Synthesis of quasi-free-standing bilayer graphene nanoribbons on SiC surfaces

Scaling graphene down to nanoribbons is a promising route for the implementation of this material into devices. Quantum confinement of charge carriers in such nanostructures, combined with the electric field-induced break of symmetry in AB-stacked bilayer graphene, leads to a band gap wider than that obtained solely by this symmetry breaking. Consequently, the possibility of fabricating AB-stacked bilayer graphene nanoribbons with high precision is very attractive for the purposes of applied and basic science. Here we show a method, which includes a straightforward air annealing, for the preparation of quasi-free-standing AB-bilayer nanoribbons with different widths on SiC(0001). Furthermore, the experiments reveal that the degree of disorder at the edges increases with the width, indicating that the narrower nanoribbons are more ordered in their edge termination. In general, the reported approach is a viable route towards the large-scale fabrication of bilayer graphene nanostructures with tailored dimensions and properties for specific applications

Industry-supported meta-analyses compared with meta-analyses with non-profit or no support: Differences in methodological quality and conclusions

<p>Abstract</p> <p>Background</p> <p>Studies have shown that industry-sponsored meta-analyses of drugs lack scientific rigour and have biased conclusions. However, these studies have been restricted to certain medical specialities. We compared all industry-supported meta-analyses of drug-drug comparisons with those without industry support.</p> <p>Methods</p> <p>We searched PubMed for all meta-analyses that compared different drugs or classes of drugs published in 2004. Two authors assessed the meta-analyses and independently extracted data. We used a validated scale for judging the methodological quality and a binary scale for judging conclusions. We divided the meta-analyses according to the type of support in 3 categories: industry-supported, non-profit support or no support, and undeclared support.</p> <p>Results</p> <p>We included 39 meta-analyses. Ten had industry support, 18 non-profit or no support, and 11 undeclared support. On a 0–7 scale, the median quality score was 6 for meta-analyses with non-profit or no support and 2.5 for the industry-supported meta-analyses (P < 0.01). Compared with industry-supported meta-analyses, more meta-analyses with non-profit or no support avoided bias in the selection of studies (P = 0.01), more often stated the search methods used to find studies (P = 0.02), searched comprehensively (P < 0.01), reported criteria for assessing the validity of the studies (P = 0.02), used appropriate criteria (P = 0.04), described methods of allocation concealment (P = 0.05), described methods of blinding (P = 0.05), and described excluded patients (P = 0.08) and studies (P = 0.15). Forty percent of the industry-supported meta-analyses recommended the experimental drug without reservations, compared with 22% of the meta-analyses with non-profit or no support (P = 0.57).</p> <p>In a sensitivity analysis, we contacted the authors of the meta-analyses with undeclared support. Eight who replied that they had not received industry funding were added to those with non-profit or no support, and 3 who did not reply were added to those with industry support. This analysis did not change the results much.</p> <p>Conclusion</p> <p>Transparency is essential for readers to make their own judgment about medical interventions guided by the results of meta-analyses. We found that industry-supported meta-analyses are less transparent than meta-analyses with non-profit support or no support.</p

An original phylogenetic approach identified mitochondrial haplogroup T1a1 as inversely associated with breast cancer risk in BRCA2 mutation carriers

