10,814 research outputs found
Detector and Telescope Development for ProtoEXIST and Fine Beam Measurements of Spectral Response of CZT Detectors
We outline our plan to develop ProtoEXIST, a balloon-borne prototype
experiment for the Energetic X-ray Imaging Survey Telescope (EXIST) for the
Black Hole Finder Probe. EXIST will consist of multiple wide-field hard X-ray
coded-aperture telescopes. The current design of the EXIST mission employs two
types of telescope systems: high energy telescopes (HETs) using CZT detectors,
and low energy telescopes (LETs) using Si detectors. With ProtoEXIST, we will
develop and demonstrate the technologies required for the EXIST HETs. As part
of our development efforts, we also present recent laboratory measurements of
the spectral response and efficiency variation of imaging CZT detectors on a
fine scale (~0.5 mm). The preliminary results confirm the need for multi-pixel
readouts and small inter-pixel gaps to achieve uniform spectral response and
high detection efficiency across detectors.Comment: 9 pages, 12 figures, 1 table, appears in SPIE 2005 proceedings (5898:
UV, X-ray, and Gamma-ray Space Instrumentation for Astronomy XIV
Boar rearing: the influence of group vs individual penning from weaning to 27 weeks of age
We compared mating performance and soundness of feet and legs of boars which were reared in group vs individual pens. Individually penned boars consumed more feed from 6 to 12 weeks of age and were heavier at 12 weeks of age. However, individually penned boars also were more unsound and tended to score lower in mating tests.; Swine Day, Manhattan, KS, November 11, 198
Proton acceleration in analytic reconnecting current sheets
Particle acceleration provides an important signature for the magnetic collapse that accompanies a solar flare. Most particle acceleration studies, however, invoke magnetic and electric field models that are analytically convenient rather than solutions of the governing magnetohydrodynamic equations. In this paper a self-consistent magnetic reconnection solution is employed to investigate proton orbits, energy gains, and acceleration timescales for proton acceleration in solar flares. The magnetic field configuration is derived from the analytic reconnection solution of Craig and Henton. For the physically realistic case in which magnetic pressure of the current sheet is limited at small resistivities, the model contains a single free parameter that specifies the shear of the velocity field. It is shown that in the absence of losses, the field produces particle acceleration spectra characteristic of magnetic X-points. Specifically, the energy distribution approximates a power law ~ξ-3/2 nonrelativistically, but steepens slightly at the higher energies. Using realistic values of the “effective” resistivity, we obtain energies and acceleration times that fall within the range of observational data for proton acceleration in the solar corona
Dust Stratification in Young Circumstellar Disks
We present high-resolution infrared spectra of four YSOs (T Tau N, T Tau S,
RNO 91, and HL Tau). The spectra exhibit narrow absorption lines of 12CO, 13CO,
and C18O as well as broad emission lines of gas phase12CO. The narrow
absorption lines of CO are shown to originate from the colder circumstellar
gas. We find that the line of sight gas column densities resulting from the CO
absorption lines are much higher than expected for the measured extinction for
each source and suggest the gas to dust ratio is measuring the dust settling
and/or grain coagulation in these extended disks. We provide a model of
turbulence, dust settling and grain growth to explain the results. The
techniques presented here allow us to provide some observationally-motivated
bounds on accretion disk alpha in protostellar systems
Vibronic coupling explains the ultrafast carotenoid-to-bacteriochlorophyll energy transfer in natural and artificial light harvesters
The initial energy transfer in photosynthesis occurs between the
light-harvesting pigments and on ultrafast timescales. We analyze the
carotenoid to bacteriochlorophyll energy transfer in LH2 Marichromatium
purpuratum as well as in an artificial light-harvesting dyad system by using
transient grating and two-dimensional electronic spectroscopy with 10 fs time
resolution. We find that F\"orster-type models reproduce the experimentally
observed 60 fs transfer times, but overestimate coupling constants, which leads
to a disagreement with both linear absorption and electronic 2D-spectra. We
show that a vibronic model, which treats carotenoid vibrations on both
electronic ground and excited state as part of the system's Hamiltonian,
reproduces all measured quantities. Importantly, the vibronic model presented
here can explain the fast energy transfer rates with only moderate coupling
constants, which are in agreement with structure based calculations.
