Resource Requirements for Fault-Tolerant Quantum Simulation: The Transverse Ising Model Ground State

We estimate the resource requirements, the total number of physical qubits and computational time, required to compute the ground state energy of a 1-D quantum Transverse Ising Model (TIM) of N spin-1/2 particles, as a function of the system size and the numerical precision. This estimate is based on analyzing the impact of fault-tolerant quantum error correction in the context of the Quantum Logic Array (QLA) architecture. Our results show that due to the exponential scaling of the computational time with the desired precision of the energy, significant amount of error correciton is required to implement the TIM problem. Comparison of our results to the resource requirements for a fault-tolerant implementation of Shor's quantum factoring algorithm reveals that the required logical qubit reliability is similar for both the TIM problem and the factoring problem.Comment: 19 pages, 8 figure

Thermally activated resonant tunnelling in GaAs/AlGaAs triple barrier tunnelling structures

A thermally activated resonant tunnelling feature has been observed in the current-voltage characteristics (I(V)) of triple barrier resonant tunnelling structures (TBRTS) due to alignment of the n=1 confined states in the two quantum wells (QWs) within the active region. With rising sample temperature, the tunnelling current of the resonant feature increases in magnitude, showing a small negative differential resistance region which is discernable even at 293K. This behaviour is unique to multiple barrier devices and cannot be observed in conventional double barrier resonant tunnelling structures. Symmetric TBRTS, of nominal well widths 67Å and asymmetric QW, with decreasing second well widths, nominally 64Å to 46Å, have been studied with temperature dependent resonant tunnelling behaviour observed in both symmetric and asymmetric designs. Activation energies have been extracted from Arrhenius plots of the magnitude of the thermally activated peak current for each device design. This activation energy decreases as the second well width is decreased due to alignment occurring at increasingly greater bias and as such at energies closer to the Fermi level in the emitter region of the devices. Experimentally determined activation energies are in good agreement with theoretical values obtained by modelling the device I(V) characteristic

Capacity-Allocation Methods for Reducing Urban Traffic Congestion

It is unlikely that roadway construction or vehicle automation will be able to alleviate most major urban congestion in the near future (5-15 years). What else can be done to reasonably reduce congestion? Several approaches to reducing congestion by capacity allocation are reviewed: laissez-faire allocation, allocation by passenger load, ramp metering, road and parking pricing, allocation by trip purpose, rationing, and mixed strategies. These approaches are qualitatively compared against four criteria: effectiveness at reducing congestion, economic efficiency, income distribution effects, and flexibility of access for urgent trips. Recommendations are made regarding capacity-allocation measures with potential to reduce congestion and to increase economic efficiency. The equity impacts of these measures are identified and methods for mitigating these effects are proposed. Congestion pricing, together with free but metered on-ramps at freeways for nonpayers or with subsidies for lower-income households at1 are found to deserve further study and an incremental method of adoption is outlined

Baseline albumin-bilirubin (ALBI) in Western patients with hepatocellular carcinoma treated with stereotactic body radiotherapy (SBRT)

Purpose: To assess the baseline albumin-bilirubin (ALBI) score as a predictor of toxicity and survival in a prospective cohort of Western patients with hepatocellular carcinoma (HCC) treated with stereotactic body radiation therapy (SBRT) in 2 prospective trials. Methods and Materials: The study included 102 patients with Child-Pugh class A liver disease who received 6-fraction SBRT for HCC. Univariate and multivariable logistic regression investigated factors associated with toxicity, defined as an increase in Child-Pugh score ≥ 2 within 3 months of SBRT. Univariate and multivariable Cox regression analyses investigated factors predictive of overall survival (OS). The ALBI score was analyzed as a continuous and binary variable in separate analyses. Results: On multivariable analysis of toxicity, including the ALBI score as a continuous variable, the ALBI score (odds ratio [OR] per 0.1-unit increase, 1.51; 95% confidence interval [CI] 1.23-1.85; P = .00074), mean liver dose (OR, 1.31; 95% CI 1.02-1.68; P = .036), and dose received by 800 cm3 of normal liver (OR, 1.10; 95% CI 1.01-1.20; P = .028) were significant. When the ALBI score was included as a dichotomous variable, the ALBI grade remained a significant predictor of toxicity (OR, 7.44; 95% CI 2.34-23.70; P = .00069). On multivariable analysis of OS, including the ALBI score as a continuous variable, the ALBI score (hazard ratio [HR] per 0.1-unit increase, 1.09; 95% CI 1.03-1.17; P = .004), tumor thrombus (HR, 1.94; 95% CI 1.23-3.07; P = .004), and treatment in trial 1 versus trial 2 (HR, 1.92; 95% CI 1.23-3.03; P = .004) were significant. Similarly, when the ALBI score was included as a binary variable, the ALBI grade, tumor thrombus, and trial were significant predictors of OS. When the ALBI score was considered, the Child-Pugh score (A6 vs A5) was not significant in multivariable models analyzing toxicity or survival. Concordance statistics indicated models containing the ALBI score were superior to those containing the Child-Pugh score. Conclusions: The baseline ALBI score was more discriminating than the Child-Pugh score in predicting OS and toxicity in patients with Child-Pugh class A liver disease. The ALBI score should be used as a factor for stratification in future HCC SBRT trials

The Multi-Object, Fiber-Fed Spectrographs for SDSS and the Baryon Oscillation Spectroscopic Survey

