Laser-Generated Plasmas as X-Ray Sources in the keV-Range

This report will give an introduction to the X-line emission processes in laser-generated plasmas according to a plasma physical point of view. After a short discussion of the experimental results using laser pulses in the range of ? 10 J and irreadiances of 1 to 100 MW/cm² and of first conclusions about the temperature scaling and the dependence of the emission concerning the atomic number of the target material some models of laser-generated plasmas are analysed. The simple hot-spot model neglects any hydrodynamics and only solves for the rate equations. We discuss the underlying collisional-radiative model and evaluate the numerical results of a more complete model for the spatial and temporal plasma evolution including the hydrodynamics. The applications of such plasmas as small, strong, short sources of X-rays in the keV range is discussed with regard to the lithographic replication of sub-μm structures and to the EXAFS spectroscopy. Laser-generated plasmas are compared with conventional X-ray tubes (with rotating anode) and with synchrotrons. The question of amplified spontaneous emission in the XUV range (superradicant X-ray sources) is only shortly touched upon. In conclusion some comments are given to the recoil momentum effects of the ablating plasma on the target are given (rocket model).     

Theory of surface force-constant changes in body-centered cubic lattices

A calculation has been made of force-constant changes at the (100) and (110) surfaces of body-centered cubic crystals. A model consisting of first, second and third-neighbor Lennard-Jones interactions together with harmonic angle-bending interactions is employed. The parameters characterizing the interactions are chosen to fit the equilibrium lattice spacing, the elastic constants, and certain phonon frequencies at high symmetry points in the Brillouin zone. The procedure consists of first calculating the static displacements produced by the creation of the surface and then calculating the change in force constants produced by the cubic and quartic anharmonic terms in the potential energy. Specific results have been obtained for chromium, iron, tungsten, and molybdenum.     

Theory of surface polaritons in n-type silicon in the presence of a dc current,including the electron thermal pressure gradient

A theoretical investigation has been made of the effect of a drift current, including the electron thermal pressure gradient, on surface polaritons in n-type Si. The polariton propagation and drift current directions are taken to be either parallel or antiparallel. Retardation is included, but damping is neglected. The specular reflection approach of Kliewer and Fuchs is used to obtain the polariton dispersion relation. The results show that the drift current and surface polaritons interact, leading to evanescent waves for certain frequencies. However, no wave amplification is obtained.     

Countercurrent gas-liquid flow in parallel vertical tubes

The subject of this paper is the flow between an upper reservoir, containing a liquid, and a lower reservoir, containing a gas, interconnected by parallel vertical tubes. The characteristics of the combined system are predicted from a knowledge of the behavior of flow in individual tubes. Numerous modes of possible operation are described analytically and demonstrated experimentally. The effects of system geometry, changes in gas supply characteristics, operating procedure and two-phase flow regimes on the transitions between modes and system stability are presented. Predictions are made for the limiting case of a large number of identical parallel channels.     

Compressibility effects on waves in stratified two-phase flow

Ardron (1980) presented both one-dimensional and two-dimensional analyses of wave propagation in horizontal stratified two-phase flow. He compared the two approaches and concluded that the comparison helped to improve confidence in the use of one-dimensional approximations for the analysis of complex systems such as nuclear reactors.There are several assumptions in Ardron's developments. When alternative assumptions are made the results change. By examining the consequences of several possible assumptions we have learned from this example that considerable care may be necessary in the reduction of a multi-dimensional two-phase flow problem to a simpler form.This paper presents a more complete two-dimensional solution of this problem and discusses the limitations of the approximate solutions.     

Correlated electromigration of H in the switchable mirror YH(3-delta)

Electromigration of hydrogen in YH(3-delta) is studied by exploiting the H concentration dependence of the optical transmission of YH(3-delta). We find the effective valence Z* of H in YH(3-delta) to be negative. Its value is dominated by a huge wind-force-like term, i.e., Z* approximately K/rho, with K approximately -60 mOmega cm. This value is 3 orders of magnitude larger than typical for H in metals. In an Arrhenius plot, the ratio of hydrogen and electron fluxes extrapolates to unity at infinite temperature, suggesting a one-to-one correlation of hydrogen and electron hopping. We discuss our results in the light of strong electron correlation theories which predict each proton to bind two electrons in a sort of Zhang-Rice singlet.     

Cluster chemistry. partial hydrogenation of coordinated isocyanide on a ruthenium cluster carbonyl.

Addition of dihydrogen to Ru₃(CO)₁₁(CNBu^t) affords HRu₃(CO)₉(HC:NB as the major product; this complex and four other minor products were identified from their IR, NMR and mass spectra.     

Some primitives for the portable programming of array and vector processors

A high-level language for array and vector processors is analyzed by the methods of denotational semantics. The analysis leads to the identification of a set of primitives suitable for the portable programming of array and vector processors. Discussion of the primitives includes consideration of the efficiency with which they may be implemented on different machines, and their possible application to portable programming, the design of intermeiate languages, and the design of future array and vector processors.     

Orthogonal designs II

Orthogonal designs are a natural generalization of the Baumert-Hall arrays which have been used to construct Hadamard matrices. We continue our investigation of these designs and show that orthogonal designs of type (1,k) and ordern exist for everyk < n whenn = 2 ^t+2?3 andn = 2 ^t+2?5 (wheret is a positive integer). We also find orthogonal designs that exist in every order 2n and others that exist in every order 4n. Coupled with some results of earlier work, this means that theweighing matrix conjecture ‘For every ordern ≡ 0 (mod 4) there is, for eachk ?n, a square {0, 1, ? 1} matrixW = W(n, k) satisfyingWW ^t =kIn’ is resolved in the affirmative for all ordersn = 2^t+1?3,n = 2^t+1?5 (t a positive integer). The fact that the matrices we find are skew-symmetric for allk < n whenn ≡ 0 (mod 8) and because of other considerations we pose three other conjectures about weighing matrices having additional structure and resolve these conjectures affirmatively in a few cases. In an appendix we give a table of the known results for orders ? 64.