43,685 research outputs found
Failure Analysis of Nickel-hydrogen Cell Subjected to Simulated Low Earth Orbit Cycling
A nickel-hydrogen cell completed 10,080 simulated low earth orbit charge/discharge cycles at depths-of-discharge ranging from 50 to 80 percent prior to failure. The cell is of the Air Force design, rated at 50 ampere-hours, 8.9 cm (3.5 inches) in diameter. Upon disassembly, the end of the polysulfone core supporting the electrode stack was found to have fractured. This allowed the electrode stack to expand. A massive short was found at the inner diameter of the electrodes centered roughly at plate set 34 to 37 from the positive end of the electrode stack. The damaged area extended through approximately one third of the electrode stack, with the effect becoming progressively less with distance from plate set 34 to 37. Measured thicknesses of the positive plates were significantly greater than the initial specification values. The postulated cause of failure is that positive plate growth caused fracture of the shoulder from the end of the polysulfone core on which the electrodes are mounted. The electrode stack relieved and pressure points were created at the area near the inner diameter of the plates at the tab attachment. A short occurred at a pressure point between opposing plates and propagated to other electrode sets due to thermal and mechanical stresses caused by the short
Multiple scattering of light by atoms with internal degeneracy
An analytical microscopic theory for the resonant multiple scattering of
light by cold atoms with arbitrary internal degeneracy is presented. It permits
to calculate the average amplitude and the average intensity for one-photon
states of the full transverse electromagnetic field in a dilute medium of
unpolarized atoms. Special emphasis is laid upon an analysis in terms of
irreducible representations of the rotation group. It allows to sum explicitly
the ladder and maximally crossed diagrams, giving the average intensity in the
Boltzmann approximation and the interference corrections responsible for weak
localization and coherent backscattering. The exact decomposition into field
modes shows that the atomic internal degeneracy contributes to the
depolarization of the average intensity and suppresses the interference
corrections. Static as well as dynamic quantities like the transport velocity,
diffusion constants and relaxation times for all field modes and all atomic
transitions are derived.Comment: Corrected minor errors. Slightly extended version of the article
appeared in prin
Extinction for two parabolic stochastic PDE's on the lattice
It is well known that, starting with finite mass, the super-Brownian motion
dies out in finite time. The goal of this article is to show that with some
additional work, one can prove finite time die-out for two types of systems of
stochastic differential equations on the lattice Z^d. Our first system involves
the heat equation on the lattice Z^d, with a nonlinear noise term u(t,x)^gamma
dB_x(t), with 1/2 <= gamma < 1. The B_x are independent Brownian motions. When
gamma = 1/2, the measure which puts mass u(t,x) at x is a super-random walk and
it is well-known that the process becomes extinct in finite time a.s.
Finite-time extinction is known to be a.s. false if gamma = 1. For 1/2 < gamma
< 1, we show finite-time die-out by breaking up the solution into pieces, and
showing that each piece dies in finite time. Our second example involves the
mutually catalytic branching system of stochastic differential equations on
Z^d, which was first studied by Dawson and Perkins. Roughly speaking, this
process consists of 2 superprocesses with the continuous time simple random
walk as the underlying spatial motion. Furthermore, each process stimulates
branching and dying in the other process. By using a somewhat different
argument, we show that, depending on the initial conditions, finite time
extinction of one type may occur with probability 0, or with probability
arbitrarily close to 1
NASA 50 amp hour nickel cadmium battery waste heat determination
A process for determining the waste heat generated in a 50-ampere-hour, nickel cadmium battery as a function of the discharge rate is described and results are discussed. The technique involved is essentially calibration of the battery as a heat transfer rate calorimeter. The tests are run at three different levels of battery activity, one at 40-watts of waste heat generated, one at 60, and one at 100. Battery inefficiency ranges from 14 to 18 percent at discharge rates of 284 to 588 watts, respectively and top-of-cell temperatures of 20 C
Entrepreneurship and Growth
In the year 2000 at a meeting in Lisbon, leaders of the European Union (EU) articulated a set of goals for the Union, which have come to be called the Lisbon Strategy or Lisbon Agenda. The agenda had three main goals: to promote growth through innovation, to create a learning economy, and to bring about social and environmental renewal. Exactly what the last goal implies is not clear, at least to me, but the intent and substance behind the first two certainly is. Research spending was to rise across the EU, university enrollments would rise with them, and a more friendly environment for innovation would be created as markets continued to be liberalized and integrated. The EU leaders meeting in Lisbon set the year 2010 as their goal for fulfilling this agenda. The year 2010 has come and gone. Today, growth rates in Europe are even lower than they were in 2000. Research and university budgets have been cut â sometimes drastically â across the EU. These developments are, of course, largely a response to the recent financial crisis and its impact on state finances. But the crisis would not have been nearly as severe as it has been, if EU countries had been well on their way to fulfilling the goals of the Lisbon Agenda when the crisis hit. The EUâs failure to come anywhere near meeting the goals set out in the year 2000 stems, I shall argue, to underlying structural factors and ideological perspectives, which constitute major obstacles to the kind of knowledge-based, innovative society that the EU leaders dreamed of in Lisbon more than a decade ago. This paper attempts to identify what these obstacles are.Entrepreneurship; Economic Growth; Human Capital; European Union
Atmospheric density models
An atmospheric model developed by Jacchia, quite accurate but requiring a large amount of computer storage and execution time, was found to be ill-suited for the space shuttle onboard program. The development of a simple atmospheric density model to simulate the Jacchia model was studied. Required characteristics including variation with solar activity, diurnal variation, variation with geomagnetic activity, semiannual variation, and variation with height were met by the new atmospheric density model
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