AC-Calorimetry at High Pressure and Low Temperature

Recent developments of the AC-calorimetric technique adapted for the needs of high pressure experiments are discussed. A semi-quantitative measurement of the specific heat with a Bridgman-type of pressure cell as well as a diamond anvil cell is possible in the temperature range 0.1 K < T < 10 K. The pressure transmitting medium used to ensure good pressure conditions determines to a great extent via its thermal conductivity the operating frequency and thus the accessible temperature range. Investigations with different pressure transmitting media for T > 1.5 K reveal for solid He a cut-off frequency which is considerably higher than for steatite. Experiments below 1 K and pressures above 10 GPa clearly show that the pressure dependence of the linear temperature coefficient of the specific heat can be measured. It is in qualitative agreement to a related quantity obtained quasi-simultaneously by electrical resistivity measurements on the same sample.Comment: 14 pages, 7 figures. The manuscript with high resoultion figures (pdf-file, about 1Mb) can be downloaded from http://www.cpfs.mpg.de/~wilhelm

Welthandel: Frei und fair? Handelsabkommen in der Kritik

Vielfach wird behauptet, die globale Einkommensverteilung entwickle sich dramatisch auseinander und die unfaire globale Weltwirtschaftsordnung sei schuld daran. Stehen »fair trade« und »free trade« im Widerspruch zueinander oder nicht? Mit der Diskussion dieser Frage führen Gabriel Felbermayr, ifo Institut, und Wilhelm Kohler, Universität Tübingen, in das Thema ein. Für Christoph Scherrer, Universität Kassel, bieten die modernen Handelsabkommen eher einen »Schutz der Starken statt der Schwachen«. Die neuen Abkommen schützen die kapital- und forschungsstarken Unternehmen und sichern Investoren, die über erhebliche Finanzmittel verfügen. Als eine sinnvolle Alternative erscheint ihm, »das Regelwerk des Welthandels nach entwicklungspolitischen, sozialen und ökologischen Prinzipien auszurichten«. Richard Senti, ETH Zürich, macht darauf aufmerksam, dass mit den regionalen Integrationsabkommen so etwas wie eine zweite Welthandelsordnung entstanden ist, die im Widerstreit mit der WTO steht. Die regionalen Freihandelszonen haben in der jüngsten Vergangenheit ein starkes Eigenleben entwickelt, dass es ihnen schwer fallen werde, sich in die Welthandelsordnung einzubringen. Johannes Wallacher, Hochschule für Philosophie München, sieht sowohl Chancen als auch Risiken. Internationale Handelsbeziehungen bieten Chancen für mehr Wohlstand, aber bedingen auch höheren Anpassungsdruck. Peter-Christian Müller-Graff, Universität Heidelberg, sieht für klassische Freihandelsabkommen, die nur den Markzugang thematisieren, keine Zukunft. Sie bedürfen »der Anreicherung durch Schutzstandards und geeigneter und verlässlicher Mechanismen des Rechtsschutzes für die Marktakteure und gegebenenfalls auch der Mechanismen für Fälle gravierender asymmetrischer Entwicklungen«. Denn der Handel mit Produkten beinhalte mehr als isolierte Außenwirtschaftspolitik, er habe längst Fragen von Gesundheits-, Sozial-, Verbraucher- und Umweltpolitik erreicht. Nach Ansicht von Heribert Dieter, Stiftung Wissenschaf

Characterization of spotted hyena, Crocuta crocuta microsatellite loci

We have isolated 10 polymorphic microsatellite loci in the spotted hyena,Crocuta crocuta.The loci displayed between eight and 14 alleles in a minimum of 12 individuals tested. These loci will be used to investigate relatedness within social groups, the genetic structure of populations, sexual selection, and mate choice in spotted hyenas

