Preparation of Chiral Cholestanofluorene and Its Electron-Rich Derivatives for Isolation of a Stable Cation−Radical Salt

A simple and practical synthesis of a variety of chiral fluorene derivatives is described where a cholestane moiety is attached to the carbon 9 of the fluorene ring system from readily available starting materials. An appropriately substituted fluorene derivative (i.e., R = OMe) forms a highly colored (chiral) cation−radical that can be isolated as robust hexachloroantimonate salt. Interestingly, the simplest cholestanofluorene (i.e., R = H) can also be transformed into a dibromo derivative (i.e., R = Br), a precursor to the (poly)cholestanofluorenes where the cholestane moieties will serve not only as groups that impart chirality but also allow them to be soluble in common organic solvents. The details of these works are described

Hexabenzo[4.4.4]propellane: A Helical Molecular Platform for the Construction of Electroactive Materials

Helical hexabenzo[4.4.4]propellane (a relative of hexaphenylethane) and its derivatives are synthesized and their structures are established by X-ray crystallography. Isolation and X-ray crystallographic characterization of a robust trication-radical salt of hexamethoxypropellane derivative confirms that its framework is stable toward oxidative (aliphatic) C−C bond cleavage. It is also demonstrated that propellane can be easily brominated at the 4,4‘-positions of the biphenyl linkages for its usage as a molecular platform for the preparation of electroactive materials

A Versatile Synthesis of Electroactive Stilbenoprismands for Effective Binding of Metal Cations

A versatile synthesis of a new class of polyaromatic receptors (stilbenoprismands) containing a Δ-shaped cavity similar to that of the π-prismand together with an intimately coupled electroactive stilbenoid moiety was accomplished via an efficient intramolecular McMurry coupling reaction. The presence of the Δ-shaped cavity in stilbenoprismands allows an efficient binding of a single silver cation as probed by 1H NMR spectroscopy. Electron-rich stilbenoprismands undergo a ready oxidation to their highly robust cation−radical and dicationic salts. X-ray structure determination of a representative dicationic stilbenoprismand showed that the charges were largely localized on the tetraarylethylene moiety, which results in a twisting of the ethylenic C═C bond by ∼35°. Moreover, the electronic coupling among the stilbenoid and π-prismand moieties in various stilbenoprismands was briefly probed by optical methods

Stabilizer Slicing: Coherent Error Cancellations in LDPC Codes

Coherent errors are a dominant noise process in many quantum computing architectures. Unlike stochastic errors, these errors can combine constructively and grow into highly detrimental overrotations. To combat this, we introduce a simple technique for suppressing systematic coherent errors in low-density parity-check (LDPC) stabilizer codes, which we call stabilizer slicing. The essential idea is to slice low-weight stabilizers into two equally-weighted Pauli operators and then apply them by rotating in opposite directions, causing their overrotations to interfere destructively on the logical subspace. With access to native gates generated by 3-body Hamiltonians, we can completely eliminate purely coherent overrotation errors, and for overrotation noise of 0.99 unitarity we achieve a 135-fold improvement in the logical error rate of Surface-17. For more conventional 2-body ion trap gates, we observe an 89-fold improvement for Bacon-Shor-13 with purely coherent errors which should be testable in near-term fault-tolerance experiments. This second scheme takes advantage of the prepared gauge degrees of freedom, and to our knowledge is the first example in which the state of the gauge directly affects the robustness of a code's memory. This work demonstrates that coherent noise is preferable to stochastic noise within certain code and gate implementations when the coherence is utilized effectively.Comment: 6 pages, 9 figure

Changing lifestyles and consumption patterns in developing countries: A scenario analysis for China and India

China and India are the world's largest developing economies and also two of the most populous countries. China, which now has more than 1.3 billion people, is expected to grow to more than 1.4 billion by 2050, and India with a population of 1 billion will overtake China to be the most populous country with about 1.6 billion population. These two countries are home to 37% of the world's population today. In addition, China and India have achieved notable success in their economic development characterised by a high rate of gross domestic product (GDP) growth in the last two decades. Together the two countries account already for almost a fifth of world GDP. The most direct and significant result of economic growth in India and China is the amazing improvement in quality of life (or at least spending power) for an increasing share of the population. The populations of both the countries have experienced a transition from ‘poverty’ to ‘adequate food and clothing’; today growing parts of the population are getting closer to ‘well to do lifestyles’. These segments of the society are not satisfied any more with enough food and clothes, but are also eager to obtain a quality life of high nutrient food, comfortable living, health care and other quality services. The theme of this paper is to analyse how the major drivers contributed to the environmental consequences in the past, and to take a forward look at the environmental impacts of these driving forces in China and India. The paper identifies population, affluence and technology to be the major driving forces in environmental pollution for these two countries then applies the simple equation of Impact=Population×Affluence×Technology, or I=PAT to evaluate the effects of changes in these drivers on CO2 emissions

Radial fingering in a Hele-Shaw cell: a weakly nonlinear analysis

The Saffman-Taylor viscous fingering instability occurs when a less viscous fluid displaces a more viscous one between narrowly spaced parallel plates in a Hele-Shaw cell. Experiments in radial flow geometry form fan-like patterns, in which fingers of different lengths compete, spread and split. Our weakly nonlinear analysis of the instability predicts these phenomena, which are beyond the scope of linear stability theory. Finger competition arises through enhanced growth of sub-harmonic perturbations, while spreading and splitting occur through the growth of harmonic modes. Nonlinear mode-coupling enhances the growth of these perturbations with appropriate relative phases, as we demonstrate through a symmetry analysis of the mode coupling equations. We contrast mode coupling in radial flow with rectangular flow geometry.Comment: 36 pages, 5 figures, Latex, added references, to appear in Physica D (1998

Disfluency in dialogue:an intentional signal from the speaker?

Disfluency is a characteristic feature of spontaneous human speech, commonly seen as a consequence of problems with production. However, the question remains open as to why speakers are disfluent: Is it a mechanical by-product of planning difficulty, or do speakers use disfluency in dialogue to manage listeners' expectations? To address this question, we present two experiments investigating the production of disfluency in monologue and dialogue situations. Dialogue affected the linguistic choices made by participants, who aligned on referring expressions by choosing less frequent names for ambiguous images where those names had previously been mentioned. However, participants were no more disfluent in dialogue than in monologue situations, and the distribution of types of disfluency used remained constant. Our evidence rules out at least a straightforward interpretation of the view that disfluencies are an intentional signal in dialogue. © 2012 Psychonomic Society, Inc