Concurrent processing simulation of the space station

The development of a new capability for the time-domain simulation of multibody dynamic systems and its application to the study of a large angle rotational maneuvers of the Space Station is described. The effort was divided into three sequential tasks, which required significant advancements of the state-of-the art to accomplish. These were: (1) the development of an explicit mathematical model via symbol manipulation of a flexible, multibody dynamic system; (2) the development of a methodology for balancing the computational load of an explicit mathematical model for concurrent processing; and (3) the implementation and successful simulation of the above on a prototype Custom Architectured Parallel Processing System (CAPPS) containing eight processors. The throughput rate achieved by the CAPPS operating at only 70 percent efficiency, was 3.9 times greater than that obtained sequentially by the IBM 3090 supercomputer simulating the same problem. More significantly, analysis of the results leads to the conclusion that the relative cost effectiveness of concurrent vs. sequential digital computation will grow substantially as the computational load is increased. This is a welcomed development in an era when very complex and cumbersome mathematical models of large space vehicles must be used as substitutes for full scale testing which has become impractical

Crystalline To Amorphous Transformation In Ion-implanted Silicon: A Composite Model

The transformation of silicon to the amorphous state by implanted ions was studied both experimentally and theoretically. Experimentally, the amount of transformed silicon and the critical ion dose necessary to amorphized the entire implanted layer were determined by ESR. How the critical dose varies with ion mass (Li, N, Ne, Ar, and Kr), ion energy (20-180 keV), and implant temperature (77-475 K) was determined. Theoretically, several phenomenological models were used to analyze these data. The overlap-damage model was used to determine the critical dose from the data, the size of the amorphous region around the ion track, and the degree of overlap damage required for amorphization. For all implants, the first ion created only predamage, while the second or third ion into the same region caused the amorphous transformation. The critical-energy-density model was in good agreement with the measured critical doses. This model assumed that a region would become amorphous if the energy density deposited into atomic processes by the ions exceeded the critical energy density of 6x1023 eV/cm3. For high-temperature implantations, out-diffusion models can explain the temperature dependence of the critical dose. Although the analysis is not completely definitive, the critical-energy-density model may also be valid at high temperature if diffusion of the damage energy is taken into account. This out-diffusion of energy from around the ion track occurs via a thermally activated process. Probably, the energy moves with the out-diffusion of the vacancies from the ion track

Strain Effects On The ESR Spectrum From Antimony Donors In Germanium

The electron-spin-resonance spectra from surface-strained (but not externally stressed) antimony-doped germanium are investigated in detail. Experimental data are given for the linewidth, line asymmetry, and line-shape reversal feature as well as for the changes in donor concentration, temperature, and surface conditions. The donors of interest occur in a surface layer several microns thick. A theoretical analysis is based on the Kohn-Luttinger formulation for a shallow donor electron, which is forced by surface strain to predominately occupy a [111] conduction-band valley minimum. A substantial distribution in strain among the donor sites is necessary to account for the line-structure features. These features are predicted by a distribution function, which is calculated by using a narrowed Lorentzian line for a homogeneous line shape and a Gaussian strain distribution that determines the inhomogeneous broadening caused by strain-induced g-value variations. The one order of magnitude increase in linewidth with angle is attributed primarily to a g-3 dependence of the linewidth on strain. The asymmetry shape ratio of about 3 is attributed primarily to variations in the valley-population probabilities at different donor sites. The line-shape reversal feature is caused by an angular-dependent variation in the change of the g value with valley-population coefficients. For detailed calculations, distributed strain along the predominately occupied valley axis is assumed. It is found that the average compressive strain along the [111] axis is 10-4 with an accuracy of about 40% and that the Gaussian strain width is 0.6x10-4. This average strain corresponds to a predominant valley occupation of 99%. Our analysis can be used as a semiquantitative tool for determining strain conditions in Ge(Sb). © 1975 The American Physical Society

Snake-Oil Security Claims the Systematic Misrepresentation of Product Security in the E-Commerce Arena

