531 research outputs found
Post-Minkowskian Hamiltonians in modified theories of gravity
The aim of this note is to describe the computation of post-Minkwoskian
Hamiltonians in modified theories of gravity. Exploiting a recent relation
between amplitudes of massive scalars and Hamiltonians for relativistic
point-particles, we define a post-Minkowskian potential at second order in
Newton's constant arising from modifications in General
Relativity. Using this result we calculate the associated contribution to the
scattering angle for binary black holes at second post-Minkowskian order,
showing agreement in the non relativistic limit with previous results for the
bending angle of a massless particle around a static massive source in
theories.Comment: 11 pages, new calculations added (v2. submitted to Physics Letter B
Analysis and Design of High Speed Serial Interfaces for Automotive Applications
The demand for an enriched end-user experience and increased performance in next generation
electronic applications is never ending, and it is a common trend for a wide spectrum
of applications owing to different markets, like computing, mobile communication and automotive.
For this reason High Speed Serial Interface have become widespread components for
nowadays electronics with a constant demand for power reduction and data rate increase.
In the frame of gigabit serial systems, the work discussed in this thesis develops in two
directions: on one hand, the aim is to support the continuous data rate increase with the
development of novel link modeling approaches that will be employed for system level evaluation
and as support in the design and characterization phases. On the other hand, the
design considerations and challenges in the implementation of the transmitter, one of the
most delicate blocks for the signal integrity performance of the link, are central.
The first part of the activity regarding link performance predictions lead to the development
of an enhanced statistical simulation approach, capable to account for the transmitter
waveform shape in the ISI analysis, a characteristic that is missed by the available state-ofthe-
art simulation approaches. The proposed approach has been extensively tested by comparison
with traditional simulation approaches (Spice-like simulators) and validated against
experimental characterization of a test system, with satisfactory results.
The second part of the activity consists in the design of a high speed transmitter in a
deeply scaled CMOS technology, spanning from the concept of the circuit, its implementation
and characterization. Targets of the design are to achieve a data rate of 5 Gb/s with
a minimum voltage swing of 800 mV, thus doubling the data rate of the current transmitter
implementation, and reduce the power dissipation adopting a voltage mode architecture.
The experimental characterization of the fabricated lot draws a twofold picture, with some
of the performance figures showing a very good qualitative and quantitative agreement with
pre-silicon simulations, and others revealing a poor performance level, especially for the eye
diagram. Investigation of the root causes by the analysis of the physical silicon design, of the
bonding scheme of the prototypes and of the pre-silicon simulations is reported. Guidelines
for the redesign of the circuit are also given.Nel panorama delle applicazioni elettroniche il miglioramento delle performance di un prodotto
da una generazione alla successiva ha lo scopo di offrire all\u2019utilizzatore finale nuove
funzioni e migliorare quelle esistenti. Negli ultimi anni grazie al costante avanzamento della
tecnologia integrata, si \ue8 assistito ad un enorme sviluppo della capacit\ue0 computazionale dei
dispositivi in tutti i segmenti di mercato, quali ad esempio l\u2019information technology, la comunicazione
mobile e l\u2019automotive. La conseguente necessit\ue0 di mettere in comunicazione
dispostivi diversi all\u2019interno della stessa applicazione e di traferire grosse quantit\ue0 di dati ha
provocato una capillare diffusione delle interfacce seriali ad alta velocit\ue0, o High Speed Serial
Interfaces (HSSIs). La necessit\ue0 di ridurre il consumo di potenza e aumentare il bit rate per
questo tipo di applicazioni \ue8 diventata dunque un ambito di ricerca di estremo interesse.
Il lavoro discusso in questa tesi si colloca nell\u2019ambito della trasmissione di dati seriali a
bit rate superiori ad 1Gb/s e si sviluppa in due direzioni: da un lato, a sostegno del continuo
aumento del bit rate nelle nuove generazioni di interfacce, \ue8 stato affrontato lo sviluppo di
nuovi approcci di modellazione del sistema, che possano essere impiegati nella valutazione
delle prestazioni dell\u2019interfaccia e a supporto delle fasi di progettazione e di caratterizzazione.
