1,030 research outputs found
Resonances in Fock Space: Optimization of a SASER device
We model the Fock space for the electronic resonant tunneling through a
double barrier including the coherent effects of the electron-phonon
interaction. The geometry is optimized to achieve the maximal optical phonon
emission required by a SASER (ultrasound emitter) device.Comment: 4 pages, 3 figures, to be published in Proceedings of the VI Latin
American Workshop on Nonlinear Phenomena, special issue of Physica
Multipole Amplitudes of Pion Photoproduction on Nucleons up to 2GeV within Dispersion Relations and Unitary Isobar Model
Two approaches for analysis of pion photo- and electroproduction on nucleons
in the resonance energy region are checked at using the results of
GWU(VPI) partial-wave analysis of photoproduction data. The approaches are
based on dispersion relations and unitary isobar model. Within dispersion
relations good description of photoproduction multipoles is obtained up to
. Within unitary isobar model, modified with increasing energy by
incorporation of Regge poles, and with unified Breit-Wigner parametrization of
resonance contributions, good description of photoproduction multipoles is
obtained up to .Comment: 23 pages, LaTe
Self-organization in a phonon laser
We make an adaptation of laser modelling equations to describe the behavior
of a phonon laser (saser). Our saser consists of an AlGaAs/GaAs double barrier
heterostructure designed to generate an intense beam of transversal acoustic
(TA) phonons. To study our system, we begin with a Hamiltonian that describes
the decay of primary longitudinal optical phonons (LO_1) into secondary (LO_2)
and TA (LO_1 -> LO_2 + TA) and its inverse process (recombination). Using this
Hamiltonian, a set of coupled equations of motion for the phonons is obtained.
We also consider the interaction between the phonons and its reservoirs. These
interactions are introduced in the equations of motion leading to a set of
coupled Langevin equations. In order to obtain an expression to describe our
saser we apply, in the Langevin equations, an adiabatic elimination of some
variables of the subsystem. Following the method above we obtain the value of
the injection threshold for the operation of our phonon laser. At this
threshold occurs a phase transition from a disordered to a coherent state. It
is shown that it is not necessary a big "optical" pumping to get a sasing
region.Comment: 4 figure
Relativistic D-brane Scattering is Extremely Inelastic
We study the effects of quantum production of open strings on the
relativistic scattering of D-branes. We find strong corrections to the brane
trajectory from copious production of highly-excited open strings, whose
typical oscillator level is proportional to the square of the rapidity. In the
corrected trajectory, the branes rapidly coincide and remain trapped in a
configuration with enhanced symmetry. This is a purely stringy effect which
makes relativistic brane collisions exceptionally inelastic. We trace this
effect to velocity-dependent corrections to the open-string mass, which render
open strings between relativistic D-branes surprisingly light. We observe that
pair-creation of open strings could play an important role in cosmological
scenarios in which branes approach each other at very high speeds.Comment: 30 pages; added references and a comment about velocity-dependent
masse
The emission of X-rays by fission fragments
Approximately 5% of the Îł-ray transitions in fission fragments are internally converted, giving rise to X-rays. X-ray energies are characteristic of Z, but yields depend strongly and not smoothly on Z and A of the fragments and on time. If these biases can be accepted, X-rays can be used to identify the atomic number of fission fragments. More generally, internal conversion and X-ray emission must be interpreted in the context of detailed knowledge of Îł-ray transitions.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/43110/1/10967_2005_Article_BF02039468.pd
Expressed Protein Selenoester Ligation
Herein, we describe the development and application of a novel expressed protein selenoester ligation (EPSL) methodology for the one-pot semi-synthesis of modified proteins. EPSL harnesses the rapid kinetics of ligation reactions between modified synthetic selenopeptides and protein aryl selenoesters (generated from expressed intein fusion precursors) followed by in situ chemoselective deselenization to afford target proteins at concentrations that preclude the use of traditional ligation methods. The utility of the EPSL technology is showcased through the efficient semi-synthesis of ubiquitinated polypeptides, lipidated analogues of the membrane-associated GTPase YPT6, and site-specifically phosphorylated variants of the oligomeric chaperone protein Hsp27 at high dilution.Sameer S. Kulkarni, Emma E. Watson, Joshua W. C. Maxwell, Gerhard Niederacher, Jason Johansen-Leete, Susanne Huhmann, Somnath Mukherjee, Alexander R. Norman, Julia Kriegesmann, Christian F. W. Becker, and Richard J. Payn
