Synthesis and structure of stable cis-dimethyl complex of oxotungsten(VI)

Oxotungsten(VI) complex cis-[WO(L^tBu)Me₂] (L^tBu = methylamino-N,N-bis(2-methylene-4-methyl-6-tert-butylphenolate) dianion) was prepared by the transmetallation reaction of [WO(L^tBu)Cl₂] (either cis or trans isomer) with methyl magnesium iodide. This unexpectedly stable dialkyl complex can be activated by Et₂AlCl to catalyze the ring-opening metathesis polymerization of norbornene.     

A novel strategy for the preparation of naturally occurring phosphocitrate and its partially esterified derivatives

A novel method for the synthesis of phosphocitrate (1, PC) starting from triethyl ester of citric acid and MeOPCl2 is described. The method is based on selective stepwise hydrolysis of ester moieties from the intermediate Me-O-P(O)(Cl)(Z) (Z = triethylcitrate), 4a, which also allows one to prepare partially esterified derivatives of PC with good yield and purity without chromatographic purifications.     

Copolymerisation properties of siloxy‐substituted bis(indenyl)zirconocene catalysts: modified rheological behaviour

The combination of the copolymerisation ability and vinyl end group selectivity of siloxy substitution of ethylene‐bridged bis(indenyl)zirconium dichlorides suggest these catalyst as potential ones for the production of polyethylene containing small amounts of long chain branching. The role of the polymerisation conditions with these highly active catalysts can clearly be seen. Furthermore low contents of multiple branches may occur, even though the probability of attaching several macromonomers into one chain is low. The effect on melt rheological behaviour depends on both the amount of long chain branching and the length of the branch. Moreover the position of the siloxy group is very important. Polymers synthesized with catalysts, where the siloxy group is in position 1, give peculiar rheological behaviour resembling cross‐linked networks although the polymers are completely soluble.     

Interplay of colloidal stability of cellulose nanocrystals and their dispersibility in cellulose acetate butyrate matrix

Cellulose nanocrystals (CNC) prepared from eucalyptus cellulose CNCs were modified by the reaction with methyl adipoyl chloride, CNCm, or with a mixture of acetic and sulfuric acid, CNCa. The CNC were either dispersed at 0.1 wt% in the pure solvents ethyl acetate (EA), tetrahydrofuran (THF) and dimethylformamide (DMF) or in cellulose acetate butyrate (CAB) solutions prepared in these solvents at 0.9 wt%. The colloidal behavior of these dispersions was systematically investigated using a phase separation analyzer LUMiReader^®. The mechanical properties and morphological features of the films resulting from the mixtures of CAB and CNC were determined by dynamic mechanical analysis, optical microscopy and atomic force microscopy, respectively. Regardless the functional group attached to the surface of CNC, the best colloidal stability was observed for dispersions prepared in CAB/DMF solution. Higher degree of substitution of modified CNCs favored the colloidal stability in EA and THF. Composite films prepared from CAB/DMF solutions were more homogeneous and presented better mechanical performance than those prepared in CAB/EA or CAB/THF. The mechanical performance of composites and neat CAB prepared from DMF was CAB/CNCs > CAB/CNCm > CAB/CNCa > CAB, indicating that the modification weakens the percolation process, which is mediated by H bonding.     

Measurement of the sign of the spectroscopic quadrupole moment for the 2(1)+ state in 70Se: no evidence for oblate shape

Using a method whereby molecular and atomic ions are independently selected, an isobarically pure beam of 70Se ions was postaccelerated to an energy of 206 MeV using REX-ISOLDE. Coulomb-excitation yields for states in the beam and target nuclei were deduced by recording deexcitation gamma rays in the highly segmented MINIBALL gamma-ray spectrometer in coincidence with scattered particles in a silicon detector. At these energies, the Coulomb-excitation yield for the first 2+ state is expected to be strongly sensitive to the sign of the spectroscopic quadrupole moment through the nuclear reorientation effect. Experimental evidence is presented here for a prolate shape for the first 2+ state in 70Se, reopening the question over whether there are, as reported earlier, deformed oblate shapes near to the ground state in the light selenium isotopes.     

How log-normal is your country? An analysis of the statistical distribution of the exported volumes of products

We have considered the statistical distributions of the volumes of 1131 products exported by 148 countries. We have found that the form of these distributions is not unique but heavily depends on the level of development of the nation, as expressed by macroeconomic indicators like GDP, GDP per capita, total export and a recently introduced measure for countries’ economic complexity called fitness. We have identified three major classes: a) an incomplete log-normal shape, truncated on the left side, for the less developed countries, b) a complete log-normal, with a wider range of volumes, for nations characterized by intermediate economy, and c) a strongly asymmetric shape for countries with a high degree of development. Finally, the log-normality hypothesis has been checked for the distributions of all the 148 countries through different tests, Kolmogorov-Smirnov and Cramér-Von Mises, confirming that it cannot be rejected only for the countries of intermediate economy.     

Stoichiometric Determination of Carbon in Ceramic Materials by Low Energy Deuteron Activation Analysis

The ¹²C(d,n)¹³N reaction, at 2 MeV, was used for the stoichiometric determination of carbon in reference materials and sintered pellets of SiC ceramics. The preliminary results show higher percentage of carbon on the surface in comparison to the core of the sintered ceramics, indicating the existence of carbon contamination on the surface, possibly caused by the sintering process itself.     

Thermische Marangonikonvektion in Tropfen unter Mikrogravitation bei Beachtung der Tropfendeformation

Übersicht Die hier vorgestellten Ergebnisse sind Teil eines Forschungsprojektes mit dem Ziel, Marangonikonvektion unter Schwerelosigkeit mittels transienter Temperaturfelder zu beeinflussen. In dieser Veröffentlichung werden Lösungen für stationäre Strömungsfelder unter Vorgabe des Temperaturfeldes an der Oberfläche eines frei schwebenden Tropfens präsentiert. In der bestehenden Literatur wird zur Berechnung dieser Ergebnisse die freie Oberfläche des Tropfens als nicht deformierte Kugel vorgegeben. Im Vergleich dazu ergibt sich die Oberfläche in den hier vorgestellten Ergebnissen als Teil der Lösung. Das Strömungsfeld im Tropfen wird für verschiedene Reynolds-Zahlen 0Re5000 und Kapillarzahlen 10Ca1000 dargestellt.

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Thermal Marangoni convection in drops under microgravity taking into account their deformation

Summary The investigations presented here are part of a microgravity project in which the reduction of thermal Marangoni convection by using a transient heat source is studied experimentally and theoretically. This publication shows the results of the theoretical considerations concerning steady state fluid motion in a drop under microgravity induced by a given temperature field at the surface of the drop. In contrast to the literature where the surface is assumed to be an underformed sphere the position of the surface is part of the solutions obtained. The solutions have been computed for Reynolds numbers 0Re5000 and capillary numbers 10Ca1000.