Introduction: Individuals carrying pathogenic mutations in the BRCA1 and BRCA2 genes have a high lifetime risk of breast cancer. BRCA1 and BRCA2 are involved in DNA double-strand break repair, DNA alterations that can be caused by exposure to reactive oxygen species, a main source of which are mitochondria. Mitochondrial genome variations affect electron transport chain efficiency and reactive oxygen species production. Individuals with different mitochondrial haplogroups differ in their metabolism and sensitivity to oxidative stress. Variability in mitochondrial genetic background can alter reactive oxygen species production, leading to cancer risk. In the present study, we tested the hypothesis that mitochondrial haplogroups modify breast cancer risk in BRCA1/2 mutation carriers. Methods: We genotyped 22,214 (11,421 affected, 10,793 unaffected) mutation carriers belonging to the Consortium of Investigators of Modifiers of BRCA1/2 for 129 mitochondrial polymorphisms using the iCOGS array. Haplogroup inference and association detection were performed using a phylogenetic approach. ALTree was applied to explore the reference mitochondrial evolutionary tree and detect subclades enriched in affected or unaffected individuals. Results: We discovered that subclade T1a1 was depleted in affected BRCA2 mutation carriers compared with the rest of clade T (hazard ratio (HR) = 0.55; 95% confidence interval (CI), 0.34 to 0.88; P = 0.01). Compared with the most frequent haplogroup in the general population (that is, H and T clades), the T1a1 haplogroup has a HR of 0.62 (95% CI, 0.40 to 0.95; P = 0.03). We also identified three potential susceptibility loci, including G13708A/rs28359178, which has demonstrated an inverse association with familial breast cancer risk. Conclusions: This study illustrates how original approaches such as the phylogeny-based method we used can empower classical molecular epidemiological studies aimed at identifying association or risk modification effects.Peer reviewe

Genome-Wide Association Study in BRCA1 Mutation Carriers Identifies Novel Loci Associated with Breast and Ovarian Cancer Risk

BRCA1-associated breast and ovarian cancer risks can be modified by common genetic variants. To identify further cancer risk-modifying loci, we performed a multi-stage GWAS of 11,705 BRCA1 carriers (of whom 5,920 were diagnosed with breast and 1,839 were diagnosed with ovarian cancer), with a further replication in an additional sample of 2,646 BRCA1 carriers. We identified a novel breast cancer risk modifier locus at 1q32 for BRCA1 carriers (rs2290854, P = 2.7×10-8, HR = 1.14, 95% CI: 1.09-1.20). In addition, we identified two novel ovarian cancer risk modifier loci: 17q21.31 (rs17631303, P = 1.4×10-8, HR = 1.27, 95% CI: 1.17-1.38) and 4q32.3 (rs4691139, P = 3.4×10-8, HR = 1.20, 95% CI: 1.17-1.38). The 4q32.3 locus was not associated with ovarian cancer risk in the general population or BRCA2 carriers, suggesting a BRCA1-specific associat

In-situ transmission electron microscopy on high-temperature phase transitions of Ge-Sb-Te alloys

