Using EBSD and TEM-Kikuchi patterns to study local crystallography at the domain boundaries of lead zirconate titanate

Reliable EBSD mapping of 90° domains in a tetragonal ferroelectric perovskite has been achieved for the first time, together with reliable automated orientation determination from TEM-Kikuchi patterns. This has been used to determine misorientation angles at 90° domain boundaries and thus local <i>c</i>/<i>a</i> ratios. The sources of orientation noise/error and their effects on the misorientation angle data have been thoroughly analyzed and it is found that this gives a cosine distribution of misorientation angles about the mean with a characteristic width related to the width of the orientation noise distribution. In most cases, a good agreement is found between local <i>c</i>/<i>a</i> ratios and global measurements by X-ray diffraction, but some clear discrepancies have also been found suggesting that real local variations are present, perhaps as a consequence of compositional inhomogeneities

v-K-data for silica from lifetime measurements under step-shaped loading history

Different methods were applied so far in order to determine subcritical crack growth for silica. Mostly, fracture mechanics standard tests with macro cracks were used for this purpose. In this report, we evaluated the subcritical crack growth curves from lifetime tests on silica bending specimens. The survivors were then tested under increased stress. Crack growth rates down to v=10$^{-12}$m/s were reached in this way. In the plot of v=f(K/K$_{Ic}$) slight material differences could be eliminated and suitable agreement with macro-crack results by Wiederhorn and Bolz [1] on DCB-specimens and Michalske et al. [2] on DCDC-specimens could be stated

Temperature dependence and mechanisms for vortex pinning by periodic arrays of Ni dots in Nb films

Pinning interactions between superconducting vortices in Nb and magnetic Ni dots were studied as a function of current and temperature to clarify the nature of pinning mechanisms. A strong current dependence is found for a square array of dots, with a temperature dependent optimum current for the observation of periodic pinning, that decreases with temperature as (1-T/Tc)3/2. This same temperature dependence is found for the critical current at the first matching field with a rectangular array of dots. The analysis of these results allows to narrow the possible pinning mechanisms to a combination of two: the interaction between the vortex and the magnetic moment of the dot and the proximity effect. Moreover, for the rectangular dot array, the temperature dependence of the crossover between the low field regime with a rectangular vortex lattice to the high field regime with a square configuration has been studied. It is found that the crossover field increases with decreasing temperature. This dependence indicates a change in the balance between elastic and pinning energies, associated with dynamical effects of the vortex lattice in the high field range.Comment: 12 text pages (revtex), 6 figures (1st jpeg, 2nd-6th postscript) accepted in Physical Review

Kinetic analysis of the early signaling steps of the human chemokine receptor CXCR4

G protein-coupled receptors (GPCRs) are biological switches that transduce extracellular stimuli into intracellular responses in the cell. Temporally resolving GPCR transduction pathways is key to understanding how cell signaling occurs. Here, we investigate the kinetics and dynamics of the activation and early signaling steps of the chemokine receptor CXCR4 in response to its natural ligands CXCL12 and macrophage migration inhibitory factor (MIF), using Förster resonance energy transfer-based approaches. We show that CXCR4 presents a multifaceted response to CXCL12, with receptor activation (≈0.6s) followed by a rearrangement in the receptor/G protein complex (≈1s), a slower dimer rearrangement (≈1.7s) and prolonged G protein activation (≈4s). In comparison, MIF distinctly modulates every step of the transduction pathway, indicating distinct activation mechanisms and reflecting the different pharmacological properties of these two ligands. Our study also indicates that CXCR4 exhibits some degree of ligand-independent activity, a relevant feature for drug development. SIGNIFICANCE STATEMENT: The CXCL12/CXCR4 axis represents a well-established therapeutic target for cancer treatment. We demonstrate that CXCR4 exhibits a multifaceted response that involves dynamic receptor dimer rearrangements, which is kinetically embedded between receptor-G protein complex rearrangements and G protein activation. The alternative endogenous ligand MIF behaves opposite to CXCL12 in each assay studied and does not lead to G protein activation. This detailed understanding of the receptor activation may aid in the development of more specific drugs against this target

Electronic excitation of furfural as probed by high-resolution vacuum ultraviolet spectroscopy, electron energy loss spectroscopy, and ab initio calculations

