Utilizing data collected from the 1980 public-use sample of the U.S. Census, we examine the effect of percentage foreign born in the labor force upon aggregate self-employment rate in 272 SMSAs. Because mean self-employment among the foreign born was higher than among the native born, an increased percentage in the foreign born in a SMSA labor force caused increased aggregate self-employment. Also, as a result of renewed immigration during the 1970s, and the resulting increase in the foreign-born component of the civilian labor force, nonfarm self-employment in the United States increased about 3% above what would have been expected from a comparable “influx” of native-born workers. Depending on which method of estimation one selects, this immigration-prompted increase explains from 16% to 52% of the decade's total increase in nonfarm self-employment, a surprising reversal of nearly 10 decades of uninterrupted decrease. Rate of self-employment among immigrants had no effect upon the rate of or returns to self-employment of native-born workers in general or native blacks in particular.
Power consumption and reliability are key issues in space system applications. During the flight, electro-magnetic radiation may cause single event damage effects including SEUs, SEFIs, SETs and others. In order to mitigate these problems, a system with dynamic and partial reconfiguration capabilities is proposed. This approach provides a possibility to reconfigure parts of the design during the operation thus making the system flexible, fault tolerant and less power-consuming. Two partial reconfiguration methodologies are proposed and compared in terms of power consumption, flexibility, and size of memory footprints.
<p>One major environmental constraint during exploration missions is the presence of charged dust-like particles, which are present on the Moon, Mars, comets and asteroids. From an analysis of the effects of lunar dust on Extra-Vehicular Activity (EVA) systems during the six Apollo missions that landed on the lunar surface, it was found that these effects can take many forms such as external vision obscuration, false instrument readings, dust coating and contamination, loss of traction, clogging of mechanisms, abrasion, thermal control problems and seal failures. One of the most serious effects is the compromising of astronaut health by irritation and inhalation of lunar dust.</p><p>Therefore, it is of utmost importance to characterise the properties of the dust particles present on the exploration sites and their transportation mechanisms to enable efficient mitigation techniques to be put in place.</p><p>The overall objective of the DUSTER project is to develop instrumentation and technologies to study dust particles and electrostatic transportation for planetary and small body exploration missions. Specifically, the aim is to design, manufacture and test in a relevant environment a compact multi-sensor instrument for in situ analysis of dust properties (mechanical and electrical) and electrostatic transportation that can be used on a small lunar lander. To that end, the instrument includes:</p><p>- A dust collector: electrodes biased at high potential to attract/collect dust particles, coupled to an electrometer</p><p>- Langmuir probes</p><p>- E-field probes</p><p>Using this instrument, the following parameters will be derived:</p><p>- Charging level of dust as a function of the environmental parameters (illumination, plasma density and temperature)</p><p>- (gravity + cohesive forces)/charge ratio distribution of dust layer</p><p>These two parameters will allow the determination of the electric field needed to attract/collect dust according to the environmental conditions (illumination, plasma density and temperature), which, among other applications, will allow designing electrostatic dust mitigation devices and dust sample collectors.</p>
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