Ion flotation of dichromate and of complexed cyanide: Surfactants for qualitative analysis

Ion flotation studies have shown that a surface-active agent is useful for qualitative analysis of complex ions in dilute aqueous solution, with the surfactant forming a particulate complex with the complex ion of concern. Experiments with a monovalent, cationic surfactant have established the prevalence of Cr₂O₇ ²⁻ (HCrO₄ ⁻) and not CrO₄ ²⁻; of [Fe(CN)₆]⁴⁻ and [Fe(CN)₅H₂O]³⁻; and of [FeFe(CN)₆]²⁻ and not [FeFe(CN)₆]⁻ or [Fe(CN)₆]³⁻. The results can be contrasted to those with ions that do not form particulate complexes with the surfactant, such as HPO₄ ²⁻ and phenolate; with the latter, no qualitative analytical information can be gained. Ion flotation appears to be a promising technique in general for the determination of ionic species present in aqueous solution; the surfactant must react with the ion of significance to form a particulate complex and the initial surfactant concentration must be controlled carefully.     

Nonaqueous potentiometry of coal-derived asphaltenes and model nitrogen-containing compounds in acetophenone and nitrobenzene

A series of 34 nitrogen-containing compounds with a wide range of basicities was examined under differential nonaqueous potentiometric conditions in acetophenone and nitrobenzene. These compounds could be resolved into five classes based on pK_aand half-neutralization-potential (HNP) values. Asphaltenes isolated from the vacuum still overhead (VSO) and vacuum still bottoms (VSB) fractions of the H-coal process were titrated under similar conditions. The titration results of both asphaltenes indicated the presence of two classes of nitrogen-containing compounds, a titratable class of the pyridine-ring or aniline type and a nontitratable class.     

Sulphated polysaccharides from Indian samples of Enteromorpha compressa (Ulvales,Chlorophyta): Isolation and structural features

Heteroglycan and xyloglucan rich fractions were extracted from Indian samples of Enteromorpha compressa in 25% yield by sequential extractions with water and alkali. This heteroglycan is sulfated and has an apparent molecular mass of 55 kDa. Chemical structural analysis of this polysaccharide revealed a branched structure having 1,4- and 1,2,4-linked rhamnose 3-sulphate, 1,4-linked glucose, 1,3- and 1,6- linked galactose, 1,4- and terminally linked glucuronic acid and 1,4-linked xylose partially sulfated on O-2. Chemical and spectroscopic analysis showed that the 4-M KOH extracted hemicellulosic fraction contained an unusual β-(1,4)-linked linear xyloglucan. Enzyme hydrolysis and analysis of the resulting fragments by matrix-assisted laser desorption ionization-time of flight-mass spectrometry (MALDI-TOF-MS) showed that this linear polymer contained partially sulfated Glc₃Xyl₂ or Glc₄Xyl₂ as oligomeric building subunits.     

Mechanical and tribological behavior of alumina and alumina‐CNT reinforced hybrid unsaturated polyester composites

Micro‐ and nano‐scale wear behavior of alumina vis‐á‐vis alumina‐carbon nanotube‐reinforced hybrid composites has been studied. In comparison to the pristine alumina, the alumina‐carbon nanotube hybrid reinforcement resulted in reduced scratch depth and lower frictional coefficient. Addition of carbon nanotube has effectively modified the pristine alumina into a superior wear resistant filler. POLYM. COMPOS., 37:1577–1586, 2016. © 2014 Society of Plastics Engineers     

Dual material gate junctionless tunnel field effect transistor

This paper proposes a junctionless tunnel field effect transistor (JLTFET) with dual material gate (DMG) structure and the performance was studied on the basis of energy band profile modulation. The two-dimensional simulation was carried out to show the effect of conduction band minima on the abruptness of transition between the ON and OFF states, which results in low subthreshold slope (SS). Appropriate selection of work function for source and drain side gate metal of a double metal gate JLTFET can also significantly reduce the subthreshold slope (SS), OFF state leakage and hence gives improved I _ON/I _OFF.     

Minimization of exit burr in face milling of medium carbon steel by exit edge beveling

Elimination, or reduction, of burrs formed during machining is drawing focus of manufacturers and researchers since long or suppressing a burr regarding its formation or removal of it through a suitable deburring process. Deburring is an extra process often required to undertake, and it involves additional time and cost. Presence of burr may cause several problems, such as difficulty in assembly, dimensional inaccuracy, injury to the operator, etc. Like other industries, avoidance of burr on milled component surfaces in railways is of concern. In the present investigation, formation of burr in face milling is tried to reduce by beveling the exit edge of blocks of medium carbon steel (45C8) which is widely used in railways for manufacture of different components. Cutting conditions are also varied to observe the effect on burr formation. It is observed that at an exit edge bevel angle of 15°, negligible burr is formed at most of the cutting conditions undertaken, and hence, recommended.     

