8,547 research outputs found
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
Randomized Algorithms for the Loop Cutset Problem
We show how to find a minimum weight loop cutset in a Bayesian network with
high probability. Finding such a loop cutset is the first step in the method of
conditioning for inference. Our randomized algorithm for finding a loop cutset
outputs a minimum loop cutset after O(c 6^k kn) steps with probability at least
1 - (1 - 1/(6^k))^c6^k, where c > 1 is a constant specified by the user, k is
the minimal size of a minimum weight loop cutset, and n is the number of
vertices. We also show empirically that a variant of this algorithm often finds
a loop cutset that is closer to the minimum weight loop cutset than the ones
found by the best deterministic algorithms known
Advanced recovery systems wind tunnel test report
Pioneer Aerospace Corporation (PAC) conducted parafoil wind tunnel testing in the NASA-Ames 80 by 120 test sections of the National Full-Scale Aerodynamic Complex, Moffett Field, CA. The investigation was conducted to determine the aerodynamic characteristics of two scale ram air wings in support of air drop testing and full scale development of Advanced Recovery Systems for the Next Generation Space Transportation System. Two models were tested during this investigation. Both the primary test article, a 1/9 geometric scale model with wing area of 1200 square feet and secondary test article, a 1/36 geometric scale model with wing area of 300 square feet, had an aspect ratio of 3. The test results show that both models were statically stable about a model reference point at angles of attack from 2 to 10 degrees. The maximum lift-drag ratio varied between 2.9 and 2.4 for increasing wing loading
The Effect of Low Stem Temperatures and Stem Incisions on the Translocation of Water
Author Institution: Department of Botany and Plant Pathology, The Ohio State University, Columbus 1
Universal decay law in charged-particle emission and exotic cluster radioactivity
A linear universal decay formula is presented starting from the microscopic
mechanism of the charged-particle emission. It relates the half-lives of
monopole radioactive decays with the -values of the outgoing particles as
well as the masses and charges of the nuclei involved in the decay. This
relation is found to be a generalization of the Geiger-Nuttall law in
radioactivity and explains well all known cluster decays. Predictions on the
most likely emissions of various clusters are presented.Comment: 2 figure
Control of Partitioning and Export of Carbon in Leaves of Higher-Plants
Within source leaves, partition of assimilated carbon and export are regulated to both leaf and plant ontogeny and to environmental conditions. System goals, adaptive responses, control mechanisms, and information flow are developed from the viewpoint that a well-adapted plant is an integrated system. Regulation of partitioning and export involves both feedforward control and feedback homeostasis. Export is controlled by regulation of metabolism which supplies assimilated material to be translocated, by control of efflux into the free space of material destined for export, and by regulation of phloem loading. Control of export by the latter two processes depends on responsive metabolic processes that can supply sucrose and other transport molecules upon demand. An integrated model incorporating these features posits that control of export by mechanisms located in the source leaves is an important means of regulating translocation
Hydrodynamic modeling of towed buoyant submarine antenna's in multidirectional seas
Submitted in partial fulfillment of the requirements for the degree of Master of Science at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 2000A finite difference computer model is developed to simulate the exposure statistics of a radio
frequency buoyant antenna as it is towed in a three-dimensional random seaway. The model
allows the user to prescribe antenna properties (length, diameter, density, etc.), sea conditions
(significant wave height, development of sea), tow angle, and tow speed. The model then
simulates the antenna-sea interaction for the desired duration to collect statistics relating to
antenna performance. The model provides design engineers with a tool to predict antenna
performance trends, and to conduct design tradeoff studies. The floating antenna envisioned
is for use by a submarine operating at modest speed and depth
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