13,589 research outputs found
Validity and reliability of three syntactic complexity measures in narratives produced by Cantonese-speaking children
No full textA model for the formation of the active region corona driven by magnetic flux emergence
No full textAims. We present the first model that couples the formation of the corona of a solar active region to a model of the emergence of a sunspot pair. This allows us to study when, where, and why active region loops form, and how they evolve.
Methods. We use a 3D radiation magnetohydrodynamics (MHD) simulation of the emergence of an active region through the upper convection zone and the photosphere as a lower boundary for a 3D MHD coronal model. The coronal model accounts for the braiding of the magnetic fieldlines, which induces currents in the corona to heat up the plasma. We synthesize the coronal emission for a direct comparison to observations. Starting with a basically field-free atmosphere we follow the filling of the corona with magnetic field and plasma.
Results. Numerous individually identifiable hot coronal loops form, and reach temperatures well above 1 MK with densities comparable to observations. The footpoints of these loops are found where small patches of magnetic flux concentrations move into the sunspots. The loop formation is triggered by an increase in upward-directed Poynting flux at their footpoints in the photosphere. In the synthesized extreme ultraviolet (EUV) emission these loops develop within a few minutes. The first EUV loop appears as a thin tube, then rises and expands significantly in the horizontal direction. Later, the spatially inhomogeneous heat input leads to a fragmented system of multiple loops or strands in a growing envelope
Room Temperature Copper(II)-Catalyzed Oxidative Cyclization of Enamides to 2,5-Disubstituted Oxazoles via Vinylic C–H Functionalization
No full textA copper(II)-catalyzed oxidative cyclization of enamides to oxazoles via vinylic C–H bond functionalization at room temperature is described. Various 2,5-disubstituted oxazoles bearing aryl, vinyl, alkyl, and heteroaryl substituents could be synthesized in moderate to high yields. This reaction protocol is complementary to our previously reported iodine-mediated cyclization of enamides to afford 2,4,5-trisubstituted oxazoles.National Institutes of Health (U.S.) (Grant GM58160
High resolution fourier domain optical coherence tomography at 2 microns for painted objects
Get PDFOptical Coherence Tomography has been successfully applied to the non-invasive imaging of subsurface microstructure of a variety of materials from biological tissues to painted objects of art. One of the limitations of the technique is the low depth of penetration due to the strong scattering and absorption in the material. Previous studies found that for paint materials, the optimum window for large depth of penetration is around 2.2 microns. This is also true for many other materials with low water content. We have previously demonstrated OCT systems in this wavelength regime for imaging with improved depth of penetration. In this paper, we present an improved 2 micron high resolution Fourier domain OCT system using a broadband supercontinuum source. The system achieved a depth resolution of 9 microns in air (or 6 microns in paint or any polymer)
A wireless multimedia system
No full textThe complexity, robustness, image and speech quality as well as packet multiplexing issues of a reconfigurable multi-media mobile communicator are addressed. The proposed moderate complexity motion-compensated Discrete Cosine Transform (DCT) based image communicator provides an image peak signal-to-noise ratio (PSNR) of 38 dB at an average bit rate of about 25 kbits/s. The speech codec used is a low-complexity 32 kbit/s CCITT G721 standard scheme. Bandwidth efficient 16 or 64level quadrature amplitude modulation (QAM) combined with embedded low-complexity binary Bose-Chaudhuri-Hocquenghem (BCH) forward error correction coding is deployed. The 20-slot packet reservation multiple access (PRMA) scheme used supports an extra 2.4 kbit/s low-rate data channel for each speech user, in addition to providing 5-6 video-phone channels. The ADPCM/DCT/BCH/16-QAM as well as 64QAM schemes provide nearly unimpaired speech and image quality for channel SNRs in excess of 30 dB and 38 dB, respectively
A Review of silicon carbide development in MEMS applications
Get PDFDue to its desirable material properties, Silicon Carbide (SiC) hasbecome an alternative material to replace Si for MicroelectromechanicalSystems (MEMS) applications in harsh environments. To promote SiC MEMSdevelopment towards future cost-effective products, main technology areas inmaterial deposition and processes have attracted significant interest. Thedevelopments in these areas have contributed to the rapid emergence of SiCMEMS prototypes. In this paper, we give an overview of the importantdevelopments in SiC material formation and fabrication processes in recentyears. Some of the most interesting state-of-the-art SiC MEMS devices arereviewed. This highlights the major progresses in SiC MEMS developed thusfar. This paper also looks into the prospect of SiC MEMS drawing attention topotential issues
