•A unifying model is established for viscous- and friction-type bidirectional pendulum TMDs.•The homogeneous properties of two friction types, axial and tangential, are discussed.•An optimal design ...methodology is proposed and exemplified for each type.•Pros and cons of each type are shown based on extensive numerical simulations.
As a development of the classical pendulum vibration absorber, bidirectional pendulum TMDs (BTMDs) have been recently proposed, capable to resonate with the main structure along both its horizontal directions by virtue of their optimally designed three-dimensional (3D) pendulum surface. To provide BTMDs with the required energy dissipation capability, two damping mechanisms based on respectively axial and tangential friction were invented as an alternative to ordinary viscous dashpots. The first one consists of a vertical axial-friction damper connecting the BTMD to the main structure. The second one consists of a tangential friction spatially variable along the pendulum surface in proportion to the modulus of the surface gradient vector. Both mechanisms are fundamentally characterized by a nonlinear but homogeneous first-order model which makes their effectiveness independent from the excitation level. This paper compares the two friction paradigms with the classical viscous one. To this purpose, first a unifying fully nonlinear 3D model is established through Lagrangian mechanics, then an optimal design method is proposed, based on either H∞ or H2 norm minimization criteria. Extensive numerical simulations are performed to show the pros and cons of the three damping options and of the two optimization approaches. Results demonstrate that the three types exhibit a similar performance against unidirectional excitation but that the axial-friction type loses most of its effectiveness under bidirectional excitation whenever the pendulum surface is axial- or nearly axial-symmetrical, because of the insurgence of a peculiar rotational motion which virtually deactivates the friction damper. Results also show that the H∞ design criterion is more robust than the H2 design criterion, and that both criteria outperform previous simplified approaches proposed in the literature. It is concluded that, once properly designed and until stroke demand does not exceed their intrinsic stroke limitations, BTMDs are an effective vibration control strategy, which can be implemented through a variety of damping options, and that the two homogeneous friction mechanisms, and particularly the tangential one, are promising paradigms to provide amplitude-independent damping to engineering pendular systems.
The double proton transfer reaction in the guanine–cytosine (GC) base pair is studied, using density functional theory, to understand the chances of mutations under the effect of uniform electric ...fields in the order of 108 to 109 V m–1. On the basis of potential energy surfaces, reaction Gibbs energies, equilibrium constants, imaginary frequencies, forward and reverse barrier heights, tunneling-corrected rate constants, half-lives of the forward and reverse reactions, percent tautomerization, and Boltzmann distributions, it was found that fields ≥+3.60 × 109 V m–1 facilitate the mutation in the GC base pair and reduce the rectification of point mutations. Fields applied along the double proton transfer in the −x (defined in the C to G direction) direction favor the canonical over the rare tautomers. Tunneling-corrected rate constants of the forward reaction increase exponentially with stronger fields in the −x direction and follow a Gaussian curve for the reverse reaction.
Abstract
Humans have witnessed epidemics and pandemics periodically throughout history. Often, such infectious outbreaks have resulted in entire civilisations struggling against possible extinction. ...Despite recent clinical advancements and technological developments, issues of neglected sustainability and lax health hygiene practices, among others, have provided a context for the emergence of the COVID19 pandemic. Against such a backdrop, scientific communication using diversified tools could play a significant role in efforts towards preparedness and control, as well as the initiation of immediate remedial measures in the fight against epidemics and pandemics. These tools could help to increase understanding of the scientific solutions to minimise the outbreaks of infectious diseases, thereby strengthening societal immunity. This paper considers the history of epidemics/pandemics to draw attention to their occurrence, effects and potential impacts on human societies. In addition, it defines the major factors underpinning the various infectious outbreaks over the last three decades. Constructive preparation and preventative stages for authorities, scientists and researchers to check and diminish the impact of epidemics and pandemics during and post-outbreak are suggested while focusing on the need for science communication in the healthcare system. The paper also reviews recent empirical studies and WHO guidelines. Communication through appropriate communicators may help cut through the noise, share facts and boost confidence in science and governance. The impact of science communication on the interplay between government–expert–public or society could help promote positive behavioural change as well as overcome linguistic barriers.
