1435 research outputs found
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Miglioramento del ciclo termico/di lavorazione su alberi motore integrali
No full textThis article introduces the process of hardening and tempering, and describes an approach to the solution of problems on a mechanical componen
Shape Optimization Problems with Internal Constraint
No full textWe consider shape optimization problems with internal inclusion constraints,
of the form \min\big\{J(\Omega)\ :\ \Dr\subset\Omega\subset\R^d,\
|\Omega|=m\big\}, where the set \Dr is fixed, possibly unbounded, and
depends on via the spectrum of the Dirichlet Laplacian. We analyze the existence of a solution and its qualitative properties, and rise some open questions
Porting Decision Tree Building and Pruning Algorithms to Multicore using FastFlow
No full textThe whole computer hardware industry embraced multicores. For these machines, the extreme optimisation of sequential algorithms is no longer sufficient to squeeze the real machine power, which can be only exploited via thread-level parallelism. Decision tree algorithms exhibit natural concurrency that makes them suitable to be parallelised. This paper presents an approach for easy-yet-efficient porting of an implementation of the C4.5 algorithm on multicores. The approach is based on the FastFlow parallel programming environment. The strength of our porting consists in minimal changes to the original sequential code. In addition to the tree building algorithm, we consider also the so far unaddressed problem of parallelising the error-based pruning with grafting algorithm of C4.5. We devise lower bounds for the forms of parallelisations adopted, and achieve performances close to such bounds
Targeting multi cores by structured programming and data flow
No full textData flow techniques have been around since the early ’70s when they were used in compilers for sequential languages. Shortly after their intro- duction they were also considered as a possible model for parallel comput- ing, although the impact here was limited. Recently, however, data flow has been identified as a candidate for efficient implementation of various programming models on multi-core architectures. In most cases, however, the burden of determining data flow “macro” instructions is left to the programmer, while the compiler/run time system manages only the ef- ficient scheduling of these instructions. We discuss a structured parallel programming approach supporting automatic compilation of programs to macro data flow and we show experimental results demonstrating the fea- sibility of the approach and the efficiency of the resulting “object” code on different classes of state-of-the-art multi-core architectures. The ex- perimental results use different base mechanisms to implement the macro data flow run time support, from plain pthreads with condition variables to more modern and effective lock- and fence-free parallel frameworks.
Experimental results comparing efficiency of the proposed approach with those achieved using other, more classical parallel frameworks are also presented
La decomposizione ai valori singolari per l’analisi di immagini
No full textImage analysis by Singular Value Decomposition. Theory, applications and examples
Phase diagram of QCD with two degenerate staggered quarks
No full textWe present preliminary results about the critical line of QCD with two
degenerate staggered quarks at nonzero temperature and chemical potential,
obtained by the method of analytic continuation. As in our previous studies
with different numbers of colors and flavors, we find deviations from a simple
quadratic dependence on the chemical potential. We comment on the shape of the
critical line at real chemical potential and give an estimate of the curvature
of the critical line, both for quark chemical potential and isospin chemical
potential
Constraints for Service Contracts
No full textThis paper focuses on client-service interactions distinguishing between three phases: negotiate, commit and execute. The participants negotiate their behaviours, and if an agreement is reached they commit and start an execution which is guaranteed to respect the interaction scheme agreed upon. These ideas are materialised through a calculus of contracts enriched with semiring-based constraints, which allow clients to choose services and to interact with them in a safe way. A concrete representation of these constraints with logic programs and logic program combinations is straightforward, thus reducing constraint solution (and consequently the establishment of a contract) to the execution of a logic program.<br /
Proving Translation and Reduction Semantics Equivalent for Java Simple Closures: Extended Version
No full text\Lname\ is a minimal core calculus that extends Featherweight (generic) Java, \FGJ, with lambda expressions. It has been used to study properties of Simple Closure in Java, including type safety and the abstraction property. Its formalization is based on a reduction semantics and a typing system that extend those of \FGJ. is a source-to-source, translation rule system from Java 1.5 extended with lambda expressions back to ordinary Java 1.5. It has been introduced to study implementation features of closures in Java, including assignment of non local variables and relations with anonymous class objects. In this paper we prove that the two semantics commute. <br /
Measuring Gravito-magnetic Effects by Multi Ring-Laser Gyroscope
No full textWe propose an under-ground experiment to detect the general relativistic
effects due to the curvature of space-time around the Earth (de Sitter effect)
and to rotation of the planet (dragging of the inertial frames or
Lense-Thirring effect). It is based on the comparison between the IERS value of
the Earth rotation vector and corresponding measurements obtained by a
tri-axial laser detector of rotation. The proposed detector consists of six
large ring-lasers arranged along three orthogonal axes.
In about two years of data taking, the 1% sensitivity required for the
measurement of the Lense-Thirring drag can be reached with square rings of 6
side, assuming a shot noise limited sensitivity ().
The multi-gyros system, composed of rings whose planes are perpendicular to one
or the other of three orthogonal axes, can be built in several ways. Here, we
consider cubic and octahedron structures. The symmetries of the proposed
configurations provide mathematical relations that can be used to study the
stability of the scale factors, the relative orientations or the ring-laser
planes, very important to get rid of systematics in long-term measurements,
which are required in order to determine the relativistic effects
The three-dimensional gauge-glass model
No full textWe investigate the temperature-disorder (T-S) phase diagram of a
three-dimensional gauge glass model, which is a cubic-lattice nearest-neighbor
XY model with quenched random phase shifts A_xy at the bonds, by numerical
Monte Carlo simulations. We consider the uncorrelated phase-shift distribution
P(A_xy)\sim \exp[(cos A_xy)/S], which has the pure XY model and the uniform
distribution of random shifts as extreme cases at S=0 and S->infty
respectively, and which gives rise to equal magnetic and overlap correlation
functions when T=S. While the high-temperature phase is always paramagnetic, at
low temperatures there is a ferromagnetic phase for weak disorder (small S) and
a glassy phase at large disorder (large S). These three phases are separated by
transition lines with different magnetic and glassy critical behaviors. The
disorder induced by the random shifts turns out to be irrelevant at the
paramagnetic-ferromagnetic transition line, where the critical behavior belongs
to the 3D XY universality class of pure systems; disorder gives only rise to
very slowly decaying scaling corrections. The glassy critical behavior along
the finite-temperature paramagnetic-glassy transition line belongs to the
gauge-glass universality class, with a quite large critical exponent nu=3.2(4).
These transition lines meet at a multicritical point M, located at
T=S=0.7840(2). The low-temperature ferromagnetic and glassy phases are
separated by a third transition line, from M down to the T=0 axis, which is
slightly reentrant