Strong efficiency improvement of SOI-LEDs through carrier confinement

Contemporary silicon light-emitting diodes in silicon-on-insulator (SOI) technology suffer from poor efficiency compared to their bulk-silicon counterparts. In this letter, we present a new device structure where the carrier injection takes place through silicon slabs of only a few nanometer thick. Its external quantum efficiency of 1.4 • 10−4 at room temperature, with a spectrum peaking at 1130 nm, is almost two orders higher than reported thus far on SOI. The structure diminishes the dominant role of nonradiative recombination at the n+ and p+contacts, by confining the injected carriers in an SOI peninsula.\ud With this approach, a compact infrared light source can be fabricated using standard semiconductor processing steps.\u

Nonequilibrium candidate Monte Carlo: A new tool for efficient equilibrium simulation

Metropolis Monte Carlo simulation is a powerful tool for studying the equilibrium properties of matter. In complex condensed-phase systems, however, it is difficult to design Monte Carlo moves with high acceptance probabilities that also rapidly sample uncorrelated configurations. Here, we introduce a new class of moves based on nonequilibrium dynamics: candidate configurations are generated through a finite-time process in which a system is actively driven out of equilibrium, and accepted with criteria that preserve the equilibrium distribution. The acceptance rule is similar to the Metropolis acceptance probability, but related to the nonequilibrium work rather than the instantaneous energy difference. Our method is applicable to sampling from both a single thermodynamic state or a mixture of thermodynamic states, and allows both coordinates and thermodynamic parameters to be driven in nonequilibrium proposals. While generating finite-time switching trajectories incurs an additional cost, driving some degrees of freedom while allowing others to evolve naturally can lead to large enhancements in acceptance probabilities, greatly reducing structural correlation times. Using nonequilibrium driven processes vastly expands the repertoire of useful Monte Carlo proposals in simulations of dense solvated systems

Metal-insulator transition in the quarter- filled frustrated checkerboard lattice

We study the electronic structure and correlations in the geometrically frustrated two dimensional checkerboard lattice. In the large U limit considered here we start from an extended Hubbard model of spinless fermions at half-filling. We investigate the model within two distinct Green's function approaches: In the first approach a single-site representation decoupling scheme is used that includes the effect of nearest neighbor charge fluctuations. In the second approach a cluster representation leading to a 'multiorbital' model is investigated which includes intra-cluster correlations exactly and those between clusters on a mean field basis. It is demonstrated that with increasing nearest-neighbor Coulomb interaction V both approaches lead to a metal-insulator transition with an associated 'Mott-Hubbard' like gap caused by V. Within the single site approach we also explore the possibility of charge order. Furthermore we investigate the evolution of the quasiparticle bands as funtion of V

On-line planning and scheduling: an application to controlling modular printers

We present a case study of artificial intelligence techniques applied to the control of production printing equipment. Like many other real-world applications, this complex domain requires high-speed autonomous decision-making and robust continual operation. To our knowledge, this work represents the first successful industrial application of embedded domain-independent temporal planning. Our system handles execution failures and multi-objective preferences. At its heart is an on-line algorithm that combines techniques from state-space planning and partial-order scheduling. We suggest that this general architecture may prove useful in other applications as more intelligent systems operate in continual, on-line settings. Our system has been used to drive several commercial prototypes and has enabled a new product architecture for our industrial partner. When compared with state-of-the-art off-line planners, our system is hundreds of times faster and often finds better plans. Our experience demonstrates that domain-independent AI planning based on heuristic search can flexibly handle time, resources, replanning, and multiple objectives in a high-speed practical application without requiring hand-coded control knowledge

Political economy of the petroleum sector in Nigeria

The relatively slow pace of Nigeria's development has often been attributed to the phenomenon of the resource curse whereby the nature of the state as a"rentier"dilutes accountability for development and political actors are able to manipulate institutions to sustain poor governance. The impact of the political elite's resource-control and allocation of revenues on core democratic mechanisms is central to understand the obstacles to development and governance failure. Given that problems of petroleum sector governance are extremely entrenched in Nigeria, the key question is whether and how it is possible to get out of a poor equilibrium after fifty years of oil production. This paper uses a political economy perspective to analyze the governance weaknesses along the petroleum sector value chain and attempts to establish the links between challenges in sector regulation and the following major political and economic attributes: (i) strong executive control on petroleum governance in a political environment of weak checks and balances; (ii) regulatory and operating roles bundled into one institution, thereby creating conflict of interest; and (iii) manipulation of elections and political appointments. The restoration of democratic government has helped improve transparency and management of oil revenue and reforms at the federal level and proposed reforms of the petroleum sector hold much promise. At the same time, the judiciary has started to restore confidence that it will serve as a check and balance on the executive and the electoral process. Yet, these reforms are fragile and need to be deepened and institutionalized. They must be addressed not as purely technocratic matters but as issues of political economy and vested interests that must, through regulation and reform, be aligned with the public interest and a vision of Nigerian development.National Governance,Environmental Economics&Policies,Oil Refining&Gas Industry,Energy Production and Transportation,Public Sector Corruption&Anticorruption Measures

