5,189 research outputs found
The Formation of a "Primary Film" on Materials Submerged in the Sea at Port Hueneme, California
The initial stages of fouling, the accumulation
of microscopic organisms, and formation
of a primary film or slime layer, have received
but sparse attention in the literature. To cite an
example, the U.S. Naval Institute publication
Marine Fording and Its Prevention contains
hundreds of references to fouling but only
eight pertain to the primary film
Electric Polarizability of Neutral Hadrons from Lattice QCD
By simulating a uniform electric field on a lattice and measuring the change
in the rest mass, we calculate the electric polarizability of neutral mesons
and baryons using the methods of quenched lattice QCD. Specifically, we measure
the electric polarizability coefficient from the quadratic response to the
electric field for 10 particles: the vector mesons and ; the
octet baryons n, , , , and ;
and the decouplet baryons , , and .
Independent calculations using two fermion actions were done for consistency
and comparison purposes. One calculation uses Wilson fermions with a lattice
spacing of fm. The other uses tadpole improved L\"usher-Weiss gauge
fields and clover quark action with a lattice spacing fm. Our results
for neutron electric polarizability are compared to experiment.Comment: 25 pages, 20 figure
Correlation Between Student Collaboration Network Centrality and Academic Performance
We compute nodal centrality measures on the collaboration networks of
students enrolled in three upper-division physics courses, usually taken
sequentially, at the Colorado School of Mines. These are complex networks in
which links between students indicate assistance with homework. The courses
included in the study are intermediate Classical Mechanics, introductory
Quantum Mechanics, and intermediate Electromagnetism. By correlating these
nodal centrality measures with students' scores on homework and exams, we find
four centrality measures that correlate significantly with students' homework
scores in all three courses: in-strength, out-strength, closeness centrality,
and harmonic centrality. These correlations suggest that students who not only
collaborate often, but also collaborate significantly with many different
people tend to achieve higher grades. Centrality measures between simultaneous
collaboration networks (analytical vs. numerical homework collaboration)
composed of the same students also correlate with each other, suggesting that
students' collaboration strategies remain relatively stable when presented with
homework assignments targeting different skills. Additionally, we correlate
centrality measures between collaboration networks from different courses and
find that the four centrality measures with the strongest relationship to
students' homework scores are also the most stable measures across networks
involving different courses. Correlations of centrality measures with exam
scores were generally smaller than the correlations with homework scores,
though this finding varied across courses.Comment: 10 pages, 4 figures, submitted to Phys. Rev. PE
Bulletin No. 383 - Cooperative Nutritional Status Studies in the Western Region: I. Nutrient Intake
In 1947, a concerted study of the nutritional status of selected population groups was initiated in the western region of the United States. Previous dietary surveys had indicated that substantial portions of the country\u27s population were consuming lower than recommended levels of essential nutrients. Deficiency diseases that may have nutritional background, such as dental caries, anemia, and rickets, existed. Investigators reported subclinical signs of malnutrition in several areas. Few studies had been made in the West, although reports of high incidence of dental caries and suspected undernutrition had come from several western states. The regional committee thought it evident that the presence of endemic nutritional deficiencies, imbalances, and excesses should be investigated within the western region, and their causes in environmental factors or food habits should be studied. Such conditions might be widespread and cross state lines. Hence the regional approach was appropriate
Perturbative and non-perturbative studies with the delta function potential
We show that the delta function potential can be exploited along with
perturbation theory to yield the result of certain infinite series. The idea is
that any exactly soluble potential if coupled with a delta function potential
remains exactly soluble. We use the strength of the delta function as an
expansion parameter and express the second-order energy shift as an infinite
sum in perturbation theory. The analytical solution is used to determine the
second-order energy shift and hence the sum of an infinite series. By an
appropriate choice of the unperturbed system, we can show the importance of the
continuum in the energy shift of bound states.Comment: 19 pages, 2 table
Defect modes in otherwise perfect photonic crystal and photonic crystal fibres
