19,727 research outputs found
The calibration and flight test performance of the space shuttle orbiter air data system
The Space Shuttle air data system (ADS) is used by the guidance, navigation and control system (GN&C) to guide the vehicle to a safe landing. In addition, postflight aerodynamic analysis requires a precise knowledge of flight conditions. Since the orbiter is essentially an unpowered vehicle, the conventional methods of obtaining the ADS calibration were not available; therefore, the calibration was derived using a unique and extensive wind tunnel test program. This test program included subsonic tests with a 0.36-scale orbiter model, transonic and supersonic tests with a smaller 0.2-scale model, and numerous ADS probe-alone tests. The wind tunnel calibration was further refined with subsonic results from the approach and landing test (ALT) program, thus producing the ADS calibration for the orbital flight test (OFT) program. The calibration of the Space Shuttle ADS and its performance during flight are discussed in this paper. A brief description of the system is followed by a discussion of the calibration methodology, and then by a review of the wind tunnel and flight test programs. Finally, the flight results are presented, including an evaluation of the system performance for on-board systems use and a description of the calibration refinements developed to provide the best possible air data for postflight analysis work
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Association of prior depressive symptoms and suicide attempts with subsequent victimisation - analysis of population-based data from the Adult Psychiatric Morbidity Survey
Background: Symptoms of mental disorder, particularly schizophrenia, predispose to victimisation. Much less is known about the relationship between depressive symptoms and later victimisation in the general population, the influence of these symptoms on types of subsequent victimisation, or the role of symptom severity. We investigated this in nationally representative data from the UK.
Methods: Data were from the Adult Psychiatric Morbidity Survey 2007. Multivariable logistic regressions estimated association between: a. prior depressive symptoms, and b. prior depressive symptoms with suicide attempt, and types of more recent victimisation. Gender-specific associations were estimated using multiplicative interactions.
Results: Prior depressive symptoms were associated with greater odds of any recent intimate partner violence (IPV), emotional IPV, sexual victimisation, workplace victimisation, any victimisation, and cumulative victimisation (adjusted odds ratio (aOR) for increasing types of recent victimisation: 1.47, 95% confidence interval (CI): 1.14, 1.89). Prior depressive symptoms with suicide attempt were associated with any recent IPV, emotional IPV, any victimisation, and cumulative victimisation (aOR for increasing types of recent victimisation: 2.33, 95%: 1.22, 4.44).
Limitations: Self-reported recalled data on previous depressive symptoms, may have limited accuracy. Small numbers of outcomes for some comparisons resulted in imprecision of these estimates.
Conclusion: Aside from severe mental illness such as schizophrenia, previous depressive symptoms in the general population are associated with greater subsequent victimisation. Men and women with prior depressive symptoms may be vulnerable to a range of types of victimisation, and may benefit from interventions to reduce this vulnerability
The remotely piloted vehicle as an earth science research aircraft
A brief study was conducted at the Goddard Space Flight Center to identify existing remotely piloted vehicle (RPV) capabilities and to determine if the use of an RPV was advantageous and practical for Earth science investigations. A total of 17 instrument systems were identified. It was found that RPV's were considered especially valuable for dangerous missions, e.g., flights through volcano plumes and hurricanes, long duration profiles over inaccessible regions such as the Antarctic, and very low altitude ocean profiling missions
Charged Particle Motion in a Highly Ionized Plasma
A recently introduced method utilizing dimensional continuation is employed
to compute the energy loss rate for a non-relativistic particle moving through
a highly ionized plasma. No restriction is made on the charge, mass, or speed
of this particle. It is, however, assumed that the plasma is not strongly
coupled in the sense that the dimensionless plasma coupling parameter
g=e^2\kappa_D/ 4\pi T is small, where \kappa_D is the Debye wave number of the
plasma. To leading and next-to-leading order in this coupling, dE/dx is of the
generic form g^2 \ln[C g^2]. The precise numerical coefficient out in front of
the logarithm is well known. We compute the constant C under the logarithm
exactly for arbitrary particle speeds. Our exact results differ from
approximations given in the literature. The differences are in the range of 20%
for cases relevant to inertial confinement fusion experiments. The same method
is also employed to compute the rate of momentum loss for a projectile moving
in a plasma, and the rate at which two plasmas at different temperatures come
into thermal equilibrium. Again these calculations are done precisely to the
order given above. The loss rates of energy and momentum uniquely define a
Fokker-Planck equation that describes particle motion in the plasma. The
coefficients determined in this way are thus well-defined, contain no arbitrary
parameters or cutoffs, and are accurate to the order described. This
Fokker-Planck equation describes the longitudinal straggling and the transverse
diffusion of a beam of particles. It should be emphasized that our work does
not involve a model, but rather it is a precisely defined evaluation of the
leading terms in a well-defined perturbation theory.Comment: Comments: Published in Phys. Rep. 410/4 (2005) 237; RevTeX, 111
Pages, 17 Figures; Transcription error corrected in temperature equilibration
rate (3.61) and (12.44) which replaces \gamma-2 by \gamma-
Dynamical transition for a particle in a squared Gaussian potential
We study the problem of a Brownian particle diffusing in finite dimensions in
a potential given by where is Gaussian random field.
Exact results for the diffusion constant in the high temperature phase are
given in one and two dimensions and it is shown to vanish in a power-law
fashion at the dynamical transition temperature. Our results are confronted
with numerical simulations where the Gaussian field is constructed, in a
standard way, as a sum over random Fourier modes. We show that when the number
of Fourier modes is finite the low temperature diffusion constant becomes
non-zero and has an Arrhenius form. Thus we have a simple model with a fully
understood finite size scaling theory for the dynamical transition. In addition
we analyse the nature of the anomalous diffusion in the low temperature regime
and show that the anomalous exponent agrees with that predicted by a trap
model.Comment: 18 pages, 4 figures .eps, JPA styl
Effective diffusion constant in a two dimensional medium of charged point scatterers
We obtain exact results for the effective diffusion constant of a two
dimensional Langevin tracer particle in the force field generated by charged
point scatterers with quenched positions. We show that if the point scatterers
have a screened Coulomb (Yukawa) potential and are uniformly and independently
distributed then the effective diffusion constant obeys the
Volgel-Fulcher-Tammann law where it vanishes. Exact results are also obtained
for pure Coulomb scatterers frozen in an equilibrium configuration of the same
temperature as that of the tracer.Comment: 9 pages IOP LaTex, no figure
Distributed Deep Learning for Question Answering
This paper is an empirical study of the distributed deep learning for
question answering subtasks: answer selection and question classification.
Comparison studies of SGD, MSGD, ADADELTA, ADAGRAD, ADAM/ADAMAX, RMSPROP,
DOWNPOUR and EASGD/EAMSGD algorithms have been presented. Experimental results
show that the distributed framework based on the message passing interface can
accelerate the convergence speed at a sublinear scale. This paper demonstrates
the importance of distributed training. For example, with 48 workers, a 24x
speedup is achievable for the answer selection task and running time is
decreased from 138.2 hours to 5.81 hours, which will increase the productivity
significantly.Comment: This paper will appear in the Proceeding of The 25th ACM
International Conference on Information and Knowledge Management (CIKM 2016),
Indianapolis, US
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