Electromyography applied to sport ergonomics

Abstract

The improvement of electromyographic (EMG) devices for the detection of electric potentials produced in voluntary complex movements and the evolution of methodological approaches to data acquisition and computerized analysis of patterns, are responsible for the increased applications of EMG in bioengineering, rehabilitation, sport and occupational biomechanics, physiology and zoology and to a lesser extent in ergonomics. This paper describes three different EMG applications related to a sport environment using three different EMG registration and data acquisition approaches.

The first study examined the relation between the swimming action in water and its simulation using training equipment on land. It was found that with respect to the mechanical aspects of dry-land equipment and to the biomechanical differences in the execution of the front crawl action on dry land and in water, based on EMG activity of the propulsion muscles, the best results were found when using devices with accommodating resistance. Recovery muscles were best imitated using isokinetics, but despite the greater effort on land, lower EMG activity was recorded than in water. It was generally observed that whenever the swimmer acted against a mechanical resistance an important pattern deviation was noted.

Second, a study to determine the influence of ski materials on the EMG muscle activity of skiers showed systematic differences between the use of racing, soft and compact skis. The results supported the idea that the soft ski should be more highly recommended than the compact or racing ski for both general and competive use.

Finally, in a third study we found that there was a very high degree of similarity in the pattern and intensity of muscle activity in both free swimming and swimming against a mechanical resistance (MAD swimming), even though the kinesiological aspects of the movement trajectory were proved different beforehand.     

Response and noise characteristics of small-sized inorganic and organic scintillation detectors measured with vacuum and solid-state photodetectors

Response and noise properties of scintillation detectors were investigated using a ¹³⁷Cs radioactive source. The experimental setup consisted of a scintillator, photodetector, amplifier, and spectrometric analog-to-digital converter. Small-sized, cubic crystals were manufactured of stilbene, p-terphenyl and thallium-doped cesium iodide, as well as of a plastic scintillator material based on polystyrene. Vacuum and solid-state photomultipliers and a silicon PIN photodiode were used as photodetectors. The energy equivalent noise was determined for all used photodetectors. The response of various scintillators when using vacuum and semiconductor photomultipliers was found to be closely similar.     

Observed light yield of scintillation pixels: Extending the two-ray model

In this paper we propose an extended, two dimensional model describing the propagation of scintillation photons inside a cuboid crystal until they reach a PMT window. In the simplest approach the model considers two main reasons for light losses: standard absorption obeying the classical Lambert–Beer law and non-ideal reflectivity of the “mummy” covering formed by several layers of Teflon tape wrapping the sample. Results of the model calculations are juxtaposed with experimental data as well as with predictions of an earlier, one dimensional model.     

Compressively sampled light field reconstruction using orthogonal frequency selection and refinement

This paper considers the compressive sensing framework as a way of overcoming the spatio-angular trade-off inherent to light field acquisition devices. We present a novel method to reconstruct a full 4D light field from a sparse set of data samples or measurements. The approach relies on the assumption that sparse models in the 4D Fourier domain can efficiently represent light fields. The proposed algorithm reconstructs light fields by selecting the frequencies of the Fourier basis functions that best approximate the available samples in 4D hyper-blocks. The performance of the reconstruction algorithm is further improved by enforcing orthogonality of the approximation residue at each iteration, i.e. for each selected basis function. Since sparsity is better preserved in the continuous Fourier domain, we propose to refine the selected frequencies by searching for neighboring non-integer frequency values. Experiments show that the proposed algorithm yields performance improvements of more than 1 dB compared to state-of-the-art compressive light field reconstruction methods. The frequency refinement step also significantly enhances the visual quality of reconstruction results of our method by a 1.8 dB average.     

