Thermoelectric prospects of nanomaterials with spin-orbit surface bands

Nanostructured composites and nanowire arrays of traditional thermoelectrics like Bi, Bi(1-x)Sb(x) and Bi(2)Te(3) have metallic Rashba surface spin-orbit bands featuring high mobilities rivaling that of the bulk for which topological insulator behavior has been proposed. Nearly pure surface electronic transport has been observed at low temperatures in Bi nanowires with diameter around the critical diameter, 50 nm, for the semimetal-to semiconductor transition. The surface contributes strongly to the thermopower, actually dominating for temperatures T < 100 K in these nanowires. The surface thermopower was found to be -1 T microvolt/(K^2), a value that is consistent with theory. We show that surface electronic transport together with boundary phonon scattering leads to enhanced thermoelectric performance at low temperatures of Bi nanowire arrays. We compare with bulk n-BiSb alloys, optimized CsBi(4)Te(6) and optimized Bi(2)Te(3). Surface dominated electronic transport can be expected in nanomaterials of the other traditional thermoelectrics.Comment: 18 pages, 3 figure

Surface state band mobility and thermopower in semiconducting bismuth nanowires

Many thermoelectrics like Bi exhibit Rashba spin-orbit surface bands for which topological insulator behavior consisting of ultrahigh mobilities and enhanced thermopower has been predicted. Bi nanowires realize surface-only electronic transport since they become bulk insulators when they undergo the bulk semimetal-semiconductor transition as a result of quantum confinement for diameters close to 50 nm. We studied 20-, 30-, 50- and 200-nm trigonal Bi wires. Shubnikov-de Haas magnetoresistance oscillations caused by surface electrons and bulklike holes enable the determination of their densities and mobilities. Surface electrons have high mobilities exceeding 2(m^2)/(Vsec) and contribute strongly to the thermopower, dominating for temperatures T< 100 K. The surface thermopower is - 1.2 T microvolt/(K^2), a value that is consistent with theory, raising the prospect of developing nanoscale thermoelectrics based on surface bands.Comment: 19 pages. 3 figure

Landscape-scale forest loss as a catalyst of population and biodiversity change

The BioTIME database was supported by ERC AdG BioTIME 250189 and ERC PoC BioCHANGE 727440. We thank the ERC projects BioTIME and BioCHANGE for supporting the initial data synthesis work that led to this study, and the Leverhulme Centre for Anthropocene Biodiversity for continued funding of the database. Also supported by a Carnegie-Caledonian PhD Scholarship and NERC doctoral training partnership grant NE/L002558/1 (G.N.D.), a Leverhulme Fellowship and the Leverhulme Centre for Anthropocene Biodiversity (M.D.), Leverhulme Project Grant RPG-2019-402 (A.E.M. and M.D.), and the German Centre of Integrative Biodiversity Research (iDiv) Halle-Jena-Leipzig (funded by the German Research Foundation; FZT 118, S.A.B.).Global biodiversity assessments have highlighted land-use change as a key driver of biodiversity change. However, there is little empirical evidence of how habitat transformations such as forest loss and gain are reshaping biodiversity over time. We quantified how change in forest cover has influenced temporal shifts in populations and ecological assemblages from 6090 globally distributed time series across six taxonomic groups. We found that local-scale increases and decreases in abundance, species richness, and temporal species replacement (turnover) were intensified by as much as 48% after forest loss. Temporal lags in population- and assemblage-level shifts after forest loss extended up to 50 years and increased with species’ generation time. Our findings that forest loss catalyzes population and biodiversity change emphasize the complex biotic consequences of land-use change.PostprintPeer reviewe

Psychological support athletes

The article includes a review of the basic principles of psychological support for athletes before competitionСтатья включает в себя рассмотрение основных принципов психологической поддержки спортсменов перед соревнованиям

Stent-in-Stent Endovascular Correction in Right Internal Carotid Artery Restenosis: a Clinical Case

