Sol-gel niobium pentoxide coatings: Applications to photovoltaic energy conversion and electrochromism

In the last decade the sol-gel process became a promising method to synthesize materials in form of coatings, nanoscale powders and porous systems. Several products or devices made with such a process already exist on the market. This paper briefly reviews the state of the art in the development of electrochromic coatings and devices and nanocrystalline solar cells achieved during the last decade using sol-gel derived pure and doped niobium pentoxide

Avalanche dynamics, surface roughening and self-organized criticality - experiments on a 3 dimensional pile of rice

We present a two-dimensional system which exhibits features of self-organized criticality. The avalanches which occur on the surface of a pile of rice are found to exhibit finite size scaling in their probability distribution. The critical exponents are $\tau$ = 1.21(2) for the avalanche size distribution and $D$ = 1.99(2) for the cut-off size. Furthermore the geometry of the avalanches is studied leading to a fractal dimension of the active sites of $d_B$ = 1.58(2). Using a set of scaling relations, we can calculate the roughness exponent $\alpha = D - d_B$ = 0.41(3) and the dynamic exponent $z = D(2 - \tau)$ = 1.56(8). This result is compared with that obtained from a power spectrum analysis of the surface roughness, which yields $\alpha$ = 0.42(3) and $z$ = 1.5(1) in excellent agreement with those obtained from the scaling relations.Comment: 7 pages, 8 figures, accepted for publication in PR

The reliability of musculoskeletal ultrasound in the detection of cartilage abnormalities at the metacarpo-phalangeal joints

SummaryObjectiveTo assess the reliability of ultrasound (US) in detecting cartilage abnormalities at the metacarpo-phalangeal (MCP) joints in people with cartilage pathology.MethodsNine expert ultrasonographers initially achieved consensus on definitions and scanning protocols. They then examined the second to fifth MCP joints of the dominant hand of eight people with hand osteoarthritis (OA). US examinations were conducted in two rounds, with independent blinded evaluations of cartilage lesions. Global cartilage abnormalities were assessed by applying a dichotomous (presence/absence) score; in addition, the following lesions were evaluated using the same scoring system: loss of anechoic structure and/or thinning of the cartilage layer, and irregularities and/or loss of sharpness of at least one cartilage margin. Reliability was assessed using kappa (k) coefficients.ResultsThirty-two joints were examined. Intra-observer k values ranged from 0.52 to 1 for global cartilage abnormalities; k values ranged from 0.54 to 0.94 for loss of anechoic structure and/or thinning of cartilage layer and from 0.59 to 1 for irregularities and/or loss of sharpness of at least one cartilage margin. Values of k for inter-observer reliability were 0.80 for global cartilage abnormalities, 0.62 for loss of anechoic structure and/or thinning of cartilage layer, and 0.39 for irregularities and/or loss of sharpness of at least one cartilage margin.ConclusionUS is a reliable imaging modality for the detection of cartilage abnormalities in patients with cartilage pathology in the MCP joints. The analysis of specific cartilage measures showed more variable results that may be improved by modifying definitions and further standardization of US techniques

MAGNETIC EFFECTS OF TUNNELLING RECOMBINATION LUMINESCENCE IN CsI AND KCl DOPED CRYSTAL

Des cristaux de CsI et KCl dopés avec des impuretés monovalentes telles que Ag, Tl, Na, etc... et exposés à basse température à des radiations ionisantes présentent une luminescence qui persiste plusieurs heures après la fin de l'irradiation. Le processus est interprété comme une recombinaison due à un transfert d'énergie par effet tunnel entre électrons et trous piégés sur des sites voisins. L'application d'un champ magnétique extérieur (0 ⩽ B ⩽ 6T) induit dans CsI : NaI et KCl : AgCl (ou : NaCl) une forte diminution de l'intensité de la phosphorescence due à une polarisation partielle des spins électroniques des défauts. Aucun effet n'est observé dans CsI : TlI et KCl : TlCl (ou : CuCl). L'application d'un champ microonde résonant tend à compenser l'effet du champ magnétique et permet dans CsI : NaI seulement, la détection optique de la R. P. E. du centre du type trou self-trappé responsable du processus de phosphorescence.CsI and KCl crystals doped with monovalent impurities such as Ag, Tl, Na, etc... and exposed to ionising radiations at low temperature present a luminescence which persists many hours after the end of the irradiation. The process is attributed to a tunnelling recombination between nearby trapped electrons and holes. An external magnetic field (0 ⩽ B ⩽ 6T) induces in CsI : NaI and KCl : AgCl (or : NaCl) a strong reduction of the intensity of the phosphorescence caused by a partial polarization of the electron spins of the defect pairs. No effect has been found in CsI : TlI and KCl : TlCl (or : CuCl). The application of a resonant microwave field tends to compensate the magnetic field effect and allows in Csl : NaI only, the optical detection of EPR of the hole type defect responsible for the afterglow process

Optical Properties Of Dye Molecules Adsorbed On Fractal Structures

We present preliminary measurements of the optical properties of Rhodamine B molecules adsorbed or trapped in porous matrices such as Vycor 7930 glass, silica xerogels and aerogels. The electronic transfer between donor and acceptor molecules adsorbed on such fractal structures is also discussed; a fast sub-picosecond resolution experiment is proposed to study this process. © 1986.821-3165170Mandelbrot, (1982) The Fractal Geometry of Nature, , Freeman, LondonAlexander, Orbach, Density of states on fractals : « fractons » (1982) Journal de Physique Lettres, 43, pp. L-625Rammal, Toulouse, (1983) J. Phys. Lett., 44, pp. L-13Evesque, (1983) J. de Phys., 44, p. 1217Klafter, Blumen, (1984) J. Chem. Phys., 80, p. 875Even, Rademann, Jortner, Manor, Reisfeld, (1984) Phys. Rev. Lett., 52, p. 2164Woignier, (1984) Thesis, , University of MontpellierBrito Cruz, Scarparo, Srivastava, (1983) Rev. Bras. Fisica, 13, p. 37