2,389 research outputs found
Spin Polarization and Transport of Surface States in the Topological Insulators Bi2Se3 and Bi2Te3 from First Principles
We investigate the band dispersion and the spin texture of topologically
protected surface states in the bulk topological insulators Bi2Se3 and Bi2Te3
by first-principles methods. Strong spin-orbit entanglement in these materials
reduces the spin-polarization of the surface states to ~50% in both cases; this
reduction is absent in simple models but of important implications to
essentially any spintronic application. We propose a way of controlling the
magnitude of spin polarization associated with a charge current in thin films
of topological insulators by means of an external electric field. The proposed
dual-gate device configuration provides new possibilities for electrical
control of spin.Comment: 4+ pages, 3 figure
Harnessing Rural Radio for Climate Change Mitigation and Adaptation in the Philippines
The working paper documents the pilot rural radio campaign, dubbed as 'Climate Change i-Broadkas Mo', implemented by the CGIAR Research Program on Climate Change, Agriculture and Food Security in Southeast Asia (CCAFS SEA) and the Philippine Federation of Rural Broadcasters (PFRB) in strategic regions of the Philippines from 2015 to 2018. The radio campaign provided PFRB affiliated broadcasters with scripts and ready-to-be-aired (RTBA) interviews on climate-smart agriculture. The lessons learned from the project can be used to enhance the capacities of rural broadcasters on climate change reporting and to create a demand for radio-based distance learning, not only in Northern Philippines, but in similar regions in Southeast Asia
Many-body interactions in quasi-freestanding graphene
The Landau-Fermi liquid picture for quasiparticles assumes that charge
carriers are dressed by many-body interactions, forming one of the fundamental
theories of solids. Whether this picture still holds for a semimetal like
graphene at the neutrality point, i.e., when the chemical potential coincides
with the Dirac point energy, is one of the long-standing puzzles in this field.
Here we present such a study in quasi-freestanding graphene by using
high-resolution angle-resolved photoemission spectroscopy. We see the
electron-electron and electron-phonon interactions go through substantial
changes when the semimetallic regime is approached, including renormalizations
due to strong electron-electron interactions with similarities to marginal
Fermi liquid behavior. These findings set a new benchmark in our understanding
of many-body physics in graphene and a variety of novel materials with Dirac
fermions.Comment: PNAS 2011 ; published ahead of print June 27, 201
Retinal gene therapy with a large MYO7A cDNA using adeno-associated virus.
Usher 1 patients are born profoundly deaf and then develop retinal degeneration. Thus they are readily identified before the onset of retinal degeneration, making gene therapy a viable strategy to prevent their blindness. Here, we have investigated the use of adeno-associated viruses (AAVs) for the delivery of the Usher 1B gene, MYO7A, to retinal cells in cell culture and in Myo7a-null mice. MYO7A cDNA, under control of a smCBA promoter, was packaged in single AAV2 and AAV5 vectors and as two overlapping halves in dual AAV2 vectors. The 7.9-kb smCBA-MYO7A exceeds the capacity of an AAV vector; packaging of such oversized constructs into single AAV vectors may involve fragmentation of the gene. Nevertheless, the AAV2 and AAV5 single vector preparations successfully transduced photoreceptor and retinal pigment epithelium cells, resulting in functional, full-length MYO7A protein and correction of mutant phenotypes, suggesting successful homologous recombination of gene fragments. With discrete, conventional-sized dual AAV2 vectors, full-length MYO7A was detected, but the level of protein expression was variable, and only a minority of cells showed phenotype correction. Our results show that MYO7A therapy with AAV2 or AAV5 single vectors is efficacious; however, the dual AAV2 approach proved to be less effective
Doping effects on the electronic and structural properties of CoO2: An LSDA+U study
A systematic LSDA+U study of doping effects on the electronic and structural
properties of single layer CoO2 is presented. Undoped CoO2 is a charge transfer
insulator within LSDA+U and a metal with a high density of states (DOS) at the
Fermi level within LSDA. (CoO2), on the other hand, is a band
insulator with a gap of 2.2 eV. Systems with fractional doping are metals if no
charge orderings are present. Due to the strong interaction between the doped
electron and other correlated Co d electrons, the calculated electronic
structure of (CoO2) depends sensitively on the doping level x. Zone
center optical phonon energies are calculated under the frozen phonon
approximation and are in good agreement with measured values. Softening of the
phonon at doping x ~0.25 seems to indicate a strong electron-phonon
coupling in this system. Possible intemediate spin states of Co ions, Na
ordering, as well as magnetic and charge orderings in this system are also
discussed.Comment: 11 pages, 12 figure
How are “Atypical” Sulfite Dehydrogenases Linked to Cell Metabolism? Interactions between the SorT Sulfite Dehydrogenase and Small Redox Proteins
Sulfite dehydrogenases (SDHs) are enzymes that catalyze the oxidation of the toxic and mutagenic compound sulfite to sulfate, thereby protecting cells from adverse effects associated with sulfite exposure. While some bacterial SDHs that have been characterized to date are able to use cytochrome c as an electron acceptor, the majority of these enzymes prefer ferricyanide as an electron acceptor and have therefore been termed “atypical” SDHs. Identifying the natural electron acceptor of these enzymes, however, is crucial for understanding how the “atypical” SDHs are integrated into cell metabolism. The SorT sulfite dehydrogenase from Sinorhizobium meliloti is a representative of this enzyme type and we have investigated the interactions of SorT with two small redox proteins, a cytochrome c and a Cu containing pseudoazurin, that are encoded in the same operon and are co-transcribed with the sorT gene. Both potential acceptor proteins have been purified and characterized in terms of their biochemical and electrochemical properties, and interactions and enzymatic studies with both the purified SorT sulfite dehydrogenase and components of the respiratory chain have been carried out. We were able to show for the first time that an “atypical” sulfite dehydrogenase can couple efficiently to a cytochrome c isolated from the same organism despite being unable to efficiently reduce horse heart cytochrome c, however, at present the role of the pseudoazurin in SorT electron transfer is unclear, but it is possible that it acts as an intermediate electron shuttle between. The SorT system appears to couple directly to the respiratory chain, most likely to a cytochrome oxidase
- …