1435 research outputs found
Sort by
Compensation of the laser parameters fluctuations in large ring laser gyros: a Kalman filter approach
No full textHe-Ne ring laser gyroscopes are, at present, the most precise devices for
absolute angular velocity measurements. Limitations to their performance come
from the non--linear dynamics of the laser. Following the Lamb semi-classical
theory, we find a set of critical parameters affecting the time stability of
the system. We propose a method for estimating the long term drift of the laser
parameters and for filtering out the laser dynamics effects from the rotation\ud
measurement. The parameter estimation procedure, based on the perturbative
solutions of the laser dynamics, allow us to apply Kalman Filter theory for the
estimation of the angular velocity. Results of a comprehensive Monte Carlo
simulation and results of a preliminary analysis on experimental data from the
ring laser prototype G-Pisa are shown and discussed
Lattice QCD Simulations in External Background Fields
No full textWe discuss recent results and future prospects regarding the investigation,
by lattice simulations, of the non-perturbative properties of QCD and of its
phase diagram in presence of magnetic or chromomagnetic background fields.
After a brief introduction to the formulation of lattice QCD in presence of
external fields, we focus on studies regarding the effects of external fields
on chiral symmetry breaking, on its restoration at finite temperature and on
deconfinement. We conclude with a few comments regarding the effects of
electromagnetic background fields on gluodynamics
Rydberg excitation of a Bose-Einstein condensate
No full textWe have performed two-photon excitation via the 6P3/2 state to n=50-80 S or D
Rydberg state in Bose-Einstein condensates of rubidium atoms. The Rydberg
excitation was performed in a quartz cell, where electric fields generated by
plates external to the cell created electric charges on the cell walls.
Avoiding accumulation of the charges and realizing good control over the
applied electric field was obtained when the fields were applied only for a
short time, typically a few microseconds. Rydberg excitations of the
Bose-Einstein condensates loaded into quasi one-dimensional traps and in
optical lattices have been investigated. The results for condensates expanded
to different sizes in the one-dimensional trap agree well with the intuitive
picture of a chain of Rydberg excitations controlled by the dipole-dipole
interaction. The optical lattice applied along the one-dimensional geometry
produces localized, collective Rydberg excitations controlled by the
nearest-neighbour blockade
Existence and solution methods for equilibria
No full textEquilibrium problems provide a mathematical framework which includes optimization, variational inequalities, fixed-point and saddle point problems, and noncooperative games as particular cases. This general format received an increasing interest in the last decade mainly because many theoretical and algorithmic results developed for one of these models can be often extended to the others through the unifying language provided by this common format. This survey paper aims at covering the main results concerning the existence of equilibria and the solution methods for finding them.<br /
The Equivalence of Reduction and Translation Semantics of Java Simple Closures (Extended Version)
No full textFGCJ is a minimal core calculus that extends Featherweight Generic Java, FGJ, with lambda expressions for Java Simple Closures. It has been introduced to study, in a reduction semantics framework, properties of Java Simple Closures, including type safety and abstraction property. F 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, in a translation semantics framework, the design and the implementation features of lambda expressions, including simple closures, this transparency, non local variables and relations with anonymous class objects. In this paper we prove that the reduction semantics and the translation semantics commute in FGACJ. Where FGACJ is a minimal core calculus that extends FGCJ, by adding Java interfaces and anonymous class objects and that allows a restricted definition of translation semantics F
Cohomology of D-complex manifolds
No full textIn order to look for a well-behaved counterpart to Dolbeault cohomology in D-complex geometry, we study the de Rham cohomology of an almost D-complex manifold and its subgroups made up of the classes admitting invariant, respectively anti-invariant, representatives with respect to the almost D-complex structure, miming the theory introduced by Li and Zhang (2009) in [20] for almost complex manifolds. In particular, we prove that, on a 4-dimensional D-complex nilmanifold, such subgroups provide a decomposition at the level of the real second de Rham cohomology group. Moreover, we study deformations of D-complex structures, showing in particular that admitting D-Kähler structures is not a stable property under small deformations
High-fidelity quantum driving
No full textSUMMARY The ability to accurately control a quantum system is a fundamental
requirement in many areas of modern science such as quantum information
processing and the coherent manipulation of molecular systems. It is usually
necessary to realize these quantum manipulations in the shortest possible time
in order to minimize decoherence, and with a large stability against
fluctuations of the control parameters. While optimizing a protocol for speed
leads to a natural lower bound in the form of the quantum speed limit rooted in
the Heisenberg uncertainty principle, stability against parameter variations
typically requires adiabatic following of the system. The ultimate goal in
quantum control is to prepare a desired state with 100% fidelity. Here we
experimentally implement optimal control schemes that achieve nearly perfect
fidelity for a two-level quantum system realized with Bose-Einstein condensates
in optical lattices. By suitably tailoring the time-dependence of the system's
parameters, we transform an initial quantum state into a desired final state
through a short-cut protocol reaching the maximum speed compatible with the
laws of quantum mechanics. In the opposite limit we implement the recently
proposed transitionless superadiabatic protocols, in which the system perfectly
follows the instantaneous adiabatic ground state. We demonstrate that
superadiabatic protocols are extremely robust against parameter variations,
making them useful for practical applications
Getting Close Without Touching
No full textIn this paper we study the Near-Gathering problem for a set of asynchronous, anonymous, oblivious and autonomous mobile robots with limited visibility moving in Look-Compute-Move (LCM) cycles: In this problem, the robots have to get close enough to each other, so that every robot can see all the others, without touching (i.e., colliding) with any other robot. The importance of this problem might not be clear at a first sight: Solving the Near-Gathering problem, it is possible to overcome the limitations of having robots with limited visibility, and it is therefore possible to exploit all the studies (the majority, actually) done on this topic, in the unlimited visibility setting. In fact, after the robots get close enough, they are able to see all the robots in the system, a scenario similar to the one where the robots have unlimited visibility. Here, we present a collision-free algorithm for the Near-Gathering problem, the first to our knowledge, that allows a set of autonomous mobile robots to nearly gather within finite time. The collision-free feature of our solution is crucial in order to combine it with an unlimited visibility protocol. In fact, the majority of the algorithms that can be found on the topic assume that all robots occupy distinct positions at the beginning. Hence, only providing a collision-free Near-Gathering algorithm, as the one presented here, is it possible to successfully combine it with an unlimited visibility protocol, hence overcoming the natural limitations of the limited visibility scenario.In our model, distances are induced by the infinity norm. A discussion on how to extend our algorithm to models with different distance functions, including the usual Euclidean distance, is also presented
On Cohomological Decomposability of Almost-Kähler Structures
No full textWe study the J-invariant and J-anti-invariant cohomological subgroups of the
de Rham cohomology of a compact manifold M endowed with an almost-K\"ahler
structure (J, \omega, g). In particular, almost-K\"ahler manifolds satisfying a
Lefschetz type property, and solvmanifolds endowed with left-invariant
almost-complex structures are investigated
Singular SQCD Vacua and Confinement
No full textWe revisit the study of confining vacua in the softly broken N=2
supersymmetric QCD, in the light of some recent developments in our
understanding of the dynamics of N=2 gauge theories. These vacua are
characterized by an effective magnetic gauge group () and are referred to sometimes as the vacua. We further clarify the
meaning of duality arising from the matching of
semi-classical and quantum vacua. A particular attention is paid to certain
singular SCFT's of N=2 SQCD, driven into confinement phase by the adjoint mass
deformation . In some cases they occur as a result of
coalescence of different vacua as the bare mass is tuned to a critical
value