Gold mobility in the crust: From source to ore deposit formation

Gold ist ein Edelmetall mit einer geringen Konzentration in der Erdkruste (~1.2 ng·g-1), während Au-Erz heute ab einem Au-Gehalt von mehr als 1 μg·g-1 profitabel ist. Um eine Anreicherung um drei Größenordnungen zu erreichen, muss Au aus einer Quelle mobilisiert, durch ein Fluid transportiert und in der Kruste durch effiziente Fällungsmechanismen konzentriert werden. Diese Arbeit zielt darauf ab, die Quelle-Senke-Prozesse besser zu verstehen, die die Bildung von Au-Lagerstätten und ihre Metallassoziation in orogenen und kontinentalen Vulkanbögen kontrollieren. Orogene Au-Lagerstätten im Central Lapland Greenstone Belt und im Pohjanmaa Belt (Finnland) stehen für erstere, letztere für den Vulkan Nea Kameni und die hybride Epithermal-SMS-Au-Mineralisierung von Kolumbo (Griechenland). Auf der Basis dieser Untersuchungsobjekte werden folgende Forschungsschwerpunkte entwickelt: 1) Verbesserung der Au-Analyse durch Laserablation und induktiv gekoppelte Plasma-Massenspektrometrie (LA-ICP-MS) auf Presspulver-Pellets (PPP) zur Untersuchung von Au-Muttergestein und Mobilisierungsprozessen; 2) Charakterisierung der Metallquellen, die bei der Bildung von Au-reichen Lagerstätten eine Rolle spielen; 3) Untersuchung der Mobilisierungs- und Transportmechanismen von Au und anderen Metallen; 4) Untersuchung der Mineralisierungsprozesse, die zur Bildung von Au-Lagerstätten führen, und der Parameter, die die Metallassoziation steuern. Um die Prozesse, die zur Mobilisierung von Au in der Kruste führen, besser einzugrenzen, wurde eine Methode für die PPP-LA-ICPMS- Analyse entwickelt, die eine Nachweisgrenze für Au von nur 0,10-0,05 ng·g-1 erreicht und die Analyse der Au-Verteilung in Au-armen Gesteinen ermöglicht. Die Untersuchung der finnischen orogenen Au-Lagerstätten und des zugehörigen Grundgebirges zeigt, wie die Metallassoziation und der Gehalt der Lagerstätten von den lokalen Mineralisierungsbedingungen, dem Zeitpunkt der Bildung während der mehrstufigen Mineralisierungsereignisse und der Muttergesteinslithologie abhängen, die den Gehalt an Au, unedlen Metallen und Liganden in den metamorphen Fluiden steuern. Zusätzlich unterstreicht diese Studie die Rolle der magmatischen Entgasung bei der Bildung von Au-Lagerstätten in Vulkanbögen. Die Untersuchung der magmatischen Differentiation in Kolumbo zeigt, dass Au und andere chalkophile Elemente bei der Entgasung mobilisiert werden, trotz früher Schwefelsättigung. Wir stellen eine starke Korrelation zwischen der Bildung von Sulfid-Gas-Tropfen im Magma und der Mineralisierung von Kolumbo fest, was darauf hindeutet, dass metallreiche, magmatische Fluide wahrscheinlich an der Bildung von Porphyr- und epithermalen Lagerstätten teilhaben. Die Untersuchung atypischer Lagerstätten wie orogener Au-Lagerstätten mit atypischer Metallvergesellschaftung und hybrider SMS-epithermaler Lagerstätten ermöglicht ein tieferes Verständnis der Au-Mobilität in der Kruste, da sie Metallmobilisierungsprozesse aufzeigen, die in typischen Lagerstätten nicht beobachtet werden können

High-pressure annealing of a prestructured nanocrystalline precursor to obtain tetragonal and orthorhombic polymorphs of Hf3N4

Transition metal nitrides containing metal ions in high oxidation states are a significant goal for the discovery of new families of semiconducting materials. Most metal nitride compounds prepared at high temperature and high pressure from the elements have metallic bonding. However amorphous or nanocrystalline compounds can be prepared via metal-organic chemistry routes giving rise to precursors with a high nitrogen:metal ratio. Using X-ray diffraction in parallel with high pressure laser heating in the diamond anvil cell this work highlights the possibility of retaining the composition and structure of a metastable nanocrystalline precursor under high pressure-temperature conditions. Specifically, a nanocrystalline Hf3N4 with a tetragonal defect-fluorite structure can be crystallized under high-P,T conditions. Increasing the pressure and temperature of crystallization leads to the formation of a fully recoverable orthorhombic (defect cottunite-structured) polymorph. This approach identifies a novel class of pathways to the synthesis of new crystalline nitrogen-rich transition metal nitrides

