10,861 research outputs found
Charles M. Breder, Jr.: Bahamas and Florida
Dr. Charles M. Breder, a well known ichthyologist, kept meticulous field diaries throughout his career. This publication is a transcription of field notes recorded during the Bacon Andros Expeditions, and trips to Florida, Ohio and Illinois during the 1930s. Breder's work in Andros included exploration of a "blue hole", inland ecosystems, and collection of marine and terrestrial specimens. Anecdotes include descriptions of camping on the beach, the "filly-mingoes" (flamingos) of Andros Island, the Marine
Studios of Jacksonville, FL, a trip to Havana, and the birth of seahorses. This publication is part of a series of transcriptions of Dr. Breder's diaries. (PDF contains 55 pages
Population structures in the SARA and SARB reference collections of Salmonella enterica according to MLST, MLEE and microarray hybridization
In the 1980's and 1990's, population genetic analyses based on Multilocus Enzyme Electrophoresis (MLEE) provided an initial overview of the genetic diversity of multiple bacterial species, including Salmonella enterica. The genetic diversity within S. enterica subspecies enterica according to MLEE is represented by the SARA and SARB reference collections, each consisting of 72 isolates, which have been extensively used for comparative analyses. MLEE has subsequently been replaced by Multilocus Sequence Typing (MLST). Our initial MLST results indicated that some strains within the SARB collection differed from their published descriptions. We therefore performed MLST on four versions of the SARB collection from different sources and one collection of SARA, and found that multiple isolates in SARB and SARA differ in serovar from their original description, and other SARB isolates differed between different sources. Comparisons with a global MLST database allowed a plausible reconstruction of the serovars of the original collection. MLEE, MLST and microarrays were largely concordant at recognizing closely related strains. MLST was particularly effective at recognizing discrete population genetic groupings while the two other methods provided hints of higher order relationships. However, quantitative pair-wise phylogenetic distances differed considerably between all three methods. Our results provide a translation dictionary from MLEE to MLST for the extant SARA and SARB collections which can facilitate genomic comparisons based on archival insights from MLEE
Hot phonon decay in supported and suspended exfoliated graphene
Near infrared pump-probe spectroscopy has been used to measure the ultrafast
dynamics of photoexcited charge carriers in monolayer and multilayer graphene.
We observe two decay processes occurring on 100 fs and 2 ps timescales. The
first is attributed to the rapid electron-phonon thermalisation in the system.
The second timescale is found to be due to the slow decay of hot phonons. Using
a simple theoretical model we calculate the hot phonon decay rate and show that
it is significantly faster in monolayer flakes than in multilayer ones. In
contrast to recent claims, we show that this enhanced decay rate is not due to
the coupling to substrate phonons, since we have also seen the same effect in
suspended flakes. Possible intrinsic decay mechanisms that could cause such an
effect are discussed.Comment: 4 pages, 3 figure
Using humanoid robots to study human behavior
Our understanding of human behavior advances as our humanoid robotics work progresses-and vice versa. This team's work focuses on trajectory formation and planning, learning from demonstration, oculomotor control and interactive behaviors. They are programming robotic behavior based on how we humans âprogramâ behavior in-or train-each other
Numerical Regularization of Electromagnetic Quantum Fluctuations in Inhomogeneous Dielectric Media
Electromagnetic Casimir stresses are of relevance to many technologies based
on mesoscopic devices such as MEMS embedded in dielectric media, Casimir
induced friction in nano-machinery, micro-fluidics and molecular electronics.
Computation of such stresses based on cavity QED generally require numerical
analysis based on a regularization process. A new scheme is described that has
the potential for wide applicability to systems involving realistic
inhomogeneous media. From a knowledge of the spectrum of the stationary modes
of the electromagnetic field the scheme is illustrated by estimating
numerically the Casimir stress on opposite faces of a pair of perfectly
conducting planes separated by a vacuum and the change in this result when the
region between the plates is filled with an incompressible inhomogeneous
non-dispersive dielectric.Comment: 5 pages, 2 figures, submitted to PR
X 1908+075: An X-ray Binary with a 4.4 day Period
X 1908+075 is an optically unidentified and highly absorbed X-ray source that
appears in early surveys such as Uhuru, OSO-7, Ariel V, HEAO-1, and the EXOSAT
Galactic Plane Survey. These surveys measured a source intensity in the range
of 2-12 mCrab at 2-10 keV, and the position was localized to ~ 0.5 degrees. We
use the Rossi X-ray Timing Explorer (RXTE) All Sky Monitor (ASM) to confirm our
expectation that a particular Einstein IPC detection (1E 1908.4+0730) provides
the correct position for X 1908+075. The analysis of the coded mask shadows
from the ASM for the position of 1E 1908.4+0730 yields a persistent intensity ~
8 mCrab (1.5-12 keV) over a 3 year interval beginning in 1996 February.
Furthermore, we detect a period of 4.400 +- 0.001 days with a false alarm
probability < 1.0e-7 . The folded light curve is roughly sinusoidal, with an
amplitude that is 22 % of the mean flux. The X-ray period may be attributed to
the scattering and absorption of X-rays through a stellar wind combined with
the orbital motion in a binary system. We suggest that X 1908+075 is an X-ray
binary with a high mass companion star.Comment: 6 pages, two-column,"emulateapj" style, submitted to Ap
Synchronization of Chaotic Oscillators due to Common Delay Time Modulation
We have found a synchronization behavior between two identical chaotic
systems^M when their delay times are modulated by a common irregular signal. ^M
This phenomenon is demonstrated both in two identical chaotic maps whose
delay times are driven by a common^M chaotic or random signal and in two
identical chaotic oscillators whose delay times are driven by^M a signal of
another chaotic oscillator. We analyze the phenomenon by using^M the Lyapunov
exponents and discuss it in relation with generalized synchronization.^MComment: 5 pages, 4 figures (to be published in PRE
Performance of distributed mechanisms for flow admission in wireless adhoc networks
Given a wireless network where some pairs of communication links interfere
with each other, we study sufficient conditions for determining whether a given
set of minimum bandwidth quality-of-service (QoS) requirements can be
satisfied. We are especially interested in algorithms which have low
communication overhead and low processing complexity. The interference in the
network is modeled using a conflict graph whose vertices correspond to the
communication links in the network. Two links are adjacent in this graph if and
only if they interfere with each other due to being in the same vicinity and
hence cannot be simultaneously active. The problem of scheduling the
transmission of the various links is then essentially a fractional, weighted
vertex coloring problem, for which upper bounds on the fractional chromatic
number are sought using only localized information. We recall some distributed
algorithms for this problem, and then assess their worst-case performance. Our
results on this fundamental problem imply that for some well known classes of
networks and interference models, the performance of these distributed
algorithms is within a bounded factor away from that of an optimal, centralized
algorithm. The performance bounds are simple expressions in terms of graph
invariants. It is seen that the induced star number of a network plays an
important role in the design and performance of such networks.Comment: 21 pages, submitted. Journal version of arXiv:0906.378
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