Southern African summer-rainfall variability, and its teleconnections, on interannual to interdecadal timescales in CMIP5 models

23 pagesInternational audienceThis study provides the first assessment of CMIP5 model performances in simulating southern Africa (SA) rainfall variability in austral summer (Nov–Feb), and its teleconnections with large-scale climate variability at different timescales. Observed SA rainfall varies at three major timescales: interannual (2–8 years), quasi-decadal (8–13 years; QDV) and interdecadal (15–28 years; IDV). These rainfall fluctuations are, respectively, associated with El Niño Southern Oscillation (ENSO), the Interdecadal Pacific Oscillation (IPO) and the Pacific Decadal Oscillation (PDO), interacting with climate anomalies in the South Atlantic and South Indian Ocean. CMIP5 models produce their own variability, but perform better in simulating interannual rainfall variability, while QDV and IDV are largely underestimated. These limitations can be partly explained by spatial shifts in core regions of SA rainfall variability in the models. Most models reproduce the impact of La Niña on rainfall at the interannual scale in SA, in spite of limitations in the representation of ENSO. Realistic links between negative IPO are found in some models at the QDV scale, but very poor performances are found at the IDV scale. Strong limitations, i.e. loss or reversal of these teleconnections, are also noted in some simulations. Such model errors, however, do not systematically impact the skill of simulated rainfall variability. This is because biased SST variability in the South Atlantic and South Indian Oceans strongly impact model skills by modulating the impact of Pacific modes of variability. Using probabilistic multi-scale clustering, model uncertainties in SST variability are primarily driven by differences from one model to another, or comparable models (sharing similar physics), at the global scale. At the regional scale, i.e. SA rainfall variability and associated teleconnections, while differences in model physics remain a large source of uncertainty, the contribution of internal climate variability is increasing. This is particularly true at the QDV and IDV scales, where the individual simulations from the same model tend to differentiate, and the sampling error increase

A Methodology for Assessing Thermal Stratification in an HCCI Engine and Understanding the Impact of Engine Design and Operating Conditions.

HCCI is a promising advanced engine concept with the potential to pair high thermal efficiencies with ultra-low emissions. However, HCCI has so far been demonstrated only over a narrow operating range due to a lack of control over HCCI burn rates. While there is an emerging consensus about the critical role of thermal stratification on HCCI burn rates, there was a gap related to availability of a method to rapidly assess the impact of engine design or operating conditions on thermal stratification in a practical HCCI engine. The objectives of this research are to develop a novel post-processing technique for studying thermal stratification in a fired, metal HCCI engine, and use the proposed technique to understand the impact of operating conditions on the in-cylinder unburned temperature distribution. The technique is called the Thermal Stratification Analysis (TSA) and it uses the autoignition integral coupled to the mass fraction burned curve to determine a distribution of mass and temperature in the cylinder prior to combustion. The technique is then validated by comparing the TSA results to predictions from CFD simulations and experimentally measured unburned temperature distributions in an optical engine. A large amount of data was collected and processed with the TSA to determine the effects of engine design and operating conditions on the in-cylinder unburned temperature distribution and HCCI burn rates. The results show that the thermal width increases with a higher internal residual gas fraction, increasing intake temperature, advancing combustion phasing, increasing the maximum TDC temperature, and increasing the in-cylinder swirl. Finally, an innovative method for active control of the thermal stratification and HCCI burn rates with a glow plug is proposed. The results show that the glow plug is able to control combustion phasing and, more importantly, broaden the temperature distribution and lengthen the burn duration a considerable amount. The glow plug improves some of the emissions characteristics slightly and the combustion efficiency as well. The main drawbacks of using a glow plug in HCCI are the efficiency penalty associated with the energy consumed by the glow plug and the observed increase in the cycle-to-cycle variations.PHDMechanical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/102425/1/blawler_1.pd

Use of angiotensin receptor blockers and risk of dementia in a predominantly male population: prospective cohort analysis

Objective To investigate whether angiotensin receptor blockers protect against Alzheimer’s disease and dementia or reduce the progression of both diseases

Conformal loop ensembles and the stress-energy tensor

We give a construction of the stress-energy tensor of conformal field theory (CFT) as a local "object" in conformal loop ensembles CLE_\kappa, for all values of \kappa in the dilute regime 8/3 < \kappa <= 4 (corresponding to the central charges 0 < c <= 1, and including all CFT minimal models). We provide a quick introduction to CLE, a mathematical theory for random loops in simply connected domains with properties of conformal invariance, developed by Sheffield and Werner (2006). We consider its extension to more general regions of definition, and make various hypotheses that are needed for our construction and expected to hold for CLE in the dilute regime. Using this, we identify the stress-energy tensor in the context of CLE. This is done by deriving its associated conformal Ward identities for single insertions in CLE probability functions, along with the appropriate boundary conditions on simply connected domains; its properties under conformal maps, involving the Schwarzian derivative; and its one-point average in terms of the "relative partition function." Part of the construction is in the same spirit as, but widely generalizes, that found in the context of SLE_{8/3} by the author, Riva and Cardy (2006), which only dealt with the case of zero central charge in simply connected hyperbolic regions. We do not use the explicit construction of the CLE probability measure, but only its defining and expected general properties.Comment: 49 pages, 3 figures. This is a concatenated, reduced and simplified version of arXiv:0903.0372 and (especially) arXiv:0908.151

From synoptic to interdecadal variability in southern African rainfall: towards a unified view across timescales

