唐家山堰塞湖泄洪问题的研究

研究的是唐家山地震次生灾害引发的堰塞湖问题.首先对数字高程地图进行等高图像分析求解了堰塞湖不同高程水位对应的湖区面积,建立了蓄水量体积与堰塞湖水位高程的离散化模型,然后建立了神经网络模型和多元线性回归模型研究了北川降雨量与堰塞湖入库流量的关系,继而求解得到不同降雨量下每日堰塞湖水位高程.在研究泄洪过程时,首先通过对泄洪过程和溃坝过程内在机理的研究分别建立了正交多项式逼近模型和仿真模型得到溃坝时的溃口流量随时间变化的关系,继而分析求解得到溃坝时其他参数随时间变化的关系.针对淹没区的问题,综合数字高程地图和行政区域地图,利用数字地图计算了洪水到达各被淹没区域的时间,淹没范围,以便于确定撤离方案.     

HCN及其氢加成物分子间氢键问题的量子化学研究

采用量子化学(MNDO、CNDO/2)方法,探讨了HCN、H_2CNH和H_3CNH_2分子间的N…H-C氢键的构成。计算表明:HCN-HCN分子间氢键作用较强,支持了实验结果。HCN及其氢加成物H_2CNH、H_3CNH_2等分子间的氢键作用依次减弱,其随C≡N、C=N、C-N的差异而变化,碳氮链中氮原子的作用是构成N…H-C型氢键的一个决定性因素。     

Self-assembled highly ordered ethane-bridged periodic mesoporous organosilica and its application in HPLC

Monodisperse spherical periodic mesoporous organosilicas (PMOs) with ethane integrated in the framework were synthesized and their application as stationary phase for chromatographic separation is demonstrated. The ethane-PMOs were prepared by condensation of 1,2-bis(triethoxysilyl)ethane (BTSE) in basic condition using octadecyltrimethylammonium chloride (C(18)TMACl) as template and ethanol as co-solvent. The morphology and mesoporous structure of ethane-PMOs were controlled under different concentrations of sodium hydroxide (NaOH) and EtOH. The results of scanning electron microscopy (SEM), transmission electron microscopy (TEM), powder X-ray diffraction (XRD), nitrogen sorption measurement, Fourier transform infrared spectroscopy (FT-IR) and elemental analysis showed that ethane-PMOs have spherical morphology, uniform particle distribution, highly ordered pore structure, high surface area and narrow pore-size distribution. The column packed with these materials exhibits good permeability, high chemical stability and good selectivity of mixtures of aromatic hydrocarbons in normal phase high-performance liquid chromatography (HPLC).     

正电子湮没参量及其所反映物质信息的探讨

本根据正电子在凝聚态物质中的湮没机制及捕获模型,讨论了正电子湮没参量——正电子寿命谱和多普勒线形等参量所反映的物质信息,给出了各正电子湮没参量与所反映的物质信息之间的定量关系。分析了在该体系中正电子寿命参量与局域电子密度、多普勒线形参量和角关联参量与电子动量密度分布和费米面之关联。     

用手性配体改性铝锂试剂对芳香酮的还原

用手性一元酮作辅助配体,与１,２,５,６－二丙酮甘ｉＡｌｈ５对芳香酮进行对映选择 的,得到光学活性产物８个。通过与α－乙酰氧基－Ｌ－丙酰氯生成非对映异构体酯,经气相色谱分析,芳酮挑学产率为２３．３￣７１．２％。初步探讨了配体之间对称性匹配的情况。     

A Novel Approach to Synthesis of Tricyclic Diterpenoid

A novel approach has been found and the first total synthesis of (±)-Salvirecognine was accomplished by using it. In which intramolecular cyclization and Friedel-Crafts alkylation took place simultaneously to afford key intermediates for synthesis of aromatic tricyclic diterpenoids OMe PPA O O O OMe 1 2 Scheme 1 As shown in Scheme 1 intramolecular cyclization and Friedel-Crafts alkylation took place simultaneously when compound 1 was treated by PPA at 125 ℃. In which the i-pr…     

New insight into melting and crystallization behavior in semicrystalline poly(ethylene terephthalate)

After isothermal crystallization, poly(ethylene terephthalate) (PET) showed double endothermic behavior in the differential scanning calorimetry (DSC) heating scan. During the heating scans of semicrystalline PET, a metastable melt which comes from melting thinner lamellar crystal populations formed between the low and the upper endothermic temperatures. The metastable melt can recrystallize immediately just above the low melting temperature and form thicker lamellae than the original ones. The thickness and perfection depends on the crystallization time and crystallization temperature. The crystallization kinetics of this metastable melt can be determined by means of DSC. The kinetics analysis showed that the isothermal crystallization of the metastable PET melt proceeds with an Avrami exponent of n = 1.0 ∼ 1.2, probably reflecting one‐dimensional or irregular line growth of the crystal occurring between the existing main lamellae with heterogeneous nucleation. This is in agreement with the hypothesis that the melting peaks are associated with two distinct crystal populations with different thicknesses. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 53–60, 2000     

