Failure Analysis of AISI-304 Stainless Steel Styrene Storage Tank

This paper presents the failure analysis of AISI-304 stainless steel tank that was fabricated by welding and used for the storage of styrene monomers. After about 13 years of satisfactory operation, significant cracking was observed adjacent to the weld joints and in base plate near tank foundation. Weld repair was by shielded gas arc welding using AISI 308 stainless steel filler wire. The failed base plate was replaced with the new AISI 304 base plate of same thickness. After a short period of time, seepage was observed along the weld bead. Upon nondestructive testing cracks were found in the heat-affected zone and in the base plate. The failure investigation was carried out on welded and base plate samples using spectroscopy, optical and scanning electron microscopy, fractography, SEM–EDS analysis, microhardness measurements, tensile and impact testing. The results revealed transgranular cracks in the HAZ and base plate, and the failure was attributed due to stress corrosion cracking. Cracks initiated as a result of combined action of stresses developed during welding and the presence of a chloride containing environment due to seawater. It was further observed that improper welding parameters were employed for weld repair which resulted in sensitization of the structure and postweld heat treatment to remove weld sensitization and minimize the residual stresses was not done.     

Safety analysis of discrete event systems using a simplified Petri net controller

This paper deals with the problem of forbidden states in discrete event systems based on Petri net models. So, a method is presented to prevent the system from entering these states by constructing a small number of generalized mutual exclusion constraints. This goal is achieved by solving three types of Integer Linear Programming problems. The problems are designed to verify the constraints that some of them are related to verifying authorized states and the others are related to avoiding forbidden states. The obtained constraints can be enforced on the system using a small number of control places. Moreover, the number of arcs related to these places is small, and the controller after connecting them is maximally permissive.     

The role of flow‐induced microstructure in rheological behavior and nonisothermal crystallization kinetics of polyethylene/organoclay nanocomposites

The evolution of polyethylene/organoclay nanocomposite microstructure via shear and extentional flow fields was studied by tracing rheological behavior and nonisothermal crystallization kinetics. Although studying microstructure formed through flow fields, two phenomena were noticed: the breaking of three‐dimensional (3D) network containing filler–filler, filler–matrix, and matrix–matrix interactions, and organoclay platelets orientation. Utilizing nonlinear viscoelastic measurements and thermal analyses, it was proven that clay alignment was present only in large enough shear flows and all elongational flows. It was observed that regardless of the type of flow field and its magnitude, due to the breaking of 3D network, the extent of crystallization can be increased. The half‐lives of the crystallization of film samples and those samples subjected to large enough shear rates for clay platelets to be aligned decreased, proving the effect of clay orientation on crystallization rate increment. Based on endotherms observed through melting behavior studies of samples, it was proven that in elongation and large amplitude shear flows, clay orientation had resulted in forming thicker crystalline lamellae, likely because of forcing the adjacent polymer chains to align with the clay platelets. POLYM. ENG. SCI., 54:1839–1847, 2014. © 2013 Society of Plastics Engineers     

Electrical detection of cancer biomarker using aptamers with nanogap break-junctions

Epidermal growth factor receptor (EGFR) is a cell surface protein overexpressed in cancerous cells. It is known to be the most common oncogene. EGFR concentration also increases in the serum of cancer patients. The detection of small changes in the concentration of EGFR can be critical for early diagnosis, resulting in better treatment and improved survival rate of cancer patients. This article reports an RNA aptamer based approach to selectively capture EGFR protein and an electrical scheme for its detection. Pairs of gold electrodes with nanometer separation were made through confluence of focused ion beam scratching and electromigration. The aptamer was hybridized to a single stranded DNA molecule, which in turn was immobilized on the SiO(2) surface between the gold nanoelectrodes. The selectivity of the aptamer was demonstrated by using control chips with mutated non-selective aptamer and with no aptamer. Surface functionalization was characterized by optical detection and two orders of magnitude increase in direct current (DC) was measured when selective capture of EGFR occurred. This represents an electronic biosensor for the detection of proteins of interest for medical applications.     

Boost-wise pre-loaded mixture of experts for classification tasks

A modified version of Boosted Mixture of Experts (BME) is presented in this paper. While previous related works, namely BME, attempt to improve the performance by incorporating complementary features of a hybrid combining framework, they have some drawback. Analyzing the problems of previous approaches has suggested several modifications that have led us to propose a new method called Boost-wise Pre-loaded Mixture of Experts (BPME). We present a modification in pre-loading (initialization) procedure of ME, which addresses previous problems and overcomes them by employing a two-stage pre-loading procedure. In this approach, both the error and confidence measures are used as the difficulty criteria in boost-wise partitioning of problem space.