Many of the applications of photonic crystals and photonic crystal fibres require the periodic structure tohave some type of defect. In photonic crystal fibers a point defect defines the fiber core, whereas in photonic crystals a line defect acts as a waveguide, and point defects act as cavities. The modeling of these defects usually either makes use of periodic boundary conditions, by which the defect is replicated periodically, or models a photonic cyrstal of finite extent. HOwever, some applications, for example the cut-off behaviour of a defect mode where the field extends very widely, require methods that can model a defect in an otherwise infinite and perfectly periodic structure. Here we present such a method. It combines the method of fictitious sources with averaging over the Brillouin zone, and we apply it to study the long wavelength behavior of the fundamental mode of photonic crystal fibers
TransFormers for Ensuring Long-Term Operations in Lunar Extreme Environments
"Surviving Extreme Space Environments" (EE) is one of NASA's Space Technology Grand Challenges. Power generation and thermal control are the key survival ingredients that allow a robotic explorer to cope with the EE using resources available to it, for example, by harvesting the local solar energy or by utilizing an onboard radioisotope thermoelectric generator (RTG). TransFormers (TFs) are a new technology concept designed to transform a localized area within a harsh extreme environment into a survivable micro-environment by projecting energy to the precise location where robots or humans operate. For example, TFs placed at a location on the rim of Shackleton Crater, which is illuminated by solar radiation for most of the year, would be able to reflect solar energy onto robots operating in the dark cold crater. TFs utilize a shape transformation mechanism to un-fold from a compact volume to a large reflective surface, and to control how much-and where-the energy is projected, and by adjusting for the changing position of the sun. TFs would enable in-situ resource utilization (ISRU) activities within locations of high interest that would normally be unreachable because of their extreme environmen
Bures distance between two displaced thermal states
The Bures distance between two displaced thermal states and the corresponding
geometric quantities (statistical metric, volume element, scalar curvature) are
computed. Under nonunitary (dissipative) dynamics, the statistical distance
shows the same general features previously reported in the literature by
Braunstein and Milburn for two--state systems. The scalar curvature turns out
to have new interesting properties when compared to the curvature associated
with squeezed thermal states.Comment: 3 pages, RevTeX, no figure
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Quantifying sources of inter-model diversity in the cloud albedo effect
There is large diversity in simulated aerosol forcing among models that participated in the fifth Coupled Model Intercomparison Project (CMIP5), particularly related to aerosol interactions with clouds. Here we use the reported model data and fitted aerosol-cloud relations to separate the main sources of inter-model diversity in the magnitude of the cloud albedo effect. There is large diversity in the global load and spatial distribution of sulfate aerosol, as well as in global-mean cloud-top effective radius. The use of different parameterizations of aerosol-cloud interactions makes the largest contribution to diversity
in modeled radiative forcing (up to -39%, +48% about the mean estimate). Uncertainty in pre-industrial sulfate load also makes a substantial contribution (-15%, +61% about the mean estimate), with smaller contributions from inter-model differences in the historical change in sulfate load and in mean cloud fraction
Decuplet Baryon Structure from Lattice QCD
The electromagnetic properties of the SU(3)-flavor baryon decuplet are
examined within a lattice simulation of quenched QCD. Electric charge radii,
magnetic moments, and magnetic radii are extracted from the E0 and M1 form
factors. Preliminary results for the E2 and M3 moments are presented giving the
first model independent insight to the shape of the quark distribution in the
baryon ground state. As in our octet baryon analysis, the lattice results give
evidence of spin-dependent forces and mass effects in the electromagnetic
properties. The quark charge distribution radii indicate these effects act in
opposing directions. Some baryon dependence of the effective quark magnetic
moments is seen. However, this dependence in decuplet baryons is more subtle
than that for octet baryons. Of particular interest are the lattice predictions
for the magnetic moments of and for which new recent
experimental measurements are available. The lattice prediction of the
ratio appears larger than the experimental ratio, while the
lattice prediction for the magnetic moment ratio is in good
agreement with the experimental ratio.Comment: RevTeX manuscript, 34 pages plus 21 figures (available upon request
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