3,432 research outputs found
Multi-wavelength observations of the gamma-ray flaring quasar S4 1030+61 in 2009-2014
We present a study of the parsec-scale multi-frequency properties of the
quasar S4 1030+61 during a prolonged radio and gamma-ray activity. Observations
were performed within Fermi gamma-ray telescope, OVRO 40-m telescope and MOJAVE
VLBA monitoring programs, covering five years from 2009. The data are
supplemented by four-epoch VLBA observations at 5, 8, 15, 24, and 43 GHz, which
were triggered by the bright gamma-ray flare, registered in the quasar in 2010.
The S4 1030+61 jet exhibits an apparent superluminal velocity of (6.4+-0.4)c
and does not show ejections of new components in the observed period, while
decomposition of the radio light curve reveals nine prominent flares. The
measured variability parameters of the source show values typical for
Fermi-detected quasars. Combined analysis of radio and gamma-ray emission
implies a spatial separation between emitting regions at these bands of about
12 pc and locates the gamma-ray emission within a parsec from the central
engine. We detected changes in the value and direction of the linear
polarization and the Faraday rotation measure. The value of the intrinsic
brightness temperature of the core is above the equipartition state, while its
value as a function of distance from the core is well approximated by the
power-law. Altogether these results show that the radio flaring activity of the
quasar is accompanied by injection of relativistic particles and energy losses
at the jet base, while S4 1030+61 has a stable, straight jet well described by
standard conical jet theories.Comment: accepted by MNRAS, 16 pages, 14 figures, 8 tables, 5 pages of
supplementary materia
Zero Temperature Insulator-Metal Transition in Doped Manganites
We study the transition at T=0 from a ferromagnetic insulating to a
ferromagnetic metallic phase in manganites as a function of hole doping using
an effective low-energy model Hamiltonian proposed by us recently. The model
incorporates the quantum nature of the dynamic Jahn-Teller(JT) phonons strongly
coupled to orbitally degenerate electrons as well as strong Coulomb correlation
effects and leads naturally to the coexistence of localized (JT polaronic) and
band-like electronic states. We study the insulator-metal transition as a
function of doping as well as of the correlation strength U and JT gain in
energy E_{JT}, and find, for realistic values of parameters, a ground state
phase diagram in agreement with experiments. We also discuss how several other
features of manganites as well as differences in behaviour among manganites can
be understood in terms of our model.Comment: To be published in Europhysics Letter
Crystal Symmetry Lowering in Chiral Multiferroic BaTaFeSiO observed by X-Ray Magnetic Scattering
Chiral multiferroic langasites have attracted attention due to their
doubly-chiral magnetic ground state within an enantiomorphic crystal. We report
on a detailed resonant soft X-ray diffraction study of the multiferroic
BaTaFeSiO at the Fe and oxygen edges. Below
() we observe the satellite reflections ,
, and where . The dependence of the scattering intensity on X-ray polarization and
azimuthal angle indicate that the odd harmonics are dominated by the
out-of-plane (-axis) magnetic dipole while the
originates from the electron density distortions accompanying magnetic order.
We observe dissimilar energy dependences of the diffraction intensity of the
purely magnetic odd-harmonic satellites at the Fe edge. Utilizing
first-principles calculations, we show that this is a consequence of the loss
of threefold crystal symmetry in the multiferroic phase
Magnetic Ordering and Superconductivity in the REIrGe (RE = Y, La-Tm, Lu) System
We find that the compounds for RE = Y, La-Dy, crystallize in the tetragonal
Ibam (UCoSi type) structure whereas the compounds for RE = Er-Lu,
crystallize in a new orthorhombic structure with a space group Pmmn. Samples of
HoIrGe were always found to be multiphase. The compounds for RE = Y
to Dy which adopt the Ibam type structure show a metallic resistivity whereas
the compounds with RE = Er, Tm and Lu show an anomalous behavior in the
resistivity with a semiconducting increase in as we go down in
temperature from 300K. Interestingly we had earlier found a positive
temperature coefficient of resistivity for the Yb sample in the same
temperature range. We will compare this behavior with similar observations in
the compounds RERuGe and REBiPt. LaIrGe and
YIrGe show bulk superconductivity below 1.8K and 2.5K respectively.
Our results confirm that CeIrGe shows a Kondo lattice behavior and
undergoes antiferromagnetic ordering below 8.5K. Most of the other compounds
containing magnetic rare-earth elements undergo a single antiferromagnetic
transition at low temperatures (T12K) while GdIrGe,
DyIrGe and NdIrGe show multiple transitions. The
T's for most of the compounds roughly scale with the de Gennes factor.
which suggests that the chief mechanism of interaction leading to the magnetic
ordering of the magnetic moments may be the RKKY interaction.Comment: 25 pages, 16 figure
Descriptive Complexity of Deterministic Polylogarithmic Time and Space
We propose logical characterizations of problems solvable in deterministic
polylogarithmic time (PolylogTime) and polylogarithmic space (PolylogSpace). We
introduce a novel two-sorted logic that separates the elements of the input
domain from the bit positions needed to address these elements. We prove that
the inflationary and partial fixed point vartiants of this logic capture
PolylogTime and PolylogSpace, respectively. In the course of proving that our
logic indeed captures PolylogTime on finite ordered structures, we introduce a
variant of random-access Turing machines that can access the relations and
functions of a structure directly. We investigate whether an explicit predicate
for the ordering of the domain is needed in our PolylogTime logic. Finally, we
present the open problem of finding an exact characterization of
order-invariant queries in PolylogTime.Comment: Submitted to the Journal of Computer and System Science
CFD Simulation Studies on a 19 Cone Angle Hydrocyclone
Hydrocyclone being in practice for classification applicat-ions are of low cone angle typically at 10°. The details on the simulation of such hydrocyclone are well reported. The present study is an attempt to simulate the water flow behaviour inside a 3 inch 19° cone angle hydrocyclone, which in general is applied for processing intermediate size coal and is popularly know as heavy medium cyclone. A 3D axi-symmetric model of standard 3" heavy medium cyclone geometry is generated. The computational domain
is divided into unstructured grid having 115053 tetrahe-dral volumes using GAMBIT preprocessor. A segregated solver
with steady state 3-D double precision scheme was used for model computations assigning a convergence value of 1e-06. For predicting swirling flow characteristics prevailing inside the cyclone, Pressure Interpolation Scheme (PRESTO) is used. Reynolds stress model (RSM), which was reported to account with greater precision for the effects of swirl, rotation etc. was selected for turbulence calculat-ions. For obtaining the pressure field inside the system
SIMPLE algorithm scheme was used. Higher-order Quadratic Upwind Interpolation (QUICK) spatial discretisation scheme was used for field variables interpolation from cell centers to faces of the control volumes. Tangential, axial velocity profiles and pressure distributions are pres-ented and the water-split values obtained through simula-tion are compared with the experimental results
Exploring metastability via the third harmonic measurements in single crystals of - showing anomalous Peak effect
We explore the metastability effects across the order-disorder transition
pertaining to the peak effect phenomenonon in critical current density ()
via the first and the third harmonic ac susceptibility measurements in the
weakly pinned single crystals of -. An analysis of our data
suggests that an imprint of the limiting (spinodal) temperature above which
is path independent can be conveniently located in the third harmonic
data ().Comment: Accepted for publication in Phys. Rev.
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