A high-wavenumber boundary-element method for an acoustic scattering problem

In this paper we show stability and convergence for a novel Galerkin boundary element method approach to the impedance boundary value problem for the Helmholtz equation in a half-plane with piecewise constant boundary data. This problem models, for example, outdoor sound propagation over inhomogeneous flat terrain. To achieve a good approximation with a relatively low number of degrees of freedom we employ a graded mesh with smaller elements adjacent to discontinuities in impedance, and a special set of basis functions for the Galerkin method so that, on each element, the approximation space consists of polynomials (of degree $\nu$) multiplied by traces of plane waves on the boundary. In the case where the impedance is constant outside an interval $[a,b]$, which only requires the discretization of $[a,b]$, we show theoretically and experimentally that the $L_2$ error in computing the acoustic field on $[a,b]$ is ${\cal O}(\log^{\nu+3/2}|k(b-a)| M^{-(\nu+1)})$, where $M$ is the number of degrees of freedom and $k$ is the wavenumber. This indicates that the proposed method is especially commendable for large intervals or a high wavenumber. In a final section we sketch how the same methodology extends to more general scattering problems

System multilayered applied to the radiative cooling

In applied optics, the multilayered structures (MLS) take an important place in many instrumental and industrial devices. The aim of this work is to study the MLS in order to optimize the inverse greenhouse effect; it is made by a survey on theoretical formalism of the energy exchange phenomena. This optimization requires that the window materials (MLS) are good reflectors in the visible range and assuring a total transmission in the infrared zone (8-13 µm); One of the support elements, of the window, answering to these criterions is germanium, for which we have studied the thickness influence and have found that the equilibrium temperature reached by the absorber has a minimal value between 0.01 µm and 0.06 µm. However, only with germanium, the window can not products the inverse greenhouse effect. Indeed, the germanium must include other layers in order to increase the visible reflectance and the infrared transmittance (8-13µm); what forms a multilayered structure. Several system have been used, only 7 of them have been kept for this work: S1, S2, …, S7 systems. Only the following systems: S2/S1, S3/S2/S1 and MgO/S3/S2/S1 give a radiative cooling effect, with a very good result of 15 °C below ambient temperature in the case of the S6 system. To approach of the real conditions of this system realization (S6), we simulated the effects of such imperfections, as presence of air, that would be due to the quality of the layers deposition. This study is made in the case of the S7 system. As results, we found that, for zenithal angles ≤ 60°, the layers of air, for which the thickness is lower than 0.5 µm, don't present any influence on the absorber's equilibrium temperature.In applied optics, the multilayered structures (MLS) take an important place in many instrumental and industrial devices. The aim of this work is to study the MLS in order to optimize the inverse greenhouse effect; it is made by a survey on theoretical formalism of the energy exchange phenomena. This optimization requires that the window materials (MLS) are good reflectors in the visible range and assuring a total transmission in the infrared zone (8-13 µm); One of the support elements, of the window, answering to these criterions is germanium, for which we have studied the thickness influence and have found that the equilibrium temperature reached by the absorber has a minimal value between 0.01 µm and 0.06 µm. However, only with germanium, the window can not products the inverse greenhouse effect. Indeed, the germanium must include other layers in order to increase the visible reflectance and the infrared transmittance (8-13µm); what forms a multilayered structure. Several system have been used, only 7 of them have been kept for this work: S1, S2, …, S7 systems. Only the following systems: S2/S1, S3/S2/S1 and MgO/S3/S2/S1 give a radiative cooling effect, with a very good result of 15 °C below ambient temperature in the case of the S6 system. To approach of the real conditions of this system realization (S6), we simulated the effects of such imperfections, as presence of air, that would be due to the quality of the layers deposition. This study is made in the case of the S7 system. As results, we found that, for zenithal angles ≤ 60°, the layers of air, for which the thickness is lower than 0.5 µm, don't present any influence on the absorber's equilibrium temperature

