Multi-dimple phenomena in TEHL point contacts

Theoretical analysis and experimental measurement of the multiple dimples in thermal elastohydrodynamic lubrication (TEHL) point contacts have been carried out. Good agreement is found between the theoretical and experimental results. A thermal multi-spike theory is proposed to explain the multi-dimple phenomena.     

Zero point energy of the Pullen–Edmonds Hamiltonian

Here we wish to apply the newly developed Generalized Moments Expansion (GMX) to the well-known potential

Novel reactive thermosensitive polyethers – control of transition point

A new class of thermosensitive polymers based on polyethers is discussed. Using living anionic polymerisation techniques a series of homo- and block copolymers of 2,3-epoxypropanol-1 (the glycidol), ethoxy ethyl glycidol ether, its hydrophobic derivative, and ethylene oxide of different molar masses and topology (linear and comb-like) was obtained. By simple chemical modification of hydroxyl groups in polyglycidol segments hydrophobic elements were introduced into polymer chains, which allowed to control the transition point related to the lower critical solution temperature between 0 to 100°C. The relation between the transition temperature and the structure of obtained polymers is discussed.     

Cloud point phenomenon in aqueous mixtures of cationic-anionic surfactants

It used to be held that the cloud point phenomenon was only a characteris-tic of nonionic surfactants alone. Such phenomenon is rarely observed in ionicsurfactants. The present study shows that the mixture of cationic-anionic surfac-tants not only has a krafft point which is the characteristic of an ionic surfactant,but also exhibits the cloud point phenomenon obviously at certain concentrations.     

Cloud point extraction of Δ9-tetrahydrocannabinol from cannabis resin

A cloud point extraction coupled with high performance liquid chromatography (HPLC/UV) method was developed for the determination of Δ⁹-tetrahydrocannabinol (THC) in micellar phase. The nonionic surfactant “Dowfax 20B102” was used to extract and pre-concentrate THC from cannabis resin, prior to its determination with a HPLC–UV system (diode array detector) with isocratic elution. The parameters and variables affecting the extraction were investigated. Under optimum conditions (1 wt.% Dowfax 20B102, 1 wt.% Na₂SO₄, T?=?318 K, t?=?30 min), this method yielded a quite satisfactory recovery rate (~81 %). The limit of detection was 0.04 μg?mL^?1, and the relative standard deviation was less than 2 %. Compared with conventional solid–liquid extraction, this new method avoids the use of volatile organic solvents, therefore is environmentally safer.     

On the nature of the Møller-Plesset critical point

It has been suggested [F. H. Stillinger, J. Chem. Phys. 112, 9711 (2000)] that the convergence or divergence of M?ller-Plesset perturbation theory is determined by a critical point at a negative value of the perturbation parameter z at which an electron cluster dissociates from the nuclei. This conjecture is examined using configuration-interaction computations as a function of z and using a quadratic approximant analysis of the high-order perturbation series. Results are presented for the He, Ne, and Ar atoms and the hydrogen fluoride molecule. The original theoretical analysis used the true Hamiltonian without the approximation of a finite basis set. In practice, the singularity structure depends strongly on the choice of basis set. Standard basis sets cannot model dissociation to an electron cluster, but if the basis includes diffuse functions then it can model another critical point corresponding to complete dissociation of all the valence electrons. This point is farther from the origin of the z plane than is the critical point for the electron cluster, but it is still close enough to cause divergence of the perturbation series. For the hydrogen fluoride molecule a critical point is present even without diffuse functions. The basis functions centered on the H atom are far enough from the F atom to model the escape of electrons away from the fluorine end of the molecule. For the Ar atom a critical point for a one-electron ionization, which was not previously predicted, seems to be present at a positive value of the perturbation parameter. Implications of the existence of critical points for quantum-chemical applications are discussed.     

Acoustique d'un fluide au voisinage du point d'ébullition

In a previous paper (Boutin and Auriault 1993) the homogenization technique of multiscale expansions was used for investigating how acoustic waves may propagate in a bubbly fluid at finite concentration. Three different equivalent macroscopic behaviours where derived, for “large”, “medium” and “small” bubble systems, respectively. In the present paper, we extend the analysis by taking into consideration possible phase change effects. We show that phase change effects are negligible in the case of “large” bubbles, whereas they strongly modify the “medium” bubble system behaviour by decreasing the bulk modulus of several orders of magnitude. For “small” bubbles, capillary effects are dominating.     

