Variation in XANES in biotite as a function of orientation, crystal composition, and metamorphic history

Microscale analysis of ferrous:ferric iron ratios in silicate minerals has the potential to constrain geological processes but has proved challenging because textural information and spatial resolution are limited with bulk techniques, and in situ methods have limited spatial resolution. Synchrotron methods, such as XANES, have been hampered by the sensitivity of spectra to crystal orientation and matrix effects. In an attempt to break this nexus, biotites from Tanzania were characterized with a combination of optical microscopy, electron microprobe, Mössbauer analysis, electron backscatter diffraction (EBSD) and X-ray absorption near edge structure (XANES) spectroscopy. Pre-edge and edge characteristics of the FeKa absorption feature were compared to orientation information derived by EBSD and ferric iron content derived from Mössbauer analysis. Statistically significant correlations between measured spectral features and optic/crystallographic orientation were observed for individual samples. However, orientation corrections derived from these correlations did not reduce the uncertainty in Fe3+/Fetot. The observations are consistent with matrix- and ordering-dependency of the XANES features, and further work is necessary if a general formulation for orientation corrections is to be devised

Retuning of Inferior Colliculus Neurons Following Spiral Ganglion Lesions: A Single-Neuron Model of Converging Inputs

Lesions of spiral ganglion cells, representing a restricted sector of the auditory nerve array, produce immediate changes in the frequency tuning of inferior colliculus (IC) neurons. There is a loss of excitation at the lesion frequencies, yet responses to adjacent frequencies remain intact and new regions of activity appear. This leads to immediate changes in tuning and in tonotopic progression. Similar effects are seen after different methods of peripheral damage and in auditory neurons in other nuclei. The mechanisms that underlie these postlesion changes are unknown, but the acute effects seen in IC strongly suggest the “unmasking” of latent inputs by the removal of inhibition. In this study, we explore computational models of single neurons with a convergence of excitatory and inhibitory inputs from a range of characteristic frequencies (CFs), which can simulate the narrow prelesion tuning of IC neurons, and account for the changes in CF tuning after a lesion. The models can reproduce the data if inputs are aligned relative to one another in a precise order along the dendrites of model IC neurons. Frequency tuning in these neurons approximates that seen physiologically. Removal of inputs representing a narrow range of frequencies leads to unmasking of previously subthreshold excitatory inputs, which causes changes in CF. Conversely, if all of the inputs converge at the same point on the cell body, receptive fields are broad and unmasking rarely results in CF changes. However, if the inhibition is tonic with no stimulus-driven component, then unmasking can still produce changes in CF

NICE : A Computational solution to close the gap from colour perception to colour categorization

The segmentation of visible electromagnetic radiation into chromatic categories by the human visual system has been extensively studied from a perceptual point of view, resulting in several colour appearance models. However, there is currently a void when it comes to relate these results to the physiological mechanisms that are known to shape the pre-cortical and cortical visual pathway. This work intends to begin to fill this void by proposing a new physiologically plausible model of colour categorization based on Neural Isoresponsive Colour Ellipsoids (NICE) in the cone-contrast space defined by the main directions of the visual signals entering the visual cortex. The model was adjusted to fit psychophysical measures that concentrate on the categorical boundaries and are consistent with the ellipsoidal isoresponse surfaces of visual cortical neurons. By revealing the shape of such categorical colour regions, our measures allow for a more precise and parsimonious description, connecting well-known early visual processing mechanisms to the less understood phenomenon of colour categorization. To test the feasibility of our method we applied it to exemplary images and a popular ground-truth chart obtaining labelling results that are better than those of current state-of-the-art algorithms

The limitations of hibonite as a single-mineral oxybarometer for early solar system processes

