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

Unemployment Convergence in Central and Eastern European Countries: Driving Forces and Cluster Behavior

Employing a nonlinear logistic smooth transition autoregression system and comovement analysis, we find that the German business cycle has acted as a common driver affecting the cyclical behavior of unemployment rates in Central and Eastern European countries. In addition, we identify two convergence clubs in unemployment dynamics. The first comprises the Baltic States, Hungary, and Poland, and the second group of countries is composed of the Czech Republic and Slovakia. Interestingly, this classification matches the labor market policies and institutional divergences observed among these countries

Psychometric Properties of the German Version of the Pain Vigilance and Awareness Questionnaire (PVAQ) in Pain-Free Samples and Samples with Acute and Chronic Pain

The way individuals attend to pain is known to have a considerable impact on the experience and chronification of pain. One method to assess the habitual "attention to pain" is the Pain Vigilance and Awareness Questionnaire (PVAQ). With the present study, we aimed to test the psychometric properties of the German version of the PVAQ across pain-free samples and across patients with acute and chronic pain. Two samples of pain-free individuals (student sample (N = 255)/non-student sample (N = 362)) and two clinical pain samples (acute pain patients (N = 105)/chronic pain patients (N = 36)) were included in this cross-sectional evaluation of the German PVAQ. Factor structure was assessed using exploratory and confirmatory factor analyses. Reliability was assessed using internal consistency (Cronbach's alpha). Construct validity was tested by assessing correlations between PVAQ and theoretically related constructs. Exploratory factor analysis (non-student sample) and confirmatory factor analysis (student sample, acute pain patient sample) suggested that a two-factor solution best fitted our data ("attention to pain," "attention to changes in pain"). Internal consistency ranged from acceptable to good in all four samples. As hypothesized, the PVAQ correlated significantly with theoretically related constructs in all four samples, suggesting good construct validity in pain-free individuals and in pain patients. The German PVAQ shows good psychometric properties across samples of pain-free individuals and patients suffering from pain that are comparable to PVAQ versions of other languages. Thus, the German PVAQ seems to be a measure of pain vigilance equally valid as found in other countries

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

Stakeholders' views on the global guidelines for the sustainable use of non‐native trees

A large number of non‐native trees (NNTs) have been introduced globally and widely planted, contributing significantly to the world's economy. Although some of these species present a limited risk of spreading beyond their planting sites, a growing number of NNTs are spreading and becoming invasive leading to diverse negative impacts on biodiversity, ecosystem functions and human well‐being. To help minimize the negative impacts and maximize the economic benefits of NNTs, Brundu et al. developed eight guidelines for the sustainable use of NNTs globally—the Global Guidelines for the Use of NNTs (GG‐NNTs). Here, we used an online survey to assess perceptions of key stakeholders towards NNTs, and explore their knowledge of and compliance with the GG‐NNTs. Our results show that stakeholders are generally aware that NNTs can provide benefits and cause negative impacts, often simultaneously and they consider that their organization complies with existing regulations and voluntary agreements concerning NNTs. However, they are not aware of or do not apply most of the eight recommendations included in the GG‐NNTs. We conclude that effectively managing invasions linked to NNTs requires both more communication efforts using an array of channels for improving stakeholder awareness and implementation of simple measures to reduce NNT impacts (e.g. via GG‐NNTs), and a deeper understanding of the barriers and reluctance of stakeholders to manage NNT invasions. Read the free Plain Language Summary for this article on the Journal blog

Flow cytometry as a rapid analytical tool to determine physiological responses to changing O2 and iron concentration by Magnetospirillum gryphiswaldense strain MSR-1

Magnetotactic bacteria (MTB) are a diverse group of bacteria that synthesise magnetosomes, magnetic membrane-bound nanoparticles that have a variety of diagnostic, clinical and biotechnological applications. We present the development of rapid methods using flow cytometry to characterize several aspects of the physiology of the commonly-used MTB Magnetospirillum gryphiswaldense MSR-1. Flow cytometry is an optical technique that rapidly measures characteristics of individual bacteria within a culture, thereby allowing determination of population heterogeneity and also permitting direct analysis of bacteria. Scatter measurements were used to measure and compare bacterial size, shape and morphology. Membrane permeability and polarization were measured using the dyes propidium iodide and bis-(1,3-dibutylbarbituric acid) trimethine oxonol to determine the viability and ‘health’ of bacteria. Dyes were also used to determine changes in concentration of intracellular free iron and polyhydroxylakanoate (PHA), a bacterial energy storage polymer. These tools were then used to characterize the responses of MTB to different O2 concentrations and iron-sufficient or iron-limited growth. Rapid analysis of MTB physiology will allow development of bioprocesses for the production of magnetosomes, and will increase understanding of this fascinating and useful group of bacteria

Temporal Integration of Movement: The Time-Course of Motion Streaks Revealed by Masking

Temporal integration in the visual system causes fast-moving objects to leave oriented ‘motion streaks’ in their wake, which could be used to facilitate motion direction perception. Temporal integration is thought to occur over 100 ms in early cortex, although this has never been tested for motion streaks. Here we compare the ability of fast-moving (‘streaky’) and slow-moving fields of dots to mask briefly flashed gratings either parallel or orthogonal to the motion trajectory. Gratings were presented at various asynchronies relative to motion onset (from to ms) to sample the time-course of the accumulating streaks. Predictions were that masking would be strongest for the fast parallel condition, and would be weak at early asynchronies and strengthen over time as integration rendered the translating dots more streaky and grating-like. The asynchrony where the masking function reached a plateau would correspond to the temporal integration period. As expected, fast-moving dots caused greater masking of parallel gratings than orthogonal gratings, and slow motion produced only modest masking of either grating orientation. Masking strength in the fast, parallel condition increased with time and reached a plateau after 77 ms, providing an estimate of the temporal integration period for mechanisms encoding motion streaks. Interestingly, the greater masking by fast motion of parallel compared with orthogonal gratings first reached significance at 48 ms before motion onset, indicating an effect of backward masking by motion streaks