The modern commercial systems and software industry in the United States have grown up in a snake-oil salesman\u27s paradise. The largest sector of this industry by far is composed of standard commercial systems that are marketed to provide specified functionality (e.g. Internet web server, firewall, router, etc.) Such products are generally provided with a blanket disclaimer stating that the purchaser must evaluate the suitability of the product for use, and that the user assumes all liability for product behavior. In general, users cannot evaluate and cannot be expected to evaluate the security claims of a product. The ability to analyze security claims is important because a consumer may place unwarranted trust in the security abilities of a web server (or other computer device) to perform its stated purpose, thereby putting his own organization at risk, as well as third parties (consumers, business partners, etc.) All but the largest and most capable organizations lack the resources or expertise to evaluate the security claims of a product. More importantly, no reasonable and knowledgeable person would expect them to be able to do so. The normal legal presumptions of approximate equality of bargaining power and comparable sophistication in evaluating benefits and risks are grievously unjust in the context of software security. In these transactions, it is far wiser to view the general purchaser, even if that purchaser is a sizable corporation, as an ignorant consumer. Hence, often purchasers accept what appear to be either implied merchantability claims of the vendor or claims of salespersons\u27 made outside of the context of a written document. These claims frequently have little, if any, basis in fact. These standard commercial systems form the bulk of the critical infrastructure of existing Internet functionality and e-commerce systems. Often, these systems are not trustworthy, yet the use of these systems by misinformed purchasers created massive vulnerability for both purchasers and third parties (including a substantial fraction of both U.S. and international citizens). The frequent disclosure of individual credit card information from supposedly secure commercial systems illustrates an aspect of this vulnerability and raises serious questions concerning the merchantability of these systems. While it is impossible to avoid all risks, they can be reduced to a very small fraction of their current level. Vendors have willfully taken approaches and used processes that do not allow assurance of appropriate security properties, while simultaneously and recklessly misrepresenting the security properties of their products to their customers

Electron Spin Resonance In Argon-ion-implanted Silicon

A new paramagnetic center with g = 2.0029 is observed, in both n- and p-type silicon after they are heavily implanted (higher than 1017 ions/cm2) with 150-keV argon ions. © 1973 American Institute of Physics

Differentiating Phrase Structure Parsing and Memory Retrieval in the Brain

On some level, human sentence comprehension must involve both memory retrieval and structural composition. This study differentiates these two processes using neuroimaging data collected during naturalistic listening. Retrieval is formalized in terms of multiword expressions while structure-building is formalized in terms of bottom-up parsing. The results most strongly implicate Anterior Temporal regions for structure-building and Precuneus Cortex for memory retrieval

Book Reviews

Professor Hicks has done for a few great lawyers and \u27a few great books what it is hoped he may do for many more lawyers and many more books. Out of his full and intimate knowledge of the literature of our profession he has gathered and presented to us in most entertaining fashion the human as well as the intellectual and professional characteristics of a full half dozen men, each of whom holds a somewhat unique place in the development of Anglo-Saxon law

Spectroscopic ellipsometry as a sensitive monitor of materials contamination

Spectroscopic ellipsometry is demonstrated to be extremely sensitive to contamination layers in the thickness range from 0.1 nm to 10 microns. In the present experiments we deposit either a thin lubricating oil (WD-40) or mineral oil continuously onto Ir, Cu, Al, Au, and V substrates from a bubbler, and monitor its thickness growth from sub-nanometer to tens of nanometers as a function of time. Re-evaporation of contaminant oils is also monitored in real-time by ellipsometry

Rapidly decaying supernova 2010X: A candidate ".Ia" explosion

We present the discovery, photometric, and spectroscopic follow-up observations of SN 2010X (PTF 10bhp). This supernova decays exponentially with τ_d = 5 days and rivals the current recordholder in speed, SN 2002bj. SN 2010X peaks at M_r = −17 mag and has mean velocities of 10,000 km s^(−1). Our light curve modeling suggests a radioactivity-powered event and an ejecta mass of 0.16M_⊙. If powered by Nickel, we show that the Nickel mass must be very small (≈0.02 M_⊙) and that the supernova quickly becomes optically thin to γ -rays. Our spectral modeling suggests that SN 2010X and SN 2002bj have similar chemical compositions and that one of aluminum or helium is present. If aluminum is present, we speculate that this may be an accretion-induced collapse of an O-Ne-Mg white dwarf. If helium is present, all observables of SN 2010X are consistent with being a thermonuclear helium shell detonation on a white dwarf, a “.Ia” explosion. With the 1 day dynamic-cadence experiment on the Palomar Transient Factory, we expect to annually discover a few such events