2,624 research outputs found
Composite fermions close to the one-half filling of the lowest Landau level revisited
By strictly adhering to the microscopic theory of composite fermions for the
Landau-level filling fractions nu_e = p/(2 p + 1), we reproduce, with
remarkable accuracy, the surface-acoustic-wave (SAW)-based experimental results
by Willett and co-workers concerning two-dimensional electron systems with nu_e
close to 1/2. Our results imply that the electron band mass m_b, as distinct
from the composite fermion mass m_*, must undergo a substantial increase under
the conditions corresponding to nu_e approximately equal to 1/2. In view of the
relatively low aerial electronic densities n_e to which the underlying SAW
experiments correspond, our finding conforms with the experimental results by
Shashkin et al. [Phys. Rev. B 66, 073303 (2002)], concerning two-dimensional
electrons in silicon, that signal sharp increase in m_b for n_e decreasing
below approximately 2 x 10^{11} cm^{-2}. We further establish that a finite
mean-free path l_0 is essential for the observed linearity of the longitudinal
conductivity sigma_{xx}(q) as deduced from the SAW velocity shifts.Comment: 5 pages, 2 postscript figure
Cumulant expansions for atmospheric flows
The equations governing atmospheric flows are nonlinear. Consequently, the
hierarchy of cumulant equations is not closed. But because atmospheric flows
are inhomogeneous and anisotropic, the nonlinearity may manifest itself only
weakly through interactions of mean fields with disturbances such as thermals
or eddies. In such situations, truncations of the hierarchy of cumulant
equations hold promise as a closure strategy.
We review how truncations at second order can be used to model and elucidate
the dynamics of atmospheric flows. Two examples are considered. First, we study
the growth of a dry convective boundary layer, which is heated from below,
leading to turbulent upward energy transport and growth of the boundary layer.
We demonstrate that a quasilinear truncation of the equations of motion, in
which interactions of disturbances among each other are neglected but
interactions with mean fields are taken into account, can capture the growth of
the convective boundary layer even if it does not capture important turbulent
transport terms. Second, we study the evolution of two-dimensional large-scale
waves representing waves in Earth's upper atmosphere. We demonstrate that a
cumulant expansion truncated at second order (CE2) can capture the evolution of
such waves and their nonlinear interaction with the mean flow in some
circumstances, for example, when the wave amplitude is small enough or the
planetary rotation rate is large enough. However, CE2 fails to capture the flow
evolution when nonlinear eddy--eddy interactions in surf zones become
important. Higher-order closures can capture these missing interactions.
The results point to new ways in which the dynamics of turbulent boundary
layers may be represented in climate models, and they illustrate different
classes of nonlinear processes that can control wave dissipation and momentum
fluxes in the troposphere.Comment: 43 pages, 10 figures, accepted for publication in the New Journal of
Physic
Effect of storage temperature and storage duration on biodiesel properties and characteristics
Biodiesel based on vegetable oils offer the advantage being a sustainable and environmentally attractive alternative to conventional petroleum based fuel. Biodiesel is produced from any fat or oil such as soybean oil, through a refinery process called transesterification. The key issue in using vegetable oil-based fuels is oxidation stability, stoichiometric point, bio-fuel composition, antioxidants on the degradation and much oxygen with comparing to diesel gas oil. Biodiesel can be used as a pure fuel or blended with petroleum in any percentage but the standard storage and handling procedures used for biodiesel are the main issue due to the biodiesel fuel specifications. In the quest for fulfill the industry specifications standard; the fuel should be stored in a clean, dry and dark environment. In this research, three different storage temperature were study which are; low (0 – 5 °C), ambient, and high (40 – 50 °C). The key parameters that are required to store biodiesel are discussed, and the recent research advances are noted. Five types of biodiesel after storage all the samples for 2016 hours were tested plus with two product of combustion. Images analysis for combustion process was used to image appearances analysis. Under 2016 hours of storage duration, the effect of degradation was happen although the effect is not significance because the changes are still in acceptable ranges
Energetic Quantum Limit in Large-Scale Interferometers
For each optical topology of an interferometric gravitational wave detector,
quantum mechanics dictates a minimum optical power (the ``energetic quantum
limit'') to achieve a given sensitivity. For standard topologies, when one
seeks to beat the standard quantum limit by a substantial factor, the energetic
quantum limit becomes impossibly large. Intracavity readout schemes may do so
with manageable optical powers.Comment: Revised version; to be published in Proceedings of the 1999 Edoardo
Amaldi Conference on Gravitational Waves; 11 pages including figures;
manuscript is RevTex; figures are .eps; an AIP style file is include
RNA aptamers generated against oligomeric Abeta40 recognize common amyloid aptatopes with low specificity but high sensitivity.
