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Search Results: 1 - 10 of 113737 matches for " John W. Ramsay "
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Differences in Plantar Flexor Fascicle Length and Pennation Angle between Healthy and Poststroke Individuals and Implications for Poststroke Plantar Flexor Force Contributions
John W. Ramsay,Thomas S. Buchanan,Jill S. Higginson
Stroke Research and Treatment , 2014, DOI: 10.1155/2014/919486
Abstract: Poststroke plantar flexor muscle weakness has been attributed to muscle atrophy and impaired activation, which cannot collectively explain the limitations in force-generating capability of the entire muscle group. It is of interest whether changes in poststroke plantar flexor muscle fascicle length and pennation angle influence the individual force-generating capability and whether plantar flexor weakness is due to uniform changes in individual muscle force contributions. Fascicle lengths and pennation angles for the soleus, medial, and lateral gastrocnemius were measured using ultrasound and compared between ten hemiparetic poststroke subjects and ten healthy controls. Physiological cross-sectional areas and force contributions to poststroke plantar flexor torque were estimated for each muscle. No statistical differences were observed for any muscle fascicle lengths or for the lateral gastrocnemius and soleus pennation angles between paretic, nonparetic, and healthy limbs. There was a significant decrease ( ) in the paretic medial gastrocnemius pennation angle compared to both nonparetic and healthy limbs. Physiological cross-sectional areas and force contributions were smaller on the paretic side. Additionally, bilateral muscle contributions to plantar flexor torque remained the same. While the architecture of each individual plantar flexor muscle is affected differently after stroke, the relative contribution of each muscle remains the same. 1. Introduction Stroke is a leading cause of long-term adult disability in the United States. It has been reported that approximately 795,000 American adults are affected by a stroke each year and that the prevalence of stroke will increase by an estimated 25% by 2030 [1]. Muscle weakness contralateral to the brain lesion, or hemiparesis, is the most common impairment following stroke [2, 3] and is evident by a decrease in maximal voluntary strength on the paretic limb compared to the nonparetic limb [4, 5]. A combination of muscular and neurological impairments is believed to contribute to poststroke hemiparesis [6]. Since the force-generating capacity of a muscle is dependent on amount of impairment, some recent studies have identified the extent to which these changes occur after stroke. Using magnetic resonance imaging, Ramsay et al. [7] observed muscle atrophy in twelve out of fifteen lower extremity muscles. They found an overall decrease in contractile tissue of 20% in the shank area and 24% in the thigh. Similarly, Klein et al. [8] also observed muscle atrophy in the plantar flexor muscles but
Poststroke Muscle Architectural Parameters of the Tibialis Anterior and the Potential Implications for Rehabilitation of Foot Drop
John W. Ramsay,Molly A. Wessel,Thomas S. Buchanan,Jill S. Higginson
Stroke Research and Treatment , 2014, DOI: 10.1155/2014/948475
Abstract: Poststroke dorsiflexor weakness and paretic limb foot drop increase the risk of stumbling and falling and decrease overall functional mobility. It is of interest whether dorsiflexor muscle weakness is primarily neurological in origin or whether morphological differences also contribute to the impairment. Ten poststroke hemiparetic individuals were imaged bilaterally using noninvasive medical imaging techniques. Magnetic resonance imaging was used to identify changes in tibialis anterior muscle volume and muscle belly length. Ultrasonography was used to measure fascicle length and pennation angle in a neutral position. We found no clinically meaningful bilateral differences in any architectural parameter across all subjects, which indicates that these subjects have the muscular capacity to dorsiflex their foot. Therefore, poststroke dorsiflexor weakness is primarily neural in origin and likely due to muscle activation failure or increased spasticity of the plantar flexors. The current finding suggests that electrical stimulation methods or additional neuromuscular retraining may be more beneficial than targeting muscle strength (i.e., increasing muscle mass). 1. Introduction In the United States alone, about 795,000 people suffer from a new or recurrent stroke each year [1]. Stroke survivors often suffer from hemiparesis or muscle weakness on one side of the body. Foot drop commonly occurs from muscle weakness in the paretic leg and manifests itself as a decrease in dorsiflexion range of motion [2]. For many poststroke survivors, paretic limb foot drop increases the risk of stumbling and falling and decreases functional mobility [2]. It is unclear whether dorsiflexor weakness is solely due to neurological impairment following stroke or whether changes in the muscle architecture are additional contributing factors. Muscle fascicle length and pennation angle (i.e., the angle in which the fascicles insert themselves into the aponeuroses of the muscle) are two architectural parameters that can influence how a muscle generates force. Varying these two parameters can alter the functional ability of a muscle, including range of motion and total force production [3]. Therefore, changes in fascicle length or pennation angle may contribute to post-stroke dorsiflexor weakness [4]. Medical imaging techniques (e.g., ultrasonography and magnetic resonance imaging) are often used to study muscle architecture in vivo in healthy populations and patients with neurological disorders [5–11]. However, little is known about poststroke muscle architectural changes. In the
