30,443 research outputs found
Dynamical Inequality in Growth Models
A recent exponent inequality is applied to a number of dynamical growth
models. Many of the known exponents for models such as the Kardar-Parisi-Zhang
(KPZ) equation are shown to be consistent with the inequality. In some cases,
such as the Molecular Beam Equation, the situation is more interesting, where
the exponents saturate the inequality. As the acid test for the relative
strength of four popular approximation schemes we apply the inequality to the
exponents obtained for two Non Local KPZ systems. We find that all methods but
one, the Self Consistent Expansion, violate the inequality in some regions of
parameter space. To further demonstrate the usefulness of the inequality, we
apply it to a specific model, which belongs to a family of models in which the
inequality becomes an equality. We thus show that the inequality can easily
yield results, which otherwise have to rely either on approximations or general
beliefs.Comment: 6 pages, 4 figure
Demonstration of the feasibility of automated silicon solar cell fabrication
A study effort was undertaken to determine the process, steps and design requirements of an automated silicon solar cell production facility. Identification of the key process steps was made and a laboratory model was conceptually designed to demonstrate the feasibility of automating the silicon solar cell fabrication process. A detailed laboratory model was designed to demonstrate those functions most critical to the question of solar cell fabrication process automating feasibility. The study and conceptual design have established the technical feasibility of automating the solar cell manufacturing process to produce low cost solar cells with improved performance. Estimates predict an automated process throughput of 21,973 kilograms of silicon a year on a three shift 49-week basis, producing 4,747,000 hexagonal cells (38mm/side), a total of 3,373 kilowatts at an estimated manufacturing cost of 1.22 per watt
Low dimensional magnetic solids and single crystal elpasolites: Need for improved crystal growing techniques
The need for extensive crystal growing experiments to develop techniques for preparing crystals suitable for magnetic anisotropy measurements and detailed X-ray and neutron diffraction studies is rationalized on the basis of the unique magnetic properties of the materials and their hydrogen bonded structures which have many features in common with metalloenzyme and metalloprotein active sites. Single crystals of the single and mixed lanthanide species are prepared by the Bridgeman technique of gradient solidification of molten samples. The effects of crystal imperfections on the optical properties of these materials are an important part of the projected research. A series of a-amido acid complexes of first row transition metals were prepared which crystallize as infinite linear chains and exhibit low dimensional magnetic ordering (one or two) at temperature below 40 K
Novel applications of the NASA/GSFC Viterbi decoder hardware simulator
The NASA/GSFC developed an all digital, real time, programmable Viterbi decoder simulator operating at rates up to 6 Msps. With this simulator, the bit error rate (BER) performance of convolutionally encoded/Viterbi decoded Shuttle-TDRSS return link channels under pulsed radio frequency interference (RFI) conditions has been predicted. The principles of the simulator are described with special emphasis on the channel simulator and the essential interaction between CLASS software and the simulator. The sensitivity of coded BER as function of several illustrative RFI parameters is discussed for two typical Shuttle-TDRSS return link configurations
Space program: Space debris a potential threat to Space Station and shuttle
Experts estimate that more than 3.5 million man-made objects are orbiting the earth. These objects - space debris - include whole and fragmentary parts of rocket bodies and other discarded equipment from space missions. About 24,500 of these objects are 1 centimeter across or larger. A 1-centimeter man-made object travels in orbit at roughly 22,000 miles per hour. If it hit a spacecraft, it would do about the same damage as would a 400-pound safe traveling at 60 miles per hour. The Government Accounting Office (GAO) reviews NASA's plans for protecting the space station from debris, the extent and precision of current NASA and Defense Department (DOD) debris-tracking capabilities, and the extent to which debris has already affected shuttle operations. GAO recommends that the space debris model be updated, and that the findings be incorporated into the plans for protecting the space station from such debris. GAO further recommends that the increased risk from debris to the space shuttle operations be analyzed
Convergence of CI single center calculations of positron-atom interactions
The Configuration Interaction (CI) method using orbitals centered on the
nucleus has recently been applied to calculate the interactions of positrons
interacting with atoms. Computational investigations of the convergence
properties of binding energy, phase shift and annihilation rate with respect to
the maximum angular momentum of the orbital basis for the e^+Cu and PsH bound
states, and the e^+-H scattering system were completed. The annihilation rates
converge very slowly with angular momentum, and moreover the convergence with
radial basis dimension appears to be slower for high angular momentum. A number
of methods of completing the partial wave sum are compared, an approach based
on a Delta X_J = a/(J + 1/2)^n + b/(J + 1/2)^(n+1) form (with n = 4 for phase
shift (or energy) and n = 2 for the annihilation rate) seems to be preferred on
considerations of utility and underlying physical justification.Comment: 23 pages preprint RevTeX, 11 figures, submitted to PR
Discovery of a Jet-Like Structure at the High Redshift QSO CXOMP J084128.3+131107
The Chandra Multiwavelength Project (ChaMP) has discovered a jet-like
structure associated with a newly recognized QSO at redshift z=1.866. The
system was 9.4 arcmin off-axis during an observation of 3C 207. Although
significantly distorted by the mirror PSF, we use both a raytrace and a nearby
bright point source to show that the X-ray image must arise from some
combination of point and extended sources, or else from a minimum of three
distinct point sources. We favor the former situation, as three unrelated
sources would have a small probability of occurring by chance in such a close
alignment. We show that interpretation as a jet emitting X-rays via inverse
Compton (IC) scattering on the cosmic microwave background (CMB) is plausible.
This would be a surprising and unique discovery of a radio-quiet QSO with an
X-ray jet, since we have obtained upper limits of 100 microJy on the QSO
emission at 8.46 GHz, and limits of 200 microJy for emission from the putative
jet.Comment: 12 pages including 4 figures. Accepted for publication by ApJ Letter
Hybrid simulations of lateral diffusion in fluctuating membranes
In this paper we introduce a novel method to simulate lateral diffusion of
inclusions in a fluctuating membrane. The regarded systems are governed by two
dynamic processes: the height fluctuations of the membrane and the diffusion of
the inclusion along the membrane. While membrane fluctuations can be expressed
in terms of a dynamic equation which follows from the Helfrich Hamiltonian, the
dynamics of the diffusing particle is described by a Langevin or Smoluchowski
equation. In the latter equations, the curvature of the surface needs to be
accounted for, which makes particle diffusion a function of membrane
fluctuations. In our scheme these coupled dynamic equations, the membrane
equation and the Langevin equation for the particle, are numerically integrated
to simulate diffusion in a membrane. The simulations are used to study the
ratio of the diffusion coefficient projected on a flat plane and the
intramembrane diffusion coefficient for the case of free diffusion. We compare
our results with recent analytical results that employ a preaveraging
approximation and analyze the validity of this approximation. A detailed
simulation study of the relevant correlation functions reveals a surprisingly
large range where the approximation is applicable.Comment: 12 pages, 9 figures, accepted for publication in Phys. Rev.
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