3,425 research outputs found
Quasi Periodic Oscillations (QPOs) and frequencies in an accretion disk and comparison with the numerical results from non-rotating black hole computed by the GRH code
The shocked wave created on the accretion disk after different physical
phenomena (accretion flows with pressure gradients, star-disk interaction etc.)
may be responsible observed Quasi Periodic Oscillations (QPOs) in ray
binaries. We present the set of characteristics frequencies associated with
accretion disk around the rotating and non-rotating black holes for one
particle case. These persistent frequencies are results of the rotating pattern
in an accretion disk. We compare the frequency's from two different numerical
results for fluid flow around the non-rotating black hole with one particle
case. The numerical results are taken from our papers Refs.\refcite{Donmez2}
and \refcite{Donmez3} using fully general relativistic hydrodynamical code with
non-selfgravitating disk. While the first numerical result has a relativistic
tori around the black hole, the second one includes one-armed spiral shock wave
produced from star-disk interaction. Some physical modes presented in the QPOs
can be excited in numerical simulation of relativistic tori and spiral waves on
the accretion disk. The results of these different dynamical structures on the
accretion disk responsible for QPOs are discussed in detail.Comment: 13 figures, added reference, accepted for publication in Modern
Physics Letters
Aging of poled ferroelectric ceramics due to relaxation of random depolarization fields by space-charge accumulation near grain boundaries
Migration of charged point defects triggered by the local random
depolarization field is shown to plausibly explain aging of poled ferroelectric
ceramics providing reasonable time and acceptor concentration dependences of
the emerging internal bias field. The theory is based on the evaluation of the
energy of the local depolarization field caused by mismatch of the
polarizations of neighbor grains. The kinetics of charge migration assumes
presence of mobile oxygen vacancies in the material due to the intentional or
unintentional acceptor doping. Satisfactory agreement of the theory with
experiment on the Fe-doped lead zirconate titanate is demonstrated.Comment: theory and experiment, 22 pages, 3 figure
Analysis of Biomass Pyrolysis Product Yield Distribution in Thermally Thin Regime at Different Heating Rates
A better understanding of biomass pyrolysis process at various thermal regimes is fundamental to the optimization of biomass thermochemical conversion processes. In this research work, the behaviour of biomass pyrolysis in thermally thin regime was numerically investigated at different heating rates (1, 5, 10 and 20 K/s). A kinetic model, consisting of five ordinary differential equations, was used to simulate the pyrolysis process. The model equations were coupled and simultaneously solved by using fourth-order Runge-Kutta method. The concentrations of the biomass sample (Maple wood) and product species per time were simulated. Findings revealed that tar yield increased with increase in heating rate. Char yield, however, decreased with increase in heating rate. Results also showed that the extent of secondary reactions, which influenced gas yield concentration, is a function of residence time and temperature. This model can be adopted for any biomass material when the kinetic parameters of the material are known. Keywords: Biomass, pyrolysis, kinetic model, thermally thin regim
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
Evolution of superconductivity in LaO1-xFxBiS2 prepared by high pressure technique
Novel BiS2-based superconductors LaO1-xFxBiS2 prepared by the high pressure
synthesis technique were systematically studied. It was found that the high
pressure annealing strongly the lattice as compared to the LaO1-xFxBiS2 samples
prepared by conventional solid state reaction at ambient pressure. Bulk
superconductivity was observed within a wide F-concentration range of x = 0.2 ~
0.7. On the basis of those results, we have established a phase diagram of
LaO1-xFxBiS2.Comment: 11 pages, 6 figure
Relativistic Diskoseismology. I. Analytical Results for 'Gravity Modes'
We generalize previous calculations to a fully relativistic treatment of
adiabatic oscillations which are trapped in the inner regions of accretion
disks by non-Newtonian gravitational effects of a black hole. We employ the
Kerr geometry within the scalar potential formalism of Ipser and Lindblom,
neglecting the gravitational field of the disk. This approach treats
perturbations of arbitrary stationary, axisymmetric, perfect fluid models. It
is applied here to thin accretion disks. Approximate analytic eigenfunctions
and eigenfrequencies are obtained for the most robust and observable class of
modes, which corresponds roughly to the gravity (internal) oscillations of
stars. The dependence of the oscillation frequencies on the mass and angular
momentum of the black hole is exhibited. These trapped modes do not exist in
Newtonian gravity, and thus provide a signature and probe of the strong-field
structure of black holes. Our predictions are relevant to observations which
could detect modulation of the X-ray luminosity from stellar mass black holes
in our galaxy and the UV and optical luminosity from supermassive black holes
in active galactic nuclei.Comment: 31 pages, 6 figures, uses style file aaspp4.sty, prepared with the
AAS LATEX macros v4.0, significant revision of earlier submission to include
modes with axial index m>
Controllable chirality-induced geometrical Hall effect in a frustrated highly-correlated metal
A current of electrons traversing a landscape of localized spins possessing
non-coplanar magnetic order gains a geometrical (Berry) phase which can lead to
a Hall voltage independent of the spin-orbit coupling within the material--a
geometrical Hall effect. We show that the highly-correlated metal UCu5
possesses an unusually large controllable geometrical Hall effect at T<1.2K due
to its frustration-induced magnetic order. The magnitude of the Hall response
exceeds 20% of the \nu=1 quantum Hall effect per atomic layer, which translates
into an effective magnetic field of several hundred Tesla acting on the
electrons. The existence of such a large geometric Hall response in UCu5 opens
a new field of inquiry into the importance of the role of frustration in
highly-correlated electron materials.Comment: article and supplemental informatio
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