1,811 research outputs found
Distribution, Hybridization, and Taxonomic Status of Two-lined Salamanders (\u3ci\u3eEurycea bislineata\u3c/i\u3e complex) in Virginia and West Virginia
We used three diagnostic protein markers to examine salamanders of the Eurycea bislineata complex at 80 localities in Virginia and West Virginia. Two groups were strongly differentiated and met at a narrow contact zone. Rare hybridization was observed as well as limited introgression up to 5 km north and 10 km south of the contact zone. At the contact zone, 1% F1, 2% F2, 32% backcross, and 66% parental genotypes were observed. This pattern of parapatric distribution with limited hybridization and introgression argues for the recognition of Eurycea bislineata and E. cirrigera as separate species
Modeling Micro-Porous Surfaces for Secondary Electron Emission Control to Suppress Multipactor
This work seeks to understand how the topography of a surface can be engineered to control secondary electron emission (SEE) for multipactor suppression. Two unique, semi-empirical models for the secondary electron yield (SEY) of a micro-porous surface are derived and compared. The first model is based on a two-dimensional (2D) pore geometry. The second model is based on a three-dimensional (3D) pore geometry. The SEY of both models is shown to depend on two categories of surface parameters: chemistry and topography. An important parameter in these models is the probability of electron emissions to escape the surface pores. This probability is shown by both models to depend exclusively on the aspect ratio of the pore (the ratio of the pore height to the pore diameter). The increased accuracy of the 3D model (compared to the 2D model) results in lower electron escape probabilities with the greatest reductions occurring for aspect ratios less than two. In order to validate these models, a variety of micro-porous gold surfaces were designed and fabricated using photolithography and electroplating processes. The use of an additive metal-deposition process (instead of the more commonly used subtractive metal-etch process) provided geometrically ideal pores which were necessary to accurately assess the 2D and 3D models. Comparison of the experimentally measured SEY data with model predictions from both the 2D and 3D models illustrates the improved accuracy of the 3D model. For a micro-porous gold surface consisting of pores with aspect ratios of two and a 50% pore density, the 3D model predicts that the maximum total SEY will be one. This provides optimal engineered surface design objectives to pursue for multipactor suppression using gold surfaces
Time Optimal Control in Spin Systems
In this paper, we study the design of pulse sequences for NMR spectroscopy as
a problem of time optimal control of the unitary propagator. Radio frequency
pulses are used in coherent spectroscopy to implement a unitary transfer of
state. Pulse sequences that accomplish a desired transfer should be as short as
possible in order to minimize the effects of relaxation and to optimize the
sensitivity of the experiments. Here, we give an analytical characterization of
such time optimal pulse sequences applicable to coherence transfer experiments
in multiple-spin systems. We have adopted a general mathematical formulation,
and present many of our results in this setting, mindful of the fact that new
structures in optimal pulse design are constantly arising. Moreover, the
general proofs are no more difficult than the specific problems of current
interest. From a general control theory perspective, the problems we want to
study have the following character. Suppose we are given a controllable right
invariant system on a compact Lie group, what is the minimum time required to
steer the system from some initial point to a specified final point? In NMR
spectroscopy and quantum computing, this translates to, what is the minimum
time required to produce a unitary propagator? We also give an analytical
characterization of maximum achievable transfer in a given time for the two
spin system.Comment: 20 Pages, 3 figure
Building Energy Use and Conservation in Cycle VIII of the Texas Institutional Conservation Program
Sixty-two technical assistance (energy audit)
reports by twelve different consulting firms representing
fifteen independent school districts, nine
hospitals, and five colleges have been reviewed to
assess energy use characteristics and recommended
energy saving measures. Such measures include both
maintenance and operation (H&O) measures (generally
regarded as "low-cost, no-cost") and energy conservation
(ECH) measures (generally more expensive and
requiring outside skills). Implementation cost,
annual savings of energy and costs, and paybacks
were reported for all M&Os and ECHs. Measures were
broken down by the consulting firms according to
energy use characteristics and categories, and it
was determined that average costs for electricity
and gas, before implementation of M&Os and ECHs,
were 4.85/MMBTU respectively. The
total implementation cost and projected annual
savings for the M&Os are 223,000
respectively, yielding a four-month payback. The
corresponding results for implementation of ECHs are
555,000, resulting in a four-year
payback. Also, some obvious problems in the preparation
of technical assistance reports along with
the general background and implementation of the
Institutional Conservation Program in Texas,
resulting from the National Energy Act of 1978, are
discussed
Anion vacancy driven magnetism in incipient ferroelectric SrTiO3 and KTaO3 nanoparticles
Based on our analytical results [http://arxiv.org/abs/1006.3670], we predict
that undoped nanoparticles (size <10-100nm) of incipient ferroelectrics without
any magnetic ions can become ferromagnetic even at room temperatures due to the
inherent presence of a new type of magnetic defects with spin S=1, namely
oxygen vacancies, where the magnetic triplet state is the ground state in the
vicinity of the surface (magnetic shell), while the nonmagnetic singlet is the
ground state in the bulk material (nonmagnetic core). Consideration of randomly
distributed magnetic spins (S=1) had shown that magnetic properties of
incipient ferroelectric nanoparticles are strongly size and temperature
dependent due to the size and temperature dependence of their dielectric
permittivity and the effective Bohr radius proportional to permittivity. The
phase diagrams in coordinates temperature - particle radius are considered. In
particular, for particle radii less that the critical radius ferromagnetic
long-range order appears in a shell region of thickness 5 - 50 nm once the
concentration of magnetic defects exceeds the magnetic percolation threshold.
The critical radius is calculated in the mean field theory from the condition
of the magnetic defects exchange energy equality to thermal energy. For
particle radii higher than critical value only the paramagnetic phase is
possible. The conditions of the super-paramagnetic state appearance in the
assembly of nanoparticles with narrow distribution function of their sizes are
discussed also.Comment: 33 pages, 7 figures, 2 appendice
Triphenylsulfonium topophotochemistry
The products from the 193 nm irradiation of triphenylsulfonium nonaflate (TPS) embedded in a poly(methyl methacrylate) (PMMA) film have been characterized. The analysis of the photoproduct formation was performed using chromatographic techniques including HPLC, GPC and GC-MS as well as UV-vis and NMR spectroscopic methods. Two previously unreported TPS photoproducts, triphenylene and dibenzothiophene, were detected; additionally, GPC and DOSY-NMR spectroscopic analyses after irradiation suggested that TPS fragments had been incorporated into the polymer film. The irradiation of acetonitrile solutions containing 10% w/v PMMA and 1% w/v TPS in a 1 cm-path-length cuvette showed only a trace amount of triphenylene or dibenzothiophene, indicating that topochemical factors were important for the formation of these molecules. The accumulated evidence indicates that both products were formed by in-cage, secondary photochemical reactions: 2-(phenylthio)biphenyl to triphenylene, and diphenylsulfide to dibenzothiophene
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