3,615 research outputs found
New critical frontiers for the Potts and percolation models
We obtain the critical threshold for a host of Potts and percolation models
on lattices having a structure which permits a duality consideration. The
consideration generalizes the recently obtained thresholds of Scullard and Ziff
for bond and site percolation on the martini and related lattices to the Potts
model and to other lattices.Comment: 9 pages, 5 figure
Consequences of self and foreign superantigen interaction with specific VB elements of the murine TCR aB
Journal ArticleThe aB T-cell receptor (TCRaB) recognizes a ligand composed of an antigen fragment complexed with a product of the major histocompatibility complex (MHC). The repertoire of receptors is limited both by the germ line of receptor variable elements and by selective events that take place during T-cell development. The current view is that the germ-line repertoire is expressed in the thymus randomly but that only those T cells bearing receptors that successfully interact with MHC molecules expressed on thymic cortical epithelial cells are allowed to mature (Bevan and Fink 1978; Zinkernagel et al. 1978; Kisielow et al. 1988; Sha et al. 1988). Furthermore, during the process of establishing tolerance to self-antigens, this positively selected population is further reduced by the deletion or inactivation of clones whose receptors continue to interact with self-antigen/MHC ligands (Kappler et al. 1987a, 1988; MacDonald et al. 1988; Pullen et al. 1988). Thus, positive and negative selections reduce expressed receptor repertoire in the periphery to a fraction of the germ-line repertoire
Why is timing of bird migration advancing when individuals are not?
Recent advances in spring arrival dates have been reported in many migratory species but the mechanism driving these advances is unknown. As population declines are most widely reported in species that are not advancing migration, there is an urgent need to identify the mechanisms facilitating and constraining these advances. Individual plasticity in timing of migration in response to changing climatic conditions is commonly proposed to drive these advances but plasticity in individual migratory timings is rarely observed. For a shorebird population that has significantly advanced migration in recent decades, we show that individual arrival dates are highly consistent between years, but that the arrival dates of new recruits to the population are significantly earlier now than in previous years. Several mechanisms could drive advances in recruit arrival, none of which require individual plasticity or rapid evolution of migration timings. In particular, advances in nest-laying dates could result in advanced recruit arrival, if benefits of early hatching facilitate early subsequent spring migration. This mechanism could also explain why arrival dates of short-distance migrants, which generally return to breeding sites earlier and have greater scope for advance laying, are advancing more rapidly than long-distance migrants
Saturated hydrocarbon polymeric binder for advanced solid propellant and hybrid solid grains Quarterly report no. 3, 1 May - 31 Jul. 1966
Saturated hydrocarbon polymeric binder for advanced solid propellant and hybrid solid grain
Saturated hydrocarbon polymeric binder for advanced solid propellant and hybrid solid grains Quarterly report no. 2, 1 Feb. - 30 Apr. 1966
Synthesis and analysis of ethylene-neohexene copolymers with other non ketene-imine group free radicals for solid and hybrid grain propellant saturated hydrocarbon binder progra
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Characterization of mesostasis areas in mare basalts: constraining melt compositions from which apatite crystallizes
Crystallization of major silicate and oxide phases from basaltic melts produces late-stage liquids whose chemical compositions differ from the initial melt. These chemically evolved liquids crystallize phases in the interstitial mesostasis regions in lunar basaltic rocks. Enrichment of incompatible elements, including volatiles such as OH, F, Cl, is characteristic of these late-stage liquids and encourages growth of accessory phases including apatite [Ca5(PO4)2(F,Cl,OH)]. Apatite is the main volatile bearing crystalline phase in lunar rocks. It starts crystallizing after ~95% melt solidification in typical mare basalts, but could crystallize earlier, after ~85-90% solidification in KREEP basalts. Using the OH contents of apatites, several researchers have calculated water contents for parental magmas. These calculated parental magma water contents can then be used to estimate a range of values for water in the mantle source regions of mare basalts [e.g.,2-6]. Therefore, a better characterization of the mesostasis areas, and of the melts in which apatite forms, is paramount to gain further insights and constraints on water in the lunar interior, especially because important parameters such as partitioning of volatiles between late-stage melts and apatite remain poorly constrained
Critical Percolation in Finite Geometries
The methods of conformal field theory are used to compute the crossing
probabilities between segments of the boundary of a compact two-dimensional
region at the percolation threshold. These probabilities are shown to be
invariant not only under changes of scale, but also under mappings of the
region which are conformal in the interior and continuous on the boundary. This
is a larger invariance than that expected for generic critical systems.
Specific predictions are presented for the crossing probability between
opposite sides of a rectangle, and are compared with recent numerical work. The
agreement is excellent.Comment: 10 page
NONLINEAR REGRESSION FUNCTIONS FOR FORAGE NUTRIENT DISAPPEARANCE FROM BAGS INCUBATED IN THE RUMEN
Seven nonlinear regression functions are compared for fitting rumen in situ disappearance data. The standard function is based on a simple one-compartment model. In addition, we consider a time lag modification, a two-compartment model, and functions based on underlying probability models for degradation time. The empirical suitability of the seven regression functions are assessed using two in situ experiments involving forages fed to dairy cows. A function based on the loglogistic distribution is shown to have empirical and theoretical advantages
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