Increasing the ordering temperatures in oxalate-based 3D chiral magnets: the series [Ir(ppy)2(bpy)][M(II)M(III)(ox)3] x 0.5 H2O (M(II)M(III) = MnCr, FeCr, CoCr, NiCr, ZnCr, MnFe, FeFe); bpy = 2,2'-bipyridine; ppy = 2-phenylpyridine; ox = oxalate dianion)

The synthesis, structure, and physical properties of a novel series of oxalate-based bimetallic magnets obtained by using the Ir(ppy)2(bpy)]+ cation as a template of the bimetallic [M(II)M(III)(ox)3]- network are reported. The compounds can be formulated as [Ir(ppy)2(bpy)][M(II)Cr(III)(ox)3] x 0.5 H2O (M(II) = Ni, Mn, Co, Fe, and Zn) and [Ir(ppy)2(bpy)]-[M(II)Fe(III)(ox)3] x 0.5 H2O (M(II) = Fe, Mn) and crystallize in the chiral cubic space group P4(1)32 or P4(3)32. They show the well-known 3D chiral structure formed by M(II) and M(III) ions connected through oxalate anions with [Ir(ppy)2(bpy)]+ cations and water molecules in the holes left by the oxalate network. The M(II)Cr(III) compounds behave as soft ferromagnets with ordering temperatures up to 13 K, while the Mn(II)Fe(III) and Fe(II)Fe(III) compounds behave as a weak ferromagnet and a ferrimagnet, respectively, with ordering temperatures of 31 and 28 K. These values represent the highest ordering temperatures so far reported in the family of 3D chiral magnets based on bimetallic oxalate complexes.     

Counterpropagating spatial Kerr soliton in reflection gratings

We analytically predict the existence of both spatial bright and dark counterpropagating solitons in a reflection grating in the presence of the Kerr nonlinearity. The basic trapping mechanism consists of a twofold balance where diffraction is compensated by self-focusing and reflection is altered by the nonlinear-induced interferometric grating. We find that, whenever the spectral soliton profile lies within the grating stop band, bright and dark solitons exist only if the mutual phase of the counterpropagating solitons is pi or 0, respectively.     

Sufficient conditions for Benford’s law

We present two sufficient conditions for an absolutely continuous random variable to obey Benford’s law for the distribution of the first significant digit. These two sufficient conditions suggest that Benford’s law will not often be observed in everyday sets of numerical data. On the other hand, we recall that there are two processes by way of which a random variable can come close to following Benford’s law. The first of these is the multiplication of independent random variables and the second is the exponentiation of a random variable to a large power. Our working tool is the Poisson sum formula of Fourier analysis. Like the central limit theorem, Benford’s law has an asymptotic nature.     

Effect of Fill Time on the Performance of Pilot-scale ASBR and AnSBBR Applied to Sanitary Wastewater Treatment

Many lab-scale studies have been carried out regarding the effect of feed strategy on the performance of anaerobic sequencing batch reactors (ASBR); however, more detailed pilot-scale studies should be performed to assess the real applicability of this type of operation. Therefore, the objective of this work was to assess the effect of feed strategy or fill time in a 1-m³ mechanically stirred pilot-scale sequencing batch reactor, treating 0.65 m³ sanitary wastewater in 8-h cycles at ambient temperature. Two reactor configurations were used: one containing granular biomass (denominated ASBR) and the other immobilized biomass on polyurethane foam as inert support (denominated anaerobic sequencing batch biofilm reactor (AnSBBR)). The reactors were operated under five distinct feed strategies, namely: typical batch and fed-batch for 25%, 50%, 75%, and 100% of the cycle length. Stirring frequency in the ASBR was 40 rpm with two flat-blade turbine impellers and 80 rpm in the AnSBBR with two helix impellers. The results showed that both the ASBR and AnSBBR when operated under typical batch, fed-batch for 50% and 75% of the cycle length, presented improved organic matter removal efficiencies, without significant differences in performance, thus showing important operational flexibility. In addition, the reactors presented operation stability under all conditions.     

