We present ground-based and Swift observations of iPTF16fnl, a likely tidal disruption event (TDE) discovered by the intermediate Palomar Transient Factory (iPTF) survey at 66.6 Mpc. The light curve ...of the object peaked at an absolute mag . The maximum bolometric luminosity (from optical and UV) was erg s−1, an order of magnitude fainter than any other optical TDE discovered so far. The luminosity in the first 60 days is consistent with an exponential decay, with , where t0 = 57631.0 (MJD) and days. The X-ray shows a marginal detection at erg s−1 (Swift X-ray Telescope). No radio counterpart was detected down to 3 , providing upper limits for monochromatic radio luminosities of erg s−1 and erg s−1 (Very Large Array, 6.1 and 22 GHz). The blackbody temperature, obtained from combined Swift UV and optical photometry, shows a constant value of 19,000 K. The transient spectrum at peak is characterized by broad He ii and H emission lines, with FWHMs of about 14,000 km s−1 and 10,000 km s−1, respectively. He i lines are also detected at λλ 5875 and 6678. The spectrum of the host is dominated by strong Balmer absorption lines, which are consistent with a post-starburst (E+A) galaxy with an age of ∼650 Myr and solar metallicity. The characteristics of iPTF16fnl make it an outlier on both luminosity and decay timescales, as compared to other optically selected TDEs. The discovery of such a faint optical event suggests a higher rate of tidal disruptions, as low-luminosity events may have gone unnoticed in previous searches.
We present multiwavelength observations of the tidal disruption event (TDE) iPTF15af, discovered by the intermediate Palomar Transient Factory survey at redshift z = 0.07897. The optical and ...ultraviolet (UV) light curves of the transient show a slow decay over 5 months, in agreement with previous optically discovered TDEs. It also has a comparable blackbody peak luminosity of . The inferred temperature from the optical and UV data shows a value of (3-5) × 104 K. The transient is not detected in X-rays up to within the first 5 months after discovery. The optical spectra exhibit two distinct broad emission lines in the He ii region, and at later times also H emission. Additionally, emission from N iii and O iii is detected, likely produced by the Bowen fluorescence effect. UV spectra reveal broad emission and absorption lines associated with high-ionization states of N v, C iv, Si iv, and possibly P v. These features, analogous to those of broad absorption line quasars (BAL QSOs), require an absorber with column densities cm−2. This optically thick gas would also explain the nondetection in soft X-rays. The profile of the absorption lines with the highest column density material at the largest velocity is opposite that of BAL QSOs. We suggest that radiation pressure generated by the TDE flare at early times could have provided the initial acceleration mechanism for this gas. Spectral UV line monitoring of future TDEs could test this proposal.
We applied ozone source apportionment technology (OSAT) with tagged tracers coupled within the Comprehensive Air Quality Model with Extensions (CAMx) to study the region and source category ...contribution to surface ozone in the Yangtze River Delta area in summer of 2013. Results indicate that the daytime ozone concentrations in the YRD region are influenced by emissions both locally, regionally and super-regionally. At urban Shanghai, Hangzhou and Suzhou receptors, the ozone formation is mainly VOC-limited, precursor emissions form Zhejiang province dominate their O3 concentrations. At the junction area among two provinces and Shanghai city, the ozone is usually influenced by all the three areas. The daily max O3 at the Dianshan Lake in July are contributed by Zhejiang (48.5%), Jiangsu (11.7%), Anhui (11.6%) and Shanghai (7.4%), long-range transport constitutes around 20.9%. At Chongming site, the BVOC emissions rate is higher than urban region. Regional contribution results show that Shanghai constitutes 15.6%, Jiangsu contributes 16.2% and Zhejiang accounts for 25.5% of the daily max O3. The analysis of the source category contribution to high ozone in the Yangtze River Delta region indicates that the most significant anthropogenic emission source sectors contributing to O3 pollution include industry, vehicle exhaust, although the effects vary with source sector and selected pollution episodes. Emissions of NOx and VOCs emitted from the fuel combustion of industrial boilers and kilns, together with VOCs emissions from industrial process contribute a lot to the high concentrations in urban Hangzhou, Suzhou and Shanghai. The contribution from regional elevated power plants cannot be neglected, especially to Dianshan Lake. Fugitive emissions of volatile pollution sources also have certain contribution to regional O3. These results indicate that the regional collaboration is of most importance to reduce ambient ozone pollution, particularly during high ozone episodes.
