STRIDE CHARACTERISTICS RELATED TO RUNNING VELOCITY IN MAXIMAL SPRINT RUNNING

In sprinting, athletes and coaches strive to increase running speed by means of general and specific training methods. As running velocity is always the product of stride length and stride frequency, in the end, all methods aim to improve one or both of these factors. The relation between stride length, stride rate and running velocity has been discussed in the literature from different points of view. Alexander and Goldspink (1977) analysed the movement speed and stride characteristics of mammals. As they wanted to compare mammals of different sizes, they transferred stride characteristics and speed into dimensionless parameters, taking into account gravity and the length of the leg. Their conclusions should also be valid for humans. But it is not clear if these formulas can predict stride characteristics in maximal sprint running. It was the purpose of this study to analyse whether stride rate and stride length in maximal sprint running are related to running velocity as proposed by Alexander and Goldspink. A better understanding of this relationship could probably help coaches in developing sprint training strategies. In this study twenty male physical education students performed a maximal sprint over 100 meter and seventeen female students ran a 40 meter sprint. Running speed was continuously recorded by means of a velocimeter. Surface electrodes were used to record the muscle activity of four thigh muscles. These EMGrecordings were used to determine the duration of each stride cycle and to calculate mean stride rate per 5 meter-interval. The length of the lower limbs (h) and the acceleration of free fall (g) are used in the definitions of dimensionless running velocity (dV), stride rate(dSR) and stride length (dSL). The average maximal velocity of the male sprinters was 9.37 ±0.52 m/s while the female sprinters attained 7.38± 0.52 m/s. The relation between stride length and running velocity in male 100 meter performance was determined by means of linear regression analysis: dV=0.178+(1.175*dSL). This means that 87% of variance in running velocity seems to be related to differences in stride length. On the other hand variance in stride rate explains less than 20% of the variance in running speed. These findings are confirmed by the results in the 40 meter sprint of the female group: dV=(1.172*dSL)-0.0830 with 80% of variance in dV being explained by variance in dSL and 20% of dV explained by dSR. In contrast to the findings reported in the literature we found a clear linear relationship between dSL and dV, and no significant correlation between dSR and dV. These findings were confirmed in two separate analyses: one with females and another with males. The discrepancies between the results in the literature and this study can probably be explained by the fact that we analyzed pure sprint performances, in contrast to most studies analyzing differences in running speeds ranging from jogging to sprinting. In all-out sprinting, stride rate in the second 5 meter interval is already close to the maximum stride rate; from this point on differences in running speed are mainly due to changes in stride length

STUDY OF PERFORMANCE RELATED STRENGTH TESTS FOR COMPETITION LEVEL SPRINTERS

Strength is a performance determining factor in sprinting. This study investigates the significance of a variety of isokinetic tests to control strength requirements for sprinters. Eighteen competition level sprinters &1i0 0 m-time = 10.94 s, = 0.22 s) ran a 40 meter sprint and performed 24 isokinetic strength tests on the PROMETT-system Static, concentric, eccentric and plyometric contractions were executed at velocities between 0 and 300 '1s for knee-extensors, knee flexors and ankle extensors. For each movement the torque at three different joint angles was recorded. As the performance determining factors change in relation to running distance, the correlation between the recorded torques and the running speed is graphically presented in relation to running distance (72 graphs). Per type of contraction the torque with the highest correlation with running speed was selected for further analysis. To interpret these graphs three phases are distinguished in a 40 meter sprint. Phase 1 is the phase of initial acceleration (from 0 to 10 m), phase 2 is the phase of continued acceleration (from 10 to 30 m) and phase 3 is the phase of maximum running speed (30 to 40 m). The common variance in torque and running speed data is quantified by means of the determinationcoefficient. The results indicate that isokinetic strength tests can be used to evaluate sprint related strength requirements at a competition level. 30 to 50 percent of variance in running speed within each of the three phases can be declared by a single isokinetic strength test. It may be concluded that the strength of the knee flexors determines 50 % of the variance within the phase of initial acceleration. Ankle extension torques explain 45 % of the variance in running speed within phase 2, and the strength of the knee extensors determines 33 % of variance in maximum running speed. It is also remarkable that for ankle extension only tests were selected with a high movement velocity (200°/s), while for knee extension tests were selected at lower velocities (65 and 130°/s)

Ultrafast dynamics of coherent optical phonons and nonequilibrium electrons in transition metals

