4,742 research outputs found
Determination of the Equation of State of Dense Matter
Nuclear collisions can compress nuclear matter to densities achieved within
neutron stars and within core-collapse supernovae. These dense states of matter
exist momentarily before expanding. We analyzed the flow of matter to extract
pressures in excess of 10^34 pascals, the highest recorded under
laboratory-controlled conditions. Using these analyses, we rule out strongly
repulsive nuclear equations of state from relativistic mean field theory and
weakly repulsive equations of state with phase transitions at densities less
than three times that of stable nuclei, but not equations of state softened at
higher densities because of a transformation to quark matter.Comment: 26 pages, 6 figures; final versio
Conceptual design study of a Harrier V/STOL research aircraft
MCAIR recently completed a conceptual design study to define modification approaches to, and derive planning prices for the conversion of a two place Harrier to a V/STOL control, display and guidance research aircraft. Control concepts such as rate damping, attitude stabilization, velocity command, and cockpit controllers are to be demonstrated. Display formats will also be investigated, and landing, navigation and guidance systems flight tested. The rear cockpit is modified such that it can be quickly adapted to faithfully simulate the controls, displays and handling qualities of a Type A or Type B V/STOL. The safety pilot always has take command capability. The modifications studied fall into two categories: basic modifications and optional modifications. Technical descriptions of the basic modifications and of the optional modifications are presented. The modification plan and schedule as well as the test plan and schedule are presented. The failure mode and effects analysis, aircraft performance, aircraft weight, and aircraft support are discussed
Triggering the Formation of Halo Globular Clusters with Galaxy Outflows
We investigate the interactions of high-redshift galaxy outflows with
low-mass virialized (Tvir < 10,000K) clouds of primordial composition. While
atomic cooling allows star formation in larger primordial objects, such
"minihalos" are generally unable to form stars by themselves. However, the
large population of high-redshift starburst galaxies may have induced
widespread star formation in these objects, via shocks that caused intense
cooling both through nonequilibrium H2 formation and metal-line emission. Using
a simple analytic model, we show that the resulting star clusters naturally
reproduce three key features of the observed population of halo globular
clusters (GCs). First, the 10,000 K maximum virial temperature corresponds to
the ~ 10^6 solar mass upper limit on the stellar mass of GCs. Secondly, the
momentum imparted in such interactions is sufficient to strip the gas from its
associated dark matter halo, explaining why GCs do not reside in dark matter
potential wells. Finally, the mixing of ejected metals into the primordial gas
is able to explain the ~ 0.1 dex homogeneity of stellar metallicities within a
given GC, while at the same time allowing for a large spread in metallicity
between different clusters. To study this possibility in detail, we use a
simple 1D numerical model of turbulence transport to simulate mixing in
cloud-outflow interactions. We find that as the shock shears across the side of
the cloud, Kelvin-Helmholtz instabilities arise, which cause mixing of enriched
material into > 20% of the cloud. Such estimates ignore the likely presence of
large-scale vortices, however, which would further enhance turbulence
generation. Thus quantitative mixing predictions must await more detailed
numerical studies.Comment: 21 pages, 11 figures, Apj in pres
The Most Massive Black Holes in the Universe: Effects of Mergers in Massive Galaxy Clusters
Recent observations support the idea that nuclear black holes grew by gas
accretion while shining as luminous quasars at high redshift, and they
establish a relation of the black hole mass with the host galaxy's spheroidal
stellar system. We develop an analytic model to calculate the expected impact
of mergers on the masses of black holes in massive clusters of galaxies. We use
the extended Press-Schechter formalism to generate Monte Carlo merger histories
of halos with a mass 10^{15} h^{-1} Msun. We assume that the black hole mass
function at z=2 is similar to that inferred from observations at z=0 (since
quasar activity declines markedly at z<2), and we assign black holes to the
progenitor halos assuming a monotonic relation between halo mass and black hole
mass. We follow the dynamical evolution of subhalos within larger halos,
allowing for tidal stripping, the loss of orbital energy by dynamical friction,
and random orbital perturbations in gravitational encounters with subhalos, and
we assume that mergers of subhalos are followed by mergers of their central
black holes. Our analytic model reproduces numerical estimates of the subhalo
mass function. We find that the most massive black holes in massive clusters
typically grow by a factor ~ 2 by mergers after gas accretion has stopped. In
our ten realizations of 10^{15} h^{-1} Msun clusters, the highest initial (z=2)
black hole masses are 5-7 x 10^9 Msun, but four of the clusters contain black
holes in the range 1-1.5 x 10^{10} Msun at z=0. Satellite galaxies may host
black holes whose mass is comparable to, or even greater than, that of the
central galaxy. Thus, black hole mergers can significantly extend the very high
end of the black hole mass function.Comment: 13 pages, 7 figures, accepted for publication in The Astrophysical
Journa
Universal scaling of the elliptic flow data at RHIC
Recent PHOBOS measurements of the excitation function for the pseudo-rapidity
dependence of elliptic flow in Au+Au collisions at RHIC, have posed a
significant theoretical challenge. Here we show that these differential
measurements, as well as the RHIC measurements on transverse momentum satisfy a
universal scaling relation predicted by the Buda-Lund model, based on exact
solutions of perfect fluid hydrodynamics. We also show that recently found
transverse kinetic energy scaling of the elliptic flow is a special case of
this universal scaling.Comment: 4 pages, 3 figures, 1 tabl
Semi-Analytical Models for Lensing by Dark Halos: I. Splitting Angles
We use the semi-analytical approach to analyze gravitational lensing of
quasars by dark halos in various cold dark matter (CDM) cosmologies, in order
to determine the sensitivity of the prediction probabilities of images
separations to the input assumptions regarding halos and cosmologies. The mass
function of dark halos is assumed to be given by the Press-Schechter function.