The burgeoning literature on LMX differentiation has demonstrated positive and negative cross-level outcomes depending on specific boundary conditions. Although this research has provided key ...insights into the LMX phenomenon at multiple levels of analysis, we currently lack a conceptual understanding of when and why LMX differentiation may have positive or negative consequences at work. Opening the black box between LMX differentiation and work behaviors, we draw on social comparison theory to develop a conceptual model of the cross-level implications of LMX differentiation for employee emotions and discretionary behaviors. Since each LMX dyad is nested within the broader workgroup, we incorporate multilevel relationships in our theorizing. Relying on social comparison theory, we theorize that specific instances of resource allocation by leaders function as affective events that trigger social comparison emotions. More specifically, we posit that these affective events trigger an emotion appraisal process that causes relative individual LMX status and justice perceptions to interact as sources of social comparison information, influencing the type of social comparison emotion that emerges, with subsequent effects on interpersonal discretionary behavior. Overall, our social comparison perspective unravels emotional mechanisms that provide one explanation for why LMX differentiation has inconsistent effects on employee work behaviors.
Benign pleural effusions (BPEs) are more common than malignant effusions and their treatment involves treating the underlying disease process. However, in cases refractory to medical management, ...pleural interventions might be necessary. Use of indwelling pleural catheters (IPCs) has been gaining popularity for patients with refractory effusion. In this review, we will focus on reviewing the data assessing safety and efficacy of IPC in patients with BPE related to congestive heart failure (CHF), hepatic hydrothorax, end-stage renal disease (ESRD) and chylothorax.
Several small studies including the most recent randomized control trial have looked into the efficacy and safety of IPC in BPE. Majority of data come from patients having CHF and hepatic hydrothorax as the underlying cause of the effusion. Limited data are available in patients with ESRD and chylothorax. Time to pleurodesis varies but is relatively higher in this patient population. Caution must be addressed in patients with immunocompromised status given a high risk of infection.
IPCs are increasingly being used in patients with BPE refractory to medical management. They can be used both for palliation and to achieve pleurodesis in some cases. Further data in the form of randomized control trials are still needed to evaluate the efficacy and safety of its use in this patient population.
This article discusses the most relevant scholarship produced on the rise of Peruvian cuisine and Peru’s gastro-politics. It focuses on the contexts, processes and protagonists behind the attempt to ...heal and re-found the nation through food after a period of decline and terror, and on the formulation of ideas of social change aimed at shaping and promoting Peru as an entrepreneurial, vigorous but also more equal and fairer society. It also considers the smaller societal changes that nurtured these ideas, which are varied in nature and scope. Methodologically, the article explores the semantics, practices and ideologies at stake as expressed in public discourse, media content, gastronomic trends and restaurant sourcing. By unfolding central processes of the culinary project: high-end cuisine, the refiguring of indigenous people as producers and the use of cultural identity as an authenticating force, it offers a critical reading of the so-called gastronomic revolution, highlighting the ways in which claims to unity and reconciliation, particularly in the incorporation of indigenous people and their food cultures, smooth over ongoing inequalities.
Neoliberal restructuring and the feminization of export-led industries are often associated with the disempowerment of women in the workplace. Surprisingly, this disempowerment was not the case with ...a public textile company in Mahalla, an industrial city north of Cairo. Between 2006 and 2008, workers organized wildcat strikes involving around 24,000 workers. In contrast to the strike waves of the 1980s, women were integral to organizing the strikes and assumed leadership roles in them. This article argues that even as Egypt adopted structural adjustments in the 1990s that led to the decline of the historically leading sectors of textiles and yarn, exports of clothing increased. By the 2000s, the clothing sector was completely feminized and women in Mahalla were positioned in the most productive departments. This change empowered women by elevating their role and induced skeptical male colleagues to support women’s activism in the company and to build cross-gender solidarity.
