[HFe(CO)4 – A Versatile Reagent toward Dichlorophosphines,Phosphenium Salts,Phospha-alkenes and Diphosphenes

Abstract

A new entry to non classical phosphorus complexes is reported.     

Methode calorimetrique de mesure des enthalpies de formation des alliages liquides a forte tension de vapeur

The heat effects corresponding to the dissolution of solid PbSe in liquid Pb-Se alloys starting from pure Pb were measured with a direct reaction calorimeter. The partial enthalpy of formation of PbSe in the melt and the integral enthalpy of formation of the Pb-PbSe system in the liquid state referred the liquid Pb and PbSe were deduced. Then, from a very simple change of reference state, and in the knowledge of the enthalpy of PbSe, the integral enthalpy of formation of Pb-Se liquid alloys with reference to pure liquid components could be derived. The results agreed very well with those obtained previously on the dissolution of Se in Pb. The method used can be applied whenever the component to be added to the bath has a high vapor pressure.

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Zusammenfassung Die bei der Überführung von festem PbSe in flüssige Pb-Se-Legierungen auftretenden Wärmeeffekte wurden mittels direkter Reaktionskalorimetrie bestimmt. Die auf flüssiges Pb und PbSe bezogene partielle Bildungsenthalpie des Pb-PbSe-Systems im flüssigen Zustand wurde ermittelt. Durch eine geringfügige Veränderung des Referenzzustandes konnte bei Kenntnis der Enthalpie von PbSe die integrale Bildungsenthalpie von flüssigen Pb-Se-Legierungen in Bezug auf die reinen Komponenten abgeleitet werden. Die Ergebnisse stimmen gut mit denen überein, die früher für die Auflösung von Se in Pb erhalten wurden. Die Methode ist anwendbar, wenn dem Bade zuzugebende Komponenten einen hohen Dampfdruck haben.

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Pb-Se Pb-Se, . Pb-Se Pb-PbSe Pb Pb-Se. PbSe, Pb-Se . , . , .

     

A Bistable Microelectromechanical System Actuated by Spin-Crossover Molecules

We report on a bistable MEMS device actuated by spin-crossover molecules. The device consists of a freestanding silicon microcantilever with an integrated piezoresistive detection system, which was coated with a 140 nm thick film of the [Fe(HB(tz)₃)₂] (tz=1,2,4-triazol-1-yl) molecular spin-crossover complex. Switching from the low-spin to the high-spin state of the ferrous ions at 338 K led to a reversible upward bending of the cantilever in agreement with the change in the lattice parameters of the complex. The strong mechanical coupling was also evidenced by the decrease of approximately 66 Hz in the resonance frequency in the high-spin state as well as by the drop in the quality factor around the spin transition.     

Single stage purification of flax,hemp, and milkweed stem and their physical and morphological properties

Agriculture biomass is an alternative possible solution for the extraction of cellulose, compared to the classical soft and hard wood. However, the valorization of cellulose is challenging for the researchers as it involves multiple steps. In the present study, the raw fibers of flax, hemp, and milkweed stem fibers were purified in single step using hydrogen peroxide in water. By this method authors successfully extracted the purified cellulose fibers without damaging the fiber length. The purified fibers were characterized to understand the thermal, functional, crystalline, and morphological properties by thermogravimetric analysis (TGA), Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), and scanning electron microscopy (SEM). The FTIR results showed the effective removal of lignin and significant improvement in thermal stability was observed by TGA. Evidently, the SEM results showed significant improvement in the morphology compared to that of the raw fibers. XRD results showed that the treatment does not affect the crystallinity of the fibers.     

A Redox‐Active Bridging Ligand to Promote Spin Delocalization,High‐Spin Complexes,and Magnetic Multi‐Switchability

A dinuclear Co^II complex, [Co₂(tphz)(tpy)₂]ⁿ⁺ (n=4, 3 or 2; tphz: tetrapyridophenazine; tpy: terpyridine), has been assembled using the redox‐active and strongly complexing tphz bridging ligand. The magnetic properties of this complex can be tuned from spin‐crossover with T_1/2≈470 K for the pristine compound (n=4) to single‐molecule magnet with an S_T=5/2 spin ground state when once reduced (n=3) to finally a diamagnetic species when twice reduced (n=2). The two successive and reversible reductions are concomitant with an increase of the spin delocalization within the complex, promoting remarkably large magnetic exchange couplings and high‐spin species even at room temperature.     

