813 research outputs found
Numeric and fluid dynamic representation of tornadic double vortex thunderstorms
Current understanding of a double vortex thunderstorm involves a pair of contra-rotating vortices that exists in the dynamic updraft. The pair is believed to be a result of a blocking effect which occurs when a cylindrical thermal updraft of a thunderstorm protrudes into the upper level air and there is a large amount of vertical wind shear between the low level and upper level air layers. A numerical tornado prediction scheme based on the double vortex thunderstorm was developed. The Energy-Shear Index (ESI) is part of the scheme and is calculated from radiosonde measurements. The ESI incorporates parameters representative of thermal instability and blocking effect, and indicates appropriate environments for which the development of double vortex thunderstorms is likely
Frequency stabilization for mobile satellite terminals via LORAN
Digital satellite communication systems require careful management of frequency stability. Historically, frequency stability has been accomplished by continuously powered, high cost, high performance reference oscillators. Today's low cost mobile satellite communication equipment must operate under wide ranging environmental conditions, stabilize quickly after application of power, and provide adequate performance margin to overcome RF link impairments unique to the land mobile environment. Methods for frequency stabilization in land mobile applications must meet these objectives without incurring excessive performance degradation. A frequency stabilization scheme utilizing the LORAN (Long Range Navigation) system is presented
Local starburst galaxies and their descendants
Despite strong interest in the starburst (hereafter SB) phenomenon, the
concept remains ill-defined. We use a strict definition of SB to examine the
statistical properties of local SB and post-starburst (hereafter PB) galaxies.
We also seek relationships to active galaxies. Potential SB galaxies are
selected from the SDSS DR7 and their stellar content is analysed. We apply an
age dependent dust attenuation correction and derive star formation rates
(SFR), ages and masses of the young and old populations. The photometric masses
nicely agree with dynamical masses derived from the H-alpha emission line
width. To select SB galaxies, we use the birthrate parameter b=SFR/,
requiring b>=3. The PB sample is selected from the citerion EW(Hdelta_abs)>=6
A. Only 1% of star-forming galaxies are found to be SB galaxies. They
contribute 3-6% to the stellar production and are therefore unimportant for the
local star formation activity. The median SB age is 70 Myr, roughly independent
of mass. The b-parameter strongly depends on burst age. Values close to b=60
are found at ages ~10 Myr, while almost no SBs are found at ages >1 Gyr. The
median baryonic burst mass fraction of sub-L* galaxies is 5%, decreasing slowly
with mass. The median mass fraction of the recent burst in the PB sample is
5-10%. The age-mass distribution of the progenitors of the PBs is bimodal with
a break at log(M)~10.6 above which the ages are doubled. The SB and PB
luminosity functions (hereafter LFs) follow each other closely until M_r~-21,
when AGNs begin to dominate. The PB LF continues to follow the AGN LF while SB
loose significance. This suggests that the number of luminous SBs is
underestimated by about one dex at high luminosities, due to large amounts of
dust and/or AGN blending. It also indicates that the SB phase preceded the AGN
phase. We also discuss the conditions for global gas outflow caused by stellar
feedback.Comment: Accepted for publication in Astronomy and Astrophysics. This is an
extended, substantially revised and corrected version with partly modified
conclusion
Does \u27Free-Sampling\u27 Enhance the Value of Public Goods?
This study investigates whether a \u27free sampling\u27 marketing strategy induces an enduring WTP premium effect for public goods. Using data from a unique field experiment involving curbside recycling, we find that the premium effect associated with providing non-participating households a brief opportunity to participate in a curbside recycling program for free is relatively small and not enduring. It may therefore not be cost effective to offer a free-sampling participation incentive for this type (or similar types) of local public good(s)
The Effects of Aerobic vs Anaerobic Exercise on Cognitive Function in College Aged Individuals
Please download the pdf version of the abstract
A Central Partition of Molecular Conformational Space. IV. Extracting information from the graph of cells
In previous works [physics/0204035, physics/0404052, physics/0509126] a
procedure was described for dividing the -dimensional
conformational space of a molecular system into a number of discrete cells,
this partition allowed the building of a combinatorial structure from data
sampled in molecular dynamics trajectories: the graph of cells, that encodes
the set of cells in conformational space that are visited by the system in its
thermal wandering. Here we outline a set of procedures for extracting useful
information from this structure: 1st) interesting regions in the volume
occupied by the system in conformational space can be bounded by a polyhedral
cone whose faces are determined empirically from a set of relations between the
coordinates of the molecule, 2nd) it is also shown that this cone can be
decomposed into a hierarchical set of smaller cones, 3rd) the set of cells in a
cone can be encoded by a simple combinatorial sequence.Comment: added an intrduction and reference
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