Mechanism State Matrices for Spatial Reconfigurable Mechanisms

This paper improves augmented mechanism state matrices by replacing joint code with screw system notation. The proposed substitution allows for a more specific description of the joints in the mechanism and the capability to describe both spatial and planar mechanisms. Examples are provided which elucidate the proposed approach

Modeling, Analysis, and Verification of a Weld-Breaking Mechanism for Automatic Circuit Recloser Applications

The automatic circuit recloser (ACR) is responsible for protecting electrical distribution grids in the event that high voltage power lines come in contact with ground. In order to prevent damage, ACRs break the electrical continuity of the circuit through the use of a vacuum interrupter and a weld breaking mechanism. Vacuum interrupters consist of two metallic contacts in an air-tight ceramic housing. Due to the electrical interactions that take place during the interruption process, unintended welds are formed between the contacts. These welds have the ability to impede or completely stop the interruption process, thus rendering the ACR inoperable. In order to ensure that the ACR can interrupt current even when welds have formed, a mechanism is used to complement the opening force and impart an impact load on the weld. This mechanism is generally designed based on rules of thumb and engineering judgment. This thesis develops a dynamic model of an ACR, which acts as a blueprint for the further development and optimization of the weld-breaking motion. The dynamic model consists of four main submodels: the dynamic motion of the masses, the dielectric breakdown model, the contact bounce model, and the weld-strength model. The dynamic motion and the weld-strength model are developed based on first principles, while the dielectric breakdown model and the contact bounce model are determined based on experimental data. The overarching dynamic model is compared to performance data and shows good agreement

Excess mortality in US Veterans during the COVID-19 pandemic: an individual-level cohort study.

BACKGROUND: Most analyses of excess mortality during the COVID-19 pandemic have employed aggregate data. Individual-level data from the largest integrated healthcare system in the US may enhance understanding of excess mortality. METHODS: We performed an observational cohort study following patients receiving care from the Department of Veterans Affairs (VA) between 1 March 2018 and 28 February 2022. We estimated excess mortality on an absolute scale (i.e. excess mortality rates, number of excess deaths) and a relative scale by measuring the hazard ratio (HR) for mortality comparing pandemic and pre-pandemic periods, overall and within demographic and clinical subgroups. Comorbidity burden and frailty were measured using the Charlson Comorbidity Index and Veterans Aging Cohort Study Index, respectively. RESULTS: Of 5 905 747 patients, the median age was 65.8 years and 91% were men. Overall, the excess mortality rate was 10.0 deaths/1000 person-years (PY), with a total of 103 164 excess deaths and pandemic HR of 1.25 (95% CI 1.25-1.26). Excess mortality rates were highest among the most frail patients (52.0/1000 PY) and those with the highest comorbidity burden (16.3/1000 PY). However, the largest relative mortality increases were observed among the least frail (HR 1.31, 95% CI 1.30-1.32) and those with the lowest comorbidity burden (HR 1.44, 95% CI 1.43-1.46). CONCLUSIONS: Individual-level data offered crucial clinical and operational insights into US excess mortality patterns during the COVID-19 pandemic. Notable differences emerged among clinical risk groups, emphasizing the need for reporting excess mortality in both absolute and relative terms to inform resource allocation in future outbreaks

Dynamic Model of a Weld Breaking Mechanism for Automatic Circuit Recloser Applications

Automatic circuit reclosers protect electrical distribution systems by breaking the circuit should the current levels exceed an acceptable range. In the process of opening and closing the circuit, welds are formed between the contacts, making it difficult to separate the contacts again. In order to ensure that the contacts can be separated in the event of a fault, a mechanism has been constructed to impart an impact load on the weld. This mechanism has been designed and used for many years with little understanding of how the mechanism components affect the performance of the mechanism. In order to gain this understanding, a dynamic model of the mechanism was created

Hypertension Control During the Coronavirus Disease 2019 Pandemic: A Cohort Study Among U.S. Veterans