•A high O3 episode over the YRD was simulated using the CAMx modeling system.•Ozone source apportionment technology was applied to study the formation mechanism and sources of O3.•Contributions of different source regions and source categories to O3 were analyzed.
iPTF16geu Goobar, A.; Amanullah, R.; Kulkarni, S. R. ...
Science (American Association for the Advancement of Science),
04/2017, Letnik:
356, Številka:
6335
Journal Article
Recenzirano
Odprti dostop
We report the discovery of a multiply imaged, gravitationally lensed type Ia supernova, iPTF16geu (SN 2016geu), at redshift z = 0.409. This phenomenon was identified because the light from the ...stellar explosion was magnified more than 50 times by the curvature of space around matter in an intervening galaxy. We used high-spatial-resolution observations to resolve four images of the lensed supernova, approximately 0.3 arc seconds from the center of the foreground galaxy. The observations probe a physical scale of ~1 kiloparsec, smaller than is typical in other studies of extragalactic gravitational lensing. The large magnification and symmetric image configuration imply close alignment between the lines of sight to the supernova and to the lens. The relative magnifications of the four images provide evidence for substructures in the lensing galaxy.
Multi-directional impact forging (MDIF) with high strain rate shows high grain refinement efficiency and texture randomization effect in magnesium alloys. AZ61 Mg alloy was subjected to MDIF process, ...and the related grain refinement mechanisms and texture development were investigated. MDIF resulted in a homogeneous microstructure with fine grains of 11 μm and non-basal texture, which was ascribed to the consecutive twinning and dynamic recrystallization (DRX). During the early forging passes, twin-induced DRX associated with {10–11} contraction and {10–11}-{10–12} double twins, and the coalescence and intersection of {10–12} extension twins with various variants effectively refined the coarse original grains and randomized the texture. With continuous forging, continuous and discontinuous DRX subsequently took place and eventually led to the fully DRXed microstructure and double-peak texture. Besides, fine spherical β-Mg17Al12 particles were dynamically precipitated along the original grain boundaries, acting as the preferred nucleation sites for DRX by particle-stimulated nucleation mechanism (PSN). Meanwhile, these particles became effective pinning obstacles for suppressing the DRXed grain growth.
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•MDIF resulted in a homogenous microstructure with fine grains of 11 μm.•Highly efficient grain refinement was ascribed to consecutive twinning and DRX.•Twinning and DRX dominate texture development during MDIF.•Dynamic precipitates along original GBs were preferred nucleation for DRX by PSN.
RyR2 is a high-conductance intracellular calcium (Ca
) channel that controls the release of Ca
from the sarco(endo)plasmic reticulum of a variety of cells. Here, we report the structures of RyR2 from ...porcine heart in both the open and closed states at near-atomic resolutions determined using single-particle electron cryomicroscopy. Structural comparison reveals a breathing motion of the overall cytoplasmic region resulted from the interdomain movements of amino-terminal domains (NTDs), Helical domains, and Handle domains, whereas almost no intradomain shifts are observed in these armadillo repeats-containing domains. Outward rotations of the Central domains, which integrate the conformational changes of the cytoplasmic region, lead to the dilation of the cytoplasmic gate through coupled motions. Our structural and mutational characterizations provide important insights into the gating and disease mechanism of RyRs.
Nanophotonic Image Sensors Chen, Qin; Hu, Xin; Wen, Long ...
Small (Weinheim an der Bergstrasse, Germany)
12, Številka:
36
Journal Article
Recenzirano
Odprti dostop
The increasing miniaturization and resolution of image sensors bring challenges to conventional optical elements such as spectral filters and polarizers, the properties of which are determined mainly ...by the materials used, including dye polymers. Recent developments in spectral filtering and optical manipulating techniques based on nanophotonics have opened up the possibility of an alternative method to control light spectrally and spatially. By integrating these technologies into image sensors, it will become possible to achieve high compactness, improved process compatibility, robust stability and tunable functionality. In this Review, recent representative achievements on nanophotonic image sensors are presented and analyzed including image sensors with nanophotonic color filters and polarizers, metamaterial‐based THz image sensors, filter‐free nanowire image sensors and nanostructured‐based multispectral image sensors. This novel combination of cutting edge photonics research and well‐developed commercial products may not only lead to an important application of nanophotonics but also offer great potential for next generation image sensors beyond Moore's Law expectations.