Backbonding contributions to small molecule chemisorption in a metal–organic framework with open copper(i) centers

Metal–organic frameworks are promising materials for applications such as gas capture, separation, and storage, due to their ability to selectively adsorb small molecules. The metal–organic framework Cu^I-MFU-4l, which contains coordinatively unsaturated copper(i) centers, can engage in backbonding interactions with various small molecule guests, motivating the design of frameworks that engage in backbonding and other electronic interactions for highly efficient and selective adsorption. Here, we examine several gases expected to bind to the open copper(i) sites in Cu^I-MFU-4l via different electronic interactions, including σ-donation, π-backbonding, and formal electron transfer. We show that in situ Cu L-edge near edge X-ray absorption fine structure (NEXAFS) spectroscopy can elucidate π-backbonding by directly probing excitations to unoccupied backbonding orbitals with Cu d-character, even for gases that participate in other dominant interactions, such as ligand-to-metal σ-donation. First-principles calculations based on density functional theory and time-dependent density functional theory additionally reveal the backbonding molecular orbitals associated with these spectroscopic transitions. The energies of the transitions correlate with the energy levels of the isolated small molecule adsorbates, and the transition intensities are proportional to the binding energies of the guest molecules within Cu^I-MFU-4l. By elucidating the molecular and electronic structure origins of backbonding interactions between electron rich metal centers in metal–organic frameworks and small molecule guests, it is possible to develop guidelines for further molecular-level design of solid-state adsorbents for energy-efficient separations of relevance to industry.

In situ near edge X-ray absorption fine structure spectroscopy directly probes unoccupied states associated with backbonding interactions between the open metal site in a metal–organic framework and various small molecule guests.     

Engineered Bifunctional Luminescent Pillared-Layer Frameworks for Adsorption of CO2 and Sensitive Detection of Nitrobenzene in Aqueous Media

Through a dual-ligand synthetic approach, five isoreticular primitive cubic (pcu)-type pillared-layer metal–organic frameworks (MOFs), [Zn₂(dicarboxylate)₂(NI-bpy-44)] ⋅ x DMF ⋅ y H₂O, in which dicarboxylate=1,4-bdc ( 1 ), Br-1,4-bdc ( 2 ), NH₂-1,4-bdc ( 3 ), 2,6-ndc ( 4 ), and bpdc ( 5 ), have been engineered. MOFs 1 – 5 feature twofold degrees of interpenetration and have open pores of 27.0, 33.6, 36.8, 52.5, and 62.1 %, respectively. Nitrogen adsorption isotherms of activated MOFs 1′ – 5′ at 77 K all displayed type I adsorption behavior, suggesting their microporous nature. Although 1′ and 3′ – 5′ exhibited type I adsorption isotherms of CO₂ at 195 K, MOF 2′ showed a two-step gate-opening sorption isotherm of CO₂. Furthermore, MOF 3′ also had a significant influence of amine functions on CO₂ uptake at high temperature due to the CO₂–framework interactions. MOFs 1 – 5 revealed solvent-dependent fluorescence properties; their strong blue-light emissions in aqueous suspensions were efficiently quenched by trace amounts of nitrobenzene (NB), with limits of detection of 4.54, 5.73, 1.88, 2.30, and 2.26 μm , respectively, and Stern–Volmer quenching constants (K_sv) of 2.93×10³, 1.79×10³, 3.78×10³, 4.04×10³, and 3.21×10³ m ⁻¹, respectively. Of particular note, the NB-included framework, NB@ 3 , provided direct evidence of the binding sites, which showed strong host–guest π–π and hydrogen-bonding interactions beneficial for donor–acceptor electron transfer and resulting in fluorescence quenching.     

Isomaltulose Exhibits Prebiotic Activity,and Modulates Gut Microbiota,the Production of Short Chain Fatty Acids,and Secondary Bile Acids in Rats

In vitro experiments have indicated prebiotic activity of isomaltulose, which stimulates the growth of probiotics and the production of short chain fatty acids (SCFAs). However, the absence of in vivo trials undermines these results. This study aims to investigate the effect of isomaltulose on composition and functionality of gut microbiota in rats. Twelve Sprague–Dawley rats were divided into two groups: the IsoMTL group was given free access to water containing 10% isomaltulose (w/w), and the control group was treated with normal water for five weeks. Moreover, 16S rRNA sequencing showed that ingestion of isomaltulose increased the abundances of beneficial microbiota, such as Faecalibacterium and Phascolarctobacterium, and decreased levels of pathogens, including Shuttleworthia. Bacterial functional prediction showed that isomaltulose affected gut microbial functionalities, including secondary bile acid biosynthesis. Targeted metabolomics demonstrated that isomaltulose supplementation enhanced cholic acid concentration, and reduced levels of lithocholic acid, deoxycholic acid, dehydrocholic acid, and hyodeoxycholic acid. Moreover, the concentrations of propionate and butyrate were elevated in the rats administered with isomaltulose. This work suggests that isomaltulose modulates gut microbiota and the production of SCFAs and secondary bile acids in rats, which provides a scientific basis on the use of isomaltulose as a prebiotic.