12,744 research outputs found
Characterization of motor control in Parkinson’s disease: a translational electromyography-informed modeling approach
No full textI disordini assiali impattano negativamente la qualità della vita delle persone affette da Morbo di Parkinson (PD). Infatti, alterazioni del normale
ciclo del passo e anomalie posturali sono uno dei sintomi motori più invalidanti di questa malattia. I metodi per la valutazione dei disordini motori
indotti dal PD si basano sull’osservazione soggettiva di un singolo specialista che somministra scale cliniche, le quali possono mancare di ripetibilit`a
inter-operatore e intra-sessione. Negli ultimi decenni, l’analisi del movimento in clinica si è affermata come un utile strumento per la caratterizzazione
delle alterazioni motorie indotte dalla patologia e ha permesso di quantificare una riduzione nella velocit`a del passo, nella sua lunghezza
e nel range of motion articolare nell’arto inferiore. In aggiunta a questo, l’elettromiografia superficiale (sEMG) ha permesso di determinare alterazioni
nell’attività elettrica dei muscoli dell’arto inferiore nel PD se confrontata rispetto a una popolazione di controllo, sia in termini di intensit`a
che di timing di attivazione. Sebbene questi siano metodi stabiliti nella pratica clinica, risulta impossibile fornire informazioni riguardanti la relazione
causale tra l’alterata attivazione neurale e il deficit motorio nelle persone affette da PD in vivo. In questa direzione, approcci data-driven
di modellazione neuro-muscolo-scheletrica (NMSM) consentono di capire come il comando neurale sia tradotto in output meccanico. Queste simulazioni
forniscono un set di variabili che possono essere utilizzate per l’implementazione nuove metriche quantitative ed oggettive per la valutazione
del controllo motorio dell’individuo, e permettono di approfondire la comprensione nella progressione della malattia. Questi modelli possono
essere calibrati e settati per fornire un ulteriore grado di personalizzazione tramite l’incorporazione dell’attivit`a muscolare sperimentale del soggetto
nel flusso di elaborazione dei dati. Tuttavia, il trasferimento di queste tecniche in pratica clinica è ostacolato da limitazioni pratiche. Innanzitutto, non esiste una misura diretta della forza muscolare in vivo per la validazione dei risultati del modello.
Ciononostante, è generalmente accettato nella pratica utilizzare il profilo di segnale sEMG per validare i pattern di forza muscolare. Secondo, in
condizioni di laboratorio, i segnali sEMG da utilizzare come input della pipeline di modellazione vengono normalizzati rispetto alle loro contrazioni
massimali volontarie (MVC), che sono per`o difficilmente ottenibili in popolazioni affette da disordini neurologici a causa della ridotta selettività manifestata nelle contrazioni muscolari. E’ inoltre necessario un gran numero di segnali sEMG per ottenere una completa caratterizzazione del profilo
motorio del soggetto: questo pu`o rendere la preparazione dispendiosa in termini di tempo e pu`o provocare disagio e affaticamento in chi viene sottoposto alla valutazione. Infine, a causa della semplicità del loro utilizzo, tecniche di ottimizzazione statica (SO), che non richiedono alcuna conoscenza a priori sull’attivazione muscolare, sono solitamente preferite agli approcci guidati ad sEMG nella risoluzione del problema di ridondanza muscolare. Tuttavia, i modelli basati su SO assumono una strategia di controllo motorio identica tra diversi individui nell’algoritmo di distribuzione della forza, e quindi non permettendo una personalizzazione del controllo motorio adattata al soggetto.
Il presente progetto di dottorato è un primo tentativo di proporre una pipeline di modellazione informata con sEMG che sia affidabile e adatta per
l’applicazione clinica e che miri a oltrepassare le limitazioni dovute al setup sperimentale (come la necessit`a di acquisire MVC e un elevato numero di
canali sEMG) mantenendo un grado di personalizzazione accettabile nel contesto di soggetti affetti da PD.Axial disorders negatively affect the quality of life of those people affected by Parkinson’s disease (PD). Indeed, gait alterations and postural abnormalities are one of the most invalidating motor symptoms of the pathology.
