Strain development and damage accumulation under ion irradiation of polycrystalline Ge-Sb-Te alloys

The atomic displacement produced by ion irradiation with 150 keV Ar+ ions has been studied in Ge1Sb2Te4 and Ge2Sb2Te5. Electrical, optical and structural measurements have been employed to characterize the induced electrical and structural modifications. At low temperature the amorphization threshold, evaluated by in situ reflectivity measurements, is independent of the composition and the crystalline structure, and it is equal to 1 x 1013 cm-2. At room temperature, at which dynamic annealing can take place, Ge2Sb2Te5 and Ge1Sb2Te4 in the rocksalt phase exhibit the same amorphization threshold (3 x 1013 cm-2). In the trigonal structure, instead, a higher fluence is required to amorphize the Ge1Sb2Te4, compared to Ge2Sb2Te5. The observed differences between the two compositions can be explained considering the effect of dynamic annealing during ion irradiation of the trigonal phase, which is characterized by the presence of van der Waals gaps. These may act as a preferential sink for the diffusion of the displaced atoms and the filling of these gaps tunes the electronic and structural properties. Filling of about 30% of the gaps produces an electronic transition from metallic to insulating behavior. By further increasing the disorder and filling more than 70% of the gaps the films convert into the rocksalt phase

Role of interfaces on the stability and electrical properties of Ge2Sb2Te5 crystalline structures

GeSbTe-based materials exhibit multiple crystalline phases, from disordered rocksalt, to rocksalt with ordered vacancy layers, and to the stable trigonal phase. In this paper we investigate the role of the interfaces on the structural and electrical properties of Ge2Sb2Te5. We find that the site of nucleation of the metastable rocksalt phase is crucial in determining the evolution towards vacancy ordering and the stable phase. By properly choosing the substrate and the capping layers, nucleation sites engineering can be obtained, thus promoting or preventing the vacancy ordering in the rocksalt structure or the conversion into the trigonal phase. The vacancy ordering occurs at lower annealing temperatures (170 °C) for films deposited in the amorphous phase on silicon (111), compared to the case of SiO2 substrate (200 °C), or in presence of a capping layer (330 °C). The mechanisms governing the nucleation have been explained in terms of interfacial energies. Resistance variations of about one order of magnitude have been measured upon transition from the disordered to the ordered rocksalt structure and then to the trigonal phase. The possibility to control the formation of the crystalline phases characterized by marked resistivity contrast is of fundamental relevance for the development of multilevel phase change data storage

Intriguing Electrostatic Potential of CO: Negative Bond-ends and Positive Bond-cylindrical-surface

The strong electronegativity of O dictates that the ground state of singlet CO has positively charged C and negatively charged O, in agreement with ab initio charge analysis, but in disagreement with the dipole direction. Though this unusual phenomenon has been fairly studied, the study of electrostatic potential (EP) for noncovalent interactions of CO is essential for better understanding. Here we illustrate that both C and O atom-ends show negative EP (where the C end gives more negative EP), favoring positively charged species, whereas the cylindrical surface of the CO bond shows positive EP, favoring negatively charged ones. This is demonstrated from the interactions of CO with Na+, Cl-, H2O, CO and benzene. It can be explained by the quadrupole driven electrostatic nature of CO (like N2) with very weak dipole moment. The EP is properly described by the tripole model taking into account the electrostatic multipole moments, which has a large negative charge at a certain distance protruded from C, a large positive charge on C, and a small negative charge on O. We also discuss the EP of the first excited triplet COopen0

Joint CNN and Variational Model for Fully-automatic Image Colorization

International audienceThis paper aims to couple the powerful prediction of the convolutional neural network (CNN) to the accuracy at pixel scale of the variational methods. In this work, the limitations of the CNN-based image colorization approaches are described. We then focus on a CNN which is able to compute a statistical distribution of the colors for each pixel of the image based on a learning over a large color image database. After describing its limitation, the variational method of [17] is briefly recalled. This method is able to select a color candidate among a given set while performing a regularization of the result. By combining this approach with a CNN, we designed a fully automatic image coloriza-tion framework with an improved accuracy in comparison with CNN alone. Some numerical experiments demonstrate the increased accuracy performed by our method

Signifikante Unterschiede in der schriftlichen Wissenskontrolle durch ein Blended-Learning-Konzept im Rahmen eines internistischen Untersuchungskurses: eine randomisiert-kontrollierte Pilotstudie

