On the Interface Between LENS® Deposited Stainless Steel 304L Repair Geometry and Cast or Machined Components

Laser Engineered Net Shaping™ (LENS®) is being evaluated for use as a metal component repair/modification process. A component of the evaluation is to better understand the characteristics of the interface between LENS deposited material and the substrate on which it is deposited. A processing and metallurgical evaluation was made on LENS processed material fabricated for component qualification tests. A process parameter evaluation was used to determine optimum build parameters and these parameters were used in the fabrication of tensile test specimens to study the characteristics of the interface between LENS deposited material and several types of substrates. Analyses of the interface included mechanical properties, microstructure, and metallurgical integrity. Test samples were determined for a variety of geometric configurations associated with interfaces between LENS deposited material and both wrought base material or previously deposited LENS material. Thirteen different interface configurations were fabricated for evaluation representing a spectrum of deposition conditions from complete part build, to hybrid substrate-LENS builds, to repair builds for damaged or re-designed housings. Good mechanical properties and full density were observed for all configurations. When tested to failure, fracture occurred by ductile microvoid coalescence. The repair and hybrid interfaces showed the same metallurgical integrity as, and had properties similar to, monolithic LENS deposits.Mechanical Engineerin

Energy Conversion Alternatives Study (ECAS), General Electric Phase 1. Volume 2: Advanced energy conversion systems. Part 3: Direct energy conversion cycles

For abstract, see N76-23680

The ubiquitin-proteasome pathway in cancer.

Degradation by the 26S proteasome of specific proteins that have been targeted by the ubiquitin pathway is the major intracellular non-lysosomal proteolytic mechanism and is involved in a broad range of processes, such as cell cycle progression, antigen presentation and control of gene expression. Recent work, reviewed here, has shown that this pathway is often the target of cancer-related deregulation and can underlie processes, such as oncogenic transformation, tumour progression, escape from immune surveillance and drug resistance

Effects of Scale-Free Disorder on the Anderson Metal-Insulator Transition

We investigate the three-dimensional Anderson model of localization via a modified transfer-matrix method in the presence of scale-free diagonal disorder characterized by a disorder correlation function $g(r)$ decaying asymptotically as $r^{-\alpha}$. We study the dependence of the localization-length exponent $\nu$ on the correlation-strength exponent $\alpha$. % For fixed disorder $W$, there is a critical $\alpha_{\rm c}$, such that for $\alpha < \alpha_{\rm c}$, $\nu=2/\alpha$ and for $\alpha > \alpha_{\rm c}$, $\nu$ remains that of the uncorrelated system in accordance with the extended Harris criterion. At the band center, $\nu$ is independent of $\alpha$ but equal to that of the uncorrelated system. The physical mechanisms leading to this different behavior are discussed.Comment: submitted to Phys. Rev. Let

Spin ice in a field: quasi-phases and pseudo-transitions

Thermodynamics of the short-range model of spin ice magnets in a field is considered in the Bethe - Peierls approximation. The results obtained for [111], [100] and [011] fields agrees reasonably well with the existing Monte-Carlo simulations and some experiments. In this approximation all extremely sharp field-induced anomalies are described by the analytical functions of temperature and applied field. In spite of the absence of true phase transitions the analysis of the entropy and specific heat reliefs over H-T plane allows to discern the "pseudo-phases" with specific character of spin fluctuations and define the lines of more or less sharp "pseudo-transitions" between them.Comment: 18 pages, 16 figure

Critical Behaviour of 3D Systems with Long-Range Correlated Quenched Defects

A field-theoretic description of the critical behaviour of systems with quenched defects obeying a power law correlations $\sim |{\bf x}|^{-a}$ for large separations ${\bf x}$ is given. Directly for three-dimensional systems and different values of correlation parameter $2\leq a \leq 3$ a renormalization analysis of scaling function in the two-loop approximation is carried out, and the fixed points corresponding to stability of the various types of critical behaviour are identified. The obtained results essentially differ from results evaluated by double $\epsilon, \delta$ - expansion. The critical exponents in the two-loop approximation are calculated with the use of the Pade-Borel summation technique.Comment: Submitted to J. Phys. A, Letter to Editor 9 pages, 4 figure

Storage of light in atomic vapor

We report an experiment in which a light pulse is decelerated and trapped in a vapor of Rb atoms, stored for a controlled period of time, and then released on demand. We accomplish this storage of light by dynamically reducing the group velocity of the light pulse to zero, so that the coherent excitation of the light is reversibly mapped into a collective Zeeman (spin) coherence of the Rb vapor

The Causal Boundary of spacetimes revisited

We present a new development of the causal boundary of spacetimes, originally introduced by Geroch, Kronheimer and Penrose. Given a strongly causal spacetime (or, more generally, a chronological set), we reconsider the GKP ideas to construct a family of completions with a chronology and topology extending the original ones. Many of these completions present undesirable features, like those appeared in previous approaches by other authors. However, we show that all these deficiencies are due to the attachment of an ``excessively big'' boundary. In fact, a notion of ``completion with minimal boundary'' is then introduced in our family such that, when we restrict to these minimal completions, which always exist, all previous objections disappear. The optimal character of our construction is illustrated by a number of satisfactory properties and examples.Comment: 37 pages, 10 figures; Definition 6.1 slightly modified; multiple minor changes; one figure added and another replace