Carbon ad-dimer defects in carbon nanotubes

The adsorption of carbon dimers on carbon nanotubes leads to a rich spectrum of structures and electronic structure modifications. Barriers for the formation of carbon dimer induced defects are calculated and found to be considerably lower than those for the Stone-Wales defect. The electronic states introduced by the ad-dimers depend on defect structure and tube type and size. Multiple carbon ad-dimers provide a route to structural engineering of patterned tubes that may be of interest for nanoelectronics.     

Sémi-microdosage de quelques constituants du lait par séparation chromatographique

Résumé La complexité de l'état physique dans lequel se trouvent les constituants du lait à l'état naturel fait de leur séparation un problème difficilement soluble, surtout quand il s'agit d'analyser de petites quantités.Une séparation des constituants du lait est possible sur une colonne d'alumine hydratée.Le mécanisme de cette séparation réside dans un échange d'ions, résultant des propriétés conférées par la couche de graisse déposée sur le grain d'alumine hydraté.Le lactose, le premier constituant recueilli, passe par simple filtration indifféremment duh de l'alumine.Les protéides sont élués par une solution alcaline. Leh de l'alumine a une grande influence à la fois sur leur adsorption et sur leur élution. Une alumine acide retient la presque totalité des protéines, tandis qu'une alumine neutre ou légèrement alcaline en permet une élution facile.Dans les conditions de nos expériences l'alumine employée ne peut adsorber qu'une quantité déterminée de protéines. L'excès passe immédiatement dans le filtrat. Ainsi, l'on peut différencier deux fractions protéiques qui sont récoltées après le passage du lait dans la colonne: l'une dans le filtrat, quand la colonne est déjà saturée, l'autre dans l'éluat alcalin.Les phosphates minéraux sont élués par une solution acide; leur rétention n'est pas influencée par leh de la colonne.

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Summary The complexity of the physical state, in which the constituents of milk occur naturally, makes their separation a difficult problem, particularly when small quantities are to be analyzed. The constituents of milk can be separated on a column of hydrated alumina.The mechanism of this separation resides in an exchange of ions resulting from properties conferred by the layer of fat deposited on the grains of hydrated alumina.Lactose, the first constituent collected, passes through by simple filtration, indifferent to theh of the alumina.The proteins are eluted by means of an alkaline solution. Theh of the alumina has a large influence both on their adsorption and elution. An acidic alumina retains practically all of the proteins, whereas a neutral or slightly alkaline alumina makes their elution easy.Under the conditions of the author's experiments, the alumina employed could adsorb only a determinate quantity of proteins. The excess immediately passed into the filtrate. It is thus possible to differentiate two protein fractions, which are collected after the passage of the milk through the column: one in the filtrate, when the column is already saturated, the other in the alkaline eluate.The mineral phosphates are eluted by an acid solution; their retention is not influenced by theh of the column.

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Zusammenfassung Die verwickelten physikalischen Verhältnisse unter den Bestandteilen der Milch im natürlichen Zustand macht deren Trennung zu einem schwierigen Problem, besonders wenn es sich um die Analyse kleiner Mengen handelt. Diese Trennung wird durch Verwendung einer Säule von Aluminiumoxydhydrat ermöglicht. Der Trennungsmechanismus beruht auf einem Ionenaustausch zufolge jener Umstände, die sich aus der Bindung des Fettes an das gekörnte Adsorptionsmittel ergeben. Die Lactose, der zuerst erhältliche Bestandteil, passiert das Aluminiumoxyd unabhängig vomh. Die Proteide werden alkalisch eluiert. Dash des Aluminiumoxyds ist von großem Einfluß auf deren Adsorption und Elution. Saures Aluminiumoxyd hält das Eiweiß fast zur Gänze zurück, während neutrales oder schwach basisches Aluminiumoxyd die Elution erleichtert. Unter den von uns gewählten Versuchsbedingungen kann das verwendete Aluminiumoxyd nur eine bestimmte Menge der Eiweißkörper adsorbieren. Der Überschuß geht unmittelbar ins Filtrat. So lassen sich zwei Eiweißfraktionen unterscheiden, von denen sich die eine nach der Sättigung der Trennsäule im Filtrat, die andere im Eluat findet. Das anorganische Phosphat wird sauer eluiert; dessen Adsorption wird durch dash der Kolonne nicht beeinflußt.

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Avec 10 figures.     

