2,158 research outputs found
Impurities and electronic localization in graphene bilayers
We analyze the electronic properties of bilayer graphene with Bernal stacking
and a low concentration of adatoms. Assuming that the host bilayer lies on top
of a substrate, we consider the case where impurities are adsorbed only on the
upper layer. We describe non-magnetic impurities as a single orbital hybridized
with carbon's pz states. The effect of impurity doping on the local density of
states with and without a gated electric field perpendicular to the layers is
analyzed. We look for Anderson localization in the different regimes and
estimate the localization length. In the biased system, the field induced gap
is partially filled by strongly localized impurity states. Interestingly, the
structure, distribution and localization length of these states depend on the
field polarization.Comment: 7 pages, 6 figure
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
High-precision analysis of binary stars with planets. I. Searching for condensation temperature trends in the HD 106515 system
We explore the probable chemical signature of planet formation in the
remarkable binary system HD 106515. The A star hosts a massive long-period
planet with 9 MJup detected by radial velocity. We also refine stellar and
planetary parameters by using non-solar-scaled opacities when modeling the
stars. Methods. We carried out a simultaneous determination of stellar
parameters and abundances, by applying for the first time non-solar-scaled
opacities in this binary system, in order to reach the highest possible
precision. Results. The stars A and B in the binary system HD 106515 do not
seem to be depleted in refractory elements, which is different when comparing
the Sun with solar-twins. Then, the terrestrial planet formation would have
been less efficient in the stars of this binary system. Together with HD
80606/7, this is the second binary system which does not seem to present a
(terrestrial) signature of planet formation, and hosting both systems an
eccentric giant planet. This is in agreement with numerical simulations, where
the early dynamical evolution of eccentric giant planets clear out most of the
possible terrestrial planets in the inner zone. We refined the stellar mass,
radius and age for both stars and found a notable difference of 78% in R
compared to previous works. We also refined the planet mass to mp sini = 9.08
+/- 0.20 MJup, which differs by 6% compared with literature. In addition, we
showed that the non-solar-scaled solution is not compatible with the classical
solar-scaled method, and some abundance differences are comparable to NLTE or
GCE effects specially when using the Sun as reference. Then, we encourage the
use of non-solar-scaled opacities in high-precision studies such as the
detection of Tc trends.[abridged]Comment: 9 pages, 10 figures, A&A accepted. arXiv admin note: text overlap
with arXiv:1507.0812
Analytic aspects of evolution algebras
We prove that every evolution algebra A is a normed algebra, for an l1-norm defined in terms of a fixed natural basis. We further show that a normed evolution algebra A is a Banach algebra if and only if A=A1âA0, where A1 is finite-dimensional and A0 is a zero-product algebra. In particular, every nondegenerate Banach evolution algebra must be finite-dimensional and the completion of a normed evolution algebra is therefore not, in general, an evolution algebra. We establish a sufficient condition for continuity of the evolution operator LB of A with respect to a natural basis B, and we show that LB need not be continuous. Moreover, if A is finite-dimensional and B={e1,âŠ,en}, then LB is given by Le, where e=âiei and La is the multiplication operator La(b)=ab, for bâA. We establish necessary and sufficient conditions for convergence of (Lna(b))n, for all bâA, in terms of the multiplicative spectrum Ïm(a) of a. Namely, (Lna(b))n converges, for all bâA, if and only if Ïm(a)âÎâȘ{1} and Îœ(1,a)â€1, where Îœ(1,a) denotes the index of 1 in the spectrum of La.The second author acknowledges funding from: the Distinguished Visitor Programme of the
School of Mathematics and Statistics of University College Dublin, Project MTM2016-76327-
C3-2-P of the Spanish Ministry of Economy, Industry and Competitiveness, Research Group
FQM 199 of the Junta de AndalucĂa and European Union FEDER support
Normative Influences on Adolescentsâ Self-Reported Pro-Environmental Behaviors: The Role of Parents and Friends
Pro-environmental behavioral patterns are influenced by relevant othersâ actions and expectations. Studies about the intergenerational transmission of environmentalism have demonstrated that parents play a major role in their childrenâs pro-environmental actions. However, little is known about how other social agents may shape youthâs environmentalism. This cross-sectional study concentrates on the role that parents and peers have in the regulation of 12- to 19-year-oldsâ pro-environmental behaviors. We also consider the common response bias effect by examining the associations between parents, peers, and adolescentsâ pro-environmentalism in two independent data sets. Data Set 1 (N = 330) includes adolescentsâ perceptions of relevant othersâ behaviors. Data Set 2 (N = 152) includes relevant othersâ self-reported pro-environmental behavior. Our results show that parentsâ and peersâ descriptive and injunctive norms have a direct effect on adolescentsâ pro-environmental behavior and an indirect one, through personal norms. Adolescents seem to be accurate in the perception of their close onesâ environmental actions
Experimental approval of the extended flat bands and gapped subbands in rhombohedral multilayer graphene
Graphene layers are known to stack in two stable configurations, namely ABA
or ABC stacking, with drastically distinct electronic properties. Unlike the
ABA stacking, little has been done to experimentally investigate the electronic
properties of ABC graphene multilayers. Here, we report the first magneto
optical study of a large ABC domain in a graphene multilayers flake, with ABC
sequences exceeding 17 graphene sheets. The ABC-stacked multilayers can be
fingerprinted with a characteristic electronic Raman scattering response, which
persists even at room temperatures. Tracing the magnetic field evolution of the
inter Landau level excitations from this domain gives strong evidence to the
existence of a dispersionless electronic band near the Fermi level,
characteristic of such stacking. Our findings present a simple yet powerful
approach to probe ABC stacking in graphene multilayer flakes, where this highly
degenerated band appears as an appealing candidate to host strongly correlated
states.Comment: 8 pages, 4 figure
Quiste Ăłseo aneurismĂĄtico postraumĂĄtico
Se presenta un caso de quiste Ăłseo aneurismĂĄtico de localizaciĂłn superficial
en la cara externa del hĂșmero. El tumor fue tratado mediante la resecciĂłn en bloque
y relleno con hueso liofilizado. La evolución ha sido satisfactoria no habiéndose presentado
recurrencia del tumor y considerĂĄndose el enfermo completamente curado a los tres
años de realizado el tratamiento. Se establece una relación próxima en el tiempo con un
episodio traumĂĄtico, que se considera desencadenante del desarrollo tumoral y de la sintomatologĂa.A case of aneurysmal bone cyst located at the lateral periosteal surface of the humeral diaphysis is presented. The patient was treated by in-bloc tumor resection and grafting of liophylized bone. The outcome has been satisfactory without tumor recurrence. Three years after surgery the patients remains free from disease. A relationship between previous trauma and the development of tumor could be found
Fractura bipolar de clavĂcula
Se presenta un caso de fractura que afecta a ambos extremos de la clavĂcula.
Fractura tipo II de Neer del fragmento distal y fractura del extremo esternal de la clavĂcula. Se
realizĂł tratamiento quirĂșrgico mediante reducciĂłn abierta y osteosĂntesis con agujas de Kirschner
en ambas. El resultado a largo plazo ha sido satisfactorio cosmética y funcionalmente.A case of bipolar fracture affecting both ends of the clavicle is reported. The
lesion consisted of a Neer type II fracture at the distal segment and a fracture close to the proximal
joint with the sternum. Surgical treatment was carried out by open reduction and Kirschner
wire fixation stabilizing both sides. At follow up, clinical and cosmetic results are
satisfactories
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