4,279 research outputs found
Dynamics of Multidimensional Secession
We explore a generalized Seceder Model with variable size selection groups
and higher dimensional genotypes, uncovering its well-defined mean-field
limiting behavior. Mapping to a discrete, deterministic version, we pin down
the upper critical size of the multiplet selection group, characterize all
relevant dynamically stable fixed points, and provide a complete analytical
description of its self-similar hierarchy of multiple branch solutions.Comment: 4 pages, 4 figures, PR
A molecular theory for two-photon and three-photon fluorescence polarization
In the analysis of molecular structure and local order in heterogeneous samples, multiphoton excitation of fluorescence affords chemically specific information and high-resolution imaging. This report presents the results of an investigation that secures a detailed theoretical representation of the fluorescence polarization produced by one-, two-, and three-photon excitations, with orientational averaging procedures being deployed to deliver the fully disordered limits. The equations determining multiphoton fluorescence response prove to be expressible in a relatively simple, generic form, and graphs exhibit the functional form of the multiphoton fluorescence polarization. Amongst other features, the results lead to the identification of a condition under which the fluorescence produced through the concerted absorption of any number of photons becomes completely unpolarized. It is also shown that the angular variation of fluorescence intensities is reliable indicator of orientational disorder
Quantum Monte Carlo calculations of H dissociation on Si(001)
We present quantum Monte Carlo calculations for various reaction pathways of
H with Si(001), using large model clusters of the surface. We obtain
reaction energies and energy barriers noticeably higher than those from
approximate exchange-correlation functionals. In improvement over previous
studies, our adsorption barriers closely agree with experimental data. For
desorption, the calculations give barriers for conventional pathways in excess
of the presently accepted experimental value, and pinpoint the role of coverage
effects and desorption from steps.Comment: 4 pages, 1 figur
Validation of S. Pombe sequence assembly by microarray hybridization
We describe a method to make physical maps of genomes using correlative hybridization patterns of probes to random pools of BACs. We derive thereby an estimated distance between probes, and then use this estimated distance to order probes. To test the method, we used BAC libraries from Schizzosaccharomyces pombe. We compared our data to the known sequence assembly, in order to assess accuracy. We demonstrate a small number of significant discrepancies between our method and the map derived by sequence assembly. Some of these discrepancies may arise because genome order within a population is not stable; imposing a linear order on a population may not be biologically meaningful
Formation of shear bands in drying colloidal dispersions
In directionally dried colloidal dispersions regular bands can appear behind the drying front, inclined at ±45° to the drying line. Although these features have been noted to share visual similarities with shear bands in metal, no physical mechanism for their formation has ever been suggested, until very recently. Here, through microscopy of silica and polystyrene dispersions, dried in Hele-Shaw cells, we demonstrate that the bands are indeed associated with local shear strains. We further show how the bands form, that they scale with the thickness of the drying layer, and that they are eliminated by the addition of salt to the drying dispersions. Finally, we reveal the origins of these bands in the compressive forces associated with drying
Reproductive cycle of the velvet swimming crab Necora puber (L.) (Decapoda, Brachyura, Portunidae) on the east coast of Ireland
An unfished population of Necora puber, in a coastal area just south of Dublin, was sampled monthly between August 1986 and November 1987 using baited creels. The reproductive cycle was analysed using gonad stages, the incidence and size distribution of ovigerous females and developmental stages of the egg masses. Both sexes started to breed at a carapace width of about 50 mm when they were about one year old. Seven ovarian and six testicular stages were recognised, both macro- and microscopically. The ovary underwent continuous cyclical changes and there was no distinct winter resting period. All ovigerous females had developing or ripe ovaries and they may thus produce more than one brood in a season. The main breeding season started in February with the greatest number of ovigerous females found in March-June and a peak in May. Less than 10% of females were ovigerous from August to January. The main periods of larval release were April, June and August. Spawning and recovering males were present throughout the year. Differences between the observed reproductive cycle and those studied in Britain and Spain are discussed
Jump-like unravelings for non-Markovian open quantum systems
Non-Markovian evolution of an open quantum system can be `unraveled' into
pure state trajectories generated by a non-Markovian stochastic (diffusive)
Schr\"odinger equation, as introduced by Di\'osi, Gisin, and Strunz. Recently
we have shown that such equations can be derived using the modal (hidden
variable) interpretation of quantum mechanics. In this paper we generalize this
theory to treat jump-like unravelings. To illustrate the jump-like behavior we
consider a simple system: A classically driven (at Rabi frequency )
two-level atom coupled linearly to a three mode optical bath, with a central
frequency equal to the frequency of the atom, , and the two side
bands have frequencies . In the large limit we
observed that the jump-like behavior is similar to that observed in this system
with a Markovian (broad band) bath. This is expected as in the Markovian limit
the fluorescence spectrum for a strongly driven two level atom takes the form
of a Mollow triplet. However the length of time for which the Markovian-like
behaviour persists depends upon {\em which} jump-like unraveling is used.Comment: 11 pages, 5 figure
Critical dimensions of the diffusion equation
We study the evolution of a random initial field under pure diffusion in
various space dimensions. From numerical calculations we find that the
persistence properties of the system show sharp transitions at critical
dimensions d1 ~ 26 and d2 ~ 46. We also give refined measurements of the
persistence exponents for low dimensions.Comment: 4 pages, 5 figure
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