5,644 research outputs found
Development of a 60 kW alternator for SNAP-8
Design and development testing of 60 kW alternator for SNAP
NASA/GE Energy Efficient Engine low pressure turbine scaled test vehicle performance report
The low pressure turbine for the NASA/General Electric Energy Efficient Engine is a highly loaded five-stage design featuring high outer wall slope, controlled vortex aerodynamics, low stage flow coefficient, and reduced clearances. An assessment of the performance of the LPT has been made based on a series of scaled air-turbine tests divided into two phases: Block 1 and Block 2. The transition duct and the first two stages of the turbine were evaluated during the Block 1 phase from March through August 1979. The full five-stage scale model, representing the final integrated core/low spool (ICLS) design and incorporating redesigns of stages 1 and 2 based on Block 1 data analysis, was tested as Block 2 in June through September 1981. Results from the scaled air-turbine tests, reviewed herein, indicate that the five-stage turbine designed for the ICLS application will attain an efficiency level of 91.5 percent at the Mach 0.8/10.67-km (35,000-ft), max-climb design point. This is relative to program goals of 91.1 percent for the ICLS and 91.7 percent for the flight propulsion system (FPS)
The role of M cells and the long QT syndrome in cardiac arrhythmias: simulation studies of reentrant excitations using a detailed electrophysiological model
In this numerical study, we investigate the role of intrinsic heterogeneities
of cardiac tissue due to M cells in the generation and maintenance of reentrant
excitations using the detailed Luo-Rudy dynamic model. This model has been
extended to include a description of the long QT 3 syndrome, and is studied in
both one dimension, corresponding to a cable traversing the ventricular wall,
and two dimensions, representing a transmural slice. We focus on two possible
mechanisms for the generation of reentrant events. We first investigate if
early-after-depolarizations occurring in M cells can initiate reentry. We find
that, even for large values of the long QT strength, the electrotonic coupling
between neighboring cells prevents early-after-depolarizations from creating a
reentry. We then study whether M cell domains, with their slow repolarization,
can function as wave blocks for premature stimuli. We find that the inclusion
of an M cell domain can result in some cases in reentrant excitations and we
determine the lifetime of the reentry as a function of the size and geometry of
the domain and of the strength of the long QT syndrome
Multiple mechanisms of spiral wave breakup in a model of cardiac electrical activity
It has become widely accepted that the most dangerous cardiac arrhythmias are
due to re- entrant waves, i.e., electrical wave(s) that re-circulate repeatedly
throughout the tissue at a higher frequency than the waves produced by the
heart's natural pacemaker (sinoatrial node). However, the complicated structure
of cardiac tissue, as well as the complex ionic currents in the cell, has made
it extremely difficult to pinpoint the detailed mechanisms of these
life-threatening reentrant arrhythmias. A simplified ionic model of the cardiac
action potential (AP), which can be fitted to a wide variety of experimentally
and numerically obtained mesoscopic characteristics of cardiac tissue such as
AP shape and restitution of AP duration and conduction velocity, is used to
explain many different mechanisms of spiral wave breakup which in principle can
occur in cardiac tissue. Some, but not all, of these mechanisms have been
observed before using other models; therefore, the purpose of this paper is to
demonstrate them using just one framework model and to explain the different
parameter regimes or physiological properties necessary for each mechanism
(such as high or low excitability, corresponding to normal or ischemic tissue,
spiral tip trajectory types, and tissue structures such as rotational
anisotropy and periodic boundary conditions). Each mechanism is compared with
data from other ionic models or experiments to illustrate that they are not
model-specific phenomena. The fact that many different breakup mechanisms exist
has important implications for antiarrhythmic drug design and for comparisons
of fibrillation experiments using different species, electromechanical
uncoupling drugs, and initiation protocols.Comment: 128 pages, 42 figures (29 color, 13 b&w
Neutrino scattering and flavor transformation in supernovae
We argue that the small fraction of neutrinos that undergo direction-changing
scattering outside of the neutrinosphere could have significant influence on
neutrino flavor transformation in core-collapse supernova environments. We show
that the standard treatment for collective neutrino flavor transformation is
adequate at late times, but could be inadequate in the crucial shock
revival/explosion epoch of core-collapse supernovae, where the potentials that
govern neutrino flavor evolution are affected by the scattered neutrinos.
