排序方式: 共有63条查询结果,搜索用时 15 毫秒
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Liu H Yang S Balteanu I Balaj OP Fox-Beyer BS Beyer MK Bondybey VE 《Rapid communications in mass spectrometry : RCM》2004,18(13):1479-1481
A route to efficient generation of C6H4+*, potentially the benzyne radical cation, is presented. Laser vaporization of Mg+* and supersonic expansion in helium doped with o-, m-, or p-C6H4F2 yields, among other ions, o-, m-, p-C6H4F2Mg+* complexes, but no C6H4+*. Collision-induced dissociation experiments show that the o-C6H4F2Mg+* complex can be converted into C6H4+* in a mildly energetic collision, with a center-of-mass energy around 1-2 eV. These conditions can also be reached in the ion source when argon is used as a carrier gas. In this way, mass spectra containing the desired m/z 76 peak, i.e. C6H4+*, are obtained. 相似文献
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David Semrouni O. Petru Balaj Florent Calvo Catarina F. Correia Carine Clavaguéra Gilles Ohanessian 《Journal of the American Society for Mass Spectrometry》2010,21(5):728-738
The structure of the sodiated peptide GGGGGGGG-Na+ or G8-Na+ was investigated by infrared multiple photon dissociation (IRMPD) spectroscopy and a combination of theoretical methods.
IRMPD was carried out in both the fingerprint and N—H/O—H stretching regions. Modeling used the polarizable force field AMOEBA
in conjunction with the replica-exchange molecular dynamics (REMD) method, allowing an efficient exploration of the potential
energy surface. Geometries and energetics were further refined at B3LYP-D and MP2 quantum chemical levels. The IRMPD spectra
indicate that there is no free C-terminus OH and that several N—Hs are free of hydrogen bonding, while several others are
bound, however not very strongly. The structure must then be either of the charge solvation (CS) type with a hydrogen-bound
acidic OH, or a salt bridge (SB). Extensive REMD searches generated several low-energy structures of both types. The most
stable structures of each type are computed to be very close in energy. The computed energy barrier separating these structures
is small enough that G8-Na+ is likely fluxional with easy proton transfer between the two peptide termini. There is, however, good agreement between
experiment and computations in the entire spectral range for the CS isomer only, which thus appears to be the most likely
structure of G8-Na+ at room temperature. 相似文献
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浅海移动船只的宽带辐射声场在距离-频率上通常表现为有规则的干涉条纹结构,这些条纹的特性(数目和斜率)可用波导不变量理论来表征并已被用于多种水声反演问题中,如沉积层声学参数反演和宽带声源距离的估计。基于波导不变量理论和干涉条纹的结构特性,利用扩展卡尔曼滤波器分析移动船只LOFAR图中干涉条纹的距离-频率特征可对其距离进行连续估计。该方法不需要海洋环境的信息和前向拷贝声场计算,具有较高的计算效率。海试数据处理结果和GPS数据计算结果比较一致,证实了本方法的准确性。试验数据处理同样证实该方法对初始距离的选择有着较高的稳健性。 相似文献
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针对矢量水听器测向的应用要求,研究了三维水声传播问题中水平折射对声矢量场特性的影响。理论分析表明,水平折射可使质点水平位移从线性极化转变为椭圆极化,同时引起声能流方向的水平偏转。声能流方向的水平偏转导致波达方向偏离目标水平方位,对目标水平方位估计造成误差。采用虚源法仿真了倾角为2.86°的楔形波导中的三维声矢量场,并给出了空间各点处由水平折射引起的单矢量水听器目标方位估计误差。结果显示,部分区域中由水平折射引起的目标方位估计误差可达10°以上。 相似文献
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在海洋声学中,三维抛物方程模型可以有效考虑三维空间的声传播效应。然而,采用三维抛物方程模型分析三维空间内的声传播问题时,计算时间较长,并且需要消耗较大的计算机内存,因此给远距离声场的快速精确计算带来了很大困难。为此,将非均匀网格Galerkin离散化方法用于三维直角坐标系下的水声抛物方程模型中,深度算子和水平算子Galerkin离散方式由均匀网格变为非均匀网格。仿真结果表明,三维直角坐标系下非均匀网格离散的抛物方程模型,在保持计算精度、提高计算速度的同时,可以实现远距离声场的快速预报。另外,针对远距离局部海底地形与距离有关的三维声传播问题,给出了声场快速计算方法;在海底保持水平的区域,采用经典Kraken模型,重构抛物方程算法的初始场,随后依次递推求解地形与距离有关海底下的三维声场。采用改进模型,证明了远距离楔形波导声强增强效应。 相似文献
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Mircea Balaj 《Applied Mathematics Letters》2010,23(3):241-245
In this paper, using the Brouwer fixed point theorem, we establish a common fixed point theorem for a family of set-valued mappings. As applications of this result we obtain existence theorems for the solutions of two types of vector equilibrium problems, a Ky Fan-type minimax inequality and a generalization of a known result due to Iohvidov. 相似文献
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