Production of double-sided targets by electrodeposition: initial evaluation and optimization of performance

The Detector for Advanced Neutron Capture Experiments (DANCE) located at the Los Alamos Neutron Science Center is used to perform neutron capture cross-section measurements on radioactive and non-radioactive isotopes. Thin actinide targets for the DANCE detector are typically prepared by molecular deposition on thin titanium foils. For the preparation of double-sided deposits, a Teflon electrodeposition cell was constructed with two liquid chambers with a foil substrate in between, allowing electrodeposition on both sides of the foil. We have been studying the electrodeposition of uranium from isopropyl alcohol solutions using this cell. Effects of acid composition, uranium concentration, current, and deposition time will be described.     

Fusion-fission of heavy and superheavy nuclei

The process of fusion-fission of heavy and superheavy nuclei (SHE) with Z=82–122 formed in the reactions with ⁴⁸Ca and ⁵⁸Fe ions at energies near and below the Coulomb barrier has been studied. The experiments were carried out at the U-400 accelerator of the Flerov Laboratory of Nuclear Reactions (JINR) and at the XTU Tandem accelerator of the National Laboratory of Legnaro (LNL) using the time-of-flight spectrometer of fission fragments CORSET and the neutron multidetector DEMON. As a result of the experiments, mass and energy distributions (MED) of fission fragments; fission, quasifission, and evaporation residue cross sections; and multiplicities of neutrons and γ-quanta and their dependences on the mechanism of formation and decay of compound systems have been studied.     

On computing minimal realizable spectral radii of non‐negative matrices

For decades considerable efforts have been exerted to resolve the inverse eigenvalue problem for non‐negative matrices. Yet fundamental issues such as the theory of existence and the practice of computation remain open. Recently, it has been proved that, given an arbitrary (n–1)‐tuple ?? = (λ₂,…,λ_n) ∈ ?^n–1 whose components are closed under complex conjugation, there exists a unique positive real number ?(??), called the minimal realizable spectral radius of ??, such that the set {λ₁,…,λ_n} is precisely the spectrum of a certain n × n non‐negative matrix with λ₁ as its spectral radius if and only if λ₁ ? ?(??). Employing any existing necessary conditions as a mode of checking criteria, this paper proposes a simple bisection procedure to approximate the location of ?(??). As an immediate application, it offers a quick numerical way to check whether a given n‐tuple could be the spectrum of a certain non‐negative matrix. Copyright © 2004 John Wiley & Sons, Ltd.     

Irreducible representations of Virasoro-toroidal Lie algebras

Toroidal Lie algebras and their vertex operator representations were introduced in [MEY] and a class of indecomposable modules were investigated. In this work, we extend the toroidal algebra by the Virasoro algebra thus constructing a semi-direct product algebra containing the toroidal algebra as an ideal and the Virasoro algebra as a subalgebra. With the use of vertex operators and certain oscillator representations of the Virasoro algebra it is proved that the corresponding Fock space gives rise to a class of irreducible modules for the Virasoro-toroidal algebra.To A. John Coleman on the occasion of his 75th birthday     

Regioselectivity in the photochemical ring contraction of 4-diazopyrazolidine-3,5-diones to give aza-β-lactams

The photochemical decomposition of unsymmetrically substituted 4-diazopyrazolidine-3,5-diones leads to aza-β-lactams, and provides some indication of the relative migratory aptitude of nitrogen groups in the Wolff rearrangement.     

Frequency discrimination in the monkey

This study evaluated frequency discrimination ability in 11 monkeys over an extended period of time using a repeating-standard procedure and the method of constant stimuli. The intersubject variability of the difference limens for frequency (delta F) was large, as reported by other investigators, but similar in magnitude to the variability of the difference limens for intensity (delta I) from three of the same subjects in an intensity discrimination experiment. Continued training generally resulted in a rapid decrease in delta F's, followed by a longer-term, slower decrease. For one subject delta F's slowly decreased throughout a 190-week time period. This long-term training effect was specific to frequency discrimination; a similar effect was not observed for the same subject tested in an intensity discrimination experiment. Finally, delta F's from the well-trained monkeys of this study were larger than monkey delta F's from this laboratory reported in an earlier study, and than human delta F's. An anatomical explanation for the human/monkey delta F magnitude difference is explored.