Advertisement

In the past ** Richard D. Ball** has collaborated on articles with

More information about

AbstractThe purpose of this self-directed learning module is to describe the anatomy and physiology of the nerve, neuromuscular junction, and muscle as they relate to rehabilitation of diseases affecting these structures. It is a section of the chapter on rehabilitation in nerve and muscle disorders for the Self-Directed Medical Knowledge Program Study guide for practitioners and trainees in physical medicine and rehabilitation. The major clinically important structural features and relationships of the spinal cord segment, spinal roots, peripheral nerve, motor unit, and muscle fiber are outlined with structure-function correlations. Metabolic features of neuronal physiology, including axonal transport, blood-nerve barriers, and synaptic function, are reviewed as they relate to commonly encountered neurologic diseases. Lastly, skeletal muscle cell biochemistry and physiology are discussed as they relate to force generation and force maintenance.

AbstractThe purpose of this self-directed learning module is to describe the anatomy and physiology of the nerve, neuromuscular junction, and muscle as they relate to rehabilitation of diseases affecting these structures. It is a section of the chapter on rehabilitation in nerve and muscle disorders for the Self-Directed Medical Knowledge Program Study guide for practitioners and trainees in physical medicine and rehabilitation. The major clinically important structural features and relationships of the spinal cord segment, spinal roots, peripheral nerve, motor unit, and muscle fiber are outlined with structure-function correlations. Metabolic features of neuronal physiology, including axonal transport, blood-nerve barriers, and synaptic function, are reviewed as they relate to commonly encountered neurologic diseases. Lastly, skeletal muscle cell biochemistry and physiology are discussed as they relate to force generation and force maintenance.

AbstractThe purpose of this self-directed learning module is to describe the anatomy and physiology of the nerve, neuromuscular junction, and muscle as they relate to rehabilitation of diseases affecting these structures. It is a section of the chapter on rehabilitation in nerve and muscle disorders for the Self-Directed Medical Knowledge Program Study guide for practitioners and trainees in physical medicine and rehabilitation. The major clinically important structural features and relationships of the spinal cord segment, spinal roots, peripheral nerve, motor unit, and muscle fiber are outlined with structure-function correlations. Metabolic features of neuronal physiology, including axonal transport, blood-nerve barriers, and synaptic function, are reviewed as they relate to commonly encountered neurologic diseases. Lastly, skeletal muscle cell biochemistry and physiology are discussed as they relate to force generation and force maintenance.

AbstractMyosin heavy chain degradation fragments produced in vivo have been identified in chicken pectoralis muscle. The fragments were identified by electrophoresis of unfractionated extracts of chicken pectoralis muscle on sodium dodecyl sulfate/polyacrylamide gels followed by immunoblotting on nitrocellulose sheets. Monoclonal antibodies directed against the S2 and light meromyosin subfragments as well as type II myosin-specific polyclonal antibodies directed against the entire myosin heavy chain were used to characterize the fragments, which range in molecular weight from approximately 80,000 to 180,000. All fragments contain the extreme carboxy-terminal portion of the molecule and are distinct from the classical proteolytic fragments such as heavy and light meromyosin, S1, S2 or rod. These fragments appear to be produced in vivo by proteolytic cleavage of peptides from the amino-terminal (S1) end of the heavy chain while the myosin molecule is still embedded in the thick filament. Fragment concentrations are estimated to be approximately 5 to 10% of that of the intact myosin heavy chain. These fragments are not the result of artifactual damage to myosin, e.g. proteolysis or hydrodynamic shear. The techniques described in this paper provide a probe into the early stages of myosin and thick filament degradation in vivo.

AbstractWe show that recent data from HERA on the proton structure function F2 at small x and large Q2 provide a direct confirmation of the double asymptotic scaling prediction of perturbative QCD. A linear rise of ln F2 with the scaling variable σ is observed throughout the kinematic region probed at HERA, and the measured slope is in excellent agreement with the QCD prediction. This provides a direct determination of the leading coefficient of the beta function. At large values of the scaling variable ϱ the data display a small but statistically significant scaling violation.

AbstractWe show how perturbation theory may be reorganized to give splitting functions which include order by order convergent sums of all leading logarithms of x. This gives a leading twist evolution equation for parton distributions which sums all leading logarithms of x and Q2, allowing stable perturbative evolution down to arbitrarily small values of x. Perturbative evolution then generates the double scaling rise of F2 observed at HERA, while in the formal limit x → 0 at fixed Q2 the Lipatov xf-λ behaviour is eventually reproduced. We are thus able to explain why leading order perturbation theory works so well in the HERA region.

AbstractWe propose a resolution of the puzzle posed by the discrepancy between the value of the pion-nucleon sigma term inferred from pion-nucleon scattering, and that deduced from baryon mass splittings using the Zweig rule. We show that there is a significant hypercharge-dependent dynamical contribution to baryon masses which may be estimated by the solution of the Schwinger-Dyson equation for the quark self-energy. This contribution alters the relationship between baryon mass splittings and the sigma term, completely resolving the discrepancy without any need for Zweig rule violation.

We review a formalism that includes the effects of nonperturbative U(1) symmetry breaking on the QCD evolution of nonsinglet structure functions. We show that a strong scale dependence is generated in an intermediate energy range 0.5⪝Q⪝5 GeV2 GeV2 for all values of x. We show that this explains naturally the observed violation of the Gottfried sum, and allows a determination of the shape of the nonsinglet structure function, in excellent agreement with experiment. We argue that these effects may affect the determination of α, from deep-inelastic scattering.