International audienceDuring the austral summer season (November–February), southern African rainfall, south of 20°S, has been shown to vary over a range of time scales, from synoptic variability (3–7 days, mostly tropical temperate troughs) to interannual variability (2–8 years, reflecting the regional effects of El Niño–Southern Oscillation). There is also evidence for variability at quasi-decadal (8–13 years) and interdecadal (15–28 years) time scales, linked to the interdecadal Pacific oscillation and the Pacific decadal oscillation, respectively. This study aims to provide an overview of these ranges of variability and their influence on regional climate and large-scale atmospheric convection and quantify uncertainties associated with each time scale. We do this by applying k-means clustering onto long-term (1901–2011) daily outgoing longwave radiation anomalies derived from the 56 individual members of the Twentieth Century Reanalysis. Eight large-scale convective regimes are identified. Results show that 1) the seasonal occurrence of the regimes significantly varies at the low-frequency time scales mentioned above; 2) these modulations account for a significant fraction of seasonal rainfall variability over the region; 3) significant associations are found between some of the regimes and the aforementioned modes of climate variability; and 4) associated uncertainties in the regime occurrence and convection anomalies strongly decrease with time, especially the phasing of transient variability. The short-lived synoptic anomalies and the low-frequency anomalies are shown to be approximately additive, but even if they combine their respective influence at both scales, the magnitude of short-lived perturbations remains much larger

Trends and Costs Associated With Suboptimal Physical Activity Among US Women With Cardiovascular Disease

IMPORTANCE: Cardiovascular disease (CVD) is the leading cause of death and disability among women. Achievement of recommended physical activity (PA) levels is an essential component of CVD management. OBJECTIVE: To describe trends, sociodemographic factors, and health care expenditures associated with suboptimal PA among a nationally representative sample of US women with CVD. DESIGN, SETTING, AND PARTICIPANTS: This cross-sectional study used serial data from the Medical Expenditure Panel Survey from 2006 through 2015. The analyses were conducted in August 2018. Women who had self-reported and/or International Classification of Diseases, Ninth Revision, diagnosis of CVD were included. MAIN OUTCOMES AND MEASURES: Recommended PA was defined as 30 minutes or more of moderate- to vigorous-intensity exercise, 5 or more days per week. Weighted logistic regression was used to examine the associations of various sociodemographic factors with suboptimal PA, adjusted for comorbidities. A 2-part econometric model was used to assess health care expenditures. RESULTS: A total of 18 027 women were included in this study. The results were weighted to provide estimates for approximately 19.5 million adult women in the United States with CVD (mean [SD] age, 60.4 [16.9] years). More than half of the women with CVD reported suboptimal PA, a trend that increased during the 10-year period, with 58.2% (95% CI, 55.9%-60.5%) of participants reporting suboptimal PA in 2006-2007 vs 61.9% (95% CI, 59.7%-64.2%) in 2014-2015 (P = .004). The proportion of women with suboptimal PA differed by sociodemographic factors. In adjusted models, compared with non-Hispanic white women, African American women (odds ratio, 1.22; 95% CI, 1.08-1.38) and Hispanic women (odds ratio, 1.33; 95% CI, 1.13-1.58) were more likely to have suboptimal PA. Women from low- or very low-income strata (compared with high-income strata), enrolled in public insurance (compared with private insurance), and with less than high school education (compared with at least some college education) were more likely to have suboptimal PA. Health care costs among women with CVD with suboptimal PA were higher compared with those among women who met the recommended PA, and this increased through time, from a mean total health care expenditure of $12 724 (95$11 627-$13 821) in 2006-2007 to$14 820 (95% CI, $13 521-$16 119) in 2014-2015. CONCLUSIONS AND RELEVANCE: The proportion of women with CVD not meeting recommended PA is high and increasing, particularly among certain racial/ethnic and socioeconomic groups, and is associated with significant health care costs. More must be done to improve PA for secondary prevention and reduction of expenditures among women with CVD

Figuring Rhetoric: From Antistrophe to Apostrophe through Catastrophe

This essay explores rhetoric tropologically through various strophes: antistrophe, catastrophe, and apostrophe. Our purpose is to delineate problems and possibilities that these tropes pose for rhetoric in an effort to create new rhetorics. We seek to display the antistrophic and catastrophic figurations of rhetoric and then use visual lenses of photography and cinema to disrupt the figurations. Following the disruption, we seek to heighten sensibilities to other figurations, in particular an apostrophic figuration. We cast apostrophe as a figure for change because it marks a deeply felt turn toward difference and otherness. Turned as such, rhetoric becomes erotic

Fluctuating Stripes in Strongly Correlated Electron Systems and the Nematic-Smectic Quantum Phase Transition

We discuss the quantum phase transition between a quantum nematic metallic state to an electron metallic smectic state in terms of an order-parameter theory coupled to fermionic quasiparticles. Both commensurate and incommensurate smectic (or stripe) cases are studied. Close to the quantum critical point (QCP), the spectrum of fluctuations of the nematic phase has low-energy ``fluctuating stripes''. We study the quantum critical behavior and find evidence that, contrary to the classical case, the gauge-type of coupling between the nematic and smectic is irrelevant at this QCP. The collective modes of the electron smectic (or stripe) phase are also investigated. The effects of the low-energy bosonic modes on the fermionic quasiparticles are studied perturbatively, for both a model with full rotational symmetry and for a system with an underlying lattice, which has a discrete point group symmetry. We find that at the nematic-smectic critical point, due to the critical smectic fluctuations, the dynamics of the fermionic quasiparticles near several points on the Fermi surface, around which it is reconstructed, are not governed by a Landau Fermi liquid theory. On the other hand, the quasiparticles in the smectic phase exhibit Fermi liquid behavior. We also present a detailed analysis of the dynamical susceptibilities in the electron nematic phase close to this QCP (the fluctuating stripe regime) and in the electronic smectic phase.Comment: 34 pages, 5 figure. An error in the calculation of fermion self-energy correction in the smectic phase was corrected, with updated Eq. (7.5) and Eq. (E3) and Table