Further progress in ion back-flow reduction with patterned gaseous hole-multipliers

A new idea on electrostatic deviation and capture of back-drifting avalanche-ions in cascaded gaseous hole-multipliers is presented. It involves a flipped reversed-bias Micro-Hole & Strip Plate (F-R-MHSP) element, the strips of which are facing the drift region of the multiplier. The ions, originating from successive multiplication stages, are efficiently deviated and captured by such electrode. Experimental results are provided comparing the ion-blocking capability of the F-R-MHSP to that of the reversed-bias Micro-Hole & Strip Plate (R-MHSP) and the Gas Electron Multiplier (GEM). Best ion-blocking results in cascaded hole-multipliers were reached with a detector having the F-R-MHSP as the first multiplication element. A three-element F-R-MHSP/GEM/MHSP cascaded multiplier operated in atmospheric-pressure Ar/CH4 (95/5), at total gain of ~10^{5}, yielded ion back-flow fractions of 3*10^{-4} and 1.5*10^{-4}, at drift fields of 0.5 and 0.2 kV/cm, respectively. We describe the F-R-MHSP concept and the relevance of the obtained ion back-flow fractions to various applications; further ideas are also discussed.Comment: 17 pages, 11 figures, published in JINS

THE DYNAMIC SUPPORT STRUCTURE AND THE FOOT STABILITY RELATED TO RUNNING SPEED

Introduction - The alterations of the dynamic support structure in running, related to the horizontal speed increase, has been studied by several authors; Cavanagh (1989)studies the displacement of the support center and the pressure distributions; Nigg et all (1981) analyses the active and passive loader Bates (1983) study the critical variables defining the support dynamic. Simultaneously, the study of the rearfoot mobility around the horizontal axes of the subtalar joint during ground contact has been gaining in importance (Nigg et all, 1978). The above mentioned subjects are integrated in the present study for a more complete knowledge of the foot contact. Relations between the increase of running speed and respectively the variables defining the rearfoot mobility and the critical variable6 of the ground reaction forces are establish. Methods - Six sprinter of Portuguese national level carried out each of them 6 performances, barefoot, at three different speeds (Vl=3.3 7 me-I+/-0.56 ; V2=4. 37me"+/-0.37 e V,55 -44 me-I+/-0.31). The kinetic data were obtained on a force platform (Kistler 9281B, sampling frequency 1000 Hz) connected t6 the computer via A/D card (DT 2801A Data Translation). The runners speed was controlled by means of photoelectric censors that synchronized the collection of the kinetic and video images. The kinematic data was processed according to the methodology proposed by Nigg et all (1978). Results and Discussion - The obtained kinetic results are similar to those contained in the corresponding bibliographic references , in form patterns as well as in quantitative results (Cavanagh,1989 ; Nigg et a11,1981; Batee et all, 1983). Regarding the rearfoot mobility the displacement/time curves are similar to the ones presented by Nigg et all (1978) as far as barefoot runners are concerned. Significant statistical correlations (correlation coefficient, Bravais-Pearson) were ascertained showing that the running speed increase ie related to : (1) decrease of ground contact time (r=-0.96, P-ZO.01) , (2) increase of anteriorposterior speed variation (aVy) (r50.77,

Nanomaterials with high solar reflectance as an emerging path towards energy-efficient envelope systems: a review

The application of nanomaterials in the construction field is allowing the development of smart, green, durable and more efficient buildings. Among the most widely researched nanomaterials are nanosized cool pigments, which are being enforced to achieve thermal and energy-efficient facades, with the development of high reflectance and retro-reflectance coatings. Their peculiar optical and catalytic activity turns nanomaterials into suitable candidates to be used as dark coloured high solar reflectance without affecting aesthetic characteristics, thus improving the durability of coatings. The objective of this paper is to review the state-of-the-art on the benefits of using high reflectance nanopigments as coatings in building facades and their production and synthesis processes. It is thus divided into three main topics: (i) the benefits of using nanopigments on facades, (ii) the most important nanomaterials used as cool pigments and (iii) the main methods of synthesizing nanopigments. One expects that the study of near-infrared nanopigmentation synthesis processes will be able to promote and disseminate the use of nanotechnology in construction, assessing the production problems and limitation and thus helping to disseminate new products by reducing production costs and increase availability. [GRAPHICS]

