Quantum interference of electrons in a ring: tuning of the geometrical phase

We calculate the oscillations of the DC conductance across a mesoscopic ring, simultaneously tuned by applied magnetic and electric fields orthogonal to the ring. The oscillations depend on the Aharonov-Bohm flux and of the spin-orbit coupling. They result from mixing of the dynamical phase, including the Zeeman spin splitting, and of geometric phases. By changing the applied fields, the geometric phase contribution to the conductance oscillations can be tuned from the adiabatic (Berry) to the nonadiabatic (Ahronov-Anandan) regime. To model a realistic device, we also include nonzero backscattering at the connection between ring and contacts, and a random phase for electron wavefunction, accounting for dephasing due to disorder.Comment: 4 pages, 3 figures, minor change

Multilevel Analysis of Locomotion in Immature Preparations Suggests Innovative Strategies to Reactivate Stepping after Spinal Cord Injury

Locomotion is one of the most complex motor behaviors. Locomotor patterns change during early life, reflecting development of numerous peripheral and hierarchically organized central structures. Among them, the spinal cord is of particular interest since it houses the central pattern generator (CPG) for locomotion. This main command center is capable of eliciting and coordinating complex series of rhythmic neural signals sent to motoneurons and to corresponding target-muscles for basic locomotor activity. For a long-time, the CPG has been considered a black box. In recent years, complementary insights from in vitro and in vivo animal models have contributed significantly to a better understanding of its constituents, properties and ways to recover locomotion after a spinal cord injury (SCI). This review discusses key findings made by comparing the results of in vitro isolated spinal cord preparations and spinal-transected in vivo models from neonatal animals. Pharmacological, electrical, and sensory stimulation approaches largely used to further understand CPG function may also soon become therapeutic tools for potent CPG reactivation and locomotor movement induction in persons with SCI or developmental neuromuscular disorder

Topological Quantum Phase Transitions in Topological Superconductors

In this paper we show that BF topological superconductors (insulators) exibit phase transitions between different topologically ordered phases characterized by different ground state degeneracy on manifold with non-trivial topology. These phase transitions are induced by the condensation (or lack of) of topological defects. We concentrate on the (2+1)-dimensional case where the BF model reduce to a mixed Chern-Simons term and we show that the superconducting phase has a ground state degeneracy $k$ and not $k^2$. When the symmetry is $U(1) \times U(1)$, namely when both gauge fields are compact, this model is not equivalent to the sum of two Chern-Simons term with opposite chirality, even if naively diagonalizable. This is due to the fact that U(1) symmetry requires an ultraviolet regularization that make the diagonalization impossible. This can be clearly seen using a lattice regularization, where the gauge fields become angular variables. Moreover we will show that the phase in which both gauge fields are compact is not allowed dynamically.Comment: 5 pages, no figure

Cardiovascular autonomic function and MCI in Parkinson's disease

Introduction: dysautonomic dysfunction and cognitive impairment represent the most disabling non-motor features of Parkinson's Disease (PD). Recent evidences suggest the association between Orthostatic Hypotension (OH) and PD-Dementia. However, little is known on the interactions between cardiovascular dysautonomia and Mild Cognitive Impairment (MCI). We aimed to evaluate the association between cardiovascular dysautonomia and MCI in patients with PD. Methods: non-demented PD patients belonging to the PACOS cohort underwent a comprehensive instrumental neurovegetative assessment including the study of both parasympathetic and sympathetic function (30:15 ratio, Expiratory-Inspiratory ratio [E-I] and presence of Orthostatic Hypotension [OH]). Diagnosis of MCI was made according to the MDS criteria level II. Results: we enrolled 185 PD patients of whom 102 (55.1%) were men, mean age was 64.6 ± 9.7 years, mean disease duration of 5.6 ± 5.5 years with a mean UPDRS-ME score of 31.7 ± 10.9. MCI was diagnosed in 79 (42.7%) patients. OH was recorded in 52 (28.1%) patients, altered 30:15 ratio was recorded in 39 (24.1%) patients and an altered E-I ratio was found in 24 (19.1%) patients. Presence of MCI was associated with an altered 30:15 ratio (adjOR 2.83; 95%CI 1.25–6.40) but not with an altered E-I ratio, while OH was associated only with the amnestic MCI subgroup (OR 2.43; 95% CI 1.05–5.06). Conclusion: in our study sample, MCI was mainly associated with parasympathetic dysfunction in PD

Phase-space characterization of complexity in quantum many-body dynamics

We propose a phase-space Wigner harmonics entropy measure for many-body quantum dynamical complexity. This measure, which reduces to the well known measure of complexity in classical systems and which is valid for both pure and mixed states in single-particle and many-body systems, takes into account the combined role of chaos and entanglement in the realm of quantum mechanics. The effectiveness of the measure is illustrated in the example of the Ising chain in a homogeneous tilted magnetic field. We provide numerical evidence that the multipartite entanglement generation leads to a linear increase of entropy until saturation in both integrable and chaotic regimes, so that in both cases the number of harmonics of the Wigner function grows exponentially with time. The entropy growth rate can be used to detect quantum phase transitions. The proposed entropy measure can also distinguish between integrable and chaotic many-body dynamics by means of the size of long term fluctuations which become smaller when quantum chaos sets in.Comment: 10 pages, 9 figure