Radio-colouration of diamond: a spectroscopic study

We have undertaken a study of the common green or orange-brown spots at the surface of rough diamond specimens, which are caused by alpha particles emanating from radioactive sources outside the diamond. Richly coloured haloes represent elevated levels of structural damage, indicated by strong broadening of the main Raman band of diamond, intense strain birefringence, and up-doming of spots due to their extensive volume expansion. Green radio-colouration was analogously generated through the irradiation of diamond with 8.8 MeV helium ions. The generation of readily visible radio-colouration was observed after irradiating diamond with ≥10¹⁵ He ions per cm². The accumulation of such a high number of alpha particles requires irradiation of the diamond from a radioactive source over long periods of time, presumably hundreds of millions of years in many cases. In the samples irradiated with He ions, amorphisation was observed in volume areas where the defect density exceeded 5 × 10^?3 Å^?3 (or 0.03 dpa; displacements per target atom). In contrast, graphitisation as a direct result of the ion irradiation was not observed. The green colouration transformed to brown at moderate annealing temperatures (here 450 °C). The colour transformation is associated with only partial recovery of the radiation damage. The colour change is mainly due to the destruction of the GR1 centre, explained by trapping of vacancies at A defects to form the H3 centre. An activation energy of ~2.4 ± 0.2 eV was determined for the GR1 reduction. The H3 centre, in turn, causes intense yellowish-green photoluminescence under ultraviolet illumination. Radio-colouration and associated H3 photoluminescence are due to point defects created by the ions irradiated, whereas lattice ionisation is of minor importance. This is concluded from the depth distribution of the colouration and the photoluminescence intensity (which corresponds to the defect density but not the ionisation distribution pattern). The effect of the implanted He ions themselves on the colour and photoluminescence seems to be negligible, as radio-colouration and H3 emission were analogously produced through irradiation of diamond with C ions. The photoluminescence emission becomes observable at extremely low defect densities on the order of 10^?6 Å^?3 (or 0.000006 dpa) and is suppressed at moderate defect densities of ~5 × 10^?4 Å^?3 (or ~0.003 dpa). Intensely brown-coloured diamond hence does not show the H3 emission anymore. Anneals up to 1,600 °C has reduced considerably irradiation damage and radio-colouration, but the structural reconstitution of the diamond (and its de-colouration) was still incomplete.     

Early Holocene M~6 explosive eruption from Plosky volcanic massif (Kamchatka) and its tephra as a link between terrestrial and marine paleoenvironmental records

We report tephrochronological and geochemical data on early Holocene activity from Plosky volcanic massif in the Kliuchevskoi volcanic group, Kamchatka Peninsula. Explosive activity of this volcano lasted for ~1.5 kyr, produced a series of widely dispersed tephra layers, and was followed by profuse low-viscosity lava flows. This eruptive episode started a major reorganization of the volcanic structures in the western part of the Kliuchevskoi volcanic group. An explosive eruption from Plosky (M~6), previously unstudied, produced tephra (coded PL2) of a volume of 10–12 km³ (11–13 Gt), being one of the largest Holocene explosive eruptions in Kamchatka. Characteristic diagnostic features of the PL2 tephra are predominantly vitric sponge-shaped fragments with rare phenocrysts and microlites of plagioclase, olivine and pyroxenes, medium- to high-K basaltic andesitic bulk composition, high-K, high-Al and high-P trachyandesitic glass composition with SiO₂ = 57.5–59.5 wt%, K₂O = 2.3–2.7 wt%, Al₂O₃ = 15.8–16.5 wt%, and P₂O₅ = 0.5–0.7 wt%. Other diagnostic features include a typical subduction-related pattern of incompatible elements, high concentrations of all REE (>10× mantle values), moderate enrichment in LREE (La/Yb ~ 5.3), and non-fractionated mantle-like pattern of LILE. Geochemical fingerprinting of the PL2 tephra with the help of EMP and LA-ICP-MS analyses allowed us to map its occurrence in terrestrial sections across Kamchatka and to identify this layer in Bering Sea sediment cores at a distance of >600 km from the source. New high-precision ¹⁴C dates suggest that the PL2 eruption occurred ~10,200 cal BP, which makes it a valuable isochrone for early Holocene climate fluctuations and permits direct links between terrestrial and marine paleoenvironmental records. The terrestrial and marine ¹⁴C dates related to the PL2 tephra have allowed us to estimate an early Holocene reservoir age for the western Bering Sea at 1,410 ± 64 ¹⁴C years. Another important tephra from the early Holocene eruptive episode of Plosky volcano, coded PL1, was dated at 11,650 cal BP. This marker is the oldest geochemically characterized and dated tephra marker layer in Kamchatka to date and is an important local marker for the Younger Dryas—early Holocene transition. One more tephra from Plosky, coded PL3, can be used as a marker northeast of the source at a distance of ~110 km.     

