Efficient Reconstruction of Elastic Stiffnesses in Isotropic and Anisotropic Plates

Because composite materials are often used in safety critical applications, such as in aerospace, it is desirable to have a quick and reliable confirmation of their material properties. The aim of this paper is to introduce the idea of inferring elastic and/or viscoelastic material properties from plate wave measurements with a minimum amount of data. Material characterization of anisotropic materials has been a focus point of research for many years. A good review of this literature can be found in a recent review article [1]. Rokhlin and collaborators [2–4] have also studied this problem extensively, using propagation characteristics and the transmission coefficient to reconstruct elastic properties. The advantage of reconstructing the stiffnesses from the zeros of the transmission coefficient lies the the fact that in contrast to the zeros of the reflection coefficient the transmission coefficient zeros are independent of the fluid properties. A drawback of this method is that the plate must be accessible from both sides.</p

Dominance of Large Cities in China au XXe siecle

In the elastic property characterization of composite laminates with liquid-coupled ultrasound, the stiffnesses that are most easily and accurately measured in conventional single-sided reflection geometries are those of least interest to structural design engineers. Typical elastic wave measurements produce detailed maps of out-of-plane longitudinal stiffnesses, average laminate shear constants, and even mixed stiffnesses, such as C 13, C 23, etc, although these latter can be difficult to infer accurately [1]–[6]. (Further background on this topic can be found in recent reviews [7], [8].) This portion of the stiffness matrix is, however, of relatively little interest to most designers of composite structure. Of far greater interest is the longitudinal in-plane stiffness, since this property controls the effect of tensile and compressive forces on the laminate structure. Additionally, the laminate bending stiffness is another useful material property, but in this paper we concentrate on measuring the in-plane longitudinal stiffnessC 11

Towards Monitoring of Concrete Structures with Embedded Ultrasound Sensors and Coda Waves – First Results of DFG for CoDA

Due to the importance of reinforced concrete structures for modern society, damage assessment during the entire life-cycle of such structures has become a special interest in non-destructive testing. Using embedded ultrasound sensors in combination with other measurement methods, numerical modeling and self-made data collectors, tailored specifically for monitoring tasks, the German research group DFG FOR CoDA aims to investigate and develop novel methods for damage detection and rapid model updating in reinforced concrete structures. In the first stage of the project, besides the development of custom-built, low-cost data collectors, ultrasonic transducers are embedded in a large, reinforced concrete specimen on a BAM test site near Berlin. In this experiment, the influence of changing environmental conditions (mainly temperature) on the ultrasound signal is investigated using coda-wave interferometry. The results show a correlation between changes in temperature and ultrasonic velocity. Such changes must be taken into consideration in a long-term monitoring setup to distinguish between reversible and permanent changes. By correcting the data using a linear relation between concrete temperature and velocity change to remove the seasonal trends and by low-pass filtering the data to remove daily variations can remove most of the temperature influence on the ultrasound measurements

Clinical intervention based on positive psychology: what is it and how to do it?

Symposia on New Waves in Psychotherapy: Variations in CBT?, Hong Kong, 8 May 2010

A knowledge-based online workflow scheudling system

Lamb waves have been widely used in ultrasonic NDE to characterize material properties or assess material quality [1], Of the previous work on materials using phase-matched fluid-loaded coupling, most has been performed in water-coupled testing [2]. With the development of efficient non-contacting ultrasonic air-coupled transducers [3], it has become feasible to apply air-coupled ultrasonic methods to NDE. Because of the low signal noise ratio resulting from the large impedance mismatch between the air and the solid object, most work of air-coupled (AC) ultrasound is qualitative, with defects in plates and C-scan imaging being the principal objectives. As demonstrated by Safaeinili, et al. [4], however, it is possible to characterize elastic plates, both isotropic and anisotropic, by using AC ultrasound, despite the signal-to-noise ratio (SNR) penalty

Identification of novel androgen receptor corepressor, CDC25A, in prostate cancer cells

Poster Presentations - Theme 4: Cancer: 4.10The 12th Research Postgraduate Symposium (RPS 2007), Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong, 12&14 December 200

Identification of a potential auto-regulatory site upstream of the mouse Hoxb-3 gene

In prior studies of Gaussian beam reflection from immersed plates [1–5], it is shown that the reflected field or receiver voltage as a function of transducer position, at any incident angle, can be calculated or measured at constant frequency, and the 2-D calculated reflected field or receiver voltage in the incident plane is almost the same as a 3-D calculation, except for a scale factor as we show later in this paper. This is not the case, however, for the reflection and transmission frequency spectrum, which is widely used to infer the plate material parameters [6,7]. In this paper we extend the complex transducer point (CTP) to this widely used ultrasonic Lamb wave technology. We show that the reflection frequency spectrum requires a full 3-D voltage calculation to achieve the desired accuracy under all conditions. The 3-D receiver voltage frequency spectrum calculated here is compared to extensive experimental results on several materials and in different experimental configurations. The results show that the 3-D voltage spectrum calculation must be used under some conditions to make accurate deductions of material parameters

Finding linear motif pairs from protein interaction networks: a probabilistic approach.

Finding motif pairs from a set of protein sequences based on the protein-protein interaction data is a challenging computational problem. Existing effective approaches usually rely on additional information such as some prior knowledge on protein groupings based on protein domains. In reality, this kind of knowledge is not always available. Novel approaches without using this knowledge is much desirable. Recently, Tan et al. proposed such an approach. However, there are two problems with their approach. The scoring function (using chi(2) testing) used in their approach is not adequate. Random motif pairs may have higher scores than the correct ones. Their approach is also not scalable. It may take days to process a set of 5000 protein sequences with about 20,000 interactions. In this paper, our contribution is two-fold. We first introduce a new scoring method, which is shown to be more accurate than the chi-score used in Tan et al. Then, we present two efficient algorithms, one exact algorithm and a heuristic version of it, to solve the problem of finding motif pairs. Based on experiments on real datasets, we show that our algorithms are efficient and can accurately locate the motif pairs. We have also evaluated the sensitivity and efficiency of our heuristics algorithm using simulated datasets, the results show that the algorithm is very efficient with reasonably high sensitivity.link_to_OA_fulltextThe 6th Annual International Conference on Computational Systems Bioinformatics (CSB), San Diego, CA., 13-17 August 2007. In Computational Systems Bioinformatics Conference Proceedings, 2007, v. 6, p. 111-11