Tuned mass dampers (TMDs) and nonlinear energy sinks (NESs) are two viable options for passively absorbing structural vibrations. In seismic applications, a trade-off exists in their performance, ...because TMDs’ effectiveness varies with the structural stiffness while NESs’ effectiveness varies with the earthquake intensity. To investigate this trade-off systematically, a lifecycle cost- (LCC-) oriented robust analysis and design method is here proposed, in which the effectiveness of a solution is measured by the reduction it entails in the expected cost of future seismic losses. In it, structural stiffness variability is modelled using a worst-case approach with lower and upper bounds, while seismic intensity variability is inherently captured by the incremental dynamic analyses underlying every LCC evaluation. The resulting worst-case lifetime cost provides a rational metric for discussing pros and cons of TMDs and NESs, and becomes the objective function for their robust optimization. The method is applied to the design of TMDs and NESs on a variety of single- and multi-story linear building models, located in a moderate-to-high seismic hazard region. Mass ratios from 1 to 10% and structural stiffness reductions up to 4 times are considered. Results show that TMDs are consistently more effective than NESs even in the presence of large stiffness reductions, provided that structural stiffness uncertainty is considered in design. They also show that a conventional robust H
∞
design provides for TMDs a solution which is very close to that obtained by minimizing the proposed LCC metric.
Students with Attention-Deficit/Hyperactivity Disorder (ADHD) are struggling writers. Yet no comprehensive model has been validated to explain their poor writing outcomes. This study aims to test ...whether an extended version of the Not-So-Simple View of Writing (NSVW) model can describe the effects of key abilities on writing performance in students with ADHD. The sample included students with and without ADHD who completed cognitive and academic measures in the Colorado Twin Project. A Multi-Group Structural Equation Model approach revealed that multiple broad cognitive abilities predicted student writing performance and basic writing skills predicted more advanced writing skills. Model fit was excellent both for a model with writing as a single latent variable (fully latent) and as interrelated manifest variables (partially latent). Furthermore, students with and without ADHD demonstrated comparable patterns of relationships among the variables in the model. Implications for the assessment of writing difficulties in students with ADHD are discussed.
•Ball vibration absorbers using a radially-increasing friction coating are presented.•The nonholonomic model is derived and a design procedure established.•Experimental tests and simulations prove ...their advantages over conventional devices.•Their equivalent damping ratio and performance are nearly amplitude independent.
Ball vibration absorbers (BAs) are a simple, low-cost and compact way to realize the principle of tuned mass damping. The basic arrangement of a BA consists of a spherical mass rolling without sliding in a rubber-coated spherical cavity, and dissipating through rolling friction. In a conventional BA, the rubber coating is uniform along the cavity, and so is rolling friction. This makes the BA equivalent damping inversely proportional to the excitation amplitude, and its performance amplitude dependent. In this study, two new BA types are proposed. The first type, called the homogeneous BA (HBA), has a rolling friction radially increasing in proportion to the ball angular displacement. Hardly realizable in practice, this ideal friction model is homogeneous in the first order, ensuring an amplitude-independent optimal performance. The second type, called the discrete-homogeneous BA (DBA), is the stepwise approximation of the HBA. Not exactly homogeneous, its variable friction model can be easily realized through the juxtaposition of multiple coating regions, having different thickness or material quality. After establishing a unifying, fully nonlinear, nonholonomic analytical model, valid for various types of friction and viscous BAs, this paper first derives an optimal design procedure applicable to each type, then experimentally and numerically demonstrates (1) the validity of the homogeneous and discrete-homogeneous concepts, (2) their practical feasibility, (3) the accuracy of the proposed model, (4) the effectiveness of the design procedure, and (5) the superior performance of the HBA and the DBA over conventional friction absorbers.
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