691 research outputs found
Damage to fronto-parietal networks impairs motor imagery ability after stroke : a voxel-based lesion symptom mapping study
Background: mental practice with motor imagery has been shown to promote motor skill acquisition in healthy subjects and patients. Although lesions of the common motor imagery and motor execution neural network are expected to impair motor imagery ability, functional equivalence appears to be at least partially preserved in stroke patients.Aim: to identify brain regions that are mandatory for preserved motor imagery ability after stroke.Method: thirty-seven patients with hemiplegia after a first time stroke participated. Motor imagery ability was measured using a Motor Imagery questionnaire and temporal congruence test. A voxelwise lesion symptom mapping approach was used to identify neural correlates of motor imagery in this cohort within the first year post-stroke.Results: poor motor imagery vividness was associated with lesions in the left putamen, left ventral premotor cortex and long association fibres linking parieto-occipital regions with the dorsolateral premotor and prefrontal areas. Poor temporal congruence was otherwise linked to lesions in the more rostrally located white matter of the superior corona radiata. Conclusion: This voxel-based lesion symptom mapping study confirms the association between white matter tract lesions and impaired motor imagery ability, thus emphasizing the importance of an intact fronto-parietal network for motor imagery. Our results further highlight the crucial role of the basal ganglia and premotor cortex when performing motor imagery tasks
Semantic Clone Detection via Probabilistic Software Modeling
Semantic clone detection is the process of finding program elements with
similar or equal runtime behavior. For example, detecting the semantic equality
between the recursive and iterative implementation of the factorial
computation. Semantic clone detection is the de facto technical boundary of
clone detectors. This boundary was tested over the last years with interesting
new approaches. This work contributes a semantic clone detection approach that
detects clones with 0% syntactic similarity. We present Semantic Clone
Detection via Probabilistic Software Modeling (SCD-PSM) as a stable and precise
solution to semantic clone detection. PSM builds a probabilistic model of a
program that is capable of evaluating and generating runtime data. SCD-PSM
leverages this model and its model elements to finding behaviorally equal model
elements. This behavioral equality is then generalized to semantic equality of
the original program elements. It uses the likelihood between model elements as
a distance metric. Then, it employs the likelihood ratio significance test to
decide whether this distance is significant, given a pre-specified and
controllable false-positive rate. The output of SCD-PSM are pairs of program
elements (i.e., methods), their distance, and a decision whether they are
clones or not. SCD-PSM yields excellent results with a Matthews Correlation
Coefficient greater 0.9. These results are obtained on classical semantic clone
detection problems such as detecting recursive and iterative versions of an
algorithm, but also on complex problems used in coding competitions.Comment: 12 pages, 2 pages of references, 5 listings, 2 figures, 4 table
Realization of a spherical boundary by a layer of wave-guiding medium
In this paper the concept of wave-guiding medium, previously introduced for
planar structures, is defined for the spherically symmetric case. It is shown
that a quarter-wavelength layer of such a medium serves as a transformer of
boundary conditions between two spherical interfaces. As an application, the
D'B'-boundary condition, requiring vanishing of normal derivatives of the
normal components of D and B field vectors, is realized by transforming the
DB-boundary conditions. To test the theory, scattering from a spherical DB
object covered by a layer of wave-guiding material is compared to the
corresponding scattering from an ideal D'B' sphere, for varying medium
parameters of the layer
- …