Nonlinear flexural vibrations of thin-walled circular cylinders

Nonlinear flexural vibration analysis using Galerkin method in thin-walled circular cylinder

Vibration measurement by pulse differential holographic interferometry

Technique measures structural deformation of materials subjected to wide range of temperatures and other environmental conditions. Effects of convection currents are eliminated by operating a pulsed laser in double pulse mode that exposes hologram twice in quick succession

Applications of holography to vibrations, transient response, and wave propagation

Applications of holography to vibrations, transient response, and wave propagatio

Fast Ensemble Smoothing

Smoothing is essential to many oceanographic, meteorological and hydrological applications. The interval smoothing problem updates all desired states within a time interval using all available observations. The fixed-lag smoothing problem updates only a fixed number of states prior to the observation at current time. The fixed-lag smoothing problem is, in general, thought to be computationally faster than a fixed-interval smoother, and can be an appropriate approximation for long interval-smoothing problems. In this paper, we use an ensemble-based approach to fixed-interval and fixed-lag smoothing, and synthesize two algorithms. The first algorithm produces a linear time solution to the interval smoothing problem with a fixed factor, and the second one produces a fixed-lag solution that is independent of the lag length. Identical-twin experiments conducted with the Lorenz-95 model show that for lag lengths approximately equal to the error doubling time, or for long intervals the proposed methods can provide significant computational savings. These results suggest that ensemble methods yield both fixed-interval and fixed-lag smoothing solutions that cost little additional effort over filtering and model propagation, in the sense that in practical ensemble application the additional increment is a small fraction of either filtering or model propagation costs. We also show that fixed-interval smoothing can perform as fast as fixed-lag smoothing and may be advantageous when memory is not an issue

Morphing Ensemble Kalman Filters

A new type of ensemble filter is proposed, which combines an ensemble Kalman filter (EnKF) with the ideas of morphing and registration from image processing. This results in filters suitable for nonlinear problems whose solutions exhibit moving coherent features, such as thin interfaces in wildfire modeling. The ensemble members are represented as the composition of one common state with a spatial transformation, called registration mapping, plus a residual. A fully automatic registration method is used that requires only gridded data, so the features in the model state do not need to be identified by the user. The morphing EnKF operates on a transformed state consisting of the registration mapping and the residual. Essentially, the morphing EnKF uses intermediate states obtained by morphing instead of linear combinations of the states.Comment: 17 pages, 7 figures. Added DDDAS references to the introductio

A Stochastic Covariance Shrinkage Approach in Ensemble Transform Kalman Filtering

The Ensemble Kalman Filters (EnKF) employ a Monte-Carlo approach to represent covariance information, and are affected by sampling errors in operational settings where the number of model realizations is much smaller than the model state dimension. To alleviate the effects of these errors EnKF relies on model-specific heuristics such as covariance localization, which takes advantage of the spatial locality of correlations among the model variables. This work proposes an approach to alleviate sampling errors that utilizes a locally averaged-in-time dynamics of the model, described in terms of a climatological covariance of the dynamical system. We use this covariance as the target matrix in covariance shrinkage methods, and develop a stochastic covariance shrinkage approach where synthetic ensemble members are drawn to enrich both the ensemble subspace and the ensemble transformation

The nature of the pandemic:Exploring the negative impacts of the COVID-19 pandemic upon recreation visitor behaviors and experiences in parks and protected areas

