Creeping flow solution of the Leidenfrost phenomenon

Creeping flow solution of Leidenfrost phenomenon by use of Navier-Stokes, continuity, and energy equation

Boydbolt, a positive-latch, simple-release fastener

Fastener /Boydbolt/ has recently been designed to furnish positive lock and release characteristics that positively prevent accidental adverse functions of lock or release

Analysis of Layered Social Networks

Prevention of near-term terrorist attacks requires an understanding of current terrorist organizations to include their composition, the actors involved, and how they operate to achieve their objectives. To aid this understanding, operations research, sociological, and behavioral theory relevant to the study of social networks are applied, thereby providing theoretical foundations for new methodologies to analyze non-cooperative organizations, defined as those trying to hide their structure or are unwilling to provide information regarding their operations. Techniques applying information regarding multiple dimensions of interpersonal relationships, inferring from them the strengths of interpersonal ties, are explored. A layered network construct is offered that provides new analytic opportunities and insights generally unaccounted for in traditional social network analyses. These provide decision makers improved courses of action designed to impute influence upon an adversarial network, thereby achieving a desired influence, perception, or outcome to one or more actors within the target network. This knowledge may also be used to identify key individuals, relationships, and organizational practices. Subsequently, such analysis may lead to the identification of exploitable weaknesses to either eliminate the network as a whole, cause it to become operationally ineffective, or influence it to directly or indirectly support National Security Strategy

A generalized correlation of vaporization times of drops in film boiling on a flat plate

Vaporization time correlations for drops in leidenfrost state of film boiling on flat plat

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

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

SPECTRAL DECOMPOSITION OF VERTICAL GROUND REACTION FORCE CURVES

INTRODUCTION - The vertical ground re- action force component typically has two peaks. The first peak (impact peak) is caused by the impact between the foot and the ground while the lower frequency second peak (active peak) is caused by the vertical braking of the body followed by vertical push-off. Bobbert et al. (1991) pro- posed a method of decomposing the VGRF into the contribution of the support leg and the rest of the body by double differentiation of segment center of mass position data. This decomposition allowed them to determine the magnitude of the impact peak independent of the rest of the curve. The purpose of this study was to investigate a method of decomposing the VGRF curve that does not require differentiation of position data. METHODOLOGY - Five male recreational runners completed 5 trials in 3 different run- ning shoes that differed only in the density of the midsole material. VGRF data were recorded from a force platform at 1000 Hz using an analogue to digital converter. A Fourier transform was performed on each trial An inverse transform was then per- formed twice - once using the frequencies below 3 Hz and once using the frequencies above 3 Hz. Figure 1 illustrates a typical decomposition of the force curve. Peak (PK) and time to peak (TPK) values were recorded for each curve of the decomposed VGRF curve. RESULTS AND DISCUSSION - The magnitudes and times of the impact and active peaks for the decomposed VGRF are presented in Table 1. The impact peak for the soft shoe had a greater magnitude than the medium or hard shoes. This may indi- cate that this shoe midsole experienced maximum compression or that the subjects perceived the soft midsole and adjusted their kinematics. There were essentially no differences in the active PK between the soft, medium and hard midsoles. Table 1. Mean values for decomposed VGRF variables. Midsole Soft Medium Hard Impact PK 240.1 212.8 238.7 Impact TPK 28.3 26.1 26.6 Active PK 1241.2 1233.4 1244.7 Active TPK 107.9 108.7 104.0 Since the impact peak component is of a higher frequency than the active compo- nent, the decomposed VGRF curves are comparable lo the curves of Bobbert et el. (1991). These results indicate that this pro-cedure can be used to separate the true impact characteristics of the VGRF from the remainder of the curve. REFERENCES Bobbert, M.F. et al. (1991). Calculation of vertical ground reaction force estimates during running from positional data. J Biomech, Vol 24: 12 pp. 1095-1 105