Summary The Rayleigh damping model, which is pervasive in nonlinear response history analysis (RHA) of buildings, is shown to develop ‘spurious’ damping forces and lead to inaccurate response results. We prove that a viscous damping matrix constructed by superposition of modal damping matrices—irrespective of the number of modes included or values assigned to modal damping ratios—completely eliminates the ‘spurious’ damping forces. This is the damping model recommended for nonlinear RHA. Replacing the stiffness‐proportional part of Rayleigh damping by the tangent stiffness matrix is shown to improve response results. However, this model is not recommended because it lacks a physical basis and has conceptual implications that are troubling: hysteresis in damping force–velocity relationship and negative damping at large displacements. Furthermore, the model conflicts with the constant‐damping model that has been the basis for fundamental concepts and accumulated experience about the inelastic response of structures. With a distributed plasticity model, the structural response is not sensitive to the damping model; even the Rayleigh damping model leads to acceptable results. This perspective on damping provides yet another reason to employ the superior distributed plasticity models in nonlinear RHA. OpenSees software has been extended to include a damping matrix defined as the superposition of modal damping matrices. Although this model leads to a full populated damping matrix, the additional computational demands are demonstrated to be minimal. Copyright © 2015 John Wiley & Sons, Ltd.
Abstract Visual imagery is reported to play a central role m posttraumatic stress disorder (PTSD). This pilot investigation examined visual imagery ability in patients with varying degrees of posttraumatic stress. Eighty one survivors of motor vehicle accidents with either (a) diagnosed PTSD, (b) diagnosed Specific Phobia, or (c) no psychiatric diagnosis and low anxiety were assessed on a measure of vividness of visual imagery. Low Anxiety subjects displayed superior visual imagery compared to PTSD and Specific Phobic subjects. Incidence of flashbacks and nightmares, however, was associated with visual imagery ability in PTSD subjects. Findings suggest that visual imagery ability may be associated with PTSD flashbacks. These results are discussed in terms of use of imagery‐based treatments with traumatized patients, and of the need for further investigation of the role that imagery plays in posttraumatic adjustment.
The highly particular US conception of “race” is a direct outcome of the unique status of the United States as a slaveholding republic. While slavery itself has long been abolished, its dynamics were replicated in Jim Crow segregation and later in the urban ghetto. Henceforth, another ‘peculiar institution’, born of the adjoining of the hyperghetto with the carceral system, is remoulding the social meaning and significance of ‘race’ in accordance with the dictates of the deregulated economy and the post‐Keynesian state. For the first time in US history, the carceral system has become the main ‘race making’ machine. Its material stranglehold and classificatory activity have assumed a salience and reach that are wholly unprecedented in American history as well as unparalleled in any other society.
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The extension of room temperature electrochemical techniques for the study of equilibrium and charge transfer processes in aqueous systems at elevated temperatures and pressures is now well established (1, 2). Many of these studies have been designed to provide fundamental data on phenomena such as charge transfer, corrosion, acid dissociation, ion pairing, ion hydrolysis, hydrothermal precipitation and electro-deposition (1, 2).
We demonstrate very high frequency (VHF) nanomechanical resonators based upon single-crystal silicon nanowires (SiNWs), which are prepared by the bottom-up chemical synthesis. Metallized SiNW resonators operating near 200 MHz are realized with quality factor Q ≈ 2000−2500. Pristine SiNWs, with fundamental resonances as high as 215 MHz, are measured using a VHF readout technique that is optimized for these high resistance devices. The pristine resonators provide the highest Q's, as high as Q ≈ 13 100 for an 80 MHz device. SiNWs excel at mass sensing; characterization of their mass responsivity and frequency stability demonstrates sensitivities approaching 10 zeptograms. These SiNW resonators offer significant potential for applications in resonant sensing, quantum electromechanical systems, and high frequency signal processing.
Abstract This chapter starts by reflecting reflects back on the controversy triggered by “Scrutinizing the Street” and discusses the social and academic conditions of epistemic reflexivity. It moves to characterizing ethnography as “embodied and embedded” social inquiry. It develops a critique of ethnographic reason by dissecting “ethnographism”: the tendency to want to describe, interpret and explain a phenomenon based solely on the elements discerned through fieldwork. It calls for the practice of an enactive, structural, and historicized ethnography that sets out to embed the micro-actions observed in the interlocking series of nested social spaces that shape them and give them sense. Such an ethnography allows us to avoid falling into one or another of the five “organic fallacies” of participant observation: interactionism, inductivism, populism, presentism, and the hermeneutic drift. And to move beyond Clifford Geertz’s “thick description” with the “thick construction” inspired by Pierre Bourdieu, whose mission is to construct scientifically the ordinary social construction of reality. Illustrations and tips from an immersive field study of the county criminal are provided to indicate how to construct the ethnographic object by fusing theory, method, and observation.
En este trabajo-manifiesto, publicado originalmente en marzo de 1998, Pierre Bourdieu y Loïc Wacquant articulan la literatura académica y la denuncia política. En un contexto de creciente imperialismo que afecta también al campo académico, los autores abordan los modos en que los intelectuales podrían contribuir políticamente al cambio de estado de las cosas mediante la investigación social, en un espacio social que pugna por su relativa autonomía.
