28,030 research outputs found
Ising films with surface defects
The influence of surface defects on the critical properties of magnetic films
is studied for Ising models with nearest-neighbour ferromagnetic couplings. The
defects include one or two adjacent lines of additional atoms and a step on the
surface. For the calculations, both density-matrix renormalization group and
Monte Carlo techniques are used. By changing the local couplings at the defects
and the film thickness, non-universal features as well as interesting crossover
phenomena in the magnetic exponents are observed.Comment: 8 pages, 12 figures included, submitted to European Physical Journal
Formation of Electronic Nematic Phase in Interacting Systems
We study the formation of an electronic nematic phase characterized by a
broken point-group symmetry in interacting fermion systems within the weak
coupling theory. As a function of interaction strength and chemical potential,
the phase transition between the isotropic Fermi liquid and nematic phase is
first order at zero temperature and becomes second order at a finite
temperature. The transition is present for all typical, including quasi-2D,
electronic dispersions on the square lattice and takes place for arbitrarily
small interaction when at van Hove filling, thus suppressing the Lifshitz
transition. In connection with the formation of the nematic phase, we discuss
the origin of the first order transition and competition with other broken
symmetry states.Comment: revtex4, 6 pages, 6 figures; revised introduction, updated reference
Ising thin films with modulations and surface defects
Properties of magnetic films are studied in the framework of Ising models. In
particular, we discuss critical phenomena of ferromagnetic Ising films with
straight lines of magnetic adatoms and straight steps on the surface as well as
phase diagrams of the axial next-nearest neighbour Ising (ANNNI) model for thin
films exhibiting various spatially modulated phases.Comment: 6 pages, 4 figures include
More is Less: Perfectly Secure Oblivious Algorithms in the Multi-Server Setting
The problem of Oblivious RAM (ORAM) has traditionally been studied in a
single-server setting, but more recently the multi-server setting has also been
considered. Yet it is still unclear whether the multi-server setting has any
inherent advantages, e.g., whether the multi-server setting can be used to
achieve stronger security goals or provably better efficiency than is possible
in the single-server case.
In this work, we construct a perfectly secure 3-server ORAM scheme that
outperforms the best known single-server scheme by a logarithmic factor. In the
process, we also show, for the first time, that there exist specific algorithms
for which multiple servers can overcome known lower bounds in the single-server
setting.Comment: 36 pages, Accepted in Asiacrypt 201
Effect of Media Strength and pH on the Growth of Hairy Roots and Production of Gymnemic Acid from Gymnema Sylvestre
Gymnema sylvestre (Madhunashini) is one of the most important medicinal plants used as a crude drug for its preventive and therapeutic properties. Among other constituents of Gymnema, gymnemic acid is a major component responsible for biological and pharmacological actions. The present study deals with the influence of different media strength and initial medium pH on the growth of hairy roots and gymnemic acid production from Gymnema sylvestre. Higher strength of the media (1.5X) favoured the biomass production (114.64 g/L FW and 12.63 g/L DW) and gymnemic acid content (11.7 mg/g DW) in the tested range of 0.25, 0.50, 0.75, 1.0, 1.5 and 2.0 X strength. Among the different hydrogen ion concentration (pH) of 4.0, 4.5, 5.0, 5.5, 5.8, 6.0 and 6.5, initial medium pH of 6.0 favoured the biomass production (102.41 g/L FW and 11.52 g/L DW) and medium pH of 5.8 favoured the gymnemic acid production (11.30 mg/g DW)
Small x Behavior of Parton Distributions from the Observed Froissart Energy Dependence of the Deep Inelastic Scattering Cross Section
We fit the reduced cross section for deep-inelastic electron scattering data
to a three parameter ln^2 s fit, A + beta ln^2 (s/s_0), where s= [Q^2/x] (1-x)
+ m^2, and Q^2 is the virtuality of the exchanged photon. Over a wide range in
Q^2 (0.11 < Q^2 < 1200 GeV^2) all of the fits satisfy the logarithmic energy
dependence of the Froissart bound. We can use these results to extrapolate to
very large energies and hence to very small values of Bjorken x -- well beyond
the range accessible experimentally. As Q^2 --> infinity, the structure
function F_2^p(x, Q^2) exhibits Bjorken scaling, within experimental errors. We
obtain new constraints on the behavior of quark and antiquark distribution
functions at small x.Comment: 10 pages, 2 figure
Analytic Expression for the Joint x and Q^2 Dependences of the Structure Functions of Deep Inelastic Scattering
We obtain a good analytic fit to the joint Bjorken-x and Q^2 dependences of
ZEUS data on the deep inelastic structure function F_2(x, Q^2). At fixed
virtuality Q^2, as we showed previously, our expression is an expansion in
powers of log (1/x) that satisfies the Froissart bound. Here we show that for
each x, the Q^2 dependence of the data is well described by an expansion in
powers of log Q^2. The resulting analytic expression allows us to predict the
logarithmic derivatives {({\partial}^n F_2^p/{{(\partial\ln Q^2}})^n)}_x for n
= 1,2 and to compare the results successfully with other data. We extrapolate
the proton structure function F_2^p(x,Q^2) to the very large Q^2 and the very
small x regions that are inaccessible to present day experiments and contrast
our expectations with those of conventional global fits of parton distribution
functions.Comment: 4 pages, 3 figures, a few changes in the text. Version to be
published in Physical Review Letter
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