Evaluation of Parameter-based Attacks against Embedded Neural Networks with Laser Injection

Upcoming certification actions related to the security of machine learning (ML) based systems raise major evaluation challenges that are amplified by the large-scale deployment of models in many hardware platforms. Until recently, most of research works focused on API-based attacks that consider a ML model as a pure algorithmic abstraction. However, new implementation-based threats have been revealed, emphasizing the urgency to propose both practical and simulation-based methods to properly evaluate the robustness of models. A major concern is parameter-based attacks (such as the Bit-Flip Attack, BFA) that highlight the lack of robustness of typical deep neural network models when confronted by accurate and optimal alterations of their internal parameters stored in memory. Setting in a security testing purpose, this work practically reports, for the first time, a successful variant of the BFA on a 32-bit Cortex-M microcontroller using laser fault injection. It is a standard fault injection means for security evaluation, that enables to inject spatially and temporally accurate faults. To avoid unrealistic brute-force strategies, we show how simulations help selecting the most sensitive set of bits from the parameters taking into account the laser fault model.Comment: Accepted at 42nd International Conference on Computer Safety, Reliability and Security, SafeComp 202

Positive effects of ectomycorrhizal colonization on growth of seedlings of a tropical tree across a range of forest floor light conditions

In a shadehouse experiment we tested the effects of light, nutrients and ectomycorrhizal fungi (EMF) on the growth of Vatica albiramis van Slooten (Dipterocarpaceae) seedlings. We hypothesised that it is more advantageous for plants to form connections with EMF and to trade carbon for nutrients with EMF under high light than low light. The relationship between seedling growth and the proportion of ectomycorrhizal root tips was expected as positive in high light and as negative in low light. Light conditions simulated the forest understory (low; 3% full sunlight), a small gap (medium; 11%) and a large gap (high; 33%) and a fully factorial combination of nutrients (F−/+) and ectomycorrhizal colonization (EMF−/+) treatments were applied within light conditions. The application of EMF and nutrients did significantly alter seedling growth across the range of forest floor light conditions, however the key hypothesis was rejected as seedling growth under low light was not affected by increased EMF colonization of root tips (light:EMF colonization χ2 = 2.97, p = 0.23). In addition, the lack of difference in morphotype abundance across light conditions indicated that light changes may not favour the association to specific EMF in seedlings of this particular dipterocarp species. Our results suggest that antagonistic (non-beneficial to the plant) effects due to ectomycorrhizal colonization under a light constrained environment may not affect seedling growth of Vatica albirami

The ALMA Early Science View of FUor/EXor objects. IV. Misaligned Outflows in the Complex Star-forming Environment of V1647 Ori and McNeil's Nebula

We present Atacama Large Millimeter/sub-millimeter Array (ALMA) observations of the star-forming environment surrounding V1647 Ori, an outbursting FUor/EXor pre-MS star. Dust continuum and the (J = 2 - 1) $^{12}$CO, $^{13}$CO, C$^{18}$O molecular emission lines were observed to characterize the V1647 Ori circumstellar disc and any large scale molecular features present. We detect continuum emission from the circumstellar disc and determine a radius r = 40 au, inclination i = 17$^{\circ}$$^{+6}_{-9}$ and total disc mass of M$_{\mathrm{disk}}$ of ~0.1 M$_{\odot}$. We do not identify any disc structures associated with nearby companions, massive planets or fragmentation. The molecular cloud environment surrounding V1647 Ori is both structured and complex. We confirm the presence of an excavated cavity north of V1647 Ori and have identified dense material at the base of the optical reflection nebula (McNeil's Nebula) that is actively shaping its surrounding environment. Two distinct outflows have been detected with dynamical ages of ~11,700 and 17,200 years. These outflows are misaligned suggesting disc precession over ~5500 years as a result of anisotropic accretion events is responsible. The collimated outflows exhibit velocities of ~2 km s$^{-1}$, similar in velocity to that of other FUor objects presented in this series but significantly slower than previous observations and model predictions. The V1647 Ori system is seemingly connected by an "arm" of material to a large unresolved structure located ~20$"$ to the west. The complex environment surrounding V1647 Ori suggests it is in the early stages of star formation which may relate to its classification as both an FUor and EXor type object.Comment: 18 pages, 14 figures, 4 tables; accepted for publication in MNRA

