Spatio-temporal self-focusing in femtosecond pulse transmission through multimode optical fibers

We numerically investigate ultra-short pulse propagation in multimode optical fibers with launch peak powers approaching the critical power for self-focusing using a generalized multimode nonlinear Schrödinger equation approach. Nonlinear spatial and temporal effects combined with fiber dispersion govern pulse compression in space and time which can result in damage inducing intensity levels. Here we identify pulse parameters for which damage is avoided and high-power delivery through optical fiber is possible near the fiber zero-dispersion wavelength

Modal decomposition of self-focusing effects in optical fibres

When an intense beam with a transverse intensity gradient propagates in a medium with positive Kerr nonlinearity n2, the induced refractive index profile actuates a lens, focusing the beam itself. For input powers above a critical threshold, P > Pcrit, self-focusing can subjugate beam divergence, resulting in catastrophic collapse and material failure [1]. For P < Pcrit diffraction deflects energy from the focal point, and in a fibre, divergence is reflected at the core/cladding boundary instigating a periodic transverse beam profile

Fast and broadband fiber dispersion measurement with dense wavelength sampling

We report on a method to obtain dispersion measurements from spectral-domain low-coherence interferograms which enables high accuracy (~ps/(nm·km)), broadband measurements and the determination of very dense (up to 20 points/nm over 500 nm) data sets for both dispersion and dispersion slope. The method exploits a novel phase extraction algorithm which allows the phase associated with each sampling point of the interferogram to be calculated and provides for very accurate results as well as a fast measurement capability, enabling close to real time measurements. The important issue of mitigating the measurement errors due to any residual dispersion of optical elements and to environmental fluctuations was also addressed. We performed systematic measurements on standard fibers which illustrate the accuracy and precision of the technique, and we demonstrated its general applicability to challenging problems by measuring a carefully selected set of microstructured fibers: a lead silicate W-type fiber with a flat, near-zero dispersion profile; a hollow core photonic bandgap fiber with strongly wavelength dependent dispersion and dispersion slope; a small core, highly birefringent index guiding microstructured fiber, for which polarization resolved measurements over an exceptionally wide (~1000 nm) wavelength interval were obtained

Numerical modelling of the seismic performance of Romanian traditional timber-framed buildings

Traditional architecture made of timber-framed masonry (TFM) system is widespread around the world and has already been recognized as a unique cultural heritage to be preserved. These structures have shown a good seismic performance compared to other typologies because their configuration and construction details were constantly updated as soon as the builders addressed the causes of damage mechanisms when earthquakes occurred. Regarding this typology, Romanian TFM structures can be considered a representative example also because they experienced several seismic events showing their good earthquake-resistance. Although these buildings are still constructed and inhabited nowadays, no recommendation is provided in the Romanian building code and its structural behaviour is not properly characterized yet. Bearing in mind that the building’s global response depends on many parameters such as the performance of its structural elements and their interaction, the calibration of shear walls is crucial to define the non-linear behaviour under cyclic loading. A simplified modelling strategy was chosen to simulate TFM wall response consisting of an equivalent frame with linear elastic elements and non-linearities lumped at the joints by using OpenSees. After calibrating the wall response according to the experimental campaign performed at Technical University of Civil Engineering of Bucharest, the panel was adapted to model a representative Romanian TFM building whose dynamic properties were evaluated by eigenvalue analysis and their potential calibration is proposed based on the ambient vibration tests

Analysis of wheelchair sprint biomechanics on two elite athletes on an instrumented drum ergometer