Nanophotonic structures including nano‐scatters, nanoholes and metamaterials show the capabilities for spectral filtering and possess advantages over pigment‐based filters such as robust stability, tunability, high compactness, improved process compatibility. A typical application is to integrate nanophotonic filters into image sensors with the potential to suppress the crosstalk, improve the resolution and enable on‐chip spectroscopy.
We present a radio-quiet quasar at z = 0.237 discovered "turning on" by the intermediate Palomar Transient Factory (iPTF). The transient, iPTF 16bco, was detected by iPTF in the nucleus of a galaxy ...with an archival Sloan Digital Sky Survey spectrum with weak narrow-line emission characteristic of a low-ionization nuclear emission-line region (LINER). Our follow-up spectra show the dramatic appearance of broad Balmer lines and a power-law continuum characteristic of a luminous ( erg s−1) type 1 quasar 12 yr later. Our photometric monitoring with PTF from 2009-2012 and serendipitous X-ray observations from the XMM-Newton Slew Survey in 2011 and 2015 constrain the change of state to have occurred less than 500 days before the iPTF detection. An enhanced broad H /O iii λ5007 line ratio in the type 1 state relative to other changing-look quasars also is suggestive of the most rapid change of state yet observed in a quasar. We argue that the >10 increase in Eddington ratio inferred from the brightening in UV and X-ray continuum flux is more likely due to an intrinsic change in the accretion rate of a preexisting accretion disk than an external mechanism such as variable obscuration, microlensing, or the tidal disruption of a star. However, further monitoring will be helpful in better constraining the mechanism driving this change of state. The rapid "turn-on" of the quasar is much shorter than the viscous infall timescale of an accretion disk and requires a disk instability that can develop around a black hole on timescales less than 1 yr.
The high-conductance intracellular calcium (Ca
) channel RyR2 is essential for the coupling of excitation and contraction in cardiac muscle. Among various modulators, calmodulin (CaM) regulates RyR2 ...in a Ca
-dependent manner. Here we reveal the regulatory mechanism by which porcine RyR2 is modulated by human CaM through the structural determination of RyR2 under eight conditions. Apo-CaM and Ca
-CaM bind to distinct but overlapping sites in an elongated cleft formed by the handle, helical and central domains. The shift in CaM-binding sites on RyR2 is controlled by Ca
binding to CaM, rather than to RyR2. Ca
-CaM induces rotations and intradomain shifts of individual central domains, resulting in pore closure of the PCB95 and Ca
-activated channel. By contrast, the pore of the ATP, caffeine and Ca
-activated channel remains open in the presence of Ca
-CaM, which suggests that Ca
-CaM is one of the many competing modulators of RyR2 gating.
Optimization of the energy levels at the donor-acceptor interface of organic solar cells has driven their efficiencies to above 10%. However, further improvements towards efficiencies comparable with ...inorganic solar cells remain challenging because of high recombination losses, which empirically limit the open-circuit voltage (
) to typically less than 1 V. Here we show that this empirical limit can be overcome using non-fullerene acceptors blended with the low band gap polymer PffBT4T-2DT leading to efficiencies approaching 10% (9.95%). We achieve
up to 1.12 V, which corresponds to a loss of only
/
-
= 0.5 ± 0.01 V between the optical bandgap
of the polymer and
. This high
is shown to be associated with the achievement of remarkably low non-geminate and non-radiative recombination losses in these devices. Suppression of non-radiative recombination implies high external electroluminescence quantum efficiencies which are orders of magnitude higher than those of equivalent devices employing fullerene acceptors. Using the balance between reduced recombination losses and good photocurrent generation efficiencies achieved experimentally as a baseline for simulations of the efficiency potential of organic solar cells, we estimate that efficiencies of up to 20% are achievable if band gaps and fill factors are further optimized.
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