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Turbulent phenomena are among the most striking effects that both classical and quantum fluids can exhibit. While classical turbulence is ubiquitous in nature, the observation of quantum turbulence requires the precise manipulation of quantum fluids such as superfluid helium or atomic Bose-Einstein condensates. In this work we demonstrate the turbulent dynamics of a 2D quantum fluid of exciton-polaritons, hybrid light-matter quasiparticles, both by measuring the kinetic energy spectrum and showing the onset of vortex clustering. We demonstrate that the formation of clusters of quantum vortices is triggered by the increase of the incompressible kinetic energy per vortex, showing the tendency of the vortex-gas towards highly excited configurations despite the dissipative nature of our system. These results lay the basis for the investigations of quantum turbulence in two-dimensional fluids of light.

Optical bound states in the continuum (BIC) are peculiar topological states that, when realized in a planar photonic crystal lattice, are symmetry-protected from radiating in the far field despite lying within the light cone, i.e., in the energy-momentum dispersion region for which radiation can propagate out of the lattice plane. These BICs possess an invariant topological charge given by the winding number of the polarization vectors, similarly to vortices in quantum fluids, such as superfluid helium and atomic Bose-Einstein condensates. In spite of several reports of optical BICs in patterned dielectric slabs with evidence of lasing, their potential as topologically protected states with theoretically infinite lifetime has not been fully exploited, yet. Here we show Bose-Einstein condensation of polaritons, hybrid light-matter excitations, occuring in a BIC thanks to its peculiar non-radiative nature. The combination of the ultra-long BIC lifetime and the tight confinement of the waveguide geometry allow to achieve an extremely low threshold density for condensation, which is not reached in the dispersion minimum but at a saddle point in reciprocal space. By bridging bosonic condensation and symmetry-protected radiation eigenmodes, we unveil new ways of imparting topological properties onto macroscopic quantum states with unexplored dispersion features. Such an observation may open a route towards energy-efficient polariton condensation in cost-effective integrated devices, ultimately suited for the development of hybrid light-matter optical circuits

Lean fuel burning is considered as one of the most prominent methods to achieve the low temperature combustion reduces nitrogen oxides (NOx) emissions. However, as a result lean burning suffers from strong flame instabilities and a very lean operating condition near to the flame quenching limit is associated with the high risk of lean blowout (LBO) which has to be avoided. Therefore, the capability to sense the origin of LBO will provide substantial settlements to improve combustor reliability in order to achieve optimum performance, to extend engine life and to reduce maintenance cost. From the last few decades, many engine manufacturers and research institutions are working on the novel approaches based on the lean combustion concepts. For achieving desired objects, several passive control technologies were studied to improve the flame stabilization by modifying the injector geometry or flame holders in a permanent way. Adding to this, Non thermal plasma assisted combustion (NTPAC) technology is the most encouraging techniques to actively control the control the flow and combustion dynamics in consonance with real-time operating conditions without altering the combustor design. NTPAC improves the efficiency of combustors, increases flame stabilization, enhances low temperature oxidation, and extends the LBO limits, in the meantime it also reduces the significant amount of nitrogen oxides (NOx). From literature review it has been concluded that the effects of NTPAC is broadly classified into three ways: thermal effects, kinetic effects, and transport effects. Among all the NTPAC technologies, the dielectric barrier discharge (DBD) is widely considered and credit goes to the simplicity of its design and the wide range of operating modes.However, the effects of NTPAC on flame stability and LBO limits are not clearly understood yet, due to the complexity of each specific process involves in the plasma combustion. Therefore, for the better understanding of NTPAC processes, an experimental study was performed which investigates the behavior of premixed methane/air flames close to LBO limits at different operating conditions using plasma assisted lifted swirl combustor. The combustor was equipped with ring-needle shaped plasma actuator operated by sinusoidal generator at the maximum frequency of 20 kHz directly coupled with flame near to the nozzle. The test system was covered by faraday cage to avoid interference of electromagnetic fields produced through plasma discharge. The plasma actuator configuration involves a tungsten needle having a diameter of 1 mm and length equal to 46 mm. The needle was placed at the center of nozzle which referred as a high voltage (HV) electrode. However, the nozzle was acted as a grounded (GND) electrode. Electrical characterization of combustion characteristics was performed at different plasma actuation conditions and air/fuel mass flow rates. Flame behavior was also captured by high resolution CCD camera by predicting the recirculation zone produced by plasma, have the benefits of generating compact flames and allowing the high reaction rates. Acoustic measurements were performed using high sensitivity microphone. Furthermore, post processing of the microphone data involved application of Fast Fourier Transform (FFT).

