Molecular modelling and design of lubricant additives and their molecular dynamic simulations studies of Diamond-Like-Carbon (DLC) and steel surface coating

Quantitative Structure–Properties Relationship (QSPR) analysis was carried out on 30 lubricant additives while molecular dynamics simulations study was also performed to determine the dynamic binding strength between the hydrogen-containing DLC (a-C: H) sliding interface and lubricant additives. Reliable and predictable QSPR model was generated along with statistical parameters such as internal and external validations parameters such as squared correlation coefficient R² (0.807208), adjusted squared correlation coefficient R²adj (0.763674), cross-validation coefficient Q² (0.68867) and the external validation R²ext (0.6297). Two multifunctional lubricant additives were designed and they were found to have excellent anti-wear properties of 5.295 and 5.192(mm) which were better than the commercially sold lubricating oil additives, ZDDP. In addition, due to the absence of phosphorous and zinc in the molecular structures of the newly designed additives, these additives will not inhibit/limit the activity of the catalytic converter and will not form suspension or particulate matter in the car exhaust pipe. Moreover, the molecular dynamics simulation study revealed that one of the two designed lubricant additives of Benzothiazole derivatives were found to have excellent dynamic binding energies of 466.808 and 470.023?kcal/mol on DLC coating surfaces, while the second designed additive also generated better dynamic binding energies of 266.416 and 157.198?kcal/mol on steel coating surfaces than the commercially sold lubricant additive, ZDDP. This investigation will help in rational synthesis of new and better selective lubricant additives with predetermined dynamic binding energy and provides valuable information for the understanding of dynamic binding energy of additive on DLC and steel coating sliding surfaces.     

Minimum cost design of RC beams with segmentation using continuum-type optimality criteria

Economic designs of reinforced concrete beams with segmentation involving costs of concrete, reinforcing steel and formwork are considered. For practical reasons, the design variables are prescribed by means of an unknown constant and given shape function, whereas the constraints in addition to lower and upper bounds on design variables include maximum deflection in the span, flexural and shear strengths. Conditions of minimality are rigorously derived using calculus of variation on an augmented Lagrangian. An iterative procedure describing the computational aspects of the design is presented using a segmented propped cantilever beam as an example. Numerical examples are presented when the design variables involved are the depth alone or both the depth and steel ratio. A practical application of a simply supported beam is also considered and results compared with those obtained using nonlinear programming techniques (Karihaloo 1993; Kanagasundaram and Karihaloo 1990). An examination of the rate of convergence shows that the present technique is very promising.     

Minimum cost design of RC frames using the DCOC method Part II: Columns under biaxial bending actions

The DCOC-based numerical algorithms developed in Part I are generalized to the minimum cost design of RC frames in which columns are subjected to biaxial bending. All columns in each floor are assumed to have the same cross-section. Likewise, all beams are assumed to have the same section over their entire length. To account for the variation of forces along the height of the columns or the length of the beams, the steel ratio is allowed to vary freely. Real problems are solved to demonstrate the efficiency and practicability of the algorithm developed.     

Synthesis and solution properties of hydrophobically associating ionic polymers made from diallylammonium salts/sulfur dioxide cyclocopolymerization

Sulfur dioxide, N,N-diallyl-N-carboethoxymethylammonium chloride and the hydrophobic monomers N,N-diallyl-N-dodecylammonium chloride or N,N-diallyl-N-octadecylammonium chloride were cyclocopolymerized in dimethyl sulfoxide using azobisisobutyronitrile (AIBN) as the initiator to afford water-soluble cationic polyelectrolyte (CPE) having five-membered cyclic structure on the polymeric backbone. The CPE on acidic (HCl) hydrolysis of the pendent ester groups gave the corresponding cationic acid salt (CAS) which was converted to the anionic polyelectrolyte (APE) by treatment with sodium hydroxide. The solution properties of the CPE and APE containing varying amount of the hydrophobic monomers in the range 0-10 mol% were investigated by viscometric techniques. The polymers showed that concentration (C^∗_HA) of less than 1 wt% was required for the manifestation of hydrophobic association, and displayed significant hydrophobic association in salt (NaCl)-free as well as salt-added solutions.     

Mild sulfonated polyether ketone ether ketone ketone incorporated polysulfone membranes for microbial fuel cell application

To address the impediments of low power generation of Nafion, which is the main hurdle in the commercialization of microbial fuel cells (MFC), the current study focuses on developing a new PEM for MFC from mild sulfonation of PEKEKK with relatively improved physiochemical properties. In this study, mild post sulfonation of a polyether ketone ether ketone ketone (PEKEKK) has been successfully achieved using 98% H2SO4 at 90°C under reflux. 5%–30% (wt%) of sulfonated PEKEKK (SPEKEKK) loaded polysulfone (PSU) composite membranes were fabricated via a solution casting method. Ingeminating evidence of the sulfonation and structure of sulfonated polymer was proved by ¹H NMR peaks integration data and FTIR, respectively. The addition of SPEKEKK to PSU showed significant improvement in conductivity owing to the availability of more protonated sites ( SO3H) and water mediated pathways for the conduction of protons. The composite membrane containing 30 wt% SPEKEKK exhibits the highest conductivity of 0.12 S/cm at 90°C. The water uptakes and swelling ratio of the composite membranes are all higher than that of the pristine PSU membrane and show an increasing trend with increasing SPEKEKK content, thus validating the availability of water domains. Meanwhile, the lowest initial decomposition temperatures assigned to sulfonic acid groups and main chain degradation of the polysulfone/polyether ketone ether ketone ketone (PSU/SPEKEKK) composite membranes occurred at ~300°C and ~500°C respectively, which reflects an excellent thermal stability property. The experimental results indicate that the PSU/SPEKEKK membrane has the potential to greatly enhance the efficiency of MFCs.     

