Metabolic costs of load carriage with different container sizes

Abstract

Six well-trained male subjects carried boxes of varying box width and weight at varying speeds on a level treadmill until steady-state heart rates were obtained. Analysis of the steady-state data for heart rate and metabolic cost led to development of highly accurate predictor models for both factors. The metabolic-cost model accounted for over 94% of the variance (R²>0·94), and the heart-rate model accounted for over 81% of the variance present (R²>0·81). Evaluation of other models for predicting physiological response to carrying loads found their predictions to differ significantly from the data of the present study.     

The effects of a lower body exoskeleton load carriage assistive device on limits of stability and postural sway

The study investigated the effects of using a lower body prototype exoskeleton (EXO) on static limits of stability and postural sway. Measurements were taken with participants, 10 US Army enlisted men, standing on a force platform. The men were tested with and without the EXO (15 kg) while carrying military loads of 20, 40 and 55 kg. Body lean to the left and right was significantly less and postural sway excursions and maximal range of movement were significantly reduced when the EXO was used. Hurst values indicated that body sway was less random over short-term time intervals and more random over long-term intervals with the EXO than without it. Feedback to the user's balance control mechanisms most likely was changed with the EXO. The reduced sway and relatively small changes in sway with increasing load weights suggest that the EXO structure may have functioned to provide a bracing effect on the body.     

Biomechanical assessment of lateral stiffness elements in the suspension system of a backpack

The purpose of this study was to examine the change in load distribution characteristics associated with adding lateral stiffness elements (rods) to a rucksack (backpack). A load distribution mannequin was instrumented with two 3D load cells to allow determination of the load applied to the shoulders and upper torso independent of the load applied to the hips and lower trunk. Position and mass of the payload (25?kg) were fixed at the centre of the volume of the rucksack and held constant during all testing. It was hypothesized that lateral rods would provide a force bridge that transfers part of the vertical load of the pack from the upper back and shoulders to the hip belt thereby reducing the vertical load on the torso, and possibly reducing the horizontal reaction force that produces a shear load on the spine. Results showed that these active stiffness elements shifted 14% of the vertical load from the upper torso to the pelvic region with lumbar shear load remaining relatively unchanged for all combinations of shoulder strap and waist belt tension. The lateral rods also provided a mean increase of 12% in the extensor moment at the L3?–?L4 level, thus reducing some demand on the erector spinae muscles.     

Trunk muscle activity in different modes of carrying schoolbags

The daily load of carrying schoolbags is influenced by the mode of carriage. Electromyographic (EMG) activity from rectus abdominis and erector spinae was recorded bilaterally in five static conditions: no bag; shoulder bag; backpack; front pack; double pack. Nineteen students carried a load of 15% of their body weight. A double pack, with the load equally distributed in a front and a backpack, showed no significant differences in EMG activity compared with unloaded standing. The activity levels of erector spinae significantly decreased while carrying a backpack and increased with a shoulder bag and a front pack. Rectus abdominis revealed significantly higher EMG levels in the backpack trial. Asymmetrical activity between the right and the left part of the back muscles was clearly observed while carrying a shoulder bag with the weight at the right side of the body. The abdominal muscles revealed a slightly significant asymmetry for the shoulder bag and, surprisingly, also for the backpack. These findings suggest that the physical stresses associated with carrying book bags can be minimized by the design of a double pack. Asymmetry in muscle activity may indicate a failure of trunk stabilization and contribute to the development back pain.     

双目立体视觉在模型姿态监测中的应用研究

风洞试验模型姿态的实时、精确非接触测量对于提高风洞试验的精度和可信度有重要意义。但实现却十分困难,尤其是模型姿态侧滑角的实时精确测量。提出采用双目立体视觉实时、精确测量模型姿态,简要说明了硬件组成和基本原理,深入探讨了技术要点和主要算法。最后给出了测量结论。     

On the SPH tensile instability in forming viscous liquid drops

Smoothed Particle Hydrodynamics (SPH) simulations of elastic solids and viscous fluids may suffer from unphysical clustering of particles due to the tensile instability. Recent work has shown that in simulations of elastic or brittle solids the instability can be removed by an artificial stress whose form is derived from a linear perturbation analysis of the full set of governing SPH equations. While a linear analysis cannot be used to derive the corresponding form of the artificial stress for a viscous fluid, here we show that the same construction which applies to elastic solids may also work for viscous fluids provided that the constant parameter ? entering in the definition of the artificial stress is properly chosen. As a suitable test case, we model the formation of a circular van der Waals liquid drop and show that the tensile instability is removed when an artificial viscous force and energy generation term are added to the standard SPH equations of motion and energy, respectively. The optimal value of the constant ? is constrained by the ability of the model simulation to reproduce both a sufficiently smoothed density profile and the van der Waals phase diagram.     

Anomalous wear behavior of MoS2 films in moderate vacuum and dry nitrogen

440C steel thrust ball bearing races lubricated with 1 m thick sputtered films of MoS₂ were tested in the unidirectional and oscillatory modes against bare steel balls in moderate (10^–4–10^–5 Pa 10^–6–10^–7 Torr) vacuum and in 1 atmosphere of 99.999% pure ( 1 ppm water) N₂ in the same unbaked environmental chamber. Over 90% of the residual gases in the chamber vacuum consisted of H₂O vapor. The bearings operated in N₂ showed substantially longer lives compared to the specimens tested in vacuum. Scanning electron microscope (SEM) tribometry was also performed on an MoS₂ film powder-burnished onto a 440C flat. This flat was repeatedly oscillated against bare, hemispherical-tipped 440C pins on fresh wear tracks in the same type of N₂ and column vacuum of ~10^–3 Pa 10^–5 Torr itself containing over 90% residual H₂O. The SEM-generated results on the burnished film confirmed the same, atmosphere-dependent difference in wear life observed with the sputtered layers. Varying the moisture content of the burnished flat and its immediate environment by cryosorption predictably manipulated the coefficient of friction and wear life of MoS₂. The various possible causes of this perplexing phenomenon are reviewed, and a plausible hypothesis is offered attributing the unexpected wear life reduction to the physico-chemical consequences of residual H₂O hydrogen-bonding to the oxidized and/or hydrated edge and basal plane sites of MoS₂ in moderate vacuum. The site-specific sorption of water is severely hindered in 1 atm N₂ by the gas molecules disrupting the H-bonding mechanism.     

威腾500 t桥式梁运输车

介绍了威腾500t桥式梁运输车的研制与开发,着重介绍了设计要求与特点。与法国Nicolas桥式梁运输车进行了详细的对比分析,并对该设计产品的应用实例与应用效果进行了阐述。     

A CAD tool for an array of differential oscillators coupled through a broadband network

A new expression of the equations describing the locked states of two oscillators coupled through a resistor is presented in this article. This theory has led to the elaboration of a CAD tool which provides, in a short simulation time, the frequency locking region of two coupled differential oscillators. © 2012 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2012.