Bound states in the continuum (BICs)

Exciton-polaritons are hybrid light-matter excitations arising from the nonperturbative coupling of a photonic mode and an excitonic resonance. Behaving as interacting photons, they show optical third-order nonlinearities providing effects such as optical parametric oscillation or amplification. It has been suggested that polariton-polariton interactions can be greatly enhanced by inducing aligned electric dipoles in their excitonic part. However, direct evidence of a true particle-particle interaction, such as superfluidity or parametric scattering, is still missing. In this Letter, we demonstrate that dipolar interactions can be used to enhance parametric effects such as self-phase modulation in waveguide polaritons. By quantifying these optical nonlinearities, we provide a reliable experimental measurement of the direct dipolar enhancement of polariton-polariton interactions.

Exciton-polaritons are mixed light-matter particles offering a versatile solid state platform to study many-body physical effects. In this work we demonstrate an electrically controlled polariton laser, in a compact, easy-to-fabricate and integrable configuration, based on a semiconductor waveguide. Interestingly, we show that polariton lasing can be achieved in a system without a global minimum in the polariton energy-momentum dispersion. The surface cavity modes for the laser emission are obtained by adding couples of specifically designed diffraction gratings on top of the planar waveguide, forming an in-plane Fabry-Perot cavity. It is thanks to the waveguide geometry, that we can apply a transverse electric field in order to finely tune the laser energy and quality factor of the cavity modes. Remarkably, we exploit the system sensitivity to the applied electric field to achieve an electrically controlled population of coherent polaritons. The precise control that can be reached with the manipulation of the grating properties and of the electric field provides strong advantages to this device in terms of miniaturization and integrability, two main features for the future development of coherent sources from polaritonic technologies., Comment: 11 pages, 5 figures. Supplementary: 6 pages, 7 figures

We report the nonlinear optical properties of polaritons in a single quantum well GaAs microcavity. Single and double resonance cavities have been used to enhance the nonlinear effect of a nonlinear medium in high-Q quality factor cavities due to the cavity field amplification. On the other hand, such a cavity can generate polaritons, which condense (Bose–Einstein condensation) for determined conditions, such as cavity detuning and polariton density. Here, we present experimental observations of the second harmonic generation from polaritons in a GaAs microcavity, which exhibit a 2 order higher efficiency than those from the usual method. Furthermore, the efficiency is particularly high when the polariton is a photon-like particle and in a condensed state.

Topological Physics relies on the specific structure of the eigenstates of Hamiltonians. Their geometry is encoded in the quantum geometric tensor containing both the celebrated Berry curvature, crucial for topological matter, and the quantum metric. The latter is at the heart of a growing number of physical phenomena such as superfluidity in flat bands, orbital magnetic susceptibility, exciton Lamb shift, and non-adiabatic corrections to the anomalous Hall effect. Here, we report the first direct measurement of both Berry curvature and quantum metric in a two-dimensional continuous medium. The studied platform is a planar microcavity of extremely high finesse, in the strong coupling regime. It hosts mixed exciton-photon modes (exciton-polaritons) subject to photonic spin-orbit-coupling which makes emerge Dirac cones and exciton Zeeman splitting breaking time-reversal symmetry. The monopolar and half-skyrmion pseudospin textures are measured by polarisation-resolved photoluminescence. The associated quantum geometry of the bands is straightforwardly extracted from these measurements. Our results unveil the intrinsic chirality of photonic modes which is at the basis of topological photonics. This technique can be extended to measure Bloch band geometries in artificial lattices. The use of exciton-polaritons (interacting photons) opens wide perspectives for future studies of quantum fluid physics in topological systems.

Hydrogels based on poly(ethylene glycol) (PEG) are commonly used for studies related to cell fate and tissue engineering. Here we present a new covalent layer-by-layer build-up process leading to PEG coatings of nanometer size called "nanogel films". Compared to macroscopic hydrogels, such nanogels should provide a fine control over the structure and the thickness of the coating. Alternated deposition of bifunctional and tetra functional PEG molecules reacting through thiol/maleimide click chemistry is evaluated by quartz crystal microbalance. We first study parameters influencing the build-up process of such coatings and demonstrate the importance of (i) the nature of the first deposited layer, (ii) the PEG concentrations and (iii) the length of the PEG chains that appears to be the most significant parameter influencing film growth. The build-up process can be extended to a large variety of substrates like SiO2 or polymers by using an appropriate anchoring layer. Covalent functionalization of these nanogel films by proteins or enzymes is suited by modifying the biomolecules with thiol or maleimide groups and immobilizing them during the build-up process. Activity of the embedded enzymes can be maintained. Moreover ligands like biotin can be incorporated into the film and recognition by streptavidin can be modulated by playing with the number of PEG layers covering biotin. Compared to well-known PEG hydrogels, these new coatings are promising as they allow to (i) build thin nanometric coatings, (ii) finely control the amount of deposited PEG and (iii) organize the position of the embedded biomolecules inside the film layers.

