30,236 research outputs found
KC-135 aero-optical turbulent boundary layer/shear layer experiment revisited
The aero-optical effects associated with propagating a laser beam through both an aircraft turbulent boundary layer and artificially generated shear layers are examined. The data present comparisons from observed optical performance with those inferred from aerodynamic measurements of unsteady density and correlation lengths within the same random flow fields. Using optical instrumentation with tens of microsecond temporal resolution through a finite aperture, optical performance degradation was determined and contrasted with the infinite aperture time averaged aerodynamic measurement. In addition, the optical data were artificially clipped to compare to theoretical scaling calculations. Optical instrumentation consisted of a custom Q switched Nd:Yag double pulsed laser, and a holographic camera which recorded the random flow field in a double pass, double pulse mode. Aerodynamic parameters were measured using hot film anemometer probes and a five hole pressure probe. Each technique is described with its associated theoretical basis for comparison. The effects of finite aperture and spatial and temporal frequencies of the random flow are considered
The Supernova-Gamma Ray Burst Connection
Supernovae 1998bw and its corresponding relativistically expanding radio
source are coincident with the \grb source GRB 980425. We show that of six
recent SN Ib/c for which an outburst epoch can be estimated with some
reliability, four have radio outbursts and all are correlated in time and space
with BATSE \grbs. The joint probability of all six correlations is
1.5. No such correlation exists for SN Ia and SN II. The \gr\
energy associated with the SN/GRB events is ergs if
emitted isotropically. Economy of hypotheses leads us to propose that all \grbs
are associated with supernovae and that the \grb events have a quasi-isotropic
component that cannot be observed at cosmological distances and a strongly
collimated and Doppler-boosted component that can only be seen if looking
nearly along the collimation axis. Such collimation requires a high rate of
occurrence perhaps consistent with a supernova rate. The collimated flow may be
generated by core collapse to produce rotating, magnetized neutron stars. All
core collapse events may produce such jets, but only the ones that occur in
supernovae with small or missing hydrogen envelopes, Type Ib or Ic, can
propagate into the interstellar medium and yield a visible \grb. We suggest
that asymmetries in line profiles and spectropolarimetry of SN II and SN Ib/c,
pulsar runaway velocities, soft \gr repeaters and \grbs are associated
phenomena.Comment: Submitted to ApJL on May 19, 1998. Revised on Jun 15, 199
Substructure coupling for dynamic analysis and testing
Fixed interface and free interface methods of substructure coupling for dynamic analysis are discussed. Three methods for reducing the number of coordinates required by fixed interface methods are introduced. Matrix ordinary differential equations are employed to improve accuracy in free interface substructure coupling methods
A review of substructure coupling methods for dynamic analysis
The state of the art is assessed in substructure coupling for dynamic analysis. A general formulation, which permits all previously described methods to be characterized by a few constituent matrices, is developed. Limited results comparing the accuracy of various methods are presented
Revised reference model for nitric acid
A nearly global set of data on the nitric acid distribution was obtained for seven months by the Limb Infrared Monitor of the Stratosphere (LIMS) experiment on the Nimbus 7 spacecraft. The evaluation of the accuracy, precision, and resolution of these data is described, and a description of the major features of the nitric acid distributions is presented. The zonal mean for nitric acid is distributed in a stratospheric layer that peaks near 30 mb, with the largest mixing ratios occurring in polar regions, especially in winter
Multiple domestications of asian rice
In their recent Correspondence about our study showingthat there were three origins of Asian rice2, Huang and Han suggest that the
methodology that we used to infer multiple domestications was flawed as it did not take account of the strong genetic bottleneck in japonica
Phenotypic analysis of host-parasite interactions in lambs infected with Teladorsagia circumcincta
Magnetic and electric phase control in epitaxial EuTiO from first principles
We propose a design strategy - based on the coupling of spins, optical
phonons, and strain - for systems in which magnetic (electric) phase control
can be achieved by an applied electric (magnetic) field. Using first-principles
density-functional theory calculations, we present a realization of this
strategy for the magnetic perovskite EuTiO.Comment: Significantly revised for clarit
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