Study of Time-Domain Techniques for Modal Parameter Identification of a Long Suspension Bridge with Dense Sensor Arrays

While numerous studies have been published concerning the application of a variety of system identification techniques in conjunction with vibration measurements from civil infrastructure systems, there is a paucity of publications addressing the influence of algorithm-specific control parameters that impact the correct and efficient application of the selected identification scheme. Furthermore, as dense sensor arrays become widely accessible in civil infrastructure applications, voluminous amounts of multichannel data streams are becoming available for processing, thus imposing new demands on identification procedures regarding high-dimensionality (in both the spatial as well as the temporal domains) requirements that may render some methods inapplicable if careful attention is not paid to practical implementation issues. This paper provides a comprehensive study of three time-domain identification algorithms applied in conjunction with the Natural Excitation Technique in order to extract the modal parameters of a newly constructed long-span bridge that was monitored, in its virgin state, over a relatively long period of time with a state-of-the-art dense sensor array. The three methods used are: the eigensystem realization algorithm (ERA), the ERA with data correlations, and the least squares algorithm. One of the critical issues in the mentioned algorithms, is selection of the reference degree-of-freedom (DOF). Previous experiences have shown that one cannot rely on a single reference DOF for identification of all modes. Consequently, the aforementioned identification formulations were modified to include multiple reference DOF, simultaneously, or one at a time. An autonomous algorithm was presented to distinguish the genuine structural modes from spurious noise or computational modes. Based on some parameter studies, some useful guidelines for the selection of critical user-selectable parameters are presented.     

Plate heat exchangers: Recent advances

This study presents the advances in plate heat exchangers both in theory and application. It dresses the direction of various technical research and developments in the field of energy handling and conservation. The selected areas of heat transfer performance and pressure drop characteristics, general models and calculations change of phase; boiling and condensation, fouling and corrosion, and welded type plate heat exchangers and finally other related areas are highlighted.     

Positive Wire-to-Plane Coronas as Influenced by Atmospheric Humidity

A method is suggested for calculating the inception voltage and corona current in humid air. It is found that the photoelectrons distribution within the ionization layer, which depends upon the gap geometry, plays an important role in deciding whether the inception voltage increases or decreases with relative humidity. The inception voltage is one of the boundary conditions required in the theoretical analysis of the corona V-I characteristics also presented. The experimental results reported in the literature which differ widely can be explained in the light of the present findings.     

Influence of temperature,molecular weight,and molecular weight dispersity on the surface tension of polystyrene,polypropylene, and polyethylene. II. Theoretical

Experimental data for the surface tension of polystyrenes of different molecular weights (3400–200,000) and different molecular weight dispersities (1–3) and of different polyolefins are compared with the predictions of the Patterson–Rastogi and Dee–Sauer cell theories, which infer the surface tension from pressure–volume–temperature (PVT) data. PVT data for these polymers were obtained from the literature and experimentally and are fitted to the Flory–Orwoll–Vrij equation of state. Both theories predict that the surface tension will decrease linearly with increasing temperature and increase with molecular weight, thereby corroborating the experimental data. However, both theories underestimate the entropy change in the surface formation per unit area at a constant volume for low molecular weight and polydisperse systems and underestimate the effect of molecular weight dispersity on surface tension. Both theories feature two parameters, m and b, that quantify the enthalpic and entropic contributions to surface tension. The theoretical predictions are fitted to the experimental data for monodisperse polystyrene (with a molecular weight above the molecular weight of entanglement), polypropylene, and linear low‐density polyethylene to quantify the enthalpic contribution to surface tension. b is then evaluated as a function of molecular weight and molecular weight dispersity and is found to decrease with increasing molecular weight and to increase with increasing molecular weight dispersity, showing that end‐group excess at the surface has some effect on surface tension. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 2201–2212, 2002     

Dystocia: is it a major indication for caesarean section?

An unusual case of rhinocerebral zygomycosis with its clinical and histopathological features are presented. A good response was observed with oral itraconazole at a dose of 200 mg day-1 for a period of 3 months. To our knowledge, it is the first case report of this infection, involving the maxillary sinus, eye and the brain, from Madras, Tamilnadu, India.     

Modification of the standard epifluorescence microscopic method for total bacterial counts in environmental samples

Acridine orange direct count (AODC) is a popular method for determining microbial numbers in environmental samples via epifluorescence microscopy. We have found that the color of the fluorescing cells (green vs orange-red cells) depends on the level of moisture on the filter and that the percentage of green-fluorescing cells decreases when the filter is dry. Since the level of moisture can vary across the filter and is difficult to control in any case, the use of color as a basis for inferring cell activity is not justified. The proportion of cells fluorescing green on a previously dried filter can be greatly increased by remoistening the filter prior to microscopic examination. This is advantageous since cells which fluoresce green are more easily visualized than orange-red fluorescing cells. We therefore propose modification of the Standard Methods protocol for AODC to include the remoistening step.     

Generalized hydrodynamics of reaction-diffusion systems and dissipative structures

Generalized hydrodynamics (GH) are derived and used to describe a reaction-diffusion system. The derived GH equations are hyperbolic and are shown to be more general and more suitable than the conventional parabolic reaction-diffusion equations, especially in small geometries. These equations are applied to the study of dissipative structures in glycolysis and are solved numerically using the finite-element method. The solution exhibits a multitude of wave and Turing patterns. The time evolution of the calortropy production for the obtained pattern seems to correlate with the increasing complexity of the system.     

A framework for real-time implementation of low-dimensional parameterized NMPC

In this paper, a novel approach is proposed to implement low-dimensional parameterized Nonlinear Model Predictive Control (NMPC) schemes for systems showing fast dynamics. The proposed scheme is based on distributing the reconstruction of the cost function over the real lifetime of the controlled system. The framework is particularly suitable for NMPC formulations that use low dimensional control parametrization. The concrete example of a Planar Vertical Take-Off and Landing (PVTOL) aircraft stabilization problem is used to illustrate the efficiency of the proposed formulation.     

Generalized inverted exponential distribution under constant stress accelerated life test: Different estimation methods with application

Estimation of the parameters of generalized inverted exponential distribution is considered under constant stress accelerated life test. Besides the maximum likelihood method, nine different frequentist methods of estimation are used to estimate the unknown parameters. Moreover, the reliability function is estimated under use conditions based on different methods of estimation. We perform extensive simulation experiments to see the performance of the proposed estimators. As an illustration, a real data set is analyzed to demonstrate how the proposed methods may work in practice.