Das Hochtemperaturverhalten beeinflusst viele verschiedene Prozesse von der Materialherstellung bis hin zur technologischen Anwendung. In-situ Transmissionselektronenmikroskopie (TEM) bietet die Möglichkeit, die atomaren Prozesse während struktureller Phasenübergänge direkt und in Realzeit zu beobachten. In dieser Arbeit wurde in-situ TEM angewendet, um die Reversibilität des Schmelz- und Kristallisationsprozesses, sowie das anisotropen Sublimationsverhaltens von Ge-Sb-Te (GST) Dünnschichten zu untersuchen. Die gezielte Probenpräparation für die erfolgreiche Beobachtung der Hochtemperatur-Phasenübergänge wird hervorgehoben. Die notwendige Einkapselung für die Beobachtung der Flüssigphase unter Vakuumbedingungen und die erforderliche sauberer Oberfläche für den Sublimationsprozess werden detailliert beschrieben. Außerdem wird die Elektronenenergieverlustspektroskopie eingesetzt um die lokale chemische Zusammensetzung vor und nach den Übergängen zu bestimmen. Die Untersuchung der Grenzflächenstruktur und Dynamik sowohl beim Phasenübergang fest-flüssig als auch flüssig-fest zeigt Unterschiede zwischen den beiden Vorgängen. Die trigonale Phase von GST weist beim Schmelzen eine teilweise geordnete Übergangszone an der fest-flüssig-Grenzfläche auf, während ein solcher Zwischenzustand bei der Erstarrung nicht entsteht. Außerdem läuft der Schmelzvorgang zeitlich linear ab, während die Kristallisation durch eine Wurzelabhängigkeit von der Zeit mit überlagerter Start-Stopp-Bewegung beschrieben werden kann. Der Einfluss der Substrat-Grenzfläche wird diskutiert und die Oberflächenenergie von GST bestimmt. Die anisotrope Dynamik führt beim Phasenübergang fest-gasförmig der kubischen Phase von GST zur Ausbildung stabiler {111} Facetten. Dies erfolgt über die Bildung von Kinken und Stufen auf stabilen Terrassen. Die Keimbildungsrate und die bevorzugten Keimbildungsorte der Kinken wurden identifiziert und stimmen mit den Voraussagen des Terrassen-Stufen-Kinken Modells überein.High-temperature behavior influence many different processes ranging from material processing to device applications. In-situ transmission electron microscopy (TEM) provides the means for direct observation of atomic processes during structural phase transitions in real time. In this thesis, in-situ TEM is applied to investigate the reversibility of the melting and solidification processes as well as the anisotropic sublimation behavior of Ge-Sb-Te (GST) thin films. The purposeful sample preparation for the successful observation of the high-temperature phase transitions is emphasized. The required encapsulation for the observation of the liquid phase inside the vacuum conditions and the necessary clean surface for sublimation process are discussed in detail. Additionally electron energy-loss spectroscopy in the TEM is used to determine the local chemical composition before and after the phase transitions. The analysis of the interface structure and dynamic during the solid-to-liquid as well as the liquid-to-solid phase transition shows differences between both processes. The trigonal phase of GST exhibits a partially ordered transition zone at the solid-liquid interface during melting while such an intermediate state does not form during solidification. Additionally the melting process proceeds with linear dependence on time, whereas crystallization can be described as having a square-root time-dependency featuring a superimposed start-stop motion. The influence of the interface is addressed and the surface energies of GST are determined. The anisotropic dynamic of the solid-to-gas phase transition of the cubic GST phase leads to the formation of stable {111} facets. This happens via kink and step nucleation on stable terraces. The nucleation rates and the preferred kink nucleation sites are identified and are in accordance with the predictions of terrace-step-kink model

Die Geldeinkommenspolitik des sozialistischen Staates als Bestandteil der Hauptaufgabe

HUB(11) - 86 HB 1350, T. 1, 2 / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Phase Stability and Anisotropic Sublimation of Cubic Ge–Sb–Te Alloy Observed by In Situ Transmission Electron Microscopy

Phase stability and anisotropic sublimation dynamics of the cubic Ge–Sb–Te alloy have been investigated by in situ transmission electron microscopy (TEM). The starting point of the phase-transition study is an epitaxially aligned Ge₁Sb₂Te₄ grain on a Si(111) substrate. Upon in situ heating, the cubic phase remains stable up to the sublimation point without a transition to the thermodynamically stable trigonal crystal structure which is attributed to Si diffusion into the Ge₁Sb₂Te₄ grain. The sublimation process is made visible with atomic resolution. The anisotropic process leads to the formation of stable {111} facets via kink nucleation on stable steps and subsequent sublimation from those kink sites as predicated by the terrace-step-kink model. Kink nucleation sites are identified and are in accordance with the broken-bond model approach

Phase Stability and Anisotropic Sublimation of Cubic Ge–Sb–Te Alloy Observed by In Situ Transmission Electron Microscopy

Phase stability and anisotropic sublimation dynamics of the cubic Ge–Sb–Te alloy have been investigated by in situ transmission electron microscopy (TEM). The starting point of the phase-transition study is an epitaxially aligned Ge₁Sb₂Te₄ grain on a Si(111) substrate. Upon in situ heating, the cubic phase remains stable up to the sublimation point without a transition to the thermodynamically stable trigonal crystal structure which is attributed to Si diffusion into the Ge₁Sb₂Te₄ grain. The sublimation process is made visible with atomic resolution. The anisotropic process leads to the formation of stable {111} facets via kink nucleation on stable steps and subsequent sublimation from those kink sites as predicated by the terrace-step-kink model. Kink nucleation sites are identified and are in accordance with the broken-bond model approach

Phase Stability and Anisotropic Sublimation of Cubic Ge–Sb–Te Alloy Observed by In Situ Transmission Electron Microscopy

