Iron mineralogy of a Hawaiian palagonitic soil with Mars-like spectral and magnetic properties

Visible and near-IR spectral data for some palagonitic soils from Mauna Kea, Hawaii, are similar to corresponding spectral data for Mars. It is important to understand the composition, distribution, and mineralogy of the ferric-bearing phases for the best spectral analogues because the correspondence in spectral properties implies that the nature of their ferric-bearing phases may be similar to those on Mars. In order to constrain interpretations of the Martian data, a variety of palagonitic soils should be studied in order to establish to what extent differences in their spectral data correspond to differences in the mineralogy of their ferric-bearing phases. Spectral (350-2100 nm), Mossbauer, magnetic, and some compositional data for one of a suite of Hawaiian palagonitic soils are presented. The soil (HWMK1) was collected below the biologically active zone from the sides of a gully cut at 9000 ft elevation on Mauna Kea. The soil was wet sieved with freon into seven size fractions less than 1 mm

Outgassing of Ordinary Chondritic Material and Some of its Implications for the Chemistry of Asteroids, Planets, and Satellites

We used chemical equilibrium calculations to model thermal outgassing of ordinary chondritic material as a function of temperature, pressure, and bulk compositions and use our results to discuss outgassing on asteroids and the early Earth. The calculations include ~1,000 solids and gases of the elements Al, C, Ca, Cl, Co, Cr, F, Fe, H, K, Mg, Mn, N, Na, Ni, O, P, S, Si, and Ti. The major outgassed volatiles from ordinary chondritic material are CH4, H2, H2O, N2, and NH3(the latter at conditions where hydrous minerals form). Contrary to widely held assumptions, CO is never the major C-bearing gas during ordinary chondrite metamorphism. The calculated oxygen fugacity (partial pressure) of ordinary chondritic material is close to that of the quartz-fayalite-iron (QFI) buffer. Our results are insensitive to variable total pressure, variable volatile element abundances, and kinetic inhibition of C and N dissolution in Fe metal. Our results predict that Earth's early atmosphere contained CH4, H2, H2O, N2, and NH3; similar to that used in Miller-Urey synthesis of organic compounds.Comment: 72 pages, 17 figures, 3 tables; submitted to Icaru

Functional role of T-cell receptor nanoclusters in signal initiation and antigen discrimination

Antigen recognition by the T-cell receptor (TCR) is a hallmark of the adaptive immune system. When the TCR engages a peptide bound to the restricting major histocompatibility complex molecule (pMHC), it transmits a signal via the associated CD3 complex. How the extracellular antigen recognition event leads to intracellular phosphorylation remains unclear. Here, we used single-molecule localization microscopy to quantify the organization of TCR–CD3 complexes into nanoscale clusters and to distinguish between triggered and nontriggered TCR–CD3 complexes. We found that only TCR–CD3 complexes in dense clusters were phosphorylated and associated with downstream signaling proteins, demonstrating that the molecular density within clusters dictates signal initiation. Moreover, both pMHC dose and TCR–pMHC affinity determined the density of TCR–CD3 clusters, which scaled with overall phosphorylation levels. Thus, TCR–CD3 clustering translates antigen recognition by the TCR into signal initiation by the CD3 complex, and the formation of dense signaling-competent clusters is a process of antigen discrimination

The forest transition and ecological thresholds: resilience, recovery, and predictions

