524 research outputs found
Utilization of Birefringent Fiber as Sensor of Temperature Field Disturbance
The paper deals with utilization of induced birefringence sensitivity to temperature field in birefringent optical fibers. The propagating optical wave and optical fibers are described by means of coherency and Jones matrices, which are decomposed into unitary matrix and spin matrices. The development of polarization caused by temperature field is interpreted on the Poincare sphere by means of MATLAB® environment. The temperature sensitivity of Panda and bow-tie fiber has been measured for circular polarization excitation. Curves of intensity fluctuation caused by the temperature dependence are presented
Evaluation of seals for high-performance cryogenic turbomachines
An approach to computing flow and dynamic characteristics for seals or bearings is discussed. The local average velocity was strongly influenced by inlet and exit effects and fluid injection, which in turn drove zones of secondary flow. For the restricted three-dimensional model considered, the integral averaged results were in reasonable agreement with selected data. Unidirectional pressure measurements alone were insufficient to define such flow variations. However, for seal and bearing leakage correlations the principles of corresponding states were found to be useful. Also discussed are three phenomena encountered during testing of three eccentric nonrotating seal configurations for the Space Shuttle Main Engine (SSME) Program. Fluid injection, choking within a seal, and pressure profile crossover are related to postulated zones of secondary flow or separation and to direct stiffness
Large Scale Anisotropy of Cosmic Rays and Directional Neutrino Signals from Galactic Sources
We investigate the neutrino - cosmic ray connection for sources in the Galaxy
in terms of two observables: the shape of the energy spectrum and the
distribution of arrival directions. We also study the associated gamma ray
emission from these sources.Comment: Proceedings of the 2nd Cosmic Ray Anisotropy Workshop, 26-28
September 2013, Madison, Wisconsin. To appear in IOP Conference Serie
On the unimportance of memory for the time non-local components of the Kadanoff-Baym equations
The generalized Kadanoff-Baym ansatz (GKBA) is an approximation to the
Kadanoff-Baym equations (KBE), that neglects certain memory effects that
contribute to the Green's function at non-equal times. Here we present
arguments and numerical results to demonstrate the practical insignificance of
the quantities neglected when deriving the GKBA at conditions at which KBE and
GKBA are appropriate. We provide a mathematical proof that places a scaling
bound on the neglected terms, further reinforcing that these terms are
typically small in comparison to terms that are kept in the GKBA. We perform
calculations in a range of models, including different system sizes and filling
fractions, as well as experimentally relevant non-equilibrium excitations. We
find that both the GKBA and KBE capture the dynamics of interacting systems
with moderate and even strong interactions well. We explicitly compute terms
neglected in the GKBA approximation and show, in the scenarios tested here,
that they are orders of magnitude smaller than the terms that are accounted
for, i.e., they offer only a small correction when included in the full
Kadanoff-Baym equations.Comment: 14 pages, 3 figures, Supplemental information with 10 figure
Test Population Selection from Weibull-Based, Monte Carlo Simulations of Fatigue Life
Fatigue life is probabilistic and not deterministic. Experimentally establishing the fatigue life of materials, components, and systems is both time consuming and costly. As a result, conclusions regarding fatigue life are often inferred from a statistically insufficient number of physical tests. A proposed methodology for comparing life results as a function of variability due to Weibull parameters, variability between successive trials, and variability due to size of the experimental population is presented. Using Monte Carlo simulation of randomly selected lives from a large Weibull distribution, the variation in the L10 fatigue life of aluminum alloy AL6061 rotating rod fatigue tests was determined as a function of population size. These results were compared to the L10 fatigue lives of small (10 each) populations from AL2024, AL7075 and AL6061. For aluminum alloy AL6061, a simple algebraic relationship was established for the upper and lower L10 fatigue life limits as a function of the number of specimens failed. For most engineering applications where less than 30 percent variability can be tolerated in the maximum and minimum values, at least 30 to 35 test samples are necessary. The variability of test results based on small sample sizes can be greater than actual differences, if any, that exists between materials and can result in erroneous conclusions. The fatigue life of AL2024 is statistically longer than AL6061 and AL7075. However, there is no statistical difference between the fatigue lives of AL6061 and AL7075 even though AL7075 had a fatigue life 30 percent greater than AL6061
Probabilistic Analysis for Comparing Fatigue Data Based on Johnson-Weibull Parameters
Leonard Johnson published a methodology for establishing the confidence that two populations of data are different. Johnson's methodology is dependent on limited combinations of test parameters (Weibull slope, mean life ratio, and degrees of freedom) and a set of complex mathematical equations. In this report, a simplified algebraic equation for confidence numbers is derived based on the original work of Johnson. The confidence numbers calculated with this equation are compared to those obtained graphically by Johnson. Using the ratios of mean life, the resultant values of confidence numbers at the 99 percent level deviate less than 1 percent from those of Johnson. At a 90 percent confidence level, the calculated values differ between +2 and 4 percent. The simplified equation is used to rank the experimental lives of three aluminum alloys (AL 2024, AL 6061, and AL 7075), each tested at three stress levels in rotating beam fatigue, analyzed using the Johnson- Weibull method, and compared to the ASTM Standard (E739 91) method of comparison. The ASTM Standard did not statistically distinguish between AL 6061 and AL 7075. However, it is possible to rank the fatigue lives of different materials with a reasonable degree of statistical certainty based on combined confidence numbers using the Johnson- Weibull analysis. AL 2024 was found to have the longest fatigue life, followed by AL 7075, and then AL 6061. The ASTM Standard and the Johnson-Weibull analysis result in the same stress-life exponent p for each of the three aluminum alloys at the median, or L(sub 50), live
Dynamic Mode Decomposition for Extrapolating Non-equilibrium Green's Functions Dynamics
The HF-GKBA offers an approximate numerical procedure for propagating the
two-time non-equilibrium Green's function(NEGF). Here we compare the HF-GKBA to
exact results for a variety of systems with long and short-range interactions,
different two-body interaction strengths and various non-equilibrium
preparations. We find excellent agreement between the HF-GKBA and exact time
evolution in models when more realistic long-range exponentially decaying
interactions are considered. This agreement persists for long times and for
intermediate to strong interaction strengths. In large systems, HF-GKBA becomes
prohibitively expensive for long-time evolutions. For this reason, look at the
use of dynamical mode decomposition(DMD) to reconstruct long-time NEGF
trajectories from a sample of the initial trajectory. Using no more than 16\%
of the total time evolution we reconstruct the total trajectory with high
fidelity. Our results show the potential for DMD to be used in conjunction with
HF-GKBA to calculate long time trajectories in large-scale systems
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