Relatively oxidized conditions for diamond formation at Udachnaya (Siberia)

Thanks to the physical strength of diamonds and their relatively unreactive chemical nature, their mineral inclusions may remain exceptionally preserved from alteration processes and chemical exchanges with surrounding minerals, fluids and/or melts following diamond formation. Cr-bearing spinels are relatively common inclusions found in peridotitic diamonds and important oxybarometers providing information about the oxygen fugacity (fO2) of their source mantle rocks. Here, we investigated a magnesiochromite-olivine touching pair in a diamond from the Udachnaya kimberlite (Siberia) by in situ single-crystal X-ray diffraction and energy-domain synchrotron Mossbauer spectroscopy, aiming to constrain the physical-chemical conditions of diamond formation and to explore the redox state of this portion of the Siberian craton when the diamond was formed. The P-T-fO(2) entrapment conditions of the inclusion pair, determined by thermo- and oxybarometric analyses, are similar to 5.7(0.4) GPa and similar to 1015(50) ? (although entrapment at higher T and re-equilibration during subsequent mantle storage are also possible) and fO(2) near the enstatite-magnesite-olivine-diamond (EMOD) buffer. The determined fO(2) is similar to, or slightly more oxidized than, those of xenoliths from Udachnaya, but whilst the xenoliths last equilibrated with the surrounding mantle just prior to their entrainment in the kimberlite at similar to 360 Ma, the last equilibration of the inclusion pair is much older, occurring at 3.5-3.1, similar to 2 or similar to 1.8 Ga before final encapsulation in its host diamond. Hence, the similarity between xenoliths and inclusion fO(2) values indicates that the modern redox state of this portion of the Siberian lithosphere was likely attained relatively early after its formation and may have persisted for billions of years after diamond formation, at least at the local scale. Moreover, the oxygen fugacity determination for the inclusion pair provides direct evidence of diamond formation near the EMOD buffer and is consistent with recent models suggesting relatively oxidized, water-rich CHO fluids as the most likely parents for lithospheric diamonds

The impact of COVID-19 on radiological findings in patients accessing the emergency department: a multicentric study

The aim of this multicentric study is to illustrate how the COVID-19 pandemic lockdown affected the workload and outcomes of radiological examinations in emergency radiology

Diamond-inclusion system recording old deep lithosphere conditions at Udachnaya (Siberia)

Diamonds and their inclusions are unique fragments of deep Earth, which provide rare samples from inaccessible portions of our planet. Inclusion-free diamonds cannot provide information on depth of formation, which could be crucial to understand how the carbon cycle operated in the past. Inclusions in diamonds, which remain uncorrupted over geological times, may instead provide direct records of deep Earth’s evolution. Here, we applied elastic geothermobarometry to a diamond-magnesiochromite (mchr) host-inclusion pair from the Udachnaya kimberlite (Siberia, Russia), one of the most important sources of natural diamonds. By combining X-ray diffraction and Fourier-transform infrared spectroscopy data with a new elastic model, we obtained entrapment conditions, Ptrap = 6.5(2) GPa and Ttrap = 1125(32)–1140(33) °C, for the mchr inclusion. These conditions fall on a ca. 35 mW/m2 geotherm and are colder than the great majority of mantle xenoliths from similar depth in the same kimberlite. Our results indicate that cold cratonic conditions persisted for billions of years to at least 200 km in the local lithosphere. The composition of the mchr also indicates that at this depth the lithosphere was, at least locally, ultra-depleted at the time of diamond formation, as opposed to the melt-metasomatized, enriched composition of most xenoliths

T. brucei Infection Reduces B Lymphopoiesis in Bone Marrow and Truncates Compensatory Splenic Lymphopoiesis through Transitional B-Cell Apoptosis

African trypanosomes of the Trypanosoma brucei species are extracellular protozoan parasites that cause the deadly disease African trypanosomiasis in humans and contribute to the animal counterpart, Nagana. Trypanosome clearance from the bloodstream is mediated by antibodies specific for their Variant Surface Glycoprotein (VSG) coat antigens. However, T. brucei infection induces polyclonal B cell activation, B cell clonal exhaustion, sustained depletion of mature splenic Marginal Zone B (MZB) and Follicular B (FoB) cells, and destruction of the B-cell memory compartment. To determine how trypanosome infection compromises the humoral immune defense system we used a C57BL/6 T. brucei AnTat 1.1 mouse model and multicolor flow cytometry to document B cell development and maturation during infection. Our results show a more than 95% reduction in B cell precursor numbers from the CLP, pre-pro-B, pro-B, pre-B and immature B cell stages in the bone marrow. In the spleen, T. brucei induces extramedullary B lymphopoiesis as evidenced by significant increases in HSC-LMPP, CLP, pre-pro-B, pro-B and pre-B cell populations. However, final B cell maturation is abrogated by infection-induced apoptosis of transitional B cells of both the T1 and T2 populations which is not uniquely dependent on TNF-, Fas-, or prostaglandin-dependent death pathways. Results obtained from ex vivo co-cultures of living bloodstream form trypanosomes and splenocytes demonstrate that trypanosome surface coat-dependent contact with T1/2 B cells triggers their deletion. We conclude that infection-induced and possibly parasite-contact dependent deletion of transitional B cells prevents replenishment of mature B cell compartments during infection thus contributing to a loss of the host's capacity to sustain antibody responses against recurring parasitemic waves

