An X-ray plateau followed by a steep decay ("internal plateau") has been observed in both long and short gamma-ray burst (GRBs), implying that a millisecond magnetar operates in some GRBs. The sharp ...decay at the end of the plateau, marking the abrupt cessation of the magnetar's central engine, has been considered the collapse of a supra-massive magnetar into a black hole (BH) when it spins down. If this "internal plateau" is indeed evidence of a magnetar central engine, the natural expectation in some candidates would be a signature from the newborn BH. In this work, we find that GRB 070110 is a particular case which shows a small X-ray bump following its "internal plateau." We interpret the plateau as a spin-down supra-massive magnetar and the X-ray bump as fallback BH accretion. This indicates that a newborn BH is likely active in some GRBs. Therefore, GRB 070110-like events may provide further support to the magnetar central engine model and enable us to investigate the properties of the magnetar as well as the newborn BH.
Reverse time migration (RTM) is a seismic imaging method to map the subsurface reflectivity using recorded seismic waveforms. The practice in exploration seismology has long established a two-fold ...approach of seismic imaging: Using velocity modeling building to establish the long-wavelength reference velocity models, and using seismic migration to map the short-wavelength reflectivity structures. Among various seismic migration methods for different situations, RTM is the only method that is capable to use all seismic wave types that can be computed numerically. Being initiated in early 1980's, RTM seeks an image of the subsurface reflectivity as the best match in an image space between the extrapolation of time-reversed waveform data and the prediction based on estimated velocity model and source parameters. Judging the image quality in the same space of forming the images is more advantageous than the approaches of modeling and inversion which seek the solution in the model space but judge its fitness in data space. Considering that most seismic migration applications today still use primary reflection as the only signal, the capability of RTM to use all computable wave types is unique and helpful reducing the imaging artifacts due to mistaking non-primary waves as primary reflections. Hence, we refer to those RTM algorithms using only primary reflections as the first-generation RTM methods, and the RTM algorithms making a full use of primary reflections, multiple reflections and other non-primary waveform data as the second-generation RTM methods. This paper reviews the development history of the RTM along with its major challenges, current solutions, and future perspectives.
Drought is a major threat to plant growth and crop productivity. Calcium-dependent protein kinases (CDPKs, CPKs) are believed to play important roles in plant responses to drought stress. Here, we ...report that Arabidopsis thaliana CPK8 functions in abscisic acid (ABA)- and Ca2+-mediated plant responses to drought stress. The cpk8 mutant was more sensitive to drought stress than wild-type plants, while the transgenic plants overexpressing CPK8 showed enhanced tolerance to drought stress compared with wild-type plants. ABA-, H2O2-, and Ca2+-induced stomatal closing were impaired in cpk8 mutants. Arabidopsis CATALASE3 (CAT3) was identified as a CPK8-interacting protein, confirmed by yeast two-hybrid, coimmunoprecipitation, and bimolecular fluorescence complementation assays. CPK8 can phosphorylate CAT3 at Ser-261 and regulate its activity. Both cpk8 and cat3 plants showed lower catalase activity and higher accumulation of H2O2 compared with wild-type plants. The cat3 mutant displayed a similar drought stress-sensitive phenotype as cpk8 mutant. Moreover, ABA and Ca2+ inhibition of inward K+ currents were diminished in guard cells of cpk8 and cat3 mutants. Together, these results demonstrated that CPK8 functions in ABA-mediated stomatal regulation in responses to drought stress through regulation of CAT3 activity.
Abstract The arrival times of photons with different energy could be different, even when they are emitted from the same source simultaneously. Such a spectral lag is a common property among ...high-energy astrophysics phenomena like gamma-ray bursts (GRBs). The potential violation of the Lorentz invariance caused by quantum fluctuations in background spacetime metrics could cause the spectral lag. In this paper, we try to make a constraint on Lorentz invariance violation (LIV) with multiple energy bands light curves of GRBs. With a sample of 90 Swift GRBs with redshifts, we calculate their spectral offsets from four fixed energy bands within their source frame. With help from the cross-correlation function and kernel smooth procedure, we extract improved spectral shifts. By using these more general spectral lags, we obtain an upper limit on LIV, equivalent to a lower limit on the quantum-gravitational energy scale of E QG ≥ 2.2 × 10 14 GeV.
Abstract
Early optical observations of gamma-ray bursts can significantly contribute to the study of the central engine and physical processes therein. However, of the thousands observed so far, only ...a few have data at optical wavelengths in the first minutes after the onset of the prompt emission. Here we report on GRB 190106A, whose afterglow was observed in optical bands just 36 s after the Swift/BAT trigger, i.e., during the prompt emission phase. The early optical afterglow exhibits a bimodal structure followed by a normal decay, with a faster decay after ∼
T
0
+ 1 day. We present optical photometric and spectroscopic observations of GRB 190106A. We derive the redshift via metal absorption lines from Xinglong 2.16 m/BFOSC spectroscopic observations. From the BFOSC spectrum, we measure
z
= 1.861 ± 0.002. The double-peak optical light curve is a significant feature predicted by the reverse-forward external-shock model. The shallow decay followed by a normal decay in both the X-ray and optical light curves is well explained with the standard forward-shock model with late-time energy injection. Therefore, GRB 190106A offers a case study for GRB emission from both reverse and forward shocks.