Dall\u2019altro lato, si \ue8 focalizzata l\u2019attenzione sulle sfide e sulle problematiche inerenti il progetto
di uno dei blocchi pi\uf9 delicati per le prestazioni del sistema, il trasmettitore.
La prima parte della tesi ha come oggetto lo sviluppo di un approccio di simulazione
statistico innovativo, in grado di includere nell\u2019analisi degli effetti dell\u2019interferenza di intersimbolo
anche la forma d\u2019onda prodotta all\u2019uscita del trasmettitore, una caratteristica che
non \ue8 presente in altri approcci di simulazione proposti in letteratura. La tecnica proposta
\ue8 ampiamente testata mediante il confronto con approcci di simulazione tradizionali (di tipo
Spice) e mediante il confronto con la caratterizzazione sperimentale di un sistema di test, con
risultati pienamente soddisfacenti.
La seconda parte dell\u2019attivit\ue0 riguarda il progetto di un trasmettitore integrato high speed
in tecnologia CMOS a 40nm e si estende dallo studio di fattibilit\ue0 del circuito fino alla sua
realizzazione e caratterizzazione. Gli obiettivi riguardano il raggiungimento di un bit rate
pari a 5 Gb/s, raddoppiando cos\uec il bit rate dell\u2019attuale implementazione, e di una tensione
differenziale di uscita minima di 800mV (picco-picco) riducendo allo stesso tempo la potenza
dissipata mediante l\u2019adozione di una architettura Voltage Mode. I risultati sperimentali
ottenuti dal primo lotto fabbricato non delineano un quadro univoco: alcune performance
mostrano un ottimo accordo qualitativo e quantitativo con le simulazioni pre-fabbricazione,
mentre prestazioni non soddisfacenti sono state ottenute in particolare per il diagramma ad
occhio. Grazie all\u2019analisi del layout del prototipo, del bonding tra silicio e package e delle
simulazioni pre-fabbricazione \ue8 stato possibile risalire ai fattori responsabili del degrado delle
prestazioni rispetto alla previsioni pre-fabbricazione, permettendo inoltre di delineare le
linee guida da seguire nella futura progettazione di un nuovo prototipo
Gravitational shock waves and scattering amplitudes
We study gravitational shock waves using scattering amplitude techniques.
After first reviewing the derivation in General Relativity as an
ultrarelativistic boost of a Schwarzschild solution, we provide an alternative
derivation by exploiting a novel relation between scattering amplitudes and
solutions to Einstein's field equations. We prove that gravitational shock
waves arise from the classical part of a three point function with two massless
scalars and a graviton. The region where radiation is localized has a
distributional profile and it is now recovered in a natural way, thus bypassing
the introduction of singular coordinate transformations as used in General
Relativity. The computation is easily generalized to arbitrary dimensions and
we show how the exactness of the classical solution follows from the absence of
classical contributions at higher loops. A classical double copy between
gravitational and electromagnetic shock waves is also provided and for a
spinning source, using the exponential form of three point amplitudes, we infer
a remarkable relation between gravitational shock waves and spinning ones, also
known as gyratons. Using this property, we infer a family of exact solutions
describing gravitational shock waves with spin. We then compute the phase shift
of a particle in a background of shock waves finding agreement with an earlier
computation by Amati, Ciafaloni and Veneziano for particles in the high energy
limit. Applied to a gyraton, it provides a result for the scattering angle to
all orders in spin.Comment: 23 pages, published on JHE
The irony of networks
By the end of the 1970s, it became evident that hierarchies were not always the most efficient and effective solution for complex problems in increasingly plural and fragmented societies. During the last 40 years governance structures and practices in the public sector have shifted towards new logics that direct the way the public sector is functioning. This dissertation deals with use of networks as new governance systems for policy implementation and public service delivery. Based on a mixed-methods approach, three studies investigate the configurational effects of network environment, network structures and coordination practices on public network effectiveness. They improve the understanding of the joint effects of network context, the structure of interorganizational relationships and the governance practices applied in order to organize and coordinate the common efforts of networked organizations. The results show that a network, despite being a distinct resource allocation mechanism, makes use of practices primarily typical for hierarchies and markets. Therefore, networks provide a flexible governance system that allows for vertical integration, bureaucratic means of organization and managerial steering, which in turn allow networks to be successful, if coherently applied
