8,791 research outputs found
New expression for the K-shell ionization
A new expression for the total K-shell ionization cross section by electron
impact based on the relativistic extension of the binary encounter Bethe (RBEB)
model, valid from ionization threshold up to relativistic energies, is
proposed. The new MRBEB expression is used to calculate the K-shell ionization
cross sections by electron impact for the selenium atom. Comparison with all,
to our knowledge, available experimental data shows good agreement
Building multi-layer social knowledge maps with google maps API
Google Maps is an intuitive online-map service which changes people's way of navigation on Geo-maps. People can explore the maps in a multi-layer fashion in order to avoid information overloading. This paper reports an innovative approach to extend the "power" of Google Maps to adaptive learning. We have designed and implemented a navigator for multi-layer social knowledge maps, namely ProgressiveZoom, with Google Maps API. In our demonstration, the knowledge maps are built from the Interactive System Design (ISD) course at the School of Information Science, University of Pittsburgh. Students can read the textbooks and reflect their individual and social learning progress in a context of pedagogical hierarchical structure
Comparison of Four Space Propulsion Methods for Reducing Transfer Times of Manned Mars Mission
We assess the possibility of reducing the travel time of a manned mission to
Mars by examining four different propulsion methods, and keeping the mass at
departure under 2,500 tonnes, for a fixed architecture. We evaluated
representative systems of three different state of the art technologies
(chemical, nuclear thermal, and electric), and one advance technology, the
"Pure Electro-Magnetic Thrust" (PEMT) concept (proposed by Rubbia). A mission
architecture mostly based on the Design Reference Architecture 5.0 is assumed
in order to estimate the mass budget, that influences the performance of the
propulsion system. Pareto curves of the duration of the mission and time of
flight versus mass of mission are drawn. We conclude that the ion engine
technology, combined with the classical chemical engine, yields the shortest
mission times for this architecture with the lowest mass, and that chemical
propulsion alone is the best to minimise travel time. The results obtained
using the PEMT suggest that it could be a more suitable solution for farther
destinations than Mars.Comment: Change in title, abstract and presentation so to clarify the main
results. 14 pages, 7 figures and 2 table
Knowledgezoom for java: A concept-based exam study tool with a zoomable open student model
This paper presents our attempt to develop a personalized exam preparation tool for Java/OOP classes based on a fine-grained concept model of Java knowledge. Our goal was to explore two most popular student model-based approaches: open student modeling and problem sequencing. The result of our work is a Java exam preparation tool, Knowledge Zoom. The tool combines an open concept-level student model component, Knowledge Explorer and a concept-based sequencing component, Knowledge Maximizer into a single interface. This paper presents both components of Knowledge Zoom, reports results of its evaluation, and discusses lessons learned. © 2013 IEEE
Spin dependent Momentum Distributions in Deformed Nuclei
We study the properties of the spin dependent one body density in momentum
space for odd--A polarized deformed nuclei within the mean field approximation.
We derive analytic expressions connecting intrinsic and laboratory momentum
distributions. The latter are related to observable transition densities in
{\bf p}--space that can be probed in one nucleon knock--out reactions from
polarized targets. It is shown that most of the information contained in the
intrinsic spin dependent momentum distribution is lost when the nucleus is not
polarized. Results are presented and discussed for two prolate nuclei,
Ne and Mg, and for one oblate nucleus, Ar. The effects of
deformation are highlighted by comparison to the case of odd--A nuclei in the
spherical model.Comment: Latex 2.09. 25 pages and 6 figures (available from
[email protected]), to appear in Ann. of Phy
Nuclear Pairing in the T=0 channel revisited
Recent published data on the isoscalar gap in symmetric nuclear matter using
the Paris force and the corresponding BHF single particle dispersion are
corrected leading to an extremely high proton-neutron gap of
MeV at . Arguments whether this value can be reduced due
to screening effects are discussed. A density dependent delta interaction with
cut off is adjusted so as to approximately reproduce the nuclear matter values
with the Paris force.Comment: 4 pages, 4 figure
Global Cosmological Parameters Determined Using Classical Double Radio Galaxies
A sample of 20 powerful extended radio galaxies with redshifts between zero
and two were used to determine constraints on global cosmological parameters.
Data for six radio sources were obtained from the VLA archive, analyzed, and
combined with the sample of 14 radio galaxies used previously by Guerra & Daly
to determine cosmological parameters. The results are consistent with our
previous results, and indicate that the current value of the mean mass density
of the universe is significantly less than the critical value. A universe with
of unity is ruled out at 99.0% confidence, and the best fitting
values of in matter are and
assuming zero space curvature and zero cosmological
constant, respectively. Note that identical results obtain when the low
redshift bin, which includes Cygnus A, is excluded; these results are
independent of whether the radio source Cygnus A is included. The method does
not rely on a zero-redshift normalization.
The radio properties of each source are also used to determine the density of
the gas in the vicinity of the source, and the beam power of the source. The
six new radio sources have physical characteristics similar to those found for
the original 14 sources. The density of the gas around these radio sources is
typical of gas in present day clusters of galaxies. The beam powers are
typically about .Comment: 39 pages includes 21 figures, accepted to Ap
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