Leak detection in gas pipeline networks using an efficient state estimator. Part II. Experimental and field evaluation

In Part-I of this two part paper, a method is proposed for on-line leak detection and identification in gas pipeline networks using flow and pressure measurements. Simulations on two illustrative networks were used to demonstrate the applicability of the proposed method. In this paper, the performance of the proposed leak detection and identification methodology was evaluated using experiments with compressed air on a laboratory scale network. The on-line applicability of the proposed methodology was demonstrated through field level leak detection tests carried out on a 204.7 km long pipeline in India, supplying natural gas to a power plant. The laboratory and field tests demonstrated that the proposed methodology can be used for quick on-line detection of leaks, and locating the leaks reasonably accurately.     

Multivariable optimization studies of cathode catalyst layer of a polymer electrolyte membrane fuel cell

The amount of current generated in a polymer electrolyte membrane fuel cell (PEMFC) depends strongly on the local conditions in a cathode such as available oxygen, surface area available for the reactions, amount of ionomer, and amount of electro-catalyst. In the present work, design parameters of a cathode catalyst layer are optimized to achieve the maximum current density at a given operating voltage. The decision variables are chosen such that they can be realized experimentally. To understand the effect of the model fidelity on the decision variables, optimization is performed with a single phase model and a two-phase model with and without membrane. Other objective functions such as maximization of current generation per catalyst loading, minimization of catalyst layer cost per power and minimization of cell cost per power are also considered to study the effects of the objective functions on the decision variables.     

Analysis of a thermal storage unit containing multiple phase change materials dispersed with high conductivity particles

This paper investigates numerically the combined effect of employing multiple Phase change materials (PCMs) and dispersion of high conductivity particles on the thermal performance of an energy storage unit. The key parameters that govern the performance have been identified following a simple reduction of variables. Among the different parameters, melting temperature of the PCMs, latent heat and melting temperature difference between two consecutive PCMs (ΔT_m) are found to have a significant influence on the performance. A case study considering a 3-PCM unit to study the effect of key parameters during melting has been presented. The results show that for the 3-PCM unit, the performance is better when the second and third PCMs placed have their latent heats larger than the first PCM. It has been recommended to have ΔT_m1 > ΔT_m2 for the 3-PCM unit in order achieve more melting.

     

A finite element study of the indentation mechanics of an adhesively bonded layered solid

The objective of this work is to study the mechanics of indentation of an adhesively bonded layered solid. To this end, several (plane strain) finite element simulations of wedge indentation of a ductile strip which is adhesively bonded to a rigid substrate are conducted by varying the properties of the adhesive layer. The stress fields below the indenter tip and at the strip-adhesive interface are examined for various depths of indentation. The effects of the adhesive properties on the above features of the finite element solution, as well as on the hardness versus penetration characteristics, are investigated. The above results are also compared with those for an unbonded strip resting on a frictionless surface. It is found that once yielding commences in the adhesive layer, the state of stress in it is comprised of a shear stress and a superposed hydrostatic compression. Also, it is observed that increasing the yield strength of the adhesive layer significantly delays the onset of the decreasing phase of the hardness versus penetration curve, whereas, changing the elastic modulus of the adhesive has negligible effect on it.     

Realisation of transmission zeros with two RC parallel ladders

The polynomial decompositions due to Calahan and Horowitz can be effectively used for the synthesis of passive RC parallel ladders to realise any zeros of transmission including those on the positive real axis. Only two ladders are sufficient. One of the ladders will be connected via a voltage amplifier having a gain of ±1.     

Pulsed Anodic Anodisation of Porous Silicon Films

Porous Silicon is conventionally made by dc anodisation of silicon. In this paper we have studied the luminescence of porous silicon made by pulsed anodisation as a function of duty cycle and HF concentration. Specifically we show for the first time that the luminescence can be tuned over a wide range in energy.     

A Three-dimensional Numerical Study of Mixed Mode (I and II) Crack Tip Fields in Elastic–plastic Solids

The stress fields near a crack front in a ductile solid are essentially three-dimensional (3D) in nature. The objective of this paper is to investigate the structure of these fields and to establish the validity of two-dimensional (2D) plane stress and plane strain approximations near the crack front under mixed mode (combined modes I and II) loading. To this end, detailed 3D and 2D small strain, elastic–plastic finite element simulations are carried out using a boundary layer (small scale yielding) formulation. The plastic zones and radial, angular and thickness variations of the stresses are studied corresponding to different levels of remote elastic mode mixity and applied load, as measured by the plastic zone size with respect to the plate thickness. The 3D results are compared with those obtained from 2D simulations and asymptotic solutions. It is found that, in general, plane stress conditions prevail at a distance from the crack front exceeding half the plate thickness, although it could be slightly smaller for mode II predominant loading. The implications of the 3D stress distribution on micro-void growth near the crack front are briefly discussed.     

Variable step-size Griffiths’ algorithm for improved performance of feedforward/feedback active noise control

A new robust computationally efficient variable step-size LMS algorithm is proposed and it is applied for secondary path (SP) identification of feedforward and feedback active noise control (ANC) systems. The proposed variable step-size Griffiths’ LMS (VGLMS) algorithm not only uses a step-size, but also the gradient itself, based on the cross-correlation between input and the desired signal. This makes the algorithm robust to both stationary and non-stationary observation noise and the additional computational load involved for this is marginal. Further, in terms of convergence speed and error, it is better than those by the Normalized LMS (NLMS) and the Zhang’s method (Zhang in EURASIP J. Adv. Signal Process. 2008(529480):1–9, 2008). The convergence rate of the feedforward and feedback ANC systems with the VGLMS algorithm for SP identification is faster (by a factor of 2 and 3, respectively) compared with that using NLMS algorithm. For feedforward ANC, its convergence rate is faster (3 times) compared with Akhtar’s algorithm (Akhtar in IEEE Trans Audio Speech Lang Process 14(2), 2006). Also, for higher main path lengths compared with SP, the proposed algorithm is computationally efficient compared with Akhtar’s algorithm.     

rexB of bacteriophage lambda is an anti-cell death gene

In Escherichia coli, programmed cell death is mediated through "addiction modules" consisting of two genes; the product of one gene is long-lived and toxic, whereas the product of the other is short-lived and antagonizes the toxic effect. Here we show that the product of lambdarexB, one of the few genes expressed in the lysogenic state of bacteriophage lambda, prevents cell death directed by each of two addiction modules, phd-doc of plasmid prophage P1 and the rel mazEF of E. coli, which is induced by the signal molecule guanosine 3',5'-bispyrophosphate (ppGpp) and thus by amino acid starvation. lambdaRexB inhibits the degradation of the antitoxic labile components Phd and MazE of these systems, which are substrates of ClpP proteases. We present a model for this anti-cell death effect of lambdaRexB through its action on the ClpP proteolytic subunit. We also propose that the lambdarex operon has an additional function to the well known phenomenon of exclusion of other phages; it can prevent the death of lysogenized cells under conditions of nutrient starvation. Thus, the rex operon may be considered as the "survival operon" of phage lambda.