Emergent quantum confinement at topological insulator surfaces

Bismuth-chalchogenides are model examples of three-dimensional topological insulators. Their ideal bulk-truncated surface hosts a single spin-helical surface state, which is the simplest possible surface electronic structure allowed by their non-trivial $\mathbb{Z}_2$ topology. They are therefore widely regarded ideal templates to realize the predicted exotic phenomena and applications of this topological surface state. However, real surfaces of such compounds, even if kept in ultra-high vacuum, rapidly develop a much more complex electronic structure whose origin and properties have proved controversial. Here, we demonstrate that a conceptually simple model, implementing a semiconductor-like band bending in a parameter-free tight-binding supercell calculation, can quantitatively explain the entire measured hierarchy of electronic states. In combination with circular dichroism in angle-resolved photoemission (ARPES) experiments, we further uncover a rich three-dimensional spin texture of this surface electronic system, resulting from the non-trivial topology of the bulk band structure. Moreover, our study reveals how the full surface-bulk connectivity in topological insulators is modified by quantum confinement.Comment: 9 pages, including supplementary information, 4+4 figures. A high resolution version is available at http://www.st-andrews.ac.uk/~pdk6/pub_files/TI_quant_conf_high_res.pd

NF-κB mediated enhancement of potassium currents by the chemokine CXCL1/growth related oncogene in small diameter rat sensory neurons

<p>Abstract</p> <p>Background</p> <p>Inflammatory processes play important roles in both neuropathic and inflammatory pain states, but the effects of inflammation <it>per se </it>within the sensory ganglia are not well understood. The cytokine growth-related oncogene (GRO/KC; CXCL1) shows strong, rapid upregulation in dorsal root ganglion (DRG) in both nerve injury and inflammatory pain models. We examined the direct effects of GRO/KC on small diameter DRG neurons, which are predominantly nociceptive. Whole cell voltage clamp technique was used to measure voltage-activated potassium (K) currents in acutely cultured adult rat small diameter sensory neurons. Fluorescently labeled isolectin B4 (IB4) was used to classify cells as IB4-positive or IB4-negative.</p> <p>Results</p> <p>In IB4-negative neurons, voltage-activated K current densities of both transient and sustained components were increased after overnight incubation with GRO/KC (1.5 nM), without marked changes in voltage dependence or kinetics. The average values for the slow and fast decay time constants at 20 mV were unchanged by GRO/KC. The amplitude of the fast inactivating component increased significantly with no large shifts in the voltage dependence of inactivation. The increase in K currents was completely blocked by co-incubation with protein synthesis inhibitor cycloheximide (CHX) or NF-κB inhibitors pyrrolidine dithiocarbamate (PDTC) or quinazoline (6-Amino-4-(4-phenoxypheny lethylamino;QNZ). In contrast, the voltage-activated K current of IB4-positive neurons was unchanged by GRO/KC. GRO/KC incubation caused no significant changes in the expression level of eight selected voltage-gated K channel genes in quantitative PCR analysis.</p> <p>Conclusion</p> <p>The results suggest that GRO/KC has important effects in inflammatory processes via its direct actions on sensory neurons, and that activation of NF-κB is involved in the GRO/KC-induced enhancement of K currents.</p

The space group classification of topological band insulators

Topological band insulators (TBIs) are bulk insulating materials which feature topologically protected metallic states on their boundary. The existing classification departs from time-reversal symmetry, but the role of the crystal lattice symmetries in the physics of these topological states remained elusive. Here we provide the classification of TBIs protected not only by time-reversal, but also by crystalline symmetries. We find three broad classes of topological states: (a) Gamma-states robust against general time-reversal invariant perturbations; (b) Translationally-active states protected from elastic scattering, but susceptible to topological crystalline disorder; (c) Valley topological insulators sensitive to the effects of non-topological and crystalline disorder. These three classes give rise to 18 different two-dimensional, and, at least 70 three-dimensional TBIs, opening up a route for the systematic search for new types of TBIs.Comment: Accepted in Nature Physic

Emergence of non-centrosymmetric topological insulating phase in BiTeI under pressure

The spin-orbit interaction affects the electronic structure of solids in various ways. Topological insulators are one example where the spin-orbit interaction leads the bulk bands to have a non-trivial topology, observable as gapless surface or edge states. Another example is the Rashba effect, which lifts the electron-spin degeneracy as a consequence of spin-orbit interaction under broken inversion symmetry. It is of particular importance to know how these two effects, i.e. the non-trivial topology of electronic states and Rashba spin splitting, interplay with each other. Here we show, through sophisticated first-principles calculations, that BiTeI, a giant bulk Rashba semiconductor, turns into a topological insulator under a reasonable pressure. This material is shown to exhibit several unique features such as, a highly pressure-tunable giant Rashba spin splitting, an unusual pressure-induced quantum phase transition, and more importantly the formation of strikingly different Dirac surface states at opposite sides of the material.Comment: 5 figures are include