Heterologous Expression and Patch-Clamp Recording of P2X Receptors in HEK293 Cells

P2X receptors (P2XRs) are ligand-gated ion channels gated by extracellular adenosine 5′-triphosphate (ATP) and play a critical role in mediating ATP-induced purinergic signaling in physiological and pathological processes. Heterologous expression of P2XR in human embryonic kidney 293 (HEK293) cells and measurement of P2XR-mediated currents using patch-clamp recording technique have been widely used to study the biophysical and pharmacological properties of these receptors. Combination of electrophysiology with site-directed mutagenesis and structural information has shed light on the molecular basis for receptor activation and mechanisms of actions by receptor antagonists and modulators. It is anticipated that such methodologies will continue helping us to provide more mechanistic understanding of P2XRs and to test novel receptor antagonists and allosteric modulators for therapeutical purposes. In this chapter, we describe protocols of transiently or stably expressing the P2XR in HEK293 cells and measuring P2XR-mediated currents by using whole-cell recording

Monocular Vision-Based Pose Estimation of Uncooperative Spacecraft

Activities in outer space have entered a new era of growth, fostering human development and improving key Earth-based applications such as remote sensing, navigation, and telecommunication. The recent creation of SpaceX's Starlink constellation as well as the steep increase in CubeSat launches are expected to revolutionize the way we use space and extend the current capabilities of satellite-based technology. However, this steep increase in the number of human-made objects is rapidly leading to higher collision risks in congested Earth orbits. This has led to questioning whether this trend is sustainable on the long term, and ultimately to the need to tackle sustainability in space.The recent decade has seen considerable efforts by Space Agencies to both prevent major collisions in orbit via Active Debris Removal (ADR) missions and to extend the lifetime of the functioning satellites with On-Orbit Servicing (OOS). Unfortunately, the approach and capture of space debris objects is complicated by the fact that these targets are uncooperative and cannot aid close-proximity operations, leading to critical challenges in the estimation of their relative position and attitude (pose) with respect to the servicer spacecraft. Several missions have been proposed as technology demonstrators of debris removal and servicing technologies, in which passive monocular cameras are combined with active sensors to improve the robustness and accuracy of the navigation system. Yet, despite the inherent challenges that come together with the use of monocular cameras in space, navigation systems based on a single camera are becoming an attractive alternative to systems based on active sensors, due to their reduced mass, power consumption and system complexity. The research work presented in this thesis aims at developing and validating a robust and accurate monocular camera-based pose estimation system compliant with navigation requirements of both ADR and OOS missions. \\Two fundamental open challenges are addressed:\begin{enumerate}\item The robustness and applicability of image processing algorithms and pose estimation methods.\item The validation of relative navigation filters and their interface with image processing and pose estimation.\end{enumerate}\noindent This research begins with a survey on the robustness and applicability of existing monocular vision-based pose estimation systems. After identifying the characteristics and limitations of each subsystem implemented in state-of-the-art architectures, a comparative assessment of the current solutions is given at different levels of the pose estimation process, in order to bring a novel and broad perspective. Special focus is put on the improved robustness of novel image processing schemes and pose estimators based on Convolutional Neural Networks (CNN). The limitations and drawbacks of the validation of current pose estimation schemes with synthetic images are further discussed, together with the critical trade-offs for the selection of visual-based navigation filters.Building on the results of the survey, a novel framework is introduced to enable a robust and accurate pose estimation. Two investigated CNNs are used at image processing level to identify a set of pre-selected features on the target spacecraft, which are fed to a pose estimator prior to the navigation filter (loosely-coupled) or directly to the navigation filter as measurements (tightly-coupled). A novel method to derive covariance matrices directly from the CNN heatmaps is introduced to improve the modeling of the feature detection uncertainty prior to pose estimation. The performance results indicate that a tightly-coupled approach can guarantee an advantageous coupling between the rotational and translational states within the filter, while reflecting a representative measurements covariance. Synthetic monocular images of the European Space Agency's Envisat spacecraft are used to generate datasets for training, validation and testing of the CNN. Likewise, the images are used to recreate a representative close-proximity scenario for the validation of the proposed filter.This research work then extends the validation from a purely synthetic one to a more comprehensive on-ground validation. To this end, ESA's GNC Rendezvous, Approach and Landing Simulator testbed is used to validate the proposed CNN-based pose estimation system on representative rendezvous scenarios, with special focus on solving the domain shift problem which characterizes CNNs trained on synthetic datasets when tested on more realistic imagery. To solve the domain shift problem, a novel augmentation technique focused on texture randomization was introduced, aimed at improving the CNN robustness against previously unseen target textures. The results prove an increase in robustness towards realistic imagery, as randomizing the texture of the target spacecraft during training allows the CNN to generalize textures and to focus on the shape of the target. However, a performance decrease in highly adverse illumination conditions or low camera exposures suggests that additional augmentation techniques are required to tackle the domain shift from an illumination standpoint. In response to this need and in order to extend the on-ground validation to the entire navigation system, this research work proceeds by introducing the on-ground validation of a CNN-based Unscented Kalman Filter. The validation is carried out at Stanford's robotic Testbed for Rendezvous and Optical Navigation on a dataset of realistic laboratory images, which simulate rendezvous trajectories of a servicer spacecraft to the Tango spacecraft from the PRISMA mission. The validation is performed at different levels of the navigation system by first training and testing the adopted CNN on SPEED+, the next generation spacecraft pose estimation dataset with specific emphasis on domain shift between a synthetic domain and a laboratory domain. A novel data augmentation scheme based on light randomization is proposed to improve the CNN robustness under adverse viewing conditions. Next, the entire navigation system is tested on two representative rendezvous trajectories. Results indicate that the inclusion of a new scheme to adaptively scale the heatmaps-based measurement error covariance improves filter robustness by returning centimeter-level position errors and moderate attitude accuracies at steady-state. Thanks to the proposed adaptive method, the filter does not diverge in periods of low measurements accuracy, suggesting that a proper representation of the measurements uncertainty combined with an adaptive measurement error covariance is key in improving the navigation robustness.Space Systems Egineerin

