Active cleaning technique for removing contamination from optical surfaces in space

Plasma cleaning experiments were completed on hydrocarbon contaminant films, experiments were initiated to determine a satisfactory technique for depositing contaminant films, and an experiment was conducted to determine whether specimens are being thermally cleaned rather than plasma cleaned. Results of plasma cleaning experiments on hydrocarbon contaminant films showed that the optical properties of mirrors and gratings could be satisfactorily restored. Results on fused silica optical flats were inconclusive because of the insensitivity of measurement techniques to the contaminant films. White thermal control surfaces, degraded by the hydrocarbon contaminant film, could not be restored by oxygen plasma exposure. The reflectance of silvered FEP Teflon thermal control surfaces could be restored by plasma cleaning. Experiments with a silicone contaminant indicated that it could not be easily polymerized onto surfaces with ultraviolet radiation. Results of the thermal cleaning experiment showed that the polymerized hydrocarbon contaminant film could not be removed by heating in vacuum to a temperature in excess of that expected during plasma cleaning

Small linear wind tunnel saltation experiments: Some experiences

Since the wind tunnels proposed to be used for the Space Station Planetology Experiments are of a rather limited size, some experience and techniques used for saltation experiments in a small linear wind tunnel may be of interest. Three experiments will be presented. The first concerns a length effect of saltation mass flux in which the size of the wind tunnel exaggerates the physical process taking place. The second experiment concerns a nonoptical technique that does not interfere with flow and by which momentum flux to the floor may be measured. The technique may also be used to calculate saltation flux (using appropriate assumptions). The third experiment concerns the use of the momentum equation to estimate momentum fluxes by difference

Toward a history of the space shuttle. An annotated bibliography

This selective, annotated bibliography discusses those works judged to be most essential for researchers writing scholarly studies on the Space Shuttle's history. A thematic arrangement of material concerning the Space Shuttle will hopefully bring clarity and simplicity to such a complex subject. Subjects include the precursors of the Space Shuttle, its design and development, testing and evaluation, and operations. Other topics revolve around the Challenger accident and its aftermath, promotion of the Space Shuttle, science on the Space Shuttle, commercial uses, the Space Shuttle's military implications, its astronaut crew, the Space Shuttle and international relations, the management of the Space Shuttle Program, and juvenile literature. Along with a summary of the contents of each item, judgments have been made on the quality, originality, or importance of some of these publications. An index concludes this work

Breaks, Good and Bad: The Inner Life of Research

Once in a while, if you are lucky, you will get to read a technical research article which has some soul. The rest are corpses. Corpses are fine for their purpose, but they never real the inner life, the dynamic mechanism. An outstanding exception is the recent best seller in science, The Double Helix; which details the very human development of a very important theoretical model

Chiropteran Mortality

The study of chiropteran mortality is a difficult one because observations concerning mass mortality, predation, and fatal accidents are sporadic and unexpected. Almost every known predaceous animal preys on bats from time to time; but (with one or two rare exceptions) do so only when an occasional opportunity presents itself, and do not specialize in bat predation. Our knowledge of bat pathology is meager. Mass-mortalities have been reported only from sight observations, and the causative organisms rarely ascertained, because of the unexpected encounter. The relationships between human and chiropteran diseases are becoming much better understood; this study is mostly oriented toward man, and not toward the cause and effect of disease in the chiroptera. The longevity of certain bats is known to range between 15 and 20 years; but their unique activities make them rather prone to accident. They become impaled on such sharp objects as barbed wire, and locust, burdock, and cactus spines. They fall into water holes and drown, get entrapped in tar pits, get electrocuted on high-power lines, etc., but remain among the most abundant mammals on earth today. We have attempted to assemble the literature on all known causes of mortality in bats but cannot, of course, cite all noted occurrences

Uniformity and Diversity in Payment Systems

The rules governing the transfer of value between users of payment systems differ among payment systems. Rules allocating loss from unauthorized payment, erroneous payment, and the reversibility of payment vary according to whether payment is made by check, credit or debit card, wholesale wire transfer, or letter of credit. Thirty-five years after the New Payments Code failed to attract enough support to become law, academics and practitioners recently have proposed that payment system rules be uniform. This Article rejects this initially attractive position. It argues that the optimal standardization of payment system rules allows diverse rules among payment systems. The case for uniformity implicitly judges the reduction in information costs resulting from standardization to exceed the benefits from a choice among payment instruments with different rules. The Article argues that the proponents for uniformity overestimate the savings in information costs and ignore or underestimate the benefits to payment system users of different rules governing payment instruments. The technology for transferring value and predominant use of particular payment instruments differs, as does the capacity of payment system users and providers to avoid or reduce loss. Even cognitive error or unawareness of payment system rules among consumers does not always justify a single consumer-specific rule for consumer payments. While current law does not necessarily offer optimal diversity, diverse rules among some payment systems would be preferable to uniformity

Feasibility study of an Integrated Program for Aerospace vehicle Design (IPAD). Volume 3: Support of the design process

The user requirements for computer support of the IPAD design process are identified. The user-system interface, language, equipment, and computational requirements are considered

A Nonlinear Super-Exponential Rational Model of Speculative Financial Bubbles

Keeping a basic tenet of economic theory, rational expectations, we model the nonlinear positive feedback between agents in the stock market as an interplay between nonlinearity and multiplicative noise. The derived hyperbolic stochastic finite-time singularity formula transforms a Gaussian white noise into a rich time series possessing all the stylized facts of empirical prices, as well as accelerated speculative bubbles preceding crashes. We use the formula to invert the two years of price history prior to the recent crash on the Nasdaq (april 2000) and prior to the crash in the Hong Kong market associated with the Asian crisis in early 1994. These complex price dynamics are captured using only one exponent controlling the explosion, the variance and mean of the underlying random walk. This offers a new and powerful detection tool of speculative bubbles and herding behavior.Comment: Latex document of 24 pages including 5 eps figure