We present the design and performance of the multi-object fiber spectrographs for the Sloan Digital Sky Survey (SDSS) and their upgrade for the Baryon Oscillation Spectroscopic Survey (BOSS). Originally commissioned in Fall 1999 on the 2.5-m aperture Sloan Telescope at Apache Point Observatory, the spectrographs produced more than 1.5 million spectra for the SDSS and SDSS-II surveys, enabling a wide variety of Galactic and extra-galactic science including the first observation of baryon acoustic oscillations in 2005. The spectrographs were upgraded in 2009 and are currently in use for BOSS, the flagship survey of the third-generation SDSS-III project. BOSS will measure redshifts of 1.35 million massive galaxies to redshift 0.7 and Lyman-alpha absorption of 160,000 high redshift quasars over 10,000 square degrees of sky, making percent level measurements of the absolute cosmic distance scale of the Universe and placing tight constraints on the equation of state of dark energy. The twin multi-object fiber spectrographs utilize a simple optical layout with reflective collimators, gratings, all-refractive cameras, and state-of-the-art CCD detectors to produce hundreds of spectra simultaneously in two channels over a bandpass covering the near ultraviolet to the near infrared, with a resolving power R = \lambda/FWHM ~ 2000. Building on proven heritage, the spectrographs were upgraded for BOSS with volume-phase holographic gratings and modern CCD detectors, improving the peak throughput by nearly a factor of two, extending the bandpass to cover 360 < \lambda < 1000 nm, and increasing the number of fibers from 640 to 1000 per exposure. In this paper we describe the original SDSS spectrograph design and the upgrades implemented for BOSS, and document the predicted and measured performances.Comment: 43 pages, 42 figures, revised according to referee report and accepted by AJ. Provides background for the instrument responsible for SDSS and BOSS spectra. 4th in a series of survey technical papers released in Summer 2012, including arXiv:1207.7137 (DR9), arXiv:1207.7326 (Spectral Classification), and arXiv:1208.0022 (BOSS Overview

Task-specific reach-to-grasp training after stroke: Development and description of a home-based intervention

© The Author(s) 2015. This series of articles for rehabilitation in practice aims to cover a knowledge element of the rehabilitation medicine curriculum. Nevertheless they are intended to be of interest to a multidisciplinary audience. The competency addressed in this article is to transparently describe the process of developing a complex intervention for people after stroke as part of a feasibility randomised controlled trial. Objective: To describe and justify the development of a home-based, task-specific upper limb training intervention to improve reach-to-grasp after stroke and pilot it for feasibility and acceptability prior to a randomized controlled trial. Intervention description: The intervention is based on intensive practice of whole reach-to-grasp tasks and part-practice of essential reach-to-grasp components. A 'pilot' manual of activities covering the domains of self-care, leisure and productivity was developed for the feasibility study. The intervention comprises 14 hours of therapist-delivered sessions over six weeks, with additional self-practice recommended for 42 hours (i.e. one hour every day). As part of a feasibility randomized controlled trial, 24 people with a wide range of upper limb impairment after stroke experienced the intervention to test adherence and acceptability. The median number of repetitions in one-hour therapist-delivered sessions was 157 (interquartile range IQR 96-211). The amount of self-practice was poorly documented. Where recorded, the median amount of practice was 30 minutes (interquartile range 22-45) per day. Findings demonstrated that the majority of participants found the intensity, content and level of difficulty of the intervention acceptable, and the programme to be beneficial. Comments on the content and presentation of the self-practice material were incorporated in a revised 'final' intervention manual. Discussion: A comprehensive training intervention to improve reach-to-grasp for people living at home after stroke has been described in accordance with the Template for Intervention Description and Replication (TIDieR) reporting guidelines. The intervention has been piloted, and found to be acceptable and feasible in the home setting. Trial registration: ISRCTN5671658

The prevalence and incidence of mental ill-health in adults with autism and intellectual disabilities

The prevalence, and incidence, of mental ill-health in adults with intellectual disabilities and autism were compared with the whole population with intellectual disabilities, and with controls, matched individually for age, gender, ability-level, and Down syndrome. Although the adults with autism had a higher point prevalence of problem behaviours compared with the whole adult population with intellectual disabilities, compared with individually matched controls there was no difference in prevalence, or incidence of either problem behaviours or other mental ill-health. Adults with autism who had problem behaviours were less likely to recover over a two-year period than were their matched controls. Apparent differences in rates of mental ill-health are accounted for by factors other than autism, including Down syndrome and ability level

Stable-isotope techniques to investigate sources of plant water

Stable isotopologues of water (mainly 1H216O, HD16O and 1H218O) have been used for decades as tracers of the Earth's water cycle. In this chapter, we briefly describe the theoretical background and state-of-the-art techniques of the use of water stable isotopes to investigate the sources of plant water. We aim to provide the basic understanding of stable isotope fractionation within the Earth's critical zone that is relevant for studies of plant water sources. We then present a practical guide of their most common applications in field studies and the most common and up-to-date laboratory procedures. We finally introduce the existing statistical approaches for estimating the relative contributions of water sources to plant transpiration. By acknowledging the advantages and limitations of each approach, we aim to provide an overview of the current techniques to researchers in the fields of plant ecophysiology, ecohydrology and forest ecology, so that they can make informed decisions when designing their experiments