1,824 research outputs found
Cosmological tests of an axiverse-inspired quintessence field
No full textInspired by the string axiverse idea, it has been suggested that the recent transition from decelerated to accelerated cosmic expansion is driven by an axion-like quintessence field with a sub-Planckian decay constant. The scenario requires that the axion field be rather near the maximum of its potential but is less finely tuned than other explanations of cosmic acceleration. The model is parametrized by an axion decay constant f, the axion mass m, and an initial misalignment angle |θi| which is close to π. In order to determine the m and θi values consistent with observations, these parameters are mapped onto observables: the Hubble parameter H(z) at an angular-diameter distance dA(z) to redshift z=0.57, as well as the angular sound horizon of the cosmic microwave background (CMB). Measurements of the baryon acoustic oscillation (BAO) scale at z≃0.57 by the BOSS survey and Planck measurements of CMB temperature anisotropies are then used to probe the {m,f,θi} parameter space. With current data, CMB constraints are the most powerful, allowing a fraction of only ∼0.2 of the parameter-space volume. Measurements of the BAO scale made using the SPHEREx or SKA experiments could go further, observationally distinguishing all but ∼10-2 or ∼10-5 of the parameter-space volume (allowed by simple priors) from the ΛCDM model
Air pollution at Rochester, NY: Long-term trends and multivariate analysis of upwind SO2 source impacts
No full textThere have been many changes in the air pollutant sources in the northeastern United States since 2001. To assess the effect of these changes, trend analyses of the monthly average values were performed on PM2.5 and its components including major ions, elemental carbon (EC), organic carbon (OC), and gaseous pollutant concentrations measured between 2001 (in some cases 1999) and 2015 at the NYS Department of Environmental Conservation sites in Rochester, NY. Mann-Kendall regression with Sen's slope was applied to estimate the trends and seasonality. Using piecewise regression, significant reductions in the air pollution of Rochester area were observed between 2008 and 2010 when a 260 MW coal-fired power plant was decommissioned, new heavy-duty diesel trucks had to be equipped with catalytic regenerator traps, and the economic recession that began in 2008 reduced traffic and other activities. The monthly average PM2.5 mass showed a downward trend (− 5 μg/m3; − 41%) in Rochester between 2001 and 2015. This change is largely due to reductions in particulate sulfate that showed a 65% decrease. The sulfate concentrations were compared to changes in SO2 emissions in seventeen upwind source domains, and other systematic changes by multivariate linear regression. Selectivity ratio obtained from target projection discriminated the most important source domains that are SO2 emissions from Georgia for winter, North Carolina for transition (spring and fall) and Ohio along with other influences for summer. North Carolina and Michigan were identified as the main sources for entire period. These observations suggest that any further reductions in the specified regional SO2 emissions would result in a proportional decrease in sulfate in Rochester
A Unified Framework To Design Time-Constrained Control Systems and its Application to Attitude Control of a Rigid Spacecraft
No full textThis paper presents a unified educational framework for introducing and analyzing different time-constrained control methodologies for nonlinear systems. The formulation covers asymptotic, finite-time, fixed-time, predefined-time, and prescribed-time control approaches. For each methodology, the control design requirements are outlined, followed by the controller formulation and stability analysis using a generic second-order strict-feedback nonlinear system model. This unified treatment allows for a cohesive learning journey to understand the theoretical foundations and relative merits of the various time-constrained control strategies. To illustrate the practical utility of these techniques, the frameworks are applied to the attitude control problem for a rigid spacecraft. Comparative simulation results highlight the convergence behavior and tracking performance achieved by each method on this aerospace vehicle application. The unified presentation provides a pedagogical approach for the systematic study of time-constrained control methodologies of relevance for aerospace systems. This formulation can serve as an educational resource in aerospace control curricula for exposing students to these advanced nonlinear control techniques. Copyright (C) 2024 The Authors. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0/
Risk Taking in Opportunity Evaluation