Nitrate is one of the main inorganic nitrogen sources for plants. Nitrate absorption from soils is achieved through the combined activities of specific nitrate transporters. Nitrate transporter 2.1 ...(NRT2.1) is the major component of the root high‐affinity nitrate transport system in Arabidopsis thaliana. Studies to date have mainly focused on transcriptional control of NRT2.1. Here, we show that NRT2.1 protein stability is also regulated in response to nitrogen nutrition availability. When seedlings were transferred to nitrate‐limited conditions, the apparent half‐life of NRT2.1 in roots increased from 3 to 9 h. This stabilization of NRT2.1 protein occurred rapidly, even prior to the transcriptional stimulation of NRT2.1. Furthermore, we revealed that phosphorylation at serine 28 (Ser28) of NRT2.1 is involved in regulating the stability of this protein. Substitution of Ser28 by alanine resulted in unstable NRT2.1, and this loss‐of‐phosphorylation mutant (NRT2.1S28A) failed to complement the growth‐restricted phenotype of the nrt2.1 mutant when a low concentration of nitrate was the sole nitrogen source. These results demonstrate that phosphorylation at Ser28 is crucial for NRT2.1 protein stabilization and accumulation in response to nitrate limitation.
Nitrate transporter 2.1 (NRT2.1) is a major component of the root high‐affinity nitrate transport system in Arabidopsis. Here, we show that stabilization of NRT2.1 protein occurred rapidly in response to nitrogen nutrition availability, and phosphorylation at serine 28 (Ser28) of NRT2.1 is involved in regulating the stability of this protein.
Gamma-ray bursts are most luminous explosions in the universe. Their ejecta are believed to move towards Earth with a relativistic speed. The interaction between this “relativistic jet” and a ...circumburst medium drives a pair of (forward and reverse) shocks. The electrons accelerated in these shocks radiate synchrotron emission to power the broad-band afterglow of GRBs. The external shock theory is an elegant theory, since it invokes a limit number of model parameters, and has well predicted spectral and temporal properties. On the other hand, depending on many factors (e.g. the energy content, ambient density profile, collimation of the ejecta, forward vs. reverse shock dynamics, and synchrotron spectral regimes), there is a wide variety of the models. These models have distinct predictions on the afterglow decaying indices, the spectral indices, and the relations between them (the so-called “closure relations”), which have been widely used to interpret the rich multi-wavelength afterglow observations. This review article provides a complete reference of all the analytical synchrotron external shock afterglow models by deriving the temporal and spectral indices of all the models in all spectral regimes, including some regimes that have not been published before. The review article is designated to serve as a useful tool for afterglow observers to quickly identify relevant models to interpret their data. The limitations of the analytical models are reviewed, with a list of situations summarized when numerical treatments are needed.
Abstract
Conjugate addition of ethanol and subsequent oxidation with bis (trifluoroacetoxy)iodobenzene (PIFA) allowed for the inner ethoxylation of 3‐oxo‐N‐confused tetraphenylporphyrin (
ONCP
). ...First oxidation of
ONCP
with PIFA followed by treatment with ethanol gave two more N‐confused phlorins derivatives
5
and
6
.
The weak short gamma-ray burst (GRB) 170817A was accompanied by the GW170817 gravitational-wave event and is believed to have been produced by an off-beam relativistic jet. Here, we use the and ...relations to determine its Lorentz factor Γ and the viewing angle from the edge of the jet of GRB 170817A. Our results indicate that and , corresponding to an on-axis and erg. Therefore, the GRB was an intrinsically weak short GRB. We also find that the afterglow emission was in good agreement with the follow-up multiband observations and that the radio emissions at around 20 days may have come from the off-axis jet. Interestingly, the Doppler factor and luminosity follow a universal relation for GRBs and blazars, thus suggesting that they may share a similar radiation mechanism.
cis‐Linked cyclotetraphenylene dimer 2c‐CTPE and trimer 3c‐CTPE were synthesized via Pt‐mediated cyclization of cis‐diboronated tetraphenylethene. The structure of 2c‐CTPE has been confirmed by ...single crystal X‐ray diffraction. The strain energy of 2c‐CTPE and 3c‐CTPE was calculated to be 86.28 ⋅ kJ mol−1 and 9.23 kJ ⋅ mol−1, respectively. 2c‐CTPE and 3c‐CTPE are typical AIEgens and show mechanofluorochromic properties. The comparisons of cis‐linked cyclotetraphenylenes with gem‐linked cyclotetraphenylenes were also discussed.
Two cis‐connected cyclic tetraphenylethylenes, 2c‐CTPE and 3c‐CTPE, were synthesized by platinum‐mediated cyclization. The strain energy of 2c‐CTPE is up to 86.28 kJ ⋅ mol−1. 2c‐CTPE and 3c‐CTPE demonstrates typical Aggregation‐Induced Emission (AIE) characteristics. Moreover, both 2c‐CTPE and 3c‐CTPE display mechanofluorochromic properties.
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