We report the linear and nonlinear optical properties of single GaAs nanowires with polytypism effect. Electron transmission microscopy experiments show that the nanowires contain wurtzite segments as well as zinc blende segments with two different crystallographic orientations. Time-resolved photoluminescence spectroscopy of single nanowires shows ultrafast radiative recombination lifetimes in the range of 20–70 ps as a consequence of the charge scattering in the type-II band alignment between WZ and ZB segments and or by the high surface area of the nanowires. Polarization resolved second harmonic generation in the nanowires found to be highly sensitive to the crystallography of the nanowires. All three crystal axes orientations of the nanowires were determined. Furthermore, the volume fraction of the ZB segments oriented in the [0–11] and in the [01–1] directions was precisely determined for the first time by optical measurement besides the TEM technique.

Topological physics relies on the structure of the eigenstates of the Hamiltonians. The geometry of the eigenstates is encoded in the quantum geometric tensor

Large single-crystal flakes of 2D perovskite are able to sustain strong polariton nonlinearities at room temperature., Polaritonic devices exploit the coherent coupling between excitonic and photonic degrees of freedom to perform highly nonlinear operations with low input powers. Most of the current results exploit excitons in epitaxially grown quantum wells and require low-temperature operation, while viable alternatives have yet to be found at room temperature. We show that large single-crystal flakes of two-dimensional layered perovskite are able to sustain strong polariton nonlinearities at room temperature without the need to be embedded in an optical cavity formed by highly reflecting mirrors. In particular, exciton-exciton interaction energies are shown to be spin dependent, remarkably similar to the ones known for inorganic quantum wells at cryogenic temperatures, and more than one order of magnitude larger than alternative room temperature polariton devices reported so far. Because of their easy fabrication, large dipolar oscillator strengths, and strong nonlinearities, these materials pave the way for realization of polariton devices at room temperature.

The development of techniques able to check the structural health of a wind blade is very important. An innovative and promising technique applicable at this aim is the SMArt thermography. It exploits the electro-thermal properties of SMArt composites, in order to detect the structural flaws using an embedded source. Such a system enables a built-in, fast, cost-effective and in-depth assessment of the structural damage as it overcomes the limitations of standard thermography. With the aim for developing a reliable diagnostic method based on SMArt thermography, a preliminary numerical model was implemented in order to simulate the heating and the subsequent cooling of a GFRP composite laminate with embedded SMA wires. The heat source was represented by the Joule effect originated in the SMA wires and supplied as power density. The analysis of the resulting thermal maps at different values of power density provided the optimal levels of current amplitude and period to be applied in the subsequent experimental applications.

In this work, we studied the effect of some growth parameters on the polarization behavior of InAs/GaAs closely stacked quantum dot (CSQDs). In particular, we focused on the surface reconstruction time of GaAs spacer, its thickness and the number of QD layers. We found that the most effective parameter to enhance the TM/TE intensity ratio is the surface reconstruction time of the GaAs spacer before the subsequent QD deposition. By varying this parameter between 20 s and 120 s, a TM/TE ratio as high as 0.86 has been achieved. A further fine tuning of GaAs spacer thickness and QD layer number increased this ratio up to a value of 0.92 in structures containing only 3 QD layers.

In this work we experimentally demonstrate for the first time spontaneous generation of two-dimensional exciton-polariton X-waves. X-waves belong to the family of localized packets, which are capable of sustaining their shape with no spreading even in the linear regime. This allows to keep the packet shape and size for very low densities and very long times compared, for instance, to soliton waves, which always necessitate a nonlinearity to compensate the diffusion. Here we exploit the polariton nonlinearity and unique structured dispersion, comprising both positive- and negative-mass curvatures, to trigger an asymmetric four wave mixing in the momentum space. This ultimately enables self-formation of a spatial X-wave front. By means of ultrafast imaging experiments we observe the early reshaping of the initial Gaussian packet into the X-pulse and its propagation even for vanishing small densities. This allows us to outline the crucial effects and parameters driving the phenomena and to tune the degree of peak superluminal propagation, which we found to be in a good agreement with numerical simulations., 10 pages, 6 figures, 2 ancillary movie files

This work explores the conditions to obtain the extension of the PL emission beyond 1.3 μm in InGaAs quantum dot (QD) structures growth by MOCVD. We found that, by controlling the In incorporation in the barrier embedding the QDs, the wavelength emission can be continuously tuned from 1.25 μm up to 1.4 μm at room temperature. However, the increase in the overall strain of the structures limits the possibility to increase the maximum gain in the QD active device, where an optical density as high as possible is required. By exploring the kinetics of QD surface reconstruction during the GaAs overgrowth, we are able to obtain, for the first time, emission beyond 1.3 μm from InGaAs QDs grown on GaAs matrix. The wavelength is tuned from 1.26 μm up to 1.33 μm and significant improvements in terms of line shape narrowing and room temperature efficiency are obtained. The temperature-dependent quenching of the emission efficiency is reduced down to a factor of 3, the best value ever reported for QD structures emitting at 1.3 μm .

