15,104 research outputs found
Using temporal distributions of transient events to characterize cosmological source populations
The brightest events in a time series of cosmological transients obey an
observation time dependence which is often overlooked. This dependence can be
exploited to probe the global properties of electromagnetic and gravitational
wave transients (Howell et al. 2007a, Coward & Burman 2005). We describe a new
relation based on a peak flux--observation time distribution and show that it
is invariant to the luminosity distribution of the sources (Howell et al.
2007b). Applying this relation, in combination with a new data analysis filter,
to \emph{Swift} gamma-ray burst data, we demonstrate that it can constrain
their rate density.Comment: published in proceedings of FRONTIERS OF FUNDAMENTAL AND
COMPUTATIONAL PHYSICS: 10th International Symposium, AIP,1246,203, (2010
An improved method for estimating source densities using the temporal distribution of Cosmological Transients
It has been shown that the observed temporal distribution of transient events
in the cosmos can be used to constrain their rate density. Here we show that
the peak flux--observation time relation takes the form of a power law that is
invariant to the luminosity distribution of the sources, and that the method
can be greatly improved by invoking time reversal invariance and the temporal
cosmological principle. We demonstrate how the method can be used to constrain
distributions of transient events, by applying it to Swift gamma-ray burst data
and show that the peak flux--observation time relation is in good agreement
with recent estimates of source parameters. We additionally show that the
intrinsic time dependence allows the method to be used as a predictive tool.
Within the next year of Swift observation, we find a 50% chance of obtaining a
peak flux greater than that of GRB 060017 -- the highest Swift peak flux to
date -- and the same probability of detecting a burst with peak flux > 100
photons s^{-1} cm^{-2} within 6 years.Comment: Submitted to ApJ Letter
Multidimensionality of Entrepreneurial Firm-level Processes: Do the Dimensions Covary?
Covariance (or not) among the first-order dimensions of firm-level entrepreneurial processes underpins a fundamental and non-trivial difference between the entrepreneurial orientation and entrepreneurial posture constructs. Utilizing a typology developed for multi-dimensional constructs, we operationalized each construct according to its specific conceptualization (relationships among the dimensions) and compared and contrasted each construct in an identical nomological network. Although we found support for both theories, the entrepreneurial orientation construct was more robust in explaining additional variance in growth. Additionally, our findings suggest that the means through which the first-order dimensions are operationalized—latent vs. summates— significantly affect the analysis
Southern Corn Rootworm (Coleoptera: Chrysomelidae) Adult Emergence and Population Growth Assessment After Selection With Vacuolar ATPase-A double-stranded RNA Over Multiple Generations
The southern corn rootworm, Diabrotica undecimpunctata howardi Barber (Coleoptera: Chrysomelidae), was exposed over multiple generations to vacuolar (v)ATPase-A double-stranded (ds)RNA, first as adults and later, as neonate larvae. During adult selection, high mortality and lower fecundity were observed in the RNAi-selected cages after beetles were exposed to sublethal dsRNA concentrations that varied between LC40 and LC75. During larval selection, a delay in adult emergence and effects on population growth parameters were observed after neonates were exposed to sublethal dsRNA concentrations that varied between LC50 and LC70. Some of the parameters measured for adult emergence such as time to reach maximum linear adult emergence, time elapsed before attaining linear emergence, termination point of the linear emergence, and total days of linear emergence increase, were significantly different between RNAi-selected and control colonies for at least one generation. Significant differences were also observed in population growth parameters such as growth rate, net reproductive rate, doubling time, and generation time. After seven generations of selection, there was no indication that resistance evolved. The sublethal effects caused by exposures of southern corn rootworm to dsRNAs can affect important life history traits and fitness especially through delays in adult emergence and reduction in population growth. Although changes in susceptibility did not occur, the observation of sublethal effects suggests important responses to potential selection pressure. Assuming resistance involves a recessive trait, random mating between susceptible and resistant individuals is an important factor that allows sustainable use of transgenic plants, and delays in adult emergence observed in our studies could potentially compromise this assumption
