3,321 research outputs found
The first stars of the Rho Ophiuchi Dark Cloud. XMM-Newton view of Rho Oph and its neighbors
Star formation in molecular clouds can be triggered by the dynamical action
of winds from massive stars. Furthermore, X-ray and UV fluxes from massive
stars can influence the life time of surrounding circumstellar disks. We
present the results of a 53 ks XMM-Newton observation centered on the Rho
Ophiuchi A+B binary system. Rho Ophiiuchi lies in the center of a ring of dust,
likely formed by the action of its winds. This region is different from the
dense core of the cloud (L1688 Core F) where star formation is at work. X-rays
are detected from Rho Ophiuchi as well as a group of surrounding X-ray sources.
We detected 89 X-ray sources, 47 of them have at least one counterpart in 2MASS
+ All-WISE catalogs. Based on IR and X-ray properties, we can distinguish
between young stellar objects (YSOs) belonging to the cloud and background
objects. Among the cloud members, we detect 3 debris disk objects and 22
disk-less / Class III young stars. We show that these stars have ages in
Myr, and are significantly older than the YSOs in L1688. We speculate that they
are the result of an early burst of star formation in the cloud. An X-ray
energy of ergs has been injected into the surrounding
medium during the past Myr, we discuss the effects of such energy budget in
relation to the cloud properties and dynamics.Comment: 17 pages, 9 figures, 7 tables. Accepted for publication to Astronomy
& Astrophysic
Bis[μ-N-(diethylamino-κN)dimethylsilylanilido-κ2 N:N]bis[chloridocobalt(II)]
In the title binuclear CoII complex, [Co2(C12H21N2Si)2Cl2], an inversion center is located at the mid-point between the two Co atoms in the dimeric molecule. The bidentate N-silylated anilide ligand coordinates the CoII atom in an N,N′-chelating mode and provides the anilide N atom as a bridge to link two CoII atoms. The two ends of the N—Si—N chelating unit exhibit different affinities for the metal atom. The Co—Nanilide bond is 2.031 (6) Å and Co—Namino bond is 2.214 (6) Å. The four-coordinate Co atom presents a distorted tetrahedral geometry, while the dimeric aggregation exhibits a (CoN)2 rhombus core with 1.998 (6) Å as the shortest sides and shows a ladder structure composed of Co, N and Si atoms
Picocyanobacteria and deep-ocean fluorescent dissolved organic matter share similar optical properties
Marine chromophoric dissolved organic matter (CDOM) and its related fluorescent components (FDOM), which are widely distributed but highly photobleached in the surface ocean, are critical in regulating light attenuation in the ocean. However, the origins of marine FDOM are still under investigation. Here we show that cultured picocyanobacteria, Synechococcus and Prochlorococcus, release FDOM that closely match the typical fluorescent signals found in oceanic environments. Picocyanobacterial FDOM also shows comparable apparent fluorescent quantum yields and undergoes similar photo-degradation behaviour when compared with deep-ocean FDOM, further strengthening the similarity between them. Ultrahigh-resolution mass spectrometry (MS) and nuclear magnetic resonance spectroscopy reveal abundant nitrogen-containing compounds in Synechococcus DOM, which may originate from degradation products of the fluorescent phycobilin pigments. Given the importance of picocyanobacteria in the global carbon cycle, our results indicate that picocyanobacteria are likely to be important sources of marine autochthonous FDOM, which may accumulate in the deep ocean
Selective Calixarene Directed Synthesis of MXene Plates, Crumpled Sheets, Spheres and Scrolls
Fully exploiting the electronic and mechanical properties of 2D laminar materials not only requires efficient and effective means of their exfoliation into low dimensional layers, but also necessitates a means of changing their morphology so as to explore any enhancement that this may offer. MXenes are a rapidly emerging new class of such laminar materials with unique properties. However, access to other morphologies of MXenes has not yet been fully realised. To this end we have developed the synthesis of MXenes (Ti2C) as plates, crumpled sheets, spheres and scrolls, which involves selective intercalation of p-phosphonic calix[n]arenes, with control in morphology arising from the choice of the size of the macrocycle, n = 4, 5, 6 or 8. This opens up wider avenues of discovery/design for new morphologies from the wider family of MXenes beyond Ti2C, along with opportunities to exploit any new physico-chemical properties proffered
Holevo Cram\'er-Rao Bound for waveform estimation of gravitational waves
Detecting kilohertz gravitational waves from the post-merger remnants of
binary neutron-star mergers could enhance our understanding of extreme matter.
To enable this detection, a gravitational-wave interferometer can be detuned to
increase its kilohertz sensitivity. The precision limits of detuned
interferometers and other cavity--based quantum sensors, however, are not well
understood. The sensitivity of the standard variational readout scheme does not
reach the waveform-estimation Quantum Cram\'er-Rao Bound. We establish the
fundamental precision limit, the waveform-estimation Holevo Cram\'er-Rao Bound,
by identifying the incompatibility of the na\"ive estimates of the signal's
cosine and sine phases. For an equal weighting between the phases, we prove
that the standard scheme is indeed optimal. For unequal weights, however, we
propose an experimental realisation of a new measurement scheme to
significantly improve the sensitivity. This scheme could facilitate kilohertz
gravitational-wave astronomy and has broader applications to detuned
cavity--based quantum metrology.Comment: v2. Letter: 7 pages, 2 figures. Supplemental Material: 17 pages, 4
figures. Submitted on August 11 2023 to Physical Review Letter
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