A (1→4)-β-D-Glucuronan Excreted by a Mutant of the Rhizobium Meliloti M5N1 Strain

Abstract

A mutant of the R. meliloti M5N1 strain has been selected. This strain, R. meliloti M5N1 CS (NCIMB 40472), excretes an extracellular material composed of 2-O-Ac-β-GlcpA, 3-O-Ac-β-GlcpA, 2,3-di-O-Ac-β-GlcpA and three species of β-GlcpA residues 1→4 linked. For the culture conditions used, the weight average molecular weight of the polymer varied in the range of 6 × 10⁴ < Mw < 4 × 10⁵. High molecular weight glucuronate forms thermoreversible gels at 5 g L^?l. In the presence of divalent cation such as Ca²⁺ or trivalent cations such as Cr³⁺ or Fe^{3 +}, cross linking of the polymer occurs. This polysaccharide is the first exocellular (1→4)-β-D-glucuronan produced by a R. meliloti strain.     

Photofragmentation and photoabsorption cross sections for mass selected argon cluster ions,n=3 to 108

A tandem time-of-flight mass spectrometer is used to measure photofragmentation mass spectra and optical absorption spectra of mass selected argon cluster ions in then=3 to 108 atoms per cluster range.     

Ein einfaches analytisches Verfahren zur Berechnung des turbulenten Wärmeübergangs hinter einem hydrodynamischen Vorlauf

Zusammenfassung Es wird ein einfaches Berechnungsverfahren vorgestellt, das eine Bestimmung des turbulenten Wärmeübergangs hinter einem hydrodynamischen Vorlauf gestattet. Durch eine Anpassung der Randbedingungen in der Reynoldsnalogie an die Strömungsverhältnisse bei unterschiedlichem Beginn von Temperatur- und Geschwindigkeitsgrenzschicht wird das Verhältnis der Nusseltzahlen einer Strömung mit Vorlauf zu der ohne Vorlauf formuliert. Dieses Nusseltzahlverhältnis stellt eine Korrekturfunktion für den Einfluß unbeheizter Anlaufstrecken dar und gestattet die Wärmeübergangsberechnung hinter hydrodynamischen Vorläufen aus den bekannten Gleichungen für den gleichzeitigen Beginn von Temperatur- und Strömungsgrenzschicht. Das Verfahren ist für Rohr-und Plattenströmungen anwendbar; die Korrekturfunktion ist in beiden Fällen eine Funktion der Vorlauflänge und der thermischen Lauflänge, für die Rohrströmung zusätzlich noch Funktion der Reynoldszahl.

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A simple analytical method to calculate the turbulent heat transfer behind a hydrodynamic starting length

An analytical method is presented to calculate the turbulent heat transfer behind an hydrodynamic starting length. By modification of the boundary conditions in the Reynolds analogie with respect to the flow conditions for different running lengths of the boundary layer of temperatur and velocity the heat transfer ratio of a flow with to a flow without hydrodynamic starting length can be formulated. This heat transfer ratio is a correction function to describe the influence of an unheated starting length and allows the heat transfer calculation by using the well known heat transfer formulas for the simultaneous hydrodynamic and thermal start. The method can be applied as well to the flat plate flow as to the pipe flow. In both cases the correction function depends on the unheated starting length and the thermal running length, for the pipe flow additionaly on the Reynolds number.

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Bezeichnungen A_q turbulente Impuls-Austauschgröße - A turbulente Wärmeaustauschgröße - c_f Reibungsbeiwert - c_p spezifische Wärme - D Rohrdurchmesser - L hydrodynamischer Vorlauf - n Exponent des Grenzschicht-Potenzgesetzes - q Wärmestromdichte - R Rohrradius - s Reynoldsanalogiefaktor - T Temperatur - u Strömungsgeschwindigkeit in x-Richtung - u Schubspannungsgeschwindigkeit - x, y Koordinaten - Wärmeübergangskoeffizient - Grenzschichtdicke - Wärmeleitfähigkeit - dynamische Viskosität - Dichte - Schubspannung Kennzahlen Nu Nusseltzahl - Pr Prandtlzahl - Re Reynoldszahl - St Stantonzahl Indizes D Rohrströmung - E Rohreintritt - F Fluid - L mit hydrodynamischem Vorlauf - m Rohrmitte - T Temperaturgrenzschicht - u Geschwindigkeitsgrenzschicht - w Wand - x örtlicher Wert, Platte-Rohreinlauf - Rand der Grenzschicht Herrn Professor Professor h.c. Dr. sc. techn. Romano Gregorig zum 70. Geburtstag gewidmet.     

