Mechanism of dehydration of magnesium oxalate dihydrate

The isothermal dehydration of magnesium oxalate dihydrate has been studied at various temperatures between 190 and 260°C in the presence of air. The isothermal dehydration curves show the usual sigmoidal character and display an induction period which is highest at 190°C. The dehydration velocity constant (k) values (obtained by the application of Mampel's equation) plotted vs. 1/T according to the Arrhenius equation gave a plot in which two linear sections intersect at ～215°C with activation energies of 12.3 and 18.3 kcal mole^?1 for the lower- and higher-temperature sections, respectively. This behaviour is tentatively explained in terms of a change in the mechanism of dehydration, and not the formation of some new phase other than the dihydrate and the anhydrous oxalate phases present in both the original crystalline oxalate and the sample heated at 200°C for 120 min. X-Ray patterns of the heated oxalate sample left for a few days at room temperature showed a marked sensitivity for rehydration of the anhydrous oxalate phase.     

Extremal measures for a system of orthogonal polynomials

We characterize the extremal measures of an indeterminate moment problem associated with a system of orthogonal polynomials defined by a three-term recurrence relation.     

Pyridazine Derivatives and Related Compounds,Part 221: Synthesis,Reactions, and Insecticidal Activity of 3-Amino-5,6-diaryl-1H-pyrazolo[3,4-c]pyridazines

Starting with 3-amino-5,6-diaryl-1H-pyrazolo[3,4-c]pyridazine, the syntheses of thiourea derivatives, dithiocarbamates, ethyl carbamate, phosphoranylidene amino, and substituted acetamido derivatives are described. The products were screened for their insecticidal activity against Mucsa, domestica, and Aphid, Macrosiphum pisi.

Supplemental materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental file.     

Stability of the determination of the surface impedance of an obstacle from the scattering amplitude

We prove a stability estimate of logarithmic type for the inverse problem consisting in the determination of the surface impedance of an obstacle from the scattering amplitude. We present a simple and direct proof, which is essentially based on an elliptic Carleman inequality. Copyright © 2013 John Wiley & Sons, Ltd.     

A fast and robust fictitious domain method for modelling viscous flows in complex mixers: The example of propellant make‐down

This work deals with the development of a fast three‐dimensional numerical strategy for the simulation of viscous fluid flow in complex mixing systems. The proposed method is based on a distributed Lagrange multiplier fictitious domain method and the use of the low‐cost MINI finite element. Contrary to the previous fictitious domain method developed by our group a few years ago, the underlying partial differential equations are solved here in a coupled manner using a consistent penalty technique. The method is discussed in detail and its precision is assessed by means of experimental data in the case of an agitated vessel. A comparison made with our existing fictitious domain method and its decoupled Uzawa‐based solver clearly shows the advantages of resorting to the MINI finite element and fully coupled solution strategy. The new technique is then applied to the simulation of the flow of a Newtonian viscous fluid in a three‐blade planetary mixer in the context of the production of solid propellants. Copyright © 2008 John Wiley & Sons, Ltd.     

A necklace model for vesicles simulations in 2D

The aim of this paper is to propose a new numerical model to simulate 2D vesicles interacting with a Newtonian fluid. The inextensible membrane is modeled by a chain of circular rigid particles, which are maintained in cohesion by using two different types of forces. First, a spring force is imposed between neighboring particles in the chain. Second, in order to model the bending of the membrane, each triplet of successive particles is submitted to an angular force. Numerical simulations of vesicles in shear flow have been run using FEM and the FreeFem++ software. Exploring different ratios of inner and outer viscosities, we recover the well‐known ‘tank‐treading’ and ‘tumbling’ motions predicted by a theory and experiments. Moreover, for the first time, 2D simulations of the ‘vacillating‐breathing’ regime without special ingredient such as thermal fluctuations are recovered. Copyright © 2014 John Wiley & Sons, Ltd.     

Evidences of segregated SnO2 type nanoparticles coating layered double hydroxide at moderate temperature

A series of layered double hydroxide (LDH) materials prepared by classical coprecipitation in the presence of divalent Co2+, trivalent Al3+, and tetravalent Sn4+ cations have been investigated as a function of the temperature. As illustrated for the cation composition (Co; Al; Sn) of (0.75; 0.175; 0.075), the segregation of SnO2-type nanodomains in an interphasing LDH sand-rose region is directly evidenced by transmission electron microscopy and selected area electron diffraction (TEM/SAED). At moderate temperature (400 degrees C) the local environment around the cobalt cations is strongly modified, whereas the local structure is found to be unchanged in the vicinity of the tin cations. It is explained on the basis of the breakdown of the lamellar assembly and of the partial oxidation of Co2+ cations and that tin dioxide domains are still segregated from LDH particles. Even if the tin dioxide component does not participate from a structural point of view in the LDH composition, its beneficial effect on the textural properties is significant, increasing the specific surface area and narrowing the pore size distribution.     

Pyrimidine ortho-quinodimethanes. Part 2: Synthesis of new [60]fullerene adducts based on substituted pyrimidine derivatives and their 1H NMR dynamic study

The Diels–Alder reaction of various pyrimidine ortho-quinodimethanes generated in situ with C₆₀ gives access to a variety of new fullerodihydroquinazoline derivatives. This variety is increased since substituents on the pyrimidine ring can be easily modified before or after its reaction with C₆₀. Variable temperature ¹H NMR spectra provided thermodynamic parameters related to the boat-to-boat interconversion of the cyclohexene ring fused to the fullerene moiety. The mass spectra of the prepared cycloadducts show that the retro-Diels–Alder process takes place easily with elimination of the corresponding diene molecule.     

Exploring rearrangements along the fragmentation pathways of diuron anion: A combined experimental and computational investigation

Diuron (3-(3,4-dichlorophenyl)-1,1-dimethylurea), a common herbicide from phenyl urea class, was investigated by studying the formation of several negative ions [M−H]⁻ in the gas phase and the fragmentation behaviour of the thermodynamically most probably formed isomeric anions upon linear ion acceleration/collision experiments. The collision induced dissociation experiments (CID) were carried out in a hexapole–quadrupole–hexapole hybrid system coupled to 12 T magnet with infinity ICR cell for high resolution measurements. Two distinctive main pathways were observed in the MS/MS spectrum. Sustained off-resonance irradiation (SORI) experiments inside the ICR cell reinforce the fragmentation channels obtained from linear ion acceleration experiments. The fragmentation pathways were also completely investigated by the use of B3LYP/6-311+G(2d,p)//B3LYP/6-31+G(d) level of theory. Elimination of dimethylamine takes place in a two-step process, by which two successive 1,3 proton shifts occur. The second 1,3 proton shift is concerted with the departure of dimethylamine. The driving force for the (CH₃)₂NH elimination is the formation of isocyanate group. The formed primary product ion can further decompose to release HCl through a new transition state. A stable new aromatic product ion is formed with 10π electrons. Loss of C₃H₅NO neutral from another anionic isomer of the precursor ion was also observed and is characteristic for the amide terminal of the diamide functional group. A concerted mechanism is proposed, by which N–C bond breakage and cyclization of the eliminated neutral fragment C₃H₅NO takes place simultaneously to form 1-methyl-aziridin-2-one.