Chaos motion in robot manipulators

It is shown that a simple two-link planar manipulator exhibits a phenomenon of global instability in a subspace of its configuration space. A numerical example, as well as results of a graphic simulation, is given

Household strategies for coping with poverty and social exclusion in post-crisis Russia

What strategies have Russian households used, to cope with economic hardship in the wake of recent financial crisis? Which coping strategies have been most effective in reducing poverty for different groups of households? And how have people been able to adapt to the dramatic drop in formal cash incomes? The authors look at these questions using subjective evaluations of coping strategies used by household survey respondents to mitigatethe effects of the Russian financial crisis on their welfare. The data come from two rounds (1996 and 1998) of the Russian Longitudinal Monitoring Survey. The results of their analysis show that a household's choice of survival strategy, strongly depends on its human capital: the higher its level of human capital, the more likely it is to choose an active strategy (such as finding a supplementary job, or increasing home production). Households with low levels of human capital, those headed by pensioners, and those whose members have low levels of education, are more likely to suffer social exclusion. To prevent poverty from becoming entrenched, the trend toward marginalization, and impoverishment of these groups of households, needs to be monitored, and targeted policy interventions need to be undertaken to reverse the trend.Housing&Human Habitats,VN-Acb Mis -- IFC-00535908,Poverty Assessment,Health Monitoring&Evaluation,Poverty Lines

Internal and external R&D: complements or substitutes? Evidence from a dynamic panel data model.

We examine the impact of internal and external R&D on labor productivity in a 6-year panel of 304 innovating firms. We apply a dynamic linear panel data model that allows for decreasing returns to scale in internal and external R&D with a non-linear approximation of changes in the knowledge stock. We find complementarity between internal and external R&D, with a positive impact of external R&D only evident in case of sufficient internal R&D. The findings confirm the role of internal R&D in enhancing absorptive capacity and hence the effective utilization of external knowledge. These results suggest that empirical studies examining complementarities between continuously measured practices should adopt more general non-linear specifications to allow for correct inferences.R&D; Panel data; Innovating firms; Knowledge; Empirical study; Specifications;

Testing for complementarity and substitutability in the case of multiple practices.

Recent empirical studies of firm-level performance have been concerned with establishing potential complementarity between more than two organizational practices. These papers have drawn conclusions on the basis of potentially biased estimates of pair-wise interaction effects between such practices. In this paper we develop a consistent testing framework based on multiple inequality constraints that derives from the definition of (strict) supermodularity as suggested by Athey and Stern (1998). Monte Carlo results show that the multiple restrictions test is superior for performance models with high explanatory power. If practices explain only a minor part of organizational performance no test is able to identify complementarity or substitutability in a satisfactory manner.Complementarity; Constraint; Effects; Empirical study; Firm performance; Framework; Interaction effects; Model; Models; Performance; Power; Studies; Supermodularity;

The effect of early childhood development programs on women's labor force participation and older children's schooling in Kenya

About 20,000 early childhood development centers provided day care for and prepared for primary school more than 1 million children aged three to seven (roughly 20 percent of children in that age group) in Kenya in 1995. The number of child care facilities reached 23,690 by the end of 1999. The authors analyze the effect of child care costs on households'behavior in Kenya. For households with children aged three to seven, they model household demand for mothers'participation in paid work, the participation in paid work of other household members, household demand for schooling, and household demand for child care. They find that: A) A high cost for child care discourages households from using formal child care facilities and has a negative effect on mothers'participation in market work. B) The cost of child care and the level of mothers'wages affect older children's school enrollment, but these factors affect boys'and girls'schooling differently. An increase in mothers'wages increases boys'enrollment but depresses girls'enrollment. C) Higher child care costs have no significant effect on boys'schooling but significantly decrease the number of girls in school.Children and Youth,Public Health Promotion,Primary Education,Health Monitoring&Evaluation,Early Childhood Development,Children and Youth,Primary Education,Street Children,Early Childhood Development,Youth and Governance