Highly sensitive ECL-PCR method for detection of K-ras point mutation

A highly sensitive electrochemiluminescence-polymerase chain reaction (ECL-PCR) method for K-ras point mutation detection is developed. Briefly, K-ras oncogene was amplified by a Ru(bpy)32 (TBR)-labeled forward and a biotin-labeled reverse primer, and followed by digestion with MvaI restriction enzyme, which only cut the wild-type amplicon containing its cutting site. The digested product was then adsorbed to the streptavidin-coated microbead through the biotin label and detected by ECL assay. The experiment results showed that the different genotypes can be clearly discriminated by ECL-PCR method. It is useful in point mutation detection, due to its sensitivity, safety, and simplicity.     

Sustainable composites of surface-modified cellulose with low–melting point polyamide

The present study proposed a series of sustainable polyamide/cellulose composites with up to 60% bio-based content to address environmental issues arising from using fossil-based polymers. Furthermore, it addressed one of the most challenging cellulose/polymer composites' issues, filler/matrix compatibility. Accordingly, the microcrystalline cellulose (MCC) surface was treated through the grafting of n-octadecyl isocyanate (ODI) molecules. The elemental analysis confirmed the substitution of approximately 9 ODI molecules per 100 anhydroglucose units, resulting in superhydrophobic MCC formation with a water contact angle of 130°. The surface-modified MCC was melt blended with a bio-based low–melting point polyamide, developed through copolymerization of 11-aminoundecanoic acid and 12-aminolauric acid. Scanning electron microscopy images confirmed no evidence of surface-modified MCC agglomeration, even at a high loading of 30 wt%, suggesting a uniform dispersion of the filler particles and excellent compatibility between two phases. Consequently, the storage modulus, tensile modulus, and yield stress were enhanced by 40%, 100%, and 50%, respectively, in the composite sample with 30 wt% of MCC, proving excellent stress transformation from the matrix to particles arose from good adhesion between cellulose particles and polyamide chains. Furthermore, all samples revealed suitable melt flowability and viscoelastic performances, suggesting their excellent processability, a critical property for engineered thermoplastics. On top of that, the presence of the surface-modified particles considerably decreased water uptake capacity and water vapor transmission of the polymer matrix, making it interesting for specific applications like packaging films.     

Single-cell level point mutation analysis of circulating tumor cells through droplet microfluidics

Tumor heterogeneity plays a critical role in the determination of appropriate anticancer therapy. As circulating tumor cells(CTCs) contain all tumor-related information, the genetic changes on CTCs could help us choose the appropriate treatments for different patients. Single-base mutations are very common in tumor genetic changes which may result in drug resistance. Here, we introduce a single-cell mutation detection platform based on droplet microfluidics. This platform integrates cell capsula...     

Single-cell level point mutation analysis of circulating tumor cells through droplet microfluidics

Tumor heterogeneity plays a critical role in the determination of appropriate anticancer therapy. As circulating tumor cells(CTCs) contain all tumor-related information, the genetic changes on CTCs could help us choose the appropriate treatments for different patients. Single-base mutations are very common in tumor genetic changes which may result in drug resistance. Here, we introduce a single-cell mutation detection platform based on droplet microfluidics. This platform integrates cell capsula...     

DNA origami-based nano-hunter enriches low-abundance point mutations by targeting wild-type gene segments

Point mutations can be used as biomarkers to perform diagnosis for diseases. In this study, a nanorobot for low-abundance point mutation enrichment was constructed using DNA origami. The novel design achieved limits of detection of 0.1% and 1% for synthesized DNA samples and clinical gene samples, respectively. Resettability was a key property of this method, which also involved a simpler process, lower cost and shorter detection duration than traditional enrichment methods. This novel DNA nanor...     

