The 30-cm ion thruster power processor

A power processor unit for powering and controlling the 30 cm Mercury Electron-Bombardment Ion Thruster was designed, fabricated, and tested. The unit uses a unique and highly efficient transistor bridge inverter power stage in its implementation. The system operated from a 200 to 400 V dc input power bus, provides 12 independently controllable and closely regulated dc power outputs, and has an overall power conditioning capacity of 3.5 kW. Protective circuitry was incorporated as an integral part of the design to assure failure-free operation during transient and steady-state load faults. The implemented unit demonstrated an electrical efficiency between 91.5 and 91.9 at its nominal rated load over the 200 to 400 V dc input bus range

Creep fatigue of low-cobalt superalloys: Waspalloy, PM U 700 and wrought U 700

The influence of cobalt content on the high temperature creep fatigue crack initiation resistance of three primary alloys was evaluated. These were Waspalloy, Powder U 700, and Cast U 700, with cobalt contents ranging from 0 up to 17 percent. Waspalloy was studied at 538 C whereas the U 700 was studied at 760 C. Constraints of the program required investigation at a single strain range using diametral strain control. The approach was phenomenological, using standard low cycle fatigue tests involving continuous cycling tension hold cycling, compression hold cycling, and symmetric hold cycling. Cycling in the absence of or between holds was done at 0.5 Hz, whereas holds when introduced lasted 1 minute. The plan was to allocate two specimens to the continuous cycling, and one specimen to each of the hold time conditions. Data was taken to document the nature of the cracking process, the deformation response, and the resistance to cyclic loading to the formation of small cracks and to specimen separation. The influence of cobalt content on creep fatigue resistance was not judged to be very significant based on the results generated. Specific conclusions were that the hold time history dependence of the resistance is as significant as the influence of cobalt content and increased cobalt content does not produce increased creep fatigue resistance on a one to one basis

Echoes of ECOs: gravitational-wave signatures of exotic compact objects and of quantum corrections at the horizon scale

Gravitational waves from binary coalescences provide one of the cleanest signatures of the nature of compact objects. It has been recently argued that the post-merger ringdown waveform of exotic ultracompact objects is initially identical to that of a black-hole, and that putative corrections at the horizon scale will appear as secondary pulses after the main burst of radiation. Here we extend this analysis in three important directions: (i) we show that this result applies to a large class of exotic compact objects with a photon sphere for generic orbits in the test-particle limit; (ii) we investigate the late-time ringdown in more detail, showing that it is universally characterized by a modulated and distorted train of "echoes" of the modes of vibration associated with the photon sphere; (iii) we study for the first time equal-mass, head-on collisions of two ultracompact boson stars and compare their gravitational-wave signal to that produced by a pair of black-holes. If the initial objects are compact enough as to mimic a binary black-hole collision up to the merger, the final object exceeds the maximum mass for boson stars and collapses to a black-hole. This suggests that - in some configurations - the coalescence of compact boson stars might be almost indistinguishable from that of black-holes. On the other hand, generic configurations display peculiar signatures that can be searched for in gravitational-wave data as smoking guns of exotic compact objects.Comment: 13 pages, RevTex4. v2: typo in equation 7 corrected, references added, to appear in PR

Models and Algorithms for Graph Watermarking

We introduce models and algorithmic foundations for graph watermarking. Our frameworks include security definitions and proofs, as well as characterizations when graph watermarking is algorithmically feasible, in spite of the fact that the general problem is NP-complete by simple reductions from the subgraph isomorphism or graph edit distance problems. In the digital watermarking of many types of files, an implicit step in the recovery of a watermark is the mapping of individual pieces of data, such as image pixels or movie frames, from one object to another. In graphs, this step corresponds to approximately matching vertices of one graph to another based on graph invariants such as vertex degree. Our approach is based on characterizing the feasibility of graph watermarking in terms of keygen, marking, and identification functions defined over graph families with known distributions. We demonstrate the strength of this approach with exemplary watermarking schemes for two random graph models, the classic Erd\H{o}s-R\'{e}nyi model and a random power-law graph model, both of which are used to model real-world networks

