This article contributes to explaining the rise of labor unrest in Egypt in the early 2000s, led initially by public-sector workers. Using two case studies in textile and transport, the author shows ...that perceptions of sector potential affected workers’ ability to protest and compensated for the decline in their sectors’ roles in the economy. The perceptions of underutilization due to corruption and to sector viability based on squandered profits help explain workers’ militancy and capacities to mount an extended protest campaign. These perceptions build on discourses that critique the state’s adoption of neoliberal policies associated with privatization. Workers could develop these perceptions because their sectors still played a role in the economy despite their decline. The analysis contributes to the Power Resource Approach by showing how perceptions of sector potential enhance capacities among Global South workers in declining sectors. To explain labor unrest, the author engages labor scholarship on Egypt that focuses on grievances rather than on workers’ economic position and sources of power.
Summary
The seismic performance of tuned mass dampers (TMDs) on structures undergoing inelastic deformations may largely depend on the ground motion intensity. By estimating the impact of each ...seismic intensity on the overall cost of future seismic damages, lifecycle cost (LCC) proves a rational metric for evaluating the benefits of TMDs on inelastic structures. However, no incorporation of this metric into an optimization framework is reported yet. This paper presents a methodology for the LCC‐optimal design of TMDs on inelastic structures, which minimizes the total seismic LCC of the combined building‐TMD system. Its distinctive features are the assumption of a mass‐proportional TMD cost model, the adoption of an iterative suboptimization procedure, and the initialization of the TMD frequency and damping ratios according to a conventional linear TMD design technique. The methodology is applied to the seismic improvement of the SAC‐LA benchmark buildings, taken as representative of standard steel moment‐resisting frame office buildings in LA, California. Results show that, despite their limited performance at the highest intensity levels, LCC‐optimal TMDs considerably reduce the total LCC, to an extent that depends on both the building vulnerability and the TMD unit cost. They systematically present large mass ratios (around 10%) and frequency and damping ratios close to their respective linearly designed optima. Simulations reveal the effectiveness of the proposed design methodology and the importance of adopting a nonlinear model to correctly evaluate the cost‐effectiveness of TMDs on ordinary structures in highly seismic areas.
Summary
Passive tuned mass dampers (TMDs) are widely used in controlling structural vibrations. Although their principle is well established, the search for improved arrangements is still under way. ...This effort has recently produced an innovative paradigm of bidirectional pendulum TMD (BTMD) that, moving along a specially designed three‐dimensional (3D) surface, can simultaneously control two in‐plane orthogonal structural modes. In existing versions of BTMDs, energy dissipation is provided either by ordinary horizontal viscous dampers or by an original arrangement of vertical friction dampers. In this paper, a new paradigm is proposed, in which energy dissipation comes from the tangential friction arising along the pendulum surface out of an optimal spatially variable friction coefficient pattern. Within this paradigm, if the friction coefficient is taken proportional to the modulus of the pendulum surface gradient, the dissipation model results nonlinear homogeneous in the small‐displacement domain, and the performance of the absorber, herein called the homogeneous tangential friction BTMD (HT‐BTMD), results independent from the excitation level. The present work introduces this concept, derives the analytical model of the HT‐BTMD, establishes a method for its optimal design, and numerically verifies its seismic effectiveness in comparison with viscously damped devices. The validity and feasibility of the concept are demonstrated through experimental tests on a small‐scale lab prototype, which also show the efficacy of a stepwise approximation of the homogeneous friction pattern. The new device proves a competing alternative to existing BTMDs, and homogeneous tangential friction proves a promising new paradigm to provide pendular systems with amplitude‐independent structural damping.
TRPV1 and TRPM8 are sensory nerve ion channels activated by heating and cooling, respectively. A variety of physical and chemical
stimuli activate these receptors in a synergistic manner but the ...underlying mechanisms are unclear. Both channels are voltage
sensitive, and temperature and ligands modulate this voltage dependence. Thus, a voltage-sensing mechanism has become an attractive
model to explain the generalized gating of these and other thermo-sensitive TRP channels. We show here using whole-cell and
single channel measurements that voltage produces only a partial activation of TRPV1 and TRPM8. At room temperature (20â25°C)
membrane depolarization evokes responses that saturate at â¼50â60% of the maximum open probability. Furthermore, high concentrations
of capsaicin (10 μ m ), resiniferatoxin (5 μ m ) and menthol (6 m m ) reveal voltage-independent gating. Similarly, other modes of TRPV1 regulation including heat, protein kinase C-dependent
phosphorylation, and protons enhance both the efficacy and sensitivity of voltage activation. In contrast, the TRPV1 antagonist
capsazepine produces the opposite effects. These data can be explained by an allosteric model in which voltage, temperature,
agonists and inverse agonists are independently coupled, either positively or negatively, to channel gating. Thus, voltage
acts separately but in concert with other stimuli to regulate channel activation, and, therefore, a voltage-sensitive mechanism
is unlikely to represent a final, gating mechanism for these channels.
In this article, we examine several techniques that allow for the construction of bounds estimates based on instrumental variables, even when the instruments are not valid. We introduce the plausexog ...and imperfectiv commands, which implement methods described by Conley, Hansen, and Rossi (2012, Review of Economics and Statistics 94: 260–272) and Nevo and Rosen (2012b, Review of Economics and Statistics 94: 659–671). We examine the performance of these bounds under a range of circumstances, which leads to several practical results related to the informativeness of the bounds in different situations.
•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.
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