2,913 research outputs found
Bilayer graphene under pressure: Electron-hole Symmetry Breaking, Valley Hall Effect, and Landau Levels
The electronic structure of bilayer graphene under pressure develops very
interesting features with an enhancement of the trigonal warping and a
splitting of the parabolic touching bands at the K point of the reciprocal
space into four Dirac cones, one at K and three along the T symmetry lines. As
pressure is increased, these cones separate in reciprocal space and in energy,
breaking the electron-hole symmetry. Due to their energy separation, their
opposite Berry curvature can be observed in valley Hall effect experiments and
in the structure of the Landau levels. Based on the electronic structure
obtained by Density Functional Theory, we develop a low energy Hamiltonian that
describes the effects of pressure on measurable quantities such as the Hall
conductivity and the Landau levels of the system.Comment: 11 pages, 9 figure
Magnetic Structure of Hydrogen Induced Defects on Graphene
Using density functional theory (DFT), Hartree-Fock, exact diagonalization,
and numerical renormalization group methods we study the electronic structure
of diluted hydrogen atoms chemisorbed on graphene. A comparison between DFT and
Hartree-Fock calculations allows us to identify the main characteristics of the
magnetic structure of the defect. We use this information to formulate an
Anderson-Hubbard model that captures the main physical ingredients of the
system, while still allowing a rigorous treatment of the electronic
correlations. We find that the large hydrogen-carbon hybridization puts the
structure of the defect half-way between the one corresponding to an adatom
weakly coupled to pristine graphene and a carbon vacancy. The impurity's
magnetic moment leaks into the graphene layer where the electronic correlations
on the C atoms play an important role in stabilizing the magnetic solution.
Finally, we discuss the implications for the Kondo effect.Comment: 10 pages, 10 fig
Inter-limb asymmetry during rehabilitation understanding formulas and monitoring the "magnitude" and "direction"
This article outlines how asymmetry can be used during the rehabilitation process for practitioners, and the importance of both the magnitude and direction of an inter-limb asymmetry
Fairness-aware Optimal Graph Filter Design
Graphs are mathematical tools that can be used to represent complex
real-world interconnected systems, such as financial markets and social
networks. Hence, machine learning (ML) over graphs has attracted significant
attention recently. However, it has been demonstrated that ML over graphs
amplifies the already existing bias towards certain under-represented groups in
various decision-making problems due to the information aggregation over biased
graph structures. Faced with this challenge, here we take a fresh look at the
problem of bias mitigation in graph-based learning by borrowing insights from
graph signal processing. Our idea is to introduce predesigned graph filters
within an ML pipeline to reduce a novel unsupervised bias measure, namely the
correlation between sensitive attributes and the underlying graph connectivity.
We show that the optimal design of said filters can be cast as a convex problem
in the graph spectral domain. We also formulate a linear programming (LP)
problem informed by a theoretical bias analysis, which attains a closed-form
solution and leads to a more efficient fairness-aware graph filter. Finally,
for a design whose degrees of freedom are independent of the input graph size,
we minimize the bias metric over the family of polynomial graph convolutional
filters. Our optimal filter designs offer complementary strengths to explore
favorable fairness-utility-complexity tradeoffs. For performance evaluation, we
conduct extensive and reproducible node classification experiments over
real-world networks. Our results show that the proposed framework leads to
better fairness measures together with similar utility compared to
state-of-the-art fairness-aware baselines.Comment: 12 pages, 3 figures, 9 tables. arXiv admin note: text overlap with
arXiv:2303.1145
Effects of an eccentric inner Jupiter on the dynamical evolution of icy body reservoirs in a planetary scattering scenario
