13,522 research outputs found
Development of a machine protection system for the Superconducting Beam Test Facility at Fermilab
Fermilab's Superconducting RF Beam Test Facility currently under construction
will produce electron beams capable of damaging the acceleration structures and
the beam line vacuum chambers in the event of an aberrant accelerator pulse.
The accelerator is being designed with the capability to operate with up to
3000 bunches per macro-pulse, 5Hz repetition rate and 1.5 GeV beam energy. It
will be able to sustain an average beam power of 72 KW at the bunch charge of
3.2 nC. Operation at full intensity will deposit enough energy in niobium
material to approach the melting point of 2500 {\deg}C. In the early phase with
only 3 cryomodules installed the facility will be capable of generating
electron beam energies of 810 MeV and an average beam power that approaches 40
KW. In either case a robust Machine Protection System (MPS) is required to
mitigate effects due to such large damage potentials. This paper will describe
the MPS system being developed, the system requirements and the controls issues
under consideration.Comment: 3 pp. 13th International Conference on Accelerator and Large
Experimental Physics Control Systems (ICALEPCS 2011). 10-14 Oct 2011.
Grenoble, Franc
Uniaxial and biaxial soft deformations of nematic elastomers
We give a geometric interpretation of the soft elastic deformation modes of
nematic elastomers, with explicit examples, for both uniaxial and biaxial
nematic order. We show the importance of body rotations in this non-classical
elasticity and how the invariance under rotations of the reference and target
states gives soft elasticity (the Golubovic and Lubensky theorem). The role of
rotations makes the Polar Decomposition Theorem vital for decomposing general
deformations into body rotations and symmetric strains. The role of the square
roots of tensors is discussed in this context and that of finding explicit
forms for soft deformations (the approach of Olmsted).Comment: 10 pages, 10 figures, RevTex, AmsTe
Finite element solution of low bond number sloshing
The dynamics of liquid propellant in a low Bond number environment which are critical to the design of spacecraft systems with respect to orbital propellant transfer and attitude control system were investigated. Digital computer programs were developed for the determination of liquid free surface equilibrium shape, lateral slosh natural vibration mode shapes, and frequencies for a liquid in a container of arbitrary axisymmetric shape with surface tension forces the same order of magnitude as acceleration forces. A finite volume element representation of the liquid was used for the vibration analysis. The liquid free surface equilibrium shapes were computed for several tanks at various contact angles and ullage volumes. A configuration was selected for vibration analysis and lateral slosh mode shapes and natural frequencies were obtained. Results are documented
Computational challenges of systems biology
Progress in the study of biological systems such as the heart, brain, and liver will require computer scientists to work closely with life scientists and mathematicians. Computer science will play a key role in shaping the new discipline of systems biology and addressing the significant computational challenges it poses
Radio and near-infrared observations of the steep spectrum Galactic plane radio source WKB 0314+57.8
Radio and near-infared observations towards the steep spectrum Galactic plane
radio source WKB 0314+57.8 are presented, in order to clarify the nature of
this source. The radio observations include archival and survey data, together
with new Giant Metrewave Radio Telescope observations at 617 MHz. The
near-infrared observations are in the J and K bands, from the Gemini instrument
on the Shane 3-m telescope. The radio observations show that WKB 0314+57.8 is
extended, with an very steep spectrum (with flux density proportional to
frequency to -2.5 power between 40 MHz and 1.5 GHz). The colour--magnitude
diagram constructed from near-infrared observations of the field suggests the
presence of a z approx 0.08 galaxy cluster behind the Galactic plane, reddened
by about 6 magnitudes of visual extinction. Although the steep spectrum source
has no obvious identification, two other radio sources in the field covered by
the near-infrared observations have tentative identifications with galaxies.
