The influence of solutes on kinetics and thermodynamics of liquid indium-oxygen systems

The influence of small additions of the solutes Sn, Pb, Cu, Ag, and Ti on the diffusivity, solubility, activity, and the activity coefficient of oxygen in liquid indium was studied for temperatures between 750 and 950 °C, using solid state electrochemical techniques. A sharp increase in diffusivity and a decrease in solubility of oxygen were observed in all cases when small amounts of these solutes were added to liquid indium. Further additions of these solutes moderately increased the oxygen diffusivity and decreased the oxygen solubility. The thermodynamics of liquid binary alloys of indium, In-Sn, In-Pb, In-Cu, and In-Ag were also studied up to 10 at pct of these solutes. There is evidence that the large increase in diffusivity and decrease in solubility of oxygen in indium is due to cluster formations in liquid metal. Formerly with the Union Carbide Corporation,     

供应链稳定性架构研究

供应链稳定性时供应链效率、风险和可靠性都有着重要意义.供应链稳定性是由供应链资源、信息、共同市场和企业间战略伙伴关系等要素所决定的.这些要素在供应链运营层面中有不同的表现.把握住供应链稳定框架是实现供应链稳定运营的基础.     

供应链稳定性架构研究

供应链稳定性对供应链效率、风险和可靠性都有着重要意义。供应链稳定性是由供应链资源、信息、共同市场和企业间战略伙伴关系等要素所决定的,这些要素在供应链运营层面中有不同的表现。把握住供应链稳定框架是实现供应链稳定运营的基础。     

FDA perspective on peptide formulation and stability issues

Traditionally, peptide drugs are prepared as sterile solutions and administered to patients by daily injection. However, this form of drug delivery causes pain and inconvenience to patients and thus has been poorly accepted. In addition to improving patient compliance, many novel delivery systems have been developed to address the need for prolonged, localized (targeted), or pulsatile drug action. Examples include, but are not limited to oral, nasal, or long-acting controlled release injectable dosage forms; a number of them have been approved by FDA recently. The unique characteristics and the relevant regulatory issues with respect to each type of delivery system are presented.     

The influence of the Si and Mn concentrations on the kinetics of the bainite transformation in Fe-C-Si-Mn alloys

Five Fe-C-Si-Mn alloys were investigated by dilatometry, optical microscopy, and transmission electron microscopy (TEM) analysis to determine the effects of Si and Mn content and austenitizing temperatures on the kinetics of bainite transformation. Segregation of Mn at prior austenite grain boundaries at a temperature below B_s was detected by the scanning transmission electron microscopy + energy dispersive spectroscopy (STEM + EDS) and secondary ion mass spectroscopy (SIMS) techniques. The fraction of intragranular ferrite increases with Mn content. The time needed for the initiation of the bainite transformation tends to decrease as the austenitizing temperature decreases. The results obtained were compared with those from Fe-0.38C-1.73Si and Fe-0.38C-3.11Mn alloys. Equilibrium and nonequilibrium segregation of Mn at prior austenite grain boundaries and the effect of the interaction between Si and Mn on the segregation of Mn are used to explain the results obtained and the large difference between the kinetics of the two ternary alloys and those of the Fe-C-Si-Mn alloys. This paper is based on a presentation made in the symposium “International Conference on Bainite” presented at the 1988 World Metals Congress in Chicago, IL, on September 26 and 27, 1988, under the auspices of the ASM INTERNATIONAL Phase Transformations Committee and the TMS Ferrous Metallurgy Committee.     

检测速度及其稳定性对涡流检测的影响

针对涡流检测中的检测速度及其稳定性 ,用铜管进行了一些试验 .结果表明涡流探伤仪器的检测灵敏度和可靠性程序均受到很大影响     

The influence of elastic anisotropy on dislocation stability in /gb-tin and lead

The effects of elastic anisotropy on the energy and thermodynamic stability of dislocations in β-tin and lead were assessed through computation of the dislocation energy factorK. The energy factors were utilized to construct an inverse Wulff plot, from which unstable dislocation orientations are defined by concave regions of the construction. Dislocation instabilities are predicted for β-tin near the melting point for four of six slip systems considered, the slip systems displaying the instabilities being (110) [001], (100) [001], (010) [101], and (101)[101]. An instability is predicted also for the slip system {111} <111> in lead, which is the first fcc metal found to display sufficient elastic anisotropy for instability. For the metals examined in this paper, the angular range over which instabilities occur narrows with decreasing temperature, and usually, below some critical temperature, the dislocation line becomes stable over all orientations. The occurrence of dislocation instabilities is a direct result of elastic anisotropy, and their possible influence on physical properties is discussed.     

The influence of microencapsulation using Eudragit RS100 on the hydrolysis kinetics of acetylsalicylic acid

Homogeneous Eudragit RS100 matrix microspheres containing molecularly dispersed acetylsalicylic acid (ASA) were prepared in order to investigate the effect of encapsulation on the decomposition rate of a hydrolytically susceptible drug. ASA-loaded microspheres of this non-eroding polymer matrix were analysed at predetermined time points following immersion of the microspheres in temperature controlled buffer systems at pH 1.2 or pH 12.1 at 30, 40 or 50 degrees C. The mass balance of the total amount of solutes (ASA and SA) initially located within the microsphere interior was equal to the sum of the amount of solutes remaining in the microsphere interior and the amount of solutes in the aqueous phase at any time during the course of the study. Each analysis involved the quantitation of four species; the drug and decomposition product, salicylic acid (SA), in both the microspheres phase and the external aqueous phase. A simple model system using first-order rate approximations for the concurrent Fickian diffusion and hydrolysis decomposition of the drug resulted in a multiexponential expression which adequately described the time-course profile of the drug. SA-loaded microspheres were used as a control under similar conditions to determine the magnitude of the contribution of microsphere phase hydrolysis of ASA to the overall rate of drug loss from the microspheres. Results indicated that microspheres phase hydrolysis of ASA was minimal. Even after 900 h of immersion in pH 12.1 buffer some ASA remained within the microsphere. It is postulated that the matrix incorporated drug is essentially shielded from hydrolytic attack until it is liberated into the external aqueous environment. Electrostatic association of the drug with the charged quaternary residues in the polymer along with the limiting availability of water within the microsphere may be responsible for the observed stability of ASA in aqueous swollen ASA-loaded Eudragit microspheres.     

