ANTHROPOMETRICAL DIFFERENCES BETWEEN CHINESE AND GERMANS

Introduction: It is known that anthropometrical data differ with gender, race, and age. In practice, researchers often use the statistical data obtained from previous studies for biomechanical modeling in sports. Accuracy is reduced by unsuitable racial data. Knowing the racial differences and statistical error can help scientists achieve a reasonable compromise between the accuracy of the estimates and the time required to complete the measurements. The purpose of this study was to determine anthropometrical differences between Chinese and Germans. METHODS: A method developed by Shan (1993, 1995) was utilized in this study. The process of the method is as follows: measure the characteristic profiles of a human body, reconstruct the entire body in the computer with the help of measured profiles, subdivide the body into several thousand columns, and finally calculate anthropometrical data such as segmental masses, centers of mass, radii of gyration, and moments of inertia. Sixty subjects (15 female Germans, 15 female Chinese, 15 male Germans, and 15 male Chinese) took part in this study. Correlation and regression analyses were made of body weight and/or height as independent variables. RESULTS: For the same body weight and height: the trunk of a Chinese is 1.8% (male 1.9%, female 1.7%) taller than that of a German, the leg of a German is 1.8% longer than that of a Chinese, the head of a Chinese is 2.6% (male 3.0%, female 2.3%) heavier than that of a German, and the leg of a German is 1.7% (male 1.6%, female 1.8%) heavier than that of a Chinese. The segmental masses are better estimated by body weight (r=0.6 - 0.8,

BIOMECHANICAL ANALYSIS OF SPRINTING TO IMPROVE THE INDIVIDUAL TECHNIQUE

INTRODUCTION: The aim of this study is to record dynamic and cinematic parameters during sprinting with maximum velocity. The sprint start is also examined. The motion analysis aims for an improvement of the individual technique METHODS: 21 male and 3 female runners took part in this study. Cinematic and dynamic parameters were recorded during start and fast running. In the sagitall plane the following parameters were analysed: joint-angles, velocities and acceleration of joints, centres of joints, joint forces and joint moments. These parameters were recorded with two high-speed cameras (250 Hz) and a 3- dimensional force platform (measuring area 240x80 cm). The experimental set-up allowed the recording of two successive steps on the force platform while the dynamical- and kinematical-data was synchronously obtained. Additionally the reaction time was measured. The reaction time is the time from the start signal to the moment the rear leg leaves the block,. The high-speed video data were interpreted with the software package winanalyze from Mikromak. RESULTS: Very different rotary actions of the shoulders to balance the hip action were observed. The main differences between the single athletes became evident in the velocities and the accelerations of the hip and the knee-angles. Particularly variable forces in the direction of movement (retarding stroke) came forward between the different athletes. The observed tendencies will be verfied in another study in June. OUTLOOK: After the inquiry of the general fitness of the sprinters the development of a special training-program for each athlete is intended in the next step. It will be based on the Multi-Joint-Concept form R. P. Narcessian. REFERENCES: Hay, J. G. (1993). The Biomechanics of Sports Techniques. Englewood Cliffs, N.J.: Prentice-Hall

A conjecture on the origin of dark energy

The physical origin of holographic dark energy (HDE) is investigated. The main existing explanations, namely the UV/IR connection argument of Cohen et al, Thomas' bulk holography argument, and Ng's spacetime foam argument, are shown to be not satisfactory. A new explanation of the HDE model is then proposed based on the ideas of Thomas and Ng. It is suggested that the dark energy might originate from the quantum fluctuations of spacetime limited by the event horizon of the universe. Several potential problems of the explanation are also discussed.Comment: 11 pages, no figure

Demonstration of a sub‐picosecond x‐ray streak camera

A novel design, magnetically focused, x‐ray streak camera was designed and tested using sub‐20 fs soft‐x‐ray pulses generated by high harmonic emission in a gas. The temporal resolution of the camera was demonstrated to be under 0.9 ps throughout the ultraviolet to soft‐x‐ray wavelength region. Our streak camera represents the fastest x‐ray detector developed to date. © 1996 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/69727/2/APPLAB-69-1-133-1.pd

Part-Scale Model for Fast Prediction of Thermal Distortion in DMLS Additive Manufacturing Part 2: A Quasi-Static Thermomechanical Model

The direct metal laser sintering (DMLS) additive manufacturing process can quickly produce complex parts with excellent mechanical properties. However, thermal stress accumulated in the layer-by-layer build cycles of DMLS may induce part distortion and even cause the failure of the whole build process. This paper is the second part of two companion papers that present a part-scale model for fast prediction of temperature history and part distortion in DMLS. In this paper, a quasi-static thermomechanical (QTM) model is built to estimate the thermal distortion of entire parts in DMLS. Firstly, the thermal contraction in each build cycle is modeled as a quasi-static loading process; the final thermal stress accumulated in the parts is the superposition of thermal stress generated in each build cycle. Secondly, the stress relaxation process after the parts are cut off from the substrate is modeled, and final distortion of the parts is predicted with thermal stress calculated from the thermal contraction processes. In comparison to existing transient thermomechanical models, the QTM can predict thermal distortion in DMLS with much faster computational speed, and a comparison against experiment shows less than 10% error.Mechanical Engineerin

