Realizzazione di un amplificatore lock-in digitale

Tra tutte le tecniche sviluppate per il recupero di segnali, i metodi basati sul principio di rilevazione sincrona, utilizzati dagli amplificatori lock-in, sono largamente i più usati in tutti i campi della ricerca scientifica. Gli amplificatori lock-in sono strumenti utilizzati per rilevare e misurare segnali in ambienti in cui il rumore di fondo può essere di diversi ordini di grandezza più grande del segnale che si intende misurare. In questo lavoro viene presentato un metodo per realizzare un amplificatore lock-in digitale su scheda hardware NI ELVIS II+ e software LabVIEW. In seguito viene descritto come, attraverso test opportuni, sono state analizzate le performance del sistema realizzato e sono state confrontate con i sistemi disponibili commercialmente. Infine, l’amplificatore lock-in realizzato è stato poi utilizzato in un esperimento di misura spettroscopica dell’energia di gap di un campione di Germanio per mezzo dell’effetto fotoelettrico interno.

Behaviour of the energy gap in a model of Josephson coupled Bose-Einstein condensates

In this work we investigate the energy gap between the ground state and the first excited state in a model of two single-mode Bose-Einstein condensates coupled via Josephson tunnelling. The ene:rgy gap is never zero when the tunnelling interaction is non-zero. The gap exhibits no local minimum below a threshold coupling which separates a delocalized phase from a self-trapping phase that occurs in the absence of the external potential. Above this threshold point one minimum occurs close to the Josephson regime, and a set of minima and maxima appear in the Fock regime. Expressions for the position of these minima and maxima are obtained. The connection between these minima and maxima and the dynamics for the expectation value of the relative number of particles is analysed in detail. We find that the dynamics of the system changes as the coupling crosses these points.

Utilização da instrumentação virtual em Labview para criação da interface gráfica do amplificador lock-in utilizado em estudos fisiológicos a partir da comunicação via porta serial

This work presents the development of a graphical interface to the Lock-in Amplifier, which is used in physiological studies on the motility of the gastrointestinal tract in rats and signal processing. With a simple and low cost instrumentation, the resources offered by the virtual interface of LabVIEW software allows the creation of commands similar to the actual instrument that, through communication via standard serial port, transmits data between a PC and peripheral device performing specific and particular needs in the amplifier. Created for the lock-in amplifier model SR830 Stanford Research Systems, the remote manipulation gives the user greater accessibility in the process of configuration and calibration. And, since the software is installed, there is the advantage of eliminating the need of purchase new devices to upgrade the system. The commands created were made to perform six basic modifications that are used in routine of the Biomagnetism Laboratory. The instrumentation developed has the following controls: Amplitude, Frequency, Time Constant, slope low pass filter, sensitivity and offset

Sviluppo di programma in LabVIEW per controllo di pressione in apparato Sievert

In questa tesi si propone un progetto software per il controllo automatico delle pressioni in apparato volumetrico, o apparato Sievert, dedicato allo studio dell'assorbimento e desorbimento di idrogeno nei metalli. Si introduce la fisica che regola la formazione degli idruri metallici, e i parametri di studio importanti per lo sviluppo di un sistema energetico basato sull'idrogeno. Particolare attenzione viene data alla misura di cinetica, la percentuale in peso di idrogeno assorbito/desorbito in funzione del tempo. Nel capitolo 2 si mostra il principio di funzionamento di un apparato Sievert e la realizzazione hardware dell'apparato: si compone di una serie di volumi calibrati, separati da valvole, a temperatura costante, tra cui la camera porta-campioni . La pressione al loro interno viene variata immettendo o aspirando idrogeno. Nel capitolo 3 è sviluppata la procedura di controllo software tramite LabVIEW, che si impone di impostare una pressione intermedia su un volume parziale, conoscendo la pressione finale, a volumi collegati, alla quale studiare il campione. Questo modo di lavoro permette di non agire direttamente sul campione con le immissioni e le aspirazioni di idrogeno. Il programma è stato provato con misure per materiali dalla cinetica molto veloce come il palladio(Pd). I risultati, nel capitolo 4, mostrano che il programma è in grado di controllare efficacemente le variazioni di pressioni e la misura di cinetica.

Theory and practice of automotive modal lock-in – an Indonesian case

This thesis examines the question why the automotive mode and the large technological system it creates, continues to dominate urban transport systems despite the availability of more cost-efficient alternatives. A number of theoretical insights are developed into the way these losses evolve from path dependent growth, and lead to market failure and lock-in. The important role of asymmetries of influence is highlighted. A survey of commuters in Jakarta Indonesia is used to provide a measure of transport modal lock-in (TML) in a developing country conurbation. A discrete choice experiment is used to provide evidence for the thesis central hypothesis that in such conurbations there is a high level of commuter awareness of the negative externalities generated by TML which can produce a strong level of support for its reversal. Why TML nevertheless remains a strong and durable feature of the transport system is examined with reference to the role of asymmetries of influence.

Automotive modal lock-in: The role of path dependence and large socio-economic regimes in market failure

This paper addresses less recognised factors which influence the diffusion of a particular technology. While an innovation’s attributes and performance are paramount, many fail because of external factors which favour an alternative. This paper, with theoretic input from diffusion, lock-in and path-dependency, presents a qualitative study of external factors that influenced the evolution of transportation in USA. This historical account reveals how one technology and its emergent systems become dominant while other choices are overridden by socio-political, economic and technological interests which include not just the manufacturing and service industries associated with the automobile but also government and market stakeholders. Termed here as a large socio-economic regime (LSER),its power in ensuring lock-in and continued path-dependency is shown to pass through three stages, weakening eventually as awareness improves. The study extends to transport trends in China, Korea, Indonesia and Malaysia and they all show the dominant role of an LSER. As transportation policy is increasingly accountable to address both demand and environmental concerns and innovators search for solutions, this paper presents important knowledge for innovators, marketers and policy makers for commercial and societal reasons, especially when negative externalities associated with an incumbent transportation technology may lead to market failure.

An Approximate Method For Calculation Of Fluid Force And Response Of A Circular Cylinder At Lock-In

In this paper, equations calculating lift force of a rigid circular cyclinder at lock-in uniform flow are deduced in detail. Besides, equations calculating the lift force on a long flexible circular cyclinder at lock-in are deduced based on mode analysis of a multi-degree freedom system. The simplified forms of these equations are also given. Furthermore, an approximate method to predict the forces and response of rigid circular cyclinders and long flexible circular cyclinders at lock-in is introduced in the case of low mass-damping ratio. A method to eliminate one deficiency of these equations is introduced. Comparison with experimental results show the effectiveness of this approximate method.

High-precision digital lock-in measurements of critical current and AC loss in HTS 2G-Tapes

Application of High Temperature Superconducting (HTS) has been increasingly popular since the new superconducting materials were discovered. This paper presents a new high-precision digital lock-in measurement technique which is used for measuring critical current and AC loss of the 2nd Generation HTS tape. Using a lock-in amplifier and nano-voltage meter, we can resolve signals at nano-volt level, while using a specially designed compensation coil we can cancel out inductive by adjusting the coil inductance. Furthermore, a finer correction for the inductive component can be achieved by adjusting the reference phase of the lock-in amplifier. The critical current and AC loss measurement algorithms and hardware layout are described and analyzed, and results for both numerical and experimental data under varieties of frequencies are presented. © 2008 SICE.