Phase stability and anisotropic sublimation dynamics of the cubic Ge–Sb–Te alloy have been investigated by in situ transmission electron microscopy (TEM). The starting point of the phase-transition study is an epitaxially aligned Ge₁Sb₂Te₄ grain on a Si(111) substrate. Upon in situ heating, the cubic phase remains stable up to the sublimation point without a transition to the thermodynamically stable trigonal crystal structure which is attributed to Si diffusion into the Ge₁Sb₂Te₄ grain. The sublimation process is made visible with atomic resolution. The anisotropic process leads to the formation of stable {111} facets via kink nucleation on stable steps and subsequent sublimation from those kink sites as predicated by the terrace-step-kink model. Kink nucleation sites are identified and are in accordance with the broken-bond model approach

Die russische Leidensfaehigkeit Mythos oder rationales Verhalten?

'Neues Osteuropa: Zerstoerter Staatssozialismus plus Marktwirtschaft und Demokratie? Fuenfzehn Jahre nach Beginn der Perestrojka wird allerorts Bilanz gezogen. Hoechst unterschiedlich verlaeuft der Umbau der Gesellschaft. Das Vaterland der Perestrojka -ein weites Land mit weiter Seele, geeint durch einen Menschenschlag, der die noetige charakterliche Disposition mitbringt, um die Haerten der Veraenderungen zu meistern. So will es jedenfalls das Stereotyp. Der Topos der Leidensfaehigkeit sollte erklaeren, warum besondere soziale Haerten vom Volk vielleicht mit Klagen, aber ohne massives oeffentliches Aufbegehren erduldet werden. Laesst sich dieses Verhaltensmuster in der Gegenwart wiederfinden und mit der Dolgoterpenie-Mentalitaet beschreiben oder sind andere Gruende dafuer ausschlaggebend? Im ersten Teil wendet sich die Autorin der sozialen Situation am Arbeitsplatz zu. Die Spannung zwischen Arbeit und Kapital war und ist traditionell in allen Industrielaendern Ursache heftiger Auseinandersetzungen. Der Umgang mit ihnen gibt daher Aufschluss darueber, wie eine Gesellschaft mit ihren Konflikten umgeht. Gaebe es die russische Leidensfaehigkeit, so muesste sie sich in Form von friedfertigen industriellen Beziehungen niederschlagen. Es ist nicht moeglich, eine Merkmalsmatrix zu erstellen, aus der man eindeutig ableiten koennte, wann kollektives Protestverhalten zu erwarten ist. Es wird daher eine Kombination aus makrooekonomischen und organisatorischen Faktoren vorschlagen, die ueblicherweise als relevant angenommen werden. Zunaechst thematisiert die Autorin die allgemeine Wirtschaftslage und nimmt dabei Armut, Arbeitslosigkeit und die Reaktionen darauf in den Blick. Darueber hinaus widmet sie sich dem betrieblichen Arbeitskampf, der Rolle der Gewerkschaften und dem Machtverhaeltnis zwischen Betriebsleitung und Belegschaft. Schliesslich werden die volkswirtschaftliche Faktoren, die einen Hinweis auf soziale Auseinandersetzungen jenseits der betrieblichen Organisationsstruktur geben koennen, betrachtet. Im zweiten Teil wird untersucht, wie sich Werte, Normen und individuelle Identitaeten wandeln und welche Folgen das hat. Jede Gesellschaft produziert Regeln und Menschen, die diese Regeln kennen, sich an sie halten oder wissen, wie sie sie veraendern koennen. Auf den ersten Blick gibt es die sowjetischen Massstaebe nicht mehr. Kulturelle Ueberlieferungen wirken jedoch trotz Revolutionen fort. Das wirtschaftliche und politische System hat sich immens veraendert, und die Menschen muessen sich mental anpassen, um zu ueberleben. Insofern wird es im zweiten Teil um die sozialen Folgen einer solchen Anpassungsleistung gehen.' (Textauszug)Available from http://userpage.fu-berlin.de/ / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman