Some remarks on correlations between conflict and instability

International audienceA study of the stability of classical systems under the influence of two conflicting single-well, single-variable potentials is presented. The control parameters are a so-called conflict parameter c, the distance between the two conflicting attractors, and an asymmetry parameter a which determines the relative strength of the two attractors. For convex potentials, the influence of conflict on the system stability depends on the sign of the third derivative of the conflicting potential functions, resulting in two categories called U- and V-type potentials. The introduction of a concave branch (bias) in convex conflicting potentials qualitatively changes the system behavior, by generating bifurcation and discontinuity. The cusp catastrophe can be redefined as the conflict between two such biased single-well potentials. The main interest of the new representation potentially lies in the evocative power of the control parameters a and c. The mapping of (a,c) on (u,v), the traditional control parameters of the cusp catastrophe, is given. The cusp develops above a certain critical value of the conflict parameter c

Synthesis by the polyol process and ionic conductivity of nanostructured La2Mo2O9 powders

International audienceLa2Mo2O9 nanostructured powders were synthesized by the polyol process. The effects of the nature of the polyol, the refluxing time, the hydrolysis ratio, the metal concentration and the addition of hydroxide ions, on the purity and morphology of the powders are determined. Two main morphologies are observed, the particles being in the shape of platelets or spheres, with respectively diethylene glycol or ethylene glycol as solvent. A specific surface area of 24 m2/g was reached by varying the metal concentration. The conductivity measurements were recorded on pellets that present in some cases a closed porosity, the relative density reaching 95% without any milling step. According to the synthesis parameters, the grain conductivity can be slightly increased, the total conductivity remaining only slightly lower than that of pellets made of powders synthesized by solid state reaction

Giant oxygen isotope effect on the metal-insulator transition of RNiO{sub 3} perovskites

The metal to insulator transition displayed by all the members of the perovskite family RNiO{sub 3} (R = 4f rare earth different from La) has attracted a lot of interest since it constitutes one of the few examples of this phenomenon in perfectly stoichiometric compounds. In spite of the great deal of work performed during the last six years, the mechanism responsible for the electronic localization is still a matter of controversy. The observation of unusually large O isotope shifts on the metal-insulator temperature T{sub MI} reported in this study represents an important advance since it clearly proves the dominant role of the electron lattice interaction as driving force for the transition. Moreover, the good agreement between this observation and a simple model based on the existence of Jahn-Teller polarons in the metallic state gives further qualitative and quantitative support to the polaronic picture recently suggested to account for O isotope effects in other 3d transition metal oxides containing Jahn-Teller ions

The barocaloric effect: A Spin-off of the Discovery of High-Temperature Superconductivity

Some key results obtained in joint research projects with Alex M\"uller are summarized, concentrating on the invention of the barocaloric effect and its application for cooling as well as on important findings in the field of high-temperature superconductivity resulting from neutron scattering experiments.Comment: 26 pages, 9 figure

Angiotensin inhibition enhances drug delivery and potentiates chemotherapy by decompressing tumour blood vessels

Cancer and stromal cells actively exert physical forces (solid stress) to compress tumour blood vessels, thus reducing vascular perfusion. Tumour interstitial matrix also contributes to solid stress, with hyaluronan implicated as the primary matrix molecule responsible for vessel compression because of its swelling behaviour. Here we show, unexpectedly, that hyaluronan compresses vessels only in collagen-rich tumours, suggesting that collagen and hyaluronan together are critical targets for decompressing tumour vessels. We demonstrate that the angiotensin inhibitor losartan reduces stromal collagen and hyaluronan production, associated with decreased expression of profibrotic signals TGF-β1, CCN2 and ET-1, downstream of angiotensin-II-receptor-1 inhibition. Consequently, losartan reduces solid stress in tumours resulting in increased vascular perfusion. Through this physical mechanism, losartan improves drug and oxygen delivery to tumours, thereby potentiating chemotherapy and reducing hypoxia in breast and pancreatic cancer models. Thus, angiotensin inhibitors—inexpensive drugs with decades of safe use—could be rapidly repurposed as cancer therapeutics.National Cancer Institute (U.S.) (Grant P01-CA080124)National Cancer Institute (U.S.) (Grant R01-CA126642)National Cancer Institute (U.S.) (Grant R01-CA085140)National Cancer Institute (U.S.) (Grant R01-CA115767)National Cancer Institute (U.S.) (Grant R01-CA098706)United States. Dept. of Defense. Breast Cancer Research Program (Innovator Award W81XWH-10-1-0016)Lustgarten Foundation (Dana-Farber Cancer Institute/David H. Koch Institute for Integrative Cancer Research at MIT Bridge Project Grant

Frustration wave order in iron(II) oxide spinels

Frustrated magnetic materials provide a great laboratory to study the interplay between classical order and quantum fluctuations. The authors study the frustrated magnetic ground states of two Fe spinel oxides showing that the frustration is a fluctuating characteristic that manifests itself as a “frustration wave

A family of oxide ion conductors based on the ferroelectric perovskite Na0.5Bi0.5TiO3

Oxide ion conductors find important technical applications in electrochemical devices such as solid-oxide fuel cells (SOFCs), oxygen separation membranes and sensors1, 2, 3, 4, 5, 6, 7, 8, 9. Na0.5Bi0.5TiO3 (NBT) is a well-known lead-free piezoelectric material; however, it is often reported to possess high leakage conductivity that is problematic for its piezo- and ferroelectric applications10, 11, 12, 13, 14, 15. Here we report this high leakage to be oxide ion conduction due to Bi-deficiency and oxygen vacancies induced during materials processing. Mg-doping on the Ti-site increases the ionic conductivity to ~0.01 S cm−1 at 600 °C, improves the electrolyte stability in reducing atmospheres and lowers the sintering temperature. This study not only demonstrates how to adjust the nominal NBT composition for dielectric-based applications, but also, more importantly, gives NBT-based materials an unexpected role as a completely new family of oxide ion conductors with potential applications in intermediate-temperature SOFCs and opens up a new direction to design oxide ion conductors in perovskite oxides

The constraint functions: an attempt to evaluate the constraint rate inside structures that undergo ordered magnetic frustration

International audienceWe propose a simple way to determine the constraint rate in ordered frustrated magnetic structures, based upon the calculation of the reduced energy of the system. The notion of a constraint function is illustrated using the example of the symmetrical triangular platelet, for which the evolution of constraint with the coupling constants ratio is studied. The constraint rates of some classical structures and real compounds estimated by this method are presented