10,845 research outputs found
Final technical report for NSF grant #OCE 75-20241, entitled Identification and role of the ultraplankton of the lower Chesapeake Bay region
Numbers and species identities of the most dominant small (\u3c15ÎŒm) photosynthetic Plankton were determined from samples of lower Chesapeake Bay water. The data is being compared to physical and chemical measurements of the Bay waters in an effort to determine conditions which encourage or inhibit growth of the organisms. Pure cultures of some of the more common species have been established and are being used to evaluate the roles of the organisms in terms of photosynthetic rates and utilization and excretion of nitrogen compounds
Further Observations of the Intermediate Mass Black Hole Candidate ESO 243-49 HLX-1
The brightest Ultra-Luminous X-ray source HLX-1 in the galaxy ESO 243-49
currently provides strong evidence for the existence of intermediate mass black
holes. Here we present the latest multi-wavelength results on this intriguing
source in X-ray, UV and radio bands. We have refined the X-ray position to
sub-arcsecond accuracy. We also report the detection of UV emission that could
indicate ongoing star formation in the region around HLX-1. The lack of
detectable radio emission at the X-ray position strengthens the argument
against a background AGN.Comment: 4 pages, 2 figures. Accepted 11th of Feb 2010. Contributed talk to
appear in Proceedings of "X-ray Astronomy 2009: Present Status,
Multi-Wavelength Approach and Future Perspectives", Bologna, Italy, September
7-11, 2009, AIP, eds. A. Comastri, M. Cappi, and L. Angelin
Investigating the Diversity of Wolbachia across the Spiny Ants (Polyrhachis)
Among insects, Wolbachia is an exceedingly common bacterial endosymbiont with a range of consequences of infection. Despite the frequency of Wolbachia infection, very little is known about this bacteria\u27s diversity and role within hosts, especially within ant hosts. In this study, we analyze the occurrence and diversity of Wolbachia across the spiny ants (Polyrhachis), a large and geographically diverse genus. Polyrhachis samples from throughout the host genus\u27 phylogenetic and biogeographical range were first screened for single infections of Wolbachia using the wsp gene and Sanger sequencing. The multilocus sequence typing (MLST) scheme was then used on these singly infected samples to identify the Wolbachia strains. A Wolbachia phylogeny was inferred from the Polyrhachis samples analyzed in this study as well as other Formicidae MLST profiles from the MLST online database. We hypothesized that three key host factors were impacting Wolbachia diversity within the Polyrhachis genus: biogeography, phylogeny, and species level. The results suggest that the phylogeny and biogeography of Polyrhachis hosts have no impact on Wolbachia diversity; however, species level may have some limited influence. Additionally, Wolbachia strains appear to group according to being either Old World or New World strains. Among the taxa able to form complete MLST allelic profiles, all twenty are seemingly new strains
Dynamics of a structured slug population model in the absence of seasonal variation
We develop a novel, nonlinear structured population model for the slug Deroceras reticulatum, a highly significant agricultural pest of great economic impact, in both organic and non-organic settings. In the absence of seasonal variations, we numerically explore the effect of life history traits that are dependent on an individual's size and measures of population biomass. We conduct a systematic exploration of parameter space and highlight the main mechanisms and implications of model design. A major conclusion of this work is that strong size dependent predation significantly adjusts the competitive balance, leading to non-monotonic steady state solutions and slowly decaying transients consisting of distinct generational cycles. Furthermore, we demonstrate how a simple ratio of adult to juvenile biomass can act as a useful diagnostic to distinguish between predated and non-predated environments, and may be useful in agricultural settings
The Broadband Spectrum of Galaxy Clusters
We examine whether nonthermal protons energized during a cluster merger are
simultaneously responsible for the Coma cluster's diffuse radio flux (via
secondary decay) and the departure of its intra-cluster medium (ICM) from a
thermal profile via Coulomb collisions between the quasithermal electrons and
the hadrons. Rather than approximating the influence of nonthermal
proton/thermal electron collisions as extremely rare events which cause an
injection of nonthermal, power-law electrons (the `knock-on' approximation), we
self-consistently solve (to our knowledge, for the first time) the covariant
kinetic equations for the two populations. The electron population resulting
from these collisions is out of equilibrium, yet not a power law, and
importantly displays a higher bremsstrahlung radiative efficiency than a pure
power law. Observations with GLAST will test this model directly.Comment: Accepted for publication in Ap
Reduction Operators of Linear Second-Order Parabolic Equations
The reduction operators, i.e., the operators of nonclassical (conditional)
symmetry, of (1+1)-dimensional second order linear parabolic partial
differential equations and all the possible reductions of these equations to
ordinary differential ones are exhaustively described. This problem proves to
be equivalent, in some sense, to solving the initial equations. The ``no-go''
result is extended to the investigation of point transformations (admissible
transformations, equivalence transformations, Lie symmetries) and Lie
reductions of the determining equations for the nonclassical symmetries.
