4,790 research outputs found
Scattering by a toroidal coil
In this paper we consider the Schr\"odinger operator in with
a long-range magnetic potential associated to a magnetic field supported inside
a torus . Using the scheme of smooth perturbations we construct
stationary modified wave operators and the corresponding scattering matrix
. We prove that the essential spectrum of is an
interval of the unit circle depending only on the magnetic flux across
the section of . Additionally we show that, in contrast to the
Aharonov-Bohm potential in , the total scattering cross-section
is always finite. We also conjecture that the case treated here is a typical
example in dimension 3.Comment: LaTeX2e 17 pages, 1 figur
Diffusion of gold nanoclusters on graphite
We present a detailed molecular-dynamics study of the diffusion and
coalescence of large (249-atom) gold clusters on graphite surfaces. The
diffusivity of monoclusters is found to be comparable to that for single
adatoms. Likewise, and even more important, cluster dimers are also found to
diffuse at a rate which is comparable to that for adatoms and monoclusters. As
a consequence, large islands formed by cluster aggregation are also expected to
be mobile. Using kinetic Monte Carlo simulations, and assuming a proper scaling
law for the dependence on size of the diffusivity of large clusters, we find
that islands consisting of as many as 100 monoclusters should exhibit
significant mobility. This result has profound implications for the morphology
of cluster-assembled materials
Caspase I-related protease inhibition retards the execution of okadaic acid- and camptothecin-induced apoptosis and PAI-2 cleavage, but not commitment to cell death in HL-60 cells
We have previously reported that the putative cytoprotective protease inhibitor, plasminogen activator inhibitor type 2 (PAI-2), is specifically cleaved during okadaic acid-induced apoptosis in a myeloid leukaemic cell line (Br J Cancer (1994) 70: 834â840). HL-60 cells exposed to okadaic acid and camptothecin underwent morphological and biochemical changes typical of apoptosis, including internucleosomal DNA fragmentation and PAI-2 cleavage. Significant endogenous PAI-2 cleavage was observed 9 h after exposure to okadaic acid; thus correlating with other signs of macromolecular degradation, like internucleosomal DNA fragmentation. In camptothecin-treated cells, PAI-2 cleavage was an early event, detectable after 2 h of treatment, and preceding internucleosomal DNA fragmentation. The caspase I selective protease inhibitor, YVAD-cmk, inhibited internucleosomal DNA fragmentation and PAI-2 cleavage of okadaic acid and camptothecin-induced apoptotic cells. YVAD-cmk rather sensitively and non-toxically inhibited camptothecin-induced morphology, but not okadaic acid-induced morphology. In in vitro experiments recombinant PAI-2 was not found to be a substrate for caspase I. The results suggest that caspase I selective protease inhibition could antagonize parameters coupled to the execution phase of okadaic acid- and camptothecin-induced apoptosis, but not the commitment to cell death. © 1999 Cancer Research Campaig
Resistivity scaling and critical dynamics of fully frustrated Josephson-junction arrays with on-site dissipation
We study the scaling behavior and critical dynamics of the resistive
transition in Josephson-junction arrays, at f=1/2 flux quantum per plaquette,
by numerical simulation of an on-site dissipation model for the dynamics. The
results are compared with recent simulations using the
resistively-shunted-junction model. For both models, we find that the
resistivity scaling and critical dynamics of the phases are well described by
the same critical temperature as for the chiral (vortex-lattice) transition,
with a power-law divergent correlation length. The behavior is consistent with
the single transition scenario, where phase and chiral variables order at the
same temperature, but with different dynamic exponents z for phase coherence
and chiral order.Comment: 17 pages, 13 figures, to appear in Phys. Rev.
How to observe the Efimov effect
We propose to observe the Efimov effect experimentally by applying an
external electric field on atomic three-body systems. We first derive the
lowest order effective two-body interaction for two spin zero atoms in the
field. Then we solve the three-body problem and search for the extreme
spatially extended Efimov states. We use helium trimers as an illustrative
numerical example and estimate the necessary field strength to be less than 2.7
V/angstrom.Comment: 4 pages, 2 postscript figures, psfig.sty, revte
Fermi's golden rule and exponential decay as a RG fixed point
We discuss the decay of unstable states into a quasicontinuum using models of
the effective Hamiltonian type. The goal is to show that exponential decay and
the golden rule are exact in a suitable scaling limit, and that there is an
associated renormalization group (RG) with these properties as a fixed point.
The method is inspired by a limit theorem for infinitely divisible
distributions in probability theory, where there is a RG with a Cauchy
distribution, i.e. a Lorentz line shape, as a fixed point. Our method of
solving for the spectrum is well known; it does not involve a perturbation
expansion in the interaction, and needs no assumption of a weak interaction. We
use random matrices for the interaction, and show that the ensemble
fluctuations vanish in the scaling limit. Thus the limit is the same for every
model in the ensemble with probability one.Comment: 20 pages, 1 figur
Line shape analysis of the K transition in muonic hydrogen
The K transition in muonic hydrogen was measured with a
high-resolution crystal spectrometer. The spectrum is shown to be sensitive to
the ground-state hyperfine splitting, the corresponding triplet-to-singlet
ratio, and the kinetic energy distribution in the state. The hyperfine
splitting and triplet-to-singlet ratio are found to be consistent with the
values expected from theoretical and experimental investigations and,
therefore, were fixed accordingly in order to reduce the uncertainties in the
further reconstruction of the kinetic energy distribution. The presence of
high-energetic components was established and quantified in both a
phenomenological, i.e. cascade-model-free fit, and in a direct deconvolution of
the Doppler broadening based on the Bayesian approach.Comment: 22 pages, 21 figure
A unified earthquake catalogue for the North Sea to derisk European CCS operations
Carbon capture and storage (CCS) technology is essential to European decarbonisation efforts, and several offshore CO2 storage projects are being developed in the North Sea. Understanding the geomechanical response to CO2 injection is key to both the pre-characterisation and operation of a storage reservoir. A thorough assessment of seismicity gives critical insights into the stress field and faulting around reservoirs, both key controls on the geomechanical response to injection. Seismicity also illuminates potential hydraulic pathways for leakage, be it directly by revealing the extent of faults, or indirectly through fractures imaged by measurements of seismic anisotropy. High quality seismicity data is critical to underpin all of these methods of analysis. This paper presents the most complete catalogue of seismicity in the North Sea to date. The combined data are enabling revised assessments of seismic hazard and leakage risk in the North Sea, as well as a better understanding of faulting and stress. This study shows the value of unifying disparate seismicity data, allowing for more accurate seismological analyses. These lay the foundation for better management of risks for not only geologic CO2 storage, but other offshore industries and infrastructure
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