Spin-gap opening accompanied by a strong magnetoelastic response in the S=1 magnetic dimer system Ba3BiRu2O9

Neutron diffraction, magnetization, resistivity, and heat capacity measurements on the 6H-perovskite Ba3BiRu2O9 reveal simultaneous magnetic and structural dimerization driven by strong magnetoelastic coupling. An isostructural but strongly displacive first-order transition on cooling through T*=176 K is associated with a change in the nature of direct Ru-Ru bonds within Ru2O9 face-sharing octahedra. Above T*, Ba3BiRu2O9 is an S=1 magnetic dimer system with intradimer exchange interactions J0/kB=320 K and interdimer exchange interactions J'/kB=-160 K. Below T*, a spin-gapped state emerges with \Delta\approx220 K. Ab initio calculations confirm antiferromagnetic exchange within dimers, but the transition is not accompanied by long range-magnetic order.Comment: 5 pages, 5 figures, accepted by Physical Review

Magnetic structures of βI-Li2CoSiO4 and γ0-Li2MnSiO4: crystal structure type vs. magnetic topology

The magnetic structure and properties of the candidate lithium-ion battery cathode materials Pbn21(≡Pna21) Li2CoSiO4 and P21/n Li2MnSiO4 have been studied experimentally using low-temperature neutron powder diffraction and magnetometry. Both materials undergo long-range antiferromagnetic ordering, at 14 K and 12 K respectively, due to super-super-exchange mediated by bridging silicate groups. Despite having different crystal structures (wurtzite- vs. “dipolar”-type), Li2CoSiO4 and Li2MnSiO4 have the same topology in terms of magnetic interactions, and adopt collinear magnetic structures of the same type with the propagation vectors (0,1/2,1/2) and (1/2,0,1/2) respectively. The magnetic moments in the two materials are aligned perpendicular-ly and obliquely to the distorted closed-packed layers of oxygen atoms. The experimentally observed values of the ordered magnetic moments, 2.9 μB and 4.6 μB, are close to those expected for d7 Co2+ and d5 Mn2+ re-spectively

Sodium manganese fluorosulphate with a triplite structure

The crystal structure of the NaMnSO4F fluorosulphate phase prepared by low-temperature solid-state synthesis has been solved and refined by the Rietveld analysis of synchrotron X-ray powder diffraction data. Isostructural to the naturally occurring triplite family of minerals, this compound crystallizes in monoclinic C2/c symmetry (#15) with unit cell parameters of a = 13.77027(17), b = 6.63687(8), c = 10.35113(14) Å, = 121.4795(3) and V = 806.78(2) Å3. Its structure is built of edge-sharing chains of distorted MO4F2 octahedra, which are interconnected by constituent SO4 tetrahedra to form a robust three-dimensional polyanionic framework. MO4F2 octahedra are randomly occupied by Na and Mn with close to 1:1 occupancy. This random mixing of cations among polyhedral building blocks means that there are no channels for Na-ion conduction, rendering it electrochemically inactive. The structure is discussed and compared to other known alkali metal fluorosulphates as well as to naturally occurring triplite-type minerals

Revisiting the cubic crystal structures of Sr4Nb2O9 and Sr5Nb2O10

We have synthesized polycrystalline and single crystal samples of Sr4Nb2O9 and Sr5Nb2O10 and revisited the crystal structure of the high-temperature cubic phase. By careful analysis of single-crystal X-ray diffraction (SXRD), powder synchrotron X-ray diffraction (Syn-PXRD) and powder neutron diffraction (PND) data, we arrive at a structure model in space group 4#3 (216), a subgroup of the reported 3# (225) model. The 4#3 model gives a better fit to the diffraction data, especially PND. We observed an interstitial oxide ion O3 on the 48h site near O1, which gives a tetrahedral Nb1−O polyhedron rather than an octahedral one as found in the 3# (225) model. The temperature-dependent conductivities of Sr4Nb2O9 and Sr5Nb2O10 in dried O2 were studied using impedance spectroscopy. The activation energies of Sr4Nb2O9 and Sr5Nb2O10 were estimated to be 1.18(1) eV and 1.17(4) eV respectively. This crystallographic arrangement of O1 and O3 (spread over split sites) is likely a key structural factor behind oxide ionic migration in Sr4Nb2O9 and Sr5Nb2O10

Tourism and the smartphone app: capabilities, emerging practice and scope in the travel domain.

