Energy and charge localization in irradiated DNA.

The relation between the site of energy deposition and the site of its biological action is an important question in radiobiology. Even at 77 degrees K, evidence is clear that these two sites must be separated since energy deposition is random but specific products are formed. Several processes that may contribute to this separation are: 1) hole migration and stabilization through deprotonation to give neutral oxidation product radicals; 2) electron trapping and transfer to form specific radical anions, possibly followed by protonation to give neutral reduction product radicals; and 3) recombination of spatially separated charges or radicals. These microscopic processes will be reviewed critically in an analysis using electron paramagnetic resonance spectroscopy (EPR) evidence for and against long-range transfer of energy and/or charge in frozen, hydrated DNA.     

A new system identification technique for harmonic decomposition

An extended and unifying system identification technique is presented for a class of systems that include all main signal models that arise in the harmonic decomposition problem. This technique unifies and extends the previously developed system identification techniques which are improvements on the Pisarenko harmonic decomposition (or, its spatial dual, MUSIC) as they arise in arrays of sensors. The advantages of the technique and some of its specializations include having no assumptions of stationarity on the stochastic processes involved. Another contribution of this technique is that it can also be used without any resort to probability theoretic concepts, thus bypassing the approximation of autocorrelations via time averages, yielding the system parameters exactly. This technique can be utilized to determine the dominant modes of vibrations of flexible structures as well. An analogy is established between arrays of sensors for target signal returns and those that can be used for vibrations in flexible structures. This enables the results developed for each one of these problems to be applied to the other     

Direct integration methods in dynamic problems of structural mechanics

A method of direct integration with respect to time is proposed to solve dynamic problems of structural mechanics and comparison with the well-known methods is presented.     

Residual stresses and endurance strength under tension-compression in the conditions of stress concentration

Residual stresses and endurance strength of specimens with stress concentrators are considered. The results obtained make it possible to predict the fatigue limit of strengthened parts with concentrators in the case of tension-compression.     

Statistical analysis of experimental study results on low-cycle fatigue resistance for the EI698-VD high-temperature alloy

The results of low-cycle fatigue tests of smooth cylindrical specimens made of the EI698-VD nickel-base high-temperature alloy widely used in aircraft engine industry are considered statistically. The influence of such factors as an initial level of mechanical properties, operating time and temperature of tests is evaluated. The experimental data on low-cycle fatigue (LCF) are used when determining the cyclic life for disks.     

Optical, X-ray and γ-ray observations of compact objects in globular clusters

In the past three years, a new era of study of globular clusters has begun with multiwavelength observations from the current generation of astronomical telescopes in space. We review the recent results obtained from our studies of compact binaries and x-ray sources in globulars with ROSAT and HST as well as our balloon-borne hard x-ray telescope EXITE and ground-based observations (CTIO). With ROSAT, we have obtained the most sensitive high resolution soft x-ray images of clusters which show multiple low luminosity sources in cluster cores that are likely indicative of the long-sought population of cataclysmic variables (CVs). We have obtained deep H images of two clusters with HST and found CV candidates for 3 of the ROSAT sources in the core of NGC 6397. New CTIO imaging and spectroscopy of two ‘dim source’ fields in ω-Cen are also described. With EXITE we carried out the first hard x-ray imaging observations of the cluster 47 Tuc; such studies can ultimately limit the populations of millisecond pulsars and pulsar emission mechanisms. A long ROSAT exposure on 47 Tuc also shows probable cluster diffuse emission, possibly due to hot gas from ablating millisecond pulsars. Multiwavelength studies of globular clusters may provide new constraints on problems as diverse as the origin of CVs and LMXBs and the origin of hot gas in globulars.     

Megahertz power converters for specific power systems

Some of the problems in the development of pulsewidth power converters when the switching frequency is increased from hundreds of kilohertz to tens of megahertz are highlighted. The major goal is the establishment of a ten megahertz power chain designed to operate in a distributed system from a DC power bus of 24 to 48 V. Available components and materials are discussed, and possible topologies-flyback, forward, push-pull forward, and buck converters-are examined. The performance criteria chosen for this analysis are, in the order of preference, output requirements, size and weight, efficiency, and cost     

Convective motions in liquid metals for material processings. Numerical simulation of oscillation regimes and effect of rotation

The paper is concerned with the numerical simulation and the analysis of some kinds of flow regimes which can develop in Bridgman and Czochralski systems for material processings. The flows in the liquid phase are investigated considering two-dimensional and axisymmetric models. The time-dependent regimes were studied for a zero-Prandtl-number fluid layer confined inside a two-dimensional cavity of aspect ratio (length-to-height) A=4, involving a stress-free upper surface and submitted to a horizontal temperature gradient. The range of Grashof number was varied up to the conditions at which the flow goes from oscillatory to chaotic type behaviours. The combined influence of the temperature gradients and of the rotations of the crucible and of the seed/crystal was investigated for a Czochralski model. The axisymmetric regimes were studied for a Pr_m=0.015 liquid melt confined inside a cylindrical crucible of aspect ratio (height-to-radius) A_m=2, and coupled to a viscous encapsulant liquid layer (10<Pr_e<1200) of aspect ratio A_e=0.5. A number of steady and (transient) time-dependent flow patterns are identified.     

Responses of the upper middle atmosphere (60–110 km), to the first two stratwarms of map (1982/3, 1983/4)

The global developments of the stratospheric events (～20–50 km) are briefly described using balloon and satellite data. Winds data from L.F. drift (52°N, 15°E, Europe) for heights of 90–100 km, and from M.F. radar (52°N, 107°W, Canada) for heights of 60–110 km are then compared with the stratospheric morphology.Data for 1982/3 and 1983/4 show that the planetary wave activity and warmings produced strong westward and southward perturbations in the radar winds. Satellite data from 0.1, 0.01 hPa are consistent with these winds; and also show smaller scale structures in the mesosphere than the stratosphere. The semi-diurnal tide responded strongly to the atmospheric disturbances in Europe and Canada: for the latter vertical wavelength changes occurred for heights of 70–100 km. However the correlation between these tidal fluctuations was not high indicating that the tidal adjustments were continental rather than hemispheric.     

Interpretation of hard X-ray images during the impulsive phase of a limb flare

We show that the observations of a limb flare, in which a hard X-ray (16–30 keV) source is seen at the boundary between two interacting magnetic structures, indicate the presence of hot (T ? 6 × 10⁷ K) plasma within the region. Non thermal bremsstrahlung processes do not agree with these observations. We discuss the possible causes of the heating.