The femtosecond optical pump-probe technique was used to study dynamics of photoexcited electrons and coherent optical phonons in transition metals Zn and Cd as a function of temperature and excitation level. The optical response in time domain is well fitted by linear combination of a damped harmonic oscillation because of excitation of coherent $E_{2g}$ phonon and a subpicosecond transient response due to electron-phonon thermalization. The electron-phonon thermalization time monotonically increases with temperature, consistent with the thermomodulation scenario, where at high temperatures the system can be well explained by the two-temperature model, while below $\approx$ 50 K the nonthermal electron model needs to be applied. As the lattice temperature increases, the damping of the coherent $E_{2g}$ phonon increases, while the amplitudes of both fast electronic response and the coherent $E_{2g}$ phonon decrease. The temperature dependence of the damping of the $E_{2g}$ phonon indicates that population decay of the coherent optical phonon due to anharmonic phonon-phonon coupling dominates the decay process. We present a model that accounts for the observed temperature dependence of the amplitude assuming the photoinduced absorption mechanism, where the signal amplitude is proportional to the photoinduced change in the quasiparticle density. The result that the amplitude of the $E_{2g}$ phonon follows the temperature dependence of the amplitude of the fast electronic transient indicates that under the resonant condition both electronic and phononic responses are proportional to the change in the dielectric function.Comment: 10 pages, 9 figures, to appear in Physical Review

The novel method to reduce the silica content in lignin recovered from black liquor originating from rice straw

Difficulties in the production of lignin from rice straw because of high silica content in the recovered lignin reduce its recovery yield and applications as bio-fuel and aromatic chemicals. Therefore, the objective of this study is to develop a novel method to reduce the silica content in lignin from rice straw more effectively and selectively. The method is established by monitoring the precipitation behavior as well as the chemical structure of precipitate by single-stage acidification at different pH values of black liquor collected from the alkaline treatment of rice straw. The result illustrates the significant influence of pH on the physical and chemical properties of the precipitate and the supernatant. The simple two-step acidification of the black liquor at pilot-scale by sulfuric acid 20w/v% is applied to recover lignin at pH 9 and pH 3 and gives a percentage of silica removal as high as 94.38%. Following the developed process, the high-quality lignin could be produced from abundant rice straw at the industrial-scale

Intrinsic response time of graphene photodetectors

Graphene-based photodetectors are promising new devices for high-speed optoelectronic applications. However, despite recent efforts, it is not clear what determines the ultimate speed limit of these devices. Here, we present measurements of the intrinsic response time of metal-graphene-metal photodetectors with monolayer graphene using an optical correlation technique with ultrashort laser pulses. We obtain a response time of 2.1 ps that is mainly given by the short lifetime of the photogenerated carriers. This time translates into a bandwidth of ~262 GHz. Moreover, we investigate the dependence of the response time on gate voltage and illumination laser power

Homodyne detection for measuring internal quantum correlations of optical pulses

A new method is described for determining the quantum correlations at different times in optical pulses by using balanced homodyne detection. The signal pulse and sequences of ultrashort test pulses are superimposed, where for chosen distances between the test pulses their relative phases and intensities are varied from measurement to measurement. The correlation statistics of the signal pulse is obtained from the time-integrated difference photocurrents measured.Comment: 7 pages, A4.sty include

Cumulative Effects in 100 kHz Repetition-Rate Laser-Induced Plasma Filaments in Air

[EN] Cumulative effects are crucial for applications of laser filaments, such as for the remote transfer of energy and the control of electric discharges. Up to now, studies of cumulative effects in the air of high-repetition-rate pulse trains have been performed at lower rates than 10 kHz. Herein, the nonlinear effects associated with short plasma filaments produced by pulses of moderate energy (0.4 mJ per pulse) and repetition rates up to 100 kHz are experimentally characterized. With increasing repetition rate, a decrease in absorption, fluorescence emission, and breakdown voltage and concurrently an increase in peak intensity and third-harmonic-generation efficiency are observed. Hydrodynamic simulations of the heated gas show that the observed decreases are directly related to a quasi-stationary state of reduced gas density in the filament. However, further investigations are required to fully understand the physics underpinning the observed sharp reduction of the breakdown voltage at 100 kHz repetition rates. The results may prove relevant for energy and information delivery applications by laser-induced air waveguide or electric discharge and lightning control.TJW acknowledges the support from NSAF (Grant no. U2130123), Strategic Priority Research Program of the Chinese Academy of Sciences (Grant no. XDB16), International Partnership Program of Chinese Academy of Sciences (Grant nos. 181231KYSB20200033 and 181231KYSB20200040), Shanghai Science and Technology Program (Grant no. 21511105000), and Oversea Training Program of Ministry of Science and Technology. MC acknowledges the support from UK Research and Innovation (UKRI) and the UK Engineering and Physical Sciences Research Council (EPSRC) (Fellowship "In-Tempo" EP/S001573/1), and the Royal Society (RGS\R1\201365). JCD acknowledges the support of NASA (SBIR grant 80NSSC22PB067). The authors wish to acknowledge Drs. Jean-Pierre Wolf, Jerome Kasparaian, Clara Saraceno, and Olga Kosareva for enlightening discussions.Wang, T.; Ebrahim, MH.; Afxenti, I.; Adamou, D.; Dada, AC.; Li, R.; Leng, Y.... (2023). Cumulative Effects in 100 kHz Repetition-Rate Laser-Induced Plasma Filaments in Air. Advanced Photonics Research. 4(3). https://doi.org/10.1002/adpr.2022003384

