2,425 research outputs found
On small time asymptotics for rough differential equations driven by fractional Brownian motions
We survey existing results concerning the study in small times of the density
of the solution of a rough differential equation driven by fractional Brownian
motions. We also slightly improve existing results and discuss some possible
applications to mathematical finance.Comment: This is a survey paper, submitted to proceedings in the memory of
Peter Laurenc
Sn-modification of Pt7/alumina model catalysts: Suppression of carbon deposition and enhanced thermal stability.
An atomic layer deposition process is used to modify size-selected Pt7/alumina model catalysts by Sn addition, both before and after Pt7 cluster deposition. Surface science methods are used to probe the effects of Sn-modification on the electronic properties, reactivity, and morphology of the clusters. Sn addition, either before or after cluster deposition, is found to strongly affect the binding properties of a model alkene, ethylene, changing the number and type of binding sites, and suppressing decomposition leading to carbon deposition and poisoning of the catalyst. Density functional theory on a model system, Pt4Sn3/alumina, shows that the Sn and Pt atoms are mixed, forming alloy clusters with substantial electron transfer from Sn to Pt. The presence of Sn also makes all the thermally accessible structures closed shell, such that ethylene binds only by Ï-bonding to a single Pt atom. The Sn-modified catalysts are quite stable in repeated ethylene temperature programmed reaction experiments, suggesting that the presence of Sn also reduces the tendency of the sub-nano-clusters to undergo thermal sintering
A reevaluation of achromatic spatio-temporal vision: nonoriented filters are monocular, they adapt, and can be used for decision making at high flicker speeds
Masking, adaptation, and summation paradigms have been used to investigate the characteristics of early spatio-temporal vision. Each has been taken to provide evidence for (i) oriented and (ii) nonoriented spatial-filtering mechanisms. However, subsequent findings suggest that the evidence for nonoriented mechanisms has been misinterpreted: those experiments might have revealed the characteristics of suppression (eg, gain control), not excitation, or merely the isotropic subunits of the oriented detecting mechanisms. To shed light on this, we used all three paradigms to focus on the âhigh-speedâ corner of spatio-temporal vision (low spatial frequency, high temporal frequency), where cross-oriented achromatic effects are greatest. We used flickering Gabor patches as targets and a 2IFC procedure for monocular, binocular, and dichoptic stimulus presentations. To account for our results, we devised a simple model involving an isotropic monocular filter-stage feeding orientation-tuned binocular filters. Both filter stages are adaptable, and their outputs are available to the decision stage following nonlinear contrast transduction. However, the monocular isotropic filters (i) adapt only to high-speed stimuliâconsistent with a magnocellular subcortical substrateâand (ii) benefit decision making only for high-speed stimuli (ie, isotropic monocular outputs are available only for high-speed stimuli). According to this model, the visual processes revealed by masking, adaptation, and summation are related but not identical
Aerosol optical properties during INDOEX based on measured aerosol particle size and composition
The light scattering and light absorption as a function of wavelength and relative humidity due to aerosols measured at the Kaashidhoo Climate Observatory in the Republic of the Maldives during the INDOEX field campaign has been calculated. Using size-segregated measurements of aerosol chemical composition, calculated light scattering and absorption has been evaluated against measurements of light scattering and absorption. Light scattering coefficients are predicted to within a few percent over relative humidities of 20â90%. Single scattering albedos calculated from the measured elemental carbon size distributions and concentrations in conjunction with other aerosol species have a relative error of 4.0% when compared to measured values. The single scattering albedo for the aerosols measured during INDOEX is both predicted and observed to be about 0.86 at an ambient relative humidity of 80%. These results demonstrate that the light scattering, light absorption, and hence climate forcing due to aerosols over the Indian Ocean are consistent with the chemical and physical properties of the aerosol at that location
Different genome stability proteins underpin primed and naĂŻve adaptation in E. coli CRISPR-Cas immunity
CRISPR-Cas is a prokaryotic immune system built from capture and integration of invader DNA into CRISPR (Clustered Regularly Interspaced Short Palindromic Repeats) loci, termed âAdaptationâ, which is dependent on Cas1 and Cas2 proteins. In Escherichia coli, Cascade-Cas3 degrades invader DNA to effect immunity, termed âInterferenceâ. Adaptation can interact with interference (âprimedâ), or is independent of it (ânaĂŻveâ). We demonstrate that primed adaptation requires the RecG helicase and PriA protein to be present. Genetic analysis of mutant phenotypes suggests that RecG is needed to dissipate R-loops at blocked replication forks. Additionally, we identify that DNA polymerase I is important for both primed and naive adaptation, and that RecB is needed for naĂŻve adaptation. Purified Cas1-Cas2 protein shows specificity for binding to and nicking forked DNA within single strand gaps, and collapsing forks into DNA duplexes. The data suggest that different genome stability systems interact with primed or naĂŻve adaptation when responding to blocked or collapsed invader DNA replication. In this model, RecG and Cas3 proteins respond to invader DNA replication forks that are blocked by Cascade interference, enabling DNA capture. RecBCD targets DNA ends at collapsed forks, enabling DNA capture without interference. DNA polymerase I is proposed to fill DNA gaps during spacer integration
