Abstract
We report on analysis of observations of the bright transient X-ray pulsar Swift J0243.6+6124 obtained during its 2017-2018 giant outburst with Insight-HXMT, NuSTAR, and Swift observatories. ...We focus on the discovery of a sharp state transition of the timing and spectral properties of the source at super-Eddington accretion rates, which we associate with the transition of the accretion disk to a radiation pressure dominated (RPD) state, the first ever directly observed for magnetized neutron star. This transition occurs at slightly higher luminosity compared to already reported transition of the source from sub- to super-critical accretion regime associate with onset of an accretion column. We argue that this scenario can only be realized for comparatively weakly magnetized neutron star, not dissimilar to other ultra-luminous X-ray pulsars (ULPs), which accrete at similar rates. Further evidence for this conclusion is provided by the non-detection of the transition to the propeller state in quiescence which strongly implies compact magnetosphere and thus rules out magnetar-like fields.
Visualizing individual molecules with chemical recognition is a longstanding target in catalysis, molecular nanotechnology and biotechnology. Molecular vibrations provide a valuable 'fingerprint' for ...such identification. Vibrational spectroscopy based on tip-enhanced Raman scattering allows us to access the spectral signals of molecular species very efficiently via the strong localized plasmonic fields produced at the tip apex. However, the best spatial resolution of the tip-enhanced Raman scattering imaging is still limited to 3-15 nanometres, which is not adequate for resolving a single molecule chemically. Here we demonstrate Raman spectral imaging with spatial resolution below one nanometre, resolving the inner structure and surface configuration of a single molecule. This is achieved by spectrally matching the resonance of the nanocavity plasmon to the molecular vibronic transitions, particularly the downward transition responsible for the emission of Raman photons. This matching is made possible by the extremely precise tuning capability provided by scanning tunnelling microscopy. Experimental evidence suggests that the highly confined and broadband nature of the nanocavity plasmon field in the tunnelling gap is essential for ultrahigh-resolution imaging through the generation of an efficient double-resonance enhancement for both Raman excitation and Raman emission. Our technique not only allows for chemical imaging at the single-molecule level, but also offers a new way to study the optical processes and photochemistry of a single molecule.
We present X-ray timing results of the new black hole candidate MAXI J1535−571 during its 2017 outburst from Hard X-ray Modulation Telescope (Insight-HXMT) observations taken from 2017 September 6 to ...23. Following the definitions given by Belloni, we find that the source exhibits transitions from the low/hard state to the hard intermediate state, and eventually to the soft intermediate state. Quasi-periodic oscillations (QPOs) are found in the intermediate states, which suggest different types of QPOs. With the large effective area of Insight-HXMT at high energies, we are able to present the energy dependence of the QPO amplitude and centroid frequency up to 100 keV, which has rarely been explored by previous satellites. We also find that the phase lag at the type-C QPOs centroid frequency is negative (soft lag) and strongly correlated with the centroid frequency. Assuming a geometrical origin of type-C QPOs, the source is consistent with being a high-inclination system.
Tracking the formation and full evolution of polar cap ionization patches in the polar ionosphere, we directly observe the full Dungey convection cycle for southward interplanetary magnetic field ...(IMF) conditions. This enables us to study how the Dungey cycle influences the patches' evolution. The patches were initially segmented from the dayside storm enhanced density plume at the equatorward edge of the cusp, by the expansion and contraction of the polar cap boundary due to pulsed dayside magnetopause reconnection, as indicated by in situ Time History of Events and Macroscale Interactions during Substorms (THEMIS) observations. Convection led to the patches entering the polar cap and being transported antisunward, while being continuously monitored by the globally distributed arrays of GPS receivers and Super Dual Auroral Radar Network radars. Changes in convection over time resulted in the patches following a range of trajectories, each of which differed somewhat from the classical twin‐cell convection streamlines. Pulsed nightside reconnection, occurring as part of the magnetospheric substorm cycle, modulated the exit of the patches from the polar cap, as confirmed by coordinated observations of the magnetometer at Tromsø and European Incoherent Scatter Tromsø UHF radar. After exiting the polar cap, the patches broke up into a number of plasma blobs and returned sunward in the auroral return flow of the dawn and/or dusk convection cell. The full circulation time was about 3 h.
