19,869 research outputs found
A study of early stopping, ensembling, and patchworking for cascade correlation neural networks
The constructive topology of the cascade correlation algorithm makes it a popular choice for many researchers wishing to utilize neural networks. However, for multimodal problems, the mean squared error of the approximation increases significantly as the number of modes increases. The components of this error will comprise both bias and variance and we provide formulae for estimating these values from mean squared errors alone. We achieve a near threefold reduction in the overall error by using early stopping and ensembling. Also described is a new subdivision technique that we call patchworking. Patchworking, when used in combination with early stopping and ensembling, can achieve an order of magnitude improvement in the error. Also presented is an approach for validating the quality of a neural network’s training, without the explicit use of a testing dataset
An analysis of the gust-induced overspeed trends of helicopter rotors
Equations for analyzing the potential gust-induced overspeed tendency of helicopter rotors are presented. A parametric analysis was also carried out to illustrate the sensitivity of rotor angular acceleration to changes in rotor lift, propulsive force, tip speed, and forward velocity
Decuplet baryon magnetic moments in a QCD-based quark model beyond quenched approximation
We study the decuplet baryon magnetic moments in a QCD-based quark model
beyond quenched approximation. Our approach for unquenching the theory is based
on the heavy baryon perturbation theory in which the axial couplings for baryon
- meson and the meson-meson-photon couplings from the chiral perturbation
theory are used together with the QM moment couplings. It also involves the
introduction of a form factor characterizing the structure of baryons
considered as composite particles. Using the parameters obtained from fitting
the octet baryon magnetic moments, we predict the decuplet baryon magnetic
moments. The magnetic moment is found to be in good agreement with
experiment: is predicted to be compared to the
experimental result of (2.02 0.05) .Comment: 19 pages, 2 figure
TDIR: Time-Delay Interferometric Ranging for Space-Borne Gravitational-Wave Detectors
Space-borne interferometric gravitational-wave detectors, sensitive in the
low-frequency (mHz) band, will fly in the next decade. In these detectors, the
spacecraft-to-spacecraft light-travel times will necessarily be unequal and
time-varying, and (because of aberration) will have different values on up- and
down-links. In such unequal-armlength interferometers, laser phase noise will
be canceled by taking linear combinations of the laser-phase observables
measured between pairs of spacecraft, appropriately time-shifted by the light
propagation times along the corresponding arms. This procedure, known as
time-delay interferometry (TDI), requires an accurate knowledge of the
light-time delays as functions of time. Here we propose a high-accuracy
technique to estimate these time delays and study its use in the context of the
Laser Interferometer Space Antenna (LISA) mission. We refer to this ranging
technique, which relies on the TDI combinations themselves, as Time-Delay
Interferometric Ranging (TDIR). For every TDI combination, we show that, by
minimizing the rms power in that combination (averaged over integration times
s) with respect to the time-delay parameters, we obtain estimates
of the time delays accurate enough to cancel laser noise to a level well below
the secondary noises. Thus TDIR allows the implementation of TDI without the
use of dedicated inter-spacecraft ranging systems, with a potential
simplification of the LISA design. In this paper we define the TDIR procedure
formally, and we characterize its expected performance via simulations with the
\textit{Synthetic LISA} software package.Comment: 5 pages, 2 figure
Addressing Ethical Issues in Studying Men’s Traumatic Stress
Like many human experiences, traumatic stress is highly gendered. Over the past several decades, a sub-stantial number of empirical studies have explored ethical issues in traumatic stress research. However, these studies have typically reported female samples or failed to account for the influence of gender in their analyses of mixed-sex samples. By extension, ethical issues that are relevant to male participants in traumatic stress research are poorly understood. After briefly exploring why the vulnerabilities of male participants are under-explored in traumatic stress research, this article highlights many ethical issues that are important to address when men participate in traumatic stress research, concluding with some sugges-tions for how these might be taken up to advance the field
Enskog Theory for Polydisperse Granular Mixtures II. Sonine Polynomial Approximation
The linear integral equations defining the Navier-Stokes (NS) transport
coefficients for polydisperse granular mixtures of smooth inelastic hard disks
or spheres are solved by using the leading terms in a Sonine polynomial
expansion. Explicit expressions for all the NS transport coefficients are given
in terms of the sizes, masses, compositions, density and restitution
coefficients. In addition, the cooling rate is also evaluated to first order in
the gradients. The results hold for arbitrary degree of inelasticity and are
not limited to specific values of the parameters of the mixture. Finally, a
detailed comparison between the derivation of the current theory and previous
theories for mixtures is made, with attention paid to the implication of the
various treatments employed to date.Comment: 26 pages, to be published in Phys. Rev.
Seasonal oxygen cycling and primary production in the Sargasso Sea
The hydrographic record at Station S in the Sargasso Sea shows the development of a subsurface oxygen maximum within the euphotic zone which must be of photosynthetic origin. Consideration of insolation, heat budgets and available 3He/3H data yields an estimate of the order of 5 M m−2 y−1 for the vertically integrated oxygen production rate. Gas exchange calculations reveal a similar oxygen flux leaving the surface, and examination of respiration cycles below the euphotic zone yields consistent results. Such results point to new production of the order of 50 g C m−2 y−1. By using a more realistic mixed layer-thermocline model (Klein and Coste, 1984) it appears that the flux of nutrients into the euphotic zone is sufficient to support such a production. The pulse-like nature of nutrient injection implied by this model raises the possibility of a spatially variable efficiency of recycling which may account for the disparity between the above observations and the level of new production inferred from 14C and 12N incubation techniques
Stabilization of nonlinear velocity profiles in athermal systems undergoing planar shear flow
We perform molecular dynamics simulations of model granular systems
undergoing boundary-driven planar shear flow in two spatial dimensions with the
goal of developing a more complete understanding of how dense particulate
systems respond to applied shear. In particular, we are interested in
determining when these systems will possess linear velocity profiles and when
they will develop highly localized velocity profiles in response to shear. In
previous work on similar systems we showed that nonlinear velocity profiles
form when the speed of the shearing boundary exceeds the speed of shear waves
in the material. However, we find that nonlinear velocity profiles in these
systems are unstable at very long times. The degree of nonlinearity slowly
decreases in time; the velocity profiles become linear when the granular
temperature and density profiles are uniform across the system at long times.
We measure the time required for the velocity profiles to become linear
and find that increases as a power-law with the speed of the shearing
boundary and increases rapidly as the packing fraction approaches random close
packing. We also performed simulations in which differences in the granular
temperature across the system were maintained by vertically vibrating one of
the boundaries during shear flow. We find that nonlinear velocity profiles form
and are stable at long times if the difference in the granular temperature
across the system exceeds a threshold value that is comparable to the glass
transition temperature in an equilibrium system at the same average density.
Finally, the sheared and vibrated systems form stable shear bands, or highly
localized velocity profiles, when the applied shear stress is lowered below the
yield stress of the static part of the system.Comment: 11 pages, 14 figure
Low-speed inducers for cryogenic upper-stage engines
Two-phase, low-speed hydrogen and oxygen inducers driven by electric motors and applicable to the tug engine were designed and constructed. The oxygen inducer was tested in liquid and two-phase oxygen. Its head and flow performance were approximately as designed, and it was able to accelerate to full speed in 3 seconds and produce its design flow and head. The analysis of the two-phase data indicated that the inducer was able to pump with vapor volume fractions in excess of 60 percent. The pump met all of its requirements (duration of runs and number of starts) to demonstrate its mechanical integrity
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