Extraction of uranium(IV) from phosphoric acid solutions with 1-phenyl-3-methyl-4-benzoylpyrazolone-5 (PMBP)

The extraction of uranium(IV) from phosphoric acid solutions with PMBP and PMBP-TOPO mixtures has been studied. The synergic extraction with PMBP-TOPO is more effective than the simple chelate extraction with PMBP and both systems are more effective than the synergic extraction of uranium(VI) with DEHPA-TOPO. It is established that the complexes extracted are U(PMBP)(4) and U(PMBP)(4).TOPO for the chelate and synergic extraction respectively. The most probable uranium(VI) species in the aqueous phase (2.9-6.33M H(3)PO(4)) is the neutral complex U(H(5)P(2)O(8))(4). Analytical methods suitable for determination of uranium in phosphoric acid solutions have been developed. The highest sensitivity is achieved by combining the synergic extraction with the uranium(IV)-arsenazo III colour reaction.     

Rapid Convergence to Frequency for Substitution Tilings of the Plane

This paper concerns self-similar tilings of the Euclidean plane. We consider the number of occurrences of a given tile in any domain bounded by a Jordan curve. For a large class of self-similar tilings, including many well-known examples, we give estimates of the oscillation of this number of occurrences around its average frequency times the total number of tiles in the domain, which depend only on the Jordan curve.     

A semi-implicit monotone difference scheme for an initial-boundary value problem of a strongly degenerate parabolic equation modeling sedimentation-consolidation processes

We prove the convergence of a semi-implicit monotone finite difference scheme approximating an initial-boundary value problem for a spatially one-dimensional quasilinear strongly degenerate parabolic equation, which is supplied with two different inhomogeneous flux-type boundary conditions. This problem arises in the modeling of the sedimentation-consolidation process. We formulate the definition of entropy solution of the model in the sense of Kru kov and prove convergence of the scheme to the unique entropy solution of the problem, up to satisfaction of one of the boundary conditions.

     

Linearly repetitive Delone sets are rectifiable

We show that every linearly repetitive Delone set in the Euclidean d  -space R^d${\mathbb{R}}^d$, with d?2$d?2$, is equivalent, up to a bi-Lipschitz homeomorphism, to the integer lattice Z^d${\mathbb{Z}}^d$. In the particular case when the Delone set X   in R^d${\mathbb{R}}^d$ comes from a primitive substitution tiling of R^d${\mathbb{R}}^d$, we give a condition on the eigenvalues of the substitution matrix which ensures the existence of a homeomorphism with bounded displacement from X   to the lattice βZ^d$\beta {\mathbb{Z}}^d$ for some positive β. This condition includes primitive Pisot substitution tilings but also concerns a much broader set of substitution tilings.     

EPR Equilibration Study of the O–H Bond Dissociation Enthalpy in a Benzyl Phenolic Antioxidant

The equilibrium of the reaction galvinoxyl radical + 4,4′-methylene-bis(2,6-di-tert-butyl-phenol) (IOH) ⇆ hydrogalvinoxyl + 4,4′-methylene-bis(2,6-di-tert-butyl-phenoxyl radical) was monitored by electron paramagnetic resonance spectroscopy between 213 and 293 K. The equilibrium constant was calculated for each temperature point and correlated to T ⁻¹ applying the Van't Hoff relationship lnK _R = (−ΔH _R ⁰/RT) + (ΔS _R ⁰/R). The reaction enthalpy was found to be 12.0 ± 0.9 kJ/mol and the bond strength in IOH (BDE_(O–H)) = 340.7 ± 3.0 kJ/mol. The thermochemical stabilization of the involved phenoxyls is discussed. Authors' address: Sara N. Mendiara, Departamento de Química, Facultad de Ciencias Exactas y Naturales, Universidad Nacional de Mar del Plata, Funes 3350, Mar del Plata 7600, Argentina     

ESR equilibrium measurements of the O?H bond energy in α-tocopherol

ESR equilibrium measurements in radical buffer systems yield a value of 76.0 kcal/mol for the O? H bond energy in α-tocopherol.     

Response of PETN detonators to elevated temperatures

In the present study, commercially available detonators with pentaerythritol tetranitrate (PETN) were subjected to elevated temperatures. The detonators were thermally ignited over a range of heating rates to measure ignition delay time and assess detonator violence. The violence of the detonator was quantified by measuring the velocity of the detonator closure disc (or “flyer”). The maximum flyer velocity of a thermally ignited detonator was comparable in magnitude to that obtained by initiating a room temperature pristine detonator with an exploding bridge wire (under the same confinement); however, the high flyer velocity was not an indication of deflagration to detonation transition (DDT) in the thermally ignited detonator. The detonator responded more violently than a thermally ignited detonator when initiated at 95% of the ignition delay time. Inoperability thresholds were also measured by varying the detonator temperature and the threshold was found to be sensitive at detonator temperatures below the melting point of PETN.     

Convergence of a level‐set algorithm in scalar conservation laws

This article is concerned with the convergence of the level‐set algorithm introduced by Aslam (J Comput Phys 167 (2001), 413–438) for tracking the discontinuities in scalar conservation laws in the case of linear or strictly convex flux function. The numerical method is deduced by the level‐set representation of the entropy solution: the zero of a level‐set function is used as an indicator of the discontinuity curves and two auxiliary states, which are assumed continuous through the discontinuities, are introduced. We rewrite the numerical level‐set algorithm as a procedure consisting of three big steps: (a) initialization, (b) evolution, and (c) reconstruction. In (a), we choose an entropy admissible level‐set representation of the initial condition. In (b), for each iteration step, we solve an uncoupled system of three equations and select the entropy admissible level‐set representation of the solution profile at the end of the time iteration. In (c), we reconstruct the entropy solution using the level‐set representation. We prove the convergence of the numerical solution to the entropy solution in for every , using ‐weak bounded variation (BV) estimates and a cell entropy inequality. In addition, some numerical examples focused on the elementary wave interaction are presented. © 2014 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 31: 1310–1343, 2015     

EPR Equilibration Measurement of the C–H Bond Enthalpy in the Methylene Groups of 1,3,5-Trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl)benzene (Irganox)

On the basis of previous and current studies, it has been possible to evaluate and compare the bond dissociation energies of the phenol (O–H) bond and of the methylene and methyl (C–H) bonds in Irganox (trade name) by means of electron paramagnetic resonance records of galvinoxyl–irganoxyl hydrogen transfer reaction equilibria. The bond dissociation enthalpy of the C–H methylene and methyl bonds in Irganox was found to be 339.0 ± 3.0 kJ/mol, very close to the previously found value of 340.7 ± 3.0 kJ/mol for the O–H bond of some benzyl–phenolic antioxidant.     

Study of the aggregation of nonylammonium chloride in aqueous solutions of sodium chloride by vapor pressure osmometry

We determined osmotic coefficients from vapor pressure osmometry (VPO) measurements on aqueous solutions of nonylammonium chloride in the presence of NaCl at 30°C. VPO data were subsequently used to determine the critical micelle concentration (CMC) of the solutions of this surfactant. The values of this parameter obtained from VPO are well correlated with those obtained from light scattering. No premicellar aggregation was observed at surfactant concentrations below the CMC. The osmotic coefficients below the CMC may be evaluated from the extended form of the Debye–Hückel equation. Above the CMC, the dependence of the osmotic coefficient on the surfactant concentration was indicative of the occurrence of aggregation rather than the interactions in the system. Some comments are made on the uncertainty in the value of some parameters in micellar solutions and possible source of error using the VPO technique in these solutions.