The mission of the Universal Protein Resource (UniProt) (http://www.uniprot.org) is to provide the scientific community with a comprehensive, high-quality and freely accessible resource of protein sequences and functional annotation. It integrates, interprets and standardizes data from literature and numerous resources to achieve the most comprehensive catalog possible of protein information. The central activities are the biocuration of the UniProt Knowledgebase and the dissemination of these data through our Web site and web services. UniProt is produced by the UniProt Consortium, which consists of groups from the European Bioinformatics Institute (EBI), the SIB Swiss Institute of Bioinformatics (SIB) and the Protein Information Resource (PIR). UniProt is updated and distributed every 4 weeks and can be accessed online for searches or downloads.

The gluon momentum density xg ( x , Q 2 ) of the proton was extracted at Q 2 = 20 GeV 2 for small values of x between 4 × 10 −4 and 10 −2 from the scaling violations of the proton structure function F 2 measured recently by ZEUS in deep inelastic neutral current ep scattering at HERA. The extraction was performed in two ways. Firstly, using a global NLO fit to the ZEUS data on F 2 at low x constrained by measurementsfrom NMC at larger x ; and secondly using published approximate methods for the solution of the GLAP QCD evolution equations. Consistent results are obtained. A substantial increase of the gluon density is found at small x in comparison with the NMC result obtained at larger values of x .

In this work, the deposition of Y thin films by laser beams with 0.5 ps and 5 ps pulse durations at different laser fluences (1.2–6.4 J/cm2) is reported. The morphology of the deposited films and of the ablated target surface is investigated by scanning electron microscopy analyses. The present results show that the films, well adherent to the substrates, are characterized by a high abundance of sub-micrometric particulates with average size less than 0.3 μm, whose density decreases with increasing laser fluence. The formation of columnar structures observed on the target surface seems to be responsible of the poor film homogeneity. Acceptable deposition rate in the range of 0.08–0.16 A/pulse with 5 ps pulse duration is found; on the contrary with 0.5 ps pulse duration, it is not possible to get information on deposition rate as a function of the laser fluence due to the high non-uniformity of the films. A comparison with the results previously obtained in ns regime is presented and discussed. The achievements of our investigation will be useful to optimize the synthesis of photocathodes based on Y films for the production of bright electron beams in radio-frequency photoinjectors.

In this paper an associative-parametric approach is proposed in order to model the mesh of an aeronautical concept starting from a set of high-level structural primitives. This approach allows the designer to carry out the geometric modelling and the automatic mesh generation within one software environment in a fast and interactive way. The structural optimisation process is then simplified, with a relevant man-hours saving. A lower number of data transfers between different software is, moreover, involved with less problems related to the data corruption. To assure orders of continuity higher than C0 between adjacent instances, a suitable mathematical description of the structural primitives has been proposed. This description assures the maintenance of the required continuity constraints when the mesh is modified. Appropriate schemes of dependences are identified to guarantee the automatic propagation of the modifications complying with the continuity constraints.

A pulsed neutron source has been realized at the Beam Test Facility (BTF) of the National Laboratory of Frascati, near Rome (Italy). Neutrons are produced sending high energy (510 MeV) electrons to impinge on an optimized Tungsten target. This kind of source produces neutrons with an energy spectrum that spans over more than 9 decades of energy (from few meV up to hundred of MeV), even if most of them have energy around 1 MeV. This source may be suitable for calibrating neutron sensitive devices with response in the MeV region, as well as it could be efectively used for material and nuclear science investigations. Neutron and photon rates and their spectra have been measured along well designed extraction lines, by using a Bonner Sphere Spectrometer (BSS). This works describes the experimental apparatus used to produce neutrons and the first experimental results: measured neutron and photon fluences are compared with Monte Carlo predictions performed with FLUKA and MCNPX, respectively.

In this work we present a time-resolved magneto-luminescence investigation (up to 8 T) of InGaAs V-shaped quantum wires (QWRs) with different In content, as a function of temperature and the applied magnetic field. The states of the wires were investigated by CW PL and quantitatively compared with the results of a numerical solution of the two-dimensional Schrodinger equation. Time-resolved experiments performed in magnetic field at different temperatures indicate the existence of a competition between the electron confinement occurring in deep QWRs at low temperature, and the magnetic confinement prevailing in shallower QWRs.

We present a systematic study of electronic levels and recombination lifetimes for rectangular and V-shaped quantum wires (QWRs) in a magnetic field B. In both cases, the effect of B is a modification of the subband dispersion consisting mainly in a flattening at small values of the wave vector: this feature is explained with the appearance of Landau levels inside the wire profile, and it becomes more pronounced with growing magnetic field. As a consequence, an increase in the calculated free-carrier lifetime with the field strength is found. This behaviour is experimentally observed in InxGa1-xAs/GaAs V-shaped quantum wires with an In content x = 0.10, where the exciton is ionised and the recombination mechanism is supposed to be a free-carrier one; a quantitative agreement between theory and experiment is found.

