those obtained in the statistical
quasiclassical method of Lee and Scully in the Weyl-Wigner picture. It is also
verified that propagating the Wigner distribution along the classical
trajectories the amount of error is less than that coming from propagating the
Gaussian distribution along classical trajectories.Comment: 20 pages, REVTEX, no figures, 3 tables include
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