     

Electrochemical investigation of the anodic corrosion of Pb–Ca–Sn–Li grid alloy in H2SO4 solution

The steady-state and anodic corrosion of Pb–0.17 wt.% Ca–0.88 wt.% Sn, and Pb–0.17 wt.% Ca–0.88 wt.% Sn–0.06 wt.% Li alloys in 4.5 M H₂SO₄ at 25 °C were studied using cyclic voltammetry, linear sweep voltammetry, and electrochemical impedance spectroscopy. The experimental results show that the lithium added to Pb–Ca–Sn alloy increases corrosion resistance in equilibrium potential and inhibits the growth of the anodic corrosion layer.     

Speech Recognition-Based Automated Visual Acuity Testing with Adaptive Mel Filter Bank

One of the most commonly reported disabilities is vision loss, which can be diagnosed by an ophthalmologist in order to determine the visual system of a patient. This procedure, however, usually requires an appointment with an ophthalmologist, which is both time-consuming and expensive process. Other issues that can arise include a lack of appropriate equipment and trained practitioners, especially in rural areas. Centered on a cognitively motivated attribute extraction and speech recognition approach, this paper proposes a novel idea that immediately determines the eyesight deficiency. The proposed system uses an adaptive filter bank with weighted mel frequency cepstral coefficients for feature extraction. The adaptive filter bank implementation is inspired by the principle of spectrum sensing in cognitive radio that is aware of its environment and adapts to statistical variations in the input stimuli by learning from the environment. Comparative performance evaluation demonstrates the potential of our automated visual acuity test method to achieve comparable results to the clinical ground truth, established by the expert ophthalmologist’s tests. The overall accuracy achieved by the proposed model when compared with the expert ophthalmologist test is 91.875%. The proposed method potentially offers a second opinion to ophthalmologists, and serves as a cost-effective pre-screening test to predict eyesight loss at an early stage.     

The Influence of KrF Excimer Laser Annealing on Magnetic and Structural Properties of FePt/PtIr Thin Films

A series of 60-nm FePt thin films were deposited by RF magnetron sputtering system on Si/SiO₂ substrate. Platinum–iridium alloy was deposited as a buffer film between the FePt thin film and Si/SiO₂ substrate. These films were annealed by KrF excimer laser annealing with 248 nm of wavelength. The number of laser pulses which were applied on the film was varied from 3 to 20. The A₁ to L₁₀ phase transformation of FePt was confirmed by X-ray diffraction. Three pulses of laser were not sufficient for A₁ to L₁₀ phase transformation. A maximum order parameter of 0.91 was obtained after applying 18 pulses of laser. The roughness of films changed in different pulses, and the films were in the best condition after applying 18 pulses; the roughness was 3.51 nm and its morphology that was observed from AFM was 129 nm. The maximum coercivity was 0.61 MA/m. The coercivity increased with the application of different pulses of laser. Increasing coercivity to the maximum value of 0.61 MA/m related to grain growth. Coercivity of samples in 3, 6, 9, 12, 18, and 20 pulses was 0.24, 0.402, 0.488, 0.522, 0.64, and 0.6 MA/m respectively. Determining the grain growth under condition of annealing was done by field emission scanning electron microscopy (FESEM). Growth of all specimens was calculated with imager software. Grain size in as deposited and 3, 6, 9, 12, and 18 pulses of laser was 15, 20, 29, 44, 47, and 59 respectively.     

Control of morphology and optical properties of PbS nanostructured thin films by deposition parameters: study of mechanism

PbS thin films were grown on glass substrates by chemical bath deposition (CBD) using lead nitrate, thiourea and sodium hydroxide in aqueous solutions at three different temperatures (22, 36 and 50?°C). The microstructure and morphology evolution of the films were investigated using X-ray diffraction, scanning electron microscopy and atomic force microscopy. Optical properties were studied using UV–Vis–IR spectroscopy. The results indicate that temperature plays an important role in controlling the morphology and optical properties of nanostructured PbS thin films through changing deposition mechanism. The active deposition mechanism changed from cluster to ion-by-ion mechanism with an increase in deposition temperature from 22 to 50?°C, and consequently, film properties such as morphology, optical absorption and preferred orientation changed completely.