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S Longhi

Publications and source records attributed to S Longhi.

At least 19 recordsLinked to original sources
PubMed2006

SPINE bioinformatics and data-management aspects of high-throughput structural biology.

SPINE (Structural Proteomics In Europe) was established in 2002 as an integrated research project to develop new methods and technologies for high-throughput structural biology. Development areas were broken down into workpackages and this article gives an overview of ongoing activity in the bioinformatics workpackage. Developments cover target selection, target registration, wet and dry laboratory data management and structure annotation as they pertain to high-throughput studies. Some individual projects and developments are discussed in detail, while those that are covered elsewhere in this issue are treated more briefly. In particular, this overview focuses on the infrastructure of the software that allows the experimentalist to move projects through different areas that are crucial to high-throughput studies, leading to the collation of large data sets which are managed and eventually archived and/or deposited.

Computational Biology↗
PubMed2006

Observation of dynamic localization in periodically curved waveguide arrays.

We report on a direct experimental observation of dynamic localization (DL) of light in sinusoidally-curved lithium-niobate waveguide arrays which provides the optical analog of DL for electrons in periodic potentials subjected to ac electric fields as originally proposed by Dunlap and Kenkre [Phys. Rev. B 34, 3625 (1986)10.1103/PhysRevB.34.3625]. The theoretical condition for DL in a sinusoidal field is experimentally demonstrated.

Journal Article↗
PubMed2006

Imaging of Bloch oscillations in erbium-doped curved waveguide arrays.

We report a direct observation of Bloch-like dynamics of light in curved waveguide arrays manufactured in Er:Yb-doped phosphate glass by femtosecond laser writing. The green upconversion fluorescence emitted by excited erbium ions is exploited to image the flow of the guided pump light at approximately 980 nm along the array. Direct and clear evidence of periodic light breathing for single-waveguide excitation, closely related to Bloch oscillations, is reported.

Journal Article↗
PubMed2005

Slow light in periodic superstructure Bragg gratings.

A theoretical and experimental analysis of group velocity reduction in periodic superstructure Bragg gratings is presented. Experimental demonstration of group velocity reduction of sub-nanosecond pulses at the wavelength of optical communications is reported using a Moiré fiber grating.

Journal Article↗
PubMed2005

Beam dynamics and wave packet splitting in a periodically curved optical waveguide: multimode effects.

A theoretical and experimental analysis of beam dynamics and wave packet splitting of light in a periodically bent optical waveguide, a phenomenon recently observed [Phys. Rev. Lett. 94, 073002 (2005)] which is the optical equivalent of adiabatic stabilization of atoms in intense and high-frequency laser fields, is presented in the multimode operational regime. Inhibition of wave packet splitting is theoretically predicted and experimentally observed for higher-order mode excitation.

Journal Article↗
PubMed2005

Dose-finding study of weekly docetaxel, anthracyclines plus fluoropyrimidines as first-line treatment in advanced breast cancer.

BACKGROUND: The efficacy and safety of prolonged fluoropyrimidines, either intravenously or orally, prompted their integration with taxanes and anthracyclines in the treatment of advanced breast cancer (ABC). We conducted three subsequent dose-finding studies on first-line chemotherapy in ABC with anthracyclines, either epirubicin (E) or doxorubicin (A), and docetaxel (T), both given on days 1 and 8 every 3 weeks, plus continuous infusion (CI) 5-fluorouracil (F) or capecitabine (X). PATIENTS AND METHODS: Sixty-two patients (37% dominant visceral disease, 48% locally advanced disease, 45% two or more sites involved), received different doses of T (60--80 mg/m(2)), A (40--50 mg/m(2)) or E (60--90 mg/m(2)) and X (1,650 and 2,000 mg/m(2)), or CI F at a fixed daily dose of 200 mg/m(2). Cardiac function was monitored at baseline and then every four cycles by echocardiography. RESULTS: The median number of cycles per patient with all regimens was four (range one to eight). Haematological and gastrointestinal toxicity defined the maximum tolerated doses, at T-80/E-90 mg/m(2) with TEF, T-70/A50/X-2,000 mg/m(2) with TAX and T-70/E-80/X-1,650 mg/m(2) with TEX. Two patients treated with TEF developed transient cardiac toxicity (dilatative cardiomyopathy and coronary subtotal stenosis requiring stenting) after cumulative E doses of 400 mg and 1,100 mg/m(2), respectively. Fifty-nine patients were evaluable for response; the overall response rates (ORR) were comparable between regimens (54% with TEF, 71% with TAX and 86% with TEX), with an 81% ORR in 31 patients with locally advanced disease. CONCLUSIONS: The addition of fluoropyrimidines to weekly, intermittent ET is well tolerated and active in ABC.

