Electrospray ionization tandem mass spectrometry in high-throughput screening of homogeneous catalysts

The frontispiece shows an illustration by John Tenniel and an excerpt from the 1865 edition of Lewis Carroll's "Alice in Wonderland". Because everything in Wonderland runs counter to logic, the Queen of Hearts declares in Alice's trial "Sentence first-verdict afterwards". High-throughput screening of catalysts, as it is conventionally practiced, does "Synthesis first-screening afterwards" which, as is argued in this review, also backwards. Given the particular constraints present in organometallic complexes, it is more efficient to develop a selective synthesis only when it has already been determined that a structure is likely to be better. The consequence is that screening methods must be able to handle ill-defined mixtures. Electrospray ionization tandem mass spectrometry is presented as a technical solution to this problem.     

高能强子–强子碰撞中喷注性质的蒙特卡洛研究

在喷注“圆锥判定法”的基础上,对高能强子–强子碰撞中产生的喷注(微喷注)的性质进行了蒙特卡洛研究.采用以喷注动量为z轴的“喷注坐标系”,给出了表征喷注性质的各物理量在新坐标系中的分布情况.结果表明,圆锥判定法能够作为一种有效手段来对高能强子–强子碰撞和相对论重离子碰撞中发生的硬和半硬过程开展实验研究.由有喷注事件和无喷注事件的多重数分布可以看到,E_t=2GeV是用圆锥法确定喷注的合理的横能截断值.     

NMR of Colossal Magnetoresistive Manganites and Expanded Lattice Intermetallics at High Pressure

A survey is given of NMR studies of colossal magnetoresistive manganese perovskites (RE,Ca,Sr,Ba)MnO₃ (RE = rare earth) and the interstitially modified permanent magnet materials, RE₂Fe₁₇A _x (A = N,C,H) at ambient pressure and at applied pressures of up to 10 kbar. The different pressure behavior of the Mn hyperfine field found in the metallic and in the insulating manganite compounds is discussed and related to the micro- and macroscopic properties of these magnetically inhomogeneous materials. In the RE₂Fe₁₇A _x compounds a different pressure behavior of the hyperfine field at the RE sites with different number and type of interstitial atom neighbors is discussed in terms of local compressibility. The influence of the interstitial modification and the applied pressure on the RE hyperfine field and quadrupole splitting is analyzed and the impact of the chemical pressure and covalent effects on these quantities is compared. A comparison of the behavior of the magnetic state of the 4f electron shell with pressure and with interstitial modification is made and the relation to the magnetocrystalline anisotropy is discussed.     

High-field high-speed MAS resolution enhancement in 1H NMR spectroscopy of solids

Resolution in ¹H NMR spectra of solids can be significantly enhanced with fast magic-angle spinning and high magnetic fields. A variable field and spinning speed study up to 25 T and 40 kHz shows that the homogeneous line broadening is inversely proportional to the product of magnetic field strength and spinning speed. The combination of high field and fast speed yields a ¹H linewidth approaching the intrinsic limit determined by anisotropy of magnetic susceptibility. An analysis of the anisotropic magnetic susceptibility line broadening is presented.     

Porosity of ill-posed problems

We prove that in several classes of optimization problems, including the setting of smooth variational principles, the complement of the set of well-posed problems is -porous.

     

Higher-Order Corrections to the Effective Gravitational Action from Noether Symmetry Approach

Higher-order corrections of the Einstein–Hilbert action of general relativity can be recovered by imposing the existence of a Noether symmetry to a class of theories of gravity where the Ricci scalar R and its d'Alembertian R are present. In several cases, it is possible to get exact cosmological solutions or, at least, to simplify the dynamics by recovering constants of motion. The main result is that a Noether vector seems to rule the presence of higher-order corrections of gravity.