Angular factorization of matrices

Let Q denote a selfadjoint matrix (or operator of finite rank). The factorization of I + Q into the form $\text{I + Q = (I ? W) D(I ? W}{}^1\text{)}$ is considered. The well-known case where W is constrained to be lower triangular while D is diagonal is extended to quadrangular and other generalized-canonical forms. The case where Q is not selfadjoint is also developed. Applications for these results may be found in the realm of multivariate-stochastic approximation, and signal extraction.     

Breakup temperature of target spectators in 197Au + 197Au collisions at E/A = 1000 MeV

Breakup temperatures were deduced from double ratios of isotope yields for target spectators produced in the reaction ¹⁹⁷Au + ¹⁹⁷Au at 1000 MeV per nucleon. Pairs of ^3,4He and ^6,7Li isotopes and pairs of ^3,4He and H isotopes (p, d and d, t) yield consistent temperatures after feeding corrections, based on the quantum statistical model, are applied. The temperatures rise with decreasing impact parameter from 4 MeV for peripheral to about 10 MeV for the most central collisions. The good agreement with the breakup temperatures measured previously for projectile spectators at an incident energy of 600 MeV per nucleon confirms the universality established for the spectator decayat relativistic bombarding energies. The measured temperatures also agree with the breakup temperatures predicted by the statistical multifragmentation model. For these calculations a relation between the initial excitation energy and mass was derived which gives good simultaneous agreement for the fragment charge correlations. The energy spectra of light charged particles, measured at τ_lab = 150°, exhibit Maxwellian shapes with inverse slope parameters much higher than the breakup temperatures. The statistical multifragmentation model, because Coulomb repulsion and sequential decay processes are included, yields light-particle spectra with inverse slope parameters higher than the breakup temperatures but considerably below the measured values. The systematic behavior of the differences suggests that they are caused by light-charged-particle emission prior to the final breakup stage.     

On the use of bioluminescence for estimating shear stresses over a rippled seabed

The bioluminescence emitted by micro-planktonic organisms has been adopted to detect shear stresses within oscillating flows over small scale bedforms. To this aim, an experimental campaign has been planned in order to optimize optical detectors and to address peculiar needs of biological organisms.     

Fibre-end micro-lens system for endoscopic erbium-laser surgery applications

A sapphire micro-lens system in combination with a zirconium-fluoride (ZrF₄) fibre has been designed and constructed as a surgical tool for focusing Er:YAG-laser radiation. It both refocuses the laser radiation transmitted through a 350 µm core fibre to a spot diameter of 570 µm at a working distance of 7.6 mm, and protects the distal fibre end from damage. An accurate and uncomplicated visualization of the focus position of the erbium-laser beam is realized by coupling a HeNe aiming laser into the cladding of the fibre. In vitro cutting experiments reveal the high cutting precision with minimal thermal damage of the surrounding tissue and the high damage resistance of the system. It may render the use of the erbium laser possible in a wide range of endoscopic applications.     

Production of an 8.0 MeV 7Be ion beam at the Naples TTT-3 accelerator

For an improved determination of the ⁷Be(p, γ)⁸B absolute cross section, the reaction is studied in inverse kinematics. The study involves a ⁷Be radioactive ion beam of 8.0 MeV, a windowless H2 gas target, and an efficient recoil separator for the detection of the ⁸B residual nuclides. The techniques used to produce such a beam as well as the first direct observation of ⁸B are reported.     

A mountain pass method for the numerical solution of semilinear wave equations

Summary It is well-known that periodic solutions of semilinear wave equations can be obtained as critical points of related functionals. In the situation that we studied, there is usually an obvious solution obtained as a solution of linear problem. We formulate a dual variational problem in such a way that the obvious solution is a local minimum. We then find additional non-obvious solutions via a numerical mountain pass algorithm, based on the theorems of Ambrosetti, Rabinowitz and Ekeland. Numerical results are presented.Research supported in part by grant DMS-9208636 from the National Science FoundationResearch supported in part by grant DMS-9102632 from the National Science Foundation     

Studies in Sol-Gel Glasses with Incorporation of Cu and Fe, using PAS, X-ray Diffraction and EPR

SiO₂ Glasses with incorporation of either Cu or Fe were prepared by the sol-gel process and annealed in air at temperatures within the range of 100 to 500°C. The samples were characterized using Visible Photoacoustic Absorption Spectroscopy (PAS), X-ray powder diffraction and Electron Paramagnetic Resonance (EPR). Under the annealing both systems show significant changes in composition, producing an evolution in the optical absorption spectra. In both systems, the formation of the metal oxide particles is observed after annealing at or above 300°C. The optical and EPR spectra are interpreted in terms of the coordination of the metal ions using the ligand field theory. It is observed that the color of the samples has strong change with both the type of metal incorporated and with the annealing temperature.     

A contribution to the characterization of the aerosol sources in São Paulo

Fine and coarse particles in suspension in the atmosphere were collected on two Teflon filters with a dichotomous sampler. The concentration of Al, Br, Ca, Ce, Cl, Co, Cr, Fe, K, La, Mn, Na, P, Pb,, S, Sb, Sc, Se, Si, Sm, Th, V and Zn was determined by ED-XRF and INAA. The elemental concentration was analyzed by means of linear correlation coefficients, enrichment factors and principal factors analysis in order to identify the aerosol sources. The main sources of the aerosol particles were the marine ones, resuspended soil, fuel-oil combustion, phosphatic rocks, refuse incineration and residual high-temperature processes.     

Capillary GC-MS — Stable isotope dilution analysis of methylmalonic acid in plasma: A candidate reference method for the diagnosis and the follow-up of methylmalonic acidaemias

Summary Because methylmalonic acid (MMA) accumulates in the body fluids of patients suffering from inherited metabolic disorders involving its pathway, the quantitation of this metabolite is not only fundamental to diagnosis but is also important in the follow-up of affected patients under treatment.We describe the method set up and used in our laboratory for the measurement of MMA in body fluids and propose its application to plasma as the reference method for the biochemical diagnosis and follow-up of methylmalonic acidaemias.