Enhancing light-extraction efficiency of OLEDs with high- and low-refractive-index organic–inorganic hybrid materials

High- and low-refractive-index hybrid materials were prepared by an in situ acid-free sol–gel process for internal and external light-extraction layers in organic light-emitting diodes (OLEDs). A random copolymer of methyl methacrylate (MMA) and 3-(trimethoxysilyl) propyl methacrylate (MSMA), poly(MMA-co-MSMA), which was capped with trialkoxysilane in MSMA units, was used as a precursor. The precursor was further reacted with titanium(IV) isopropoxide (TTIP) and tetraethyl orthosilicate (TEOS) to synthesize the high- and low-refractive-index hybrid materials, respectively, in which TiO₂ and SiO₂ nanoparticles were well dispersed, respectively, in the polymer matrix. After the reactions with TTIP and TEOS, the refractive index increased to 1.81 and decreased to 1.44 from 1.50 of the precursor, respectively. The luminance, power, and current efficiency of the OLED with an external light-extraction layer were enhanced by 21.3, 28.6, and 29.1%, respectively, those of the OLED with an internal light-extraction layer were increased by 62.4, 76.9, and 59.2%, respectively, and those of the device with combined ELEL and ILEL were enhanced by 62.7, 77.2, and 59.3%, respectively, when compared to values for the reference OLED without an internal or external light-extraction layer. These results indicate that high- and low-refractive-index materials are desirable for enhancement in light-extraction efficiency, and they can provide practical solutions for various applications such as OLED displays and lighting.     

Extrusion of silicon-rich AlMgSi alloys

As a part of on-going research on phase transformations during the deformation of light alloys, the effect of silicon excess on the extrudability and mechanical properties of the standard AlMgSi1 alloy within AA6082 alloy is investigated in this study. The AlMgSi1 alloy and three experimental aluminum alloys with a silicon content of 1.98%, 3.73% and 5.51% were direct-chilled cast into billets 95 mm in diameter, homogenized at 540 °C for 4 h and extruded into 12 mm diameter rods at different extrusion speeds. The results showed that an increase in the silicon content reduced the extrudability of the AlMgSi1 alloy by lowering the limiting extrusion speed. However, the extruded alloys with 3.73% and 5.51% silicon, generally characterized by a fine grained microstructure, exhibited higher strength levels compared with the 1.98% silicon alloy. Nonetheless, the mechanical properties of these alloys, in the T6 temper condition, were below those of the AlMgSi1 base alloy.     

Changes of fluorescent spectral features after successive rare earth doping of gadolinium oxide powders

We present a complex fluorescence study of a series of gadolinium oxide polycrystalline powders singly, doubly and triply doped with trivalent rare earth ions (Er³⁺, Tb³⁺, and Dy³⁺), to explore a possibility of their use as materials for white light emitting diodes. The excitation and luminescence spectra along with the decay kinetics were measured in the temperature range from 6 to 300 K. The luminescence efficiency was studied within the visible spectral range, i.e. −400 nm to 750 nm under excitation by 355 nm third harmonic Nd:YAG laser pulses. Singly doped Er³⁺ sample gave stronger luminescence signals, but others showed significantly larger decay lifetimes. The successive rare earths doping leads to substantial changes of the spectral positions due to the up-conversion processes. In the singly (Er³⁺) doped sample, following the time resolved spectrum and decay curves, there are two different types of emissions: at 660 nm and at shorter wavelengths (below 640 nm) the red emission's lifetime is ten times longer than at shorter wavelengths. The singly doped sample shows unclear temperature-dependence of luminescence with lifetime at 550 nm (the longest at 100 K, similarly at 6 K and 300 K) and achieved luminous efficacy 73.5 lm/W.     

基于DM642的结构光图像中心线提取

提出了一种基于DM642的中心线提取算法,针对TMS320DM642嵌入式平台的特性,采用3×3最亮邻接点加权平均法提取结构光带中心线,并对其进行优化.该方法与其他一些基于MATLAB的传统中心线提取算法相比,不仅提高了提取速度和精度,而且大大减少了类似模板法等需用的卷积运算量,实时性好,适合在大数据量背景下的嵌入式平台应用,通过图像处理板卡的PCI接口,可以方便地实现处理数据的及时上传.     

TYIN tegnestue Architects. Integrating On-Site Education and Practice

Founded by Andreas Grøntvedt Gjertsen and Yashar Hanstad, TYIN tegnestue Architects grew out of an initiative to provide sleeping accommodation for an orphanage in Thailand when the principals were only third-year architecture students. Norwegian architect Lisbet Harboe explains how the student-architects built up a practice while in schools by refocusing their studies and those of their peers on learning through their own experiences of construction.