Based on its advanced computing capabilities and ubiquity, the smartphone has rapidly been adopted as a tourism travel tool.With a growing number of users and a wide varietyof applications emerging, the smartphone is fundamentally altering our current use and understanding of the transport network and tourism travel. Based on a review of smartphone apps, this article evaluates the current functionalities used in the domestic tourism travel domain and highlights where the next major developments lie. Then, at a more conceptual level, the article analyses how the smartphone mediates tourism travel and the role it might play in more collaborative and dynamic travel decisions to facilitate sustainable travel. Some emerging research challenges are discussed

Structure evolution of Na2O2 from room temperature to 500 oC

Na2O2 is one of the possible discharge products from sodium-air batteries. Here we report the evolution of the structure of Na2O2 from room temperature to 500 oC using variable-temperature neutron and synchrotron X- ray powder diffraction. A phase transition from α-Na2O2 to β-Na2O2 is observed in the neutron diffraction measurements above 400 oC and the crystal structure of β-Na2O2 is determined from neutron diffraction data at 500 oC. α-Na2O2 adapts a hexagonal 6#2 (No. 189) structure and β-Na2O2 adapts a tetragonal I41/acd (No. 142) structure. The thermal expansion coefficients of α-Na2O2 is a = 2.98×10–5 K–1, c = 2.89×10–5 K–1 and V = 8.96×10–5 K–1 up to 400 oC and a ~10% volume expansion occurs during the phase transition from α- Na2O2 to β-Na2O2 due to the re-alignment/rotation of O22– groups. Both phases are electronic insulators according to DFT calculations with band gaps (both indirect) of 1.75 eV (α-Na2O2) and 2.56 eV (β-Na2O2). Impedance analysis from room temperature to 400 oC revealed a significant enhancement of conductivity at T ≥ 275 oC. α-Na2O2 shows higher conductivity (~10 times at T ≤ 275 oC and ~3 times at T > 275 oC) in O2 compared to in Ar. We confirmed, by dielectric analysis, that this enhanced conductivity is dominated by ionic conduction

Integrated Polyphenol-Based Hydrogel Templating Method for Functional and Structured Oxidic Nanomaterials

A straightforward fabrication method for tunable nanomaterials remains a key objective in the research areas of template chemistry, catalysis, and energy storage materials. A growing focus in materials chemistry is the development of structuring methods that are simple, scalable, and, at the same time, feasible with environmentally benign chemicals. We present a hydrogel-mediated templating method that yields customizable, porous transition-metal oxides. The protocol is extremely simple and includes predominately naturally occurring compounds. For example, the incorporation of sacrificial polymer latex into a polyphenolic hydrogel network produces xerogel composites with various filler contents. Voids are generated simultaneously during the pyrolysis of the dried gel, allowing for controlling the three-dimensional (3D) arrangement of titania nanocrystals. As a proof of concept, we use the produced macroporous titania as a negative electrode (anode) material in lithium-ion batteries. We demonstrate that the gel-derived macroporous anatase significantly reduces the capacity loss compared to its commercial or nonporous analogues. The modularity of this one-pot templating protocol is further demonstrated by the fabrication of titanate nanostructures and porous zirconia

Glucocorticoid Receptor Confers Resistance to Antiandrogens by Bypassing Androgen Receptor Blockade

