6,917 research outputs found
Microdetermination of urea in urine using p-dimethylaminobenzaldehyde /PDAB/
Adaptation of the p-dimethylaminobenzaldehyde method for determining urea concentration in urine is an improved micromechanical method. Accuracy and precision are satisfactory. This method avoids extra steps of deproteinizing or removing normal urinary chromogens
Intelligent redundant actuation system requirements and preliminary system design
Several redundant actuation system configurations were designed and demonstrated to satisfy the stringent operational requirements of advanced flight control systems. However, this has been accomplished largely through brute force hardware redundancy, resulting in significantly increased computational requirements on the flight control computers which perform the failure analysis and reconfiguration management. Modern technology now provides powerful, low-cost microprocessors which are effective in performing failure isolation and configuration management at the local actuator level. One such concept, called an Intelligent Redundant Actuation System (IRAS), significantly reduces the flight control computer requirements and performs the local tasks more comprehensively than previously feasible. The requirements and preliminary design of an experimental laboratory system capable of demonstrating the concept and sufficiently flexible to explore a variety of configurations are discussed
Flash of photons from the early stage of heavy-ion collisions
The dynamics of partonic cascades may be an important aspect for particle
production in relativistic collisions of nuclei at CERN SPS and BNL RHIC
energies. Within the Parton-Cascade Model, we estimate the production of single
photons from such cascades due to scattering of quarks and gluons q g -> q
gamma, quark-antiquark annihilation q qbar -> g gamma, or gamma gamma, and from
electromagnetic brems-strahlung of quarks q -> q gamma. We find that the latter
QED branching process plays the dominant role for photon production, similarly
as the QCD branchings q -> q g and g -> g g play a crucial role for parton
multiplication. We conclude therefore that photons accompanying the parton
cascade evolution during the early stage of heavy-ion collisions shed light on
the formation of a partonic plasma.Comment: 4 pages including 3 postscript figure
Deep Convolutional Neural Networks as strong gravitational lens detectors
Future large-scale surveys with high resolution imaging will provide us with
a few new strong galaxy-scale lenses. These strong lensing systems
however will be contained in large data amounts which are beyond the capacity
of human experts to visually classify in a unbiased way. We present a new
strong gravitational lens finder based on convolutional neural networks (CNNs).
The method was applied to the Strong Lensing challenge organised by the Bologna
Lens Factory. It achieved first and third place respectively on the space-based
data-set and the ground-based data-set. The goal was to find a fully automated
lens finder for ground-based and space-based surveys which minimizes human
inspect. We compare the results of our CNN architecture and three new
variations ("invariant" "views" and "residual") on the simulated data of the
challenge. Each method has been trained separately 5 times on 17 000 simulated
images, cross-validated using 3 000 images and then applied to a 100 000 image
test set. We used two different metrics for evaluation, the area under the
receiver operating characteristic curve (AUC) score and the recall with no
false positive (). For ground based data our
best method achieved an AUC score of and a
of . For space-based data our best
method achieved an AUC score of and a
of . On space-based data adding dihedral invariance to the CNN
architecture diminished the overall score but achieved a higher no
contamination recall. We found that using committees of 5 CNNs produce the best
recall at zero contamination and consistenly score better AUC than a single
CNN. We found that for every variation of our CNN lensfinder, we achieve AUC
scores close to within .Comment: 9 pages, accepted to A&
Parton cascade description of relativistic heavy-ion collisions at CERN SPS energies ?
We examine Pb+Pb collisions at CERN SPS energy 158 A GeV, by employing the
earlier developed and recently refined parton-cascade/cluster-hadronization
model and its Monte Carlo implementation. This space-time model involves the
dynamical interplay of perturbative QCD parton production and evolution, with
non-perturbative parton-cluster formation and hadron production through cluster
decays. Using computer simulations, we are able to follow the entwined
time-evolution of parton and hadron degrees of freedom in both position and
momentum space, from the instant of nuclear overlap to the final yield of
particles. We present and discuss results for the multiplicity distributions,
which agree well with the measured data from the CERN SPS, including those for
K mesons. The transverse momentum distributions of the produced hadrons are
also found to be in good agreement with the preliminary data measured by the
NA49 and the WA98 collaboration for the collision of lead nuclei at the CERN
SPS. The analysis of the time evolution of transverse energy deposited in the
collision zone and the energy density suggests an existence of partonic matter
for a time of more than 5 fm.Comment: 16 pages including 7 postscript figure
Isoscalar-isovector mass splittings in excited mesons
Mass splittings between the isovector and isoscalar members of meson nonets
arise in part from hadronic loop diagrams which violate the Okubo-Zweig-Iizuka
rule.
Using a model for these loop processes which works qualitatively well in the
established nonets, I tabulate predictions for the splittings and associated
isoscalar mixing angles in the remaining nonets below about 2.5 GeV, and
explain some of their systematic features.
The results for excited vector mesons compare favorably with experiment.Comment: 8 RevTeX pages, including 1 LaTeX figure.
CMU-HEP93-23/DOE-ER-40682-4
Heavy resonance production in high energy nuclear collisions
We estimate freezeout conditions for , , and quarks in high energy
nuclear collisions. Freezeout is due either to loss of thermal contact, or to
particles ``wandering'' out of the region of hot matter. We then develop a
thermal recombination model in which both single-particle (quark and antiquark)
and two-particle (quark-antiquark) densities are conserved. Conservation of
two-particle densities is necessary because quarks and antiquarks are always
produced in coincidence, so that the local two-particle density can be much
larger than the product of the single-particle densities. We use the freezeout
conditions and recombination model to discuss heavy resonance production at
zero baryon density in high energy nuclear collisions.Comment: revtex, 15 pages, no figures, KSUCNR-009-9
Constrained neural network training and its application to hyperelastic material modeling
Neural networks (NN) have been studied and used widely in the field of computational mechanics, especially to approximate material behavior. One of their disadvantages is the large amount of data needed for the training process. In this paper, a new approach to enhance NN training with physical knowledge using constraint optimization techniques is presented. Specific constraints for hyperelastic materials are introduced, which include energy conservation, normalization and material symmetries. We show, that the introduced enhancements lead to better learning behavior with respect to well known issues like a small number of training samples or noisy data. The NN is used as a material law within a finite element analysis and its convergence behavior is discussed with regard to the newly introduced training enhancements. The feasibility of NNs trained with physical constraints is shown for data based on real world experiments. We show, that the enhanced training outperforms state-of-the-art techniques with respect to stability and convergence behavior within FE simulations
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