Vibrational absorption sidebands in the Coulomb blockade regime of single-molecule transistors

Current-driven vibrational non-equilibrium induces vibrational sidebands in single-molecule transistors which arise from tunneling processes accompanied by absorption of vibrational quanta. Unlike conventional sidebands, these absorption sidebands occur in a regime where the current is nominally Coulomb blockaded. Here, we develop a detailed and analytical theory of absorption sidebands, including current-voltage characteristics as well as shot noise. We discuss the relation of our predictions to recent experiments.Comment: 7 pages, 6 figures; revised discussion of relation to experimen

Rhythmic inhibition allows neural networks to search for maximally consistent states

Gamma-band rhythmic inhibition is a ubiquitous phenomenon in neural circuits yet its computational role still remains elusive. We show that a model of Gamma-band rhythmic inhibition allows networks of coupled cortical circuit motifs to search for network configurations that best reconcile external inputs with an internal consistency model encoded in the network connectivity. We show that Hebbian plasticity allows the networks to learn the consistency model by example. The search dynamics driven by rhythmic inhibition enable the described networks to solve difficult constraint satisfaction problems without making assumptions about the form of stochastic fluctuations in the network. We show that the search dynamics are well approximated by a stochastic sampling process. We use the described networks to reproduce perceptual multi-stability phenomena with switching times that are a good match to experimental data and show that they provide a general neural framework which can be used to model other 'perceptual inference' phenomena

The physical environment and multi-professional teamwork in three newly built stroke units

Purpose: To explore multi-professional teamwork in relation to the physical environment in three newly built or renovated stroke units. Materials and methods: An observational study was undertaken. The participants were all staff members of a multi-professional team working in the reviewed stroke units. The data were collected using behavioural mapping and semi-structured observations, and they were analysed by content analysis and descriptive statistics. Results: Out of all the observations in the behavioural mapping, very few were of two or more members from the team together with a patient. None of the included stroke units had a co-location for all the members of the multi-professional team. Three main categories emerged from the analysis of the interviews: (i) the hub of the unit; (ii) the division of places; and (iii) power imbalance. All the categories reflected the teamwork in relation to parts of the physical environment. Conclusion: The design of the physical environment is important for multi-professional teamwork. Emphasis must be placed on better understanding the impact of the physical environment and on incorporating the evidence related to multi-professional teamwork during the design of stroke units.IMPLICATIONS FOR REHABILITATION Understanding the link between the physical environment and effective teamwork can lead to more tailored and supportive design solutions. The design of the physical environment should be considered as a vital part of effective teamwork in stroke units. The physical environment should include shared workstations, allowing team members to meet and communicate face to face

Metal-insulator transitions: Influence of lattice structure, Jahn-Teller effect, and Hund's rule coupling

We study the influence of the lattice structure, the Jahn-Teller effect and the Hund's rule coupling on a metal-insulator transition in AnC60 (A= K, Rb). The difference in lattice structure favors A3C60 (fcc) being a metal and A4C60 (bct) being an insulator, and the coupling to Hg Jahn-Teller phonons favors A4C60 being nonmagnetic. The coupling to Hg (Ag) phonons decreases (increases) the value Uc of the Coulomb integral at which the metal-insulator transition occurs. There is an important partial cancellation between the Jahn-Teller effect and the Hund's rule coupling.Comment: 4 pages, RevTeX, 3 eps figure, additional material available at http://www.mpi-stuttgart.mpg.de/docs/ANDERSEN/fullerene

Adaptive Optimization of Wave Functions for Fermion Lattice Models

We present a simulation algorithm for Hamiltonian fermion lattice models. A guiding trial wave function is adaptively optimized during Monte Carlo evolution. We apply the method to the two dimensional Gross-Neveu model and analyze systematc errors in the study of ground state properties. We show that accurate measurements can be achieved by a proper extrapolation in the algorithm free parameters.Comment: 4 pages, 6 figures (Encapsulated PostScript

Optical excitations in organic molecules, clusters and defects studied by first-principles Green's function methods