The residual stresses introduced into a component as a result of the mechanical processes necessary for its manufacture significantly influence of fatigue behaviour. The application of loads themselves can, however, alter the initial residual stress distribution, so it is feasible to believe that the residual stress field of a fatigue-stressed structure develops over its entire lifespan. The aim of this article is to analyse the development that the residual stresses initially present in a welded butt joint undergo following the application of the external cyclic load. Comparisons between two residual stress measurements, conducted on the same joint before and after the application of fatigue cycles, have made it possible to obtain interesting information regarding the development of residua stresses in components subjected to fatigue. In particular, it has been found that unlike what is commonly reported, there are particular conditions where the application of a cyclic load results in an increase in the residual stresses initially present, rather than their relaxation. This phenomenon should be taken into consideration in order to avoid unexpected failure in components subjected to fatigue.

InGaAs/GaAs V-shaped quantum wires grown in grooves with either (111) or (411) sidewalls have been studied by ps-transient photoluminescence as a function of the excitation intensity. The optical nonlinearity associated with the screening of the internal piezoelectric field is temporally monitored by the blue-shift of the spectrally resolved photoluminescence, occurring in the first 150 ps after the laser pulse, followed by the recovery of the unperturbed energy resonance at longer delays. Such an energy shift strongly depends on the photoexcited carrier density and reaches a maximum value of about 14 meV in the (411) wires. Despite their larger piezoelectric field, we observe a smaller energy shift in wires with (111) sidewalls, due to the enhanced confinement which localizes the wire wave-function at the bottom of the groove. The observed energy shifts are consistent with the theoretical calculation of the polarization charge density induced by the strain via the piezoelectric effect.

Summary Background Gastro-oesophageal reflux is common in preterm newborns; at present, no studies have evaluated the efficacy of sodium alginate in this population. Aim To evaluate the effect of sodium alginate on gastro-oesophageal reflux features in preterm newborns by combined pH and impedance monitoring (pH-MII). Methods Thirty-two symptomatic preterm newborns underwent a 24 h pH-MII, during which each baby was fed eight times. Sodium alginate was given four times at alternate meals [drug-given (DG) vs. drug-free (DF) meals]. Gastro-oesophageal reflux features (i.e. number, acidity, duration and height of gastro-oesophageal reflux) after DG and DF meals were compared by Wilcoxon signed ranks test. Results Sodium alginate significantly decreased the number of acid gastro-oesophageal reflux detected either by pH monitoring (DG vs. DF: median 17.00 vs. 29.00, P = 0.002) and MII (DG vs. DF: 4.0 vs. 6.00, P = 0.050), and also acid oesophageal exposure (DG vs. DF: 4.0% vs. 7.6%, P = 0.030), without any influence on non-acid gastro-oesophageal reflux. Furthermore, it decreased the number of gastro-oesophageal reflux reaching proximal oesophagus (DG vs. DF: 5.50 vs. 7.50, P = 0.030). Conclusions The use of sodium alginate in preterm infants seems to be promising, because this drug decreases gastro-oesophageal reflux acidity and height with the advantage of a nonsystemic way of action and a more favourable safety profile over H2 blockers and PPIs.

Natural dyes have been used extensively in the past for many purposes, such us to colour fibers and to produce inks, watercolours and paints, but their use declined rapidly after the discovery of synthetic colours. Nowadays we witness a renewed interest, as natural dyes are neither toxic nor polluting. In this work, physical and chemical properties of four selected dyes, namely red (Madder), yellow (Weld and Turmeric) and blue (Woad) colours, produced by means of traditional techniques at the Museo dei Colori Naturali (Lamoli, Italy), have been investigated. The chromatic properties have been studied through the reflectance spectroscopy, a non-invasive technique for the characterisation of chromaticity. Reflection spectra both from powders and egg-yolk tempera models have been acquired to provide the typical features of the dyes in the UV-vis spectral range. Moreover, to assess the feasibility of laser cleaning procedures, tempera layers were investigated after irradiation with an excimer laser. Micro Raman spectroscopy, Scanning Electron Microscopy and Energy Dispersive X-Ray analyses have complemented the survey, returning compositional and morphological information as well. Efforts have been made to give scientific feedback to the production processes and to support the research activity in the restoration of the artworks where these dyes were employed.

The aim of this work is the development of microstructural numerical models of metallic foams. In particular, attention is focused on closed cell foam made of aluminium alloy. By means of a finite elements code, the material cellular structure was shaped in different ways: firstly the Kelvin cell, with both plane and curved walls; finally an ellipsoidal cell defined by random dimensions, position and orientation has been adopted as base unit. In order to validate the foam numerical models, static tests were performed to obtain the typical stress–strain curves and then compared with the numerical analysis results.

In this contribution we report on an optical nonlinearity featuring colloidal seeded grown CdSe/CdS nanorods (NRs). It consists of a photoluminescence (PL) blueshift of single rod spectra with increasing laser power and a transient, power-dependent redshift of the spectra studied by time resolved PL measurement, strictly related to the multicarrier scattering occurring at high excitation density. We attribute this nonlinearity to a photo-induced screening of an internal field, originating from the piezoelectric polarization induced at the core/shell interface.

