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281.
We explore how the Peccei-Quinn (PQ) axion parameter space can be constrained by the frequency-dependence dimming of radiation from astrophysical objects. To do so we perform accurate calculations of photon-axion conversion in the presence of a variable magnetic field. We propose several tests where the PQ axion parameter space can be explored with current and future astronomical surveys: the observed spectra of isolated neutron stars, occultations of background objects by white dwarfs and neutron stars, the light-curves of eclipsing binaries containing a white dwarf. We find that the lack of dimming of the light-curve of a detached eclipsing white dwarf binary recently observed, leads to relevant constraints on the photon-axion conversion. Current surveys designed for Earth-like planet searches are well matched to strengthen and improve the constraints on the PQ axion using astrophysical objects radiation dimming. 相似文献
282.
283.
The synthesis and liquid crystalline properties of novel achiral amides (Ia–g, IIa–g and IVa,b), achiral Schiff's bases (IIIa–g and Va–g), chiral amides (VI, VII) and chiral Schiff's bases (VIII–XI) incorporating a 1,3,4-oxadiazole ring are reported. All amides of the series I and II display an enantiotropic smectic A phase. The amide IVa,b did not show mesomorphic properties. Amides of the series Ia–g and IIa–g contain a flexible n-tetradecylthio chain, the other terminal substituent is an n-alkoxy chain and n-alkyl chain, respectively (n?=?4–10) and the 1,3,4-oxadiazole is in the terminal rigid core. Amides Ia–g have broader mesomorphic range and higher thermal stability than the corresponding amides IIa–g. Amides IVa,d contain the 1,3,4-oxadiazole ring in the centre of the rigid core and two flexible alkoxy chains as flexible terminal substituents. Thus, the mesomorphic properties are favoured if 1,3,4-oxadiazole is shifted to a terminal position of the rigid core. Schiff's bases IIIa–g display an enantiotropic dimorphism smectic C–smectic A. Schiff's bases IIIa–g have a broader mesomorphic range than the analogous amides Ia–g. Schiff's bases Va–g exhibit a dimorphism smectic A–nematic, and in contrast to this the analogous amide IVa,b did not show mesomorphism. The chiral amides VI and VII and chiral Schiff's bases X and XI did not show mesomorphic properties and only the chiral Schiff's bases VIII and IX display a chiral smectic C phase in a short mesomorphic range. A density functional theory theoretical study at the B3LYP/6–311++G(d,p) level was performed in order to analyse the structural features that must be related with the mesomorphic behaviour of the reported compounds. 相似文献
284.
Let Y be a closed manifold with a locally flat submanifold \({Z\subset Y}\) and X be a manifold with a boundary \({\partial X}\) . In this paper we construct the algebraic surgery theory of a stratified space that is homeomorphic to \({Y\cup X}\) with transversal intersection \({Y\cap X= Z=\partial X}\) . We develop the algebraic surgery theory of Ranicki to this case and we obtain relations between the introduced spectra that realize the obstruction groups and the structure sets. 相似文献
285.
Jesper J. H. B. Sattler Ines D. Gonzalez‐Jimenez Lin Luo Brien A. Stears Andrzej Malek David G. Barton Beata A. Kilos Mark P. Kaminsky Tiny W. G. M. Verhoeven Eline J. Koers Marc Baldus Bert M. Weckhuysen 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2014,126(35):9405-9410
A novel catalyst material for the selective dehydrogenation of propane is presented. The catalyst consists of 1000 ppm Pt, 3 wt % Ga, and 0.25 wt % K supported on alumina. We observed a synergy between Ga and Pt, resulting in a highly active and stable catalyst. Additionally, we propose a bifunctional active phase, in which coordinately unsaturated Ga3+ species are the active species and where Pt functions as a promoter. 相似文献
286.
Jain V Jimenez A Maldarelli C Tu RS 《Langmuir : the ACS journal of surfaces and colloids》2008,24(18):9923-9928
We describe a rationally designed peptide with tunable surface activity, where the dynamics of surface activity are an outcome of helical folding. Our rationally designed model peptide is surface-active only as an alpha-helix. We apply circular dichroism to show that the folded population can be controlled with changes in electrolyte concentration, and we apply pendant bubble tensiometry to explore dynamic surfactant activity. This study shows a peptide that responds to environmental stimuli with dynamic folding and surface activity. Extending this concept to selective binding peptides will lead to new tools, where dynamic surface activity is coupled to targeted binding. 相似文献
287.
An innovative way to improve fire‐retardant properties of different polymers by applying intumescent coatings on their surface has been studied. Two polymers have been investigated: polypropylene and polycarbonate. The surfaces were first subjected to a flaming treatment in order to clean them and to increase their wettability and thus improve the adhesion of the coatings. Two different formulations were then applied: a transparent intumescent varnish, based on an acrylic resin, and an intumescent coating based on polyvinylacetate resin. Different parameters have been obtained using several fire tests. The cone calorimeter, the limiting oxygen index and UL94 tests have been carried out to evaluate the fire‐retardant properties obtained for both the intumescent coating and the intumescent varnish. Results clearly evidence an outstanding improvement of the fire‐retardant properties using intumescent coatings without any incorporation of flame retardants in the bulk. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
288.
289.
Ma H Gibson EA Dittmer PJ Jimenez R Palmer AE 《Journal of the American Chemical Society》2012,134(5):2488-2491
Fluorescence resonance energy transfer (FRET)-based genetically encoded metal-ion sensors are important tools for studying metal-ion dynamics in live cells. We present a time-resolved microfluidic flow cytometer capable of characterizing the FRET-based dynamic response of metal-ion sensors in mammalian cells at a throughput of 15 cells/s with a time window encompassing a few milliseconds to a few seconds after mixing of cells with exogenous ligands. We have used the instrument to examine the cellular heterogeneity of Zn(2+) and Ca(2+) sensor FRET response amplitudes and demonstrated that the cluster maps of the Zn(2+) sensor FRET changes resolve multiple subpopulations. We have also measured the in vivo sensor response kinetics induced by changes in Zn(2+) and Ca(2+) concentrations. We observed an ~30 fold difference between the extracellular and intracellular sensors. 相似文献
290.
Gibson EA Gaudiosi DM Kapteyn HC Jimenez R Kane S Huff R Durfee C Squier J 《Optics letters》2006,31(22):3363-3365
Efficient reflection grisms for pulse-compression and material-dispersion compensation have been designed and demonstrated in a 40 fs, 300 microJ, 5 kHz downchirped pulse amplification system for the first time to our knowledge. A grism design for 800 nm femtosecond laser pulse dispersion compensation applications is realized by using standard, commercial diffraction gratings. 相似文献