Classes of small-world networks

We study the statistical properties of a variety of diverse real-world networks. We present evidence of the occurrence of three classes of small-world networks: (a) scale-free networks, characterized by a vertex connectivity distribution that decays as a power law; (b) broad-scale networks, characterized by a connectivity distribution that has a power law regime followed by a sharp cutoff; and (c) single-scale networks, characterized by a connectivity distribution with a fast decaying tail. Moreover, we note for the classes of broad-scale and single-scale networks that there are constraints limiting the addition of new links. Our results suggest that the nature of such constraints may be the controlling factor for the emergence of different classes of networks.     

Changes of the polymerization mechanism depending on the monomer and solvent for a homogeneous Ziegler-type initiating system

The homogeneous system resulting from the reaction between tetrabenzylzirconium and triethylaluminium is an active catalyst for the polymerization of styrene, and p-methyl-, α-methyl and p-chlorostyrenes. The molecular weights and the structures of the resulting polymers are highly dependent on the nature of the monomer and on the reaction medium. In toluene, styrene and p-methylstyrene give essentially linear unsaturated dimers, whereas p-chlorostyrene leads to a polymer with a high molecular weight. In methylene dichloride higher oligomers and a polymer are obtained simultaneously from all the monomers. The comparative behaviour of the styrene derivatives was examined in copolymerization experiments under various experimental conditions. The ratios of monomer incorporation were compared with those reported in the literature for related systems. The results show that, according to the monomer and the reacting medium, the same catalytic system is able to induce polymerizations of the “coordinated anionic”, radical and cationic type.     

Atrial natriuretic peptide level and intracardiac pressure in cardiac transplant recipients

Summary Blood pressures and plasma atrial natriuretic peptide (ANP) concentrations have been measured in venous and intracardiac sites in 11 patients (10 men and 1 woman) given cardiac transplants.The mean plasma ANP level was 214.4 pg·ml^–1 in the superior veina cava and 281 pg·ml^–1 in the right atrium. This significantly higher level was maintained in the right ventricle (269) and in the pulmonary artery (295). The level in controls was 25 pg·ml^–1. Intra cardiac and mean arterial pressures were in normal range in all patients, and there was no correlation between plasma ANP level and intracardiac pressure.The data suggest that in cardiac transplant patients right atrial pressure does not have a primary role in releasing ANP. The transplanted heart is denervated and remains so for many months after operation, thus suggesting that innervation is not obligatory for ANP secretion. Further studies are required to determine the relative contribution of donor and recipient atrial tissues to ANP secretion.     

Quantification by magnetic resonance spectroscopy of metabolites in seminal plasma able to differentiate different forms of azoospermia

The aim was to determine whether proton magnetic resonance spectroscopy (1H-MRS) of metabolites such as glycerophosphorylcholine (GPC), choline, citrate and lactate in human seminal plasma can be used to differentiate (i) different azoospermic patients and (ii) different forms of spermatogenic failure including those who had undergone radiation therapy or chemotherapy. Semen samples were provided by men with obstructive azoospermia and spermatogenic failure who had serum follicle stimulating hormone (FSH) values within the normal range and either more or less than normal. Four prominent constituents of seminal plasma were identified by 1H-MRS: GPC, choline, citrate and lactate. The peak area ratios of choline/citrate as well as choline/lactate were significantly different (P < 0.01) between groups with spermatogenic failure and obstructive azoospermia. When the serum FSH values were normal in men with spermatogenic failure and obstructive azoospermia, a significant difference was found in the GPC/choline ratio (P < 0.001). When the FSH values were normal, the GPC/choline ratio appeared to be a very important parameter able to differentiate not only between cases of spermatogenic failure and obstructive azoospermia but also between different forms of spermatogenic failure. These results demonstrate the potential use of 1H-MRS on human seminal plasma in a new approach in the management of male infertility.      

ELECTROPHYSIOLOGICAL EFFECTS OF FENFLURAMINE OR COMBINED VITAMIN B6 AND MAGNESIUM ON CHILDREN WITH AUTISTIC BEHAVIOUR

The authors compared the effects of fenfluramine or combined vitamin B6 and magnesium treatment on the evoked potential conditioning of 12 children whose autistic behaviour had improved clinically following treatment. The children who were clinically sensitive to combined vitamin B6 and magnesium developed a conditioning phenomenon and the fenfluramine-sensitive children showed an enhancement of the Cz evoked response amplitude. Results are discussed with reference to behaviour modifications observed during treatment.     

The danger present to the spinal cord arterial vasculature during surgery of nerve-tissue tumors of the posterior mediastinum]

The authors report one case of posterior mediastinal neurinoma with a Adamkiewicz artery arising at an atypical site. They stress the spinal cord complications following thoracic surgery. The value of spinal cord arteriography during preoperative examinations and for prevention of complications is discussed.