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The isomer distribution of branched glycerol dialkyl glycerol tetraethers (brGDGTs) in soils has been shown to correlate to the local mean annual temperature. Here, we explore the use of brGDGT distributions as proxy for the elevation at which soil organic carbon is preferentially mobilized in the Central Himalaya. Soil brGDGT distributions collected along an altitudinal profile, spanning elevations from 200 to 4,450 m asl, are linearly correlated to elevation. We use this calibration to trace the provenance of soil organic matter in suspended sediments of rivers draining the Himalaya. BrGDGT distributions of fluvial sediments reflect the mean elevation of the soil cover in most catchments. Inverse modeling of the brGDGT data set suggests similar relative contribution to soil organic carbon mobilization from different land covers within a factor 2. We conclude that riverine soil organic carbon export in the Himalaya mostly occurs pervasively and is at the catchment scale insensitive to anthropogenic perturbations. Plain Language Summary: Soil degradation influences the global climate and has direct impacts on the ability of soils to deliver economic and ecological services. Identifying the source of eroded soil‐derived carbon entrained in sediments of large rivers remains challenging. In this contribution, we use the temperature‐sensitive signature of soil microbe‐derived organic molecules to trace the source of soil carbon exported in river sediments of the rapidly eroding Central Himalaya of Nepal. Molecular signatures of soils, sampled over a wide range of elevations, and hence temperatures are plotted on an elevation profile. River sediments are then compared to soil signatures in order to identify elevations of preferential soil export through rivers. Our data shows that soil‐derived carbon is sampled uniformly over most of the catchments, indicating that soil export by Himalayan rivers is not driven by localized human perturbations such as agriculture or deforestation. Key Points: A calibration for soil branched glycerol dialkyl glycerol tetraether (brGDGT) signals against an elevation profile is developedThe provenance of soil organic matter in riverine suspended sediments is traced based on corresponding brGDGT distributionsSoil organic carbon in most river sediments originates from the entire soil‐covered catchment, indicating uniform soil organic matter export [ABSTRACT FROM AUTHOR]

X-ray emission spectroscopy (XES) at the O Kα threshold has been used to investigate the electronic structure of a microporous pure calcined zeolite with the crystal structure of the MFI-type framework (silicalite), a deboronated MFI zeolite (DB-MFI), a pure mesoporous cubic MCM-48 material, a MCM-48 loaded with copper and zinc oxide nanoparticles (Cu/ZnO-MCM-48), and a crystalline layered silicic acid H-RUB-18. For comparison, the XES O Kα spectrum of pure α-quartz has also been recorded. In the nonresonant energy regime the XES O Kα spectra for all these compounds look very similar indicating that the electronic structure of the micro- and mesoporous silica materials is very similar to that of quartz. In the resonant regime, however, the spectra exhibit significant differences. In all the materials under study, the resonant XES O Kα spectra recorded at photon energies close to the positions of the O K edges show Raman-type inelastic peaks with an energy loss of 11 eV, originating from electronic excitations within these insulating materials. The prominent features in the XES O Kα spectra of α-quartz and H-RUB-18 are analyzed by means of quantum chemical ab initio cluster calculations. [ABSTRACT FROM AUTHOR]

The reduction of Cu(II) oxide species in siliceous matrixes of different porosity (MFI, FAU, MCM-48) and in alumosilicate MFI is analyzed by temperature-programmed reduction in hydrogen (TPR), by X-ray absorption fine structure and by transmission electron microscopy. The results indicate that hydrogen activation, which is a key step for the autocatalytic reduction mechanism, is not initiated unless the Cu metal nuclei formed exceed a critical size.

