Using a damper amplification factor to increase energy dissipation in structures

AbstractFluid dampers are an important tool for dissipating unwanted vibrations in a range of engineering structures. This paper examines the effects of amplifying the displacements transferred to a non-linear damper, to increase the effectiveness of the damper in a range of situations commonly encountered in civil engineering structures. These include, (i) the ability to “fine tune” the required damping for a particular size damper, (ii) the ability to have a set of the same size dampers, but with different amplification factors to achieve a specific damping task, and (iii) to increase the sensitivity of the damper to small movements which effectively extends the range over which the damper works. Through numerical simulations and experimental tests conducted on a non-linear damper, we quantify the potential advantages of adding an amplification factor and the range of parameters where the benefit to this device is significant. The example of a two-storey structure is used as a test case and real-time dynamic substructuring tests are used to assess the complete system performance using a range of different amplification factors. The results show that the structural performance is most improved for frequencies close to resonance and that the amplification factor has an effective limit that for the case considered in this study is of approximately 3. The effects of the mechanism compliance are also assessed

Supporting brace sizing in structures with added linear viscous fluid dampers: A filter design solution

Viscous fluid dampers have proved to be effective in suppressing unwanted vibrations in a range of engineering structures. When dampers are fitted in a structure, a brace is typically used to attach them to the main structure. The stiffness of this brace can significantly alter the effectiveness of the damper, and in structures with multiple dampers, this can be a complex scenario to model. In this paper, we demonstrate that the effects of the brace compliance on the damper performance can be modelled by way of a first-order filter. We use this result to formulate a procedure that calculates the stiffness required by the supporting brace to provide a specified effectiveness of the damping action. The proposed procedure assumes that viscous dampers have been sized in a previous design step based on any optimal methodology in which, as is usually the case, the presence of supporting braces and their dynamic effects were neglected. Firstly considering a one degree-of-freedom system, we show that the proposed method ensures a desired level of damper efficiency for all frequencies within a selected bandwidth. Then the analysis is extended to the case of multi-degree-of-freedom systems to show that the design criteria can be applied in a straightforward and successful manner to more complex structures

Los Sangurimas, una obra narrativa polémica

Con la literatura ecuatoriana de los años treinta se produce un cambio importante, tanto en la temática como en la estructura de su narrativa. Dentro del romanticismo, durante el siglo XIX, dos escritores llaman ya la atención en este movimiento: Juan Montalvo Fiallos y Juan León Mera. El primero, por la pureza del lenguaje, el aspecto combativo de su temática y por ser precursor del modernismo. El segundo, por la calidad de su trabajo literario, al cumplir con lo cánones dictados por los maestros europeos. En el siglo XX y, dentro de la vanguardia hispanoamericana, dos escritores se imponen por lo innovador de sus enunciados: Pablo Palacio y José de la Cuadra. Palacio, al romper tabúes sociales y De la Cuadra, por tener la reputación de ser uno de los iniciadores más fuertes del realismo mágico en Sur América. Los Sangurimas, de José de la Cuadra, es una obra narrativa que describe el comportamiento de una dinastía que impone su presión. Las personas -familiares y vecinos- están sometidas al proceder hegemónico de un hombre que hace imperar su voluntad y arrasa con todo enunciado o individuo que se cruce en su camino. Esta obra denuncia y, a la vez, afirma el abuso de un caciquismo que operaba en cualquier aldea, grande o pequeña, que se convertía en víctima de este mal endémico de los siglos XIX y XX en Hispanoamérica. Asimismo, en Los Sangurimas encontramos analogías en la estructura, el tema y los personajes que están cargados de pasiones, bajo el ojo director del trópico. Todo esto para hacer hincapié y analizar el tratamiento de lo improbable, del mito y de la leyenda.In the thirties, the Ecuadorian literature experiments an important change in its themes as well as in its narrative structure. When romanticism was in vogue in the 19th Century, Two Ecuadorian writers already call our attention powerfully: Juan Montalvo for the purity of his prose, the spirited aspect of his themes and because he was a precursor of modernism. Juan León Mera, on the other hand, was highly regarded for his excellent narrative work, especially for following the norms dictated by the European masters. In the 20th Century, in the Hispanic American vanguard era two writers stand out: Pablo Palacio when he breaks social taboos and De la Cuadra one of the stronger initiators of magic realism in South America. Los Sangurimas, by José de la Cuadra, is a narrative work that describes the outrageous behavior of a dynasty. The people �family and neighbors- are submitted to one man� hegemonic power, abuses and repression are intolerable. Los Sangurimas denounce and, at the same time, affirms the cruelty of caciquismo which acted in any village, large or small, becoming an endemic characteristic of the 19th and 20th Centuries in Latin America. Likewise, in this work we find analogies in the structure, the themes, and the characters which are introduced by the geography. All this is done, with the purpose to emphasize and to analyze the improbable, the mythic and the legendary

