Relating in situ gas measurements to the surface outgassing properties of cometary nuclei

The sensitivity of the gas flow field to changes in different initial conditions has been studied for the case of a highly simplified cometary nucleus model. The nucleus model simulated a homogeneously outgassing sphere with a more active ring around an axis of symmetry. The varied initial conditions were the number density of the homogeneous region, the surface temperature, and the composition of the flow (varying amounts of H2O and CO2) from the active ring. The sensitivity analysis was performed using the Polynomial Chaos Expansion (PCE) method. Direct Simulation Monte Carlo (DSMC) was used for the flow, thereby allowing strong deviations from local thermal equilibrium. The PCE approach can be used to produce a sensitivity analysis with only four runs per modified input parameter and allows one to study and quantify non-linear responses of measurable parameters to linear changes in the input over a wide range. Hence the PCE allows one to obtain a functional relationship between the flow field properties at every point in the inner coma and the input conditions. It is for example shown that the velocity and the temperature of the background gas are not simply linear functions of the initial number density at the source. As probably expected, the main influence on the resulting flow field parameter is the corresponding initial parameter (i.e. the initial number density determines the background number density, the temperature of the surface determines the flow field temperature, etc.). However, the velocity of the flow field is also influenced by the surface temperature while the number density is not sensitive to the surface temperature at all in our model set-up. Another example is the change in the composition of the flow over the active area. Such changes can be seen in the velocity but again not in the number density. Although this study uses only a simple test case, we suggest that the approach, when applied to a real case in 3D, should assist in identifying the sensitivity of gas parameters measured in situ by, for example, the Rosetta spacecraft to the surface boundary conditions and vice versa.

Comparison of 3D kinetic and hydrodynamic models to ROSINA-COPS measurements of the neutral coma of 67P/Churyumov-Gerasimenko

67P/Churyumov-Gerasimenko (67P) is a Jupiter-family comet and the object of investigation of the European Space Agency mission Rosetta. This report presents the first full 3D simulation results of 67P’s neutral gas coma. In this study we include results from a direct simulation Monte Carlo method, a hydrodynamic code, and a purely geometric calculation which computes the total illuminated surface area on the nucleus. All models include the triangulated 3D shape model of 67P as well as realistic illumination and shadowing conditions. The basic concept is the assumption that these illumination conditions on the nucleus are the main driver for the gas activity of the comet. As a consequence, the total production rate of 67P varies as a function of solar insolation. The best agreement between the model and the data is achieved when gas fluxes on the night side are in the range of 7% to 10% of the maximum flux, accounting for contributions from the most volatile components. To validate the output of our numerical simulations we compare the results of all three models to in situ gas number density measurements from the ROSINA COPS instrument. We are able to reproduce the overall features of these local neutral number density measurements of ROSINA COPS for the time period between early August 2014 and January 1 2015 with all three models. Some details in the measurements are not reproduced and warrant further investigation and refinement of the models. However, the overall assumption that illumination conditions on the nucleus are at least an important driver of the gas activity is validated by the models. According to our simulation results we find the total production rate of 67P to be constant between August and November 2014 with a value of about 1 × 10²⁶ molecules s⁻¹.

