Surface Conductivity of Si(100) and Ge(100) Surfaces Determined from Four-Point Transport Measurements Using an Analytical N-Layer Conductance Model

An analytical N-layer model for charge transport close to a surface is derived from the solution of Poisson's equation and used to describe distance-dependent electrical four-point measurements on the microscale. As the N-layer model comprises a surface channel, multiple intermediate layers and a semi-infinite bulk, it can be applied to semiconductors in combination with a calculation of the near-surface band-bending to model very precisely the measured four-point resistance on the surface of a specific sample and to extract a value for the surface conductivity. For describing four-point measurements on sample geometries with mixed 2D-3D conduction channels often a very simple parallel-circuit model has so far been used in the literature, but the application of this model is limited, as there are already significant deviations, when it is compared to the lowest possible case of the N-layer model, i.e. the 3-layer model. Furthermore, the N-layer model is applied to published distance-dependent four-point resistance measurements obtained with a multi-tip scanning tunneling microscope (STM) on Germanium(100) and Silicon(100) with different bulk doping concentrations resulting in the determination of values for the surface conductivities of these materials.Comment: 11 pages, 6 color figure

Surface and Step Conductivities on Si(111) Surfaces

Four-point measurements using a multi-tip scanning tunneling microscope (STM) are carried out in order to determine surface and step conductivities on Si(111) surfaces. In a first step, distance-dependent four-point measurements in the linear configuration are used in combination with an analytical three-layer model for charge transport to disentangle the 2D surface conductivity from non-surface contributions. A termination of the Si(111) surface with either Bi or H results in the two limiting cases of a pure 2D or 3D conductance, respectively. In order to further disentangle the surface conductivity of the step-free surface from the contribution due to atomic steps, a square four-probe configuration is applied as function of the rotation angle. In total this combined approach leads to an atomic step conductivity of $\sigma_\mathrm{step} = (29 \pm 9)$ $\mathrm{\Omega}^{-1} \mathrm{m}^{-1}$ and to a step-free surface conductivity of $\sigma_\mathrm{surf} = (9 \pm 2) \cdot 10^{-6}\,\mathrm{\Omega}^{-1}/\square$ for the Si(111)-(7$\times$7) surface.Comment: Main paper: 5 pages, 4 figures, Supplemental material: 6 pages, 3 figures. The Supplemental Material contains details on the sample preparation and measurement procedure, additional experimental results for Si(111) samples with different doping levels, and the description of the three-layer conductance mode

Evidence for topological band inversion of the phase change material Ge2Sb2Te5

We present an angle-resolved photoemission study of a ternary phase change material, namely Ge2Sb2Te5, epitaxially grown on Si(111) in the metastable cubic phase. The observed upper bulk valence band shows a minimum at Gamma-bar being 0.3 eV below the Fermi level E_F and a circular Fermi contour around Gamma-bar with a dispersing diameter of 0.27-0.36 Anstroms^-1. This is in agreement with density functional theory calculations of the Petrov stacking sequence in the cubic phase which exhibits a topological surface state. The topologically trivial cubic KH stacking shows a valence band maximum at Gamma in line with all previous calculations of the hexagonal stable phase exhibiting the valence band maximum at Gamma for a trivial Z_2 topological invariant nu_0 and away from Gamma for non-trivial nu_0. Scanning tunneling spectroscopy exhibits a band gap of 0.4 eV around E_F

Variations in Rainbow Trout Immune Responses against A. salmonicida: Evidence of an Internal Seasonal Clock in Oncorhynchus mykiss

publishedVersio

Strong and Weak 3D Topological Insulators Probed by Surface Science Methods

The contributions of surface science methods to discover and improve 3D topological insulator materials are reviewed herein, illustrated with examples from the authors’ own work. In particular, it is demonstrated that spin-polarized angular-resolved photoelectron spectroscopy is instrumental to evidence the spin-helical surface Dirac cone, to tune its Dirac point energy toward the Fermi level, and to discover novel types of topological insulators such as dual ones or switchable ones in phase change materials. Moreover, procedures are introduced to spatially map potential fluctuations by scanning tunneling spectroscopy and to identify topological edge states in weak topological insulators. © 2020 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinhei

Sex differences in associations of comorbidities with incident cardiovascular disease:Focus on absolute risk

