199,527 research outputs found
Covalent bonding of antibodies of polystyrene latex beads: A concept
Technique facilitates purification of vaccines and production of immunoadsorption columns exhibiting relatively long stability. Information interests biochemists, medical researchers, and pharmaceutical manufacturers
Cardiotachometer with linear beat-to-beat frequency response
Cardiotachometer detects and displays the human heart rate during physiological studies. It provides linear response to the heart rate, records heart rate during rest and under heavy stress, provides a beat-to-beat indication of changes in heart rate, and is relatively free of interfering signals from activities other than the heart rate
Viscosity and Thermal Relaxation for a resonantly interacting Fermi gas
The viscous and thermal relaxation rates of an interacting fermion gas are
calculated as functions of temperature and scattering length, using a many-body
scattering matrix which incorporates medium effects due to Fermi blocking of
intermediate states. These effects are demonstrated to be large close to the
transition temperature to the superfluid state. For a homogeneous gas in
the unitarity limit, the relaxation rates are increased by nearly an order of
magnitude compared to their value obtained in the absence of medium effects due
to the Cooper instability at . For trapped gases the corresponding ratio
is found to be about three due to the averaging over the inhomogeneous density
distribution. The effect of superfluidity below is considered to leading
order in the ratio between the energy gap and the transition temperature.Comment: 7 pages, 3 figure
Multifluid, Magnetohydrodynamic Shock Waves with Grain Dynamics II. Dust and the Critical Speed for C Shocks
This is the second in a series of papers on the effects of dust on
multifluid, MHD shock waves in weakly ionized molecular gas. We investigate the
influence of dust on the critical shock speed, v_crit, above which C shocks
cease to exist. Chernoff showed that v_crit cannot exceed the grain
magnetosound speed, v_gms, if dust grains are dynamically well coupled to the
magnetic field. We present numerical simulations of steady shocks where the
grains may be well- or poorly coupled to the field. We use a time-dependent,
multifluid MHD code that models the plasma as a system of interacting fluids:
neutral particles, ions, electrons, and various ``dust fluids'' comprised of
grains with different sizes and charges. Our simulations include grain inertia
and grain charge fluctuations but to highlight the essential physics we assume
adiabatic flow, single-size grains, and neglect the effects of chemistry. We
show that the existence of a phase speed v_phi does not necessarily mean that C
shocks will form for all shock speeds v_s less than v_phi. When the grains are
weakly coupled to the field, steady, adiabatic shocks resemble shocks with no
dust: the transition to J type flow occurs at v_crit = 2.76 v_nA, where v_nA is
the neutral Alfven speed, and steady shocks with v_s > 2.76 v_nA are J shocks
with magnetic precursors in the ion-electron fluid. When the grains are
strongly coupled to the field, v_crit = min(2.76 v_nA, v_gms). Shocks with
v_crit < v_s < v_gms have magnetic precursors in the ion-electron-dust fluid.
Shocks with v_s > v_gms have no magnetic precursor in any fluid. We present
time-dependent calculations to study the formation of steady multifluid shocks.
The dynamics differ qualitatively depending on whether or not the grains and
field are well coupled.Comment: 43 pages with 17 figures, aastex, accepted by The Astrophysical
Journa
A large scale extinction map of the Galactic Anticenter from 2MASS
We present a 127deg x 63deg extinction map of the Anticenter of the Galaxy,
based on and colour excess maps from 2MASS. This 8001 square degree
map with a resolution of 4 arcminutes is provided as online material. The
colour excess ratio / is used to determine the power law index of
the reddening law (\beta) for individual regions contained in the area (e.g.