Size-frequency distribution of boulders ≥7 m on comet 67P/Churyumov-Gerasimenko

Aims. We derive for the first time the size-frequency distribution of boulders on a comet, 67P/Churyumov-Gerasimenko (67P), computed from the images taken by the Rosetta/OSIRIS imaging system. We highlight the possible physical processes that lead to these boulder size distributions. Methods. We used images acquired by the OSIRIS Narrow Angle Camera, NAC, on 5 and 6 August 2014. The scale of these images (2.44−2.03 m/px) is such that boulders ≥7 m can be identified and manually extracted from the datasets with the software ArcGIS. We derived both global and localized size-frequency distributions. The three-pixel sampling detection, coupled with the favorable shadowing of the surface (observation phase angle ranging from 48° to 53°), enables unequivocally detecting boulders scattered all over the illuminated side of 67P. Results. We identify 3546 boulders larger than 7 m on the imaged surface (36.4 km2), with a global number density of nearly 100/km2 and a cumulative size-frequency distribution represented by a power-law with index of −3.6 +0.2/−0.3. The two lobes of 67P appear to have slightly different distributions, with an index of −3.5 +0.2/−0.3 for the main lobe (body) and −4.0 +0.3/−0.2 for the small lobe (head). The steeper distribution of the small lobe might be due to a more pervasive fracturing. The difference of the distribution for the connecting region (neck) is much more significant, with an index value of −2.2 +0.2/−0.2. We propose that the boulder field located in the neck area is the result of blocks falling from the contiguous Hathor cliff. The lower slope of the size-frequency distribution we see today in the neck area might be due to the concurrent processes acting on the smallest boulders, such as i) disintegration or fragmentation and vanishing through sublimation; ii) uplifting by gas drag and consequent redistribution; and iii) burial beneath a debris blanket. We also derived the cumulative size-frequency distribution per km2 of localized areas on 67P. By comparing the cumulative size-frequency distributions of similar geomorphological settings, we derived similar power-law index values. This suggests that despite the selected locations on different and often opposite sides of the comet, similar sublimation or activity processes, pit formation or collapses, as well as thermal stresses or fracturing events occurred on multiple areas of the comet, shaping its surface into the appearance we see today.

Assessment of the mineral density and mineral content of the equine third metacarpal and first phalanx bone by dual energy x-ray absorptiometry

In the first part of this methodological study eleven metacarpi of 9 skeletally normal horses were examined from 4 directions by dual energy x-ray absorptiometry (DXA). The differences between the dorsopalmar-palmarodorsal and lateromedial-mediolateral (opposite sites) bone mineral density (BMD) values were found to be nonsignificant. In the second part of the study the precision of the Norland XR-26 densitometer was tested by measuring 34 metacarpal bones and 34 proximal phalanges, each of them three times, from a single direction. The difference between the individual measurements of the first phalanges and of the metacarpal bones originating from the right or the left side of the same horse were not significant, nor did the age or breed have a significant effect on BMD or bone mineral content (BMC). However, both BMD and BMC are greater in the metacarpal bones than in the proximal phalanges and are higher in geldings than in mares or to stallions, while the BMD or BMC values of mares and stallions did not differ from each other significantly. These data point to the necessity of further BMD studies in a higher number of patients.

Ethnic differences in macular pigment density and distribution

PURPOSE: Many epidemiologic studies suggest a number of risk factors that may be associated with progression of age-related maculopathy (ARM). In this study, the authors investigate ethnic differences in macular pigment density (MPD) and macular pigment (MP) distribution. METHODS: Inclusion criteria were healthy subjects, aged 35 to 49 years, visual acuity >or=20/20, race ethnicity white non-Hispanic (WNH) or African. All subjects underwent the following examinations: best-corrected ETDRS visual acuity (VA), measurements of MPD, and spatial distribution of MP with a modified confocal scanning laser ophthalmoscope according to a standard protocol. MPD maps were calculated from autofluorescence images recorded at 488 nm and 514 nm. Central macular pigment density (MPDc) was quantified from MPD maps within 0.5 degrees around the center of the fovea. RESULTS: In total, 118 healthy subjects (61 women, 57 men) aged 35 to 49 years (mean, 42.5 +/- 3.6 years) were recruited for the study. Sixty-seven healthy subjects were WNH and 51 were African. Visual acuity ranged from 20/20 to 20/16 in the study eye. Significant differences were found among MPDc between the group of WNH (MPDc, 0.36 +/- 0.13 density units [DU]; P < 0.0001) and African subjects (MPDc, 0.59 +/- 0.14 DU). A parafoveal ring was significantly more frequent in African subjects than in WNH subjects (86% [African] vs. 68% [WNH]; P < 0.0001). CONCLUSIONS: This study demonstrates that ethnicity plays a role in MPD values and in MP distribution. The association of different distribution patterns and their relevance as possible prognostic factors for diseases leading to oxidative retinal damage requires further studies.

