1435 research outputs found
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Il Mediterraneo di Ranieri: alcune considerazioni su una fonte agiografica pisana del XII secolo
No full textRIASSUNTO Nella Vita di San Ranieri il Mediterraneo e, in particolare, la pre- senza pisana nel mare nostrum hanno un peso non indifferente. La ‘mediterraneità’ di Ranieri non risiede soltanto e banalmente nel fat- to che questo santo pisano del XII secolo definisce pienamente la sua conversione a Gerusalemme dopo averla raggiunta su un navi- glio mercantile, ma emerge in numerosi aspetti della sua vicenda umana, nei miracoli a lui attribuiti e nel contesto in cui si sviluppa la sua azione. Nel testo si trovano infatti indicazioni molto precise sui modi e i mezzi di navigazione, sulle relazioni commerciali e di- plomatiche instaurate da Pisa con i vari dominî costieri e su eventi importanti del panorama geopolitico del ventennio 1140-1160. SUMMARY In "The Life of Saint Rainerius", the Mediterranean and the presence of Pisa in this sea are important. Rainerius is 'Mediterranean' not only because this twelfth-century Pisan saint completes its full conversion in Jerusalem after he reached the holy town on a merchant ship, but because Mare Nostrum is present in several moments of his life, in miracles attributed to him and in the context where he acts. So it's possible to find in this text informations about ways and tools of navigation, trade relations and diplomatic relationships established by Pisa commune with various domains in the coastal and geopolitical landscape of 1140-1160
Secure token passing at application level
No full textSUMMARY We introduce an application level implementation of a token passing operation. After an introduction that explains the conceptual principles, we describe exhaustively the state machines that implement our solution. The security requirements are carefully considered, since the token is a sensitive resource, but without introducing scalability limit
L'affinità e la concentrazione. I meccanismi molecolari della regolazione del metabolismo.
Get PDFConcentration and affinity of reactants determine the chemical equilibrium, and the biological reactions between proteins and their ligands behave like chemical reactions at a constant temperature. In cells, affinity between proteins and ligands can be regulated through changes in protein structure induced either by molecular effectors or by covalent reactions. Hemoglobin affinity towards oxygen is regulated by two different molecular mechanisms: the oxygen cooperative effect and proton and diphosphoglycerate allosteric effects. Metabolic pathways are made of sequences of enzymatic proteins, where the product of a given enzymatic reaction is a substrate of the enzyme positioned next in the metabolic pathway. One or few pacemaker enzymes, placed in strategic positions, regulate the metabolic pathways. The pacemaker enzymes are regulated in their catalytic activity by metabolites and/or covalent reactions and, through these mechanisms, they regulate the whole metabolism. Given the same metabolic conditions, the regulation of the same metabolic pathways placed in different human tissues can be very different
Observation of Stückelberg oscillations in accelerated optical lattices
No full textWe report the experimental observation of St\"{u}ckelberg oscillations of
matter waves in optical lattices. Extending previous work on Landau-Zener
tunneling of Bose-Einstein condensates in optical lattices, we study the
effects of the accumulated phase between two successive crossings of the
Brillouin zone edge. Our results agree well with a simple model for multiple
Landau-Zener tunneling events taking into account the band structure of the
optical lattice
Equilibrium and off-equilibrium trap-size scaling in 1D ultracold bosonic gases
No full textWe study some aspects of equilibrium and off equilibrium quantum dynamics of
dilute bosonic gases in the presence of a trapping potential. We consider
systems with a fixed number of particles N and study their scaling behavior
with increasing the trap size. We focus on one-dimensional (1D) bosonic
systems, such as gases described by the Lieb-Liniger model and its
Tonks-Girardeau limit of impenetrable bosons, and gases constrained in optical
lattices as described by the Bose-Hubbard model. We study their quantum
(zero-temperature) behavior at equilibrium and off equilibrium during the
unitary time evolution arising from changes of the trapping potential, which
may be instantaneous or described by a power-law time dependence, starting from
the equilibrium ground state for a initial trap size. Renormalization-group
scaling arguments, analytical and numerical calculations show that the
trap-size dependence of the equilibrium and off-equilibrium dynamics can be
cast in the form of a trap-size scaling in the low-density regime,
characterized by universal power laws of the trap size, in dilute gases with
repulsive contact interactions and lattice systems described by the
