9,643 research outputs found
Brassica genomics: a complement to, and early beneficiary of, the Arabidopsis sequence.
Those studying the genus Brassica will be among the early beneficiaries of the now-completed Arabidopsis sequence. The remarkable morphological diversity of Brassica species and their relatives offers valuable opportunities to advance our knowledge of plant growth and development, and our understanding of rapid phenotypic evolution
AMPHIBIAN DISTRIBUTION IN THE GEORGIA SEA ISLANDS: IMPLICATIONS FROM THE PAST AND FOR THE FUTURE
We summarized amphibian distributions for 12 coastal islands in Georgia, USA. Occurrence among islands was correlated with life history traits, habitats, island size, distance to other islands, and island geological age. Species’ distributions were determined from published literature. Island sizes and vegetation types were derived from 2011 Georgia Department of Natural Resources habitat maps, which included both federal and state vegetation classification systems. Species occurring on more islands tended to have greater total reproductive output (i.e., life span >4 years, and annual egg production >1,000 eggs) and adults had tolerance of brackish environs. Larger islands had greatÂer area of freshwater wetlands, predominantly short hydroperiod (<6 months). Species tied to long hydroperiod wetlands (>6 months) were more restricted in their distribution across islands. Overall, larger islands supported more species, but the correlation was weaker for geologically younger HoÂlocene islands (age <11,000 years). While Euclidean distance between islands does not necessarily preclude inter-island dispersal, inhospitable habitat for amphibians (brackish tidal marshes and creeks interspersed with wide rivers) suggests that inter-island dispersal is very limited. The paucity of recent occurrence data for amphibians in this dynamic coastal region, let alone standardized annual moniÂtoring data, hinders efforts to model species’ vulnerability in a region susceptible to sea level rise and development pressure. The most common survey method, standardized amphibian vocal surveys, will detect Anuran reproductive efforts, but is unlikely to ascertain if breeding was successful or to detect salamanders. While it will not replace actual population data, consideration of critical life-history traits and breeding habitat availability can be used to direct management to support long-term species perÂsistence in changing environs. Even common amphibians in coastal conservation areas of Georgia are vulnerable to increasing population isolation caused by unsuitable habitat
Intrinsic Cavity QED and Emergent Quasi-Normal Modes for Single Photon
We propose a special cavity design that is constructed by terminating a
one-dimensional waveguide with a perfect mirror at one end and doping a
two-level atom at the other. We show that this atom plays the intrinsic role of
a semi-transparent mirror for single photon transports such that quasi-normal
modes (QNM's) emerge spontaneously in the cavity system. This atomic mirror has
its reflection coefficient tunable through its level spacing and its coupling
to the cavity field, for which the cavity system can be regarded as a two-end
resonator with a continuously tunable leakage. The overall investigation
predicts the existence of quasi-bound states in the waveguide continuum. Solid
state implementations based on a dc-SQUID circuit and a defected line resonator
embedded in a photonic crystal are illustrated to show the experimental
accessibility of the generic model.Comment: 4 pages,5 figures, Comments welcom
Unstable recurrent patterns in Kuramoto-Sivashinsky dynamics
We undertake a systematic exploration of recurrent patterns in a
1-dimensional Kuramoto-Sivashinsky system. For a small, but already rather
turbulent system, the long-time dynamics takes place on a low-dimensional
invariant manifold. A set of equilibria offers a coarse geometrical partition
of this manifold. A variational method enables us to determine numerically a
large number of unstable spatiotemporally periodic solutions. The attracting
set appears surprisingly thin - its backbone are several Smale horseshoe
repellers, well approximated by intrinsic local 1-dimensional return maps, each
with an approximate symbolic dynamics. The dynamics appears decomposable into
chaotic dynamics within such local repellers, interspersed by rapid jumps
between them.Comment: 11 pages, 11 figure
Study of intermixing in a GaAs/AlGaAs quantum-well structure using doped spin-on silica layers
