3,976 research outputs found
The minimum free-stream wind speed for initiating motion of surface material on Mars
Estimates of the minimum free-stream wind speed that is required for initiating the motion of surficial material on Mars have ranged from 30 to about 200 meters per second. Thus the best value for this quantity is not well established. Graphical comparison of much of the pertinent data taken in the laboratory and in the field on Earth provides a minimum value for the Bagnold coefficient of 0.08 and this in turn provides a minimum value for the threshold friction velocity of 1.3 meters per second for initiating motion of particulate matter on Mars at low elevations where the pressure is 7 millibars. The most appropriate value of the ratio of friction velocity to free-stream velocity for putative unstable condition appears to be 0.026. Thus the minimum free-stream wind speed for initiating motion is obtained as 50 meters per second. If the surface material on Mars, however, is less cohesive than that on earth, the minimum value may be smaller
Ages of White Dwarf-Red Subdwarf Systems
We provide the first age estimates for two recently discovered white
dwarf-red subdwarf systems, LHS 193AB and LHS 300AB. These unusual systems
provide a new opportunity for linking the reliable age estimates for the white
dwarfs to the (measurable) metallicities of the red subdwarfs. We have obtained
precise photometry in the bands and spectroscopy covering
from 6000\AA to 9000\AA for the two new systems, as well as for a comparison
white dwarf-main sequence red dwarf system, GJ 283 AB. Using model grids
available in the literature, we estimate the cooling age as well as
temperature, surface gravity, mass, progenitor mass and {\it total} lifetimes
of the white dwarfs. The results indicate that the two new systems are probably
ancient thick disk objects with ages of at least 6-9 Gyr. We also conduct
searches of red dwarf and white dwarf compendia from SDSS data and the
L{\'e}pine Shara Proper Motion (LSPM) catalog for additional common proper
motion white dwarf-red subdwarf systems. Only seven new candidate systems are
found, which indicates the rarity of these systems.Comment: accepted for publication in Ap
Using multi-rater and test-retest data to detect overlap within and between psychological scales
Correlations estimated in single-source data provide uninterpretable estimates of empirical overlap between scales. We describe a model to adjust correlations for errors and biases using testâretest and multi-rater data and compare adjusted correlations among individual items with their human-rated semantic similarity (SS). We expected adjusted correlations to predict SS better than unadjusted correlations and exceed SS in absolute magnitude. While unadjusted and adjusted correlations predicted SS rankings equally well across all items, adjusted correlations were superior where items were judged most semantically redundant in meaning. Retest- and agreement-adjusted correlations were usually higher than SS, whereas unadjusted correlations often underestimated SS. We discuss uses of testâretest and multi-rater data for identifying construct redundancy and argue SS often underestimates variablesâ empirical overlap
Recommended from our members
Functional Imaging of the Outer Retinal Complex using High Fidelity Imaging Retinal Densitometry
We describe a new technique, high fidelity Imaging Retinal Densitometry (IRD), which probes the functional integrity of the outer retinal complex. We demonstrate the ability of the technique to map visual pigment optical density and synthesis rates in eyes with and without macular disease. A multispectral retinal imaging device obtained precise measurements of retinal reflectance over space and time. Data obtained from healthy controls and 5 patients with intermediate AMD, before and after photopigment bleaching, were used to quantify visual pigment metrics. Heat maps were plotted to summarise the topography of rod and cone pigment kinetics and descriptive statistics conducted to highlight differences between those with and without AMD. Rod and cone visual pigment synthesis rates in those with AMD (vâ=â0.043âSD 0.019âmin-1 and vâ=â0.119âSD 0.046âmin-1, respectively) were approximately half those observed in healthy controls (vâ=â0.079âSD 0.024âmin-1 for rods and vâ=â0.206âSD 0.069âmin-1 for cones). By mapping visual pigment kinetics across the central retina, high fidelity IRD provides a unique insight into outer retinal complex function. This new technique will improve the phenotypic characterisation, diagnosis and treatment monitoring of various ocular pathologies, including AMD
Recommended from our members
Comparison of Interactions Between Control and Mutant Macrophages
This paper presents a preliminary study on macrophages migration in Drosophila embryos, comparing two types of cells. The study is carried out by a framework called macrosight which analyses the movement and interaction of migrating macrophages. The framework incorporates a segmentation and tracking algorithm into analysing motion characteristics of cells after contact. In this particular study, the interactions between cells is characterised in the case of control embryos and Shot3 mutants, where the cells have been altered to suppress a specific protein, looking to understand what drives the movement. Statistical significance between control and mutant cells was found when comparing the direction of motion after contact in specific conditions. Such discoveries provide insights for future developments in combining biological experiments to computational analysis
Effects of mechanically separated dairy cow slurry on grazing performance
Abstract Inorganic fertilisers are widely used to fertilise grasslands in dairy systems. Increasing the nutrient use efficiency of slurry applied as an alternative or supplementary fertiliser could reduce the volume of purchased fertiliser. This would reduce costs and improve security of future fertiliser supply since slurry is produced on farm. Slurry separation could increase the potential for fertilising grazed grassland with slurry. This experiment compared the effects on milk yields of fertilising grazing swards with the liquid fraction of separated slurry, whole slurry or inorganic fertiliser. Three groups of 12 core cows were grazed for two 24 day rotations on 2 day paddocks between 18 and 24 days after fertiliser treatment application in a put and take design. Nutrient use efficiency was significantly higher (P<0.05) from the liquid fraction of separated slurry (12.2 kg kgN -1 ) compared to whole slurry (8.0 kg kgN -1 ) application. This effect was most likely due to a combination of improved soil infiltration and reduced sward contamination
Galactic planetary nebulae with Wolf-Rayet nuclei. II. A consistent observational data set
We present high resolution spectrophotometric data for 34 galactic planetary
nebulae with [WC] nuclei (WRPNe).The sample includes PNe with early and late
[WC] stars and some WELS. Physical conditions and chemical abundances have been
derived and expansion velocities were estimated for most objects of the sample.
