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.

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.

Modelling regular and estimable inverse demand systems : a distance function approach

To be useful for policy simulation in the current climate of rapid structural change, inverse demand systems must remain regular over substanstial variations in quantities. The distance function is a convenient vehicle for generating such systems. It also allows convenient imposition of prior ideas about the structure of preferences required for realistic policy work. While the distance function directly yields Hicksian inverse demand functions via the Shepard-Hanoch lemma, they are usually explicit in the unobservable level of utility (u), but lack a closed-form representation in terms of the observable variables. Note however that the unobservability of u need not hinder estimation. A simple one-dimensional numerical inversion allows the estimation of the distance function via the parameters of the implied Marshallian inverse demand functions. This paper develops the formal theory for using distance functions in this context, and reports on initial trials on the operational feasibility of the method.

The influence of leisure preference, life priority and making time on regular participation in leisure time physical activity

Using an attitude-behaviour theory approach this study examined the direct and indirect influence of preference, life priority and time allocation on regular participation in leisure-time physical activity (LTPA). The crosssectional study used self-report questionnaires to collect data from a random sample of 250 people aged 19 to 87 years living in an Australian city. The findings suggest that people’s regular participation in LTPA is not directly influenced by their preference for it. Rather, making LTPA a high life priority and allocating time for LTPA are intervening factors that explain the relationship. The outcomes emphasise the importance of encouraging the formation of a preference for physical activity in young children. They suggest all levels of government and the leisure profession emphasise work/life balance by prioritising LTPA, educating people about time management and helping them to develop time management skills.

Studentship and oppositional behaviour within physical education teacher education : a case study ; and, Between the rings and under the gym mat : a narrative

This thesis represents a part of a program of study that is reaching a closure. The broadest brush that could be applied to my work is that it concerns Physical Education Teacher Education (PETE), that it focuses on aspects of professional socialisation, and that it involves various case studies utilising naturalistic inquiry. Whilst it would be impossible and naive to believe that the reading of these texts will produce the meanings that I encourage, or have internalised, nevertheless the order of reading is at least something that I can argue for. Read in the order I suggest throughout the thesis I am hopeful that my subjectivities, and the learning and understandings I have reached may become clear. The purpose of this two part thesis is an exploration of the interplay or dialectic that exists between PETE students, academic staff and the subject matter within PETE. I have had to come to understand the limitations and advantages of insider research as the work has been completed at my University in the School of Human Movement and Sports Science where I have worked for twenty years. This thesis examines the extent to which studentship and oppositional behaviour underlies the dialectic that exists between the students and the various discourses within the program. I have written the study in two very different formats, one, a collection of stories about PETE and the other, an interpretative case study conducted during 1993 and 1994. Within the case study, studentship and oppositional behaviour were viewed as a measure of the extent to which students react and push against the forces of socialisation within their PETE program that is seen to represent dominant discourses, The following broad research questions were considered to enable the above analysis. 1. What is the nature of studentship and oppositional behaviour in a high status subject within PETE compared to a subject that is seen by students to be of little relevance and of low status? 2. How are studentship and oppositional behaviour related to students subjective warrants? 3. How are the studentship and oppositional behaviours exhibited by students related to the pedagogy and discourses reflected in the knowledge, beliefs and practices within the two sites. The starting point for this research was a study conducted as a totally separate research task (Swan, 1992) that investigated the hierarchies of subject knowledge within a PETE site and investigated the influence of such hierarchies upon student intention. A great deal of meta analysis exists about the manner in which a technocratic rationality pervades PETE but very little case study material of what this means to students and academic staff within such institutions is available. The stories in Between The Rings And Under The Gym Mat, which is the second part of this thesis, represent ‘the data’ differently from the case study, but they speak their own truth. At times the nature of the story is indistinguishable from the reality of the case study. Wexler (1992) undertook an ethnographic study about identity formation in three very different high schools, and published the findings in a book entitled Becoming Somebody. His introductory words about the nature of the social story he tells, are significant to this study and story. Social history is recounted by creative intervention that can only be made from culturally accessible materials. Ethnography is neither an objective realist, nor subjective imaginist account. Rather, it is an historical artefact that is mediated by elaborated distancing of culturally embedded and internally contradictory (but seemingly independent and coherent) concepts that take on a life of their own as theory. So, this is not ‘news from nowhere,’ but a theoretically structured story where both the story and its structure are part of my times. (p.6) The case study before you is organised with an analysis of studentship and oppositional behaviour detailed in chapter one. The following chapter conceptualises studentship and oppositional behaviour in relation to particular themes of professional socialisation, resistance to oppression and youth culture. Chapter three locates the case study to the major paradigmatic debates about the value and nature of the subject matter content within PETE, Chapter four outlines the case site, the research process and the research dilemma’s confronted in this study. The remaining three chapters are the case record as I can best understand it. In Between the Rings and under the Gym Mat (part B) the story most directly concerned with studentship and oppositional behaviour, is called Tale of Two Classes’. It takes on a very different reality to the case study (part A) and much can be said about the reality of lived experience which can be portrayed in narrative form as opposed to a clinical case study. Many of the other stories pose similar images that are contradictory and never quite complete. I have written a separate methodological section for the narrative stories. It is my intention that the case study and the series of stories should be viewed as essentially complementary, but also a discrete representation of a part of PETE. As part of the Ed D program I have undertaken four discrete research tasks as the starting point for this research I have referred to the first one (Hierarchies of Subject knowledge within PETE). I also undertook an action research project about ‘Teaching Poorly by Choice.’ A further piece of research was a somewhat reflective effort to draw together what this has all meant to me from a subjective and reflexive perspective. Such efforts are often seen as being self indulgent, as subjectivity in the form of lived experience sits uneasily in academia. A final paper involved an evaluation of Between the Rings and Under the Gym Mat from a pedagogical perspective by PETE professionals around the world. And that's the way things turned out.

Internet security applications of the Munn rings

Effective multiple clustering systems, or clusterers, have important applications in information security. The aim of the present article is to introduce a new method of designing multiple clusterers based on theMunn rings and describe a class of optimal clusterers which can be obtained in this construction.