Multiparton Interactions in Photoproduction at HERA

The high energy photoproduction of jets is being observed at the ep collider, HERA. It may be that the HERA centre-of-mass energy is sufficiently large that the production of more than one pair of jets per ep collision becomes possible, owing to the large number density of the probed gluons. We construct a Monte Carlo model of such multiparton interactions and study their effects on a wide range of physical observables. The conclusion is that multiple interactions could have very significant effects upon the photoproduction final state and that this would for example make extractions of the gluon density in the photon rather difficult. Total rates for the production of many (i.e. > 2) jets could provide direct evidence for the presence of multiple interactions, although parton showering and hadronization significantly affect low transverse energy jets.Comment: 21 pages, 8 figures include

Influence of Constraining Barrier on the 5th Lumbar and 1st Sacral joint Compressive Force during Manual Lifting

The purpose of this study was to examine the mechanical stresses on the lower back as the response of different heights of constraining barrier. Ten male subjects lifted a load from the floor to the knuckle height under the non-constrained and the constrained conditions with 4 different heights of constraining barrier (80%, 100%, 120% and 140% of knee height). The constrained condition was defined as the condition where a load was placed on the floor behind a certain level of bar. When lifting of the constrained conditions, subjects significantly increased the peak compressive forces at L5/S1 compared to the non-constrained (3868.8 ± 527.5 N, 4175.0 ± 486.0 N, 4162.4 ± 462.3 N, 4136.0 ± 553.1 N, 4079.4 ± 468.9 N for 0%, 80%, 100%, 120% and 140% barrier height conditions respectively). The subjects moved the load further from L5/S1 in the horizontal direction when lifting during the constrained conditions. While lifting during the constrained conditions subjects generated an increase in the sacral angle and a decrease of the knee flexion. The peak compressive forces at L5/S1 showed a statistically significant quadratic trend. However, the magnitude of the difference of peak compressive forces during the constrained conditions was small

The Effect of Shoe Type on a Golfer's Stability

The role of the shoe in the golf swing should be to provide a solid base of support for the application of forces. Because there is a large mediolateral component to the reaction forces at the feet during the swing, a shoe is required that is effective in providing mediolateral stability. Without the necessary stability, changes in the kinetics and kinematics of the swing may occur that could lead to inaccurate ball placement. To study the role of stability, twelve right-handed male golfers where asked to hit golf balls into an indoor driving net using a five iron golf club. All subjects were experienced golfers with self-reported handicaps of twelve or less. In-shoe pressure measurements using a Tekscan in-shoe pressure measurement system were recorded in each shoe simultaneously at 100 Hz. Ground reaction forces for each foot were collected for the same trials using two separate A.M.T.I. force platform systems sampling at 319 Hz. Identification of address and contact involved the use of a pressure sensor beneath the ball and the hitting surface. A light was iluminated while the golfer was in the address position (AD) as well as at contact (CON). This circuit was also interfaced to a microcomputer via an analog to digital converter so that AD and CON could be identified in the ground reaction force data. These positions were verified and maximum backswing (MB) was identified using a 200 Hz NEC high speed video camera. The shoe types consisted of two golf shoes, one athletic golf shoe, one running shoe, and one cross-training shoe. Analysis focused on changes in the movement of the center of pressure (COP) at the ground-shoe and shoe-foot interface, as well as position of the center of pressure at address, maximum backswing and contact. Comparison of the movement of the COP was used to indicate the relative stability of each shoe. The occurrence of the maximum deviation of the COP in the anteroposterior and medio-Iateral direction relative to MB and CON was assessed both in-shoe and at the ground-shoe interface. The results may provide evidence regarding the stability associated with golf shoes as compared with a cross-trainer or running shoe

THE EFFECT OF STEP-HEIGHT ON THE KNEE ANGLES AND IN-SHOE PRESSURE DISTRIBUTIONS DURING STEP-AEROBICS

INTRODUCTION A recent trend in indoor exercise is step-aerobics. This form of aerobic exercise involves the rhythmic stepping up to and down from a fixed platform to the beat of the accompanying "pop" music. In the past, substantial research has been done on the kinematics of the climbing of actual architectural stairs (Andriacchi et al., 1980; McFayden and Winter, 1988; Laubenthal et al., 1972) but no studies, to date, have been done to explore the kinematics of this new fitness phenomenon. Therefore, the purpose of this investigation was to study the biomechanics of step aerobics. Specifically, the effect of the step-height on the knee angles and in-shoe pressure distributions of subjects performing step aerobics was evaluated. It was hoped that the results of this study could be used to help determine any possible biomechanical health concerns of participation in step aerobics

Inelastic diffraction and color-singlet gluon-clusters in high-energy hadron-hadron and lepton-hadron collisions