Adult↗
PubMed2005

Measles virus nucleoprotein induces cell-proliferation arrest and apoptosis through NTAIL-NR and NCORE-FcgammaRIIB1 interactions, respectively.

Measles virus (MV) nucleoprotein (N) is a cytosolic protein that is released into the extracellular compartment after apoptosis and/or secondary necrosis of MV-infected cells in vitro. Thus, MV-N becomes accessible to inhibitory cell-surface receptors: FcgammaRIIB and an uncharacterized nucleoprotein receptor (NR). MV-N is composed of two domains: NCORE (aa 1-400) and NTAIL (aa 401-525). To assess the contribution of MV-N domains and of these two receptors in suppression of cell proliferation, a human melanoma HT144 cell line expressing (HT144IIB1) or lacking FcgammaRIIB1 was used as a model. Specific and exclusive NCORE-FcgammaRIIB1 and NTAIL-NR interactions were shown. Moreover, NTAIL binding to human NR predominantly led to suppression of cell proliferation by arresting cells in the G0/G1 phases of the cell cycle, rather than to apoptosis. NCORE binding to HT144IIB1 cells primarily triggered caspase-3 activation, in contrast to HT144IIB1/IC- cells lacking the FcgammaRIIB1 intra-cytoplasmic tail, thus demonstrating the specific inhibitory effect of the NCORE-FcgammaRIIB1 interaction. MV-N- and NCORE-mediated apoptosis through FcgammaRIIB1 was inhibited by the pan-caspase inhibitor zVAD-FMK, indicating that apoptosis was dependent on caspase activation. By using NTAIL deletion proteins, it was also shown that the region of NTAIL responsible for binding to human NR and for cell growth arrest maps to one of the three conserved boxes (Box1, aa 401-420) found in N of Morbilliviruses. This work unveils novel mechanisms by which distinct domains of MV-N may display different immunosuppressive activities, thus contributing to our comprehension of the immunosuppressive state associated with MV infection. Finally, MV-N domains may be good tools to target tumour cell proliferation and/or apoptosis.

Animals↗
PubMed2004

Ray and wave instabilities in twisted graded-index optical fibers.

We study ray and wave propagation in an elliptical graded-index optical fiber or lens with a twisted axis and show analytically the existence of an instability for both ray trajectories and beam moments in a finite range of axis twist rate embedded within the spatial frequencies of periodically focused rays for the untwisted fiber. By considering the paraxial ray equations and the paraxial wave dynamics in a rotating frame that follows the fiber axis twist, we reduce the dynamical problem of ray trajectories to the classical Blackburn's pendulum, which shows a dynamical instability, corresponding to classical diverging trajectories, due to the competing effects of confining potential, Coriolis force, and centrifugal force. A closed set of linear evolution equations for generalized beam moments are also derived from the paraxial wave equation in the rotating reference frame, revealing the existence of a dynamical moment instability in addition to the trajectory instability. A detailed analysis of beam propagation is presented in case of a Gaussian beam, and different dynamical regimes are discussed.

Journal Article↗
PubMed2003

Sub-100-ps amplitude-modulation mode-locked Tm-Ho:BaY2F8 laser at 2.06 microm.

We report the generation of sub-100-ps pulse trains near the 2.06-microm wavelength in an actively mode-locked diode-pumped Tm-Ho:BaYF laser operating at room temperature. Transform-limited, 97-ps Gaussian pulses at a 100-MHz repetition rate with an average power in excess of 20 mW and with a carrier wavelength tunable by approximately 50 nm near 2.066 microm are demonstrated.

Journal Article↗
PubMed2003

Quantum-mechanical analogy of beam propagation in waveguides with a bent axis: dynamic-mode stabilization and radiation-loss suppression.

Wave propagation in an optical waveguide with a bent axis is studied under the scalar and paraxial wave approximations, and the quantum mechanical analogy with the electron dynamics in an atomic potential interacting with an intense electromagnetic field is highlighted. In particular we show that for a truncated parabolic waveguide with a periodically curved axis, a dynamic mode splitting with reduced radiation losses can be observed, which is fully analogous to the phenomenon of wave packet dichotomy and ionization quenching found in strong-field atomic physics.

Journal Article↗
PubMed2002

Pulse dynamics in actively mode-locked lasers with frequency shifting.

