Mechanical response of reaction phases of the TiAl/steel brazed joint under a tensile load

This article offers a study of a mechanical response of the TiAl/Steel brazed joint. The (i) intermetallic reaction layer’s phases, (ii) the residue filler, and the (iii) base metals constitute the complex structure considered. The study features TiAl and 42CrMo steel brazed with an AgCuTi filler metal. The analysis includes the microstructural study and an evaluation of mechanical properties of the brazed joint. In addition, the fracture behavior of the joint under a tensile loading in situ is studied in the context of the impact that reaction phases may have on the joint properties. The results of the study indicate that the complex joint structure is due to the presence of a ternary intermetallic reaction layer, as well as the presence of intermetallics in the filler residue. The multilayered structure includes Ti₃Al+AlCuTi+AlCu₂Ti ternary intermetallic reaction layer, Ag(Cu) residue filler, AlCu₂Ti intermetallic dispersed in the residue braze and TiC layer. The hardness sequence of the structure has been established. The crack initiation, its propagation, and an ultimate fracture are associated primarily with Ti₃Al+AlCuTi+AlCu₂Ti ternary intermetalics layer.     

Determination of Thermal Conductivity of Silicate Matrix for Applications in Effective Media Theory

Silicate materials have an irreplaceable role in the construction industry. They are mainly represented by cement-based- or lime-based materials, such as concrete, cement mortar, or lime plaster, and consist of three phases: the solid matrix and air and water present in the pores. Therefore, their effective thermal conductivity depends on thermal conductivities of the involved phases. Due to the time-consuming experimental determination of the effective thermal conductivity, its calculation by means of homogenization techniques presents a reasonable alternative. In the homogenization theory, both volumetric content and particular property of each phase need to be identified. For porous materials the most problematic part is to accurately identify thermal conductivity of the solid matrix. Due to the complex composition of silicate materials, the thermal conductivity of the matrix can be determined only approximately, based on the knowledge of thermal conductivities of its major compounds. In this paper, the thermal conductivity of silicate matrix is determined using the measurement of a sufficiently large set of experimental data. Cement pastes with different open porosities are prepared, dried, and their effective thermal conductivity is determined using a transient heat-pulse method. The thermal conductivity of the matrix is calculated by means of extrapolation of the effective thermal conductivity versus porosity functions to zero porosity. Its practical applicability is demonstrated by calculating the effective thermal conductivity of a three-phase silicate material and comparing it with experimental data.     

Cascade delta-sigma modulator with pseudo-differential comparator-based switched-capacitor gain stage

A low-power, multi-stage delta-sigma modulator with comparator-based switched-capacitor (CBSC) gain stages is presented. The presented design eliminates the need for operational amplifiers and replaces them by comparators with current sources at their outputs to alleviate the effects of continued technology scaling on analog and mixed-signal circuits. The proposed technique significantly reduces power consumption and can be applied to switched-capacitor delta-sigma modulators of arbitrary order. Based on the proposed methodology, a 2-1 cascade, single-bit, pseudo-differential switched-capacitor delta-sigma modulator is developed and achieves a SNDR of 76.8 dB with an oversampling ratio of 64 at a clock frequency of 8 MHz.     

A one-dimensional plug-flow model of a counter-current spray drying tower

A one-dimensional numerical model for a detergent slurry drying process in a counter-current spray drying tower is developed for the prediction of the gas and droplet/particle temperature profiles within the tower. The model accommodates droplets/particles over a range of sizes. A semi-empirical slurry droplet drying model is integrated with a counter-current tower simulation based on mass, energy and particulate phase momentum balances in order to calculate the drying rate and the particle residence time within the tower. The coupled first order ordinary differential equations for the two phases are solved numerically using the iterative shooting method in an algorithm developed within MATLAB. The predictions of the numerical model are compared with industrial pilot plant data. The results are found to vary significantly with the specified size distribution of the droplets. Despite the simplicity of the model in ignoring the coalescence, agglomeration, wall deposition and re-entrainment, the model gives reasonable agreement with the experimental data.     

Low energy architecture for a severe US climate: Design and evaluation of a hybrid ventilation strategy

Natural ventilation, relying on openings in the façade, is applicable to a limited range of climates, sites and building types. Advanced naturally ventilated buildings, such as those using stacks to encourage buoyancy driven airflow, or hybrid buildings, which integrate both natural and mechanical systems, can extend the range of buildings and climate within which natural ventilation might be used.     

Scheduling algorithm for VOQ switches

A variety of matching schemes for VOQ switches that provide high throughput for uniform traffic have been proposed. The dual round robin matching (DRRM) scheme has performance similar to iSLIP and lower implementation complexity. DRRM with exhaustive service (EDRRM) algorithm was created as modification of DRRM algorithm with goal to improve performance of DRRM algorithm for bursty and non-uniform traffic conditions. Under extremely unbalanced arrival traffic, an exhaustive service policy may lead to unfairness and starvation. This paper proposes matching scheme for VOQ switches that provides high throughput almost the same as EDRRM scheme and avoid unfairness and starvation under unbalanced traffic.     

Endoscopic wedge-shaped lung biopsy--initial experience

The authors publish their initial experience with wedge-shaped pulmonary biopsy by the endoscopic route. The group is formed by 18 patients who were indicated for the operation on account of a disseminated pulmonary process in order to assess the micromorphological appearance of the affected lung tissue. Two patients developed a complication during operation which therefore was completed by minor thoracotomy. In who patients the authors observed after operation slow expansion of the pulmonary parenchyma. No death after the operation was recorded. The authors assume, based on their initial experience, that this operation will soon be included among common diagnostic operations and will help to facilitate the diagnosis and selection of treatment in patients with disseminated lung disease.     

Inhibition of DNA cytosine methyltransferase by chemopreventive selenium compounds, determined by an improved assay for DNA cytosine methyltransferase and DNA cytosine methylation

The organoselenium compounds benzyl selenocyanate (BSC) and 1,4-phenylenebis(methylene)selenocyanate (p-XSC), as well as sodium selenite, are effective chemopreventive agents for various chemically induced tumors in animal models at both the initiation and postinitiation stages. The mechanisms involved at the postinitiation stage are not clear. Because several lines of evidence indicate that inhibition of excess DNA (cytosine-5)-methyltransferase (Mtase) may be a sufficient factor for the suppression or reversion of carcinogenesis, we examined the effects of sodium selenite, BSC, p-XSC and benzyl thiocyanate (BTC), the sulfur analog of BSC, on Mtase activity in nuclear extracts of human colon carcinomas, and of p-XSC on the Mtase activity of HCT116 human colon carcinoma cells in culture. For this purpose, we developed an improved Mtase assay, in which the incorporation of the methyl-[3H] group from S-adenosyl[methyl-3H]methionine into deoxycytidine of poly(dI-dC)-poly(dI-dC), is specifically determined by HPLC with radioflow detection after enzymatic hydrolysis, enhancing specificity and reliability. In a variation, using SssI methyltransferase and labeled S-adenosylmethionine, the overall methylation status of DNA in various tissues can also be compared. Selenite, BSC and p-XSC inhibited Mtase extracted from a human colon carcinoma with IC50s of 3.8, 8.1 and 5.2 microM, respectively; BTC had no effect. p-XSC also inhibited the Mtase activity and growth of human colon carcinoma HCT116 cells, with an IC50 of approximately 20 microM. The improved Mtase assay should prove to be a reliable method for screening potential Mtase inhibitors, especially using cells in culture. We suggest that inhibition of Mtase may be a major mechanism of chemoprevention by selenium compounds at the postinitiation stage of carcinogenesis.