Coil combination using linear deconvolution in k-space for phase imaging

Background: The combination of multi-channel data is a critical step for the imaging of phase and susceptibility contrast in magnetic resonance imaging (MRI). Magnitude-weighted phase combination methods often produce noise and aliasing artifacts in the magnitude images at accelerated imaging sceneries. To address this issue, an optimal coil combination method through deconvolution in k-space is proposed in this paper. Methods: The proposed method firstly employs the sum-of-squares and phase aligning method to yield a complex reference coil image which is then used to calculate the coil sensitivity and its Fourier transform. Then, the coil k-space combining weights is computed, taking into account the truncated frequency data of coil sensitivity and the acquired k-space data. Finally, combining the coil k-space data with the acquired weights generates the k-space data of proton distribution, with which both phase and magnitude information can be obtained straightforwardly. Both phantom and in vivo imaging experiments were conducted to evaluate the performance of the proposed method. Results: Compared with magnitude-weighted method and MCPC-C, the proposed method can alleviate the phase cancellation in coil combination, resulting in a less wrapped phase. Conclusions: The proposed method provides an effective and efficient approach to combine multiple coil image in parallel MRI reconstruction, and has potential to benefit routine clinical practice in the future

Investigation on gas-liquid two-phase flow centrifugal pump performances for different rotational speeds

International audiencePerformance characteristics of a centrifugal pump under gas-liquid mixture are presented, using a direct coupled single-stage, single-suction centrifugal pump. Both experimental and numerical simulations comparison are carried out, for three different rotational speeds and different inlet gas volume fractions, the results of which are presented, based on dimensionless coefficients from similarity laws. The numerical results show that good agreement is obtained with experimental data at nominal rotational speed for several flow coefficients. It is found that the running of the pump is near the sudden break down of the present pump when the inlet void fraction is below 7%. However, numerical results are less sensitive to rotational speed effects compared with experiment ones; the influence of decreasing rotational speed on pump performances is more and more pronounced when inlet gas void fraction increases and flow coefficient decreases. Froude number effects are taken into account in order to explain part of these differences

Parsec-scale jet properties of the gamma-ray quasar 3C 286

The quasar 3C~286 is one of two compact steep spectrum sources detected by the {\it Fermi}/LAT. Here, we investigate the radio properties of the parsec(pc)-scale jet and its (possible) association with the $\gamma$-ray emission in 3C~286. The Very Long Baseline Interferometry (VLBI) images at various frequencies reveal a one-sided core--jet structure extending to the southwest at a projected distance of $\sim$1 kpc. The component at the jet base showing an inverted spectrum is identified as the core, with a mean brightness temperature of $2.8\times 10^{9}$~K. The jet bends at about 600 pc (in projection) away from the core, from a position angle of $-135^\circ$ to $-115^\circ$. Based on the available VLBI data, we inferred the proper motion speed of the inner jet as $0.013 \pm 0.011$ mas yr$^{-1}$ ($\beta_{\rm app} = 0.6 \pm 0.5$), corresponding to a jet speed of about $0.5\,c$ at an inclination angle of $48^\circ$ between the jet and the line of sight of the observer. The brightness temperature, jet speed and Lorentz factor are much lower than those of $\gamma$-ray-emitting blazars, implying that the pc-scale jet in 3C~286 is mildly relativistic. Unlike blazars in which $\gamma$-ray emission is in general thought to originate from the beamed innermost jet, the location and mechanism of $\gamma$-ray emission in 3C~286 may be different as indicated by the current radio data. Multi-band spectrum fitting may offer a complementary diagnostic clue of the $\gamma$-ray production mechanism in this source.Comment: 9 pages, 4 figures, accept for publication in MNRA

Effects of polysaccharide from Lycium barbarum in alloxan-induced diabetic mice

A study was undertaken to evaluate the effects of polysaccharide from Lycium barbarum (LBP) in alloxan-induced diabetic mice. The various parameters studied included body weight, fasting blood glucose levels, total cholesterol (TC) and triglyceride (TG) in diabetic and normal mice. LBP treatment(20, 40 mg/ kg body weight) for 28 days resulted in a significant decrease in the concentration of fasting blood glucose (FBG), total cholesterol (TC) and triglyceride (TG) in diabetes mellitus mice. Furthermore, LBP significantly increased body weight (bw). The data demonstrated LBP at the dose of 40 mg/kg bw exhibited the optimal effect

Energy Dissipation and Air Entrainment in a Stepped Storm Waterway: an Experimental Study

For the last three decades, research focused on steep stepped chutes. Few studies considered flat-slope stepped geometries such as stepped storm waterways or culverts. In this study, experiments were conducted in a large, flat stepped chute (~3.4 degrees) based upon a Froude similitude. Three basic flow regimes were observed: nappe flow without hydraulic jump, transition flow, and skimming flow. Detailed air-water flow measurements were conducted. The results allow a complete characterization of the air concentration and bubble count rate distributions, as well as an accurate estimate of the rate of energy dissipation. The flow resistance, expressed in terms of a modified friction slope, was found to be about 2.5 times greater than in smooth-chute flow. A comparison between smooth- and stepped-invert flows shows that greater aeration and larger residence times take place in the latter geometry. The result confirms the air-water mass transfer potential of stepped cascades, even for flat slopes

