1,372 research outputs found
Giant magneto-optical response in non-magnetic semiconductor BiTeI driven by bulk Rashba spin splitting
We study the magneto-optical (MO) response of polar semiconductor BiTeI with
giant bulk Rashba spin splitting at various carrier densities. Despite being
non-magnetic, the material is found to yield a huge MO activity in the infrared
region under moderate magnetic fields (<3 T). By comparison with
first-principles calculations, we show that such an enhanced MO response is
mainly due to the intraband transitions between the Rashba-split bulk
conduction bands in BiTeI, which give rise to distinct novel features and
systematic doping dependence of the MO spectra. We further predict an even more
pronounced enhancement in the low-energy MO response and dc Hall effect near
the crossing (Dirac) point of the conduction bands
Power-Law Distributions in a Two-sided Market and Net Neutrality
"Net neutrality" often refers to the policy dictating that an Internet
service provider (ISP) cannot charge content providers (CPs) for delivering
their content to consumers. Many past quantitative models designed to determine
whether net neutrality is a good idea have been rather equivocal in their
conclusions. Here we propose a very simple two-sided market model, in which the
types of the consumers and the CPs are {\em power-law distributed} --- a kind
of distribution known to often arise precisely in connection with
Internet-related phenomena. We derive mostly analytical, closed-form results
for several regimes: (a) Net neutrality, (b) social optimum, (c) maximum
revenue by the ISP, or (d) maximum ISP revenue under quality differentiation.
One unexpected conclusion is that (a) and (b) will differ significantly, unless
average CP productivity is very high
Observable Signatures of EMRI Black Hole Binaries Embedded in Thin Accretion Disks
We examine the electromagnetic (EM) and gravitational wave (GW) signatures of
stellar-mass compact objects (COs) spiraling into a supermassive black hole
(extreme mass-ratio inspirals or EMRIs), embedded in a thin, radiation-pressure
dominated, accretion disk. At large separations, the tidal effect of the
secondary CO clears a gap. We show that the gap refills during the late
GW-driven phase of the inspiral, leading to a sudden EM brightening of the
source. The accretion disk leaves an imprint on the GW through its angular
momentum exchange with the binary, the mass increase of the binary members due
to accretion, and its gravity. We compute the disk-modified GWs both in an
analytical Newtonian approximation and in a numerical effective-one-body
approach. We find that disk-induced migration provides the dominant
perturbation to the inspiral, with weaker effects from the mass accretion onto
the CO and hydrodynamic drag. Depending on whether a gap is present, the
perturbation of the GW phase is between 10 and 1000 radians per year,
detectable with the future Laser Interferometer Space Antenna (LISA) at high
significance. The Fourier transform of the disk-modified GW in the stationary
phase approximation is sensitive to disk parameters with a frequency trend
different from post-Newtonian vacuum corrections. Our results suggest that
observations of EMRIs may place new sensitive constraints on the physics of
accretion disks.Comment: 42 pages, 8 figures, 3 tables, submitted to Phys. Rev.
Gas barrier properties of oxyfluorinated graphene filled polytetrafluoroethylene nanocomposites
Menus for Feeding Black Holes
Black holes are the ultimate prisons of the Universe, regions of spacetime
where the enormous gravity prohibits matter or even light to escape to
infinity. Yet, matter falling toward the black holes may shine spectacularly,
generating the strongest source of radiation. These sources provide us with
astrophysical laboratories of extreme physical conditions that cannot be
realized on Earth. This chapter offers a review of the basic menus for feeding
matter onto black holes and discusses their observational implications.Comment: 27 pages. Accepted for publication in Space Science Reviews. Also to
appear in hard cover in the Space Sciences Series of ISSI "The Physics of
Accretion onto Black Holes" (Springer Publisher
Preparation and characterization of in situ polymerized cyclic butylene terephthalate/graphene nanocomposites
Graphene reinforced cyclic butylene terephthalate (CBT) matrix nanocomposites were prepared and characterized by mechanical and thermal methods. These nanocomposites containing different amounts of graphene (up to 5 wt%) were prepared by melt mixing with CBT that was polymerized in situ during a subsequent hot pressing. The nanocomposites and the neat polymerized CBT (pCBT) as reference material were subjected to differential scanning calorimetry (DSC), dynamical mechanical analysis (DMA), thermogravimetrical analysis (TGA) and heat conductivity measurements. The dispersion of the grapheme nanoplatelets was characterized by transmission electron microscopy (TEM). It was established that the partly exfoliated graphene worked as nucleating agent for crystallization, acted as very efficient reinforcing agent (the storage modulus at room temperature was increased by 39 and 89% by incorporating 1 and 5 wt.% graphene, respectively). Graphene incorporation markedly enhanced the heat conductivity but did not influence the TGA behaviour due to the not proper exfoliation except the ash content
Extreme mass ratio inspiral rates: dependence on the massive black hole mass
We study the rate at which stars spiral into a massive black hole (MBH) due
to the emission of gravitational waves (GWs), as a function of the mass M of
the MBH. In the context of our model, it is shown analytically that the rate
approximately depends on the MBH mass as M^{-1/4}. Numerical simulations
confirm this result, and show that for all MBH masses, the event rate is
highest for stellar black holes, followed by white dwarfs, and lowest for
neutron stars. The Laser Interferometer Space Antenna (LISA) is expected to see
hundreds of these extreme mass ratio inspirals per year. Since the event rate
derived here formally diverges as M->0, the model presented here cannot hold
for MBHs of masses that are too low, and we discuss what the limitations of the
model are.Comment: Accepted to CQG, special LISA issu
Observation of confined current ribbon in JET plasmas
we report the identification of a localised current structure inside the JET
plasma. It is a field aligned closed helical ribbon, carrying current in the
same direction as the background current profile (co-current), rotating
toroidally with the ion velocity (co-rotating). It appears to be located at a
flat spot in the plasma pressure profile, at the top of the pedestal. The
structure appears spontaneously in low density, high rotation plasmas, and can
last up to 1.4 s, a time comparable to a local resistive time. It considerably
delays the appearance of the first ELM.Comment: 10 pages, 6 figure
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