SummaryThe treatment of advanced prostate cancer has been transformed by novel antiandrogen therapies such as enzalutamide. Here, we identify induction of glucocorticoid receptor (GR) expression as a common feature of drug-resistant tumors in a credentialed preclinical model, a finding also confirmed in patient samples. GR substituted for the androgen receptor (AR) to activate a similar but distinguishable set of target genes and was necessary for maintenance of the resistant phenotype. The GR agonist dexamethasone was sufficient to confer enzalutamide resistance, whereas a GR antagonist restored sensitivity. Acute AR inhibition resulted in GR upregulation in a subset of prostate cancer cells due to relief of AR-mediated feedback repression of GR expression. These findings establish a mechanism of escape from AR blockade through expansion of cells primed to drive AR target genes via an alternative nuclear receptor upon drug exposure

Complex 5d magnetism in a novel S = ½ trimer system, the 12L hexagonal perovskite Ba4BiIr3O12

The 12L hexagonal perovskite Ba4BiIr3O12 has been synthesized for the first time and characterized using high-resolution neutron and synchrotron x-ray diffraction as well as physical properties measurements. The structure contains Ir3O12 linear face-sharing octahedral trimer units, bridged by corner-sharing BiO6 octahedra. The average electronic configurations of Ir and Bi are shown to be 4+(d5) and 4+(s1) respectively, the same as for the S = ½ dimer system Ba3BiIr2O9 which undergoes a spin-gap opening with a strong magnetoelastic effect at T* = 74 K. Anomalies in magnetic susceptibility, heat capacity, electrical resistivity and unit cell parameters indeed reveal an analogous effect at T* ≈ 215 K in Ba4BiIr3O12. However, the transition is not accompanied by the opening of a gap in spin excitation spectrum, because antiferromagnetic coupling among s = ½ Ir4+ (d5) cations leads to the formation of a S = ½ doublet within the trimers, vs. S = 0 singlets within dimers. The change in magnetic state of the trimers at T* leads to a structural distortion, the energy of which is overcompensated for by the formation of S = ½ doublets. Extending this insight to the dimer system Ba3BiIr2O9 sheds new light on the more pronounced low-temperature anomalies observed for that compound

Impacts of coastal infrastructure on shoreline response to major hurricanes in southwest Louisiana

© The Author(s), 2022. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Cadigan, J., Bekkaye, J., Jafari, N., Zhu, L., Booth, A., Chen, Q., Raubenheimer, B., Harris, B., O’Connor, C., Lane, R., Kemp, G., Day, J., Day, J., & Ulloa, H. Impacts of coastal infrastructure on shoreline response to major hurricanes in southwest Louisiana. Frontiers in Built Environment, 8, (2022): 885215. https://doi.org/10.3389/fbuil.2022.885215.The Rockefeller Wildlife Refuge, located along the Chenier Plain in Southwest Louisiana, was the location of the sequential landfall of two major hurricanes in the 2020 hurricane season. To protect the rapidly retreating coastline along the Refuge, a system of breakwaters was constructed, which was partially completed by the 2020 hurricane season. Multi-institutional, multi-disciplinary rapid response deployments of wave gauges, piezometers, geotechnical measurements, vegetation sampling, and drone surveys were conducted before and after Hurricanes Laura and Delta along two transects in the Refuge; one protected by a breakwater system and one which was the natural, unprotected shoreline. Geomorphological changes were similar on both transects after Hurricane Laura, while after Delta there was higher inland sediment deposition on the natural shoreline. Floodwaters drained from the transect with breakwater protection more slowly than the natural shoreline, though topography profiles are similar, indicating a potential dampening or complex hydrodynamic interactions between the sediment—wetland—breakwater system. In addition, observations of a fluidized mud deposit in Rollover Bayou in the Refuge are presented and discussed in context of the maintenance of wetland elevation and stability in the sediment starved Chenier Plain.Funding for the study has been partially provided by the National Science Foundation through grants NSF 2139882, 2139883, 1829136, 1848650, and 1939275, as well as through the United States Army Corps of Engineers Regional Sediment Management program. Student support provided through the National Science Foundation Graduate Research Fellowship Program and the Louisiana Coastal Science Assistantship Program