In-orbit background simulation of a type-B CATCH satellite

The Chasing All Transients Constellation Hunters (CATCH) space mission plans to launch three types of micro-satellites (A, B, and C). The type-B CATCH satellites are dedicated to locating transients and detecting their time-dependent energy spectra. A type-B satellite is equipped with lightweight Wolter-I X-ray optics and an array of position-sensitive multi-pixel Silicon Drift Detectors. To optimize the scientific payloads for operating properly in orbit and performing the observations with high sensitivities, this work performs an in-orbit background simulation of a type-B CATCH satellite using the Geant4 toolkit. It shows that the persistent background is dominated by the cosmic X-ray diffuse background and the cosmic-ray protons. The dynamic background is also estimated considering trapped charged particles in the radiation belts and low-energy charged particles near the geomagnetic equator, which is dominated by the incident electrons outside the aperture. The simulated persistent background within the focal spot is used to estimate the observation sensitivity, i.e. 4.22$\times$10$^{-13}$ erg cm$^{-2}$ s$^{-1}$ with an exposure of 10$^{4}$ s and a Crab-like source spectrum, which can be utilized further to optimize the shielding design. The simulated in-orbit background also suggests that the magnetic diverter just underneath the optics may be unnecessary in this kind of micro-satellites, because the dynamic background induced by charged particles outside the aperture is around 3 orders of magnitude larger than that inside the aperture.Comment: 24 pages, 13 figures, 7 tables, accepted for publication in Experimental Astronom

Volume Regulated Anion Channel Currents of Rat Hippocampal Neurons and Their Contribution to Oxygen-and-Glucose Deprivation Induced Neuronal Death

Volume-regulated anion channels (VRAC) are widely expressed chloride channels that are critical for the cell volume regulation. In the mammalian central nervous system, the physiological expression of neuronal VRAC and its role in cerebral ischemia are issues largely unknown. We show that hypoosmotic medium induce an outwardly rectifying chloride conductance in CA1 pyramidal neurons in rat hippocampal slices. The induced chloride conductance was sensitive to some of the VRAC inhibitors, namely, IAA-94 (300 µM) and NPPB (100 µM), but not to tamoxifen (10 µM). Using oxygen-and-glucose deprivation (OGD) to simulate ischemic conditions in slices, VRAC activation appeared after OGD induced anoxic depolarization (AD) that showed a progressive increase in current amplitude over the period of post-OGD reperfusion. The OGD induced VRAC currents were significantly inhibited by inhibitors for glutamate AMPA (30 µM NBQX) and NMDA (40 µM AP-5) receptors in the OGD solution, supporting the view that induction of AD requires an excessive Na+-loading via these receptors that in turn to activate neuronal VRAC. In the presence of NPPB and DCPIB in the post-OGD reperfusion solution, the OGD induced CA1 pyramidal neuron death, as measured by TO-PRO-3-I staining, was significantly reduced, although DCPIB did not appear to be an effective neuronal VRAC blocker. Altogether, we show that rat hippocampal pyramidal neurons express functional VRAC, and ischemic conditions can initial neuronal VRAC activation that may contribute to ischemic neuronal damage

SiO2-carbon nanocomposite anodes with a 3D interconnected network and porous structure from bamboo leaves

To seek for a low-cost, green and sustainable method of preparing nanostructured carbon electrode materials, we are inspired by natural biomaterials. An amorphous SiO2-carbon nanocomposite (SiO2-C/NCs) with three-dimensional (3D) interconnected network and hierarchical porous structure is synthesized by thermal decomposition of abandoned bamboo leaves at 700 degrees C in N-2 atmosphere. The characterization results indicate that the SiO2-C/NCs inherited the natural hierarchical structure of the bamboo leaves. Compared with the commercialized graphite anode and other artificial nanostructured carbon materials, the SiO2-C/NCs anode shows a high lithium-storage capacity of 586.2 mA h g(-1) at 200 mA g(-1), with impressive good cycle stability (294.7 mA h g(-1) after 190 cycles) and ultra-high coulombic efficiency close to 100%. After 160 cycles at varied current densities from 200 mA g(-1) to 2000 mA g(-1), this anode still maintains a high discharge of 117.4 mA h g(-1). This simple, green and sustainable strategy will open a new avenue for large-scale preparation and application of nanostructured electrode materials from biomass materials

Marine Oil Spill Detection Based on the Comprehensive Use of Polarimetric SAR Data

As a major marine pollution source, oil spills largely threaten the sustainability of the coastal environment. Polarimetric synthetic aperture radar remote sensing has become a promising approach for marine oil spill detection since it could effectively separate crude oil and biogenic look-alikes. However, on the sea surface, the signal to noise ratio of Synthetic Aperture Radar (SAR) backscatter is usually low, especially for cross-polarized channels. In practice, it is necessary to combine the refined detail of slick-sea boundary derived from the co-polarized channel and the highly accurate crude slick/look-alike classification result obtained based on the polarimetric information. In this paper, the architecture for oil spill detection based on polarimetric SAR is proposed and analyzed. The performance of different polarimetric SAR filters for oil spill classification are compared. Polarimetric SAR features are extracted and taken as the input of Staked Auto Encoder (SAE) to achieve high accurate classification between crude oil, biogenic slicks, and clean sea surface. A post-processing method is proposed to combine the classification result derived from SAE and the refined boundary derived from VV channel power image based on special density thresholding (SDT). Experiments were conducted on spaceborne fully polarimetric SAR images where both crude oil and biogenic slicks were presented on the sea surface

