Damage identification of supporting structures with a moving sensory system

© 2017 Elsevier Ltd An innovative approach to identify local anomalies in a structural beam bridge with an instrumented vehicle moving as a sensory system across the bridge. Accelerations at both the axle and vehicle body are measured from which vehicle-bridge interaction force on the structure is determined. Local anomalies of the structure are estimated from this interaction force with the Newton's iterative method basing on the homotopy continuation method. Numerical results with the vehicle moving over simply supported or continuous beams show that the acceleration responses from the vehicle or the bridge structure are less sensitive to the local damages than the interaction force between the wheel and the structure. Effects of different movement patterns and moving speed of the vehicle are investigated, and the effect of measurement noise on the identified results is discussed. A heavier or slower vehicle has been shown to be less sensitive to measurement noise giving more accurate results

Mössbauer hyperfine parameters of iron species in the course of Geobacter-mediated magnetite mineralization

Amorphous ferric iron species (ferrihydrite or akaganeite of <5 nm in size) is the only known solid ferric iron oxide that can be reductively transformed by dissimilatory iron-reducing bacteria to magnetite completely. The lepidocrocite crystallite can be transformed into magnetite in the presence of abiotic Fe(II) at elevated pH or biogenic Fe(II) with particular growth conditions. The reduction of lepidocrocite by dissimilatory iron-reducing bacteria has been widely investigated showing varying results. Vali et al. (Proc Natl Acad Sci USA 101:16121-16126, 2004) captured a unique biologically mediated mineralization pathway where the amorphous hydrous ferric oxide transformed to lepidocrocite was followed by the complete reduction of lepidocrocite to single-domain magnetite. Here, we report the 57Fe Mössbauer hyperfine parameters of the time-course samples reported in Vali et al. (Proc Natl Acad Sci USA 101:16121-16126, 2004). Both the quadrupole splittings and linewidths of Fe(III) ions decrease consistently with the change of aqueous Fe(II) and transformations of mineral phases, showing the Fe(II)-mediated gradual regulation of the distorted coordination polyhedrons of Fe 3+ during the biomineralization process. The aqueous Fe(II) catalyzes the transformations of Fe(III) minerals but does not enter the mineral structures until the mineralization of magnetite. The simulated abiotic reaction between Fe(II) and lepidocrocite in pH-buffered, anaerobic media shows the simultaneous formation of green rust and its gradual transformation to magnetite plus a small fraction of goethite. We suggested that the dynamics of Fe(II) supply is a critical factor for the mineral transformation in the dissimilatory iron-reducing cultures. © 2011 The Author(s).published_or_final_versionSpringer Open Choice, 21 Feb 201

Fiber-coupled light-emitting diode with a capillary-bonded hemispherical lens

A hemispherical lens capillary-bonded to an InGaN flip-chip light-emitting diode (LED) is demonstrated to efficiently couple light to a plastic optical fiber. The BK-7 hemispherical lens is bonded onto a circularly shaped LED chip with inclined sidewalls cut by laser-micromachining, so that lateral emissions are effectively suppressed. Capillary bonding minimizes air-gap between chip and lens enabling transmission of evanescent waves, thus maximizing overall optical transmission. With the lens attached, emission divergence from the assembly is significantly reduced, diverting rays into the acceptance cone of the fiber. Fiber coupling efficiency as high as 53.8% has been demonstrated. © 2011 IEEE.published_or_final_versio

Fitting Nonlinear Ordinary Differential Equation Models with Random Effects and Unknown Initial Conditions Using the Stochastic Approximation Expectation–Maximization (SAEM) Algorithm

The past decade has evidenced the increased prevalence of irregularly spaced longitudinal data in social sciences. Clearly lacking, however, are modeling tools that allow researchers to fit dynamic models to irregularly spaced data, particularly data that show nonlinearity and heterogeneity in dynamical structures. We consider the issue of fitting multivariate nonlinear differential equation models with random effects and unknown initial conditions to irregularly spaced data. A stochastic approximation expectation–maximization algorithm is proposed and its performance is evaluated using a benchmark nonlinear dynamical systems model, namely, the Van der Pol oscillator equations. The empirical utility of the proposed technique is illustrated using a set of 24-h ambulatory cardiovascular data from 168 men and women. Pertinent methodological challenges and unresolved issues are discussed

