A mathematical model for a single screen barrier in open-plan offices

In open-plan offices, single screen barriers are widely used to separate individual workplaces as a means of improving acoustical privacy. In this paper, a general model for calculating the insertion loss of a single screen barrier in the presence of a floor and a ceiling is developed using the image source technique. In addition to the acoustical properties of the floor and ceiling, this model also takes the sound absorption of the screen, the sound transmission through the screen and the interference between the sound waves into account. This model is able to separate the contribution of reflected sound and diffracted sound from the total sound pressure level at the receiving point, which can help indicate how best to improve the acoustical design of an open office. The mean differences between the predicted 1/3 octave band insertion loss values behind the screen and the corresponding measured results are within 2 dB.     

PDAs and Lab Works—A New Way to Make Chemical Measurements

Computer-controlled data acquisition is rapidly becoming the rule rather than the exception in general chemistry laboratories. The LabWorks learning system is one of many computer-controlled data acquisition interfaces that allow students to quickly obtain and analyze chemistry data. This article explains how communication is established between a personal digital assistant (PDA) and the LabWorks interface. This project continues work previously accomplished using an HP 48 calculator to communicate with the LabWorks interface. The PDA has more computing power, more storage ability, and the Windows CE operating system provides a more user-friendly interface than the handheld graphing calculator. Sample experimental data is provided as an example of how this LabWorks/Palm PC combination can be applied to inexpensively enhance laboratory learning.     

Quasi-classical trajectory calculations on the H + O2 reaction

Quasi-classical trajectory calculations have been performed on the H + O₂ system. Significant reaction probabilities are obtained when the initial energy is in rotation or vibration, or a combination of the two, but not when the initial energy is in translation. The opacity function shows a bimodal dependence on the impact parameter, with a small peak at 0.9 Å < b < 1.5 Å and a very prominent peak at 2.5 Å < b < 3.3 Å. The product scattering angles and product energy distributions also depend on b and to a limited extent on the initial energy distribution. The observations can be largely interpreted in terms of the nature of the motion on the potential energy surface, while the effects of rotational energy on the reaction follow qualitatively from statistical phase-space theory.     

Some trimethylphosphineoxide complexes of lanthanide and indium tris-(bis-trimethylsilylamides)

The reactions of the 3-coordinated metal tris-(bis-trimethylsilylamides) M[N(SiMe₃)₂]₃ (ML₃; where M = La, Pr, Eu, Gd and In) with trimethylphosphineoxide Me₃PO(L′) have been studied. All of these metals gave 1:1 complexes ML₃(L′) which dissociated on heating in vacuo. The Pr and Eu complexes gave interesting pseudo-contact shifted ¹H NMR spectra which are qualitatively in accord with the expected molecular structure. Variable temperature NMR measurements proved the restricted rotation of the silylamide (L) ligands occurs around the M–N axes. Evidence is also presented for unstable 5-coordinated complexes ML₃(L′)₂. The gadolinium 1:1 complex gave a very broad NMR spectrum and its ESR spectrum is being investigated.     

Central limit theorems under weak dependence

This article is motivated by a central limit theorem of Ibragimov for strictly stationary random sequences satisfying a mixing condition based on maximal correlations. Here we show that the mixing condition can be weakened slightly, and construct a class of stationary random sequences covered by the new version of the theorem but not Ibragimov's original version. Ibragimov's theorem is also extended to triangular arrays of random variables, and this is applied to some kernel-type estimates of probability density.     

Some rotating,time-dependent Bianchi type VIII cosmologies with heat flow

A number of explicit, rotating and expanding cosmological solutions of the Einstein field equations are presented. They have homogeneous hypersurfaces of Bianchi type VIII, and they are locally rotationally symmetric. The source is a perfect fluid with heat flow. The thermodynamic properties of the models are discussed.     

Asymptotic normality of some kernel-type estimators of probability density

Central limit theorems are proved for some kernel-type estimators of probability density in the case where the observations form a strictly random sequence satisfying the ?-mixing condition with a certain logarithmic mixing rate.     

Predictors of speech intelligibility in rooms

Three different types of acoustical measures were compared as predictors of speech intelligibility in rooms of varied size and acoustical conditions. These included signal-to-noise measures, the speech transmission index derived from modulation transfer functions, and useful/detrimental sound ratios obtained from early/late sound ratios, speech, and background levels. The most successful forms of each type of measure were of similar prediction accuracy, but the useful/detrimental ratios based on a 0.08-s early time interval were most accurate. Several physical measures, although based on very different calculation procedures, were quite strongly related to each other.     

Recent developments in picosecond photochronoscopy

Recent developments in the techniques of generation and measurement of picosecond and sub-picosecond pulses from mode-locked lasers are reviewed. Particular attention is paid to frequency tunable, bandwidth-limited pulses from dye lasers, especially the cw dye laser. In measurement the main emphasis is put on the rapid advances of the last few years in ultra-fast streak-cameras, ans the recent developments in streak-camera synchronization to a cw mode-locked laser is described. Future prospects for shorter wavelenght pulses in the uv and vuv are briefly considered.