13,476 research outputs found
Sticky Particles and Stochastic Flows
Gaw\c{e}dzki and Horvai have studied a model for the motion of particles
carried in a turbulent fluid and shown that in a limiting regime with low
levels of viscosity and molecular diffusivity, pairs of particles exhibit the
phenomena of stickiness when they meet. In this paper we characterise the
motion of an arbitrary number of particles in a simplified version of their
model
Crop-raiding Baboons (Papio anubis) and Defensive Farmers: A West African perspective
Baboons are often reported as the worst crop-raiders in Africa, but there has been little observation of the actual behavioural-ecology of their crop-raiding, especially in West Africa. The paper examines the crop-raiding behaviour of a group of habituated baboons (Gamgam group) near the village of Gashaka on the south-western border of Gashaka Gumti National Park, Nigeria. Data were collected during the wet and dry crop seasons via scan sampling and ad libitum techniques. For scan sampling the activity of each observed individual was noted every 2.5 min. For ad libitum data any activity relevant to crop-raiding was noted when it occurred, including the reactions of farmers who were guarding their fields. Descriptive statistics were generated and trends in baboon and human behaviour examined. Sixty-nine percent of Gamgam group’s raids were successful. Farmers only prevented or reduced the time baboons spent in fields on 28.9% of all raids. Crops eaten varied from ripe maize to scavenging for scraps of sweet potato in harvested fields. Maize (ripe and dried) was the most frequently eaten crop. All members of Gamgam group, including weaned infants, ate all crops, but only adult males ate bananas. Observations suggested that baboons used cheek pouches to store food before moving to a safer locality to eat, to avoid farmers’ attacks and intragroup competition. Deterrent methods included guarding, fences of fish net, poisoned baits, olfactory, visual and auditory scaring devices. Guarding presence in fields was not regular. In the wet season guards reacted to baboon crop-raiding on 54% of raids and in the dry season on 44%. On average it took farmers 23 min to react to baboons in their fields. The two most common reactions of guards were shouting and chasing baboons. Observations do not suggest that any one particular defence method can prevent baboon crop-raiding
Studies on the use of supercritical ammonia for ceramic nitride synthesis and fabrication
The extractability of ammonia halides (including ammonium thiocyanate) formed as byproducts from the synthesis of Si(NH)2 via ammonolysis of the corresponding silicon tetrahalides using supercritical NH3 as the extraction medium was investigated. It was found that the NH4SCN byproduct of ammonolysis of Si(SCN)4 can be almost completely extracted from the insoluble Si(NH)2 forming a promising system for the synthesis of pure Si(NH)2, one of the best precursors for Si3N4. In addition it was found that Si3N4, AlN, BN, and Si(NH)2 are insoluble in SC ammonia. Also discussed are design considerations for a supercritical ammonia extraction unit
Irreversible thermodynamics of creep in crystalline solids
We develop an irreversible thermodynamics framework for the description of
creep deformation in crystalline solids by mechanisms that involve vacancy
diffusion and lattice site generation and annihilation. The material undergoing
the creep deformation is treated as a non-hydrostatically stressed
multi-component solid medium with non-conserved lattice sites and
inhomogeneities handled by employing gradient thermodynamics. Phase fields
describe microstructure evolution which gives rise to redistribution of vacancy
sinks and sources in the material during the creep process. We derive a general
expression for the entropy production rate and use it to identify of the
relevant fluxes and driving forces and to formulate phenomenological relations
among them taking into account symmetry properties of the material. As a simple
application, we analyze a one-dimensional model of a bicrystal in which the
grain boundary acts as a sink and source of vacancies. The kinetic equations of
the model describe a creep deformation process accompanied by grain boundary
migration and relative rigid translations of the grains. They also demonstrate
the effect of grain boundary migration induced by a vacancy concentration
gradient across the boundary
Modeling and Analysis of Power Processing Systems (MAPPS), initial phase 2
The overall objective of the program is to provide the engineering tools to reduce the analysis, design, and development effort, and thus the cost, in achieving the required performances for switching regulators and dc-dc converter systems. The program was both tutorial and application oriented. Various analytical methods were described in detail and supplemented with examples, and those with standardization appeals were reduced into computer-based subprograms. Major program efforts included those concerning small and large signal control-dependent performance analysis and simulation, control circuit design, power circuit design and optimization, system configuration study, and system performance simulation. Techniques including discrete time domain, conventional frequency domain, Lagrange multiplier, nonlinear programming, and control design synthesis were employed in these efforts. To enhance interactive conversation between the modeling and analysis subprograms and the user, a working prototype of the Data Management Program was also developed to facilitate expansion as future subprogram capabilities increase
A simulation model for wind energy storage systems. Volume 1: Technical report
A comprehensive computer program for the modeling of wind energy and storage systems utilizing any combination of five types of storage (pumped hydro, battery, thermal, flywheel and pneumatic) was developed. The level of detail of Simulation Model for Wind Energy Storage (SIMWEST) is consistent with a role of evaluating the economic feasibility as well as the general performance of wind energy systems. The software package consists of two basic programs and a library of system, environmental, and load components. The first program is a precompiler which generates computer models (in FORTRAN) of complex wind source storage application systems, from user specifications using the respective library components. The second program provides the techno-economic system analysis with the respective I/O, the integration of systems dynamics, and the iteration for conveyance of variables. SIMWEST program, as described, runs on the UNIVAC 1100 series computers
A survey of the testate amoeba genus Difflugia Leclerc, 1815 based on specimens in the E. Penard and C.G. Ogden collections of the Natural History Museum, London. Part 2: Species with shells that are pyriform or elongate.
© 2014 The Author(s). Protistology © 2014 Protozoological Society Affiliated with RAS. All articles published by Protistology are permanently accessible online immediately upon publication, without subscription charges or registration barriers
Anisotropy, Itineracy, and Magnetic Frustration in High-Tc Iron Pnictides
Using first-principle density functional theory calculations combined with
insight from a tight-binding representation, dynamical mean field theory, and
linear response theory, we have extensively investigated the electronic
structures and magnetic interactions of nine ferropnictides representing three
different structural classes. The calculated magnetic interactions are found to
be short-range, and the nearest () and next-nearest () exchange
constants follow the universal trend of J_{1a}/2J_{2}\sim 1, despite their
itinerant origin and extreme sensitivity to the z-position of As. These results
bear on the discussion of itineracy versus magnetic frustration as the key
factor in stabilizing the superconducting ground state. The calculated spin
wave dispersions show strong magnetic anisotropy in the Fe plane, in contrast
to cuprates.Comment: Fig.4 updated: Phys. Rev. Lett (in press
- …