4,985 research outputs found
Preparation and Characterization of Nanostructured CaCu2.90 Zn0.10 Ti4O12 Ceramic
Nanostructure CaCu2.90Zn0.10Ti4O12 (CCZTO)
electronic ceramic was synthesized by semi‐wet route.
The objective of this route is to enable the calcination and
sintering processes to go for completion in shorter time
and at lower temperature.The samples were
characterized by XRD, TEM, SEM and EDX analyses. The
crystallite size of the CCZTO ceramic, obtained by XRD
using Debye Scherrer formula, range from 38‐74nm
which is in good agreement with the particle size observed
by TEM analysis. It was observed clearly that the grain size
significantly increased with an increase in sintering
duration. Dielectric measurements were carried out by
LCR meter in the temperature range, 300‐ 500K, at few
selected frequencies. It was also observed that the dielectric
constant and dielectric loss of CCZTO are temperature
independent in higher frequency whereas temperature
dependent in low frequency region. The ceramics exhibit
high dielectric constant of 1.35 x 10
4
at 1 kHz
Scaling of NonOhmic Conduction in Strongly Correlated Systems
A new scaling formalism is used to analyze nonlinear I-V data in the vicinity
of metal-insulator transitions (MIT) in five manganite systems. An exponent,
called the nonlinearity exponent, and an onset field for nonlinearity, both
characteristic of the system under study, are obtained from the analysis. The
onset field is found to have an anomalously low value corroborating the
theoretically predicted electronically soft phases. The scaling functions above
and below the MIT of a polycrystalline sample are found to be the same but with
different exponents which are attributed to the distribution of the MIT
temperatures. The applicability of the scaling in manganites underlines the
universal response of the disordered systems to electric field
Study of Low Energy Spin Rotons in the Fractional Quantum Hall Effect
Motivated by the discovery of extremely low energy collective modes in the
fractional quantum Hall effect (Kang, Pinczuk {\em et al.}), with energies
below the Zeeman energy, we study theoretically the spin reversed excitations
for fractional quantum Hall states at and 3/7 and find qualitatively
different behavior than for . We find that a low-energy,
charge-neutral "spin roton," associated with spin reversed excitations that
involve a change in the composite-fermion Landau level index, has energy in
reasonable agreement with experiment.Comment: Postscript figures included. Accepted in Phys. Rev. B (Rapid
Communication
Broadband X-ray properties of black holes GRS 1758-258 and 1E 1740.7-2942: AstroSat and NuSTAR results
We present the results on broadband X-ray properties of persistent black hole
binaries GRS 1758258 and 1E 1740.72942 using AstroSat, NuSTAR and
Swift-XRT observations carried out during 20162022. We perform spectral
modeling of both sources after eliminating the contamination in their
\textit{LAXPC} spectra from nearby X-ray sources. Preliminary spectral
modelling using Comptonization and line emission ( 6.4 keV) models
suggest that GRS 1758258 occupies both dim-soft state (
keV, , of Eddington luminosity L) and hard
state (, =445 keV, =15 % L)
that requires a multi-colour disc blackbody model ( keV)
occasionally. 1E 1740.72942 instead is found only in hard state
(=1.672.32, =516 keV, =12 % L).
