On the imaging of electron transport in semiconductor quantum structures by scanning-gate microscopy: successes and limitations

This paper presents a brief review of scanning-gate microscopy applied to the imaging of electron transport in buried semiconductor quantum structures. After an introduction to the technique and to some of its practical issues, we summarise a selection of its successful achievements found in the literature, including our own research. The latter focuses on the imaging of GaInAs-based quantum rings both in the low magnetic field Aharonov-Bohm regime and in the high-field quantum Hall regime. Based on our own experience, we then discuss in detail some of the limitations of scanning-gate microscopy. These include possible tip induced artefacts, effects of a large bias applied to the scanning tip, as well as consequences of unwanted charge traps on the conductance maps. We emphasize how special care must be paid in interpreting these scanning-gate images.Comment: Special issue on (nano)characterization of semiconductor materials and structure

La firma electrónica

Los cambios normativos que introdujo la Ley de Comercio Electrónico imponen modificaciones a figuras como la oferta misma, pues el uso de esta nueva herramienta debe producir tantos efectos como los manuscritos utilizados en el comercio. El rol determinante de la CNUDMI y el trabajo interno por comar vacíos normativos son objeto de estudio por los autores.

Cellular localisation by immunolabelling and transmission electron microscopy of oxaloacetate decarboxylase or its individual subunits synthesised in Escherichia coli

The genes oadGAB encoding the oxaloacetate decarboxylase γ, α and β-subunits from Klebsiella pneumoniae were expressed in Escherichia coli. Using different expression vectors, the entire enzyme or its individual subunits were synthesised. The expression was evidenced immunologically in whole cells with polyclonal antibodies raised against the purified oxaloacetate decarboxylase. The expressed α-subunit or a combination of a and β-subunits were shown to reside in the cytoplasm, while the entire oxaloacetate decarboxylase or a γα-complex were located mostly in the cytoplasmic membrane. Interestingly, overexpression of the γα-complex or the entire oxaloacetate decarboxylase in E. coli led to a significant immunogold labelling in the cytoplasm, indicating that the a-subunit was not completely complexed to the membrane-bound γ or βγ-subunit

On the Complexity of Finding Second-Best Abductive Explanations

While looking for abductive explanations of a given set of manifestations, an ordering between possible solutions is often assumed. The complexity of finding/verifying optimal solutions is already known. In this paper we consider the computational complexity of finding second-best solutions. We consider different orderings, and consider also different possible definitions of what a second-best solution is

On the Hyperbolicity of Lorenz Renormalization

We consider infinitely renormalizable Lorenz maps with real critical exponent $\alpha>1$ and combinatorial type which is monotone and satisfies a long return condition. For these combinatorial types we prove the existence of periodic points of the renormalization operator, and that each map in the limit set of renormalization has an associated unstable manifold. An unstable manifold defines a family of Lorenz maps and we prove that each infinitely renormalizable combinatorial type (satisfying the above conditions) has a unique representative within such a family. We also prove that each infinitely renormalizable map has no wandering intervals and that the closure of the forward orbits of its critical values is a Cantor attractor of measure zero.Comment: 63 pages; 10 figure

Delayed post-ischaemic neuroprotection following systemic neural stem cell transplantation involves multiple mechanisms

Recent evidence suggests that neural stem/precursor cells (NPCs) promote recovery in animal models with delayed neuronal death via a number of indirect bystander effects. A comprehensive knowledge of how transplanted NPCs exert their therapeutic effects is still lacking. Here, we investigated the effects of a delayed transplantation of adult syngenic NPCs—injected intravenously 72 h after transient middle cerebral artery occlusion—on neurological recovery, histopathology and gene expression. NPC-transplanted mice showed a significantly improved recovery from 18 days post-transplantation (dpt) onwards, which persisted throughout the study. A small percentage of injected NPCs accumulated in the brain, integrating mainly in the infarct boundary zone, where most of the NPCs remained undifferentiated up to 30 dpt. Histopathological analysis revealed a hitherto unreported very delayed neuroprotective effect of NPCs, becoming evident at 10 and 30 dpt. Tissue survival was associated with downregulation of markers of inflammation, glial scar formation and neuronal apoptotic death at both mRNA and protein levels. Our data highlight the relevance of very delayed degenerative processes in the stroke brain that are intimately associated with inflammatory and glial responses. These processes may efficaciously be antagonized by (stem) cell-based strategies at time-points far beyond established therapeutic windows for pharmacological neuroprotectio

Activity of comet 103P/Hartley 2 at the time of the EPOXI mission fly-by

Comet 103P/Hartley~2 was observed on Nov. 1-6, 2010, coinciding with the fly-by of the space probe EPOXI. The goal was to connect the large scale phenomena observed from the ground, with those at small scale observed from the spacecraft. The comet showed strong activity correlated with the rotation of its nucleus, also observed by the spacecraft. We report here the characterization of the solid component produced by this activity, via observations of the emission in two spectral regions where only grain scattering of the solar radiation is present. We show that the grains produced by this activity had a lifetime of the order of 5 hours, compatible with the spacecraft observations of the large icy chunks. Moreover, the grains produced by one of the active regions have a very red color. This suggests an organic component mixed with the ice in the grains.Comment: 11 pages, 7 figures, Icarus in pres