3,926 research outputs found
Baryon Dynamics, Dark Matter Substructure, and Galaxies
By comparing a collisionless cosmological N-body simulation (DM) to an SPH
simulation with the same initial conditions, we investigate the correspondence
between the dark matter subhalos produced by collisionless dynamics and the
galaxies produced by dissipative gas dynamics in a dark matter background. When
galaxies in the SPH simulation become satellites in larger groups, they retain
local dark matter concentrations (SPH subhalos) whose mass is typically five
times their baryonic mass. The more massive subhalos of the SPH simulation have
corresponding subhalos of similar mass and position in the DM simulation; at
lower masses, there is fairly good correspondence, but some DM subhalos are in
different spatial positions and some suffer tidal stripping or disruption. The
halo occupation statistics of DM subhalos -- the mean number of subhalos,
pairs, and triples as a function of host halo mass -- are very similar to those
of SPH subhalos and SPH galaxies. Gravity of the dissipative baryon component
amplifies the density contrast of subhalos in the SPH simulation, making them
more resistant to tidal disruption. Relative to SPH galaxies and SPH subhalos,
the DM subhalo population is depleted in the densest regions of the most
massive halos. The good agreement of halo occupation statistics between the DM
subhalo and SPH galaxy populations leads to good agreement of their two-point
correlation functions and higher order moments on large scales. The depletion
of DM subhalos in dense regions depresses their clustering at R<1 Mpc/h. In
these simulations, the "conversation" between dark matter and baryons is mostly
one-way, with dark matter dynamics telling galaxies where to form and how to
cluster, but the "back talk" of the baryons influences small scale clustering
by enhancing the survival of substructure in the densest environments.Comment: 32 pages including 16 figs. Submitted to ApJ. PDF file with higher
quality versions of Figs 2 and 3 available at
http://www.astronomy.ohio-state.edu/~dhw/Preprints/subhalo.pd
Radio Emission from an Ultraluminous X-Ray Source
The physical nature of ultraluminous x-ray sources is uncertain. Stellar mass
black holes with beamed radiation and intermediate mass black holes with
isotropic radiation are two plausible explanations. We discovered radio
emission from an ultraluminous x-ray source in the dwarf irregular galaxy NGC
5408. The x-ray, radio and optical fluxes as well as the x-ray spectral shape
are consistent with beamed relativistic jet emission from an accreting stellar
black hole. If confirmed, this would suggest that the ultraluminous x-ray
sources may be stellar-mass rather than intermediate mass black holes. However,
interpretation of the source as a jet-producing intermediate-mass black hole
cannot be ruled out at this time.Comment: 8 pages, one color figure. appeared in Science 299: 365-367 (January
17, 2003
Nucleosynthesis constraints on the neutron star-black hole merger rate
We derive constraints on the time-averaged event rate of neutron star-black
hole (NS-BH) mergers by using estimates of the population-integrated production
of heavy rapid neutron-capture (r-process) elements with nuclear mass numbers A
> 140 by such events in comparison to the Galactic repository of these chemical
species. Our estimates are based on relativistic hydrodynamical simulations
convolved with theoretical predictions of the binary population. This allows us
to determine a strict upper limit of the average NS-BH merger rate of ~6*10^-5
per year. We quantify the uncertainties of this estimate to be within factors
of a few mostly because of the unknown BH spin distribution of such systems,
the uncertain equation of state of NS matter, and possible errors in the
Galactic content of r-process material. Our approach implies a correlation
between the merger rates of NS-BH binaries and of double NS systems.
Predictions of the detection rate of gravitational-wave signals from such
compact-object binaries by Advanced LIGO and Advanced Virgo on the optimistic
side are incompatible with the constraints set by our analysis.Comment: 5 pages, 3 figures; accepted for publication in ApJ
Sub-Inertial Gravity Modes in the B8V Star KIC 7760680 Reveal Moderate Core Overshooting and Low Vertical Diffusive Mixing
KIC 7760680 is so far the richest slowly pulsating B star, by exhibiting 36
consecutive dipole () gravity (g-) modes. The monotonically decreasing
period spacing of the series, in addition to the local dips in the pattern
confirm that KIC 7760680 is a moderate rotator, with clear mode trapping in
chemically inhomogeneous layers. We employ the traditional approximation of
rotation to incorporate rotational effects on g-mode frequencies. Our detailed
forward asteroseismic modelling of this g-mode series reveals that KIC 7760680
is a moderately rotating B star with mass M. By
simultaneously matching the slope of the period spacing, and the number of
modes in the observed frequency range, we deduce that the equatorial rotation
frequency of KIC 7760680 is 0.4805 day, which is 26\% of its Roche break
up frequency. The relative deviation of the model frequencies and those
observed is less than one percent. We succeed to tightly constrain the
exponentially-decaying convective core overshooting parameter to . This means that convective core overshooting can
coexist with moderate rotation. Moreover, models with exponentially-decaying
overshoot from the core outperform those with the classical step-function
overshoot. The best value for extra diffusive mixing in the radiatively stable
envelope is confined to (with in cm sec), which is notably smaller than theoretical
predictions.Comment: 12 Figures, 2 Tables, all data publicly available for download;
accepted for publication in Astrophysical Journa
Nucleosynthesis in dynamical and torus ejecta of compact binary mergers
We present a comprehensive study of r-process element nucleosynthesis in the
ejecta of compact binary mergers (CBMs) and their relic black-hole (BH)-torus
systems. The evolution of the BH-accretion tori is simulated for seconds with a
