36,854 research outputs found
Pion-mass dependence of three-nucleon observables
We use an effective field theory (EFT) which contains only short-range
interactions to study the dependence of a variety of three-nucleon observables
on the pion mass. The pion-mass dependence of input quantities in our
``pionless'' EFT is obtained from a recent chiral EFT calculation. To the order
we work at, these quantities are the 1S0 scattering length and effective range,
the deuteron binding energy, the 3S1 effective range, and the binding energy of
one three-nucleon bound state. The chiral EFT input we use has the inverse 3S1
and 1S0 scattering lengths vanishing at mpi_c=197.8577 MeV. At this
``critical'' pion mass, the triton has infinitely many excited states with an
accumulation point at the three-nucleon threshold. We compute the binding
energies of these states up to next-to-next-to-leading order in the pionless
EFT and study the convergence pattern of the EFT in the vicinity of the
critical pion mass. Furthermore, we use the pionless EFT to predict how doublet
and quartet nd scattering lengths depend on mpi in the region between the
physical pion mass and mpi=mpi_c.Comment: 24 pages, 9 figure
Effective field theory description of halo nuclei
Nuclear halos emerge as new degrees of freedom near the neutron and proton
driplines. They consist of a core and one or a few nucleons which spend most of
their time in the classically-forbidden region outside the range of the
interaction. Individual nucleons inside the core are thus unresolved in the
halo configuration, and the low-energy effective interactions are short-range
forces between the core and the valence nucleons. Similar phenomena occur in
clusters of He atoms, cold atomic gases near a Feshbach resonance, and some
exotic hadrons. In these weakly-bound quantum systems universal scaling laws
for s-wave binding emerge that are independent of the details of the
interaction. Effective field theory (EFT) exposes these correlations and
permits the calculation of non-universal corrections to them due to
short-distance effects, as well as the extension of these ideas to systems
involving the Coulomb interaction and/or binding in higher angular-momentum
channels. Halo nuclei exhibit all these features. Halo EFT, the EFT for halo
nuclei, has been used to compute the properties of single-neutron, two-neutron,
and single-proton halos of s-wave and p-wave type. This review summarizes these
results for halo binding energies, radii, Coulomb dissociation, and radiative
capture, as well as the connection of these properties to scattering
parameters, thereby elucidating the universal correlations between all these
observables. We also discuss how Halo EFT's encoding of the long-distance
physics of halo nuclei can be used to check and extend ab initio calculations
that include detailed modeling of their short-distance dynamics.Comment: 104 pages, 31 figures. Topical Review for Journal of Physics G. v2
incorporates several modifications, particularly to the Introduction, in
response to referee reports. It also corrects multiple typos in the original
submission. It corresponds to the published versio
A mathematical model of the CH-53 helicopter
A mathematical model suitable for real time simulation of the CH-53 helicopter is presented. This model, which is based on modified nonlinear classical rotor theory and nonlinear fuselage aerodynamics, will be used to support terminal-area guidance and navigation studies on a fixed-base simulator. Validation is achieved by comparing the model response with that of a similar aircraft and by a qualitative comparison of the handling characteristics made by experienced pilots
Experiment K-6-17. Structural changes and cell turnover in the rats small intestine induced by spaceflight
The purpose of this project was to test the hypothesis that the generalized, whole body decrease in synthetic activity associated with microgravity conditions of space flight as evidenced by negative nitrogen balance and muscle atrophy (Nicogossian and Parker, 1982; Oganov, 1981), as well as inhibited lymphocyte proliferation (Bechler and Cogoli, 1986), would be evident in cells characterized by a rapid rate of turnover. As a model, researchers chose to study the turnover of mucosal cells lining the jejunum of the small intestine, since these cells are among the most rapidly proliferating in the body. Under normal conditions, epithelial cells that line the small intestine are continually produced in the crypts of Lieberkuhn. These cells migrate out of the crypts onto intestinal villi, are progressively pushed up the villus as new crypt cells are formed, and ultimately reach the tip of villi where they are then descquamated. In rats, the entire process, from initial proliferation in crypts to desquamation, takes approximately 2 days (Cairnie et al., 1965; Lipkin, 1973). In this study, researchers determined the mitotic index for mucosal cells lining the proximal, middle, and distal regions of the jejunum in rats from three treatment groups (synchronous control, vivarium control and flight), and measured the depth of the crypts of Lieberkuhn and the length of villi present in each of the three jejunal regions sampled
Retirement Responses to Early Social Security Benefit Reductions
This paper evaluates potential responses to reductions in early Social Security retirement benefits. Using the Health and Retirement Study (HRS) linked to administrative records, we find that Social Security coverage is quite uneven in the older population: one-quarter of respondents in their late 50’s lacks coverage under the Disability Insurance program, and one-fifth lacks coverage for old-age benefits. Among those eligible for benefits, respondents who subsequently retired early appear quite similar initially to those who later filed for normal retirement benefits, but both groups were healthier and better educated than those who later filed for disability benefits. Next we investigate the potential impact of curtailing, and then eliminating, early Social Security benefits. A life-cycle model of retirement behavior provides estimated parameters used to simulate the effects of cutting early Social Security benefits on retirement pathways. We find that cutting early Social Security benefits would boost the probability of normal retirement by twice as much as it would the probability of disability retirement.
