20,194 research outputs found
Shock-Wave Heating Model for Chondrule Formation: Prevention of Isotopic Fractionation
Chondrules are considered to have much information on dust particles and
processes in the solar nebula. It is naturally expected that protoplanetary
disks observed in present star forming regions have similar dust particles and
processes, so study of chondrule formation may provide us great information on
the formation of the planetary systems.
Evaporation during chondrule melting may have resulted in depletion of
volatile elements in chondrules. However, no evidence for a large degree of
heavy-isotope enrichment has been reported in chondrules. In order to meet this
observed constraint, the rapid heating rate at temperatures below the silicate
solidus is required to suppress the isotopic fractionation.
We have developed a new shock-wave heating model taking into account the
radiative transfer of the dust thermal continuum emission and the line emission
of gas molecules and calculated the thermal history of chondrules. We have
found that optically-thin shock waves for the thermal continuum emission from
dust particles can meet the rapid heating constraint, because the dust thermal
emission does not keep the dust particles high temperature for a long time in
the pre-shock region and dust particles are abruptly heated by the gas drag
heating in the post-shock region. We have also derived the upper limit of
optical depth of the pre-shock region using the radiative diffusion
approximation, above which the rapid heating constraint is not satisfied. It is
about 1 - 10.Comment: 58 pages, including 5 tables and 15 figures, accepted for publication
in The Astrophysical Journa
Macroscopic detection of the strong stochasticity threshold in Fermi-Pasta-Ulam chains of oscillators
The largest Lyapunov exponent of a system composed by a heavy impurity
embedded in a chain of anharmonic nearest-neighbor Fermi-Pasta-Ulam oscillators
is numerically computed for various values of the impurity mass . A
crossover between weak and strong chaos is obtained at the same value
of the energy density (energy per degree of freedom)
for all the considered values of the impurity mass . The threshold \epsi
lon_{_T} coincides with the value of the energy density at which a
change of scaling of the relaxation time of the momentum autocorrelation
function of the impurity ocurrs and that was obtained in a previous work ~[M.
Romero-Bastida and E. Braun, Phys. Rev. E {\bf65}, 036228 (2002)]. The complete
Lyapunov spectrum does not depend significantly on the impurity mass . These
results suggest that the impurity does not contribute significantly to the
dynamical instability (chaos) of the chain and can be considered as a probe for
the dynamics of the system to which the impurity is coupled. Finally, it is
shown that the Kolmogorov-Sinai entropy of the chain has a crossover from weak
to strong chaos at the same value of the energy density that the crossover
value of largest Lyapunov exponent. Implications of this result
are discussed.Comment: 6 pages, 5 figures, revtex4 styl
Three-dimensional calculation of shuttle charging in polar orbit
The charged particles environment in polar orbit can be of sufficient intensity to cause spacecraft charging. In order to gain a quantitative understanding of such effects, the Air Force is developing POLAR, a computer code which simulates in three dimensions the electrical interaction of large space vehicles with the polar ionospheric plasma. It models the physical processes of wake generation, ambient ion collection, precipitating auroral electron fluxes, and surface interactions, including secondary electron generation and backscattering, which lead to vehicle charging. These processes may be followed dynamically on a subsecond timescale so that the rapid passage through intense auroral arcs can be simulated. POLAR models the ambient plasma as isotropic Maxwellian electrons and ions (0+, H+), and allows for simultaneous precipitation of power-law, energetic Maxwellian, and accelerated Gaussian distributions of electrons. Magnetic field effects will be modeled in POLAR but are currently ignored
A systematic review of factors associated with side-effect expectations from medical interventions
Background: Fear of side-effects can result in non-adherence to medical interventions, such as medication and chemotherapy. Side-effect expectations have been identified as strong
predictors of later perception of side-effects. However, research investigating predictors of side-effect expectations is disparate.
Objective: To identify factors associated with side-effect expectations.
Search strategy: We systematically searched Embase, Ovid MEDLINE, Global Health, PsycARTICLES, PsycINFO, Web of Science and Scopus.
