31,388 research outputs found
Particles from comet Kohoutek detected by the micrometeoroid experiment on HEOS 2
HEOS B measurements on particles ejected from comet Kohoutek reflect average particle rate as a function of particle speed and mass in relation to random distribution with known speed from the interplanetary region. The micrometeoroid experiment detector onboard the satellite passed through the orbital plane of the comet and encountered ejected particles for approximately two months
Flux Enhancement of Slow-moving Particles by Sun or Jupiter: Can they be Detected on Earth?
Slow-moving particles capable of interacting solely with gravity might be
detected on Earth as a result of the gravitational lensing induced focusing
action of the Sun. The deflection experienced by these particles are inversely
proportional to the square of their velocities and as a result their focal
lengths will be shorter. We investigate the velocity dispersion of these
slow-moving particles, originating from distant point-like sources, for
imposing upper and lower bounds on the velocities of such particles in order
for them to be focused onto Earth. We find that fluxes of such slow-moving and
non-interacting particles must have speeds between ~0.01 and ~0.14 times the
speed of light, . Particles with speeds less than ~0.01 c will undergo way
too much deflection to be focused, although such individual particles could be
detected. At the caustics, the magnification factor could be as high as ~10E+6.
We impose lensing constraints on the mass of these particles in order for
them to be detected with large flux enhancements to be greater than E-9 eV. An
approximate mass density profile for Jupiter is used to constrain particle
velocities for lensing by Jupiter. We show that Jupiter could potentially focus
particles with speeds as low as ~0.001c, which the Sun cannot. As a special
case, the perfect alignment of the planet Jupiter with the Sun is also
considered.Comment: 20 Pages, 5 figure
Fracture strength and Young's modulus of ZnO nanowires
The fracture strength of ZnO nanowires vertically grown on sapphire
substrates was measured in tensile and bending experiments. Nanowires with
diameters between 60 and 310 nm and a typical length of 2 um were manipulated
with an atomic force microscopy tip mounted on a nanomanipulator inside a
scanning electron microscope. The fracture strain of (7.7 +- 0.8)% measured in
the bending test was found close to the theoretical limit of 10% and revealed a
strength about twice as high as in the tensile test. From the tensile
experiments the Young's modulus could be measured to be within 30% of that of
bulk ZnO, contrary to the lower values found in literature.Comment: 5 pages, 3 figures, 1 tabl
Two-Electron Photon Emission From Metallic Quantum Wells
Unusual emission of visible light is observed in scanning tunneling
microscopy of the quantum well system Na on Cu(111). Photons are emitted at
energies exceeding the energy of the tunneling electrons. Model calculations of
two-electron processes which lead to quantum well transitions reproduce the
experimental fluorescence spectra, the quantum yield, and the power-law
variation of the intensity with the excitation current.Comment: revised version, as published; 4 pages, 3 figure
Trilingual conversations: a window into multicompetence
A recurrent theme in the literature on trilingual language use is the question of whether there is a specific “trilingual competence.” In this paper we consider this question in the light of codeswitching patterns in two dyadic trilingual conversations between a mother and daughter conducted in (Lebanese) Arabic, French, and English. Quantitative and qualitative analysis of codeswitching in both conversants shows that, despite the fact that both subjects are fluent in all three languages, uses of switching are significantly different for mother and daughter across a number of features, including relative frequency of different switch types, and the incidence of hybrid constructions involving items from two or more languages. The subjects appear to display qualitatively distinct profiles of competence in the trilingual mode. This in turn leads to the conclusion that the facts of trilingual language use are best characterized in terms of “multicompetence” (Cook, 1991). The paper concludes with some further reflections on the uniqueness of trilingual language use (an “old chestnut” in
trilingualism research, cf. Klein, 1995)
Effect of pyridoxal deficiency on biotin content of N. sitophila
Effect of pyridoxal deficiency on biotin content of N. sitophil
Social Simulation of Stock Markets: Taking It to the Next Level
This paper studies the use of social simulation in linking micro level investor behaviour and macro level stock market dynamics. Empirical data from a survey on individual investors\' decision-making and social interaction was used to formalize the trading and interaction rules of the agents of the artificial stock market SimStockExchange. Multiple simulation runs were performed with this artificial stock market, which generated macro level results, like stock market prices and returns over time. These outcomes were subsequently compared to empirical macro level data from real stock markets. Partial qualitative as well as quantitative agreement between the simulated asset returns distributions and the asset returns distributions of the real stock markets was found.Agent-Based Computational Finance, Artificial Stock Markets, Behavioral Finance, Micro-Macro Links, Multi-Agent Simulation, Stock Market Characteristics
Quantification of antithrombin isoform proportions in plasma samples of healthy subjects, sepsis patients, and in antithrombin concentrates
Antithrombin (AT) circulates in plasma in two isoforms, AT-alpha (90-95%) and AT-beta (5-10%). AT isoform proportions were measured in plasma samples of 17 healthy subjects and 26 posttraumatic or postoperative septic patients, as well as in 4 commercially available AT concentrates. Total AT was immune-purified from plasma and concentrates. Micellar electrokinetic chromatography was used to analytically separate and quantify the isoforms. Compared with plasma samples of healthy donors, septic plasmas revealed significantly reduced AT activity (p < 0.001) and beta-isoform content (p < 0.05). AT-beta correlated inversely with urea and creatinine serum concentrations (p < 0.01), indicating a relationship between better renal function and higher beta-isoform content. beta-Isoform neither correlated with age, gender, and 28-day mortality, nor with plasma concentrations of various inflammatory and organ function parameters. The commercial AT concentrate, which is equivalent to the current WHO standard, had an AT-beta content close to that found in plasma of healthy subjects. The availability of this novel quantitative AT isoform assay allows, for the first time, a closer look at the role of AT isoforms in hemostasis and sepsis pathophysiology. Copyright (C) 2002 S. Karger AG, Basel
Using EBSD and TEM-Kikuchi patterns to study local crystallography at the domain boundaries of lead zirconate titanate
Reliable EBSD mapping of 90° domains in a tetragonal ferroelectric perovskite has been achieved for the first time, together with reliable automated orientation determination from TEM-Kikuchi patterns. This has been used to determine misorientation angles at 90° domain boundaries and thus local <i>c</i>/<i>a</i> ratios. The sources of orientation noise/error and their effects on the misorientation angle data have been thoroughly analyzed and it is found that this gives a cosine distribution of misorientation angles about the mean with a characteristic width related to the width of the orientation noise distribution. In most cases, a good agreement is found between local <i>c</i>/<i>a</i> ratios and global measurements by X-ray diffraction, but some clear discrepancies have also been found suggesting that real local variations are present, perhaps as a consequence of compositional inhomogeneities
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