Using EFT to analyze low-energy Compton scattering from protons and light nuclei
We discuss the application of an effective field theory (EFT) which
incorporates the chiral symmetry of QCD to Compton scattering from the proton
and deuteron. We describe the chiral EFT analysis of the proton Compton
scattering database presented in our recent review (arXiv:1203.6834), which
gives: alpha^{(p)}=10.5 +/- 0.5(stat) +/- 0.8(theory); beta^{(p)}= 2.7 +/-
0.5(stat) +/- 0.8(theory), for the electric and magnetic dipole polarizability
of the proton. We also summarize the chiral EFT analysis of the world data on
coherent Compton scattering from deuterium presented in arXiv:1203.6834. That
yields: alpha^{(s)}=10.5 +/- 2.0(stat) +/- 0.8(theory); beta^{(s)}=3.6 +/-
1.0(stat) +/- 0.8(theory).Comment: 5 pages. Invited talk, presented by Phillips at the 11th Conference
on the Intersections of Nuclear and Particle Physics (CIPANP 2012), St.
Petersburg, FL, May 201
Nucleon Polarisabilities at and Beyond Physical Pion Masses
We examine the results of Chiral Effective Field Theory (EFT) for the
scalar- and spin-dipole polarisabilities of the proton and neutron, both for
the physical pion mass and as a function of . This provides chiral
extrapolations for lattice-QCD polarisability computations. We include both the
leading and sub-leading effects of the nucleon's pion cloud, as well as the
leading ones of the resonance and its pion cloud. The analytic
results are complete at NLO in the -counting for pion masses close
to the physical value, and at leading order for pion masses similar to the
Delta-nucleon mass splitting. In order to quantify the truncation error of our
predictions and fits as \% degree-of-belief intervals, we use a Bayesian
procedure recently adapted to EFT expansions. At the physical point, our
predictions for the spin polarisabilities are, within respective errors, in
good agreement with alternative extractions using experiments and
dispersion-relation theory. At larger pion masses we find that the chiral
expansion of all polarisabilities becomes intrinsically unreliable as
approaches about MeV---as has already been seen in other observables.
EFT also predicts a substantial isospin splitting above the physical
point for both the electric and magnetic scalar polarisabilities; and we
speculate on the impact this has on the stability of nucleons. Our results
agree very well with emerging lattice computations in the realm where EFT
converges. Curiously, for the central values of some of our predictions, this
agreement persists to much higher pion masses. We speculate on whether this
might be more than a fortuitous coincidence.Comment: 39 pages LaTeX2e (pdflatex) including 12 figures as 16 .pdf files
using includegraphics. Version approved for publication in EPJA includes
modifications, clarifications and removal of typographical errors in
refereeing and publication proces
Resonance tube igniter
Reasonance induced in stoichiometric mixtures of gaseous hydrogen-oxygen produces temperatures /over 1100 deg F/ high enough to cause ignition. Resonance tube phenomenon occurs when high pressure gas is forced through sonic or supersonic nozzle into short cavity. Various applications for the phenomenon are discussed
- …