958 research outputs found
A dissociation between stopping and switching actions following a lesion of the pre-supplementary motor area
AbstractIntroductionAlthough the pre-supplementary motor area (pre-SMA) is one of the most frequently reported areas of activation in functional imaging studies, the role of this brain region in cognition is still a matter of intense debate. Here we present a patient with a focal lesion of caudal pre-SMA who displays a selective deficit in updating a response plan to switch actions, but shows no impairment when required to withhold a response – stopping.Materials & methodsThe patient and a control group underwent three tasks designed to measure different aspects of cognitive control and executive function.ResultsThe pre-SMA patient displayed no impairment when responding in the face of distracting stimuli (Eriksen flanker paradigm), or when required to halt an on-going response (STOP task). However, a specific deficit was observed when she was required to rapidly switch between response plans (CHANGE task).ConclusionsThese findings suggest that the caudal pre-SMA may have a particularly important role in a network of brain regions required for rapidly updating and implementing response plans. The lack of any significant impairment on other measures of cognitive control suggests that this is not likely due to a global deficit in cognitive control. We discuss the implications of these results in the context of current theories of pre-SMA function
Radiation Pressure and Photon Momentum in Negative-Index Media
Radiation pressure and photon momentum in negative-index media are no
different than their counterparts in ordinary (positive-index) materials. This
is because the parameters responsible for these properties are the admittance,
sqrt(epsilon/mu), and the group refractive index n_g of the material (both
positive entities), and not the phase refractive index, n=sqrt(epsilon*mu),
which is negative in negative-index media. One approach to investigating the
exchange of momentum between electromagnetic waves and material media is via
the Doppler shift phenomenon. In this paper we use the Doppler shift to arrive
at an expression for the radiation pressure on a mirror submerged in a
negative-index medium. In preparation for the analysis, we investigate the
phenomenon of Doppler shift in various settings, and show the conditions under
which a so-called "inverse" Doppler shift could occur. We also argue that a
recent observation of the inverse Doppler shift upon reflection from a
negative-index medium cannot be correct, because it violates the conservation
laws.Comment: 14 pages, 8 figures, 17 equations, 5 reference
Deducing radiation pressure on a submerged mirror from the Doppler shift
Radiation pressure on a flat mirror submerged in a transparent liquid,
depends not only on the refractive index n of the liquid, but also on the phase
angle psi_0 of the Fresnel reflection coefficient of the mirror, which could be
anywhere between 0^{\circ} and 180^{\circ}. Depending on the value of psi_0,
the momentum per incident photon picked up by the mirror covers the range
between the Abraham and Minkowski values, i.e., the interval
(2\hbarw_0/nc,2n\hbarw_0/c). Here \hbar is the reduced Planck constant, w_0 is
the frequency of the incident photon, and c is the speed of light in vacuum. We
argue that a simple experimental setup involving a dielectric slab of
refractive index n, a vibrating mirror placed a short distance behind the slab,
a collimated, monochromatic light beam illuminating the mirror through the
slab, and an interferometer to measure the phase of the reflected beam, is all
that is needed to deduce the precise magnitude of the radiation pressure on a
submerged mirror. In the proposed experiment, the transparent slab plays the
role of the submerging liquid (even though it remains detached from the mirror
at all times), and the adjustable gap between the mirror and the slab simulates
the variable phase-angle psi_0. The phase of the reflected beam, measured as a
function of time during one oscillation period of the mirror, then provides the
information needed to determine the gap-dependence of the reflected beam's
Doppler shift and, consequently, the radiation pressure experienced by the
mirror.Comment: 9 pages, 2 figures, 13 equation
Malware Detection using Machine Learning and Deep Learning
Research shows that over the last decade, malware has been growing
exponentially, causing substantial financial losses to various organizations.
Different anti-malware companies have been proposing solutions to defend
attacks from these malware. The velocity, volume, and the complexity of malware
are posing new challenges to the anti-malware community. Current
state-of-the-art research shows that recently, researchers and anti-virus
organizations started applying machine learning and deep learning methods for
malware analysis and detection. We have used opcode frequency as a feature
vector and applied unsupervised learning in addition to supervised learning for
malware classification. The focus of this tutorial is to present our work on
detecting malware with 1) various machine learning algorithms and 2) deep
learning models. Our results show that the Random Forest outperforms Deep
Neural Network with opcode frequency as a feature. Also in feature reduction,
Deep Auto-Encoders are overkill for the dataset, and elementary function like
Variance Threshold perform better than others. In addition to the proposed
methodologies, we will also discuss the additional issues and the unique
challenges in the domain, open research problems, limitations, and future
directions.Comment: 11 Pages and 3 Figure
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