1435 research outputs found
Sort by
Tunnelling rates for the nonlinear Wannier-Stark problem
No full textSUMMARY We present a method to numerically compute accurate tunnelling rates for a
Bose-Einstein condensate which is described by the nonlinear Gross-Pitaevskii
equation. Our method is based on a sophisticated real-time integration of the
complex-scaled Gross-Pitaevskii equation, and it is capable of finding the
stationary eigenvalues for the Wannier-Stark problem. We show that even weak
nonlinearities have significant effects in the vicinity of very sensitive
resonant tunnelling peaks, which occur in the rates as a function of the Stark
field amplitude. The mean-field interaction induces a broadening and a shift of
the peaks, and the latter is explained by analytic perturbation theory
Study of the systematic errors in the calculation of renormalization constants of the topological susceptibility on the lattice
No full textSUMMARY We present a study of the systematic effects in the nonperturbative
evaluation of the renormalization constants which appear in the
field-theoretical determination of the topological susceptibility in pure
Yang-Mills theory. The study is performed by computing the renormalization
constants on configurations that have been calibrated by use of the
Ginsparg-Wilson formalism and by cooling
Analysis of systematic errors in the calculation of renormalization constants of the topological susceptibility on the lattice
No full textSUMMARY A Ginsparg-Wilson based calibration of the topological charge is used to
calculate the renormalization constants which appear in the field-theoretical
determination of the topological susceptibility on the lattice. A systematic
comparison is made with calculations based on cooling. The two methods agree
within present statistical errors (3%-4%). We also discuss the independence of
the multiplicative renormalization constant Z from the background topological
charge used to determine it
Behaviour-aware discovery of Web service compositions
No full textA major challenge for Service-oriented Computing is how to discover and compose (Web) services to build complex applications. We present a matchmaking system that exploits both semantics and behavioural information to discover service compositions capable of satisfying a client request
Contract-based Service Aggregation
No full textWe present a methodology for the automated selection and aggregation of (Web) services with the purpose of satisfying client queries. A key ingredient of our approach is the notion of service contract, which consists of signature (WSDL),
ontology information (OWL), and behaviour specification (YAWL).
The methodology inputs a registry of service contracts and a client service contract, and it automatically generates aggregated contracts that fulfil the request. By trace inspection we first individuate candidate sets of contracts that
could satisfy the query collectively. For each candidate set, we generate the contract of the aggregate by suitably building its control- and data-flow, and we verify whether it actually complies with the request
Nonabelian Confinement near Nontrivial Conformal Vacua
No full textWe discuss some aspects of confinement and dynamical symmetry breaking in the
so-called nonabelian Argyres-Douglas vacua, which occur very generally in
supersymmetric theories. These systems are characterized by strongly-coupled
nonabelian monopoles and dyons; confinement and dynamical symmetry breaking are
caused by the condensation of monopole composites, rather than by condensation
of single weakly-coupled monopoles. In general, there are strong constraints on
which kind of monopoles can appear as the infrared degrees of freedom, related
to the proper realization of the global symmetry of the theory. Drawing
analogies to some of the phenomena found here, we make a speculation on the
ground state of the standard QCD
Scalable accessibility of a recoverable database using wandering tokens
No full textIn a large distributed system there is usually the need to keep a record of the state of the components: one example is the database of the resources available in a Grid. The design of such database should take into account that the size of the system is not constant, and may vary of orders of magnitude: manual intervention to reconfigure the system in order to meet accessibility requirements may be problematic,and a source of unreliability.We present a scheme that provides scalable accessibility to such a database, focussing on the performance of update operations. The scalable implementation of update operations enables ubiquitous replication of the database, thus bringing at reach the scalability of read operations. Each component of the system regulates automatically the relevant operational parameters with a kind of feedback, which is based on probabilistic considerations. Many aspect of the scheme are in fact probabilistic, and we introduce a simple model that describes the performance of the system. The overall approach as well as certain performance figures that cannot be forecast analitically, are explored with simulation
Inference of Approximated Motifs with Conserved Relations
No full textIn this paper we define a new class of problems that
generalizes that of finding repeated motifs. The novelty
lies in the addition of constraints on the motifs in terms
of relations that must hold between pairs of positions of
the motifs. We will hence denote them as "relational
motifs". For this class of problems we give an algorithm
that is a suitable extension of the KMR paradigm
and, in particular, of the KMRC as it uses a
degenerate alphabet. The algorithm contains several improvements
with respect to KMRC that result especially useful
when---as it is required for relational motifs---the inference
is made by partially overlapping shorter motifs, rather
than concatenating them like in KMR.
The efficiency, correctness and completeness of the algorithm is assured
by several non-trivial properties that we prove in this paper. Finally, we
list some possible applications and we focus on one of them:
the study of 3D structures of proteins
Steam and exothermic reactions as alternative techniques to control soil-borne disease in basil
No full textSUMMARY The search for non-chemical methods to control soil-borne pathogens has recently intensified ahead of the forthcoming phase-out of the fumigant methyl bromide in 2005. Indeed, none of the previously available alternatives match methyl bromide wide-spectrum control. Here, we tested two pre-planting treatments: steaming with a soil-steaming machine and exothermic reaction by incorporation into the soil of potassium hydroxide (KOH), a substance that causes an exothermic reaction with water. Experiments were conducted from 2003 to 2005 in open-field conditions by assessing the effectiveness of steam and exothermic reaction against Fusarium oxysporum f.sp. basilici and Sclerotinia minor on basil. The results show that steam combined with exothermic reaction reduce the incidence of Fusarium wilt (77–96%) better than steam only (70–89%). The control of Sclerotinia minor was better with potassium hydroxide (94–92%) than with steam only (83–87%). Further, we evaluated the effects of the treatments on microbial population, yield and weed control. Here, the treatments induced the following major effects: (1) a reduction of more than 99% of the number of Fusarium oxysporum colonies in soil; (2) an increase of about 200% in Trichoderma spp. in soil; (3) a drastic increase in the plant yield, from 6.9–7.5 g for the control to 23.0–25.5 gr for steam treatments; (4) a high reduction of plants per square meter of 94–95% for Amaranthus retroflexus, of 96–99% for Portulaca oleracea, of 93–94% for Chenopodium spp. and of 86–90% for Hordeum vulgare, using both steam and exothermic reactions. Similar results were obtained with steam only. Therefore, our results evidence the potential of this approach to control various soil-borne pathogens. Steam and exothermic reaction are thus promising alternatives to chemical soil disinfestation for high-value crops
Funzionalità e flessibilità degli schemi di classificazione tradizionali applicati a un CMS (Content Management System): faccette, CDD, JITA
No full textIn questa presentazione sono illustrati tre schemi di classificazione diversi così come sono stati applicati a tre weblog diversi. Per ciascuno schema sono state evidenziate le funzionalità e le caratteristiche nonché i limiti e si è spiegato per quale motivo sia stato scelto uno schema piuttosto che un altro. Gli schemi e i blog analizzati sono: uno schema di classificazione basato sul principio delle faccette per il blog Biblioatipici; la Classificazione Decimale Dewey per il blog Atipicheletture e infine lo schema di classificazione JITA per il blog personale di Andrea Marchitelli