Recovering three-dimensional shape around a corner using ultrafast time-of-flight imaging

The recovery of objects obscured by scattering is an important goal in imaging and has been approached by exploiting, for example, coherence properties, ballistic photons or penetrating wavelengths. Common methods use scattered light transmitted through an occluding material, although these fail if the occluder is opaque. Light is scattered not only by transmission through objects, but also by multiple reflection from diffuse surfaces in a scene. This reflected light contains information about the scene that becomes mixed by the diffuse reflections before reaching the image sensor. This mixing is difficult to decode using traditional cameras. Here we report the combination of a time-of-flight technique and computational reconstruction algorithms to untangle image information mixed by diffuse reflection. We demonstrate a three-dimensional range camera able to look around a corner using diffusely reflected light that achieves sub-millimetre depth precision and centimetre lateral precision over 40 cm×40 cm×40 cm of hidden space.MIT Media Lab ConsortiumUnited States. Defense Advanced Research Projects Agency. Young Faculty AwardMassachusetts Institute of Technology. Institute for Soldier Nanotechnologies (Contract W911NF-07-D-0004

High Prevalence and Genetic Diversity of HCV among HIV-1 Infected People from Various High-Risk Groups in China

BACKGROUND: Co-infection with HIV-1 and HCV is a significant global public health problem and a major consideration for anti-HIV-1 treatment. HCV infection among HIV-1 positive people who are eligible for the newly launched nationwide anti-HIV-1 treatment program in China has not been well characterized. METHODOLOGY: A nationwide survey of HIV-1 positive injection drug uses (IDU), former paid blood donors (FBD), and sexually transmitted cases from multiple provinces including the four most affected provinces in China was conducted. HCV prevalence and genetic diversity were determined. We found that IDU and FBD have extremely high rates of HCV infection (97% and 93%, respectively). Surprisingly, people who acquired HIV-1 through sexual contact also had a higher rate of HCV infection (20%) than the general population. HIV-1 subtype and HCV genotypes were amazingly similar among FBD from multiple provinces stretching from Central to Northeast China. However, although patterns of overland trafficking of heroin and distinct HIV-1 subtypes could be detected among IDU, HCV genotypes of IDU were more diverse and exhibited significant regional differences. CONCLUSION: Emerging HIV-1 and HCV co-infection and possible sexual transmission of HCV in China require urgent prevention measures and should be taken into consideration in the nationwide antiretroviral treatment program

The chromosome content and genotype of two wheat cell lines and of their somatic fusion product with oat

Somatic hybridization seeks to genetically combine phylogenetically distant parents. An effective system has been established in bread wheat (Triticum aestivum L.) involving protoplasts from a non-totipotent cell line adapted to in vitro culture (T1) in combination with totipotent protoplasts harvested from embryogenic calli (T2). Here, we report the karyotype and genotype of T1 and T2. Line T1 carries nine A (A-genome of wheat), seven B (B-genome of wheat) and eight D (D-genome of wheat) genome chromosomes, while T2 cells have 12 A, 10 B and 12 D genome chromosomes. Rates of chromosome aberration in the B- and D-genomes were more than 25%, higher than in the A-genome. DNA deletion rates were 55.6% in T1 and 19.4% in T2, and DNA variation rates were 8.3% in T1 and 13.9% in T2. Rate of DNA elimination was B- > D- > A-genome in both T1 and T2. The same set of cytological and genetic assays was applied to a derivative of the somatic fusion between protoplasts of T1, T2 and oat (Avena sativa L.). The regenerant plants were near euploid with respect to their wheat complement. Six wheat chromosome arms—4AL, 3BS, 4BL, 3DS, 6DL and 7DL—carried small introgressed segments of oat chromatin. A genotypic analysis of the hybrid largely confirmed this cytologically-based diagnosis

Measles on the Edge: Coastal Heterogeneities and Infection Dynamics

Mathematical models can help elucidate the spatio-temporal dynamics of epidemics as well as the impact of control measures. The gravity model for directly transmitted diseases is currently one of the most parsimonious models for spatial epidemic spread. This model uses distance-weighted, population size-dependent coupling to estimate host movement and disease incidence in metapopulations. The model captures overall measles dynamics in terms of underlying human movement in pre-vaccination England and Wales (previously established). In spatial models, edges often present a special challenge. Therefore, to test the model's robustness, we analyzed gravity model incidence predictions for coastal cities in England and Wales. Results show that, although predictions are accurate for inland towns, they significantly underestimate coastal persistence. We examine incidence, outbreak seasonality, and public transportation records, to show that the model's inaccuracies stem from an underestimation of total contacts per individual along the coast. We rescue this predicted ‘edge effect’ by increasing coastal contacts to approximate the number of per capita inland contacts. These results illustrate the impact of ‘edge effects’ on epidemic metapopulations in general and illustrate directions for the refinement of spatiotemporal epidemic models