Migratory insertion in N-heterocyclic carbene complexes of palladium; an experimental and DFT study

The first authenticated example of migration of a methyl group from palladium(II) to a coordinated N-heterocyclic carbene is described.     

Exploring hydrothermally grown potassium titanate fibers by STEM-in-SEM/EDX and XRD.

During lab-scale experiments on the reforming of methanol by means of water at supercritical conditions (T > 374 degrees C, p > 22.1 MPa), a tubular reactor with a titanium liner was exposed to an aqueous solvent containing methanol (5 wt%) and KHCO3 (0.3 wt%). At the end of the run, a fibrous precipitate was found at two positions in the reactor. The material was studied in a field emission scanning electron microscope equipped with an energy dispersive X-ray analysis unit (FESEM/EDX). A thin-film support technique using carbon-filmed TEM grids was applied to perform scanning transmission-type imaging (STEM-in-SEM operation) and transmission current measurements. The analysis of the hydrothermally grown fibers resulted in a potassium titanate species composed of approximately K2TiO3, which has been confirmed by X-ray diffraction (XRD).     

Synthesis,bonding properties and ether activation reactivity of cyclobutadienyl-ligated hybrid uranocenes

A series of hybrid uranocenes consisting of uranium(iv) sandwiched between cyclobutadienyl (Cb) and cyclo-octatetraenyl (COT) ligands has been synthesized, structurally characterized and studied computationally. The dimetallic species [(η⁴-Cb′′′′)(η⁸-COT)U(μ:η²:η⁸-COT)U(THF)(η⁴-Cb′′′′)] (1) forms concomitantly with, and can be separated from, monometallic [(η⁴-Cb′′′′)U(THF)(η⁸-COT)] (2) (Cb′′′′ = 1,2,3,4-tetrakis(trimethylsilyl)cyclobutadienyl, COT = cyclo-octatetraenyl). In toluene solution at room temperature, 1 dissociates into 2 and the unsolvated uranocene [(η⁴-Cb′′′′)U(η⁸-COT)] (3). By applying a high vacuum, both 1 and 2 can be converted directly into 3. Using bulky silyl substituents on the COT ligand allowed isolation of base-free [(η⁴-Cb′′′′)U{η⁸-1,4-(ⁱPr₃Si)₂C₈H₆}] (4), with compounds 3 and 4 being new members of the bis(annulene) family of actinocenes and the first to contain a cyclobutadienyl ligand. Computational studies show that the bonding in the hybrid uranocenes 3 and 4 has non-negligible covalency. New insight into actinocene bonding is provided by the complementary interactions of the different ligands with uranium, whereby the 6d orbitals interact most strongly with the cyclobutadienyl ligand and the 5f orbitals do so with the COT ligands. The redox-neutral activation of diethyl ether by [(η⁴-Cb′′′′)U(η⁸-C₈H₈)] is also described and represents a uranium-cyclobutadienyl cooperative process, potentially forming the basis of further small-molecule activation chemistry.

The synthesis, structure and bonding in a series of hybrid uranocenes consisting of cyclobutadienyl and cyclo-octatetraenyl ligands is described.     

On the Nonlinear Dynamic State Reconstruction Problem for Chemical/Biochemical Reaction Systems in the Presence of Model Uncertainty

A new approach to the unmeasurable state reconstruction problem for nonlinear chemical reaction systems in the presence of model uncertainty is proposed. In particular, a new robust nonlinear state estimation method is developed that explicitly uses all the available useful information associated with: (i) a dynamic model inevitably characterized by uncertainty, and (ii) a set of sensor measurements in order to accurately reconstruct other key quantities/variables that cannot be measured on-line due to physical and/or technical limitations. The problem of interest is conveniently formulated and addressed within the context of singular partial differential equations (PDE) theory, leading to a nonlinear state estimator that possesses a state-dependent gain computed through the solution of a system of first-order singular PDEs. A set of necessary and sufficient conditions is presented that ensure the existence and uniqueness of a locally analytic solution to the aforementioned system of singular PDEs, and a series solution method that can be easily implemented via a MAPLE code is developed. Under these conditions, the convergence of the estimation error or the mismatch between the actual unmeasurable states and their estimates is analyzed and characterized in the presence of model uncertainty. Finally, the performance of the proposed nonlinear etimator and its convergence properties are evaluated in an illustrative biochemical reaction system that exhibits nonlinear behavior coupled with parametric uncertainty, and the estimation objective is to accurately reconstruct the unmeasurable substrate concentration using the available cell mass concentration measurements and the model of the system under consideration.     

