13,307 research outputs found
Rotor burst protection criteria and implications
Current aircraft design practices to minimize the hazard from rotor bursts are described. The consequences of non-contained engine failures and the impact of rotor burst protection systems on aircraft design are discussed
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Derivation of near-optimal pump schedules for water distribution by simulated annealing
The scheduling of pumps for clean water distribution is a partially discrete non-linear problem with many variables. The scheduling method described in this paper typically produces costs within 1% of a linear program-based solution, and can incorporate realistic non-linear costs that may be hard to incorporate in linear programming formulations. These costs include pump switching and maximum demand charges. A simplified model is derived from a standard hydraulic simulator. An initial schedule is produced by a descent method. Two-stage simulated annealing then produces solutions in a few minutes. Iterative recalibration ensures that the solution agrees closely with the results from a full hydraulic simulation
Persistence of Antarctic polar stratospheric clouds
The persistence of Polar Stratospheric Clouds (PSCs) observed by the Stratospheric Aerosol Measurement (SAM) 2 satellite sensor over a 9-year period is compared and contrasted. Histograms of the SAM 2 1.0 micron extinction ratio data (aerosol extinction normalized by the molecular extinction) at an altitude of 18 km in the Antarctic have been generated for three 10-day periods in the month of September. Statistics for eight different years (1979 to 1982 and 1984 to 1987) are shown in separate panels for each figure. Since the SAM 2 system is a solar occultation experiment, observations are limited to the edge of the polar night and no measurements are made deep within the vortex where temperatures could be colder. For this reason, use is made of the NMC global gridded fields and the known temperature-extinction relationship to infer additional information on the occurrence and areal coverage of PSCs. Calculations of the daily areal coverage of the 195 K isotherm will be presented for this same period of data. This contour level lies in the range of the predicted temperature for onset of the Type 1 particle enhancement mode at 50 mb (Poole and McCormick, 1988b) and should indicate approximately when formation of the binary HNO3-H2O particles begins
Airborne aerosol lidar
The objectives are: to analyze dual polarization lidar measurements of aerosols and polar stratospheric clouds (PSCs) obtained aboard the NASA Ames DC-8 aircraft during the 1989 Airborne Arctic Stratospheric Expedition (AASE); and to combine lidar, SAM II, and other AASE data with theoretical modeling calculations to study PSC characteristics. A summary of progress and results is given
Tellipsoid: Exploiting inter-gene correlation for improved detection of differential gene expression
Motivation: Algorithms for differential analysis of microarray data are vital
to modern biomedical research. Their accuracy strongly depends on effective
treatment of inter-gene correlation. Correlation is ordinarily accounted for in
terms of its effect on significance cut-offs. In this paper it is shown that
correlation can, in fact, be exploited {to share information across tests},
which, in turn, can increase statistical power.
Results: Vastly and demonstrably improved differential analysis approaches
are the result of combining identifiability (the fact that in most microarray
data sets, a large proportion of genes can be identified a priori as
non-differential) with optimization criteria that incorporate correlation. As a
special case, we develop a method which builds upon the widely used two-sample
t-statistic based approach and uses the Mahalanobis distance as an optimality
criterion. Results on the prostate cancer data of Singh et al. (2002) suggest
that the proposed method outperforms all published approaches in terms of
statistical power.
Availability: The proposed algorithm is implemented in MATLAB and in R. The
software, called Tellipsoid, and relevant data sets are available at
http://www.egr.msu.edu/~desaikeyComment: 19 pages, Submitted to Bioinformatic
Weak-wave advancement in nearly collinear four-wave mixing
We identify a new four-wave mixing process in which two nearly collinear pump
beams produce phase-dependent gain into a weak bisector signal beam in a
self-defocusing Kerr medium. Phase matching is achieved by weak-wave
advancement caused by cross-phase modulation between the pump and signal beams.
We relate this process to the inverse of spatial modulational instability and
suggest a time-domain analog.Comment: 7 pages, 3 figure
Relative intensity squeezing by four-wave mixing with loss: an analytic model and experimental diagnostic
Four-wave mixing near resonance in an atomic vapor can produce relative
intensity squeezed light suitable for precision measurements beyond the
shot-noise limit. We develop an analytic distributed gain/loss model to
describe the competition of mixing and absorption through the non-linear
medium. Using a novel matrix calculus, we present closed-form expressions for
the degree of relative intensity squeezing produced by this system. We use
these theoretical results to analyze experimentally measured squeezing from a
Rb vapor and demonstrate the analytic model's utility as an experimental
diagnostic.Comment: 10 pages, 5 figure
Comparison of two- and three-dimensional Navier-Stokes solutions with NASA experimental data for CAST-10 airfoil
The two-dimensional (2-D) and three-dimensional Navier-Stokes equations are solved for flow over a NAE CAST-10 airfoil model. Recently developed finite-volume codes that apply a multistage time stepping scheme in conjunction with steady state acceleration techniques are used to solve the equations. Two-dimensional results are shown for flow conditions uncorrected and corrected for wind tunnel wall interference effects. Predicted surface pressures from 3-D simulations are compared with those from 2-D calculations. The focus of the 3-D computations is the influence of the sidewall boundary layers. Topological features of the 3-D flow fields are indicated. Lift and drag results are compared with experimental measurements
Automatic signal range selector for metering devices Patent
Voltage range selection apparatus for sensing and applying voltages to electronic instruments without loading signal sourc
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