A heterogeneous peer-to-peer network testbed

In this paper, we describe a heterogeneous peer-to-peer network testbed, which is developed as part of a joint research project to investigate novel resource discovery and content distribution protocols in a heterogeneous wired/wireless environment. We describe the testbed requirements, the testbed architecture, the multi-functional wireless node, and the software architecture. We also describe some of the proposed protocols to be developed and tested on the testbed. © 2009 IEEE.published_or_final_versionThe 1st International Conference on Ubiquitous and Future Networks (ICUFN 2009), Hong Kong, 7-9 June 2009. In Proceedings of the 1st ICUFN, 2009, p. 46-5

Trade-offs between high yields and greenhouse gas emissions in irrigation wheat cropland in China

Although the concept of producing higher yields with reduced greenhouse gas (GHG) emissions is a goal that attracts increasing public and scientific attention, the trade-off between high yields and GHG emissions in intensive agricultural production is not well understood. Here, we hypothesize that there exists a mechanistic relationship between wheat grain yield and GHG emission, and that could be transformed into better agronomic management. A total 33 sites of on-farm experiments were investigated to evaluate the relationship between grain yield and GHG emissions using two systems (conventional practice, CP; high-yielding systems, HY) of intensive winter wheat (<i>Triticum aestivum</i> L.) in China. Furthermore, we discussed the potential to produce higher yields with lower GHG emissions based on a survey of 2938 farmers. Compared to the CP system, grain yield was 39% (2352 kg ha⁻¹) higher in the HY system, while GHG emissions increased by only 10%, and GHG emission intensity was reduced by 21%. The current intensive winter wheat system with farmers' practice had a median yield and maximum GHG emission rate of 6050 kg ha⁻¹ and 4783 kg CO₂ eq ha⁻¹, respectively; however, this system can be transformed to maintain yields while reducing GHG emissions by 26% (6077 kg ha⁻¹, and 3555 kg CO₂ eq ha⁻¹). Further, the HY system was found to increase grain yield by 39% with a simultaneous reduction in GHG emissions by 18% (8429 kg ha⁻¹, and 3905 kg CO₂ eq ha⁻¹, respectively). In the future, we suggest moving the trade-off relationships and calculations from grain yield and GHG emissions to new measures of productivity and environmental protection using innovative management technologies

Recent Developments in Enantioselective Transition Metal Catalysis Featuring Attractive Noncovalent Interactions between Ligand and Substrate.

Enantioselective transition metal catalysis is an area very much at the forefront of contemporary synthetic research. The development of processes that enable the efficient synthesis of enantiopure compounds is of unquestionable importance to chemists working within the many diverse fields of the central science. Traditional approaches to solving this challenge have typically relied on leveraging repulsive steric interactions between chiral ligands and substrates in order to raise the energy of one of the diastereomeric transition states over the other. By contrast, this Review examines an alternative tactic in which a set of attractive noncovalent interactions operating between transition metal ligands and substrates are used to control enantioselectivity. Examples where this creative approach has been successfully applied to render fundamental synthetic processes enantioselective are presented and discussed. In many of the cases examined, the ligand scaffold has been carefully designed to accommodate these attractive interactions, while in others, the importance of the critical interactions was only elucidated in subsequent computational and mechanistic studies. Through an exploration and discussion of recent reports encompassing a wide range of reaction classes, we hope to inspire synthetic chemists to continue to develop asymmetric transformations based on this powerful concept.The EPSRC are acknowledged in manuscript as they provide a studentship to one of the authors

Warm-Hot Gas in and around the Milky Way: Detection and Implications of OVII Absorption toward LMC X-3

X-ray absorption lines of highly-ionized species such as OVII at about zero redshift have been firmly detected in the spectra of several active galactic nuclei. However, the location of the absorbing gas remains a subject of debate. To separate the Galactic and extragalactic contributions to the absorption, we have obtained Chandra LETG-HRC and FUSE observations of the black hole X-ray binary LMC X--3. A joint analysis of the detected OVII and Ne IX Kalpha lines, together with the non-detection of the OVII Kbeta and OVIII Kalpha lines, gives the measurements of the temperature, velocity dispersion, and hot oxygen column density. The X-ray data also allow us to place a 95% confidence lower limit to the Ne/O ratio as 0.14. The OVII line centroid and its relative shift from the Galactic OI Kalpha absorption line, detected in the same observations, are inconsistent with the systemic velocity of LMC X--3 ($+310 {\rm km s^{-1}}$). The far-UV spectrum shows OVI absorption at Galactic velocities, but no OVI absorption is detected at the LMC velocity at $> 3\sigma$ significance. Both the nonthermal broadening and the decreasing scale height with the increasing ionization state further suggest an origin of the highly-ionized gas in a supernova-driven galactic fountain. In addition, we estimate the warm and hot electron column densities from our detected OVII Kalpha line in the LMC X--3 X-ray spectra and from the dispersion measure of a pulsar in the LMC vicinity. We then infer the O/H ratio of the gas to be $\gtrsim 8 \times 10^{-5}$, consistent with the chemically-enriched galactic fountain scenario. We conclude that the Galactic hot interstellar medium should in general substantially contribute to zero-redshift X-ray absorption lines in extragalactic sources.Comment: 11 pages, accepted for publication in Ap