Characterization of silicon carbide surfaces of 6H- 15R- and 3Cpolytypes by optical second-harmonic generation in comparison with X-ray diffraction techniques

Abstract. Second-harmonic (SH) generation is a versatile method applicable to in-situ characterization of even noncentrosymmetric media like silicon carbide (SiC). In particular, the azimuthal rotational anisotropy of the SH response from SiC observed in reflection allows identification of various polytypes. The nonlinear-optical results are compared to X-ray diffraction data. The abundance of information obtained through the SH studies makes characteristic fingerprinting of the 6H, 15R, and 3C polytypes of SiC is possible. The spatial resolution of the optical sampling was about 50 µm in the lateral direction with a typical penetration depth of 100 nm for the fundamental radiation. Defect regions of different crystallographic structures in large SiC samples were identified by observing the spatially resolved dependence of the SH intensity. 42.65.Nx; 78.66; 42.70.N Silicon carbide (SiC) is a widely studied semiconductor that crystallizes in over 200 known polytypes. The most common structure is α-SiC, which consists of a mixture of hexagonal polytypes (6H, 4H) and the rhombohedral polytype 15R PACS: As already demonstrated in other studies on centrosymmetric materials like silicon, second-harmonic generation (SHG) has proved to be a sensitive tool for studying a large variety of surface and interface structural and electronic properties. Although SHG from non-centrosymmetric materials is not restricted to the surface but is also possible in the bulk material SHG studies in reflection geometry provide substantial crystallographic information on the near-surface region. The generation depth of the second-harmonic (SH) radiation detected in reflection of approximately λ/2π, where λ is the fundamental wavelength, allows higher surface specificity, as compared to the typical interaction lengths of several micrometers in conventional X-ray diffraction techniques in back-reflection geometry (X-ray examination of SiC cf. [4]). The tensorial properties of the second-order susceptibility, which characterizes the SHG effect, provide information on the crystal structure in case of non-centrosymmetric materials in the near-surface region by investigating its azimuthal rotational anisotropy. Although studies on non-centrosymmetric gallium arsenide (GaAs) demonstrated sensitively surface reconstruction changes In the present work, we demonstrate that SHG is a versatile tool to characterize the crystalline structure of SiC. By investigating the rotational anisotropy of the SH response of various polytypes of SiC, we could fingerprint the most important species 6H, 15R and 3C, which are revealed by different crystalline structures. We were also able to distinguish between bulk and surface contributions to the SH signal from cubic and hexagonal SiC by differences in the rotationa

Characteristics, management and attainment of lipid target levels in diabetic and cardiac patients enrolled in Disease Management Program versus those in routine care: LUTZ registry

<p>Abstract</p> <p>Background</p> <p>Since 2002 the sick funds in Germany have widely implemented disease management programs (DMPs) for patients with type 2 diabetes mellitus (DM) and coronary heart disease (CHD). Little is known about the characteristics, treatment and target attainment lipid levels of these patients enrolled in DMPs compared to patients in routine care (non-DMP).</p> <p>Methods</p> <p>In an open, non-interventional registry (LUTZ) in Germany, 6551 physicians documented 15,211 patients with DM (10,110 in DMP, 5101 in routine care) and 14,222 (6259 in DMP, 7963 in routine care) over a follow-up period of 4 months. They received the NCEP ATP III guidelines as a reminder on lipid level targets.</p> <p>Results</p> <p>While demographic characteristics of DMP patients were similar to routine care patients, the former had higher rates of almost all cardiovascular comorbidities. Patients in DMPs received pharmacological treatment (in almost all drug classes) more often than non-DMP patients (e.g. antiplatelets: in DM 27.0% vs 23.8%; in CHD 63.0% vs. 53.6%). The same applied for educational measures (on life style changes and diet etc.). The rate of target level attainment for low density lipoprotein cholesterol (LDL-C) < 100 mg/dl was somewhat higher in DMP patients at inclusion compared to non-DMP patients (DM: 23.9% vs. 21.3%; CHD: 30.6% vs. 23.8%) and increased after 4 months (DM: 38.3% vs. 36.9%; CHD: 49.8% vs. 43.3%). Individual LDL-C target level attainment rates as assessed by the treating physicians were higher (at 4 months in DM: 59.6% vs. 56.5%; CHD: 49.8% vs 43.3%). Mean blood pressure (BP) and HbA_1cvalues were slightly lowered during follow-up, without substantial differences between DMP and non-DMP patients.</p> <p>Conclusion</p> <p>Patients with DM, and (to a greater extent) with CHD in DMPs compared to non-DMP patients in routine care have a higher burden of comorbidities, but also receive more intensive pharmacological treatment and educational measures. The present data support that the substantial additional efforts in DMPs aimed at improving outcomes resulted in quality gains for achieving target LDL-C levels, but not for BP or HbA_1c. Longer-term follow-up is needed to substantiate these results.</p

Short- and Long-range Neural Synchrony in Grapheme–Color Synesthesia

Grapheme–color synesthesia is a perceptual phenomenon where single graphemes (e.g., the letter “E”) induce simultaneous sensations of colors (e.g., the color green) that were not objectively shown. Current models disagree as to whether the color sensations arise from increased short-range connectivity between anatomically adjacent grapheme- and color-processing brain structures or from decreased effectiveness of inhibitory long-range connections feeding back into visual cortex. We addressed this issue by examining neural synchrony obtained from EEG activity, in a sample of grapheme–color synesthetes that were presented with color-inducing versus non-color-inducing graphemes. For color-inducing graphemes, the results showed a decrease in the number of long-range couplings in the theta frequency band (4–7 Hz, 280–540 msec) and a concurrent increase of short-range phase-locking within lower beta band (13–20 Hz, 380–420 msec at occipital electrodes). Because the effects were both found in long-range synchrony and later within the visual processing stream, the results support the idea that reduced inhibition is an important factor for the emergence of synesthetic colors

Estimating Mode Effects in Panel Surveys: A Multitrait Multimethod Approach

Kroh M, Karmann A, Kühne S. Estimating Mode Effects in Panel Surveys: A Multitrait Multimethod Approach. In: Cernat A, Sakshaug JW, eds. Measurement Error in Longitudinal Data. Oxford: Oxford University Press; 2021: 89-109