5,859 research outputs found
On the mechanism for orbital-ordering in KCuF3
The Mott insulating perovskite KCuF3 is considered the archetype of an
orbitally-ordered system. By using the LDA+dynamical mean-field theory (DMFT)
method, we investigate the mechanism for orbital-ordering (OO) in this
material. We show that the purely electronic Kugel-Khomskii super-exchange
mechanism (KK) alone leads to a remarkably large transition temperature of T_KK
about 350 K. However, orbital-order is experimentally believed to persist to at
least 800 K. Thus Jahn-Teller distortions are essential for stabilizing
orbital-order at such high temperatures.Comment: 4 pages, 5 figure
The Bodies of The Condemned: The Return of the Body as the Object of State Power
This paper provides a historical analysis of the genealogy of American policing and attempts to explain the return of state power to individual bodies. It argues that this return was informed by French counterinsurgency strategies in Algeria. Through engagement with Foucault\u27s analysis of power and surveillance practices, it aims to shed light on and help us better understand and combat police brutality today
Shikata Ga Nai: Statelessness and Sacrifice for Japanese-American Volunteers During the Second World War
Through a Philosophical analysis of the nature of Internment Camps as well as oral histories of veterans who volunteered to serve in the US military from the camps, this paper will argue that the internment of Japanese Americans during WWII was an event that the Supreme Court and surrounding legal discourse placed outside of legal jurisdiction. Those within the camps were thus condemned to a life lacking political qualification and juridical personhood. Faced with the dangers of this condition, interned Japanese Americans who served in the U.S. Army consciously laid claim to the American political community through the sacrifice of their lives. These soldiers, therefore, performed a thoroughly political act of resistance rather than of pure patriotism
The Dynamical Evolution of Be star disks
We present a novel theoretical tool to analyze the dynamical behaviour of a
Be disk fed by non-constant decretion rates. It is mainly based on the computer
code HDUST, a fully three-dimensional radiative transfer code that has been
successfully applied to study several Be systems so far, and the SINGLEBE code
that solves the 1D viscous diffusion problem. We have computed models of the
temporal evolution of different types of Be star disks for different dynamical
scenarios. By showing the behaviour of a large number of observables
(interferometry, polarization, photometry and spectral line profiles), we show
how it is possible to infer from observations some key dynamical parameters of
the disk.Comment: IAU 272 symposium proceedings, 3 pages, 1 figur
Non-LTE Monte Carlo Radiative Transfer: II. Non-Isothermal Solutions for Viscous Keplerian Disks
We discuss the basic hydrodynamics that determines the density structure of
the disks around hot stars. Observational evidence supports the idea that these
disks are Keplerian (rotationally supported) gaseous disks. A popular scenario
in the literature, which naturally leads to the formation of Keplerian disks,
is the viscous decretion model. According to this scenario, the disks are
hydrostatically supported in the vertical direction, while the radial structure
is governed by the viscous transport. This suggests that the temperature is one
primary factor that governs the disk density structure. In a previous study we
demonstrated, using 3-D NLTE Monte Carlo simulations, that viscous keplerian
disks can be highly non-isothermal. In this paper we build upon our previous
work and solve the full problem of the steady-state non-isothermal viscous
diffusion and vertical hydrostatic equilibrium. We find that the
self-consistent solution departs significantly from the analytic isothermal
density, with potentially large effects on the emergent spectrum. This implies
that non-isothermal disk models must be used for a detailed modeling of Be star
disks.Comment: 22 pages, 9 figures, Ap
Dynamical evolution of the mass function and radial profile of the Galactic globular cluster system
Evolution of the mass function (MF) and radial distribution (RD) of the
Galactic globular cluster (GC) system is calculated using an advanced and a
realistic Fokker-Planck (FP) model that considers dynamical friction,
disc/bulge shocks and eccentric cluster orbits. We perform hundreds of FP
calculations with different initial cluster conditions, and then search a
wide-parameter space for the best-fitting initial GC MF and RD that evolves
into the observed present-day Galactic GC MF and RD. By allowing both MF and RD
of the initial GC system to vary, which is attempted for the first time in the
present Letter, we find that our best-fitting models have a higher peak mass
for a lognormal initial MF and a higher cut-off mass for a power-law initial MF
than previous estimates, but our initial total masses in GCs, M_{T,i} =
1.5-1.8x10^8 Msun, are comparable to previous results. Significant findings
include that our best-fitting lognormal MF shifts downward by 0.35 dex during
the period of 13 Gyr, and that our power-law initial MF models well-fit the
observed MF and RD only when the initial MF is truncated at >~10^5 Msun. We
also find that our results are insensitive to the initial distribution of orbit
eccentricity and inclination, but are rather sensitive to the initial
concentration of the clusters and to how the initial tidal radius is defined.
If the clusters are assumed to be formed at the apocentre while filling the
tidal radius there, M_{T,i} can be as high as 6.9x10^8 Msun, which amounts to
~75 per cent of the current mass in the stellar halo.Comment: To appear in May 2008 issue of MNRAS, 386, L6
Cyclic Variability of the Circumstellar Disc of the Be Star Tau. II. Testing the 2D Global Disc Oscillation Model
Aims. In this paper we model, in a self-consistent way, polarimetric,
photometric, spectrophotometric and interferometric observations of the
classical Be star Tauri. Our primary goal is to conduct a critical
quantitative test of the global oscillation scenario. Methods. We have carried
out detailed three-dimensional, NLTE radiative transfer calculations using the
radiative transfer code HDUST. For the input for the code we have used the most
up-to-date research on Be stars to include a physically realistic description
for the central star and the circumstellar disc. We adopt a rotationally
deformed, gravity darkened central star, surrounded by a disc whose unperturbed
state is given by a steady-state viscous decretion disc model. We further
assume that disc is in vertical hydrostatic equilibrium. Results. By adopting a
viscous decretion disc model for Tauri and a rigorous solution of the
radiative transfer, we have obtained a very good fit of the time-average
properties of the disc. This provides strong theoretical evidence that the
viscous decretion disc model is the mechanism responsible for disc formation.
With the global oscillation model we have successfully fitted spatially
resolved VLTI/AMBER observations and the temporal V/R variations of the
H and Br lines. This result convincingly demonstrates that the
oscillation pattern in the disc is a one-armed spiral. Possible model
shortcomings, as well as suggestions for future improvements, are also
discussed.Comment: 14 pages, 9 figures, accepted to A&
High-dispersion spectroscopic monitoring of the Be/X-ray binary A0535+26/V725 Tau I: The long-term profile variability
We report on optical high-dispersion spectroscopic monitoring observations of
the Be/X-ray binary A0535+26/V725 Tau, carried out from November 2005 to March
2009. The main aim of these monitoring observations is to study spectral
variabilities in the Be disc, on both the short (a week or so) and long (more
than hundreds of days) timescales, by taking long-term frequent observations.
Our four-year spectroscopic observations indicate that the V/R ratio, i.e., the
relative intensity of the violet (V) peak to the red (R) one, of the
double-peaked H-alpha line profile varies with a period of 500 days. The H-beta
line profile also varies in phase with the H-alpha profile. With these
observations covering two full cycles of the V/R variability, we reconstruct
the 2-D structure of the Be disc by applying the Doppler tomography method to
the H-alpha and H-beta emission line profiles, using a rigidly rotating frame
with the V/R variability period. The resulting disc structure reveals
non-axisymmetric features, which can be explained by a one-armed perturbation
in the Be disc. It is the first time that an eccentric disc structure is
directly detected by using a method other than the interferometric one.Comment: (10 pages, 9 figures, accepted to MNRAS
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