The effects of stellar winds on the magnetospheres and potential habitability of exoplanets

Context: The principle definition of habitability for exoplanets is whether they can sustain liquid water on their surfaces, i.e. that they orbit within the habitable zone. However, the planet's magnetosphere should also be considered, since without it, an exoplanet's atmosphere may be eroded away by stellar winds. Aims: The aim of this paper is to investigate magnetospheric protection of a planet from the effects of stellar winds from solar-mass stars. Methods: We study hypothetical Earth-like exoplanets orbiting in the host star's habitable zone for a sample of 124 solar-mass stars. These are targets that have been observed by the Bcool collaboration. Using two wind models, we calculate the magnetospheric extent of each exoplanet. These wind models are computationally inexpensive and allow the community to quickly estimate the magnetospheric size of magnetised Earth-analogues orbiting cool stars. Results: Most of the simulated planets in our sample can maintain a magnetosphere of ~5 Earth radii or larger. This suggests that magnetised Earth analogues in the habitable zones of solar analogues are able to protect their atmospheres and is in contrast to planets around young active M dwarfs. In general, we find that Earth-analogues around solar-type stars, of age 1.5 Gyr or older, can maintain at least a Paleoarchean Earth sized magnetosphere. Our results indicate that planets around 0.6 - 0.8 solar-mass stars on the low activity side of the Vaughan-Preston gap are the optimum observing targets for habitable Earth analogues.Comment: 8 pages, 3 figures, accepted to Astronomy and Astrophysic

Bone Mass and Strength in Older Men With Type 2 Diabetes: The Osteoporotic Fractures in Men Study

The effects of type 2 diabetes mellitus (T2DM) on bone volumetric density, bone geometry, and estimates of bone strength are not well established. We used peripheral quantitative computed tomography (pQCT) to compare tibial and radial bone volumetric density (vBMD, mg/cm3), total (ToA, mm2) and cortical (CoA, mm2) bone area and estimates of bone compressive and bending strength in a subset (n = 1171) of men (≥65 years of age) who participated in the multisite Osteoporotic Fractures in Men (MrOS) study. Analysis of covariance–adjusted bone data for clinic site, age, and limb length (model 1) and further adjusted for body weight (model 2) were used to compare data between participants with (n = 190) and without (n = 981) T2DM. At both the distal tibia and radius, patients with T2DM had greater bone vBMD (+2% to +4%, model 1, p < .05) and a smaller bone area (ToA −1% to −4%, model 2, p < .05). The higher vBMD compensated for lower bone area, resulting in no differences in estimated compressive bone strength at the distal trabecular bone regions. At the mostly cortical bone midshaft sites of the radius and tibia, men with T2DM had lower ToA (−1% to −3%, p < .05), resulting in lower bone bending strength at both sites after adjusting for body weight (−2% to −5%, p < .05) despite the lack of difference in cortical vBMD at these sites. These data demonstrate that older men with T2DM have bone strength that is low relative to body weight at the cortical-rich midshaft of the radius despite no difference in cortical vBMD. © 2010 American Society for Bone and Mineral Researc

Estimating magnetic filling factors from Zeeman–Doppler magnetograms

V.S., S.P.M., and A.J.F.acknowledge funding from the European Research Council (ERC) under the European Unions Horizon 2020 research and innovation programme (grant agreement No. 682393 AWESoMeStars). S.B.S. acknowledges funding via the Austrian Space Application Programme (ASAP) of the Austrian Research Promotion Agency (FFG) within ASAP11, the FWF NFN project S11601-N16 and the sub-project S11604-N16. A. A.V. acknowledges funding received from the Irish Research Council Laureate Awards 2017/2018.Low-mass stars are known to have magnetic fields that are believed to be of dynamo origin. Two complementary techniques are principally used to characterize them. Zeeman–Doppler imaging (ZDI) can determine the geometry of the large-scale magnetic field while Zeeman broadening can assess the total unsigned flux including that associated with small-scale structures such as spots. In this work, we study a sample of stars that have been previously mapped with ZDI. We show that the average unsigned magnetic flux follows an activity-rotation relation separating into saturated and unsaturated regimes. We also compare the average photospheric magnetic flux recovered by ZDI, BV, with that recovered by Zeeman broadening studies, BI. In line with previous studies, BV ranges from a few % to ~20% of BI. We show that a power-law relationship between BV and BI exists and that ZDI recovers a larger fraction of the magnetic flux in more active stars. Using this relation, we improve on previous attempts to estimate filling factors, i.e., the fraction of the stellar surface covered with magnetic field, for stars mapped only with ZDI. Our estimated filling factors follow the well-known activity-rotation relation, which is in agreement with filling factors obtained directly from Zeeman broadening studies. We discuss the possible implications of these results for flux tube expansion above the stellar surface and stellar wind models.Publisher PDFPeer reviewe