Beneficial effects of aggressive low-density lipoprotein cholesterol lowering in women with stable coronary heart disease in the Treating to New Targets (TNT) study

OBJECTIVE: To examine by secondary analysis of the Treating to New Targets (TNT) study whether the benefits of intensive versus standard levels of lipid lowering are equally applicable to women. METHODS: A total of 10 001 patients (1902 women) with stable coronary heart disease (CHD) were randomised to double-blind treatment with atorvastatin 10 or 80 mg/day for a median follow-up of 4.9 years. RESULTS: In women and men, intensive treatment with atorvastatin 80 mg significantly reduced the rate of major cardiovascular events compared with atorvastatin 10 mg. Among women, the relative and absolute reductions were 27% and 2.7%, respectively (hazard ratio (HR) = 0.73, 95% confidence interval (CI) 0.54 to 1.00, p = 0.049). In men, the corresponding rate reductions were 21% and 2.2% (HR = 0.79, 95% CI 0.69 to 0.91, p = 0.001). The number needed to treat value (to prevent one cardiovascular event over 4.9 years compared with patients treated with atorvastatin 10 mg) for atorvastatin 80 mg was 29 for women and 30 for men. Rates of death of non-cardiovascular origin in the atorvastatin 80 mg and atorvastatin 10 mg were 3.6% and 1.6%, respectively (p = 0.004) among women, and 2.8% and 3.1% (p = 0.47) among men. CONCLUSION: Intensive lipid-lowering treatment with atorvastatin 80 mg produced significant reductions in relative risk for major cardiovascular events compared with atorvastatin 10 mg in both women and men with stable CHD.

Mothers adjust egg size to helper number in a cooperatively breeding cichlid

Mothers should adjust the size of propagules to the selective forces to which these offspring will be exposed. Usually, a larger propagule size is favored when young are exposed to high mortality risk or conspecific competition. Here we test 2 predictions on how egg size should vary with these selective agents. When offspring are cared for by parents and/or alloparents, protection may reduce the predation risk to young, which may allow mothers to invest less per single offspring. In the cooperatively breeding cichlid Neolamprologus pulcher, brood care helpers protect group offspring and reduce the latters' mortality rate. Therefore, females are expected to reduce their investment per egg when more helpers are present. In a first experiment, we tested this prediction by manipulating the helper number. In N. pulcher, helpers compete for dispersal opportunities with similar-sized individuals of neighboring groups. If the expected future competition pressure on young is high, females should increase their investment per offspring to give them a head start. In a second experiment, we tested whether females produce larger eggs when perceived neighbor density is high. Females indeed reduced egg size with increasing helper number. However, we did not detect an effect of local density on egg size, although females took longer to produce the next clutch when local density was high. We argue that females can use the energy saved by adjusting egg size to reduced predation risk to enhance future reproductive output. Adaptive adjustment of offspring size to helper number may be an important, as yet unrecognized, strategy of cooperative breeders.

Osteocyte lacunar density and area in newly formed bone of the augmented sinus

OBJECTIVES Osteocytes, the most common cells of the bone, are buried in lacunae. Density and area of the osteocyte lacunae change with increasing maturation of the newly formed bone. Evaluation of osteocyte lacunae can therefore provide insights into the process of graft consolidation. MATERIALS AND METHODS Here, we determined the osteocyte lacunar density (number of osteocyte lacunae per bone area; N.Ot/BAr) and the osteocyte lacunar area in μm(2) (Lac.Ar) in histological specimens 6 and 12 weeks after the sinuses of 10 minipigs were augmented with Bio-Oss(®) , a deproteinized bovine bone mineral, and Ostim(®) , an aqueous paste of synthetic nanoparticular hydroxyapatite. The region of interest was defined by the following criteria: (i) >1 mm from the host bone, (ii) >0.5 mm from the sinus mucosa, (iii) minimum area of 0.2 mm(2) , and (iv) bone tissue spanning at least two bone substitute particles. RESULTS The overall osteocyte lacunar density was significantly higher in the Bio-Oss(®) group than in the Ostim(®) group and decreased during the observation period at a similar range in both groups. The osteocyte lacunar area was smaller in the Bio-Oss(®) group than the Ostim(®) group but there was no significant change within the groups over time. CONCLUSIONS These results suggest that bone substitutes affect the osteocyte lacunar density and the osteocyte lacunar area in the newly formed bone within the augmented sinus in this particular model situation. These measures can provide insights into the maturation of newly formed bone in the augmented sinus.

