Phase transition to chimera state in two populations of oscillators interacting via a common external environment

We consider two populations of coupled oscillators, interacting each other through a common external environment. The external environment is synthesized by the contributions from all oscillators of both populations. Such indirect coupling via an external medium arises naturally in many fields, e.g., dynamical quorum sensing in coupled biological and chemical systems. We analyze the existence and stability of a variety of stationary states on the basis of the OttAntonsen reduction method, which reveals that the interaction via an external environment gives rise to unusual collective behaviors such as the uniform drifting, non-uniform drifting and chimera states. We present a complete bifurcation diagram, which provides the underlying mechanism of the phase transition towards chimera state with the route of incoherence → uniform drift → non-uniform drift → chimera.

Seismic Performance Assessment, Retrofitting and Loss Estimation of an Existing Non-Engineered Building in Nepal

<p>The non-engineered building built before 2004 remained after Gorkha earthquake although such structures demonstrate seismic deficient. Therefore, the present study aims to carry out detail seismic performance of such building to investigate as-built seismic performance and its performance after intervention of retrofit measures. Two in situ tests were performed, which includes Schmidt hammer test and ambient vibration test. The adaptive pushover analysis and dynamic time history analyses were performed for as-built and retrofitted building. The retrofit measures increase the stiffness and maximum base shear capacity of the buildings. In addition, such retrofit measures improved single storey drift concentration in existing building such that uniform drift profile can be attained. Furthermore, the probability of exceeding damage states can be significantly reduced and mainly found to be more effective in minimizing higher damage states, such as partial collapse and collapse states. The maximum expected annual loss occurs between 0.1 g and 0.2 g PGA (Peak Ground Acceleration). It was revealed that the steel braced building was found to be relatively more effective in enhancing the seismic performance, whereas reinforced concrete shear wall found more economic feasible retrofit measure for this particular building.</p>

An Optimal Seismic Force Pattern for Uniform Drift Distribution

The force distribution proposed by codes, which in many cases is framed in the equivalent static force procedure, likely leads to design structures with non-uniform drift distribution in terms of inter-storey drift and ductility demands. This can lead to an unbalanced drift demand at certain storeys. This phenomenon may also amass cyclic damage to the dissipative elements at this very storey, therefore increasing the probability of premature failure for low-cycle fatigue. This work proposes a new force design distribution that accounts for higher mode effects and limits the displacement concentration at any storey thus improving the dissipative capacity of the whole structures. The main advantage of the proposed method stands in its formulation, which allows to spare any previous set up with structural analyses. The proposed force distribution has been applied to multi-degree-of-freedom systems to check its effectiveness, and the results have been compared with other proposals. In addition, in order to obtain a further validation of the proposed force distribution, the results obtained by using a genetic algorithm have been evaluated and compared. Additionally, the results provided in this work validate the proposed procedure to develop a more efficient lateral load pattern.

Design Development of a Four-Story Strongback Braced Frame

Conventional braced frames tend to concentrate damage in one or a few stories during large earthquakes, indicative of “weak” or “soft” story behavior. To mitigate this behavior, several studies have proposed a modified braced frame, or “strongback”, that utilizes an essentially elastic vertical steel truss to impose a uniform drift distribution. While a subassemblage experimental test and past numerical studies have shown that the strongback system can successfully delay or prevent weak or soft story behavior, the dynamic behavior of this system has not been systematically assessed or evaluated. This study defines the design space for a four-story strongback system. The ability of the strongback to mitigate weak story behavior under a far-field suite of ground motions was assessed using the performance-based methodology in FEMA P695.

Seismic design and response of steel multi-tiered concentrically braced frames in Canada

This article investigates the seismic design and response of steel multi-tiered concentrically braced frames (MT-BFs) in which braces meet at columns between diaphragms. The seismic design provisions of CSA S16-14 are described and illustrated for three-tiered Type MD (moderately ductile) and five-tiered Type LD (limited ductile) braced frames. Analysis methods are proposed to evaluate the in-plane flexural demand on columns. The seismic response of the frames is examined through nonlinear response history analysis. As assumed in design, inelastic deformations tend to concentrate in one tier over the frame height, causing non-uniform drift demands and in-plane bending moments in the columns. CSA S16 provisions predicted well the frame in-plane flexural response and result in acceptable ductility demands on the braces. An extended seismic analysis and design approach that accounts for vertical distribution of brace tension yielding along the frame height is proposed for frames that exceed the limits prescribed in CSA S16.

Incremental Dynamic Analysis of Shape Memory Alloy Braced Steel Frames

Incremental Dynamic Analysis (IDA) is a technique to determine the overall seismic performance of structures under varied intensities of earthquakes. In this paper, the seismic performance of four-story steel braced frames equipped with superelastic Shape Memory Alloy (SMA) braces is assessed by performing IDA. The seismic response of SMA-braced frames was compared to that of corresponding Buckling-Restrained Braced Frames (BRBFs). Based on the results of this comparative study, the SMA-braced frames were generally effective in reducing maximum interstory drifts and permanent roof deformations. In addition, the SMA-braced frames demonstrated more uniform drift distribution over the height of the building. As the intensity of earthquake excitation increases, a higher response reduction can be expected for SMA-braced frames.

Characterization of Silicon Oxides Formed by Light-Induced Anodisation for Silicon Solar Cell Surface Passivation

ABSTRACTIn this paper we report the properties of the anodic silicon dioxide film formed using light-induced anodisation (LIA) method and its potential to be used as surface passivation layer of p-type silicon surfaces of silicon solar cells. The high uniformity of the formed oxide is possibly due to the uniform drift of the positive charge carriers in the silicon to the surface being anodised. The oxide grows at higher rate than that in nitric acid, an oxide layer with thickness of 18 nm can be formed by anodising for 10 min with 15 V bias in 0.5 M sulphuric acid. After annealing in oxygen and then forming gas at 400 °C for 30 min, an average effective carrier lifetime of 120 μs was measured by quasi-steady state photoluminance on 180 μm p-type 3-5 Ohm cm Cz silicon wafers, with a value of 110 μs being measured for the same wafers passivated by a thermally-grown oxide of the same thickness. The properties of the anodic silicon dioxide layers formed by LIA have been characterized by ellipsometry, x-ray photoelectron spectroscopy, quasi-steady state photoluminance and Fourier transform infrared spectroscopy.

Strengthening Research in the Longitudinal Frames of Prefabricated Structures with Viscous Dampers

For the lack of research in the longitudinal frame of prefabricated structure for its weak lateral stiffness, pushover analysis is conducted to evaluate the seismic performance of a fabricated concrete frame. Based on case study, the strengthening strategies with viscous dampers are analyzed. In view of the undesirable drift distribution and failure mode in the existing building, it is believed that arrangement of dampers should be designed to attain a uniform drift distribution. Based on the nonlinear time history analysis method, the strategy of damper allocation in vertical direction of the structure is investigated .Results indicate that a proper design might be attained based on the property of existing system, leading to a uniform drift distribution and better seismic performance.