Aptamers are useful molecular recognition tools in research, diagnostics, and therapy. Despite promising results in other fields, aptamer use has remained scarce in amyloid research, including Alzheimer's disease (AD). AD is a progressive neurodegenerative disease believed to be caused by neurotoxic amyloid beta-protein (Abeta) oligomers. Abeta oligomers therefore are an attractive target for development of diagnostic and therapeutic reagents. We used covalently-stabilized oligomers of the 40-residue form of Abeta (Abeta40) for aptamer selection. Despite gradually increasing the stringency of selection conditions, the selected aptamers did not recognize Abeta40 oligomers but reacted with fibrils of Abeta40, Abeta42, and several other amyloidogenic proteins. Aptamer reactivity with amyloid fibrils showed some degree of protein-sequence dependency. Significant fibril binding also was found for the naĂŻve library and could not be eliminated by counter-selection using Abeta40 fibrils, suggesting that aptamer binding to amyloid fibrils was RNA-sequence-independent. Aptamer binding depended on fibrillogenesis and showed a lag phase. Interestingly, aptamers detected fibril formation with > or =15-fold higher sensitivity than thioflavin T (ThT), revealing substantial beta-sheet and fibril formation undetected by ThT. The data suggest that under physiologic conditions, aptamers for oligomeric forms of amyloidogenic proteins cannot be selected due to high, non-specific affinity of oligonucleotides for amyloid fibrils. Nevertheless, the high sensitivity, whereby aptamers detect beta-sheet formation, suggests that they can serve as superior amyloid recognition tools
Inelastic light scattering from a Mott insulator
We propose to use Bragg spectroscopy to measure the excitation spectrum of
the Mott insulator state of an atomic Bose gas in an optical lattice. We
calculate the structure factor of the Mott insulator taking into account both
the selfenergy corrections of the atoms and the corresponding dressing of the
atom-photon interaction. We determine the scattering rate of photons in the
stimulated Raman transition and show that by measuring this scattering rate in
an experiment, in particular the excitation gap of the Mott insulator can be
determined.Comment: 4 pages, 7 figures, LaTeX, submitted to PR
Continuous bioprocessing: the real thing this time? 10(th) Annual bioProcessUK Conference, December 3-4, 2013, London, UK.
The Annual bioProcessUK Conference has acted as the key networking event for bioprocess scientists and engineers in the UK for the past 10 years. The following article is a report from the sessions that focused on continuous bioprocessing during the 10(th) Annual bioProcessUK Conference (London, December 2013). These sessions were organized by the 'EPSRC Centre for Innovative Manufacturing in Emergent Macromolecular Therapies' hosted at University College London. A plenary lecture and workshop provided a forum for participants to debate topical issues in roundtable discussions with industry and academic experts from institutions such as Genzyme, Janssen, Novo Nordisk, Pfizer, Merck, GE Healthcare and University College London. The aim of these particular sessions was to understand better the challenges and opportunities for continuous bioprocessing in the bioprocessing sector
Bootstrapping the empirical distribution of a stationary process with change-point
© 2019, Institute of Mathematical Statistics. All rights reserved. When detecting a change-point in the marginal distribution of a stationary time series, bootstrap techniques are required to determine critical values for the tests when the pre-change distribution is unknown. In this paper, we propose a sequential moving block bootstrap and demonstrate its validity under a converging alternative. Furthermore, we demonstrate that power is still achieved by the bootstrap under a non-converging alternative. We follow the approach taken by Peligrad in [14], and avoid assumptions of mixing, association or near epoch dependence. These results are applied to a linear process and are shown to be valid under very mild conditions on the existence of any moment of the innovations and a corresponding condition of summability of the coefficients
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