The flare of radiation from the tidal disruption and accretion of a star can be used as a marker for supermassive black holes that otherwise lie dormant and undetected in the centres of distant ...galaxies. Previous candidate flares have had declining light curves in good agreement with expectations, but with poor constraints on the time of disruption and the type of star disrupted, because the rising emission was not observed. Recently, two 'relativistic' candidate tidal disruption events were discovered, each of whose extreme X-ray luminosity and synchrotron radio emission were interpreted as the onset of emission from a relativistic jet. Here we report a luminous ultraviolet-optical flare from the nuclear region of an inactive galaxy at a redshift of 0.1696. The observed continuum is cooler than expected for a simple accreting debris disk, but the well-sampled rise and decay of the light curve follow the predicted mass accretion rate and can be modelled to determine the time of disruption to an accuracy of two days. The black hole has a mass of about two million solar masses, modulo a factor dependent on the mass and radius of the star disrupted. On the basis of the spectroscopic signature of ionized helium from the unbound debris, we determine that the disrupted star was a helium-rich stellar core.
Electrical switching of an antiferromagnet Wadley, P.; Howells, B.; Železný, J. ...
Science (American Association for the Advancement of Science),
02/2016, Letnik:
351, Številka:
6273
Journal Article
Recenzirano
Odprti dostop
Antiferromagnets are hard to control by external magnetic fields because of the alternating directions of magnetic moments on individual atoms and the resulting zero net magnetization. However, ...relativistic quantum mechanics allows for generating current-induced internal fields whose sign alternates with the periodicity of the antiferromagnetic lattice. Using these fields, which couple strongly to the antiferromagnetic order, we demonstrate room-temperature electrical switching between stable configurations in antiferromagnetic CuMnAs thin-film devices by applied current with magnitudes of order 10⁶ ampere per square centimeter. Electrical writing is combined in our solid-state memory with electrical readout and the stored magnetic state is insensitive to and produces no external magnetic field perturbations, which illustrates the unique merits of antiferromagnets for spintronics.
On May 21, 2019 at 03:02:29 UTC Advanced LIGO and Advanced Virgo observed a short duration gravitational-wave signal, GW190521, with a three-detector network signal-to-noise ratio of 14.7, and an ...estimated false-alarm rate of 1 in 4900 yr using a search sensitive to generic transients. If GW190521 is from a quasicircular binary inspiral, then the detected signal is consistent with the merger of two black holes with masses of 85_{-14}^{+21} M_{⊙} and 66_{-18}^{+17} M_{⊙} (90% credible intervals). We infer that the primary black hole mass lies within the gap produced by (pulsational) pair-instability supernova processes, with only a 0.32% probability of being below 65 M_{⊙}. We calculate the mass of the remnant to be 142_{-16}^{+28} M_{⊙}, which can be considered an intermediate mass black hole (IMBH). The luminosity distance of the source is 5.3_{-2.6}^{+2.4} Gpc, corresponding to a redshift of 0.82_{-0.34}^{+0.28}. The inferred rate of mergers similar to GW190521 is 0.13_{-0.11}^{+0.30} Gpc^{-3} yr^{-1}.
We found that exposure of mice and rats to male but not female experimenters produces pain inhibition. Male-related stimuli induced a robust physiological stress response that results in ...stress-induced analgesia. This effect could be replicated with T-shirts worn by men, bedding material from gonadally intact and unfamiliar male mammals, and presentation of compounds secreted from the human axilla. Experimenter sex can thus affect apparent baseline responses in behavioral testing.
Bringing physics to life at the submesoscale Lévy, Marina; Ferrari, Raffaele; Franks, Peter J. S. ...
Geophysical research letters,
07/2012, Letnik:
39, Številka:
14
Journal Article
Recenzirano
Odprti dostop
A common dynamical paradigm is that turbulence in the upper ocean is dominated by three classes of motion: mesoscale geostrophic eddies, internal waves and microscale three‐dimensional turbulence. ...Close to the ocean surface, however, a fourth class of turbulent motion is important: submesoscale frontal dynamics. These have a horizontal scale of O(1–10) km, a vertical scale of O(100) m, and a time scale of O(1) day. Here we review the physical‐chemical‐biological dynamics of submesoscale features, and discuss strategies for sampling them. Submesoscale fronts arise dynamically through nonlinear instabilities of the mesoscale currents. They are ephemeral, lasting only a few days after they are formed. Strong submesoscale vertical velocities can drive episodic nutrient pulses to the euphotic zone, and subduct organic carbon into the ocean's interior. The reduction of vertical mixing at submesoscale fronts can locally increase the mean time that photosynthetic organisms spend in the well‐lit euphotic layer and promote primary production. Horizontal stirring can create intense patchiness in planktonic species. Submesoscale dynamics therefore can change not only primary and export production, but also the structure and the functioning of the planktonic ecosystem. Because of their short time and space scales, sampling of submesoscale features requires new technologies and approaches. This paper presents a critical overview of current knowledge to focus attention and hopefully interest on the pressing scientific questions concerning these dynamics.
