The 3C/3D line ratio in Ni XIX: New Ab Initio theory and experimental results

We report a fully relativistic close-coupling calculation of the electron impact excitation of Ni xix to derive the 3C/3D line intensity ratio, with an uncertainty of 5%. Convergence of the calculation with respect to both channel coupling effects and the many interacting Rydberg series of resonances has been achieved. New measurements in an electron beam ion trap agree with our calculation. We show that the 3C/3D x-ray line ratio depends sensitively on both electron energy and beamwidth in an optically thin plasma. Accounting for this dependence improves the accuracy of the Ni abundance determination in astrophysical sources.     

Electronic assignment as 1 A′(ππ*)-1 A′ of the 2980 Å system of 2-aminopyridine by rotational band contour analysis

In 2-aminopyridine the electronic origin band of the 2980 å electronic system, the longest wavelength system which has been observed, is shown to be a type B-type A hybrid band containing 55 ± 10 per cent of type A character. It follows that the electronic transition is ¹ A′-¹ A′ which implies a π*-π and not a π*-n electron promotion.

The degree of type A character is interpreted as indicating a swing of the transition moment by 10 ± 10° from the b axis of pyridine (the in-plane axis perpendicular to C ₂). Since it is expected that the first π*-π transition in pyridine has its transition moment polarized along the b axis the amino-group does not seem to perturb the pyridine transition strongly in this respect.

The changes of rotational constants from the ground to the excited state in 2-aminopyridine are very similar to those in aniline and probably reflect similar changes in geometry, namely a substantial contraction of the C-NH₂ bond, an opening of the internal ring angle adjacent to the substituent and a benzene-like expansion of the ring.

The origin of the 0-0 band is at 33471·1 ± 0·1 cm^-1.     

An extension of Willard’s Finite Basis Theorem: Congruence meet-semidistributive varieties of finite critical depth

Ross Willard proved that every congruence meet-semidistributive variety of algebras that has a finite residual bound and a finite signature can be axiomatized by some finite set of equations. We offer here a simplification of Willards proof, avoiding its use of Ramseys Theorem. This simplification also extends Willards theorem by replacing the finite residual bound with a weaker condition.In Celebration of the Sixtieth Birthday of Ralph N. McKenzieReceived February 26, 2004; accepted in final form August 2, 2004.     

Colloidal interactions and transport in nematic liquid crystals

We describe a new nematic liquid-crystal colloid system which is characterized by both charge stabilization of the particles and an interaction force. We estimate the effective charge of the particles by electrophoretic measurements and find that in such systems the director anchoring energy W is very low and the particles have little director distortion around them. The interaction force is created by producing a radial distribution of the nematic order parameter around a locally isotropic region created by ir laser heating. We theoretically describe this as being due to the induced flexoelectric polarization, the quadrupolar symmetry of which provides the required long-range force acting on charged particles.     

Bi2223带材临界电流沿长度方向的统计分布

本文采用四引线法测量了Bi2223带材临界电流沿长度方向的分布,采用正态分布、对数正态分布、威布尔分布和最小极值分布对临界电流分布进行了拟合检验,确定了临界电流的最优统计分布模型.     

Coding and enumeration of trees that can be laid upon a hexagon lattice

A tree that can be superimposed upon a hexagon lattice is called a hexagon lattice tree. A method for mechanically coding, enumerating and drawing these objects is described, and has been tested for trees with up to ten vertices. For storage and information transmission, the code uses an expanded version of theN-tuple code in which edge vector elements having one of four possible values are inserted. For establishing uniqueness, it is used in combination with a hexagon lattice reference grid whose vertices are numbered sequentially in the tightest possible outward spiral. Published rules for the derivation ofN-tuple codes by hand are commented on, and a small error pointed out.     