Single or Combined Maquet III Osteotomy: Long Term Results

INTRODUCTION: In 1963, based on biomechanics studies, Maquet proposed the advancement of the patellar tendon insertion as a mean of treating patellofemoral pain. The rationale for this procedure was a reduction in the patellofemoral compression force vector by changing the angular relationship between patella tendon and quadriceps tendon. One of the additional procedures, on a malalign knee, was performing a cupuliform osteotomy above the tibial tuberosity (COATT). OBJECTIVES: Evaluating, on a retrospective and comparative trial, the clinical and radiological long-term outcomes of the patients who underwent a single (M) or combined (MC) Maquet III osteotomy, in order to determine if this surgery as or not fulfilled its initially objectives. METHODS: All surgical records of the Service, between 1970 and 1991, were reviewed. We identify 116 cases registered as “M” or “MC” Maquet III osteotomy. A questionnaire as been prepared for collecting data. We evaluated the preoperative complaints, postoperative complications and range of motion recovery time, as well as the postoperative pain absence period. All patients underwent an objective assessment by the Visual Analog Scale (VAS) and the Kujala Patellofemoral Scoring System (KPFSS). A radiological assessment was also made in order to evaluate the arthrosis degree and compartment affected, the Bicondylo-Patellar Angle (BPA) and the Caton-Deschamps Index (CDI). Mann-Whitney, t-Student and Chi-Square tests were applied for statistical evaluation. p <0.05 was considered statistically significant. RESULTS: According to the study criteria, from the 116 selected patients we could review in our clinics 49 Maquet III osteotomies (n= 25 “M” group vs n=24 “MC” group) . On the “M” group, the average age at surgery was 37.6 ±12.0 years and the postoperative follow-up 27.1 ±3.15 years, versus 56,5 ±6,8 years at surgery and a 23,2 ±3,4 postoperative follow up years on the “MC” group. Prior range of motion was accomplished 4.8 ±3.5 months after surgery on the “M” group versus 6,7 ±3,5 months on the “MC” group (p=0,017). About complications, on the “M” group we have 16,0% (n=4) versus 16,6% (n=4) (p=0,763). The “M” group presented40% (n=10) patients who haven’t referred pain until nowadays versus 38,5% (n=5) (p=0,85), and the average period of of pain absence was 20.5 ±5.7 years on the “M” group versus 11,0 ±1,7 (p=0,001). At the COX score, 58,3% (n=14) of the “M” group had good to excellent outcomes versus 53,8% (n=7) (p=0,793). VAS at rest was 1.7 ±0.7, in activity 4.4±3.0 and KPFSS 61.9 ±22.3 points on the “M” group versus 1,1 ±0,3 (p=0,016), 4,3 ±2,0 (p=0,883) and 54,7 ± 16,9 (p=0,364) points on the “MC” group. Radiologically, BPA was 6.3 ±3.9° and CDI 0.9 ±0.1 on the “M” group versus 11,8 ±3,9 (p=0,000) and 0,9 ±0,2 (p=0,99) on the “MC” group. Nowadays, at the“M” group,58,3% (n=14) had a grade I/II of Kellgren&Lawrence at patellofemoral joint and 79,2.% (n=19) at the femorotibial joint versus 53,8% (n=7) (p=0,793) and 46,2% (n=6) (p=0,041). CONCLUSION: With a cut off follow-up period higher than 20 years, the Maquet III group presented58,3% of good to excellent outcomes with patients presenting a majority of low grade osteoarthritic knee. The COATT procedure hasn’t increased the postoperative complications nor worsen the funcional outcomes. On the other side, the femorotibial grade of arthritis was higher on this group