Performances under representative pressure and temperature conditions of the gas chromatography-mass spectrometry space experiment to investigate Titan's atmospheric composition

In the frame of the calibration of the aerosol collector and pyrolyser, and gas chromatography-mass spectrometry experiments of the Huygens probe arrived at Titan, systematic experimental studies were led to estimate the influence of the operating conditions on the analyses that should have been achieved in the Titan's atmosphere. The primary objective of this study was to estimate the influence of operating conditions variations induced by (i) instrumental modifications made shortly before the probe launch which can have changed the operating pressures; (ii) the change of the probe environmental conditions (pressure, temperature) during its descent in the atmosphere; (iii) a possible deviation of pressure and temperature regulations from their nominal values because of the long journey of the instrument in space, or of other external events. The secondary objective of this work was to create an analytical database that can be used as a reference to treat the chromatograms obtained in situ, and help to identify chromatographically the analyzed species, complementary to mass spectrometry. Beyond the application to a specific instrument, this work was also useful to experimentally estimate the fundamental evolution of the separation as a function of the changes of operating conditions with time. The obtained results show (i) the significant influence of inlet and outlet pressure variation on the time of analysis, but not on the separation power. It thus enables to significantly shorten the analysis duration, and thus to analyze more compounds within the fixed time of analysis of the instrument; (ii) the significant influence of temperature on the retention. In this frame, the enthalpies of exchange between the gas phase and the stationary phase of the species were determined to be used to retrieve the analyzed species in case of deviation of the operating temperature; (iii) that the possible aging of the columns does not have influence on the columns efficiency and separation power; (iv) the analytical capabilities of the gas chromatography-mass spectrometry experiment within operating conditions representative of those encountered in situ. Finally, in spite of possible operating condition changes, it is shown that results coming from the gas chromatograph-mass spectrometer experiment, which are currently under analysis, could bring important information on the Titan's atmosphere and its history.     

Pyridine•BrF3, the missing link for clean fluorinations of aromatic derivatives

This work demonstrates the unique features of the never used before Py?BrF(3) complex in the field of aromatic organic fluorinations. The main disadvantage of the noncomplexed BrF(3) is the fact that usually, in addition to the desired fluorination, a parallel electrophilic aromatic bromination takes place as well. Use of the Py?BrF(3) complex reduces this electrophilic bromination, which is observed with most reagents based on fluorine and bromine [BrF].     

Acrolein polymerization: Monodisperse,homo, and hybrido microspheres,synthesis, mechanism,and reactions

Monodisperse polyacrolien (PA) microspheres were obtained by a single step process via two mechanisms: (a) aqueous polymerization of acrolein under alkaline conditions and (b) aqueous radical polymerization of acrolein by irradiation with a cobalt source. The diameter of the former microspheres can be varied from 0.04 up to 8 μm. The monodispersity of the system is also discussed. The diameter of the latter microspheres can be varied up to 0.2 μm. Hybrido PA microspheres were formed by grafting PA microspheres of average diameter of 0.1 μm obtained by irradiation onto the surface of PA microspheres produced by the alkaline mechanism. The aldehyde content of the microspheres prepared by irradiation is much higher than those of the microspheres formed under alkaline conditions. The aldehyde groups were used for the covalent binding of ligands containing primary amino groups, such as proteins and drugs, in a single step under physiological pH.     

Dimension Reduction for the Landau-de Gennes Model on Curved Nematic Thin Films

We use the method of \(\Gamma \)-convergence to study the behavior of the Landau-de Gennes model for a nematic liquid crystalline film attached to a general fixed surface in the limit of vanishing thickness. This paper generalizes the approach in Golovaty et al. (J Nonlinear Sci 25(6):1431–1451, 2015) where we considered a similar problem for a planar surface. Since the anchoring energy dominates when the thickness of the film is small, it is essential to understand its influence on the structure of the minimizers of the limiting energy. In particular, the anchoring energy dictates the class of admissible competitors and the structure of the limiting problem. We assume general weak anchoring conditions on the top and the bottom surfaces of the film and strong Dirichlet boundary conditions on the lateral boundary of the film when the surface is not closed. We establish a general convergence result to an energy defined on the surface that involves a somewhat surprising remnant of the normal component of the tensor gradient. Then we exhibit one effect of curvature through an analysis of the behavior of minimizers to the limiting problem when the substrate is a frustum.     

On the local structure of doubly laced crystals

Let g be a Lie algebra all of whose regular subalgebras of rank 2 are type A₁×A₁, A₂, or C₂, and let B be a crystal graph corresponding to a representation of g. We explicitly describe the local structure of B, confirming a conjecture of Stembridge.