Palladium catalyzed hydrodechlorination of alfa-chloroacetophenones by hydrogen transfer from the H2O-CO system

PdC12(PPh3)2, in combination with an extra amount of PPh3, is an excellent catalyst precursor for the hydrodechlorination of alfa-chloroacetophenone to acetophenone by hydrogen transfer from the H2O-CO system. The reaction occurs with concomitant evolution of CO2. Under typical reaction conditions (50-70\ub0C 40-80 atm, substrate/Pd/P = 2000/l1/50, H2O/substrate = 8- 12/1, the reaction occurs in 70-80% yield in 2 h, using ethanol or dioxane as a solvent ([Pd] = 5x1O-4 mol xl-1. When the catalyst precursor is employed without adding an additional amount of PPh3 extensive decomposition to metallic palladium occurs. Also Pd/C is active in promoting the hydrodechlorination reaction. As expected the reaction rate increases upon increasing concentration of catalyst, carbon monoxide pressure and temperature. The yield is slightly influenced by the concentration of the substrate. The effect of the concentration of H20 is the most significant. In ethanol as a solvent at low concentration of water the reaction rate increases to reach a plateau above 6-7 x1O-2 molxl-1 of water. On the basis of the fact that it is known that (i) the precursor is reduced to a Pd(0) species by the H2O-CO system, even in the presence of hydrochloric acid, which is freed during the course of the hydrodechlorination reaction and that (ii) the starting alfa-chloroacetophenone oxidatively adds to Pd(0) to give Pd(CH2COPh)Cl(PPh3)2 (I) and that (iii) this complex reacts with hydrochloric acid to give acetophenone and PdCl2(PPh3)2 (II), it is proposed that the hydrodechlorination reaction proceeds via the intermediacy of a species analogous to complex (I) and that (II) is reduced to the Pd(0) complex through the intercation of CO and H2O with the metal center to give a species having a Pd-(COOH) moiety, which after beta-hydride abstraction gives a palladium-hydride species with concomitant evolution of CO2. The hydride gives off a proton and reduces Pd(II) returning a Pd(O) species back to the catalytic cycle. We found also that complex (I) is reduced to a Pd(0) complex with formation of acetophenone through the action of H2O and CO. It is proposed that this reaction, which may be at the base of a different catalytic path, occurs via the intermediacy of a species having a H-Pd-(CH2COPh) which, after reductive elimination of acetophenone give the Pd(0) complex starting a new catalytic cycle. In the case of the Pd/C catalyzed hydrodechlorination it is suggested that H2O and CO interacts on the surface of the metal to give a hydride and evolution of CO2 and that this hydride displaces a chloride anion from a+chloroacetophenone absorbed on the catalytic surface to give the hydrodechlorination product