Judiciously 3‐partitioning 3‐uniform hypergraphs

Bollobás, Reed, and Thomason proved every 3‐uniform hypergraph ? with m edges has a vertex‐partition V()=V₁?V₂?V₃ such that each part meets at least edges, later improved to 0.6m by Halsegrave and improved asymptotically to 0.65m+o(m) by Ma and Yu. We improve this asymptotic bound to , which is best possible up to the error term, resolving a special case of a conjecture of Bollobás and Scott.     

CONTROLLING THE 3D NANOSCALE ORGANIZATION OF BULK HETEROJUNCTION POLYMER SOLAR CELLS

In this study,the three dimensional nanoscale organization in the photoactive layers of poly(3-hexylthiophene) (P3HT) and a methanofullerene derivative (PCBM) is revealed by transmission electron tomography.After annealing treatment,either at elevated temperature or during slow solvent evaporation,nanoscale interpenetrating networks are formed with high crystalline order and favorable concentration gradients of both components through the thickness of the photoactive layer.Such a tailored morphology acco...     

A Multi‐Electrode Approach for On‐Line Characterisation of Size and Shape

A multi‐electrode approach is proposed for on‐line characterisation of particle size and shape in dilute particulate suspensions. Based on an electrozone principle, the approach uses four electrodes in a tube rather than two electrodes across an aperture employed in conventional methods. The outer two electrodes are used for current injection, while the inner two electrodes yield voltage measurement. A sensor designed in this way can reduce errors of false counts and oversizing that may occur in conventional methods, thus providing more accurate particle sizing. It is also possible to use the signal slope along with signal peak for particle size and shape characterisation. Both theoretical modelling and experiments were conducted, showing that particle aspect ratio along with particle diameter can be obtained, for example, for cylindrical particles.     

Field evaporation end forms of tungsten

The anomalous field ion images consisting of bright bands of variable width parallel to the 〈111〉 zones, previously reported for tungsten pulse evaporated in helium at 78 K, have also been observed with neon as imaging gas. For both gases the upper limit to the pulse lengths for production of the bands is about 1 ms. The influence of the ratio, R, of pulse height to the total evaporation voltage on the intensity distribution in field ion images of tungsten has been studied for helium and neon together with the effect of residual gases peculiar to ion pumped stainless steel UHV systems (H₂, CH₄ and CO). It is found that when R is raised to a certain level traces of residual gases if present in sufficient quantities, can produce, with tungsten, images with intensity distributions similar to those found with molybdenum after slow evaporation. These are attributed to preferential adsorption of the residual gases on different parts of the specimen and, depending on the nature of the adsorbate, leading to a promotion or a reduction of the ionization probability of the imaging gas. It is pointed out that before an image can be described as typical of a particulaelement or alloy, the conditions of prior evaporation should be carefully controlled.     

The differential thermal analysis behavior of lead zirconate titanate materials

Differential thermal analysis has been used to examine the reactions involved in the formation of lead zirconate titanate and related materials. The reaction of PbO and TiO₂ produced an exothermic peak near 600°C, while mixtures of PbO and ZrO₂ gave endothermic peak at 760°C. Lead titanate and lead zirconate mixtures showed no evidence of reaction below 900°C. Evidence is presented which suggests that PbO and PbTiO₃ react in the vicinity of 750°C. For ternary mixtures of PbO, titanate, the thermograms indicate a complicated behavior between 600–800°C, depending on the ratios of the reactant materials. The results suggest that the calcination reaction to form lead zirconate titanate is a more complex process than has been recognized. Data on the various phase transitions for the lead zirconate titanate materials are also presented.     

Noninvasive determination of human cortisol and dehydroepiandrosterone sulfate using liquid chromatography-tandem mass spectrometry

Liquid chromatography-tandem mass spectrometry (LC-MS/MS) for measurements of steroids in human saliva has garnered increased interest in the area of clinical psychoneuroendocrinological research. However, performance characteristics of LC-MS/MS methods for the analysis of steroids in saliva are limited. Human saliva samples were collected via passive drool. Cortisol and dehydroepiandrosterone sulfate (DHEA-S) in the samples were extracted together, resolved on a C18-A column, and analyzed using tandem mass spectrometry. The LC-MS/MS method had limits of quantitation of 0.03 and 0.06 ng/mL for DHEA-S and cortisol, respectively. Method evaluations showed coefficient variation (%CV) of inter-assay ranging 4.6–17.9% for DHEA-S and cortisol, recoveries of 102.4–109.5% for DHEA-S and 94.6–98.3% for cortisol, and assay linearity with R² = 0.9964 for DHEA-S (1.0–25.0 ng/mL) and R² = 0.997 (1.0–25.0 ng/mL) for cortisol. No cross contamination among samples was observed. Human saliva showed 20% and 18% ion enhancement effect for DHEA-S and cortisol assay, respectively. No interference by ten common steroids was detected. Regression analysis of method comparisons with laboratory-developed test (LDT) method revealed R² = 0.9688 (LC-MS/MS = 0.9665 LDT-LC-MS/MS − 0.7355) for cortisol, and R² = 0.9039 (LC-MS/MS = 1.0173 LDT-LC-MS/MS + 3.6797) for DHEA-S. Reference ranges for young adults were determined to be 0.3–5.9 ng/mL for females and 0.1–5.6 ng/mL for males for salivary cortisol, and 0.6–7.4 ng/mL for females and 0.6–10.1 ng/mL for males for salivary DHEA-S. An LC-MS/MS method for quantifying cortisol and DHEA-S in human saliva was developed and validated for clinical and psychoneuroendocrinological research that require noninvasive means of measuring these hormones.