Magnetic jam in the corona of the Sun
No full textThe outer solar atmosphere, the corona, contains plasma at temperatures of more than a million K, more than 100 times hotter that solar surface. How this gas is heated is a fundamental question tightly interwoven with the structure of the magnetic field in the upper atmosphere. Conducting numerical experiments based on magnetohydrodynamics we account for both the evolving three-dimensional structure of the atmosphere and the complex interaction of magnetic field and plasma. Together this defines the formation and evolution of coronal loops, the basic building block prominently seen in X-rays and extreme ultraviolet (EUV) images. The structures seen as coronal loops in the EUV can evolve quite differently from the magnetic field. While the magnetic field continuously expands as new magnetic flux emerges through the solar surface, the plasma gets heated on successively emerging fieldlines creating an EUV loop that remains roughly at the same place. For each snapshot the EUV images outline the magnetic field, but in contrast to the traditional view, the temporal evolution of the magnetic field and the EUV loops can be different. Through this we show that the thermal and the magnetic evolution in the outer atmosphere of a cool star has to be treated together, and cannot be simply separated as done mostly so far
Reconfigurable tri-band H-shaped antenna with frequency selectivity feature for compact wireless communication systems
Get PDFThis is the post-print version of the Article. The published version can be accessed from the link below - Copyright @ 2011 IETThis study presents an H-shaped reconfigurable antenna for wireless applications. The antenna consists of an H-shape radiator and a CPW printed on a circuit board and a varactor diode connecting the upper and lower arms of the H-shape radiator for reconfigurability. The uniqueness of the antenna lies on the ability to select the operating mode and frequencies electronically using a varactor diode. By selecting the DC-bias voltages of 11.5, 10 and 8 V across the varactor diode, which in turn selects the corresponding varactor capacitances of 2, 4 and 6 pF, the antenna can be controlled to operate in three different modes, namely a single-band mode to cover the GSM1900, a dual-band mode at 1.88 and 2.4 GHz to cover the GSM1900 and Bluetooth/WLAN, respectively and a tri-band mode at 1.57, 1.88 and 2.4 GHz to cover the GSM1900, WLAN and GPS, respectively. Furthermore, by varying the varactor capacitance from 7 to 13 pF, the GPS and WLAN bands can be tuned by 11.44% (1.57-1.4 GHz) and 6.46% (2.4-2.25 GHz), respectively, yet keeping the 1.88-GHz band unchanged. Detailed studies on the antenna's performance are carried out to investigate the behaviour of the antenna at each resonant frequency in each operating mode.This work is supported by the Measurements for Innovators (MFI) program and the National Measurement Office, an Executive Agency of the Department for Business, Innovation and Skills
APOLIPOPROTEIN AIMILANO PARTIAL LECITHIN - CHOLESTEROL ACYLTRANSFERASE DEFICIENCY DUE TO LOW-LEVELS OF A FUNCTIONAL ENZYME
No full textThe cholesterol esterification process was analyzed in 19 carriers of the apolipoprotein AIMilano (AIM) variant and in 19 age-sex matched controls by measuring lecithin: cholesterol acyltransferase (LCAT) mass, activity (i.e., cholesterol esterification with a standard p in the presence of the endogenous substrate). The AIM subjects had lower LCAT mass (3.30 ± 0.85 μg/ml), activity (71.1 ± 36.4 nmol/ml per h) and cholesterol esterification rate (23.6 ± 12.5 nmol/ml per h) compared to controls (5.22 ± 0.74 μg/ml, 121.6 ± 54.6 nmol/ml0 per h and 53.6 ± 29.9 nmol/ml per h, respectively). The specific LCAT activity, i.e., LCAT activity per μg of LCAT, was similar in the two groups, indicating that the LCAT protein in the AIM carriers is structurally and functionally normal. However, the specific cholesterol esterification rate was 23% lower in the AIM subjects (8.03 ± 6.01 nmol/h per μg) compared to controls (10.49 ± 5.86 nmol/h per μg; P < 0.05). The capacity of HDL3, purified from both AIm and control plasma, to act as substrates for cholesterol esterification was similar, thus suggesting that other mechanism(s) may be in play. Carriers with a relative abundance of abnormal, small HDL3b particles had the most altered cholesterol esterification pattern. Upon evaluating all AIM subjects, a complex relationship between HDL structure, plasma lipid-lipoprotein levels and cholesterol esterification emerged, making the AIMilano condition a unique model for the study of the mechanisms regulating the cholesterol esterification-transfer process in man
- …
