125 research outputs found
Coulomb impurity in graphene
We consider the problem of screening of an electrically charged impurity in a
clean graphene sheet. When electron-electron interactions are neglected, the
screening charge has a sign opposite to that of the impurity, and is localized
near the impurity. Interactions between electrons smear out the induced charge
density to give a large-distance tail that follows approximately, but not
exactly, an r^{-2} behavior and with a sign which is the same as that of the
impurity.Comment: 10 pages, 3 figures; (v2) Corrected sign error in Eq. (13); (v3)
corrected figure
Quantum Mechanics of Particle on a torus knot: Curvature and Torsion Effects
Constraints play an important role in dynamical systems. However, the subtle
effect of constraints in quantum mechanics is not very well studied. In the
present work we concentrate on the quantum dynamics of a point particle moving
on a non-trivial torus knot. We explicitly take into account the role of
curvature and torsion, generated by the constraints that keep the particle on
the knot. We exploit the "Geometry Induced Potential (GIP) approach" to
construct the Schrodinger equation for the dynamical system, obtaining thereby
new results in terms of particle energy eigenvalues and eigenfunctions. We
compare our results with existing literature that completely ignored the
contributions of curvature and torsion. In particular, we explicitly show how
the "knottedness" of the path influences the results. In the process we have
revealed a (possibly un-noticed) "topological invariant".Comment: Revised version (to be uploaded, with no change in conclusions),
accepted in EP
SU(2)-invariant spin liquids on the triangular lattice with spinful Majorana excitations
We describe a new class of spin liquids with global SU(2) spin rotation
symmetry in spin 1/2 systems on the triangular lattice, which have real
Majorana fermion excitations carrying spin S = 1. The simplest
translationally-invariant mean-field state on the triangular lattice breaks
time-reversal symmetry and is stable to fluctuations. It generically possesses
gapless excitations along 3 Fermi lines in the Brillouin zone. These intersect
at a single point where the excitations scale with a dynamic exponent z = 3. An
external magnetic field has no orbital coupling to the SU(2) spin
rotation-invariant fermion bilinears that can give rise to a transverse thermal
conductivity, thus leading to the absence of a thermal Hall effect. The Zeeman
coupling is found to gap out two-thirds of the z = 3 excitations near the
intersection point and this leads to a suppression of the low temperature
specific heat, the spin susceptibility and the Wilson ratio. We also compute
physical properties in the presence of weak disorder and discuss possible
connections to recent experiments on organic insulators.Comment: 26 pages, 11 figure
Fostering Human Learning in Sequential Decision-Making: Understanding the Role of Evaluative Feedback
Cognitive rehabilitation, STEM skill acquisition, and coaching games such as
chess often require tutoring decision-making strategies. The advancement of
AI-driven tutoring systems for facilitating human learning requires an
understanding of the impact of evaluative feedback on human decision-making and
skill development. To this end, we conduct human experiments using Amazon
Mechanical Turk to study the influence of evaluative feedback on human
decision-making in sequential tasks. In these experiments, participants solve
the Tower of Hanoi puzzle and receive AI-generated feedback while solving it.
We examine how this feedback affects their learning and skill transfer to
related tasks. We also explore various computational models to understand how
people incorporate evaluative feedback into their decision-making processes
Reducing inter-cluster TDMA interference by adaptive MAC allocation in sensor networks
Abstract This paper presents a Self-Reorganizing Slot Allocation (SRSA
Physical Context Detection using Wearable Wireless Sensor Networks
This paper presents the architecture of a wearable sensor network and a Hidden Markov Model (HMM) processingframework for stochastic identification of body postures andphysical contexts. The key idea is to collect multi-modal sensor data from strategically placed wireless sensors over a human subject’s body segments, and to process that using HMM in order to identify the subject’s instantaneous physical context. The key contribution of the proposed multi-modal approach is a significant extension of traditional uni-modal accelerometry in which only the individual body segment movements, without their relative proximities and orientation modalities, is used for physical context identification. Through real-life experiments with body mounted sensors it is demonstrated that while the unimodal accelerometry can be used for differentiating activityintensive postures such as walking and running, they are not effective for identification and differentiation between lowactivity postures such as sitting, standing, lying down, etc. In the proposed system, three sensor modalities namely acceleration, relative proximity and orientation are used for context identification through Hidden Markov Model (HMM) based stochastic processing. Controlled experiments using human subjects are carried out for evaluating the accuracy of the HMMidentified postures compared to a naïve threshold based mechanism over different human subjects
A 3 year old girl presented with abdominal distention since birth with developmental delay
This article has no abstract. The first 100 words appear below:
A 3 year old girl, 3rd issue of consanguineous parents from the Feni District (south part of Bangladesh) immunized as per EPI schedule presented at the outpatient department with the history of progressive abdominal distension and not growing well since birth. She had also the history of developmental delay and recurrent respiratory tract infection. Still she can not stand without the support and unable to make a sentence completely. Her brother died at 5 months of age with abdominal distention with unknown cause. She had no history of jaundice, hematemesis, melena, convulsion and craving for food
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