A preliminary shield design for a SNAP-8 power system

A preliminary shield design for a nuclear power system utilizing a SNAP-8 reactor for space base application is presented. A representative space base configuration was selected to set the geometry constraints imposed on the design. The base utilizes two independent power packages each with a reactor operating at 600 kwt and each producing about 50 kwe. The crew compartment is located about 200 feet from each reactor and is large enough in extent to intercept a total shadow angle of 60 deg measured about the center line of each reactor

Probable solar flare doses encountered on an interplanetary mission as calculated by the MCFLARE code

The computer program, MCFLARE, uses Monte Carlo methods to simulate solar flare occurrences during an interplanetary space voyage. The total biological dose inside a shielded crew compartment due to the flares encountered during the voyage is determined. The computer program evaluates the doses obtained on a large number of trips having identical trajectories. From these results, a dose D sub p having a probability p of not being exceeded during the voyage can be determined as a function of p for any shield material configuration. To illustrate the use of the code, a trip to Mars and return is calculated, and estimated doses behind several thicknesses of aluminum shield and water shield are presented

The design of a Pulse Position Modulated /PPM/ optical communication system

Design of pulse position modulation optical communication syste

Взаємодія засобів контамінованої лексичної когезії в тексті англійських мультимодальних літературних казок Філіпа Арда (Interaction of modes of contaminated lexical cohesion in the text of English multimodal literary fairy tales written by Philip Ardagh)

В означеній статті проаналізовано переплетення вербальних та невербальних засобів контамінованої лексичної когезії в тексті англійської мультимодальної літературної казки Філіпа Арда. Інтеракцію між вербальною та невербальною складовими розглянуто за ознакою наявності іконічних та параграфемних/графічних вкраплень у вербальну складову: мікро-, мезо-, макровкраплень у межах синтаксичної одиниці, надфразної єдності та фрагмента тексту казки. (Combination and convergence of atypical components in modern fictional text cause formation of contaminated cohesion in English multimodal literary fairy tale. Contaminated cohesion identifies relation between different semiotic modes of verbal component and nonverbal component, i.e. interpretation of verbal components depends on nonverbal components in multimodal fictional text, and vice versa. The article reviews interweaving of verbal components and nonverbal components of contaminated lexical cohesion in the text of English multimodal literary fairy tales written by Philip Ardagh. The verbal component of contaminated lexical cohesion consists of reiteration, synonyms, antonyms, parallel constructions / chiastic structure, literary and colloquial words, onomatopoeia. Interaction between verbal component and nonverbal component is considered according to the iconic, paragraphemic/graphic inclusions in the verbal component, i.e. availability of the micro-, meso- and macro inclusions in a sentence, a microtext and a fragment of English multimodal literary fairy tale. Semiotic and narrative interpretation of the text of English multimodal literary fairy tale written by Philip Ardagh is based on GeM (genre and multimodality) model used for structual and semiotic ranging of modes of contaminated cohesion. This model provides data on different genres using combinations of text, layout, graphics, pictures and diagrams. In this model, the text of English multimodal literary fairy tale is analyzed on five levels of structure including content structure, rhetorical structure, layout structure, navigation structure, linguistic structure.

Sum-of-squares lower bounds for planted clique

Finding cliques in random graphs and the closely related "planted" clique variant, where a clique of size k is planted in a random G(n, 1/2) graph, have been the focus of substantial study in algorithm design. Despite much effort, the best known polynomial-time algorithms only solve the problem for k ~ sqrt(n). In this paper we study the complexity of the planted clique problem under algorithms from the Sum-of-squares hierarchy. We prove the first average case lower bound for this model: for almost all graphs in G(n,1/2), r rounds of the SOS hierarchy cannot find a planted k-clique unless k > n^{1/2r} (up to logarithmic factors). Thus, for any constant number of rounds planted cliques of size n^{o(1)} cannot be found by this powerful class of algorithms. This is shown via an integrability gap for the natural formulation of maximum clique problem on random graphs for SOS and Lasserre hierarchies, which in turn follow from degree lower bounds for the Positivestellensatz proof system. We follow the usual recipe for such proofs. First, we introduce a natural "dual certificate" (also known as a "vector-solution" or "pseudo-expectation") for the given system of polynomial equations representing the problem for every fixed input graph. Then we show that the matrix associated with this dual certificate is PSD (positive semi-definite) with high probability over the choice of the input graph.This requires the use of certain tools. One is the theory of association schemes, and in particular the eigenspaces and eigenvalues of the Johnson scheme. Another is a combinatorial method we develop to compute (via traces) norm bounds for certain random matrices whose entries are highly dependent; we hope this method will be useful elsewhere

Performance Charts for a Turbojet System

Convenient charts are presented for computing the thrust, fuel consumption, and other performance values of a turbojet system. These charts take into account the effects of ram pressure, compressor pressure ratio, ratio of combustion-chamber-outlet temperature to atmospheric temperature, compressor efficiency, turbine efficiency, combustion efficiency, discharge-nozzle coefficient, losses in total pressure in the inlet to the jet-propulsion unit and in the combustion chamber, and variation in specific heats with temperature. The principal performance charts show clearly the effects of the primary variables and correction charts provide the effects of the secondary variables. The performance of illustrative cases of turbojet systems is given. It is shown that maximum thrust per unit mass rate of air flow occurs at a lower compressor pressure ratio than minimum specific fuel consumption. The thrust per unit mass rate of air flow increases as the combustion-chamber discharge temperature increases. For minimum specific fuel consumption, however, an optimum combustion-chamber discharge temperature exists, which in some cases may be less than the limiting temperature imposed by the strength temperature characteristics of present materials