Friedel–crafts crosslinking methods for polystyrene modification. IV. Macromolecular structure of crosslinked particles

Crosslinked polystyrene particles were prepared by Friedel–Crafts suspension crosslinking of polystyrene using 2,4-dichloromethyl-2,5-dimethyl benzene as crosslinking agent. The polymer was dissolved in nitrobenzene and reaction occurred in a 70 wt % aqueous solution of ZnCl₂ with poly(vinyl alcohol) as a suspending agent. The spherical particles produced were swollen in toluene, chloroform, and tetrahydrofuran to determine their equilbrium polystyrene volume fraction. Analysis of the crosslinked macromolecular structure gave values of number-average molecular weight between crosslinks of M?_c = 900–5900 increasing as the nominal crosslinking ratio X decreased from 0.75 to 0.0625 mol of crosslinking agent per mole of polystyrene repeating unit. Porosimetric analysis contributed to the understanding of the importance of the pore structure for swelling behavior.     

Comparison of three digestion methods for the determination of the aqua regia soluble content of lead,cadmium and chromium in sewage sludges by ETAAS

A procedure for the determination of the aqua regia soluble content of lead, cadmium and chromium in a sewage sludge reference material (CRM 145R) by electrothermal atomic absorption spectrometry (ETAAS) is described. A comparison of the dissolution procedure proposed in the certification report, to an oven-assisted digestion and a proposed microwave digestion procedure is performed. In the ETAAS method developed, 1 g of Pt proved to be an appropriate modifier for each of the above heavy metals. Possible sources of error at each analytical step are addressed. The metal contents obtained with the proposed method are in a good agreement at 95% significance level with the certified values given for CRM 145R.     

Topological properties of the solution set of a class of nonlinear evolutions inclusions

In the paper we study the topological structure of the solution set of a class of nonlinear evolution inclusions. First we show that it is nonempty and compact in certain function spaces and that it depends in an upper semicontinuous way on the initial condition. Then by strengthening the hypothesis on the orientor field F(t, x), we are able to show that the solution set is in fact an R -set. Finally some applications to infinite dimensional control systems are also presented.     

Domination on Sets and in H p

In this paper we characterize the subsets E of the unit disk with the following property : ${\rm If}\ 0\ < \ p \ \leq \infty\ {\rm and}\ f \ \epsilon\ H^{p},\ 0 \ < \ ||f||_{p}\ <c \ < \infty $ then there exists $ {\cal G}\epsilon {H^{p}} $ such that $|{\cal G}(z)|\leq |f(z)|\ {\rm on}\ E\ {\rm and}\ ||{\cal G}||_{p}$ . A similar characterisation is given also for the case of the disk algebra.     

Concurrent Delay Testing in Totally Self-Checking Systems

Prompt detection of even small delay faults, sometimes before causing critical paths to fail, gains importance since stricter test quality requirements for high performance and high density VLSI circuits have to be satisfied in critical applications. This can be achieved by using concurrent delay testing.In this paper a novel idea for concurrent detection of two-rail path delay faults is introduced. It is shown that TSC two-rail code error indicators that monitor pairs of paths with similar propagation delays can be used for concurrent delay testing. Our technique is applied to TSC two-rail code checkers as well as to duplication systems which are the most widely used TSC systems. The design of TSC two-rail code checkers and TSC duplication systems with respect to two-rail path delay faults is achieved for first time in the open literature.