THE ART ATHLETE: A SPORTS BIOMECHANICS PERSPECTIVE

Overuse injuries are as much a problem for ‘art athletes’ (dancers and musicians and performing artists generally) as they are for those we more commonly term ‘athletes’. Lower back injuries in male ballet dancers are certainly commonplace. 3D motion analysis in combination with 3D Static Strength Predicting analysis showed that compressive forces at L5/S1 were above the National Institute of Occupational Safety and Health ‘Back Compression Design Limit’ (~ 4,500N) and shear forces were high (~ 530 N) for male dancers performing two commonly used classical lifts. A research design for the use of an opto-reflective motion analysis (Vicon) to investigate shoulder joint loading in cellists and violinists will also be presented

Regulation of the galactose pathway in Saccharomyces cerevisiae: induction of uridyl transferase mRNA and dependency on GAL4 gene function

In Saccharomyces cerevisiae, utilization of galactose requires four inducible enzyme activities. Three of these activities (galactose-1-phosphate uridyl transferase, EC 2.7.7.10; uridine diphosphogalactose 4-epimerase, EC 5.1.3.2; and galactokinase, EC 2.7.1.6) are specified by three tightly linked genes (GAL7, GAL10, and GAL1, respectively) on chromosome II, whereas the fourth, galactose transport, is specified by a gene (GAL2) located on chromosome XII. Although classic genetic analysis has revealed both positive and negative regulatory genes that coordinately affect the appearance of all four enzyme activities, neither the basic events leading to the appearance of enzyme activities nor the roles of the regulatory genes have yet been determined. Regulation of inducible enzyme activity could be mediated by events related to transcription, translation, or enzyme activation. For the purpose of studying galactose pathway induction and its regulation, we have developed an immunoprecipitation assay that enables us to detect the GAL7 specified uridyl transferase polypeptide in yeast extracts and among the polypeptides synthesized in an RNA-dependent in vitro translation system. Use of this immunoprecipitation assay in conjunction with in vivo labeling experiments demonstrates the presence of [(3)H]leucine-labeled transferase in extracts prepared from cells grown in galactose but not from cells grown in glucose. This galactose-specific induction of transferase polypeptide is mediated by the de novo appearance of a functional mRNA species whose synthetic capacity is detectable by the combination of in vitro translation and immunoprecipitation. The appearance of functional transferase mRNA depends on wild-type expression of the positive regulatory gene, GAL4. Cells carrying a nonsense (amber) mutation in the GAL4 gene fail to produce the transferase mRNA, whereas a nonsense suppressor of the GAL4 amber mutant regains the galactose-specific mRNA response. Our results establish that the induction of the GAL7 specified uridyl transferase activity is mediated by de novo appearance of a functional mRNA and that this galactose-specific response is dependent on a wild-type GAL4 gene product

Engineering model 8-cm thruster subsystem

An Engineering Model (EM) 8 cm Ion Thruster Propulsion Subsystem was developed for operation at a thrust level 5 mN (1.1 mlb) at a specific impulse 1 sub sp = 2667 sec with a total system input power P sub in = 165 W. The system dry mass is 15 kg with a mercury-propellant-reservoir capacity of 8.75 kg permitting uninterrupted operation for about 12,500 hr. The subsystem can be started from a dormant condition in a time less than or equal to 15 min. The thruster has a design lifetime of 20,000 hr with 10,000 startup cycles. A gimbal unit is included to provide a thrust vector deflection capability of + or - 10 degrees in any direction from the zero position. The EM subsystem development program included thruster optimization, power-supply circuit optimization and flight packaging, subsystem integration, and subsystem acceptance testing including a cyclic test of the total propulsion package