Determination of swelling behavior and morphological properties of poly(acrylamide‐co‐itaconic acid) and poly(acrylic acid‐co‐itaconic acid) copolymeric hydrogels

Poly(acrylamide‐co‐itaconic acid) (PAAmIA) and poly(acrylic acid‐co‐itaconic acid) (PAAIA) copolymeric hydrogels were prepared with different compositions via free‐radical polymerization. Ethylene glycol dimethacrylate (EGDMA) was used as an original crosslinker for these monomers. Gelation percentages of the monomers were studied in detail and it was found that addition of IA into the monomer mixture decreased the gelation percentage. The variation in swelling values (%) with time, temperature, and pH was determined for all hydrogels. PAA, which is the most swollen hydrogel, has the swelling percentage value of 2000% at pH = 7.4, 37°C. Swelling behaviors were explained with detailed SEM micrographs, which show the morphologic differences between dry and swollen hydrogels. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 5994–5999, 2006     

Numerical investigation on stress concentration of corrosion pit

Localized (pitting) corrosion has been observed in steel and high-strength aluminium alloys in aqueous environments and has been identified as a potential origin for fatigue crack nucleation. In the present study, under uniaxial tension loading, stress distribution at the semi-elliptical corrosion pits has been investigated by conducting a series of three-dimensional semi-elliptical pitted models, systematically. Based on the finite element analyses, it is concluded that pit aspect ratio (a/2c) is a main parameter affecting stress concentration factor (SCF). An attempt has been made to construct simple equations to SCF depending on characteristic of pit parameters. At the bottom of hemispherical pit, contribution of secondary (premature) pit formation to SCF is very pronounced.     

Investigating the current distribution of parallel-configured quantum point contacts under quantum Hall conditions

Journal of Computational Electronics - Electric-field-controlled charge transport is a crucial concept of modern computers, embodied, namely in field-effect transistors. The metallic gate voltage...     

Simulation assisted capacity improvement of cement grinding circuit: Case study cement plant

Extensive sampling campaign was performed around the cement grinding circuit of a cement plant in Turkey, for different production types of cement, as CEM I 42.5, CEM II 32.5/42.5/52.5, for the modelling and simulation purposes. During the sampling surveys; samples were collected from around the circuit for the steady state condition of the operation and, following a crash stop, from inside the mill. The size distributions of the samples were determined down to 2 μm by the combination of sieving and laser sizing methods. By using the size distributions around the circuit and control room data mass balance studies were performed. Then equipments in the circuit; ball mill, air-classifier and filter, were modelled individually by using the appropriate model structures. After modelling the circuit, simulation studies were performed for capacity improvement, mainly by the ball size optimization. By implementing the proposed optimization, the capacity of the circuit was increased up to 12.7–20.5% for different production types, hence; the overall specific energy consumption of the circuit was reduced, as predicted in simulation studies.     

Psychological adjustment of children with mild and moderately severe asthma

In chronic hepatitis B virus (HBV) infection seroconversion from hepatitis B e antigen (HBeAg) to hepatitis B e antibody (HBeAb) may be followed either by remission of the disease with low-level viraemia, or by continuing inflammation with high-level viraemia. In both situations the virus may acquire a mutation in the precore sequence which prevents it from encoding HBeAg. We now show that the number of amino acid substitutions in the HBV core is low in viral sequences from patients with HBeAg positive chronic liver disease and HBeAg negative HBeAb positive patients in remission, but the frequency of substitutions is high in HBeAg, negative HBeAb positive patients with active liver disease. Furthermore we show that these substitutions cluster in the promiscuous CD4+ T-helper-cell epitope and in HBV core/e antibody binding determinants, but are not found in regions recognized by major histocompatability complex (MHC) restricted cytotoxic T lymphocytes. Sequential viral sequences from patients before and after HBeAg/HbeAb seroconversion shows that core mutations arise either at the same time or after the precore stop mutation which prevents the virus from encoding HBeAg. These results are consistent with the hypothesis that after clearance of HBeAg, mutations in regions of the virus recognized by CD4+ helper T cells and B cells allow persistence of the HBe negative virus in HBeAb positive patients with viraemia and active hepatitis.     

Static and Fatigue Properties of the Cold and Warm Compacted Sintered Aluminium Alloy Alumix 431 (Al‐5.5 Zn‐2.5 Mg‐1.5 Cu)

In this work, the densification behaviour, sintering characteristics, hardness, strength, tensile and fatigue properties of the Alumix 431 alloy (Al, Zn, Mg and Cu alloy) produced using the conventional press and sinter process in different pressures and temperatures are investigated. For this purpose, specimens were produced under pressures between 300 and 500 MPa at 50 MPa intervals at room temperature (RT), and 80 °C in the first step. In the second step, specimens were produced at the compaction pressure of 230 MPa under RT and 180 MPa with 80 °C for tensile and fatigue testing which provided same densities. Specimens were sintered under five different sintering conditions. The dimensional change in warm compacted samples is lower than that of cold compacted samples. Tensile and fatigue properties of warm (180 MPa pressure) and cold (230 MPa pressure) compacted specimens are almost equal due to the same densities.     

A new method for determination of fine particle breakage

Material characterization plays a crucial role by means of equipments efficiency and overall circuit performance. Material properties such as grindability, breakage, crushability, mineralogy can easily be determined by laboratory studies. These parameters are required for modeling and simulation works.Breakage behaviour of material is important for size reduction equipments and it is defined by breakage distribution function. Commonly, single particle breakage method is used to determine breakage behaviour of materials which assumes that breakage is not size dependent. As new surfaces formed material behaviour changes so particle size effect should also be introduced into the grinding model structure. Determination of fine particle breakage becomes important. This will make models more reliable. With this aim a bed breakage method was developed for determination of fine particle breakage. In this study new breakage model is presented and effects of different breakage distribution functions on breakage rate and discharge function is investigated. The bed breakage test results are compared with single size drop-weight test results in the aspect of modeling. It was observed that, the breakage rate and discharge function variation by size indicates a characteristic change at fine size ranges compared to regular curve.