62 research outputs found
Quantifying biodiversity trade-offs in the face of widespread renewable and unconventional energy development
The challenge of balancing biodiversity protection with economic growth is epitomized by the development of renewable and unconventional energy, whose adoption is aimed at stemming the impacts of global climate change, yet has outpaced our understanding of biodiversity impacts. We evaluated the potential conflict between biodiversity protection and future electricity generation from renewable (wind farms, run-of-river hydro) and non-renewable (shale gas) sources in British Columbia (BC), Canada using three metrics: greenhouse gas (GHG) emissions, electricity cost, and overlap between future development and conservation priorities for several fish and wildlife groups - small-bodied vertebrates, large mammals, freshwater fish - and undisturbed landscapes. Sharp trade-offs in global versus regional biodiversity conservation exist for all energy technologies, and in BC they are currently smallest for wind energy: low GHG emissions, low-moderate overlap with top conservation priorities, and competitive energy cost. GHG emissions from shale gas are 1000 times higher than those from renewable sources, and run-of-river hydro has high overlap with conservation priorities for small-bodied vertebrates. When all species groups were considered simultaneously, run-of-river hydro had moderate overlap (0.56), while shale gas and onshore wind had low overlap with top conservation priorities (0.23 and 0.24, respectively). The unintended cost of distributed energy sources for regional biodiversity suggest that trade-offs based on more diverse metrics must be incorporated into energy planning.Peer reviewe
Kepler Observations of V447 Lyr: An Eclipsing U Gem Cataclysmic Variable
We present the results of an analysis of data covering 1.5 years of the dwarf
nova V447 Lyr. We detect eclipses of the accretion disk by the mass donating
secondary star every 3.74 hrs which is the binary orbital period. V447 Lyr is
therefore the first dwarf nova in the Kepler field to show eclipses. We also
detect five long outbursts and six short outbursts showing V447 Lyr is a U Gem
type dwarf nova. We show that the orbital phase of the mid-eclipse occurs
earlier during outbursts compared to quiescence and that the width of the
eclipse is greater during outburst. This suggests that the bright spot is more
prominent during quiescence and that the disk is larger during outburst than
quiescence. This is consistent with an expansion of the outer disk radius due
to the presence of high viscosity material associated with the outburst,
followed by a contraction in quiescence due to the accretion of low angular
momentum material. We note that the long outbursts appear to be triggered by a
short outburst, which is also observed in the super-outbursts of SU UMa dwarf
novae as observed using Kepler.Comment: Accepted by MNRA
Long-term monitoring in IC4665: Fast rotation and weak variability in very low mass objects
We present the combined results of three photometric monitoring campaigns
targeting very low mass (VLM) stars and brown dwarfs in the young open cluster
IC4665 (age ~40 Myr). In all three runs, we observe ~100 cluster members,
allowing us for the first time to put limits on the evolution of spots and
magnetic activity in fully convective objects on timescales of a few years. For
20 objects covering masses from 0.05 to 0.5 Msol we detect a periodic flux
modulation, indicating the presence of magnetic spots co-rotating with the
objects. The detection rate of photometric periods (~20%) is significantly
lower than in solar-mass stars at the same age, which points to a mass
dependence in the spot properties. With two exceptions, none of the objects
exhibit variability and thus spot activity in more than one season. This is
contrary to what is seen in solar-mass stars and indicates that spot
configurations capable of producing photometric modulations occur relatively
rarely and are transient in VLM objects. The rotation periods derived in this
paper range from 3 to 30h, arguing for a lack of slow rotators among VLM
objects. The periods fit into a rotational evolution scenario with pre-main
sequence contraction and moderate (40-50%) angular momentum losses due to wind
braking. By combining our findings with literature results, we identify two
regimes of rotational and magnetic properties, called C- and I-sequence. Main
properties on the C-sequence are fast rotation, weak wind braking, Halpha
emission, and saturated activity levels, while the I-sequence is characterised
by slow rotation, strong wind braking, no Halpha emission, and linear
activity-rotation relationship. Rotation rate and stellar mass are the primary
parameters that determine in which regime an object is found. (abridged)Comment: 16 pages, 10 figures, accepted for publication in MNRA
Rotation, activity, and lithium abundance in cool binary stars
We have used two robotic telescopes to obtain time-series high-resolution
spectroscopy and V I and/or by photometry for a sample of 60 active stars.