Counterintuitively, the vibrational levels on the carotenoid electronic ground
state play a central role in the excited state population transfer to
bacteriochlorophyll as the resonance between the donor-acceptor energy gap and
vibrational ground state energies is the physical basis of the ultrafast energy
transfer rates in these systems
Optically induced forces and torques:Interactions between nanoparticles in a laser beam
Distinctive optical forces and torques arise between nanoparticles irradiated by intense laser radiation. These forces, associated with a pairwise process of stimulated scattering, prove to enable the possibility of producing significant modifications to both the form and magnitude of interparticle forces, with additional contributions arising in the case of dipolar materials. Moreover, such forces have the capacity to generate unusual patterns of nanoscale response, entirely controlled by the input beam characteristics- principally the optical frequency, intensity, and polarization. Based on quantum electrodynamical theory, a general result is secured for the laser-induced force under arbitrary conditions, incorporating both static and dynamic coupling mechanisms. Specific features of the results are identified for pairs of particles with prolate cylindrical symmetry, e.g., carbon nanotubes, where it is shown that the laser-induced forces and torques are sensitive functions of the pair spacing and orientation, and the laser beam geometry; significantly, they can be either repulsive or attractive according to conditions. For nanoparticles trapped in a Laguerre-Gaussian laser beam the results also reveal additional and highly distinctive torques that suggest further possibilities for nanomanipulation with light. The paper concludes with a discussion on several potential applications of such forces. © 2005 The American Physical Society
Lectures on Supersymmetry Breaking
We review the subject of spontaneous supersymmetry breaking. First we
consider supersymmetry breaking in a semiclassical theory. We illustrate it
with several examples, demonstrating different phenomena, including metastable
supersymmetry breaking. Then we give a brief review of the dynamics of
supersymmetric gauge theories. Finally, we use this dynamics to present various
mechanisms for dynamical supersymmetry breaking. These notes are based on
lectures given by the authors in 2007, at various schools.Comment: 47 pages. v2: minor correction
The Fermi-Pasta-Ulam recurrence and related phenomena for 1D shallow-water waves in a finite basin
In this work, different regimes of the Fermi-Pasta-Ulam (FPU) recurrence are
simulated numerically for fully nonlinear "one-dimensional" potential water
waves in a finite-depth flume between two vertical walls. In such systems, the
FPU recurrence is closely related to the dynamics of coherent structures
approximately corresponding to solitons of the integrable Boussinesq system. A
simplest periodic solution of the Boussinesq model, describing a single soliton
between the walls, is presented in an analytical form in terms of the elliptic
Jacobi functions. In the numerical experiments, it is observed that depending
on a number of solitons in the flume and their parameters, the FPU recurrence
can occur in a simple or complicated manner, or be practically absent. For
comparison, the nonlinear dynamics of potential water waves over nonuniform
beds is simulated, with initial states taken in the form of several pairs of
colliding solitons. With a mild-slope bed profile, a typical phenomenon in the
course of evolution is appearance of relatively high (rogue) waves, while for
random, relatively short-correlated bed profiles it is either appearance of
tall waves, or formation of sharp crests at moderate-height waves.Comment: revtex4, 10 pages, 33 figure
Cohort Profile: The Health Survey for England
To monitor the health of the public in England, UK, the Central Health Monitoring Unit within the UK Department of Health commissioned an annual health examination survey, which became known as the Health Survey for England (HSE). The first survey was completed in 1991. The HSE covers all of England and is a nationally representative sample of those residing at private residential addresses. Each survey year consists of a new sample of private residential addresses and people. The HSE collects detailed information on mental and physical health, health-related behaviour, and objective physical and biological measures in relation to demographic and socio-economic characteristics of people aged 16 years and over at private residential addresses. There are two parts to the HSE; an interviewer visit, to conduct an interview and measure height and weight, then a nurse visit, to carry out further measurements and take biological samples. Since 1994, survey participants aged 16 years and over have been asked for consent to follow-up through linkage to mortality and cancer registration data, and from 2003, to the Hospital Episode Statistics database, thus converting annual cross-sectional survey data into a longitudinal study. Annual survey data (1994–2009) are available through the UK Data Archive
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