Modeling the Radio Background from the First Black Holes at Cosmic Dawn: Implications for the 21 cm Absorption Amplitude

We estimate the 21 cm Radio Background from accretion onto the first intermediate-mass Black Holes between $z\approx 30$ and $z\approx 16$. Combining potentially optimistic, but plausible, scenarios for black hole formation and growth with empirical correlations between luminosity and radio-emission observed in low-redshift active galactic nuclei, we find that a model of black holes forming in molecular cooling halos is able to produce a 21 cm background that exceeds the Cosmic Microwave Background (CMB) at $z \approx 17$ though models involving larger halo masses are not entirely excluded. Such a background could explain the surprisingly large amplitude of the 21 cm absorption feature recently reported by the EDGES collaboration. Such black holes would also produce significant X-ray emission and contribute to the $0.5-2$ keV soft X-ray background at the level of $\approx 10^{-13}-10^{-12}$ erg sec$^{-1}$ cm$^{-2}$ deg$^{-2}$, consistent with existing constraints. In order to avoid heating the IGM over the EDGES trough, these black holes would need to be obscured by Hydrogen column depths of $N_\text{H} \sim 5 \times 10^{23} \text{cm}^{-2}$. Such black holes would avoid violating contraints on the CMB optical depth from Planck if their UV photon escape fractions were below $f_{\text{esc}} \lesssim 0.1$, which would be a natural result of $N_\text{H} \sim 5 \times 10^{23} \text{cm}^{-2}$ imposed by an unheated IGM.Comment: 10 pages, 7 figures, accepted to ApJ, replacement to match submitted versio

Calibration of the EDGES High-Band Receiver to Observe the Global 21-cm Signature from the Epoch of Reionization

The EDGES High-Band experiment aims to detect the sky-average brightness temperature of the $21$-cm signal from the Epoch of Reionization (EoR) in the redshift range $14.8 \gtrsim z \gtrsim 6.5$. To probe this redshifted signal, EDGES High-Band conducts single-antenna measurements in the frequency range $90-190$ MHz from the Murchison Radio-astronomy Observatory in Western Australia. In this paper, we describe the current strategy for calibration of the EDGES High-Band receiver and report calibration results for the instrument used in the $2015-2016$ observational campaign. We propagate uncertainties in the receiver calibration measurements to the antenna temperature using a Monte Carlo approach. We define a performance objective of $1$~mK residual RMS after modeling foreground subtraction from a fiducial temperature spectrum using a five-term polynomial. Most of the calibration uncertainties yield residuals of $1$~mK or less at $95\%$ confidence. However, current uncertainties in the antenna and receiver reflection coefficients can lead to residuals of up to $20$ mK even in low-foreground sky regions. These dominant residuals could be reduced by 1) improving the accuracy in reflection measurements, especially their phase 2) improving the impedance match at the antenna-receiver interface, and 3) decreasing the changes with frequency of the antenna reflection phase.Comment: Updated to match version accepted by Ap