Orbital solutions are presented for 26 SB2 and 19 SB1 systems with
unprecedented phase coverage and accuracy. The total of 6,609 R=55,000 echelle
spectra are also used to systematically determine effective temperatures,
gravities, metallicities, rotational velocities, lithium abundances and
absolute H{\alpha}-core fluxes as a function of time. The photometry is used to
infer unspotted brightness, V - I and/or b - y colors, spot-induced brightness
amplitudes and precise rotation periods. Our data are complemented by
literature data and are used to determine rotation-temperature-activity
relations for active binary components. We also relate lithium abundance to
rotation and surface temperature. We find that 74% of all known
rapidly-rotating active binary stars are synchronized and in circular orbits
but 26% are rotating asynchronously of which half have Prot > Porb and e > 0.
Because rotational synchronization is predicted to occur before orbital
circularization active binaries should undergo an extra spin-down besides tidal
dissipation. We suspect this to be due to a magnetically channeled wind with
its subsequent braking torque. We find a steep increase of rotation period with
decreasing effective temperature for active stars. For inactive, single giants
with Prot > 100 d, the relation is much weaker. Our data also indicate a
period-activity relation for H{\alpha} of the form RH{\alpha} \propto P - 0.24
for binaries and RH{\alpha} \propto P -0.14 for singles. Lithium abundances in
our sample increase with effective temperature. On average, binaries of
comparable effective temperature appear to exhibit 0.25 dex less surface
lithium than singles. We also find a trend of increased Li abundance with
rotational period of form log n(Li) \propto - 0.6 log Prot
Rotation of young stars in Cepheus OB3b
We present a photometric study of I-band variability in the young association Cepheus OB3b. The study is sensitive to periodic variability on time-scales of less than a day, to more than 20 d. After rejection of contaminating objects using V, I, R and narrow-band Hα photometry, we find 475 objects with measured rotation periods, which are very likely pre-main-sequence members of the Cep OB3b star-forming region.
We revise the distance and age to Cep OB3b, putting it on the self-consistent age and distance ladder of Mayne & Naylor. This yields a distance modulus of 8.8 ± 0.2 mag, corresponding to a distance of 580 ± 60 pc, and an age of 4–5 Myr.
The rotation period distribution confirms the general picture of rotational evolution in young stars, exhibiting both the correlation between accretion (determined in this case through narrow-band Hα photometry) and rotation expected from disc locking, and the dependence of rotation upon mass that is seen in other star-forming regions. However, this mass dependence is much weaker in our data than found in other studies. Comparison to the similarly aged NGC 2362 shows that the low-mass stars in Cep OB3b are rotating much more slowly. This points to a possible link between star-forming environment and rotation properties. Such a link would call into question models of stellar angular momentum evolution, which assume that the rotational period distributions of young clusters and associations can be assembled into an evolutionary sequence, thus ignoring environmental effects
Astrophysical magnetic fields and nonlinear dynamo theory
The current understanding of astrophysical magnetic fields is reviewed,
focusing on their generation and maintenance by turbulence. In the
astrophysical context this generation is usually explained by a self-excited
dynamo, which involves flows that can amplify a weak 'seed' magnetic field
exponentially fast. Particular emphasis is placed on the nonlinear saturation
of the dynamo. Analytic and numerical results are discussed both for small
scale dynamos, which are completely isotropic, and for large scale dynamos,
where some form of parity breaking is crucial. Central to the discussion of
large scale dynamos is the so-called alpha effect which explains the generation
of a mean field if the turbulence lacks mirror symmetry, i.e. if the flow has
kinetic helicity. Large scale dynamos produce small scale helical fields as a
waste product that quench the large scale dynamo and hence the alpha effect.
