The carbene/carbenoid chemistry of lithium and tin cyclopropylidenoids

In Chapter I of this dissertation, the Skattebol-type rearrangement (in THF solution at -78(DEGREES)) of anti-7-bromo-syn-7-lithiobicyclo4.1.0hept-2-ene (34-anti) and its C(\u277)-epimer (34-syn) is investigated. The following discoveries demonstrate that, in solution, this rearrangement proceeds through a carbenoid: (a) carbenoid 34-anti undergoes 1,3-rearrangement and generates the carbenoid coupling products 42-syn and 42-anti 17 times faster than does 34-syn, (b) the coupling products 42-syn and 42-anti are formed in a much different ratio from 34-anti (7.5 to 1) than from 34-syn (1.5 to 1), (c) no carbene trapping products were formed in the presence of a large excess of isobutylene, cyclohexene, or triethylsilane, and (d) the saturated analogs of 34-anti and 34-syn (i.e., 89-anti and 89-syn, respectively) do not generate the corresponding free cyclopropylidene under the same reaction conditions (or under a variety of other reaction conditions which are investigated in Chapter II);In Chapter III, the pyrolysis reactions of anti-7-bromo-syn-7-trimethylstannylbicyclo4.1.0hept-2-ene (35-anti) and its C(\u277)-epimer (35-syn) are studied, in hopes of observing the Skattebol rearrangement of the corresponding cyclopropylidene. The results of the gas-phase pyrolysis studies are not easily understood. In the solution phase, however, the pyrolysis reactions of 35-anti and 35-syn have both been discovered to involve initial C-Br bond heterolysis, with no carbene involvement. The reaction of 35-anti involves an ionic 1,3-rearrangement (through double bond participation), and that of 35-syn involves an ionic opening of the cyclopropyl ring (favored by the stereochemistry of the bromine group);Chapter IV describes the solution-phase pyrolysis reactions of the saturated analogs of 35-anti and 35-syn (205-anti and 205-syn, respectively). Both reactions again involve initial C-Br bond heterolysis. The major reaction pathway of 205-anti is C-Br bond heterolysis, leading to a cyclopropyl ion pair, which, in the absence of cation traps, loses trimethyltin bromide, to generate the corresponding cyclopropylidene. The major reaction pathway of 205-syn is ionic opening of the cyclopropyl ring (again favored by the stereochemistry of the bromine group)

Space-efficient detection of unusual words

Detecting all the strings that occur in a text more frequently or less frequently than expected according to an IID or a Markov model is a basic problem in string mining, yet current algorithms are based on data structures that are either space-inefficient or incur large slowdowns, and current implementations cannot scale to genomes or metagenomes in practice. In this paper we engineer an algorithm based on the suffix tree of a string to use just a small data structure built on the Burrows-Wheeler transform, and a stack of $O(\sigma^2\log^2 n)$ bits, where $n$ is the length of the string and $\sigma$ is the size of the alphabet. The size of the stack is $o(n)$ except for very large values of $\sigma$. We further improve the algorithm by removing its time dependency on $\sigma$, by reporting only a subset of the maximal repeats and of the minimal rare words of the string, and by detecting and scoring candidate under-represented strings that $\textit{do not occur}$ in the string. Our algorithms are practical and work directly on the BWT, thus they can be immediately applied to a number of existing datasets that are available in this form, returning this string mining problem to a manageable scale.Comment: arXiv admin note: text overlap with arXiv:1502.0637

Introduction to the Plasma Issue

The study of the physics of ionized gases has had a long and complicated history. The word "plasma" was first coined by Langmuir and Tonks in 1929 to denote a gas in which an important fraction of the molecules are dissociated into ions and electrons, the gas as a whole remaining electrically neutral. The laboratory study of plasmas, of course, had been pursued long before that, many important discoveries in the realm of gas discharge phenomena having been made in the 1800's. These studies, continuing into the Twentieth Century as exemplified by the work of Langmuir, served as the foundation for many practical electronic devices used for the generation, rectification, and control of electrical energy. The plasmas used in these devices usually have a low-charge density, and the fractional ionization is ordinarily less than one per cent. This small percentage of ionization is sufficient to provide good electrical conductivity which can be controlled externally, but it is difficult to study theoretically because of the numerous competing processes involving neutral atoms, metastable atoms, ions, electrons, and collective oscillations of ions and electrons

Decoupling of Mechanical Structures with Piezoceramic Stacks

A review of the development and realisation of an adaptive interface for decoupling of two mechanical systems is presented. An approach is utilized to design an adaptronical system by means of rapid-prototyping on the basis of a simulation. The method includes the calculation of the dynamic behaviour of the mechanical structure with the help of FEM. The FE-model of the mechanical structure is reduced and embedded as modal state-space-model with the numerical simulation software MATLAB/ Simulink. Actuators and sensors are integrated into the mechanical structure. Based on the resulting dynamical behaviour of the mechanical structure an adaptive control algorithm for the decoupling of structural vibrations is developed. Experimental tests are performed to confirm and to update the simulations. The hardware-in-the-loop-simulation is performed with the commercial rapid-prototyping dSpace-system. This procedure allows the development and the evaluation of more complex adaptive mechanical structures

Modeling the Miocene Climatic Optimum. Part I: Land and Atmosphere

This study presents results from the Community Climate System Model 3 (CCSM3) forced with early to middle Miocene (~20–14 Ma) vegetation, topography, bathymetry, and modern CO2. A decrease in the meridional temperature gradient of 6.5°C and an increase in global mean temperature of 1.5°C are modeled in comparison with a control simulation forced with modern boundary conditions. Seasonal poleward displacements of the subtropical jet streams and storm tracks compared to the control simulation are associated with changes in Hadley circulation and significant cooling of the polar stratosphere, consistent with previously predicted effects of global warming. Energy budget calculations indicate that reduced albedo and topography were responsible for Miocene warmth in the high-latitude Northern Hemisphere while a combination of increased ocean heat transport and reduced albedo was responsible for relative warmth in the high-latitude Southern Hemisphere, compared to the present. Model–data analysis suggests Miocene climate was significantly warmer and wetter than simulated here, consistent with previous uncoupled Miocene models and supports recent reconstructions of Miocene CO2 substantially higher than present