AbstractWe determine the strong coupling αs from a next-to-leading order analysis of processes used for the NNPDF2.1 parton determination, which includes data from neutral and charged current deep-inelastic scattering, Drell–Yan and inclusive jet production. We find αs(MZ)=0.1191±0.0006exp, where the uncertainty includes all statistical and systematic experimental uncertainties, but not purely theoretical uncertainties, which are expected to be rather larger. We study the dependence of the results on the dataset, by providing further determinations based respectively on deep-inelastic data only, and on HERA data only. The deep-inelastic fit gives the consistent result αs(MZ)=0.1177±0.0009exp, but the result of the HERA-only fit is only marginally consistent. We provide evidence that individual data subsets can have runaway directions due to poorly determined PDFs, thus suggesting that a global dataset is necessary for a reliable determination.

AbstractThe FONLL general-mass variable-flavour number scheme provides a framework for the matching of a calculation in which a heavy quark is treated as a massless parton to one in which the mass dependence is retained throughout. We describe how the usual formulation of FONLL can be extended in such a way that the heavy quark parton distribution functions are freely parameterized at some initial scale, rather than being generated entirely perturbatively. We specifically consider the case of deep-inelastic scattering, in view of applications to PDF determination, and the possible impact of a fitted charm quark distribution on F2c is assessed.

AbstractWe discuss the inclusion of running coupling effects in perturbative small x evolution equations. We show that a running coupling BFKL-like x-evolution equation is fully compatible, up to higher twist corrections, with the standard factorized perturbative evolution of parton distributions. We then use this result, combined with the well-known Airy asymptotics, to prove that the oscillations which are present in the running-coupling BFKL solution do not affect the associated splitting functions, which instead remain smooth in the small x limit. This allows us to give a prescription to include running-coupling corrections in the small-x resummation of scaling violations. We show that these corrections are small in the HERA region.

AbstractWe reconsider the high energy resummation of photoproduction, electroproduction and hadroproduction cross-sections, in the light of recent progress in the resummation of perturbative parton evolution to NLO in logarithms of Q2 and x. We show in particular that the when the coupling runs the dramatic enhancements seen at fixed coupling, due to infrared singularities in the partonic cross-sections, are substantially reduced, to the extent that they are largely accounted for by the usual NLO and NNLO perturbative corrections. This leads to a novel explanation of the large K-factors commonly found in perturbative calculations of hadroproduction cross-sections. We give numerical estimates of high energy resummation effects for inclusive B-production, inclusive jets, Drell–Yan and vector boson production, along with their rapidity distributions. We find that resummation modifies the B-production cross-section at the LHC by at most 15%, but that the enhancement of gluonic W-production may be as large as 50% at large rapidities.

AbstractWe present the determination of a set of parton distributions of the nucleon, at next-to-leading order, from a global set of deep-inelastic scattering data: NNPDF1.0. The determination is based on a Monte Carlo approach, with neural networks used as unbiased interpolants. This method, previously discussed by us and applied to a determination of the nonsinglet quark distribution, is designed to provide a faithful and statistically sound representation of the uncertainty on parton distributions. We discuss our dataset, its statistical features, and its Monte Carlo representation. We summarize the technique used to solve the evolution equations and its benchmarking, and the method used to compute physical observables. We discuss the parametrization and fitting of neural networks, and the algorithm used to determine the optimal fit. We finally present our set of parton distributions. We discuss its statistical properties, test for its stability upon various modifications of the fitting procedure, and compare it to other recent parton sets. We use it to compute the benchmark W and Z cross sections at the LHC. We discuss issues of delivery and interfacing to commonly used packages such as LHAPDF.

AbstractWe present a computation of the inclusive Drell–Yan production cross-section in perturbative QCD to all orders in the limit of high partonic centre-of-mass energy. We compare our results to the fixed order NLO and NNLO results in MS¯ scheme, and provide predictions at N3LO and beyond. Our expressions may be used to obtain fully resummed results for the inclusive cross-section.

AbstractWe present a determination of the parton distributions of the nucleon from a global set of hard scattering data using the NNPDF methodology at LO and NNLO in perturbative QCD, thereby generalizing to these orders the NNPDF2.1 NLO parton set. Heavy quark masses are included using the so-called FONLL method, which is benchmarked here at NNLO. We demonstrate the stability of PDFs upon inclusion of NNLO corrections, and we investigate the convergence of the perturbative expansion by comparing LO, NLO and NNLO results. We show that the momentum sum rule can be tested with increasing accuracy at LO, NLO and NNLO. We discuss the impact of NNLO corrections on collider phenomenology, specifically by comparing to recent LHC data. We present PDF determinations using a range of values of αs, mc and mb. We also present PDF determinations based on various subsets of the global dataset, show that they generally lead to less accurate phenomenology, and discuss the possibility of future PDF determinations based on collider data only.

AbstractWe present an NLO perturbative analysis of all available data on the polarized structure function g1 (x, Q2) with the aim of making a quantitative test of the validity of the Bjorken sum rule, of measuring αs and of deriving helicity fractions. We take particular care over the small x extrapolation, since it is now known that Regge behaviour is unreliable at perturbative scales. For fixed α5, we find that if all the most recent data are included gA = 1.19 ± 0.09, confirming the Bjorken sum rule at the 8% level. We further show that the value of αs is now reasonably well constrained by scaling violations in the structure function data, despite the fact that it cannot yet be reliably fixed by the value of the Bjorken sum: our final result is as(mz) = −0.008+0.010. We also confirm earlier indications of a sizeable positive gluon polarization in the nucleon.

We review recent HERA data on the structure function F2 at small x and large Q2. We show that the salient features of the data are revealed by comparing them to the double asymptotic scaling behaviour which F2 is predicted to satisfy in perturbative QCD.

Advertisement