With this in mind, the microscopic theory of the alpha effect is revisited in
full detail and recent results for the loss of helical magnetic fields are
reviewed.Comment: 285 pages, 72 figures, accepted by Phys. Re
COVID-19 trajectories among 57 million adults in England: a cohort study using electronic health records
BACKGROUND:
Updatable estimates of COVID-19 onset, progression, and trajectories underpin pandemic mitigation efforts. To identify and characterise disease trajectories, we aimed to define and validate ten COVID-19 phenotypes from nationwide linked electronic health records (EHR) using an extensible framework.
METHODS:
In this cohort study, we used eight linked National Health Service (NHS) datasets for people in England alive on Jan 23, 2020. Data on COVID-19 testing, vaccination, primary and secondary care records, and death registrations were collected until Nov 30, 2021. We defined ten COVID-19 phenotypes reflecting clinically relevant stages of disease severity and encompassing five categories: positive SARS-CoV-2 test, primary care diagnosis, hospital admission, ventilation modality (four phenotypes), and death (three phenotypes). We constructed patient trajectories illustrating transition frequency and duration between phenotypes. Analyses were stratified by pandemic waves and vaccination status.
FINDINGS:
Among 57 032 174 individuals included in the cohort, 13 990 423 COVID-19 events were identified in 7 244 925 individuals, equating to an infection rate of 12·7% during the study period. Of 7 244 925 individuals, 460 737 (6·4%) were admitted to hospital and 158 020 (2·2%) died. Of 460 737 individuals who were admitted to hospital, 48 847 (10·6%) were admitted to the intensive care unit (ICU), 69 090 (15·0%) received non-invasive ventilation, and 25 928 (5·6%) received invasive ventilation. Among 384 135 patients who were admitted to hospital but did not require ventilation, mortality was higher in wave 1 (23 485 [30·4%] of 77 202 patients) than wave 2 (44 220 [23·1%] of 191 528 patients), but remained unchanged for patients admitted to the ICU. Mortality was highest among patients who received ventilatory support outside of the ICU in wave 1 (2569 [50·7%] of 5063 patients). 15 486 (9·8%) of 158 020 COVID-19-related deaths occurred within 28 days of the first COVID-19 event without a COVID-19 diagnoses on the death certificate. 10 884 (6·9%) of 158 020 deaths were identified exclusively from mortality data with no previous COVID-19 phenotype recorded. We observed longer patient trajectories in wave 2 than wave 1.
INTERPRETATION:
Our analyses illustrate the wide spectrum of disease trajectories as shown by differences in incidence, survival, and clinical pathways. We have provided a modular analytical framework that can be used to monitor the impact of the pandemic and generate evidence of clinical and policy relevance using multiple EHR sources.
FUNDING:
British Heart Foundation Data Science Centre, led by Health Data Research UK
Finishing the euchromatic sequence of the human genome
The sequence of the human genome encodes the genetic instructions for human physiology, as well as rich information about human evolution. In 2001, the International Human Genome Sequencing Consortium reported a draft sequence of the euchromatic portion of the human genome. Since then, the international collaboration has worked to convert this draft into a genome sequence with high accuracy and nearly complete coverage. Here, we report the result of this finishing process. The current genome sequence (Build 35) contains 2.85 billion nucleotides interrupted by only 341 gaps. It covers ∼99% of the euchromatic genome and is accurate to an error rate of ∼1 event per 100,000 bases. Many of the remaining euchromatic gaps are associated with segmental duplications and will require focused work with new methods. The near-complete sequence, the first for a vertebrate, greatly improves the precision of biological analyses of the human genome including studies of gene number, birth and death. Notably, the human enome seems to encode only 20,000-25,000 protein-coding genes. The genome sequence reported here should serve as a firm foundation for biomedical research in the decades ahead
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