Gauge fields, geometric phases, and quantum adiabatic pumps

Quantum adiabatic pumping of charge and spin between two reservoirs (leads) has recently been demonstrated in nanoscale electronic devices. Pumping occurs when system parameters are varied in a cyclic manner and sufficiently slowly that the quantum system always remains in its ground state. We show that quantum pumping has a natural geometric representation in terms of gauge fields (both Abelian and non-Abelian) defined on the space of system parameters. Tunneling from a scanning tunneling microscope tip through a magnetic atom could be used to demonstrate the non-Abelian character of the gauge field.     

The spatial logistic map as a simple prototype for spatiotemporal chaos

A spatial extension of the logistic map-termed spatial logistic map-is found to display the same basic universality classes as the commonly studied diffusively coupled logistic lattice despite being vastly simpler. By analyzing the escape rates and the Lyapunov spectra it is shown that the main attractors of the spatial logistic map are stable and hence that it is a good candidate for serving as a prototype for the class of coupled map lattices which it is a part of. The spatial logistic map is then employed to provide an analytical derivation for the recently discovered linear scaling of the wavelength under increasing coupling ranges.     

Consideration of molecular weight during compound selection in virtual target-based database screening

Virtual database screening allows for millions of chemical compounds to be computationally selected based on structural complimentary to known inhibitors or to a target binding site on a biological macromolecule. Compound selection in virtual database screening when targeting a biological macromolecule is typically based on the interaction energy between the chemical compound and the target macromolecule. In the present study it is shown that this approach is biased toward the selection of high molecular weight compounds due to the contribution of the compound size to the energy score. To account for molecular weight during energy based screening, we propose normalization strategies based on the total number of heavy atoms in the chemical compounds being screened. This approach is computationally efficient and produces molecular weight distributions of selected compounds that can be selected to be (1) lower than that of the original database used in the virtual screening, which may be desirable for selection of leadlike compounds or (2) similar to that of the original database, which may be desirable for the selection of drug-like compounds. By eliminating the bias in target-based database screening toward higher molecular weight compounds it is anticipated that the proposed procedure will enhance the success rate of computer-aided drug design.     

A new model of crystal packing

A new, conceptually simple model of crystal packing is proposed which uses "packing patterns" to describe unit cells in terms of molecular building blocks.     

A result about a selection problem of Michael

It is shown that a continuum that is an space in the sense of Michael must be hereditarily decomposable. This improves known results, thereby providing more evidence that such continua must be dendrites.

     

Existence and uniqueness of rectilinear slit maps

We consider a generalization of the parallel slit uniformization in which the angle of inclination of each image slit is assigned independently. Koebe proved that for domains of finite connectivity there is, up to a normalization, a unique rectilinear slit map achieving any given angle assignment. Koebe's theorem is partially extended to domains of infinite connectivity. A uniqueness result is shown for domains of countable connectivity and arbitrary angle assignments, and an existence result is proved for arbitrary domains under the assumption that the angle assignment is continuous and has finite range. In order to prove the existence result a new extremal length tool, called the crossing-module, is introduced. The crossing-module allows greater freedom in the family of admissible arcs than the classical module. Several results known for the module are extended to the crossing-module. A generalization of Jenkins' module condition for the parallel slit problem is given for the rectilinear slit problem in terms of the crossing-module and it is shown that rectilinear slit maps satisfying this crossing-module condition exist.

     

The identification of tyre induced vehicle interior noise

Sound transmission into a vehicle is classified as either airborne or structure borne sound. From the point view of noise control, the reduction of noise transferred by different paths requires different solutions. Coherence function analysis is often used to identify transmission paths. However it can be difficult to separate the airborne from structure borne components. The principle of acoustic reciprocity offers a convenient method for overcoming this difficulty. The principal states that the transfer function between an acoustic volume velocity source and an acoustic receiver is independent of a reversal of the position of source and receiver. The work done on this study involves exciting a stationary tyre and measuring the surface velocity of the tyre at a number of discrete points. The acoustic transfer functions between each point on the tyre and a receiver point are measured reciprocally. Two sets of measurements are then combined to yield a measure of the sound pressure due to a point force on the tyre via the acoustic transmission path only. This technique also provides information on the relative contributions of various regions of the tyre wall to the resultant noise. Also the sound radiation characteristics, the horn effect, and resonance at the wheel housing are identified through the reciprocal measurement.     

Crystal Structure of Bis[hydrobis(3-phenylpyrazolyl)(5-phenylpyrazolyl)borato]-zinc(II)

Abstract  

The X-ray crystal structure of (C₅₄ H₄₂ B₂ N₁₂ Zn)*2(C H Cl₃) is reported. The title compound is a chloroform-solvated neutral complex crystallizing in the Triclinic space group, P − 1, with two half complexes (each located on a crystallographic center of inversion) and two full chloroform molecules appearing in the asymmetric unit. The capping ligands are related by symmetry and together form, essentially, an octahedral coordination sphere. Strain is apparent in the complex as indicated by asymmetric bond distances and angles. Final statistical data: R = 4.60% with I > 2σ(I), a = 11.2912(8) ?, b = 14.7912(11) ?, c = 17.0047(13) ?, α = 72.3560(10)°, β = 89.8950(10)°, γ = 88.1010(10)°, Z = 2.