A survey of acoustic conditions in semi-open plan classrooms in the United Kingdom

This paper reports the results of a large scale, detailed acoustic survey of 42 open plan classrooms of varying design in the UK each of which contained between 2 and 14 teaching areas or classbases. The objective survey procedure, which was designed specifically for use in open plan classrooms, is described. The acoustic measurements relating to speech intelligibility within a classbase, including ambient noise level, intrusive noise level, speech to noise ratio, speech transmission index, and reverberation time, are presented. The effects on speech intelligibility of critical physical design variables, such as the number of classbases within an open plan unit and the selection of acoustic finishes for control of reverberation, are examined. This analysis enables limitations of open plan classrooms to be discussed and acoustic design guidelines to be developed to ensure good listening conditions. The types of teaching activity to provide adequate acoustic conditions, plus the speech intelligibility requirements of younger children, are also discussed.     

Relativity and the lead-acid battery

The energies of the solid reactants in the lead-acid battery are calculated ab?initio using two different basis sets at nonrelativistic, scalar-relativistic, and fully relativistic levels, and using several exchange-correlation potentials. The average calculated standard voltage is 2.13?V, compared with the experimental value of 2.11?V. All calculations agree in that 1.7-1.8?V of this standard voltage arise from relativistic effects, mainly from PbO2 but also from PbSO4.     

Vocal Fold Vibration and Phonation Start in Aspirated, Unaspirated, and Staccato Onset

Objectives/Hypotheses

Singers learn to produce well-controlled tone onsets by accurate synchronization of glottal adduction and buildup of subglottal pressure. Spectrographic analyses have shown that the higher spectrum partials are present also at the vowel onset in classically trained singers’ performances. Such partials are produced by a sharp discontinuity in the waveform of the transglottal airflow, presumably produced by vocal fold collision.

Study Design

After hearing a prompt series of a triad pattern, six singer subjects sang the same triad pattern on the vowel /i/ (1) preceded by an aspirated /p/, (2) preceded by an unaspirated /p/, and (3) without any preceding consonant in staccato.

Methods

Using high-speed imaging we examined the initiation of vocal fold vibration in aspirated and unaspirated productions of the consonant /p/ as well as in the staccato tones.

Results

The number vibrations failing to produce vocal fold collision were significantly higher in the aspirated /p/ than in the unaspirated /p/ and in the staccato tones. High frequency ripple in the audio waveform was significantly delayed in the aspirated /p/.

Conclusions

Initiation of vocal fold collision and the appearance of high-frequency ripple in the vowel /i/ are slightly delayed in aspirated productions of a preceding consonant /p/.     

Harmonic tori in De Sitter spaces S^{2n}_1

We show that all superconformal harmonic immersions from genus one surfaces into de Sitter spaces $S^{2n}_{1}$ with globally defined harmonic sequence are of finite-type and hence result merely from solving a pair of ordinary differential equations. As an application, we prove that all Willmore tori in $S^{3}$ without umbilic points can be constructed in this simple way.     

Tripodal Thiols as Ligands for Molecular Magnets: Very Strong Antiferromagnetic Exchange Interactions in Vanadium(III) Clusters

The synthesis, structural and magnetic characterisation of [V^III₃O(tmme)₂(diimine)₂Cl] [diimine=2,2′‐bipyridine ( 1 ) or 1,10‐phenanthroline ( 2 )] and (HNEt₃)₂[V^III₄O(tmme)₄] ( 3 ) is reported, in which H₃tmme is tris(mercaptomethyl)ethane, MeC(CH₂SH)₃, the thiol analogue of the famous tripodal alcohol ligands typified by H₃thme [tris(hydroxymethyl)ethane, MeC(CH₂OH)₃]. Complexes 1 and 3 have “T‐shaped” and square topologies, respectively, and the latter is centred on a rare example of a square‐planar oxide. The tri‐thiolate ligands bind the periphery of the clusters and provide such strong antiferromagnetic exchange pathways that in both cases only a single total spin state is occupied up to room temperature, in the absence of metal–metal bonding. Magnetic data, electronic structure calculations and electrochemical data are reported.     