DESIGN: Retrospective cohort study. OBJECTIVE: We sought to examine whether disruptions in follow-up intervals contributed to hypertension control. BACKGROUND: Disruptions in health care were widespread during the coronavirus disease 2019 pandemic. PATIENTS AND METHODS: We identified a cohort of individuals with hypertension in both prepandemic (March 2019-February 2020) and pandemic periods (March 2020-February 2022) in the Veterans Health Administration. First, we calculated follow-up intervals between the last prepandemic and first pandemic blood pressure measurement during a primary care clinic visit, and between measurements in the prepandemic period. Next, we estimated the association between the maintenance of (or achieving) hypertension control and the period using generalized estimating equations. We assessed associations between follow-up interval and control separately for periods. Finally, we evaluated the interaction between period and follow-up length. RESULTS: A total of 1,648,424 individuals met the study inclusion criteria. Among individuals with controlled hypertension, the likelihood of maintaining control was lower during the pandemic versus the prepandemic (relative risk: 0.93; 95% CI: 0.93, 0.93). Longer follow-up intervals were associated with a decreasing likelihood of maintaining controlled hypertension in both periods. Accounting for follow-up intervals, the likelihood of maintaining control was 2% lower during the pandemic versus the prepandemic. For uncontrolled hypertension, the likelihood of gaining control was modestly higher during the pandemic versus the prepandemic (relative risk: 1.01; 95% CI: 1.01, 1.01). The likelihood of gaining control decreased with follow-up length during the prepandemic but not pandemic. CONCLUSIONS: During the pandemic, longer follow-up between measurements contributed to the lower likelihood of maintaining control. Those with uncontrolled hypertension were modestly more likely to gain control in the pandemic

Excess Mortality Among Patients in the Veterans Affairs Health System Compared With the Overall US Population During the First Year of the COVID-19 Pandemic.

IMPORTANCE: During the first year of the COVID-19 pandemic, there was a substantial increase in the rate of death in the United States. It is unclear whether those who had access to comprehensive medical care through the Department of Veterans Affairs (VA) health care system had different death rates compared with the overall US population. OBJECTIVE: To quantify and compare the increase in death rates during the first year of the COVID-19 pandemic between individuals who received comprehensive medical care through the VA health care system and those in the general US population. DESIGN, SETTING, AND PARTICIPANTS: This cohort study compared 10.9 million enrollees in the VA, including 6.8 million active users of VA health care (those with a visit in the last 2 years), with the general population of the US, with deaths occurring from January 1, 2014, to December 31, 2020. Statistical analysis was conducted from May 17, 2021, to March 15, 2023. MAIN OUTCOMES AND MEASURES: Changes in rates of death from any cause during the COVID-19 pandemic in 2020 compared with previous years. Changes in all-cause death rates by quarter were stratified by age, sex, race and ethnicity, and region, based on individual-level data. Multilevel regression models were fit in a bayesian setting. Standardized rates were used for comparison between populations. RESULTS: There were 10.9 million enrollees in the VA health care system and 6.8 million active users. The demographic characteristics of the VA populations were predominantly male (>85% in the VA health care system vs 49% in the general US population), older (mean [SD], 61.0 [18.2] years in the VA health care system vs 39.0 [23.1] years in the US population), and had a larger proportion of patients who were White (73% in the VA health care system vs 61% in the US population) or Black (17% in the VA health care system vs 13% in the US population). Increases in death rates were apparent across all of the adult age groups (≥25 years) in both the VA populations and the general US population. Across all of 2020, the relative increase in death rates compared with expected values was similar for VA enrollees (risk ratio [RR], 1.20 [95% CI, 1.14-1.29]), VA active users (RR, 1.19 [95% CI, 1.14-1.26]), and the general US population (RR, 1.20 [95% CI, 1.17-1.22]). Because the prepandemic standardized mortality rates were higher in the VA populations prior to the pandemic, the absolute rates of excess mortality were higher in the VA populations. CONCLUSIONS AND RELEVANCE: In this cohort study, a comparison of excess deaths between populations suggests that active users of the VA health system had similar relative increases in mortality compared with the general US population during the first 10 months of the COVID-19 pandemic

Natural allelic variation underlying a major fitness trade-off in Arabidopsis thaliana

Plants can defend themselves against a wide array of enemies, from microbes to large animals, yet there is great variability in the effectiveness of such defences, both within and between species. Some of this variation can be explained by conflicting pressures from pathogens with different modes of attack. A second explanation comes from an evolutionary tug of war, in which pathogens adapt to evade detection, until the plant has evolved new recognition capabilities for pathogen invasion. If selection is, however, sufficiently strong, susceptible hosts should remain rare. That this is not the case is best explained by costs incurred from constitutive defences in a pest-free environment. Using a combination of forward genetics and genome-wide association analyses, we demonstrate that allelic diversity at a single locus, ACCELERATED CELL DEATH 6 (ACD6), underpins marked pleiotropic differences in both vegetative growth and resistance to microbial infection and herbivory among natural Arabidopsis thaliana strains. A hyperactive ACD6 allele, compared to the reference allele, strongly enhances resistance to a broad range of pathogens from different phyla, but at the same time slows the production of new leaves and greatly reduces the biomass of mature leaves. This allele segregates at intermediate frequency both throughout the worldwide range of A. thaliana and within local populations, consistent with this allele providing substantial fitness benefits despite its marked impact on growth