Composite mixed finite elements on plane quadrilaterals

Mixed finite elements over a plane convex quadrilateral are obtained by assembling two Raviart-Thomas mixed finite elements over triangles. The macroelement is given by an eliminating procedure of the degrees of freedom related to the common edge to the two triangles. This procedure results in a finite element with a space of interpolating functions containing the polynomials of degree ? l, where l is the greater integer for which the same property is satisfied by the relevant Raviart-Thomas [Mathematical Aspects of Finite Element Methods, Roma 1975, I. Galligani and E. Magenes, Eds., Lecture Notes in Mathematics Vol. 606, Springer-Verlag, Berlin, 1975] mixed finite element. The interpolation error is estimated by means of the technique of almost equivalent affine element as given by Ciavaldini and Nédélec [Rev. Fr. Autom. Inf. Recher. Opérationnelle Ser. Rouge R2 , 29–45 (1974)]. © 1993 John Wiley & Sons, Inc.     

Sedimentvolumina von polydispersem Schiefer

Zusammenfassung Es wird der Einfluß der Wertigkeit und Konzentration verschiedener Elektrolyte auf die Ausflockung und die Sedimentation polydisperser Suspensionen von Schiefer untersucht. Die dreiwertigen Ionen unterscheiden sich in ihrer Wirksamkeit deutlich von den zweiwertigen, die sich untereinander sehr ähnlich verhalten. Einwertige Kationen wurden wegen ihrer Bedeutungslosigkeit für das der vorliegenden Arbeit zugrundeliegende technische Problem nicht in die Untersuchung einbezogen.Der durch die Wertigkeit der Kationen bedingte charakteristische Verlauf der Sedimentationskurven erlaubt unter Umständen Aussagen über Komplexbildungen in Elektrolytlösungen.Außer den von Egolf und McCabe angenommenen Phasen der Sedimentation tritt unter Umständen eine Wachstumsperiode auf, deren Abhängigkeit von den Versuchsbedingungen diskutiert wird.Die kleinsten Sedimentvolumina werden durch zweiwertige Kationen bei Schwellenwertskonzentration erreicht. Die Bedeutung der Versuchsergebnisse für die betriebsmäßige Ton- und Schieferschlammeindickung wird erörtert.

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Résumé L'influence de la valence et de la concentration de divers électrolytes sur la flocculation et la sédimentation des suspensions polydisperses de schiste a été étudiée. Les ions trivalents se distinguent dans leur activité, nettement des ions bivalents qui se comportent entre eux, d'une facon fort semblable. Etant donné que les ions monovalents ne présentent aucun intérêt en ce qui concerne le problème technique qui fut à la base de la présente étude, ils n'ont pas été inclus dans les expériences.L'allure caractéristique des courbes de sédimentation qui dépend de la valence des cations permet, sous certaines circonstances, la mise en évidence de la formation des complexes dans des solutions d'électrolytes.A part des phases de sédimentation décrites par Egolf et McCabe, il apparaît, sous certaines circonstances, une période de croissance dont la dépendance des conditions expérimentales est discutée.Les volumes de sédimentation les plus petits sont atteints en utilisant des cations bivalents à la concentration critique. La portée des résultats expérimentaux sur l'épaississement industriel des boues d'argile et de schiste est discutée.

     

Highly diastereoselective synthetic route to enantiopure beta(2)-amino acids and gamma-amino alcohols using a fluorinated oxazolidine (Fox) as chiral auxiliary

The alkylation reactions of an amide enolate derived from a trifluoromethylated oxazolidine (Fox) chiral auxiliary occur with a complete diastereoselectivity and in good yields with various electrophiles. This reaction provides a versatile and straightforward strategy for the synthesis of beta(2)-amino acids and gamma-amino alcohols in enantiopure form.     

Heteroleptic [n]Chromoarenophanes: ansa Complexes Derived from [Cr(η5‐C5H5)(η6‐C6H6)]

The synthesis of ansa complexes has been studied intensively owing to their importance as homogeneous catalysts and as precursors of metal‐containing polymers. However, paramagnetic non‐metallocene derivatives are rare and have been limited to examples with vanadium and titanium. Herein, we report an efficient procedure for the selective dilithiation of paramagnetic sandwich complex [Cr(η⁵‐C₅H₅)(η⁶‐C₆H₆)], which allows the preparation of a series of [n]chromoarenophanes (n=1, 2, 3) that feature silicon, germanium, and tin atoms at the bridging positions. The electronic and structural properties of these complexes were probed by X‐ray diffraction analysis, cyclic voltammetry, and by UV/Vis and EPR spectroscopy. The spectroscopic parameters for the strained and less strained complexes (i.e., with multiple‐atom linkers) indicate that the unpaired electron resides primarily in a d orbital on chromium(I); this result was also supported by density functional theory (DFT) calculations. We did not observe a correlation between the experimental UV/Vis and EPR data and the degree of molecular distortion in these ansa complexes. The treatment of tin‐bridged complex [Cr(η⁵‐C₅H₄)(η⁶‐C₆H₅)SntBu₂] with [Pt(PEt₃)₃] results in the non‐regioselective insertion of the low‐valent Pt⁰ fragment into the C_ipso? Sn bonds in both the five‐ and six‐membered rings, thereby furnishing a bimetallic complex. This observed reactivity suggests that ansa complexes of this type are promising starting materials for the synthesis of bimetallic complexes in general and also underline their potential to undergo ring‐opening processes to yield new metal‐containing polymers.     

Determination of trace elements Fe,cu and Zn in the Algerian cancerous plasma using X-ray fluorescence (XRF)

Cancers are among the leading causes of morbidity and mortality in the world. The purpose of this study was to conduct a survey on the effect of minerals on cancer risk in the Algerian population. One hundred and seventy-eight plasma samples were used to analyze the concentrations of iron (Fe), copper (Cu), and zinc (Zn) in cancerous patients and also in healthy subjects using the X-ray florescence technique (XRF). Samples were classified according to the age and gender of the donors. An empirical formula was developed for the concentration of Zinc, Copper and Iron in cancer patients according to the age. The averages iron, copper and zinc concentrations in mg/kg for control and Cancer disease groups were (1493 ± 105; 1496 ± 86), (1172 ± 229; 1078 ± 283) and (1266 ± 202; 1344 ± 208) respectively. The ANOVA One-Way test was applied. For both genders of control and cancer disease groups it shows a significant decrease rate of copper for global and female gender and a significant increase rate of zinc for global and male gender (p < 0.05). The results indicate that the Cu and Zn concentration could show helpful tools for diagnosis and preventive treatment of cancer diseases.     

Zur Konstitution des MgCO3·3H2O

Zusammenfassung Die Ultrarot-Absorption obiger Verbinding wurde untersucht. Sie erlaubt keinen sicheren Schluß auf die Konstitution dieser Verbindung als basisches Hydrogencarbonat.Mit einer Abbildung