Sharif Digital Repository

This research explored the influences of shielding gases on the appearance of weld beads and the microstructures and mechanical properties of thin-wall samples using conventional gas metal arc welding as the heat source by using 5356 aluminium alloy welding wire as the raw materials and nitrogen (N2) and argon (Ar) as the shielding gases. The results showed that under the same parameters and after mono-layer single-bead welding was performed using N2 as the shielding gas, the bead height was higher, the bead width was narrower, and the penetration depth was shallower. The grain size of the thin-wall sample protected by N2 was 43.5–47.8 % smaller than that obtained under Ar protection.... 

In this paper, we describe a carbon dioxide mineralization process and its associated solid products. These solid products include amorphous silica, iron hydroxides and magnesium carbonates. These products were subjected to various characterization tests, and the results are published here. It was found that the iron hydroxides from this process can have different crystalline properties, and their formation depended very much on the pH of the reaction conditions. Different forms of magnesium carbonate were also obtained, and the type of carbonate precipitated was found to be dependent on the carbonation temperature. Hydromagnesite was obtained mainly at low temperatures, while dypingite was... 

Employing a proper pulse shaper in the conventional split Hopkinson pressure bar (SHPB) test helps to achieve dynamic equilibrium condition and to fulfill a constant strain rate condition in the test specimen. To this end, the parameters affecting the incident pulse shape, i.e., pulse shaper thickness, pulse shaper diameter, striker bar length and striker bar velocity are experimentally studied. Moreover, simulation results, validated by experimental data together with wave propagation analysis, are exploited to provide general guidelines to properly design a pulse shaper. It is recommended to use a relatively large diameter pulse shaper for testing work-hardening materials. Also, for... 

In this work the effects of backwash pressure, duration of acid and sodium hydroxide backwashing, sodium hydroxide concentration, and the duration of forward washing on performance of permeate flux recovery (PFR) were investigated. A two-level fractional factorial design (FFD) was used to design the experiments. The ability of back propagation neural network (BPNN) and radial basis function neural network (RBFNN) in predicting the performance of cleaning-in-place (CIP) of hydrophilic polyethersulfone (PES) membrane were investigated. It is found that BPNN has better ability in predicting the PFR performance than RBFNN. The best architecture of BPNN was a network consisting of 1 hidden layer... 

Distant, dusty and extremely luminous galaxies form a key component of the high redshift universe, tracing the period of intense cosmic activity that ultimately gave rise to the present-day universe. These highly luminous galaxies, first detected in the ground-based submillimeter region, are however optically very faint, which hampers identification of the optical counterpart and the measurement of a redshift. We are developing a new direct-detection submm spectrograph DESHIMA. By taking advantage of the rapidly advancing technology of superconducting microresonators, DESHIMA will revolutionize the appearance and capabilities of a submm spectrograph. There will no longer be large grating... 

Quasi-ultrafine (quasi-UF) particulate matter (PM0.25) and its components were measured in indoor and outdoor environments at four retirement communities in Los Angeles Basin, California, as part of the Cardiovascular Health and Air Pollution Study (CHAPS). The present paper focuses on the characterization of the sources, organic constituents and indoor and outdoor relationships of quasi-UF PM. The average indoor/outdoor ratios of most of the measured polycyclic aromatic hydrocarbons (PAHs), hopanes, and steranes were close to or slightly lower than 1, and the corresponding indoor-outdoor correlation coefficients (R) were always positive and, for the most part, moderately strong (median R... 

A simple and effective procedure is proposed for spectrophotometric determination of catecholamines; Dopamine (1), L-Dopa (2) and Adrenaline (3). It was found that the reduction of Ag+ to silver nanoparticles (Ag-NPs) by these catecholamines in the presence of polyvinylpyrrolidone (PVP) as a stabilizing agent produced very intense surface plasmon resonance peak of Ag-NPs. The plasmon absorbance of the Ag-NPs allows the quantitative spectrophotometric detection of the catecholamines. The calibration curves derived from the changes in absorbance at λ = 440 nm were linear with concentration of Dopamine, Levodopa and Adrenaline in the range of 3.2×10-6- 2.0x10-5 M, 1.6x10-7 - 1.0×10-5 M,... 

In analysing the structural organization of a social network, identifying important nodes has been a fundamental problem. The concept of network centrality deals with the assessment of the relative importance of a particular node within the network. Most of the traditional network centrality definitions have a high computational cost and require full knowledge of network topological structure. On the one hand, in many applications we are only interested in detecting the top-k central nodes of the network with the largest values considering a specific centrality metric. On the other hand, it is not feasible to efficiently identify central nodes in a large real-world social network via... 

Let G be a graph on n vertices with r := [n/2] and let γ 1 ≥ · · · ≥ γ n be adjacency eigenvalues of G. Then the Ḧuckel energy of G, HE(G), is defined as [Equation presented] The concept of Hückel energy was introduced by Coulson as it gives a good approximation for the π-electron energy of molecular graphs. We obtain two upper bounds and a lower bound for HE(G). When n is even, it is shown that equality holds in both upper bounds if and only if G is a strongly regular graph with parameters (n, k, γ, μ) = (4t2 + 4t + 2, 2t2 + 3t + 1, t2 + 2t, t2 + 2t + 1), for positive integer t. Furthermore, we will give an infinite family of these strongly regular graph whose construction was communicated... 

Nonlinear propagation has been demonstrated to have a significant impact on ultrasound imaging. An efficient computational algorithm is presented to simulate nonlinear ultrasound propagation through layered liquid and tissue-equivalent media. Results are compared with hydrophone measurements. This study was undertaken to investigate the role of nonlinear propagation in high frequency ultrasound micro-imaging. The acoustic field of a focused transducer (20 MHz centre frequency, f-number 2.5) was simulated for layered media consisting of water and tissue-mimicking phantom, for several wide-bandwidth source pulses. The simulation model accounted for the effects of diffraction, attenuation and... 

