Anderson Acceleration for Fixed-Point Iterations

This paper concerns an acceleration method for fixed-point iterations that originated in work of D. G. Anderson [J. Assoc. Comput. Mach., 12 (1965), pp. 547-560], which we accordingly call Anderson acceleration here. This method has enjoyed considerable success and wide usage in electronic structure computations, where it is known as Anderson mixing; however, it seems to have been untried or underexploited in many other important applications. Moreover, while other acceleration methods have been extensively studied by the mathematics and numerical analysis communities, this method has received relatively little attention from these communities over the years. A recent paper by H. Fang and Y. Saad [Numer. Linear Algebra Appl., 16 (2009), pp. 197-221] has clarified a remarkable relationship of Anderson acceleration to quasi-Newton (secant updating) methods and extended it to define a broader Anderson family of acceleration methods. In this paper, our goals are to shed additional light on Anderson acceleration and to draw further attention to its usefulness as a general tool. We first show that, on linear problems, Anderson acceleration without truncation is essentially equivalent in a certain sense to the generalized minimal residual (GMRES) method. We also show that the Type 1 variant in the Fang-Saad Anderson family is similarly essentially equivalent to the Arnoldi (full orthogonalization) method. We then discuss practical considerations for implementing Anderson acceleration and illustrate its performance through numerical experiments involving a variety of applications

Is the red dragon green? An examination of the antecedents and consequences of environmental proactivity in China

China is the world’s second largest economy and the largest emitter of carbon dioxide, yet we know little about environmental proactivity in the most populated country in the world. We address this gap through a survey of 161 Chinese companies with two respondents per firm (N = 322) where we seek to identify the antecedents and consequences of environmental proactivity. We identify two categorizations of environmental proactivity: Environmental operational improvements and environmental reporting. We find that ecological motivations and regulatory stakeholder pressure are positively related to both types of environmental proactivity, and external stakeholder pressure is negatively related to environmental reporting. Furthermore, we find that (1) if a firm is environmentally proactive (as it relates to either measure) and they are ecologically motivated, there is a positive and significant cost advantage, and (2) if a firm makes use of environmental operational improvement and they are competitively motivated, there is a positive and significant reputation advantage. Implications for researchers, managers, and policy-makers in China are discussed

Empirical Archetypes for Strong Corporate Environmental Performance

We examine 45 existing case studies of firms with strong corporate environmental performance (CEP) to empirically identify four organizational configurations for successful sustainability. These four configurations represent different combinations of variables describing a firm’s external environment, organizational structure, and its strategy-related activities. More specifically, these configurations vary in having a benign or challenging external environment, a mechanistic or organic structure, a low-cost or differentiation strategy, hands-on or hands-off participation by the top-management-team, high or low consideration given to stakeholders, and a short or long-term time orientation. Taken together the four organizational configurations introduce an understanding of equifinality for achieving CEP. In other words, given an adequate variety of ingredients, there are multiple recipes for successful sustainability. Implications for scholars, practitioners, and policy-makers and other stakeholders are discussed

Coherent versus Incoherent Light Scattering from a Quantum Dot

We analyze the light scattered by a single InAs quantum dot interacting with a resonant continuous-wave laser. High resolution spectra reveal clear distinctions between coherent and incoherent scattering, with the laser intensity spanning over four orders of magnitude. We find that the fraction of coherently scattered photons can approach unity under sufficiently weak or detuned excitation, ruling out pure dephasing as a relevant decoherence mechanism. We show how spectral diffusion shapes spectra, correlation functions, and phase-coherence, concealing the ideal radiatively-broadened two-level system described by Mollow.Comment: to appear in PRB 85, 23531

Combining the high-dose/refuge strategy and self-limiting transgenic insects in resistance management - a test in experimental mesocosms