Background: Taking a medical history and performing a physical examination represent basic medical skills. However, numerous national and international studies show that medical students and physicians-to-be demonstrate substantial deficiencies in the proper examination of individual organ systems.Aim: The objective of this study was to conduct a randomized controlled pilot study to see if, in the context of a bedside clinical examination course in internal medicine, an additional app-based blended-learning strategy resulted in (a) higher satisfaction, better self-assessments by students when rating their history-taking skills (b1) and their ability to perform physical examinations (b2), as well as (c) higher multiple-choice test scores at the end of the course, when compared to a traditional teaching strategy.Methods: Within the scope of a bedside course teaching the techniques of clinical examination, 26 students out of a total of 335 students enrolled in the 2012 summer semester and 2012/2013 winter semester were randomly assigned to two groups of the same size. Thirteen students were in an intervention group (IG) with pre- and post-material for studying via an app-based blended-learning tool, and another 13 students were in a control group (CG) with the usual pre- and post-material (handouts). The IG was given an app specifically created for the history-taking and physical exam course, an application program for smartphones enabling them to view course material directly on the smartphone. The CG received the same information in the form of paper-based notes. Prior to course begin, all of the students filled out a questionnaire on sociodemographic data and took a multiple-choice pretest with questions on anamnesis and physical examination. After completing the course, the students again took a multiple-choice test with questions on anamnesis and physical examination.Results: When compared to the CG, the IG showed significantly more improvement on the multiple-choice tests after taking the clinical examination course (p=0.022). This improvement on the MC tests in the IG significantly correlated with the amount of time spent using the app (Spearman's rho=0.741, p=0.004).Conclusion: When compared to conventional teaching, an app-based blended-learning approach leads to improvement in test scores, possibly as a result of more intensive preparation for and review of the clinical examination course material.Hintergrund: Die Erhebung der Anamnese und die Durchführung körperlicher Untersuchungstechniken stellen eine grundlegende Kompetenz des ärztlichen Handelns dar. Allerdings zeigen zahlreiche nationale und internationale Studien, dass bei Medizinstudierenden und angehenden Ärzten erhebliche Defizite in der korrekten Durchführung der körperlichen Untersuchung einzelner Organsysteme vorliegen.Zielsetzung: Ziel der vorliegenden Studie war es, in einer randomisiert-kontrollierten Pilotstudie zu überprüfen, ob im Rahmen eines internistischen Bedside-Teaching ein zusätzliches App-basiertes Blended-Learning-Konzept im Vergleich zum klassischen Lehrkonzept (a) zu einer höheren Zufriedenheit, zu einer besseren Selbsteinschätzung der Studierenden bezüglich der Anamneseerhebung (b1) und der Durchführung der körperlichen Untersuchung (b2), als auch (c) zu besseren Multiple-Choice (MC)-Prüfungsergebnissen am Ende des Kurses führt.Methodik: Im Rahmen des internistischen Untersuchungskurses / Bedside-Teaching wurden von insgesamt 335 Studierenden des Sommersemesters 2012 und des Wintersemesters 2012/2013 26 Studierende randomisiert zwei gleich großen Gruppen zugewiesen: 13 Studierende einer Interventionsgruppe (IG) mit Vor- und Nachbereitungsmaterial anhand eines App-basierten Blended-Learning-Konzepts und 13 Studierende einer Kontrollgruppe (KG) mit konventionellem Vor- und Nachbereitungsmaterial (Handout). Die IG erhielt eine auf den Anamnese- und Untersuchungskurs zugeschnitte App, ein Anwendungsprogramm für Smartphones, das es ermöglicht, Lehrmaterial für den Untersuchungskurs direkt auf dem Smartphone einzusehen. Die KG erhielt dieselben Informationen anhand von Skripten. Vor Beginn des Untersuchungskurses füllten alle Studierenden Fragebögen zu soziodemographischen Daten aus und nahmen an einer Eingangs-MC-Klausur mit MC-Fragen zur Anamnese und körperlicher Untersuchung teil. Nach Abschluss des Untersuchungskurses nahmen die Studierenden erneut an einer MC-Klausur mit MC-Fragen zu Anamnese und körperlicher Untersuchung teil.Ergebnisse: Die IG zeigte im Vergleich zur KG eine signifikant höhere Verbesserung in den MC-Klausuren nach Durchlaufen des Untersuchungskurses (p=0,022). Die Verbesserung in den MC-Klausuren korrelierte in der IG signifikant mit der zeitlichen Beschäftigung mit der App (Spearmans rho=0.741, p=0.004). Schlussfolgerung: Ein App-basiertes Blended-Learning-Konzept führt im Vergleich zum klassischen Lehrkonzept, möglicherweise durch einer intensivere Vor- und Nachbereitung des klinischen Untersuchungskurses, zu einer Verbesserung in den Prüfungsergebnissen