Derailment is one of the most hazardous occurrences affecting the safety of railroad cars that must be prevented. The potential threat of derailment could be especially significant when length of tangent between vertical curves isn't long enough. Although the length of tangent between vertical curves could be relevant to railway safety, no research had been conducted to study its effect on derailment risk. The primary objective of this paper was to investigate the effect of tangent length between vertical curves on derailment. This study consisted of three major components: (1) review of 1999-2008 derailment reports in Iran, (2) a regression analysis, and (3) recommendation model for... 

Physical separation methods, especially membrane technology, can be a good substitute for biological wastewater treatment, due to its simple constructions and operations. There are many papers and patents in this field. Membranes need to be cleaned periodically to be able to operate economically, and need to be replaced after a while. Several factors can influence the membrane cleaning procedure, including pressure of backwash, acid and base concentration, duration of forward washing, and duration of acid-base backwashing. In this study the effect of these parameters was investigated to find an optimum condition which could result in a good polyethersulphone (PES) membrane cleaning with less... 

In this work, the process of starch removal from starchy wastewater using a hydrophilic polyethersulfone membrane was investigated. The pore size of the membrane was 0.65 μm and the pattern of stream in plate and frame handmade membrane module was cross-flow. To design the layout of the experiments, response surface methodology was applied. The performance of the filtration process was evaluated by calculating the (chemical oxygen demand) COD removal percentage (rejection factor) and permeate flux. In this study, five operative parameters were investigated, including trans-membrane pressure, flow rate and temperature of feed, pH, and the COD concentration of starch wastewater. Two models... 

Hydrocarbon contaminations due to their volatility, solubility and biodegradability properties can enter the vadose zone and adversely influence the soil properties. Recently, some deep and superficial signs of oil pollution have emerged in the soils around the refinery of Sarkhoun. In order to assess the exact type and behavior of pollutants, evaluate the environmental attributes and measure some important factors of oil contamination in this region, and also to see how pollution transfer in the underground environment, this study has been done. Materials & methods Sarkhoun refinery is located 50 kilometers away from ar Abbas in the northeast direction. The area is mostly composed of Marne... 

Tributhyl phosphate (TBP) decomposition in supercritical water oxidation (SCWO) was performed with and without catalyst, at different temperatures ranging from 370 to 480 °C, and different reaction times. Ag2O, CuO, Fe2O3, MgO, and ZnO synthesized by supercritical water were examined in TBP decomposition as the catalyst. TBP structure decomposed under the non-catalytic reaction; nevertheless, the results indicated that the use of catalysts improved the reaction efficiency, which calculated based on total organic carbon (TOC) removal, by far. However, TOC removal using Fe2O3 was 20% higher than the non-catalytic reaction. Having the ability in completion of the redox cycle, iron oxide... 

A new inelastic mechanism, detwinning-induced plasticity (DIP), is proposed to model the response of NiTi SMAs to cyclic loading, based on thermodynamic considerations. DIP is incorporated into a constitutive framework for NiTi SMA. The constitutive framework also includes well-established inelastic mechanisms of phase transformation, transformation-induced plasticity, residual martensite, and detwinning. The model is constructed at the single crystal scale using the framework of thermodynamics and a crystal plasticity formulation. An explicit scale-transition rule is adopted for the simulation of polycrystalline materials, allowing direct comparison of the model predictions with published... 

The studies on forced migrants' digitally mediated communication and transnational practices have not sufficiently addressed contexts in which migrants are imposed with strong regulations on their physical mobility and information and communication technology (ICT), Internet, and social media uses. This article studied Internet and social media uses, digital divides (access, use, and the impact of Internet and social media), and digital transnational practices among Afghans in Iran. More than three million Afghans live in different legal, economic, and social positions in Iran. The analysis was based on surveys with 2003 Afghan refugees, other legally authorized Afghan immigrants, and... 

Some mechanical and metallurgical properties of hollow and solid long forged products are compared. The metallurgical properties include such micro- and macro-structural characteristics as the grain size and grain flow patterns. Mechanical evaluation was performed by means of hardness testing. Some theoretical analyses were also carried out. The results indicate that the hollow or mandrel forged products possess better properties. Both the mechanical and metallurgical properties are more uniform and homogeneous through the thickness direction in such products. By contrast, in the solid forged parts, there is a gradient in the micro- and macro-structural properties from the surface to the... 

Physiological and photobiochemical changes and growth in the heterotrophic strain Chlorella vulgaris g120 were studied during trophic conversion from heterotrophic to phototrophic growth regime. After the exposure of the Chlorella g120 culture to light, it revealed a significant activity of the electron transport (450–700 μmol e− m−2 s−1 as measured by chlorophyll fluorescence) and high PSII photochemical yield Fv/Fm between 0.7 and 0.8. Fast fluorescence induction kinetics showed that PSII electron acceptors in the plastoquinone pool remained partly oxidized, indicating no downregulation of PSII electron transport. The data further revealed that high photobiochemical activity is lost in... 

Classic identifiability analysis of flow barriers in incompressible single-phase flow reveals that it is not possible to identify the location and permeability of low-permeability barriers from production data (wellbore pressures and rates), and that only averaged reservoir properties in between wells can be identified. We extend the classic analysis by including compressibility effects. We use two approaches: a twin experiment with synthetic production data for use with a time-domain parameter-estimation technique, and a transfer-function formalism in the form of bilaterally coupled four-ports allowing for an analysis in the frequency domain. We investigate the identifiability, from noisy...