KINETIC ENERGY OF BODY SEGMENTS IN DROP JUMP

INTRODUCTION - In sport movements, such as sprinting and jumping, where the ability to produce explosive movement is extremely important, the elastic characteristics of the muscle-skeletal system are decisive. Drop jump (DJ) exercises are often used as a training method to develop the mechanical and control capabilities of the neuromuscular system. DJ has also been used to obtain very important data about the degree of adaptability of the locomotor system to increasing amounts of mechanical load, using different dropping heights. The purpose of this study is to analyse the changes of the kinetic energy of body segments (KE) in relation to the increase o! mechanical load, both in the stretching and push-off phases. These changes are related to the angular kinematics of joints and to the relative length changes on some of the extensor muscles. METHODS - Four elite sprinters (height 17855 cm, body mass 69.34.5 kg) performed 6 DJ from 25, 40, 55 and 70 cm. Ground reaction forces were recorded at 500Hz and vertical peak and vertical net impulse were calculated. Simultaneously, angular kinematic data of the ankle, knee and hip joints were calculated using video analysis system (120 Hz). We used Visser et al. (1990) model to calculate the relative length changes (%L) of gastrocnemius (G), rectus femoris (RF) and biceps femoris (BF) muscles. The joint angular velocity (~)) and relative muscle length changes velocity (%L.s-') were also calculated. The KE energy of the foot, lower leg, thigh and upper body mass centres were calculated from the kinematic and anthropometric data. RESULTS - The basic results are showed on the table, AVG and SD values, both for the stretching and shortening phases of the ground contact period. CONCLUSION - The KE of the body segments at the end of push-off was higher on DJ25 and DJ40, Wen compared with the KE at touchdown, presenting a positive energetic balance. At DJ55, the energetic balance was null and at DJ70 was negative. The stretching and shortening velocities increased in all muscles with the increase of DJ height. Nevertheless, no differences were found on vertical jumping achievement between DJ executed from different heights. The subjects were able to reduce the increasing stretching load producing higher vertical net impulses during the downward movement. REFERENCES Visser J.J.. Hoogkamer, J., Bobbert, M.F. and Huijing, P.A.(1990). Eur J Appl Physiol, 61: 453-46

A dynamic method for charging-up calculations: the case of GEM

The simulation of Micro Pattern Gaseous Detectors (MPGDs) signal response is an important and powerful tool for the design and optimization of such detectors. However, several attempts to simulate exactly the effective charge gain have not been completely successful. Namely, the gain stability over time has not been fully understood. Charging-up of the insulator surfaces have been pointed as one of the responsible for the difference between experimental and Monte Carlo results. This work describes two iterative methods to simulate the charging-up in one MPGD device, the Gas Electron Multiplier (GEM). The first method uses a constant step for avalanches time evolution, very detailed, but slower to compute. The second method uses a dynamic step that improves the computing time. Good agreement between both methods was reached. Despite of comparison with experimental results shows that charging-up plays an important role in detectors operation, should not be the only responsible for the difference between simulated and measured effective gain, but explains the time evolution in the effective gain.Comment: Minor changes in grammatical statements and inclusion of some important information about experimental setup at section "Comparison with experimental results

