Cycle to cycle variability in a repetitive upper extremity task

The purpose of this study was to examine the variability in muscle activity at rest and work during a repetitive task. A total of 20 participants performed a bimanual push task using three frequencies (4, 8, 16 pushes/min), three loads (1 kg, 2 kg, 4 kg) and two grip conditions (no grip, 30% maximum). The coefficient of variation (CoV) of muscle activity was determined for the anterior deltoid, biceps brachii, extensor digitorum and flexor digitorum superficialis. Faster push frequencies and heavier loads had lower work–rest ratio CoV and higher mean muscle activity (p < 0.01). Sixteen pushes per minute produced the lowest CoV for the anterior deltoid (p < 0.01), while the 1- kg load produced the lowest CoV for the extensor digitorum and flexor digitorum superficialis (p < 0.01). Changes were driven by the rest phase rather than by the work phase, except for grip decreasing forearm muscle CoV. These findings underscore the importance of variability at rest and indicate that low variability of muscle activity is associated with ergonomic risk factors.

Practitioner Summary: Decreased motor variability has been associated with pain and injury. A cyclical push task, evaluated in terms of work and rest phases, found that greater workloads increased variability primarily due to changes in the rest phase. Muscle variability, especially for the rest phase, may provide insight into injury risk.     

Quantitative Characterization of the Fracture Surface of Si Single Crystals by Confocal Microscopy

Experiments are conducted to study the dislocation nucleation conditions at the crack tip in {110}〈110〉 oriented Si single crystals. Specimens with surface cracks are first statically loaded at elevated temperatures for a prolonged period of time to initiate and move dislocations away from the crack tip, then cooled down to room temperature and loaded to fracture to measure the fracture toughness. Fractographic analysis of the fracture surfaces is performed. Distinct wavy patterns on the fracture surface at the initial cleavage crack front are observed, which is attributed to the existence of local mixed mode I/mode III stresses resulting from the inhomogeneous dislocation activity. Confocal microscopy is employed to quantify the fracture surface roughness. The results show that the increase of fracture toughness is directly associated with the increased area of the rough surface, which is characterized by the roughness number or the fractal dimension increment. Our results also demonstrate that dislocation nucleation can occur only at discrete sites. The spacing between these dislocation nucleation sources is of the order of 1 μm. A simple model is developed for the relationship between the fracture toughness and the surface roughness parameters, which is in good agreement with the experimental results.     

无机纳米粉体制造技术的现状及展望

介绍了无机纳米粉体的制造技术和最新进展，着重介绍了超重力技术制备纳米粉体材料的进展和应用状况，讨论了目前无机纳米粉体制造技术中存在的问题，并总结了其应用和前景。     

SAGA: sparse and geometry-aware non-negative matrix factorization through non-linear local embedding

This paper presents a new non-negative matrix factorization technique which (1) allows the decomposition of the original data on multiple latent factors accounting for the geometrical structure of the manifold embedding the data; (2) provides an optimal representation with a controllable level of sparsity; (3) has an overall linear complexity allowing handling in tractable time large and high dimensional datasets. It operates by coding the data with respect to local neighbors with non-linear weights. This locality is obtained as a consequence of the simultaneous sparsity and convexity constraints. Our method is demonstrated over several experiments, including a feature extraction and classification task, where it achieves better performances than the state-of-the-art factorization methods, with a shorter computational time.     

超细钛酸锶系列功能材料的制备技术及进展

钛酸锶(SrTiO3)陶瓷是一种新兴的多功能电子陶瓷材料，由于其优异的电学性能而在很多领域有着广泛的应用。综述了SrTiO3粉体的主要制备技术及新进展，并对其加以比较。指出液相化学合成法是现阶段制备SrTiO3的主要方法，而作为液相法之一的直接沉淀法由于具有设备简单、操作方便、粉体粒径小、粒度分布窄、易于掺杂等优点有着诱人的工业应用前景。     

Effects of carbonation on the pore structure of non-hydraulic lime mortars

The pore structures of carbonated non-hydraulic lime mortars made with a range of different aggregates and concentrations of lime have been determined using mercury intrusion porosimetry (MIP). MIP data have been correlated with scanning electron microscopy images and other porosity data. During carbonation there is an increase in pore volume in the ∼ 0.1 μm pore diameter range across all mortar types which is attributed to the transformation of portlandite to calcite. Also there is a monotonic increase in the volumes of pores with diameters below 0.03 μm. A model is proposed for the changes in pore structure caused by carbonation. This attributes the increase in the volume of sub 0.03 μm pores to the attachment of calcite crystals to the surface of aggregate particles, and in some cases to the surface of portlandite crystals. This phenomenon may explain the continuing presence of portlandite in mortars that, apparently, have fully carbonated.     

PDC Control Design for Non-holonomic Wheeled Mobile Robots with Delayed Outputs

This paper presents a new technique for tracking-error model-based Parallel Distributed Compensation (PDC) control for non-holonomic vehicles where the outputs (measurements) of the system are delayed and the delay is constant. Briefly, this technique consists of rewriting the kinematic error model of the mobile robot tracking problem into a TS fuzzy representation and finding a stabilizing controller by solving LMI conditions for the tracking-error model. The state variables are estimated by nonlinear predictor observer where the outputs are delayed by a constant delay. To illustrate the efficiency of the proposed approach a comparison between the TS fuzzy observer and the nonlinear predictor observer is shown. For this study the reference trajectory is built by taking into account the acceleration limits of the mobile robot. All experiments are implemented on simulation and the real-time platform.     

Optimization Model for the Sustainable Water Resource Management of River Basins

Water Resources Management - This paper presents a new methodology for the sustainable and optimal allocation of water for a river basin management area. The model distinguishes between short and...     

Condensation/Hydrogenation of Biomass-Derived Oxygenates in Water/Oil Emulsions Stabilized by Nanohybrid Catalysts

The synthesis of fuel-range molecules by condensation of biomass-derived furfural and acetone has been studied in a biphasic emulsion system. Nanohybrids composed of basic oxide nanoparticles fused to carbon nanotubes have been used to simultaneously stabilize water/oil emulsions and catalyze the condensation reaction. Under the same conditions, higher conversions and higher fractions of fuel-range condensation products (C₈?CC₁₃) have been obtained in the emulsion compared to those obtained in the single phase. Furthermore, when using metallized nanohybrids these emulsions have been used to hydrogenate the oil-soluble condensation products. Both model compounds and synthetic bio-oil mixtures have been used to demonstrate that catalytic emulsion systems could be effective for upgrading complex mixtures, such as pyrolysis oil.