Five different hydrous layer silicates (HLSs) containing fer layers (ferrierite-type layers) were obtained by hydrothermal syntheses from mixtures of silicic acid, water and tetraalkylammonium/tetraalkylphosphonium hydroxides. The organic cations had been added as structure directing agents (SDA). A characteristic feature of the structures is the presence of strong to medium strong hydrogen bonds between the terminal silanol/siloxy groups of neighbouring layers. The five-layered silicates differ chemically only with respect to the organic cations. Structurally, they differ with respect to the arrangement of the fer layers relative to each other, which is distinct for every SDA-fer-layer system. RUB-20 (containing tetramethylammonium) and RUB-40 (tetramethylphosphonium) are monoclinic with stacking sequence AAA and shift vectors between successive layers 1aO + 0b0 + 0.19c0 and 1a0 + 0b0 + 0.24c0, respectively. RUB-36 (diethyldimethylammonium), RUB-38 (methyltriethylammonium) and RUB-48 (trimethylisopropylammonium) are orthorhombic with stacking sequence ABAB and shift vectors 0.5a0 + 0b0 ± 0.36c0, 0.5a0 + 0b0 + 0.5c0 and 0.5a0 + 0b0 ± 0.39c0, respectively. Unprecedented among the HLSs, two monoclinic materials are made up of fer layers which possess a significant amount of ordered defects within the layer. The ordered defects involve one particular Si-O-Si bridge which is, to a fraction of ca. 50%, hydrolyzed to form nests of two uSi-OH groups. When heated to 500-600 °C in air, the HLSs condense to form framework silicates. Although all layered precursors were moderately to well ordered, the resulting framework structures were of quite different crystallinity. The orthorhombic materials RUB-36, -38 and -48, general formula SDA4Si36O72(OH)4, which possess very strong hydrogen bonds (d[O...O] 2.4 Å), transform into a fairly or well ordered CDO-type silica zeolite RUB-37. The monoclinic materials RUB-20 and -40, general formula SDA2Si18O36(OH)2OH, possessing medium strong hydrogen bonds (d[O...O] 2.65 Å) are transformed into poorly ordered framework silicates. Some rules of thumb can be established concerning the successful zeolite synthesis via a topotactic condensation of layered precursors. Favourably, the precursor (i) possesses already a well ordered structure without defects, (ii) contains strong inter-layer hydrogen bonds and does not contain strong intra-layer hydrogen bonds and (iii) contains a suitable cation. The nature of the organic cation (size, geometry, flexibility, thermal stability) plays a key role in the formation of a microporous tectosilicate with well ordered structure. RUB-36 which meets these criteria yields a well ordered condensation product (RUB-37). [ABSTRACT FROM AUTHOR]

Upcoming high-intensity laser systems will be able to probe the quantum-induced nonlinear regime of electrodynamics. So far unobserved QED phenomena such as the discovery of a nonlinear response of the quantum vacuum to macroscopic electromagnetic fields can become accessible. In addition, such laser systems provide for a flexible tool for investigating fundamental physics. Primary goals consist in verifying so far unobserved QED phenomena. Moreover, strong-field experiments can search for new light but weakly interacting degrees of freedom and are thus complementary to accelerator-driven experiments. I review recent developments in this field, focusing on photon experiments in strong electromagnetic fields. The interaction of particle-physics candidates with photons and external fields can be parameterized by low-energy effective actions and typically predict characteristic optical signatures. I perform first estimates of the accessible new-physics parameter space of high-intensity laser facilities such as POLARIS and ELI. [ABSTRACT FROM AUTHOR]

The derivation of a convergent series representation for the quantum electrodynamic effective action obtained by two of us (S.R.V. and D.R.L.) in [Can. J. Phys. 71, 389 (1993)] is reexamined. We present more details of our original derivation. Moreover, we discuss the relation of the electric-magnetic duality to the integral representation for the effective action, and we consider the application of nonlinear convergence acceleration techniques that permit the efficient and reliable numerical evaluation of the quantum correction to the Maxwell Lagrangian. [ABSTRACT FROM AUTHOR]

In an attempt to reduce the incidence of skin cancer, cancer foundations have run educational campaigns which encourage the general population to limit their solar UVR exposures. An important part of these campaigns, in particular in Australia, but also more recently in Europe and the U.S., has been the adoption of protective measures such as sunscreens, hats, sunglasses and clothing. The protective properties of fabrics and clothing against ultraviolet radiation (UVR) have been known for some time, but recently there has been considerable interest in quantifying the degree of protection. This has been generated, in part, by the requirements for occupational protection for outdoor workers as well as the provision of UVR protection for the recreational market. The quantification of UVR protection has been laboratory based using in vitro test methods. Development of a standard test method has become an important part of the testing process' and this paper presents results from an intercomparison involving five independent testing laboratories. Agreement is good, in particular for samples with protection factors below 50. Technical difficulties and sources of errors associated with the measurements are discussed. [ABSTRACT FROM AUTHOR]