57,264 research outputs found
Fairness in overloaded parallel queues
Maximizing throughput for heterogeneous parallel server queues has received
quite a bit of attention from the research community and the stability region
for such systems is well understood. However, many real-world systems have
periods where they are temporarily overloaded. Under such scenarios, the
unstable queues often starve limited resources. This work examines what happens
during periods of temporary overload. Specifically, we look at how to fairly
distribute stress. We explore the dynamics of the queue workloads under the
MaxWeight scheduling policy during long periods of stress and discuss how to
tune this policy in order to achieve a target fairness ratio across these
workloads
Analysis of recent type Ia supernova data based on evolving dark energy models
We study characters of recent type Ia supernova (SNIa) data using evolving
dark energy models with changing equation of state parameter w. We consider
sudden-jump approximation of w for some chosen redshift spans with double
transitions, and constrain these models based on Markov Chain Monte Carlo
(MCMC) method using the SNIa data (Constitution, Union, Union2) together with
baryon acoustic oscillation A parameter and cosmic microwave background shift
parameter in a flat background. In the double-transition model the Constitution
data shows deviation outside 1 sigma from LCDM model at low (z < 0.2) and
middle (0.2 < z < 0.4) redshift bins whereas no such deviations are noticeable
in the Union and Union2 data. By analyzing the Union members in the
Constitution set, however, we show that the same difference is actually due to
different calibration of the same Union sample in the Constitution set, and is
not due to new data added in the Constitution set. All detected deviations are
within 2 sigma from the LCDM world model. From the LCDM mock data analysis, we
quantify biases in the dark energy equation of state parameters induced by
insufficient data with inhomogeneous distribution of data points in the
redshift space and distance modulus errors. We demonstrate that location of
peak in the distribution of arithmetic means (computed from the MCMC chain for
each mock data) behaves as an unbiased estimator for the average bias, which is
valid even for non-symmetric likelihood distributions.Comment: 12 pages, 6 figures, published in the Phys. Rev.
Comparison of speech intelligibility in cockpit noise using SPH-4 flight helmet with and without active noise reduction
Active Noise Reduction (ANR) is a new technology which can reduce the level of aircraft cockpit noise that reaches the pilot's ear while simultaneously improving the signal to noise ratio for voice communications and other information bearing sound signals in the cockpit. A miniature, ear-cup mounted ANR system was tested to determine whether speech intelligibility is better for helicopter pilots using ANR compared to a control condition of ANR turned off. Two signal to noise ratios (S/N), representative of actual cockpit conditions, were used for the ratio of the speech to cockpit noise sound pressure levels. Speech intelligibility was significantly better with ANR compared to no ANR for both S/N conditions. Variability of speech intelligibility among pilots was also significantly less with ANR. When the stock helmet was used with ANR turned off, the average PB Word speech intelligibility score was below the Normally Acceptable level. In comparison, it was above that level with ANR on in both S/N levels
A simulation model for wind energy storage systems. Volume 1: Technical report
A comprehensive computer program for the modeling of wind energy and storage systems utilizing any combination of five types of storage (pumped hydro, battery, thermal, flywheel and pneumatic) was developed. The level of detail of Simulation Model for Wind Energy Storage (SIMWEST) is consistent with a role of evaluating the economic feasibility as well as the general performance of wind energy systems. The software package consists of two basic programs and a library of system, environmental, and load components. The first program is a precompiler which generates computer models (in FORTRAN) of complex wind source storage application systems, from user specifications using the respective library components. The second program provides the techno-economic system analysis with the respective I/O, the integration of systems dynamics, and the iteration for conveyance of variables. SIMWEST program, as described, runs on the UNIVAC 1100 series computers
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