13 págs.; 7 figs.; 8 tabs.© 2015 AIP Publishing LLC. The electronic spectroscopy of isolated furfural (2-furaldehyde) in the gas phase has been investigated using high-resolution photoabsorption spectroscopy in the 3.5-10.8 eV energy-range, with absolute cross section measurements derived. Electron energy loss spectra are also measured over a range of kinematical conditions. Those energy loss spectra are used to derive differential cross sections and in turn generalised oscillator strengths. These experiments are supported by ab initio calculations in order to assign the excited states of the neutral molecule. The good agreement between the theoretical results and the measurements allows us to provide the first quantitative assignment of the electronic state spectroscopy of furfural over an extended energy range.F.F.S. and P.L.V. acknowledge the Portuguese Foundation for Science and Technology (FCT-MEC) through Grant Nos. SFRH/BPD/68979/2010 and SFRH/BSAB/105792/2014, respectively, the research Grant Nos. PTDC/FIS-ATO/1832/ 2012 and UID/FIS/00068/2013. P.L.V. also acknowledges his Visiting Research Fellow position at Flinders University, Adelaide, South Australia. The Patrimoine of the University of Liège, the Fonds National de la Recherche Scientifique, and the Fonds de la Recherche Fondamentale Collective of Belgium have also supported this research. E.L. and R.F.C.N. thank CNPq (Brazil) and the Science Without Borders Programme for opportunities to study abroad. The authors wish to acknowledge the beam time at the ISA synchrotron at Aarhus University, Denmark. The research leading to these results has received funding from the European Community’s Seventh Framework Programme (Grant No. FP7/2007-2013) CALIPSO under Grant Agreement No. 312284. D.B.J. thanks the Australian Research Council for financial support provided through a Discovery Early Career Research Award. M.J.B. also thanks the Australian Research Council for some financial support, while M.J.B. and M.C.A.L. acknowledge the Brazilian agencies CNPq and FAPEMIG for financial support. F.B. and G.G. acknowledge partial financial support from the Spanish Ministry MINECO (Project No. FIS2012-31230) and the EU COST Action No. CM1301 (CELINA). Finally, R.F.C., M.T.do N.V., M.H.F.B., and M.A.P.L. acknowledge support from the Brazilian agency CNPq.Peer Reviewe

Instability of the rhodium magnetic moment as origin of the metamagnetic phase transition in alpha-FeRh

Based on ab initio total energy calculations we show that two magnetic states of rhodium atoms together with competing ferromagnetic and antiferromagnetic exchange interactions are responsible for a temperature induced metamagnetic phase transition, which experimentally is observed for stoichiometric alpha-FeRh. A first-principle spin-based model allows to reproduce this first-order metamagnetic transition by means of Monte Carlo simulations. Further inclusion of spacial variation of exchange parameters leads to a realistic description of the experimental magneto-volume effects in alpha-FeRh.Comment: 10 pages, 13 figures, accepted for publication in Phys. Rev.

Transverse Phase Locking for Vortex Motion in Square and Triangular Pinning Arrays

We analyze transverse phase locking for vortex motion in a superconductor with a longitudinal DC drive and a transverse AC drive. For both square and triangular arrays we observe a variety of fractional phase locking steps in the velocity versus DC drive which correspond to stable vortex orbits. The locking steps are more pronounced for the triangular arrays which is due to the fact that the vortex motion has a periodic transverse velocity component even for zero transverse AC drive. All the steps increase monotonically in width with AC amplitude. We confirm that the width of some fractional steps in the square arrays scales as the square of the AC driving amplitude. In addition we demonstrate scaling in the velocity versus applied DC driving curves at depinning and on the main step, similar to that seen for phase locking in charge-density wave systems. The phase locking steps are most prominent for commensurate vortex fillings where the interstitial vortices form symmetrical ground states. For increasing temperature, the fractional steps are washed out very quickly, while the main step gains a linear component and disappears at melting. For triangular pinning arrays we again observe transverse phase locking, with the main and several of the fractional step widths scaling linearly with AC amplitude.Comment: 10 pages, 14 postscript figure

Structural Requirements for Dihydrobenzoxazepinone Anthelmintics: Actions against Medically Important and Model Parasites: Trichuris muris, Brugia malayi, Heligmosomoides polygyrus, and Schistosoma mansoni

Nine hundred million people are infected with the soil-transmitted helminths Ascaris lumbricoides (roundworm), hookworm, and Trichuris trichiura (whipworm). However, low single-dose cure rates of the benzimidazole drugs, the mainstay of preventative chemotherapy for whipworm, together with parasite drug resistance, mean that current approaches may not be able to eliminate morbidity from trichuriasis. We are seeking to develop new anthelmintic drugs specifically with activity against whipworm as a priority and previously identified a hit series of dihydrobenzoxazepinone (DHB) compounds that block motility of ex vivo Trichuris muris. Here, we report a systematic investigation of the structure–activity relationship of the anthelmintic activity of DHB compounds. We synthesized 47 analogues, which allowed us to define features of the molecules essential for anthelmintic action as well as broadening the chemotype by identification of dihydrobenzoquinolinones (DBQs) with anthelmintic activity. We investigated the activity of these compounds against other parasitic nematodes, identifying DHB compounds with activity against Brugia malayi and Heligmosomoides polygyrus. We also demonstrated activity of DHB compounds against the trematode Schistosoma mansoni, a parasite that causes schistosomiasis. These results demonstrate the potential of DHB and DBQ compounds for further development as broad-spectrum anthelmintics