8,372 research outputs found
Localized modes of binary mixtures of Bose-Einstein condensates in nonlinear optical lattices
The properties of the localized states of a two component Bose-Einstein
condensate confined in a nonlinear periodic potential [nonlinear optical
lattice] are investigated. We reveal the existence of new types of solitons and
study their stability by means of analytical and numerical approaches. The
symmetry properties of the localized states with respect to the NOL are also
investigated. We show that nonlinear optical lattices allow the existence of
bright soliton modes with equal symmetry in both components, bright localized
modes of mixed symmetry type, as well as, dark-bright bound states and bright
modes on periodic backgrounds. In spite of the quasi 1D nature of the problem,
the fundamental symmetric localized modes undergo a delocalizing transition
when the strength of the nonlinear optical lattice is varied. This transition
is associated with the existence of an unstable solution, which exhibits a
shrinking (decaying) behavior for slightly overcritical (undercritical)
variations in the number of atoms.Comment: 13 pages, 14 figure
Quantum-tunneling dynamics of a spin-polarized Fermi gas in a double-well potential
We study the exact dynamics of a one-dimensional spin-polarized gas of
fermions in a double-well potential at zero and finite temperature. Despite the
system is made of non-interacting fermions, its dynamics can be quite complex,
showing strongly aperiodic spatio-temporal patterns during the tunneling. The
extension of these results to the case of mixtures of spin-polarized fermions
in interaction with self-trapped Bose-Einstein condensates (BECs) at zero
temperature is considered as well. In this case we show that the fermionic
dynamics remains qualitatively similar to the one observed in absence of BEC
but with the Rabi frequencies of fermionic excited states explicitly depending
on the number of bosons and on the boson-fermion interaction strength. From
this, the possibility to control quantum fermionic dynamics by means of
Feshbach resonances is suggested.Comment: Accepted for publication in Phys. Rev.
Soliton ratchets induced by ac forces with harmonic mixing
The ratchet dynamics of a kink (topological soliton) of a dissipative
sine-Gordon equation in the presence of ac forces with harmonic mixing (at
least bi-harmonic) of zero mean is studied. The dependence of the kink mean
velocity on system parameters is investigated numerically and the results are
compared with a perturbation analysis based on a point particle representation
of the soliton. We find that first order perturbative calculations lead to
incomplete descriptions, due to the important role played by the soliton-phonon
interaction in establishing the phenomenon. The role played by the temporal
symmetry of the system in establishing soliton ratchets is also emphasized. In
particular, we show the existence of an asymmetric internal mode on the kink
profile which couples to the kink translational mode through the damping in the
system. Effective soliton transport is achieved when the internal mode and the
external force get phase locked. We find that for kinks driven by bi-harmonic
drivers consisting of the superposition of a fundamental driver with its first
odd harmonic, the transport arises only due to this {\it internal mode}
mechanism, while for bi-harmonic drivers with even harmonic superposition, also
a point-particle contribution to the drift velocity is present. The phenomenon
is robust enough to survive the presence of thermal noise in the system and can
lead to several interesting physical applications.Comment: 9 pages, 13 figure
Matter-wave 2D solitons in crossed linear and nonlinear optical lattices
It is demonstrated the existence of multidimensional matter-wave solitons in
a crossed optical lattice (OL) with linear OL in the direction and
nonlinear OL (NOL) in the direction, where the NOL can be generated by a
periodic spatial modulation of the scattering length using an optically induced
Feshbach resonance. In particular, we show that such crossed linear and
nonlinear OL allows to stabilize two-dimensional (2D) solitons against decay or
collapse for both attractive and repulsive interactions. The solutions for the
soliton stability are investigated analytically, by using a multi-Gaussian
variational approach (VA), with the Vakhitov-Kolokolov (VK) necessary criterion
for stability; and numerically, by using the relaxation method and direct
numerical time integrations of the Gross-Pitaevskii equation (GPE). Very good
agreement of the results corresponding to both treatments is observed.Comment: 8 pages (two-column format), with 16 eps-files of 4 figure
Compactons in Nonlinear Schr\"odinger Lattices with Strong Nonlinearity Management
The existence of compactons in the discrete nonlinear Schr\"odinger equation
in the presence of fast periodic time modulations of the nonlinearity is
demonstrated. In the averaged DNLS equation the resulting effective inter-well
tunneling depends on modulation parameters {\it and} on the field amplitude.
This introduces nonlinear dispersion in the system and can lead to a
prototypical realization of single- or multi-site stable discrete compactons in
nonlinear optical waveguide and BEC arrays. These structures can dynamically
arise out of Gaussian or compactly supported initial data.Comment: 4 pages, 4 figure
Review about comorbidities of behavioural disorders in children and adolescents: The focus on attention-deficit/hyperactivity disorder
Disruptive behavior disorders (DBD) present high comorbidity rate mainly for opposite-defiant disorders that are frequent among children, adolescents and adults affected by with attention deficit and hyperactivity disorder (ADHD), probably as result of common temperamental risk factors such as attention, distraction, impulsivity. ADHD tend to manifest in about 50% of individuals diagnosed as disruptive behavioral disorders
Behavioural disorders in children and adolescents: A conceptual review about the therapeutic alliance with family and school
Aim: In disruptive behavioral disorders, given the wide range of symptomatic manifestations and the complexity of the sociofamiliar contexts in which they develop, it is now proven that more visible and more stable results can be achieved over time through multimodal and multidimensional interventions. These are accomplished through the integration of psychotherapeutic interventions for the child and parents, counseling interventions for all the various practitioners who come into contact with the child in school, sports, and social settings, through the possibility of organizing multiple settings in patient can be followed by several health professionals such as child and adolescent neuropsychiatrist, neuropsychomotricist, occupation therapist, psychologist
Adiabatic Compression of Soliton Matter Waves
The evolution of atomic solitary waves in Bose-Einstein condensate (BEC)
under adiabatic changes of the atomic scattering length is investigated. The
variations of amplitude, width, and velocity of soliton are found for both
spatial and time adiabatic variations. The possibility to use these variations
to compress solitons up to very high local matter densities is shown both in
absence and in presence of a parabolic confining potential.Comment: to appear in J.Phys.
Forensic considerations on violent parasomnias during lifespan
Nocturnal parasomnias are a group of sleep complex manifestation that don't alter the sleep macrostructure, but when persistent during adulthood may be assume violent aspects with relevant forensic implications about the guiltiness
The behavioral parenting interventions (BPT) for support and mandatory integrative therapy for children and adolescents affected by disruptive behavioural disorders: A brief review
The behavioral parenting interventions (BPT), commonly abbreviated as parent training, is a program conducted by an expert with the specific purpose of improving or modifying parental practices in order to promote the child's well-being, increasing parenting skills in the daily management of the child, problem solving and reducing the level of parenting and family stress. BPT presents many positive effects on children or adolescents affected by neurodevelopmental disorder such as ADHD, autism and cognitive dysfunction but BPT appears to improve also other proximal outcomes such as parenting competence and parenting stress
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