Electron-induced rippling in graphene

We show that the interaction between flexural phonons, when corrected by the exchange of electron-hole excitations, may place the graphene sheet very close to a quantum critical point characterized by the strong suppression of the bending rigidity of the membrane. Ripples arise then due to spontaneous symmetry breaking, following a mechanism similar to that responsible for the condensation of the Higgs field in relativistic field theories. In the presence of membrane tensions, ripple condensation may be reinforced or suppressed depending on the sign of the tension, following a zero-temperature buckling transition in which the order parameter is given essentially by the square of the gradient of the flexural phonon field.Comment: 4 pages, 3 figure

Educación para la sostenibilidad en las escuelas de negocios indias: informe de la situación

Sustainability issues, given their potential scale of impact and urgency, have captured the imagination of both corporations and academic institutions everywhere. This paper examines how such problems and their potential solutions have been incorporated into higher education, particularly business school education in India. With over 3,600 business schools in the public and private sector, business education in India has proliferated. However, students by and large still remain unexposed to sustainability and disaster management concepts in their curriculum.  The underlying factors for this include, lack of institutional capacity, issues related to faculty motivation and incentives, lack of recruiter interest and limited availability to high quality resource material.  Further, while several schools in India focus on sectors relevant to sustainability, inter-organizational linkages have not developed and business school generally operate independently.  This paper examines the way forward to deeply integrate sustainability principles into the core curriculum of business schools. Measures suggested include creating communities of practice among academia and industry, building a resource base of teaching materials for easy access by faculty, and several measures to strengthen institutional capacity.Debido a su alto potencial de impacto y urgencia, los asuntos relacionados con la sostenibilidad han capturado la imaginación tanto de las empresas privadas, como de las instituciones académicas en todas partes. Este artículo examina cómo dichos problemas y sus soluciones potenciales han sido incorporados en la educación superior, particularmente en la educación de negocios de India. Con unas 3,600 escuelas de negocios en los sectores público y privado, la educación de negocios en India ha proliferado. Sin embargo, los estudiantes, en general, siguen sin tener contacto con conceptos de sosteniblidad y gestión de desastres en sus currículos. Los factores subyacentes a esta situación incluyen la falta de capacidad institucional, los probelmas relacionados con la motivación e incentivos de los profesores universitarios, la falta de interés de los reclutadores y la limitada disponibilidad de material de consulta de alta calidad. Además, mientras que varias escuelas de negocios de India se enfocan en sectores relevantes para la sostenibilidad, los vínculos interorganizacionales no han sido desarrollados y las escuelas de negocios operan en general independientemente. Este artículo examina el camino a seguir para integrar principios de sostenibilidad de manera profunda a los currículos básicos de las escuelas de negocios. Las medidas que se sugieren incluyen la creación de comunidades prácticas entre la academia y la industria, la construcción de materiales pedagógicos de fácil acceso para profesores universitarios y diferentes medidas para fortalecer la capacidad institucional

Disorder-induced pseudodiffusive transport in graphene nanoribbons.

We study the transition from ballistic to diffusive and localized transport in graphene nanoribbons in the presence of binary disorder, which can be generated by chemical adsorbates or substitutional doping. We show that the interplay between the induced average doping (arising from the nonzero average of the disorder) and impurity scattering modifies the traditional picture of phase-coherent transport. Close to the Dirac point, intrinsic evanescent modes produced by the impurities dominate transport at short lengths giving rise to a regime analogous to pseudodiffusive transport in clean graphene, but without the requirement of heavily doped contacts. This intrinsic pseudodiffusive regime precedes the traditional ballistic, diffusive, and localized regimes. The last two regimes exhibit a strongly modified effective number of propagating modes and a mean free path which becomes anomalously large close to the Dirac point

Geometric phases in semiconductor spin qubits: Manipulations and decoherence

We describe the effect of geometric phases induced by either classical or quantum electric fields acting on single electron spins in quantum dots in the presence of spin-orbit coupling. On one hand, applied electric fields can be used to control the geometric phases, which allows performing quantum coherent spin manipulations without using high-frequency magnetic fields. On the other hand, fluctuating fields induce random geometric phases that lead to spin relaxation and dephasing, thus limiting the use of such spins as qubits. We estimate the decay rates due to piezoelectric phonons and conduction electrons in the circuit, both representing dominant electric noise sources with characteristically differing power spectra.Comment: 17 pages, 8 figures, published versio

Space VLBI Observations of 3C371

We present the first space VLBI observations of 3C~371, carried out at a frequency of 4.8 GHz. The combination of the high resolution provided by the orbiting antenna Highly Advanced Laboratory for Communications and Astronomy (HALCA) and the high sensitivity of the VLBA allows imaging of the jet of 3C~371 with an angular resolution of approximately 0.26 mas, which for this relatively nearby source corresponds to $\sim$ 0.4 h$^{-1}$ pc. Comparison between two epochs separated by 66 days reveals no apparent motions in the inner 7 mas jet structure above an upper limit of $\sim 1.4 h^{-1}$ c. This value, the absence of detectable counterjet emission from the presumably symmetric jet, plus the presence of extended double-lobe structure, are consistent with the knots in the jet being stationary features such as standing shocks. The jet intensity declines with the angular distance from the core as $\phi^{-1.68}$. This is more gradual than that derived for 3C~120, $\phi^{-1.86}$, for which there is evidence for strong intereactions between the jet and ambient medium. This suggests that in 3C~371 there is a greater level of {\it in situ} acceleration of electrons and amplification of magnetic field. We interpret sharp bends in the jet at sites of off-center knots as further evidence for the interaction between the jet and external medium, which may also be responsible for the generation of standing recollimation shocks. These recollimation shocks may be responsible for the presumably stationary components. The radio properties of 3C~371 are intermediate between those of other radio galaxies with bright cores and those of BL Lacertae objects.Comment: 5 pages, 4 figures. Accepted for publication in Ap

Hall-effect and resistivity measurements in CdTe and ZnTe at high pressure: Electronic structure of impurities in the zincblende phase and the semi-metallic or metallic character of the high-pressure phases

We carried out high-pressure resistivity and Hall-effect measurements in single crystals of CdTe and ZnTe up to 12 GPa. Slight changes of transport parameters in the zincblende phase of CdTe are consitent with the shallow character of donor impurities. Drastic changes in all the transport parameters of CdTe were found around 4 GPa, i.e. close to the onset of the cinnabar to rock-salt transition. In particular, the carrier concentration increases by more than five orders of magnitude. Additionally, an abrupt decrease of the resistivity was detected around 10 GPa. These results are discussed in comparison with optical, thermoelectric, and x-ray diffraction experiments. The metallic character of the Cmcm phase of CdTe is confirmed and a semi-metallic character is determined for the rock-salt phase. In zincblende ZnTe, the increase of the hole concentration by more than two orders of magnitude is proposed to be due to a deep-to-shallow transformation of the acceptor levels. Between 9 and 11 GPa, transport parameters are consistent with the semiconducting character of cinnabar ZnTe. A two orders of magnitude decrease of the resistivity and a carrier-type inversion occurs at 11 GPa, in agreement with the onset of the transition to the Cmcm phase of ZnTe. A metallic character for this phase is deduced.Comment: 20 pages, 4 figure

Vector cross product differential and difference equations in R^3 and in R^7

Through a matrix approach of the 2-fold vector cross product in R^3 and in R^7, some vector cross product di erential and di erence equations are studied. Either the classical theory or convenient Drazin inverses, of elements belonging to the class of index 1 matrices, are applied.MTM2017-83506-C2-2-P (Spain)info:eu-repo/semantics/publishedVersio