2,644 research outputs found
Enhancing simulation of efficiency with analytical tools
Some means of combining both computer simulation and anlytical techniques are indicated in order to mutually enhance their efficiency as design tools and to motivate those involved in engineering design to consider using such combinations. While the idea is not new, heavy reliance on computers often seems to overshadow the potential utility of analytical tools. Although the example used is drawn from the area of dynamics and control, the principles espoused are applicable to other fields. In the example the parameter plane stability analysis technique is described briefly and extended beyond that reported in the literature to increase its utility (through a simple set of recursive formulas) and its applicability (through the portrayal of the effect of varying the sampling period of the computer). The numerical values that were rapidly selected by analysis were found to be correct for the hybrid computer simulation for which they were needed. This obviated the need for cut-and-try methods to choose the numerical values, thereby saving both time and computer utilization
Large Space Telescope (LST) Pointing Control System (PCS) analytical Advanced Technical Development (ATD) program
The large space telescope (LST) pointing control system (PCS) advanced technical development (ATD) program is described. The approach used is to describe the overall PCS development effort, showing how the analytical ATD program elements fit into it. Then the analytical ATD program elements are summarized
X-ray source characteristics and detection efficiencies of prototype Lixiscopes
The radioactive X-ray sources and scintillator screens used in prototype Lixiscope units are described. Some of those considerations necessary for the optimization of future Lixiscope designs are stressed as well as some semi-quantitative information on the present prototype devices
Passive stability of a spinning Skylab
The results of an analytical investigation of the rotational dynamics of a spinning Skylab space station are presented. The passive stability of motion of a simplified model consisting of a rigid core body with two attached flexible appendages is investigated. The parameter plane stability technique is applied to the specific Skylab case to determine its transient response to external disturbances
Pensions in the laboratory: the role of commitment and reputation for deferred compensation in multi-period labor contracts
This paper examines the relationship between firmsâ wage offers and workersâ supply of effort in a multi-period environment. If firms are able to commit to a schedule of wage payments, in equilibrium they will offer deferred compensation: first-period productivity is positive and wages are zero, while last-period productivity is zero and wages are positive. Workers respond to deferred compensation by supplying sufficient effort to avoid dismissal. In the absence of commitment, firms pay zero wages and workers supply low effort. The experiment produces strong evidence of these predictions. With commitment, we frequently observe deferred compensation and relatively high worker effort. In the absence of commitment, we observe no deferred compensation, much lower wages, and little worker effort. A third treatment where commitment is not possible, but firms are able to build a reputation, produces an intermediate result. Finally, we also find some evidence of gift exchange, in particular in the absence of commitment when deferred compensation does not work
Deferred compensation and gift exchange: an experimental investigation into multi-period labor markets
This paper examines the relationship between firmsâ wage offers and workersâ
supply of effort using a three-period experiment. In equilibrium, firms will offer deferred
compensation: first period productivity is positive and wages are zero, while third period
productivity is zero and wages are positive. The experiment produces strong evidence
that deferred compensation increases worker effort; in about 70 percent of cases subjects
supplied the optimal effort given the wage offer, and there was a strong effort response to
future-period wages. We also find some evidence of gift exchange; worker players
increased the effort levels in response to above equilibrium wage offers by a human, but
not in response to similar offers by a computer. Finally, we find that firm players who are
initially hesitant to defer compensation learn over time that it is beneficial to do so
Worst-case space radiation environments for geocentric missions
Worst-case possible annual radiation fluences of energetic charged particles in the terrestrial space environment, and the resultant depth-dose distributions in aluminum, were calculated in order to establish absolute upper limits to the radiation exposure of spacecraft in geocentric orbits. The results are a concise set of data intended to aid in the determination of the feasibility of a particular mission. The data may further serve as guidelines in the evaluation of standard spacecraft components. Calculations were performed for each significant particle species populating or visiting the magnetosphere, on the basis of volume occupied by or accessible to the respective species. Thus, magnetospheric space was divided into five distinct regions using the magnetic shell parameter L, which gives the approximate geocentric distance (in earth radii) of a field line's equatorial intersect
Out-of-pile creep behavior of uranium carbide
Compression creep tests were investigated on various UC-based fuel materials having a variation in both density and composition. Specimens were prepared by casting and by hot pressing. Steady-state creep rates were measured under vacuum at 1400 to 1800 C in the stress range 500-4000 psi
Absolute stability analysis of attitude control systems for large boosters
Absolute stability analysis of attitude control systems for large launch vehicle
High-Temperature Alkali Vapor Cells with Anti-Relaxation Surface Coatings
Antirelaxation surface coatings allow long spin relaxation times in
alkali-metal cells without buffer gas, enabling faster diffusion of the alkali
atoms throughout the cell and giving larger signals due to narrower optical
linewidths. Effective coatings were previously unavailable for operation at
temperatures above 80 C. We demonstrate that octadecyltrichlorosilane (OTS) can
allow potassium or rubidium atoms to experience hundreds of collisions with the
cell surface before depolarizing, and that an OTS coating remains effective up
to about 170 C for both potassium and rubidium. We consider the experimental
concerns of operating without buffer gas and with minimal quenching gas at high
vapor density, studying the stricter need for effective quenching of excited
atoms and deriving the optical rotation signal shape for atoms with resolved
hyperfine structure in the spin-temperature regime. As an example of a
high-temperature application of antirelaxation coated alkali vapor cells, we
operate a spin-exchange relaxation-free atomic magnetometer with sensitivity of
6 fT/sqrt(Hz) and magnetic linewidth as narrow as 2 Hz.Comment: 8 pages, 5 figures. The following article appeared in Journal of
Applied Physics and may be found at http://link.aip.org/link/?jap/106/11490
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