Comparison of CID spectra of singly charged polypeptide antibiotic precursor ions obtained by positive-ion vacuum MALDI IT/RTOF and TOF/RTOF, AP-MALDI-IT and ESI-IT mass spectrometry

Various classes of polypeptide antibiotics, including blocked linear peptides (gramicidin D), side-chain-cyclized peptides (bacitracin, viomycin, capreomycin), side-chain-cyclized depsipeptides (virginiamycin S), real cyclic peptides (tyrocidin, gramcidin S) and side-chain-cyclized lipopeptides (polymyxin B and E, amfomycin), were investigated by low-energy collision induced dissociation (LE-CID) as well as high-energy CID (HE-CID). Ion trap (IT) based instruments with different desorption/ionization techniques such as electrospray ionization (ESI), atmospheric pressure matrix-assisted laser desorption/ionization (AP-MALDI) and vacuum MALDI (vMALDI) as well as a vMALDI-time-of-flight (TOF)/curved field-reflectron instrument fitted with a gas collision cell were used. For optimum comparability of data from different IT instruments, the CID conditions were standardized and only singly charged precursor ions were considered. Additionally, HE-CID data obtained from the TOF-based instrument were acquired and compared with LE-CID data from ITs. Major differences between trap-based and TOF-based CID data are that the latter data set lacks abundant additional loss of small neutrals (e.g. ammonia, water) but contains product ions down to the immonium-ion-type region, thereby allowing the detection of even single amino-acid (even unusual amino acids) substitutions. For several polypeptide antibiotics, mass spectrometric as well as tandem mass spectrometric data are shown and discussed for the first time, and some yet undescribed minor components are also reported. De novo sequencing of unusually linked minor components of (e.g. cyclic) polypeptides is practically impossible without knowledge of the exact structure and fragmentation behavior of the major components. Finally, the described standardized CID condition constitutes a basic prerequisite for creating a searchable, annotated MS(n)-database of bioactive compounds. The applied desorption/ionization techniques showed no significant influence on the type of product ions (neglecting relative abundances of product ions formed) observed, and therefore the type of analyzer connected with the CID process mainly determines the type of fragment ions.     

Formation and Characterisation of the Silver Hydride Nanocluster Cation [Ag3H2((Ph2P)2CH2)]+ and Its Release of Hydrogen

Multistage mass spectrometry and density functional theory (DFT) were used to characterise the small silver hydride nanocluster, [Ag₃H₂L]⁺ (where L=(Ph₂P)₂CH₂) and its gas‐phase unimolecular chemistry. Collision‐induced dissociation (CID) yields [Ag₂HL]⁺ as the major product while laser‐induced dissociation (LID) proceeds via H₂ formation and subsequent release from [Ag₃H₂L]⁺, giving rise to [Ag₃L]⁺ as the major product. Deuterium labelling studies on [Ag₃D₂L]⁺ prove that the source of H₂ is from the hydrides and not from the ligand. Comparison of TD‐DFT absorption patterns obtained for the optimised structures with action spectroscopy results, allows assignment of the measured features to structures of precursors and products. Molecular dynamics “on the fly” reveal that AgH loss is favoured in the ground state, but H₂ formation and loss is preferred in the first excited state S₁, in agreement with CID and LID experimental findings. This indicates favourable photo‐induced formation of H₂ and subsequent release from [Ag₃H₂L]⁺, an important finding in context of metal hydrides as a hydrogen storage medium, which can subsequently be released by heating or irradiation with light.     

有序多级孔N/Nd/TiO_2的制备及其在可见光下催化降解甲基橙的性能

以聚苯乙烯为胶晶模板,采用溶胶-凝胶法制备了有序多级孔N/Nd/TiO_2(1),其结构和形貌经SEM,XRD,XPS和N2吸附-脱附表征。研究了1在可见光下催化降解甲基橙的性能。结果表明:1为有序大孔/介孔多级结构,大孔孔道/介孔孔窗呈相互通透三维有序结构,大孔孔道内径约230 nm,介孔孔窗约30 nm,比表面积为125.50 m~2·g~(-1),比孔容为1.124 5 cm~3·g~(-1)。1催化甲基橙的脱色率为42.76%。     

四级涡轮多叶片排三元N-S解网络并行计算

在科学与工程计算国家重点实验室SGI工作站网络上，基于PVM并行软件平台，发展了多叶片三元N-S解并行计算程序，对一四级动力涡轮内部流场进行了计算和初步分析．     

稻杆的热溶剂提质及多级分离

采用1-甲基萘(1-MN)为溶剂,在不同温度下(250、300、350 ℃)对稻秆进行热溶剂提质及多级分离,获得3种主要固体产物:低分子量萃取物(soluble)、高分子量萃取物(deposit)和萃取残渣(residue),以及少量气体产物和液体产物。对各组分的元素组成、化学结构、物理化学特性等进行了详细分析,并采用ICP-MS测定了其碱金属和碱土金属(AAEM)含量。结果发现,低分子量萃取物收率随着温度的升高而增大,350 ℃时碳基收率达到33.48%。3种固体产物的碳含量和氧含量随着温度的升高而分别升高和降低,350 ℃时soluble、deposit的碳含量分别高达82.36%、80.59%,氧含量分别低至9.50%、12.03%,稻杆原样中高达86.99%的氧以H₂O或CO₂的形式释放。soluble几乎无灰,deposit的灰含量也低于1.50%。3种固体产物的高位发热量显著高于稻杆原样。FT-IR结果表明,稻杆热溶剂处理过程中除发生了脱水反应、脱羧基反应外,还有明显的芳香化反应。soluble和deposit的Na、Mg和K含量极低,而且随温度的升高其含量逐渐降低。总之,热溶剂提质及多级分离法实现了温和条件下的生物质脱水脱氧提质,并获得低灰低氧含量、高碳含量和发热量的多种产物,此方法有较好的应用前景。     