Gd‐DTPA‐Dopamine‐Bisphytanyl Amphiphile: Synthesis,Characterisation and Relaxation Parameters of the Nanoassemblies and Their Potential as MRI Contrast Agents

Here, a new amphiphilic magnetic resonance imaging (MRI) contrast agent, a Gd^III‐chelated diethylenetriaminepentaacetic acid conjugated to two branched alkyl chains via a dopamine spacer, Gd‐DTPA‐dopamine‐bisphytanyl (Gd‐DTPA‐Dop‐Phy), which is readily capable of self‐assembling into liposomal nanoassemblies upon dispersion in an aqueous solution, is reported. In vitro relaxivities of the dispersions were found to be much higher than Magnevist, a commercially available contrast agent, at 0.47 T but comparable at 9.40 T. Analysis of variable temperature ¹⁷O NMR transverse relaxation measurements revealed the water exchange of the nanoassemblies to be faster than that previously reported for paramagnetic liposomes. Molecular reorientation dynamics were probed by ¹H NMRD profiles using a classical inner and outer sphere relaxation model and a Lipari–Szabo “model‐free” approach. High payloads of Gd^III ions in the liposomal nanoassemblies made solely from the Gd‐DTPA‐Dop‐Phy amphiphiles, in combination with slow molecular reorientation and fast water exchange makes this novel amphiphile a suitable candidate to be investigated as an advanced MRI contrast agent.     

Nanostructure changes in protic ionic liquids (PILs) through adding solutes and mixing PILs

The effect of adding primary n-alcohols with aliphatic chains and hexane on the nanostructure of a series of 14 protic ionic liquids (PILs) was explored using small and wide angle X-ray scattering (SAXS and WAXS). PILs were investigated with primary, secondary and tertiary ammonium cations containing different alkyl chain lengths, with and without hydroxyl substitution of the alkyl chain. Formate or nitrate anions were paired with these cations. The PILs which had no identified intermediate range order between 5-16 ? had very low solubilities of the solutes. The other PILs, which had non-polar domains present, were mostly miscible with the primary alcohols of ethanol, propanol and butanol. When the alkyl chain length of the alcohols was similar to the PILs then the alcohols co-partitioned with the alkylammonium cation components of the PILs and caused either an increase or decrease in the size of the non-polar domains, depending on whether the alcohol chain length was longer or shorter than that of the cation in the PIL respectively. For ethylammonium nitrate (EAN) with propanol or butanol and propylammonium nitrate (PAN) with butanol, the difference between the alcohol chain length and the alkyl chain length was too great to lead to a modified nanostructure, and instead large aggregates were present. The solubility of hexane in the alkylammonium nitrate PILs had a very strong correlation to the alkyl chain length. The addition of hexane had very little effect on the non-polar domain sizes, which was attributed to it not being orientated in alignment with the alkylammonium cations in the non-polar domains. Lastly, seven binary PIL-PIL solution series were investigated using SAXS and WAXS to show how the nanostructure of these systems can be fine tuned to control the size and structure of the non-polar domains.     

Activating water: important effects of non-leaving groups on the hydrolysis of phosphate triesters

The high rate of spontaneous hydrolysis of tris-2-pyridyl phosphate (TPP) is explained by the activating effects of the non-leaving ("spectator") groups on P-OAr cleavage, and not by intramolecular catalysis. Previous work on phosphate-transfer reactions has concentrated on the contributions to reactivity of the nucleophile and the leaving group, but our results make clear that the effects of the non-leaving groups on phosphorus can be equally significant. Rate measurements for three series of phosphate triesters showed that sensitivities to the non-leaving groups are substantial for spontaneous hydrolysis reactions, although significantly smaller for reactions with good nucleophiles. There are clear differences between triaryl and dialkyl aryl triesters in sensitivities to leaving and non-leaving groups with the more reactive triaryl systems showing lower values for both β(LG) and β(NLG). Intramolecular catalysis of the hydrolysis of TPP by the neighbouring pyridine nitrogens is insignificant, primarily because of their low basicity.