3,327 research outputs found
Horava-Lifshitz gravity: tighter constraints for the Kehagias-Sfetsos solution from new solar system data
We analytically work out the perturbation induced by the Kehagias-Sfetsos
(KS) space-time solution of the Horava-Lifshitz (HL) modified gravity at long
distances on the two-body range for a pair of test particles A and B orbiting
the same mass M. We apply our results to the most recently obtained
range-residuals \delta\rho for some planets of the solar system (Mercury, Mars,
Saturn) ranged from the Earth to effectively constrain the dimensionsless KS
parameter \psi_0 for the Sun. We obtain \psi_0 >= 7.2 x 10^-10 (Mercury),
\psi_0 >= 9 x 10^-12 (Mars), \psi_0 >= 1.7 x 10^-12 (Saturn). Such lower bounds
are tighter than other ones existing in literature by several orders of
magnitude. We also preliminarily obtain \psi_0 >= 8 x 10^-10 for the system
constituted by the S2 star orbiting the Supermassive Black Hole (SBH) in the
center of the Galaxy.Comment: LaTex2e, 15 pages, 1 table, 3 figures, 31 references. Version
matching the one at press in International Journal of Modern Physics D
(IJMPD
Three-dimensional viscous flow analysis inside a turbine volute
A three-dimensional numerical method has been developed to analyze the complex flow field inside a turbine volute. Comparisons are made between solutions with different boundary conditions
Secondary Electron Yield Measurements of Fermilab's Main Injector Vacuum Vessel
We discuss the progress made on a new installation in Fermilab's Main
Injector that will help investigate the electron cloud phenomenon by making
direct measurements of the secondary electron yield (SEY) of samples irradiated
in the accelerator. In the Project X upgrade the Main Injector will have its
beam intensity increased by a factor of three compared to current operations.
This may result in the beam being subject to instabilities from the electron
cloud. Measured SEY values can be used to further constrain simulations and aid
our extrapolation to Project X intensities. The SEY test-stand, developed in
conjunction with Cornell and SLAC, is capable of measuring the SEY from samples
using an incident electron beam when the samples are biased at different
voltages. We present the design and manufacture of the test-stand and the
results of initial laboratory tests on samples prior to installation.Comment: 3 pp. 3rd International Particle Accelerator Conference (IPAC 2012)
20-25 May 2012, New Orleans, Louisian
Three-Dimensional Flow Analysis Inside Consortium Impeller at Design and Off-Design Conditions
Three-dimensional flow fields inside the Consortium impeller were analyzed with a Navier-Stokes code. The numerical results at the design and off-design conditions are compared with the experimental data
Studies of turbulence and transportation in Alcator C-Mod ohmic plasmas with phase contrast imaging and comparisons with gyrokinetic simulations
Mortality following Traumatic Brain Injury among Individuals Unable to Follow Commands at the Time of Rehabilitation Admission: A National Institute on Disability and Rehabilitation Research Traumatic Brain Injury Model Systems Study
Severe traumatic brain injury (TBI) has been associated with increased mortality. This study characterizes long-term mortality, life expectancy, causes of death, and risk factors for death among patients admitted within the National Institute on Disability and Rehabilitation Research (NIDRR) TBI Model Systems Programs (TBIMS) who lack command following at the time of admission for inpatient TBI rehabilitation. Of the 8084 persons enrolled from 1988 and 2009, 387 from 20 centers met study criteria. Individuals with moderate to severe TBI who received inpatient rehabilitation were 2.2 times more likely to die than individuals in the U.S. general population of similar age, gender, and race, with an average life expectancy (LE) reduction of 6.6 years. The subset of individuals who were unable to follow commands on admission to rehabilitation was 6.9 times more likely to die, with an average LE reduction of 12.2 years. Relative to the U.S. general population matched for age, gender, and race/ethnicity, these non–command following individuals were more than four times more likely to die of circulatory conditions, 44 times more likely to die of pneumonia, and 38 times more likely to die of aspiration pneumonia. The subset of individuals with TBI who are unable to follow commands upon admission to inpatient rehabilitation are at a significantly increased risk of death when compared with the U.S. general population and compared with all individuals with moderate to severe TBI receiving inpatient rehabilitation. Respiratory causes of death predominate, compared with the general population
When Models Interact with their Subjects: The Dynamics of Model Aware Systems
A scientific model need not be a passive and static descriptor of its
subject. If the subject is affected by the model, the model must be updated to
explain its affected subject. In this study, two models regarding the dynamics
of model aware systems are presented. The first explores the behavior of
"prediction seeking" (PSP) and "prediction avoiding" (PAP) populations under
the influence of a model that describes them. The second explores the
publishing behavior of a group of experimentalists coupled to a model by means
of confirmation bias. It is found that model aware systems can exhibit
convergent random or oscillatory behavior and display universal 1/f noise. A
numerical simulation of the physical experimentalists is compared with actual
publications of neutron life time and {\Lambda} mass measurements and is in
good quantitative agreement.Comment: Accepted for publication in PLoS-ON
Validation in Fusion Research: Towards Guidelines and Best Practices
Because experiment/model comparisons in magnetic confinement fusion have not
yet satisfied the requirements for validation as understood broadly, a set of
approaches to validating mathematical models and numerical algorithms are
recommended as good practices. Previously identified procedures, such as
verification, qualification, and analysis of error and uncertainty, remain
important. However, particular challenges intrinsic to fusion plasmas and
physical measurement therein lead to identification of new or less familiar
concepts that are also critical in validation. These include the primacy
hierarchy, which tracks the integration of measurable quantities, and
sensitivity analysis, which assesses how model output is apportioned to
different sources of variation. The use of validation metrics for individual
measurements is extended to multiple measurements, with provisions for the
primacy hierarchy and sensitivity. This composite validation metric is
essential for quantitatively evaluating comparisons with experiments. To mount
successful and credible validation in magnetic fusion, a new culture of
validation is envisaged.Comment: 27 pages, 1 table, 6 figure
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