In this work, we evaluate the residual stress field originated by a new welding process named Friction Stir Welding. We analysed aluminium alloy butt-welded joints. Both similar and dissimilar joints have been considered in 2024-T3 and 6082-T6 aluminium alloy 0.8 and 3 mm thick. For each joint, the longitudinal and transversal residual stress distribution have been obtained in a direction normal to the weld cord. In the thicker dissimilar joints, the longitudinal residual stress distribution is very similar to the distribution present in the traditional welded joints. It presents, in fact, a tensile region near the weld cord, which is balanced by compressive regions away. On the contrary, other joints present a low compressive stress at the weld toe, which began tensile away. Moreover, the effect of the shoulder geometry on the residual stress field was evaluated on 1.5 mm thick joints.

Artistic yellow pigments, commonly employed from antiquity, were investigated by morphological, spectrophotometric and compositional analyses. Namely, scanning electron microscopy–energy dispersive X-ray (SEM/EDX) characterisations and reflectance, attenuated total reflection–Fourier transform infrared spectroscopy (ATR-FTIR) and Raman spectroscopy were carried out on egg yolk tempera models to discriminate the pigments. The models were irradiated with excimer KrF (248 nm) laser at different working conditions, and the effects induced on colour were related to chemical and physical modifications through the same analyses, as a function of laser parameters. It came out that the effects on the pictorial layers are always related to the modifications of the binding medium and, in addition, the laser radiation induces dehydration and transformation of iron oxides in natural earths. Copyright © 2009 John Wiley & Sons, Ltd.

Due to their delta-like density of states, quantum dots (QDs) were expected to improve laser device performances with respect to quantum wells (QWs). Nevertheless, some important drawbacks limit this technology. For instance, QD laser still suffers from a low value of the modal gain, due to the low areal density of QDs, and inhomogeneous broadening, especially when multistacked layers are used. In this paper, we demonstrate that a linear increase of the QD modal gain with the QD layers number, as typically achieved in multi-QW lasers, is possible by a careful control of the Stranski-Krastanov QDs growth and QDs stacking optimization. A low-transparency current density of 10 A/cm(2) per QD layer and a modal gain of 6 cm(-1) per QD layer Were achieved from laser structures containing up to seven QD layers. We demonstrate 10-Gb/s direct modulation (until a temperature of 50 degrees C and high T-0 (110 K) from a single-mode device containing six QD layers.

The aim of the MAPEC_LIFE (Monitoring Air Pollution Effects on Children for Supporting Public Health Policy) study is to evaluate the associations between the concentrations of air pollutants and early biological effects in children living in five Italian towns (Brescia, Torino, Lecce, Perugia and Pisa) characterised by varying levels of air pollution. This paper presents the results of micronucleus cytome assays performed on the oral mucosa cells of subjects living in Lecce (Puglia, Italy) and their relationship to factors associated with indoor/outdoor exposure and lifestyles. The study was conducted on 6-8-year-old schoolchildren living in Lecce. The micronucleus cytome assay was performed on exfoliated buccal cells collected from the oral mucosa of children using a soft-bristled toothbrush. Micronuclei were evaluated only in normal differentiated cells. Overall, 43.0% of the samples tested were positive, with an average frequency of 0.28 MN/1000 differentiated cells. Data analysis shows positive associations between the frequency of MN in the children’s buccal mucosa cells and obesity, heavy traffic and smoking mothers, while outdoor sports seem to have the opposite effect. These data will be integrated with data from the other cities involved in the MAPEC_LIFE study and could be used

The Hanbury Brown--Twiss effect is one of the celebrated phenomenologies of modern physics that accommodates equally well classical (interferences of waves) and quantum (correlations between indistinguishable particles) interpretations. The effect was discovered in the late thirties with a basic observation of Hanbury Brown that radio-pulses from two distinct antennas generate signals on the oscilloscope that wiggle similarly to the naked eye. When Hanbury Brown and his mathematician colleague Twiss took the obvious step to propose bringing the effect in the optical range, they met with considerable opposition as single-photon interferences were deemed impossible. The Hanbury Brown--Twiss effect is nowadays universally accepted and, being so fundamental, embodies many subtleties of our understanding of the wave/particle dual nature of light. Thanks to a novel experimental technique, we report here a generalized version of the Hanbury Brown--Twiss effect to include the frequency of the detected light, or, from the particle point of view, the energy of the detected photons. In addition to the known tendencies of indistinguishable photons to arrive together on the detector, we find that photons of different colors present the opposite characteristic of avoiding each others. We postulate that fermions can be similarly brought to exhibit positive (boson-like) correlations by frequency filtering., 18 pages, includes supplementary material of the derivations

We study the electronic structure of CdTe spheres (dots) and tetrapods by absorption, fluorescence, and photoluminescence-excitation (PLE) spectroscopy. A series of quantum dots with different diameter and tetrapods with varying arm length and diameter is investigated in solution at room temperature. We observe a significant impact of the geometrical shape of the nanocrystals on the optical response. In particular we find a double peak in the emission of tetrapods as a characteristic feature of this nanocrystal geometry. We observe a pronounced Stokes shift for the tetrapod and dot samples which depends sensitively on the crystal size. (c) 2005 Elsevier Ltd. All rights reserved.

