EXOSAT spectra of some bright QSO's

This paper reports on EXOSAT observations of four bright QSO's and active galaxies. The QSO PHL 1657 has a simple spectrum that can be fit with power law plus some low energy absorption. A soft excess is observed for both MR 2251 and E 1352.24+1830. Finally, PKS 2126-158 was detected and the results are consistent with a 0.7 energy index.     

Optimal Design Strategy of Switching Converters Employing Current in jected Control

This paper analyzes a buck/boost regulator employing current-injected control (CIC). It reveals the complex interactions between the dc loop and the current-injected loop and underlines the fundamental principle that governs the loop gain determination. Three commonly used compensation techniques are compared. The integral and lead/lag compensation are shown to be most desirable for performance optimization and stability.     

Modeling international cooperation in human space exploration for the twenty-first century.

The policy process of international cooperation in space exploration. including optimistic and pessimistic scenarios for the twenty-first century, is modeled and examined in this study. In the optimistic scenario, international cooperation involves a balanced and interdependent distribution of capabilities between states, their respective national space agencies and communities of space scientists and space engineers. Cooperation is characterized by interstate participation in critical path components and joint research and development. In the pessimistic scenario, international cooperation is structured and dominated politically and economically by powerful states vis-a-vis weaker states. Cooperation is limited to coordination of separate nationally approved projects and augmentation of capabilities in noncritical path components. On the basis of these two scenarios, policy predictions and implications relevant to exploration missions in the twenty-first century, such as a human-tended lunar base and human missions to Mars, are presented and discussed.     

Low-harmonic three-phase inverters with nonpulsating terminalcurrents

A basic class of three-phase inverters with nonpulsating terminal currents, namely, the four-topology four-inductor four-capacitor class is derived and studied. The expressions of duty-ratios required for low-harmonic dc-to-three-phase-ac conversion, ranges of output voltage variation, and component stresses for given specifications of inverters are derived. The characteristics of inverters include low-harmonic power conversion, low component stresses, variable-frequency variable-amplitude output voltages of values both below and above the dc input value, and the use of minimum number of inductors to achieve nonpulsating terminal currents     

Changing world-changing nature of conflicts-a critical role formilitary radar

The upheaval in world geopolitical structure is changing the nature of international security and the nature of possible future conflicts. A review of the character of these future conflicts points to new critical roles for military radars. This paper is not an overview of all future military radar possibilities but rather it assesses the nature of future conflicts and identifies certain critical radar systems and technologies that are the keystone to favorable resolution of these conflicts     

Non-conservative forces on LAGEOS I and II

The behavior of the empirically determined along-track accelerations from the LAGEOS satellites has been attributed to a variety of physical phenomena. Of these, the models for Yarkovsky thermal drag, anisotropic reflectivity and Yarkovsky-Schach drag are dependent on the spin axis orientation of the satellite. This investigation explores the utilization of these models in an attempt to recover the spin axis orientation history, particularly for the LAGEOS I satellite.     

Modeling of liquid encapsulated gallium melts

Liquid encapsulation crystal growth from the melt plays an important role in space processing. Use of an encapsulant may avoid evaporation of volatile components and may control thermocapillary flow, which becomes important in microgravity. In the present work the fluid physics of encapsulated liquid gallium is studied analytically and numerically in preparation to forthcoming experiments. It is shown that flow in the viscous encapsulant is essentially negligible and that liquid encapsulation reduces flow velocities in the encapsulated electronic melt. Flow velocity in the gallium is the main parameter in the studies.     

Novel hybrid 12-pulse boost-type rectifier with controlled output voltage

Novel hybrid 12-pulse line interphase transformer (LIT) rectifier systems with integrated single-switch or two-switch boost-type output stage that ensure a constant output voltage independent of mains and load conditions are proposed for supplying actuators of future more electric aircraft. The principle of operation, the dimensioning, and the system control are discussed. The theoretical considerations are experimentally confirmed for a 10 kW laboratory prototype. Finally, the single-and the two-switch system are comparatively evaluated concerning the level of input current ripple, power factor, and overall efficiency.     

Computerized Medical Devices: Trends, Problems, and Safety

Virtually all of the medical devices utilizing electronics will contain a micro or minicomputer by 1990. These devices accounted for $7 billion in U.S. sales in 1984. Their capabilities can provide the means for new or greatly improved medical procedures, and ensure greater patient safety. However, these benefits can easily be compromised if ``computer safety' is not practiced in the design, manufacturing, testing and clinical use of these devices. Along with a trend to wider usage, the number of recalls of medical devices due to computer-related problems has approximately doubled in the last five years. ``Computer-caused' problems are often not recognized or reported as such, resulting in an underestimation of the prevalence of this type of problem. Our study of technical factors causing problems in computerized devices revealed that software quality assurance (SQA), the quality of the ac power, and electromagnetic interference are primary factors. Selected design and QA techniques that are well-known in military-aerospace industries can be used to prevent the most prevalent problems occurring in computerized medical devices, without significantly affecting overall device manufacturing costs.