Carbonate diagenesis and feldspar alteration in fracture-related bleaching zones (Buntsandstein,central Germany): possible link to CO<Subscript>2</Subscript>-influenced fluid–mineral reactions

Fracture-related bleaching of Lower Triassic Buntsandstein red beds of central Germany was related to significant carbonate diagenesis and feldspar alteration caused by CO₂-rich fluids. Using cathodoluminescence microscopy and spectroscopy combined with electron microprobe analysis and stable carbon isotope study, two major fluid–mineral interactions were detected: (1) zoned, joint-filling calcites and zoned pore-filling calcite cements, the latter replacing an earlier dolomite, were formed during bleaching. During the calcite formation and dolomite–calcite transformation, iron was incorporated into the calcite cement crystal cores due to Fe availability from the coeval bleaching. The dedolomitisation was ultimately associated with a volume increase. The related permeability decrease implies a certain degree of sealing and increasing retention of CO₂, and the volume increase offers a minor CO₂ sink. Carbonate-rich sandstone, therefore, can provide advantages for underground CO₂ storage especially when situated in the fringes of the reservoir. (2) Alkali-feldspar alteration due to the bleaching fluids is reflected in cathodoluminescence spectra predominantly by the modulation of a brown luminescence emission peak (~620 nm). This peak represents a newly discovered effect related to alkali-feldspar alteration not solely associated with bleaching. Its modulation by the bleaching is interpreted to be due to Na depletion or a lattice defect in the Si–O bonds of the SiO₄-tetrahedron. Alteration reflected by this luminescence feature has a destructive effect on the feldspars implying the possibility of diminished rock integrity due to bleaching and, hence, CO₂-rich fluids. Two further CL spectral changes related to bleaching occur, (a) decreased intensity between around 570 nm assigned to Mn-depletion, and (b) increased amplitude and wavelength shift of the red (~680 nm) band. Converging evidence from carbonate and feldspar diagenesis, stable carbon isotope data and analysis of fracture directions suggests that CO₂ fluids contributed to a significant extent to the bleaching phenomena and alteration in the studied Buntsandstein strata.     

Crowdsourcing urban form and function

Urban form and function have been studied extensively in urban planning and geographical information science. However, gaining a greater understanding of how they merge to define the urban morphology remains a substantial scientific challenge. Toward this goal, this paper addresses the opportunities presented by the emergence of crowdsourced data to gain novel insights into form and function in urban spaces. We are focusing in particular on information harvested from social media and other open-source and volunteered datasets (e.g. trajectory and OpenStreetMap data). These data provide a first-hand account of form and function from the people who define urban space through their activities. This novel bottom-up approach to study these concepts complements traditional urban studies to provide a new lens for studying urban activity. By synthesizing recent advancements in the analysis of open-source data, we provide a new typology for characterizing the role of crowdsourcing in the study of urban morphology. We illustrate this new perspective by showing how social media, trajectory, and traffic data can be analyzed to capture the evolving nature of a city’s form and function. While these crowd contributions may be explicit or implicit in nature, they are giving rise to an emerging research agenda for monitoring, analyzing, and modeling form and function for urban design and analysis.     

The Need for Ultraviolet to Understand the Chemical Evolution of the Universe and Cosmology.

We identify an important set of key areas where an advanced observational Ultraviolet capability would have major impact on studies of cosmology and Galaxy formation in the young Universe. Most of these are associated with the Universe at z < 3–4. We address the issues associated with Dark matter evidence in the local Universe and the impact of the Warm-Hot Intergalactic Medium WHIM on the local Baryon count. The motivations to make ultraviolet (UV) studies of supernovae (SNe) are reviewed and discussed in the light of the results obtained so far by means of IUE and HST observations. It appears that UV studies of SNe can, and do lead to fundamental results not only for our understanding of the SN phenomenon, such as the kinematics and the metallicity of the ejecta, but also for exciting new findings in Cosmology, such as the tantalizing evidence for “dark energy” that seems to pervade the Universe and to dominate its energetics. The need for additional and more detailed UV observations is also considered and discussed.Finally we show the enormous importance of the UV for abundance evolution in the Intergalactic Medium (IGM), and the importance of the He II studies to identify re-ionization epochs, which can only be done in the UV.     

Energy release in air showers

A simulation study of the energy released in air due to the development of an extensive air shower has been carried out using the CORSIKA code. The contributions to the energy release from different particle species and energies as well as the typical particle densities are investigated. Special care is taken of particles falling below the energy threshold of the simulation which contribute about 10% to the total energy deposition. The dominant contribution to the total deposition stems from electrons and positrons from sub-MeV up to a few hundred MeV, with typical transverse distances between particles exceeding 1 mm for 10 EeV showers.     