Multi-period stochastic portfolio optimization: Block-separable decomposition

We consider a multiperiod stochastic programming recourse model for stock portfolio optimization. The presence of various risk and policy constraints leads to significant period-by-period linkage in the model. Furthermore, the dimensionality of the model is large due to many securities under consideration. We propose exploiting block separable recourse structure as well as methods of inducing such structure within nested L-shaped decomposition. We test the model and solution methodology with a base consisting of the Standard & Poor 100 stocks and experiment with several variants of the block separable technique. These are then compared to the standard nested period-by-period decomposition algorithm. It turns out that for financial optimization models of the kind that are discussed in this paper, significant computational efficiencies can be gained with the proposed methodology.     

Multiple-Subarc Gradient-Restoration Algorithm, Part 2: Application to a Multistage Launch Vehicle Design

In Part 1 (see Ref. 2), a multiple-subarc gradient-restoration algorithm (MSGRA) was developed with the intent of enhancing the robustness of gradient-restoration algorithms and also enlarging the field of applications. Indeed, MSGRA can be applied to optimal control problems involving multiple subsystems as well as discontinuities in the state and control variables at the interface between contiguous subsystems.In Part 2 (this paper), MSGRA is applied to compute the optimal trajectory for a multistage launch vehicle design, specifically, a rocket-powered spacecraft ascending from the Earth surface to a low Earth orbit (LEO). Single-stage, double-stage, and triple-stage configurations are considered. For multistage configurations, discontinuities in the mass occur at the interfaces between consecutive stages.The numerical results show that, given the current levels of the engine specific impulse and spacecraft structural factor, the single-stage version is not feasible at this time, while the double-stage and triple-stage versions are feasible. Further increases in the specific impulse and decreases in the structural factor are needed if the single-stage configuration has to become feasible.Also, the numerical results show that the optimal trajectory requires initially maximum thrust, followed by modulated thrust so as to satisfy the maximum acceleration constraint, followed by nearly zero thrust for coasting flight, followed by a final burst with moderate thrust so as to increase the spacecraft velocity to the circular velocity needed for LEO insertion. The above properties of the optimal thrust time history are useful for developing the guidance scheme approximating in real time the optimal trajectory for a launch vehicle design.     

Measuring Risk for Income Streams

A measure of risk is introduced for a sequence of random incomes adapted to some filtration. This measure is formulated as the optimal net present value of a stream of adaptively planned commitments for consumption. The new measure is calculated by solving a stochastic dynamic linear optimization problem which, for finite filtrations, reduces to a deterministic linear programming problem.We analyze properties of the new measure by exploiting the convexity and duality structure of the stochastic dynamic linear problem. The measure depends on the full distribution of the income process (not only on its marginal distributions) as well as on the filtration, which is interpreted as the available information about the future. The features of the new approach are illustrated by a numerical example.     

包米勒PLC在蛇形造波机设计中的关键技术研究

蛇形造波机是一种在海洋工程研究领域中,用于模拟大范围海浪的阵列式实验设备。为了进一步提高大范围海浪模拟的精度,蛇形造波机同步控制性能的提高具有十分重要的意义。针对包米勒PLC的运动控制技术进行研究,提出了基于其具有多级主从式结构的蛇形造波机同步运动控制系统,实现所有造波单元的严格同步控制。针对上位机和各PLC间数据量大、传输速度慢的问题,采用无损数据压缩和线性数据插值降低数据量,并应用多线程以太网通讯方式提高数据传输速率。另外由于该系统机械结构惯量大和总体负载大的特点,存在启停过程中电机过流问题。为此提出了一种基于余弦函数的拟合算法优化造波机启动和停止过程。在各个性能指标的验证实验中,该系统运行稳定,数据传输速度快,同步性能高,完全满足大范围海浪模拟要求。     

几种4-氨基吡啶衍生物的多级质谱裂解途径

为获得高效的海洋生物毒素河豚毒素(TTX)解毒剂,合成了一系列4-氨基吡啶类衍生物N-二异丙基磷酰化氨基酸-N-4-氨基吡啶;研究了N-二异丙基磷酰化氨基酸-N-4-氨基吡啶的多级质谱(ESI-MS/MS)裂解方式;提出了碎片离子m/z=95的裂解途径,并推测了其重排机理.结果表明,该类化合物具有相同分子量的碎片离子c/c′,是由两种母离子a或b离子裂解得到的.通过在吡啶环上引入氯原子可证实该裂解途径;而碎片离子m/z=95源于离子重排.