Lego-like spheres and tori

Given a connected surface \({\mathbb {F}}^2\) with Euler characteristic \(\chi \) and three integers \(b>a\ge 1<k\), an \((\{a,b\};k)\)-\({\mathbb {F}}^2\) is a \({\mathbb {F}}^2\)-embedded graph, having vertices of degree only k and only a- and b-gonal faces. The main case are (geometric) fullerenes (5, 6; 3)-\({\mathbb {S}}^2\). By \(p_a\), \(p_b\) we denote the number of a-gonal, b-gonal faces. Call an \((\{a,b\};k)\)-map lego-admissible if either \(\frac{p_b}{p_a}\), or \(\frac{p_a}{p_b}\) is integer. Call it lego-like if it is either \(ab^f\)-lego map, or \(a^fb\)-lego map, i.e., the face-set is partitioned into \(\min (p_a,p_b)\) isomorphic clusters, legos, consisting either one a-gon and \(f=\frac{p_b}{p_a}\,b\)-gons, or, respectively, \(f=\frac{p_a}{p_b}\,a\)-gons and one b-gon; the case \(f=1\) we denote also by ab. Call a \((\{a,b\};k)\)-map elliptic, parabolic or hyperbolic if the curvature \(\kappa _b=1+\frac{b}{k}-\frac{b}{2}\) of b-gons is positive, zero or negative, respectively. There are 14 lego-like elliptic \((\{a,b\};k)\)-\({\mathbb {S}}^2\) with \((a,b)\ne (1,2)\). No \((\{1,3\};6)\)-\({\mathbb {S}}^2\) is lego-admissible. For other 7 families of parabolic \((\{a,b\};k)\)-\({\mathbb {S}}^2\), each lego-admissible sphere with \(p_a\le p_b\) is \(a^fb\) and an infinity (by Goldberg–Coxeter operation) of \(ab^f\)-spheres exist. The number of hyperbolic \(ab^f\,(\{a,b\};k)\)-\({\mathbb {S}}^2\) with \((a,b)\ne (1,3)\) is finite. Such \(a^f b\)-spheres with \(a\ge 3\) have \((a,k)=(3,4),(3,5),(4,3),(5,3)\) or (3, 3); their number is finite for each b, but infinite for each of 5 cases (a, k). Any lego-admissible \((\{a,b\};k)\)-\({\mathbb {S}}^2\) with \(p_b=2\le a\) is \(a^f b\). We list, explicitly or by parameters, lego-admissible \((\{a,b\};k)\)-maps among: hyperbolic spheres, spheres with \(a\in \{1,2\}\), spheres with \(p_b\in \{2,\frac{p_a}{2}\}\), Goldberg–Coxeter’s spheres and \((\{a,b\};k)\)-tori. We present extensive computer search of lego-like spheres: 7 parabolic (\(p_b\)-dependent) families, basic examples of all 5 hyperbolic \(a^fb\) (b-dependent) families with \(a\ge 3\), and lego-like \((\{a,b\};3)\)-tori.     

Central limit theorems for realized volatility under hitting times of an irregular grid

We consider a continuous semi-martingale sampled at hitting times of an irregular grid. The goal of this work is to analyze the asymptotic behavior of the realized volatility under this rather natural observation scheme. This framework strongly differs from the well understood situations when the sampling times are deterministic or when the grid is regular. Indeed, neither Gaussian approximations nor symmetry properties can be used. In this setting, as the distance between two consecutive barriers tends to zero, we establish central limit theorems for the normalized error of the realized volatility. In particular, we show that there is no bias in the limiting process.     

Linear-programming extended formulations for the single-item lot-sizing problem with backlogging and constant capacity

Recently, several authors [8, 10] have argued for the use of extended formulations to tighten production planning models. In this work we present two linear-programming extended formulations of the constant-capacity lot-sizing problem with backlogging. The first one applies to the problem with a general cost function and has O(n³) variables and constraints. This improves on the more straightforward O(n⁴) Florian and Klein [2] type formulation. The second one applies when the costs satisfy the Wagner-Whitin property but it has O(n²) variables and O(n³) constraints. As a by-product, we positively answer an open question of Miller and Wolsey [4] about the tightness of an extended formulation for the continuous mixing set. This text presents research results of the Belgian Program on Interuniversity Poles of Attraction initiated by the Belgian State, Prime Minister's Office, Science Policy Programming. The research was carried out with financial support of the Growth Project G1RD-1999-00034 (LISCOS) of the European Community. The scientific responsibility is assumed by the author.