8,275 research outputs found
Synthesis of cubic diamond in the graphite-magnesium carbonate and graphite-K2Mg(CO3)(2) systems at high pressure of 9-10 GPa region
Cubic diamond was synthesized with two systems, (1) graphite with pure magnesium carbonate (magnesite) and (2) graphite with mixed potassium and magnesium carbonate at pressures and temperatures above 9.5 GPa, 1600 degrees C and 9 GPa, 1650 degrees C, respectively. At these conditions (1) the pure magnesite is solid, whereas (2) the mixed carbonate exists as a melt. In this pressure range, graphite seems to be partially transformed into hexagonal diamond. Measured carbon isotope delta(13)C values for all the materials suggest that the origin of the carbon source to form cubic diamond was the initial graphite powder, and not the carbonates
Gravitational waves from nonspinning black hole-neutron star binaries: dependence on equations of state
We report results of a numerical-relativity simulation for the merger of a
black hole-neutron star binary with a variety of equations of state (EOSs)
modeled by piecewise polytropes. We focus in particular on the dependence of
the gravitational waveform at the merger stage on the EOSs. The initial
conditions are computed in the moving-puncture framework, assuming that the
black hole is nonspinning and the neutron star has an irrotational velocity
field. For a small mass ratio of the binaries (e.g., MBH/MNS = 2 where MBH and
MNS are the masses of the black hole and neutron star, respectively), the
neutron star is tidally disrupted before it is swallowed by the black hole
irrespective of the EOS. Especially for less-compact neutron stars, the tidal
disruption occurs at a more distant orbit. The tidal disruption is reflected in
a cutoff frequency of the gravitational-wave spectrum, above which the spectrum
amplitude exponentially decreases. A clear relation is found between the cutoff
frequency of the gravitational-wave spectrum and the compactness of the neutron
star. This relation also depends weakly on the stiffness of the EOS in the core
region of the neutron star, suggesting that not only the compactness but also
the EOS at high density is reflected in gravitational waveforms. The mass of
the disk formed after the merger shows a similar correlation with the EOS,
whereas the spin of the remnant black hole depends primarily on the mass ratio
of the binary, and only weakly on the EOS. Properties of the remnant disks are
also analyzed.Comment: 27pages, 21 figures; erratum is added on Aug 5. 201
On the Origin of Lyman Blobs at High Redshift: Submillimetric Evidence for a Hyperwind Galaxy at z=3.1
The most remarkable class of high-redshift objects observed so far is
extended Ly emission-line blobs found in an over-density region at
redshift 3.1. They may be either a dust-enshrouded, extreme starburst galaxy
with a large-scale galactic outflow (superwind) or cooling radiation from dark
matter halos. Recently one of these Ly blobs has been detected at
submillimeter wavelengths (450 and 850 m). Here we show that its
rest-frame spectral energy distribution between optical and far-infrared is
quite similar to that of Arp 220, which is a typical ultraluminous
starburst/superwind galaxy in the local universe. This suggests strongly that
the superwind model proposed by Taniguchi & Shioya is applicable to this
Ly blob. Since the blob is more luminous in the infrared by a factor of
30 than Arp 220, it comprises a new population of hyperwind galaxies at high
redshift.Comment: 4 pages, 1 figure. ApJ (Letters), in pres
Quantum Hall Effect, Screening and Layer-Polarized Insulating States in Twisted Bilayer Graphene
We investigate electronic transport in dual-gated twisted bilayer graphene.
Despite the sub-nanometer proximity between the layers, we identify independent
contributions to the magnetoresistance from the graphene Landau level spectrum
of each layer. We demonstrate that the filling factor of each layer can be
independently controlled via the dual gates, which we use to induce Landau
level crossings between the layers. By analyzing the gate dependence of the
Landau level crossings, we characterize the finite inter-layer screening and
extract the capacitance between the atomically-spaced layers. At zero filling
factor, we observe magnetic and displacement field dependent insulating states,
which indicate the presence of counter-propagating edge states with inter-layer
coupling.Comment: 4 pages, 3 figure
Exploring binary-neutron-star-merger scenario of short-gamma-ray bursts by gravitational-wave observation
We elucidate the feature of gravitational waves (GWs) from binary neutron
star merger collapsing to a black hole by general relativistic simulation. We
show that GW spectrum imprints the coalescence dynamics, formation process of
disk, equation of state for neutron stars, total masses, and mass ratio. A
formation mechanism of the central engine of short -ray bursts, which
are likely to be composed of a black hole and surrounding disk, therefore could
be constrained by GW observation.Comment: Accepted to PR
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