10,573 research outputs found
Study of the long-term evolution of the accretion dynamics of GX 339-4
We study the dynamical behaviour of the galactic black hole source GX 339-4
during 2002-2011 outbursts using RXTE, Swift(XRT), XMM-Newton(PN) archival
data. We present the spectral evolution of the source using four outbursts data
and discuss their similarities/differences between outbursts. We infer that the
second peak in 2002/03 and 2004/05 outbursts can be due to a second instant of
triggered instability in the accretion disc due to irradiation from the central
X-ray source after peak-I. This propagates in viscous time scale and takes
~80-90 days after peak-I to produce peak-II. This unifies all four outbursts
having a long rising time of ~90 days. The dynamical evolution of accretion
parameters have been studied by modeling the individual observed spectrum with
two-component accretion disc model where a Keplerian accretion disc produces
the soft photons and the hard part of the spectrum originates from a hot
sub-Keplerian central corona. A generic mathematical model has been proposed to
understand the evolution of accretion parameters for sources like GX 339-4
which have longer rising time. Also, the possible differences of physical
scenario for outbursts with shorter rising time are also discussed.Comment: Accepted for publication in mnra
Anti-chiral edge states in an exciton polariton strip
We present a scheme to obtain anti-chiral edge states in an exciton-polariton
honeycomb lattice with strip geometry, where the modes corresponding to both
edges propagate in the same direction. Under resonant pumping the effect of a
polariton condensate with nonzero velocity in one linear polarization is
predicted to tilt the dispersion of polaritons in the other, which results in
an energy shift between two Dirac cones and the otherwise flat edge states
become tilted. Our simulations show that due to the spatial separation from the
bulk modes the edge modes are robust against disorder.Comment: 6 pages, 5 figure
RVB gauge theory and the Topological degeneracy in the Honeycomb Kitaev model
We relate the Z gauge theory formalism of the Kitaev model to the SU(2)
gauge theory of the resonating valence bond (RVB) physics. Further, we
reformulate a known Jordan-Wigner transformation of Kitaev model on a torus in
a general way that shows that it can be thought of as a Z gauge fixing
procedure. The conserved quantities simplify in terms of the gauge invariant
Jordan-Wigner fermions, enabling us to construct exact eigen states and
calculate physical quantities. We calculate the fermionic spectrum for flux
free sector for different gauge field configurations and show that the ground
state is four-fold degenerate on a torus in thermodynamic limit. Further on a
torus we construct four mutually anti-commuting operators which enable us to
prove that all eigenstates of this model are four fold degenerate in
thermodynamic limit.Comment: 12 pages, 3 figures. Added affiliation and a new section,
'Acknowledgements'.Typos correcte
Chemical mechanical polishing of thin film diamond
The demonstration that Nanocrystalline Diamond (NCD) can retain the superior
Young's modulus (1,100 GPa) of single crystal diamond twinned with its ability
to be grown at low temperatures (<450 {\deg}C) has driven a revival into the
growth and applications of NCD thin films. However, owing to the competitive
growth of crystals the resulting film has a roughness that evolves with film
thickness, preventing NCD films from reaching their full potential in devices
where a smooth film is required. To reduce this roughness, films have been
polished using Chemical Mechanical Polishing (CMP). A Logitech Tribo CMP tool
equipped with a polyurethane/polyester polishing cloth and an alkaline
colloidal silica polishing fluid has been used to polish NCD films. The
resulting films have been characterised with Atomic Force Microscopy, Scanning
Electron Microscopy and X-ray Photoelectron Spectroscopy. Root mean square
roughness values have been reduced from 18.3 nm to 1.7 nm over 25 {\mu}m,
with roughness values as low as 0.42 nm over ~ 0.25 {\mu}m. A polishing
mechanism of wet oxidation of the surface, attachment of silica particles and
subsequent shearing away of carbon has also been proposed.Comment: 6 pages, 6 figure
A Field Theory for Partially Polarized Quantum Hall States
We propose a new effective field theory for partially polarized quantum Hall
states. The density and polarization for the mean field ground states are
determined by couplings to two Chern-Simons gauge fields. In addition there is
a -model field, \mh, which is necessary both to preserve the
Chern-Simons gauge symmetry that determines the correlations in the ground
state, and the global SU(2) invariance related to spin rotations. For states
with non zero polarization, the low energy dynamics is that of a ferromagnet.
In addition to spin waves, the spectrum contains topological solitons, or
skyrmions, just as in the fully polarized case. The electric charge of the
skyrmions is given by , where is the filling
fraction, the magnitude of the polarization, and the topological
charge. For the special case of full polarization, the theory involves a single
scalar field and a single Chern-Simons field in addition to the -model
field, \mh. We also give a heuristic derivation of the model lagrangians for
both full and partial polarization, and show that in a mean field picture, the
field \mh is necessary in order to take into account the Berry phases
originating from rotations of the electron spins.Comment: RevTex, 9 page
Pump induced Autler-Townes effect and A-T mixing in a four level atoms
It is shown by theoretical simulation that tuning of the pump power can
induce mixing and crossing of Autler-Townes(A-T)components of closely spaced
transitions in atoms. Pump radiation also leads to small shifts of the central
hole of A-T doublet. Off-resonance pumping gives an asymmetry in the A-T
components and by controlling pump frequency detuning it is also possible to
mix the A-T components.Comment: 10 Pages, 3 figur
Seismic Design of Geosynthetic Reinforced Soil Walls
In this paper, the design geogrid/geotextile reinforced retaining walls are summarized. Design of geosynthetics reinforced walls includes internal and external stability analyses. Seismic analyses also considered for design of geosynthetics reinforced walls. Many designers do not have all of the tools required to complete all of the components of the stability analysis for site conditions. Most current geosynthetics reinforced soil retaining wall design software products do not address all of the components of the stability analysis. This paper is directed towards researchers, practitioners, and regulators, and gives guidance for future research and development of codes for reinforced soil walls
Coupled channel description of 16O+142,144,146Nd scattering around the Coulomb barrier using a complex microscopic potential
Angular distributions of elastic scattering and inelastic scattering from 2+ 1 state are measured for 16O+142,144,146Nd systems at several energies in the vicinity of the Coulomb barrier. The angular distributions are systematically analyzed in coupled channel framework. Renormalized double folded real optical and coupling potentials with DDM3Y interaction have been used in the calculation. Relevant nuclear densities needed to generate the potentials are derived from shell model wavefunctions. A truncated shell model calculation has been performed and the calculated energy levels are compared with the experimental ones. To simulate the absorption, a 'hybrid' approach is adopted. The contribution to the imaginary potential of couplings to the inelastic channels, other than the 2+ 1 target excitation channel, is calculated in the Feshbach formalism. This calculated imaginary potential along with a short ranged volume Woods-Saxon potential to simulate the absorption in fusion channel reproduces the angular distributions for 16O+146Nd quite well. But for 16O+142,144Nd systems additional surface absorption is found to be necessary to fit the angular distribution data. The variations of this additional absorption term with incident energy and the mass of the target are explored. © 2003 Elsevier Science B.V. All rights reserved
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