Periodic Changes In Direction Research Articles

Термофорез как причина периодической смены направления конвекции магнитной жидкости в вертикальных каналах

The results of experiments with magnetic fluid based on undecane with magnetite particles size of of 6 nm and their volume fraction of 16 % are analyzed. Convection in two vertical connected channels with a square section of 3.2×3.2 mm 2 and a height of 50 mm was studied. Two equally probable stationary convection directions are observed in the undecane when heated from below. In the magnetic fluid, instead of a stationary flow, a periodic change of direction was observed: the flow upward in one channel and downward in the other, spontaneously and periodically (~ 1 hour) changed to the flow in the opposite direction. The oscillations are associated with the instability of the convective flow due to the thermodiffusion separation of particles. A formula for the characteristic separation time, which is determined by the thermodiffusion parameters of the medium, was obtained. In the channel, with upward flow, the trajectories of colloidal particles are deviate towards the wall due to thermophoresis, and part of the particles falls into the trap – a thin (~0.01 mm) diffusion boundary layer. In another channel, the fluid flows down, and the trajectories of colloidal particles deviate from the wall due to thermophoresis, and the boundary layer loses particles. The concentration difference between the channels increases and ends with a change in the convection direction. The experimental thermograms show a linear change in the buoyancy force in the channels over time. The formula for the rate of accumulation (loss) of concentration in the boundary layer is obtained. The Soret coefficient of the magnetic fluid by processing the experimental thermograms using the found formula was measured 0.25 K –1 .

Physical Education of Russian Students in the XX and XXI Centuries

Анализ физического воспитания в нашей стране позволяет констатировать, что его развитие характеризуется периодической сменой направленности и приоритетов содержания. Эти приоритеты напрямую связаны с внешней политикой государства, с состоянием и уровнем здоровья нации, с новыми теоретическими и практическими научными разработками ведущих ученых и педагогов страны. Смена направленности - довольно частое явление в отечественном физическом воспитании в высших учебных заведениях. Причина такого явления заключается прежде всего в том, что создание методики физической культуры в образовательных учреждениях нашей страны проходило в условиях, когда еще не были разработаны основные компоненты научно-методических основ самой дисциплины. На разных этапах становления предмета учебно-воспитательный процесс ориентировался на разные цели: военная подготовка; подготовка к трудовой деятельности; коммунистическое воспитание и формирование нового человека; подготовка к сдаче норм комплекса ГТО; подготовка спортивного резерва; формирование компетенций и т. д.

Modeling Optimal Strategies for Finding a Resource-Linked, Windborne Odor Plume: Theories, Robotics, and Biomimetic Lessons from Flying Insects.

Male moths locate females by navigating along her pheromone plume, often flying hundreds of meters en route. As the first male to find a calling female is most apt to be her mate, this can be termed "a race to find the female" and it is assumed to be under strong selective pressure for efficiency and rapidity. Locating a distant, odor-linked resource involves two strategies. The first is to contact the outer envelope of the odor plume. When wind direction is relatively invariant, the plume stretches and then crosswind flights may be favored, although when wind direction shifts over 60°, upwind and downwind paths may be optimal. Alternatively, the path may be random with respect to the direction of wind flow, with periodic changes in direction, as in either Lévy or Random Walks. After first detecting the pheromone, a second strategy follows: moths navigate along the plume by heading upwind when the pheromone is detected, with crosswind casting to re-establish contact if the plume is lost. This orientation path is not straightforward in nature, however, because atmospheric turbulence fragments the plume, thereby creating large odor gaps. Furthermore, a shifting wind direction can lead the responder out of the plume. One way to explore which strategies are optimal for enabling initial contact with the plume and subsequent navigation is through modeling of plumes' dispersal and of insects' flight strategies. Our simulations using the flight characteristics of the male gypsy moth (Lymantria dispar) suggest that search strategies similar to Lévy Walks are most apt to result in a high probability of contact with plumes. Although a searching trajectory aimed predominately crosswind performed almost as well as those with a random orientation when wind direction was relatively stable, downwind biased trajectories were least successful. A random orientation with respect to immediate wind flow, as used in our simulations of Lévy and Random Walks, seems optimal both for initial discovery of the plume and likelihood of locating an odor source. In the two available direct field observations, moths adopted a random orientation with respect to concurrent wind direction.

