112 research outputs found
Instability and `Sausage-String' Appearance in Blood Vessels during High Blood Pressure
A new Rayleigh-type instability is proposed to explain the `sausage-string'
pattern of alternating constrictions and dilatations formed in blood vessels
under influence of a vasoconstricting agent. Our theory involves the nonlinear
elasticity characteristics of the vessel wall, and provides predictions for the
conditions under which the cylindrical form of a blood vessel becomes unstable.Comment: 4 pages, 4 figures submitted to Physical Review Letter
Direct estimation of genome mutation rates from pedigrees in free-ranging baleen whales
Current low germline mutation rate (𝜇) estimates in baleen whales have greatly influenced research ranging from assessments of whaling impacts to evolutionary cancer biology. However, the reported rates were subject to methodological errors and uncertainty. We estimated 𝜇 directly from pedigrees in natural populations of four baleen whale species and the results were similar to primates. The implications of revised 𝜇 values include pre-exploitation population sizes at 14% of previous genetic diversity-based estimates and the conclusion that 𝜇 in itself is insufficient to explain low cancer rates in gigantic mammals (i.e., Peto’s Paradox). We demonstrate the feasibility of estimating 𝜇 from whole genome pedigree data in natural populations, which has wide-ranging implications for the many ecological and evolutionary inferences that rely on 𝜇
Higher Yield and Fewer Weeds in Four-Species Grass/Legume Mixtures Than in Monocultures: Results from the First Year at 20 Sites of Cost Action 852
Utilisation of grass/legume mixtures instead of grass monocultures is a sensible alternative for low input, efficient agricultural systems that reduce production costs, promote environmental policy and maintain a living countryside. Consequently, widely adapted forage legumes will become increasingly important. Instability of simple grass / legume mixtures with only one grass and one legume species is a major problem (Wachendorf et al., 2001). An experiment was established in 39 sites in Europe, Australia and Canada within COST Action 852 to: (1) assess the benefits of grass / legume mixtures in terms of forage production, (2) test whether the combination of fast and slow-growing species improves the stability of the mixtures and (3) assess response patterns over a large environmental gradient
Suppression of Star Formation in the central 200 kpc of a z = 1.4 Galaxy Cluster [Erratum added]
We present the results of an extended narrow-band H{\alpha} study of the
massive galaxy cluster XMMU J2235.3-2557 at z = 1.39. This paper represents a
follow up study to our previous investigation of star-formation in the cluster
centre, extending our analysis out to a projected cluster radius of 1.5 Mpc.
Using the Near InfraRed Imager and Spectrograph (NIRI) on Gemini North we
obtained deep H narrow-band imaging corresponding to the rest-frame wavelength
of H{\alpha} at the cluster's redshift. We identify a total of 163 potential
cluster members in both pointings, excluding stars based on their near-IR
colours derived from VLT/HAWK-I imaging. Of these 163 objects 14 are
spectroscopically confirmed cluster members, and 20% are excess line-emitters.
We find no evidence of star formation activity within a radius of 200 kpc of
the brightest cluster galaxy in the cluster core. Dust-corrected star formation
rates (SFR) of excess emitters outside this cluster quenching radius, RQ \sim
200 kpc, are on average = 2.7 \pm 1.0 M\odot yr-1, but do not show
evidence of increasing star-formation rates toward the extreme 1.5 Mpc radius
of the cluster. No individual cluster galaxy exceeds an SFR of 6 M\odot yr-1 .
