Tractable Simulation of Error Correction with Honest Approximations to Realistic Fault Models

In previous work, we proposed a method for leveraging efficient classical simulation algorithms to aid in the analysis of large-scale fault tolerant circuits implemented on hypothetical quantum information processors. Here, we extend those results by numerically studying the efficacy of this proposal as a tool for understanding the performance of an error-correction gadget implemented with fault models derived from physical simulations. Our approach is to approximate the arbitrary error maps that arise from realistic physical models with errors that are amenable to a particular classical simulation algorithm in an "honest" way; that is, such that we do not underestimate the faults introduced by our physical models. In all cases, our approximations provide an "honest representation" of the performance of the circuit composed of the original errors. This numerical evidence supports the use of our method as a way to understand the feasibility of an implementation of quantum information processing given a characterization of the underlying physical processes in experimentally accessible examples.Comment: 34 pages, 9 tables, 4 figure

Post-Uruguay Round price linkages between developed and developing countries

The Uruguay Round Agreement on Agriculture attempted to lower distortions in the global agricultural markets. However, the significant fall in commodity prices in late 1990s may have reduced the incentives for both developed and developing countries to better integrate into the world markets. This study analyzes price linkages and adjustment between developed and developing countries during the post-Uruguay Round period. Prices of two key commodity markets, long-grain rice and medium-hard wheat, are assembled for major exporters and producers. Results from the multivariate cointegration analysis suggest partial market integration between developed and developing countries in the post-Uruguay Round period. Developed countries are found to be price leaders in these two markets, and in most cases, the changes in their prices have relatively large impacts on those of the developing countries. The new entrants into world markets (Vietnam and Argentina) have faced considerable price adjustment due to changes in the developed countries' prices.Price linkages ,Wheat markets ,Rice markets ,Uruguay Round Agreement on Agriculture (URAA) ,Doha Developmental Round of the World Trade Organization (WTO) ,

Monolayer MoS2 strained to 1.3% with a microelectromechanical system

We report on a modified transfer technique for atomically thin materials integrated onto microelectromechanical systems (MEMS) for studying strain physics and creating strain-based devices. Our method tolerates the non-planar structures and fragility of MEMS, while still providing precise positioning and crack free transfer of flakes. Further, our method used the transfer polymer to anchor the 2D crystal to the MEMS, which reduces the fabrication time, increases the yield, and allowed us to exploit the strong mechanical coupling between 2D crystal and polymer to strain the atomically thin system. We successfully strained single atomic layers of molybdenum disulfide (MoS2) with MEMS devices for the first time and achieved greater than 1.3% strain, marking a major milestone for incorporating 2D materials with MEMS We used the established strain response of MoS2 Raman and Photoluminescence spectra to deduce the strain in our crystals and provide a consistency check. We found good comparison between our experiment and literature.Published versio

Applying autonomy to distributed satellite systems: Trends, challenges, and future prospects

While monolithic satellite missions still pose significant advantages in terms of accuracy and operations, novel distributed architectures are promising improved flexibility, responsiveness, and adaptability to structural and functional changes. Large satellite swarms, opportunistic satellite networks or heterogeneous constellations hybridizing small-spacecraft nodes with highperformance satellites are becoming feasible and advantageous alternatives requiring the adoption of new operation paradigms that enhance their autonomy. While autonomy is a notion that is gaining acceptance in monolithic satellite missions, it can also be deemed an integral characteristic in Distributed Satellite Systems (DSS). In this context, this paper focuses on the motivations for system-level autonomy in DSS and justifies its need as an enabler of system qualities. Autonomy is also presented as a necessary feature to bring new distributed Earth observation functions (which require coordination and collaboration mechanisms) and to allow for novel structural functions (e.g., opportunistic coalitions, exchange of resources, or in-orbit data services). Mission Planning and Scheduling (MPS) frameworks are then presented as a key component to implement autonomous operations in satellite missions. An exhaustive knowledge classification explores the design aspects of MPS for DSS, and conceptually groups them into: components and organizational paradigms; problem modeling and representation; optimization techniques and metaheuristics; execution and runtime characteristics and the notions of tasks, resources, and constraints. This paper concludes by proposing future strands of work devoted to study the trade-offs of autonomy in large-scale, highly dynamic and heterogeneous networks through frameworks that consider some of the limitations of small spacecraft technologies.Postprint (author's final draft

Spatial scale and small area population statistics for England and Wales

It is well-known that the results of analyses of aggregate data, such as those provided as outputs from censuses, are dependent on the size and shape of the zones used to report the data. However, many users of aggregate census data do not consider how far the zones utilised in their analyses capture spatial information about the population sub-groups they are studying. In addition, future data collection strategies should account for such issues. This article takes as its focus England and Wales, and it seeks to assess how far output areas (OAs) and aggregations of OAs capture information in selected population sub-groups and, therefore, how important it might be to use zones of a particular size in order to properly analyse the geographies of these sub-groups. The article uses the index of dissimilarity, Dxy (for groups x and y), and variograms to assess spatial variation in population sub-groups as represented by counts for OAs, lower layer super output areas (LSOAs), middle layer super output areas (MSOAs) and local authority districts (LAs), all produced as outputs from the Census in England and Wales. The analyses show how much information is contained at each spatial scale for sub-categories relating to age, ethnic group, housing tenure, car or van availability, qualifications, employment, limiting long-term illness (LLTI) and National Statistics Socio-economic Classification (NS-SeC). The amount of variation contained by each level of the hierarchy of zones differs markedly by population sub-group. LAs capture most (83%) of the variation in the spread of the population by the binary categorisation of White/Black, Asian and Minority Ethnic (far more than for any other variable), but there remains considerable local variation. The results suggest that zones larger than OAs are not geographically detailed enough to enable meaningful analysis of local-level differences between places and thus any alternative to the Census in the United Kingdom (with England and Wales as a specific case) must provide zones equivalent in size to OAs. If estimates are available only for larger areas then much information will be lost and our ability to explore how sub-group characteristics, or the relationships between variables, differ between localities will be considerably diminished. The results also provide evidence on some of the ways in which the population of England and Wales was geographically distributed in 2011

Prehypertensive blood pressures and regional cerebral blood flow independently relate to cognitive performance in midlife

Background High blood pressure is thought to contribute to dementia in late life, but our understanding of the relationship between individual differences in blood pressure ( BP ) and cognitive functioning is incomplete. In this study, cognitive performance in nonhypertensive midlife adults was examined as a function of resting BP and regional cerebral blood flow ( rCBF ) responses during cognitive testing. We hypothesized that BP would be negatively related to cognitive performance and that cognitive performance would also be related to rCBF responses within areas related to BP control. We explored whether deficits related to systolic BP might be explained by rCBF responses to mental challenge. Methods and Results Healthy midlife participants (n=227) received neuropsychological testing and performed cognitive tasks in a magnetic resonance imaging scanner. A pseudocontinuous arterial spin labeling sequence assessed rCBF in brain areas related to BP in prior studies. Systolic BP was negatively related to 4 of 5 neuropsychological factors (standardized β&gt;0.13): memory, working memory, executive function, and mental efficiency. The rCBF in 2 brain regions of interest was similarly related to memory, executive function, and working memory (standardized β&gt;0.17); however, rCBF responses did not explain the relationship between resting systolic BP and cognitive performance. Conclusions Relationships at midlife between prehypertensive levels of systolic BP and both cognitive and brain function were modest but suggested the possible value of midlife intervention. </jats:sec