Bose-Hubbard model. The scaling functions corresponding to several physically
interesting observables are computed. Our results are of experimental relevance
for systems of cold atomic gases trapped by tunable confining potentials
Universality of the glassy transitions in the two-dimensional +- J Ising model
No full textWe investigate the zero-temperature glassy transitions in the square-lattice
+- J Ising model, with bond distribution ; p=1 and p=1/2 correspond to the pure Ising model and
to the Ising spin glass with symmetric bimodal distribution, respectively. We
present finite-temperature Monte Carlo simulations at p=4/5, which is close to
the low-temperature paramagnetic-ferromagnetic transition line located at
p=0.89, and at p=1/2. Their comparison provides a strong evidence that the
glassy critical behavior that occurs for , , is
universal, i.e., independent of p. Moreover, we show that glassy and magnetic
modes are not coupled at the multicritical zero-temperature point where the
paramagnetic-ferromagnetic transition line and the T=0 glassy transition line
meet. On the theoretical side we discuss the validity of finite-size scaling in
glassy systems with a zero-temperature transition and a discrete Hamiltonian
spectrum. Because of a freezing phenomenon which occurs in a finite volume at
sufficiently low temperatures, the standard finite-size scaling limit in terms
of does not exist: the renormalization-group invariant quantity
should be used instead as basic variable
Accelerating sequential programs using FastFlow and self-offloading
No full textFastFlow is a programming environment specifically targeting cache-coherent shared-memory multi-cores. FastFlow is implemented as a stack of C++ template libraries built on top of lock-free (fence-free) synchronization mechanisms. In this paper we present a further evolution of FastFlow enabling programmers to offload part of their workload on a dynamically created software accelerator running on unused CPUs. The offloaded function can be easily derived from pre-existing sequential code. We emphasize in particular the effective trade-off between human productivity and execution efficiency of the approach.</p
LIBERO: a LIghtweight BEhaviouRal skeletOn framework
No full textWe describe a lightweight prototype framework designed for experimentation with behavioural skeletons. A behavioural skeleton is a component implementing a well-known parallelism exploitation pattern and a rule-based autonomic manager taking care of some non-functional feature related to the parallel computation. Our prototype supports multiple autonomic managers within the same behavioural skeleton, each taking care of a different functional concern. The different managers in the behavioural skeleton coordinate themselves in such a way that a global, user-provided SLA can be satisfied. We discuss experiments that validate the manager coordination protocol, and the overall prototype functionality.
The prototype is built on top of plain Java and employs JBoss rules for management.
We present experimental results that demonstrate the operation of our prototype and allow overheads to be evaluated
Qd-type methods for quasiseparable matrices
No full textIn the last few years many numerical techniques for computing eigenvalues of structured rank matrices have been proposed. Most of them arebased on iterations since, in the symmetric case, the rank structure is preserved and high accuracy is guaranteed. In the unsymmetriccase, however, the algorithm destroys the rank structure, which is instead preserved if iterations are used. We consider a wideclass of quasiseparable matrices which can be represented in terms of the same parameters involved in their Neville factorization. Thisclass, if assumptions are made to prevent possible breakdowns, is closed under steps. Moreover, we propose an implicit shifted method with a linear cost per step, which resembles the qd method for tridiagonal matrices. We show that for totally nonnegativequasiseparable matrices the algorithm is stable and breakdowns cannot occur, if the Laguerre shift, or other shift strategy preservingnonnegativity, is used. Computational evidence shows that good accuracy is obtained also when applied to symmetric positive definitematrices.<br /
StochKit-FF: Efficient Systems Biology on Multicore Architectures
No full textThe stochastic modelling of biological systems is an informative, and in some cases, very adequate technique, which may however result in being more expensive than other modelling approaches, such as differential equations. We present StochKit-FF, a parallel version of StochKit, a reference toolkit for stochastic simulations. StochKit-FF is based on the FastFlow programming toolkit for multicores and exploits the novel concept of selective memory. We experiment StochKit-FF on a model of HIV infection dynamics, with the aim of extracting information from efficiently run experiments, here in terms of average and variance and, on a longer term, of more structured data