Probing the phase diagram of CeRu_2Ge_2 by thermopower at high pressure

The temperature dependence of the thermoelectric power, S(T), and the electrical resistivity of the magnetically ordered CeRu_2Ge_2 (T_N=8.55 K and T_C=7.40 K) were measured for pressures p < 16 GPa in the temperature range 1.2 K < T < 300 K. Long-range magnetic order is suppressed at a p_c of approximately 6.4 GPa. Pressure drives S(T) through a sequence of temperature dependences, ranging from a behaviour characteristic for magnetically ordered heavy fermion compounds to a typical behaviour of intermediate-valent systems. At intermediate pressures a large positive maximum develops above 10 K in S(T). Its origin is attributed to the Kondo effect and its position is assumed to reflect the Kondo temperature T_K. The pressure dependence of T_K is discussed in a revised and extended (T,p) phase diagram of CeRu_2Ge_2.Comment: 7 pages, 6 figure

Multiple low-temperature skyrmionic states in a bulk chiral magnet

Magnetic skyrmions are topologically protected nanoscale spin textures with particle-like properties. In bulk cubic helimagnets, they appear under applied magnetic fields and condense spontaneously into a lattice in a narrow region of the phase diagram just below the magnetic ordering temperature, the so-called A-phase. Theory, however, predicts skyrmions to be locally stable in a wide range of magnetic fields and temperatures. Our neutron diffraction measurements reveal the formation of skyrmion states in large areas of the magnetic phase diagram, from the lowest temperatures up to the A-phase. We show that nascent and disappearing spiral states near critical lines catalyze topological charge changing processes, leading to the formation and destruction of skyrmionic states at low temperatures, which are thermodynamically stable or metastable depending on the orientation and strength of the magnetic field. Skyrmions are surprisingly resilient to high magnetic fields: the memory of skyrmion lattice states persists in the field polarized state, even when the skyrmion lattice signal has disappeared. These findings highlight the paramount role of magnetic anisotropies in stabilizing skyrmionic states and open up new routes for manipulating these quasi-particles towards energy-efficient spintronics applications

Intra- and interchain interactions in (Cu1/2¬Au1/2)CN, (Ag1/2¬Au1/2)CN, and (Cu1/3Ag1/3Au1/3)CN and their effect on one-, two- and three-dimensional order

Mixed-metal cyanides, (Cu1/2Au1/2)CN, (Ag1/2Au1/2)CN and (Cu1/3Ag1/3Au1/3)CN, adopt an AuCN-type structure in which metal-cyanide chains pack on a hexagonal lattice with metal atoms arranged in sheets. The interactions between and within the metal-cyanide chains are investigated using density-functional-theory (DFT) calculations, 13C solid-state NMR (SSNMR) and X-ray pair distribution function (PDF) measurements. Long-range metal and cyanide order is found within the chains: (–Cu–NC–Au–CN–)∞, (–Ag–NC–Au–CN–)∞ and (–Cu–NC–Ag–NC–Au–CN–)∞. Although Bragg diffraction studies establish that there is no long-range order between chains, X-ray PDF results show that there is local order between chains. In (Cu1/2Au1/2)CN and (Ag1/2Au1/2)CN, there is a preference for unlike metal atoms occurring as nearest neighbours within the metal sheets. A general mathematical proof shows that the maximum average number of heterometallic nearest-neighbour interactions on a hexagonal lattice with two types of metal atom is four. Calculated energies of periodic structural models show that those with four unlike nearest neighbours are most favourable. Of these, models in space group Immm give the best fits to the X-ray PDF data out to 8 Å, providing good descriptions of the short- and medium-range structures. This result shows that interactions beyond those of nearest neighbours must be considered when determining the structures of these materials. Such interactions are also important in (Cu1/3Ag1/3Au1/3)CN, leading to the adoption of a structure in Pmm2 containing mixed Cu-Au and silver-only sheets arranged to maximise the numbers of CuˑˑˑAu nearest- and next-nearest-neighbour interactions

1 m long multilayer-coated deformable piezoelectric bimorph mirror for adjustable focusing of high-energy X-rays