THE ANTAGONIST MUSCLE PATTERN IN ELBOW EXTENSION OFA THROWING TASK

INTRODUCTION The myoelectric activity in fast human movements is characterised by a phasic pattern with two fundamental events: the first agonist burst, responsible for the initial limb acceleration, and an antagonist impulse. The accurate definition of the antagonist burst role, and the relative participation of peripheral and central sources on its control, are not clearly defined in the literature (Angel, 1977; Marsden et al., 1983). The purpose of the present study was (1) to characterise the antagonistic pattern on the elbow extension when subjects had to throw a dart onto a target, and (2) to analyse the antagonist changes when subjects throw with different accuracy/speed demands. Experiments were performed on 13 subjects. Surface EMG were recorded from triceps and biceps brachii with active bipolar electrodes. Electrogoniometers wore used on shoulder and elbow joints. RESULTS The antagonist EMG contained a phasic burst (ANT) which began between the movement onset and the end of the agonist activation, with an usual co-contraction duration of less than 30 ms. The time interval between the movement onset and the beginning of ANT was normally higher than the EMG latency necessary for spindle influences, considered to be less than 20 ms (Tarkka, 1986). In our results, ANT always began during the acceleration phase and, in most cases, developed its maximum intensity around the moment of elbow peak velocity. So, the antagonist burst represents more than an impulse braking preventing full extension, and we must admit its participation in the control of the duration of the acceleration phase. Antagonist modifications with velocity indicated an amplitude increase, measured by the integrated EMG. without relevant temporal changes. Two subjects presented an alternative way of braking the movement, when the accuracy constraints were absent, based, on the increase of the joint stiffness through the co-contraction of agonist and antagonist muscles. This kind of movement braking resulted in a reduced timing accuracy demand when compared with the active braking, produced by the antagonist phasic burst (Ghez & Martin, 1 982). CONCLUSION The timing of the antagonist phasic burst invite us (1) to associate it with the control of the end of the acceleration phase and (2) to accept that it could be influenced by the muscular response to stretch, although modulated by higher central commands. (3) The general tendency was to maintain the temporal structure of antagonist EMG among conditions and to increase its intensity with the increase of the throwing velocity. (4) Two subjects presented an alternative way of braking the movement when the accuracy constraints wers absent. REFERENCES Angel, R. (1977). Antagonist muscle activity during rapid arm movements. Central versus proprioceptive influences. J. Neuroi, Neuros., Psychia t., 40: 683-686. Ghez, C., & Martin, J. (1 982). The control of rapid limb movement in the cat. Ill - Agonist- Antagonist coupling. Exp: Br. Res., 45: 1 15 - 125. Marsden, C., Obeso, J., & Rothwell, J. (1983). The function of the antagonist muscle during fast limb movements in man. J. Physiol., 335: 1 - 13. Tarkka, 1. (1986). Short and long latency reflexes in human muscles following electrical and mechanical stimulation. Acta Physiol. Scand., 128. Supplem. 557: 1-32

Simulation of VUV electroluminescence in micropattern gaseous detectors: the case of GEM and MHSP

Electroluminescence produced during avalanche development in gaseous avalanche detectors is an useful information for triggering, calorimetry and tracking in gaseous detectors. Noble gases present high electroluminescence yields, emitting mainly in the VUV region. The photons can provide signal readout if appropriate photosensors are used. Micropattern gaseous detectors are good candidates for signal amplification in high background and/or low rate experiments due to their high electroluminescence yields and radiopurity. In this work, the VUV light responses of the Gas Electron Multiplier and of the Micro-Hole Strip Plate, working with pure xenon, are simulated and studied in detail using a new and versatile C++ toolkit. It is shown that the solid angle subtended by a photosensor placed below the microstructures depends on the operating conditions. The obtained absolute EL yields, determined for different gas pressures and as functions of the applied voltage, are compared with those determined experimentally.Comment: Accepted for publication in Journal of Instrumentatio

Simulation of gain stability of THGEM gas-avalanche particle detectors

Charging-up processes affecting gain stability in Thick Gas Electron Multipliers (THGEM) were studied with a dedicated simulation toolkit. Integrated with Garfield++, it provides an effective platform for systematic phenomenological studies of charging-up processes in MPGD detectors. We describe the simulation tool and the fine-tuning of the step-size required for the algorithm convergence, in relation to physical parameters. Simulation results of gain stability over time in THGEM detectors are presented, exploring the role of electrode-thickness and applied voltage on its evolution. The results show that the total amount of irradiated charge through electrode's hole needed for reaching gain stabilization is in the range of tens to hundreds of pC, depending on the detector geometry and operational voltage. These results are in agreement with experimental observations presented previously