49 research outputs found
Hamstring muscles: Architecture and innervation
Knowledge of the anatomical organization of the hamstring muscles is necessary to understand their functions, and to assist in the development of accurate clinical and biomechanical models. The hamstring muscles were examined by dissection in six embalmed human lower limbs with the purpose of clarifying their gross morphology. In addition to obtaining evidence for or against anatomical partitioning ( as based on muscle architecture and pattern of innervation), data pertaining to architectural parameters such as fascicular length, volume, physiological cross-sectional area, and tendon length were collected. For each muscle, relatively consistent patterns of innervation were identified between specimens, and each was unique with respect to anatomical organization. On the basis of muscle architecture, three regions were identified within semimembranosus. However, this was not completely congruent with the pattern of innervation, as a primary nerve branch supplied only two regions, with the third region receiving a secondary branch. Semitendinosus comprised two distinct partitions arranged in series that were divided by a tendinous inscription. A singular muscle nerve or a primary nerve branch innervated each partition. In the biceps femoris long head the two regions were supplied via a primary nerve branch which divided into two primary branches or split into a series of branches. Being the only muscle to cross a single joint, biceps femoris short head consisted of two distinct regions demarcated by fiber direction, with each innervated by a separate muscle nerve. Architecturally, each muscle differed with respect to parameters such as physiological cross-sectional area, fascicular length and volume, but generally all partitions within an individual muscle were similar in fascicular length. The long proximal and distal tendons of these muscles extended into the muscle bellies thereby forming elongated musculotendinous junctions. Copyright (C) 2005 S. Karger AG, Basel
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An analysis of the saturation of a high gain FEL
We study the saturated state of an untapered free electron laser in the Compton regime, arising after exponential amplification of an initial low level of radiation by an initially monoenergetic, unbunched electron beam. The saturated state of the FEL is described by oscillations about an equilibrium state. Using the two invariants of the motion, and certain assumptions motivated by computer simulations, we provide approximate analytic descriptions of the radiation field and electron distribution in the saturation regime. We first consider a one-dimensional approximation, and later extend our approach to treat an electron beam of finite radial extent. Of note is a result on the radiated power in the case of an electron beam with small radius
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X-ray characterization of oxidized tantalum nitride
Sputter deposited non-stoichiometric tantalum nitride films are oxidized in air between 200 and 500{degrees}C to form a passive film. The oxidized films have been studied with x-ray absorption near edge spectroscopy (XANES) and extended x-ray absorption near edge spectroscopy (EXAFS). Films exposed to KOH formed a non-protective surface layer identified in low angle XANES and EXAFS as KTaO{sub 3}. Auger electron and x-ray photoelectron spectroscopies were also used to characterize these films
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Diffusion rate for the emittance growth due to periodic crossings of nonlinear coupled resonances
Assuming that many betatron oscillations occur between crossings so that the betatron phase is uncorrelated from one crossing to the next, we estimate the diffusion rate for the emittance growth due to periodic crossing of coupled nonlinear resonances. It was shown that the diffusion rate is more or less independent of the frequency, but it is inversely proportional to the modulation amplitude
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An assessment of the risk significance of human errors in selected PSAs and operating events
Sensitivity studies based on Probabilistic Safety Assessments (PSAs) for a pressurized water reactor and a boiling water reactor are described. In each case human errors modeled in the PSAs were categorized according to such factors as error type, location, timing, and plant personnel involved. Sensitivity studies were then conducted by varying the error rates in each category and evaluating the corresponding change in total core damage frequency and accident sequence frequency. Insights obtained are discussed and reasons for differences in risk sensitivity between plants are explored. A separate investigation into the role of human error in risk-important operating events is also described. This investigation involved the analysis of data from the USNRC Accident Sequence Precursor program to determine the effect of operator-initiated events on accident precursor trends, and to determine whether improved training can be correlated to current trends. The findings of this study are also presented. 5 refs., 15 figs., 1 tab
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Reduction of FEL gain due to wiggler errors
For an FEL operating in the exponential regime before saturation, we consider the effect on the gain of longitudinal velocity variations arising from wiggler field errors. The average gain reduction and the width of the output power distribution are expressed in terms of the mean square average of the ponderomotive phase shift per gain length. A scheme for correcting the electron trajectory using position monitors and dipole correctors is analyzed. Analytic results are compared with numerical simulations. Our work is directly applicable to the design of FEL amplifiers and the results are encouraging for the feasibility of such devices. 13 refs., 2 figs