Hybrid Rockets as Post-Boost Stages and Kick Motors

Hybrid rockets are attractive as post-boost stages and kick motors due to their inherent safety and low cost, but it is not clear from previous research which oxidizer is most suitable for maximizing ΔV within a fixed envelope size, or what impact O/F shift and nozzle erosion will have on ΔV. A standard hybrid rocket design is proposed and used to clarify the impact of component masses on ΔV within three 1 m3 envelopes of varying height-to-base ratios. Theoretical maximum ΔV are evaluated first, assuming constant O/F and no nozzle erosion. Of the four common liquid oxidizers: H2O2 85 wt%, N2O, N2O4, and LOX, H2O2 85 wt% is shown to result in the highest ΔV, and N2O is shown to result in the highest density ΔV, which is the ΔV normalized for motor density. When O/F shift is considered, the ΔV decreases by 9% for the N2O motor and 12% for the H2O2 85 wt% motor. When nozzle erosion is also considered, the ΔV decreases by another 7% for the H2O2 85 wt% motor and 4% for the N2O motor. Even with O/F shift and nozzle erosion, the H2O2 85 wt% motor can accelerate itself (916 kg) upwards of 4000 m/s, and the N2O motor (456 kg) 3550 m/s.

Peculiarities of Functional and Motor Fitness of 1St–5Th Year Students of Special Medical Department

The objective of the study was to determine the age-related peculiarities of functional and motor fitness of students of a special medical department of higher education institutions. Material and methods. The study participants were 1st year (n = 34); 2nd year (n = 14); 3rd year (n = 58); 4th year (n = 21); 5th year (n = 16) male students. One group was organized in each year of study, which added up to five experimental groups. All the students participated in physical education classes twice a week. To solve the tasks set, the following research methods were used: analysis of scientific literature, pedagogical observation, pedagogical testing, formative experiment, index method, biomedical methods, and methods of mathematical statistics. During classes, the study used the method of strictly regulated exercise (motor density of the class was 50-70%), for developing general endurance – the continuous method with covering a distance of 1,000-2,000 m (heart rate: 120-150 beats per minute), circuit and repetition methods. Results. The study results show positive changes in the functional state of the respiratory system and speed and strength abilities in the 1st-5th year students of the special medical department (p < 0.05). Conclusions. A successful development of the basic functional body systems and motor abilities in 1st-5th year students can be achieved under the influence of pedagogical conditions, namely: the method of strictly regulated exercise using exercise equipment (motor density of the class was 50-70%); the continuous method with covering a distance of 1,000-2,000 m at a slow pace (heart rate: 120-150 beats per minute); circuit and repetition methods. By the results of comparative analysis of the functional and motor fitness, the 1st-5th year male students of the special medical department show better results in tests for assessing the cardiovascular and respiratory systems, speed and strength abilities. In the 18-22 age range, according to the Ruffier index, there is an increase in the number of male students of the special medical department with a “good” and “satisfactory” cardiovascular system state and a decrease in the number of students with a “bad” result.

The differences in energy system demands of competitive male tennis play between fast and slow courts

This study investigated the energy system demand differences between matches played on fast courts and on slow courts of high-performance male players. Matches of Grand Slam matches played by Russian players were analysed. External indicators as such in-point playing time as a proportion of total match time were used to conduct the analysis. Data analysis found significant differences in all measured external indicators such as average match playing time, number of points and in-point time. Results also found a significant difference between match motor density (the percentage of total match time that made up effective playing time) for the two surface types, with the slow surface (clay) match motor density being significantly higher than that of the fast surface (grass and hard court), 14.5% and 12.9%, respectively. Subsequent analysis of point length reveals clay courts that slow courts had a significantly higher percentage of points that lasted more than 10 seconds whilst fast courts has a higher percentage of points under 10 seconds in length. It can be concluded that due to the length of the points, tennis primarily employs the ATP-PCr energy system for energy use, dipping into the anaerobic lactic acid energy pathways more on clay court matches. Whilst the aerobic pathways are not employed heavily in-point, they are still essential, possibly even more on clay court due to greater taxation on the anaerobic lactic acid pathway, as they provide the basis for ATP re-synthesis between points. This signals toward endurance as a major component of fitness in tennis.

A Brownian ratchet model explains the biased sidestepping movement of single-headed kinesin-3 KIF1A

The kinesin-3 motor KIF1A is involved in long-ranged axonal transport in neurons. In order to ensure vesicular delivery, motors need to navigate the microtubule lattice and overcome possible roadblocks along the way. The single-headed form of KIF1A is a highly diffusive motor that has been shown to be a prototype of Brownian motor by virtue of a weakly-bound diffusive state to the microtubule. Recently, groups of single-headed KIF1A motors were found to be able to sidestep along the microtubule lattice, creating left-handed helical membrane tubes when pulling on giant unilamellar vesicles in vitro. A possible hypothesis is that the diffusive state enables the motor to explore the microtubule lattice and switch protofilaments, leading to a left-handed helical motion. Here we study microtubule rotation driven by single-headed KIF1A motors using fluorescene-interference contrast (FLIC) microscopy. We find an average rotational pitch of ≃ 1.4 μm which is remarkably robust to changes in the gliding velocity, ATP concentration and motor density. Our experimental results are compared to stochastic simulations of Brownian motors moving on a two-dimensional continuum ratchet potential, which quantitatively agree with the FLIC experiments. We find that single-headed KIF1A sidestepping can be explained as a consequence of the intrinsic handedness and polarity of the microtubule lattice in combination with the diffusive mechanochemical cycle of the motor.