It is proposed, that ``the colorless objects'' which manifest themselves in large-rapidity-gap events are color-singlet gluon-clusters due to self-organized criticality (SOC), and that optical-geometrical concepts and methods are useful in examing the space-time properties of such objects. A simple analytical expression for the $t$-dependence of the inelastic single diffractive cross section $d\sigma/dt$ ($t$ is the four-momentum transfer squared) is derived. Comparison with the existing data and predictions for future experiments are presented. The main differences and similarities between the SOC-approach and the ``Partons in the Pomeron (Pomeron and Reggeon)''-approach are discussed.Comment: 12 pages, 2 figure

In-Shoe Pressure Distribution During Ergometer Rowing In Novice And Experienced Rowers

Distribution of foot pressure during rowing has been minimally investigated. Foot pressure distribution is most likely altered with experience ca using an increase in stability and thus efficiency duirng the rowing stroke. This study evaluated in-shoe pressure distribution differences between novice and experienced collegiate rowers during rowing on the Concept II ergometer. In shoe pressure was measured in ten subjects, five novice and five experienced, while rowing at a stroke rate of 32-34 strokes per minute. The subjects wore the same model shoe with a Tekscan in-shoe pressure measurement system placed inside each shoe, only the dominant foot was studied. Data were sampled at a rate of 100 Hz. The following variables at the shoe-foot interface were investigated during the drive and the recovery of the stroke: peak forefoot pressure, peak rearfoot pressure, and displacement of the mediolateral and longitudinal center of pressure (COP). Peak pressures were investigated to discover how the pressure is distributed during the stroke. Comparison of the COP was used to indicate the stabililty of the foot during the drive phase. The experienced rowers had a high proportion of the total in-shoe pressure in the forefoot during the drive. Generally there was less pressure exerted on the recovery phase in the experienced subjects. These subjects also had a less variable mediolateral COP and an increase in the longitudinal COP plot. To apply force correctly during the drive it seems to be necessary to place a high proportion of the pressure in the forefoot. The trend toward decreased pressure on the recovery in the experienced rowers may reflect an increased efficiency due to experience. The decrease in the mediolateral COP deviation would appear to be related to increased stability. The longitudinal COP plot showed that with experience the plantar surface in contact with the shoe during the drive increases

Charged Particle Multiplicity in Diffractive Deep Inelastic Scattering

The recent data from H1 Collaboration on hadron multiplicity in diffractive DIS has been studied in the framework of perturbative QCD as a function of invariant diffractive mass. The formulas obtained explain the observed excess of particle production in diffractive DIS relative to that in DIS and $e^+e^-$ annihilation. It is shown that the results are sensitive to the quark--gluon structure of the Pomeron. Namely, the data say in favour of a super-hard gluon distribution at the initial scale.Comment: 12 pages, 3 figures; to be published in Phys. Rev.

Colorless and colored gluon-clusters in nucleon?

It is suggested that virtual gluon-clusters exist in nucleon, and that such colorless and colored objects manifest themselves in the small $x_B$ region of inelastic lepton-nucleon scattering processes. The relationship between the space-time properties of such clusters and the striking features observed in these scattering processes is discussed. A phase-space model is used to show how quantitative results can be obtained in such an approach. The results of this model-calculation are in reasonable agreement with the existing data. Further experiments are suggested.Comment: to be published in Phys. Rev.

Unitarization of Gluon Exchange Amplitudes and Rapidity Gaps at the Tevatron

Rapidity gaps between two hard jets at the Tevatron have been interpreted as being due to the exchange of two gluons which are in an overall color-singlet state. We show that this simple picture involves unitarity violating amplitudes. Unitarizing the gluon exchange amplitude leads to qualitatively different predictions for the fraction of $t$-channel color singlet exchange events in forward $qq$, $qg$ or $gg$ scattering, which better fit Tevatron data.Comment: 21 pages, Revtex, 7 postscript figures included via epsf.sty. Compressed postscript file of complete paper also available at http://pheno.physics.wisc.edu/pub/preprints/1998/madph-98-1024.ps.Z or at ftp://pheno.physics.wisc.edu/pub/preprints/1998/madph-98-1024.ps.

A Semi-Analytical Analysis of Texture Collapse

This study presents a simplified approach to studying the dynamics of global texture collapse. We derive equations of motion for a spherically symmetric field configuration using a two parameter ansatz. Then we analyse the effective potential for the resulting theory to understand possible trajectories of the field configuration in the parameter space of the ansatz. Numerical results are given for critical winding and collapse time in spatially flat non-expanding, and flat expanding universes. In addition, the open non-expanding and open-expanding cases are studied.Comment: 12 pages, figures available from author, BROWN-HET-895, uses phyzz