An automated micromethod for the separation of monosaccharides by partition chromatography

Summary The conditions for a separation of monosaccharid.es and their automatic determination on the microscale have been studied. The separation is based upon partition chromatography on an anion-exchange resin in its sulphate form with ethanol -water as the eluent. The eluate is analysed colorimetrically with orcinol as the colour reagent. Microgram quantities in complicated mixtures of monosaccharides can be determined in less than three hours.

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Zusammenfassung Die Arbeitsbedingungen für die Trennung und automatische Bestimmung von Monosacchariden im Mikromaßstab wurden untersucht. Die Trennung wird verteilungschromatographisch an einem Anionenaustauscherharz in Sulfatform mit Äthanol-Wasser als Eluent ausgeführt. Das Eluat wird kolorimetrisch mit Orcin als Farbreagens durchgeführt. In Monosaccharidgemischen lassen sich Mikrogrammengen in weniger als 3 Stunden bestimmen.

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Résumé On a étudié les conditions de séparation des monosaccharides et leur dosage automatique à l'échelle micro. La séparation repose sur la Chromatographie de partage sur une résine échangeuse anionique sous sa forme sulfate, avec le mélange éthanol-eau comme éluant. On analyse par colorimétrie l'éluat avec l'orcinol comme réactif coloré. On peut doser des quantités de l'ordre du microgramme dans des mélanges complexes de monosaccharides en moins de 3 heures.

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The financial support of the Swedish Technical Research Council is gratefully acknowledged. Thanks are also due to Dr.H. W. Holy, Teehnicon Instruments Co., Chertsey, Great Britain, for a gift of specially prepared ion-exchange resin.     

Chemically modified cellulose micro- and nanofibrils as paper-strength additives

Chemically modified cellulose micro- and nanofibrils were successfully used as paper strength additives. Three different kinds of cellulose nanofibrils (CNFs) were studied: carboxymethylated CNFs, periodate-oxidised carboxymethylated CNFs and dopamine-grafted carboxymethylated CNFs, all prepared from bleached chemical fibres of dissolving grade, and one microfibrillated cellulose from unbleached kraft fibres. In addition to mechanical characterization of the final paper sheets the fibril retention, sheet density and sheet morphology were also studied as a function of addition of the four different cellulose fibrils. In general, the cellulose fibrils, when used as additives, significantly increased the tensile strength, Young’s modulus and strain-at-break of the paper sheets. The effects of the different fibrils on these properties were compared and evaluated and used to analyse the underlying mechanisms behind the strengthening effect. The strength-enhancing effect was most pronounced for the periodate-oxidised CNFs when they were added together with polyvinyl amine (PVAm) or poly(dimethyldiallylammonium chloride) (pDADMAC). The addition of periodate-oxidised CNFs, with pDADMAC as retention aid, resulted in a 37% increase in tensile strength at a 2 wt% addition and an 89% increase at a 15 wt% addition (from 67 to 92 and 125 kNm/kg, respectively) compared to a reference with only pDADMAC. Wet-strong sheets with a wet tensile index of 30 kNm/kg were also obtained when periodate-oxidised CNFs and PVAm were combined. This significant increase in wet strength is suggested to be the result of a formation of cross-links between the aldehyde groups, introduced by the periodate oxidation, and hydroxyl groups on the lignocellulosic fibres and the primary amines of PVAm. Even though less significant, there was also an increase in wet tensile strength when pDADMAC was used together with periodate-oxidised fibrils which shows that the aldehyde groups are able to increase the wet strength without the presence of the primary amines of the PVAm. As an alternative method to strengthen the fibre network, carboxymethylated CNFs grafted with dopamine, by an ethyl dimethylaminopropyl carbodiimide coupling, were used as a strength additive. When used as an additive, these CNFs showed a strong propensity to form films on and around the fibres and significantly increased the mechanical properties of the sheets. Their addition resulted in an increase in the Young´s modulus by 41%, from 5.1 to 7.2 GPa, and an increase in the tensile strength index of 98% (from 53 to 105 kNm/kg) with 5 wt% retained dopamine-grafted CNFs.     

High-resolution VUV spectroscopy using pulsed laser sources

The resonance spectroscopic techniques - level-crossing, optical double resonance and quantum-beat spectroscopy - have been employed following pulsed laser excitation. The use of pulsed lasers has enabled spectroscopic studies of atomic structures and radiative lifetimes in the UV/VUV spectral region.