粉粒体两相流的电容层析成象测量

粉粒体系统中的固相浓度分布的在线测量是十分困难的问题．电容层析成象技术是一种近年来发展起来的非侵入式快速浓度场测量技术．它不干扰流场，不受流动中颗粒浓度、加速度、不透明等因素的制约．本文讨论其测量原理、应用、近期进展、存在的主要问题及其解决的对策．     

ac Conductivity of mixed spinel NiAl0.7Cr0.7Fe0.6O4

ac Conductivity measurements are carried out across the metal to insulator transition in NiAl_0.7Cr_0.7Fe_0.6O₄. The low frequency data is analyzed using Summerfield scaling theory for hopping conductivity. The exponent of the scaling behavior has significantly different values in the conducting and insulating regimes. The hopping frequency and the zero frequency conductivity are found to increase with temperature, slowly in the metallic regime and rapidly in the insulating regime.     

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Length-dependent DNA separations using multiple end-attached peptide nucleic acid amphiphiles in micellar electrokinetic chromatography

End-labeled free-solution electrophoresis (ELFSE) is an alternative approach to gel-based methods for size-based electrophoretic separation of DNA. In ELFSE, an electrically neutral "drag-tag" is appended to DNA to add significant hydrodynamic drag, thereby breaking its constant charge-to-friction ratio. Current drag-tag architecture relies on covalent attachment of polymers to each DNA molecule. We have recently proposed the use of micellar drag-tags in conjunction with sequence-specific hybridization of peptide nucleic acid amphiphiles (PNAAs). This work investigates the effect of multiple PNAA attachment on DNA resolution using MEKC. Simultaneous PNAA hybridization allows for the separation of long DNA targets, up to 1012 bases, using micellar drag-tags. Each PNAA handle independently interacts with the micellar phase, reducing the overall mobility of this complex relative to individual PNAA binding. The sequence- and size-based dependence of this separation technique is maintained with multiple PNAA binding over a range of DNA sizes. Results are accurately described by ELFSE theory, yielding alpha=54 for single-micelle tagging and alpha=142 for dual-micelle tagging. This method is the first example of a non-covalent drag-tag used to separate DNA of 1000 bases based on both size and sequence.     

Nonadiabatic electron dynamics in the exit channel of Na-molecule optical collisions

We study optical collisions of Na atoms with N(2), CO, C(2)H(2), and CO(2) molecules in a crossed-beam experiment. Excited electronic states of the collision complex are selectively populated during the collision. We measure the relative population of the Na(3p) fine-structure levels after the collision and observe in this way the nonadiabatic transitions occuring in the final phase of the collision process. For the NaCO, NaC(2)H(2), and NaCO(2) systems new ab initio potential surfaces were generated. The theoretical analysis of the nonadiabatic electron dynamics on the excited potential surfaces is made within the classical-path formalism. The results are in good qualitative agreement with the experimental data and provide insight into the nonadiabatic mechanisms prevailing during the evolution in the upper 3p manifold. The differences between the different collisional systems are related to the presence and system-specific locations of conical intersections and avoided crossing seams in the excited potential surfaces.     

Intermolecular potential for Ar+NH3 from differential cross sections

¹H- {¹³C} and ¹H- {¹⁵N} heteronuclear double resonance experiments are used to determine the transition frequencies in the ¹³C and ¹⁵N N.M.R. spectra of isotopically entriched samples of methyl cyanide dissolved in the nematic mesophase of p-ethoxybenzylidene-p-butyl aniline. It is found that σ_∥ - σ_⊥ in the -C ≡ N group has values of 307 and 452 p.p.m. for ¹³C and ¹⁵N respectively, and these are rationalized in terms of Pople's LCAO theory of nuclear shielding.     

Local canted spin behaviour in Co1.4−x Zn x Ge0.4Fe1.2O4 spinels: A macroscopic, mesoscopic and microscopic study

DC magnetization, neutron depolarization and neutron diffraction (with both polarized and unpolarized neutrons) measurements have been reported for the Co_1.1−x Zn _x Ge_0.1Fe_1.2O₁ spinels with x=0.5, 0.6 and 0.7. Neutron depolarization and neutron diffraction measurements confirm the presence of a long range ferrimagnetic ordering of the local canted spins in these ferrite samples. The observed features of low field magnetization have been explained under the framework of thermally activated domain wall movement of ferrimagnetic arrangement of local canted spins. An important role of magnetic anisotropy (due to the presence of Co²⁺ ions) in establishing the magnetic ordering and domain kinetics in these ferrites has been observed.