Space Shuttle separation mechanisms

The development of space shuttle separation devices is reviewed to illustrate the mechanisms involved in separating the orbiter from the Boeing 747 carrier aircraft and from the externally mounted propellant tank. Other aspects of the separation device development discussed include design evolution, operational experience during the orbiter approach and landing tests, and the work to be accomplished before an operational system becomes a reality

Postsynaptic Ca2+, but not cumulative depolarization, is necessary for the induction of associative plasticity in Hermissenda

The neuronal modifications that underlie associative memory in Hermissenda have their origins in a synaptic interaction between the visual and vestibular systems, and can be mimicked by contiguous in vitro stimulation of these converging pathways. At the offset of vestibular stimulation (i.e., hair cell activity), the B photoreceptors are briefly released from synaptic inhibition resulting in a slight depolarization (2–4 mV). If contiguous pairings of light-induced depolarization and presynaptic vestibular activity occur in close temporal succession, this depolarization “accumulates” and has been hypothesized to culminate in a sustained rise in intracellular Ca2+ and a resultant Ca(2+)-mediated phosphorylation of K+ channels as well as an associated increase in input resistance. Here we demonstrate that this cumulative depolarization is neither necessary nor sufficient for the biophysical modifications of the B cell membrane indicative of memory formation. Consistent with several recent reports of one-trial learning in Hermissenda, one pairing of light with mechanical stimulation of the vestibular hair cells resulted in a rise in neuronal input resistance across the B cell membrane that was attenuated by a prepairing iontophoretic injection of the Ca2+ chelator EGTA (25 mM), indicating that this potentiation was Ca2+ dependent. However, the use of a single pairing negates the possibility of an accumulation of depolarization across trials. In a subsequent experiment, B photoreceptors underwent a cumulative depolarization, and a coincident rise in input resistance, during multiple pairings of light and hair cell stimulation. However, if the B photoreceptor was voltage clamped at its initial resting potential before and after each pairing, thus eliminating the cumulative depolarization, the rise in resistance not only persisted, but was enhanced. Moreover, if unpaired light presentations were followed by a current-induced depolarization (to mimic cumulative depolarization), no increase in input resistance was detected. To assess directly the effect of a cumulative depolarization on the voltage-dependent Ca2+ current, an analysis of the inward current on the B cell soma membrane was conducted. It was determined that (1) the inward current may undergo a partial inactivation during sustained depolarization, (2) the peak current was depressed during repetitive depolarizations, and (3) the peak current underwent a steady- state inactivation, such that it was reduced when elicited from holding potentials more positive than -60 mV. The analysis of this current suggests that pairings of light and presynaptic activity would reduce voltage-dependent Ca2+ influx when those pairings are conducted at depolarized membrane potentials, such as during cumulative depolarization

The global financial crisis and development thinking

The global financial crisis has not only dealt a major blow to the global economy, but also shaken confidence in economic management in the developed world and the economic models that guide it. The crisis has revealed major market failures, especially in the housing bubble and its transmission to the financial system, but also glaring state failures that propagated and exacerbated the crisis. Will the events of the past two years lead to major shifts in thinking about development economics, and should they? This paper assesses that question for several key domains of development thinking, including the market-state balance, macroeconomic management, globalization, development financing, and public spending. On the one hand, changed global circumstances and new awareness of vulnerability should lead to some policy changes, as developing countries take steps to reduce and buffer risks, including risks generated in developed countries. At the same time, the crisis should largely reinforce the Post-Washington Consensus on development that has emerged over the past decade -- a world view that aims to achieve private sector-driven growth but sees a facilitating role for the state, promotes engaging with the global economy in ways that advance development, and values pragmatism, experimentation, and evidence-based policymaking over ideology.Debt Markets,Economic Theory&Research,Banks&Banking Reform,Climate Change Economics,Emerging Markets

Vacuum-stripped silicone binder for thermal-control paint

Silicone elastomer is placed in evacuating system, heated to 160 C and held at this temperature for 24 hours. Elastomer is then cooled to room temperature in vacuum, producing upgraded, low outgassing polymer of increased molecular weight

The Response of Normal Shocks in Diffusers

The frequency response of a normal shock in a diverging channel is calculated for application to problems of pressure oscillations in ramjet engines. Two limits of a linearized analysis arc discussed: one represents isentropic flow on both sides of a shock wave; the other may be a crude appr'l'I;imation to the influence of flow separation induced hy the wave. Numerical results arc given, and the influences of the shock wave on oscillations in the engine are discus,ed

Scintillation detector for carbon-14

Detector consists of plastic, cylindrical double-wall scintillation cell, which is filled with gas to be analyzed. Thin, inner cell wall is isolated optically from outer (guard) scintillator wall by evaporated-aluminum coating. Bonding technique provides mechanical support to cell wall when device is exposed to high temperatures

Modeling pressure oscillations in Ramjets

Pressure oscillations in ramjet engines are approximated as one-dimensional motions and treated within linear acoustics. The exhaust nozzle is represented by the admittance function for a short choked nozzle. New results have been obtained for the quasi-steady response of a normal shock wave in the diffuser. Acoustic fields in the inlet region and in the combustion chamber are matched to provide an analytical expression of the criterion for linear stability. Combustion processes are accommodated but not treated in detail. As examples, data are discussed for two liquid-fueled engines, one having axial dump and one having side dumps

No more cutting class ? reducing teacher absence and providing incentives for performance

Expanding and improving basic education in developing countries requires, at a minimum, teachers who are present in the classroom and motivated to teach, but this essential input is often missing. This paper describes the findings of a series of recent World Bank and other studies on teacher absence and incentives for performance. Surprise school visits reveal that teachers are absent at high rates in countries such as India, Indonesia, Uganda, Ecuador, and Zambia, reducing the quality of schooling for children, especially in rural, remote, and poor areas. More broadly, poor teacher management and low levels of teacher accountability afflict many developing-country education systems. The paper presents evidence on these shortcomings, but also on the types of incentives, management, and support structures that can improve motivation and performance and reduce avoidable absenteeism. It concludes with policy options for developing countries to explore as they work to meet Education for All goals and improve quality.Tertiary Education,Primary Education,Education For All,Teaching and Learning,Secondary Education