A central topic in modeling land use change is to understand the forest transition from deforestation to net reforestation. Agricultural land use change is the main driver of this phenomenon; classically, agricultural land expands considerably to feed a growing population, and then declines as efficiency gains are realized, marginal farmland is abandoned, and rural populations move to cities. As a result, existing models have focused on the socioeconomic and demographic factors that drive agricultural intensification. However, in doing so, these models often neglect the role of ecological feedback effects and thresholds. These ecological thresholds can cause rapid shifts in ecosystems, such as forest collapse, based on small changes in parameters, and are very difficult to predict. The existence of these thresholds implies that agricultural expansion carries a risk of forest collapse. We aim to use realistic models to assess the risk of collapse in forest cover, dependence on key parameters, and strategies to avoid it. To address the risk of forest collapse, we develop and analyze a differential equation model that incorporates both agricultural intensification and ecological thresholds. We use parameter values from the literature to adapt this model to boreal and tropical forests. We analyze the model with bifurcation diagrams, simulations of key resilience metrics, and fitted time series of real-world data for China, Costa Rica, and Vietnam. Our analysis shows that there is a risk of forest collapse, and that the system is particularly sensitive to agricultural parameters. We find that regardless of the mechanism by which collapse occurs, there is a critical value of 20-25% forest cover. In scenarios of interest (i.e. forest transitions), initial deforestation would result in collapse if left unchecked. We estimate model parameters at multiple points along historical time series, which allows us to infer the risk of collapse and identify historical patterns. This shows that forest transitions can be caused by more varied parameter patterns than classically assumed in the literature; in particular, rates of land conversion and agricultural abandonment rate may remain elevated, instead of declining after intensification. The agricultural abandonment rate is a key advance predictor of collapse at long time horizons, but at the brink of a crisis forest collapse can best be avoided by reducing the forest conversion rate. We argue that ecological threshold effects should be acknowledged in forest transition models not only for ecological accuracy but also to ensure prudent forest management, particularly in the face of emerging risks such as climate change

Vacuum entanglement probes for ultra-cold atom systems

This study explores the transfer of nonclassical correlations from an ultra-cold atom system to a pair of pulsed laser beams. Through nondestructive local probe measurements, we introduce an alternative to destructive techniques for mapping BEC entanglement. Operating at ultralow temperatures, the setup emulates a relativistic vacuum field, using lasers as Unruh-DeWitt detectors for phonons. The vacuum holds intrinsic entanglement, transferable to distant probes briefly interacting with it - a phenomenon termed ``entanglement harvesting''. Our study accomplishes two primary objectives: first, establishing a mathematical equivalence between a pair of pulsed laser probes interacting with an effective relativistic field and the entanglement harvesting protocol; and second, to closely examine the potential and persisting obstacles for realising this protocol in an ultra-cold atom experiment.Comment: 12 pages and 3 figures, including the Supplemental Material / Appendice

Dysregulated oscillatory connectivity in the visual system in autism spectrum disorder

Autism spectrum disorder is increasingly associated with atypical perceptual and sensory symptoms. Here we explore the hypothesis that aberrant sensory processing in autism spectrum disorder could be linked to atypical intra- (local) and interregional (global) brain connectivity. To elucidate oscillatory dynamics and connectivity in the visual domain we used magnetoencephalography and a simple visual grating paradigm with a group of 18 adolescent autistic participants and 18 typically developing control subjects. Both groups showed similar increases in gamma (40-80 Hz) and decreases in alpha (8-13 Hz) frequency power in occipital cortex. However, systematic group differences emerged when analysing intra- and interregional connectivity in detail. First, directed connectivity was estimated using non-parametric Granger causality between visual areas V1 and V4. Feedforward V1-to-V4 connectivity, mediated by gamma oscillations, was equivalent between autism spectrum disorder and control groups, but importantly, feedback V4-to-V1 connectivity, mediated by alpha (8-13 Hz) oscillations, was significantly reduced in the autism spectrum disorder group. This reduction was positively correlated with autistic quotient scores, consistent with an atypical visual hierarchy in autism, characterized by reduced top-down modulation of visual input via alpha-band oscillations. Second, at the local level in V1, coupling of alpha-phase to gamma amplitude (alpha-gamma phase amplitude coupling) was reduced in the autism spectrum disorder group. This implies dysregulated local visual processing, with gamma oscillations decoupled from patterns of wider alpha-band phase synchrony (i.e. reduced phase amplitude coupling), possibly due to an excitation-inhibition imbalance. More generally, these results are in agreement with predictive coding accounts of neurotypical perception and indicate that visual processes in autism are less modulated by contextual feedback information

