150 research outputs found
Proof Analysis in Temporal Logic
No full textThe logic of time is one of the most interesting modal logics, and its importance is widely acknowledged both for philosophical and formal reasons.
In this thesis, we apply the method of internalisation of Kripke-style semantics into the syntax of sequent calculus to the proof-theoretical analysis of temporal logics.
Sequent systems for different flows of time are obtained as modular extensions of a basic temporal calculus, through the addition of appropriate mathematical rules that correspond to the properties of temporal frames: a general and uniform treatment is thus achieved for a wide range of temporal logics. All the calculi enjoy remarkable structural properties, in particular are contraction and cut free.
Linear discrete time is analysed by means of two infinitary calculi. The first is obtained by means of a rule with infinitely many premises, and the second through a new definition of provability which admits, under certain conditions, derivation trees with infinite branches.
The first calculus enjoys the desired structural properties, but the presence of an infinitary rule is harmful for proof analysis. Two finitary systems are identified by replacing the infinitary rule with a weaker finitary rule, and by bounding the number of its premises, respectively. Corresponding, somehow complementary, conservativity results are proved with respect to adequate fragments of the original calculus.
The second calculus stems from a closure algorithm which exploits the fixed-point equations
for temporal operators and gives saturated sets of closure formulas from a given formula.
Finitisation is obtained in the form of an upper bound to the proof-search procedure, and decidability follows as a major consequence
L’édition critique du Viage al Purgatory de Ramon de Perellos entre tradition et innovation,
No full textIl contributo prende in considerazione i testimoni del Viage al Purgatory de Ramon de Perellos e ne analizza alcuni loci in previsione della produzione dell'edizione critica dell'opera
Decidability for Priorean Linear Time Using a Fixed-Point Labelled Calculus
No full textA labelled sequent calculus is proposed for Priorean linear time logic, the rules of which reflect a natural closure algorithm derived from the fixed-point properties of the temporal operators. All the rules of the system are finitary, but proofs may contain infinite branches. Soundness and completeness of the calculus are stated with respect to a notion of provability based on a condition on derivation trees: A sequent is provable if and only if no branch leads to a ‘fulfilling sequent,’ the syntactical counterpart of a countermodel for an invalid sequent. Decidability is proved through a terminating proof search procedure, with an exponential bound to the branches of derivation trees for valid sequents, calculated on the length of the characteristic temporal formula of the endsequent
Simulazione numerica del processo di combustione in motori ad elevate prestazioni con codice di calcolo tridimensionale
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Fractal Graphene Patch Antennas and the THz Communications Revolution
No full textFractal antennas have and are continuing to receive attention in regard to the futureof wireless communications. This is because of their wide- and multi-band capabilities, theopportunity of fractal geometries to drive multiple resonances, and, the ability to make smallerand lighter antennas with fewer components and radiative elements with higher gains. Smallscale (i.e. on the micro- and nano-scale) and ultra high frequency (in the Terahertz or THz range)fractal antennas composed of Graphene have the potential to enhance wireless communicationsat a data rate that is unprecedented, i.e.∼1012bits per second. A Fractal Graphene antennais a high-frequency tuneable antenna for radio communications in the THz spectrum, enablingunique applications such as wireless nano-networks. This is because (mono-layer) Grapheneis a one-atom-thick two-dimensional allotrope of Carbon with the highest known electricalconductivity that is currently unavailable in any other material, including metals such as Goldand Silver. Thus, combining the properties of Graphene with the self-affine characteristics ofa fractal at the micro- and nano-scale, provides the potential to revolutionise communications,at least in the near field (the order of a few metres) for low power systems. In this paper, weconsider the basic physics and some of the principle mathematical models associated with thedevelopment of this new disruptive technology in order to provide a guide to those engagedin current and future research, a fractal Graphene antenna being an example of an advancedmaterial for demanding applications. This includes some example simulations on the THz fieldpatterns generated by a fractal patch antenna composed of Graphene whose conductivity istaken to scale with the inverse of the frequency according to a ‘Drude’ model. The approachto generating THz sources using Graphene is also explored based on Infrared laser pumping toinduce a THz photo-current
A Preliminary Study of a Graphene Fractal Sierpinski Antenna
No full textWe provide a preliminary study of a Graphene fractal antenna operating at THz frequencies with the opportunity to modulate the emission. There are a number of advantages of the fractal design, namely multiband/wideband ability, and, a smaller, lighter and simpler configuration for higher gain, that can benefit from the coupling with Graphene, the thinnest and strongest of materials exhibiting very high electrical conductivity and tunability. This paper proposes a conceptual background for the study and presents some preliminary results on the electromagnetic emission simulations undertake
Discussion of Boretti, A., 'Is there any support in the long term tide gauge data to the claims that parts of Sydney will be swamped by rising sea levels?'