Reflection properties of both sources are studied by applying relativistic
reflection model RELXILL to the broadband spectra. Our results from
\textit{AstroSat} and \textit{NuSTAR} consistently unveiled the presence of a
Comptonizing region along with an ionized reflection region (ionization
parameter =2.73.8 and 2.74.7 erg cm s in GRS 1758258
and 1E 1740.72942 respectively) in both sources. Reflection modeling
revealed GRS 1758258 to have a high metal abundance
( times solar metal abundance) and inclination angle
() of . In case of 1E 1740.72942, is constrained to
be . Finally, we discuss the implication of our findings in the
context of accretion dynamics by comparing our results with the previous
studies.Comment: Accepted for publication in MNRA
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
Orbiting Membranes in M-theory on AdS_7 x S^4 Background
We study classical solutions describing rotating and boosted membranes on
AdS_7 x S^4 background in M-theory. We find the dependence of the energy on the
spin and R-charge of these solutions. In the flat space limit we get E ~
S^{2/3}, while for AdS at leading order E-S grows as S^{1/3}. The membranes on
AdS_4 x S^7 background have briefly been studied as well.Comment: 13 pages, latex, v2: a note and refs. added, some typos correcte
Nonlinear DC-response in Composites: a Percolative Study
The DC-response, namely the - and - charateristics, of a variety
of composite materials are in general found to be nonlinear. We attempt to
understand the generic nature of the response charactersistics and study the
peculiarities associated with them. Our approach is based on a simple and
minimal model bond percolative network. We do simulate the resistor network
with appropritate linear and nonlinear bonds and obtain macroscopic nonlinear
response characteristics. We discuss the associated physics. An effective
medium approximation (EMA) of the corresponding resistor network is also given.Comment: Text written in RevTEX, 15 pages (20 postscript figures included),
submitted to Phys. Rev. E. Some minor corrections made in the text, corrected
one reference, the format changed (from 32 pages preprint to 15 pages
Classical integrability of Schrodinger sigma models and q-deformed Poincare symmetry
We discuss classical integrable structure of two-dimensional sigma models
which have three-dimensional Schrodinger spacetimes as target spaces. The
Schrodinger spacetimes are regarded as null-like deformations of AdS_3. The
original AdS_3 isometry SL(2,R)_L x SL(2,R)_R is broken to SL(2,R)_L x U(1)_R
due to the deformation. According to this symmetry, there are two descriptions
to describe the classical dynamics of the system, 1) the SL(2,R)_L description
and 2) the enhanced U(1)_R description. In the former 1), we show that the
Yangian symmetry is realized by improving the SL(2,R)_L Noether current. Then a
Lax pair is constructed with the improved current and the classical
integrability is shown by deriving the r/s-matrix algebra. In the latter 2), we
find a non-local current by using a scaling limit of warped AdS_3 and that it
enhances U(1)_R to a q-deformed Poincare algebra. Then another Lax pair is
presented and the corresponding r/s-matrices are also computed. The two
descriptions are equivalent via a non-local map.Comment: 20 pages, no figure, further clarification and references adde
Orange IV stabilizes silk fibroin microemulsions
Silk fibroin (SF) is a natural biopolymer that has been extensively studied in various applications due to its impressive mechanical properties and biocompatibility. Recently, SF-based particles have been proposed as controlled drug delivery systems. A new and efficient method to prepare SF microemulsions (SF-MEs) was developed by oil-in-water emulsions using high-pressure homogenization to promote emulsification. During SF-ME production, the secondary structure of SF changed to a more stable conformation (from random coil to -sheets), thus allowing the formation of small and stable (140.7 ± 1.9 nm; polydispersity index, 0.25) SF microparticles (SF-MPs). The efficiency of SF-MP formation was 60%. Orange IV was used as a model compound for incorporation and release studies, although its incorporation into the SF-MEs significantly improved particle size and size distribution over at least 4 wk compared to traditional stabilizers (e.g., poloxamer 407, transcutol, Tween 80, and SDS). This should be a call of attention when using dyes as model compounds since they can influence particle properties and lead to misinterpretation of the results. Orange IV showed an incorporation efficiency of 91% and a controlled release over time. Stable SF-MP formulations, further enhanced by orange IV incorporation, provide an innovative method with potential application in pharmaceutical development due to its associated high biocompatibility and release profile.The authors thank the FCT Strategic Project PEst-OE/EQB/LA0023/2013 and the project "BioHealth - Biotechnology and Bioengineering Approaches to Improve Health Quality," Ref. NORTE-07-0124-FEDER-000027, cofunded by the Programa Operacional Regional do Norte (ON.2 - O Novo Norte), QREN, FEDER. We would also like to acknowledge CRA - Unita di Ricerca di Apicoltura and Bachicoltura Padova (Italy) for the supply of B. mori silkworm cocoons, and Andreia Vasconcelos for technical support
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