5,745 research outputs found
Behavior and Breakdown of Higher-Order Fermi-Pasta-Ulam-Tsingou Recurrences
We investigate numerically the existence and stability of higher-order
recurrences (HoRs), including super-recurrences, super-super-recurrences, etc.,
in the alpha and beta Fermi-Pasta-Ulam-Tsingou (FPUT) lattices for initial
conditions in the fundamental normal mode. Our results represent a considerable
extension of the pioneering work of Tuck and Menzel on super-recurrences. For
fixed lattice sizes, we observe and study apparent singularities in the periods
of these HoRs, speculated to be caused by nonlinear resonances. Interestingly,
these singularities depend very sensitively on the initial energy and the
respective nonlinear parameters. Furthermore, we compare the mechanisms by
which the super-recurrences in the two model's breakdown as the initial energy
and respective nonlinear parameters are increased. The breakdown of
super-recurrences in the beta-FPUT lattice is associated with the destruction
of the so-called metastable state and hence is associated with relaxation
towards equilibrium. For the alpha-FPUT lattice, we find this is not the case
and show that the super-recurrences break down while the lattice is still
metastable. We close with comments on the generality of our results for
different lattice sizes
The ionizing sources of luminous compact HII regions in the RCW106 and RCW122 clouds
Given the rarity of young O star candidates, compact HII regions embedded in
dense molecular cores continue to serve as potential sites to peer into the
details of high-mass star formation. To uncover the ionizing sources of the
most luminous and compact HII regions embedded in the RCW106 and RCW122 giant
molecular clouds, known to be relatively nearby (2-4 kpc) and isolated, thus
providing an opportunity to examine spatial scales of a few hundred to a
thousand AU in size. High spatial resolution (0.3"), mid-infrared spectra
(R=350), including the fine structure lines [ArIII] and [NeII], were obtained
for four luminous compact HII regions, embedded inside the dense cores within
the RCW106 and RCW122 molecular cloud complexes. At this resolution, these
targets reveal point-like sources surrounded by nebulosity of different
morphologies, uncovering details at spatial dimensions of <1000AU. The
point-like sources display [ArIII] and [NeII] lines - the ratios of which are
used to estimate the temperature of the embedded sources. The derived
temperatures are indicative of mid-late O type objects for all the sources with
[ArIII] emission. Previously known characteristics of these targets from the
literature, including evidence of disk or accretion suggest that the identified
sources may grow more to become early-type O stars by the end of the star
formation process
Knowledge and Behavior Improvement Through a Skin Cancer Action Approach Exhibit
The purpose of the project reported here was to reduce the risk of skin cancer through an educational exhibit. Educational exhibits including brochures, conversation with Extension agents, wide-brimmed hats, and sunscreen were used to educate agriculturalists. Pre- and post-surveys queried participants regarding sun habits, knowledge of risk factors, perceived risk, and history of skin cancer. The results showed an increased use of wide-brimmed hats (p=0.00), sun-protective clothing (p=0.00), and knowledge of skin cancer risk factors (p= 0.014). A trend toward increasing sunscreen use and decreasing sole use of baseball caps was also seen
Beta defensin-2 is reduced in central but not in distal airways of smoker COPD patients
Background: Altered pulmonary defenses in chronic obstructive pulmonary disease (COPD) may promote distal airways bacterial colonization. The expression/activation of Toll Like receptors (TLR) and beta 2 defensin (HBD2) release by epithelial cells crucially affect pulmonary defence mechanisms. Methods: The epithelial expression of TLR4 and of HBD2 was assessed in surgical specimens from current smokers COPD (s-COPD; n = 17), ex-smokers COPD (ex-s-COPD; n = 8), smokers without COPD (S; n = 12), and from non-smoker non-COPD subjects (C; n = 13). Results: In distal airways, s-COPD highly expressed TLR4 and HBD2. In central airways, S and s-COPD showed increased TLR4 expression. Lower HBD2 expression was observed in central airways of s-COPD when compared to S and to ex-s-COPD. s-COPD had a