02. PETIT

1 . Thus, bone tissue has an intrinsic &quot;mechanostat&quot; which regulates bone functional adaptation. As with any homeostatic control system, bone&apos;s mechanostat J Musculoskelet Neuronal Interact 2010; 10(2):128-135 Abstract Harold Frost first proposed the existence of several mechanical thresholds in bone, two of which determine whether bone is added to, or lost from, the skeleton. Recent evidence from bone biology helps elucidate the role of osteocytes in determining these mechanical thresholds. Specifically, when mechanical stimuli fall below the resorption threshold, osteocyte apoptosis occurs, followed by bone resorption. Conversely, mechanical loading maintains osteocytes viability, and consequently, no bone is lost. With a greater than customary mechanical stimulus, osteocytes perturbation from pulsatile fluid flow results in release of anabolic factors and subsequent bone formation. Osteocytes also play a pivotal role in bone remodeling in response to alterations in the mechanical environment. In particular, osteocyte apoptosis results in bone turnover in disuse as well as in response to greater than customary mechanical stimuli due to microdamage accumulation. Given the important role of osteocytes in bone modeling and remodeling, these cells provide an ideal target for both drug therapies and exercise to prevent bone fragility

Growing bones: how important is exercise?

Purpose of review: The aim of this review is to summarize what is known about the relationship between childhood physical activity and bone mineral mass, bone geometry and bone strength. Recent findings: A number of studies consistently show a beneficial effect of childhood physical activity on bone mineral accretion. Recent data suggest that hormonal milieu, stage of maturation and the type of activity influence how much and where (periosteal or endocortical surfaces) new bone is laid down in response to loading. Individuals who are consistently active during adolescence reach adulthood with better bone geometry, and greater bone strength. Pre and early puberty are an opportune time to introduce osteogenic activities. Summary: It is clear (in our opinion) that mechanical loading dominates bone adaptation during growth, and other factors such as nutrition, disease and hormonal milieu may mediate the effect. The exact prescription for optimal bone development is not yet clearly defined, but activities that induce moderate to high-impact with fast strain rates in unusual patterns have a positive effect on bone development, even with only a few loading cycles. Inserting rest between activity bouts has promise as a means of optimizing the bone response to loading in brief period

Bone mass and structure are enhanced following a 2-year randomized controlled trial of exercise in prepubertal boys

Exercise during growth has a positive influence on bone mineral accrual, yet little is known about how bone geometry and strength adapt to loading during growth. Our primary objective was to compare changes in proximal femur bone geometry and strength between 31 prepubertal (Tanner Stage 1) boys who participated in a school-based, high-impact circuit intervention (12 min, three times a week) for 20 months and 33 maturity-matched controls. Our secondary objective was to compare changes in total body (TB), proximal femur (PF), and lumbar spine (LS) bone mineral content (BMC) and bone area (BA) in these groups. We assessed geometric variables and bone strength at the narrow neck (NN), intertrochanteric (TR) region, and femoral shaft regions by applying the Hip Structure Analysis program to proximal femur dual energy X-ray absorptiometry scans (DXA, Hologic QDR 4500). Further, we assessed total body, lumbar spine, and proximal femur BMC and BA by DXA and derived total body lean mass and fat mass from total body scans. Intervention (10.2 ± 0.5 years) and control boys (10.1 ± 0.5 years) had similar baseline height (140.8 vs. 141.3 cm) and weight (36.9 vs. 35.4 kg), and average 20-month physical activity scores (Physical Activity Questionnaire for Children, PAQ-C) and calcium intakes (861 vs. 852 mg/day, food frequency questionnaire). Twenty-month height and weight changes were not significantly different between groups; lean mass changed more (P < 0.05) in intervention boys (22.8%) than control boys (18.6%). At the NN region, intervention boys had greater bone expansion on both the periosteal (+2.6%, P = 0.1) and endosteal (+2.7%, P = 0.2) surfaces, resulting in significantly greater changes in section modulus (bone bending strength) (+7.5%, P = 0.02, ANCOVA, adjusting for height change, final Tanner Stage, and baseline bone values). Changes at the intertrochanteric and femoral shaft regions were not significantly different between groups. Femoral neck (FN) BMC changes were significantly greater in intervention boys (+4.3%, P < 0.01); changes in BA and BMC for other regions were not significantly different between groups. In summary, a school-based, high-impact exercise intervention implemented three times a week for 12 min is an effective strategy for site-specific gains in bone strength at the narrow neck region of the proximal femu

