Silica-supported metallocenes: stereochemical comparison between homogeneous and heterogeneous catalysis

Propylene was polymerized in the presence of the isospecific Et(Ind)₂ZrCl₂ (Et: ethylene, Ind: indenyl) and the aspecific (Ind)₂ZrCl₂ complexes in solution and anchored to SiO₂ and SiO₂/MAO (MAO: methylaluminoxane) supports. From the stereochemical analysis of the polypropene samples obtained it can be deduced that (i) the same active species is formed when a metallocene is in solution and when it is anchored to the SiO₂/MAO support and (ii) a completely different active species is formed when the metallocene is anchored to the silica. The fact that both systems Et(Ind)₂ZrCl₂ SiO₂ and (Ind)₂ZrCl₂ SiO₂ produce the same prevailingly isospecific polymer suggests that only isospecific centers are formed in this case, independently of the metallocene stereochemical structure.     

3D printed honeycomb bilayer structures based on polylactic acid as lightweight microwave absorbing materials

3D printed honeycomb structures constituted by neat polylactic acid (PLA) and conductive PLA (PLAc) with different cell sizes and thicknesses were manufactured through 3D printing technology based on material extrusion (MEX). These structures were arranged into bi-layer honeycomb structures (BHS) for evaluation of the microwave absorbing properties at the X-band (8.2–12.4 GHz) and Ku-band (12.4–18 GHz) frequency ranges. The effects of cell size, sample thickness, layer thickness ratio and the nature of the top layer on the electromagnetic attenuation performance of BHS samples were investigated in terms of reflection loss (RL). The components geometric characteristics and the arrangement of the layers exerted great influence on the RL values and effective absorption bandwidth (EAB). Overall the bilayer structures with 5 mm total thickness presented the best EM response in terms of EAB and minimum RL, where the component with the larger cell size (7.7 mm), PLAc (1 mm) as the top layer and PLA (4 mm) as the bottom layer exhibited the best results with RL values of −41 dB and EAB of 9.5 GHz. The BHS system with 7.7 mm cell size was more efficient in Ku band frequency range, whereas that with 3.5 mm cell size gave better response in the X-band frequency range. Therefore, RL values and EAB can be adjustable by modifying the building strategy of the printed parts, such as thickness of the sample, cell size and thickness distribution of the conductive and non-conductive layers. The findings in this work show the importance of the building strategy to fabricate components with controllable BHS and improved properties for microwave absorption application.     

Tools for the eigenvalue distribution in a non-Hermitian setting

Under mild trace norm assumptions on the perturbing sequence, we extend a recent perturbation result based on a theorem by Mirsky. The analysis concerns the eigenvalue distribution and localization of a generic (non-Hermitian) complex perturbation of a bounded Hermitian sequence of matrices. Some examples of application are considered, ranging from the product of Toeplitz sequences to the approximation of PDEs with given boundary conditions. A final discussion on open questions and further lines of research ends the note.     

Diesel particulate abatement via wall-flow traps based on perovskite catalysts

It is probably redundant to stress how extensive are nowadays the attempts to reduce the diesel particulate emissions from automotive and stationary sources. The present paper looks into a technology relied on a catalytic trap based on a SiC wall-flow monolith lined with suitable catalysts for the sake of promoting a more complete and faster regeneration after particulate capture. All the major steps of the catalytic filter preparation are dealt with, including: the synthesis and choice of the proper catalyst and trap materials, the development of an in situ catalyst deposition technique, the bench testing of the derived catalytic wall-flow. The best catalyst selected was the perovskite La0.9K0.1Cr0.9O3-delta. The filtration efficiency and the pressure drop of the catalytic and non-catalytic monoliths were evaluated on a diesel engine bench under various operating conditions.     

Analysis of 21-deoxycortisol, a marker of congenital adrenal hyperplasia, in blood by atmospheric pressure chemical ionization and electrospray ionization using multiple reaction monitoring

Congenital adrenal hyperplasia (CAH) is an autosomal recessive disorder mainly caused by 21-hydroxylase deficit (21-OHD). Deletions or mutations of the CYP21 gene induce the impairment of glucocorticoid and mineralcorticoid synthesis. 17-Hydroxyprogesterone (17-OHP) is the hormonal marker in patients, but not in the heterozygous subjects. Excess 17-OHP is hydroxylated into 21-deoxycortisol (21-DF), and therefore 21-DF can be used as a specific marker for diagnosis of heterozygous individuals. We report an analytical method for analysis of 21-DF in blood samples using electrospray (ESI) and atmospheric pressure chemical ionization (APCI), showing that ESI is very sensitive for the analysis of this marker molecule. The multiple reaction monitoring (MRM) approach was used to increase the specificity and the sensitivity of the method.     

Sample handling strategies for the determination of biophenols in food and plants

The analysis of phenols in samples of plant and food origin attracts considerable attention. However, sample handling is often an ignored feature of the analysis. This review highlights the importance of sample extraction in an analysis and the problems that can arise during this step. Many questions remain unanswered and there is a need to more carefully validate extraction efficiencies. Although many new procedures have been developed the use of traditional techniques still dominates.     

Amino Acid Oxidation: A Combined Study of Cysteine Oxo Forms by IRMPD Spectroscopy and Simulations

The redox activity of cysteine sulfur allows numerous post‐translational protein modifications involved in the oxidative regulation of metabolism, in metal binding, and in signal transduction. A combined approach based on infrared multiple photon dissociation spectroscopy at the Centre Laser Infrarouge d'Orsay (CLIO) free electron laser facility, calculations of IR frequencies, and finite temperature ab initio molecular dynamics simulations has been employed to characterize the gas‐phase structures of deprotonated cysteine sulfenic, sulfinic, and sulfonic acids, [cysSO_x]^? (x=1, 2, 3, representing the number of S‐bound oxygen atoms), which are key intermediates in the redox‐switching chemistry of proteins. The ions show different structural motifs owing to preferential binding of the proton to either the carboxylate or sulfur‐containing group. Due to the decreasing basicity of the sulfenic, sulfinic, and sulfonic terminals, the proton bound to SO^? in [cysSO]^? migrates to the carboxylate in [cysSO₃]^?, whereas it turns out to be shared in [cysSO₂]^?. Evidence is gathered that a mixture of close‐lying low‐energy conformers is sampled for each cysteine oxo form in a Paul ion trap at room temperature.     

The optimal sequential information acquisition structure: A rational utility-maximizing perspective

We consider a rational utility maximizer decision maker (DM) who must gather two pieces of information from a set of multidimensional products before making a choice. We analyze the resulting sequential information acquisition process where the DM tries to find the best possible product subject to his information acquisition constraint. In addition, we introduce publicly observable signals that allow the DM to update his expected utility functions following a standard Bayesian learning rule. Even though it seems intuitively plausible to assume that the transmission of positive and credible information may lead DMs to accept any product signaled more eagerly, this paper illustrates how transmitting credible positive information is not sufficient to decrease the rejection probability faced by the information sender on its set of products. A significant difference in product rejection probabilities arises depending on the characteristic on which signals are issued, as will be illustrated numerically for both risk-neutral and risk-averse DMs.