These observations indicate that WKB 0314+57.8 is a relic source in a cluster
of galaxies, not a pulsar.Comment: 6 pages, to appear in MNRAS, typos correcte
X-ray Polarization Signatures of Compton Scattering in Magnetic Cataclysmic Variables
Compton scattering within the accretion column of magnetic cataclysmic
variables (mCVs) can induce a net polarization in the X-ray emission. We
investigate this process using Monte Carlo simulations and find that
significant polarization can arise as a result of the stratified flow structure
in the shock-ionized column. We find that the degree of linear polarization can
reach levels up to ~8% for systems with high accretion rates and low
white-dwarf masses, when viewed at large inclination angles with respect to the
accretion column axis. These levels are substantially higher than previously
predicted estimates using an accretion column model with uniform density and
temperature. We also find that for systems with a relatively low-mass white
dwarf accreting at a high accretion rate, the polarization properties may be
insensitive to the magnetic field, since most of the scattering occurs at the
base of the accretion column where the density structure is determined mainly
by bremsstrahlung cooling instead of cyclotron cooling.Comment: 7 pages, 8 figures, accepted by MNRA
COMMUNITY SUPPORTED AGRICULTURE: FILLING A NICHE MARKET
In less than a decade, the number of Community Supported Agriculture (CSA) projects has grown to more than 400. Our research suggests that CSA shareholders' social objectives dominate their decision to join. Standard economic objectives and "club-related" objectives contribute to the decision, but are clearly secondary. Our research also suggests the CSA movement will continue to grow. Its emphasis on social objectives, its inability to supply food year around, and the ongoing development of size-neutral organic technologies, however, will probably keep it from becoming a major market channel in the next century.Agribusiness,
TOLERANCE AND IMMUNITY TO MATERNALLY DERIVED INCOMPATIBLE IgG2a-GLOBULIN IN MICE
Progeny mice were confronted with maternal γ-globulin of a different allotype by either back-cross mating, intercross mating, or by foster nursing. In all cases, many mice subsequently produced alloantibodies directed against the incompatible maternal type of IgG2a-globulin. In one series of experiments, immunologic tolerance to the maternally derived γ-globulin was demonstrated to exist in the period before formation of spontaneous antibody. The state of tolerance was then lost, unless maintenance injections of foreign γ-globulin were given. These studies demonstrate in a natural situation that maternally derived foreign proteins can first induce a state of immunological tolerance which is followed, after disappearance of the antigen, by a state of immunity. As such, this parallels the experimental induction of tolerance to foreign proteins by neonatal injections
High Speed Photometry of SDSS J013701.06-091234.9
We present high speed photometry of the Sloan Digital Sky Survey cataclysmic
variable SDSS J013701.06-091234.9 in quiescence and during its 2003 December
superoutburst. The orbital modulation at 79.71\pm0.01 min is double humped; the
superhump period is 81.702\pm0.007 min. Towards the end of the outburst late
superhumps with a period of 81.29\pm0.01 min were observed. We argue that this
is a system of very low mass transfer rate, and that it probably has a long
outburst interval.Comment: 5 pages, 8 figures. Accepted for publication in MNRA
An Adaptive Computational Model for Predicting the Density Distribution of the Proximal Femur
A custom algorithm was developed to simulate adaptive boneremodeling. The process of adaptive bone remodeling can besimulated with a self-optimizing finite element method (FEM). Thebasic remodeling rule attempts to obtain a constant value for thestrain energy per unit bone mass, by adapting density. The precisesolution is dependent on the loads, initial conditions and theparameters in the remodeling rule. The aim of this study was toidentify how the bone density distribution of the proximal femurwas affected by parameters which govern the remodeling process.The forces at different phases of the gait cycle were applied asboundary conditions. The bone density distributions from theseforces were averaged to estimate the density distribution in theproximal femur. The effect of varying the spatial influencefunction, and the influence range on the converged solution wereinvestigated. It was shown that varying these parameters withinreasonable upper and lower bounds had very little impact on thequalitative form of the converged solution. In all cases, thesolutions obtained are comparable with the actual density in theproximal femur, as measured by DEXA scans
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