Understanding the white-light flare on 2012 March 9 : Evidence of a two-step magnetic reconnection

We attempt to understand the white-light flare (WLF) that was observed on 2012 March 9 with a newly constructed multi-wavelength solar telescope called the Optical and Near-infrared Solar Eruption Tracer (ONSET). We analyzed WLF observations in radio, H-alpha, white-light, ultraviolet, and X-ray bands. We also studied the magnetic configuration of the flare via the nonlinear force-free field (NLFFF) extrapolation and the vector magnetic field observed by the Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamics Observatory (SDO). Continuum emission enhancement clearly appeared at the 3600 angstrom and 4250 angstrom bands, with peak contrasts of 25% and 12%, respectively. The continuum emission enhancement closely coincided with the impulsive increase in the hard X-ray emission and a microwave type III burst at 03:40 UT. We find that the WLF appeared at one end of either the sheared or twisted field lines or both. There was also a long-lasting phase in the H-alpha and soft X-ray bands after the white-light emission peak. In particular, a second, yet stronger, peak appeared at 03:56 UT in the microwave band. This event shows clear evidence that the white-light emission was caused by energetic particles bombarding the lower solar atmosphere. A two-step magnetic reconnection scenario is proposed to explain the entire process of flare evolution, i.e., the first-step magnetic reconnection between the field lines that are highly sheared or twisted or both, and the second-step one in the current sheet, which is stretched by the erupting flux rope. The WLF is supposed to be triggered in the first-step magnetic reconnection at a relatively low altitude.Comment: 4 pages, 4 figures, published in A&A Lette

Expression and distribution of HIF-1α, HIF-2α, VEGF, VEGFR-2 and HIMF in the kidneys of Tibetan sheep, plain sheep and goat

Background: The objective of this study was to detect the expression and distribution characteristics of five proteins (the hypoxia-inducible factor 1alpha [HIF-1a], HIF-2a, vascular endothelial growth factor [VEGF], VEGF-2 receptor [VEGFR-2] and hypoxia-induced mitogenic factor [HIMF]) in kidney of Tibetan sheep, plain sheep and goat. The results will provide the basic information for the comparative study of sheep breeds living at different altitudes.Materials and methods: The kidney tissues were collected from healthy adult Tibetan sheep, plain sheep and goats and made into paraffin sections. Histological characteristics were assessed by haematoxylin and eosin staining. Expressions of HIF-1a, HIF-2a, VEGF, VEGFR-2 and HIMF proteins were measured by immunohistochemical staining.Results: Immunohistochemistry results showed that the positive expression signals of HIF-1a, HIF-2a, VEGF and VEGFR-2 were detected in epithelial cells of renal tubules and collecting tubules, renal corpuscles in the kidneys of the three sheep breeds. Positive expression signals of HIMF were detected in epithelial cells of proximal tubules and distal tubules in Tibetan sheep and epithelial cells of distal tubules in goat. Immunostaining intensity of HIF-1a, HIF-2a, VEGF and VEGFR-2 proteins in Tibetan sheep was significantly higher than that in both plain sheep and goat (p < 0.05). Immunostaining intensity of HIMF in Tibetan sheep was higher than goat (p < 0.05). Positive expression signals of HIMF were not detected in plain sheep.Conclusions: The expression and distribution characteristics of HIF-1a, HIF-2a, VEGF, VEGFR-2 and HIMF in the studied kidney tissues suggested that these proteins may be related to the physiological regulation of Tibetan sheep kidney in hypoxia environment, and therefore might be important regulating proteins for Tibetan sheep to adapt to high altitude hypoxia environment

A Novel 2-D Multibeam Antenna Without Beamforming Network

© 2016 IEEE. A novel design of multibeam array antenna without feeding network is presented in this communication. This array antenna consists of 3 × 3 microstrip patches as radiators. In this design, a feeding network is avoided where each patch is fed by a probe. Furthermore, whatever patch is excited, the input power can be coupled to all patches through four microstrip lines located between the radiating elements. In addition, nine radiation beams can be implemented depending on different field distributions that are generated by exciting each patch individually. The proposed antenna has a simple single-layered structure and does not suffer from a complex feeding network compared with traditional multibeam antennas. The experimental results demonstrate that the scanning ranges of the nine beams are ±24° and ±45° in the vertical and horizontal directions, respectively. Moreover, measured gain for the nine beams of the implemented antenna varies from 9.06 to 10.45 dBi

Kinetics and mechanism of heterogeneous oxidation of sulfur dioxide by ozone on surface of calcium carbonate

Sulfate particles play a key role in the air quality and the global climate, but the heterogeneous formation mechanism of sulfates on surfaces of atmospheric particles is not well established. Carbonates, which act as a reactive component in mineral dust due to their special chemical properties, may contribute significantly to the sulfate formation by heterogeneous processes. This paper presents a study on the oxidation of SO₂ by O₃ on CaCO₃ particles. Using Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS), the formation of sulfite and sulfate on the surface was identified, and the roles of O₃ and water in oxidation processes were determined. The results showed that in the presence of O₃, SO₂can be oxidized to sulfate on the surface of CaCO₃ particles. The reaction is first order in SO₂ and zero order in O₃. The reactive uptake coefficient for SO₂ [(0.6–9.8)×10¹⁴ molecule cm^-3] oxidation by O₃ [(1.2–12)×10¹⁴ molecule cm^-3] was determined to be (1.4±0.3)×10^-7 using the BET area as the reactive area and (7.7±1.6)×10^-4 using the geometric area. A two-stage mechanism that involves adsorption of SO₂ followed by O₃ oxidation is proposed and the adsorption of SO₂ on the CaCO₃ surface is the rate-determining step. The proposed mechanism can well explain the experiment results. The atmospheric implications were explored based on a box model calculation. It was found that the heterogeneous reaction might be an important pathway for sulfate formation in the atmosphere

Accuracy of EGN model in ultra-wideband optical fiber communication systems

The efficient and accurate evaluation of the transmission performance of high-capacity optical communication systems has always attracted significant research attentions. The enhanced Gaussian noise (EGN) model is considered as an excellent solution to predict the system performance taking into account linear and nonlinear transmission impairments. Since the conventional form of the EGN model is complicated and intractable for a fast computation, the closed-form simplification has been regarded as a direction to significantly reduce the computational complexity. However, the accuracy of such a closed-form EGN model becomes a main concern in the application of ultra-wideband optical communication systems. In this work, we have investigated the accuracy of the closed-form EGN model for ultra-wideband optical fiber communication systems, where the performance of the system using electronic dispersion compensation, multi-channel nonlinearity compensation and full-field nonlinearity compensation has been evaluated in terms of symbol rate, number of channels and signal power. Our work will provide an insight on the application of the EGN model in next-generation ultra-wideband long-haul optical fiber communication networks

Heavily tin-doped indium oxide nano-pyramids as high-performance gas sensor

Heavily Sn-doped In2O3nano-pyramids with a Sn percentage of 19.97% by weight have been prepared by sputtering technique. The nano-pyramids with smooth facets and a sharp tip have been achieved by deposition on Sn-metal particles, leading to a diameter of ∼100nm. The gas sensors realized from these pyramids are highly sensitive to ethanol gas, and the sensitivity is about 133.99 against 200ppm ethanol at 250°C. Good sensitivity characteristics have been obtained even at a low temperature of down to 50°C. The high response and low working temperature demonstrate the potential application of heavily Sn-doped In2O3 nano-pyramids for fabricating gas sensors