Key Points
Submesoscale physics control ecology locally, but also feedback to basin scales
Strong gradients in community structure are created at the submesoscale
Despite recent innovations, sampling the submesoscale remains a major challenge
We have studied similar to 2100 early-type galaxies in the SDSS DR3 which have been detected by the GALEX Medium Imaging Survey (MIS), in the redshift range 0 < z < 0.11. Combining GALEX UV ...photometry with corollary optical data from the SDSS, we find that, at a 95% confidence level, at least similar to 30% of galaxies in this sample have UV to optical colors consistent with some recent star formation within the last Gyr. In particular, galaxies with an NUV - r color less than 5.5 are very likely to have experienced such recent star formation, taking into account the possibility of a contribution to NUV flux from the UV upturn phenomenon. We find quantitative agreement between the observations and the predictions of a semianalytical Lambda CDM hierarchical merger model and deduce that early-type galaxies in the redshift range 0 < z < 0.11 have similar to 1%-3% of their stellar mass in stars less than 1 Gyr old. The average age of this recently formed population is similar to 300-500 Myr. We also find that "monolithically" evolving galaxies, where recent star formation can be driven solely by recycled gas from stellar mass loss, cannot exhibit the blue colors (NUV - r < 5.5) seen in a significant fraction ( similar to 30%) of our observed sample.
Abstract
Determination of the lithium depletion boundary (LDB), i.e., the observational limit below which the cores of very low-mass objects do not reach high enough temperatures for Li destruction, ...has been used to obtain ages for several open clusters and stellar associations younger than 200 Myr—which until now has been considered the practical upper limit on the range of applicability of this method. In this work, we show that the LDB method can be extended to significant older ages than previously thought. Intermediate resolution optical spectra of six L-type candidate members in the Hyades cluster obtained using Optical System for Imaging and Low Resolution Integrated Spectroscopy at the 10.4 m Gran Telescopio Canarias are presented. The
670.8 nm resonance doublet is clearly detected only in the two faintest and coolest of these objects, which are classified as L3.5 to L4 brown dwarf (BD) cluster members with luminosities around 10
−4
solar. Lithium depletion factors are estimated for our targets with the aid of synthetic spectra and they are compared with predictions from evolutionary models. An LDB age of 650 ± 70 Myr for the Hyades provides a consistent description of our data using a set of state-of-the-art evolutionary models for BDs calculated by Baraffe et al.
Developing a mechanistic understanding of the impact of food structure and composition on human health has increasingly involved simulating digestion in the upper gastrointestinal tract. These ...simulations have used a wide range of different conditions that often have very little physiological relevance, and this impedes the meaningful comparison of results. The standardized protocol presented here is based on an international consensus developed by the COST INFOGEST network. The method is designed to be used with standard laboratory equipment and requires limited experience to encourage a wide range of researchers to adopt it. It is a static digestion method that uses constant ratios of meal to digestive fluids and a constant pH for each step of digestion. This makes the method simple to use but not suitable for simulating digestion kinetics. Using this method, food samples are subjected to sequential oral, gastric and intestinal digestion while parameters such as electrolytes, enzymes, bile, dilution, pH and time of digestion are based on available physiological data. This amended and improved digestion method (INFOGEST 2.0) avoids challenges associated with the original method, such as the inclusion of the oral phase and the use of gastric lipase. The method can be used to assess the endpoints resulting from digestion of foods by analyzing the digestion products (e.g., peptides/amino acids, fatty acids, simple sugars) and evaluating the release of micronutrients from the food matrix. The whole protocol can be completed in ~7 d, including ~5 d required for the determination of enzyme activities.
Anthropogenic increases in atmospheric greenhouse gas
concentrations are the main driver of current and future climate change. The
integrated assessment community has quantified anthropogenic ...emissions for
the shared socio-economic pathway (SSP) scenarios, each of which represents
a different future socio-economic projection and political environment.
Here, we provide the greenhouse gas concentrations for these SSP scenarios
– using the reduced-complexity climate–carbon-cycle model MAGICC7.0. We
extend historical, observationally based concentration data with SSP
concentration projections from 2015 to 2500 for 43 greenhouse gases with monthly and latitudinal resolution. CO2 concentrations by 2100 range
from 393 to 1135 ppm for the lowest (SSP1-1.9) and highest (SSP5-8.5)
emission scenarios, respectively. We also provide the concentration
extensions beyond 2100 based on assumptions regarding the trajectories of fossil
fuels and land use change emissions, net negative emissions, and the
fraction of non-CO2 emissions. By 2150, CO2 concentrations in the
lowest emission scenario are approximately 350 ppm and approximately plateau
at that level until 2500, whereas the highest fossil-fuel-driven scenario
projects CO2 concentrations of 1737 ppm and reaches concentrations
beyond 2000 ppm by 2250. We estimate that the share of CO2 in the total
radiative forcing contribution of all considered 43 long-lived greenhouse
gases increases from 66 % for the present day to roughly 68 % to 85 % by
the time of maximum forcing in the 21st century. For this estimation,
we updated simple radiative forcing parameterizations that reflect the Oslo
Line-By-Line model results. In comparison to the representative concentration pathways (RCPs), the five main SSPs
(SSP1-1.9, SSP1-2.6, SSP2-4.5, SSP3-7.0, and SSP5-8.5) are more evenly spaced
and extend to lower 2100 radiative forcing and temperatures. Performing two
pairs of six-member historical ensembles with CESM1.2.2, we estimate the
effect on surface air temperatures of applying latitudinally and seasonally
resolved GHG concentrations. We find that the ensemble differences in the
March–April–May (MAM) season provide a regional warming in higher northern
latitudes of up to 0.4 K over the historical period, latitudinally averaged
of about 0.1 K, which we estimate to be comparable to the upper bound
(∼5 % level) of natural variability. In comparison to the
comparatively straight line of the last 2000 years, the greenhouse gas
concentrations since the onset of the industrial period and this studies'
projections over the next 100 to 500 years unequivocally depict a
“hockey-stick” upwards shape. The SSP concentration time series derived in
this study provide a harmonized set of input assumptions for long-term
climate science analysis; they also provide an indication of the wide set of
futures that societal developments and policy implementations can lead to –
ranging from multiple degrees of future warming on the one side to
approximately 1.5 ∘C warming on the other.
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