Composition of impact melt particles and the effects of post‐impact alteration in suevitic rocks at the Yaxcopoil‐1 drill core,Chicxulub crater,Mexico

Abstract Petrographical and chemical analysis of melt particles and alteration minerals of the about 100 m‐thick suevitic sequence at the Chicxulub Yax‐1 drill core was performed. The aim of this study is to determine the composition of the impact melt, the variation between different types of melt particles, and the effects of post‐impact hydrothermal alteration. We demonstrate that the compositional variation between melt particles of the suevitic rocks is the result of both incomplete homogenization of the target lithologies during impact and subsequent post‐impact hydrothermal alteration. Most melt particles are andesitic in composition. Clinopyroxene‐rich melt particles possess lower SiO₂ and higher CaO contents. These are interpreted by mixing of melts from the silicate basement with overlying carbonate rocks. Multi‐stage post‐impact hydrothermal alteration involved significant mass transfer of most major elements and caused further compositional heterogeneity between melt particles. Following backwash of seawater into the crater, palagonitization of glassy melt particles likely caused depletion of SiO₂, Al₂O₃, CaO, Na₂O, and enrichment of K₂O and FeO_tot during an early alteration stage. Since glass is very susceptible to fluid‐rock interaction, the state of primary crystallization of the melt particles had a significant influence on the intensity of the post‐impact hydrothermal mass transfer and was more pronounced in glassy melt particles than in well‐crystallized particles. In contrast to other occurrences of Chicxulub impactites, the Yax‐1 suevitic rocks show strong potassium metasomatism with hydrothermal K‐feldspar formation and whole rock K₂0 enrichment, especially in the lower unit of the suevitic sequence. A late stage of hydrothermal alteration is characterized by precipitation of silica, analcime, and Na‐bearing Mg‐rich smectite, among other minerals. This indicates a general evolution from a silica‐undersaturated fluid at relatively high potassium activities at an early stage toward a silica‐oversaturated fluid at relatively high sodium activities at later stages in the course of fluid rock interaction.     

Temperature-jump induced cation exchange kinetics in (Co<Subscript>0.1</Subscript>Mg<Subscript>0.9</Subscript>)<Subscript>2</Subscript>SiO<Subscript>4</Subscript> olivine: an in situ optical spectroscopic study

In the olivine crystal structure, cations are distributed over two inequivalent octahedral sites, M1 and M2. Kinetics of cation exchange between the two octahedral sites in (Co_0.1Mg_0.9)₂SiO₄ single crystal have been studied in the temperature range from 600 to 800°C by monitoring the time evolution of the absorbance of Co²⁺ ions in M1 or M2 sites using optical spectroscopy after rapid temperature jumps. It was found from such temperature-jump induced relaxation experiments that with increasing temperature the absorbance of Co²⁺ ions in the M1 site decreases while that in the M2 site increases. This indicates a tendency of Co²⁺ cations to populate the M2 site with increasing temperatures and vice versa. The experimental relaxation data can be modeled using a triple exponential equation based on theoretical analysis. Activation energies of 221 ± 4 and 213 ± 10 kJ/mol were derived from relaxation experiments on the M2 site and M1 site, respectively, for the cation exchange processes in (Co_0.1Mg_0.9)₂SiO₄ olivine. Implications for cation diffusion at low temperatures are discussed.     

Reconstructing seawater δO from paired coral δO and Sr/Ca ratios: Methods, error analysis and problems, with examples from Tahiti (French Polynesia) and Timor (Indonesia)

We compare several statistical routines that may be used to calculate δ¹⁸O_sw and SSS from paired coral Sr/Ca and δ¹⁸O measurements. Typically, the δ¹⁸O_coral-SST relationship is estimated by linear regression of coral δ¹⁸O vs. SST. If this method is applied, evidence should be given that at a particular site SST and SSS do not co-vary. In the tropical oceans, SST and δ¹⁸O_sw (SSS) often co-vary, and this will bias the estimate of the regression slope of δ¹⁸O_coral-SST. Using a stochastic model, we show that covariance leads to a bias in the coefficients of the univariate regression equations. As the slope of the δ¹⁸O_coral-SST relationship has known, we propose to insert this value for γ₁ in the regression models. This requires that the constants of the regression equations are removed. To omit the constants, we propose to center the regression equations (i.e., to remove the mean values from the variables). The statistical error propagation is calculated to assess our ability to resolve past variations in δ¹⁸O_sw (SSS). At Tahiti, we find that the combined analytical uncertainties of coral δ¹⁸O and Sr/Ca equal the amplitude of the seasonal cycle of δ¹⁸O_sw (SSS). Therefore, we cannot resolve the seasonal cycle of SSS at Tahiti. At Timor, the error of reconstructed δ¹⁸O_sw (SSS) is lower than the magnitude of seasonal variations of δ¹⁸O_sw (SSS), and the seasonal cycle of δ¹⁸O_sw (SSS) can be resolved.