A Multi-Code Analysis Toolkit for Astrophysical Simulation Data
The analysis of complex multiphysics astrophysical simulations presents a
unique and rapidly growing set of challenges: reproducibility, parallelization,
and vast increases in data size and complexity chief among them. In order to
meet these challenges, and in order to open up new avenues for collaboration
between users of multiple simulation platforms, we present yt (available at
http://yt.enzotools.org/), an open source, community-developed astrophysical
analysis and visualization toolkit. Analysis and visualization with yt are
oriented around physically relevant quantities rather than quantities native to
astrophysical simulation codes. While originally designed for handling Enzo's
structure adaptive mesh refinement (AMR) data, yt has been extended to work
with several different simulation methods and simulation codes including Orion,
RAMSES, and FLASH. We report on its methods for reading, handling, and
visualizing data, including projections, multivariate volume rendering,
multi-dimensional histograms, halo finding, light cone generation and
topologically-connected isocontour identification. Furthermore, we discuss the
underlying algorithms yt uses for processing and visualizing data, and its
mechanisms for parallelization of analysis tasks.Comment: 18 pages, 6 figures, emulateapj format. Resubmitted to Astrophysical
Journal Supplement Series with revisions from referee. yt can be found at
http://yt.enzotools.org
Brief of Amici Curiae Professors Ronald A. Cass, David F. Forte, James L. Huffman, Donald J. Kochan, Jesse J. Richardson and Reed Watson in Support of Petitioners
The Court of Federal Claims ruled that the Klamath, Yurok and Hoopa (hereafter Tribes) reserved water rights in the Klamath River Basin are of a volume at least equal to the amount of water the Environmental Protection Agency has determined to be necessary to trigger endangered species protection. In the absence of an adjudication in state or federal court and contrary to the long history of federal deference (both by Congressional enactment and judicial precedent) to state adjudication of water rights, the Federal Circuit affirmed and thus preempted, without the participation of affected parties including petitioners, the State of Oregonâs ongoing adjudication of Klamath Basin water rights.
Independent of the 5th Amendment takings issue at the root of this case, the Federal Circuitâs decision raises serious federalism issues that this Court should address. Few matters are of more importance to western states like Oregon than the allocation of scarce water resources. For a century and a half this Court and Congress have mandated federal court deference to the statesâ administration and adjudication of water rights. Deference is particularly important to the wise administration of this scarce resource where there is an ongoing state court adjudication and where no federal interest will be compromised. As with asserting any reserved rights claims of its own, the federal government has every opportunity to exercise its role as trustee for the Tribes in the state court adjudication
Hypernovae/GRB in the Galactic Center as possible sources of Galactic Positrons
The observation of a strong and extended positron-electron line annihilation
emission in the central regions of the Galaxy by INTEGRAL-SPI, consistent with
the Galactic bulge geometry, without any counterpart in the gamma-ray range,
neither at high energy nor in the 1809 keV Al decay line, is
challenging. Leaving aside the geometrical question, we address the problem of
the adequate positron sources, showing the potentiality of a new category of SN
Ic, exemplified by SN2003dh, which is associated to a gamma-ray burst. This
kind of supernova/hypernova/GRB event is interpreted as the result of a bipolar
Wolf-Rayet explosion, which produces a large amount of Ni and ejects it
at high velocity along the rotation axis. The bulk of positrons resulting from
Co decay escapes in the surrounding medium due to the rapid thinning of
the ejecta in the polar direction. We show that a rate of about 0.02
SN2003dh-like events per century in the central region of the Galaxy is
sufficient to explain the positron flux detected by INTEGRAL-SPI. In order to
explain this flux by SN Ia events alone, a rate of 0.5 per century is
necessary, much higher than indicated by Galactic evolutionary models applied
to the bulge. Further observations of late light curves of SNe Ia and SNe Ic in
the bulge of spiral galaxies, together with 3D hydrodynamic calculations of
anisotropic ejections of Ni in SN Ic/GRB events, will allow to estimate
the separate contributions of SNe Ia and SNe Ic to positron injection.Comment: 7 pages, 0 figures, accepted for publication in Astrophysical Journal
Letters, 2003 12 0
Kinetics of submicron oleic acid aerosols with ozone: A novel aerosol mass spectrometric technique
The reaction kinetics of submicron oleic (9-octadecanoic (Z)-) acid aerosols with ozone was studied using a novel aerosol mass spectrometric technique. In the apparatus a flow of size-selected aerosols is introduced into a flow reactor where the particles are exposed to a known density of ozone for a controlled period of time. The aerosol flow is then directed into an aerosol mass spectrometer for particle size and composition analyses. Data from these studies were used to: (a) quantitatively model the size-dependent kinetics process, (b) determine the aerosol size change due to uptake of ozone, (c) assess reaction stoichiometry, and (d) obtain qualitative information about the volatility of the reaction products. The reactive uptake probability for ozone on oleic acid particles obtained from modeling is 1.6 (±0.2) Ă 10^(â3) with an upper limit for the reacto-diffusive length of âŒ10 nm. Atmospheric implications of the results are discussed
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