Newtonian hydrodynamics code including viscosity effects, pseudo-Newtonian
gravity for rotating BHs, and an energy-dependent two-moment closure scheme for
the transport of electron neutrinos and antineutrinos. The investigated cases
are guided by relativistic double neutron star (NS-NS) and NS-BH merger models,
producing ~3-6 Msun BHs with rotation parameters of A~0.8 and tori of 0.03-0.3
Msun. Our nucleosynthesis analysis includes the dynamical (prompt) ejecta
expelled during the CBM phase and the neutrino and viscously driven outflows of
the relic BH-torus systems. While typically ~20-25% of the initial
accretion-torus mass are lost by viscously driven outflows, neutrino-powered
winds contribute at most another ~1%, but neutrino heating enhances the viscous
ejecta significantly. Since BH-torus ejecta possess a wide distribution of
electron fractions (0.1-0.6) and entropies, they produce heavy elements from
A~80 up to the actinides, with relative contributions of A>130 nuclei being
subdominant and sensitively dependent on BH and torus masses and the exact
treatment of shear viscosity. The combined ejecta of CBM and BH-torus phases
can reproduce the solar abundances amazingly well for A>90. Varying
contributions of the torus ejecta might account for observed variations of
lighter elements with 40<Z<56 relative to heavier ones, and a considerable
reduction of the prompt ejecta compared to the torus ejecta, e.g. in highly
asymmetric NS-BH mergers, might explain the composition of heavy-element
deficient stars.Comment: 7 pages, 4 figures, only changed title compared to previous version,
accepted for publication in Proceedings of Science (Nuclei in the Cosmos
XIII, Debrecen
Comprehensive nucleosynthesis analysis for ejecta of compact binary mergers
We present the first comprehensive study of r-process element nucleosynthesis
in the ejecta of compact binary mergers (CBMs) and their relic black-hole
(BH)-torus systems. The evolution of the BH-accretion tori is simulated for
seconds with a Newtonian hydrodynamics code including viscosity effects,
pseudo-Newtonian gravity for rotating BHs, and an energy-dependent two-moment
closure scheme for the transport of electron neutrinos and antineutrinos. The
investigated cases are guided by relativistic double neutron star (NS-NS) and
NS-BH merger models, producing ~3-6 Msun BHs with rotation parameters of A~0.8
and tori of 0.03-0.3 Msun. Our nucleosynthesis analysis includes the dynamical
(prompt) ejecta expelled during the CBM phase and the neutrino and viscously
driven outflows of the relic BH-torus systems. While typically ~20-25% of the
initial accretion-torus mass are lost by viscously driven outflows,
neutrino-powered winds contribute at most another ~1%, but neutrino heating
enhances the viscous ejecta significantly. Since BH-torus ejecta possess a wide
distribution of electron fractions (0.1-0.6) and entropies, they produce heavy
elements from A~80 up to the actinides, with relative contributions of A>130
nuclei being subdominant and sensitively dependent on BH and torus masses and
the exact treatment of shear viscosity. The combined ejecta of CBM and BH-torus
phases can reproduce the solar abundances amazingly well for A>90. Varying
contributions of the torus ejecta might account for observed variations of
lighter elements with 40<Z<56 relative to heavier ones, and a considerable
reduction of the prompt ejecta compared to the torus ejecta, e.g. in highly
asymmetric NS-BH mergers, might explain the composition of heavy-element
deficient stars.Comment: 30 pages, 22 figures; revised version, accepted by MNRAS; appendix
added with test results for neutrino transpor
Hydraulic Fracture Monitoring: A Jonah Field Case Study
Hydraulic fracturing involves the injection of a fluid to fracture oil and gas reservoirs, and thus increase their permeability. The process creates numerous microseismic events, which can be used to monitor subsurface operations. In this study we introduce a novel microearthquake relocation workflow based on crosswell seismic observations and in-situ velocity measurements, and then apply it to data from two hydraulic fracture stages conducted at the Jonah field (Wyoming). The relocation is carried out by global optimization of a probability density function including P- and S-wave traveltimes, as well as source-receiver azimuths. By averaging multiple cross-well observations, we reorient the three component receivers and reduce the scatter of measured azimuth values by 50-60%. By simultaneously relocating the observed microearthquake ensemble for one fracture stage, we derive a more reliable image of the average fracture orientation and reduce the scatter of microearthquake locations by 20-40% as compared to conventional approaches. For the two stages of fracturing investigated, the microearthquakes are found to follow a NW-SE trend that places constraints on the local stress field and on the newly created fluid paths.Massachusetts Institute of Technology. Earth Resources Laboratory; Schlumberger-Doll Research Cente
Perancangan Sistem Informasi Data Bibit pada Balai Penyuluhanpertanian Perikanan dan Kehutanan (Bp3k) Kec. Sitinjau Laut
BP3K kecamatan setinjau laut merupakan badan unit daerah yang fokus di bidangpenyulahan, pertanian perikanan dan kehutanan. âDalam melakukan pengolahandata BP3K masih menggunakan penginputan data ke dalam buku besar dan belummemiliki suatu sistem penyimpanan data secara komputerisasi yang mampumengedit atau mengolah kembali data yang di simpan sehingga sering mengalamiketerlambatan dan kesalahan dalam pencarian data dan penyajian resi/laporanâ.Berdasarkan permasalahan di atas maka diusulkan penerapan program aplikasiyang dikembangkan menjadi sebuah program aplikasi dengan bahasapemrograman dan terintegrasi dengan database. Hasil yang dicapai yaituberupa sebuah rancangan sistem informasi terkomputerisasi berbasis databaseyang dapat memudahkan pihak BP3K dalam mengolah data khususnya masalahbibit masuk atau penyaluran bibit dan memberikan laporan secaracepat dan tepat waktu. Dengandibangunnya aplikasi berbasis komputer ini, diharapkan semua kendala yang adadapat teratasi dengan baik sehingga terwujud sistem yang efektif dan efisien
- âŠ