Evaluation of the benefit of emergency vaccination in a foot-and-mouth disease free country with low livestock density

Foot-and-mouth disease (FMD) is highly contagious and one of the most economically devastating diseases of cloven-hoofed animals. Scientific-based preparedness about how to best control the disease in a previously FMD-free country is therefore essential for veterinary services. The present study used a spatial, stochastic epidemic simulation model to compare the effectiveness of emergency vaccination with conventional (non-vaccination) control measures in Switzerland, a low-livestock density country. Model results revealed that emergency vaccination with a radius of 3 km or 10 km around infected premises (IP) did not significantly reduce either the cumulative herd incidence or epidemic duration if started in a small epidemic situation where the number of IPs is still low. However, in a situation where the epidemic has become extensive, both the cumulative herd incidence and epidemic duration are reduced significantly if vaccination were implemented with a radius of 10 km around IPs. The effect of different levels of conventional strategy measures was also explored for the non-vaccination strategy. It was found that a lower compliance level of farmers for movement restrictions and delayed culling of IPs significantly increased both the cumulative IP incidence and epidemic duration. Contingency management should therefore focus mainly on improving conventional strategies, by increasing disease awareness and communication with stakeholders and preparedness of culling teams in countries with a livestock structure similar to Switzerland; however, emergency vaccination should be considered if there are reasons to believe that the epidemic may become extensive, such as when disease detection has been delayed and many IPs are discovered at the beginning of the epidemic.

High-density large-scale field emitter arrays for x-ray free electron laser cathodes

High brightness electron sources are of great importance for the operation of the hard X-ray free electron lasers. Field emission cathodes based on the double-gate metallic field emitter arrays (FEAs) can potentially offer higher brightness than the currently used ones. We report on the successful application of electron beam lithography for fabrication of the large-scale single-gate as well as double-gate FEAs. We demonstrate operational high-density single-gate FEAs with sub-micron pitch and total number of tips up to 106 as well as large-scale double-gate FEAs with large collimation gate apertures. The details of design, fabrication procedure and successful measurements of the emission current from the single- and double-gate cathodes are presented.

Mapping tree density at a global scale

The global extent and distribution of forest trees is central to our understanding of the terrestrial biosphere. We provide the first spatially continuous map of forest tree density at a global scale. This map reveals that the global number of trees is approximately 3.04 trillion, an order of magnitude higher than the previous estimate. Of these trees, approximately 1.39 trillion exist in tropical and subtropical forests, with 0.74 trillion in boreal regions and 0.61 trillion in temperate regions. Biome-level trends in tree density demonstrate the importance of climate and topography in controlling local tree densities at finer scales, as well as the overwhelming effect of humans across most of the world. Based on our projected tree densities, we estimate that over 15 billion trees are cut down each year, and the global number of trees has fallen by approximately 46% since the start of human civilization.

Oral Lutein Supplementation Enhances Macular Pigment Density and Contrast Sensitivity but Not in Combination With Polyunsaturated Fatty Acids.

Purpose It has been shown that lutein and zeaxanthin accumulate in the macula where they enhance contrast sensitivity and may reduce the risk of progression to advanced age-related macular degeneration (AMD). Furthermore, omega-3 long-chain polyunsaturated fatty acids (PUFA) might further reduce this risk. However, controversy exists regarding whether PUFA may reduce the bioavailability of lutein. Methods This was a prospective 12-month, randomized, open label study evaluating the effect of supplementation with lutein, other antioxidants, and minerals on contrast sensitivity (CS) and macular pigment optical density (MPOD) in patients with age-related maculopathy. A total of 79 patients were randomized to either lutein (10 mg) and antioxidant supplement or lutein and antioxidant supplement in combination with PUFA. Patients received supplementation for a period of 6 months and were followed for a total of 12 months. Results Serum lutein and zeaxanthin increased significantly by the first follow-up visit at 1 month, and remained elevated throughout the intervention period of 6 months in the lutein-only group but not in the lutein+PUFA group. Macular pigment optical density and CS increased significantly in the lutein-only group (P < 0.005) but not in the lutein+PUFA group (P = 0.059) compared to baseline. Best-corrected visual acuity remained unchanged during the entire study period in both groups. Conclusions Addition of PUFA may reduce the bioavailability of lutein and therefore lessen the beneficial effect on macular pigment and CS. This needs to be considered when prescribing lutein supplements to patients with low lutein levels. (ClinicalTrials.gov number, NCT00563979.).