In this work the analysis, fabrication and optical characterization of a circular two-dimensional photonic crystal (2D-CPC) nano-resonator based on a air/GaAs/air slab waveguide are presented. Four InAs/InGaAs quantum dots (QDs) stacked layers emitting around 1300 nm were embedded in a GaAs waveguide layer grown on an Al0.7Ga0.3As sacrificial layer. The nano-resonator was realized by drilling 2D-PC air holes arranged in a circular lattice configuration through electron beam lithography (EBL), inductively coupled plasma (ICP) etching and wet selective etching of the Al0.7Ga0.3As sacrificial layer in order to release the membrane. The spectral response of the active circular nano-cavity has been simulated by using a three dimensional finite-difference time-domain method (3D-FDTD) as a function of both the inner and outer holes radius/period ratios of the photonic crystal structure. Good agreement between the calculated resonance and the experimental results, recorded from the nano-cavity by a mu PL setup, has been achieved. (c) 2007 Elsevier B.V. All rights reserved.

Polaritons in microcavities are versatile quasi-2D bosonic particles with a high degree of coherence and strong nonlinearities, thanks to their hybrid light-matter character. In their condensed form, they display striking quantum hydrodynamic features analogous to atomic Bose-Einstein condensates, such as long-range order coherence, superfluidity and quantized vorticity. Their variegated dispersive and dissipative properties, however, set significant differences from their atomic counterpart. In this work, we report the unique phenomenology that is observed when a pulse of light impacts the polariton vacuum: the condensate that is instantaneously formed does not splash in real space but instead coheres into an enigmatic structure, featuring concentric rings and, most notably, a sharp and bright peak at the center. Using a state-of-the-art ultrafast imaging with 50 fs time steps, we are able to track the dynamics of the polariton mean-field wavefunction in both real and reciprocal space. The observation of the real-space collapse of the condensate into an extremely localized---resolution limited---peak is at odd with the repulsive interactions of polaritons and their positive effective mass. An unconventional mechanism is therefore at play to account for our observations. Our modeling suggests that self-trapping due to a local heating of the crystal lattice---that can be described as a collective polaron formed by a polariton condensate---could be involved. These observations hint at the fascinating fluid dynamics of polaritons in conditions of extreme intensities and ultrafast times., Comment: New version complete with revised theoretical interpretation and added material. 8 pages, 5 figures, supplementary 12 pages, 15 figures. Supplementary videos: https://drive.google.com/folderview?id=0B0QCllnLqdyBZUNXMTdTNUNhdUk

An InGaAs/GaAs quantum-dot (QD) microcavity light-emitting diode (MCLED) emitting at 1.3 μm at room temperature was analyzed. The long wavelength emission of 1.3 μm emission was achieved by using InGaAs quantum dots which were directly grown on GaAs by metallorganic chemical vapor deposition. Electroluminescence bright emission peaked at 1298 nm was exhibited by the device with full width at half maximum of 6.5 meV. The results show linear dependence of optical output power as function of injection current.

Residual stresses develop during most manufacturing processes involving material deformation, heat treatment, machining or processing operations that transform the shape or change the properties of a material. They have a not negligible effect on the material strength, especially on fatigue. For this reason, it is important that some knowledge of the internal stress state can be deduced either from measurements or from modelling predictions. The object of this paper is forecasting the modification and the evolution that a residual stress field, originated by welding, suffers after chip-forming machining, such as milling and cutting. Numerical results have been critically compared to experimental measurements and show the potentiality but also the limitations of numerical techniques.

Microphotoluminescence studies of annealed In(x)Ga(1 − x)N(y)As(1 − y)/GaAs quantum wells fabricated by molecular beam epitaxy for optical emission in the 1.3 µm spectral range revealed several sharp peaks about 2–7 meV wide in the emission spectra. The intensity of the discrete lines decreased strongly with increasing lattice temperature and was absent in as-grown (unannealed) quantum wells. Such quantum dot-like emission lines are attributed to the recombination of excitons strongly localized at alloy fluctuations composed of In–N-rich clusters.

