The Essence of Quintessence and the Cost of Compression

Standard two-parameter compressions of the infinite dimensional dark energy model space show crippling limitations even with current Type Ia supernova (SN Ia) data unless strong priors are imposed. First, they cannot cope with rapid evolutionour best fit to the latest SN Ia data shows late and very rapid evolution to w0 = -2.85. However, all of the standard parameterizations (incorrectly) claim that this best fit is ruled out at more than 2 primarily because they track it well only at very low redshift, z 0.2. Furthermore, they incorrectly rule out the observationally compatible region w ≪ -1 for z > 1. Second, the parameterizations give wildly different estimates for the redshift of acceleration, which vary from zacc = 0.14 to zacc = 0.59. Although these failings are largely cured by including higher order terms (3 parameters), this results in new degeneracies and opens up large regions of previously ruled out parameter space. All of this casts serious doubt on the usefulness of the standard two-parameter compressions in the coming era of high-precision dark energy cosmology and emphasizes the need for decorrelated compressions with at least three parameters

CMB polarization power spectra contributions from a network of cosmic strings

We present the first calculation of the possible (local) cosmic string contribution to the cosmic microwave background polarization spectra from simulations of a string network (rather than a stochastic collection of unconnected string segments). We use field-theory simulations of the Abelian Higgs model to represent local U(1) strings, including their radiative decay and microphysics. Relative to previous estimates, our calculations show a shift in power to larger angular scales, making the chance of a future cosmic string detection from the B-mode polarization slightly greater. We explore a future ground-based polarization detector, taking the CLOVER project as our example. In the null hypothesis (that cosmic strings make a zero contribution) we find that CLOVER should limit the string tension mu to G mu < 0.12x10(-6) (where G is the gravitational constant), above which it is likely that a detection would be possible

Visualization of Charge Distribution in a Lithium Battery Electrode

We describe a method for direct determination and visualization of the distribution of charge in a composite electrode. Using synchrotron X-ray microdiffraction, state-of-charge profiles in-plane and normal to the current collector were measured. In electrodes charged at high rate, the signatures of nonuniform current distribution were evident. The portion of a prismatic cell electrode closest to the current collector tab had the highest state of charge due to electronic resistance in the composite electrode and supporting foil. In a coin cell electrode, the active material at the electrode surface was more fully charged than that close to the current collector because the limiting factor in this case is ion conduction in the electrolyte contained within the porous electrode

Optimizing baryon acoustic oscillation surveys – I. Testing the concordance ?CDM cosmology

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Effect of Surface Microstructure on Electrochemical Performance of Garnet Solid Electrolytes

Cubic garnet phases based on Al-substituted Li₇La₃Zr₂O₁₂ (LLZO) have high ionic conductivities and exhibit good stability versus metallic lithium, making them of particular interest for use in next-generation rechargeable battery systems. However, high interfacial impedances have precluded their successful utilization in such devices until the present. Careful engineering of the surface microstructure, especially the grain boundaries, is critical to achieving low interfacial resistances and enabling long-term stable cycling with lithium metal. This study presents the fabrication of LLZO heterostructured solid electrolytes, which allowed direct correlation of surface microstructure with the electrochemical characteristics of the interface. Grain orientations and grain boundary distributions of samples with differing microstructures were mapped using high-resolution synchrotron polychromatic X-ray Laue microdiffraction. The electrochemical characteristics are strongly dependent upon surface microstructure, with small grained samples exhibiting much lower interfacial resistances and better cycling behavior than those with larger grain sizes. Low area specific resistances of 37 Ω cm² were achieved; low enough to ensure stable cycling with minimal polarization losses, thus removing a significant obstacle toward practical implementation of solid electrolytes in high energy density batteries

Dual-Channel, Molecular-Sieving Core/Shell ZIF@MOF Architectures as Engineered Fillers in Hybrid Membranes for Highly Selective CO₂ Separation

A novel core/shell porous crystalline structure was prepared using a large pore metal organic framework (MOF, UiO-66-NH₂, pore size, ∼ 0.6 nm) as core surrounded by a small pore zeolitic imidazolate framework (ZIF, ZIF-8, pore size, ∼ 0.4 nm) through a layer-by-layer deposition method and subsequently used as an engineered filler to construct hybrid polysulfone (PSF) membranes for CO₂ capture. Compared to traditional fillers utilizing only one type of porous material with rigid channels (either large or small), our custom designed core/shell fillers possess clear advantages via pore engineering: the large internal channels of the UiO-66-NH₂ MOFs create molecular highways to accelerate molecular transport through the membrane, while the thin shells with small pores (ZIF-8) or even smaller pores generated at the interface by the imperfect registry between the overlapping pores of ZIF and MOF enhance molecular sieving thus serving to distinguish slightly larger N₂ molecules (kinetic diameter, 0.364 nm) from smaller CO₂ molecules (kinetic diameter, 0.33 nm). The resultant core/shell ZIF@MOF and as-prepared hybrid PSF membranes were characterized by transmission electron microscopy, X-ray diffraction, wide-angle X-ray scattering, scanning electron microscopy, Fourier transform infrared, thermogravimetric analysis, differential scanning calorimetry, and contact angle tests. The dependence of the separation performance of the membranes on the MOF/ZIF ratio was also studied by varying the number of layers of ZIF coatings. The integrated PSF-ZIF@MOF hybrid membrane (40 wt % loading) with optimized ZIF coating cycles showed improved hydrophobicity and excellent CO₂ separation performance by simultaneously increasing CO₂ permeability (CO₂ permeability of 45.2 barrer, 710% higher than PSF membrane) and CO₂/N₂ selectivity (CO₂/N₂ selectivity of 39, 50% higher than PSF membrane), which is superior to most reported hybrid PSF membranes. The strategy of using dual-channel molecular sieving core/shell porous crystals in hybrid membranes thus provides a promising means for CO₂ capture from flue gas

Crystal Structure of an Indigo@Silicalite Hybrid Related to the Ancient Maya Blue Pigment

The structure of the indigo@silicalite pigment, an analog of ancient Maya Blue, has been determined by combining X-ray Laue microdiffraction and powder diffraction techniques. After the adsorption of indigo into the calcined (monoclinic) silicalite sample, the powder diffraction pattern contained peaks from both orthorhombic (major phase) and monoclinic (minor phase) silicalite. Assuming that the orthorhombic phase was induced by the adsorption of indigo, Laue microdiffraction was used to map the unit cell changes (and thereby the indigo distribution) within a single crystal. It was found to be highly heterogeneous with empty monoclinic and indigo-induced orthorhombic domains. The Laue diffraction data indicated that the space group of the orthorhombic domains was <i>Pnma</i> rather than <i>P2</i>₁2₁2₁. With this information, the indigo@silicalite structure could be solved and refined from the powder diffraction data. The starting positions for two independent indigo molecules, described as rigid bodies, were obtained by simulated annealing, with a first molecule positioned in the straight channel and the second one in the sinusoidal channel. The positions and occupancies of these molecules and the positions of the framework atoms were then refined using the Rietveld method. Approximately four indigo molecules per unit cell were found, two per independent site, and possible local arrangements are suggested. The size of the indigo molecule prevents the structure from being fully ordered