Spectroscopic and optical properties of nanosystems and point defects are discussed within the framework of Green's function methods. We use an approach based on evaluating the self-energy in the so-called GW approximation and solving the Bethe-Salpeter equation in the space of single-particle transitions. Plasmon-pole models or numerical energy integration, which have been used in most of the previous GW calculations, are not used. Fourier transforms of the dielectric function are also avoided. This approach is applied to benzene, naphthalene, passivated silicon clusters (containing more than one hundred atoms), and the F center in LiCl. In the latter, excitonic effects and the $1s \to 2p$ defect line are identified in the energy-resolved dielectric function. We also compare optical spectra obtained by solving the Bethe-Salpeter equation and by using time-dependent density functional theory in the local, adiabatic approximation. From this comparison, we conclude that both methods give similar predictions for optical excitations in benzene and naphthalene, but they differ in the spectra of small silicon clusters. As cluster size increases, both methods predict very low cross section for photoabsorption in the optical and near ultra-violet ranges. For the larger clusters, the computed cross section shows a slow increase as function of photon frequency. Ionization potentials and electron affinities of molecules and clusters are also calculated.Comment: 9 figures, 5 tables, to appear in Phys. Rev. B, 200

Financing IRPTN operations : considerations for cities implementing I(R)PTNs in South Africa

The case for investment in road-based public transport in South Africa is provided in the Public Transport Strategy for South Africa (2007) and subsequent policy positions by the national Department of Transport (DOT). This gave rise to the Integrated (Rapid) Public Transport Networks (I(R)PTNs) to be implemented in then 12 (now 13) priority cities. To support this implementation, the national Department of Transport created a conditional grant to the priority municipalities, first called the Public Transport Infrastructure Fund (PTIF), then the Public Transport Infrastructure and Systems Grant (PTISG) and now the Public Transport Infrastructure Grant (PTIG) and the Public Transport Network Operations Grant (PTNOG). Planning, establishment and rollout of the I(R)PTNs in the 13 cities, over the seven years to 2014, has highlighted the real costs of these systems. There is an emerging recognition of the extent of the I(R)PTN operational costs. Initial expectations were that fare income from passengers would cover the operating costs (at least the direct operating costs) of the system. However, implementation in a number of cities to date has shown that the fare box is not sufficient to cover the direct operating costs of the I(R)PTNs, unless the fares in the new system are increased significantly above the current costs of existing public transport. Such an increase would not be economically feasible for passengers and consequently introduce unacceptable affordability issues and open the way for competition with the I(R)PTN. As a result, cities have to consider alternative avenues to finance the direct operating costs of their I(R)PTNs. Some income sources are directly related to the new transport system (including advertising on the I(R)PTNs and congestion charges), some are commercial revenue options, and some are funding options from Municipal resources (eg increases in the rates bill, equitable share, services income). This paper explores the range of income options available to cities and the potential contribution to offsetting the shortfall. Based on the evidence to date, the operational shortfalls of I(R)PTNs in South Africa are greater than anticipated and, despite the opportunities for additional funding explored here, it is likely that significant shortfalls will remain. This presents a financial risk for city treasuries with whom rests the ultimate responsibility for covering the I(R)PTN costs. A continued conversation about funding for I(R)PTNs is therefore urgently required.Paper presented at the 34th Annual Southern African Transport Conference 6-9 July 2015 "Working Together to Deliver - Sakha Sonke", CSIR International Convention Centre, Pretoria, South Africa.The Minister of Transport, South AfricaTransportation Research Board of the US

IRPTN vehicle financing options and considerations

The roll-out of comprehensive public transport networks in our major cities is requiring considerable up-front investment by government. The acquisition of the bus fleet presents the second largest component of capital expenditure by the implementing municipalities. Various fleet financing models have been adopted including the use of national grant funding and debt. This paper sets out to describe the various financing models that have been used to date and highlight their implications with respect to various criteria including cost, risk and complexity. The paper then moves on to discuss the concern of municipal treasuries surrounding the potential consolidation of the buses onto the books of the municipalities and evaluates the effectiveness of the move to finance the buses ?off-balance sheet?. The rationale for the National Department of Transport?s (?NDOT?) preference for the use of Export Credit Agency financing (?ECAs?) as the financing route of choice is also discussed. The paper then addresses the outcomes of an on- versus off-balance sheet financing structure, and the implications on both the financing model and the underlying institutional structure. An alternate model is then introduced which proposes a hybrid between the debt financing options used thus far in an attempt to mitigate the short comings present in the existing models.Paper presented at the 34th Annual Southern African Transport Conference 6-9 July 2015 "Working Together to Deliver - Sakha Sonke", CSIR International Convention Centre, Pretoria, South Africa.The Minister of Transport, South AfricaTransportation Research Board of the US