The Diamond Light Source (DLS) beamline I15-1 measures atomic pair distribution functions (PDF) using scattering of 40-80 keV X-rays. A unique focusing element was needed to condense these X-rays from an initial large cross section (11.0 mm H × 4.2 mm V) into a required spot size of FWHM ≈680 μm (H) × 20 μm (V) at a variable position between the sample and the detector. The large numerical aperture is achieved by coating a silicon substrate over 1 m long with three multilayer stripes of Bragg angle 4.2 mrad. One stripe selects X-rays of each energy 40.0, 65.4, and 76.6 keV. Sixteen piezoelectric bimorph actuators attached to the sides of the mirror substrate adjusted the reflecting surface’s shape. Focal spots of vertical width < 15 μm were obtained at three positions over a 0.92 m range, with fast, easy switching from one focal position to another. Minimized root mean square slope errors were close to 0.5 μrad after subtraction of a uniform curvature. Reflectivity curves taken along each stripe showed consistent high peaks with generally small angular variation of peak positions. This is the first application of a 1 m long multilayercoated bimorph mirror at a synchrotron beamline. Data collected with its help on a slice of a lithium ion battery’s cathode are presented

Volume and pressure dependences of the electronic, vibrational, and crystal structures of Cs2CoC l4: identification of a pressure-induced piezochromic phase at high pressure

This work investigates the high-pressure structure of Cs2CoCl4 and how it affects the electronic and vibrational properties using optical absorption, Raman spectroscopy, x-ray diffraction, and x-ray absorption in the 0-15 GPa range. In particular, we focus on the electronic and local structures of Co2+, since compression of Cs2CoCl4 yields structural transformations associated with change of coordination around Co2+, which are eventually responsible for the intense piezochromism at 7 GPa. This study provides a complete characterization of the electronic and vibrational structures of Cs2CoCl4 in the Pnma phase as a function of the cell volume and the local CoCl4 bond length, RCo-Cl, as well as its corresponding equation of state. In addition, our interest is to elucidate whether the phase transition undergone by Cs2CoCl4 at 7 GPa leads to a perovskite-layer-type structure where Co2+ is sixfold coordinated, decomposes into CsCl+CsCoCl3, or it involves an unknown phase with different coordination sites for Co2+. We show that Co2+ is sixfold coordinated in the high-pressure phase. The analysis of optical spectra and x-ray diffraction data suggests the formation of an interconnected structure of exchange-coupled Co2+ through edge-sharing octahedra at high pressure.Financial support from the Spanish Ministerio de Economía y Competitividad (Project No. MAT2015-69508-P) and MALTA-CONSOLIDER (Ref. No. MAT2015-71070-REDC) is acknowledged. We also acknowledge financial support and facilities from the Synchrotron SOLEIL (Proposal Ref. No. 20100989) and Synchrotron DIAMOND (Project Ref. No. EE1655). I.H. thanks the EU FP7 for his Marie Curie CIG grant (Grant No. MC-CIG 303535)

Engraftment of engineered ES cell–derived cardiomyocytes but not BM cells restores contractile function to the infarcted myocardium

Cellular cardiomyoplasty is an attractive option for the treatment of severe heart failure. It is, however, still unclear and controversial which is the most promising cell source. Therefore, we investigated and examined the fate and functional impact of bone marrow (BM) cells and embryonic stem cell (ES cell)–derived cardiomyocytes after transplantation into the infarcted mouse heart. This proved particularly challenging for the ES cells, as their enrichment into cardiomyocytes and their long-term engraftment and tumorigenicity are still poorly understood. We generated transgenic ES cells expressing puromycin resistance and enhanced green fluorescent protein cassettes under control of a cardiac-specific promoter. Puromycin selection resulted in a highly purified (>99%) cardiomyocyte population, and the yield of cardiomyocytes increased 6–10-fold because of induction of proliferation on purification. Long-term engraftment (4–5 months) was observed when co-transplanting selected ES cell–derived cardiomyocytes and fibroblasts into the injured heart of syngeneic mice, and no teratoma formation was found (n = 60). Although transplantation of ES cell–derived cardiomyocytes improved heart function, BM cells had no positive effects. Furthermore, no contribution of BM cells to cardiac, endothelial, or smooth muscle neogenesis was detected. Hence, our results demonstrate that ES-based cell therapy is a promising approach for the treatment of impaired myocardial function and provides better results than BM-derived cells