439 research outputs found
Reversible modifications of linear dispersion - graphene between boron nitride monolayers
Electronic properties of the graphene layer sandwiched between two hexagonal
boron nitride sheets have been studied using the first-principles calculations
and the minimal tight-binding model. It is shown that for the ABC-stacked
structure in the absence of external field the bands are linear in the vicinity
of the Dirac points as in the case of single-layer graphene. For certain atomic
configuration, the electric field effect allows opening of a band gap of over
230 meV. We believe that this mechanism of energy gap tuning could
significantly improve the characteristics of graphene-based field-effect
transistors and pave the way for future electronic applications.Comment: 5 pages, v2 with slightly modified introduction and summar
QED2+1 in graphene: symmetries of Dirac equation in 2+1 dimensions
It is well-known that the tight-binding Hamiltonian of graphene describes the
low-energy excitations that appear to be massless chiral Dirac fermions. Thus,
in the continuum limit one can analyze the crystal properties using the
formalism of quantum electrodynamics in 2+1 dimensions (QED2+1) which provides
the opportunity to verify the high energy physics phenomena in the condensed
matter system. We study the symmetry properties of 2+1-dimensional Dirac
equation, both in the non-interacting case and in the case with constant
uniform magnetic field included in the model. The maximal symmetry group of the
massless Dirac equation is considered by putting it in the Jordan block form
and determining the algebra of operators leaving invariant the subspace of
solutions. It is shown that the resulting symmetry operators expressed in terms
of Dirac matrices cannot be described exclusively in terms of gamma matrices
(and their products) entering the corresponding Dirac equation. It is a
consequence of the reducibility of the considered representation in contrast to
the 3+1-dimensional case. Symmetry algebra is demonstrated to be a direct sum
of two gl(2,C) algebras plus an eight-dimensional abelian ideal. Since the
matrix structure which determines the rotational symmetry has all required
properties of the spin algebra, the pseudospin related to the sublattices (M.
Mecklenburg and B. C. Regan, Phys. Rev. Lett. 106, 116803 (2011)) gains the
character of the real angular momentum, although the degrees of freedom
connected with the electron's spin are not included in the model. This seems to
be graphene's analogue of the phenomenon called "spin from isospin" in high
energy physics
Quadratic integrals of motions for the systems of identical particles-quantum case
The quantum dynamical systems of identical particles admitting an additional
integral quadratic in momenta are considered. It is found that an appropriate
ordering procedure exists which allows to convert the classical integrals into
their quantum counterparts. The relation to the separation of variables in
Schroedinger equation is discussed.Comment: 6 pages, no figure
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A computer adaptive measure of delay discounting
Delay discounting has been linked to important behavioral, health, and social outcomes, including academic achievement, social functioning and substance use, but thoroughly measuring delay discounting is tedious and time consuming. We develop and consistently validate an efficient and psychometrically sound computer adaptive measure of discounting. First, we develop a binary search–type algorithm to measure discounting using a large international data set of 4,190 participants. Using six independent samples ( = 1,550), we then present evidence of concurrent validity with two standard measures of discounting and a measure of discounting real rewards, convergent validity with addictive behavior, impulsivity, personality, survival probability; and divergent validity with time perspective, life satisfaction, age and gender. The new measure is considerably shorter than standard questionnaires, includes a range of time delays, can be applied to multiple reward magnitudes, shows excellent concurrent, convergent, divergent, and discriminant validity—by showing more sensitivity to effects of smoking behavior on discounting.Nehru Trust for Cambridge University, Cambridge Overseas Trus
-Deformation of Poincar\'e Superalgebra with Classical Lorentz Subalgebra and its Graded Bicrossproduct Structure
The -deformed Poincar{\'e} superalgebra written in Hopf
superalgebra form is transformed to the basis with classical Lorentz subalgebra
generators. We show that in such a basis the -deformed Poincare
superalgebra can be written as graded bicrossproduct. We show that the
-deformed superalgebra acts covariantly on -deformed
chiral superspace.Comment: 13 pages, late
Computational personality recognition in social media
A variety of approaches have been recently proposed to automatically infer users' personality from their user generated content in social media. Approaches differ in terms of the machine learning algorithms and the feature sets used, type of utilized footprint, and the social media environment used to collect the data. In this paper, we perform a comparative analysis of state-of-the-art computational personality recognition methods on a varied set of social media ground truth data from Facebook, Twitter and YouTube. We answer three questions: (1) Should personality prediction be treated as a multi-label prediction task (i.e., all personality traits of a given user are predicted at once), or should each trait be identified separately? (2) Which predictive features work well across different on-line environments? (3) What is the decay in accuracy when porting models trained in one social media environment to another
Molecular basis of tRNA recognition by the Elongator complex
The highly conserved Elongator complex modifies transfer RNAs (tRNAs) in their wobble base position, thereby regulating protein synthesis and ensuring proteome stability. The precise mechanisms of tRNA recognition and its modification reaction remain elusive. Here, we show cryo–electron microscopy structures of the catalytic subcomplex of Elongator and its tRNA-bound state at resolutions of 3.3 and 4.4 Å. The structures resolve details of the catalytic site, including the substrate tRNA, the iron-sulfur cluster, and a SAM molecule, which are all validated by mutational analyses in vitro and in vivo. tRNA binding induces conformational rearrangements, which precisely position the targeted anticodon base in the active site. Our results provide the molecular basis for substrate recognition of Elongator, essential to understand its cellular function and role in neurodegenerative diseases and cancer
Elimination of Schistosomiasis Transmission in Zanzibar: Baseline Findings before the Onset of a Randomized Intervention Trial.
Gaining and sustaining control of schistosomiasis and, whenever feasible, achieving local elimination are the year 2020 targets set by the World Health Organization. In Zanzibar, various institutions and stakeholders have joined forces to eliminate urogenital schistosomiasis within 5 years. We report baseline findings before the onset of a randomized intervention trial designed to assess the differential impact of community-based praziquantel administration, snail control, and behavior change interventions. In early 2012, a baseline parasitological survey was conducted in ∼20,000 people from 90 communities in Unguja and Pemba. Risk factors for schistosomiasis were assessed by administering a questionnaire to adults. In selected communities, local knowledge about schistosomiasis transmission and prevention was determined in focus group discussions and in-depths interviews. Intermediate host snails were collected and examined for shedding of cercariae. The baseline Schistosoma haematobium prevalence in school children and adults was 4.3% (range: 0-19.7%) and 2.7% (range: 0-26.5%) in Unguja, and 8.9% (range: 0-31.8%) and 5.5% (range: 0-23.4%) in Pemba, respectively. Heavy infections were detected in 15.1% and 35.6% of the positive school children in Unguja and Pemba, respectively. Males were at higher risk than females (odds ratio (OR): 1.45; 95% confidence interval (CI): 1.03-2.03). Decreasing adult age (OR: 1.04; CI: 1.02-1.06), being born in Pemba (OR: 1.48; CI: 1.02-2.13) or Tanzania (OR: 2.36; CI: 1.16-4.78), and use of freshwater (OR: 2.15; CI: 1.53-3.03) showed higher odds of infection. Community knowledge about schistosomiasis was low. Only few infected Bulinus snails were found. The relatively low S. haematobium prevalence in Zanzibar is a promising starting point for elimination. However, there is a need to improve community knowledge about disease transmission and prevention. Control measures tailored to the local context, placing particular attention to hot-spot areas, high-risk groups, and individuals, will be necessary if elimination is to be achieved
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