1,721,337 research outputs found
Femtosecond laser writing of integrated optical structures in glasses
No full textIn this paper, we describe how among the many variables in fs laser waveguide writing, the repetition rate has the most important role as it influences the heat accumulation between laser pulses, which determines the regime of modification and the resulting morphological change. Chapter Contents: • 12.1 Introduction • 12.2 Fundamentals of buried medication of glasses with focused femtosecond laser pulses • 12.2.1 Nonlinear absorption • 12.2.2 Relaxation and material modification • 12.2.2.1 Pulse energy • 12.2.2.2 Repetition rate • 12.2.2.3 Focusing • 12.3 Femtosecond laser waveguide writing in glasses • 12.3.1 Low repetition rate fabrication • 12.3.1.1 Fused silica glass • 12.3.1.2 Silicate and phosphate glasses • 12.3.1.3 Chalcogenide glasses • 12.3.2 High repetition rate fabrication • 12.3.2.1 Fused silica glass • 12.3.2.2 Silicate and phosphate glasses • 12.3.2.3 Chalcogenide glasses • 12.3.3 Ion migration in high repetition rate modification of multicomponent glasses • 12.3.4 Comparison of low and high repetition rate processing • 12.4 Applications • 12.4.1 Photonic devices • 12.4.1.1 Bragg grating waveguides for telecom/sensing • 12.4.1.2 Active devices • 12.4.1.3 3D architectures for astronomy • 12.4.1.4 Directional couplers for quantum information • 12.4.2 Microfluidic devices • 12.4.2.1 Hybrid FLICE for particle filter • 12.4.2.2 Liquid-liquid dynamic interfaces • 12.4.2.3 Refractive index sensor • 12.5 Conclusions • References
Laser fabrication of anti-icing surfaces: A review
Full text linkIn numerous fields such as aerospace, the environment, and energy supply, ice generation and accretion represent a severe issue. For this reason, numerous methods have been developed for ice formation to be delayed and/or to inhibit ice adhesion to the substrates. Among them, laser micro/nanostructuring of surfaces aiming to obtain superhydrophobic behavior has been taken as a starting point for engineering substrates with anti-icing properties. In this review article, the key concept of surface wettability and its relationship with anti-icing is discussed. Furthermore, a comprehensive overview of the laser strategies to obtain superhydrophobic surfaces with anti-icing behavior is provided, from direct laser writing (DLW) to laser-induced periodic surface structuring (LIPSS), and direct laser interference patterning (DLIP). Micro-/nano-texturing of several materials is reviewed, from aluminum alloys to polymeric substrates
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Optical plasma spectroscopy as a tool for monitoring laser welding processes
No full textIn this work we present experimental results of the joint application of the two previously mentioned spectroscopic techniques (electron temperature and correlation analysis) to a real-time laser welding monitoring case study. The two signals have been calculated starting from selected chemical species
composing the plasma spectra. Experimental evidence is given of the correlation between the recorded signals
and the occurrence of weld defects intentionally generated by varying the laser power and the travel speed. An optical sensor prototype was used, that embeds a fiber-coupled
miniature spectrometer having a dynamic spectral range from 390 nm to 580 nm and a resolution of 0.3 nm.
Such a prototype employed data acquisition and real-time spectra analysis algorithms for both the previously mentioned spectroscopic techniques, e.g. the electron temperature and the correlation coefficients. A high power CO2 laser source was used with maximum output power of 6 kW. The laser-metal interaction zone was
shielded by an argon flow. The plasma optical emission was collected by a quartz collimator and transmitted
to the optical sensor by a 50 μm core-diameter optical fiber. Spectral lines from three different chemical
species (Mn(I), Fe(I), Cr(I)) composing the plasma plume and the stainless steel alloy were used for the
acquisition of the electron temperature and the correlation signals. Compared to other optical sensors, the main advantage of this system is that it has a great flexibility upon variation of the welding metal or the joint geometries. In fact once the chemical composition of the alloy was known and most plasma emission lines are identified, only a slight calibration of the software settings is necessary
Sorting of particles using inertial focusing and laminar vortex technology: A review
Full text linkThe capability of isolating and sorting specific types of cells is crucial in life science, particularly for the early diagnosis of lethal diseases and monitoring of medical treatments. Among all the micro-fluidics techniques for cell sorting, inertial focusing combined with the laminar vortex technology is a powerful method to isolate cells from flowing samples in an efficient manner. This label-free method does not require any external force to be applied, and allows high throughput and continuous sample separation, thus offering a high filtration efficiency over a wide range of particle sizes. Although rather recent, this technology and its applications are rapidly growing, thanks to the development of new chip designs, the employment of new materials and microfabrication technologies. In this review, a comprehensive overview is provided on the most relevant works which employ inertial focusing and laminar vortex technology to sort particles. After briefly summarizing the other cells sorting techniques, highlighting their limitations, the physical mechanisms involved in particle trapping and sorting are described. Then, the materials and microfabrication methods used to implement this technology on miniaturized devices are illustrated. The most relevant evolution steps in the chips design are discussed, and their performances critically analyzed to suggest future developments of this technology
Modellazione del trattamento termico mediante laser pulsato ad alta brillanza per la strutturazione superficiale di un acciaio ipereutettoidico
No full textIl lavoro analizza gli effetti di un singolo impulso laser di una sorgente in fibra, eseguito nel regime di parametri laser tale da permettere l’indurimento e la rifusione della superficie di un acciaio ipereutettoidico. I parametri laser investigati sono stati la potenza laser, l’energia dell’impulso e la distanza di focalizzazione, il cui effetto è stato determinato valutando la forma, l’ampiezza e la durezza della zona trattata. È stato formulato un modello agli elementi finiti del trattamento termico, calibrato con prove sperimentali, che ha permesso di definire i parametri di processo che garantiscono l’indurimento senza fusione, o la fusione del substrato senza l’insorgere di cricche. Questi risultati sono utili per progettare pattern per la strutturazione via laser di superfici in acciaio
La penetrazione della società dell'informazione in Lombardia
No full textL'indagine di avvale di un campione stratificato di 3.000 famiglie lombarde distinte in 7 differenti tipologie. Il capitolo passa in rassegna differenti tecnologie (telefono cellulare, moneta elettronica, televisione digitale e Internet) differenziando i comportamenti, i tassi di penetrazione, e le aspettative future degli utilizzatori
L'uso di Internet nelle famiglie lombarde
No full textIl capitolo analizza i comportamenti delle famiglie lombarde, relativamente all'utilizzo di Internet, distinguendo gli "heavy users" dagli utilizzatori occasionali.
L'analisi segnala un giudizio molto positivo da parte degli utilizzatori (punteggio di 7,8 in una scala da 1 a 10), mentre permangono negative le valutazioni relative ai costi del servizio e alla sicurezza
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