4,956 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
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
Exact steady-state velocity of ratchets driven by random sequential adsorption
We solve the problem of discrete translocation of a polymer through a pore,
driven by the irreversible, random sequential adsorption of particles on one
side of the pore. Although the kinetics of the wall motion and the deposition
are coupled, we find the exact steady-state distribution for the gap between
the wall and the nearest deposited particle. This result enables us to
construct the mean translocation velocity demonstrating that translocation is
faster when the adsorbing particles are smaller. Monte-Carlo simulations also
show that smaller particles gives less dispersion in the ratcheted motion. We
also define and compare the relative efficiencies of ratcheting by deposition
of particles with different sizes and we describe an associated
"zone-refinement" process.Comment: 11 pages, 4 figures New asymptotic result for low chaperone density
added. Exact translocation velocity is proportional to (chaperone
density)^(1/3
Tetramerisation of a frustrated spin-1/2 chain
We investigate a model of a frustrated spin-1/2 Heisenberg chain coupled to
adiabatic phonons with a general form of magnetoelastic coupling. For large
enough frustration and lattice coupling a new tetramerised phase with three
different bond lengths is found. We argue that the zig-zag spin-1/2 chain
LiVO might be a good candidate to observe such a phase
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