Control of density fluctuations and electron transport in the reversed-field pinch

Contrary to what has been observed thus far collision-induced light scattering (CILS) can be completely polarized. This exceptional behavior characterizes the very far wing of the binary CILS spectrum by gaseous helium. This conclusion is drawn from an experimental study of the depolarization ratio of He (2) in a much extended, previously unexplored, spectral domain. Our analysis shows that this property, unique thus far, is mainly due to an almost perfect cancellation between polarization and exchange pair polarizability contributions to the depolarized spectrum, taking place at internuclear distances shorter than the atomic diameter.     

Momentum transport from nonlinear mode coupling of magnetic fluctuations

A cause of observed anomalous plasma momentum transport in a reversed-field pinch is determined experimentally. Magnetohydrodynamic theory predicts that nonlinear interactions involving triplets of tearing modes produce internal torques that redistribute momentum. Evidence for the nonlinear torque is acquired by detecting the correlation of momentum redistribution with the mode triplets, with the elimination of one of the modes in the triplet, and with the external driving of one of the modes.     

Liposomal Gd-DTPA: effect of encapsulation on enhancement of hepatoma model by MRI

Liposomes entrapping gadolinium-DTPA (Gd-DTPA) were synthesized from 60 mole percent egg phosphatidylcholine (EPC) and 40 mole percent cholesterol or EPC alone entrapping Gd-DTPA in diameters of 100 and 200 nm. Rats bearing Morris hepatoma in their flanks were imaged by MR pre- and post-contrast with free Gd-DTPA and liposomal Gd-DTPA for up to four hours after IV contrast. Comparison of images after free and liposomal Gd-DTPA showed dramatic differences in tumor and organ enhancement. Liposomal Gd-DTPA enhancement of tumor corresponded more closely to histologically proven vascularized portions of tumor than free Gd-DTPA. Hepatic enhancement was greater with liposomal than free Gd-DTPA and time course of liver, kidney and tumor enhancement was prolonged. The 100-nm EPC Gd-DTPA liposomes caused the greatest enhancement. Gd-DTPA liposomes may be useful as liver and blood pool contrast agents. By varying lipid composition and vesicle size, patterns of enhancement may be selectively modified.     

Qualitative properties of modified equations

Suppose that a consistent one-step numerical method of orderr is applied to a smooth system of ordinary differential equations.Given any integer m 1, the method may be shown to be of orderr + m as an approximation to a certain modified equation. Ifthe method and the system have a particular qualitative propertythen it is important to determine whether the modified equationsinherit this property. In this article, a technique is introducedfor proving that the modified equations inherit qualitativeproperties from the method and the underlying system. The techniqueuses a straightforward contradiction argument applicable toarbitrary one-step methods and does not rely on the detailedstructure of associated power series expansions. Hence the conclusionsapply, but are not restricted, to the case of Runge-Kutte methods.The new approach unifies and extends results of this type thathave been derived by other means: results are presented forintegral preservation, reversibility, inheritance of fixed points.Hamiltonian problems and volume preservation. The techniquealso applies when the system has an integral that the methodpreserves not exactly, but to order greater than r. Finally,a negative result is obtained by considering a gradient systemand gradient numerical method possessing a global property thatis not shared by the associated modified equations.     

Topological analysis of the charge density response of a Ni4 cluster to a probe H2 molecule

Local density self-consistent field (SCF) discrete variationalX calculations are performed on a Ni₄ tetrahedron interacting with a probe H₂ molecule in special geometries. Optimized basis functions generated from the spherically averaged SCF potential are used. Topological charge-density analyses and binding energy calculations are used to study a portion of the energy surface for the approach of the H₂ molecule toward the Ni₄ tetrahedron. The effect of the H₂ molecule on Ni-Ni, Ni-H bonds and changes in the H-H covalent bond are investigated with the help of the field and various data at its critical points. The qualitative relationship between these data and the calculated binding energies is exploited.