Industry-wide corporate fraud: The truth behind the Volkswagen scandal

Corporate fraud committed under climate mitigation pressures is becoming more frequently observed in line with the ever increasing environmental standards and relevant regulation enforcements. One example is the Volkswagen Emission Gate Scandal. Using firm-level panel data of major automobile manufacturers from 2000 to 2015, this study empirically identifies the motives behind the corporate deception scandal. We develop a conceptual model summarising the factors affecting decision-making, and the firms' environmentally responsible investments (ERIs) including the truthfulness of related public communications. Our findings identify legal and regulatory pressures, the firm's existing level of ERIs competency and expertise, pressures from emission regulation, market competitors, consumers, owners, or shareholders as the key factors inducing the scandal. The empirical findings show that firms are more likely to experience corporate fraud if their senior managers are paid with substantial variable components that may lead them to engage in riskier business behaviour and to be more short-term focused, thereby supporting the well-established contract theory. To avoid corporate fraud and engage in legitimate business competitiveness, we suggest that firms should focus on technological innovation as well as improving corporate governance and leverage ratios to effectively control and monitor management. In addition, policy makers should be more realistic about practical and commercial limitations in the policy-setting process, and take on a more supporting role in achieving technological innovations and effective corporate governance. In summary, we argue that cleaner production is not only the result of technologically progress and research, but importantly it also involves issues associated with corporate governance and business ethics

ADRC-based model predictive current control for PMSMs fed by three-phase four-switch inverters

© 2016 IEEE.A novel automatic disturbances rejection control (ADRC)-based model predictive current control (MPCC) strategy is developed for permanent magnet synchronous motors (PMSMs) fed by three-phase four-switch inverters, an after-fault-topology for fault-tolerant three-phase six-switch inverters. The mathematical model of a PMSM fed by a three-phase four-switch inverter is built firstly. Then the ADRC and MPCC are respectively designed, with the former being used to realize disturbance estimation and disturbance compensation while the latter being used to reduce stator current ripple and improve the quality of the torque and speed control. The resultant ADRC-based MPCC PMSM fed by an unhealthy inverter has fault-tolerant effective with dynamical performance very close to an ADRC-based MPCC PMSM fed by a healthy inverter. On the other hand, compared with PI-based MPCC PMSM fed by an unhealthy inverter, it possesses better dynamical response behavior and stronger robustness as well as smaller THD index of three-phase stator current in the presence of variation of load torque. The simulation results validate the feasibility and effectiveness of the proposed scheme

Anisotropic step-flow growth and island growth of GaN(0001) by molecular beam epitaxy

GaN(0001) thin films are grown using radio frequency plasma assisted molecular beam epitaxy. By changing the growth temperature, anisotropic growth rate behavior is observed in both the step-flow growth mode and the 2D island growth mode. Tunneling scanning microscopy reveals, in the step-flow growth mode, strong influences from the growth anisotropy on the shape of the terrace edges, resulting in striking differences between hexagonal and cubic films. In the 2D nucleation growth mode, triangularly shaped islands are formed. The significance of growth anisotropy to growing high quality GaN films is discussed.published_or_final_versio

Spatial and temporal variations of aerosols around Beijing in summer 2006: Model evaluation and source apportionment

Regional aerosol model calculations were made using the Weather Research and Forecasting (WRF)-Community Multiscale Air Quality (CMAQ) and WRF-chem models to study spatial and temporal variations of aerosols around Beijing, China, in the summer of 2006, when the Campaigns of Air Quality Research in Beijing and Surrounding Region 2006 (CAREBeijing) intensive campaign was conducted. Model calculations captured temporal variations of primary (such as elemental carbon. (EC)) and secondary (such as sulfate) aerosols observed in and around Beijing. The spatial distributions of aerosol optical depth observed by the MODTS satellite sensors were also reproduced over northeast China. Model calculations showed distinct differences in spatial distributions between primary and secondary aerosols in association with synoptic-scale meteorology. Secondary aerosols increased in air around Beijing on a scale of about 1000 × 1000 km2 under an anticyclonic pressure system. This air mass was transported northward from the high anthropogenic emission area extending south of Beijing with continuous photochemical production. Subsequent cold front passage brought clean air from the north, and polluted air around Beijing was swept to the south of Beijing. This cycle was repeated about once a week and was found to be responsible for observed enhancements/reductions of aerosols at the intensive measurement sites. In contrast to secondary aerosols, the spatial distributions of primary aerosols (EC) reflected those of emissions, resulting in only slight variability despite the changes in synopticscale meteorology. In accordance with these results, source apportionment simulations revealed that primary aerosols around Beijing were controlled by emissions within 100 km around Beijing within the preceding 24 h, while emissions as far as 500 km and within the preceding 3 days were found to affect secondary aerosols. Copyright 2009 by the American Geophysical Union

Broadband gradient impedance matching using an acoustic metamaterial for ultrasonic transducers

2016-2017 > Academic research: refereed > Publication in refereed journal201804_a bcmaVersion of RecordPublishe