Analytical and numerical computation of air-gap magnetic fields in brushless motors with surface permanent magnets

This paper extends the theory of the air-gap magnetic field in permanent-magnet (PM) brushless motors. Scalar and vector potential solutions to the field equations are brought together to unify many of the important practical methods already in use. The theory admits a more general representation of the magnetization vector than has been previously assumed, including both the radial and tangential components, and variation with radius. The work is applied in the design of PM motors where there is a requirement to minimize noise and torque ripple, and maximize efficiency, and a continuing need for improvements in the accuracy and rigor of design calculations. The air-gap flux-density distribution is at the heart of the design process, and it is desirable to study different magnetization patterns, including imperfections in the magnetization, for a wide range of magnet shapes. This paper shows the application of the analytical solutions in comparison with a new finite-element procedure, with test results on a prototype motor, and with simpler, older methods of calculation based on magnetic equivalent circuits. The comparison brings out many interesting points in relation to the accuracy and the speed and practicality of the various methods

Effect of nitrogen, sulfur, and planting rate on dryland malt barley

Non-Peer ReviewedDryland malting barley (Hordeum vulgare L.) experiments were initiated in north central Montana to evaluate the effects of planting, N, and S rates on grain yield and quality. Planting rates of 10, 15, and 20 seeds/ft2, nitrogen (N) rates of 0, 30, and 60 lbs N/acre, and S rates of 0, 10, and 20 lbs/acre were applied in all possible combinations to Metcalfe barley at 11 locations in 2004 and 2005. Optimal grain yields were generally achieved with a planting rate of 15 seeds/ft2, but 10 seeds/ft2 produced grain with the highest kernel plumpness and the highest grain protein content. Barley responses to N were similar to previously published data (i.e. increasing N resulted in higher yield and protein content but lower kernel plumpness). Sulfur fertilization had little effect on grain quality but increasing S significantly lowered grain yields at several locations

Femorofemoral crossover grafts for claudication: A safe and reliable procedure

Objective:To evaluate the role of femorofemoral crossover grafts in patients with disabling claudication.Design:Retrospective study.Setting:University hospital.Materials:Two hundred and eleven patients with iliac artery disease undergoing femorofemoral crossover grafts for disabling claudication.Chief outcome measures:Perioperative mortality, follow-up cumulative graft patency, limb loss, survival, graft infection and false aneurysm formation were evaluated to determine the immediate and long-term outcome of the procedure.Main results:Primary and secondary graft patency at 5 years was 72% and 89% respectively. There were no perioperative deaths (zero 30 day mortality). Dacron was used in 66 patients (31%) and PTFE in 145 (69%). There were no differences in patency between the two graft materials but eight Dacron grafts (12.1%) were removed because of complications (false aneurysm or infection) compared to four PTFE grafts (2.7%)(p < 0.001 Chi-square). Five patients (2%) have undergone a major lower limb amputation. Forty-one patients (19%) have required subsequent inflow procedures which represents a cumulative need for inflow of 5% per year.Conclusions:Femorofemoral crossover grafts are a safe and reliable procedure in patients with disabling claudication caused by unilateral iliac artery disease

A simple nonlinear model of a generic axisymmetric wave energy converter

The aim of this work is to develop a simple nonlinear model of a wave energy converter (WEC) for capturing power from ocean waves and converting it into electrical power. A generic axisymmetric device is considered, which consists of a vertical circular cylinder surrounded by a circular annulus. The nonlinear system of equations of motion of this generic WEC are derived; these include the nonlinear term arising from viscous drag due to boundary layer separation. The expressions for radiation damping and added mass are determined by dimensional analysis. These equations are then solved numerically and the results are displayed graphically in a number of figures. Consideration of these graphs leads to conclusions that should be taken into account by the design engineer

Gray Whales (Eschrichtius robustus) in the Western Chukchi and East Siberian Seas

During joint Soviet-American shipboard surveys in autumn 1979 and 1980, numerous sightings of gray whales (Eschrichtius robustus) were made in the western Chukchi and East Siberian seas. Gray whales were observed well offshore in ice-free water in 1979, but near the Chukotka coast in 1980. During the 1980 survey, gray whales were observed further west than previously recorded, with three animals seen at 174 08 E longitude, well into the East Siberian Sea. Based on indirect evidence of gray whale behavior and typical prey organisms identified in bottom samples, we assume gray whales are feeding in the western Chukchi Sea during summer and fall. Movement of these animals further west into the East Siberian Sea may occur regularly when ice conditions permit, but it may also be a response to increasing population size over the past several decades, and gray whales may be reoccupying habitat unused during periods of low population caused by commercial whaling.Key words: gray whale, Eschrichtius robustus, cetacean, Chukchi Sea, East Siberian SeaMots cl&eacute;s: baleine grise de Californie, Eschrichtius robustus, c&eacute;tac&eacute;, mer Tchouktche, mer de Sib&eacute;rie Oriental