No full textBoretti (2012) claims that sea-level records show insufficient acceleration to support the projections of sea-level rise that are used worldwide for planning and policy-making. Unfortunately, his claim is based more on flawed qualitative reasoning than on quantitative analysis. We replicate Boretti's methodology of fitting quadratic functions to tide-gauge observations from Fremantle and Sydney, in order to estimate the sea-level acceleration. However, we also evaluate the uncertainty in these estimates (a crucial step, omitted by Boretti), and thereby show that the observed accelerations are statistically consistent with the projections of the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. Our finding is the same when we repeat this analysis using two data sets which have smaller uncertainties, one from satellite altimeters and the other from a sea-level reconstruction. We therefore conclude that Boretti's claim is without foundation
Author Correction: Chlorination disadvantages and alternative routes for biofouling control in reverse osmosis desalination (npj Clean Water, (2019), 2, 1, (2), 10.1038/s41545-018-0024-8)
No full textIn the original version of this Review Article the affiliation and address for Lorenzo Rosa were incorrectly given as “University of Parma, Department of Information Engineering, Parma 43121, Italy”
Human Bone-Marrow-Derived Stem-Cell-Seeded 3D Chitosan–Gelatin–Genipin Scaffolds Show Enhanced Extracellular Matrix Mineralization When Cultured under a Perfusion Flow in Osteogenic Medium
No full textTissue-engineered bone tissue grafts are a promising alternative to the more conventional use of natural donor bone grafts. However, choosing an appropriate biomaterial/scaffold to sustain cell survival, proliferation, and differentiation in a 3D environment remains one of the most critical issues in this domain. Recently, chitosan/gelatin/genipin (CGG) hybrid scaffolds have been proven as a more suitable environment to induce osteogenic commitment in undifferentiated cells when doped with graphene oxide (GO). Some concern is, however, raised towards the use of graphene and graphene-related material in medical applications. The purpose of this work was thus to check if the osteogenic potential of CGG scaffolds without added GO could be increased by improving the medium diffusion in a 3D culture of differentiating cells. To this aim, the level of extracellular matrix (ECM) mineralization was evaluated in human bone-marrow-derived stem cell (hBMSC)-seeded 3D CGG scaffolds upon culture under a perfusion flow in a dedicated custom-made bioreactor system. One week after initiating dynamic culture, histological/histochemical evaluations of CGG scaffolds were carried out to analyze the early osteogenic commitment of the culture. The analyses show the enhanced ECM mineralization of the 3D perfused culture compared to the static counterpart. The results of this investigation reveal a new perspective on more efficient clinical applications of CGG scaffolds without added GO
Event-based Classification with Recurrent Spiking Neural Networks on Low-end Micro-Controller Units
No full textDue to its intrinsic sparsity both in time and space, event-based data is optimally suited for edge-computing applications that require low power and low latency. Time varying signals encoded with this data representation are best processed with Spiking Neural Networks (SNN). In particular, recurrent SNNs (RSNNs) can solve temporal tasks using a relatively low number of parameters, and therefore support their hardware implementation in resource-constrained computing architectures. These premises propel the need of exploring the properties of these kinds of structures on low-power processing systems to test their limits both in terms of computational accuracy and resource consumption, without having to resort to full-custom implementations. In this work, we implemented an RSNN model on a low-end, resource-constrained ARM-Cortex-M4-based Micro Controller Unit (MCU). We trained it on a down-sampled version of the N-MNIST event-based dataset for digit recognition as an example to assess its performance in the inference phase. With an accuracy of 97.2%, the implementation has an average energy consumption as low as 4.1μJ and a worst-case computational time of 150.4μs per time-step with an operating frequency of 180 MHz, so the deployment of RSNNs on MCU devices is a feasible option for small image vision real-time tasks
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