Introduction. Wheelchair athletics requires the maximization of pushing technique throughout the full length of the race, with particular attention to the transition from start to full speed. The use of dynamometric handrims, introduced for complete propulsion analysis has only recently made available with lightweight portable solutions for athletics [1]. Drum ergometers have also showed to be effective for the study several disciplines in the analysis of propulsion techniques [2]. The use of force plates under the wheels only accounts for the first start push; the use of IMU can instead follow the action along the full race in both simulated or track measurements [3]. In the present work, the combination of a validated drum ergometer, IMU sensors and EMG analysis was adopted to study and compare the sprint biomechanics of two elite athletes on a simulated 100m sprint. Methods. A drum ergometer [2] was adapted to host the athletics wheelchairs restrained at the front wheels. Inertial disks were applied to the drums to match the equivalent linear inertia of each subject (Figure 1.a). A set of Inertial sensors was placed on the hands and wheels of the athletes. Eight EMG sensors were placed on trapezius descendens (TD) right, deltoideus anterior (DA) right, latissimus dorsi (LD) right, pectoralis major (PM) right, biceps brachii (BB) left & right and triceps brachii (TB) left & right. IMU and EMG were captured with a MuscleLab system from Ergomotion. Two elite wheelchair athletes of Italian National Team, D.G. (T 53, 77kg, 100m P.B. 15.92s) and G.S. (T54, 56kg, 100m P.B. 14.93s) volunteered for the study and performed 5 repetitions of a simulated 100m sprint. As previous researchers, two events related to hand-to-rim contact were evaluated using hand acceleration profiles: Hand contact (HC) and Hand Release (HR). As a result, the Push Phase (PP), and the Recovery Phase (RP), were calculated, together with the Total Push Angle (TPA). Similarly to other experiences [4], athletes were asked to perform static maximal voluntary pushes against the blocked drum resistance at three hand positions on the rim: HC, HR and an intermediate position. Isometric tangential push forces at the rim were calculated from the peak torque recorded at the drum and normalized to body weight BW as in Figure 1.b. EMG moving 50 ms window RMS signals were normalized to the trial maximum value: a threshold of 20% was chosen to consider the muscle activation pattern in a polar graph as in Figure 1.c. Results. Simulated best sprint time on the drum ergometer resulted 15.25s for D.G. and 14.72s for G.S., very close to their personal best, thus confirming the validity of the equivalent intertial drum ergometer. Highest isometric forces were obtained at the HC position as shown in Figure 1.b. EMG results presented in Figure 1.c showed how the two athletes adopted different pushing techniques at 5th and 25th push. Both athletes shift forward the HC and HR position at higher speed and widen their TPA, but G.S. TPA increase is more evident. Clock polar diagram allow to capture the differences in muscle coordination among athletes and the change of activation from slow to high speed. Discussion. The use of wireless sensors for IMU and EMG analysis allows for the extension of the method to track tests, in combination with the collection of loads from instrumented handrims that are under development

Microbending effects in hollow-core photonic bandgap fibers

We developed a model for the study of how microbends affect the operation of hollow-core photonic bandgap fibers. Increased loss due to intermodal coupling is predicted. Preliminary experimental observations are in good agreement with the model’s predictions

Dispersion-shifted all-solid high index-contrast microstructured optical fiber for nonlinear applications at 1.55µm

We report the fabrication of an all-solid highly nonlinear microstructured optical fiber. The structured preform was made by glass extrusion using two types of commercial lead silicate glasses that provide high index-contrast. Effectively single-moded guidance was observed in the fiber at 1.55µm. The effective nonlinearity and the propagation loss at this wavelength were measured to be 120W/km respectively at 1.55µm. These predictions are consistent with the experimentally determined dispersion of +12.5ps/nm/km at 1.55µm. Tunable and efficient four-wave-mixing based wavelength conversion was demonstrated at wavelengths around 1.55µm using a 1.5m length of the fiber

Application of an integrated hydrological nowcasting chain on Liguria Region

Presentación realizada en la 3rd European Nowcasting Conference, celebrada en la sede central de AEMET en Madrid del 24 al 26 de abril de 2019

Influence of an Interaction between Lithium Salts and a Functional Polymorphism in SLC1A2 on the History of Illness in Bipolar Disorder

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