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**Attilio Stella**

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**Attilio Stella**

Professore ordinario di Meccanica statistica nell'Università di Padova

- s.c.r. 12 settembre 2000, s.e 27 maggio 2008

Birth: March 9, 1949 in Alexandria (Egypt)

Nationality: Italian

Civil status: Married with Alessandra Turco; two sons, Pietro and Giulio.

Academic credentials: Laurea in Fisica "cum laude", obtained on June 20, 1972 at the University of Padova, Italy. Doctor in de Wetenschappen (Ph.D. with, greatest distinction) on May 14, 1981 at the Katholieke Universiteit Leuven, Leuven, Belgium.

Current position: Full Professor (Professore Ordinario) of theoretical physics (Meccanica Statistica). Physics Department, University of Padova (since November 1993). Courses in statistical mechanics.

Previous appointments (Italy) Full Professor (Professore Straordinario) of theoretical physics (Teoria dei Campi). November 1990, Department of Physics, University of Bologna. Courses in statistical physics.

Associate Professor of theoretical physics. March 1988, Department of Physics, University of Padova. Courses in statistical mechanics and structure of matter.

Permanent Research Fellow (Ricercatore Confermato). 1981, Department of Physics, University of Padova. Teaching activities in general physics and structure of matter.

Temporary Research Fellow ( Borsista arrd Contrattista ministeriale). November 1972, Department of Physics, University of Padova. Instructor of theoretical physics.

Visiting positions abroad and in International Organizations:

April-July 1978: Visiting fellow at the Laboratorium voor Technische Natuurkunde, University of Delft, The Netherlands, with a grant of the "A. Della Riccia" Foundation (prof. J. M. J. van Leeuwen).

1978/79: Postdoctoral research fellow (postdoctoraal navorser) at the Institucit voor Theoretische Fysica of the University of Leuven, Belgium.

1979/80 and 1980/81: Visiting professor (gastdocent) at the Instituut voor Theoretische Fysica, University of Leuven, Belgium. Course on "Capita selecta uit de wiskundige en theoretische natuurkunde" (advanced statistical mechanics).

June-July 1981, September 1984 , September 1985 and September 1986: Visiting fellow (visiteur) at the Departement de Physique Theorique of the University of' Geneva, Switzerland (prof. C. P. Enz).

March 1982: Visiting professor (Lector) at the Physics Department of the University of Leuven, Belgium. 3rd Cycle course on "Special Topics in the theory of critical phenomena and lattice models".

September-October 1983 and February 1984: Visiting fellow at the Theoretical Physics Department of the University of Oxford, UK, with a fellowship of the Accademia Nazionale dei Lincei - Royal Society (prof. R. B. Stinchconrbe).

November 1984: Visiting Professor at the Department of Physics, Pennsylvania State University, State College, PA, USA (prof. M. W. Cole).

October-December 1985: Visiting Associate Professor at the Department of' Physics and Astronomy, University of Maryland, College Park, MD, USA (prof. Th. L. Einstein).

March 1987 Visiting research fellow at the CBPF of Rio de Janeiro and the Physics Departments of the Universities of Natal and Masseio (Brazil). Grant of CBPq, Brazil (prof. C. Tsallis).

May-June 1987 Visiting Professor (Lector) at the University of Leuven (Belgium). 3rd Cycle course on "Fractals in Physics".

June-July and August-October 1988: Visiting research Fellow at the Department of Physics and Astronomy, University of Maryland, MD, USA (prof. M.E. Fisher and T.L. Einstein).

July 1988: Visiting research fellow at the Department of Physics, Pennsylvania State University, State College, PA, USA (prof. M.W. Cole).

August-September 1992: Visiting research fellow at the Department of Physics, Pennsylvania State University (Prof. M.W. Cole) and at the Department of Physics and Astronomy, University of Maryland, (prof. T.L. Einstein).

September-October 1993: Visiting Fellow at the Physics Department of Penn State University, State College, PA, USA (prof. R. J. Banavar).

February and April-May 1994: Visiting Fellow at the Physics Department, Oxford University, UK. Grant of the Royal Society-Accademia Nazionale dei Lincei (prof. J.M. Yeomans).

July 1994: Visiting Fellow at the Department of Physics, University of Maryland, College Park (prof. T.L. Einstein).

June-July 1995: Visiting Fellow at the Department of Physics, University of Maryland, College Park (prof. T.L. Einstein).

September-October 1995: Visiting Professor at the Instituut vor Theoretische Fysica, Katholieke Universiteit Leuven, Belgium. Graduate course on "Many-body systems: phase transitions, critical phenomena" at the "Institute for intensive theoretical studies".

September 1996: Visiting Fellow at the Department of Physics, University of Maryland, College Park, MD, USA (prof. T. L. Einstein).