The COVID-19 pandemic dramatically affected parks and protected areas and overall recreation visitation across the United States. While outdoor recreation has been demonstrated to be beneficial, especially during a pandemic, the resulting increase in recreation visitation raises concerns regarding the broader influence of social, situational, ecological, and behavioral factors upon overall visitor experiences. This study investigated the extent to which recreation visitors’ behaviors and experiences have been impacted by the COVID-19 pandemic within the White Mountain National Forest (WMNF). A modified drop-off pick-up survey method was employed to collect population-level data from WMNF visitors from June to August of 2020 (n=317), at the height of the pandemic. Results from this mixed-method study suggest social factors (e.g., crowding and conflict), situational factors (e.g., access and closures), ecological factors (e.g., vegetation damage), behavioral factors (e.g., substitution), and sociodemographic factors (e.g., gender and income) significantly influenced overall visitor decision-making and experience quality within the WMNF. For example, more than one-third of visitors indicated the pandemic had either a major or severe impact upon their WMNF recreation experience. A more nuanced investigation of qualitative data determined that the majority of pandemic-related recreation impacts revolved around the themes of social impacts, general negative recreation impacts, situational and ecological impacts, and behavioral adaptation impacts. Moreover, historically marginalized populations (e.g., low-income households and females) within the sample reported significantly higher recreation experience impacts during the pandemic. This study demonstrates the influence of the pandemic upon outdoor recreation visitor experiences and behaviors and considers outdoor recreation as a central component within the broader social-ecological systems framework. This study demonstrates the influence of the pandemic upon outdoor recreation visitor experiences and behaviors and considers resource users a central component within the broader social-ecological systems conceptual framework. MANAGEMENT IMPLICATIONS: This study found that during the peak of the COVID-19 pandemic, social, situational, ecological, behavioral, and sociodemographic factors significantly influenced overall visitor decision-making andexperience quality: · Social and general recreation impacts were most common, with approximately 56% of the sample reporting these issues. · Results suggest significant crowding and conflict impacts stemmed from interactions between in-state and out-of-state visitors, largely based upon perceived violations of pandemic protocols. · Moreover, historically marginalized populations stated unique recreation impacts during the pandemic. For instance, visitors from low-income households reported significantly less substitution options as opposed to high-income visitors. · Female visitors perceived significantly more pandemic-related conflict than male visitors. Study findings suggest visitor crowding and conflict should be prioritized by resource managers, especially amongst historically marginalized populations. Resource managers should consider adopting a broader social-ecological systems approach to parks and protected areas management, particularly during a global pandemic

Variation in beliefs about 'fracking' between the UK and US

In decision-making on the politically-contentious issue of unconventional gas development, the UK Government and European Commission are attempting to learn from the US experience. Although economic, environmental, and health impacts and regulatory contexts have been compared cross-nationally, public perceptions and their antecedents have not. We conducted similar online panel surveys of national samples of UK and US residents simultaneously in September 2014 to compare public perceptions and beliefs affecting such perceptions. The US sample was more likely to associate positive impacts with development (i.e., production of clean energy, cheap energy, and advancing national energy security). The UK sample was more likely to associate negative impacts (i.e., water contamination, higher carbon emissions, and earthquakes). Multivariate analyses reveal divergence cross-nationally in the relationship between beliefs about impacts and support/opposition – especially for beliefs about energy security. People who associated shale gas development with increased energy security in the UK were over three times more likely to support development than people in the US with this same belief. We conclude with implications for policy and communication, discussing communication approaches that could be successful cross-nationally and policy foci to which the UK might need to afford more attention in its continually evolving regulatory environment

The role of health and wellbeing in shaping local park experiences during the COVID-19 pandemic

Parks and protected areas (PPAs) serve a critical role in society as natural reprieves for restoring both mental and physical health. The restorative power of nature was even more evident during the COVID-19 pandemic, when visitation to local PPAs increased dramatically. Resource managers within local PPAs are growing concerned regarding the influence of increasing recreation visitation levels upon health, wellbeing, and overall visitor experience quality. This study examined the influence of social, ecological, and situational factors on visitors' health, wellbeing, and satisfaction in a local PPA setting in New England. On-site intercept surveys were conducted with local PPA visitors from September 2020 to August 2021 (n = 539) across both spatial and temporal scales. Structural equation modeling and binary logistic regression analyses suggest that social, situational, and ecological factors were significant predictors of visitor health, wellbeing, and overall satisfaction. Health outcomes (e.g., health improvement) fully mediated the relationship between situational factors (e.g., signage, COVID-19 visitation) and satisfaction and partially mediated the relationship between social factors (e.g., crowding, place attachment) and satisfaction. While ecological factors (e.g., trail and resource degradation) had no direct relationship with health outcomes, they showed a strong negative relationship with visitor satisfaction. Study findings suggest that as local PPA visitation increased during the pandemic, health outcomes also increased significantly, serving to mitigate certain negative impacts, and ultimately enhance overall experience quality. These findings lend themselves to an integration of health and wellbeing, visitor use management, and social-ecological systems conceptual frameworks and provide critical theoretical and managerial insights. Management implications: This study found that as local park and protected area visitation (PPA) increased during the pandemic, health and wellbeing outcomes also increased significantly, serving to mitigate certain negative impacts, and ultimately enhance overall experience quality. Results indicate additional signage, increasing sense of place, and reducing ecological impacts should be top priorities for resource managers. Finally, study findings validate the critical role that local PPAs and resource managers play in providing opportunities for enhanced health and wellness, particularly during a global pandemic, epitomizing the mantra healthy parks and healthy people.</p