Determination of the equilibrium melting point of the β-form of polypropylene

The melting behavior of the -form of isotactic polypropylene (-iPP) was investigated as a function of crystallization time and temperature. Calcium suberate, a selective -nucleating agent was used to produce samples that consist entirely of -form i-PP. The experimental melting points were recorded at different crystallization times and were extrapolated to the start of the crystallization process in order to eliminate the effect of lamellar thickening. Using the non-linear Hoffman—Weeks approach to correlate these extrapolated experimental melting temperatures with the corresponding crystallization temperatures, an equilibrium melting point of 209°C was obtained for -iPP. The equilibrium melting point estimated through the non-linear Hoffman—Weeks analysis is about 30°C higher than that (T _m ⁰=177°C) obtained on the basis of the linear extrapolation. These results are consistent with earlier claims that a linear extrapolation of T _m–T _c data leads to an underestimation of the equilibrium melting point. The results obtained for -iPP exemplify the importance of accounting for both the isothermal lamellar thickening effects and the non-linearity in the T _m–T _c correlation, when the determination of an equilibrium melting point is carried out using a procedure based on the predictions of the Lauritzen—Hoffman secondary nucleation theory.This revised version was published online in November 2005 with corrections to the Cover Date.     

Mise au point de la chromatographie et du dosage du tungstène

Summary The chromatographic separation and determination of tungsten has been considered in the cases in which it occurs alone in solution or accompanied by chromium, vanadium, molybdenum, and iron. Two different types of chromatographic tests have been studied: usual partition chromatography and tests according to conditions B (different solvents for saturation, development, and contamination). To achieve a precise determination of tungsten and the absence of all interference, the usual partition chromatography must be adopted. The reproducibility of the determination of tungsten in this case is of the order of ±2 to 3% for 10g of the separated element. Under the conditions of the test B, the reproducibility of the determination of separated tungsten may be just as good (±3 to 4%) if use is made of conventional references and corresponding diagrams such as we recommend. Otherwise, the stains determined in the usual manner yield a deficit of 14% with respect to the deposited tungsten. In this study, the interfering factors play a predominant role from both the quantitative and qualitative points of view. This is the first time that we have been able to accomplish the determination of individual stains of chromatographed elements, remaining on the spot, of which a portion has been dispersed in the paper during the development. The chromatogram obtained under the separating conditions is much less beautiful since it leads to the migration of only the iron and the molybdenum, but it is this which is recommended to produce a perfect determination of tungsten. In the two cases of chromatography, the excess iron is separated from the tungsten during the development.

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Zusammenfassung Die chromatographische Trennung und Bestimmung von Wolfram in reinen Lösungen und in Gegenwart von Chrom, Vanadium, Molybdän und Eisen wurde untersucht. Hierzu wurden zwei verschiedene chromatographische Verfahren angewendet: die übliche Verteilung und eine Methode unter Anwendung verschiedener Lösungsmittel zur Sättigung, zur Entwicklung und als Zusatzmittel. Um eine genaue und störungsfreie Wolframbestimmung auszuführen, muß man die übliche Verteilungschromatographie anwenden. In diesem Falle ist die Reproduzierbarkeit der Wolframbestimmung in der Größenordnung von ±2 bis 3% für 10g des abgetrennten Elements. Bei Anwendung der zweiten Methode kann die Reproduzierbarkeit ebenfalls gut sein (± 3 bis 4%), wenn man sich eines geeigneten Standards und entsprechender, von uns empfohlener Diagramme bedient. Andernfalls ergeben die nach der üblichen Art bestimmten Chromatogrammflecken ein Defizit von 14% gegenüber dem angewandten Wolfram. Störungsfaktoren spielen hier eine vorherrschende Rolle, sowohl in qualitativer wie in quantitativer Hinsicht. Erstmalig hatten wir in diesem Falle an der Auftragstelle verbliebene Flecken eines Elementes zu bestimmen, von dem ein Teil während der Entwicklung sich auf dem Papier verteilt hatte. Das nach der üblichen Verteilungschromatographie erhaltene Chromatogramm ist zwar viel weniger schön, da nur das Eisen und das Molybdän wandern. Für eine perfekte Wolframbestimmung ist es aber zu empfehlen. Überschüssiges Eisen wird in beiden Fällen durch die chromatographische Entwicklung vom Wolfram abgetrennt.

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Les techniciensG. Wantier etA. Orban ont participé aux expériences.     

