1435 research outputs found
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Universality class of 3D site-diluted and bond-diluted Ising systems
No full textWe present a finite-size scaling analysis of high-statistics Monte Carlo
simulations of the three-dimensional randomly site-diluted and bond-diluted
Ising model. The critical behavior of these systems is affected by
slowly-decaying scaling corrections which make the accurate determination of
their universal asymptotic behavior quite hard, requiring an effective control
of the scaling corrections. For this purpose we exploit improved Hamiltonians,
for which the leading scaling corrections are suppressed for any thermodynamic
quantity, and improved observables, for which the leading scaling corrections
are suppressed for any model belonging to the same universality class.
The results of the finite-size scaling analysis provide strong numerical
evidence that phase transitions in three-dimensional randomly site-diluted and
bond-diluted Ising models belong to the same randomly dilute Ising universality
class. We obtain accurate estimates of the critical exponents, ,
, , , ,
, and of the leading and next-to-leading correction-to-scaling
exponents, and
Oltre i libri e i cataloghi: crediti formativi e tirocini nelle biblioteche dell'Università di Pisa ovvero innovative forme di apprendimento in biblioteca
No full textRIASSUNTO Con il passaggio dalla società dell'informazione alla società della conoscenza, le biblioteche si trovano a giocare un ruolo centrale nel paradigma innovativo dell'apprendimento, arrivando persino a cambiare il nome, trasformandosi in case delle tecnologie, case delle simulazioni, case dell'apprendimento flessibile. Il Decreto Ministeriale n. 509 del 1999, che ha dato inizio alla riforma universitaria italiana, ha introdotto negli ordinamenti didattici i CFU (Crediti formativi universitari) che possono essere acquisiti anche svolgendo attività didattica e tirocini nelle biblioteche delle Università. Tale novità ha inciso fortemente sulle biblioteche dell'Ateneo pisano, che sono entrate a pieno titolo nel campo della formazione, in quanto gli studenti che le frequentano possono seguire "Corsi sulla ricerca bibliografica", oppure "Seminari sull’uso degli strumenti bibliografici" o effettuare tirocini o stages, valevoli per l'acquisizione di CFU da inserire nel proprio curriculum. Assistiamo quindi alla trasformazione della biblioteca in specifico "ambiente di apprendimento", dove si impara applicando diverse metodologie: seguendo progetti specifici, mediante l'approccio tutoriale, collaborando in gruppi ristretti, comunque sempre in linea con le tendenze pedagogiche del costruttivismo. SUMMARY In this text we analyze the library as a learninig environment where we can experiment new kinds of knowledge and where we select and personalize digital skills in a context of lifelong learning
Francescanesimo al femminile: la Provincia Tusciae fra XIII e XIV secolo
No full textRIASSUNTO Nell’intento di ricostruire una mappa dell’espansione sul territorio delle fondazioni francescane femminili, si dà in questo articolo un primo censimento documentario e bibliografico dei monasteri presenti sul territorio della Provincia Tusciae dei Frati Minori nel periodo che va dalla seconda decade del XIII secolo, fino allo scorcio del secolo successivo. Confrontando i dati si nota che ad una prima forte espansione temporale degli insediamenti femminili francescani, che segnò la fondazione di ben sette monasteri entro il 1230 (Firenze, Siena, Lucca, Arezzo, Cortona, Pisa e Castelfiorentino), seguì un più lento radicamento sul territorio. Gli insediamenti documentati erano ubicati in città di notevole importanz,a nella parte della Toscana allora più economicamente avanzata, cui si aggiunsero centri minori pur sempre rilevanti. In alcuni centri si nota anche la tendenza alla moltiplicazione degli insediamenti, come nei casi di Firenze, Siena e Pisa. Dalla verifica delle scelte topotetiche fatte dai monasteri clariani rispetto alle città di loro riferimento si nota inoltre che, per la maggior parte, essi sono localizzati in sito extraurbano, fuori delle porte cittadine. SUMMARY The paper presents the first documentary and bibliographic census of female franciscan convents in the area of Provincia Tusciae. The article analyzes the convents of Poor Clares which were active in Tuscany in XIII and XIV centuries
La bonifica del catalogo e il controllo di qualità: strumenti, tempi, strategie
No full textRIASSUNTO Nell'articolo si affrontano le tematiche della bonifica e del controllo di qualità del catalogo, sinora poco presenti in letteratura professionale. L'analisi trae spunto dall'esperienza di chi scrive maturata nel contesto del catalogo unico on-line delle biblioteche dell'Università di Pisa, consultabile all'indirizzo . Dopo una spiegazione introduttiva del concetto di bonifica del catalogo, l'autrice passa a delineare la nascita del catalogo unico dell'ateneo pisano - sorto nel 2000 dalla fusione di singoli cataloghi, ospitati su reti locali, non comunicanti tra loro - e i successivi interventi di "pulizia" apportati manualmente o in maniera automatica. L'ultima parte dell'articolo è dedicata al controllo di qualità delle nuove registrazioni catalografiche che arricchiscono man mano l'opac; tale monitoraggio, effettuato costantemente, dovrebbe accompagnare e seguire l'intervento di bonifica del