Inclusion criteria: Studies were included if they investigated associations between any predictive factor and expectations of side-effects from any medical intervention.
Data extraction and synthesis: We extracted information about participant characteristics, medication, rates of side-effects expected, and predictors of side-effect expectations. Data
were narratively synthesised.
Main results: We identified sixty-four citations, reporting on seventy-two studies. Predictors fell into five categories: personal characteristics; clinical characteristics; psychological traits and state; presentation format of information; and information sources used. Using verbal risk descriptors (e.g. ‘common’) compared to numerical descriptors (e.g. percentages), having
lower quality of life or wellbeing, and currently experiencing symptoms were associated with increased side-effect expectations.
Discussion and conclusions: Decreasing unrealistic side-effect expectations may lead to decreased experience of side-effects and increased adherence to medical interventions.
Widespread communications about medical interventions should describe the incidence of side-effects numerically. Evidence suggests that clinicians should take particular care with patients with lower quality of life, who are currently experiencing symptoms and who have previously experienced symptoms from treatment. Further research should investigate
different clinical populations and aim to quantify the impact of the media and social media on side-effect expectations
Heat sterilizable and impact resistant Ni-Cd battery development Quarterly report, 1 Apr. - 30 Jun. 1969
Electrochemistry, battery engineering, and impact tests of heat sterilizable nickel cadmium cell
Zeta-Functions for Non-Minimal Operators
We evaluate zeta-functions at for invariant non-minimal
2nd-order vector and tensor operators defined on maximally symmetric even
dimensional spaces. We decompose the operators into their irreducible parts and
obtain their corresponding eigenvalues. Using these eigenvalues, we are able to
explicitly calculate for the cases of Euclidean spaces and
-spheres. In the -sphere case, we make use of the Euler-Maclaurin formula
to develop asymptotic expansions for the required sums. The resulting
values for dimensions 2 to 10 are given in the Appendix.Comment: 26 pages, additional reference
Galaxies Probing Galaxies in PRIMUS - I. Sample, Spectroscopy, and Characteristics of the z~0.5 MgII-Absorbing Circumgalactic Medium
Spectroscopy of background QSO sightlines passing close to foreground
galaxies is a potent technique for studying the circumgalactic medium (CGM).
QSOs are effectively point sources, however, limiting their potential to
constrain the size of circumgalactic gaseous structures. Here we present the
first large Keck/LRIS and VLT/FORS2 spectroscopic survey of bright (B_AB <
22.3) background galaxies whose lines of sight probe MgII 2796, 2803 absorption
from the CGM around close projected foreground galaxies at transverse distances
10 kpc < R_perp < 150 kpc. Our sample of 72 projected pairs, drawn from the
PRIsm MUlti-object Survey (PRIMUS), includes 48 background galaxies which do
not host bright AGN, and both star-forming and quiescent foreground galaxies
with stellar masses 9.0 < log M_*/M_sun < 11.2 at redshifts 0.35 < z_f/g < 0.8.
We detect MgII absorption associated with these foreground galaxies with
equivalent widths 0.25 Ang 2sigma significance in 20
individual background sightlines passing within R_perp < 50 kpc, and place
2sigma upper limits on W_2796 of <0.5 Ang in an additional 11 close sightlines.
Within R_perp < 50 kpc, W_2796 is anticorrelated with R_perp, consistent with
analyses of MgII absorption detected along background QSO sightlines.
Subsamples of these foreground hosts divided at log M_*/M_sun = 9.9 exhibit
statistically inconsistent W_2796 distributions at 30 kpc < R_perp < 50 kpc,
with the higher-M_* galaxies yielding a larger median W_2796 by 0.9 Ang.
Finally, we demonstrate that foreground galaxies with similar stellar masses
exhibit the same median W_2796 at a given R_perp to within <0.2 Ang toward both
background galaxies and toward QSO sightlines drawn from the literature.
Analysis of these datasets constraining the spatial coherence scale of
circumgalactic MgII absorption is presented in a companion paper.Comment: 36 pages, 18 figures, 5 tables. Accepted to Ap
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