Saponification of ethyl acetate in 2,6-lutidine + water near its critical point

We have measured the rate of saponification of ethyl acetate (CH₃COOC₂H₅) in 2,6-lutidine (2,6-DMP)?+?water (H₂O) near and far away from its critical point by electrical conductivity experiment. We found that the rate of saponification slowed in the one-phase region at temperatures near the critical point. This behaviour is evidence in support of critical slowing down. Moreover, the experimental results were compared with those of the same reaction in a different critical mixture of 2-butoxyethanol?+?H₂O [Y.W. Kim, Int. J. Thermophys. 25, 1025 (2004)].     

Mise au point du microdosage speetrophotométrique direct du cobalt sur papier

Résumé On a mis au point une technique nouvelle de mesure des concentrations des solutions de cobalt par spectrophotométrie ( = 850 m) directe sur papier de son complexe coloré avec l'-nitroso--naphtol. Cette technique est applicable aux taches chromatographiées avec une reproductibilité d'au moins 1% pour des concentrations comprises entre 0,1 et 3g. La technique préconisée peut Être recommandée pour sa rapidité et sa reproductibilité qui dépassent ce qu'il est permis d'attendre en travaillant sur des solutions ou en photométrie en lumière blanche.

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Summary A new method has been developed for measuring concentrations of solutions of cobalt by spectrophotometry ( = 850 m) directly on paper containing its colored complexes with-nitroso--naphthol. This technique is applicable to chromatographic stains with a reproducibility of at least 1% for the concentrations between 0.1 and 3g. This technique may be recommended because of its rapidity and reproducibility which exceeds that to be expected when working with solutions or in photometry in white light.

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Zusammenfassung Ein neues Verfahren der Konzentrationsbestimmung von Kobaltlösungen durch direkte Spektrophotometrie ( = 850 m) auf Papier wird beschrieben. Es lÄßt sich auf Chromatogrammflecken von 0,1 bis 3g mit einer Reproduzierbarkeit von mindestens 1% anwenden. Das vorgeschlagene Verfahren empfiehlt sich wegen seiner raschen Durchführbarkeit und Reproduzierbarkeit, die besser sind, als man bei photometrischer Untersuchung von Lösungen im Weißlicht erwarten darf.

     

Does SDS micellize under methane hydrate-forming conditions below the normal Krafft point?

Sodium dodecyl sulfate (SDS) can accelerate nucleation and growth of gas hydrates in a quiescent system. The objective of this paper is to investigate whether or not SDS micelles form in the meta-stable region of methane hydrates by the direct measurement of aqueous SDS concentration. The SDS solubility in water with high-pressure methane is identical to that under atmospheric pressure at a temperature range of 270-282 K; thus, the Krafft point under these methane hydrate-forming conditions does not shift from the normal Krafft point (281-289 K) under atmospheric pressure. The mole fraction of methane in SDS solution is independent of aqueous SDS concentration at a hydrate-forming condition. These results suggest that at temperatures below the normal Krafft point, no SDS micelles are present in the aqueous phase even in a high-pressure methane environment.     

Do vectors point the way to understanding energy transfer in molecular collisions?

This tutorial review examines the proposition that vector properties reveal more about the underlying potential energy surfaces controlling the inelastic exchange of energy in intermolecular collisions than conventional scalar measurements. Exciting recent experimental progress is summarized in the form of six selected cases studies. The new information that has been extracted is compared with the predictions of complementary theory. Likely future prospects and promising avenues for further progress are discussed. The treatment should appeal to all those with interests in the forces governing intermolecular interactions, especially in gas-phase collisions.     

Sierpiński-triangle fractal crystals with the C_(3v) point group

Self-similar fractals are of importance in both science and engineering. Metal-organic Sierpin′ ski triangles are particularly attractive for applications in gas separation, catalysis and sensing. Such fractals are constructed in this study by using 1208 V-shaped 4,400-dicyano-1,10:30,100-terphenyl molecules and Fe atoms on Au(1 1 1), and studied in detail by low-temperature scanning tunneling microscopy. Density functional theory calculations are employed to rationalize the invisible Fe atoms in STM images. Monte Carlo simulations are performed to understand the formation mechanism of the surface-supported fractal crystals.     

Locating a double vacancy or Stone–Wales point defect on a hexagonal quantum grid

Journal of Mathematical Chemistry - A graphene nano-ribbon structure can be modelled by a 3-regular hexagonal grid. We convert this to a rectangular coordinate system in order to identify uniquely...