Disordered Flat Phase in a Solid on Solid Model of Fcc(110) Surfaces and Dimer States in Quantum Spin-1/2 Chains

We present a restricted solid on solid hamiltonian for fcc (110) surfaces. It is the simplest generalization of the exactly solvable BCSOS model which is able to describe a $(2\times 1)$ missing-row reconstructed surface. We study this model by mapping it onto a quantum spin-1/2 chain of the Heisenberg type, with second and third neighbor $S^z_iS^z_j$ couplings. The ground state phase diagram of the spin-chain model is studied by exact diagonalization of finite chains up to $N=28$ sites, as well as through analytical techniques. We find four phases in the phase diagram: two ordered phases in which the spins have a N\'eel-type of long range order (an unreconstructed and a missing-row reconstructed phase, in the surface language), a spin liquid phase (representing a rough surface), and an intermediate dimer phase which breaks translational invariance and has a doubly degenerate ground state, corresponding to a disordered flat surface. The transition from the $(2\times 1)$ reconstructed phase to the disordered flat phase belongs to the $2D$ Ising universality class. A critical (preroughening) line with varying exponents separates the unreconstructed phase from the disordered flat phase. The possible experimental signatures of the disordered flat phase are discussed.Comment: 20 pages (10 Figures available upon request), REVTEX, SISSA PREPRINT 1/94/CM/S

La biblioteca postmoderna.

This study examines the shift from a "modern" to a "postmodern" approach in the field of library and information science. As a result of a thorough review of the literature about the topic, the author argues that the postmodern library is characterized by a new way of understanding the reality, which is no longer based on the objective and rational way typical of the modern age, but on a more fragmented and composite point of view, as highlighted by the theorists of postmodernism. This increases the focus on cultural diversity, and calls into question the role of the library as a tool for organizing a unique and dominant knowledge. Given these assumptions, the postmodern library is closely connected to some relevant factors of the current debate, such as the centrality of the user and the ability to facilitate the access to a wide range of documents

Performance Analysis of a DEKF for Available Bandwidth Measurement

The paper presents a characterisation analysis of a measurement algorithm based on a Discrete-time Extended Kalman Filter (DEKF), which has recently been proposed for the estimation and tracking of end-to-end available bandwidth. The analysis is carried out by means of simulations for different rates of variations of the available bandwidth and permits assessing the performance of the measurement algorithm for different values of the filter parameters, that is, the covariance matrixes of the measurement and process noise

La lingua biforcuta delle biblioteche. Un’intervista con Rossana Morriello e Michele Santoro, curatori del volume La biblioteca e l’immaginario

Intervista sul libro "La biblioteca e l'immaginario

DinSAR monitoring of the landslide activity affecting a stretch of motorway in the Campania region of Southern Italy

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On federated single sign-on in e-government interoperability frameworks

We consider the problem of handling digital identities within serviceoriented architecture (SOA) architectures. We explore federated, single signon (SSO) solutions based on identity managers and service providers. After an overview of the different standards and protocols, we introduce a middlewarebased architecture to simplify the integration of legacy systems within such platforms. Our solution is based on a middleware module that decouples the legacy system from the identity-management modules.We consider both standard point-to-point service architectures, and complex government interoperability frameworks, and report experiments to show that our solution provides clear advantages both in terms of effectiveness and performance

Local moments and magnetic order in the two-dimensional Anderson-Mott transition

We study the role of electronic correlation in a disordered two-dimensional model by using a variational wave function that can interpolate between Anderson and Mott insulators. Within this approach, the Anderson-Mott transition can be described both in the paramagnetic and in the magnetic sectors. In the latter case, we find evidence for the formation of local magnetic moments that order before the Mott transition. The charge gap opening in the Mott insulator is accompanied by the vanishing of the $\lim_{q\to 0} \overline{}$ (the bar denoting the impurity average), which is related to the compressibility fluctuations. The role of a frustrating (second-neighbor) hopping is also discussed, with a particular emphasis to the formation of metastable spin-glass states.Comment: 4+epsilon pages, 5 figure

Hernia of Foramen of Morgagni in Adult: Case Report of Laparoscopic Repair

The videolaparoscopic repair of a diaphragmatic hernia of Morgagni by external knot tying technique is described. A 69-year-old woman with subocclusive symptoms by intrathoracic migration of abdominal viscera had an immediate and complete postoperative recovery. The hernial sac was not excised. A four-year follow-up shows no hernia recurrence. This case indicated that the laparoscopic approach can be considered a suitable and safe procedure for treatment of Morgagni's hernia