Taking account of this effect, and the way it couples to entropy and
composition, will require a new paradigm in supernova modeling.Comment: 5 pages, 3 figure
Halo Modification of a Supernova Neutronization Neutrino Burst
We give the first self-consistent calculation of the effect of the scattered
neutrino halo on flavor evolution in supernovae. Our example case is an O-Ne-Mg
core collapse supernova neutronization neutrino burst. We find that the
addition of the halo neutrinos produces qualitative and quantitative changes in
the final flavor states of neutrinos. We also find that the halo neutrinos
produce a novel distortion of the neutrino flavor swap. Our results provide
strong motivation for tackling the full multidimensional and
composition-dependent aspects of this problem in the future.Comment: 14 pages, 13 figures, 1 tabl
Gonadal hormones, but not sex, affect the acquisition and maintenance of a Go/No-Go odor discrimination task in mice
In mice, olfaction is crucial for identifying social odors (pheromones) that signal the presence of suitable mates. We used a custom-built olfactometer and a thirst-motivated olfactory discrimination Go/No-Go (GNG) task to ask whether discrimination of volatile odors is sexually dimorphic and modulated in mice by adult sex hormones. Males and females gonadectomized prior to training failed to learn even the initial phase of the task, which involved nose poking at a port in one location obtaining water at an adjacent port. Gonadally intact males and females readily learned to seek water when male urine (S+) was present but not when female urine (Sā) was present; they also learned the task when non-social odorants (amyl acetate, S+; peppermint, Sā) were used. When mice were gonadectomized after training the ability of both sexes to discriminate urinary as well as non-social odors was reduced; however, after receiving testosterone propionate (castrated males) or estradiol benzoate (ovariectomized females), task performance was restored to pre-gonadectomy levels. There were no overall sex differences in performance across gonadal conditions in tests with either set of odors; however, ovariectomized females performed more poorly than castrated males in tests with non-social odors. Our results show that circulating sex hormones enable mice of both sexes to learn a GNG task and that gonadectomy reduces, while hormone replacement restores, their ability to discriminate between odors irrespective of the saliency of the odors used. Thus, gonadal hormones were essential for both learning and maintenance of task performance across sex and odor type.We thank David Giese for help in programming the apparatus used in GNG testing and Alberto Cruz-Martin for comments on an early version of the manuscript. This work was supported by NIDCD grant DC008962 to JAC. (DC008962 - NIDCD grant)Accepted manuscrip
An evaluation of the presence of pathogens on broilers raised on poultry litter treatment-treated litter
Two trials were conducted to evaluate the presence of salmonella, campylobacter, and generic Escherichia coli on broilers raised on Poultry Litter Treatment (PLTĀ®)-enhanced litter in comparison with those raised on untreated litter. Two Company A farms included three houses on each farm as the treated group and three houses per farm as controls. Two complete growouts were evaluated on each farm. The Company B study included 10 farms with two paired houses per farm, one house as the treated group and one house as the control. One growout was evaluated per farm. The pathogen sampling consisted of litter sampling and whole bird rinses on the farm and in the processing plant. Litter pH, ammonia concentration, total litter bacteria, temperatures, and humidity were also recorded. The study with Company A resulted in lower mean levels of pH, ammonia concentration, total litter bacteria, litter E. coli, and bird rinse counts for salmonella and E. coli in houses treated with PLTĀ®. The results for Company B closely resembled those for Company A, but also included campylobacter data, which showed no difference between treated and control groups. The data indicate that PLTĀ® may be a beneficial component for on-farm pathogen reduction
Algorithms for FFT Beamforming Radio Interferometers
Radio interferometers consisting of identical antennas arranged on a regular
lattice permit fast Fourier transform beamforming, which reduces the
correlation cost from in the number of antennas to
. We develop a formalism for describing this process and
apply this formalism to derive a number of algorithms with a range of
observational applications. These include algorithms for forming arbitrarily
pointed tied-array beams from the regularly spaced Fourier-transform formed
beams, sculpting the beams to suppress sidelobes while only losing
percent-level sensitivity, and optimally estimating the position of a detected
source from its observed brightness in the set of beams. We also discuss the
effect that correlations in the visibility-space noise, due to cross-talk and
sky contributions, have on the optimality of Fourier transform beamforming,
showing that it does not strictly preserve the sky information of the
correlation, even for an idealized array. Our results have applications to a
number of upcoming interferometers, in particular the Canadian Hydrogen
Intensity Mapping Experiment--Fast Radio Burst (CHIME/FRB) project.Comment: 17 pages, 4 figures, accepted to Ap
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