钯催化卤代芳烃的胺化反应的研究进展

钯催化卤代芳烃的胺化是合成芳胺化合物的重要方法,综述了近年来钯催化卤代芳烃与胺等不同含氮化合物的胺化反应研究进展,重点讨论了钯催化剂配体的结构、反应物比例、溶剂及温度等因素对反应的影响.     

Ge掺杂n型Sn基Ⅷ型单晶笼合物的制备及热电传输特性

采用Sn自熔剂法制备了具有n型传导的Ⅷ型Ba₈Ga_16-xGe_xSn₃₀ （0 ≤ x ≤ 1.0）单晶笼合物,并对其结构和热电特性进行研究. 研究结果表明：Ge在单晶中的实际含量较少,随着掺杂量的增加样品的晶格常数略有减小,Ge掺杂后样品的载流子浓度较掺杂前低,迁移率增加;所有样品的Seebeck系数均为负值,且绝对值较未掺杂样品低,但Ge掺杂后样品的电导率提高了62%;x=0.5的样品在500 K附近取得最大ZT值1.25. 关键词： Ⅷ型笼合物 n型传导 热电性能     

Online assessment of students’ reasoning when solving example-eliciting tasks: using conjunction and disjunction to increase the power of examples

ZDM – Mathematics Education - We argue that examples can do more than serve the purpose of illustrating the truth of an existential statement or disconfirming the truth of a universal...     

Identification of G‐nerve agents at picogram levels from complex organic samples containing hydrocarbon interferences by aqueous extraction,followed by derivatization and liquid chromatography‐mass spectrometry analysis

The chromatograms obtained from the gas chromatography‐electron ionization mass spectrometric (GC‐EI‐MS) analysis of extracts containing G‐nerve agents in the presence of diesel, gasoline, etc., are dominated by hydrocarbon backgrounds that “mask” the G‐nerve agents, leading to severe difficulties in identification. This paper presents a practical solution for this challenge by transferring the G‐nerve agents from the organic phase into the aqueous phase using liquid‐liquid extraction (LLE), followed by derivatization with 2‐[(dimethylamino)methyl]phenol (2‐DMAMP), allowing ultrasensitive LC‐ESI‐MS/MS analysis of the G‐derivatives. The proposed approach enables rapid identification of trace amounts of G‐nerve agents with limits of identification (LOIs) at the pg/mL scale.     

Cluster chemical ionization and deuterium exchange mass spectrometry in supersonic molecular Beams

A cluster-based chemical ionization method has been developed that produces protonated molecular ions from molecules introduced through a supersonic molecular beam interface. Mixed clusters of the analyte and a clustering agent (water or methanol) are produced in the expansion region of the beam, and are subsequently ionized by “fly through” electron impact (EI) ionization, which results in a mass spectrum that is a combination of protonated molecular ion peaks together with the conventional EI fragmentation pattern. The technique is presented and discussed as a tool complementary to electron impact ionization in supersonic molecular beams. Surface-induced dissociation on a rhenium oxide surface is also applied to simplify the mass spectra of clusters and reveal the analyte spectrum. The high gas flow rates involved with the supersonic molecular beam interface that enable the easy introduction of the clustering agents also have been used to introduce deuterating agents. An easy-to-use, fast, and routine on-line deuterium exchange method was developed to exchange active hydrogens (NH, OH). This method, combined with electron impact ionization, is demonstrated and discussed in terms of the unique information available through the EI fragmentation patterns, its ability to help in isomer identification, and possible applications with fast gas chromatography-mass spectrometry in supersonic molecular beams.     

Symmetrical gas-phase dissociation of noncovalent protein complexes via surface collisions

Previous gas-phase dissociation experiments of protein-protein complexes have resulted in product ion distributions that are asymmetric by charge and mass, providing limited insight into the chemical nature of subunit organization and interaction. In these experiments, a symmetric charge distribution results from an "energy sudden" collision of protein-protein complexes with a surface, indicating that it may be possible to probe the suboligomeric structure of noncovalent complexes in the gas phase. It is proposed that energy sudden surface activation of cytochrome C homodimers results in dissociation without significant unfolding of one of the monomeric subunits. Previously proposed mechanisms for the dissociation of protein-protein complexes are discussed in the context of these results. These experiments demonstrate the potential to preserve the structural details of subunit interaction within a protein-protein complex and help elucidate the asymmetric nature of macromolecular dissociation in the gas phase.     

Enumerating traceless matrices over compact discrete valuation rings

We show that the non-separable Banach space SL∞ is primary. This is achieved by directly solving the infinite-dimensional factorization problem in SL∞. In particular, we bypass Bourgain’s localization method.     

Experimental study of the dynamics of magneto-rheological fluid droplet impact

The kinematics of a magneto-rheological fluid droplet impact on a smooth surface, subjected to external magnetic field, was studied theoretically and experimentally. A time-dependent one-dimensional model of the impact, as typified by the droplet top center point height kinematics is developed. A series of experiments were conducted in order to validate the theoretical model. The shape changes generated during the impact process were recorded using a digital high-speed camera. Our novel kinematical model based on a variable damping function shows very good agreement with the experimental data for a wide range of Mason and Reynolds numbers.