Low-power spontaneous oscillations driven by band-filling effect.

We predict that self-sustained oscillations can be generated in a semiconductor nanocavity in which the dominant effect is band-filling dispersion. Linear stability analysis, validated through numerical integration of a mean-field model, leads us to envisage oscillations typically at tens of gigahertz, with onset at much lower input power (~100 µW) compared with those driven by two-photon absorption.

Optimizing pump-probe switching ruled by free-carrier dispersion.

We address theoretically and numerically pump-probe switching in a nonlinear semiconductor nanocavity where tuning is achieved via a dominant mechanism of free-carrier plasma dispersion. By using coupled-mode approach we give a set of guidelines to optimize the switching performances both in terms of avoiding self-pulsation and keeping switching power to the minimum, ending up by showing that such devices can achieve high-performances with relatively low-power consumption.

Laparoscopic, three-port and SILS cholecystectomy: a retrospective study.

INTRODUCTION: The aim of this study was to compare the results of classic laparoscopic, three-port and SILS cholecystectomy. MATERIALS AND METHODS: We conducted a retrospective study of data collected between January 2010 and December 2012 pertaining to 159 selected patients with symptomatic gallstones. 57 underwent laparoscopic cholecystectomy, 51 three-port cholecystectomy and 48 SILS cholecystectomy. We then compared the groups with respect to mean operating time, intraoperative complications, postoperative pain, duration of hospitalization and final aesthetic result. RESULTS: The mean operating time was significantly higher in the SILS cholecystectomy group (93 minutes) than in the other two groups. There were no intraoperative complications. There were no significant differences in the duration of hospitalization among the three groups. Patients in the SILS cholecystectomy group reported significantly less pain 3, 6 and 12 hours after surgery. The aesthetic results at 1 and 6 months' follow-up were also decidedly better. CONCLUSIONS: On the basis of this study, SILS cholecystectomy is a feasible, safe procedure. In any case, it should be used in selected patients only and carried out by a dedicated team with strong experience in laparoscopy. The main advantages of this technique are a reduction in post-operative pain and improved aesthetic result, at the price, however, of its greater technical difficulty and longer operating times. Future studies are in any case necessary to evaluate any other benefits of this method.

Temporal gap solitons and all-optical control of group delay in line-defect waveguides.

We show that a model based on anticrossing between highly group velocity-mismatched gap-guided and index-guided modes describes gap soliton propagation in photonic crystal waveguides. Such nonlinear solutions can be exploited for exploring new regimes such as all-optical control of group velocity (dispersionless slow light) over a submillimeter length scale, and propagation beyond the linear modal cutoff. The results are validated by means of finite-difference time domain simulations.

Step-index optical waveguide produced by multi-step ion implantation in LiNbO3.

The refractive indexes, material attenuation and damage fractions of a multi-step ion implanted Lithium Niobate (LiNbO3) waveguide were analyzed as functions of the annealing temperatures. An almost flat damage depth profile was designed to reduce the uncertainties related to the indexes profile shape, thus providing a better test-case for the characterizations. The measurements performed on the fabricated optical waveguides confirmed the predicted step-index profiles showing that the light is confined inside the damaged layer. The low measured attenuation (less than 0.8 dB/cm @ 632.8 nm) makes the obtained waveguide attractive for device fabrication.

Retrieval of Bragg grating transmission spectra by post-process removal of spurious Fabry-Pérot oscillations.

Efficient post-process suppression is demonstrated of spurious Fabry-Pérot oscillations, introduced by multiple cavity effects in transmission spectra measurements of various Bragg grating devices. These devices were fabricated within access waveguides and terminated with cleaved facets. The tool, based on a curve-fitting to an equivalent scattering matrix model, is shown to extract transmission spectra of devices, without a-priori knowledge of their properties. Simple and complex grating structure spectra are successfully extracted and compare well with simulated results. The technique exhibits robust behaviour for varying facet conditions and device geometries, outperforming classical averaging techniques.

Closure of the stop-band in photonic wire Bragg gratings.

