An intrinsic link between long-term UV/optical variations and X-ray loudness in quasars

Observations have shown that UV/optical variation amplitude of quasars depend on several physi- cal parameters including luminosity, Eddington ratio, and likely also black hole mass. Identifying new factors which correlate with the variation is essential to probe the underlying physical processes. Combining ~ten years long quasar light curves from SDSS stripe 82 and X-ray data from Stripe 82X, we build a sample of X-ray detected quasars to investigate the relation between UV/optical variation amplitude ($\sigma_{rms}$) and X-ray loudness. We find that quasars with more intense X-ray radiation (com- pared to bolometric luminosity) are more variable in UV/optical. Such correlation remains highly significant after excluding the effect of other parameters including luminosity, black hole mass, Ed- dington ratio, redshift, rest-frame wavelength (i.e., through partial correlation analyses). We further find the intrinsic link between X-ray loudness and UV/optical variation is gradually more prominent on longer timescales (up to 10 years in the observed frame), but tends to disappear at timescales < 100 days. This suggests a slow and long-term underlying physical process. The X-ray reprocessing paradigm, in which UV/optical variation is produced by a variable central X-ray emission illuminating the accretion disk, is thus disfavored. The discovery points to an interesting scheme that both the X-ray corona heating and UV/optical variation is quasars are closely associated with magnetic disc turbulence, and the innermost disc turbulence (where corona heating occurs) correlates with the slow turbulence at larger radii (where UV/optical emission is produced).Comment: 9 pages, 4 figures, 1 table, accepted by Ap

Thermochemical oxidation of methane induced by high-valence metal oxides in a sedimentary basin

Thermochemical oxidation of methane (TOM) by high-valence metal oxides in geological systems and its potential role as a methane sink remain poorly understood. Here we present evidence of TOM induced by high-valence metal oxides in the Junggar Basin, located in northwestern China. During diagenesis, methane from deeper source strata is abiotically oxidized by high-valence Mn(Fe) oxides at 90 to 135 °C, releasing 13C-depleted CO2, soluble Mn2+ and Fe2+. Mn generally plays the dominant role compared to Fe, due to its lower Gibbs free energy increment during oxidation. Both CO2 and metal ions are then incorporated into authigenic calcites, which are characterized by extremely negative δ13C values (−70 to −22.5‰) and high Mn content (average MnO = 5 wt.%). We estimate that as much as 1224 Tg of methane could be oxidized in the study area. TOM is unfavorable for gas accumulation but may act as a major methane sink in the deep crustal carbon cycle.This study was supported by funds from the Natural Science Foundation of China to W.-X.H. (41830425, 41230312) and X.-L.W. (41573054), the Fundamental Research Funds for the Central Universities to X.-L.W. (020614380056), and the Outstanding PhD Candidate Program of Nanjing University to X.K

Simultaneous Conversion of Polarization and Frequency via Time‐Division‐Multiplexing Metasurfaces

AbstractMetasurfaces are artificially engineered two‐dimensional materials composed of sub‐wavelength meta‐atoms, which have shown unprecedented capabilities in manipulating the amplitude, phase, frequency, and polarization states of electromagnetic waves. Specifically, polarization control can be attained via suitable anisotropic, linear, and time‐invariant designs, while frequency conversion is realized via nonlinear or time‐varying platforms. Simultaneous manipulations of polarization and frequency would be of considerable practical interest in many application scenarios, but remain unattainable with current approaches. Here, a time‐division‐multiplexing metasurface is proposed to realize the simultaneous conversion of polarization and frequency. The platform relies on time‐modulated polarization switches and, by varying the duty cycle and time delays of the polarization channels, can arbitrarily rotate the polarization at the central frequency of operation, and synthesize various polarization states at selected harmonic frequencies. Theoretical predictions are validated via measurements on a prototype operating at microwave frequencies, providing the first experimental evidence of simultaneous polarization and frequency conversions via time‐division‐multiplexing metasurfaces. The outcomes open a new pathway in manipulating the electromagnetic waves via time‐varying metasurfaces, and may be of interest for a broad variety of applications in scenarios ranging from polarization imaging to quantum optics

Poly[dimethyl­ammonium [aquadi-μ2-oxalato-yttriate(III)] trihydrate]

The title complex, {(C2H8N)[Y(C2O4)2(H2O)]·3H2O}n, was obtained accidentally under hydro­thermal conditions. The YIII atom is chelated by four oxalate ligands and one water mol­ecule resulting in a distorted tricapped trigonal–prismatic geometry. Each oxalate ligand bridges two YIII atoms, thus generating a three-dimensional network with cavities in which the ammonium cations and lattice water mol­ecules reside. Various O—H⋯O and N—H⋯O hydrogen-bonding inter­actions stabilize the crystal structure. The title complex is isotypic with the Eu and Dy analogues

A promising new class of high-temperature alloys: Eutectic high-entropy alloys

High-entropy alloys (HEAs) can have either high strength or high ductility, and a simultaneous achievement of both still constitutes a tough challenge. The inferior castability and compositional segregation of HEAs are also obstacles for their technological applications. To tackle these problems, here we proposed a novel strategy to design HEAs using the eutectic alloy concept, i.e. to achieve a microstructure composed of alternating soft fcc and hard bcc phases. As a manifestation of this concept, an AlCoCrFeNi 2.1 (atomic portion) eutectic high-entropy alloy (EHEA) was designed. The as-cast EHEA possessed a fine lamellar fcc/B2 microstructure, and showed an unprecedented combination of high tensile ductility and high fracture strength at room temperature. The excellent mechanical properties could be kept up to 700°C. This new alloy design strategy can be readily adapted to large-scale industrial production of HEAs with simultaneous high fracture strength and high ductility

The association between S100A13 and HMGA1 in the modulation of thyroid cancer proliferation and invasion

Additional file 5: Figure S3. Lentivirus-mediated S100A13 knockdown was utilized to detect the effect on migration capability with scratch-wound assays in TPC1 cell

Frequency tuning behaviour of terahertz quantum cascade lasers revealed by a laser beating scheme

In the terahertz frequency range, the commercialized spectrometers, such as the Fourier transform infrared and time domain spectroscopies, show spectral resolutions between a hundred megahertz and a few gigahertz. Therefore, the high precision frequency tuning ability of terahertz lasers cannot be revealed by these traditional spectroscopic techniques. In this work, we demonstrate a laser beating experiment to investigate the frequency tuning characteristics of terahertz quantum cascade lasers (QCLs) induced by temperature or drive current. Two terahertz QCLs emitting around 4.2 THz with identical active regions and laser dimensions (150 μm wide and 6 mm long) are employed in the beating experiment. One laser is operated as a frequency comb and the other one is driven at a lower current to emit a single frequency. To measure the beating signal, the single mode laser is used as a fast detector (laser self-detection). The laser beating scheme allows the high precision measurement of the frequency tuning of the single mode terahertz QCL. The experimental results show that in the investigated temperature and current ranges, the frequency tuning coefficients of the terahertz QCL are 6.1 MHz/0.1 K (temperature tuning) and 2.7 MHz/mA (current tuning) that cannot be revealed by a traditional terahertz spectrometer. The laser beating technique shows potential abilities in high precision linewidth measurements of narrow absorption lines and multi-channel terahertz communications