Simulation of the Unsteady Gas Flow through a Three-way Automotive Catalyst

This paper describes a model of a 1.8-litre four-cylinder four-stroke gasoline engine fitted with a close-coupled three-way catalyst (TWC). Designed to meet EURO 3 emissions standards, the engine includes some advanced emission control features in addition to the TWC, namely: variable valve timing (VVT), swirl control plates, and exhaust gas recirculation (EGR). Gas flow is treated as one-dimensional (1D) and unsteady in the engine ducting and in the catalyst. Reflection and transmission of pressure waves at the boundaries of the catalyst monolith are modelled. In-cylinder combustion is represented by a two-zone burn model with dissociation and reaction kinetics. A single Wiebe analysis of measured in-cylinder pressure data is used to determine the mass fraction burned as a function of crank angle (CA) at each engine speed. Measured data from steady-state dynamometer tests are presented for operation at wide open throttle (WOT) over a range of engine speeds. These results include CA-resolved traces of pressure at various locations throughout the engine together with cycle-averaged traces of gas composition entering the catalyst as indicated by a fast-response emissions analyser. Simulated engine performance and pressure wave action throughout the engine are well validated by the measured data.

Effects of tip structure on the generation of metal clusters by an STM tip: a way to control the orientation of nanocrystallites?

The role of the crystalline orientation of the STM tip in the generation of metal clusters is studied by atom dynamics simulations. When a (111) facet is facing the surface, the process is accompanied by a perturbation of the surface stronger than that observed for more open tip structures. This implies a technological application: the possibility of orienting a nanocrystallite deposited on a tip according to the changes observed in the force on the tip.

An economical route to one-way quantum computation

We assess the effects of a realistic intrinsic model for imperfections in cluster states by introducing noisy cluster states and characterizing their role in the one-way computational model. A suitable strategy to counter-affect these non-idealities is represented by the use of small clusters, stripped of any redundancy, which leads to the search for compact schemes for one-way quantum computation. In light of this, we quantitatively address the behavior of a simple four-qubit cluster which simulates a controlled-NOT under the influences of our model for decoherence. Our scheme can be particularly useful in an all-optical setup and the strategy we address can be directly applied in those, experimental situations where small cluster states can be constucted.

Natural three-qubit interactions in one-way quantum computing

We address the effects of natural three-qubit interactions on the computational power of one-way quantum computation. A benefit of using more sophisticated entanglement structures is the ability to construct compact and economic simulations of quantum algorithms with limited resources. We show that the features of our study are embodied by suitably prepared optical lattices, where effective three-spin interactions have been theoretically demonstrated. We use this to provide a compact construction for the Toffoli gate. Information flow and two-qubit interactions are also outlined, together with a brief analysis of relevant sources of imperfection.

Experimental demonstration of decoherence-free one-way information transfer

We report the experimental demonstration of a one-way quantum protocol reliably operating in the presence of decoherence. Information is protected by designing an appropriate decoherence-free subspace for a cluster state resource. We demonstrate our scheme in an all-optical setup, encoding the information into the polarization states of four photons. A measurement-based one-way information-transfer protocol is performed with the photons exposed to severe symmetric phase-damping noise. Remarkable protection of information is accomplished, delivering nearly ideal outcomes.

One-way quantum computing in a decoherence-free subspace

We introduce a novel scheme for one-way quantum computing (QC) based on the use of information encoded qubits in an effective cluster state resource. With the correct encoding structure, we show that it is possible to protect the entangled resource from phase damping decoherence, where the effective cluster state can be described as residing in a decoherence-free subspace (DFS) of its supporting quantum system. One-way QC then requires either single or two-qubit adaptive measurements. As an example where this proposal can be realized, we describe an optical lattice set-up where the scheme provides robust quantum information processing. We also outline how one can adapt the model to provide protection from other types of decoherence.

No Easy Way Through: Black Workers and Race Leadership at the Nadir

It is difficult, even excruciating, to imagine the staggering descent from high optimism to despondency experienced by many African Americans who lived between emancipation and the dawn of the twentieth century. For historians living in the post–civil rights era, recapturing the scale, velocity, and brutality of that dramatic fall has been hampered by two conceptual problems. The first of these, undergirded by prominent trends in the formerly “new” social history, is a widely shared enthusiasm for illuminating those hidden corners of daily life where men and women on the receiving end of Jim Crow continued to wield a degree of control. “Agency” has been the buzzword for a generation of scholarship that emphasizes the staying power and persistence of black Southerners in the face of relentless assaults on their social and economic status, their civil rights, and even, at times, their collective existence. This is, in many ways, an understandable reaction to an earlier consensus that relegated black historical initiative to the margins of a national fable cleansed of unseemly violence and sharp social conflict, but it can also be problematic.