Correlated charge polarization in a chain of coupled quantum dots

Coherent charge transfer in a linear array of tunnel-coupled quantum dots, electrostatically coupled to external gates, is investigated using the Bethe ansatz for a symmetrically biased Hubbard chain. Charge polarization in this correlated system is shown to proceed via two distinct processes: formation of bound states in the metallic phase, and charge transfer processes corresponding to a superposition of antibound states at opposite ends of the chain in the Mott-insulating phase. The polarizability in the insulating phase of the chain exhibits a universal scaling behavior, while the polarization charge in the metallic phase of the model is shown to be quantized in units of $e/2$.Comment: 9 pages, 3 figures, 1 tabl

Investigation of the effect of hot water and water vapour treatments on the strength of thermally conditioned E-glass fibres

The processing and reuse of end-of-life composite products in an environmentally friendly manner is an important challenge facing the industry. The development of an economically viable process for regenerating the properties of thermally recycled glass fibres would have significant technological, economic and environmental impacts. Thermal recycling processes for composites are relatively technologically advanced; however, they present a substantial challenge when considering their use for recycling of glass fibre reinforced materials. A combination of exposure to elevated temperatures in the region 450 – 600 °C and to mechanical damage has been shown to cause significant strength loss in glass fibres of up to 90 % of their original value. The recovered fibres are thus unsuitable for use as reinforcement in a second generation composite. Methods of strength recovery that may be applied to such recycled fibres are therefore of interest, particularly if these methods are relatively technologically straightforward. An investigation of possible strength recovery methods using hot water or water vapour was carried out on E-glass fibres. The methods were derived from similar studies on silica in which significant strengthening effects were presented alongside theoretical frameworks to explain the phenomenon [1–3]; a maximum threefold increase in strength following water vapour treatment at 250 °C was demonstrated on silica artificially weakened by abrasion

An Outbreak of Salmonella typhimurium at a teaching hospital

An outbreak of Salmonella typhimurium infection in December 1996 affected 52 patients, relatives, and staff of a large teaching hospital in southeast Queensland. Assorted sandwiches were identified as the vehicle of transmission. This article describes the outbreak investigation and demonstrates the importance of food hygiene and timely public health interventions

Capacity of Second-Growth Douglas-fir and Western Hemlock Stump Anchors for Cable Logging

The use of small instead of large stumps for cable logging anchors will usually result in applied loads approaching the load capacity of the anchors more closely. The use of small stump anchors is then contingent on better means of assessing their capacity. The results of field load tests of Douglas-fir and western hemlock stump anchors are reported. Ultimate loads were modeled as power functions of DBH. In addition, the relation between load and movement relationships for the stumps are modeled using a hyperbolic function that also provides an estimate of ultimate load. Practical use of the model equations requires knowledge of failure statistics and the acceptance of a probabilistic anchor capacity. Probability is applied to the re-rigging required when an anchor fails to perform adequately and to total pull-out failure

Coherent Resonant Tunneling Through an Artificial Molecule

Coherent resonant tunneling through an artificial molecule of quantum dots in an inhomogeneous magnetic field is investigated using an extended Hubbard model. Both the multiterminal conductance of an array of quantum dots and the persistent current of a quantum dot molecule embedded in an Aharanov-Bohm ring are calculated. The conductance and persistent current are calculated analytically for the case of a double quantum dot and numerically for larger arrays using a multi-terminal Breit-Wigner type formula, which allows for the explicit inclusion of inelastic processes. Cotunneling corrections to the persistent current are also investigated, and it is shown that the sign of the persistent current on resonance may be used to determine the spin quantum numbers of the ground state and low-lying excited states of an artificial molecule. An inhomogeneous magnetic field is found to strongly suppress transport due to pinning of the spin-density-wave ground state of the system, and giant magnetoresistance is predicted to result from the ferromagnetic transition induced by a uniform external magnetic field.Comment: 23 pages, 12 figure

Disorder and Interaction in 2D: Exact diagonalization study of the Anderson-Hubbard-Mott model

We investigate, by numerically calculating the charge stiffness, the effects of random diagonal disorder and electron-electron interaction on the nature of the ground state in the 2D Hubbard model through the finite size exact diagonalization technique. By comparing with the corresponding 1D Hubbard model results and by using heuristic arguments we conclude that it is \QTR{it}{unlikely} that there is a 2D metal-insulator quantum phase transition although the effect of interaction in some range of parameters is to substantially enhance the non-interacting charge stiffness.Comment: 13 pages, 2 figures Revised version. Accepted for publication in Phys. Rev. Let

Transport Properties of One-Dimensional Hubbard Models

We present results for the zero and finite temperature Drude weight D(T) and for the Meissner fraction of the attractive and the repulsive Hubbard model, as well as for the model with next nearest neighbor repulsion. They are based on Quantum Monte Carlo studies and on the Bethe ansatz. We show that the Drude weight is well defined as an extrapolation on the imaginary frequency axis, even for finite temperature. The temperature, filling, and system size dependence of D is obtained. We find counterexamples to a conjectured connection of dissipationless transport and integrability of lattice models.Comment: 10 pages, 14 figures. Published versio

Control of quantum interference in molecular junctions: Understanding the origin of Fano and anti- resonances

We investigate within a coarse-grained model the conditions leading to the appearance of Fano resonances or anti-resonances in the conductance spectrum of a generic molecular junction with a side group (T-junction). By introducing a simple graphical representation (parabolic diagram), we can easily visualize the relation between the different electronic parameters determining the regimes where Fano resonances or anti-resonances in the low-energy conductance spectrum can be expected. The results obtained within the coarse-grained model are validated using density-functional based quantum transport calculations in realistic T-shaped molecular junctions.Comment: 5 pages, 5 figure

An Axiomatic Setup for Algorithmic Homological Algebra and an Alternative Approach to Localization

In this paper we develop an axiomatic setup for algorithmic homological algebra of Abelian categories. This is done by exhibiting all existential quantifiers entering the definition of an Abelian category, which for the sake of computability need to be turned into constructive ones. We do this explicitly for the often-studied example Abelian category of finitely presented modules over a so-called computable ring $R$, i.e., a ring with an explicit algorithm to solve one-sided (in)homogeneous linear systems over $R$. For a finitely generated maximal ideal $\mathfrak{m}$ in a commutative ring $R$ we show how solving (in)homogeneous linear systems over $R_{\mathfrak{m}}$ can be reduced to solving associated systems over $R$. Hence, the computability of $R$ implies that of $R_{\mathfrak{m}}$. As a corollary we obtain the computability of the category of finitely presented $R_{\mathfrak{m}}$-modules as an Abelian category, without the need of a Mora-like algorithm. The reduction also yields, as a by-product, a complexity estimation for the ideal membership problem over local polynomial rings. Finally, in the case of localized polynomial rings we demonstrate the computational advantage of our homologically motivated alternative approach in comparison to an existing implementation of Mora's algorithm.Comment: Fixed a typo in the proof of Lemma 4.3 spotted by Sebastian Posu

Study of direct versus orbital entry for Mars missions. Volume 6 - Appendix D - Subsystem studies and parametric data Final report

Subsystems analyses and parametric data on configurations for direct versus orbital entry for Mars mission