1,721,248 research outputs found
Action Observation for Neurorehabilitation in Apraxia
Full text linkNeurorehabilitation and brain stimulation studies of post-stroke patients suggest that action-observation effects can lead to rapid improvements in the recovery of motor functions and long-term motor cortical reorganization. Apraxia is a clinically important disorder characterized by marked impairment in representing and performing skillful movements [gestures], which limits many daily activities and impedes independent functioning. Recent clinical research has revealed errors of visuo-motor integration in patients with apraxia. This paper presents a rehabilitative perspective focusing on the possibility of action observation as a therapeutic treatment for patients with apraxia. This perspective also outlines impacts on neurorehabilitation and brain repair following the reinforcement of the perceptual-motor coupling. To date, interventions based primarily on action observation in apraxia have not been undertaken
Cognitive social and affective neuroscience of patients with spinal cord injury
Full text linkA successful human-environment interaction requires a continuous integration of information
concerning body parts, object features and affective dynamics. Multiple neuropsychological
studies show that tools can be integrated into the representation of one's own body. In
particular, a tool that participates in the conscious movement of the person is added to the
dynamic representation the body – often called “Body schema” – and may even affect social
interaction. In light of this the wheelchair is treated as an extension of the disabled body,
essentially replacing limbs that don't function properly, but it can also be a symbol of frailty
and weakness.
In a series of experiments, I studied plastic changes of action, tool and body representation in
individuals with spinal cord injury (SCI). Due to their peripheral loss of sensorimotor
functions, in the absence of brain lesions and spared higher order cognitive functions, these
patients represent an excellent model to study this topic in a multi-faceted way, investigating
both fundamental mechanisms and possible therapeutic interventions.
In a series of experiments, I developed new behavioral methods to measure the
phenomenological aspects of tool embodiment (Chapter 3), to study its functional and neural
correlates (Chapter 4) and to assess the possible computational model underpinning these
phenomena (Chapter 5). These tasks have been used to describe changes in tool, action and
body representation following the injury (Chapter 3 and 4), but also social interactions
(Chapter 7), with the aim of giving a complete portrait of change following such damage.
I found that changes in the function (wheelchair use) and the structure (body brain
disconnection) of the physical body, plastically modulate tool, action and body representation.
Social context and social interaction are also shaped by the new configuration of bodily
representations. Such a high degree of plasticity suggests that our sense of body is not given
at once, but rather it is constantly constructed and adapted through experience
Large scale GW calculations
Full text linkWe present GW calculations of molecules, ordered and disordered solids and interfaces, which employ an efficient contour deformation technique for frequency integration and do not require the explicit evaluation of virtual electronic states nor the inversion of dielectric matrices. We also present a parallel implementation of the algorithm which takes advantage of separable expressions of both the single particle Green's function and the screened Coulomb interaction. The method can be used starting from density functional theory calculations performed with semilocal or hybrid functionals. We applied the newly developed technique to GW calculations of systems of unprecedented size, including water/semiconductor interfaces with thousands of electrons
Design of defect spins in piezoelectric aluminum nitride for solid-state hybrid quantum technologies
Full text link: Spin defects in wide-band gap semiconductors are promising systems for the realization of quantum bits, or qubits, in solid-state environments. To date, defect qubits have only been realized in materials with strong covalent bonds. Here, we introduce a strain-driven scheme to rationally design defect spins in functional ionic crystals, which may operate as potential qubits. In particular, using a combination of state-of-the-art ab-initio calculations based on hybrid density functional and many-body perturbation theory, we predicted that the negatively charged nitrogen vacancy center in piezoelectric aluminum nitride exhibits spin-triplet ground states under realistic uni- and bi-axial strain conditions; such states may be harnessed for the realization of qubits. The strain-driven strategy adopted here can be readily extended to a wide range of point defects in other wide-band gap semiconductors, paving the way to controlling the spin properties of defects in ionic systems for potential spintronic technologies
Those are your legs: The effect of visuo-spatial perspective on visuo-tactile interactions and body ownership
No full textVibrationally resolved optical excitations of the nitrogen-vacancy center in diamond
Full text linkA comprehensive description of the optical cycle of spin defects in solids requires the understanding of the electronic and atomistic structure of states with different spin multiplicity, including singlet states which are particularly challenging from a theoretical standpoint. We present a general framework, based on spin-flip time-dependent density function theory, to determine the excited state potential energy surfaces of the many-body singlet states of spin defects; we then predict the vibrationally resolved absorption spectrum between singlet shelving states of a prototypical defect, the nitrogen-vacancy center in diamond. Our results, which are in very good agreement with experiments, provide an interpretation of the measured spectra and reveal the key role of specific phonons in determining absorption processes, and the notable influence of non-adiabatic interactions. The insights gained from our calculations may be useful in defining strategies to improve infrared-absorption-based magnetometry and optical pumping schemes. The theoretical framework developed here is general and applicable to a variety of other spin defects and materials
Machine learning dielectric screening for the simulation of excited state properties of molecules and materials
No full text: Accurate and efficient calculations of absorption spectra of molecules and materials are essential for the understanding and rational design of broad classes of systems. Solving the Bethe-Salpeter equation (BSE) for electron-hole pairs usually yields accurate predictions of absorption spectra, but it is computationally expensive, especially if thermal averages of spectra computed for multiple configurations are required. We present a method based on machine learning to evaluate a key quantity entering the definition of absorption spectra: the dielectric screening. We show that our approach yields a model for the screening that is transferable between multiple configurations sampled during first principles molecular dynamics simulations; hence it leads to a substantial improvement in the efficiency of calculations of finite temperature spectra. We obtained computational gains of one to two orders of magnitude for systems with 50 to 500 atoms, including liquids, solids, nanostructures, and solid/liquid interfaces. Importantly, the models of dielectric screening derived here may be used not only in the solution of the BSE but also in developing functionals for time-dependent density functional theory (TDDFT) calculations of homogeneous and heterogeneous systems. Overall, our work provides a strategy to combine machine learning with electronic structure calculations to accelerate first principles simulations of excited-state properties
LOOK AT YOUR LEGS: THE EFFECT OF VISUO-SPATIAL PERSPECTIVE ON VISUO-TACTILE INTERACTIONS AND LEG EMBODIMENT
No full textNonempirical Range-Separated Hybrid Functional with Spatially Dependent Screened Exchange
Full text linkElectronic structure calculations based on density functionaltheory(DFT) have successfully predicted numerous ground-state propertiesof a variety of molecules and materials. However, exchange and correlationfunctionals currently used in the literature, including semilocaland hybrid functionals, are often inaccurate to describe the electronicproperties of heterogeneous solids, especially systems composed ofbuilding blocks with large dielectric mismatch. Here, we present adielectric-dependent range-separated hybrid functional, screened-exchangerange-separated hybrid (SE-RSH), for the investigation of heterogeneousmaterials. We define a spatially dependent fraction of exact exchangeinspired by the static Coulomb-hole and screened-exchange (COHSEX)approximation used in many-body perturbation theory, and we show thatthe proposed functional accurately predicts the electronic structureof several nonmetallic interfaces, three- and two-dimensional, pristine,and defective solids and nanoparticles
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