No full textIn spite of compelling advances in the notion of entrepreneurial opportunities in the past decade, the construct still undergo serious critics such as being metaphorical and not literal. One paramount reason for this shortfall is due to lack of instruments to evaluate objectively varieties of components of business opportunities such as risk and uncertainty. The process of discovering an opportunity starts from a subjective process of recognition, and it then involves further evaluation such as risk assessment to transmit it to an objective value. However, we know little about how the transformation from subjective to the objective state takes place within opportunity evaluation. Using Risky Framing concept, we contribute to this gap in knowledge. We use survey data of proxy entrepreneurs and examine their responses against a control group of non-entrepreneurs. Results show that the both groups adopt different risk levels when they confront opportunity scenarios. In addition, the risk levels adopted by the entrepreneurs was significantly greater than their non-entrepreneur counterparts. These findings provide new insights in the process of entrepreneurial alertness. The results discussed and implications for the future contributions are provide
Multivariate analysis of upwind SO2 emission influences on air pollution in Rochester, NY
No full textIntelligent Control for Aerospace Engineers: A Novel Educational Framework
No full textThe integration of intelligent control techniques into aerospace engineering education remains a challenge. This paper presents a novel approach for teaching intelligent control specifically designed for aerospace engineers, bridging the gap between theoretical foundations and practical applications. The proposed framework encompasses a comprehensive curriculum covering model-based and model-free approaches, leveraging neural networks, reinforcement learning, and other computational intelligence techniques. It emphasizes hands-on experiences through simulation-based exercises, hardware-in-the-loop experiments, and design projects tailored to different aerospace vehicle categories, including multi-rotor UAVs, helicopters, fixed-wing aircraft, and Hypersonic Flight Vehicles. The framework also addresses assessment methods, industry collaborations, and case studies to enhance student learning outcomes
Invasive haemodynamic assessment shows the obesity-HFpEF phenotype is common amongst patients with symptomatic AF
No full textArrhythmias and Device Therapy - Atrial Fibrillation (AF), Pathophysiology and Mechanisms, Mechanisms for Heart Failure and Cardiac ComplicationsAbstract not availableJ. Ariyaratnam, A.D. Elliott, R.S. Mishima, M. Emami, K. Kadhim, M.E. Middeldorp, P. Sander
The Air Pollution at Rochester: Long-Term Trends
No full textThere have been a number of changes in the sources of air pollutant in the northeastern United States since 2001. Trend analyses of monthly averages were performed on PM 2.5, ionic species, elemental carbon (EC), organic carbon (OC) and gaseous pollutants collected between 2001 and 2015 for NYS Department of Environmental Conservation sites in Rochester. Non-parametric (Mann-Kendall regression with Sen’s slope) and parametric (weighted linear and non-linear regressions) approaches were applied to estimate the trends and seasonality. We fitted the different models to monthly averages of each species for each month over the 15 years of available data. Separating the data by month removes their seasonal dependence. The unequal number of attainable samples averaged to provide monthly asset value was accounted for by weighting each month proportional to its number of available daily concentration values. Sulfate and nitrate showed downward trends. For almost all of the species over the whole, the weighted linear parametric modeling yielded steeper slopes than the non-parametric Mann-Kendall approach. For sulfate, the slopes = -0.20 and -0.15 μg m -3 year -1, respectively. These trends will be compared to changes in emissions in the upwind source domain
Remote monitoring of implantable cardioverter defibrillators: a systematic review and meta-analysis of randomised controlled trials
No full textArrhythmias and Device Therapy - Device Therapy, Home and Remote Patient MonitoringAbstract not availableM. Stefil, C.J. O'shea, M. Middeldorp, J.M. Hendriks, D.H. Lau, M. Emami, A. Thiyagarajah, J. Ariyaratnam, J. Fitzgerald, G. Young, K. Roberts-Thomson, P. Sander
Invasively diagnosed HFpEF in AF associated with functional remodelling of the left atrial appendage: implications for stroke risk
No full textIn section: Arrhythmias and Device Therapy – Atrial Fibrillation (AF), Pathophysiology and Mechanisms, Mechanisms for StrokeAbstract not availableJ. Ariyaratnam, R.S. Mishima, K. Kadhim, M. Emami, C. Gallagher, D.H. Lau, P. Sanders, A.D. Elliot
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