Fast Prediction Of Thermal Distortion In Metal Powder Bed Fusion Additive Manufacturing: Part 2, A Quasi-static Thermo-mechanical Model

The additive manufacturing (AM) process metal powder bed fusion (PBF) can quickly produce complex parts with mechanical properties comparable to that of wrought materials. However, thermal stress accumulated during Metal PBF may induce part distortion and even cause failure of the entire process. This manuscript is the second part of two companion manuscripts that collectively present a part-scale simulation method for fast prediction of thermal distortion in Metal PBF. The first part provides a fast prediction of the temperature history in the part via a thermal circuit network (TCN) model. This second part uses the temperature history from the TCN to inform a model of thermal distortion using a quasi-static thermo-mechanical model (QTM). The QTM model distinguished two periods of Metal PBF, the thermal loading period and the stress relaxation period. In the thermal loading period, the layer-by-layer build cycles of Metal PBF are simulated, and the thermal stress accumulated in the build process is predicted. In the stress relaxation period, the removal of parts from the substrate is simulated, and the off-substrate part distortion and residual stress are predicted. Validation of part distortion predicted by the QTM model against both experiment and data in literature showed a relative error less than 20%. This QTM, together with the TCN, offers a framework for rapid, part-scale simulations of Metal PBF that can be used to optimize the build process and parameters

Fast Prediction Of Thermal Distortion In Metal Powder Bed Fusion Additive Manufacturing: Part 1, A Thermal Circuit Network Model

The additive manufacturing (AM) process metal powder bed fusion (PBF) can quickly produce complex parts with mechanical properties comparable to wrought materials. However, thermal stress accumulated during PBF induces part distortion, potentially yielding parts out of specification and frequently process failure. This manuscript is the first of two companion manuscripts that introduce a computationally efficient distortion and stress prediction algorithm that is designed to drastically reduce compute time when integrated in to a process design optimization routine. In this first manuscript, we introduce a thermal circuit network (TCN) model to estimate the part temperature history during PBF, a major computational bottleneck in PBF simulation. In the TCN model, we are modeling conductive heat transfer through both the part and support structure by dividing the part into thermal circuit elements (TCEs), which consists of thermal nodes represented by thermal capacitances that are connected by resistors, and then building the TCN in a layer-by-layer manner to replicate the PBF process. In comparison to conventional finite element method (FEM) thermal modeling, the TCN model predicts the temperature history of metal PBF AM parts with more than two orders of magnitude faster computational speed, while sacrificing less than 15% accuracy. The companion manuscript illustrates how the temperature history is integrated into a thermomechanical model to predict thermal stress and distortion

Balancing hydrogen adsorption/desorption by orbital modulation for efficient hydrogen evolution catalysis

Hydrogen adsorption/desorption behavior plays a key role in hydrogen evolution reaction (HER) catalysis. The HER reaction rate is a trade-off between hydrogen adsorption and desorption on the catalyst surface. Herein, we report the rational balancing of hydrogen adsorption/desorption by orbital modulation using introduced environmental electronegative carbon/nitrogen (C/N) atoms. Theoretical calculations reveal that the empty d orbitals of iridium (Ir) sites can be reduced by interactions between the environmental electronegative C/N and Ir atoms. This balances the hydrogen adsorption/ desorption around the Ir sites, accelerating the related HER process. Remarkably, by anchoring a small amount of Ir nanoparticles (7.16 wt%) in nitrogenated carbon matrixes, the resulting catalyst exhibits significantly enhanced HER performance. This includs the smallest reported overpotential at 10 mA cm(-2) (4.5 mV), the highest mass activity at 10 mV (1.12 A mg(Ir)(-1)) and turnover frequency at 25 mV (4.21 H2 s(-1)) by far, outperforming Ir nanoparticles and commercial Pt/C

Measurement of the branching fractions of psi(2S) -> 3(pi+pi-) and J/psi -> 2(pi+pi-)

Using data samples collected at sqrt(s) = 3.686GeV and 3.650GeV by the BESII detector at the BEPC, the branching fraction of psi(2S) -> 3(pi+pi-) is measured to be [4.83 +- 0.38(stat) +- 0.69(syst)] x 10^-4, and the relative branching fraction of J/psi -> 2(pi+pi-) to that of J/psi -> mu+mu- is measured to be [5.86 +- 0.19(stat) +- 0.39(syst)]% via psi(2S) -> (pi+pi-)J/psi, J/psi -> 2(pi+pi-). The electromagnetic form factor of 3(pi+pi-) is determined to be 0.21 +- 0.02 and 0.20 +- 0.01 at sqrt(s) = 3.686GeV and 3.650GeV, respectively.Comment: 17pages, 7 figures, submitted to Phys. Rev.