Structure of the Hilbert-space of the infinite-dimensional Hubbard model

An iterative procedure for the explicit construction of the nontrivial subspace of all symmetry-adapted configurations with non-zero weight in the ground-state of the infinite-dimensional Hubbard model is developed on the basis of a symmetrized representation of the transition operators on a sequence of Bethe-Lattices of finite depth. The relation ship between these operators and the well known mapping of the infinite-dimensional Hubbard model onto an effective impurity problem coupled to a (self-consistent) bath on non-interacting electrons is given. As an application we calculate the properties of various Hubbard stars and give estimates for the half-filled Hubbard model with up to 0.1% accuracy.Comment: accepted for publication in EJP

Influence of structural disorder and large-scale geometric fluctuations on the Coherent Transport of Metallic Junctions and Molecular Wires

Structural disorder is present in almost all experimental measurements of electronic transport through single molecules or molecular wires. To assess its influence on the conductance is computationally demanding, because a large number of conformations must be considered. Here we analyze an approximate recursive layer Green function approach for the ballistic transport through quasi one-dimensional nano-junctions. We find a rapid convergence of the method with its control parameter, the layer thickness, and good agreement with existing experimental and theoretical data. Because the computational effort rises only linearly with system size, this method permits treatment of very large systems. We investigate the conductance of gold- and silver wires of different sizes and conformations. For weak electrode disorder and imperfect coupling between electrode and wire we find conductance variations of approximately 20%. Overall we find the conductance of silver junctions well described by the immediate vicinity of narrowest point in the junction, a result that may explain the observation of well-conserved conductance plateaus in recent experiments on silver junctions. In an application to flexible oligophene wires, we find that strongly distorted conformations that are sterically forbidden at zero temperature, contribute significantly to the observed average zero-bias conductance of the molecular wire

Analytical investigation of nonrecoverable stall

A lumped parameter model of the TF34 engine is formulated to study nonrecoverable stall. Features of the model include forward and reverse flow, radial flow in the fan, and variable corrected speed. The purpose of the study is to point out those parameters to which recoverability is highly sensitive but are not well known. Experimental research may then be directed toward identification of the parameters in that category. Compressor performance in the positive flow region and radial flow in the fan are shown to be important but unknown parameters determining recoverability. Other parameters such as compressor performance during reverse flow and in-stall efficiency have relatively small impact on recoverability

Inuit settlement in the Clyde area during “contact-exploration” times (ca. 1820-1895)

Dans son classique The Central Eskimo (1888), Frank Boas laisse fortement entendre qu’au moment de son périple le plus septentrional, les Inuit utilisaient très peu le littoral de la Terre de Baffin entre la baie Home au nord et le détroit d’Éclipse, qui correspond aujourd’hui à la région de la rivière Clyde. Une étude ethnohistorique concernant les établissements inuit de cette région avant la présence européenne s’est avérée décevante à cause du manque de références temporelles associées à l’information reçue des aînés de Clyde. Néanmoins, l’utilisation avec les informateurs d’indices temporels tirés de la littérature a donné de meilleurs résultats. Le présent article met en lien des souvenirs d’Inuit de Clyde avec trois récits concernant des Inuit du 19e siècle dans la région. Le plus ancien de ceux-ci (1820) se déroule à l’emplacement presque exact du village moderne de Clyde River, les deux autres, dans la décennie suivant le séjour de Boas. Ces comptes rendus, conjugués à l’information recueillie par Mathiassen (1928) auprès d’Inuit de Pond Inlet au sujet de leur lieu de naissance et de leurs déplacements, semblent indiquer que la région de Clyde était loin d’être inconnue des Inuit, même s’ils ne l’occupaient peut-être pas de façon intensive.Boas, in his classic The Central Eskimo (1888), strongly implied that at the time of his most northerly journey the Baffin Island coast between northern Home Bay and Eclipse Sound, what is today the Clyde River area, was at most only lightly utilised by Inuit. Ethnohistorical inquiry about Inuit settlement in the area prior to a European presence was frustrated by a lack of temporal referencing for much of the information received from Clyde elders. However, more success was achieved by using temporally situated literature references as cues for informants. This paper relates Clyde Inuit recollections to three reports about 19th century Inuit in the region. The earliest of these (1820) occurred almost at the site of modern Clyde River, while the other two reports are both within a decade of Boas’s journey. These accounts, coupled with Mathiassen’s (1928) information from Inuit at Pond Inlet about their birthplaces and travels, suggest that the Clyde area, while perhaps not intensively occupied, was far from unknown to Inuit

Spatial audio in small display screen devices

Our work addresses the problem of (visual) clutter in mobile device interfaces. The solution we propose involves the translation of technique-from the graphical to the audio domain-for expliting space in information representation. This article presents an illustrative example in the form of a spatialisedaudio progress bar. In usability tests, participants performed background monitoring tasks significantly more accurately using this spatialised audio (a compared with a conventional visual) progress bar. Moreover, their performance in a simultaneously running, visually demanding foreground task was significantly improved in the eye-free monitoring condition. These results have important implications for the design of multi-tasking interfaces for mobile devices