Random Networks Tossing Biased Coins

In statistical mechanical investigations on complex networks, it is useful to employ random graphs ensembles as null models, to compare with experimental realizations. Motivated by transcription networks, we present here a simple way to generate an ensemble of random directed graphs with, asymptotically, scale-free outdegree and compact indegree. Entries in each row of the adjacency matrix are set to be zero or one according to the toss of a biased coin, with a chosen probability distribution for the biases. This defines a quick and simple algorithm, which yields good results already for graphs of size n ~ 100. Perhaps more importantly, many of the relevant observables are accessible analytically, improving upon previous estimates for similar graphs

Exchangeable Random Networks

We introduce and study a class of exchangeable random graph ensembles. They can be used as statistical null models for empirical networks, and as a tool for theoretical investigations. We provide general theorems that carachterize the degree distribution of the ensemble graphs, together with some features that are important for applications, such as subgraph distributions and kernel of the adjacency matrix. These results are used to compare to other models of simple and complex networks. A particular case of directed networks with power-law out--degree is studied in more detail, as an example of the flexibility of the model in applications.Comment: to appear on "Internet Mathematics

Maintenance of vascular integrity: Role of nitric oxide and other bradykinin mediators

In the blood-vessel wall, the endothelium plays a key functional role by generating several substances that modulate vascular smooth muscle tone, as well as growth, and platelet function. This review focuses on the role of the endothelial L-arginine/nitric oxide signal transduction pathway in the maintenance of vascular integrity. Functional alterations of this pathway may be important in cardiovascular disease, because depressed activity of this protective mechanism leads to impaired relaxation and is also associated with reduced antithrombotic properties of the endothelial layer. Many of the beneficial effects of ACE inhibitor therapy may be mediated through their ability to enhance the physiological roles of nitricoxid

11th European Headache Federation Congress jointly with 31st Congress of the Italian Society for the Study of Headaches : Rome, Italy. 01-03 December 2017

. Aims of the study were explore the relationship between peripheral chromatic and central visual dysfunction evaluating also the presence of functional receptor impairment in patients with migraine, with and without aura examined interictally

Nifedipine inhibits superoxide production induced by pulsatile stretch in human aortic endothelial cells

Dihydropiridine calcium channel blocker nifedipine restores nitric oxide-mediated vasodilation in human hypertension. The mechanims involved have not been fully characterized but may relate to endothelial protection. Mechanical forces such as pulsatile stretch are involved in superoxide anion production. To clarify the effect of nifedipine on the balance between nitric oxide and superoxide anion, human cultured aortic endothelial cells were exposed to pulsatile stretch in the presence and in the absence of this compound. Rhytmic stretching was given for 1 hour by a computerized Flexercell strain unit (10% average elongation, 50 cycles per minute). Superoxide anion production was measured as the superoxide dismutase-inhibitable reduction of cytochrome c. Stretch-induced production of superoxide anion was inhibited in a concentration-dependent manner by nifedipine [6.2±0.9 vs 2.1±0.6* and 4.8±0.4*, 2.4±0.5* nmol/60 min/105 cells for stretch vs control and stetch plus nifedipine (10−7 and 10−6 M), respectively; n=6; *P<0.05 vs stretch]. This antioxidant activity of nifedipine may exert vascular protective effects in human endothelial cells. Thus, nifedipine may affect mechanical forces which, as determinants of the balance between nitric oxide and superoxide anion, are likely to play a key role in the pathophysiology of hypertensive vascular diseas

Preparation and characterisation of titania/hydroxyapatite composite coatings obtained by sol-gel process

In the present work a titania network encapsulating a hydroxyapatite particulate phase is proposed as a bioceramic composite coating. The coating on a titanium substrate was produced starting from a sol containing a mixture of titania colloidal particles and hydroxyapatite submicron particles using the dip-coating technique. The microstructure, the morphology and the surface chemical composition of the coating were characterised using X-ray diffraction (XRD), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS), respectively. Adhesion tests were also performed. These analyses showed that the obtained coating was chemically clean, homogeneous, rough, porous, with a low thickness and well-defined phase composition as well as a good adhesion to the substrate. Copyright © 2001 Elsevier Science Ltd