Multielement atomic absorption analysis using Hadamard transform spectroscopy with a new computation and superposition procedure

The application of Hadamard transform spectroscopy (HTS) to analytical atomic spectroscopy has been investigated. A theoretical examination of the signal to noise ratio indicates that HTS offers a slight multiplex advantage over single slit scanning of the spectrum for the measurement of intense lines, as in atomic absorption, but is disadvantageous for measuring small signals in atomic emission and fluorescence. Using a simple HT spectrometer Mg and Pb were determined simultaneously by flame atomic absorption spectrometry. Sensitivities similar to those of conventional systems were obtained but, owing to instrumental imperfections and a short data collection time, detection limits were worse. Optimum system performance was obtained when the mask interval width was equal to the width of the image of the spectrometer entrance slit. Greater spectral detail was revealed by superposition of a set of computed spectra in which the starting point of each spectrum was displaced from the others by a distance less than the interval width of the Hadamard mask. This approach gave improved spectra without increased instrumental complexity.     

Balanced sets in an independence structure induced by a submodular function

A submodular (and non-decreasing) function on a set induces an independence structure; the notion of a “balanced” set in this situation helps us determine whether a given independence structure is induced by any submodular function other than its own rank function, answering a question of U. S. R. Murty and I. Simon. The notion “balanced” also has a natural meaning when one independence structure is induced from another across a bipartite graph.     

The mass spectra of alkylbenzenes—II. The formation of [M ? methyl]+ from tri- and tetra-methylbenzenes

A study of the [M ? methyl]⁺ ion in the mass spectra of ring-deuterated tri- and tetramethylbenzenes has confirmed the partial randomisation of hydrogen and deuterium atoms observed by other workers. The results can be explained by postulating randomisation of the peripheral entities, followed by several cycles of ring expansion and contraction, prior to fragmentation.     

Silicon doping of MBE-grown GaAs films

Two concentration ranges of silicon doping in MBE-grown GaAs films have been investigated in some detail. In lightly doped films, with a free-electron concentration of ≈10¹⁶cm^?3, low-temperature photoluminescence spectra have been analysed to develop a model to account for spectral features previously attributed to Ge and Si acceptor levels. In heavily doped films, a maximum free-electron concentration of ≈7×10¹⁸ cm^?3 has been obtained, which is only rather weakly dependent on growth conditions and the nature of the arsenic species (As₂ or As₄). Transmission electron microscopy has shown that no significant precipitation effects occur when higher Si fluxes are used but there is evidence for autocompensation. The maximum PL intensity (300 K) is found at a lower free electron concentration then with Sn-doped films, and is more sharply peaked, but there is no evidence for an anomalous Moss-Burstein shift.     

Rear leit observation

We have observed light emission from the rear of CaF₂-roughened Al-I-Au tunnel sandwiches. Like the forward emitted light, its spectral intensity shows a sharp drop at energies > 2.5 eV. We interpret the results in terms of both emissions being mediated by a common surface or interface plasmon; the plasmon is damped above 2.5 eV by excitation of an interband transition in Au.     

Density functional theories which are upper bounds to the Hartree-fock limit in one dimension

We begin by constructing the Hartree-Fock density matrix for two model systems, polynomial wavefunctions and the equal-density orbitals. The former yields the generalization of a well-known results for the harmonic oscillator whilst the latter permits the derivation of a density functional theory.     

Observation of muon neutrino disappearance with the MINOS detectors in the NuMI neutrino beam

This Letter reports results from the MINOS experiment based on its initial exposure to neutrinos from the Fermilab NuMI beam. The rates and energy spectra of charged current nu(mu) interactions are compared in two detectors located along the beam axis at distances of 1 and 735 km. With 1.27 x 10(20) 120 GeV protons incident on the NuMI target, 215 events with energies below 30 GeV are observed at the Far Detector, compared to an expectation of 336+/-14 events. The data are consistent with nu(mu) disappearance via oscillations with |Delta(m)2/32|=2.74 +0.44/-0.26 x10(-3)eV(2) and sin(2)(2theta(23))>0.87 (68% C.L.).     

Noise thresholds for optical quantum computers

In this Letter we numerically investigate the fault-tolerant threshold for optical cluster-state quantum computing. We allow both photon loss noise and depolarizing noise (as a general proxy for all local noise), and obtain a threshold region of allowed pairs of values for the two types of noise. Roughly speaking, our results show that scalable optical quantum computing is possible for photon loss probabilities <3 x 10(-3), and for depolarization probabilities <10(-4).