AIM: To examine sex differences in associations of obesity, type-2 diabetes, hypertension, and atrial fibrillation (AF) with incident cardiovascular disease (CVD), focusing on absolute risk measures.METHODS AND RESULTS: We included a total of 7994 individuals (mean age 49.1 years; 51.2% women) without prior CVD from the PREVEND (Prevention of Renal and Vascular End-stage Disease) cohort with a median follow-up of 12.5 years. Using Poisson regression, we calculated the increase in absolute as well as relative CVD risk associated with a comorbidity using incidence rate differences (IRD = IR comorbidity-IR no-comorbidity) and incidence rate ratios (IRR = IR comorbidity/IR no-comorbidity), respectively. Sex differences were presented as women-to-men differences (WMD = IRD women-IRD men) and women-to-men ratios (WMR = IRR women/IRR men). Absolute CVD risk was lower in women than in men (IR women: 6.73 vs. IR men: 14.58 per 1000 person-years). While increase in absolute CVD risk associated with prevalent hypertension was lower in women than in men [WMD: -6.12, 95% confidence interval: (-9.84 to -2.40), P = 0.001], increase in absolute CVD risk associated with prevalent obesity [WMD: -4.25 (-9.11 to 0.61), P = 0.087], type-2 diabetes [WMD: -1.04 (-14.36 to 12.29), P = 0.879] and AF [WMD: 18.39 (-39.65 to 76.43), P = 0.535] did not significantly differ between the sexes. Using relative risk measures, prevalent hypertension [WMR: 1.49%, 95% confidence interval: (1.12-1.99), P = 0.006], type-2 diabetes [WMR: 1.73 (1.09-2.73), P = 0.019], and AF [WMR: 2.53 (1.12-5.70), P = 0.025] were all associated with higher CVD risk in women than in men. CONCLUSION: Increase in absolute risk of developing CVD is higher in hypertensive men than in hypertensive women, but no substantial sex-related differences were observed among individuals with obesity, type-2 diabetes and AF. On a relative risk scale, comorbidities, in general, confer a higher CVD risk in women than in men.</p

Sex differences in associations of comorbidities with incident cardiovascular disease: focus on absolute risk

AIM: To examine sex differences in associations of obesity, type-2 diabetes, hypertension, and atrial fibrillation (AF) with incident cardiovascular disease (CVD), focusing on absolute risk measures. METHODS AND RESULTS: We included a total of 7994 individuals (mean age 49.1 years; 51.2% women) without prior CVD from the PREVEND (Prevention of Renal and Vascular End-stage Disease) cohort with a median follow-up of 12.5 years. Using Poisson regression, we calculated the increase in absolute as well as relative CVD risk associated with a comorbidity using incidence rate differences (IRD = IR(comorbidity)−IR(no-comorbidity)) and incidence rate ratios (IRR = IR(comorbidity)/IR(no-comorbidity)), respectively. Sex differences were presented as women-to-men differences (WMD = IRD(women)−IRD(men)) and women-to-men ratios (WMR = IRR(women)/IRR(men)). Absolute CVD risk was lower in women than in men (IR(women): 6.73 vs. IR(men): 14.58 per 1000 person-years). While increase in absolute CVD risk associated with prevalent hypertension was lower in women than in men [WMD: −6.12, 95% confidence interval: (−9.84 to −2.40), P = 0.001], increase in absolute CVD risk associated with prevalent obesity [WMD: −4.25 (−9.11 to 0.61), P = 0.087], type-2 diabetes [WMD: −1.04 (−14.36 to 12.29), P = 0.879] and AF [WMD: 18.39 (−39.65 to 76.43), P = 0.535] did not significantly differ between the sexes. Using relative risk measures, prevalent hypertension [WMR: 1.49%, 95% confidence interval: (1.12–1.99), P = 0.006], type-2 diabetes [WMR: 1.73 (1.09–2.73), P = 0.019], and AF [WMR: 2.53 (1.12–5.70), P = 0.025] were all associated with higher CVD risk in women than in men. CONCLUSION: Increase in absolute risk of developing CVD is higher in hypertensive men than in hypertensive women, but no substantial sex-related differences were observed among individuals with obesity, type-2 diabetes and AF. On a relative risk scale, comorbidities, in general, confer a higher CVD risk in women than in men

Sex differences in associations of comorbidities with incident cardiovascular disease:Focus on absolute risk