Aims. We analyze the dynamics of small body reservoirs under the effects of an eccentric inner giant planet resulting from a planetary scattering event around a 0.5 M⊙ star. Methods. First, we used a semi-analytical model to define the properties of the protoplanetary disk that lead to the formation of three Jupiter-mass planets. Then, we carried out N-body simulations assuming that the planets are close to their stability limit together with an outer planetesimal disk. In particular, the present work focused on the analysis of N-body simulations in which a single Jupiter-mass planet survives after the dynamical instability event. Results. Our simulations produce outer small body reservoirs with particles on prograde and retrograde orbits, and other ones whose orbital plane flips from prograde to retrograde and back again along their evolution (“Type-F particles”). We find strong correlations between the inclination i and the ascending node longitude Ω of Type-F particles. First, Ω librates around 90° or/and 270°. This property represents a necessary and sufficient condition for the flipping of an orbit. Moreover, the libration periods of i and Ω are equal and they are out to phase by a quarter period. We also remark that the larger the libration amplitude of i, the larger the libration amplitude of Ω. We analyze the orbital parameters of Type-F particles immediately after the instability event (post IE orbital parameters), when a single Jupiter-mass planet survives in the system. Our results suggest that the orbit of a particle can flip for any value of its post IE eccentricity, although we find only two Type-F particles with post IE inclinations i ≲ 17°. Finally, our study indicates that the minimum value of the inclination of the Type-F particles in a given system decreases with an increase in the eccentricity of the giant planet.Fil: Zanardi, Macarena. Universidad Nacional de La Plata. Facultad de Ciencias AstronĂłmicas y GeofĂsicas; Argentina. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - La Plata. Instituto de AstrofĂsica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias AstronĂłmicas y GeofĂsicas. Instituto de AstrofĂsica La Plata; ArgentinaFil: de Elia, Gonzalo Carlos. Universidad Nacional de La Plata. Facultad de Ciencias AstronĂłmicas y GeofĂsicas; Argentina. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - La Plata. Instituto de AstrofĂsica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias AstronĂłmicas y GeofĂsicas. Instituto de AstrofĂsica La Plata; ArgentinaFil: Di Sisto, Romina Paula. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - La Plata. Instituto de AstrofĂsica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias AstronĂłmicas y GeofĂsicas. Instituto de AstrofĂsica La Plata; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias AstronĂłmicas y GeofĂsicas; ArgentinaFil: Naoz, S.. University of California at Los Angeles; Estados UnidosFil: Li, G.. Harvard-Smithsonian Center for Astrophysics; Estados UnidosFil: Guilera, O. M.. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - La Plata. Instituto de AstrofĂsica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias AstronĂłmicas y GeofĂsicas. Instituto de AstrofĂsica La Plata; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias AstronĂłmicas y GeofĂsicas; ArgentinaFil: Brunini, A.. Universidad Nacional de la Patagonia Austral; Argentin
Unitarity bounds and RG flows in time dependent quantum field theory
We generalize unitarity bounds on operator dimensions in conformal field
theory to field theories with spacetime dependent couplings. Below the energy
scale of spacetime variation of the couplings, their evolution can strongly
affect the physics, effectively shifting the infrared operator scaling and
unitarity bounds determined from correlation functions in the theory. We
analyze this explicitly for large- double-trace flows, and connect these to
UV complete field theories. One motivating class of examples comes from our
previous work on FRW holography, where this effect explains the range of
flavors allowed in the dual, time dependent, field theory.Comment: 38 page
Effects of combined strength and power training on physical performance and interlimb asymmetries in adolescent female soccer players
Purpose: This study examined the effects of an 8-week combined strength and power training (CSPT) intervention on physical performance and inter-limb asymmetries in adolescent female soccer players.
Methods: Thirty-seven adolescent female soccer players (age: 16.1±1.1 yrs) were randomly assigned to a control (CG, n = 18) and experimental group (EG, n = 19). EG performed CSPT twice a week, which consisted of strength and power exercises that trained the major muscles of the lower body and trunk musculature. Pre- and post-intervention tests included unilateral and bilateral horizontal and countermovement jump tests, a 40-m sprint test (10 and 30-m split times), a 10-m sprint with a 180º change of direction (COD) test and a multiple COD test (V-cut test). Asymmetries were also analyzed in the unilateral tests.
Results: Significant group by time interaction of the improvement between pre and post-tests were observed for speed (Effect size (ES): -1.30 to -1.16) and COD tests (ES: -0.62 to -0.61) but not in jumping (ES: -0.09 to 0.28) and inter-limb asymmetries tests (ES: -0.13 to 0.57). Conclusions: The short-term in-season CSPT program induced greater speed and COD performance improvements compared to soccer training alone in adolescent female soccer players
- …