Complex refractive index of non-spherical particles in the vis-NIR region - application to Bacillus Subtilis spores

A method is presented for the estimation of optical constants in the ultraviolet-visible-near-infrared (UVVis-NIR) region of nonspherical particles in a suspension at concentrations where multiple scattering issignificant. The optical constants are obtained by an inversion technique using the adding-doubling method to solve the radiative transfer equation in combination with the single scattering theories for modelling scattering by nonspherical particles. Two methods for describing scattering by single scatteringare considered: the T-matrix method and the approximate but computationally simpler Rayleigh-Gans-Debye (RGD) approximation. The method is then applied to obtain the optical constants of Bacillussubtilis spores in the wavelength region 400-1200 nm. It is found that the optical constants obtained using the RGD approximation matches those obtained using the T-matrix method to within experimental error

Debris Disks: Probing Planet Formation

Debris disks are the dust disks found around ~20% of nearby main sequence stars in far-IR surveys. They can be considered as descendants of protoplanetary disks or components of planetary systems, providing valuable information on circumstellar disk evolution and the outcome of planet formation. The debris disk population can be explained by the steady collisional erosion of planetesimal belts; population models constrain where (10-100au) and in what quantity (>1Mearth) planetesimals (>10km in size) typically form in protoplanetary disks. Gas is now seen long into the debris disk phase. Some of this is secondary implying planetesimals have a Solar System comet-like composition, but some systems may retain primordial gas. Ongoing planet formation processes are invoked for some debris disks, such as the continued growth of dwarf planets in an unstirred disk, or the growth of terrestrial planets through giant impacts. Planets imprint structure on debris disks in many ways; images of gaps, clumps, warps, eccentricities and other disk asymmetries, are readily explained by planets at >>5au. Hot dust in the region planets are commonly found (<5au) is seen for a growing number of stars. This dust usually originates in an outer belt (e.g., from exocomets), although an asteroid belt or recent collision is sometimes inferred.Comment: Invited review, accepted for publication in the 'Handbook of Exoplanets', eds. H.J. Deeg and J.A. Belmonte, Springer (2018

Using sequential structure to improve visuomotor control

In daily life, people make rapid, goal-directed movements to interact with their environment. Since these movements are goal-directed, the outcome of the movement is important. A plan is typically formulated to make the movement using visual information about target location before the movement is initiated. However, in dynamic environments people need to track the location of an object if it moves during the reach. Additionally, it would be beneficial to motor performance to learn the distribution of target locations over multiple reaches. In this paper we develop a simple model that describes how people might exploit the sequential structure over a series of trials to improve rapid visuomotor control. We then present empirical data from a sequential tracking task that investigates how people's knowledge of the location of objects is updated over trials to improve pointing performance. The model is able to predict when people will hit and miss targets with reasonable success. Interestingly, the results suggest that not only are people able to use sequential information but also look for it even when it does not exist.Anna Ma-Wyatt and Daniel Navarr

Seeing and ballistic pointing at perisaccadic targets.

We studied the effects of visual references and the level of illumination on the localization of stimuli flashed briefly near the start of saccades. A translucent shutter made it possible to remove visual references, but admit light, at different times after saccadic onset. The results show that post-saccadic visual references are not necessary for compression: a consistent compression of verbally reported relative stimulus distances is found at all shutter latencies and at all post-shutter levels of illumination. They also show that positions indicated by blind pointing show no compression except when visual references remain in view for a substantial time after saccades. These results confirm that the visual system uses multiple representations of space and suggest that it weights them differently for different tasks and different viewing conditions. No single map is used exclusively for conscious perception or for motor action, and conscious perception is always subject to compression at the time of saccades