The dynamics of wave packet splitting in a dissipative Schrödinger-like dynamical system is theoretically studied by considering the model of an amplitude-modulated mode-locked laser with frequency shifting provided by an intracavity frequency modulation. It is shown that as the strength of the frequency modulation is increased, a bifurcation takes place which corresponds to a transition from a single-pulse steady-state oscillation to a two-pulse coherent oscillatory dynamics. An analytical model for pulse splitting bifurcation and onset of two-mode oscillatory dynamics, based on a Gaussian pulse analysis, is presented and compared with numerical simulations.

Journal Article↗
PubMed2002

Measurement of superluminal optical tunneling times in double-barrier photonic band gaps.

Tunneling of optical pulses at 1.5 microm wavelength through double-barrier periodic fiber Bragg gratings is experimentally investigated in this paper. Tunneling time measurements as a function of the barrier distance show that, far from resonances of the structure, the transit time is paradoxically short--implying superluminal propagation--and almost independent of the barrier distance. This result is in agreement with theoretical predictions based on phase-time analysis and provides, in the optical context, an experimental evidence of the analogous phenomenon in quantum mechanics of nonresonant superluminal tunneling of particles across two successive potential barriers.

Journal Article↗
PubMed2002

Experimental observation of superluminal pulse reflection in a double-Lorentzian photonic band gap.

We report on the experimental observation of superluminal reflection of picosecond optical pulses at 1.5 microm using a specially designed 30-cm-long fiber Bragg grating (FBG) that realizes a spectral reflectivity profile given by the superposition of two closely spaced Lorentzian lines. Probing pulses of 380 ps duration tuned midway between the two Lorentzian lines are reflected without appreciable distortion with a measured peak pulse advancement of approximately 60 ps. The achievement of the negative group delay is due to the interference of the two resonance modes of the FBG structure and has a close connection to the phenomenon of negative group velocity for pulse propagation in an inverted medium possessing a doublet line.

Journal Article↗
PubMed2002

Stability of periodic paraxial optical systems.

Based on ray propagation of paraxial geometric optics, we show that any stable periodic paraxial system or optical resonator becomes unstable in presence of stochastic perturbations of the the periodic sequence along which the rays are propagated. The exponential divergence with distance of ray displacements from the optical axis bears a close connection to the phenomenon of Anderson localization in disordered systems. The stability of the periodic focusing system is restored when finite aperture effects are accounted for and complex paraxial optics is used to describe wave propagation.

Journal Article↗
PubMed2002

Soft sensors for control of nitrogen and phosphorus removal from wastewaters by neural networks.

In this paper, we describe the results of research aimed to evaluate the possibility of using a neural network (NN) model for predicting biological nitrogen and phosphorus removal processes in activated sludge, utilising oxidation reduction potential (ORP) and pH as NN inputs. Based on N and P concentrations predictions obtained via the NN, a strategy for controlling sequencing batch reactors (SBRs) phases duration, optimising pollutants removal and saving energy, is proposed. The NN model allowed us to reproduce the concentration trends (change in slope, or process end), with satisfactory accuracy. The NN results were generally in good agreement with the experimental data. These results demonstrated that NN models can be used as "soft on-line sensors" for controlling biological processes in SBRs. By monitoring ORP and pH, it is possible to recognise the N and P concentrations during different SBRs phases and, consequently, to identify the end of the biological nutrient removal processes. This information can then be used to design control systems.

Hydrogen-Ion Concentration↗
PubMed2001

Superluminal optical pulse propagation at 1.5 microm in periodic fiber Bragg gratings.

We report on the experimental observation of superluminal tunneling of picosecond optical pulses in a periodic fiber Bragg grating. Optical pulses of 380-ps duration, generated by an externally-modulated single-frequency erbium-ytterbium laser operating near 1.5-microm wavelength, were propagated at a group velocity greater than approximately 1.97 times the speed of light in vacuum across a 2-cm long fiber grating. Owing to the very large ratio between the thickness of the barrier (2 cm) and the wavelength of probing optical pulses ( approximately 1.5 microm), our experiment allows for the observation of superluminal tunneling in the optical region by direct optoelectronic time-domain measurements.

Journal Article↗
PubMed2001

Experimental observation of spectral oscillations in frequency modulation laser operation.

The experimental observation of transient coherent oscillations in the optical frequency spectrum of an Er-Yb solid-state laser with internal frequency modulation (FM) is reported. These oscillations, which arise in the presence of a slight detuning between the modulation frequency and the cavity axial mode separation, are transiently observed when the modulator is switched on and appear as a damped breathing of laser spectral width superimposed to the relaxation oscillation dynamics of the laser intensity. The experimental results are in good agreement with the theoretical predictions which take into account both the fast dynamics of spectral oscillations and the slow dynamics of relaxation oscillations for the codoped Er-Yb laser system.

Journal Article↗