Minimum path decompositions of oriented cubic graphs

Pullman [3] conjectured that if k is an odd positive integer, then every orientation of a regular graph of degree k has a minimum decomposition which contains no vertex which is both the initial vertex of some path in the decomposition and the terminal vertex of some other path in the decomposition. In this paper, the conjecture is established for cubic graphs, and its connection with Kelly's conjecture for tournaments is described.     

Structural aspects of the product from glyoxal and tetrakis(ethoxycarbonylamino)ethane

The base-promoted addition of glyoxal to 1,1,2,2-tetrakis(ethoxycarbonylamino)ethane in DMF gives a product mixture containing mostly 1,1′,3,3′-tetrakis(ethoxycarbonyl)-4,4′,5,5,'-tetrahydroxy-2,2′-biimidazolidyl. An alternate structure containing a tetraazadecalin system was considered less likely, since the most significant peak in the mass spectrum of this product and a tetraacetate derivative corresponded to half the mass of the parent ion. Two-dimensional nmr spectra on the major hplc fraction are more consistent with the biimidazolidinyl structure (very low J_vic and lack of NOE enhancement). A HETCOSY spectrum on the mixture allowed assignment of ¹H nmr shifts.     

Network parameters for crosslinking of chains with length and site distribution

Polymer chains are crosslinked to form a network. The chains are polydispersed, with an arbitrary distribution of weight and functionality. Crosslinks may form in three different ways: direct coupling (homopolymerization), direct coupling with propagation, and coupling through copolymerization with small monomers. Various network parameters are calculated. We give computational formulae for gel point, weight fraction soluble, weight fraction pendant, weight fraction effective, concentration of effective junctions, concentration of effective network strands, and the entanglement trapping factor. These formulae give exact values for systems that previously have only been solved using simplifying approximations. Examples show that such simplification may lead to sizable errors in the computation of network parameters.     

A variable temperature EPR study of Mn-doped NH4Cl0.9I0.1 single crystal at 170 GHz: Zero-field splitting parameter and its absolute sign

EPR measurements have been carried out on a single crystal of Mn(2+)-doped NH(4)Cl(0.9)I(0.1) at 170-GHz in the temperature range of 312-4.2K. The spectra have been analyzed (i) to estimate the spin-Hamiltonian parameters; (ii) to study the temperature variation of the zero-field splitting (ZFS) parameter; (iii) to confirm the negative absolute sign of the ZFS parameter unequivocally from the temperature-dependent relative intensities of hyperfine sextets at temperatures below 10K; and (iv) to detect the occurrence of a structural phase transition at 4.35K from the change in the structure of the EPR lines with temperature below 10K.     

Enantioselective aldol reaction of chiral acyl thiazolidine thione derived boron enolates

The compatability of an acyl thiazolidine thione as a chiral auxillary in boron enolate chemistry has been demonstrated by an enantioselective aldol condensation. The aldol products provide direct access to chiral β-lactams.     

Efficient N-sulfenylation of 2-azetidinones using S-substituted thiophthalimides

Reaction of N-unsubstituted β-lactams with various S-substituted thiophthalimides provides an efficient route to the corresponding N-thio-2-azetidinones.     

Pressure dependence of elastic behaviour and force constants of GaP

The six third order elastic constants of GaP have been obtained from measurements of the effect of hydrostatic and uniaxial pressures on ultrasonic wave velocities. The valence force field model has been used to obtain the bond-bending and stretching force constants. Confirmatory evidence is added to the hypotheses that zinc blende structure crystals undergo the densification transition under pressure when (1) a modified Born stability criterion that $\text{1}\text{2}\text{(C}{}_{11}\text{? C}{}_{12}\text{)}\text{B}$ equals about 0.2 is reached at the phase transition pressure P_t, and (2) the ratio $\text{β}{}_{\mathrm{t}}\text{α}{}_{\mathrm{t}}$ of the second order bond-bending β_t to bond-stretching α_t, force constants is about 0.1. These findings suggest that a macroscopic shear takes place at the transition     

Anomalous optical response with variation in band filling in linear chain conductors

We report the polarized infrared reflectance of ($\text{N}$-methylphenazinium)_x (phenazine)_1-x(tetracyanoquinodimethanide), (NMP)_x(Phen)_1-x(TCNQ) for 0.5≤x≤1.0. We demonstrate that the “Drude edge” in TCNQ salts is related to the conduction electron charge density. An anomalous rapid red shift of the plasma frequency, observed for $\text{x ～}\text{2}\text{3}$, may signal the emptying of the conduction electrons from half of the chains and/or a crossover from small U/W (coulomb repulsion/bandwidth) to large U/W behavior.     

Variable-temperature (295—15 K) raman spectra of dodecacarbonyl-triangulo-ruthenium(O) and -osmium(O), M3(CO)12 (M = Ru,Os)

Laser Raman spectra of solid dodecacarbonyl-triangulo-ruthenium(0) and -osmium(0), M₃(CO)₁₂ (M = Ru, Os), have been recorded at 295, 200, 100 and 15 K using a surface scanning technique to avoid sample decomposition. The data indicate that neither compound undergoes a phase change throughout the temperature range investigated. Contrary to earlier measurements at room temperature only, site-symmetry and correlation effects are more widespread than hitherto suspected.