The effect of locomotion on early visual contrast processing in humans

Most of our knowledge about vision comes from experiments in which stimuli are presented to immobile human subjects or animals. In the case of human subjects, movement during psychophysical, electrophysiological or neuroimaging experiments is considered to be a source of noise to be eliminated. Animals used in visual neuroscience experiments are typically restrained and, in many cases, anaesthetized. In reality however, vision is often used to guide the motion of awake, ambulating organisms. Recent work in mice has shown that locomotion elevates visual neuronal response amplitudes (Erisken et al., 2014; Fu et al., 2014; Lee et al., 2014; Mineault et al., 2016; Niell and Stryker, 2010) and reduces long-range gain control (Ayaz et al., 2013). Here we use both psychophysics and steady-state electrophysiology to ask whether similar effects of locomotion on early visual processing can be measured in humans. Our psychophysical results show that brisk walking has little effect on subjects’ ability to detect briefly-presented contrast changes and that co-oriented flankers are, if anything, more effective masks when subjects are walking. Our electrophysiological data were consistent with the psychophysics, indicating no increase in stimulus-driven neuronal responses whilst walking and no reduction in surround suppression. In summary we find evidence that early contrast processing is altered by locomotion in humans but in a manner that differs from that reported in mice. The effects of locomotion on very low-level visual processing may differ on a species-by-species basis and may reflect important differences in the levels of arousal associated with locomotion

Humans use different statistics for sequence analysis depending on the task

Despite its long history (Luce, 1986) the study of sequential effects has mostly been confined to simple binary tasks such as two-alternative forced choice tasks (2AFC). Here we present experimental results from a choice task with three rather than two alternatives (3AFC) as well as a novel model that can explain them. We find that humans change the statistics they use to analyse a sequence depending on the task constraints, relying on first-order transition probabilities in a 2AFC but event relative frequencies (i.e., zeroth-order transition probabilities) in a 3AFC.Dinis Gökaydin, Anna Ma-Wyatt, Daniel Navarro, Amy Perfor

The Relationship Between HR Practices and Firm Performance: Examining Causal Order

Significant research attention has been devoted to examining the relationship between HR practices and firm performance, and the research support has assumed HR as the causal variable. Using data from 45 business units (with 62 data points), this study examines how measures of HR practices correlate with past, concurrent, and future operational performance measures. The results indicate that correlations with performance measures at all three times are both high and invariant, and that controlling for past or concurrent performance virtually eliminates the correlation of HR with future performance. Implications are discussed

What the HLA-I!-Classical and Non-classical HLA Class I and Their Potential Roles in Type 1 Diabetes

Purpose of review: Hyperexpression of classical HLA class I (HLA-I) molecules in insulin-containing islets has become a widely accepted hallmark of type 1 diabetes pathology. In comparison, relatively little is known about the expression, function and role of non-classical subtypes of HLA-I. This review focuses on the current understanding of the non-classical HLA-I subtypes: HLA-E, HLA-F and HLA-G, within and outside the field of type 1 diabetes, and considers the possible impacts of these molecules on disease etiology. Recent findings: Evidence is growing to suggest that non-classical HLA-I proteins are upregulated, both at the RNA and protein levels in the pancreas of individuals with recent-onset type 1 diabetes. Moreover, associations between non-classical HLA-I genotypes and age at onset of type 1 diabetes have been reported in some studies. As with classical HLA-I, it is likely that hyperexpression of non-classical HLA-I is driven by the release of diffusible interferons by stressed β cells (potentially driven by viral infection) and exacerbated by release of cytokines from infiltrating immune cells. Non-classical HLA-I proteins predominantly (but not exclusively) transduce negative signals to immune cells infiltrating at the site of injury/inflammation. We propose a model in which the islet endocrine cells, through expression of non-classical HLA-I are fighting back against the infiltrating immune cells. By inhibiting the activity and function on NK, B and select T cells, the non-classical HLA-I, proteins will reduce the non-specific bystander effects of inflammation, while at the same time still allowing the targeted destruction of β cells by specific islet-reactive CD8+ T cells.This article is freely available via Open Access. Click on the Publisher URL to access it via the publisher's site.We are pleased to acknowledge financial support via a JDRF Career Development Award (5-CDA-2014-221-A-N), a JDRF Strategic Research Agreement (JDRF 2-SRA-2018-474-S-B), an MRC Project Grant (MR/P010695/1) and project grants from Diabetes UK (15/0005156 & 16/0005480) to SJR. GL was supported by the Diabetes Research Institute Foundation. IG has a project grant from National Institute of Health (UC4 DK104155).published version, accepted version (12 month embargo