The laser-induced breakdown spectroscopy technique is employed for compositional analyses of thin films produced by pulsed laser ablation of multielemental targets. Information about the atomic concentration of the chemical species from the irradiated target is inferred by means of the optical emission spectra of the plasma generated during laser ablation. The atomic concentration percentages and the atomic concentration ratios of the elements of Co-based magnetic alloy targets are deduced from the integrated intensities of selected emission lines of the alloy components. The experimental results show that Co atomic percentage concentration and CSi/CCoand CCr/CCoatomic concentration ratios are in agreement with the corresponding values obtained by traditional compositional analysis techniques. On the contrary, Si atomic percentage concentration values are in disagreement, since the used emission lines have significant self-absorption values. Therefore, the work proves that laser-induced breakdown spectroscopy is adequate for elemental concentration measurements provided an accurate choice of the emission lines. © 2006 Elsevier B.V. All rights reserved

In this work we present the realization of an experimental setup to measure the absorption spectrum of low planar density active media in nanoscale devices. The experimental technique employs in-plane light transmission through a waveguide embedding the active medium. It has been applied to the investigation of the room temperature optical properties of low density self-assembled InGaAs/GaAs quantum dots (QDs), emitting around 1.3 mu m. A detailed analysis of the obtained spectra showed the occurrence of a Stokes shift which after inspection turned out to be related to the thermally activated carrier migration throughout the QD ensemble.

Laser induced breakdown spectroscopy was employed in the restoration process of the bust of St. Gregory the Armenian. It was applied to carry out elemental chemical analyses of different details of the bust. The analyses showed that all the investigated pieces are covered by polluted layers, rich mainly in calcium which can be removed by laser ablation. The investigations performed on the cleaned surfaces confirm that the hair is composed essentially of silver and the stole of copper and that no foils were added during the stages of artwork realization. The interesting finding is that the decorative coating of the stole was realized in gold, instead of the supposed brass.

The 40 MHz bunched muon beam set up at CERN was used in May 2003 to make a full test of the drift tubes local muon trigger. The main goal of the test was to prove that the integration of the various devices located on a muon chamber was adequately done both on the hardware and software side of the system. Furthermore the test provided complete information about the general performance of the trigger algorithms in terms of efficiency and noise. Data were collected with the default configuration of the trigger devices and with several alternative configurations at various angles of incidence of the beam. Tests on noise suppression and di-muon trigger capability were performed.

Laser induced breakdown spectroscopy was used to investigate the composition of a gun found in the Adriatic seabed and kept in the “S. Castromediano” Provincial Museum in Lecce (Italy). Optical emission spectra of the laser-induced plasma from the surface of the piece of ordnance were recorded before and after its restoration. The metal alloy of the gun was determined through the identification of characteristic atomic emissions and confirmed through microanalysis carried out by energy dispersion X-ray spectroscopy. Experimental results evidenced that the gun is of bronze and revealed that elements composing the encrustation and noxious for the object conservation, such as calcium, were removed successfully during the cleaning operation. Performed elemental analyses confirmed that laser induced breakdown spectroscopy is a useful diagnostic tool to test the restoration degree of artworks.

The aim of this work is to evaluate by numerical simulation the real stress state of a welded component subjected to a sinusoidal external load. In particular, the relaxation process of the residual stress, due to the application of a cyclic external load, has been studied. Longitudinal welded joints, laser welded and 3 mm thick, are analysed in this work following the residual stress evolution during a fatigue test. A numerical procedure, implemented by the ABAQUS code, carries out the residual stress field originated by a welding process and it is taken as a pre-stress condition in the present ABAQUS simulations. In order to evaluate the influence of the amplitude level on the residual stress relaxation, eight different sinusoidal loads at the load ratio R = 0.1 are applied to the model. The results show a significant reduction in the initial residual stress level, even after the first load cycle. They offer a very precise explanation of the fatigue behaviour of this kind of welded joints, confirming the behaviour experimentally observed.

A detailed analysis of the excitonic transitions of 8 InGaAsP MQWs grown by MOCVD into a InGaAsP barriers with different composition has permitted to experimentally determine the band offset for InGaAsP/InGaAsP heterostructures. We find a value of about 44% referred to the valence band, which is lower than the value reported for unstrained structure (≈ 56%) and in good agreement with the value estimated by a theoretical model specifically developed to design the structure. Additionally, we compared the values of the activation energies, obtained from the fits to exciton transition PL intensity, with the carrier confinement energy evaluated theoretically. The obtained activation energies confirms that in such heterostructures the unipolar detrapping of carriers is more efficient than the exciton escape. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Although photons in vacuum are massless particles that do not appreciably interact with each other, significant interactions appear in suitable nonlinear media, leading to hydrodynamic behaviours typical of quantum fluids(1-6). Here, we show the generation and manipulation of vortex-antivortex pairs in a coherent gas of strongly dressed photons (polaritons) flowing against an artificial potential barrier created and controlled by a light beam in a semiconductor microcavity. The optical control of the polariton flow allows us to reveal new quantum hydrodynamical phenomenologies such as the formation of vortex pairs upstream from the optical barrier, a case of ultra-short time excitation of the quantum flow, and the generation of vortices with counterflow trajectories. Additionally, we demonstrate how to permanently trap and store quantum vortices hydrodynamically generated in the wake of a defect. These observations are supported by time-dependent simulations based on the non-equilibrium Gross-Pitaevskii equation(7).