Focusing and Compression of Ultrashort Pulses through Scattering Media

Light scattering in inhomogeneous media induces wavefront distortions which pose an inherent limitation in many optical applications. Examples range from microscopy and nanosurgery to astronomy. In recent years, ongoing efforts have made the correction of spatial distortions possible by wavefront shaping techniques. However, when ultrashort pulses are employed scattering induces temporal distortions which hinder their use in nonlinear processes such as in multiphoton microscopy and quantum control experiments. Here we show that correction of both spatial and temporal distortions can be attained by manipulating only the spatial degrees of freedom of the incident wavefront. Moreover, by optimizing a nonlinear signal the refocused pulse can be shorter than the input pulse. We demonstrate focusing of 100fs pulses through a 1mm thick brain tissue, and 1000-fold enhancement of a localized two-photon fluorescence signal. Our results open up new possibilities for optical manipulation and nonlinear imaging in scattering media

Parmenides reloaded

I argue for a four dimensional, non-dynamical view of space-time, where becoming is not an intrinsic property of reality. This view has many features in common with the Parmenidean conception of the universe. I discuss some recent objections to this position and I offer a comparison of the Parmenidean space-time with an interpretation of Heraclitus' thought that presents no major antagonism.Comment: 11 pages, accepted for publication in Foundations of Scienc

Непрямое сравнение эффективности и безопасности апалутамида и даролутамида для лечения неметастатического кастрационнорезистентного рака предстательной железы по результатам двух независимых исследований с поправкой на разницу между популяциями пациентов

.Введение. Апалутамид и даролутамид являются ингибиторами андрогенных рецепторов нового поколения, которые продемонстрировали превосходную эффективность у пациентов с неметастатическим кастрационно-резистентным раком предстательной железы, получающих андрогендепривационную терапию (АДТ). На сегодняшний день нет исследований по прямому сравнению этих 2 препаратов.Цель исследования – непрямое сравнение эффективности и переносимости апалутамида и даролутамида.Материалы и методы. Был применен метод согласованного скорректированного непрямого сравнения (matchingadjusted indirect comparison, MAIC) данных рандомизированного плацебо-контролируемого исследования III фазы SPARTAN (апалутамид + АДТ), которые были уравновешены по основным исходным клиническим параметрам, с опубликованными обобщенными данными исследования ARAMIS (даролутамид + АДТ) для их сопоставления. Для оценки всех конечных точек эффективности, включая выживаемость без метастазирования, повышение уровня простатического специфического антигена (ПСА), выживаемость без прогрессирования, а также общую выживаемость, были рассчитаны отношения рисков (ОР) и 95 % доверительные интервалы (ДИ). Для оценки конечных точек по безопасности (частота нежелательных явлений и серьезных нежелательных явлений) рассчитывали отношения шансов.Результаты. Перед уравновешиванием данных в исследованиях SPARTAN и ARAMIS наблюдались значимые различия по уровню ПСА (медиана 7,8 нг/мл против 9,2 нг/мл), числу пациентов со статусом 1 по шкале Eastern Cooperative Oncology Group (23 % против 31 %), частоте использования препаратов для модификации костной ткани (10 % против 4 %), медиане времени с момента установления первичного диагноза (94,9 мес против 85,4 мес) и числу пациентов из США (35 % против 12 %) и Европы (50 % против 64 %). После уравновешивания данных (n = 455) мы установили, что режим, включающий апалутамид + АДТ, с высокой долей вероятности более эффективен, чем даролутамид + АДТ, по выживаемости без метастазирования (98,3 %; ОР 0,70; 95 % ДИ 0,51–0,98), повышениюуровня ПСА (~100 %; ОР 0,46; 95 % ДИ 0,33–0,64) и выживаемости без прогрессирования (93,2 %; ОР 0,79; 95 % ДИ 0,59–1,08). Показатели общей выживаемости и переносимости не различались значительно при сравнении групп апалутамид + АДТ и даролутамид + АДТ.Заключение. Результаты анализа данных 2 важнейших исследований III фазы по неметастатическому кастрационно-резистентному раку предстательной железы с помощью метода MAIC указывают на то, что апалутамид + АДТ является более эффективной схемой лечения, чем даролутамид + АДТ, по показателям выживаемости без прогрессирования и повышению уровня ПСА, в то время как общая выживаемость и профиль безопасности этих 2 режимов не различаются.