5,901 research outputs found
Spontaneous and TMS-related EEG changes as new biomarkers to measure anti-epileptic drug effects
TMS as a pharmacodynamic indicator of cortical activity of a novel anti-epileptic drug, XEN1101
Diagnosing order by disorder in quantum spin systems
In this paper we study the frustrated J1-J2 quantum Heisenberg model on the
square lattice for J2 > 2J1, in a magnetic field. In this regime the classical
system is known to have a degenerate manifold of lowest energy configurations,
where standard thermal order by disorder occurs. In order to study its quantum
version we use a path integral formulation in terms of coherent states. We show
that the classical degeneracy in the plane transverse to the magnetic field is
lifted by quantum fluctuations. Collinear states are then selected, in a
similar pattern to that set by thermal order by disorder, leaving a Z2
degeneracy. A careful analysis reveals a purely quantum mechanical effect given
by the tunneling between the two minima selected by fluctuations. The effective
description contains two planar (XY -like) fields conjugate to the total
magnetization and the difference of the two sublattice magnetizations. Disorder
in either or both of these fields produces the locking of their conjugate
observables. Furthermore, within this scenario we argue that the quantum state
is close to a product state.Comment: 8 pages, 3 figure
Long time dynamics following a quench in an integrable quantum spin chain: local versus non-local operators and effective thermal behavior
We study the dynamics of the quantum Ising chain following a zero-temperature
quench of the transverse field strength. Focusing on the behavior of two-point
spin correlation functions, we show that the correlators of the order parameter
display an effective asymptotic thermal behavior, i.e., they decay
exponentially to zero, with a phase coherence rate and a correlation length
dictated by the equilibrium law with an effective temperature set by the energy
of the initial state. On the contrary, the two-point correlation functions of
the transverse magnetization or the density-of-kinks operator decay as a
power-law and do not exhibit thermal behavior. We argue that the different
behavior is linked to the locality of the corresponding operator with respect
to the quasi-particles of the model: non-local operators, such as the order
parameter, behave thermally, while local ones do not. We study which features
of the two-point correlators are a consequence of the integrability of the
model by analizing their robustness with respect to a sufficiently strong
integrability-breaking term.Comment: 18 pages, 11 figures, published version. Extensive changes, one
author adde
The emotional side of post-traumatic stress reaction during COVID-19 pandemic: an Italian survey
A neurally-interfaced hand prosthesis tuned inter-hemispheric communication
Purpose: This work investigates how a direct bidirectional connection between brain and hand prosthesis modifies the bi-hemispheric sensorimotor system devoted to the movement control of the lost limb. Hand prostheses are often unable to satisfy users' expectations, mostly due to the poor performance of their interfacing system. Neural Interfaces implanted inside nerves of the stump offer the advantage of using the bidirectional neural pathways 'naturally' dispatching signals to control proper hand actions and feed-back sensations. Learning to control a neurally-interfaced hand prosthesis and decode sensory information was previously observed to reduce the inter-hemispheric asymmetry of cortical motor maps and the clinical symptoms of phantom limb syndrome. Methods: Electroencephalographic (EEG) data was analysed using Functional Source Separation (FSS), a semi-blind method that incorporates prior knowledge about the signal of interest into data decomposition to give access to cortical patch activities. Results: Bi-hemispheric cortices showed normalization of their activity (topographical and spectral patterns) and of functional connectivity between homologous hand controlling areas, during the delivery of the motor command to the cybernetic prosthesis. Conclusions: The re-establishment of central-peripheral communication with the lost limb induced by a neurally-interfaced hand prosthesis produces beneficial plastic reorganization, not only restructuring contralateral directly-connected control areas, but also their functional balance within the bi-hemispheric system necessary for motor control
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