2,814 research outputs found
Combustion of solid carbon rods in zero and normal gravity
In order to investigate the mechanism of carbon combustion, spectroscopic carbon rods were resistance ignited and burned in an oxygen environment in normal and zero gravity. Direct mass spectrometric sampling was used in the normal gravity tests to obtain concentration profiles of CO2, CO, and O2 as a function of distance from the carbon surface. The experimental concentrations were compared to those predicted by a stagnant film model. Zero gravity droptower tests were conducted in order to assess the effect of convection on the normal gravity combustion process. The ratio of flame diameter to rod diameter as a function of time for oxygen pressures of 5, 10, 15, and 20 psia was obtained for three different diameter rods. It was found that this ratio was inversely proportional to both the oxygen pressure and the rod diameter
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D- Formation by Charge-Transfer Collisions of 0.3 to 10-keV Deuterium Ions and Atoms in Cesium, Rubidium, and Sodium Vapors
Apparatus for simultaneous ion counting and current recording in mass spectrometry
Ion counting system is coupled to the last dynode of an Allen-type electron multiplier on the mass analyzer of a double focusing mass spectrometer. This leaves the anode available for an electrometer, making possible simultaneous measurements. Coupling is achieved by a ferrite core transformer and associated circuitry
Spin Polarization and Magneto-Coulomb Oscillations in Ferromagnetic Single Electron Devices
The magneto-Coulomb oscillation, the single electron repopulation induced by
external magnetic field, observed in a ferromagnetic single electron transistor
is further examined in various ferromagnetic single electron devices. In case
of double- and triple-junction devices made of Ni and Co electrodes, the single
electron repopulation always occurs from Ni to Co electrodes with increasing a
magnetic field, irrespective of the configurations of the electrodes. The
period of the magneto-Coulomb oscillation is proportional to the single
electron charging energy. All these features are consistently explained by the
mechanism that the Zeeman effect induces changes of the Fermi energy of the
ferromagnetic metal having a non-zero spin polarizations. Experimentally
determined spin polarizations are negative for both Ni and Co and the magnitude
is larger for Ni than Co as expected from band calculations.Comment: 4 pages, 3 figures, uses jpsj.sty, submitted to J. Phys. Soc. Jp
Penalized PET/CT Reconstruction Algorithms With Automatic Realignment for Anatomical Priors
Two algorithms for solving misalignment issues in penalized PET/CT reconstruction using anatomical priors are proposed. Both approaches are based on a recently published joint motion estimation and image reconstruction method. The first approach deforms the anatomical image to align it with the functional one while the second approach deforms both images to align them with the measured data. Our current implementation alternates between alignment estimation and image reconstruction. We have chosen parallel level sets (PLSs) as a representative anatomical penalty, incorporating a spatially variant penalty strength. The performance was evaluated using simulated nontime-of-flight data generated with an XCAT phantom in the thorax region. We used the attenuation map in the anatomical prior. The results demonstrated that both methods can estimate the misalignment and deform the anatomical image accordingly. However, the performance of the first approach depends highly on the workflow of the alternating process. The second approach shows a faster convergence rate to the correct alignment and is less sensitive to the workflow. The presence of anatomical information improves the convergence rate of misalignment estimation for the second approach but slow it down for the first approach. Both approaches show improved performance in misalignment estimation as the data noise level decreases
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Ecological theatre and the evolutionary game: how environmental and demographic factors determine payoffs in evolutionary games
In the standard approach to evolutionary games and replicator dynamics, differences in fitness can be interpreted as an excess from the mean Malthusian growth rate in the population. In the underlying reasoning, related to an analysis of "costs" and "benefits", there is a silent assumption that fitness can be described in some type of units. However, in most cases these units of measure are not explicitly specified. Then the question arises: are these theories testable? How can we measure "benefit" or "cost"? A natural language, useful for describing and justifying comparisons of strategic "cost" versus "benefits", is the terminology of demography, because the basic events that shape the outcome of natural selection are births and deaths. In this paper, we present the consequences of an explicit analysis of births and deaths in an evolutionary game theoretic framework. We will investigate different types of mortality pressures, their combinations and the possibility of trade-offs between mortality and fertility. We will show that within this new approach it is possible to model how strictly ecological factors such as density dependence and additive background fitness, which seem neutral in classical theory, can affect the outcomes of the game. We consider the example of the Hawk-Dove game, and show that when reformulated in terms of our new approach new details and new biological predictions are produced
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Charge-State Dependence of Electron Loss From H by Collisions with Heavy, Highly Stripped Ions
Weak decays of 4He-Lambda
We measured the lifetime and the mesonic and non-mesonic decay rates of the
4He-Lambda hypernucleus. The hypernuclei were created using a 750 MeV/c
momentum K- beam on a liquid 4He target by the reaction 4He(K-,pi-)4He-Lambda.
The 4He-Lambda lifetime was directly measured using protons from Lambda p -> n
p non-mesonic decay (also referred to as proton-stimulated decay) and was found
to have a value of tau = 245 +/- 24 ps. The mesonic decay rates were determined
from the observed numbers of pi-'s and pi0's as Gamma_pi-/Gamma_tot = 0.270 +/-
0.024 and Gamma_pi0/Gamma_tot = 0.564 +/- 0.036, respectively, and the values
of the proton- and neutron-stimulated decay rates were extracted as
Gamma_p/Gamma_tot = 0.169 +/- 0.019 and Gamma_n/Gamma_tot <= 0.032 (95% CL),
respectively. The effects of final-state interactions and possible 3-body
Lambda N N decay contributions were studied in the context of a simple model of
nucleon-stimulated decay. Nucleon-nucleon coincidence events were observed and
were used in the determination of the non-mesonic branching fractions. The
implications of the results of this analysis were considered for the empirical
Delta I = 1/2 rule and the decay rates of the 4H-Lambda hypernucleus.Comment: 15 pages, 11 figures, published in PRC, revised content to match
published versio
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Charge-Transfer and Impact-Ionization Cross Sections for Highly Stripped Carbon and Niobium Ions Incident on Argon and Hydrogen
An asymptotic form of the reciprocity theorem with applications in x-ray scattering
The emission of electromagnetic waves from a source within or near a
non-trivial medium (with or without boundaries, crystalline or amorphous, with
inhomogeneities, absorption and so on) is sometimes studied using the
reciprocity principle. This is a variation of the method of Green's functions.
If one is only interested in the asymptotic radiation fields the generality of
these methods may actually be a shortcoming: obtaining expressions valid for
the uninteresting near fields is not just a wasted effort but may be
prohibitively difficult. In this work we obtain a modified form the reciprocity
principle which gives the asymptotic radiation field directly. The method may
be used to obtain the radiation from a prescribed source, and also to study
scattering problems. To illustrate the power of the method we study a few
pedagogical examples and then, as a more challenging application we tackle two
related problems. We calculate the specular reflection of x rays by a rough
surface and by a smoothly graded surface taking polarization effects into
account. In conventional treatments of reflection x rays are treated as scalar
waves, polarization effects are neglected. This is a good approximation at
grazing incidence but becomes increasingly questionable for soft x rays and UV
at higher incidence angles.
PACs: 61.10.Dp, 61.10.Kw, 03.50.DeComment: 19 pages, 4 figure
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