New approach to the stereoselective synthesis of the [4.5] spiroketal moiety of papulacandins

An efficient approach for the stereoselective construction of the spiroketal moiety of papulacandins, based on the condensation of the protected derivative of D-arabino-1,4-lactone 2 with the α-lithiated carbanion of β-phenylsulfonyl dihydrofuran 1, is described.     

Sopra un teorema del calcolo delle variazioni del sig. lindeberg

Rendiconti del Circolo Matematico di Palermo Series 1 -     

Estudios sobre acidos hidroxámicos VII. Reconocimiento específico de ésteres fórmicos,su investigación en mezclas,especialmente con otros ésteres carboxílicos

Resumen Se propone una técnica para el reconocimiento específico de microcantidades de ésteres fórmicos, basada en su transformación en ácido formohidroxámico mediante hidroxilaminolisis en medio hidro-alcohólico amoniacal. En las condiciones elegidas no son causa de error los otros ésteres carboxílicos, ni la mayor parte de las sustancias cuyos grupos funcionales reaccionan con la hidroxilamina en medio alcalino de hidróxido o carbonato de sodio o potasio. El método permite reconocer el radical formilo procedente de ésteres fórmicos en diluciones de una parte por millón, con una sensibilidad de 5g. Los ésteres fórmicos no resultan interferidos por cantidades mil a diez mil veces superiores de otros ésteres carboxílicos.

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Summary A working technique is suggested for the specific detection of micro quantities of esters of formic acid. It is based on the conversion into formhydroxamic acid esters by means of hydroxylaminolysis in aqueous-alcoholic, ammoniacal medium. Under the chosen conditions, no interference is offered by the other carboxylic acids or by most of the compounds, whose functional groups react, in alkaline medium, with hydroxylamine, i. e., in the presence of the hydroxides or carbonates of sodium or potassium. The method permits the detection of the formyl radical, obtained from formic acid esters, in dilutions of 11000 000, with the corresponding limit of identification of 5g. It was found that the identification of formic acid ester was not disturbed by 1000 to 10000 times the quantity of the other carboxylic acid esters.

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Zusammenfassung Eine Arbeitstechnik für den spezifischen Nachweis von Mikromengen von Ameisensäureestern wird vorgeschlagen. Sie beruht auf der Umwandlung in Formhydroxamsäure mittels Hydroxylaminolyse in wäßrig-alkoholischem, ammoniakalischem Medium. Unter den gewählten Bedingungen stören weder die übrigen Carbonsäureester noch die meisten derjenigen Substanzen, deren funktionelle Gruppen mit dem Hydroxylamin in alkalischem Medium, das heißt in Gegenwart der Hydroxyde oder Carbonate des Natriums oder Kaliums, reagieren. Die Methode erlaubt den Nachweis des Formylradikals, das aus Ameisensäureestern entsteht, in Verdünnungen von 11000 000, wobei die Erfassungsgrenze 5g beträgt. Es stellte sich heraus, daß der Nachweis der Ameisensäureester durch 1000-bis 10 000mal größere Mengen der übrigen Carbonsäureester nicht gestört wird.

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Résumé Les auteurs recommandent une technique de travail pour l'identification spécifique de microquantités d'esters formiques. Elle repose sur leur transformation en acide formhydroxamique par hydroxylaminolyse en milieu hydroalcoholique ammoniacal. Dans les conditions choisies, aucune perturbation n'est apportée par la présence des autres esters carboniques ni par celle de la plupart des substances dont les groupes fonctionnels réagissent sur l'hydroxylamine en milieu alcalin, c'est-à-dire en présence d'hydroxyde ou de carbonate de sodium ou de potassium. La méthode permet l'identification du radical formyle qui se forme à partir des esters formiques à des dilutions de 11000 000 avec une limite de sensibilité de 5g. Il apparaît que cette identification des esters formiques n'est pas perturbée par la présence de quantités 1000 à 10 000 fois plus grandes des autres esters carboniques.

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Presentado en la 8as Sesiones Químicas Argentinas. La Plata, V, 1956.

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Expresamos nuestro agradecimiento al Dr.Carlos Torres, de Cadya, S. A., por los ésteres facilitados para la realizatión del trabajo.