Background. Carotid artery restenosis is a rare complication of carotid stenting. The Carotid Revascularization Endarterectomy versus Stenting Trial (CREST) reveals an in-stent restenosis rate of 0–6 %, a fairly low value given an extensive study sampling of patients. Restenosis still lacks an adequate explanation in endovascular carotid surgery. Intravascular ultrasound visualisation, drug-coated balloons, stent reimplantation or reconstructive surgery have actively been used since relatively recently to tackle restenosis. Drug-coated balloons may fail in certain cases due to hampered restenosis angioplasty in a markedly rigid neointimal hyperplasia. Surgical reconstruction also possessed drawbacks, mostly due to obstacles in the stent removal and the procedure infeasibility in high-risk surgical patients.Materials and methods. The article describes a clinical case of stent-in-stent restenosis correction with drug-coated balloon-expandable re-stenting of right internal carotid artery and a long-term prognosis estimation with optical coherence tomography.Results and discussions. This tactic was adopted due to haemodynamically and clinically significant internal carotid artery restenosis, the patient’s denial of carotid endarterectomy and insufficiently effective balloon angioplasty. The choice of the correction technique was conclusive basing on a negative stent deformation testing that showed the lack of deforming stress factors at internal carotid artery restenosis. Intravascular imaging greatly enhances our ability to understand and assess endovascular processes.Conclusion. We consider clinically significant restenoses in previously stented carotid arteries as requiring further research effort, with the clinical case presented describing an individual solution

Spectroscopic study of the optical counterpart to the fast X-ray transient IGR J17544-2619 based on observations at the 1.5-m RTT-150 telescope

© 2017, Pleiades Publishing, Inc. We present the results of our long-term photometric and spectroscopic observations at the Russian–Turkish RTT-150 telescope for the optical counterpart to one of the best-known sources, representatives of the class of fast X-ray transients, IGR J17544-2619. Based on our optical data, we have determined for the first time the orbital and physical parameters of the binary system by the methods of Doppler spectroscopy.We have calculated theoretical spectra of the optical counterpart by applying non- LTE corrections for selected lines and obtained the parameters of the stellar atmosphere (T eff = 33 000 K, log g = 3.85, R = 9.5 R ⊙ , and M = 23 M ⊙ ). The latter suggest that the optical star is not a supergiant as has been thought previously

Improved measurements of ICRF antenna input impedance at ASDEX Upgrade during ICRF coupling studies

A new set of diagnostics has been implemented on ASDEX Upgrade to measure the input impedance of the ICRF antennas, in the form of a voltage and current probe pair installed on each feeding line of every antenna. Besides allowing the measurement of the reflection coefficient Γ of each antenna port, the probes have two advantages: first, they are located close to the antenna ports (∼3 m) and thus the measurements are not affected by the uncertainties due to the transmission and matching network; second, they are independent of matching conditions. These diagnostics have been used to study the behavior of the ASDEX Upgrade antennas while changing the plasma shape (low to high triangularity) and applying magnetic perturbations (MPs) via saddle coils. Scans in the separatrix position Rsep were also performed. Upper triangularity δo was increased from 0.1 to 0.3 (with the lower triangularity δu kept roughly constant at 0.45) and significant decreases in |Γ| (up to ∼30%, markedly improving antenna coupling) and moderate changes in phase (up to ∼5°) of Γ on each feeding line were observed approximately at δo ≥ 0.29. During MPs (in ∼0.5 s pulses with a coil current of 1 kA), a smaller response was observed: 6% - 7% in |Γ|, with changes in phase of ∼5° apparently due to Rsep scans only. As |Γ| is usually in the range 0.8 - 0.9, this still leads to a significant increase in possible coupled power. Numerical simulations of the antenna behavior were carried out using the FELICE code; the simulation results are in qualitative agreement with experimental measurements. The results presented here complement the studies on the influence of gas injection and MPs on the ICRF antenna performance presented in [4]