The effect of two different dopants, P and Ga, in spin-on glass (SOG) films on impurity-free vacancy disordering (IFVD) in GaAs/AlGaAs quantum-well structures has been investigated. It is observed that by varying the annealing and baking temperatures, P-doped SOG films created a similar amount of intermixing as the undoped SOG films. This is different from the results of other studies of P-doped SiOâ‚‚ and is ascribed to the low doping concentration of P, indicating that the doping concentration of P in the SiOâ‚‚ layer is one of the key parameters that may control intermixing. On the other hand, for all the samples encapsulated with Ga-doped SOG layers, significant suppression of the intermixing was observed, making them very promising candidates with which to achieve the selective-area defect engineering that is required for any successful application of IFVD.One of the authors (H.H.T.) acknowledges a fellowship
awarded to him by the Australian Research Council
Deflection of Slow Light by Magneto-Optically Controlled Atomic Media
We present a semi-classical theory for light deflection by a coherent
-type three-level atomic medium in an inhomogeneous magnetic field or
an inhomogeneous control laser. When the atomic energy levels (or the Rabi
coupling by the control laser) are position-dependent due to the Zeeman effect
by the inhomogeneous magnetic field (or the inhomogeneity of the control field
profile), the spatial dependence of the refraction index of the atomic medium
will result in an observable deflection of slow signal light when the
electromagnetically induced transparency happens to avoid medium absorption.
Our theoretical approach based on Fermat's principle in geometrical optics not
only provides a consistent explanation for the most recent experiment in a
straightforward way, but also predicts the new effects for the slow signal
light deflection by the atomic media in an inhomogeneous off-resonant control
laser field.Comment: 4 pages, 3 figure
Numerical investigation on hydrodynamic performance of a novel shaftless rim-driven counter-rotating thruster considering gap fluid
Shaftless rim-driven thruster (RDT) has recently become the research focus for marine propulsion, primarily due to low vibration, low noise, and energy saving as its advantage. This study is based on CFD theory and used the Ansys-Fluent software to examine the hydrodynamic performance of a novel rim-driven counter-rotating thruster (RDCRT). It takes a No.19A+Ka4-70 duct propeller and a 20 kW RDT as examples, as it verifies the feasibility of the simulation method. It establishes three geometric models for RDCRT's hydrodynamic performance to determine whether it is necessary to consider the motor stator/rotor gap. It examines the flow distribution characteristics of the gap fluid friction force and flow channel and investigates the gap's influence on the hydrodynamic performance. Relevant case studies indicate that, when considering the gap, the calculation outcomes of the simulation model are between the stationary model and the rotational model of the rotor inner wall when ignoring the gap. In the Forward and Aft regions, the total frictional power of the gap channel correspondingly accounts for 1.7% and 1.35% of the rated power. Additionally, compared to situations with a gap, the pressure coefficient of the inner surface of the Forward and Aft rim without a gap is more significant. Thus, the hydrodynamic simulation model should not ignore the gap. For the RDCRT, the thrust coefficient, the torque coefficient, and the maximum efficiency value are more significant than those of the single-propeller RDT, hence validating its advantages
Controlling Quasibound States in 1D Continuum Through Electromagnetic Induced Transparency Mechanism
We study the coherent scattering process of a single photon confined in an
one-dimensional (1D) coupled cavity-array, where a -type three-level
atom is placed inside one of the cavities in the array and behaves as a
functional quantum node (FQN). We show that, through the electromagnetic
induced transparency (EIT) mechanism, the -type FQN bears complete
control over the reflection and transmission of the incident photon along the
cavity-array. We also demonstrate the emergence of a quasibound state of the
single photon inside a secondary cavity constructed by two distant FQN's as two
end mirrors, from which we are motivated to design an all-optical single photon
storage device of quantum coherence.Comment: 8 pages, 6 figure
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