Phosphorus losses from land to water will be impacted by climate change and land management for food production, with detrimental impacts on aquatic ecosystems. Here we use a unique combination of ...methods to evaluate the impact of projected climate change on future phosphorus transfers, and to assess what scale of agricultural change would be needed to mitigate these transfers. We combine novel high-frequency phosphorus flux data from three representative catchments across the UK, a new high-spatial resolution climate model, uncertainty estimates from an ensemble of future climate simulations, two phosphorus transfer models of contrasting complexity and a simplified representation of the potential intensification of agriculture based on expert elicitation from land managers. We show that the effect of climate change on average winter phosphorus loads (predicted increase up to 30% by 2050s) will be limited only by large-scale agricultural changes (e.g., 20-80% reduction in phosphorus inputs).The impact of climate change on phosphorus (P) loss from land to water is unclear. Here, the authors use P flux data, climate simulations and P transfer models to show that only large scale agricultural change will limit the effect of climate change on average winter P loads in three catchments across the UK.
The composition of asteroids and their connection to meteorites provide insight into geologic processes that occurred in the early Solar System. We present spectra of the Nightingale crater region on ...near-Earth asteroid Bennu with a distinct infrared absorption around 3.4 micrometers. Corresponding images of boulders show centimeters-thick, roughly meter-long bright veins. We interpret the veins as being composed of carbonates, similar to those found in aqueously altered carbonaceous chondrite meteorites. If the veins on Bennu are carbonates, fluid flow and hydrothermal deposition on Bennu's parent body would have occurred on kilometer scales for thousands to millions of years. This suggests large-scale, open-system hydrothermal alteration of carbonaceous asteroids in the early Solar System.
Spacecraft missions have observed regolith blankets of unconsolidated subcentimetre particles on stony asteroids
. Telescopic data have suggested the presence of regolith blankets also on ...carbonaceous asteroids, including (101955) Bennu
and (162173) Ryugu
. However, despite observations of processes that are capable of comminuting boulders into unconsolidated materials, such as meteoroid bombardment
and thermal cracking
, Bennu and Ryugu lack extensive areas covered in subcentimetre particles
. Here we report an inverse correlation between the local abundance of subcentimetre particles and the porosity of rocks on Bennu. We interpret this finding to mean that accumulation of unconsolidated subcentimetre particles is frustrated where the rocks are highly porous, which appears to be most of the surface
. The highly porous rocks are compressed rather than fragmented by meteoroid impacts, consistent with laboratory experiments
, and thermal cracking proceeds more slowly than in denser rocks. We infer that regolith blankets are uncommon on carbonaceous asteroids, which are the most numerous type of asteroid
. By contrast, these terrains should be common on stony asteroids, which have less porous rocks and are the second-most populous group by composition
. The higher porosity of carbonaceous asteroid materials may have aided in their compaction and cementation to form breccias, which dominate the carbonaceous chondrite meteorites
.
Fast radio bursts (FRBs) are brief, bright, extragalactic radio flashes
. Their physical origin remains unknown, but dozens of possible models have been postulated
. Some FRB sources exhibit repeat ...bursts
. Although over a hundred FRB sources have been discovered
, only four have been localized and associated with a host galaxy
, and just one of these four is known to emit repeating FRBs
. The properties of the host galaxies, and the local environments of FRBs, could provide important clues about their physical origins. The first known repeating FRB, however, was localized to a low-metallicity, irregular dwarf galaxy, and the apparently non-repeating sources were localized to higher-metallicity, massive elliptical or star-forming galaxies, suggesting that perhaps the repeating and apparently non-repeating sources could have distinct physical origins. Here we report the precise localization of a second repeating FRB source
, FRB 180916.J0158+65, to a star-forming region in a nearby (redshift 0.0337 ± 0.0002) massive spiral galaxy, whose properties and proximity distinguish it from all known hosts. The lack of both a comparably luminous persistent radio counterpart and a high Faraday rotation measure
further distinguish the local environment of FRB 180916.J0158+65 from that of the single previously localized repeating FRB source, FRB 121102. This suggests that repeating FRBs may have a wide range of luminosities, and originate from diverse host galaxies and local environments.