     

Elemental fluorine. Part 13. Gas-liquid thin film microreactors for selective direct fluorination

Continuous flow gas-liquid thin film microreactors have been effectively used for the selective fluorination of a range of 1,3-dicarbonyl and aromatic substrates and, additionally, the conversion of aromatic disulfides to the corresponding sulfur pentafluorides. Scale-up was demonstrated by the application of a three channel microreactor device fabricated by replication of a single channel system.     

The influence of surface coordination on field evaporation processes in tungsten

The sequence of evaporation of atoms on (111), (332), (433), and (411) surfaces of tungsten has been observed in the field ion microscope for the evaporation of successive layers. Atoms with many different types of surface coordination were observed to evaporate. The data were processed to give the relative probabilities of evaporation (ρ) for each type of atom using a statistical procedure adapted to give probability limits for the ρ values. The results showed that for (111) surfaces the ρ values were the same with helium or neon as image gas and that in general differences in ρ values between differently coordinated atoms at 78 K were observed to be greater than at 20 K. At both these temperatures however the atoms with high surface coordination generally had lower ρ values. With (111), (332) and (433) surfaces the atomic arrangement allowed prediction of surface diffusion paths and with atoms in (111) surfaces an easy diffusion path was essential before evaporation could occur. Amongst atoms which had a diffusion path available, ρ values were relatively lower when the path had a saddle point protruding from the surface and which allowed the atom to be subjected to a higher field. On (411) surfaces diffusion paths are less predictable and the correlation with ρ was less.     

Adhesion of amphipathic molecules to solid surfaces

Summary Oil/water contact angles, coefficient of friction and electron diffraction have been used to study the adsorption of three long chain surface-active substances (a fatty acid, a sulphate and a substituted amine, from aqueous solution on to electropolished copper, aluminium and iron. According to the p_H of the solution, the adsorption occurs by one of the following processes (a) physical adsorption, (b) chemisorption, (c) adherence of a precipitate, (d) sensitised adsorption to form a mixed film. Certain applications e.g. lubrication and the prevention of fretting corrosion, are discussed in relation to the structure and rate of adsorption of the four types of film. The first requirement for an efficient lubricant film is the chemisorption of the long chain compound as a basic metal soap. The film is considerably strengthened by subsequent adsorption of a less polar compound, such as cholesterol, by process (d). A suitable vehicle for the two compounds is an oil/water emulsion.Electron diffraction has been used to determine the physical and chemical nature of the electropolished metal surfaces. Adsorbed monolayers can only be detected on extremely smooth surfaces. A new technique is described for depositing insoluble monolayers on reactive metals, which avoids the roughening of the metal surface experienced in the normal Langmuir-Blodgett method.

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Zusammenfassung Randwinkel öl-Wasser, Reibungskoeffizient und Elektronenstrahlbeugung wurden benutzt zum Studium der Adsorption dreier langkettiger Substanzen (eine Fettsäure, ein Sulfat und ein substituiertes Amin) aus wäßriger Lösung heraus auf elektropoliertes Kupfer, Aluminium und Eisen. Entsprechend dem p_H-Wert der Lösung geschieht die Adsorption durch einen der folgenden Prozesse:a) Physikalische Adsorption, b) Chemisorption, c) Haftung eines Niederschlags und d) sensibilisierte Adsorption unter Bildung eines Mischfilms.Einige Anwendungen, z. B. Schmierung und die Verhinderung von Reibungskorrosion, wurden unter BerÜcksichtigung der Struktur und der Adsorptionsgeschwindigkeit der vier genannten Typen von Adsorptionsschichten diskutiert. Die erste Bedingung fÜr wirksame Schmierung ist die Chemisorption der langkettigen Substanz als basische, metallorganische VerdÜnnung (Seife). Der erhaltene Adsorptionsfilm erfährt eine beachtliche Verfestigung durch nachfolgende Adsorption (nach dem Prozeß d) einer schwächer polaren Substanz, wie des Cholesterols. Ein brauchbarer Träger fÜr beide Komponenten ist eine öl-Wasser-Emulsion.Zur Aufklärung der chemischen und physikalischen Eigenschaften der elektropolierten Metalloberflächen wurde die Elektronenstrahlbeugung eingesetzt. Adsorbierte Monoschichten können nur auf extrem ebenen Oberflächen beobachtet werden. Zur Verhinderung der Aufrauhung von Metalloberflächen, wie sie von der Langmuir-Blodgett-Methode her bekannt ist, wurde eine neue Auftragungstechnik fÜr unlösliche Monoschichten auf reaktionsfähige Metalloberflächen entwickelt.

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This work was carried out during the tenure of Consolidated Zinc Studentships at Trinity Hall, Cambridge, on the part of two of the authors (R. B. W. & J. A. S.). Further financial support was provided by Almin Limited and C. S. I. R. O. (Australia).     

Quantum Monte Carlo study of the Ne atom and the Ne+ ion

We report all-electron and pseudopotential calculations of the ground-state energies of the neutral Ne atom and the Ne(+) ion using the variational and diffusion quantum Monte Carlo (DMC) methods. We investigate different levels of Slater-Jastrow trial wave function: (i) using Hartree-Fock orbitals, (ii) using orbitals optimized within a Monte Carlo procedure in the presence of a Jastrow factor, and (iii) including backflow correlations in the wave function. Small reductions in the total energy are obtained by optimizing the orbitals, while more significant reductions are obtained by incorporating backflow correlations. We study the finite-time-step and fixed-node biases in the DMC energy and show that there is a strong tendency for these errors to cancel when the first ionization potential (IP) is calculated. DMC gives highly accurate values for the IP of Ne at all the levels of trial wave function that we have considered.