Optimization conditions of UV-C radiation combined with ultrasound-assisted extraction of cherry tomato (Lycopersicon esculentum) lycopene extract
The aim of this work was to study the effect of UV-C radiation on ultrasound assisted extraction
(UAE) of cherry tomato bioactive compounds. Cherry tomatoes were exposed to two UV-C radiation
doses (0.5 and 1.0 J cm−2
) and stored at 20 ± 0.5 oC for 7 days. Next, they were lyophilized, and
the bioactive compounds were extracted by UAE at 20 KHz. To evaluate the effectiveness of the
extraction process of the bioactive compounds, a CCRD (central composite rotational design) was
used together with RSM (response surface methodology), for extraction times from 4 to 12 minutes
and concentrations (g of lyophilized product / L of ethanol) of 1:10, 1:20 and 1:30. The extracts
obtained from the irradiated tomatoes presented 5.8 times more lycopene content than the controls
and higher antioxidant activity was obtained for 4 and 8 min, in the concentrations 1:10 and 1:20 (m
v−1). Through numerical model optimization, optimal extraction conditions were obtained. The results
demonstrated that by previously irradiating tomatoes with UV-C light, the UAE yielded considerably
higher amounts of lycopene and other bioactives.CNPq (National Council of Technological and Scientific
Development, Brazil), Erasmus Mundus action 2; Fellow
Mundus Project; Department of Chemical Engineering and Food Engineering
(UFSC - Brazil) and the Department of Food Engineering (UAlg - Portugal) .info:eu-repo/semantics/publishedVersio
Metaphor, Meaning and Translation
Over the last decades, metaphor has been subject to intensive research within philoso-phy, psychology, psychiatry, pedagogics, etc., whereas there has been less focus on the study of metaphor as a linguistic utterance. But to a translator metaphor is a very intriguing practical linguistic problem. How do we translate for instance the Danish metaphor blæksprutte? In this article, we will discuss to what extent ordinary dictionaries may be of use (can you look up the metaphor blæksprutte?) and will describe the data-base of metaphors that we are establishing with examples from economic and political texts in Danish, French and Italian. The database is organized as a thesaurus where metaphorical utterances are categorized under Meaning and Source domain and where translators may find inspiration when having to render metaphors in the three lan-guages
Network management as a contingent activity. A configurational analysis of managerial behaviors in different network settings
ABSTRACTNetwork managers engage in several day-to-day activities, including bridging, networking, and stabilizing relationships. Still, when should they opt for one activity or another? Our study s..
Da Aldeia à Academia, da Academia à Aldeia: os desafios da Universidade frente às demandas dos Povos Originários
Este artigo é fruto de experiências no ensino superior envolvendo orientações de pesquisas científicas com estudantes indígenas. O objetivo do artigo é problematizar os alcances do fazer ciência com estudantes indígenas, seguindo os moldes acadêmicos tradicionais. As reflexões partem da hipótese de que a linguagem é o dispositivo limiar tanto para emancipação quanto para a continuidade de uma exclusão para com estudantes indígenas. Fundamentado em diferentes documentos e pesquisas sobre o tema, o artigo discute sobre as dificuldades dos estudantes indígenas para assimilar os ritos acadêmicos, ao mesmo tempo em que indaga sobre o compartilhamento de conhecimentos entre a universidade e populações indígenas, frente às demandas que garantirão a dignidade e sobrevivência dos povos originários
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