Analysis of Ultrasonic Backscatter for Porosity Characterization in Graphite-Epoxy Composites

This paper summarizes recent work on the use of ultrasonic back-scatter for the estimation of porosity levels in continuous-fiber-reinforced, layered graphite-epoxy composites. This work is a continuation of previous work described in Refs. 1–3, which addresses the effect of porosity on (1) azimuthal angle backscatter scans, and (2) the spectral characteristics of backscatter

Effect of Bottom-Surface Reflections on Backscatter from Porosity in a Composite Layer

Polar backscattering from a fiber-reinforced composite which contains regions of porosity, has been investigated in a number of papers [1]–[7]. Several scattering mechanisms appear to contribute to the backscattered signal. Roughly speaking the components of the backscattered signal can be attributed to effects of finite beam width, to the structuring of the material and to the existence of porosity

Activation of the steroid and xenobiotic receptor, SXR, induces apoptosis in breast cancer cells

<p>Abstract</p> <p>Background</p> <p>The steroid and xenobiotic receptor, SXR, is an orphan nuclear receptor that regulates metabolism of diverse dietary, endobiotic, and xenobiotic compounds. SXR is expressed at high levels in the liver and intestine, and at lower levels in breast and other tissues where its function was unknown. Since many breast cancer preventive and therapeutic compounds are SXR activators, we hypothesized that some beneficial effects of these compounds are mediated through SXR.</p> <p>Methods</p> <p>To test this hypothesis, we measured proliferation of breast cancer cells in response to SXR activators and evaluated consequent changes in the expression of genes critical for proliferation and cell-cycle control using quantitative RT-PCR and western blotting. Results were confirmed using siRNA-mediated gene knockdown. Statistical analysis was by t-test or ANOVA and a P value ≤ 0.05 was considered to be significant.</p> <p>Results</p> <p>Many structurally and functionally distinct SXR activators inhibited the proliferation of MCF-7 and ZR-75-1 breast cancer cells by inducing cell cycle arrest at the G1/S phase followed by apoptosis. Decreased growth in response to SXR activation was associated with stabilization of p53 and up-regulation of cell cycle regulatory and pro-apoptotic genes such as p21, PUMA and BAX. These gene expression changes were preceded by an increase in inducible nitric oxide synthase and nitric oxide in these cells. Inhibition of iNOS blocked the induction of p53. p53 knockdown inhibited up-regulation of p21 and BAX. We infer that NO is required for p53 induction and that p53 is required for up-regulation of cell cycle regulatory and apoptotic genes in this system. SXR activator-induced increases in iNOS levels were inhibited by siRNA-mediated knockdown of SXR, indicating that SXR activation is necessary for subsequent regulation of iNOS expression.</p> <p>Conclusion</p> <p>We conclude that activation of SXR is anti-proliferative in p53 wild type breast cancer cells and that this effect is mechanistically dependent upon the local production of NO and NO-dependent up-regulation of p53. These findings reveal a novel biological function for SXR and suggest that a subset of SXR activators may function as effective therapeutic and chemo-preventative agents for certain types of breast cancers.</p

To understand the expression profile and function of heparanase in the adult spinal cord

The presence of porosity in a structural material generally has a detrimental effect on the strength and mechanical properties of the component [1]. Excessive porosity is especially undesirable in laminated composites such as graphite-epoxy as it substantially degrades the interlaminar shear strength, the compressive strength and the transverse flexural strength, Detailed morphological knowledge of the pores such as their geometrical shape, orientation and location of occurrence in the laminate is valuable in several areas. In the nondestructive evaluation of porosity in composites using ultrasound, such morphological data will aid the model development of the interaction of the ultrasonic field with the voids and help the interpretation of the ultrasonic measurement results. In the investigation of the effects of defects, data on the pore morphology serve as inputs to models of the stress distribution around the defects and the interaction between the defects

The Early Development of Modern Chinese Insurance Business: The Case of the China United Assurance Society Ltd.

The presence of porosity in a fiber-reinforced composite may have a critical effect on the composite’s mechanical properties and service performance. Detection and characterization of porosity by ultrasonic means have, therefore, received considerable attention in recent years. The frequency dependence of ultrasonic attenuation has been used to find the volume fraction and pore size of gas porosity in aluminum alloys, [1]–[3], and in graphite-epoxy composites [4], The use of ultrasonic backscatter measurements to characterize the volume fraction has been reported in Refs. [5]–[6]. A theoretical model to analyze the backscatter from a porous unidirectionally fiber-reinforced composite has been established in [7]. In the present paper, the approach of Ref. [7] is extended to multi-ply fiber-reinforced composites. It has been shown experimentally by several investigators, [8]–[9], that polar backscatter from a multi-ply composite shows an amplitude dependence on the azimuthal angle, which is characterized by a pattern of peaks and valleys. The peaks occur when the propagation vector of the incident pulse is normal to the direction of the fibers in one of the plies of the multi-ply layup

Morphological science research: Where do we go from here?

The potential of ultrasonic polar backscatter measurements for detecting and characterizing porosity in composite laminates has been investigated in a number of laboratories[l–l1]. The objective of this study was to evaluate the influence of the nature of the composite’s surface on such measurements. The deleterious effects of bleeder cloth impressions, previously noted by Bar-Cohen[12], led to the hypothesis that the periodic surface features due to bleeder cloth impressions remaining after the cure process contribute significantly to the received backscattered signal, possibly masking the anisotropy of backscatter which is used to estimate porosity