碱金属钾对Ni基催化剂纤维素水蒸气气化活性的影响

采用两段式催化气化方式研究了生物质热解气化过程中碱金属的挥发对Ni基催化剂活性的影响。实验结果表明,负载K盐的纤维素水蒸气催化气化过程中,K挥发后会在催化剂表面沉积,而少量K的存在和表面沉积不但能够提高镍基催化剂的抗积炭能力,而且有助于提高其催化活性,产生更多的氢气。然而纤维素中K的浓度过大,将会抑制Ni基催化剂的效果;K在催化剂上的沉积随催化剂循环次数的增加而增加,K的含量愈高,对催化剂的抑制效果愈明显,从而缩短了催化剂的使用寿命。     

Measurement of the positive muon anomalous magnetic moment to 0.7 ppm

A higher precision measurement of the anomalous g value, a(mu)=(g-2)/2, for the positive muon has been made at the Brookhaven Alternating Gradient Synchrotron, based on data collected in the year 2000. The result a(mu(+))=11 659 204(7)(5)x10(-10) (0.7 ppm) is in good agreement with previous measurements and has an error about one-half that of the combined previous data. The present world average experimental value is a(mu)(expt)=11 659 203(8)x10(-10) (0.7 ppm).     

Precise Measurement of Muon Capture on the Proton

The aim of the μCap experiment is a 1% measurement of the singlet capture rate Λ _S for the basic electro-weak reaction μ + p → n + ν_μ. This observable is sensitive to the weak form-factors of the nucleon, in particular to the induced pseudoscalar coupling constant g _P . It will provide a rigorous test of theoretical predictions based on the Standard Model and effective theories of QCD. The present method is based on high precision lifetime measurements of μ⁻ in hydrogen gas and the comparison with the free μ⁺ lifetime. The μ⁻ experiment will be performed in ultra-clean, deuterium-depleted H₂ gas at 10 bar. Low density compared to liquid H₂ is chosen to avoid uncertainties due to ppμ formation. A time projection chamber acts as a pure hydrogen active target. It defines the muon stop position in 3D and detects rare background reactions. Decay electrons are tracked in cylindrical wire-chambers and a scintillator array covering 75% of 4π. This revised version was published online in August 2006 with corrections to the Cover Date.     

Measurement of the positive muon lifetime and determination of the Fermi constant to part-per-million precision

We report a measurement of the positive muon lifetime to a precision of 1.0 ppm; it is the most precise particle lifetime ever measured. The experiment used a time-structured, low-energy muon beam and a segmented plastic scintillator array to record more than 2×10(12) decays. Two different stopping target configurations were employed in independent data-taking periods. The combined results give τ(μ(+)) (MuLan)=2?196?980.3(2.2) ps, more than 15 times as precise as any previous experiment. The muon lifetime gives the most precise value for the Fermi constant: G(F) (MuLan)=1.166?378?8(7)×10(-5) GeV(-2) (0.6 ppm). It is also used to extract the μ(-)p singlet capture rate, which determines the proton's weak induced pseudoscalar coupling g(P).     

Phase-alternated compositeπ/2 pulses for solid state quadrupole echo NMR spectroscopy

Phase-alternated compositeπ/2 pulses have been constructed for spinI=1 to overcome quadrupole interaction effects in solid state nuclear magnetic resonance (NMR) spectroscopy. Magnus expansion approach is used to design these sequences in a manner similar to the NMR coherent averaging theory. It is inferred that the symmetric phase-alternated compositeπ/2 pulses reported here are quite successful in producing quadrupole echo free from phase distortions. This effectiveness of the present composite pulses is due to the fact that most of them are of shorter durations as compared to the ones reported in literature. In this theoretical procedure, irreducible spherical tensor operator formalism is employed to simplify the complexity involved in the evaluation of Magnus expansion terms. It has been argued in this paper that compositeπ/2 pulse sequences for this purpose can also be derived from the broadband inversionπ pulses which are designed to compensate electric field gradient (efg) inhomogeneity in spinI=1 nuclear quadrupole resonance (NQR) spectroscopy.     

Search for Lorentz and CPT violation effects in Muon spin precession

The spin precession frequency of muons stored in the (g-2) storage ring has been analyzed for evidence of Lorentz and CPT violation. Two Lorentz and CPT violation signatures were searched for a nonzero delta omega a(=omega a mu+ - omega a mu-) and a sidereal variation of omega a mu+/-). No significant effect is found, and the following limits on the standard-model extension parameters are obtained: bZ = -(1.0+/-1.1) x 10(-23) GeV; (m mu dZ0 + HXY)=(1.8+/-6.0) x 10(-23) GeV; and the 95% confidence level limits b perpendicular mu+ <1.4 x 10(-24) GeV and b perpendicular mu- <2.6 x 10(-24) GeV.     

用于EAST上低杂波平行波数测量的磁探针设计与测试

针对EAST上2.45GHz低杂波,完成了低杂波平行波数测量磁探针的设计、仿真与测试。利用有限元仿真软件COMSOL Multiphysics 5.2对磁探针尺寸进行仿真优化,确定了单匝环、矩形缝以及陶瓷片厚度等影响磁探针耦合性能的关键尺寸。测试结果表明,该磁探针对2.45GHz低杂波有良好的耦合性能和鉴别波极化的能力,与仿真结果一致。研究结果为EAST装置上低杂波平行波数测量诊断系统的建立提供重要的参考依据,从而为进一步开展高密度低杂波电流驱动实验研究提供必要的实验数据。     

Correspondence between zero angular momentum transfer cross sections of (6Li, 6He) reactions and the Gamow-Teller strength

The (⁶Li, ⁶He) cross sections on targets between ⁶Li and ⁴⁸Ca have been measured. The cross section due to zero angular momentum transfer appears to be correlated with the known Gamow-Teller strength. The reaction mechanism sometimes is dominated by multistep processes.     

Molecular dynamics simulations of the enzyme Catechol-O-Methyltransferase: methodological issues1

Results from extensive 70 ns all-atom molecular dynamics simulations of catechol-O-methyltransferase (COMT) enzyme are reported. The simulations were performed with explicit TIP3P water and Mg^2?+ ions. Four different crystal structures of COMT, with and without different ligands, were used. These simulations are among the most extensive of their kind and as such served as a stability test for such simulations. On the methodological side we found that the initial energy minimization procedure may be a crucial step: particular hydrogen bonds may break, and this can initiate an irreversible loss of protein structure that becomes observable in longer time scales of the order of tens of nanoseconds. This has important implications for both molecular dynamics and quantum mechanics–molecular mechanics simulations.