不稳定原子核β衰变强度的实验测量方法

原子核的β衰变是指原子核放射出β粒子或俘获电子而进行的转变。对β衰变强度S_β(E)的精确测量,对探索不稳定原子核的结构、揭秘恒星核合成过程、验证β衰变理论等方面均存在着重要意义。实验上,为了测量β衰变强度,一种方法是利用β-γ符合测量或者全吸收谱仪对β衰变产物进行直接测量,这种方法可以给出子核在Q_β窗口内的衰变信息。另一种方法是利用在中等能区(100~400 MeV/u)进行的电荷交换反应,如(p,n)或(3He,t),通过微分截面的高精度测量获得子核的β衰变强度,这种方法可以用于研究子核在Q_β窗外的衰变强度,但是对束流强度有较高的要求,尚无法系统研究产额较低的不稳定原子核。有鉴于此,本文提出对不稳定核素的电荷交换反应总截面进行系统测量,结合核反应理论,这种方法有望约束不稳定核素在质子发射阈下的Gamow-Teller跃迁的总强度。最后简要介绍了已开展和计划开展的工作。     

Ni/MgAl(O) 催化剂上高温焦炉煤气中焦油组分的催化转化

 采用共沉淀-水热法合成了一系列 Ni/MgAl(O) 催化剂. 用甲苯和萘的混合物作为焦油模型化合物, 在固定床反应器上研究了该催化剂直接催化转化具有较低水蒸气/碳摩尔比的高温焦炉煤气中焦油为小分子气体的反应. 考察了催化剂组成、水蒸气/碳摩尔比和反应条件等对催化剂性能的影响. 结果表明, Mg/Al 摩尔比为 3 时 Ni/MgAl(O) 催化剂表现出最优的催化性能. 在 700~800 oC 和水蒸气/碳摩尔比为 0.68 的反应条件下, 15%Ni/Mg3Al(O) 催化剂能将甲苯和萘完全转化为 CO 和 CH4 等小分子气体. 在反应气中引入 0.05% H2S(摩尔分数) 气体的实验表明, 该催化剂在焦油催化转化反应中具有较好的抗硫能力. 另外, 在催化剂中加入少量 Pt 助剂能显著提高催化剂活性.     

人体尿液中青霉素G代谢物的确认

建立了利用电场轨道阱回旋共振组合质谱仪(LTQ-Orbitrap)检测人体尿样中青霉素G及其代谢产物的分析方法。目标化合物分离鉴定选用PLRP-S聚合色谱柱,以含0.1%(体积比)甲酸溶液-乙腈为流动相,梯度洗脱分离后,选用Data-dependent MSn模式进行全扫描分析。尿样中首次检出青霉素甲酰化代谢产物(m/z 381)。青霉素新代谢物的发现对食品安全及法医毒物分析具有重要意义。     

无溶剂体系中固定化脂肪酶Candida sp. 99-125催化合成油酸低碳醇酯

采用固定化脂肪酶Candida sp.99-125在无溶剂体系中催化合成油酸低碳醇酯,考察了加酶量、温度、酸醇摩尔比和醇结构对油酸酯化率的影响。结果表明,加酶量为底物质量的3%,最适温度为20℃,酸与醇摩尔比为1∶1,甲醇对该酶有一定的毒性,由于空间位阻效应,该酶对伯醇具有高选择性,对仲醇、叔醇的选择性低,且对长链脂肪酸催化活性高,对带支链的多元酸、多元醇活性低。该酶重复使用5次,酶活性基本没有降低。与传统的化学法相比,用该酶催化合成酯类化合物的色泽更浅。     

BDIE·[Zn-(O-iPr)2]催化剂的制备及其催化二氧化碳共聚研究

近年来,人们更加关注二氧化碳与氧化环己烯的共聚反应,因为其共聚产物聚碳酸亚环己酯,有比其它类型的脂肪族聚碳酸酯更高的Tg和热分解温度[1].过去的10年间,科研人员研制出多种应用于二氧化碳与氧化环己烯共聚反应的催化剂,主要有二乙基锌助剂、羧酸锌、双金属催化剂(PBM)、稀土类以及高位阻类催化体系等[2].其中Coates等[3]在1998年报道的β二亚胺合锌型化合物进行二氧化碳与氧化环己烯共聚,其催化效率高达6.92×104gpolymer molcat.此后,催化剂的研究更多集中在高位阻二亚胺锌体系和SalenCr体系上.不断有文章报道其它的β二亚胺合锌高…     

Highly stable phospholipid unilamellar vesicles from spontaneous vesiculation: A DLS and SANS study

Spontaneously formed unilamellar vesicles (ULV) composed of short- and long-chain phospholipids, dihexanoyl phosphorylcholine (DHPC) and dimyristoyl phosphorylcholine (DMPC), respectively, were doped with a negatively charged lipid, dimyristoyl phosphorylglycerol (DMPG), and studied with small-angle neutron scattering (SANS) and dynamic light scattering (DLS). Upon dilution, the spontaneous formation of vesicles was found to take place from bilayered micelles, or so-called "bicelles". SANS and DLS data show that ULV with narrow size distributions are highly stable at low lipid (C(lp) < 0.50 wt %) and NaCl salt (C(s)) concentrations. ULV size was found to be independent of both C(lp) and C(s) when they were below 0.33 and 0.5 wt %, respectively. Surface charge and salinity were found to be important factors in preparing ULV of a certain size. This observation is not in complete agreement with previous experimental results and cannot be completely explained with current theoretical predictions based on equilibrium calculations for catanionic surfactant mixtures. ULV size is found to be invariant over a wide range of temperatures, both below and above the phase-transition temperature, T(M), of DMPC, and was stable for periods of weeks and months, even after sonication.     

Synthesis of Macroporous PMMA/Silica Nanocomposite Monoliths in Supercritical Carbon Dioxide

Summary: Macroporous monoliths consisting of silica nanoparticles embedded in poly(methyl methacrylate) (PMMA) were synthesized in supercritical CO₂. Well‐dispersed silica particles, pretreated with functional 3‐(trimethoxysilyl)propyl methacrylate (MPS), were to form colloidal PMMA nanocomposites followed by a sol‐gel transition forming interconnected structures resulting in micron‐sized pores with specific areas between 1 and 7 m² · g⁻¹. SEM and TEM results revealed uniform morphological characteristics of the composite materials and good dispersions of the silica nanoparticles.

SEM micrograph of PMMA/Silica nanocomposites forming interconnected macroporous monolith. The average size of the silica particles is 50 nm.     

Numerical study on Moore-Penrose inverse of tensors via Einstein product

Numerical Algorithms - The notation of Moore-Penrose inverse of matrices has been extended from matrix space to even-order tensor space with Einstein product. In this paper, we give the numerical...