Some flight mechanics considerations for the Voyager mission
Voyager mission study considerations including launch opportunities, trajectory design, performance capability of Saturn V launch vehicle, and vehicle load relief contro
On the gravitational wave background from compact binary coalescences in the band of ground-based interferometers
This paper reports a comprehensive study on the gravitational wave (GW)
background from compact binary coalescences. We consider in our calculations
newly available observation-based neutron star and black hole mass
distributions and complete analytical waveforms that include post-Newtonian
amplitude corrections. Our results show that: (i) post-Newtonian effects cause
a small reduction in the GW background signal; (ii) below 100 Hz the background
depends primarily on the local coalescence rate and the average chirp
mass and is independent of the chirp mass distribution; (iii) the effects of
cosmic star formation rates and delay times between the formation and merger of
binaries are linear below 100 Hz and can be represented by a single parameter
within a factor of ~ 2; (iv) a simple power law model of the energy density
parameter up to 50-100 Hz is sufficient to be used
as a search template for ground-based interferometers. In terms of the
detection prospects of the background signal, we show that: (i) detection (a
signal-to-noise ratio of 3) within one year of observation by the Advanced LIGO
detectors (H1-L1) requires a coalescence rate of for binary neutron stars (binary black holes); (ii) this limit on
could be reduced 3-fold for two co-located detectors, whereas the
currently proposed worldwide network of advanced instruments gives only ~ 30%
improvement in detectability; (iii) the improved sensitivity of the planned
Einstein Telescope allows not only confident detection of the background but
also the high frequency components of the spectrum to be measured. Finally we
show that sub-threshold binary neutron star merger events produce a strong
foreground, which could be an issue for future terrestrial stochastic searches
of primordial GWs.Comment: A few typos corrected to match the published version in MNRA
Phenology satellite experiment
The detection of a phenological event (the brown wave-vegetation senescence) for specific forest and crop types using ERTS-1 imagery is described. Data handling techniques included computer analysis and photo interpretation procedures. Computer analysis of ERTS-1 multispectral scanner digital tapes in all bands was used to give the relative changes of spectral reflectance with time of forests and specified crops. These data were obtained for a number of the study's twenty-four sites located within four north-south corridors across the United States. Analysis of ground observation photography and ERTS-1 imagery for sites in the Appalachian Corridor and Mississippi Valley Corridor indicates that the recession of vegetation development can be detected very well. Tentative conclusions are that specific phenological events such as crop maturity or leaf fall can be mapped for specific sites and possibly for entire regions
On transversally elliptic operators and the quantization of manifolds with -structure
An -structure on a manifold is an endomorphism field
\phi\in\Gamma(M,\End(TM)) such that . Any -structure
determines an almost CR structure E_{1,0}\subset T_\C M given by the
-eigenbundle of . Using a compatible metric and connection
on , we construct an odd first-order differential operator ,
acting on sections of , whose principal symbol is of the
type considered in arXiv:0810.0338. In the special case of a CR-integrable
almost -structure, we show that when is the generalized
Tanaka-Webster connection of Lotta and Pastore, the operator is given by D
= \sqrt{2}(\dbbar+\dbbar^*), where \dbbar is the tangential Cauchy-Riemann
operator.
We then describe two "quantizations" of manifolds with -structure that
reduce to familiar methods in symplectic geometry in the case that is a
compatible almost complex structure, and to the contact quantization defined in
\cite{F4} when comes from a contact metric structure. The first is an
index-theoretic approach involving the operator ; for certain group actions
will be transversally elliptic, and using the results in arXiv:0810.0338,
we can give a Riemann-Roch type formula for its index. The second approach uses
an analogue of the polarized sections of a prequantum line bundle, with a CR
structure playing the role of a complex polarization.Comment: 31 page
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