Transformations linearizing the determining equations are obtained in the
general case and under different additional constraints. A nontrivial example
illustrating applications of reduction operators to finding exact solutions of
equations from the class under consideration is presented. An observed
connection between reduction operators and Darboux transformations is
discussed.Comment: 31 pages, minor misprints are correcte
Dialogue based interfaces for universal access.
Conversation provides an excellent means of communication for almost all people. Consequently, a conversational interface is an excellent mechanism for allowing people to interact with systems. Conversational systems are an active research area, but a wide range of systems can be developed with current technology. More sophisticated interfaces can take considerable effort, but simple interfaces can be developed quite rapidly. This paper gives an introduction to the current state of the art of conversational systems and interfaces. It describes a methodology for developing conversational interfaces and gives an example of an interface for a state benefits web site. The paper discusses how this interface could improve access for a wide range of people, and how further development of this interface would allow a larger range of people to use the system and give them more functionality
Evidence of a Curved Synchrotron Spectrum in the Supernova Remnant SN 1006
A joint spectral analysis of some Chandra ACIS X-ray data and Molonglo
Observatory Synthesis Telescope radio data was performed for 13 small regions
along the bright northeastern rim of the supernova remnant SN 1006. These data
were fitted with a synchrotron radiation model. The nonthermal electron
spectrum used to compute the photon emission spectra is the traditional
exponentially cut off power law, with one notable difference: The power-law
index is not a constant. It is a linear function of the logarithm of the
momentum. This functional form enables us to show, for the first time, that the
synchrotron spectrum of SN 1006 seems to flatten with increasing energy. The
effective power-law index of the electron spectrum is 2.2 at 1 GeV (i.e., radio
synchrotron-emitting momenta) and 2.0 at about 10 TeV (i.e., X-ray
synchrotron-emitting momenta). This amount of change in the index is
qualitatively consistent with theoretical models of the amount of curvature in
the proton spectrum of the remnant. The evidence of spectral curvature implies
that cosmic rays are dynamically important instead of being "test" particles.
The spectral analysis also provides a means of determining the critical
frequency of the synchrotron spectrum associated with the highest-energy
electrons. The critical frequency seems to vary along the northeastern rim,
with a maximum value of 1.1e17 (0.6e17 - 2.1e17) Hz. This value implies that
the electron diffusion coefficient can be no larger than a factor of ~4.5-21
times the Bohm diffusion coefficient if the velocity of the forward shock is in
the range 2300-5000 km/s. Since the coefficient is close to the Bohm limit,
electrons are accelerated nearly as fast as possible in the regions where the
critical frequency is about 1.0e17 Hz.Comment: 41 pages, 8 figures, accepted by Ap
High-quality Phase-Shifted Bragg grating sensor inscribed with only one laser pulse in a polymer optical fiber
We present the first phase-shifted polymer optical fiber Bragg grating sensor inscribed with only one KrF laser pulse. The phase shift defect was created directly during the grating inscription process by placing a very narrow blocking aperture, in the center of the UV beam. One laser pulse with a duration of 15 ns and energy 6.3 mJ is adequate to introduce a refractive index change of 0.69Ă10-4 in the fiber core. The high-quality produced Bragg grating structure rejects 16.3 dB transmitted power, thus providing 97.6% reflectivity, which is well suited for photonic applications. The transmission notch depth is about 10 dB and very sharp notches of 3 dB width ranging from 14 pm is reported. The temperature, strain, and pressure response of the sensor has been characterized showing promising results in applications that require high-precision measurements. The ability to inscribe these high-quality sensors effectively can significantly reduce their production cost in industry
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