No. 25: Complex Movements, Confused Responses: Labour Migration in South Africa

The end of apartheid undermined the rationale for apartheid-era immigration. Immigration from Europe (which had been declining in the 1980s) dwindled to almost nothing as the new government dissociated itself from the racist immigration policies of the apartheid era. At the same time, downsizing and mine closures in the 1990s led to a dramatic decline in employment opportunities for African migrants in the mining industry. Tens of thousands of local and foreign migrants were retrenched. Although the industry has recovered somewhat, and continues to employ some foreign workers, the overall numbers of temporary migrant workers remain far below the levels of the 1970s and 1980s. The end of apartheid also brought new forms of labour migration to and from South Africa including a marked growth in irregular labour migration from neighbouring countries and the rest of Africa and a major brain drain of skilled professionals, primarily to OECD countries. Since 2000, there have been two further changes. First, the volume of migration from Zimbabwe has grown dramatically as a result of that country\u27s political and economic crisis. Secondly, South Africa adopted a new skills-based labour migration policy. The first section of this paper briefly reviews the post-apartheid decline in permanent immigration and legal temporary labour migration to South Africa. The next section examines some of the new migration trends that have become increasingly important over the last two decades. Finally, the paper examines the current institutional context established by the 2002 Immigration Act. In conclusion, the paper discusses the attractiveness of South Africa for African migrants and the main challenges that face the country in the coming years concerning international migration

Eulerian and Newtonian dynamics of quantum particles

We derive the classical equations of hydrodynamic type (Euler equation and the continuity equation) from which the Schrodinger equation follows as a limit case. It is shown that the statistical ensemble corresponding to quantum system and described by the Schrodinger equation, can be considered as an inviscid gas obeying the ideal gas law with quickly oscillating sign-alternating temperature. This statistical ensemble performs the complex movements consisting of smooth average movement and fast oscillations. It is shown that average movements of statistical ensemble are described by Schrodinger equation. A model of quantum motion within the limits of classical mechanics which corresponds to the considered hydrodynamic system is suggested.Comment: 25 page

Distinct Cortical Circuit Mechanisms for Complex Forelimb Movement and Motor Map Topography

SummaryCortical motor maps are the basis of voluntary movement, but they have proven difficult to understand in the context of their underlying neuronal circuits. We applied light-based motor mapping of Channelrhodopsin-2 mice to reveal a functional subdivision of the forelimb motor cortex based on the direction of movement evoked by brief (10 ms) pulses. Prolonged trains of electrical or optogenetic stimulation (100–500 ms) targeted to anterior or posterior subregions of motor cortex evoked reproducible complex movements of the forelimb to distinct positions in space. Blocking excitatory cortical synaptic transmission did not abolish basic motor map topography, but the site-specific expression of complex movements was lost. Our data suggest that the topography of movement maps arises from their segregated output projections, whereas complex movements evoked by prolonged stimulation require intracortical synaptic transmission

Analysis of complex movements

In most everyday repetitive movements such as walking, sitting, and reaching, humans exhibit large degrees of regularity. However, at the other end of the movement spectrum, in complex movement tasks, such as retrieving an object from a cluttered environment or choosing balance positions for transporting a large, unwieldy object, humans are inventive problem solvers. Therefore, in the quest to understand the human movement system, it would be essential to know if general movements have regularities across subjects as it would provide an essential scaffold in the development of more detailed dynamic movement models. This research mainly aims to learn the principles behind large-scale arbitrary movements, particularly regarding variations between different subjects. For example, given a goal-directed task, do the movements appear similar across subjects, or are movements very individualized? The tasks for the research covers developing an interactive virtual reality environment to capture goal-directed whole-body human movements, getting insights into the regularities underlying those motion capture data (kinematics), and finally analyzing the corresponding energy cost by using a forty-eight degree of freedom dynamic human model (dynamics). The results illustrate that humans chose trajectories that are economical in energetic cost while accomplishing goal-directed tasks.Computer Science

