104 research outputs found
Experimental Evidence For Self-Similar Structures In The Aggregation Of Porphyrins In Aqueous Solutions
We have studied the aggregation of the porphyrin t-HâPagg in aqueous solution by light scattering. The intensity profile of the elastically scattered light, studied in the exchanged wave-vector range 0.2 †q †31.4 ÎŒ mâ»Âč, indicates that the aggregation produces large monodisperse clusters having a fractal structure, and is driven by diffusion-limited aggregation kinetics. Additional measurements performed at different q values confirm such a picture giving a hydrodynamic radius R(H) consistent with the radius of gyration R(g) measured by elastic scattering. This is explained taking into account the qÂČ dependence observed in the mean decay rate of the intensity-intensity correlation function and the effect on this latter dynamical quantity of anisotropies in the cluster structure
Catheter ablation of ventricular tachycardia in patients with structural heart disease using cooled radiofrequency energy Results of a prospective multicenter study
AbstractOBJECTIVESThe purpose of this multicenter study was to evaluate the safety and efficacy of a radiofrequency (RF) catheter ablation system with internal saline irrigation.BACKGROUNDCatheter ablation of ventricular tachycardia (VT) associated with structural heart disease is more difficult than ablation of idiopathic VT. The larger size of responsible reentrant circuits contributes to the difficulty in achieving an adequate ablation lesion with conventional techniques. Recently, cooling of the ablation electrode by saline irrigation has been shown to increase RF lesion size.METHODSThe patient population included 146 patients who participated in the Cooled RF Ablation System clinical trial and underwent an attempt at ablation of VT occurring in the presence of structural heart disease. The duration of follow-up was 243 ± 153 days.RESULTSCatheter ablation was acutely successful, as defined by elimination of all mappable VTs, in 106 patients (75%). In 59 patients (41%), no VT of any type was inducible after ablation. Twelve patients (8%) experienced a major complication. After catheter ablation, 66 patients (46%) developed one or more episodes of a sustained ventricular arrhythmia.CONCLUSIONSThe results of this study demonstrate that catheter ablation of all mappable forms of sustained VT can be performed with high initial success and a moderate incidence of major complications (8%)
Studies of the plume emission during the femtosecond and nanosecond ablation of graphite in nitrogen
Stabilization of mid-sized silicon nanoparticles by functionalization with acrylic acid
We present an enhanced method to form stable dispersions of medium-sized silicon nanoparticles for solar cell applications by thermally induced grafting of acrylic acid to the nanoparticle surface. In order to confirm their covalent attachment on the silicon nanoparticles and to assess the quality of the functionalization, X-ray photoelectron spectroscopy and diffuse reflectance infrared Fourier spectroscopy measurements were carried out. The stability of the dispersion was elucidated by dynamic light scattering and Zeta-potential measurements, showing no sign of degradation for months
Driving electromagnetic field enhancements in tailored gold surface nanostructure: optical properties and macro scale simulations
A COMPARATIVE STUDY ON THE FEEDING COMPETITION OF THE EUROPEAN PERCH PERCA FLUVIATILIS L. AND THE RUFFE GYMNOCEPHALUS CERNUUS (L.) IN LAKE PIEDILUCO (UMBRIA, ITALY).
The abundance of European perch in Lake Piediluco has significantly dwindled in the last few years. The present study on diet overlap between perch and ruffe was prompted by the rapid expansion of the ruffe stock in the lake. This species was first found in the lake in 1996 and has since become one of the most abundant. The degree of diet overlap between the two species was analyzed by using data on the stomach contents of 275 European perch and 328 ruffe. Results are expressed as abundance (%N), occurrence (%S), weight percentage (%W) and index of predominance (Ip). The diet overlap index (α) was calculated by means of Schoenerâs formula using the %W of each food item. As an estimate of the diet width of both species, we used Levinsâ indexes of niche breadth (B) and standardized measurement of niche breadth (BA). Both species are strictly carnivorous, feeding mainly on invertebrates: the most important diet components were dipterans and crustaceans, but the European perch also feeds on fish. In the perch, the Levins index was greater (B=4.332) than that calculated for the ruffe (B=2.262). During the ontogenesis of the European perch, there is a rather pronounced diet shift: dipterans form the largest portion of the diet at all ages, though in older perch fish-eating becomes increasingly evident. Benthic crustaceans tend to be consumed in greater quantities by the 3+ age-class, though they are also found in the stomachs of specimens of all ages. Ruffe, by contrast, do not display a pronounced ontogenetic diet shift.
The index of diet overlap between the two species was rather high, the maximum α value being 0.853; values indicate a high degree of diet overlap in the younger ageclasses (1+, 2+ and 3+), with a greater differentiation between the diets of the two species emerging as the age of the perch increased.
Our research also clarified some of the biological characteristics of the European perch in Lake Piediluco, namely, theoretical growth in length, weight at length and relative weight. These analyses enabled us to compare the growth characteristics of the European perch during periods when ruffe stocks differed in terms of abundance. All of the results indicate that the growth conditions of the European perch population in Lake Piediluco are steadily worsening. This provides indirect confirmation of a negative interaction with the ruffe
On the influence of the mass ablated by a laser pulse on thin film morphology and optical properties
To know and to control experimental parameters
that play a role in laser ablation is vital to define film
properties. Among the others, laser fluence is commonly
used. Yet, when plasma expansion dynamics takes place
through an ambient gas, the relation between the ablated
mass per pulse and gas mass is critical and till now it was
poorly investigated. While the gas mass is fixed by the
pressure in the deposition chamber, the ablated mass is not
unequivocally determined by the laser fluence. For a given
fluence value the ablated mass changes as a function of the
irradiated target area. Here, we show that nanostructured
silver thin films deposited keeping unaltered the laser fluence,
while changing in a controlled way the irradiated area
and hence the ablated mass per pulse, display markedly
differentiated morphological and optical properties, as
evidenced by electron microscopy and UVâVis and Raman
spectroscopies
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