Anomalous spin-related quantum phase in mesoscopic hole rings

We have obtained numerically exact results for the spin-related geometric quantum phases that arise in p-type semiconductor ring structures. The interplay between gate-controllable (Rashba) spin splitting and quantum-confinement-induced mixing between hole-spin states causes a much higher sensitivity of magnetoconductance oscillations to external parameters than previously expected. Our results imply a much-enhanced functionality of hole-ring spin-interference devices and shed new light on recent experimental findings.

Ring strain in boroxine rings: computational and experimental considerations

B3LYP/6-311+G(d) calculations indicate that (HBO)₃ (4) and (HBO)₄ (5) possess (zero-point energy corrected) strain enthalpies of 11.4 and 31.6 kJ mol⁻¹, respectively. The absence of eight-membered (RBO)₄ rings is attributed to a combination of ring strain and the lability of the B---O bond. The synthesis, characterization and molecular structure of (PhBO)₃·pyridine (1) are described and chemical phenomena related to the addition of amines to triorganoboroxine rings are rationalized in terms of relief of ring strain in 4.

Cell division protein ftsZ: running rings around bacteria, chloroplasts and mitochondria

Of all the proteins involved in prokaryotic cell division FtsZ is one of the earliest acting and most widely distributed, being found in all but a few species. We discuss several recent discoveries of FtsZ in eukaryotic cells and the protein’s role in the division of chloroplasts and mitochondria, organelles that are of bacterial origin.

Nest-tree selection by the threatened brush-tailed phascogale (phascogale tapoatafa) (marsupialia: dasyuridae) in a highly fragmented agricultural landscape

The conservation of roosting and nesting resources is of critical concern for many hollow-dependent species around the world. We investigated the nest-tree requirements of the threatened brush-tailed phascogale (Phascogale tapoatafa) in a highly cleared agricultural landscape in south-eastern Australia. We documented the physical characteristics of selected nest trees and describe the spatial and temporal patterns of nest-tree use as revealed by radio-tracking. Nine phascogales (seven females, two males) were radio-tracked between March and July 1999 in an area where most woodland habitat is confined to linear strips along roads and streams or small patches and scattered trees in cleared farmland. Female phascogales were monitored for 13–35 days over periods of 5–15 weeks and two males were monitored for 2 and 9 days respectively. A total of 185 nest-tree fixes was collected and all nests occupied by phascogales were in standing trees. Eighty-three nest trees were identified, ranging in diameter at breast height (dbh) from 25 to 171 cm, with a mean dbh for the trees used by each individual phascogale of >80 cm. Phascogales did not discriminate between canopy tree species in selecting nest trees, but showed highly significant selection for trees in the largest size class. All individuals used multiple nest trees, with the seven females occupying an average of 11.4 nest trees from a mean of 25 diurnal locations. The number of nest trees continued to increase throughout the study, suggesting that more would be identified during a longer or more intensive study. Occupied nest trees were located throughout each individual’s home range, highlighting the importance of a continuous spatial distribution of suitable nest trees across the landscape. Nest trees were also located in adjacent farmland up to 225 m from roadside vegetation, demonstrating the value that scattered clumps and even single trees in farmland can have for wildlife conservation.

A general rooted tree drawing algorithm

A general rooted tree drawing algorithm is designed in this paper. It satisfies the basic aesthetic criteria and can be well applied to binary trees. Given an area, any complex tree can be drawn within the area in users' favorite styles. The algorithm is efficient with O(LxNxlogN) time complexity and self-adaptive as well.

Extending abelian groups to rings

For any abelian group G and any function f : G → G we define a commutative binary operation or `multiplication' on G in terms of f. We give necessary and sufficient conditions on f for G to extend to a commutative ring with the new multiplication. In the case where G is an elementary abelian p-group of odd order, we classify those functions which extend G to a ring and show, under an equivalence relation we call weak isomorphism, that there are precisely six distinct classes of rings constructed using this method with additive group the elementary abelian p-group of odd order p².

The origin of ring strain and conformational flexibility in Tri- and Tetrasiloxane Rings and their heavier group 14 congeners

Never change a winning team. Since the appearance of the first volume in 1994 this series has become a well respected forum, and like its highly successful predecessors, this sixth volume again brings together leading experts from academia and industry to provide a comprehensive and critical survey of the frontiers of current industrial and university research. - Synthesis and characterization of new organosilicon compounds - Applications in polymer and materials science - Summary of the latest research results The result is a unique compendium with two volumes of first-hand information, vital for all experts working in this field.

Comparison of the flexibility of eight-membered tetrasiloxane and stannasiloxane rings: a crystallographic and computational study

The syntheses and crystal structures of the eight-membered cyclo-stannasiloxanes cyclo-[t-Bu(OH)Si(OSnt-Bu₂O)₂Si(OH)t-Bu] (1) and cyclo-{t-Bu₂Si[OSn(CH₂SiMe₃)₂O]₂Sit-Bu₂} (2) as well as the synthesis of the six-membered cyclo-stannasiloxane cyclo-{t-Bu₂Si[OSn(CH₂SiMe₃)₂]₂O} (3) are reported. Compound 1 crystallizes as its trans isomer, but the cis isomer dominates in solution. In agreement with the experimentally obtained results, ab initio and DFT calculations on the model compounds cyclo-(H₂SiO)₄ (4), cyclo-[H₂Si(OSnH₂)OSiH₂] (5), cyclo-O(H₂SiOSnH₂)₂O (6), and cyclo-[H₂Si(OSiH₂)OSnH₂] (7) indicate that the energetic preference to adopt puckered structures increases and the ring flexibility decreases with an increasing number of tin atoms in the ring. The rich diversity of puckered conformations is attributed to the steric demand of the different organic substituents.

Novel 10- and 20- membered tin- and silicon-containing rings: synthesis, complexation behavior and conversion into a lewis acidic polymer

Reaction of the dimethylsilylmethyl-substituted tetraorganotin derivative CH₂[CH₂Sn(Ph₂)CH₂Si(H)Me₂]₂ (1) and CH₂[CH₂Sn(Ph₂)CH₂Si(i-PrO)Me₂]₂ (3), respectively, with mercuric chloride afforded the novel silicon- and tin-containing 10- and 20-membered rings cyclo-CH₂[CH₂Sn(Cl₂)CH₂Si(Me₂)]₂O (4) and cyclo-CH₂[CH₂Sn(Cl₂)CH₂Si(Me₂)OSi(Me₂)CH₂Sn(Cl₂)CH₂]₂CH₂ (5). Both compounds 4 and 5 can be converted into the soluble Lewis acidic polymer poly-[Si(Me₂)CH₂Sn(Cl₂)(CH₂)₃Sn(Cl₂)CH₂Si(Me₂)O] (8). ¹¹⁹Sn NMR studies indicate that 4 acts as a bidentate Lewis acid toward chloride ions, exclusively forming the 1:1 complex [cyclo-CH₂[CH₂Sn(Cl₂)CH₂Si(Me₂)]₂O·Cl]-[(Ph₃P)₂N]⁺ (7). The molecular structures as determined by single-crystal X-ray diffraction analysis of 4 and 7 are reported.