This is the author accepted manuscript. The final version is available from Wiley via the DOI in this record.The high-dose/refuge strategy has been the primary approach for resistance management in transgenic crops engineered with Bacillus thuringiensis toxins. However, there are continuing pressures from growers to reduce the size of Bt toxin-free refugia, which typically suffer higher damage from pests. One complementary approach is to release male transgenic insects with a female-specific self-limiting gene. This technology can reduce population sizes and slow the evolution of resistance by introgressing susceptible genes through males. Theory predicts that it could be used to facilitate smaller refugia or reverse the evolution of resistance. In this study, we used experimental evolution with caged insect populations to investigate the compatibility of the self-limiting system and the high-dose/refuge strategy in mitigating the evolution of resistance in diamondback moth, Plutella xylostella. The benefits of the self-limiting system were clearer at smaller refuge size, particularly when refugia were inadequate to prevent the evolution of resistance. We found that transgenic males in caged mesocosms could suppress population size and delay resistance development with 10% refugia and 4% - 15% initial resistance allele frequency. Fitness costs in hemizygous transgenic insects are particularly important for introgressing susceptible alleles into target populations. Fitness costs of the self-limiting gene in this study (P. xylostella OX4139 line L) were incompletely dominant, and reduced fecundity and male mating competitiveness. The experimental evolution approach used here illustrates some of the benefits and pitfalls of combining mass-release of self-limiting insects and the high dose/refuge strategy, but does indicate that they can be complementary.This work was supported by the Biotechnology and Biological Sciences Research Council [grant numbers BB/L00948X/1 to MBB and NA, and BB/L00819X/1&2 to BR]

Cost Effectiveness of Protease Inhibitor Monotherapy Versus Standard Triple Therapy in the Long-Term Management of HIV Patients: Analysis Using Evidence from the PIVOT Trial

BACKGROUND: Protease inhibitor (PI) monotherapy can maintain virological suppression in the majority of patients once it has been established on triple therapy and may also have the potential for substantial cost savings arising from the use of fewer drugs. However, the cost effectiveness of PI monotherapy has yet to be demonstrated. OBJECTIVES: In this study we examine the cost effectiveness of PI monotherapy with prompt return to combination therapy in the event of viral load rebound compared with ongoing triple therapy (OT) in patients with suppressed viral load on combination antiretroviral therapy (ART) in the UK. METHODS: The analysis used data from the PIVOT trial in which HIV-positive adults with suppressed viral load for ≥24 weeks on combination ART were randomised to maintain OT or to a strategy of PI monotherapy with prompt return to combination therapy if viral load rebounded. A cost-effectiveness analysis including long-term modelling was conducted. Main outcomes included UK National Health Service (NHS) costs and quality-adjusted life-years (QALYs) with comparative results presented as incremental cost-effectiveness ratios. RESULTS: PI monotherapy was cost saving as a result of large savings in ART drug costs while being no less effective in terms of QALYs in the within-trial analysis and marginally less effective with lifetime modelling. In the base-case analysis over 3 years, the incremental total cost per patient was -£6424.11 (95 % confidence interval -7418.84 to -5429.38) and incremental QALYs were 0.0051 (95 % CI -0.0479 to 0.0582), resulting in PI monotherapy 'dominating' OT. Multiple scenario analyses found that PI monotherapy was cost saving with no marked differences in QALYs. Modelling of lifetime costs and QALYs showed that PI monotherapy was associated with significant cost savings and was marginally less effective; PI monotherapy was cost effective at accepted cost-effectiveness thresholds in all but one scenario analysis. CONCLUSIONS: Under most assumptions, PI monotherapy appears to be a cost-effective treatment strategy compared with OT for HIV-infected patients who have achieved sustained virological suppression

Optimal face-to-face coupling for fast self-folding kirigami

Kirigami-inspired designs can enable self-folding three-dimensional materials from flat, two-dimensional sheets. Hierarchical designs of connected levels increase the diversity of possible target structures, yet they can lead to longer folding times in the presence of fluctuations. Here, we study the effect of rotational coupling between levels on the self-folding of two-level kirigami designs driven by thermal noise in a fluid. Naturally present due to hydrodynamic resistance, we find that optimization of this coupling as control parameter can significantly improve a structure's self-folding rate and yield

Peripheral neuropathy in HIV patients in sub-Saharan Africa failing first-line therapy and the response to second-line ART in the EARNEST trial.