Orion, Perseus, Taurus, Auriga, Monoceros, Camelopardalis, Cassiopeia). On
average we find a dominant value of \beta=1.8+-0.2 for the individual clouds,
in agreement with the canonical value for the interstellar medium. We also show
that there is an internal scatter of \beta values in these regions, and that in
some areas more than one dominant \beta value is present. This indicates large
scale variations in the dust properties. The analysis of the A_V values within
individual regions shows a change in the slope of the column density
distribution with distance. This can either be attributed to a change in the
governing physical processes in molecular clouds on spatial scales of about 1pc
or an A_V dilution with distance in our map.Comment: 18 pages, 29 Figures, 1 Table, Accepted for publication by MNRAS, A
version with higher resolution figures can be found at
http://astro.kent.ac.uk/~df
Mapping warm molecular hydrogen with Spitzer's Infrared Array Camera (IRAC)
Photometric maps, obtained with Spitzer's Infrared Array Camera (IRAC), can
provide a valuable probe of warm molecular hydrogen within the interstellar
medium. IRAC maps of the supernova remnant IC443, extracted from the Spitzer
archive, are strikingly similar to spectral line maps of the H2 pure rotational
transitions that we obtained with the Infrared Spectrograph (IRS) instrument on
Spitzer. IRS spectroscopy indicates that IRAC Bands 3 and 4 are indeed
dominated by the H2 v=0-0 S(5) and S(7) transitions, respectively. Modeling of
the H2 excitation suggests that Bands 1 and 2 are dominated by H2 v=1-0 O(5)
and v=0-0 S(9). Large maps of the H2 emission in IC433, obtained with IRAC,
show band ratios that are inconsistent with the presence of gas at a single
temperature. The relative strengths of IRAC Bands 2, 3, and 4 are consistent
with pure H2 emission from shocked material with a power-law distribution of
gas temperatures. CO vibrational emissions do not contribute significantly to
the observed Band 2 intensity. Assuming that the column density of H2 at
temperatures T to T+dT is proportional to T raised to the power -b for
temperatures up to 4000 K, we obtained a typical estimate of 4.5 for b. The
power-law index, b, shows variations over the range 3 to 6 within the set of
different sight-lines probed by the maps, with the majority of sight-lines
showing b in the range 4 to 5. The observed power-law index is consistent with
the predictions of simple models for paraboloidal bow shocks.Comment: 27 pages, including 11 figures. Accepted for publication in Ap
p-Wave stabilization of three-dimensional Bose-Fermi solitons
We explore bright soliton solutions of ultracold Bose-Fermi gases, showing
that the presence of p-wave interactions can remove the usual collapse
instability and support stable soliton solutions that are global energy minima.
A variational model that incorporates the relevant s- and p-wave interactions
in the system is established analytically and solved numerically to probe the
dependencies of the solitons on key experimental parameters. Under attractive
s-wave interactions, bright solitons exist only as meta-stable states
susceptible to collapse. Remarkably, the presence of repulsive p-wave
interactions alleviates this collapse instability. This dramatically widens the
range of experimentally-achievable soliton solutions and indicates greatly
enhanced robustness. While we focus specifically on the boson-fermion pairing
of 87Rb and 40K, the stabilization inferred by repulsive p-wave interactions
should apply to the wider remit of ultracold Bose-Fermi mixtures.Comment: 9 pages, 6 figure
NGC 4314. III. Inflowing Molecular Gas Feeding a Nuclear Ring of Star Formation
NGC 4314 is an early-type barred galaxy containing a nuclear ring of recent
star formation. We present CO(1-0) interferometer data of the bar and
circumnuclear region with 2.3 x 2.2 arcsec spatial resolution and 13 km/s
velocity resolution acquired at the Owens Valley Radio Observatory . These data
reveal a clumpy circumnuclear ring of molecular gas. We also find a peak of CO
inside the ring within 2 arcsec of the optical center that is not associated
with massive star formation. We construct a rotation curve from these CO
kinematic data and the mass model of Combes et al. (1992). Using this rotation
curve, we have identified the location of orbital resonances in the galaxy.
Assuming that the bar ends at corotation, the circumnuclear ring of star
formation lies between two Inner Lindblad Resonances, while the nuclear stellar
bar ends near the IILR. Deviations from circular motion are detected just
beyond the CO and H-alpha ring, where the dust lanes along the leading edge of
the bar intersect the nuclear ring. These non-circular motions along the minor
axis correspond to radially inward streaming motions at speeds of 20 - 90 km/s
and clearly show inflowing gas feeding an ILR ring. There are bright HII
regions near the ends of this inflow region, perhaps indicating triggering of
star formation by the inflow.Comment: 25 pages, uses aasms.sty. 7 Postscript figures, 12 JPEG figures.
Figures may be retrieved from
ftp://clyde.as.utexas.edu/pub/N4314COfigs.tar.g
Woe from stones: commemoration, identity politics and Estonia's 'War of Monuments'
No abstract available
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