Corn stover fractions and bioenergy

Information is presented on structure, composition, and response to enzymes of corn stover related to barriers for bioconversion to ethanol. Aromatic compounds occurred in most tissue cell walls. Ferulic acid esterase treatment before cellulase treatment significantly improved dry weight loss and release of phenolic acids and sugars in most fractions over cellulase alone. Leaf fractions were considerably higher in dry weight loss and released sugars with esterase treatment, but stem pith cells gave up the most phenolic acids. Results help identify plant fractions more appropriate for coproducts and bioconversion and those more suitable as residues for soil erosion control.     

Bone mineral density of lumbar spine and proximal femur in healthy males

The aim of this study was to investigate the relationship between BMD and age at lumbar spine and proximal femur in Turkish males. Two hundred ninety healthy males (aged 20-59 years) were investigated. BMD of the lumbar spine had its peak at ages 30-39, however, the peak for the proximal femur was between the ages of 20 and 29. There was a significant decrease in BMD at proximal femur after these peak values with increasing age. In conclusion, there was a significant correlation between age and the proximal femoral BMD in males and age has a strong predictive power on proximal femur BMD score. This revised version was published online in August 2006 with corrections to the Cover Date.     

On a theorem of Shchepin and Repovš concerning the smoothness of compacta

We show that a theorem of Shchepin and Repovš concerning the smoothness of compacta follows from the theory of semicontinuous relations.     

Superelastic percolation network of polyacrylamide (PAAm)–kappa carrageenan (κC) composite

The elasticity of the polyacrylamide (PAAm)-kappa carrageenan (κC) composite was determined as a function of (w/v-%) κC content at 40 °C. The gel composites studied contained various percentages (w/v-%) of κC. The elasticity of the swollen PAAm-κC composite was characterized by using the tensile testing technique. This study investigated the elasticity and the percolation threshold of PAAm-κC composite as a function of κC content. It is understood that the compressive elastic modulus decreases up to 1 (w/v-%) of κC and then increases at contents above 1(w/v-%) of κC. The critical exponent of elasticity y was determined between 1 and 1.6 (w/v-%) of κC and found to be 0.68. The observed elastic percolation threshold is consistent with the suggested values of the superelastic percolation network.     

Equilibrium Formation of Stable All‐Silicon Versions of 1,3‐Cyclobutanediyl

Main group analogues of cyclobutane‐1,3‐diyls are fascinating due to their unique reactivity and electronic properties. So far only heteronuclear examples have been isolated. Here we report the isolation and characterization of all‐silicon 1,3‐cyclobutanediyls as stable closed‐shell singlet species from the reversible reactions of cyclotrisilene c‐Si₃Tip₄ (Tip=2,4,6‐triisopropylphenyl) with the N‐heterocyclic silylenes c‐[(CR₂CH₂)(NtBu)₂]Si: (R=H or methyl) with saturated backbones. At elevated temperatures, tetrasilacyclobutenes are obtained from these equilibrium mixtures. The corresponding reaction with the unsaturated N‐heterocyclic silylene c‐(CH)₂(NtBu)₂Si: proceeds directly to the corresponding tetrasilacyclobutene without detection of the assumed 1,3‐cyclobutanediyl intermediate.     

Access to Enantiopure Advanced Intermediates en Route to Madangamines

The synthesis of enantiopure ABCE and ABCD tetracyclic advanced intermediates en route to madangamine alkaloids and studies for the construction of the triunsaturated 15-membered D ring of madangamine B and the saturated 13-membered D ring of madangamine E are reported.     

Ionisation energy,electron affinity,and mass spectral decomposition mechanisms of RDX isomers upon electron attachment and electron ionisation

ABSTRACT

The structures, ionisation energies (IE), and electron affinities (EA) of 1,3,5-trinitro-1,3,5-triazacyclohexane (RDX) isomers upon loss and gain of an electron were calculated using density functional theory (DFT) methods. The adiabatic electron affinities (EA_ad) range from 1 to 2 eV. The vertical detachment energies are between 1.3 and 4.0 eV. The adiabatic ionisation energies (IE_ad) are in the 9.9–10.2 eV range. The vertical ionisation energies are in the 10.4–10.9 eV range. It is shown that NO₂^?/NO₂ loss would be common in anions and cations, respectively. Isomerisation and N—N bond dissociation accompany cation and anion formation, respectively. The suggested mass spectral fragmentation products for the cations along the S₀ surface are 84, 130, and 176 amu, in agreement with earlier mass spectrometry studies.     

Exact Solution of a Generalized ANNNI Model on a Cayley Tree

We consider the Ising model on a rooted Cayley tree of order two with nearest neighbor interactions and competing next nearest neighbor interactions restricted to spins belonging to the same branch of the tree. This model was studied by Vannimenus who found a new modulated phase, in addition to the paramagnetic, ferromagnetic, antiferromagnetic phases and a (+ + - -) periodic phase. Vannimenus’s results are based on an analysis of the recurrence equations (relating the partition function of an n ? generation tree to the partition function of its subsystems containing (n ?1) generations) and most results are obtained numerically. In this paper we analytically study the recurrence equations and obtain some exact results: critical temperatures and curves, number of phases, partition function.