The qweak experiment: A search for new physics at the tev scale by measurement of the proton's weak charge
Desmond Ramsay,]W.;
Nucleus , 2007,
Abstract: the observed coupling of the proton to the z-boson, i.e. the ?weak charge? of the proton, varies with distance scale. the coupling has already been accurately measured at short distances by high energy experiments. qweak will make the measurement at a momentum transfer of only 0.3 (gev/c)2. the ?running? of the coupling from high to low energy can be calculated by correcting for the effect of clouds of virtual particles in the vacuum. because the corrections depend on all of nature’s particles, not only those which have been discovered, a difference between the calculated and measured low energy weak charge could signal new physics. a measurement of qweak to 4% will be sensitive to new physics at the few tevscale. the qweak experiment will use the fact that the parity-violating longitudinal analyzing power, az, is proportional to the proton’s weak charge. the experiment plans to measure the predicted az of -0.3 ppm with a combined statistical and systematic uncertainty of 2.2%, corresponding to a total uncertainty of 4% in qweak. this requires a statistical precision of 5 x , which can be achieved in 2200 hours with an 85% polarized, 180 μa electron beam incident on a 0.35 m liquid hydrogen target. a synchronous data acquisition system will integrate the detector current signals over each spin state and extract the helicity correlated, parity violating component.
The TRIUMF Parity Violation Experiment
W. D. Ramsay
Physics , 1997,
Abstract: An experiment (E497) is underway at TRIUMF to measure the angle-integrated, parity violating longitudinal analyzing power, Az, in proton-proton elastic scattering, to a precision of +/- 0.2 x 10^-7. The experiment uses a 221 MeV longitudinally polarized proton beam incident on a 40 cm liquid hydrogen target. The beam energy is carefully chosen so that the contribution to Az from the J=0 parity mixed partial wave (1S0-3P0) integrates to zero over the acceptance of the apparatus, leaving the experiment sensitive mainly (>95%) to Az arising from the 3P2-1D2, J=2 wave. To minimize sources of systematic error, the TRIUMF ion source and cyclotron parameters have been refined to the extent that helicity correlated beam changes are at an extremely low level, and specialized instrumentation on the E497 beamline is able to measure residual helicity correlated modulations to a precision consistent with the goals of the experiment. A data taking run in February-March, 1997 logged approximately 12% of the desired data and produced a preliminary result, Az = (1.1 +/- 0.4 +/- 0.4) x 10^-7, where the error is statistical only.
Physics in a Mirror: The TRIUMF 221 MeV pp Parity Violation Experiment
W. D. Ramsay
Physics , 1999,
Abstract: We measure the difference in the scattering probability when an experiment scattering longitudinally polarized 221 MeV protons from liquid hydrogen is replaced by its mirror image. The result depends on the interplay between the weak and strong interactions in the interesting region near the surface of the proton. The experiment is technically very challenging and requires elaborate precautions to measure and correct for various sources of systematic error.
Parity Violation in pp and np Experiments
W. D. Ramsay
Physics , 2002, DOI: 10.1063/1.1607131
Abstract: Parity violation experiments involving only two nucleons provide a way to study the non-leptonic, strangeness conserving part of the weak interaction in a clean measurement free of nuclear structure uncertainties. Although simple in principle, the experiments are technically very demanding and great pains must be taken both in the preparation of the incident polarized beams and the measurement of the resultant parity violating asymmetries, which may be masked by a multitude of systematic effects. At low and intermediate energies, pp experiments are sensitive to the medium range part of the parity violating nucleon-nucleon force, usually parameterized in terms of rho and omega meson exchange. I review existing pp measurements with particular emphasis on the recent 221 MeV pp measurement at TRIUMF which permitted the weak meson-nucleon coupling constants h^{pp}_rho and h^{pp}_omega to be determined separately for the first time. The np experiments, on the other hand, are used to extract the weak pion nucleon coupling, f_pi, describing the longest range part of the parity violating nucleon-nucleon force. The np system is the only two nucleon system that is sensitive to f_pi. I also review these experiments, with specific details of the np -> d gamma experiment now under preparation at Los Alamos National Laboratory.
Selected Parity Violation Experiments
W. D. Ramsay
Physics , 2004,
Abstract: I start by reviewing existing $\vec{p}p$ measurements with particular emphasis on the recent 221 MeV $\vec{p}p$ measurement at TRIUMF which permitted the weak meson-nucleon coupling constants $h^{pp}_\rho$ and $h^{pp}_\omega$ to be determined separately for the first time. I then review $\vec{n}p$ experiments, with specific details of the $\vec{n}p \to d\gamma$ experiment now under preparation at Los Alamos National Laboratory. This experiment will provide a clean measurement of the weak pion nucleon coupling, $f_\pi$. Finally, I discuss $\vec{e}p$ parity violation experiments, particularly the Gzero experiment under way at Jefferson Lab in Virginia. This experiment will measure the weak form factors $G_E^z$ and $G_M^z$, allowing the distribution of strange quarks in the quark sea to be determined.