Visible light-mediated cobalt and photoredox dual-catalyzed asymmetric reductive coupling of biaryl dialdehydes and aryl iodides

Secondary alcohols bearing both axial and central chirality comprise attractive biological activity, and also exhibit excellent chiral induction in asymmetric reactions. However, only very limited asymmetric catalytic approaches were developed for their catalytic synthesis. We herein describe visible light-mediated cobalt-catalyzed asymmetric reductive Grignard-type addition of axially prochiral biaryl dialdehydes with aryl iodides, leading to the direct construction of axially chiral secondary alcohols bearing aldehyde groups. Preliminary mechanistic studies indicate efficient kinetic recognition of diastereomers might occur to improve the diastereoselectivity, which might open a new avenue for the challenging cascade construction of multiple chiral elements. This protocol features excellent enantio- and diastereoselectivity, green and mild conditions, simple operation, and broad substrate scope, providing a modular platform for the synthesis of secondary axially chiral alcohols

OGD induced VRAC activation requires Na- +loading through glutamate receptors.

<p><b>A</b>. In the presence of 40 µM AP-5 and 30 µM NBQX in the OGD solution to inhibit ionotropic glutamate receptors, the 25 min OGD induced neuronal electrophysiological changes seen in the <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0016803#pone-0016803-g003" target="_blank">Fig. 3A</a> were largely attenuated. Also, the activation of VRAC in the reperfusion stage was significantly inhibited. <b>B</b>. Shows the differences in the outward current amplitudes between 6 min and 20 min post-OGD under the following conditions: 1) control; 2) in the presence of DNDS+ bicuculline +furosemide in the OGD and 3) in the presence of AP-5+NBQX in the OGD solution. * Indicates that the difference between the control and AP-5+NBQX groups was statistically significant at <i>p</i><0.05.</p

The effects of NPPB and DCPIB on OGD induced pyramidal neuron death.

<p>Besides the control group (in aCSF, <b>A</b>), the hippocampal slices were randomly divided into three groups after 25 min OGD treatment to receive the following post-OGD treatment: 1) in bath solution (<b>B</b>. OGD); 2) bath solution+100 µM NPPB (<b>C.</b> NPPB); and 3) bath solution+10 µM DCPIB (<b>D.</b> DCPIB). The fluorescence density of the TO-PRO-3-I staining is proportional to the neuronal death. Between the aCSF control and the OGD group, the neuronal death increased by 5.3 fold (3.2±0.6 in aCSF <i>vs</i>. 16.9±1.9 in OGD, n = 13). The neuronal death was reduced to 6.0 ±0.5 (n = 20) by 100 µM NPPB, and to 9.4±1.1 (n = 20) by 10 µM DCPIB. Both NPPB and DCPIB were added in the reperfusion bath solution to inhibit post-OGD VRAC. All the fluorescence intensity values are arbitrary. **. The difference between the OGD and NPPB or DCPIB groups is statistically significant at <i>p</i>≤0.01t. <b>†</b>. The difference between the NPPB and DCPIB groups is statistically significant at <i>p</i>≤0.05.</p

The post-OGD VRAC induced from rat hippocampal pyramidal neurons.

<p><b>A</b>. Shows a neuronal recording during a 40 min of OGD perfusion. The OGD first induced a progressive activation of membrane conductance accompanied by a downward shift in the holding currents, and was then followed by an anoxic depolarization (AD) at 25 min after OGD onset. A 40 min OGD treatment typically resulted in an irreversible change in neuronal electrophysiology. For the recordings shown in <b>B</b>-1, <b>C</b>-1 and <b>D-</b>1, the OGD exposure was shortened to 25 min, where the OGD-induced neuronal electrophysiological changes were readily reversible at ∼6 min after withdrawal of OGD (reperfusion). In the reperfusion stage, the voltage step protocol was delivered at the time points of “<b>a</b>” and “<b>b</b>” to obtain the I-V curves (<b>B</b>2, <b>C</b>-2 and <b>D</b>-2, the voltage step induced current traces are not shown). The presence of a strong outwardly rectifying chloride conductance and a progressive increase of conductance in the reperfusion stage were disclosed by the I-V curves shown <b>B</b>-2, where the I-V curves obtained from 6 min and 20 min post-OGD can be compared. Both of the I-V curves showed a strong outward rectification and reversed at −40 mV. During the time period from 6 min to 20 min, the amplitude of the outward currents at +100 mV increased by 32% (1542±116 pA at “<b>a</b>” <i>vs</i>. 2041±65 at “<b>b</b>”). *: indicates a statistical significance of difference at <i>p<</i>0.05. In the recording of <b>C</b>-1, an inhibitor cocktail for Cl^- cotransporter and GABA_A, i.e., 200 µM furosemide+400 µM DNDS+20 µM bicuculline, was applied to the reperfusion solution that did not prevent the outgrowing of outward chloride currents (<b>C</b>-2, 1460±126 pA at “<b>a</b>” <i>vs</i>. 1857±207 at “<b>b</b>”, <i>p</i>>0.05). The recording in <b>D</b>-1 showed that 100 µM NPPB not only prevented the outward anion conductance from further growing, but actually inhibited the outward currents to below the control level measured at 6 min in the reperfusion stage (1347±156 pA at “<b>a</b>” <i>vs</i>. 1013±89 at “<b>b</b>”).</p