14,900 research outputs found
Solving Set Constraint Satisfaction Problems using ROBDDs
In this paper we present a new approach to modeling finite set domain
constraint problems using Reduced Ordered Binary Decision Diagrams (ROBDDs). We
show that it is possible to construct an efficient set domain propagator which
compactly represents many set domains and set constraints using ROBDDs. We
demonstrate that the ROBDD-based approach provides unprecedented flexibility in
modeling constraint satisfaction problems, leading to performance improvements.
We also show that the ROBDD-based modeling approach can be extended to the
modeling of integer and multiset constraint problems in a straightforward
manner. Since domain propagation is not always practical, we also show how to
incorporate less strict consistency notions into the ROBDD framework, such as
set bounds, cardinality bounds and lexicographic bounds consistency. Finally,
we present experimental results that demonstrate the ROBDD-based solver
performs better than various more conventional constraint solvers on several
standard set constraint problems
Dynamics of the formation of a hydrogel by a pathogenic amyloid peptide: islet amyloid polypeptide
Many chronic degenerative diseases result from aggregation of misfolded polypeptides to form amyloids. Many amyloidogenic polypeptides are surfactants and their assembly can be catalysed by hydrophobic-hydrophilic interfaces (an air-water interface in-vitro or membranes in-vivo). We recently demonstrated the specificity of surface-induced amyloidogenesis but the mechanisms of amyloidogenesis and more specifically of adsorption at hydrophobic-hydrophilic interfaces remain poorly understood. Thus, it is critical to determine how amyloidogenic polypeptides behave at interfaces. Here we used surface tensiometry, rheology and electron microscopy to demonstrate the complex dynamics of gelation by full-length human islet amyloid polypeptide (involved in type II diabetes) both in the bulk solution and at hydrophobic-hydrophilic interfaces (air-water interface and phospholipids). We show that the hydrogel consists of a 3D supramolecular network of fibrils. We also assessed the role of solvation and dissected the evolution over time of the assembly processes. Amyloid gelation could have important pathological consequences for membrane integrity and cellular functions
Making Optimum Use of the Limited Agricultural Resources of the Tribal Areas of S.W. Matabeleland
A ZJE article on agricultural rural development in Rhodesia's province of South West |Matebeleland.The title of this paper requires that it should at least:-
a) Define the area under consideration.
b) Outline its physical characteristics so that its agricultural resources
may be established.
c) Outline its socio-economic environment in order to discover what pressures
there are on these resources, and to establish the development needs of the region.
d) Propose how to make best use of the resources in the light of (c) above
Tribal Trust Land Development Corporation Limited: Rural Development in Rhodesia
A Zimbabwe Journal of Economics conference paper on the need for rural development in Rhodesia (now Zimbabwe.
Discovery of distant high luminosity infrared galaxies
We have developed a method for selecting the most luminous galaxies detected
by IRAS based on their extreme values of R, the ratio of 60 micron and B-band
luminosity. These objects have optical counterparts that are close to or below
the limits of Schmidt surveys. We have tested our method on a 1079 deg^2 region
of sky, where we have selected a sample of IRAS sources with 60 micron flux
densities greater than 0.2 Jy, corresponding to a redshift limit z~1 for
objects with far-IR luminosities of 10^{13} L_sun. Optical identifications for
these were obtained from the UK Schmidt Telescope plates, using the likelihood
ratio method. Optical spectroscopy has been carried out to reliably identify
and measure the redshifts of six objects with very faint optical counterparts,
which are the only objects with R>100 in the sample. One object is a
hyperluminous infrared galaxy (HyLIG) at z=0.834. Of the remaining, fainter
objects, five are ultraluminous infrared galaxies (ULIGs) with a mean redshift
of 0.45, higher than the highest known redshift of any non-hyperluminous ULIG
prior to this study. High excitation lines reveal the presence of an active
nucleus in the HyLIG, just as in the other known infrared-selected HyLIGs. In
contrast, no high excitation lines are found in the non-hyperluminous ULIGs. We
discuss the implications of our results for the number density of HyLIGs at z<1
and for the evolution of the infrared galaxy population out to this redshift,
and show that substantial evolution is indicated. Our selection method is
robust against the presence of gravitational lensing if the optical and
infrared magnification factors are similar, and we suggest a way of using it to
select candidate gravitationally lensed infrared galaxies.Comment: 6 pages, accepted for publication in A&
Inlet spillage drag tests and numerical flow-field analysis at subsonic and transonic speeds of a 1/8-scale, two-dimensional, external-compression, variable-geometry, supersonic inlet configuration
Accurate spillage drag and pressure data are presented for a realistic supersonic inlet configuration. Results are compared with predictions from a finite-differencing, inviscid analysis computer procedure. The analytical technique shows good promise for the evaluation of inlet drag, but necessary refinements were identified. A detailed description of the analytical procedure is contained in the Appendix
What are riparian ecosystems and why are we worried about them
Riparian areas represent less than 2 percent of all terrestrial ecosystems, but they are functionally on of the most important features within natural landscapes. They are characterized by high biotic production and diversity; they moderate flood intensity and store water; and they maintain high water quality by acting as nutrient and sediment sinks. These ecological functions make them valuable areas for a variety of human uses including agriculture, timber and livestock production, recreation, and housing. Human use, however, has resulted in severe degradation of the functional health of many riparian ecosystems. Recognition of the value of the systems and the magnitude of existing and continuing degradation has generated a concerted effort by natural resources managers and researchers to develop strategies to protect and restore riparian areas. Issues requiring particular attention are (1) development of a generally accepted definition of riparian ecosystems, (2) development of a functionally useful classification scheme of riparian areas, (3) quantification of the specific ways that human use causes ecological dysfunction, (4) collection of data from which we can objectively prioritize efforts to preserve extant systems, and (5) development of ecologically sound strategies for the restoration of degraded areas
Variation in individual growth rates and population abundances of ephemerellid mayflies
Individual growth and densities of six taxa of ephemerellid mayflies were examined in relation to differences in temperature and food among streams of western North America. For most taxa, growth rate was not a simple function of either temperature or food. Growth periods of taxa differed relative to seasonal changes in temperature. As a result of the interaction between size and temperature, growth rates and shapes of the growth curve varied among taxa. The significance of temperature for life history phenomena therefore cannot be easily generalized to explain phenological patterns among stream insects. Also, little evidence was found that implicated food as the cause for observed differences in growth rates among most sites. Growth rates in streams with high rates of algal production (open sites) were similar to growth rates in streams with low algal production (shaded sites). Only sites with long periods of ice cover, and presumably low availability of food, showed marked reduction in individual growth rates. Densities, however, varied strongly across sites: open streams had higher densities than shaded streams. These results imply that populations in streams may be near carrying capacity and that per capita food availability is similar among streams. The presence of such interactions between individual and population processes may help explain patterns at individual, population, and ecosystem levels of organization. Variation in Individual Growth Rates and Population Densities of Ephemerellid Mayflies. Available from: http://www.researchgate.net/publication/271857398_Variation_in_Individual_Growth_Rates_and_Population_Densities_of_Ephemerellid_Mayflies [accessed Jul 10, 2015]
The inception of Symplectic Geometry: the works of Lagrange and Poisson during the years 1808-1810
The concept of a symplectic structure first appeared in the works of Lagrange
on the so-called "method of variation of the constants". These works are
presented, together with those of Poisson, who first defined the composition
law called today the "Poisson bracket". The method of variation of the
constants is presented using today's mathematical concepts and notations.Comment: Presented at the meeting "Poisson 2008" in Lausanne, July 2008.
Published in Letters in Mathematical Physics. 22 page
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