The mass density profile of dark halos is alternatively taken to be the
singular isothermal sphere (SIS), the Navarro-Frenk-White (NFW) profile, or the
generalized NFW profile. The cosmologies include: the Einstein-de Sitter model
(SCDM), the open model (OCDM), and the flat \Lambda-model (LCDM). As expected,
we find that the lensing probability is extremely sensitive to the mass density
profile of dark halos, and somewhat less so to the mean mass density in the
universe, and the amplitude of primordial fluctuations. NFW halos are very much
less effective in producing multiple images than SIS halos. However, none of
these models can completely explain the current observations: the SIS models
predict too many large splitting lenses, while the NFW models predict too few
small splitting lenses. This indicates that there must be at least two
populations of halos in the universe. A combination of SIS and NFW halos can
reasonably reproduce the current observations if we choose the mass for the
transition from SIS to NFW to be ~ 10^{13} solar masses. Additionally, there is
a tendency for CDM models to have too much power on small scales, i.e. too much
mass concentration; and it appears that the cures proposed for other apparent
difficulties of CDM would help here as well, an example being the warm dark
matter (WDM) variant which is shown to produce large splitting lenses fewer
than the corresponding CDM model by one order of magnitude.Comment: 46 pages, including 13 figures. Revised version with significant
improvemen
Optimal Constraints on Local Primordial Non-Gaussianity from the Two-Point Statistics of Large-Scale Structure
One of the main signatures of primordial non-Gaussianity of the local type is
a scale-dependent correction to the bias of large-scale structure tracers such
as galaxies or clusters, whose amplitude depends on the bias of the tracers
itself. The dominant source of noise in the power spectrum of the tracers is
caused by sampling variance on large scales (where the non-Gaussian signal is
strongest) and shot noise arising from their discrete nature. Recent work has
argued that one can avoid sampling variance by comparing multiple tracers of
different bias, and suppress shot noise by optimally weighting halos of
different mass. Here we combine these ideas and investigate how well the
signatures of non-Gaussian fluctuations in the primordial potential can be
extracted from the two-point correlations of halos and dark matter. On the
basis of large -body simulations with local non-Gaussian initial conditions
and their halo catalogs we perform a Fisher matrix analysis of the two-point
statistics. Compared to the standard analysis, optimal weighting- and
multiple-tracer techniques applied to halos can yield up to one order of
magnitude improvements in \fnl-constraints, even if the underlying dark
matter density field is not known. We compare our numerical results to the halo
model and find satisfactory agreement. Forecasting the optimal
\fnl-constraints that can be achieved with our methods when applied to
existing and future survey data, we find that a survey of
volume resolving all halos down to 10^{11}\hMsun at
will be able to obtain \sigma_{\fnl}\sim1 (68% cl), a factor of
improvement over the current limits. Decreasing the minimum mass of
resolved halos, increasing the survey volume or obtaining the dark matter maps
can further improve these limits, potentially reaching the level of
\sigma_{\fnl}\sim0.1. (abridged)Comment: V1: 23 pages, 12 figures, submitted to PRD. V2: 24 pages, added
appendix and citations, matched to PRD published versio
Determination of 2-methoxy-3-alkylpyrazines in wine by gas chromatography/mass spectrometry
2-Methoxy-3-alkylpyrazines have been isolated for the first time from a Sauvignon blanc wine by using a combination of distillation or headspace sampling and trapping by an ion-exchange resin. 2-Methoxy-3-isobutylpyrazine has been identified by gas chromatography/mass spectrometry as the major methoxypyrazine in a New Zealand Sauvignon blanc and, with the aid of 2-methoxy-d3-3-isobutylpyrazine as internal standard, its concentration has been determined as 35 ± 2 ppt. The method can be applied to small wine samples (< 60 ml) and detection limits are below the olfactory thresholds
Gravitational Lensing by Galaxy Groups in the Hubble Deep Field
We investigate strong lensing of galaxies in the Hubble Deep Field by
foreground groups and clusters of galaxies with masses from to
10^{15} \MSun. Over this mass range, groups with the profile of Navarro,
Frenk, & White (1995) are less efficient than singular isothermal spheres at
producing multiple images of galaxies, by factors of to
. This difference highlights the sensitivity of the lensing cross
section to the central density profile. Nonetheless, with either profile we
find that the expected number of galaxies lensed by groups in the Hubble Deep
Field is at most , consistent with the lack of clearly identified
group lens systems.Comment: 33 pages, 12 EPS figures, accepted by Ap
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