21,666 research outputs found
Form Factors Calculated on the Light-Front
A consistent treatment of decay is given on the
light-front. The to transition form factors are calculated in the
entire physical range of momentum transfer for the first time. The
valence-quark contribution is obtained using relativistic light-front wave
functions. Higher quark-antiquark Fock-state of the -meson bound state is
represented effectively by the configuration, and its effect
is calculated in the chiral perturbation theory. Wave function renormalization
is taken into account consistently. The contribution dominates
near the zero-recoil point ( GeV), and decreases rapidly as
the recoil momentum increases. We find that the calculated form factor
follows approximately a dipole -dependence in the entire range
of momentum transfer.Comment: Revtex, 19 pages, 9 figure
A simplified model of the source channel of the Leksell Gamma Knife: testing multisource configurations with PENELOPE
A simplification of the source channel geometry of the Leksell Gamma
Knife, recently proposed by the authors and checked for a single
source configuration (Al-Dweri et al 2004), has been used to calculate the dose
distributions along the , and axes in a water phantom with a
diameter of 160~mm, for different configurations of the Gamma Knife including
201, 150 and 102 unplugged sources. The code PENELOPE (v. 2001) has been used
to perform the Monte Carlo simulations. In addition, the output factors for the
14, 8 and 4~mm helmets have been calculated. The results found for the dose
profiles show a qualitatively good agreement with previous ones obtained with
EGS4 and PENELOPE (v. 2000) codes and with the predictions of
GammaPlan. The output factors obtained with our model agree
within the statistical uncertainties with those calculated with the same Monte
Carlo codes and with those measured with different techniques. Owing to the
accuracy of the results obtained and to the reduction in the computational time
with respect to full geometry simulations (larger than a factor 15), this
simplified model opens the possibility to use Monte Carlo tools for planning
purposes in the Gamma Knife.Comment: 13 pages, 8 figures, 5 table
Walk Through Solar System Times: An Exhibit with an Astrobiology Emphasis
In this astrobiology outreach project, we attempt to present the research of the Goddard Center for Astrobiology (GCA) in the context of the history of the Solar System. GCA research emphasizes the origin and formation of complex pre-biotic organic materials in extraterrestrial environments and explores whether the delivery of these primordial materials and water to the early Earth enabled the emergence and evolution of life. The content expounds on areas that are usually not touched upon in a timeline of the Earth's formation. The exhibit addresses the questions: How did our solar system form? How is the formation of our solar systems similar or different from others? How did the organic molecules we observe in space get to the Earth? What conditions are most suitable for life? We will address the issues and challenges of designing the exhibit and of explaining advanced astrobiology research topics to the public
Validation of the English and Chinese versions of the Quick-FLIC quality of life questionnaire.
A useful measure of quality of life should be easy and quick to complete. Recently, we reported the development and validation of a shortened Chinese version of the Functional Living Index-Cancer (FLIC), which we called the Quick-FLIC. In the present study of 327 English-speaking and 221 Chinese-speaking cancer patients, we validated the English version of the Quick-FLIC and further assessed the Chinese version. The 11 Quick-FLIC items were administered alongside the 11 remaining items of the full FLIC, but there appeared to be little context effect. Validity of the English version of the Quick-FLIC was attested by its strong correlation with two other measures of quality of life, and its ability to detect differences between patients with different performance status and treatment status (each P<0.001). Its internal consistency (alpha=0.86) and test-retest reliability (intraclass correlation=0.76) were also satisfactory. The measure was responsive to changes in performance status (P<0.001). The Chinese version showed similar characteristics. The Quick-FLIC behaved in ways that are highly comparable with the FLIC, even though the Quick-FLIC comprised only 11 items whereas the FLIC comprised 22. Further research is required to see whether the use of shorter instruments can improve data quality and response rates, but the fact that shorter instruments place less burden on the patients is itself inherently important
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