reduced HBD2 gene expression as demonstrated by real-time PCR on micro-dissected bronchial epithelial cells. Furthermore, HBD2 expression positively correlated with FEV1/FVC ratio and inversely correlated with the cigarette smoke exposure. In a bronchial epithelial cell line (16 HBE) IL-1β significantly induced the HBD2 mRNA expression and cigarette smoke extracts significantly counteracted this IL-1 mediated effect reducing both the activation of NFkB pathway and the interaction between NFkB and HBD2 promoter. Conclusions: This study provides new insights on the possible mechanisms involved in the alteration of innate immunity mechanisms in COPD. © 2012 Pace et al
Quasielastic K-nucleus scattering
Quasielastic K^+ - nucleus scattering data at q=290, 390 and 480 MeV/c are
analyzed in a finite nucleus continuum random phase approximation framework,
using a density-dependent particle-hole interaction. The reaction mechanism is
consistently treated according to Glauber theory, keeping up to two-step
inelastic processes. A good description of the data is achieved, also providing
a useful constraint on the strength of the effective particle-hole interaction
in the scalar-isoscalar channel at intermediate momentum transfers. We find no
evidence for the increase in the effective number of nucleons participating in
the reaction which has been reported in the literature.Comment: 21 pages, uses REVTeX and epsfig, 9 postscript figures; replaced
version corrects a few minor errors in the tex
Electroexcitation of the P33(1232), P11(1440), D13(1520), S11(1535) at Q^2=0.4 and 0.65(GeV/c)^2
Using two approaches: dispersion relations and isobar model, we have analyzed
recent high precision CLAS data on cross sections of \pi^0, \pi^+, and \eta
electroproduction on protons, and the longitudinally polarized electron beam
asymmetry for p(\vec{e},e'p)\pi^0 and p(\vec{e},e'n)\pi^+. The contributions of
the resonances P33(1232), P11(1440), D13(1520), S11(1535) to \pi
electroproduction and S11(1535) to \eta electroproduction are found. The
results obtained in the two approaches are in good agreement with each other.
There is also good agreement between amplitudes of the \gamma^* N \to S11(1535)
transition found in \pi and \eta electroproduction. For the first time accurate
results are obtained for the longitudinal amplitudes of the P11(1440),
D13(1520) and S11(1535) electroexcitation on protons.Comment: 9 pages, 9 figure
Deep inelastic scattering and final state interaction in an exactly solvable relativistic model
In the theory of deep inelastic scattering (DIS) the final state interaction
(FSI) between the struck quark and the remnants of the target is usually
assumed to be negligible in the Bjorken limit. This assumption, still awaiting
a full validation within nonperturbative QCD, is investigated in a model
composed by two relativistic particles, interacting via a relativistic harmonic
oscillator potential, within light-cone hamiltonian dynamics. An
electromagnetic current operator whose matrix elements behave properly under
Poincar\'e transformations is adopted. It is shown that: i) the parton model is
recovered, once the standard parton model assumptions are adopted; and ii) when
relativistic, interacting eigenfunctions are exactly taken into account for
both the initial and final states, the values of the structure functions,
averaged over small, but finite intervals of the Bjorken variable , coincide
with the results of the parton model in the Bjorken limit.Comment: 26 pages, to appear in Phys. Rev. C (May 1998
Universal continuous-variable quantum computation: Requirement of optical nonlinearity for photon counting
Although universal continuous-variable quantum computation cannot be achieved
via linear optics (including squeezing), homodyne detection and feed-forward,
inclusion of ideal photon counting measurements overcomes this obstacle. These
measurements are sometimes described by arrays of beam splitters to distribute
the photons across several modes. We show that such a scheme cannot be used to
implement ideal photon counting and that such measurements necessarily involve
nonlinear evolution. However, this requirement of nonlinearity can be moved
"off-line," thereby permitting universal continuous-variable quantum
computation with linear optics.Comment: 6 pages, no figures, replaced with published versio
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