Acoustic emission technique for leak detection in an end shield of a pressurised heavy water reactor

This paper discusses the successful application of the Acoustic Emission Technique (AET) for detection and location of leak paths present on the inaccessible side of an end shield of a Pressurised Heavy Water Reactor (PHWR). The methodology was based on the fact that air and water leak AE signals have different characteristic features. Baseline data was generated from a sound end-shield of a PHWR for characterizing the background noise. A mock up end-shield system with saw cut leak paths was used to verify the validity of the methodology. It was found that air leak signals under pressurisation (as low as 3 psi) could be detected by frequency domain analysis. Signals due to air leaks from various locations of a defective end-shield were acquired and analysed. It was possible to detect and locate leak paths. Presence of detected leak paths were further confirmed by alternate test.     

Electric field-induced concentration and capture of DNA onto microtips

Simple, high-yield concentration of DNA is important for high-throughput genetic analysis and disease diagnosis. Glass-based microfilters are popular but the process requires centrifugation steps with cumbersome chemical processes. As an alternative, a concentration method using an electric field has been explored previously, but with limited efficiency. In this paper, electric field-induced concentration and capture of DNA are studied by using high-aspect-ratio microtips coated with a gold layer. The microtips are immersed longitudinally into a solution of 100???L containing ??-phage DNA. After DNA concentration using an electric field, the microtips are withdrawn from the solution. Under AC- and biased AC fields, DNA is concentrated by electrophoresis (EP), dielectrophoresis (DEP), and electroosmotic flow (EOF). To reduce capillary effects in the withdrawal process, the microtips are coated with positively charged poly-l-lysine (PLL). The pattern of captured DNA is analyzed by fluorescence microscopy. DEP attracts DNA molecules at the edges of microtips, where the highest gradient of electric field exists. EP attracts DNA onto the surface of microtips following the vectors of an electric field. EOF generates vortexes that deliver DNA onto microtips. Using this method, 85% of DNA is captured on the PLL-coated microtips after three sequential captures. The concentration mechanism can potentially facilitate rapid and simple preparation of DNA for downstream analysis.     

Structural integrity assessment of the containment structure of a pressurised heavy water nuclear reactor using impact echo technique

The impact echo technique is based on the use of transient stress waves for non-destructive detection of flaws in concrete structures. Impact-echo testing has been carried out for assessment of the structural integrity of the ring beam of a pressurised heavy water nuclear reactor. In order to develop the test procedure for carrying out impact echo testing, mock up calibration blocks were made. The detectability of the impact echo system has also been established in terms of the depth and the lateral dimension of the detectable flaw for the ring beam under consideration. Based on the optimised test parameters identified with the help of the studies carried out on the mock up blocks, impact echo testing was carried out on the ring beam of the reactor containment structure, for assessing its structural integrity.     

Field equations for incompressible non-viscous fluids using artificial intelligence

In this article, we introduce new field equations for incompressible non-viscous fluids, which can be treated similarly to Maxwell’s electromagnetic equations based on artificial intelligence algorithms. Lagrangian and Hamiltonian formulations are used to arrive at field equations that are solved using convolutional neural networks. Four linear differential equations, which describe the two fields, namely, the dynamic pressure and the vortex fields, are derived, and these can be used in place of Euler’s equation. The only assumption while deriving this equation is that the dynamic pressure and vortex fields obey the superposition principle. The important finding to be noted is that Euler’s fluid equations can be converted into field equations analogous to Maxwell’s electromagnetic equations. We solve the flow problem for laminar flow past a cylinder, sphere, and cone in two dimensions similar to the conduction in a uniform electric field and arrive at closed-form expressions. These closed-form expressions, which are obtained for the potentials of fluid flow, are similar to the streamline potential functions in the case of fluid dynamics.

     

Drawing behaviour of metal–composite sandwich structures

The drawing behaviour of metal–composite sandwich structures is investigated as a function of the constituent material properties and the process variables of blank preheat temperature and blank-holder force. Materials include three grades of aluminium alloy as the skin layer material and two types of reinforced polypropylene composite as the core layer material. Blank-holder force has a significant effect on the failure mode of the metal–composite system with lower forces resulting in wrinkling as the dominate mode and higher forces resulting in splitting and fracture. Increasing preheat temperature decreases the failure in the composite core however it will increase the severity of wrinkling in the outer flange and sidewall.     

MARKOV DECISION PROCESSES WITH UNCERTAIN TRANSITION RATES: SENSITIVITY AND MAX HYPHEN MIN CONTROL

Solution techniques for Markov decision problems rely on exact knowledge of the transition rates, which may be difficult or impossible to obtain. In this paper, we consider Markov decision problems with uncertain transition rates represented as compact sets. We first consider the problem of sensitivity analysis where the aim is to quantify the range of uncertainty of the average per‐unit‐time reward given the range of uncertainty of the transition rates. We then develop solution techniques for the problem of obtaining the max‐min optimal policy, which maximizes the worst‐case average per‐unit‐time reward. In each of these problems, we distinguish between systems that can have their transition rates chosen independently and those where the transition rates depend on each other. Our solution techniques are applicable to Markov decision processes with fixed but unknown transition rates and to those with time‐varying transition rates.     

Effect of microstructure on micromechanical performance of dry cortical bone tissues

The mechanical properties of bone depend on composition and structure. Previous studies have focused on macroscopic fracture behavior of bone. In the present study, we performed microindentation studies to understand the deformation properties and microcrack–microstructure interactions of dry cortical bone. Dry cortical bone tissues from lamb femurs were tested using Vickers indentation with loads of 0.245–9.8 N. We examined the effect of bone microstructure on deformation and crack propagation using scanning electron microscopy (SEM). The results showed the significant effect of cortical bone microstructure on indentation deformation and microcrack propagation. The indentation deformation of the dry cortical bone was basically plastic at any applied load with a pronounced viscoelastic recovery, in particular at lower loads. More microcracks up to a length of approximately 20 μm occurred when the applied load was increased. At loads of 4.9 N and higher, most microcracks were found to develop from the boundaries of haversian canals, osteocyte lacunae and canaliculi. Some microcracks propagated from the parallel direction of the longitudinal interstitial lamellae. At loads 0.45 N and lower, no visible microcracks were observed.     

Nonlinear surface acoustic waves on an isotropic solid

A systematic derivation of the approximate coupled amplitude equations governing the propagation of a quasi-monochromatic Rayleigh surface wave on an isotropic solid is presented, starting from the non-linear governing differential equations and the non-linear free-surface boundary conditions, using the method of mulitple scales. An explicit solution of these equations for a signalling problem is obtained in terms of hyperbolic functions. In the case of monochromatic excitation, it is shown that the second harmonic amplitude grows initially at the expense of the fundamental and that the amplitudes of the fundamental and second harmonic remain bounded for all time.     

Acoustic emission source location on a cylindrical surface

Acoustic emission (AE) is a stress wave, generated in a structural material when it is stimulated by perturbations. One of the important features of this technique is to detect the location of the AE source in the structure from the differences in the times of arrival of stress waves at several sensors placed on it. A generalized mathematical formalism for the evaluation of the path travelled by an acoustic wave on the surface of a structure, on the concept of geodesics, is presented. Based on this concept, a mathematical method is developed for the calculation of the coordinates of an AE source on a cylindrical surface by three AE sensors. This concept has not been attempted analytically so far, to our knowledge.