ABSTRACT
We present results from spectroscopic observations of AT 2018hyz, a transient discovered by the All-Sky Automated Survey for Supernova survey at an absolute magnitude of MV ∼ −20.2 mag, in ...the nucleus of a quiescent galaxy with strong Balmer absorption lines. AT 2018hyz shows a blue spectral continuum and broad emission lines, consistent with previous TDE candidates. High cadence follow-up spectra show broad Balmer lines and He i in early spectra, with He ii making an appearance after ∼70–100 d. The Balmer lines evolve from a smooth broad profile, through a boxy, asymmetric double-peaked phase consistent with accretion disc emission, and back to smooth at late times. The Balmer lines are unlike typical active galactic nucleus in that they show a flat Balmer decrement (Hα/Hβ ∼ 1.5), suggesting the lines are collisionally excited rather than being produced via photoionization. The flat Balmer decrement together with the complex profiles suggests that the emission lines originate in a disc chromosphere, analogous to those seen in cataclysmic variables. The low optical depth of material due to a possible partial disruption may be what allows us to observe these double-peaked, collisionally excited lines. The late appearance of He ii may be due to an expanding photosphere or outflow, or late-time shocks in debris collisions.
Archean cratons have map patterns and rock associations that are diagnostic of the Wilson Cycle. The North China Craton (NCC) consists of several distinctly different tectonic units, but the ...delineation and understanding of the significance of individual sutures and the rocks between them has been controversial. We present an actualistic tectonic division and evolution of the North China Craton based on Wilson Cycle and comparative tectonic analysis that uses a multi-disciplinary approach in order to define sutures, their ages, and the nature of the rocks between them, to determine their mode of formation and means of accretion or exhumation, and propose appropriate modern analogues. The eastern unit of the craton consists of several different small blocks assembled between 2.6 and 2.7Ga ago, that resemble fragments of accreted arcs from an assembled archipelago similar to those in the extant SW Pacific. A thick Atlantic-type passive margin developed on the western side of the newly assembled Eastern Block by 2.6–2.5Ga. A >1300km-long arc and accretionary prism collided with the margin of the Eastern Block at 2.5Ga, obducting ophiolites and ophiolitic mélanges onto the block, and depositing a thick clastic wedge in a foreland basin farther into the Eastern Block. This was followed by an arc-polarity reversal, which led to a short-lived injection of mantle wedge-derived melts to the base of the crust that led to the intrusion of mafic dikes and arc-type granitoid (TTG) plutons with associated metamorphism. By 2.43Ga, the remaining open ocean west of the accreted arc closed with the collision of an oceanic plateau now preserved as the Western Block with the collision-modified margin of the Eastern Block, causing further deformation in the Central Orogenic Belt. 2.4–2.35Ga rifting of the newly amalgamated continental block formed a rift along its center, and new oceans within the other two rift arms, which removed a still-unknown continental fragment from its northern margin. By 2.3Ga an arc collided with a new Atlantic-type margin developed over the rift sequence along the northern margin of the craton, and thus was converted to an Andean margin through arc-polarity reversal.
Andean margin tectonics affected much of the continental block from 2.3 to 1.9Ga, giving rise to a broad E-W swath of continental margin magmas, and retro-arc sedimentary basins including a foreland basin superimposed on the passive northern margin. The horizontal extent of these tectonic components is similar to that across the present-day Andes in South America. From 1.88 to 1.79Ga a granulite facies metamorphic event was superimposed across the entire continental block with high-pressure granulites and eclogites in the north, and medium-pressure granulites across the whole craton to the south. The scale and duration of this post-collisional event is similar to that in Central Asia that resulted from the Cenozoic India-Asia collision. The deep crustal granulites and volcanic rocks on the surface today, interpreted to be anatectic melts from deep crustal granulites, are similar to high-grade metamorphic rocks and partial melts presently forming at mid-crustal levels beneath Tibet. Structural fabrics in lower-crustal migmatites related to this event reveal that they flowed laterally parallel to the collision boundary, in a way comparable to what is speculated to be happening in the deep crust of the Himalayan/Tibetan foreland. We relate this continent-continent collision to the collision of the North China Craton with the postulated Columbia (Nuna) Continent. The NCC broke out of the Columbia Continent between 1753–1673Ma, as shown by the formation of a suite of anorthosite, mangerite, charnockite, and alkali-feldspar granites in an ENE-striking belt along the northern margin of the craton, whose intrusion was followed by the development of rifts and graben, mafic dike swarms, and eventually an Atlantic-type passive margin that signaled the beginning of a long period of tectonic quiescence and carbonate deposition for the NCC during Sinian times, which persisted into the Paleozoic. The style of tectonic accretion in the NCC changed at circa 2.5Ga, from an earlier phase of accretion of arcs that are presently preserved in horizontal lengths of several hundred kilometers, to the accretion and preservation of linear arcs several thousand kilometers long with associated oceanic plateaus, microcontinents, and accretionary prisms. The style of progressively younger and westward outward accretion of different tectonic components is reminiscent of the style of accretion in the Superior Craton, and may signal the formation of progressively larger landmasses at the end of the Archean (perhaps like the Kenorland Continent), then into the Paleoproterozoic, culminating in the assembly of the Columbia (Nuna) Continent at 1.9–1.8Ga.
