4,662 research outputs found
Global surfaces of section in the planar restricted 3-body problem
The restricted planar three-body problem has a rich history, yet many
unanswered questions still remain. In the present paper we prove the existence
of a global surface of section near the smaller body in a new range of energies
and mass ratios for which the Hill's region still has three connected
components. The approach relies on recent global methods in symplectic geometry
and contrasts sharply with the perturbative methods used until now.Comment: 11 pages, 1 figur
Pseudo-distances on symplectomorphism groups and applications to flux theory
Starting from a given norm on the vector space of exact 1-forms of a compact
symplectic manifold, we produce pseudo-distances on its symplectomorphism group
by generalizing an idea due to Banyaga. We prove that in some cases (which
include Banyaga's construction), their restriction to the Hamiltonian
diffeomorphism group is equivalent to the distance induced by the initial norm
on exact 1-forms. We also define genuine "distances to the Hamiltonian
diffeomorphism group" which we use to derive several consequences, mainly in
terms of flux groups.Comment: 21 pages, no figure; v2. various typos corrected, some references
added. Published in Mathematische Zeitschrif
Studies of Electron-Beam Penetration and Free-Carrier Generation in Diamond Films
Experimental observations of the energyâdependent electronâbeam penetration in type IIâA natural diamond are reported. The experimental data are compared with results obtained from numerical Monte Carlo simulations, and the results are in very good agreement. The results also reveal that a threshold energy of about 125 keV is necessary for complete penetration for a 35 ÎŒm sample. It is found that over the 30â180 keV range, the energy dependence of the penetration depth and total path length exhibits a powerâlaw relation. Monte Carlo simulations have also been performed to investigate the excess carrierâgeneration profiles within diamond for a set of incident eâbeam energy distributions. The simulation results demonstrate the feasibility of tailoring the internal source function, and hence influencing the diffusion currents, the internal electric fields, and charge injection through the contacts
A room temperature 19-channel magnetic field mapping device for cardiac signals
We present a multichannel cardiac magnetic field imaging system built in
Fribourg from optical double-resonance Cs vapor magnetometers. It consists of
25 individual sensors designed to record magnetic field maps of the beating
human heart by simultaneous measurements on a grid of 19 points over the chest.
The system is operated as an array of second order gradiometers using
sophisticated digitally controlled feedback loops.Comment: 3 pages, 3 figures, submitted to Applied Physics Letter
Studies of High Field Conduction in Diamond for Electron Beam Controlled Switching
Experimental studies on a vertical metalâdiamondâsilicon switch structure have been conducted for potential pulsed power applications. Both the dc currentâvoltage characteristics and the transient switching response have been measured for a range of voltages. With a 1 ÎŒm diamond film, the switch has been seen to withstand electric fields up to 1.8 MV/cm. Our results show a polarity dependence which can be associated with current injection at the asymmetric contacts. Polarity effects were also observed in the presence of eâbeam excitation, and arise due to nonuniform carrier generation near the diamondâsilicon interface. Our switching transients were seen to follow the shape of the eâbeam for a negative bias at the silicon substrate. For positive voltage values exceeding about 80 V however, the switch is seen to go into a persistentâphotocurrent mode. This effect is a result of free carrier trapping within diamond and is enhanced by the double injection process
Microclimate 1997-1999 in primary forest, secondary forest and agroforestry systems in central Amazonia.
Rainfall, average maximum and minimum air temperature, and relative air humidity as measured at the Embrapa weather station all show that 1997 was a strong El Nino (ENSO) year.bitstream/item/181106/1/ID-5199-34-49.pdfFinal Report 1996-1999
Incoherent Transport through Molecules on Silicon in the vicinity of a Dangling Bond
We theoretically study the effect of a localized unpaired dangling bond (DB)
on occupied molecular orbital conduction through a styrene molecule bonded to a
n++ H:Si(001)-(2x1) surface. For molecules relatively far from the DB, we find
good agreement with the reported experiment using a model that accounts for the
electrostatic contribution of the DB, provided we include some dephasing due to
low lying phonon modes. However, for molecules within 10 angstrom to the DB, we
have to include electronic contribution as well along with higher dephasing to
explain the transport features.Comment: 9 pages, 5 figure
Isotope effects in underdoped cuprate superconductors: a quantum phenomenon
We show that the unusual doping dependence of the isotope effects on
transition temperature and zero temperature in - plane penetration depth
naturally follows from the doping driven 3D-2D crossover, the 2D quantum
superconductor to insulator transition (QSI) in the underdoped limit and the
change of the relative doping concentration upon isotope substitution. Close to
the QSI transition both, the isotope coefficient of transition temperature and
penetration depth approach the coefficient of the relative dopant
concentration, and its divergence sets the scale. These predictions are fully
consistent with the experimental data and imply that close to the underdoped
limit the unusual isotope effect on transition temperature and penetration
depth uncovers critical phenomena associated with the quantum superconductor to
insulator transition in two dimensions.Comment: 6 pages, 3 figure
Parasite infections in a social carnivore: Evidence of their fitness consequences and factors modulating infection load
There are substantial individual differences in parasite composition and infection load in wildlife populations. Few studies have investigated the factors shaping this heterogeneity in large wild mammals or the impact of parasite infections on Darwinian fitness, particularly in juveniles. A host's parasite composition and infection load can be shaped by factors that determine contact with infective parasite stages and those that determine the host's resistance to infection, such as abiotic and social environmental factors, and age. Hostâparasite interactions and synergies between coinfecting parasites may also be important. We test predictions derived from these different processes to investigate factors shaping infection loads (fecal egg/oocyte load) of two energetically costly gastrointestinal parasites: the hookworm Ancylostoma and the intracellular Cystoisospora, in juvenile spotted hyenas (Crocuta crocuta) in the Serengeti National Park, in Tanzania. We also assess whether parasite infections curtail survival to adulthood and longevity. Ancylostoma and Cystoisospora infection loads declined as the number of adult clan members increased, a result consistent with an encounterâreduction effect whereby adults reduced encounters between juveniles and infective larvae, but were not affected by the number of juveniles in a clan. Infection loads decreased with age, possibly because active immune responses to infection improved with age. Differences in parasite load between clans possibly indicate variation in abiotic environmental factors between clan den sites. The survival of juveniles (<365 days old) to adulthood decreased with Ancylostoma load, increased with age, and was modulated by maternal social status. Highâranking individuals with low Ancylostoma loads had a higher survivorship during the first 4 years of life than highâranking individuals with high Ancylostoma loads. These findings suggest that high infection loads with energetically costly parasites such as hookworms during early life can have negative fitness consequences
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