Strain imaging of a Cu2S switching device

Strain imaging of electrochemical behavior of a solid electrolyte Cu₂S in switching devices for nonvolatile memories is presented. The precipitation and dissolution of Cu, and the nonstoichiometry changes cause changes in volume. Strain imaging we have proposed detects the volume changes through the surface displacements using scanning probe microscopy and provides high resolution images. We observed the distributions of the electrochemical reactions in Cu₂S and located the Cu bridges causing switching.     

Machine learning for atomic forces in a crystalline solid: Transferability to various temperatures

Recently, machine learning has emerged as an alternative, powerful approach for predicting quantum‐mechanical properties of molecules and solids. Here, using kernel ridge regression and atomic fingerprints representing local environments of atoms, we trained a machine‐learning model on a crystalline silicon system to directly predict the atomic forces at a wide range of temperatures. Our idea is to construct a machine‐learning model using a quantum‐mechanical dataset taken from canonical‐ensemble simulations at a higher temperature, or an upper bound of the temperature range. With our model, the force prediction errors were about 2% or smaller with respect to the corresponding force ranges, in the temperature region between 300 K and 1650 K. We also verified the applicability to a larger system, ensuring the transferability with respect to system size.     

Non-Newtonian flow and normal stress phenomena in solutions of polystyrene in toluene

Summary Non-Newtonian flow and normal stress phenomena are studied with solutions of polystyrene in toluene with varying temperature, concentration and molecular weight.The temperature dependence of normal and shear stresses of a solution with fixed concentration can be described in terms of the shift factor,a _T , which is commonly used in the study of linear viscoelastic phenomena of polymeric systems.From the measurements of normal and shear stresses the elasticity contribution to flow behavior of polymer solution can be evaluated, and its dependences on concentration and molecular weight are discussed. Each of the tested solutions shows more or less non-Newtonian viscosity behavior, especially very strongly in solutions with high concentration and high molecular weight. And these solutions are mainly Hookean in shear, but non-Hookean character appears in solutions with high concentration and with rather low molecular weight.The zeroshear viscosityversus concentration relationship is found to obey ac ⁵-dependence in a certain range of concentration, while in the same concentration range the reciprocal of steady shear compliance shows ac ^1,5 c ²-dependence. The zeroshear viscosityversus molecular weight relationship of solutions at a fixed concentration obeys the well-knownM ^3,4-dependence above a certain critical value of molecular weight which is dependent on the concentration. While the reciprocal of compliance is almost independent of molecular weight above this value, and it seems to be somewhat affected by the type of polymers such as molecular weight heterogeneity and/or degree of branching of the polymer.

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Zusammenfassung Nicht-Newtonsches Fließen und Normalspannungsphänomene wurden an Lösungen von Polystyrol in Toluol bei verschiedenen Temperaturen und Konzentrationen sowie bei verschiedenem Molekulargewicht untersucht.Die Temperaturabhängigkeit der Normal- und Schubspannungen einer Lösung bestimmter Konzentration kann durch den Schift-Faktora _T , der allgemein bei der Betrachtung linearer viskoelastischer Phänomene polymerer Systeme gebraucht wird, beschrieben werden. Aus den Messungen der Normal- und Schubspannungen wurde der Elastizitätsbeitrag zu dem Fließverhalten der polymeren Lösung abgeleitet und seine Abhängigkeit von der Konzentration und dem Molekulargewicht diskutiert.Jede der geprüften Lösungen zeigte mehr oder weniger nicht-Newtonsches Viskositätsverhalten, besonders stark ausgeprägt in Lösungen mit hoher Konzentration und hohem Molekulargewicht. Die Lösungen zeigten bei Scherbeanspruchung hauptsächlichHookeschen Charakter. Der nicht-Hookesche Charakter trat eher auf in Lösungen mit hoher Konzentration und bei niedrigerem Molekulargewicht.Die Anfangsviskositäts-Konzentrationsbeziehunggehorcht einerc ⁵-Abhängigkeit in einem gewissen Konzentrationsbereich, während bei derselben Konzentration der reziproke Wert der Komplianz (Nachgiebigkeit) bei stationärem Scheren einec ^1,5- bisc ²-Abhängigkeit aufweist. Oberhalb eines gewissen kritischen Wertes des Molekulargewichts, der von der Konzentration abhängt, gilt die bekannteM ^3,4-Beziehung zwischen der Anfangsviskosität und dem Molekulargewicht.Der reziproke Wert der Komplianz (Nachgiebigkeit) hängt fast nicht von dem Molekulargewicht oberhalb eines kritischen Wertes ab, aber das scheint durch den Typ der polymeren Substanz, wie Polymolekularität oder durch den Verzweigungsgrad, beeinflußt zu sein.

     

Palladium‐Catalyzed Aza‐Wittig‐Type Condensation of Isoxazol‐5(4H)‐ones with Aldehydes

This paper describes the development of a palladium‐catalyzed decarboxylative inter‐ and intramolecular condensation reaction of isoxazol‐5(4 H)‐ones with carbonyl compounds in the presence of PPh₃, giving various 2‐azabuta‐1,3‐dienes or pyrroles in moderate to high yields.     

Rationally designed macrocyclic peptides as synergistic agonists of LPS-induced inflammatory response

Toll-like receptor 4 (TLR4) plays an important role in the regulation of the innate and adaptive immune response. Both agonists and antagonists of TLR4 are of considerable interest as drug leads for various disease indications. We herein report the rational design of two myeloid differentiation factor 2 (MD2)-derived macrocyclic peptides as TLR4 modulators, using the Rosetta Macromolecular Modeling software. The designed cyclic peptides, but not their linear counterparts, displayed synergistic activation of TLR signaling when co-administered with lipopolysaccharide (LPS). Although the understanding of the mechanism of action of these peptides remains elusive, these results underscore the utility of peptide cyclization for the discovery of biologically active agents, and also provide valuable tools for the investigation of TLR4 signaling.