Eden growth model for aggregation of charged particles

The stochastic Eden model of charged particles aggregation in two-dimensional systems is presented. This model is governed by two parameters: screening length of electrostatic interaction, $\lambda$, and short range attraction energy, $E$. Different patterns of finite and infinite aggregates are observed. They are of following types of morphologies: linear or linear with bending, warm-like, DBM (dense-branching morphology), DBM with nucleus, and compact Eden-like. The transition between the different modes of growth is studied and phase diagram of the growth structures is obtained in $\lambda, E$ co-ordinates. The detailed aggregate structure analysis, including analysis of their fractal properties, is presented. The scheme of the internal inhomogeneous structure of aggregates is proposed.Comment: Revtex, 9 pages with 12 postscript figure

Deterministic growth model of Laplacian charged particle aggregates

The results of the computer simulation of the aggregates growth of the similarly charged particles in the framework of deterministic Laplacian growth model on a square lattice are presented. Cluster growth is controlled by three parameters ${p, E,\lambda}$, where $p$ - Laplacian growth parameter, $E$ - energy of a particle sticking to a cluster, $\lambda$ - the screening length of electrostatic interactions. The phase diagram of cluster growth is built in the co-ordinates ${E,\lambda}$. The zones of different cluster morphology are selected: I-the zone of finite X-like structures,II-the zone of infinite ramified structures, controlled by electrostatic interactions, III-the zone of infinite structures with electrostatic interactions effectively switched off. Simple electrostatic estimations of the locations of the zone boundaries are presented. It is shown that in general case within the zone II the continuous change of $D_f$, controlled by parameters ${p, E,\lambda}$, takes place. In the degeneration limit when the given model transforms into deterministic version of the Eden model (at $p=0$), the crossover from linear $(D_f=1)$ to compact $(D_f=2)$ structures is observed when passing through the boundary between the zones I and II.Comment: REVTEX, 3 pages with 4 postscript figure

The state and dynamics of nonprofit sector in Ukraine

У статті обґрунтовано економічне значення діяльності некомерційного сектору. Проаналізовано стан некомерційного сектору провідних економік світу та України. Емпірично доведено залежність всієї економічної системи від розвитку українських некомерційних організацій. В процесі дослідження застосовано кореляційний аналіз для виявлення зв’язку між загальним обсягом ВВП, ВВП на душу населення та ВВП некомерційних організацій, що обслуговують домашні господарства. Проаналізовано вплив некомерційного сектору на людський розвиток. Розраховано коефіцієнт кореляції між Індексом людського розвитку та валовим прибутком некомерційних організацій, а також середні мінімальні витрати некомерційного сектору України на людський розвиток, що необхідні для його максимізації.В статье обосновано экономическое значение деятельности некоммерческого сектора. Проанализировано состояние некоммерческого сектора ведущих экономик мира и Украины. Эмпирически доказана зависимость всей экономической системы от развития украинских некоммерческих организаций. В процессе исследования использован корреляционный анализ для выявления связи между общим объемом ВВП, ВВП на душу населения и ВВП некоммерческих организаций, обслуживающих домашние хозяйства. Проанализировано влияние некоммерческого сектора на развитие общества. Рассчитаны коэффициент корреляции между Индексом человеческого развития и валовой прибылью некоммерческих организаций, а также средние минимальные расходы некоммерческого сектора Украины на человеческое развитие, необходимые для его максимизации.The economic importance of non-profit sector is studied in the article. The state and dynamics of the world’s non-profit sector and nonprofits in Ukraine are analyzed. The dependence of the entire economic system on the development of Ukrainian non-profit organizations is empirically proven. Correlation analysis to identify the relationship between the total volume of GDP, GDP per capita and GDP of non-profit institutions serving households is used. The non-profit sector impact on the human development is analyzed. The coefficient of correlation between the Human Development Index and gross profit of nonprofits and also the average minimum costs of the nonprofit sector in Ukraine on human development in order to his maximize are calculated

Development of human locomotion

Neural control of locomotion in human adults involves the generation of a small set of basic patterned commands directed to the leg muscles. The commands are generated sequentially in time during each step by neural networks located in the spinal cord, called Central Pattern Generators. This review outlines recent advances in understanding how motor commands are expressed at different stages of human development. Similar commands are found in several other vertebrates, indicating that locomotion development follows common principles of organization of the control networks. Movements show a high degree of flexibility at all stages of development, which is instrumental for learning and exploration of variable interactions with the environment

Humans running in place on water at simulated reduced gravity

On Earth only a few legged species, such as water strider insects, some aquatic birds and lizards, can run on water. For most other species, including humans, this is precluded by body size and proportions, lack of appropriate appendages, and limited muscle power. However, if gravity is reduced to less than Earth's gravity, running on water should require less muscle power. Here we use a hydrodynamic model to predict the gravity levels at which humans should be able to run on water. We test these predictions in the laboratory using a reduced gravity simulator

Integral functions of electron lateral distribution and their fluctuations in electron-photon cascades

