The Nakhlites Sample Multiple Igneous Units: Evidence From 40Ar/39Ar Chronology And Geochemistry

No abstract available

Exploring Mars at the nanoscale: applications of transmission electron microscopy and atom probe tomography in planetary exploration

The upcoming Mars Sample Return (MSR) mission aims to deliver small quantities of Martian rocks to the Earth. Investigating these precious samples requires the development and application of techniques that can extract the greatest amount of high quality data from the minimum sample volume, thereby maximising science return from MSR. Atom probe tomography (APT) and transmission electron microscopy (TEM) are two complementary techniques that can obtain nanoscale structural, geochemical and, in the case of atom probe, isotopic information from small sample volumes. Here we describe how both techniques operate, as well as review recent developments in sample preparation protocols. We also outline how APT has been successfully applied to extraterrestrial materials in the recent past. Finally, we describe how we have studied Martian meteorites using TEM and APT in close coordination in order to characterise the products of water/rock interactions in t h e cru st of Ma r s – a k ey sc ie n ce goal of MSR. Our results provide new insights into the Martian hydrosphere and the mechanisms of anhydrous-hydrous mineral replacement. In light of the unique results provided by these tools, APT and TEM should form a crucial part at the culmination of a correlative analytical pipeline for MSR mission materials

Improved Understanding of Atomic Ordering in Y4SixAl2- xO9- xNxMaterials Using a Combined Solid-State NMR and Computational Approach

Ceramics based around silicon aluminum oxynitrides are of both fundamental structural chemistry and technological interest. Certain oxynitride crystal structures allow very significant compositional variation through extensive Si/N exchange for Al/O, which implies a degree of atomic ordering. In this study, solid-state 29Si MAS NMR and variable field 1D and 2D 27Al MAS NMR measurements are combined with density functional theory calculations of both the structural and NMR interaction parameters for various points across the Y4Si2O7N2-Y4Al2O9 compositional range. This series provides numerous possibilities for significant variation of atomic ordering in the local ditetrahedral (Si,Al)2O7-xNx units. The two slightly structurally inequivalent aluminum sites in Y4Al2O9 are unambiguously assigned to the observed resonances. Computational findings on Y4Si2O7N2 demonstrate that the single observed 29Si NMR resonance covers a range of local inequivalent silicon environments. For the first time, the MAS NMR and neutron diffraction data from the Y4SiAlO8N structure have been directly reconciled, thus establishing aspects of atomic order and disorder that characterize this system. This comparison suggests that, although the diffraction data indicates long-range structural order supporting a highly crystalline character, the short-range information afforded by the solid-state NMR measurements indicates significant atomic disorder throughout the (Si,Al)2O7-xNx units

Mitochondrial variant enrichment from high-throughput single-cell RNA-seq resolves clonal populations

Reconstructing lineage relationships in complex tissues can reveal mechanisms underlying development and disease. Recent methods combine single-cell transcriptomics with mitochondrial DNA variant detection to establish lineage relationships in primary human cells, but are not scalable to interrogate complex tissues. To overcome this limitation, here we develop a technology for high-confidence detection of mitochondrial mutations from high-throughput single-cell RNA-sequencing. We use the new method to identify skewed immune cell expansions in primary human clonal hematopoiesis

Making things happen : a model of proactive motivation

Being proactive is about making things happen, anticipating and preventing problems, and seizing opportunities. It involves self-initiated efforts to bring about change in the work environment and/or oneself to achieve a different future. The authors develop existing perspectives on this topic by identifying proactivity as a goal-driven process involving both the setting of a proactive goal (proactive goal generation) and striving to achieve that proactive goal (proactive goal striving). The authors identify a range of proactive goals that individuals can pursue in organizations. These vary on two dimensions: the future they aim to bring about (achieving a better personal fit within one’s work environment, improving the organization’s internal functioning, or enhancing the organization’s strategic fit with its environment) and whether the self or situation is being changed. The authors then identify “can do,” “reason to,” and “energized to” motivational states that prompt proactive goal generation and sustain goal striving. Can do motivation arises from perceptions of self-efficacy, control, and (low) cost. Reason to motivation relates to why someone is proactive, including reasons flowing from intrinsic, integrated, and identified motivation. Energized to motivation refers to activated positive affective states that prompt proactive goal processes. The authors suggest more distal antecedents, including individual differences (e.g., personality, values, knowledge and ability) as well as contextual variations in leadership, work design, and interpersonal climate, that influence the proactive motivational states and thereby boost or inhibit proactive goal processes. Finally, the authors summarize priorities for future researc

Motion sickness: effect of the frequency of lateral oscillation

Introduction: low-frequency lateral oscillation is a cause of motion sickness in some forms of transport. However, the relationship between occurrence of sickness and the frequency of lateral oscillation is not known. This paper presents a study of motion sickness with lateral oscillation at frequencies between 0.0315 Hz and 0.20 Hz. Method: there were 120 subjects, in 6 groups of 20, who were exposed for up to 30 min to sinusoidal lateral oscillation with a peak velocity of 1.0 ms-1 at one of six frequencies (0.0315, 0.05, 0.08, 0.125, 0.16, 0.20 Hz). Subjects provided ratings of their motion sickness symptoms at 1-min intervals. Results: there was a highly significant effect of the frequency of lateral oscillation on the occurrence of mild nausea. Discussion: the present results have been combined with those from a previous experiment conducted with higher frequencies of oscillation to produce a frequency weighting for motion sickness caused by lateral oscillation over the range 0.0315 to 0.8 Hz. Conclusions: mild nausea caused by lateral oscillation may be predicted by an acceleration frequency weighting that is independent of frequency from 0.0315 to 0.25 Hz and reduces at 12 dB per octave (i.e., proportional to displacement) from 0.25 to 0.8 Hz. This weighting differs from the frequency weighting currently used for predicting motion sickness caused by vertical oscillation. The frequency weighting for lateral oscillation may not be applicable in those environments in which there is roll motion during lateral oscillation

Low frequency motions and motion sickness on a tilting train

Tilting trains have been developed to reduce rail transport times by allowing greater train speeds without increased discomfort from increased lateral acceleration. It is reported that passengers on tilting trains experience motion sickness, but there have been few published studies of motions of tilting trains and the associated sickness. This paper presents the motion and motion sickness on an experimental tilting train during two trials: the first involved 200 subjects on five return journeys, the second involved 445 subjects and 14 return journeys. For each journey, lateral and vertical translational accelerations and roll velocities were measured in the passenger car-body. Simultaneously, subjects assessed their motion sickness at periodic intervals using an illness rating scale. The characteristics of the translational acceleration and roll velocity were investigated for each journey and the covariant relationships between the low frequency motions were explored. Illness ratings were found to be correlated with the vertical acceleration and roll velocity. A single motion variable is considered insufficient to predict motion sickness on tilting trains

Crystallisation and Alteration of the Yamato Nakhlites

No abstract available

Reassessing the Geochemical Evolution of the Nakhlite Meteorites as Multiple Martian lava Flows

No abstract available