A statistical study was developed to find fundamental relationships between the
nebular and central star parameters.We found evidence for a strong unexpected
electron temperature gradient in WRPNe which is related to nebular excitation.
Abundance ratios indicate that there seems to be no preferential stellar mass
for the WR phenomenon to occur in the nucleus of a planetary nebula. The PNe M
1-25 and M 1-32 were found to have very small Ne/O ratios.Our data confirm the
trend of the electron density decreasing with decreasing spectral type, which
was interpreted as evidence that [WC] stars evolve from late to early [WC]
types. On the other hand, the expansion velocities do not show the increase
with decreasing spectral type, that one might expect in such a scenario. Two
objects with very late [WC] central stars, K 2-16 and PM 1-188, do not follow
the general density sequence, being of very low density for their spectral
types. We suggest that the stars either underwent a late helium flash (the
``born again'' scenario) or that they have had a particularly slow evolution
from the AGB. The 6 WELS of our sample follow the same density vs. [WC]-type
relation as the bona fide WRPNe, but they tend to have smaller expansion
velocities. The comparison between the WRPNe in the Magellanic Clouds and in
the Galaxy indicates that metallicity affects the [WR] phenomenon in central
stars of planetary nebulae.Comment: 20 pages, including 2 figures and 3 tables. Paper accepted in
Astronomy and Astrophysics, 200
A randomised trial of the effect of omega-3 polyunsaturated fatty acid supplements on the human intestinal microbiota
Objective; Omega-3 polyunsaturated fatty acids (PUFAs) have anticolorectal cancer (CRC) activity. The intestinal microbiota has been implicated in colorectal carcinogenesis. Dietary omega-3 PUFAs alter the mouse intestinal microbiome compatible with antineoplastic activity. Therefore, we investigated the effect of omega-3 PUFA supplements on the faecal microbiome in middle-aged, healthy volunteers (n=22).
Design A randomised, open-label, cross-over trial of 8 weeksâ treatment with 4âg mixed eicosapentaenoic acid/docosahexaenoic acid in two formulations (soft-gel capsules and Smartfish drinks), separated by a 12-week âwashoutâ period. Faecal samples were collected at five time-points for microbiome analysis by 16S ribosomal RNA PCR and Illumina MiSeq sequencing. Red blood cell (RBC) fatty acid analysis was performed by liquid chromatography tandem mass spectrometry.
Results; Both omega-3 PUFA formulations induced similar changes in RBC fatty acid content, except that drinks were associated with a larger, and more prolonged, decrease in omega-6 PUFA arachidonic acid than the capsule intervention (p=0.02). There were no significant changes in α or ÎČ diversity, or phyla composition, associated with omega-3 PUFA supplementation. However, a reversible increased abundance of several genera, including Bifidobacterium, Roseburia and Lactobacillus was observed with one or both omega-3 PUFA interventions. Microbiome changes did not correlate with RBC omega-3 PUFA incorporation or development of omega-3 PUFA-induced diarrhoea. There were no treatment order effects.
Conclusion; Omega-3 PUFA supplementation induces a reversible increase in several short-chain fatty acid-producing bacteria, independently of the method of administration. There is no simple relationship between the intestinal microbiome and systemic omega-3 PUFA exposure.
Trial registration number; ISRCTN18662143
Do Children\u27s Advocacy Centers improve familiesâ experiences of child sexual abuse investigations?
Abstract Objective The Children\u27s Advocacy Center (CAC) model of child abuse investigation is designed to be more child and family-friendly than traditional methods, but there have been no rigorous studies of their effect on children\u27s and caregiversâ experience. Data collected as part of the Multi-Site Evaluation of Children\u27s Advocacy Centers were used to examine whether CACs improve caregiversâ and children\u27s satisfaction with investigations. Methods Nonoffending caregiver and child satisfaction were assessed during research interviews, including the administration of a 14-item Investigation Satisfaction Scale (ISS) for caregivers. Two hundred and twenty-nine sexual abuse cases investigated through a CAC were compared to 55 cases investigated in communities with no CAC. Results Hierarchical linear regression results indicated that caregivers in CAC cases were more satisfied with the investigation than those from comparison sites, even after controlling for a number of relevant variables. There were few differences between CAC and comparison samples on children\u27s satisfaction. Children described moderate to high satisfaction with the investigation, while a minority expressed concerns about their experience. Conclusions The CAC model shows promise for improving familiesâ experiences, but to build upon this promise, agencies will need to systematize procedures for refining and adapting the model as new research becomes available
- âŠ