Monte Carlo simulated lateral distribution functions for electrons of EPC developing in lead, at superhigh energies (.1-1 PeV) for depths t or = 60 c.u. delta t=1t. c.u. are presented. The higher moment characteristics, i.e., variation, asymmetry, excess, are presented along with analytical solutions for the same characteristics at fixed observation level calculated to theory approximations A and B by using numerical inversion of the Laplace transformation. The conclusion is made of a complex, usually non-Gaussian shape of the function of the particle number distribution within a circle of given radius at fixed depth

Tapping into rhythm generation circuitry in humans during simulated weightlessness conditions

An ability to produce rhythmic activity is ubiquitous for locomotor pattern generation and modulation. The role that the rhythmogenesis capacity of the spinal cord plays in injured populations has become an area of interest and systematic investigation among researchers in recent years, despite its importance being long recognized by neurophysiologists and clinicians. Given that each individual interneuron, as a rule, receives a broad convergence of various supraspinal and sensory inputs and may contribute to a vast repertoire of motor actions, the importance of assessing the functional state of the spinal locomotor circuits becomes increasingly evident. Air-stepping can be used as a unique and important model for investigating human rhythmogenesis since its manifestation is largely facilitated by a reduction of external resistance. This article aims to provide a review on current issues related to the "locomotor" state and interactions between spinal and supraspinal influences on the central pattern generator (CPG) circuitry in humans, which may be important for developing gait rehabilitation strategies in individuals with spinal cord and brain injuries

Coupling of upper and lower limb pattern generators during human crawling at different arm/leg speed combinations

A crawling paradigm was performed by healthy adults to examine inter-limb coupling patterns and to understand how central pattern generators (CPGs) for the upper and lower limbs are coordinated. Ten participants performed hands-and-feet crawling on two separate treadmills, one for the upper limbs and another one for the lower limbs, the speed of each of them being changed independently. A 1:1 frequency relationship was often maintained even when the treadmill speed was not matched between the upper and lower limbs. However, relative stance durations in the upper limbs were only affected by changes of the upper limb treadmill speed, suggesting that although absolute times are adjusted, the relative proportions of stances and swing do not adapt to changes in lower limb treadmill speeds. With large differences between treadmill speeds, changes in upper and lower limb coupling ratio tended to occur when the upper limbs stepped at slower speeds than the lower limbs, but more rarely the other way around. These findings are in sharp contrast with those in the cat, where forelimbs always follow the rhythm of the faster moving hindlimbs. However, the fact that an integer frequency ratio is often maintained between the upper and lower limbs supports evidence of coupled CPG control. We speculate that the preference for the upper limb to decrease step frequency at lower speeds in humans may be due to weaker ascending propriospinal connections and/or a larger influence of cortical control on the upper limbs which allows for an overriding of spinal CPG control

Locomotor-like leg movements evoked by rhythmic arm movements in humans

Motion of the upper limbs is often coupled to that of the lower limbs in human bipedal locomotion. It is unclear, however, whether the functional coupling between upper and lower limbs is bi-directional, i.e. whether arm movements can affect the lumbosacral locomotor circuitry. Here we tested the effects of voluntary rhythmic arm movements on the lower limbs. Participants lay horizontally on their side with each leg suspended in an unloading exoskeleton. They moved their arms on an overhead treadmill as if they walked on their hands. Hand-walking in the antero-posterior direction resulted in significant locomotor-like movements of the legs in 58% of the participants. We further investigated quantitatively the responses in a subset of the responsive subjects. We found that the electromyographic (EMG) activity of proximal leg muscles was modulated over each cycle with a timing similar to that of normal locomotion. The frequency of kinematic and EMG oscillations in the legs typically differed from that of arm oscillations. The effect of hand-walking was direction specific since medio-lateral arm movements did not evoke appreciably leg air-stepping. Using externally imposed trunk movements and biomechanical modelling, we ruled out that the leg movements associated with hand-walking were mainly due to the mechanical transmission of trunk oscillations. EMG activity in hamstring muscles associated with hand-walking often continued when the leg movements were transiently blocked by the experimenter or following the termination of arm movements. The present results reinforce the idea that there exists a functional neural coupling between arm and legs

Locomotor patterns in cerebellar ataxia

Several studies demonstrated how cerebellar ataxia (CA) affects gait, resulting in deficits in multi-joint coordination and stability. Nevertheless, how lesions of cerebellum influence the locomotor muscle pattern generation is still unclear. To better understand the effects of CA on locomotor output, here we investigated the idiosyncratic features of the spatiotemporal structure of leg muscle activity and impairments in the biomechanics of CA gait. To this end, we recorded the electromyographic (EMG) activity of 12 unilateral lower limb muscles and analyzed kinematic and kinetic parameters of 19 ataxic patients and 20 age-matched healthy subjects during overground walking. Neuromuscular control of gait in CA was characterized by a considerable widening of EMG bursts and significant temporal shifts in the center of activity due to overall enhanced muscle activation between late swing and mid-stance. Patients also demonstrated significant changes in the intersegmental coordination, an abnormal transient in the vertical ground reaction force and instability of limb loading at heel strike. The observed abnormalities in EMG patterns and foot loading correlated with the severity of pathology (clinical ataxia scale, ICARS) and the changes in the biomechanical output. The findings provide new insights into the physiological role of cerebellum in optimizing the duration of muscle activity bursts and the control of appropriate foot loading during locomotion