Effect of heart rate monitoring on increasing motor density of physical education lessons in children with autism spectrum disorder

We apply continuous monitoring of heart rate at physical training lessons in children with autism spectrum disorder and assess its impact on increasing motor density of physical training lessons. The study engaged children with motor dynamic stereotype. The choice of this group is due to the need to properly dose the physical load: the number of repetitions, intensity and sequence of exercises to increase the motor density of physical training lessons and increase the time of work in the moderate intensity zone. The estimation of motor density of training sessions was carried out using the method of timing and was calculated by the formula of the ratio of motor activity to the total observation time in percent. The control technique we used, allowed us to increase the motor density of physical training lessons from 62.5 to 72.5 %. In the main part of the lesson time in the moderate power zone at the initial stage was 3 minutes. At the end of the study in the experimental group, this value increased by 33.3 %. Electronic monitoring of heart rate at the lessons in students with autism spectrum disorder allows for effective control of physical activity, which increases the motor density of classes without worsening the psycho-emotional state of the child.

‘Switch-like’ transition from random to directed motility of microtubules by a yeast dynein

Processive transport by multiple molecular motors that step stochastically, requires a form of mechanical coupling. In a quantitative microtubule (MT) gliding assay with yeast cytoplasmic dynein, we investigate the nature of this coupling by examining the effect of MT length and motor density on transport. We find speed and velocity have a length dependence for low motor numbers, but are independent of MT length for high motor densities. The dependence of speed, velocity and degree of randomness of MT transport is best understood when evaluated in terms of the numbers of motors bound to a filament. A model of collective transport of MTs, based on stochastic stepping and asymmetric detachment rates, reproduces the experimental trends of decreasing diffusivity with increasing number of motors. Additionally, the model predicts a ‘switch-like’ increase in directionality of MT transport above a threshold number of motors. Such a rapid transition from random to directed motility with increasing numbers of yeast dyneins, could play a role in vivo during mitosis in the ‘search and orientation’ of the Saccharomyces cerevisiae nucleus.

Improvement of medical-pedagogical observation as a method for preventing the development of prepathological condition in young athletes

Background: In the practice of training young athletes in recent years, there has been a tendency to one-sided development. Currently, existing protocols, medical-pedagogical surveillance (MPS) is imperfect, do not enable to collect complete information about young athlete in the course of training which required for the correction of the training process and optimise post-physical stressing recovery. Aim of the study is to assess the effectiveness of the improved protocol implementation- medical-pedagogical observations of children engaged in sport schools in Uzbekistan.Methods: The study was performed over 120 sports school students. Medical-pedagogical supervision (MPS) was conducted in the morning and evening sessions in different periods of the annual cycle. Study participants were divided into 2 groups and each includes 60 people, depending on the applied Protocol MPS. During the training, led timing classes, noted what the athlete using a symbol. At the end of training calculated duration of physical stress and motor density lesson finding the percent of the time the physical stress to the total training duration. Special attention was paid to the nature of the training process: the number of lessons per week correct their location, the duration and structure of activities, their common and motor density. During exercise, every 10-15 minutes counting the pulse.Results: Density of the training depended on the degree of preparedness of young athletes and in the elementary group it was 58%, middle- 63%, high- 70%. According to the current Protocol MPS failed to identify the presence of fatigue of young athletes and to assess its degree. In middle physical stress distributed such a way that the ratio of general physical training and special physical stress was equal parts, warm-up was 18-20%, the majority- 60%, final was 15-18%. In older group warm-up 10-15% of the entire training duration, the major part- 80% and the final 5-10%. The density classes are 65-80%. Reorganization showed that the number of basic groups of chronic diseases was decreased 1.2-2.5 times in most classes of diseases, whereas in control group these indicators in 2015, by contrast, has grown in 1.5-2.2 times in comparison with 2014.Conclusions: Conduct medical-pedagogical supervision on advanced protocols and corresponding reorganization of the training process and rationalization of physical stress allowed to improve the dynamics of their physical development without deviations from age-related standards of physical fitness and reducing rates of infection.

Transport efficiency of membrane-anchored kinesin-1 motors depends on motor density and diffusivity

In eukaryotic cells, membranous vesicles and organelles are transported by ensembles of motor proteins. These motors, such as kinesin-1, have been well characterized in vitro as single molecules or as ensembles rigidly attached to nonbiological substrates. However, the collective transport by membrane-anchored motors, that is, motors attached to a fluid lipid bilayer, is poorly understood. Here, we investigate the influence of motors’ anchorage to a lipid bilayer on the collective transport characteristics. We reconstituted “membrane-anchored” gliding motility assays using truncated kinesin-1 motors with a streptavidin-binding peptide tag that can attach to streptavidin-loaded, supported lipid bilayers. We found that the diffusing kinesin-1 motors propelled the microtubules in the presence of ATP. Notably, we found the gliding velocity of the microtubules to be strongly dependent on the number of motors and their diffusivity in the lipid bilayer. The microtubule gliding velocity increased with increasing motor density and membrane viscosity, reaching up to the stepping velocity of single motors. This finding is in contrast to conventional gliding motility assays where the density of surface-immobilized kinesin-1 motors does not influence the microtubule velocity over a wide range. We reason that the transport efficiency of membrane-anchored motors is reduced because of their slippage in the lipid bilayer, an effect that we directly observed using single-molecule fluorescence microscopy. Our results illustrate the importance of motor–cargo coupling, which potentially provides cells with an additional means of regulating the efficiency of cargo transport.