3,121 research outputs found
Electrically tunable piezoelectric bimorph cantilever for energy harvesting
Con la presente tesi viene esaminato un metodo per modificare la frequenza di risonanza di trasduttori piezoelettrici mediante applicazione di carichi elettrici esterni.
L'elaborato inizia con la presentazione dei cristalli utilizzati nel lavoro di tesi, concentrandosi sul processo di fabbricazione di un bimorph cantilever impiegato come convertitore elettromeccanico di energia, la cui frequenza di risonanza è modellizzata analiticamente mediante la legge di Newton e il modello di Euler-Bernoulli.
Su tale struttura vengono condotte misure mediante shaker elettrodinamico e analizzatore d'impedenza, ai fini di giusticare il modello analitico presentato.
Con lo scopo di sincronizzare la frequenza di risonanza del cantilever con la vibrazione dell'ambiente per massimizzare la potenza disponibile, viene proposto un algoritmo MPPT secondo l'approccio Perturba e Osserva (P&O), al quale è fornita in ingresso la tensione efficace di un layer di materiale piezoelettrico. Valutare la sua risposta in tensione, presenta dei limiti applicativi che hanno portato a prendere in considerazione un approccio totalmente diff�erente, basato sullo sfasamento tra la tensione di un trasduttore piezoelettrico e il segnale di accelerazione impiegato come eccitazione.
Misure sperimentali sono state condotte con l'obiettivo di validare l'efficacia di quest'ultimo approccio qualora si voglia sincronizzare la frequenza di risonanza dei piezo con segnali di vibrazione reali
M-theory on AdS_4xM^{111}: the complete Osp(2|4)xSU(3)xSU(2) spectrum from harmonic analysis
We reconsider the Kaluza Klein compactifications of D=11 supergravity on
AdS_4x(G/H)_7 manifolds that were classified in the eighties, in the modern
perspective of AdS_4/CFT_3 correspondence. We focus on one of the three N=2
cases: (G/H)_7=M^{111}=SU(3)xSU(2)xU(1)/SU(2)xU(1)'xU(1)''. Relying on the
systematic use of the harmonic analysis techniques developed in the eighties by
one of us (P. Fre') with R. D'Auria, we derive the complete spectrum of long,
short and massless Osp(2|4)xSU(3)xSU(2) unitary irreducible representations
obtained in this compactification. Our result also provides a general scheme
for the other N=2 compactifications. Furthermore, it is a necessary comparison
term in the AdS_4/CFT_3 correspondence: the complete AdS/CFT match of the
spectra that we obtain will provide a much more stringent proof of the AdS/CFT
correspondence than in the S^7 case, since the structure of the superconformal
field theory on the M2-brane world volume must be such as to reproduce, at the
level of composite operators, the flavor group representations, the conformal
dimensions and the hypercharges that we obtain in the present article. The
investigation of the match is left to future publications. Here we provide an
exhaustive construction of the Kaluza Klein side of our spectroscopy.Comment: 65 page
Exact results for the low energy AdS(4)XCP(3) string theory
We derive the Thermodynamic Bethe Ansatz equations for the relativistic sigma
model describing the AdS(4)XCP(3) string II A theory at strong coupling (i.e.
in the Alday-Maldacena decoupling limit). The corresponding Y-system involves
an infinite number of Y functions and is of a new type, although it shares a
peculiar feature with the Y-system for AdS(4)XCP(3). A truncation of the
equations at level p and a further generalisation to generic rank N allow us an
alternative description of the theory as the N=4, p= \infty representative in
an infinite family of models corresponding to the conformal cosets CP(N-1)_p X
U(1), perturbed by a relevant composite field \phi(N,p) =\phi_[CP(N-1)_p] X
\phi[U(1)] that couples the two independent conformal field theories. The
calculation of the ultraviolet central charge confirms the conjecture by Basso
and Rej and the conformal dimension of the perturbing operator, at every N and
p, is obtained using the Y-system periodicity. The conformal dimension of
\phi[CP(N-1)_p] matches that of the field identified by Fendley while
discussing integrability issues for the purely bosonic CP(N-1) sigma model.Comment: Latex fil
Effects of the antioxidant moieties of dissolved organic matter on triplet-sensitized phototransformation processes: Implications for the photochemical modeling of sulfadiazine
A model assessment of the potential of river water to induce the photochemical attenuation of pharmaceuticals downstream of a wastewater treatment plant (Guadiana River, Badajoz, Spain)
Energy conversion processes with perovskite-type materials
Mixed oxides derived from the perovskite structure by combination of A- and
B-site elements and by partial substitution of oxygen provide an immense
playground of physico-chemical properties. Here, we account for own research
conducted at the Paul Scherrer Institute on perovskite-type oxides and
oxynitrides used in electrochemical, photo(electro)chemical and catalytic
processes aiming at facing energy relevant issues
Micropower Design of an Energy Autonomous RF Tag for UWB Localization Applications
This paper describes the architecture and the micropower design criteria of a battery-less, energy autonomous, individually addressable RF tag for UWB localization applications, with a focus on baseband circuitry. The tag includes a UHF rectifier, power conversion and management circuits, an addressable wake-up radio module, a microcontroller-based control unit, and circuits for UWB localization. The proposed circuit is suitable for UWB localization either by using passive backscattering of received UWB pulses, or by using active UWB pulses generators. Power for operation is scavenged from a modulated UHF carrier also used for addressing purposes. The circuit is implemented on discrete components in a 3.12 cm2 PCB area. The circuit can wake-up from fully discharged states and operates at distances as high as 10.8 m from a 2W-ERP source in the UHF 865–868 MHz RFID band with a +1.8 dBi receiving antenna. The quiescent power consumption of the tag is 3.88 μW, and the average power consumption at an addressing and activation rate of one time per second is 4.7 μW. The effectiveness of UWB localization was tested in a localization system based on time-difference-of-arrival (TDOA) estimations, consisting of multiple UWB readers and UHF transmitters
(R) e (S)-2,2'-diidrossi-3,3'-dimetossi-5,5'-diallil-6,6'-dibromo-1,1'-bifenile un derivato chirale del <i>bis</i>-eugenolo
La presente comunicazione
descrive la sintesi dell’equivalente bromurato chirale 2 del bis-eugenolo. La stabilitÃ
conformazionale del composto 2, e quindi la possibilità di isolare i due enantiomeri, potrebbe
influenzare sostanzialmente la bioattivita’ della molecola
A Distributed, Passivity-Based Control of Autonomous Mobile Sensors in an Underwater Acoustic Network
This paper presents a cooperative and distributed control law for multiple Autonomous Underwater Vehicles (AUVs) executing a mission while meeting mutual communication constraints. Virtual couplings define interaction control forces between neighbouring vehicles. Moreover, the couplings are designed to enforce a desired vehicle-vehicle and vehicle-target spacing. The whole network is modelled in the passive, energy-based, port-Hamiltonian framework. Such framework allows to prove closed-loop stability using the whole system kinetic and virtual potential energy by constructing a suitable Lyapunov function. Furthermore, the robustness to communication delays is also demonstrated. Simulation results are given to illustrate the effectiveness of the proposed approach
- …