Assessments to evaluate PD-related motor impairments are based on the subjective observation of an individual physician delivering clinical scales, which might lack of intra-session and inter-operator repeatability. In the last couple of decades, clinical gait analysis has become a useful instrument to characterize motor alterations induced by the disease, and leaded
to quantify a reduction in gait speed, step length and lower-limb joints range of motion. In addition to this, the adoption of surface electromyography (sEMG) allowed to determine abnormalities in lower-limb muscle activity in PD when compared to healthy controls, both in terms of magnitude and timing of the activation profile. Even though those are established
tools in the clinical practice, they do not provide information on the causal relationship between the altered neural activation and the disrupted joint kinematics in people suffering from PD in vivo. In this direction, data-driven neuromusculoskeletal modeling (NMSM) approaches enable to understand how neural command is translated into mechanical output. These
simulations provide sets of variables which can be used to implement new quantitative objective metrics for assessing individuals’ neural motor control allowing to gain insights on the disease progression. These models, informed via the subject’s true muscle activity, can be calibrated and tuned to provide a higher degree of personalization.
Yet, the translation into clinical environments of NMSM techniques is still hampered due to practical limitations. First of all there is no direct measurement of muscle force in vivo to validate the model outcomes. However, it is generally accepted in the common practice to use sEMG profile to validate patterns of muscular force. Second, in laboratory conditions, sEMG signals to be used as input for the modeling pipeline are normalized with respect to their associated maximum voluntary contraction (MVC), which
is unattainable in neurological populations due to the reduced muscle voluntary selectivity. In addition to this, a high number of sEMG signals are necessary in order to obtain a full characterization of the motor functions, making the subject’s preparation time long and cumbersome, causing discomfort and fatigue. Finally, due to their simplicity of use, static optimization (SO) techniques, that do not require any a priori knowledge on the muscle activation, are usually preferred over sEMG-driven approaches when solving the muscle redundancy problem. Nonetheless, SO modeling based approaches assume identical neuromuscular control strategies between individuals and tasks in the muscle force distribution algorithm, thus not
allowing a tailored personalization of the subject’s motor control.
Therefore, the present doctoral project is a first attempt to propose a reliable sEMG-informed modeling pipeline suitable for clinical application aiming to overcome the experimental setup limitations (i.e., the need for MVC collection and the requirement of a high number of sEMG signals) while maintaining a proper degree of model personalization in the context of people with PD.
Results linked with this project might provide quantitative and repeatable metric defining a new set of possible biomechanical biomarkers which can objectively report on the motor capacity of the patient, reducing the possible sources of variability affecting the clinical scales. Moreover, the model-based estimation of in vivo variables may provide additional information to clinicians that could be used to plan intervention treatments aiming to restore and improve muscle forces
Design of a free-space optical link based on multipole-phase division multiplexing
No full textIn recent decades, control of the spatial structure of electromagnetic waves has boosted the research of new modulation formats for telecommunications and quantum applications. In particular, the exploitation of orthogonal spatial modes as distinct information carriers in the so-called spatial-division multiplexing has been dominated so far by beams carrying orbital angular momentum (OAM). However, practical solutions based on OAM-mode multiplexing still suffer from critical issues related, for instance, to efficient generation and long distance transmissions in free space. In a more general approach to wavefront propagation, we have recently introduced an innovative framework based on beams with harmonic phases characterized by multipole structures devoid of phase singularities, referred to as multipole-phase beams. This new paradigm offers efficient multiplexing and sorting in a full-optical and compact architecture based on conformal transformations, promising, moreover, to overcome the limits of previous solutions in free-space transmissions. The generalization to high orders of multipole phase is considered here, investigating a possible layout for a free space optical link. Numerical simulations are performed and discussed to validate the theory and show the potentialities of this new framework for telecommunications, both at the classical and single photon regimes
