A method of recognition of hand drawn line patterns

Method of recognition of hand drawn line pattern

Mechanism for current saturation and energy dissipation in graphene transistors

From a combination of careful and detailed theoretical and experimental studies, we demonstrate that the Boltzmann theory including all scattering mechanisms gives an excellent account, with no adjustable parameters, of high electric field transport in single as well as double-oxide graphene transistors. We further show unambiguously that scattering from the substrate and superstrate surface optical (SO) phonons governs the high field transport and heat dissipation over a wide range of experimentally relevant parameters. Models that neglect SO phonons altogether or treat them in a simple phenomenological manner are inadequate. We outline possible strategies for achieving higher current and complete saturation in graphene devices.Comment: revtex, 5 pages, 3 figures, to appear in Phys. Rev. Lett

Dipole trap model for the metallic state in gated silicon-inversion layers

In order to investigate the metallic state in high-mobility Si-MOS structures, we have further developed and precised the dipole trap model which was originally proposed by B.L. Altshuler and D.L. Maslov [Phys. Rev. Lett.\ 82, 145 (1999)]. Our additional numerical treatment enables us to drop several approximations and to introduce a limited spatial depth of the trap states inside the oxide as well as to include a distribution of trap energies. It turns out that a pronounced metallic state can be caused by such trap states at appropriate energies whose behavior is in good agreement with experimental observations.Comment: 16 pages, 10 figures, submitte

Shockley-Ramo theorem and long-range photocurrent response in gapless materials

Scanning photocurrent maps of gapless materials, such as graphene, often exhibit complex patterns of hot spots positioned far from current-collecting contacts. We develop a general framework that helps to explain the unusual features of the observed patterns, such as the directional effect and the global character of photoresponse. We show that such a response is captured by a simple Shockley-Ramo-type approach. We examine specific examples and show that the photoresponse patterns can serve as a powerful tool to extract information about symmetry breaking, inhomogeneity, chirality, and other local characteristics of the system.Comment: 7 pgs, 3 fg

Cyclic loading behavior of saturated sand with different fabrics

The undrained response of saturated sand under cyclic loading has been a subject of long-standing interest. Although it has been recognized for long, the effect of fabric remians a critical problem that is not yet well understood. In this paper, cyclic triaxial test results from a strategically designed experimental program are presented to demonstrate how significant the effect of fabric can be on the undrained cyclic behavior of sand under different combinations of initial state and initial stress conditions. A significant finding of the study is that loose sand specimens, prepared by different reconstitution methods and thus having different initial fabrics, exhibit similar failure modes under the conventional symmetrical loading condition, but they show distinct failure patterns under the non-symmetrical cyclic loading condition. A qualitative explanation of the macroscopic observations is also proposed from a microscopic perspective, which sheds light on the mechanisms involved. RÉSUMÉ : Le sujet de la réponse du sable saturé sous chargement cyclique non drainé a suscité de l’intérêt depuis longtemps. Cependant il est reconnu que l’effet de la structure reste un problème clef qui n’est pas encore bien compris. Dans cet article, les résultats d’essais triaxiaux cycliques faits dans le cadre d’un programme expérimental conçu spécialement sont présentés afin de démontrer la signifiance de l’effet de structure sur le comportement non drainé du sable soumis à différentes combinaisons d’état initial et contraintes initiales. L’un des résultats les plus importants est que les spécimens de sable lâche préparés par des methods différentes de reconstitution, et donc avec des structures initiales différentes, montrent les mêmes modes de rupture sous chargement symétrique, mais différents schémas de rupture sous chargement non symétrique. Une explication qualitative de ces observations faites à l’échelle macroscopique est donnée d’un point de vue microscopique, éclairant les mécanismes impliqués.postprin