Utilities in the sky?: Comparison of space-based and terrestrial solar power systems

Could huge arrays of space-based solar power systems one day supply utility scale electricity to the electric power grid on earth? How realistic a possibility is this option for alternative energy supply at the moment? Finley R. Shapiro, USA compares space-based and terrestrial solar power systems.     

Three-dimensional structure of the cloud of a carbon pellet evaporated in plasma of Wendelstein 7-AS stellarator

Experiments performed on a Wendelstein 7-AS stellarator revealed asymmetry of the cloud of an ablating carbon pellet. The cloud is elongated in the direction of large radius toward stronger fields, that is, opposite to the direction expected due to the toroidal drift. In order to study the effect in more detail, the three-dimensional structure of the cloud was analyzed by computer tomography. The results confirmed asymmetry of the cloud. This asymmetry is related to a drift flow existing in the plasma and directed along large radius toward stronger fields. The drift velocity is numerically estimated at ～300 m/s.     

Specific features of kinetics of molecular beam epitaxy of compounds in the GaN-AlN system

The effect of growth conditions (V/III ratio, substrate temperature) on the properties of materials in AlN-GaN systems is discussed. A concept of the growth of the AlN/AlGaN/GaN multilayer heterostructure, which provides the improvement of crystal quality and surface morphology of the layers, is suggested and realized. The improvement of the properties of GaN in the AlN/AlGaN/GaN/AlGaN multilayer heterostructure is confirmed by a considerable increase in electron mobility in the two-dimensional electron gas formed at the upper heterointerface GaN/Al_0.3Ga_0.7N.     

Modeling and optimization of preparatory work and stoping in a coal mine panel

The problem on optimization of the prepration and stoping process variables based on the maximum discounted net revenue for the period of panel mining in a coal mine has been formualted and numerically solved. The optimized data are presented for the fully-mechanized production face in coal bed no. 19 in Kostromovskaya Mine. The authors also offer a new production face preparation scheme and illustrate its efficiency in terms of Kostromovskaya Mine.     

Automated instrumentation to measure rock mass stresses in parallel-drilled holes

The prototype of a new-developed program-instrumentation system provides automated measurement and processing of data on stresses in a rock mass by employing the parallel-hole method. The respective instrumentation and the procedure for execution of tests on stress evaluation within a rock mass are also briefed on. Recorder software provides the prompt control of the entire process with visualized parameters, thus contributing to the proper decision-making with account for experimental conditions and expediency to go on with downhole tests.     

Educational status and resources for child care as predictors of TBE vaccination coverage in schoolchildren of an endemic area in Austria

Since the introduction of the Austrian tick-borne encephalitis (TBE) vaccination program in 1981 vaccination coverage of children has not been investigated sufficiently. Numerous socioeconomic and demographic factors have been identified as being associated with low vaccination coverage in childhood for most vaccinations. This study focuses on parental educational status and on resources for child care as determinants of tick-borne encephalitis (TBE) vaccination coverage of schoolchildren in an endemic TBE area of Austria. The target population were children in the first, fourth and seventh year of school education in Styria, Austria. Therefore, the sample consisting of 2470 children was divided into three age groups, children aged 7, 10 and 13 years. We performed a representative cross-sectional study. The information concerning the vaccination status of each child was recorded by means of an anonymous questionnaire given to the parents by the classroom teachers. This procedure ensured a high overall response rate of 79.8%. The prevalence of at least one TBE vaccination was 93.9% for the 7 year old, 97.8% for the 10 and 97.9% for the 13 year old. The lowest vaccination rates were found in families with four or more children (94.0%) and for those children who had unemployed parents (92.9%). The multivariate analysis indicates that TBE vaccination coverage is affected by a large number of children in the family (p = 0.0003), an urban place of residence (p = 0.0001) and by a low level of education of the mother (p = 0.013). The results suggest that, though overall high coverage in schoolchildren, vaccination programmes should be focused on large and socially deprived families.     

Stabilization of unstable equilibrium postures of a two-link pendulum using a flywheel

The planar double-link pendulum has three unstable equilibrium postures. We want to design control laws to stabilize each unstable posture. A flywheel equips the first link. This flywheel is actuated by an electrical drive. The control signal (voltage) is applied to the drive, and our double-link pendulum is an underactuated system. We show that this system is controllable. The number of unstable modes, one or two, depends on the posture. Then, the control laws are designed to suppress the unstable modes, using the linear models of the motion near each unstable equilibrium posture. These control laws are nonlinear, since the saturation of the voltage is taken into account explicitly. Numerical investigations of the nonlinear models with the designed control laws are presented in each case. This article was submitted by the authors in English.     

Numerical and experimental study of the virtual quadrupedal walking robot-semiquad

SemiQuad is a prototyped walking robot with a platform and two double-link legs. Thus, it is a five-link mechanism. The front leg models identical motions of two quadruped's front legs, the back leg models identical motions of two quadruped's back legs. The legs have passive (uncontrolled) feet that extend in the frontal plane. Due to this the robot is stable in the frontal plane. This robot can be viewed as a "virtual" quadruped. Four DC motors drive the mechanism. Its control system comprises a computer, hardware servo-systems and power amplifiers. The locomotion of the prototype is planar curvet gait. In the double support our prototype is statically stable and over actuated. In the single support it is unstable and under actuated system. There is no flight phase. We describe here the scheme of the mechanism, the characteristics of the drives and the control strategy. The dynamic model of the planar walking is recalled for the double, single support phases and for the impact instant. An intuitive control strategy is detailed. The designed control strategy overcomes the difficulties appeared due to unstable and under actuated motion in the single support.Due to the control algorithm the walking regime consists of the alternating different phases. The sequence of these phases is the following. A double support phase begins. A fast bend and unbend of the front leg allows a lift-off of the front leg. During the single support on the back leg the distance between the two leg tips increases. Then an impact occurs and a new double support phase begins. A fast bend and unbend of the back leg allows the lift-off of the back leg. During the single support on the front leg the distance between the two leg tips decreases to form a cyclic walking gait.The experiments give results that are close to those of the simulation.Funding for SemiQuad was primarily provided by the CNRS and the region Pays de La Loire.     

拒绝黑屏·WPS2007的五大独门绝技

近日,微软在中国再次针对盗版进行打击,装有盗版WinXP的用户将不得不接受每小时一次的黑屏提示,装有盗版Office的用户也会收到相关的提示信息。与此相对应的是,金山的WPS仍旧一如既往地针对个人用户完全免费,新版本的WPS2007不但可以满足绝大多数用户处理文档、电子表格的需求,更有几大独门绝技……