gravity constrained by PPN parameters and stochastic background of gravitational waves
We analyze seven different viable -gravities towards the Solar System
tests and stochastic gravitational waves background. The aim is to achieve
experimental bounds for the theory at local and cosmological scales in order to
select models capable of addressing the accelerating cosmological expansion
without cosmological constant but evading the weak field constraints. Beside
large scale structure and galactic dynamics, these bounds can be considered
complimentary in order to select self-consistent theories of gravity working at
the infrared limit. It is demonstrated that seven viable -gravities under
consideration not only satisfy the local tests, but additionally, pass the
above PPN-and stochastic gravitational waves bounds for large classes of
parameters.Comment: 23 pages, 8 figure
Identification of novel risk factors for community-acquired Clostridium difficile infection using spatial statistics and geographic information system analyses
Background: The rate of community-acquired Clostridium difficile infection (CA-CDI) is increasing. While receipt of antibiotics remains an important risk factor for CDI, studies related to acquisition of C. difficile outside of hospitals are lacking. As a result, risk factors for exposure to C. difficile in community settings have been inadequately studied. Main objective: To identify novel environmental risk factors for CA-CDI Methods: We performed a population-based retrospective cohort study of patients with CA-CDI from 1/1/2007 through 12/31/2014 in a 10-county area in central North Carolina. 360 Census Tracts in these 10 counties were used as the demographic Geographic Information System (GIS) base-map. Longitude and latitude (X, Y) coordinates were generated from patient home addresses and overlaid to Census Tracts polygons using ArcGIS; ArcView was used to assess "hot-spots" or clusters of CA-CDI. We then constructed a mixed hierarchical model to identify environmental variables independently associated with increased rates of CA-CDI. Results: A total of 1,895 unique patients met our criteria for CA-CDI. The mean patient age was 54.5 years; 62% were female and 70% were Caucasian. 402 (21%) patient addresses were located in "hot spots" or clusters of CA-CDI (p<0.001). "Hot spot" census tracts were scattered throughout the 10 counties. After adjusting for clustering and population density, age â„ 60 years (p = 0.03), race (<0.001), proximity to a livestock farm (0.01), proximity to farming raw materials services (0.02), and proximity to a nursing home (0.04) were independently associated with increased rates of CA-CDI. Conclusions: Our study is the first to use spatial statistics and mixed models to identify important environmental risk factors for acquisition of C. difficile and adds to the growing evidence that farm practices may put patients at risk for important drug-resistant infections
Grain Surface Models and Data for Astrochemistry
AbstractThe cross-disciplinary field of astrochemistry exists to understand the formation, destruction, and survival of molecules in astrophysical environments. Molecules in space are synthesized via a large variety of gas-phase reactions, and reactions on dust-grain surfaces, where the surface acts as a catalyst. A broad consensus has been reached in the astrochemistry community on how to suitably treat gas-phase processes in models, and also on how to present the necessary reaction data in databases; however, no such consensus has yet been reached for grain-surface processes. A team of âŒ25 experts covering observational, laboratory and theoretical (astro)chemistry met in summer of 2014 at the Lorentz Center in Leiden with the aim to provide solutions for this problem and to review the current state-of-the-art of grain surface models, both in terms of technical implementation into models as well as the most up-to-date information available from experiments and chemical computations. This review builds on the results of this workshop and gives an outlook for future directions
Gluon polarization in the nucleon from quasi-real photoproduction of high-pT hadron pairs
We present a determination of the gluon polarization Delta G/G in the
nucleon, based on the helicity asymmetry of quasi-real photoproduction events,
Q^2<1(GeV/c)^2, with a pair of large transverse-momentum hadrons in the final
state. The data were obtained by the COMPASS experiment at CERN using a 160 GeV
polarized muon beam scattered on a polarized 6-LiD target. The helicity
asymmetry for the selected events is = 0.002 +- 0.019(stat.) +-
0.003(syst.). From this value, we obtain in a leading-order QCD analysis Delta
G/G=0.024 +- 0.089(stat.) +- 0.057(syst.) at x_g = 0.095 and mu^2 =~ 3
(GeV}/c)^2.Comment: 10 pages, 3 figure
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