Adiabatic solution of a tilted hydrostatic thrust bearing

Solutions are presented for thermal effects on tilted hydrostatic thrust bearings. The governing Reynolds equation is solved simultaneously with the adiabatic energy equation by finite difference methods. The results show that thermal effects are significant at higher values of the bearing number and the tilt parameter.     

Homogenous and Heterogeneous Catalytic Activity of Azo-Linked Schiff Base Complexes of Mn(II), Cu(II) and Co(II)

Abstract  

Azo linked Schiff-base[L] complexes of Mn(II)(1), Cu(II)(2) and Co(II)(3) obtained by template method, in the reaction of 4-(benzeneazo) salicylaldehyde with 1,2-propanediamine in the present of metal acetate, respectively. Complexes are used as catalyst for oxidation of cyclohexene with tert-butylhydroperoxide (TBHP); oxidation of cyclohexene catalyzed by these complexes gave 2-cyclohexene-1-one and 2-cyclohexene-1-ol as major products. Conversion of cyclohexene achieved was 95–100% with (1), (2) and (3), with selectivity of 57, 92 and 100% for 2-cyclohexene-1-one, respectively. The encapsulated Cu(II) complex (Cu–NaY) catalyzes the oxidation of cyclohexene using TBHP as oxidant in good yield. (Cu–NaY) under optimized reaction condition gave three reaction products. A maximum of 100% conversion of cyclohexene has been achieved where selectivity of 2-cyclohexene-1-one was 83%.     

Role of residue 99 at the S2 subsite of factor Xa and activated protein C in enzyme specificity

It is thought that only a limited number of residues in the extended binding pocket of coagulation proteases are critical for substrate and inhibitor specificity. A candidate residue from the crystal structures of thrombin and factor Xa (FXa) that may be critical for specificity at the S2 subsite is residue 99. Residue 99 is Tyr in FXa and Thr in activated protein C (APC). To determine the role of residue 99 in S2 specificity, a Gla-domainless mutant of protein C (GDPC) was prepared in which Thr99 was replaced with Tyr of FXa. GDPC T99Y bound Ca2+ and was activated by the thrombin-thrombomodulin complex normally. The T99Y mutant, similar to FXa, hydrolyzed the chromogenic substrates with a Gly at the P2 positions. This mutant was also inhibited by antithrombin (AT) (k2 = 4.2 +/- 0.2 x 10(1) M-1 s-1), and heparin accelerated the reaction >350-fold (k2 = 1.5 +/- 0.1 x 10(4) M-1 s-1). The T99Y mutant, however, did not activate prothrombin but inactivated factor Va approximately 2-fold better than wild type. To try to switch the specificity of FXa, both Tyr99 and Gln192 of FXa were replaced with those of APC in the Gla-domainless factor X (GDFX Y99T/Q192E). This mutant was folded correctly as it bound Ca2+ with a similar affinity as GDFX and was also activated by the Russell's viper venom at similar rate, but it cleaved the chromogenic substrates with a Gly at the P2 positions poorly. The mutant, instead, cleaved the APC-specific chromogenic substrates efficiently. The Y99T/Q192E mutant became resistant to inhibition by AT in the absence of heparin but was inhibited by AT almost normally in the presence of heparin (k2 = 3.4 +/- 0.5 x 10(5) M-1 s-1). The Y99T/Q192E mutant did not inactivate factor Va, and prothrombin activation by this mutant was impaired. These results indicate that 1) residue 99 is critical for enzyme specificity at the S2 subsite, 2) a role for heparin in acceleration of FXa inhibition by AT may involve the S2-P2 modulation, and 3) the exchange of residues 99 and 192 in FXa and APC may switch the enzyme specificity with the chromogenic substrates and inhibitors but not with the natural substrates.     

Refractory Selection for High-Temperature Black Liquor Gasification

A methodology has been established for the selection of materials for refractory linings in black liquor gasifiers that are to be employed by the pulp and paper industry. As a first step, a thermodynamic software package was used to determine that black liquor smelt was composed of a liquid solution of primarily Na₂CO₃ and Na₂S under the operating conditions of the gasifier (950°C, 1 atm). Next, the software was used to predict the interaction of the black liquor smelt with various ceramics such as aluminosilicates, single component oxides, and binary oxides that are candidates for the application. Finally, experiments were performed to verify or disprove the predictions. Using sessile drop testing, contact angles were determined for molten Na₂CO₃ on candidate refractory compounds. All of the candidate ceramics were wet by molten Na₂CO₃. Among the candidates, MgAl₂O₄ was found to have the highest contact angle (∼13°). Post-mortem analysis was performed on sessile drop specimens using X-ray diffraction analysis and scanning electron microscopy with energy dispersive spectroscopy to determine if molten Na₂CO₃ had penetrated into or reacted with the ceramics. From the candidates, MgO and CeO₂ were found to have the best resistance to attack, while MgAl₂O₄ was also found to be a promising candidate.     