Key Points
Direct observations of the full Dungey cycle by tracking polar cap patches
Formation and evolution of patches modulated by dayside and nightside reconnections
The full circulation time was about 3 h
The brown planthopper (BPH), Nilaparvata lugens, is a major rice pest in Asia, and accumulated evidence indicates that this species is susceptible to RNA interference (RNAi); however, the mechanism ...underlying RNAi and parental RNAi has not yet been determined. We comprehensively investigated the repertoire of core genes involved in small interfering RNA (siRNA) and micro‐RNA (miRNA) pathways in the BPH by comparing its newly assembled transcriptome and genome with those of Drosophila melanogaster, Tribolium castaneum and Caenorhabditis elegans. Our analysis showed that the BPH possesses one drosha and two Dicer (dcr) genes, three dsRNA‐binding motif protein genes, two Argonaute (ago) genes, two Eri‐1‐like genes (eri‐1), and a Sid‐1‐like gene (sid‐1). Additionally, we report for first time that parental RNAi might occur in this species, and siRNA pathway and Sid‐1 were required for high efficiency of systemic RNAi triggered by exogenous dsRNA. Furthermore, our results also demonstrated that the miRNA pathway was involved in BPH metamorphosis as depletion of the ago1 or dcr1 gene severely impaired ecdysis. The BPH might be a good model system to study the molecular mechanism of systemic RNAi in hemimetabolous insects, and RNAi has potential to be developed to control this pest in agricultural settings.
To investigate the trend in the prevalence of gestational diabetes mellitus during 1999-2008 in women living in urban Tianjin, China.
A universal screening for gestational diabetes mellitus has ...become an integral part of the antenatal care in Tianjin, China from 1998. A total of 105,473 pregnant women living in the six urban districts of Tianjin, China, participated in the gestational diabetes mellitus screening programme between December 1998 and December 2008. The screening test consisted of a 50-g 1-h glucose test. Women who had a glucose reading ≥7.8 mmol/l at the initial screening were invited to undergo the standard 2-h oral glucose tolerance test with a 75-g glucose load. Gestational diabetes mellitus was confirmed using the World Health Organization's diagnostic criteria.
The adjusted prevalence of gestational diabetes mellitus increased by 2.8 times during 1999-2008, from 2.4 to 6.8% (P<0.0001 for linear trend). In 2008, the age-specific prevalence of gestational diabetes mellitus was the highest among women aged 30-34 years (11.3%) and lowest among women aged 25 and under (1.2%). In women aged 35 years and more, the prevalence was 5.3%.
The prevalence of gestational diabetes mellitus has markedly been increasing in a universally screened urban Chinese female population and has become an important public health problem in China.
Water contamination by dyes is a matter of concern for human health and the environment. Various methods (membrane separation, coagulation and adsorption) have been explored to remove/degrade dyes. ...However, now the exploitation of semiconductor assisted materials using renewable solar energy has emerged as a potential candidate to resolve the issue. Although, single component photocatalysts (ZnO, TiO2, ZrO2) were experimented, due to their low efficiency and stability due to the high recombination rate electron-hole pair and inefficient visible light absorption, composites of semiconductor materials are being used. Semiconductor heterojunction systems are developed by coupling two or more semiconductor components. The synergistic effect of their properties, such as adsorption and improved charge carrier migration, is observed to increase overall stability. This review covers recent progress in advanced nanocomposite materials based on g-C3N4, TiO2 and ZnO used as photocatalysts with details of enhancing the photocatalytic properties by heterojunctions, crystallinity and doping. The conclusion at the end displays a summary, research gaps and future outlook. A holistic analysis of recent progress to demonstrate the efficient heterojunctions for photodegradation with optimal conditions, this review will be helpful for the development of efficient heterostructured systems for photodegradation. This review covers references from the year 2017–2020.
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•Mechanistic development in the charge carrier's movement for dye degradation•Graphitic carbon nitride (g-C3N4) TiO2, ZnO based photocatalysts•Improved photocatalysis using heterojunctions, crystal phase and facet, doping
We perform a statistical study of electromagnetic ion cyclotron (EMIC) waves detected by the Van Allen Probes mission to investigate the spatial distribution of their occurrence, wave power, ...ellipticity, and normal angle. The Van Allen Probes have been used which allow us to explore the inner magnetosphere (1.1 to 5.8 RE). Magnetic field measurements from the Electric and Magnetic Field Instrument Suite and Integrated Science on board the Van Allen Probes are used to identify EMIC wave events for the first 22 months of the mission operation (8 September 2012 to 30 June 2014). EMIC waves are examined in H+, He+, and O+ bands. Over 700 EMIC wave events have been identified over the three different wave bands (265 H+‐band events, 438 He+‐band events, and 68 O+‐band events). EMIC wave events are observed between L = 2–8, with over 140 EMIC wave events observed below L = 4. Results show that H+‐band EMIC waves have two peak magnetic local time (MLT) occurrence regions: prenoon (09:00 < MLT ≤ 12:00) and afternoon (15:00 < MLT ≤ 17:00) sectors. He+‐band EMIC waves feature an overall stronger dayside occurrence. O+‐band EMIC waves have one peak region located in the morning sector at lower L shells (L < 4). He+‐band EMIC waves average the highest wave power overall (>0.1 nT2/Hz), especially in the afternoon sector. Ellipticity observations reveal that linearly polarized EMIC waves dominate in lower L shells.
Key Points
A statistical study of EMIC waves observed by the Van Allen Probes is performed
The occurrence and wave properties of the EMIC waves are examined
Linearly polarized EMIC waves dominate lower L shells (L < 4)
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