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We take the viewpoint that X(1576) is the tetraquark state which consists of a scalar diquark and an antiscalar-diquark in relative P-wave, and calculate its mass in the framework of the QCD sum rule approach. The numerical value of the mass mx= (1.66 =k 0.14) GeV is consistent with the experimental data. There might be some tetraquark components in the vector meson X(1576). 相似文献
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核糖核酸酶A(RNase A)的结构与功能的关系虽属已知,但大都限于水解作用方面,而关于合成作用方面的报道则颇少.根据前人用抑制剂法所得羧甲基化核糖核酸酶A的衍生物(CM-RNase A),和用合成法所得分子较简单的RNase A的类似物的研究结果,似乎RNaseA分子中的His_(119)与Lys_(41)残基与酶的合成活性无关.这些衍生物和类似物的合成活性都比它们的水解活性高,但不论它们的合成或水解活性都很显著地低于天然酶的活 相似文献
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通过改变灰化温度,灰化时间及盐酸浓度三因素设计正交试验,对样品牦牛奶粉及市售奶粉进行干法消化。用火焰原子吸收光谱法对样品中的Ca, Mg, Fe, Cu, Zn, Mn, K和Na等八种元素进行测定。实验表明,最佳消化条件为:灰化温度510 ℃,灰化时间4 h,盐酸体积比为1∶5。在最佳实验条件下,对牦牛奶粉各元素的含量做了回收实验,回收率范围在95.2%~107.3%,相对标准偏差0.38%~3.86%(n=6)。实验结果表明:牦牛奶粉营养元素含量丰富, 是营养价值极高的食品。 相似文献
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用GC/MS联用技术测定西藏酥油中的风味物质 总被引:1,自引:0,他引:1
采用水蒸汽蒸馏法提取出酥油中的风味物质,利用气相色谱-质谱联用技术对西藏酥油中的风味物质进行了分离、鉴定,共确定了34种化合物及其它们的相对含量.其中羧酸9种,酯11种,酮6种,醇2种,烯类化合物4种,苯胺类化合物和苯酚类化合物各1种.其中主要成分为己酸和辛酸,其相对含量分别为30.35%和33.22%. 相似文献
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A lattice Boltzmann–cellular automaton study on dendrite growth with melt convection in solidification of ternary alloys 下载免费PDF全文
A lattice Boltzmann(LB)–cellular automaton(CA) model is employed to study the dendrite growth of Al-4.0 wt%Cu–1.0 wt%Mg alloy. The effects of melt convection, solute diffusion, interface curvature, and preferred growth orientation are incorporated into the coupled model by coupling the LB–CA model and the CALPHAD-based phase equilibrium solver,Pan Engine. The dendrite growth with single and multiple initial seeds was numerically studied under the conditions of pure diffusion and melt convection. Effects of initial seed number and melt convection strength were characterized by newdefined solidification and concentration entropies. The numerical result shows that the growth behavior of dendrites, the final microstructure, and the micro-segregation are significantly influenced by melt convection during solidification of the ternary alloys. The proposed solidification and concentration entropies are useful characteristics bridging the solidification behavior and the microstructure evolution of alloys. 相似文献
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A new numerical method named as basic function method is proposed. It can directly discretize differential operators on unstructured grids. By expanding the basic function to approach the exact function, the central and upwind schemes of derivative are constructed. By using the second-order polynomial as a basic function and applying the flux splitting method and the combination of central and upwind schemes to suppress non-physical fluctuation near shock waves, a second-order basic function scheme of polynomial type is proposed to solve inviscid compressible flows numerically. Numerical results of typical examples for two-dimensional inviscid compressible transonic and supersonic steady flows indicate that the new scheme has high accuracy and high resolution for shock waves. Combined with the adaptive remeshing technique, satisfactory results can be obtained. 相似文献
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采用AFS-230E 型原子荧光光度计对绿豆中Se的含量及绿豆分步酶解过程中Se的形态分布进行了分析。结果表明:(1)绿豆中Se含量为54.79 μg·g-1(干重) ;(2)通过酶解,绿豆中90%以上的Se被提取出来,而水煮对Se的提取率只有19.26%,其中淀粉酶、蛋白酶和纤维素酶酶解过程对Se的提取率分别是36.64%,55.96%和5.189%,可推断,绿豆中大部分Se被蛋白结合或络合;(3)总酶解产物中Se的有机态分布系数为59.87%,远大于绿豆汤中Se的有机态分布系数(3.64%),其中淀粉酶解产物和蛋白酶解产物中Se的有机态分布系数分别为15.51%和44.36%,纤维素酶解产物中未检测到有机态Se,可见,Se在绿豆纤维素中主要以络合形式存在。回收实验表明,方法回收率为97.8%,RSD为1.1%(n=11 )。 相似文献