catalogo, al fine di assicurare il mantenimento al suo interno di standard qualitativi adeguati. SUMMARY The article examines the themes of the catalogue reclamation and quality control that have hardly been considered in professional literature so far. The analysis starts from the author’s work experience who is involved in the catalogue reclamation and quality control of Pisa University libraries opac . Catalogue reclamation is required when many of them merge into a single database, or after massive derivative cataloguing or even after retroconversion projects. In work planning staff selection is very important. The author suggests that these projects must not be given in complete outsourcing. The following section describes catalogue reclamation, referring to the University of Pisa union catalogue author's experience. This work begun in 2000 merging single university library catalogues LAN-located into a unique database. Catalogue reclamation can mainly be carried out by two means: manual and automated changes. In the first case, work methodologies definition and bibliographic tools (national and international opac) are relevant. Instead, computerized interventions are feasible only after a meticulous cases analysis strictly collaborating with systems manager. The last part of the article is dedicated to catalogue quality control by monitoring new bibliographic records and pointing out mistakes or lacks to the involved cataloguer
Orbit determination of space debris: admissible regions
No full textSUMMARY The main problem in the orbit determination of the space debris population orbiting our planet is identifying which separate sets of data belong to the same physical object. The observations of a given object during a passage above an observing station are collectively called a Too Short Arc (TSA): data from a TSA cannot allow for a complete determination of an orbit. Therefore, we have to solve first the identification problem, finding two or more TSAs belonging to the same physical object and an orbit fitting all the observations. This problem is well known for the determination of orbits of asteroids: we shall show how to apply the methods developed for preliminary orbit determination of heliocentric objects to geocentric objects. We shall focus on the definition of an admissible region for space debris, both in the case of optical observations and radar observations; then we shall outline a strategy to perform a full orbit determination
Efficient Inclusion for a Class of XML Types with Interleaving and Counting
No full textInclusion between XML types is important but expensive, and is
much more expensive when unordered types are considered. We prove here
that inclusion for XML types with interleaving and counting can be
decided in polynomial time in presence of two important restrictions:
no element appears twice in the same content model, and Kleene star
is only applied to disjunctions of single elements.
Our approach is based on the transformation of each such type into a
set of constraints that completely characterizes the
type. We then provide a complete
deduction system to verify whether the constraints of one type imply
all the constraints of another one
Perturbing QCD with external fields
No full textWe present some up-to-date results on QCD phase transition in a
chromomagnetic constant background field and in an abelian monopole background
field. Our results indicate that the QCD critical temperature is not modified
by a monopole background field, whilst it is modified by a constant
chromomagnetic field. We improve our earlier estimate of the QCD critical
parameters in a chromomagnetic background field by performing lattice
simulations with weaker fields
Two flavor QCD and confinement - II
No full textThis paper is part of a program of investigation of the chiral transition in
Nf=2 QCD, started in Phys.Rev.D72:114510,2005. Progress is reported on the
understanding of some possible systematic errors. A direct test of first order
scaling is presented
Ion dynamics and coherent structure formation following laser pulse self-channeling
No full textSUMMARY The propagation of a superintense laser pulse in an underdense, inhomogeneous
plasma has been studied numerically by two-dimensional particle-in-cell
simulations on a time scale extending up to several picoseconds. The effects of
the ion dynamics following the charge-displacement self-channeling of the laser
pulse have been addressed. Radial ion acceleration leads to the ``breaking'' of
the plasma channel walls, causing an inversion of the radial space-charge field
and the filamentation of the laser pulse. At later times a number of
long-lived, quasi-periodic field structures are observed and their dynamics is
characterized with high resolution. Inside the plasma channel, a pattern of
electric and magnetic fields resembling both soliton- and vortex-like
structures is observed
Topology, chiral and screening transitions at finite density in two colour QCD
No full textThe behaviour of the topological susceptibility in QCD with two colours and 8
flavours of quarks is studied at nonzero temperature on the lattice across the
finite density transition. It is shown that its signal drops at a
(pseudo-)critical chemical potential mu_c. The Polyakov loop and the chiral
condensate undergo their transitions at the same value. Pauli blocking
supervenes at a value of the chemical potential larger than mu_c