The treatment outcome for diffuse large B-cell lymphoma has not been improved in nearly 20 years. However, the replacement of vincristine in R-CHOP with polatuzumab vedotin, an anti-CD79b antibody ...linked to emtansine, led to a progression-free survival benefit over R-CHOP at 2 years (76.7% vs. 70.2%), with a similar safety profile.
The International Pulsar Timing Array project combines observations of pulsars from both northern and southern hemisphere observatories with the main aim of detecting ultra-low frequency (~ ...10-9--10-8 Hz) gravitational waves. Here we introduce the project, review the methods used to search for gravitational waves emitted from coalescing supermassive binary black-hole systems in the centres of merging galaxies and discuss the status of the project.
Presents a technique to directly excite Luttinger liquid collective modes in carbon nanotubes at gigahertz frequencies. By modeling the nanotube as a nano-transmission line with distributed kinetic ...and magnetic inductance as well as distributed quantum and electrostatic capacitance, we calculate the complex frequency-dependent impedance for a variety of measurement geometries. Exciting voltage waves on the nano-transmission line is equivalent to directly exciting the yet-to-be observed one-dimensional plasmons, the low energy excitation of a Luttinger liquid. Our technique has already been applied to two-dimensional plasmons and should work well for one-dimensional plasmons. Tubes of length 100 microns must be grown for gigahertz resonance frequencies. Ohmic contact is not necessary with our technique; capacitive contacts can work. Our modeling has applications in potentially terahertz nanotube transistors and RF nanospintronics.
Context.
We report the discovery of TOI 263.01 (TIC 120916706), a transiting substellar object (
R
= 0.87
R
Jup
) orbiting a faint M3.5 V dwarf (
V
= 18.97) on a 0.56 d orbit.
Aims.
We setout to ...determine the nature of the Transiting Exoplanet Survey Satellite (TESS) planet candidate TOI 263.01 using ground-based multicolour transit photometry. The host star is faint, which makes radial-velocity confirmation challenging, but the large transit depth makes the candidate suitable for validation through multicolour photometry.
Methods.
Our analysis combines three transits observed simultaneously in
r
′,
i
′, and
z
s
bands usingthe MuSCAT2 multicolour imager, three LCOGT-observed transit light curves in
g
′,
r
′, and
i
′ bands, a TESS light curve from Sector 3, and a low-resolution spectrum for stellar characterisation observed with the ALFOSC spectrograph. We modelled the light curves with P
Y
T
RANSIT
using a transit model that includes a physics-based light contamination component, allowing us to estimate the contamination from unresolved sources from the multicolour photometry. Using this information we were able to derive the true planet–star radius ratio marginalised over the contamination allowed by the photometry.Combining this with the stellar radius, we were able to make a reliable estimate of the absolute radius of the object.
Results.
The ground-based photometry strongly excludes contamination from unresolved sources with a significant colour difference to TOI 263. Furthermore, contamination from sources of the same stellar type as the host is constrained to levels where the true radius ratio posterior has a median of 0.217 and a 99 percentile of0.286. The median and maximum radius ratios correspond to absolute planet radii of 0.87 and 1.41
R
Jup
, respectively,which confirms the substellar nature of the planet candidate. The object is either a giant planetor a brown dwarf (BD) located deep inside the so-called “brown dwarf desert”. Both possibilities offer a challenge to current planet/BD formation models and make TOI 263.01 an object that merits in-depth follow-up studies.
PDF
