5,021 research outputs found
Heisenberg and Modular Invariance of N=2 Conformal Field Theory
We present a theta function representation of the twisted characters for the
rational N=2 superconformal field theory, and discuss the Jacobi-form like
functional properties of these characters for a fixed central charge under the
action of a finite Heisenberg group and modular transformations.Comment: 21 pages, Latex, 1 figure; minor typos corrected--Journal versio
Elucidating the Pd Active Sites of Bimetallic Gold-palladium Catalysts Using Chemisorption and Titration Techniques
A bimetallic nanoparticle catalyst combines two different metals on an oxide support, which can increase the selectivity towards useful products that may be too tightly bound to a monometallic catalyst. To explore the surface properties of such a system, we made a group of four PdAu bimetallic catalysts with varying gold mass loadings to compare with a parent Pd catalyst. The parent catalyst was synthesized using ion exchange, and gold was added to this parent Pd catalyst using incipient wetness impregnation (IWI) to create four bimetallic catalysts. All catalysts were characterized using H2 and CO chemisorption in tandem with O2 and H2 titration methods. The measured dispersion of the parent catalyst ranged from 60-72% which is consistent with previous measurements for catalysts synthesized with the same loading and synthesis technique. This dispersion value implies an average Pd particle diameter of about 1.8 nm. Each bimetallic catalyst was characterized using chemisorption and titration methods and the fractional gold coverage was found to be about 70%, independent of the gold loading. In parallel with the chemisorption and titration measurements, we used ICP-OES analysis to determine the gold content in the bimetallic catalysts, but these results were inconsistent with the quantities of gold used in the IWI synthesis
Cajun Crabs
A brother and sister are crabbing together at the Rockefeller Refuge in southern Louisiana. An irritating bully, Eamon teaches Caitlyn how to crab, but has an embarrassing mishap during the day. Caitlyn comes to the rescue - and has her own little revenge
Elementary Excitations in Quantum Antiferromagnetic Chains: Dyons, Spinons and Breathers
Considering experimental results obtained on three prototype compounds, TMMC,
CsCoCl3 (or CsCoBr3) and Cu Benzoate, we discuss the importance of non-linear
excitations in the physics of quantum (and classical) antiferromagnetic spin
chains.Comment: Invited at the International Symposium on Cooperative Phenomena of
Assembled Metal Complexes, November 15-17, 2001, Osaka, Japa
Demonstrating a Perimeter Trap Crop Approach to Pest Management on Summer Squash in New England
Perimeter trap cropping (PTC) involves using a trap crop, and possibly other border defenses, to encircle and protect the main cash crop like fortress walls. Six growers in Connecticut used PTC to protect commercial summer squash plantings from cucumber beetles and bacterial wilt damage. Grower surveys were used to compare PTC program results to the conventional multiple-full-field-spray system formerly used on the farms. Most growers using PTC stated that this system improved and simplified pest control, reduced pesticide use (93%) and crop loss, and saved them time and money compared to their conventional program
Charge Ordering and Spin Dynamics in NaV2O5
We report high-resolution neutron inelastic scattering experiments on the
spin excitations of NaV2O5. Below Tc, two branches associated with distinct
energy gaps are identified. From the dispersion and intensity of the spin
excitation modes, we deduce the precise zig-zag charge distribution on the
ladder rungs and the corresponding charge order (about 0.6). We argue that the
spin gaps observed in the low-T phase of this compound are primarily due to the
charge transfer.Comment: 4 pages, 5 figures, to appear in Phys. Rev. Let
Amp\`ere-Class Pulsed Field Emission from Carbon-Nanotube Cathodes in a Radiofrequency Resonator
Pulsed field emission from cold carbon-nanotube cathodes placed in a
radiofrequency resonant cavity was observed. The cathodes were located on the
backplate of a conventional -cell resonant cavity operating at
1.3-GHz and resulted in the production of bunch train with maximum average
current close to 0.7 Amp\`ere. The measured Fowler-Nordheim characteristic,
transverse emittance, and pulse duration are presented and, when possible,
compared to numerical simulations. The implications of our results to
high-average-current electron sources are briefly discussed.Comment: 5 pages, 6 figures; submitted to Applied Physics Letter
Boundary definition of a multiverse measure
We propose to regulate the infinities of eternal inflation by relating a late
time cut-off in the bulk to a short distance cut-off on the future boundary.
The light-cone time of an event is defined in terms of the volume of its future
light-cone on the boundary. We seek an intrinsic definition of boundary volumes
that makes no reference to bulk structures. This requires taming the fractal
geometry of the future boundary, and lifting the ambiguity of the conformal
factor. We propose to work in the conformal frame in which the boundary Ricci
scalar is constant. We explore this proposal in the FRW approximation for
bubble universes. Remarkably, we find that the future boundary becomes a round
three-sphere, with smooth metric on all scales. Our cut-off yields the same
relative probabilities as a previous proposal that defined boundary volumes by
projection into the bulk along timelike geodesics. Moreover, it is equivalent
to an ensemble of causal patches defined without reference to bulk geodesics.
It thus yields a holographically motivated and phenomenologically successful
measure for eternal inflation.Comment: 39 pages, 4 figures; v2: minor correction
Matching Reads to Many Genomes with the r-Index
The r-index is a tool for compressed indexing of genomic databases for exact pattern matching, which can be used to completely align reads that perfectly match some part of a genome in the database or to find seeds for reads that do not. This article shows how to download and install the programs ri-buildfasta and ri-align; how to call ri-buildfasta on an FASTA file to build an r-index for that file; and how to query that index with ri-align
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