High sporulation and overexpression of virulence factors in biofilms and reduced susceptibility to vancomycin and linezolid in recurrent Clostridium [Clostridioides] difficile infection isolates

Clostridium [Clostridioides] difficile infection (CDI) is one of the leading causes of diarrhea associated with medical care worldwide, and up to 60% of patients with CDI can develop a recurrent infection (R-CDI). A multi-species microbiota biofilm model of C. difficile was designed to evaluate the differences in the production of biofilms, sporulation, susceptibility to drugs, expression of sporulating (sigH, spo0A), quorum sensing (agrD1, and luxS), and adhesion-associated (slpA and cwp84) pathway genes between selected C. difficile isolates from R-CDI and non-recurrent patients (NR-CDI). We obtained 102 C. difficile isolates from 254 patients with confirmed CDI (66 from NR-CDI and 36 from R-CDI). Most of the isolates were biofilm producers, and most of the strains were ribotype 027 (81.374%, 83/102). Most C. difficile isolates were producers of biofilm (100/102), and most were strongly adherent. Sporulation was higher in the R-CDI than in the NR-CDI isolates (p = 0.015). The isolates from R-CDI patients more frequently demonstrated reduced susceptibility to vancomycin than isolates of NR-CDI patients (27.78% [10/36] and 9.09% [6/66], respectively, p = 0.013). The minimum inhibitory concentrations for vancomycin and linezolid against biofilms (BMIC) were up to 100 times and 20 times higher, respectively, than the corresponding planktonic MICs. Expression of sigH, spo0A, cwp84, and agrD1 was higher in R-CDI than in NR-CDI isolates. Most of the C. difficile isolates were producers of biofilms with no correlation with the ribotype. Sporulation was greater in R-CDI than in NR-CDI isolates in the biofilm model of C. difficile. The R-CDI isolates more frequently demonstrated reduced susceptibility to vancomycin and linezolid than the NR-CDI isolates in both planktonic cells and biofilm isolates. A higher expression of sporulating pathway (sigH, spo0A), quorum sensing (agrD1), and adhesion-associated (cwp84) genes was found in R-CDI than in NR-CDI isolates. All of these factors can have effect on the recurrence of the infection.Peer reviewe

Circulation of Highly Drug-Resistant Clostridium difficile Ribotypes 027 and 001 in Two Tertiary-Care Hospitals in Mexico

© 2018, Mary Ann Liebert, Inc.OBJECTIVE: To assess drug susceptibility and characterize Clostridium difficile ribotypes in isolates from two tertiary-care hospitals in Mexico. METHODS: Isolates were evaluated for genotyping, antimicrobial susceptibility testing and detection of mutations associated with drug resistance. PCR ribotyping was performed using a combination of gel-based and capillary electrophoresis-based approaches. RESULTS: MIC50 and MIC90 were ≥128 mg/L for ciprofloxacin, erythromycin, clindamycin, and rifampicin. There was no reduced susceptibility to metronidazole or tetracycline; however, reduced susceptibility to vancomycin (≥4 mg/L) and fidaxomicin (≥2 mg/L) was detected in 50 (40.3%) and 4 (3.2%) isolates, respectively. Furthermore, the rpoB Arg505Lys mutation was more frequently detected in isolates with high minimum inhibitory concentration (MIC) to rifampicin (≥32 mg/L) (OR = 52.5; 95% CI = 5.17-532.6; p < 0.000). Of the 124 C. difficile isolates recovered, 84 (66.7%) were of ribotype 027, 18 (14.5%) of ribotype 001, and the remainder were other ribotypes (353, 255, 220, 208, 176, 106, 076, 020, 019, 017, 014, 012, 003, and 002). CONCLUSION: Ribotypes 027 and 001 were the most frequent C. difficile isolates recovered in this study, and demonstrated higher MICs. Furthermore, we found four isolates with reduced susceptibility to fidaxomicin, raising a concern since this drug is currently unavailable in Mexican Hospitals.Peer reviewedFinal Accepted Versio