164 research outputs found
Crystal Structure and Chemistry of Topological Insulators
Topological surface states, a new kind of electronic state of matter, have
recently been observed on the cleaved surfaces of crystals of a handful of
small band gap semiconductors. The underlying chemical factors that enable
these states are crystal symmetry, the presence of strong spin orbit coupling,
and an inversion of the energies of the bulk electronic states that normally
contribute to the valence and conduction bands. The goals of this review are to
briefly introduce the physics of topological insulators to a chemical audience
and to describe the chemistry, defect chemistry, and crystal structures of the
compounds in this emergent field.Comment: Submitted to Journal of Materials Chemistry, 47 double spaced pages,
9 figure
Bi2Te1.6S1.4 - a Topological Insulator in the Tetradymite Family
We describe the crystal growth, crystal structure, and basic electrical
properties of Bi2Te1.6S1.4, which incorporates both S and Te in its Tetradymite
quintuple layers in the motif -[Te0.8S0.2]-Bi-S-Bi-[Te0.8S0.2]-. This material
differs from other Tetradymites studied as topological insulators due to the
increased ionic character that arises from its significant S content.
Bi2Te1.6S1.4 forms high quality crystals from the melt and is the S-rich limit
of the ternary Bi-Te-S {\gamma}-Tetradymite phase at the melting point. The
native material is n-type with a low resistivity; Sb substitution, with
adjustment of the Te to S ratio, results in a crossover to p-type and resistive
behavior at low temperatures. Angle resolved photoemission study shows that
topological surface states are present, with the Dirac point more exposed than
it is in Bi2Te3 and similar to that seen in Bi2Te2Se. Single crystal structure
determination indicates that the S in the outer chalcogen layers is closer to
the Bi than the Te, and therefore that the layers supporting the surface states
are corrugated on the atomic scale.Comment: To be published in Physical Review B Rapid Communications 16 douuble
spaced pages. 4 figures 1 tabl
Low carrier concentration crystals of the topological insulator BiTeSe
We report the characterization of BiTeSe crystals obtained by the
modified Bridgman and Bridgman-Stockbarger crystal growth techniques. X-ray
diffraction study confirms an ordered Se-Te distribution in the inner and outer
chalcogen layers, respectively, with a small amount of mixing. The crystals
displaying high resistivity () and low carrier
concentration (/cm) at 4 K were found in the central
region of the long Bridgman-Stockbarger crystal, which we attribute to very
small differences in defect density along the length of the crystal rod.
Analysis of the temperature dependent resistivities and Hall coefficients
reveals the possible underlying origins of the donors and acceptors in this
phase.Comment: 16 pages, 5 figures, accepted by PR
Advanced Differentiated Thyroid Cancer. A Complex Condition Needing a Tailored Approach
Differentiated thyroid cancers (DTCs) are slow-growing malignant tumours, including papillary and follicular carcinomas. Overall, prognosis is good, although it tends to worsen when local invasion occurs with bulky cervical nodes, or in the case of distant metastases. Surgery represents the main treatment for DTCs. However, radical excision is challenging and significant morbidity and functional loss can follow the treatment of the more advanced forms. Literature on advanced thyroid tumours, both differentiated and undifferentiated, does not provide clear and specific guidelines. This emerges the need for a tailored and multidisciplinary approach. In the present study, we report our single-centre experience of 111 advanced (local, regional, and distant) DTCs, investigating the rate of radical excision, peri-procedural and post-procedural complications, quality of life, persistence, recurrence rates, and survival rates. Results are critically appraised and compared to the existing published evidence review
Cholesterol Metabolism Is Required for Intracellular Hedgehog Signal Transduction In Vivo
We describe the rudolph mouse, a mutant with striking defects in both central nervous system and skeletal development. Rudolph is an allele of the cholesterol biosynthetic enzyme, hydroxysteroid (17-beta) dehydrogenase 7, which is an intriguing finding given the recent implication of oxysterols in mediating intracellular Hedgehog (Hh) signaling. We see an abnormal sterol profile and decreased Hh target gene induction in the rudolph mutant, both in vivo and in vitro. Reduced Hh signaling has been proposed to contribute to the phenotypes of congenital diseases of cholesterol metabolism. Recent in vitro and pharmacological data also indicate a requirement for intracellular cholesterol synthesis for proper regulation of Hh activity via Smoothened. The data presented here are the first in vivo genetic evidence supporting both of these hypotheses, revealing a role for embryonic cholesterol metabolism in both CNS development and normal Hh signaling
A neural extracellular matrix-based method for in vitrohippocampal neuron culture and dopaminergic differentiation of neural stem cells
Citizen science breathes new life into participatory agricultural research : A review
Participatory research can improve the efficiency, effectiveness, and scope of research processes, and foster social inclusion, empowerment and sustainability. Yet despite four decades of agricultural research institutions exploring and developing methods for participatory research, it has never become mainstream in the agricultural technology development cycle. Citizen science promises an innovative approach to participation in research, using the unique facilities of new digital technologies, but its potential in agricultural research participation has not been systematically probed. To this end, we conducted a critical literature review. We found that citizen science opens up four opportunities for creatively reshaping research: i) new possibilities for interdisciplinary collaboration, ii) rethinking configurations of socio-computational systems, iii) research on democratization of science more broadly, and iv) new accountabilities. Citizen science also brings a fresh perspective on the barriers to institutionalizing participation in the agricultural sciences. Specifically, we show how citizen science can reconfigure cost-motivation-accountability combinations using digital tools, open up a larger conceptual space of experimentation, and stimulate new collaborations. With appropriate and persistent institutional support and investment, citizen science can therefore have a lasting impact on how agricultural science engages with farming communities and wider society, and more fully realize the promises of participation
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