The Qweak Experiment -- A search for new physics at the TeV Scale by measurement of the proton's weak charge
Ramsay, W. D.;Collaboration, for the Qweak
High Energy Physics - Phenomenology , 2007,
Abstract: From a distance, the proton's weak charge is seen through the distorting effects of clouds of virtual particles. The effective weak charge can be calculated by starting with the measured weak coupling at the Z-pole and "running" the coupling to lower energy or, equivalently, longer distances. Because the "electroweak radiative corrections" or "loop diagrams" which give rise to the running depend not only on known particles, but on particles which have not yet been discovered, a difference between the calculated and measured weak charges may signal new physics. A measurement of Qweak to 4% will be sensitive to new physics at the few TeV scale. The Qweak experiment is based on the fact that the parity-violating longitudinal analyzing power, Az, in electron-proton scattering at low momentum transfer and small scattering angle, is proportional to the proton's weak charge. The experiment plans to measure the predicted Az of -0.3 ppm with a combined statistical and systematic uncertainty of 2.2%, corresponding to a total uncertainty of 4% of Qweak. This requires a statistical precision of 5 x 10^-9, which can be achieved in 2200 hours with an 85% polarized, 180 microamp electron beam incident on a 0.35 m liquid hydrogen target. A synchronous data acquisition system will integrate the detector current signals over each spin state and extract the helicity correlated, parity violating component.
The Qweak Experiment -- A search for new physics at the TeV Scale by measurement of the proton's weak charge
W. D. Ramsay,for the Qweak Collaboration
Physics , 2007,
Abstract: From a distance, the proton's weak charge is seen through the distorting effects of clouds of virtual particles. The effective weak charge can be calculated by starting with the measured weak coupling at the Z-pole and "running" the coupling to lower energy or, equivalently, longer distances. Because the "electroweak radiative corrections" or "loop diagrams" which give rise to the running depend not only on known particles, but on particles which have not yet been discovered, a difference between the calculated and measured weak charges may signal new physics. A measurement of Qweak to 4% will be sensitive to new physics at the few TeV scale. The Qweak experiment is based on the fact that the parity-violating longitudinal analyzing power, Az, in electron-proton scattering at low momentum transfer and small scattering angle, is proportional to the proton's weak charge. The experiment plans to measure the predicted Az of -0.3 ppm with a combined statistical and systematic uncertainty of 2.2%, corresponding to a total uncertainty of 4% of Qweak. This requires a statistical precision of 5 x 10^-9, which can be achieved in 2200 hours with an 85% polarized, 180 microamp electron beam incident on a 0.35 m liquid hydrogen target. A synchronous data acquisition system will integrate the detector current signals over each spin state and extract the helicity correlated, parity violating component.
Possible detection of two giant extrasolar planets orbiting the eclipsing polar UZ Fornacis
Stephen B. Potter,Encarni Romero--Colmenero,Gavin Ramsay,Steven Crawford,Amanda Gulbis,Sudhanshu Barway,Ewald Zietsman,Marissa Kotze,David A. H. Buckley,Darragh O'Donoghue,O. H. W. Siegmund,J. McPhate,B. Y. Welsh,John Vallerga
Physics , 2011, DOI: 10.1111/j.1365-2966.2011.19198.x
Abstract: We present new high-speed, multi-observatory, multi-instrument photometry of the eclipsing polar UZ For in order to measure precise mid-eclipse times with the aim of detecting any orbital period variations. When combined with published eclipse times and archival data spanning ~27 years, we detect departures from a linear and quadratic trend of ~60 s. The departures are strongly suggestive of two cyclic variations of 16(3) and 5.25(25) years. The two favoured mechanisms to drive the periodicities are either two giant extrasolar planets as companions to the binary (with minimum masses of 6.3(1.5)M(Jupiter) and 7.7(1.2)M(Jupiter)) or a magnetic cycle mechanism (e.g. Applegate's mechanism) of the secondary star. Applegate's mechanism would require the entire radiant energy output of the secondary and would therefore seem to be the least likely of the two, barring any further refinements in the effect of magnetic fieilds (e.g. those of Lanza et al.). The two planet model can provide realistic solutions but it does not quite capture all of the eclipse times measurements. A highly eccentric orbit for the outer planet would fit the data nicely, but we find that such a solution would be unstable. It is also possible that the periodicities are driven by some combination of both mechanisms. Further observations of this system are encouraged.
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