Household childcare choices and women's work behavior in Russia

The author models mothers'participation in the labor force, their working hours, and household demand for childcare in Russia. The model estimates the effects of the price of childcare, mothers'wages, and household income on household behavior and well-being. The theoretical model yields several predictions. To test these, reduced-form equations of the discrete and continuous household choices are estimated jointly using the method of semi-parametric full information maximum likelihood. This method controls for the correlation of error terms across outcomes, and the correlation of error terms that can result when panel data are used. The results of this analysis indicate that the extent to which mothers participate in the labor force, and for how many hours, depends on the costs of childcare and on what level of hourly wage is available to them and to other members of the household. The author's simulations show that family allowances - intended to reduce poverty - do not significantly affect the household choice of childcare arrangements. Replacing family allowances with childcare subsidies might have a strong positive effect on women's participation in the labor force and thus could be effective in reducing poverty.Primary Education,Children and Youth,Health Systems Development&Reform,Economic Theory&Research,Social Inclusion&Institutions,Youth and Governance,Children and Youth,Street Children,Primary Education,Economic Theory&Research

The emerging underclass in the Russian Federation: Income dynamics, 1992-1996

I. Introduction The transition to a market economy by the countries of Eastern Europe and the former Soviet Union has been a dramatic move from a relatively stable economic condition with equal income distribution to one with uncertainty, political and economical instability, and sharp polarization in resource distribution. The sweeping economic reforms have led the Russian Federation to eliminate most, if not all, general subsidies and significantly reduce subsidies and payments to the poor. The privatization of many activities and the process of allowing prices and exchange rates to fluctuate caused rapid economic and social changes. Since the onset of the economic transition, the establishment of a social safety net and the need to mitigate the social costs associated with the transition from a planned state economy to a market-oriented economy have been a major concern in the countries of the former Soviet Union. The political support of reforms in these countries after the end of communism and the question of political stability become vital to their governments. Poverty and inequalityareamong the factors that determine the distribution of political power. As A.B. Atkinson and J. Micklewright note, ‘‘The legitimacy of governments may be called into question if too large a gap opens between rich and poor.’

High pressure effects in fluorinated HgBa2Ca2Cu3O(8+d)

We have measured the pressure sensitivity of Tc in fluorinated HgBa2Ca2Cu3O(8+d) (Hg-1223) ceramic samples with different F contents, applying pressures up to 30 GPa. We obtained that Tc increases with increasing pressure, reaching different maximum values, depending on the F doping level, and decreases for a further increase of pressure. A new high Tc record (166 K +/- 1 K) was achieved by applying pressure (23 GPa) in a fluorinated Hg-1223 sample near the optimum doping level. Our results show that all our samples are at the optimal doping, and that fluorine incorporation decreases the crystallographic $a$-parameter concomitantly increasing the maximum attainable Tc. This effect reveals that the compression of the $a$ axes is one of the keys that controls the Tc of high temperature superconductors.Comment: 4 pages, 4 figures, submitted to Phys. Rev.

Spin Excitations in BaFe1.84Co0.16As2 Superconductor Observed by Inelastic Neutron Scattering

Superconductivity appears to compete against the spin-density-wave in Fe pnictides. However, optimally cobalt doped samples show a quasi-two-dimensional spin excitation centered at the (0.5, 0.5, L) wavevector, "the spin resonance peak", that is strongly tied to the onset of superconductivity. By inelastic neutron scattering on single crystals we show the similarities and differences of the spin excitations in BaFe1.84Co0.16As2, with respect to the spin excitations in the high-temperature superconducting cuprates. As in the cuprates the resonance occurs as an enhancement to a part of the spin excitation spectrum which extends to higher energy transfer and higher temperature. However, unlike in the cuprates, the resonance peak in this compound is asymmetric in energy.Comment: 12 pages, 6 figures; PACS # 74.70.-b, 74.20.Mn, 78.70.Nx, 74.25.Ha; corrected discussion of figures in tex