Photophysics and Photochemistry Enabled by Ligand-to-Metal-Charge-Transfer: Unusual Carbon-Carbon Bond Formation at a Zirconium Center

Six Group 4 metallocene derivatives of group 4 incorporating a redox active benzene-1,2-thiolate ligand (bdt) were prepared. These complexes were characterized using one- and two-dimensional nuclear magnetic resonance (NMR) spectroscopy. Additionally, X-ray crystallographic analyses of these complexes, with the exception of Cp2Zrbdt (Cp = cyclopentadienyl), reveal C2v symmetric structure in the solid-state. All species display electronic absorption bands that are ligand-to-metal charge transfer (LMCT) in character well into the visible region. Spectroscopic data combine with time dependent-density functional theory calculations showed fluctuation in solution which promotes non-radiative energy loss and leads to the absence of emission in solution at room temperature. Cyclic voltammograms have one reversible reduction event that is metal-centered. Except for Cp*2Hfbdt (Cp* = permethylcyclopentadienyl), the remaining five complexes exhibit an irreversible oxidation event. (MePMPMe)2ZrBn2 (MePMPMe = 3,5-dimethyl-2-(2-pyridyl)pyrrolide; Bn = benzyl) was synthesized and characterized via X-ray crystallography and NMR spectroscopy. The complex has LMCT absorption in the blue light region and is photoactive upon irradiation with blue LED. Photolysis of (MePMPMe)2ZrBn2 in the presence of excess diphenylacetylene proceeds with the formation of (MePMPMe)2(η4-C4Ph4) – the first zirconium complex featuring a coordinated cyclobutadienyl ligand. Using 4-methylbenzyl bromide as a mild oxidant, (MePMPMe)2ZrBr2 was cleanly made. A mixture of bibenzyl byproducts suggests a radical mechanism. Testing disulfide substrates lead to the formation of two new multinuclear zirconium thiophenolate complexes identified via X-ray crystallography. Expanding the substrate scope of the photoreaction by less substituted alkyne such as 1-phenyl-1-propyne, phenylacetylene, and ethynylanisole derivatives resulted in catalytic trimerization, forming benzene derivatives that are generally selective toward one isomer. Precatalyst (MePMPMe)2ZrBn2 can also tolerate benzonitrile. Preliminary experiments with 1,6-heptadiene also catalytically produced a new organic product. CO addition produced a new zirconium species that is NMR silent. Overall, the photoreaction selectivity and fast reactivity are specific to the photochemical pathway compared to thermal condition or using KC8 reductant to reduce the Zr center. Using photoactive (MePMPMe)2ZrBn2 can form new zirconium complexes and catalytically generate organic molecules with complimentary selectivity to using late transition metals catalysts. With further exploration, this methodology can be a useful tool in inorganic and organic synthesis

Efficient Human Vision Inspired Action Recognition using Adaptive Spatiotemporal Sampling

Adaptive sampling that exploits the spatiotemporal redundancy in videos is critical for always-on action recognition on wearable devices with limited computing and battery resources. The commonly used fixed sampling strategy is not context-aware and may under-sample the visual content, and thus adversely impacts both computation efficiency and accuracy. Inspired by the concepts of foveal vision and pre-attentive processing from the human visual perception mechanism, we introduce a novel adaptive spatiotemporal sampling scheme for efficient action recognition. Our system pre-scans the global scene context at low-resolution and decides to skip or request high-resolution features at salient regions for further processing. We validate the system on EPIC-KITCHENS and UCF-101 datasets for action recognition, and show that our proposed approach can greatly speed up inference with a tolerable loss of accuracy compared with those from state-of-the-art baselines. Source code is available in https://github.com/knmac/adaptive_spatiotemporal

An ultrafast 1 x M all-optical WDM packet-switched router based on the PPM header address

This paper presents an all-optical 1 x M WDM router architecture for packet routing at multiple wavelengths simultaneously, with no wavelength conversion modules. The packet header address adopted is based on the pulse position modulation (PPM) format, thus enabling the use of only a singlebitwise optical AND gate for fast header address correlation. It offers multicast as well as broadcast capabilities. It is shown that a high speed packet routing at 160 Gb/s can be achieved with a low channel crosstalk (CXT) of ~ -27 dB at a channel spacing of greater than 0.4 THz and a demultiplexer bandwidth of 500 GHz

Path integral analysis of Jarzynski's equality: Analytical results

We apply path integrals to study nonequilibrium work theorems in the context of Brownian dynamics, deriving in particular the equations of motion governing the most typical and most dominant trajectories. For the analytically soluble cases of a moving harmonic potential and a harmonic oscillator with time-dependent natural frequency, we find such trajectories, evaluate the work-weighted propagators, and validate Jarzynski's equality.Comment: 10 pages, 1 figur