Operational data analysis of MSF desalination plants. A case study of Jeddah I

Monthly operation and maintenance reports of the oldest large MSF plant in Saudi Arabia, Jeddah I, are analyzed to extract information or generic operation and design problems and to seek means for the mitigation of such problems. The accumulated records are quantified to provide estimates of equipment failure rates. Three systems are found to be the major contributors to plant outage namely, make-up water, brine recycle and sea water intake systems. Root causes of the plant unscheduled shutdowns or reductions in water production are assessed to examine generic reasons for deviations of MSF systems from standard expected performance.     

A novel symmetrical 4H–SiC MESFET: an effective way to improve the breakdown voltage

In this paper, a novel symmetrical structure (SS) of 4H–SiC metal semiconductor field effect transistor (MESFET) as an effective way to improve the breakdown voltage is presented. The key idea in this work is to improve the breakdown voltage, maximum output power density, and frequency parameters of the device using a symmetrical structure with recessed gate. The SS-MESFET modifies the electric field in the drift layer significantly. The influence of the SS-MESFET on the saturation current, breakdown voltage \((\hbox {V}_{\mathrm{BR}})\), and small-signal characteristics of the SS-MESFET are studied by numerical device simulation. Using two-dimensional device simulation, we demonstrate that the breakdown voltage \((\hbox {V}_{\mathrm{BR}})\) improved by factors 2.5 and 3.3 in comparison with an asymmetrical conventional MESFET structure (AC-MESFET) and a symmetrical conventional MESFET structure (SC-MESFET), respectively. Also, the maximum output power density \((\hbox {P}_{\mathrm{max}})\) improved about by 93 and 250 % in comparison with the AC-MESFET and SC-MESFET structures, respectively. So, the SS-MESFET shows the superior maximum available gain (MAG), unilateral power gain (U), and current gain \((\hbox {h}_{12})\) which is presenting the proposed structure is more suitable device for high power microwave applications.     

Cured melamine systems as thick fire-retardant layers deposited by combination of plasma technology and dip-coating

Melamine and melamine resins are widely used as fire-retardants for polymer building materials. Cured melamine systems are used in heat-sensitive items, such as furniture and window frames and sills. In this work, differently cured methylated poly(melamine-co-formaldehyde) (cmPMF) resins were used as fire-retardant coverage for poly(styrene) (PS) and poly(ethylene) (PE) building materials. Such polymer layers should have several tenths of micrometers thickness to produce sufficient fire retardancy. These thick layers were produced by dip-coating. To promote sufficient adhesion of such thick coating to the polyolefin substrates, also in the case of high temperatures occurring at fire exposure, the polymer substrates were firstly coated with a few hundred nanometer thick adhesion-promoting plasma polymer layer. Such thin plasma polymer layers were deposited by low-pressure plasma polymerization of allyl alcohol (ppAAl). It was assumed that the hydroxyl groups of ppAAl interact with the melamine resin; therefore, ppAAl was well suited as adhesion promoter for thick melamine resin coatings. Chemical structure and composition of polymer films were investigated using infrared-attenuated total reflectance and X-ray photoelectron spectroscopy (XPS). Peel strengths of coatings were measured. After peeling, the peeled polymer surfaces were also investigated using optical microscopy and XPS the layers for identification of the locus of peel front propagation. Thermal properties were analyzed using TGA (thermo-gravimetric analyses). Finally, the fire-retardant properties of such thick coated polymers were evaluated by exposure to flames.     

The quantitative comparison of wash fastness improvement of acid and direct dyes on wool using full backtan,syntan, and syntan/cation system

Natural tannin, synthetic tanning agent (syntan), and syntan/cationic agent were applied on wool fabric dyed with different acid and direct dyes to improve the wash fastness of dyes. In this study, a method for quantitative and exact assessment of dye removal after washing from dyed samples was used. Firstly, the optimum operating parameters for application of full backtan and syntan were determined. Then the dyed wool samples were aftertreated, using natural tannin, syntan, and syntan/cationic agent. It was found that all aftertreatments improved the wash fastness. However, aftertreatment with natural tannin improved wash fastness to the greatest extent. In the case of syntan, sequential application of cationic agent on syntaned fabric obtained further improvement in wash fastness.     

One-factor-at-a-time (OFAT) optimization of hemicellulases production from Fusarium moniliforme in submerged fermentation

Hemicellulose degrading enzymes play an important role in bioconversion of lignocellulosic and agro-industrial wastes. In this study, production of hemicellulase by six fungal isolates was determined under submerged culture using corn cobs xylan as a carbon source and enzyme inducer at different incubation periods. The results indicated that Alternaria tenuis showed the lowest enzyme productivity (156.95 ± 2.07U/l) while the highest enzyme production (2,594.44 ± 62.25 U/l) was obtained by Fusarium moniliforme. One-factor-at-a-time revealed maximum enzyme productivity of 10,950.11 ± 98.45 U/l at corn cobs xylan (6 g/l), yeast extract (4 g/l), inorganic salts (1.5 g/l KH₂PO₄, 1.0 g/l MgSO₄.7H₂O, 0.2 g/l CaCl₂, 0.4 g/l FeSO₄.7H₂O, and 0.3 g/l MnSO₄.5H₂O), initial pH (5), initial inoculum size (4%), 150 rpm, and temperature (30°C) in a submerged fermentation process.