Global development in the Twenty-first Century: the maturation of global development – responses to three critiques

Modern economic development does not travel for long in a straight line. Making sense of the periodic changes in direction is the never-ending challenge of economic analysis. My 2015 Holmes Lecture took up the challenge of explaining new twists and turns in the 21st century. Productivity and output growth are markedly lower in the developed countries, especially but not only since the great crash of 2008. The populations of the developed countries are ageing rapidly and the labour forces declining or growing slowly. Global savings are high and investment low, giving rise to historically low real interest rates.

Unidirectional motion of vehicle on sinusoidal path

The feeling of being in motion, while observing a moving train passing nearby is a common experience. It is an example of relative motion where a stationary observer experiences an illusory motion caused by a vehicle moving in the opposite direction. It is however counter-intuitive to imagine periodic changes in the direction of relative motion, while the vehicle continues to move in one direction only. To an observer, sitting inside the moving vehicle, periodic changes in direction can lead to the illusion of being in oscillatory forward and backward relative motion. This article, using a simple mathematical model describes how the unidirectional motion of vehicle on a sinusoidal path can lead to the illusion of being in periodic forward and backward relative motion. This work has emerged out of a real life experience during a train journey on the hilly curves from Kalka to Shimla.

Spontaneous Partial Rotation and Oscillation of the Protoplasm in Coleochaete and Other Chlorophyceae

Geitler, Lothar. (Botanisches Institut, Universität, Wien, Austria.) Spontaneous partial rotation and oscillation of the protoplasm in Coleochaete and other Chlorophyceae. Amer. Jour. Bot. 48(8): 738–741. 1961.—In certain differentiated cells, such as the hairs, zoosporangia, oogonia, but also in the unicellular germlings, of species of Coleochaete, Chaetotheke, and Chaetosphaeridium, there occurs regularly a spontaneous movement of the protoplasm, which expresses itself strikingly in rapid rotation or oscillation of the chromatophore. The movement occurs partially and localized in certain parts of the cell. It is comparable to no type of protoplasmic streaming known up to the present. Rotation and oscillation occur as regular, cell-specific attributes, but rotation may be converted experimentally and transiently into oscillation. Oscillation is an intermittent rotation with periodic change of direction. Exploratory researches concerning osmotic values and permeability do not yet reveal definite relationships between the several types of movement in various specialized cells and their physiological condition. However, only the hair cells of Coleochaete and Chaetotheke with rotation show selective vital-staining with neutral red; the similarly constructed ones of Chaetosphaeridium with oscillation do not.

SPONTANEOUS PARTIAL ROTATION AND OSCILLATION OF THE PROTOPLASM IN COLEOCHAETE AND OTHER CHLOROPHYCEAE

Geitler, Lothar. (Botanisches Institut, Universität, Wien, Austria.) Spontaneous partial rotation and oscillation of the protoplasm in Coleochaete and other Chlorophyceae. Amer. Jour. Bot. 48(8): 738–741. 1961.—In certain differentiated cells, such as the hairs, zoosporangia, oogonia, but also in the unicellular germlings, of species of Coleochaete, Chaetotheke, and Chaetosphaeridium, there occurs regularly a spontaneous movement of the protoplasm, which expresses itself strikingly in rapid rotation or oscillation of the chromatophore. The movement occurs partially and localized in certain parts of the cell. It is comparable to no type of protoplasmic streaming known up to the present. Rotation and oscillation occur as regular, cell‐specific attributes, but rotation may be converted experimentally and transiently into oscillation. Oscillation is an intermittent rotation with periodic change of direction. Exploratory researches concerning osmotic values and permeability do not yet reveal definite relationships between the several types of movement in various specialized cells and their physiological condition. However, only the hair cells of Coleochaete and Chaetotheke with rotation show selective vital‐staining with neutral red; the similarly constructed ones of Chaetosphaeridium with oscillation do not.