A simple nonlinear model of a generic axisymmetric wave energy converter

The aim of this work is to develop a simple nonlinear model of a wave energy converter (WEC) for capturing power from ocean waves and converting it into electrical power. A generic axisymmetric device is considered, which consists of a vertical circular cylinder surrounded by a circular annulus. The nonlinear system of equations of motion of this generic WEC are derived; these include the nonlinear term arising from viscous drag due to boundary layer separation. The expressions for radiation damping and added mass are determined by dimensional analysis. These equations are then solved numerically and the results are displayed graphically in a number of figures. Consideration of these graphs leads to conclusions that should be taken into account by the design engineer

Second order parameter-uniform convergence for a finite difference method for a partially singularly perturbed linear parabolic system

A linear system of $n$ second order differential equations of parabolic reaction-diffusion type with initial and boundary conditions is considered. The first $k$ equations are singularly perturbed. Each of the leading terms of the first $m$ equations, $mleq k$, is multiplied by a small positive parameter and these parameters are assumed to be distinct. The leading terms of the next $k-m$ equations are multiplied by the same perturbation parameter $varepsilon_m$. Since the components of the solution exhibit overlapping layers, Shishkin piecewise-uniform meshes are introduced, which are used in conjunction with a classical finite difference discretisation, to construct a numerical method for solving this problem. It is proved that in the maximum norm the numerical approximations obtained with this method are first order convergent in time and essentially second order convergent in the space variable, uniformly with respect to all of the parameters

Second order parameter-uniform convergence for a finite difference method for a partially singularly perturbed linear parabolic system

A linear system of $n$ second order differential equations of parabolic reaction-diffusion type with initial and boundary conditions is considered. The first $k$ equations are singularly perturbed. Each of the leading terms of the first $m$ equations, $mleq k$, is multiplied by a small positive parameter and these parameters are assumed to be distinct. The leading terms of the next $k-m$ equations are multiplied by the same perturbation parameter $varepsilon_m$. Since the components of the solution exhibit overlapping layers, Shishkin piecewise-uniform meshes are introduced, which are used in conjunction with a classical finite difference discretisation, to construct a numerical method for solving this problem. It is proved that in the maximum norm the numerical approximations obtained with this method are first order convergent in time and essentially second order convergent in the space variable, uniformly with respect to all of the parameters

A parameter uniform fitted mesh method for a weakly coupled system of two singularly perturbed convection-diffusion equations

In this paper, a boundary value problem for a singularly perturbed linear system of two second order ordinary differential equations of convection-diffusion type is considered on the interval [0, 1]. The components of the solution of this system exhibit boundary layers at 0. A numerical method composed of an upwind finite difference scheme applied on a piecewise uniform Shishkin mesh is suggested to solve the problem. The method is proved to be first order convergent in the maximum norm uniformly in the perturbation parameters. Numerical examples are provided in support of the theory

Modulation of DNA damage tolerance in Escherichia coli recG and ruv strains by mutations affecting PriB, the ribosome and RNA polymerase

RecG is a DNA translocase that helps to maintain genomic integrity. Initial studies suggested a role in promoting recombination, a possibility consistent with synergism between recG and ruv null alleles and reinforced when the protein was shown to unwind Holliday junctions. In this article we describe novel suppressors of recG and show that the pathology seen without RecG is suppressed on reducing or eliminating PriB, a component of the PriA system for replisome assembly and replication restart. Suppression is conditional, depending on additional mutations that modify ribosomal subunit S6 or one of three subunits of RNA polymerase. The latter suppress phenotypes associated with deletion of priB, enabling the deletion to suppress recG. They include alleles likely to disrupt interactions with transcription anti-terminator, NusA. Deleting priB has a different effect in ruv strains. It provokes abortive recombination and compromises DNA repair in a manner consistent with PriB being required to limit exposure of recombinogenic ssDNA. This synergism is reduced by the RNA polymerase mutations identified. Taken together, the results reveal that RecG curbs a potentially negative effect of proteins that direct replication fork assembly at sites removed from the normal origin, a facility needed to resolve conflicts between replication and transcription