AIM: To examine sex differences in associations of obesity, type-2 diabetes, hypertension, and atrial fibrillation (AF) with incident cardiovascular disease (CVD), focusing on absolute risk measures.METHODS AND RESULTS: We included a total of 7994 individuals (mean age 49.1 years; 51.2% women) without prior CVD from the PREVEND (Prevention of Renal and Vascular End-stage Disease) cohort with a median follow-up of 12.5 years. Using Poisson regression, we calculated the increase in absolute as well as relative CVD risk associated with a comorbidity using incidence rate differences (IRD = IR comorbidity-IR no-comorbidity) and incidence rate ratios (IRR = IR comorbidity/IR no-comorbidity), respectively. Sex differences were presented as women-to-men differences (WMD = IRD women-IRD men) and women-to-men ratios (WMR = IRR women/IRR men). Absolute CVD risk was lower in women than in men (IR women: 6.73 vs. IR men: 14.58 per 1000 person-years). While increase in absolute CVD risk associated with prevalent hypertension was lower in women than in men [WMD: -6.12, 95% confidence interval: (-9.84 to -2.40), P = 0.001], increase in absolute CVD risk associated with prevalent obesity [WMD: -4.25 (-9.11 to 0.61), P = 0.087], type-2 diabetes [WMD: -1.04 (-14.36 to 12.29), P = 0.879] and AF [WMD: 18.39 (-39.65 to 76.43), P = 0.535] did not significantly differ between the sexes. Using relative risk measures, prevalent hypertension [WMR: 1.49%, 95% confidence interval: (1.12-1.99), P = 0.006], type-2 diabetes [WMR: 1.73 (1.09-2.73), P = 0.019], and AF [WMR: 2.53 (1.12-5.70), P = 0.025] were all associated with higher CVD risk in women than in men. CONCLUSION: Increase in absolute risk of developing CVD is higher in hypertensive men than in hypertensive women, but no substantial sex-related differences were observed among individuals with obesity, type-2 diabetes and AF. On a relative risk scale, comorbidities, in general, confer a higher CVD risk in women than in men.</p

A Molecular Mechanism Underlying Genotype-Specific Intrahepatic Cholestasis Resulting From MYO5B Mutations

Altres ajuts: Supported by grants from the Nederlandse vereniging voor Gastroenterologie (to S. I. J.) and the Natural Science Foundation of China, Nos. 81873543 and 81570468 (to J. S. W.).Progressive familial intrahepatic cholestasis (PFIC) 6 has been associated with missense but not biallelic nonsense or frameshift mutations in MYO5B, encoding the motor protein myosin Vb (myoVb). This genotype-phenotype correlation and the mechanism through which MYO5B mutations give rise to PFIC are not understood. The aim of this study was to determine whether the loss of myoVb or expression of patient-specific myoVb mutants can be causally related to defects in canalicular protein localization and, if so, through which mechanism. We demonstrate that the cholestasis-associated substitution of the proline at amino acid position 600 in the myoVb protein to a leucine (P660L) caused the intracellular accumulation of bile canalicular proteins in vesicular compartments. Remarkably, the knockout of MYO5B in vitro and in vivo produced no canalicular localization defects. In contrast, the expression of myoVb mutants consisting of only the tail domain phenocopied the effects of the Myo5b-P660L mutation. Using additional myoVb and rab11a mutants, we demonstrate that motor domain-deficient myoVb inhibited the formation of specialized apical recycling endosomes and that its disrupting effect on the localization of canalicular proteins was dependent on its interaction with active rab11a and occurred at the trans -Golgi Network/recycling endosome interface. Our results reveal a mechanism through which MYO5B motor domain mutations can cause the mislocalization of canalicular proteins in hepatocytes which, unexpectedly, does not involve myoVb loss-of-function but, as we propose, a rab11a-mediated gain-of-toxic function. The results explain why biallelic MYO5B mutations that affect the motor domain but not those that eliminate myoVb expression are associated with PFIC6

Environmental change during MIS4 and MIS 3 opened corridors in the Horn of Africa for <i>Homo sapiens</i> expansion

Archaeological findings, numerical human dispersal models and genome analyses suggest several time windows in the past 200 kyr (thousands of years ago) when anatomically modern humans (AMH) dispersed out of Africa into the Levant and/or Arabia. From close to the key hominin site of Omo-Kibish, we provide near continuous proxy evidence for environmental changes in lake sediment cores from the Chew Bahir basin, south Ethiopia. The data show highly variable hydroclimate conditions from 116 to 66 kyr BP with rapid shifts from very wet to extreme aridity. The wet phases coincide with the timing of the North African Humid Periods during MIS5, as defined by Nile discharge records from the eastern Mediterranean. The subsequent record at Chew Bahir suggests stable regional hydrological setting between 58 and 32 kyr (MIS4 and 3), which facilitated the development of more habitable ecosystems, albeit in generally dry climatic conditions. This shift, from more to less variable hydroclimate, may help account for the timing of later dispersal events of AMH out of Africa