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.     

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     

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.     

Influence of DNA on the rate of ligand substitution in platinum(II) terpyridine complexes

The kinetics of substitution of pyridine or 2-methylpyridine, by iodide or thiourea, in the complexes [Pt(4'-R'terpy)(2-Rpy)](BF4)2 (R' = o-tolyl or H; R = H or CH3) has been studied, at 25 degrees C, pH 7, and various ionic strength values, in the presence of and without calf thymus DNA. The reactions occur in one observable step, and plots of kobsd against nucleophile concentration give straight lines with zero intercepts. DNA inhibits all the reactions studied without altering the rate law; the second-order rate constants k2 decrease systematically on increasing DNA concentration and are larger at higher ionic strength values. Partitioning of the ionic reactants in solution on electrostatic grounds can account for this kinetic effect in the reaction with iodide. Iodide is kept off the double helix proximity while the dicationic complexes concentrate on it. The inhibiting effect observed for the uncharged reagent thiourea can be related to the specific binding mode of the complexes to DNA. The complexes studied are effective intercalators to double helix, and this type of interaction, which prevents attack of thiourea at platinum, decreases their actual concentration in solution. The inhibiting effect is larger for [Pt(terpy)(py)]2+ that is a better intercalator. Likewise, the decrease in the rate of substitution of 2-Rpy, at a given [DNA] on decreasing ionic strength, is due to the influence of ionic strength on the complex-DNA interactions.     

Effect of a Weak Electrolyte on the Critical Micellar Concentration of Sodium Dodecyl Sulfate

The critical micellar concentration of sodium dodecyl sulfate is strongly altered bytris(hydroxy-methyl)methylammonium ions. The effect of buffer solutions containing this weak electrolyte as the counterion source has been studied using various concentrations of the acid–base system as well as modifying the pH. Results show that counterion concentrations ranging from 0 to 340 × 10⁻³M induce an appreciable diminution of the critical micellar concentration from 8 to 0.7 × 10⁻³M. The analysis of data suggests that the critical micellar concentration of sodium dodecyl sulfate depends on the concentration of weak electrolytes in a way very similar to that of strong electrolytes.     

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.     

The influence of subinhibitory concentrations of ampicillin and vancomycin on physico-chemical surface characteristics of Enterococcus faecalis 1131

The effects of growth in the presence of sub-inhibitory concentrations of ampicillin and vancomycin on physico-chemical cell surface properties of Enterococcus faecalis 1131 have been determined. Growth in the presence of antibiotics yielded increased exposure of nitrogen and oxygen at the cell surface, proportional to the amount of antibiotic added to the growth medium, probably as a result of progressive removal of lipoteichoic acid (LTA) by ampicillin and vancomycin. Bacterial isoelectric points (IEP's), derived from particulate microelectrophoresis at different suspension pH, increased concurrently. Water contact angles on bacterial lawns only varied slightly in the presence of antibiotic during growth, whereas formamide contact angles after growth in the presence of vancomycin were significantly higher than after growth in the absence of this antibiotic, yielding a strongly electron-donating character of the cell surface. Surface thermodynamical analyses indicated favourable conditions for adhesion to hexadecane and chloroform, but more negative values of interaction free energies did not necessarily coincide with increased adhesion. Bacterial adhesion to hexadecane and chloroform increased when the pH of the bacterial suspension approached the isoelectric point of the organisms, because of the minimal electrostatic interactions.     

On the symmetries of the Hubbard model: application to finite-size clusters

We evaluate the density of states of the Hubbard model at half filling on a four-site cluster with periodic boundary conditions. The results are obtained from an exact diagonalization study of the model, where theSU(2) symmetry, the Yang\(\widetilde{SU}(2)\) pseudospin symmetry and the translational invariance of the Hamiltonian are explicitly taken into account.