The relationships between the composition of hibonite with the general formula CaAl12-2x-yMgxTi4 +xTi3 +yO19, the oxidation state of Ti (Ti3 +/ΣTi, where ΣTi = Ti3 + + Ti4 +), and oxygen fugacity (fO2) were investigated experimentally. It was found that hibonite can be synthesised with a range of Ti3 +/ΣTi values at constant fO2 and with a constant Ti3 +/ΣTi value for a range of fO2s. It was also found that if hibonite with the formula CaAl12-yTi3 +yO19 (Ti3 +/ΣTi = 1) is equilibrated with a melt of CAI composition at fO2s below the iron-wüstite buffer then the resulting hibonite contained Mg, with Mg per formula unit (pfu) ~ 0.8 Ti pfu, and Ti3 +/ΣTi ~ 0.2, irrespective of the fO2. These results suggest that the availability of Mg, rather than fO2, is the key factor that determines Ti3 +/ΣTi of hibonite. The structures of synthetic samples of hibonite with the general formula CaAl12-2xMgxTi4 +xO19, where 0 ≤ X < 1, were determined by Rietveld refinement of X-ray powder diffraction data. The predominant site occupied by Ti4 + was found to change from M2 to M4 with increasing Ti content. The range of Ti concentrations over which the site occupancy changed corresponds to that observed in meteoritic hibonite. This change in the Ti4 + site produces changes in the Ti K-edge XANES spectra, particularly in the intensity of the pre-edge feature, for constant Ti3 +/ΣTi. The observed dependence of the pre-edge on the Ti4 + site was reproduced by ab initio simulations of the XANES spectra. The XANES spectra of natural hibonite with variable Ti content from the Murchison carbonaceous chondrite closely match the spectra of the synthetic samples with similar Ti contents. These differences in the spectra of meteoritic hibonite could be misinterpreted as being due to changes in Ti3 +/ΣTi, but are instead due to differences in ΣTi, which relate to the petrogenetic history. Crystal chemistry exerts a first order control on the Ti site occupancy and Ti3 +/ΣTi value of hibonite. As a result, no simple relationship between Ti3 +/ΣTi and fO2 should be expected. It is unlikely that hibonite will be useful as an oxybarometer for solar processes without Ti3 +/ΣTi standards that are compositionally matched to the unknown

The effect of CO2 on the speciation of RbBr in solution at temperatures to 579 degrees C and pressures to 0.26 GPa

Carbon dioxide- and salt-bearing solutions are common in granulite, ore-forming and magmatic environments. The presence of CO2 affects mineral solubilities, fluid miscibility, and viscosity and wetting properties, and is expected to affect salt speciation. EXAFS measurements of RbBr-H2O-CO2 fluids contained in corundum-hosted synthetic fluid inclusions (SFLINCs) have been used to investigate the effect of CO2 on salt speciation at temperatures to 579 degrees C and pressures to around 0.26 GPa. Forward modelling indicates that solute dehydration is difficult to distinguish from up to around 40% of Rb-Br ion-pairing, so results refer to the total number of nearest neighbours, which are likely to be mostly O present in waters of hydration, but may also include Br, if ion pairing is present. Additionally, results relate to the number of well-ordered neighbours in the first shell, because nearest neighbours with a high degree of disorder may be present but contribute minimally to the EXAFS signal. Analysis of the EXAFS results at the Rb edge for the CO2-free solution is consistent with previous work and shows that the number of nearest neighbours for Rb in CO2-free solutions decreases from 6 plus/minus 0.6 to 1.4 plus/minus 0.1 as temperature increases from 20 degrees C to 534 degrees C. The decrease is accompanied by a decrease in Rb-x bondlengths of 0.05 Angstroms, where x is the first shell scatterer. Results for the CO2-bearing solution are different to those for the CO2-free solution. The number of nearest neighbours is 16 and 22% less than for the CO2-bearing solution at 312 and 445 degrees C respectively. Changes in the numbers of nearest neighbours correlate well with calculated changes in the bulk solution dielectric constant; CO2-bearing and CO2-free solutions lie on the same trend, which suggests that it may be possible to calculate the number of nearest neighbours from dielectric constant. Rb-x bondlengths for the CO2-bearing solution are statistically indistinguishable to those for the CO2-free inclusions. Results for Br are worse quality than for Rb so EXAFS analysis could not be completed, however XANES spectra for CO2-free and CO2-bearing solutions are consistent with solute dehydration similar to that recorded by the Rb spectra. The conclusions of this study provide support for the notion that CO2 has a fundamental effect on the mechanics of solubility, and that these effects should be incorporated into conceptual and quantitative thermodynamic models.uids contained in corundum-hosted synthetic uid inclusions (SFLINCs) have been used to investigate the eect of CO2 on salt speciation at temperatures to 579C and pressures to around 0.26 GPa. Forward modelling indicates that solute dehydration is dicult to distinguish from up to around 40% of Rb-Br ion-pairing, so results refer to the total number of nearest neighbours, which are likely to be mostly O present in waters of hydration, but may also include Br, if ion pairing is present. Additionally, results relate to the number of well-ordered neighbours in the first shell, because nearest neighbours with a high degree of disorder may be present but contribute minimally to the EXAFS signal. Analysis of the EXAFS results at the Rb edge for the CO2-free solution is consistent with previous work and shows that the number of nearest neighbours for Rb in CO2-free solutions decreases from 6 0.6 to 1.4 0.1 as temperature increases from 20C to 534C. The decrease is accompanied by a decrease i Rb-x bondlengths of 0.05 A, where x is the rst shell scatterer. Results for the CO2-bearing solution are dierent to those for the CO2-free solution. The number of nearest neighbours is 16 and 22% less than for the CO2-bearing solution at 312 and 445C respectively. Changes in the numbers of nearest neighbours correlate well with calculated changes in the bulk solution dielectric constant; CO2-bearing and CO2-free solutions lie on the same trend, which suggests that it may be possible to calculate the number of nearest neighbours from dielectric constant. Rb-x bondlengths for the CO2-bearing solution are statistically indistinguishable to those for the CO2-free inclusions. Results for Br are worse quality than for Rb so EXAFS analysis could not be completed, however XANES spectra for CO2-free and CO2-bearing solutions are consistent with solute dehydration similar to that recorded by the Rb spectra. The conclusions of this study provide support for the notion that CO2 has a fundamental eect on the mechanics of solubility, and that these eects should be incorporated into conceptual and quantitative thermodynamic models