August 1998: Visiting Fellow at the Department of Physics- Center for Polymer Studies, Boston University, Boston, MA, USA (Padova-Boston exchange programme; prof. H. E. Stanley).

September 1998: Visit to the Massachussets Institute of Technology, Harward, MA, USA, supported by a "Bruno Rossi" fellowship (INFN-MIT exchange programme. prof. M. Kardar).

October 1998- September 1999: Visiting Scientist at Abdus Salam I.C.T.P., Trieste, in the Condensed Matter Theory Group.

Other teaching activities, in Italy and abroad:

1975/76: Instructor of mathematical methods of physics, at the University of Trento, Italy.

1980/81: Professor at the Scuola di Perfezionamento in Fisica of the University of Rome I. Course on "Complementi di Fisica Teorica" (Real space renormalization group methods).

1981/82, 1982/83 and 1983/84: Professor at the Scuola di Perfezionamento in Fisica of the University of Padova. Course on "Teoria degli stati aggregati" (critical phenomena, phase transitions and renormalization group).

from academic year 1981/82 to present: Professor (professore incaricato supplente) and/or external collaborator at the ISAS (International School for Advanced Studies), Trieste, Italy. Graduate courses on "Statistical Mechanics","Fractals in Physics" and "Polymer statistics".

1986/87 Course on "Fractals and Critical Phenomena" for the "Dottorato di Ricerca in Fisica" (Ph.D. Program) at the Department of Physics, University of Milano, Italy.

1988/89: Course on "Critical phenomena and the Renormalization Group" for the Dottorato di Ricerca in Fisica at the Department of Physics, University of Roma I. Italy.

June 1990: Course on "Advanced topics in Statistical Mechanics" for the "Dottorato di Ricerca in Fisica" at the Department of Physics, University of Bologna, Italy.

June 1991: Short course on Wetting and Polymer Statistics at the Miniworkshop on "Nonlinearity: Fractals, Pattern formation", ICTP, Trieste, Italy.

1990/91: Professor (interim) at the University of Padova. Course on Structure of Matter.

July-August 1993: Course on "Statistical Mechanics of Random Surfaces, Vesicles and Polymers" at the International School on "Recent Advances in Statistical Physics". ITU, Istanbul, Turkey.

June 1996: Course on "Renormalization group and polymer statistics" at the Institute for Mathematics and its Applications, University of Minnesota, Minneapolis. IMA tutorial on "Topology and Statistical Mechanics of Polymers".

September 1997 Course on " Polymer Statistics" at the National Graduate School of Condensed Matter Physics. INFM-ISI, Torino, Italy.

Scientific activity:

Author of about 110 papers in international refereed journals, and about 20 contributions to proceedings and books (see attached list).

The research activity is in various fields of statistical physics and the contributions can be partitioned according to the following main categories, or fields of interest.

Exact results or solutions of spin and gauge models on the lattice, of interest for the physics of cooperative phenomena and for field theory. Among these one can mention the exact demonstration that the Onsager-Yang spontaneous magnetization coincides with the appropriate derivative of the free energy with respect to the magnetic field in the two-dimensional Ising model. Another achievenent was the first formulation and solution of a gauge analogue of a spin model on Cayley tree, which provides an equivalent of the magnetic Bethe approximation for lattice gauge theories.

Study of the renormalization group as a general method for the description of the scaling properties of systems at criticality. Here one can mention the development of exact static and dynamic renormalization methods for van der Waals spin models, and the study of Griffiths-Pearce singularities (peculiarities) performed on the same systems.

Formulations of the renormalization group for quantum statistical systems (Heliurn4, XY model, Hubbard model). In this context an explicit demonstration was given that quantum effects are irrelevant in determining the universality class of the lambda transition of Helium4. Another achievement was the formulation of the first renormalization group approaches to quantum spin systems at finite temperature, and the clarification of their connections with zero temperature methods.

Optimization criteria and new appproximate methods of the renormalization group. The most remarkable contribution has been the proposal of the new approach, generally known as mean field renormalization group (MFRG). For the first time in the history of critical phenomena, in this approach the mathematical and conceptual apparatus of classical theories is directly addressed to carry on Wilson's renormalization strategy. This very flexible method has been extensively applied in the literature during the last two decades. Applications, which are still going on, concern a variety of physical contexts, ranging from quantum magnets, to disordered systems and amphiphilic monolayers.

Criteria for distinguishing between continuous and discontinuous transitions, improvements of classical approximations, including Onsager's reaction field.

Conformational properties of linear and branched polymers. In this field a large number of substantial results has been obtained. Particular impact has had the full exact determination of universal scaling behavior at the theta collapse of linear polymers in two dimensiona. This has been achieved on the basis of original correspondences between percolation theory and the interacting polymer problem. Another substantial achievement has been the prediction of a new type of collapse from linear to branched structure for polymers with competing interactions. Such collapse, which has been widely discussed in the recent literature, is expectd to have particular relevance in the context of heteropolymer and protein models.