Multi-frame scene-flow estimation using a patch model and smooth motion prior

This paper addresses the problem of estimating the dense 3D motion of a scene over several frames using a set of calibrated cameras. Most current 3D motion estimation techniques are limited to estimating the motion over a single frame, unless a strong prior model of the scene (such as a skeleton) is introduced. Estimating the 3D motion of a general scene is difficult due to untextured surfaces, complex movements and occlusions. In this paper, we show that it is possible to track the surfaces of a scene over several frames, by introducing an effective prior on the scene motion. Experimental results show that the proposed method estimates the dense scene-flow over multiple frames, without the need for multiple-view reconstructions at every frame. Furthermore, the accuracy of the proposed method is demonstrated by comparing the estimated motion against a ground truth

Intracortical Microstimulation Maps of Motor, Somatosensory, and Posterior Parietal Cortex in Tree Shrews (Tupaia Belangeri) Reveal Complex Movement Representations

Long-train intracortical microstimulation (LT-ICMS) is a popular method for studying the organization of motor and posterior parietal cortex (PPC) in mammals. In primates, LT-ICMS evokes both multi-joint and multiple body-part movements in primary motor, premotor, and posterior parietal cortex. In rodents LT-ICMS evokes complex movements of a single limb in motor cortex. Unfortunately, very little is known about motor/PPC organization in other mammals. Tree shrews are closely related to both primates and rodents and could provide insights into the evolution of complex movement domains in primates. The present study investigated the extent of cortex in which movements could be evoked with ICMS and the characteristics of movements elicited using both short-train (ST) and LT ICMS in tree shrews. We demonstrate that LT-ICMS and ST-ICMS maps are similar, with the movements elicited with ST-ICMS being truncated versions of those elicited with LT-ICMS. In addition, LT-ICMS evoked complex movements within motor cortex similar to those in rodents. More complex movements involving multiple body parts such as the hand and mouth were also elicited in motor cortex and PPC, as in primates. Our results suggest that complex movement networks present in PPC and motor cortex were present in mammals prior to the emergence of primates

On the Assessment of Stability and Patterning of Speech Movements

Speech requires the control of complex movements of orofacial structures to produce dynamic variations in the vocal tract transfer function. The nature of the underlying motor control processes has traditionally been investigated by employing measures of articulatory movements, including movement amplitude, velocity, and duration, at selected points in time. An alternative approach, first used in the study of limb motion, is to examine the entire movement trajectory over time. A new approach to speech movement trajectory analysis was introduced in earlier work from this laboratory. In this method, trajectories from multiple movement sequences are time- and amplitude-normalized, and the STI (spatiotemporal index) is computed to capture the degree of convergence of a set of trajectories onto a single, underlying movement template. This research note describes the rationale for this analysis and provides a detailed description of the signal processing involved. Alternative interpolation procedures for time-normalization of kinematic data are also considered

spike jump biomechanics in male versus female elite volleyball players

ABSTRACTThere are well-known biological differences between women and men, especially in technical-coordinative variations that contribute to sex differences in performance of complex movements lik..

Screening for Parkinson’s Disease with Response Time Barriers: A Pilot Study

Background: Although significant response time deficits (both reaction time and movement time) have been identified in numerous studies of patients with Parkinson’s disease (PD), few attempts have been made to evaluate the use of these measures in screening for PD. Methods: Receiver operator characteristic curves were used to identify cutoff scores for a unitweighted composite of two choice response tasks in a sample of 40 patients and 40 healthy participants. These scores were then cross-validated in an independent sample of 20 patients and 20 healthy participants. Results: The unit-weighted movement time composite demonstrated high sensitivity (90%) and specificity (90%) in the identification of PD. Movement time was also significantly correlated (r = 0.59, p \u3c 0.025) with the motor score of the Unified Parkinson’s Disease Rating Scale (UPDRS). Conclusions: Measures of chronometric speed, assessed without the use of biomechanically complex movements, have a potential role in screening for PD. Furthermore, the significant correlation between movement time and UPDRS motor score suggests that movement time may be useful in the quantification of PD severity