Human Serum Vitamin A and β-Carotene Contents in Relation to Locally Consumed Foods,Social Status and Gender in Kano Metropolis

Determination of the levels of vitamin A (as retinol) and β-carotene in locally consumed foods in relationship to their occurrence in the serum of individuals grouped according to different social groups and sexes was carried out in Kano metropolis. Both raw and prepared foods (meals/snacks) investigated showed the presence of β-carotene while vitamin A was only present in the latter. The levels of β-carotene in foods/snacks ranged from 2.00 – 3.40 and 88 – 1120 iu/kg in raw foods while that of vitamin A in the former was 13.00 – 23.50 iu/kg. Food/snacks derived from animal products and those made from vitamin A fortified foods showed marginally higher vitamin contents. The mean serum β-carotene and retinol concentrations of the individual grouped according to sex and social class showed significant differences between the three social groups (P < 0.05). The higher the income class, the higher the value of vitamin A and its precursor. There was no significant difference in the β-carotene and retinol concentration between males and females of low income and high income class (P > 0.05). However, there was significant difference between males and females of the medium income class (P < 0.05). These results are discussed in terms of an apparent relationship between income and serum vitamin A content.     

Kinetic modeling of oxidative dehydrogenation of propane with CO2 over MoOx/La2O3–Al2O3 in a fluidized bed

A 4-step kinetic model of CO₂-assisted oxidative dehydrogenation (ODH) of propane to C₂/C₃ olefins over a novel MoO_x/La₂O₃–γAl₂O₃ catalyst was developed. Kinetic experiments were conducted in a CREC Riser Simulator at various reaction temperatures (525–600 °C) and times (15–30 s). The catalyst was highly selective towards propylene at all combinations of the reaction conditions. Langmuir-Hinshelwood type kinetics were formulated considering propane ODH, uni- and bimolecular cracking of propane to produce a C₁-C₂ species. It was found that the one site type model adequately fitted the experimental data. The activation energy for the formation of propylene (67.8 kJ/mol) is much lower than that of bimolecular conversion of propane to ethane and ethylene (303 kJ/mol) as well as the direct cracking of propane to methane and ethylene (106.7 kJ/mol). The kinetic modeling revealed the positive effects of CO₂ towards enhancing the propylene selectivity over the catalyst.     

Thermal Effects on the Crystallization Kinetics,and Interfacial Adhesion of Single-Crystal Phase-Change Gallium

Although substrates play an important role upon crystallization of supercooled liquids, the influences of surface temperature and thermal property have remained elusive. Here, the crystallization of supercooled phase-change gallium (Ga) on substrates with different thermal conductivity is studied. The effect of interfacial temperature on the crystallization kinetics, which dictates thermo-mechanical stresses between the substrate and the crystallized Ga, is investigated. At an elevated surface temperature, close to the melting point of Ga, an extended single-crystal growth of Ga on dielectric substrates due to layering effect and annealing is realized without the application of external fields. Adhesive strength at the interfaces depends on the thermal conductivity and initial surface temperature of the substrates. This insight can be applicable to other liquid metals for industrial applications, and sheds more light on phase-change memory crystallization.     

Synthesis and viscosity of hydrophobically modified polymers containing dendritic segments

The cycloterpolymerizations of a newly synthesized dendritic quadruple‐tailed hydrophobic diallylammonium chloride with the hydrophilic monomer N,N‐diallyl‐N‐carboethoxymethylammonium chloride and sulfur dioxide afforded a series of water‐soluble cationic polyelectrolytes (CPEs) containing various proportions (0–1 mol %) of the hydrophobe. At a shear rate of 0.36 s^?1 at 30°C, salt‐free water solutions of the CPEs (4 g/dL) containing 0, 0.35, 0.53, 0.65, and 0.93 mol % of the hydrophobe had apparent viscosity values of 140, 1200, 180,000, 308,000, and 858,000 cps, respectively. The study clearly demonstrated an increase in the viscosity values with increasing incorporation of the hydrophobes. The CPEs on acidic hydrolysis of the pendant ester groups gave corresponding pH‐responsive cationic acid salts, which upon treatment with NaOH, were converted to the polybetaines (PBs), anionic polyelectrolytes (APEs), and PB/APEs containing various proportions of PB and APE fractions in the polymer chain. The effects of charge type and charge density on the polymer chain were investigated. Polymer surfactant interactions were investigated with the cationic surfactant cetyltrimethylammonium bromide; a considerable increase in the viscosity values of the CPE was observed in the presence of the surfactant. The superior viscosity behavior for the polymers containing the quadruple‐tailed hydrophobe was attributed to the blocky nature of the comonomer. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008