A Survey and Evaluation of High Energy Liquid Chemical Propulsion Systems

This report presents the results of a study to develop a procedure for evaluating liquid propellants in order (a) to select the most appropriate propellant (from among those under development) for each of several applications on each of the various missions in the NASA program, or (b) to select new propellants (from among those being proposed) for initiation or continuation of research and development. The analysis begins with a consideration of requirements--either for the specific application or for the various classes of applications. The known characteristics of the propellant or propellants to be evaluated are then put into a convenient form for evaluation. The next step is to determine whether or not there are requirements that simply cannot be met by the propellant. If the propellant passes this test, an optimum vehicle configuration using the propellant (and meeting all requirements) is estimated. (The configuration should be optimized with respect to the total resource consumption for all aspects of the mission, including R&D, production, logistics, and operation.) The total resource consumption for this configuration is then compared with that for similar configurations using other propellants (and meeting all requirements equally well). If all factors have been properly taken into account, this comparison of resource consumption will complete the evaluation. Such an evaluation may be performed several times, in increasing detail and with correspondingly increasing accuracy, as an R&D program proceeds, and the accuracy of the data as well as the cost of the next step in the program increase. The procedure is superior to those in common use in that it minimizes both the amount of analytical work and the number of points at which subjective value judgments are made

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

Can Public Debt Enhance Democracy?

This Essay draws on historical and current examples to examine the extent to which public creditors can enhance democracy by monitoring public officials in a manner that compensates for the failures of the government debtor\u27s constituents to monitor public officials. Creditors and constituents may share significant interests, depending on the structure of security arrangements for public debt and the identity of the debtors. Where interests overlap, the capacity of creditors to overcome collective action problems suffered by constituents may transform creditors into surrogates for constituents. Whether creditors are willing to play this role, however, may depend on the existence of alternatives to creditor monitoring, such as diversification and market constraints on default. The Essay concludes with an examination of the plausible scope of creditor monitoring in contemporary settings of sovereign and state and local debt

Chinch bug diseases

It has not been known until a comparatively recent date,that chinch bugs were subject to disease. In 1867 Dr. Shimer of Mt. Carroll, Ill. , presented a paper before the Academy of Natural Science of Philadelphia, in which he gave an account of a disease which so completely destroyed the chinch bugs in the vicinity of his home that it was impossible for him to find any specimens for his collection the following year. It was not then known and, unless specimens of the diseased bugs have been preserved, it probably never can be known with certainty what that disease was. Dr. Shimer only knew that it was an epidemic disease and that when the bugs died they were soon covered with a fungus or mould, which he thought to be the same as that which usually attacks dead animal matter. Sixteen years later Prof. Forbes, in his first report as State Entomologist of Illinois, gave a very full and interesting account of his careful studies of a bacterial disease, Micrococcus insectorum, which was very destructive to the bugs in Illinois in the summer of ’83. This was a true contagious disease and is conducted from bug to bug by microscopic germs as small-pox or yellow fever are conducted from man to man. Such diseases when occurring in the insect world are vastly more destructive than when occurring among human kind, as the bugs neither know the danger nor have any means of averting it. Bugs killed by this disease turn dark in color, become more or less shriveled in appearance, and when dead are not usually covered with mould

The Apple Curculio

A number of inquiries have been received at the station concerning the Apple Curculio, and I therefore give the following information concerning it. The Beetle varies much in size. The largest specimen in the station collection measures 3-16 of an inch. The beetles are often mistaken for the plum curculio, but they are easily distinguished from that species by the long, slender, somewhat curved beak and by the two prominent humps on the posterior portion of each wing-cover where the color is rust-red

Letters of Credit as Signals: Comments on Ronald Mann\u27s \u27The Role of Letters of Credit in Payment Transactions\u27

Why would buyers and sellers transact with each other through a third party that charges a significant fee for its services and that typically is authorized to make payment notwithstanding noncompliance with the very prerequisites that it has been engaged to monitor? This is the puzzle that Ronald Mann\u27s provocative and nuanced article purports to explain. Under the traditional story about the esoteric world of letters of credit, these transactions allow distant buyers and sellers to circumvent obstacles that would otherwise frustrate long-distance transactions. The traditional story explains that these credits induce buyers to approve payment prior to receiving conforming goods because the transactional structure provides buyers with documents that testify conforming goods are en route. Similarly, credits induce sellers to ship goods prior to payment because that same transactional structure assures that payment is forthcoming from a credible and creditworthy source. Mann suggests that the story is incorrect or at least incomplete. For him, the real function of the letter of credit is to solve informational asymmetries concerning the parties involved in the transaction by allowing an issuer with superior information to verify a buyer\u27s legitimacy to the distant seller or to the buyer\u27s government. I find the claim that letters of credit fill informational gaps highly plausible. Indeed, I take it to be wholly consistent with the traditional story that banks are asked to issue letters of credit because they have an informational advantage about the financial status of their customers, the applicants. It is less clear to me that what the beneficiary learns from the issuer\u27s conduct should be vaulted into a primary explanation for letters of credit. I want, therefore, to raise two issues with respect to the story that Mann tells us. One issue concerns his substantive claims about the role of letters of credit. The second is more directly related to the general theme of this conference and refleets on how Mann\u27s article may be refined, validated, or refuted by empirical work that has not yet been done