Sensory peripheral neuropathy (PN) remains a common complication in HIV-positive patients despite effective combination anti-retroviral therapy (ART). Data on PN on second-line ART is scarce. We assessed PN using a standard tool in patients failing first-line ART and for 96 weeks following a switch to PI-based second-line ART in a large Randomised Clinical Trial in Sub-Saharan Africa. Factors associated with PN were investigated using logistic regression. Symptomatic PN (SPN) prevalence was 22 % at entry (N = 1,251) and was associated (p < 0.05) with older age (OR = 1.04 per year), female gender (OR = 1.64), Tuberculosis (TB; OR = 1.86), smoking (OR = 1.60), higher plasma creatinine (OR = 1.09 per 0.1 mg/dl increase), CD4 count (OR = 0.83 per doubling) and not consuming alcohol (OR = 0.55). SPN prevalence decreased to 17 % by week 96 (p = 0.0002) following similar trends in all study groups (p = 0.30). Asymptomatic PN (APN) increased over the same period from 21 to 29 % (p = 0.0002). Signs suggestive of PN (regardless of symptoms) returned to baseline levels by week 96. At weeks 48 and 96, after adjusting for time-updated associations above and baseline CD4 count and viral load, SPN was strongly associated with TB (p < 0.0001). In summary, SPN prevalence was significantly reduced with PI-based second-line therapy across all treatment groups, but we did not find any advantage to the NRTI-free regimens. The increase of APN and stability of PN-signs regardless of symptoms suggest an underlying trend of neuropathy progression that may be masked by reduction of symptoms accompanying general health improvement induced by second-line ART. SPN was strongly associated with isoniazid given for TB treatment

Children with hyperdiploid but not triple trisomy (+4,+10,+17) acute lymphoblastic leukemia have an increased incidence of extramedullary relapse on current therapies: A single institution experience

To evaluate the outcome of children with high hyperdiploid acute lymphoblastic leukemia (hHDALL) treated at the author's institution. One hundred thirty-five consecutive children with B-precursor ALL were diagnosed between 1991 and 2002: 38 (28.1%) hHDALL and 97 (71.9%) non-hHDALL. In the hHDALL group, 11/38 (28.9%) relapsed at a median interval of 2.8 years (range: 0.8–5.0 years) with 9/11 relapses occurring at the end or after the completion of therapy. Three (27.3%) relapses were isolated hematopoietic (BM), while eight (72.7%) were either isolated extramedullary (EM) relapses ( n = 6; Testis: 4; CNS: 2) or combined hematopoietic and extramedullary relapses ( n = 2; BM + CNS: 1; BM + Testis: 1). For the non-hHDALL group, 29/97 (29.9%) relapsed. Unlike the hHDALL group, the non-hHDALL group experienced hematopoietic relapses (62%; n = 18) more frequently than isolated extramedullary (27.5%; n = 8: Testis: 1; CNS: 7) or combined hematopoietic and extramedullary relapses (10.3%; CNS + BM: 3), with 24/29 (82.8%) of the relapses occurring on therapy. Relapses in hHDALL frequently involved EM sites ( P = 0.053). Presence of triple trisomy of +4,+10,+17 at diagnosis had a protective effect against relapse ( P < 0.05). Five-year EFS for the hHDALL and non-hHDALL patients was similar, 70.5 ± 7.5% and 66.4 ± 4.9%, respectively. Five-year OS for the hHDALL patients was significantly higher than for the non-hHDALL patients, 92 ± 4.5% vs. 74.1 ± 4.5%, P = 0.038. Biologically significant differences exist between relapse patterns of hHDALL and non-hHDALL cases related to relapse sites and time periods when relapses occur. hDALL relapses continue to be chemo-sensitive. Am. J. Hematol., 2008. © 2007 Wiley-Liss, Inc.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/57520/1/21011_ftp.pd