Crack and wear behavior of SiC particulate reinforced aluminium based metal matrix composite fabricated by direct metal laser sintering process

In this investigation, crack density and wear performance of SiC particulate (SiCp) reinforced Al-based metal matrix composite (Al-MMC) fabricated by direct metal laser sintering (DMLS) process have been studied. Mainly, size and volume fraction of SiCp have been varied to analyze the crack and wear behavior of the composite. The study has suggested that crack density increases significantly after 15 volume percentage (vol.%) of SiCp. The paper has also suggested that when size (mesh) of reinforcement increases, wear resistance of the composite drops. Three hundred mesh of SiCp offers better wear resistance; above 300 mesh the specific wear rate increases significantly. Similarly, there has been no improvement of wear resistance after 20 vol.% of reinforcement. The scanning electron micrographs of the worn surfaces have revealed that during the wear test SiCp fragments into small pieces which act as abrasives to result in abrasive wear in the specimen.     

Modeling of plasma spray coating process using statistical regression analysis

This study aimed to correlate outputs of a plasma spray coating process with its input parameters. Central composite design of experiments had been followed to conduct the experiments on plasma spray coating process, in order to collect its input–output data. The effects of four input parameters, namely primary gas flow rate, stand-off distance, powder flow rate, and arc current on three outputs (responses), such as thickness, porosity, and microhardness of the coatings, had been studied using non-linear statistical regression analysis. Such an analysis yielded the response equations, and viability of these equations had been tested on a set of experimentally obtained cases. The above four process parameters were found to have varying influences on different responses. However, all the above three responses were found to be significantly dependent on primary gas flow rate.     

A Call-Admission Control (CAC) Algorithm for Providing Guaranteed QoS in Cellular Networks

Future broadband wireless access systems are expected to integrate various classes of mobile terminals (MTs), each class with a different type of quality of service (QoS) requirement. When the load on a wireless network is high, the guarantee of QoS for each class of MTs is a challenging task. This study considers two classes of MTs—profiled MTs and nonprofiled or regular MTs. It is assumed that profiled users require a guaranteed QoS. The measure of QoS is the probability of forced termination of a call that was allowed to access the network. Two previous handoff prioritization schemes—(i) prerequest scheme and (ii) guard channel scheme—decrease handoff failure (and hence forced termination). In this work, we compare and contrast both the schemes through extensive simulation and we find that neither guard channel nor channel prerequest scheme can guarantee a desired level of QoS for the profiled MTs. We then propose a novel call-admission control (CAC) algorithm that can maintain any desired level of QoS, while the successful call completion rate is very high. In the proposed algorithm, the new call arrival rate is estimated continuously, and when the estimated arrival rate is higher than a predetermined level, some new calls are blocked irrespective of the availability of channels. The objective of this new call preblocking is to maintain a cell's observed new call arrival rate at no more than the predetermined rate. We show that the proposed method can guarantee any desired level of QoS for profiled users.     

Influence of solvent composition and degree of reaction on the formation of surface microtopography in a thermoset siloxane-urethane system

The effects of solvent composition and degree of reaction prior to film formation leading to the formation of a biphasic microtopographical surface in a crosslinked siloxane-urethane coating system were explored. For the solvent composition study, a D-optimal mixture design study was carried out using methyl n-amyl ketone (MAK), toluene, ethyl 3-ethoxypropionate (EEP), butyl acetate (BA) and isopropyl alcohol (IPA) as solvents. The study revealed that the presence of slow evaporating solvents MAK, EEP and the absence of fast evaporating solvent IPA in the solvent composition with a minimal amount of BA favored formation of a structured surface. Control over the domain size could be obtained by varying the MAK:EEP ratio in solvent compositions having a fixed amount of BA. The effect of mixing time on the formation of surface domains was studied. At short mixing times (<2 h) and long mixing times (>7 h), no surface phase separation is observed, while at intermediate times a ‘window’ was found where surface microdomains of similar size are generated. Doubling the level of catalyst halves the mixing time required to generate surfaces with microdomains. Scanning electron microscopy (SEM) studies with energy dispersive X-ray mapping and dynamic mechanical analysis (DMA) were done in order to understand the development of the phases in the PDMS-polyurethane system.