Caterpillar Track Complexes in Template‐Directed Synthesis and Correlated Molecular Motion

Small alterations to the structure of a star‐shaped template totally change its mode of operation. The hexapyridyl template directs the conversion of a porphyrin dimer to the cyclic hexamer, but deleting one pyridine site changes the product to the cyclic decamer, while deleting two binding sites changes the product to the cyclic octamer. This surprising switch in selectivity is explained by the formation of 2:1 caterpillar track complexes, in which two template wheels bind inside the nanoring. Caterpillar track complexes can also be prepared by binding the hexapyridyl template inside the 8‐ and 10‐porphyrin nanorings. NMR exchange spectroscopy (EXSY) experiments show that these complexes exhibit correlated motion, in which the conrotatory rotation of the two template wheels is coupled to rotation of the nanoring track. In the case of the 10‐porphyrin system, the correlated motion can be locked by binding palladium(II) dichloride between the two templates.     

Hydrolysis and grafting of dimethylalkoxysilanes onto stainless steel

The grafting of trialkoxysilane molecules should also give rise to the formation of a siloxane network at the substrate's surface when trialkoxysilanes are used. Other candidates that might be able to act as adhesion promoters at metallic surfaces are dimethylalkoxysilanes. The advantage of dimethylalkoxysilanes is that only one silanol group is produced during the hydrolysis step, leading to the formation of a grafted monolayer onto the steel. Moreover, the chemical grafting of stainless steel, which exhibits a low surface reactivity, is of great interest for industrial applications such as adhesive bonding or coatings. The objective of this work was to chemically graft dimethylalkoxysilanes onto AISI 316L stainless steel and to analyze the grafted layer by X‐ray photoelectron spectroscopy (XPS). Investigation of the hydrolysis of these molecules in aqueous solutions was also performed by proton nuclear magnetic resonance spectroscopy (¹H NMR). The grafting of 3‐(ethoxydimethylsilyl)propylamine (APDES) and 3‐glycidoxypropyldimethylethoxysilane (GPDES) was achieved onto stainless steel after a controlled hydrolysis reaction. A pH inferior or equal to 5 was necessary to obtain a sufficient hydrolysis of silanes. XPS results have evidenced the grafting of the silanes onto stainless steel. The signal of the Si 2p peak clearly showed the formation of a covalent bond between APDES and the stainless steel surface through the O atoms giving rise to a uniform layer of adsorbed molecules. Moreover, this grafted layer is strongly stable as no removal of the alkoxysilane was observed after immersion in hot water which is very critical for these molecules. Copyright © 2015 John Wiley & Sons, Ltd.     

Approximate Simulation Techniques and Distribution of an Extended Gamma Process

In reliability theory, many papers use a standard Gamma process to model the evolution of the cumulative deterioration of a system over time. When the variance-to-mean ratio of the system deterioration level varies over time, the standard Gamma process is not convenient any more because it provides a constant ratio. A way to overcome this restriction is to consider the extended version of a Gamma process proposed by Cinlar (J Appl Probab 17:467–480, 1980). However, based on its technicality, the use of such a process for applicative purpose requires the preliminary development of technical tools for simulating its paths and for the numerical assessment of its distribution. This paper is devoted to these two points.     

Enhanced UV photosensing properties of ZnO nanowires prepared by electrodeposition and atomic layer deposition

A new process enabling the synthesis of zinc oxide (ZnO) and Al-doped ZnO nanowires (NWs) for photosensing applications is reported. By combining atomic layer deposition (ALD) for the seed layer preparation and electrodeposition for the NW growth, high-quality ZnO nanomaterials were prepared and tested as ultraviolet (UV) sensors. The obtained NWs are grown as arrays perpendicular to the substrate surface and present diameters between 70 and 130 nm depending on the Al doping, as seen from scanning electron microscopy (SEM) studies. Their hexagonal microstructure has been determined using X-ray diffraction and Raman spectroscopy. An excellent performance in UV sensing has been observed for the ZnO NWs with low Al doping, and a maximal photoresponse current of 11.1 mA has been measured. In addition, initial studies on the stability have shown that the NW photoresponse currents are stable, even after ten UV on/off cycles.