Models of membranes, vesicles and random surfaces. Here some important relations between vesicle statistics and lattice gauge problems have been discovered and applied to the study of topological and metric properties. The work on the critical properties of models of latticized random surfaces has been quite pioneeristic and inspired important subsequent developments. A review of the rich activity in this field has been recently given in a whole chapter of a recent monography ( C. Vanderzande, " Lattice Models of polymers", Cambridge University Press, Cambridge,1998).

Critical phenomena at boundary surfaces, consequenches of conformal invariance in two dimensions. Here the most important result has been the determination of the exact value of the fractal dimension of the clusters associated to critical fluctuations of Ising spins in two dimensiona. This fractal dimension was determined more than fourty years since Onsager solved the model.

Anomalous diffusion and logarithmic localization on fractal and hierarchical structures. Here the problem of Hubermann-Kerszberg's "ultradiffusion" in one dimension has been exactly solved for the first time by a dynamical renormalization group method. Also the existence of Sinai-like logarithmic diffusion for a particle subject to a biasing field on fractal structure lias been demonstraed in suitable models.

Interfacial and wetting phenomena. Of particular impact has been a recent study of the the effects of randomness on the interface fluctuations of ferromagnetic systems with more than two coexisting phases. This study proposes an original mechanism explaining very puzzling universality issues concerning the critical behavior. Another set of results concerns the wetting of fractally and self-affine rosigli surfaces. For the latter, in particular, the existence of an unexpected, roughtiess induced first-order wetting transition has been both numerically and analytically demonstrated.

Self-organized criticality. A large part of the most recent research is concentrated in this field. The results range front the determination of boundary scaling exponents for avalanche activity in sandpile models, to the formulation and solution of the, so called, inhomogeneous branching process, which has also interest per se in the context of probability theory. The models considered have applicative interest for fields like biological evolution and earthquake statistics. Of particular importance has been the discovery that prototype models like the Bak-Tang-Wiesenfeld sandpile, rather than obeying simple finite size scaling, like assumed in the literature of the last decade, show an unexpected form a multifractal scaling. The original analysis the Bak-Tarig-Wiesenfeld sandpile and of other similar models allowed to identify two different dynamical mechanisms of avalanche dynamics, leading to simple finite size and to rnultifractal scaling, respectively.

Heteropolymer models. The statistics of these models is of much current interest for problems like protein folding and polyampholites. The research in this field concentrated on understanding the cole of sequence inhomogeneities and disorder in determining the universal scaling properties at conformational transitions. A main recent achievement has been here the identification of a new, frustration dominated universality class of theta behavior for polymers with sequence disorder. This class is different from that appropriate for homogeneous polymers. Other results concern the prediction and characterization of a new type of collapse for block-copolymers and its connection with percolation theory in two dimensions.

Grants and organization activity:

Responsible of grants from NATO (Italy-US collaboration), INFM, and the Italian Ministry of University and Scientific Research. Member of the EU TMR network on "Fractals and self-organization". Member of the national commettee (Giunta) of the G-section ( theoretical condensed matter physics and cybernetics) of INFM. Local responsible of an INFN (Gruppo quarto) initiative and of an INFM research line. Organizer of international meetings and workshops at ISI, Torino, INFM-Forum, Florence, and Abdus Salam ICTP, Trieste. Member of graduate studies committee ( Collegio dei Docenti del Dottorato di Ricerca in Fisica) at the Universities of Bologna and Padova. Coordinator of graduate studies (Coordinatore del Dottorato di Ricerca in Fisica) at the Physics Department of Padova University.

Ph. D. theses supervised:

J. O. Indekeu. Static and dynamic renormalization from correlation functions and molecular fields. Leuven, 1983.

C. Vanderzande. Applications of the renormalization group in position space to quantum spin systems on a lattice. Leuven, 1984.

G. Giugliarelli. Fractally rough surfaces: wetting, adsorption and spectral properties. ISAS-Trieste, 1990.

F. Seno. Interacting models of self-avoiding paths and surfaces on the lattice: multicritical properties and universality. Padova, 1992.

M. C. Tesi. Statistical models of polymers on the lattice: universality problems and multicritical phenomena. Bologna, 1993.

E. Orlandini. Universality, topology and multicritical properties of lattice rnodels of self-avoiding surfaces and vesicles. Bologna, 1993.

G. Caldarelli. From self-organized criticality to pattern formation. Theoretical aspects and occurrence in nature. ISAS-Trieste, 1996.

G. Sartoni. Universality and interfaces in disordered media. Bologna 1996.

C. Tebaldi. Rare events dominance in non-equiluibrium critical phenomena. ISAS-Trieste, 1997.

P. Monari. Universality of heteropolymer theta collapse transitions. Padova, 1999.

M. De Menech. Multifractality and universality in sandpiles. Padova, 2000.