Massive galaxies (log M\ast /M\odot > 10.75) all have low specific SFRs (SSFRs,
i.e. SFR per unit stellar mass). At fixed stellar mass, galaxies in the cluster
centre have lower SSFRs than the rest of the cluster galaxies, which in turn
have lower SSFRs than field galaxies at the same redshift by a factor of a few
to 10. For the first time we can demonstrate through measurements of individual
SFRs that already at very early epochs (at an age of the Universe of \sim4.5
Gyr) the suppression of star-formation is an effect of the cluster environment
which persists at fixed galaxy stellar mass. [Erratum added after the original
paper]Comment: 12 pages, 6 figures, accepted for publication in MNRAS. New version:
Erratum added after the original paper (2 pages, 3 corrected figures). Due to
an error in the original computation the SFR values had to be increased by a
factor of 5. However, the results and conclusions remain largely unchange
The Agrodiversity Experiment: three years of data from a multisite study in intensively managed grasslands
Intensively managed grasslands are globally prominent ecosystems. We investigated whether experimental increases in plant diversity in intensively managed grassland communities can increase their resource use efficiency. This work consisted of a coordinated, continental-scale 33-site experiment. The core design was 30 plots, representing 15 grassland communities at two seeding densities. The 15 communities were comprised of four monocultures (two grasses and two legumes) and 11 four-species mixtures that varied in the relative abundance of the four species at sowing. There were 1028 plots in the core experiment, with another 572 plots sown for additional treatments. Sites agreed a protocol and employed the same experimental methods with certain plot management factors, such as seeding rates and number of cuts, determined by local practice. The four species used at a site depended on geographical location, but the species were chosen according to four functional traits: a fast-establishing grass, a slow-establishing persistent grass, a fast-establishing legume, and a slow-establishing persistent legume. As the objective was to maximize yield for intensive grassland production, the species chosen were all high-yielding agronomic species. The data set contains species-specific biomass measurements (yield per species and of weeds) for all harvests for up to four years at 33 sites. Samples of harvested vegetation were also analyzed for forage quality at 26 sites. Analyses showed that the yield of the mixtures exceeded that of the average monoculture in >97% of comparisons. Mixture biomass also exceeded that of the best monoculture (transgressive overyielding) at about 60% of sites. There was also a positive relationship between the diversity of the communities and aboveground biomass that was consistent across sites and persisted for three years. Weed invasion in mixtures was very much less than that in monocultures.
These data should be of interest to ecologists studying relationships between diversity and ecosystem function and to agronomists interested in sustainable intensification. The large spatial scale of the sites provides opportunity for analyses across spatial (and temporal) scales. The database can also complement existing databases and meta-analyses on biodiversity–ecosystem function relationships in natural communities by focusing on those same relationships within intensively managed agricultural grasslands
A registry-based follow-up study, comparing the incidence of cardiovascular disease in native Danes and immigrants born in Turkey, Pakistan and the former Yugoslavia: do social inequalities play a role?
<p>Abstract</p> <p>Background</p> <p>This study compared the incidence of cardiovascular disease (CVD) and acute myocardial infarction (AMI) between native Danes and immigrants born in Turkey, Pakistan and the former Yugoslavia. Furthermore, we examined whether different indicators of socioeconomic status (SES), such as employment, income and housing conditions influenced potential differences.</p> <p>Methods</p> <p>In this registry-based follow-up study individuals were identified in a large database that included individuals from two major regions in Denmark, corresponding to about 60% of the Danish population. Incident cases of CVD and AMI included fatal and non-fatal events and were taken from registries. Using Cox regression models, we estimated incidence rates at 5-year follow-up.</p> <p>Results</p> <p>Immigrant men and women from Turkey and Pakistan had an increased incidence of CVD, compared with native Danish men. In the case of AMI, a similar pattern was observed; however, differences were more pronounced. Pakistanis and Turks with a shorter duration of residence had a lower incidence, compared with those of a longer residence. Generally, no notable differences were observed between former Yugoslavians and native Danes. In men, differences in CVD and AMI were reduced after adjustment for SES, in particular, among Turks regarding CVD. In women, effects were particularly reduced among Yugoslavians in the case of CVD and in Turks in the case of CVD and AMI after adjustment for SES.</p> <p>Conclusions</p> <p>In conclusion, country of birth-related differences in the incidence of CVD and AMI were observed. At least some of the differences that we uncovered were results of a socioeconomic effect. Duration of residence also played a certain role. Future studies should collect and test different indicators of SES in studies of CVD among immigrants.</p
Plant diversity greatly enhances weed suppression in intensively managed grasslands
Weed suppression was investigated in a field experiment across 31 international sites. The study included 15 plant communities at each site, based on two grasses and two legumes, each sown in monoculture and 11 four-species mixtures varying in the relative proportions of the four species. At each site, one grass and one legume species was selected as fast establishing and the other two species were selected for persistence. Average weed biomass in mixtures over the whole experiment was 52% less (95% confidence interval, 30 to 75%) than in the most suppressive monoculture (transgressive suppression). Transgressive suppression of weed biomass persisted over each year for each mixture. Weed biomass was consistently low and relatively similar across all mixtures and years. Average sown species biomass was greater in all mixtures than in any monoculture. The suppressive effect of sown forage species on weeds in mixtures was achieved without any herbicide use. At each site, weed biomass for almost every mixture was lower than the average across the four monocultures. The average proportion of weed biomass in mixtures was less than in the most suppressive monoculture in two thirds of sites. Mixtures outyielded monocultures, and mixture yield comprised far lower weed biomass
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