Missionari oltre il deserto del Sahara, verso le sorgenti del Nilo
No full textIl saggio ricostruisce il fondamentale contributo fornito a metà Ottocento dai missionari cattolici del Vicariato apostolico dell'Africa Centrale alla scoperta dell sorgenti del Nilo. Si sofferma in particolare sull'apporto fornito da Ignaz Knoblecher, Giovanni Beltrame, Angelo Vinco, Anton Kaufmann
Perfluoropolyether (PFPE) Intermediate Molds for High-Resolution Thermal Nanoimprint Lithography
No full textAmong soft lithography techniques, Thermal Nanoimprint Lithography (NIL) is a high-throughput and low-cost process that can be applied to a broad range of thermoplastic materials. By simply applying the appropriate pressure and temperature combination, it is possible to transfer a pattern from a mold surface to the chosen material. Usually, high-resolution and large-area NIL molds are difficult to fabricate and expensive. Furthermore, they are typically made of silicon or other hard materials such as nickel or quartz for preserving their functionality. Nonetheless, after a large number of imprinting cycles, they undergo degradation and become unusable. In this paper, we introduce and characterize an innovative two-step NIL process based on the use of a perfluoropolyether (PFPE) intermediate mold to replicate sub-100 nm features from a silicon mold to the final thermoplastic material. We compare PFPE elastomeric molds with molds made of the standard polydimethylsiloxane (PDMS) elastomer, which demonstrates better resolution and fidelity of the replica process. By using PFPE intermediate molds, the nanostructured masters are preserved and the throughput of the process is significantly enhanced
An EMG-informed modelling approach for the prediction of internal variables during locomotion in Parkinson’s Disease patients: a feasibility study
No full textMABS validation through repeated execution and data mining analysis
No full textAgent Based Modelling is the most interesting and advanced approach for simulating a complex system: in a social context, the single parts and the whole are often very hard to describe in detail. Besides, there are agent based formalisms which allow to study the emergency of social behaviour with the creation and study of models, known as artificial societies. Thanks to the ever increasing computational power, it's been possible to use such models to create software, based on intelligent agents, which aggregate behaviour is complex and difficult to predict, and can be used in open and distributed systems. Data mining is born in the last decades in order to help users in finding useful knowledge from the otherwise overwhelming amount of data available nowadays from the web and the data collected every day by companies. Data Mining techniques can therefore be the keystone to reveal non-trivial knowledge expressed by the initial assumption used to build the micro-level of the model and the structure of the society of agents that emerged from the simulation
Facades of the Libreria di San Marco in Venice, The: An Interpretation of the Design Process
No full text"A new work in which I propose an interpretation of the design process Sansovino used to create the magnificent facades of the Libreria di San Marco in Venice, a masterpiece of Renaissance architecture." Sent to Marquand librarian by author Dec. 202
Optical and structural properties of low thickness lead zirconate titanate films on sapphire substrates prepared via sol-gel method
No full textLead zirconate titanate (PZT) thin films in the range of 35-90 nm were deposited on a sapphire (1000) substrate using the sol-gel preparation method by diluting a PZT solution at different levels and using dichloromethane as the solvent. The microstructure, surface morphology, and stoichiometry of the films were studied by x-ray diffraction, atomic force microscopy, and Rutherford backscattering. Very smooth films characterized by single perovskite and mixed pyrochlore/perovskite polycrystalline phases were obtained and their optical properties were studied by spectroscopic ellipsometry in the ultraviolet-visible-near-infrared region. The refractive index was evaluated by analyzing the spectroscopic ellipsometry spectra. The ellipsometric data were also used to evaluate the bandgap energy of the films. The results show that the optical parameters of the films depend on the crystalline structure and demonstrate that higher bandgaps are obtained for perovskite films as compared to pyrochlore or mixed pyrochlore/perovskite structures. Data also confirm the higher bandgap of the amorphous structure compared to the polycrystalline PZT phases
Art without an Author: Vasari’s Lives and Michelangelo’s Death
No full textMonografia sulla rappresentazione di Michelangelo nelle due edizioni delle Vite, sulla storia del libro e la questione della sua paternitàBook dedicated to the representation of Michelangelo in Vasari's Lives of the Artists, to the history of the book, and to the problem of its authorshi
- …
