Monomeric antioxidants. An 1H-NMR spectrometry study of their homopolymerization

Summary The polymerization behaviour of 3,5-di-tert-butyl-4-hydroxy-benzylmethacrylate (I), trans-3,5-di-tert-butyl-4-hydroxycinnamic acid (II), 3,5-di-tert-butyl-4-hydroxystyrene (III) and N-(3,5-ditert-butyl-4-hydroxybenzyl)maleimide (IV) was investigated. These monomeric antioxidants were polymerized in aromatic solvents, in the presence of usual radical initiators, by refluxing under nitrogen. An ¹H-NMR spectrometry method for the calculation of polymerization conversion was developed. The disappearance of the monomer double bond was followed using dibenzyl ether as an internal standard. The reactivity of these monomers, all showing the same antioxidant functionality, decreased in the order IV>I>III. The acid antioxidant (II) was not capable of polymerization.     

Time-frequency signal processing of terahertz pulses

We demonstrate that some signal-processing techniques, such as the fractional Fourier transform and the spectrogram, which are known to be effective for optical signals, can be implemented at terahertz frequencies and with available terahertz devices. These techniques, contrary to the frequency-resolved optical-gating method for pulse characterization, do not require nonlinear media, which do not exist at terahertz frequencies. Thus the fractional Fourier transform or the spectrogram offers the only possibility of characterizing terahertz pulses simultaneously in time and frequency.     

A law of interference of electromagnetic beams of any state of coherence and polarization and the Fresnel-Arago interference laws

A new general interference law is derived for the superposition of two random electromagnetic beams of any state of coherence and of any state of polarization when the beams are transmitted through polarizers and rotators. It includes, as special cases, a variety of interference laws that apply to particular situations. Some of them have a close bearing on the classic interference experiments of Fresnel and Arago that have played a basic role in elucidating the concept of polarization of light.     

Heterogeneous cationic polymerization of 1,3-dioxolane and 1,3-dioxepane using grafted BF3 on silica

Summary A BF₃ complex has been grafted onto silica and used as initiator to polymerize 1,3-dioxolane and 1,3-dioxepane. Grafting the active centers leads to a decrease of the reaction rate. The molecular weight increases steadily, parallel to the monomer conversion and the polydispersity is rapidly stabilized at a low value. MALDI-TOF mass spectrometry analysis shows that most of the polymer chains are initiated by a proton and lost a CH₂O unit. An exchange process between polymer chains bound to the silica and those remaining in the reactional medium was proposed. Finally, a semi-continuous process was investigated by adding continuously dioxolane during a 100 hours period. Received: 21 February 2001/ Revised version: 2 November 2001/ Accepted: 6 November 2001     

Evaluation of Karhunen–Loève, Spectral, and Sampling Representations for Stochastic Processes

The Karhunen–Loève, spectral, and sampling representations, referred to as the KL, SP, and SA representations, are defined and some features/limitations of KL-, SP-, and SA-based approximations commonly used in applications are stated. Three test applications are used to evaluate these approximate representations. The test applications include (1) models for non-Gaussian processes; (2) Monte Carlo algorithms for generating samples of Gaussian and non-Gaussian processes; and (3) approximate solutions for random vibration problems with deterministic and uncertain system parameters. Conditions are established for the convergence of the solutions of some random vibration problems corresponding to KL, SP, and SA approximate representations of the input to these problems. It is also shown that the KL and SP representations coincide for weakly stationary processes.     

State fusion with unknown correlation: Ellipsoidal intersection

This article focuses on the problem of fusing two prior Gaussian estimates into a single estimate, when the correlation is unknown. Existing solutions either lead to a conservative fusion result, as the chosen parametrization focuses on the fusion formulas instead of correlations, or they are computationally expensive. The contribution of this article is a novel parametrization, in which the correlation is explicitly characterized a priori to deriving the fusion formulas. Then, maximizing the correlation ensures that the fusion result is based on independent parts of the prior estimates and, simultaneously, addresses the fact that the correlation is unknown. In addition, a guaranteed improvement of the accuracy after fusion is attained. An illustrative example demonstrates the benefits of the proposed method compared to an existing fusion method.     

Promising Therapies for Atrial Fibrillation and Ventricular Tachycardia

Sudden cardiac death due to arrhythmias, such as atrial fibrillation or ventricular tachycardia, account for 15–20% of all deaths. Myocardial infarction increases the burden of atrial fibrillation and ventricular tachycardia by structural and electrical remodeling of the heart. The current management of new-onset atrial fibrillation includes electric cardioversion with very high conversion rates and pharmacologic cardioversion, with less a than 50% conversion rate. If atrial fibrillation cannot be converted, the focus becomes the control of the symptoms ensuring a constant rhythm and rate control, without considering other contributory factors such as autonomic imbalance. Recently, a huge success was obtained by developing ablation techniques or addressing the vagal nerve stimulation. On the other hand, ventricular tachycardia is more sensitive to drug therapies. However, in cases of non-responsiveness to drugs, the usual therapeutic choice is represented by stereotactic ablative therapy or catheter ablation. This review focuses on these newly developed strategies for treatment of arrhythmias in clinical practice, specifically on vernakalant and low-level tragus stimulation for atrial fibrillation and stereotactic ablative therapy for drug-refractory ventricular tachycardia. These therapies are important for the significant improvement of the management of atrial fibrillation and ventricular tachycardia, providing: (1) a safer profile than current therapies, (2) higher success rate than current solutions, (3) low cost of delivery.     

On a simplified system for steam production in nuclear power plants with pressurized water reactors

The paper develops the idea of a new system of steam production (Simplified System for Steam Production, SSSP) in nuclear power plants (NPPs) with PWR reactors, which is simplified as compared to the system used in the classical NPP of this type where steam is produced by steam generators (SGs). With the SSSP, expanders are used instead of SGs. The particularities of a NPP with a SSSP are analyzed in comparison to the classical NPP equipped with PWR and BWR reactors, which are used almost exclusively at present to produce electric energy at the industrial level.     

Poly(ethylene oxide)‐block‐polystyrene copolymers obtained by radical polymerization involving chain‐transfer processes

Poly(ethylene oxide)‐block‐polystyrene (PEO–PSt) block copolymers were prepared by radical polymerization of styrene in the presence of iodoacetate—terminated PEO (PEO‐I) as a macromolecular chain‐transfer agent. PEO‐I was synthesized by successively converting the OH end‐group of α‐methoxy ω‐hydroxy PEO to chloroacetate and then to the iodoacetate. The chain‐transfer constant of PEO‐I was estimated from the rate of consumption of the transfer agent versus the rate of consumption of the monomer (C_{tr, PEO‐I} = 0.23). Due to the involvement of degenerative transfer, styrene polymerization in the presence of PEO‐I displayed some of the characteristics of a controlled/‘living’ process, namely an increase in the molecular weight and decrease of polydispersity with monomer conversion. However, because of the slow consumption of PEO‐I due to its low chain‐transfer constant, this process was not a fully controlled one, as indicated by the polydispersity being higher than in a controlled polymerization process (1.65 versus < 1.5). The formation of PEO–PSt block copolymers was confirmed by the use of size‐exclusion chromatography and ¹H NMR spectroscopy. Copyright © 2004 Society of Chemical Industry