Immediate effect of kinesiology tape on ankle stability

BackgroundLateral ankle sprain is one of the most common musculoskeletal injuries, particularly among the sporting population. Due to such prevalence, many interventions have been tried to prevent initial, or further, ankle sprains. Current research shows that the use of traditional athletic tape can reduce the incidence of sprain recurrence, but this may be at a cost to athletic performance through restriction of motion. Kinesiology tape, which has become increasingly popular, is elastic in nature, and it is proposed by the manufacturers that it can correct ligament damage. Kinesiology tape, therefore, may be able to improve stability and reduce ankle sprain occurrence while overcoming the problems of traditional tape.AimTo assess the effect of kinesiology tape on ankle stability.Methods27 healthy individuals were recruited, and electromyography (EMG) measurements were recorded from the peroneus longus and tibialis anterior muscles. Recordings were taken from the muscles of the dominant leg during induced sudden ankle inversion perturbations using a custom-made tilting platform system. This was performed with and without using kinesiology tape and shoes, creating four different test conditions: barefoot(without tape), shoe(without tape), barefoot(with tape) and shoe(with tape). For each test condition, the peak muscle activity, average muscle activity and the muscle latency were calculated.ResultsNo significant difference (p>0.05) was found by using the kinesiology tape on any of the measured variables while the wearing of shoes significantly increased all the variables.ConclusionKinesiology tape has no effect on ankle stability and is unable to nullify the detrimental effects that shoes appear to have

Effect of ball position on the risk of injury to the lower limb joints during the hockey sweep pass in women

ObjectivesThis study aimed to determine if ball position influences the risk of lower limb non-contact injury in hockey sweep pass. It also aimed to determine a ball position that minimises excessive strain placed on the lower limb joints of the lead leg during the sweep pass.MethodsA cohort of 18 female hockey-playing volunteers (age: 19.7±1.5 years; height: 165.5±5.4 cm; body mass: 66.4±7.0 kg) were recruited. Participants performed the sweep pass using three different ball positions: in front, in line with, and behind the heel of the lead (left) foot.Motion analysis and force plate data were collected. Moments and angles in all three planes of motion for the three main lower limb joints were then calculated using Vicon software. Results were statistically analysed using SPSS software.ResultsSignificant differences (p<0.05) were found between the three tested ball positions for the mean maximum angles and moments, and mean ranges of motion produced at the lead three main lower limb joints. Positioning the ball in line with the heel of the lead foot resulted in the lowest moments and angles when compared with the other two ball positions.ConclusionsThe results indicate that positioning the ball in line with the heel of the lead foot is recommended to minimise the risk of injury to the lower limb joints during the hockey sweep pass. It is hoped that these findings will result in this position being implemented by players new to hockey or those returning to the sport following injury

Comparison of branded rugby headguards on their effectiveness in reducing impact on the head

Aim: To compare the available brands of rugby headguards and evaluate their impact attenuation properties at various locations on the cranium, with regard to concussion prevention.Methods: Seven different branded headguards were fitted onto a rigid headform and drop-tested in three different positions. An accelerometer measured the linear acceleration the headform experienced on impact with the ground. Each test involved dropping the headform from a height that generated 103.8 g on average when bare, which is the closest acceleration to the upper limit of the concussion threshold of 100 g. A mean peak acceleration for each drop position was calculated and compared with the bare baseline measurement.Results: Each headguard demonstrated a significant decrease in the mean peak acceleration from the baseline value (all p≤0.01). Overall the Canterbury Ventilator was the most effective headguard, decreasing the impact force on average by 47%. The least effective was the XBlades Elite headguard, averaging a force reduction of 27%. In five of the seven headguards, the right side of the headwear was the most effective at reducing impact force.Conclusion: Overall, the results indicate that it would be beneficial to wear a headguard during rugby in order to reduce the impact forces involved in head collisions. There was also a clear difference in performance between the tested brands, establishing the Canterbury headguard as the most effective. However, only one model of headguard from each brand was tested, so further research evaluating all other models should be considered.</p