Poly-μ-2,5-dimethylpyrazine-μ-dithiocyanato-N, S,S-dicopper(I): a three-dimensional coordination polymer containing both molecular and anionic rod ligands

Reaction of CuSCN with 2,5-dimethylpyrazine (2,5-me₂pyz) yields a polymeric material, [Cu₂(SCN)₂(2,5-me₂pyz)], which has been crystallographically characterized. The compound crystallizes in the monoclinic space group P2₁/N with a = 5.6850(2) Å, b = 6.92877(3) Å, c = 14.3575(6) Å, = 93.435(1), and Z = 2. It contains [Cu(SCN)] sheets in which each thiocyanate ligand acts in a -N,S,S-bridging mode. The sheets are bridged by 2,5-dimethylpyrazine ligands to generate a three dimensional network. The compound has also been characterized by infrared spectroscopy and thermogravimetric analysis.     

Rates of Decay and h-Processes for One Dimensional Diffusions Conditioned on Non-Absorption

Let (X _t ) be a one dimensional diffusion corresponding to the operator , starting from x>0 and T ₀ be the hitting time of 0. Consider the family of positive solutions of the equation with (0, ), where . We show that the distribution of the h-process induced by any such is , for a suitable sequence of stopping times (S _M : M0) related to which converges to with M. We also give analytical conditions for , where is the smallest point of increase of the spectral measure associated to .     

The practical use of the hole method in photoelasticity

A small circular hole has already been used in plane elasto-static photoelasticity to determine the stress tensor for any general loading situation. Originally the idea required the determination of the stress at four points at the free boundary of the hole, then it was found that more precision would be obtained if the measurements were taken at points located at a distance from the center of the hole equal to twice its radius. Later it was suggested that probably still better results would be obtained from points located at 1.4 times the radius. This paper has three objectives: (1) to improve the precision of the measurements by taking them at any point in the vicinity of the hole, which requires that the expressions giving the principal stresses be presented in a different form, as a function of the normalized variable distance from the center of the hole; (2) to show the consistent application of the method, using the values of the birefringence at various arbitrary radial locations, to plane elasto-static loading problems; and, (3) to present the application of this approach in a concise form so that its application is practical.     

Electronic structure of cubic uranium compounds

Self-consistent cellular multiple scattering techniques and photoemission energy distribution curves obtained at 20<hv<80 eV are used to study the density of states of UN and US. The calculations are based on a model using a finite cluster of atoms in a condensed-matter-like boundary potential. The main results refer to the mixing of thes, p, d, andf-states of uranium into a valence and a conduction band. Thef-states form orbitals with the ligands, within the valence and conduction bands. In the nitride the amount off character in the valence band is only 0.3 electrons and thef electrons are in two resonant levels (of each spin) in the conduction band. Only the first of these levels is occupied for the local, alternate from atom to atom, majority spin. In the sulfide the amount off character in the valence band is 0.59 electrons and the rest of thef-levels are in a resonance state (of majority spin) at the beginning of the conduction band. The conduction band is mainly of localized uranium 6d character. The theoretical results compare favorably with the photoemission data reported here.     

Pion-nucleus charge exchange reactions

This is a report on the single and double charge exchange reactions on nuclie. The emphasis is on recent experimental results and calculations. We limit ourselves to pion energies below 300 MeV. The experimental results and complexity. We present the current level of understanding of the various aspects of the charge exchange process.     

Distributor ideals in near-rings of polynomials

Partially supported by D.G.I.C.Y.T. PA 86-0471.     

Differential correlation effects in chemisorption cluster model calculations: an FCI study

The interaction of atomic hydrogen with Cu₅ and Ag₅ cluster models simulating the Cu(100) and Ag(100) surfaces has been studied at the full configuration interaction (FCI) level in order to establish the transferability of differential correlation arising from the valence shell. It is shown that pseudopotentials that deal explicitly with one electron or eleven electrons lead to differential correlation effects which agree to within 1–2 mhartree when a localization procedure is used to separate d-shell MOs from the valence ones.     

Physical and chemical evolution of PMDA-ODA during thermal imidization

The processing of poly(imide) films from poly(amic acid) solutions involves the simultaneous loss of solvent and chemical conversion, and may involve structural reorganization such as orientation or crystallization. Here, we describe weight loss, solvent sorption. Fourier transform infrared (FTIR), and wide-angle x-ray scattering (WAXS) studies during thermal imidization of the commercially important poly(imide) PMDA-ODA. The results indicate that imidization proceeds nearly to completion before significant crystallization occurs. The experimental data are interpreted in terms of a triangular phase diagram that makes it possible to plot the processing pathway during the conversion from poly(amic acid) solution to solid poly(imide). In constructing this triangular phase diagram the extent of imidization (i.e., the composition of the poly(amic acid-co-imide) copolymers during conversion) is treated as an independent thermodynamic variable. The form of the triangular phase diagram can be predicted from the Flory-Huggins lattice theory of mixing. There is inevitably a two-phase region present due to the relatively poor solubility of the poly(imide) in the poly(amic acid) solvent (NMP). The specific processing pathway taken depends on the relative amount of solvent loss and imidization during conversion. Further details about the triangular phase diagrams of poly(imides) will require such studies as solvent swelling at intermediate stages of conversion. © 1995 John Wiley & Sons, Inc.