Clinical benefit of presurgical EEG-fMRI in difficult-to-localize focal epilepsy : A single-institution retrospective review.

Objective The aim of this report is to present our clinical experience of electroencephalography–functional magnetic resonance imaging (EEG-fMRI) in localizing the epileptogenic focus, and to evaluate the clinical impact and challenges associated with the use of EEG-fMRI in pharmacoresistant focal epilepsy. Methods We identified EEG-fMRI studies (n = 118) in people with focal epilepsy performed at our center from 2003 to 2018. Participants were referred from our Comprehensive Epilepsy Program in an exploratory research effort to address often difficult clinical questions, due to complex and difficult-to-localize epilepsy. We assessed the success of each study, the clinical utility of the result, and when surgery was performed, the postoperative outcome. Results Overall, 50% of EEG-fMRI studies were successful, meaning that data were of good quality and interictal epileptiform discharges were recorded. With an altered recruitment strategy since 2012 with increased inclusion of patients who were inpatients for video-EEG monitoring, we found that this patients in this selected group were more likely to have epileptic discharges detected during EEG-fMRI (96% of inpatients vs 29% of outpatients, P<.0001). To date, 48% (57 of 118) of patients have undergone epilepsy surgery. In 10 cases (17% of the 59 successful studies) the EEG-fMRI result had a “critical impact” on the surgical decision. These patients were difficult to localize because of subtle abnormalities, apparently normal MRI, or extensive structural abnormalities. All 10 had a good seizure outcome at 1 year after surgery (mean follow-up 6.5 years). Significance EEG-fMRI results can assist identification of the epileptogenic focus in otherwise difficult-to-localize cases of pharmacoresistant focal epilepsy. Surgery determined largely by localization from the EEG-fMRI result can lead to good seizure outcomes. A limitation of this study is its retrospective design with nonconsecutive recruitment. Prospective clinical trials with well-defined inclusion criteria are needed to determine the overall benefit of EEG-fMRI for preoperative localization and postoperative outcome in focal epilepsy

Employee representation and partnership in the non-union sector: a paradox of intention?

Non-union forms of employee representation have become increasingly prominent in UK workplaces in the last 15 years. In addition, partnership working has been encouraged by New Labour, the Chartered Institute of Personnel and Development, the Confederation of British Industry and the TUC as a route to higher commitment and higher individual and organisational performance. These trends have been further encouraged by recent European Union legislation. This article seeks to examine the implied linkages between non-union employee representative mechanisms and partnership working and their influence on the effectiveness of employee voice as a conduit of high performance. The article is based on a case study organisation from within the UK finance sector, and data are drawn from semistructured interviews with managers and staff and a survey of employee attitudes. The article concludes that employers’ attempts to utilise a non-union partnership framework for organisational gain are severely constrained by structural limitations on effective employee voice