USA300 Staphylococcus aureus persists on multiple body sites following an infection

Abstract Background USA300 methicillin-resistant Staphylococcus aureus (MRSA) is a community- and hospital-acquired pathogen that frequently causes infections but also can survive on the human body asymptomatically as a part of the normal microbiota. We devised a comparative genomic strategy to track colonizing USA300 at different body sites after an initial infection. We sampled ST8 S. aureus from subjects at the site of a first known MRSA infection. Within 60 days of this infection and again 12 months later, each subject was tested for asymptomatic colonization in the nose, throat and perirectal region. 93 S. aureus strains underwent whole genome shotgun sequencing. Results Among 28 subjects at the initial sampling time, we isolated S. aureus from the nose, throat and perirectal sites from 15, 11 and 15 of them, respectively. Twelve months later we isolated S. aureus from 9 subjects, with 6, 3 and 3 strains from the nose, throat and perirectal area, respectively. Genome sequencing revealed that 23 patients (ages 0–66 years) carried USA300 intra-subject lineages (ISLs), defined as having an index infection isolate and closely related colonizing strains. Pairwise distance between strains in different ISLs was 48 to 162 single nucleotide polymorphisms (SNPs) across the core regions of the chromosome, whereas within the same ISL it was 0 to 26 SNPs. Strains in ISLs from the same subject differed in plasmid and prophage content, and contained deletions that removed the mecA-containing SCCmec and ACME regions. Five strains contained frameshift mutations in agr toxin-regulating genes. Persistence of an ISL was not associated with clinical or demographic subject characteristics. We inferred that colonization with the ISL occurred about 18 weeks before the first assessment of asymptomatic colonization. Conclusions Clonal lineages of USA300 may continue to colonize people at one or more anatomic sites up to a year after an initial infection and experience loss of the SCCmec, loss and gain of other mobile genetic elements, and mutations in the agr operon

Bone structure and volumetric BMD in overweight children: A longitudinal study

The effect of excess body fat on bone strength accrual is not well understood. Therefore, we assessed bone measures in healthy weight (HW) and overweight (OW) children. Children (9-11 yr) were classified as HW (n = 302) or OW (n = 143) based on body mass index. We assessed total (ToD) and cortical (CoD) volumetric BMD and bone area, estimates of bone strength (bone strength index [BSI]; stress-strain index [SSIp]), and muscle cross-sectional area (CSA) at the distal (8%), midshaft (50%), and proximal (66%) tibia by pQCT. We used analysis of covariance to compare bone outcomes at baseline and change over 16 mo. At baseline, all bone measures were significantly greater in OW compared with HW children (+4-15%; p 0.001), with the exception of CoD at the 50% and 66% sites. Over 16 mo, ToA increased more in the OW children, whereas there was no difference for change in BSI or ToD between groups at the distal tibia. At the tibial midshaft, SSIp was similar between groups at baseline when adjusted for muscle CSA, but low when adjusted for body fat in the OW group. At both sites, bone strength increased more in OW because of a greater increase in bone area. Changes in SSIp were associated with changes in lean mass (r = 0.70, p < 0.001) but not fat mass. In conclusion, although OW children seem to be at an advantage in terms of absolute bone strength, bone strength did not adapt to excess body fat. Rather, bone strength was adapted to the greater muscle area in OW children