Autobiographical memory specificity and cognitive style across the bipolar disorder spectrum

Bipolar disorder is characterised by intense fluctuations in mood, including the experience of severe episodes of depression, mania and hypomania. The experience of bipolar disorder can also be associated with biases in various cognitive processes, including rumination in response to positive and negative mood states and tendencies to make dysfunctional self-appraisals. Preliminary research has also suggested that bipolar disorder may be associated with deficits in the recall of specifically detailed autobiographical memories. The lack of specificity in the recall of autobiographical memories, known as the 'overgeneral' recall bias, refers to tendencies to generate generalised memory representations as the memory recall process is terminated prior to the activation of specifically detailed memories. This overgeneral recall of autobiographical memories can also contribute to ruminative thought patterns, impair the generation of effective solutions to problems, and is associated with poor illness outcomes. The overgeneral bias has been extensively researched within major depressive disorder and suicidality, but has been comparatively under-researched in bipolar disorder and in vulnerable individuals. A series of eight studies were designed to: (i) investigate the cross-sectional associations across measures of positive and negative rumination and self-appraisal with the vulnerability to hypomania, and investigate the associations of these cognitive styles with prospective mood symptoms in an at-risk sample; (ii) investigate the cognitive vulnerability to hypomania in relation to rumination, problem-solving and autobiographical memory specificity; (iii) conduct a preliminary investigation into the associations between goal-related memory processes and extreme goal-pursuit in relation to hypomania vulnerability; (iv) investigate whether the vulnerability to hypomania and future bipolar disorders is associated with similar patterns of overgeneral memory recall on a standardised cue memory task; and (v) investigate the patterns of autobiographical memory specificity within a remitted bipolar sample. The heightened vulnerability to future bipolar disorders was associated with tendencies to engage in both positive and negative forms of ruminative thought processes, and with poorer psychosocial problem-solving, however, this relationship with problem-solving was not independent of current mood symptoms. The results of two studies indicated that the heightened vulnerability to hypomania was associated with an overgeneral memory bias across two different assessments of memory specificity, in direct contrast to previous research. Individuals diagnosed with bipolar disorder also reported more extreme overgenerality during memory recall than a sample of age and gender-matched healthy controls, but were able to recall some specifically detailed negative memories in short response latencies compared to non-bipolar control participants. The research presented within this thesis supports the notion of a continuum of increasing overgenerality in the bipolar disorder spectrum, inclusive of at-risk individuals to people formally diagnosed with bipolar disorder. Although bipolar disorder appears to be associated with a trait-based overgeneral memory bias, bipolar individuals appear to have ready access to some specific negative memories even during remission from symptoms. The clinical implications of this research, methodological considerations in the assessment of memory specificity, and directions for further investigations into the nature of autobiographical memory recall in bipolar spectrum disorders are discussed.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Directly or indirectly? The role of social support in the psychological pathways underlying suicidal ideation in people with bipolar disorder

Contemporary theories of suicide, such as the Schematic Appraisals Model (SAMS), hypothesize that negative perceptions of social support are implicated in the pathways to suicidal experiences. The SAMS predicts that perceived social support influences suicidal ideation through appraisals of defeat and entrapment. However, such pathways have not been investigated with people who have bipolar disorder. This prospective four-month study tested the influence of perceived social support on later suicidal ideation via changes in defeat, entrapment, and hopelessness, in a sample of eighty euthymic participants with bipolar disorder (N = 62 at follow-up). Linear regression models tested the extent to which perceived social support at baseline predicted changes in suicidal ideation at four months directly and indirectly via changes in defeat, entrapment, and hopelessness. Perceived social support did not directly predict changes in suicidal ideation, but there was a significant indirect mediational pathway between perceived social support at baseline and changes in suicidal ideation over time, via changes in defeat, entrapment and hopelessness, supporting the SAMS. Psychological interventions which target negative perceptions of social support early, in tandem with addressing defeat, entrapment and hopelessness over time, present a potentially effective approach to counter suicidal ideation in people who experience bipolar disorder