On the particle paths and the stagnation points in small-amplitude deep-water waves

In order to obtain quite precise information about the shape of the particle paths below small-amplitude gravity waves travelling on irrotational deep water, analytic solutions of the nonlinear differential equation system describing the particle motion are provided. All these solutions are not closed curves. Some particle trajectories are peakon-like, others can be expressed with the aid of the Jacobi elliptic functions or with the aid of the hyperelliptic functions. Remarks on the stagnation points of the small-amplitude irrotational deep-water waves are also made.Comment: to appear in J. Math. Fluid Mech. arXiv admin note: text overlap with arXiv:1106.382

Universality in escape from a modulated potential well

We show that the rate of activated escape $W$ from a periodically modulated potential displays scaling behavior versus modulation amplitude $A$. For adiabatic modulation of an optically trapped Brownian particle, measurements yield $\ln W\propto (A_{\rm c} - A)^{\mu}$ with $\mu = 1.5$. The theory gives $\mu=3/2$ in the adiabatic limit and predicts a crossover to $\mu=2$ scaling as $A$ approaches the bifurcation point where the metastable state disappears.Comment: 4 pages, 3 figure

Concerted C–N/C–H Bond Formation in Highly Enantioselective Yttrium(III)-Catalyzed Hydroamination

A highly active oxazolinylborato yttrium hydroamination catalyst provides 2-methyl-pyrrolidines with excellent optical purities. The proposed mechanism, in which a yttrium(amidoalkene)amine complex reacts by concerted C–N and C–H bond formation, is supported by the rate law for conversion, substrate saturation under initial rates conditions, kinetic isotope effects, and isotopic perturbation of enantioselectivity. These features are conserved between oxazolinylborato Mg-, Y-, and Zr-mediated aminoalkene cyclizations, suggesting related transition states for all three systems. However, inversion of the products’ absolute configuration between yttrium and zirconium catalysts coordinated by the same 4S-oxazolinylborate ligands highlight dissimilar mechanisms of stereoinduction

High temperature thrust chamber for spacecraft

A high temperature thrust chamber for spacecraft (20) is provided herein. The high temperature thrust chamber comprises a hollow body member (12) having an outer surface and an internal surface (16) defining the high temperature chamber (10). The body member (12) is made substantially of rhenium. An alloy (18) consisting of iridium and at least alloying metal selected of the group consisting of rhodium, platinum and palladium is deposited on at least a portion of the internal surface (16) of the body member (12). The iridium and the alloying metal are electrodeposited onto the body member (12). A HIP cycle is performed upon the body member (12) to cause the coating of iridium and the alloying metal to form the alloy (18) which protects the body member (12) from oxidation

Effects of Fire in the Northern Great Plains

Fire has been used inconsistently to manage native and tame grasslands in the Northern Great Plains (NGP) of the north-central U.S. and south-central Canada, particularly the grasslands found in prairies, plains, agricultural land retirement programs, and moist soil sites. This has happened for three primary reasons: (1) the reduction of American Indian use of fire after 1875, (2) fire suppression and land use changes that put increasingly more acres under annual tillage since about the same time, and (3) a growing resistance to the use of fire since about 1940, largely due to media overemphasis of its harmful effects (e.g., Bambi and Smokey the Bear ). Little can be done to change the first two factors but there is ample opportunity to change human attitudes about fire. Attitudes change when the knowledge (or lack of it) changes. We believe that people have been reluctant to include fire in resource management programs in the NGP because of a lack of adequate information about the effects of fire on the soils, plants, and animals in the region. This document provides information concerning fire effects on the grassland biome of the NGP, with special emphasis on the use of fire for wildlife management. In several instances we have drawn from published literature outside the geographic region, but only to provide a more complete reference for readers and decision makers. In most instances, we only state or abstract the published findings of others without interpretation, either pro or con. Readers can fit the information into their specific circumstances. English and scientific names are from Flora of the Great Plains by the Great Plains Flora Association and from the Checklist of Vertebrates of the United States, the U.S. territories, and Canada by RC. Banks, R.W. McDiarmid, and A.L. Gardner

Prescribed Burning Guidelines in the Northern Great Plains

The use of fire to manage grasslands for wildlife is a relatively new management option for resource managers in the Northern Great Plains (NGP). Nearly all of the burning during the past 20-25 years has been conducted without the aid of specific guidelines for the region. This state-of-the-art set of recommendations was compiled because of this void. Records of 902 grassland fires (primarily on U.S. Fish and Wildlife lands), personal experiences, and synopses of other published fire research were used in developing the guidelines in this manual. Fifty-two percent of the 902 fires were in native prairie grasslands with lesser amounts in tame and native grass plantings, wetlands, and woodlands. Prescription grassland fires averaged 31 ha (77 acres) per burn. The personnel needed to safely conduct a grassland fire depended on the size of the burn, the kind of firebreaks, available equipment, and weather conditions. Costs and hours of effort to conduct fires were inversely related to burn area size. Cost ratios are extremely high for fires of less than 4 ha (10 acres). They are essentially the same for burns of 16 to 113 ha (40 to 280 acres). The two primary reasons for burning grasslands are wildlife habitat improvement and native prairie restoration. Fire use steadily increased between 1965 and 1984, but the greatest increase occurred following workshop instruction in 1978. These guidelines present a set of reasons, criteria, techniques, and examples of simple prescriptions which aid in the planning and execution of a safe and effective prescribed burning program for wildlife enhancement in grassland areas of the NGP

Effects of Fire in the Northern Great Plains

This publication is a review of selected literature about prescribed burning in the Northern Great Plains for management of wildlife. It discusses the effect of fire on soil nutrients and minerals, upland grasses and forbs, undesirable species, shrubs, trees, certain plant species, emergent vegetation in prairie wetlands, insects, nongame birds, upland game birds, waterfowl, shorebirds, small mammals, and livestock

Prescribed Burning Guidelines in the Northern Great Plains

This publication provides guidelines with reasons, criteria, techniques, and examples of simple prescriptions which aid in the planning and execution of a safe and effective prescribed burning program for wildlife enhancement in grassland areas of the Northern Great Plains

Self-organization and Mechanical Properties of Active Filament Bundles

A phenomenological description for active bundles of polar filaments is presented. The activity of the bundle results from crosslinks, that induce relative displacements between the aligned filaments. Our generic description is based on momentum conservation within the bundle. By specifying the internal forces, a simple minimal model for the bundle dynamics is obtained, capturing generic dynamic behaviors. In particular, contracted states as well as solitary and oscillatory waves appear through dynamic instabilities. The introduction of filament adhesion leads to self-organized persistent filament transport. Furthermore, calculating the tension, homogeneous bundles are shown to be able to actively contract and to perform work against external forces. Our description is motivated by dynamic phenomena in the cytoskeleton and could apply to stress-fibers and self-organization phenomena during cell-locomotion.Comment: 19 pages, 10 figure