1435 research outputs found
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Ferromagnetic-glassy transitions in three-dimensional Ising spin glasses
No full textWe investigate the ferromagnetic-glassy transitions which separate the
low-temperature ferromagnetic and spin-glass phases in the temperature-disorder
phase diagram of three-dimensional Ising spin-glass models. For this purpose,
we consider the cubic-lattice +-J (Edwards-Anderson) Ising model with bond
distribution , and present a
numerical Monte Carlo study of the critical behavior along the line that marks
the onset of ferromagnetism. The finite-size scaling analysis of the Monte
Carlo data shows that the ferromagnetic-glassy transition line is slightly
reentrant. As a consequence, for an interval of the disorder parameter p,
around p=0.77, the system presents a low-temperature glassy phase, an
intermediate ferromagnetic phase, and a high-temperature paramagnetic phase.
Along the ferromagnetic-glassy transition line magnetic correlations show a
universal critical behavior with critical exponents nu=0.96(2) and
eta=-0.39(2). The hyperscaling relation beta/nu = (1 + eta)/2 is satisfied at
the transitions, so that beta/nu = 0.305(10). This magnetic critical behavior
represents a new universality class for ferromagnetic transitions in Ising-like
disordered systems. Overlap correlations are apparently not critical and show a
smooth behavior across the transition
The entanglement entropy of 1D systems in continuous and homogenous space
No full textWe introduce a systematic framework to calculate the bipartite entanglement
entropy of a compact spatial subsystem in a one-dimensional quantum gas which
can be mapped into a noninteracting fermion system. We show that when working
with a finite number of particles N, the Renyi entanglement entropies grow as
log N, with a prefactor that is given by the central charge. We apply this
novel technique to the ground state and to excited states of periodic systems.
We also consider systems with boundaries. We derive universal formulas for the
leading behavior and for subleading corrections to the scaling. The
universality of the results allows us to make predictions for the finite-size
scaling forms of the corrections to the scaling
Quasi-long-range order in trapped systems
No full textWe investigate the effects of a trapping space-dependent potential on the
low-temperature quasi-long-range order phase of two-dimensional particle
systems with a relevant U(1) symmetry, such as quantum atomic gases. We
characterize the universal features of the trap-size dependence using scaling
arguments. The resulting scenario is supported by numerical Monte Carlo
simulations of a classical two-dimensional XY model with a space-dependent
hopping parameter whose inhomogeneity is analogous to that arising from the
trapping potential in experiments of atomic gases
Surface Control of Natural Stone Products/Controllo delle superfici di prodotti in pietra naturale
No full textThis work deals with the analysis of polished surfaces with optical methods, the characterization of surfaces with different methods and code engraving on stone materials, carried out during the Italian PRIN program 2004. Different prototypes discussed in the paper are addressed
Sette scritti politici liberi
No full textRIASSUNTO L'ipertesto contiene sette nuove traduzioni dei più importanti scritti politici di Kant, sottoposte separatamente a una licenza Creative Commons by-sa, in modo tale che siano liberamente modificabili. L'introduzione spiega le ragioni scientifiche e ideali di questa scelta. Ciascun saggio è inoltre provvisto di un'ampia annotazione della curatrice.
La forma ipertestuale permette al lettore di costruire i suoi percorsi di lettura e di confrontarsi direttamente con la versione originale tedesca.
SUMMARY A new open access Italian translation of Kant's seven major political writings. Every single essay is under a Creative Commons License by-sa, so that future translators will be able to enhance and amend this work without wasting their time in "reinventing the wheel". The curator has chosen to annotate the translation in a hypertextual form, to enable readers to select their reading route and to compare the Italian version with Kant's original German text
Potenzialità dei Sistemi CAD per la flessibilità dei sistemi produttivi
No full textPotential of CAD systems to improve the manufacturing system flexibility. Literature search and proposed approach
A 1.82 m^2 ring laser gyroscope for nano-rotational motion sensing
No full textWe present a fully active-controlled He-Ne ring laser gyroscope, operating in
square cavity 1.35 m in side. The apparatus is designed to provide a very low
mechanical and thermal drift of the ring cavity geometry and is conceived to be
operative in two different orientations of the laser plane, in order to detect
rotations around the vertical or the horizontal direction. Since June 2010 the
system is active inside the Virgo interferometer central area with the aim of
performing high sensitivity measurements of environmental rotational noise. So
far, continuous not attempted operation of the gyroscope has been longer than
30 days. The main characteristics of the laser, the active remote-controlled
stabilization systems and the data acquisition techniques are presented. An
off-line data processing, supported by a simple model of the sensor, is shown
to improve the effective long term stability. A rotational sensitivity at the
level of ten nanoradiants per squareroot of Hz below 1 Hz, very close to the
required specification for the improvement of the Virgo suspension control
system, is demonstrated for the configuration where the laser plane is
horizontal
Measuring the Virgo area tilt noise with a laser gyroscope
No full textWe report on the measurements of tilt noise performed at the Virgo site with
a ring laser gyroscope. The apparatus is a He-Ne laser operating in a square
cavity mounted on a vertical plane perpendicular to the north-south arm of the
inteferometer. We discuss the possibility of using the ring laser signal to
improve the performances of the control system of the Virgo seismic
suspensions. The comparison between the ring laser signal and the control
signals for the longitudinal translations of the inverted pendulum (IP) shows
remarkable coherence in the frequency range 20-200 mHz
Non-Abelian monopole-vortex complex
No full textIn the context of softly broken N=2 supersymmetric quantum chromodynamics
(SQCD), with a hierarchical gauge symmetry breaking SU(N+1) -> U(N) -> 1, at
scales v1 and v2, respectively, where v1 >> v2, we construct monopole-vortex
complex soliton-like solutions and examine their properties. They represent the
minimum of the static energy under the constraint that the monopole and
antimonopole positions sitting at the extremes of the vortex are kept fixed.
They interpolate the 't Hooft-Polyakov-like regular monopole solution near the
monopole centers and a vortex solution far from them and in between. The main
result, obtained in the theory with Nf=N equal-mass flavors, is concerned with
the existence of exact orientational CP(N-1) zero modes, arising from the exact
color-flavor diagonal SU(N)_{C+F} global symmetry. The "unbroken" subgroup
SU(N) \subset SU(N+1) with which the na\"ive notion of non-Abelian monopoles
and the related difficulties were associated, is explicitly broken at low
energies. The monopole transforms nevertheless according to the fundamental
representation of a new exact, unbroken SU(N) symmetry group, as does the
vortex attached to it. We argue that this explains the origin of the dual
non-Abelian gauge symmetry
Finite-size scaling in two-dimensional Ising spin glass models
No full textWe study the finite-size behavior of two-dimensional spin-glass models. We
consider the +-J model for two different values of the probability of the
antiferromagnetic bonds and the model with Gaussian distributed couplings. The
analysis of renormalization-group invariant quantities, the overlap
susceptibility, and the two-point correlation function confirms that they
belong to the same universality class. We analyze in detail the standard
finite-size scaling limit in terms of TL^(1/nu) in the +-J model. We find that
it holds asymptotically. This result is consistent with the low-temperature
crossover scenario in which the crossover temperature, which separates the
universal high-temperature region from the discrete low-temperature regime,
scales as T_c(L) ~ L^(-theta_S) with theta_S \approx 0.5