Photonic Wire Bragg Gratings, made by periodic insertion of lateral rectangular recesses into photonic wires in silicon-on-insulator, can provide large reflectivity with short device lengths because of their large index contrast. This type of design shows a counter-intuitive behaviour, as we demonstrate - using experimental and numerical data - that it can have low or null reflectance, even for large indentation values. We provide physical insight into this phenomenon by developing a model based on Bloch mode theory, and are able to find an analytical expression for the frequency at which the grating does not sustain the stop-band. Finally we demonstrate that the stop-band closing effect is a general phenomenon that may occur in various types of periodic device that can be modeled as transmission line structures.

Experimental observation of longitudinal modulation of mode fields in periodically segmented waveguides.

We present what is to our knowledge the first experimental observation by fluorescent visualization, of the evolution of the mode field profile in a periodically segmented waveguide. The experimental observations are then compared with the numerical results obtained by a finite-difference beam propagation method. Good agreement between experimental and numerical results is observed.

Hemodynamics, prolactin and catecholamine levels during hemorrhagic shock in dogs pretreated with a prolactin inhibitor (bromocriptine).

Bromocriptin, a dopaminomimetic drug, causing inhibition of prolactin secretion, was used in experiments on haemorrhagic shock in dogs. 5 dogs were treated with bromocriptine (0.4 mg.day-1) for two days; a further 5 dogs were used as control animals. 30% of the blood volume was drawn from each dog. Mean arterial blood pressure, heart rate, central venous pressure, acid-base status, prolactin, GH and catecholamine levels were checked before blood letting and monitored until 1 hour after blood letting. Animals treated with bromocriptine showed a significant decrease of the mean arterial blood pressure and of the prolactin rate and a significant increase of catecholamine levels. Control animals, instead, showed a significant increase of the prolactine and catecholamine rates. The results obtained suggest that bromocriptine can constitute an additional hypotensive factor in subjects with acute haemorrhage. A considerable amount of research work previously carried out has shown a close correlation between stress and hyper-prolactinemia. The increase of prolactinemia and the effects of bromocriptine on this hormone during surgical stress is particularly interesting due to its possible implications (Lanza V. et coll., 1983). In previous experiments involving animals it was found that Prolactin exerts positive chronotropic and hypertensive effects (Horrobin D.F., 1977) whilst bromocriptine is a potent agonist of D2 dopaminergic receptors (Thorner M.O. et coll., 1980). Dopamine was found to be particularly useful in the clinical treatment of shock thus suggesting an involvement of peripheral D2 receptors. On the basis of these observations we have considered it worthwhile to investigate the haemodynamic effects of bromocriptine in haemorrhagic shock.

[Problems of rehabilitation during permanent cardiac stimulation]. / Problemi di riabilitazione in corso di elettrostimolazione cardiaca permanente.

The importance of certain features of the classification of diseases of the His system for the purpose of planning and conducting permanent cardiac stimulation (PCE). Stability of the conduction disturbance is essential in classifying low stroke volume syndromes as due to sporadic, frequent or habitual disturbance, and the frequency of stimulation should be geared to that of the syndrome. Rehabilitation during PCE also has its psychological side. Indeed, this almost always surpasses the physical side in importance and is dependent on the patient's job, social and economic standing, and the size of his family, as well as on his own emotional blaance and psychological reactions. About 70% of subjects behave in a normal way (rational acceptance of reality and a correct balance between emotiveness and reason), 20% display anxiety and depression, and the remainder show a typical form of euphoria; in many cases, this is clearly hypomaniacal.

[Artificial pacemakers]. / Sui pacemakers artificiali.

The new generation of pacemakers satisfy three basic requirements; histocompatibility, small size, and long life. Resins have been abandoned in favour of titanium cases. These are completely sealed and there is no risk of infiltration or histotoxicity. In addition, the employment of low consumption circuits and new sources of energy, especially lithium, has enabled the working life of a pacemaker to be extended virtually to its useful limits. The application of electrical stimulation to the treatment of arrhythmia has led to the creation of automatic or magnetically controlled pacemakers that come into action with pulse volleys on the appearance of otherwise intractable rhythm disturbances.