The influence of austenite stability on the hydrogen embrittlement and stress- corrosion cracking of stainless steel

A study has been made of the HE and SCC of a type 304 and a type 310 austenitic stainless steel, and the results correlated with the presence or absence of α′ martensite, determined by means of a ferrite detector. Hydrogen induced slow crack growth (SCG) was observed at room temperature when type 304 was stressed i) in 1 psig (∼10⁵ N/m²) gaseous hydrogen, ii) after high temperature charging, and iii) while undergoing cathodic charging. The fracture surfaces corresponding to SCG were primarily transgranular and cleavage-like, and were found to be associated with α′. Conditions i) to iii) did not produce SCG in the type 310 steel, in which α′ martensite was not detected, nor did SCG occur when type 304 was stressed in gaseous hydrogen above the M_D temperature (∼110°C). These observations indicated that the formation of the martensitic phase was a prerequisite for SCG under these test conditions. Stressing of type 310 while it was undergoing cathodic charging at room temperature was found to produce shallow, nonpropagating cracks, confirming earlier reports that austenite can be embrittled by hydrogen in the absence of α′. SCC occurred in both alloys in boiling aqueous MgCl₂ (154°C) with no evidence for α′ formation. The results are discussed in terms of the mechanisms of HE and SCC. Formerly Research Associate, Department of Metallurgy and Mining Engineering, University of Illinois. Formerly Corrosion-Control Analyst with the Physical Plant at the University of Illinois.     

The influence of annealing in the ferrite-plus-austenite phase field on the stability of vanadium carbide precipitates

The influence of rapid excursions into the ferrite-plus-austenite two-phase field on V₄C₃ precipitates formed by tempering in the ferrite phase was explored. The iron-based alloy studied contained 0.14 carbon and 0.49 vanadium in wt pct. A fine distribution of V₄C₃ particles was obtained through solution treatment followed by quench and tempering at 973 K. Samples were then rapidly heated to 1088 K for various times between 50 and 300 seconds. The plate-shaped V₄C₃ precipitates in regions that maintained their original ferrite matrix exhibited a continuous coarsening and decrease in their aspect ratio with increasing hold times. The V₄C₃ precipitates in regions that transformed to austenite were observed to dissolve by a reversion process if they were below a certain size. If the V₄C₃ particles were above that size, the matrix change caused them to coarsen and reduce their aspect ratio. Based upon the size of V₄C₃ particles that did show reversion, the interphase interfacial surface energy between the V₄C₃ partieles and aus tenite in the nonequilibrium orientation relationships produced in this study was determined to be between 1125 and 1840 mJ/m². When samples where reversion was observed were retempered at 973 K, the original distribution of fine, plate-shaped V₄C₃ particles could be reproduced accompanied by a measurable secondary hardening response.     

Structural stability of short subsequences of the tropomyosin chain

The native tropomyosin molecule is a parallel, registered, alpha-helical coiled coil made from two 284-residue chains. Long excised subsequences (> or = 95 residues) form the same structure with comparable thermal stability. Here, we investigate local stability using shorter subsequences (20-50 residues) that are chemically synthesized or excised from various regions along the protein chain. Thermal unfolding studies of such shorter peptides by CD in the same solvent medium used in extant studies of the parent protein indicate very low helix content, almost no coiled-coil formation, and high thermal lability of such secondary structure as does form. This behavior is in stark contrast to extant data on leucine-zipper peptides and short "designed" synthetic peptides, many of which have high alpha-helix content and form highly stable coiled coils. The existence of short coiled coils calls into question the older idea that short subsequences of a protein have little structure. The present study supports the older view, at least in its application to tropomyosin. The intrinsic local alpha-helical propensity and helix-helix interaction in this prototypical alpha-helical protein is sufficiently weak as to require not only dimerization, but macro-molecular amplification in order to attain its native conformation in common benign media near neutral pH.     

The influence of water vapor on the fatigue crack propagation kinetics in pure aluminum single crystals

In general, water vapor accelerates the fatigue crack propagation rate in pure aluminum (99.999 pct) single crystals under Mode II or Mode I–II loading. This effect can be explained by the fact that hydrogen generated during corrosion fatigue enters into the specimen and is transported by dislocation sweeping during fatigue deformation from the surface to the interior of the crystal for a much longer distance than by diffusion. It is hydrogen which accelerates the fatigue crack propagation rate. However, for certain orientations, the reverse effect termedunusual retardation was observed, which can be explained by the blunting effect due to the presence of numerous microcracks along the secondary PSB.     

Effects of shear flow and anisotropic kinetics on the morphological stability of a binary alloy

The effect of a parallel shear flow and anisotropic interface kinetics on the onset of instability during the directional solidification of a binary alloy at constant velocity is calculated. The model for anisotropy is based on the motion of steps. A shear flow (linear Couette flow or asymptotic suction profile), parallel to the crystal-melt interface in the same direction as the step motion, decreases interface stability in that the critical solute concentration decreases. A shear flow counter to the step motion enhances stability for small shear rates; for larger shear rates, the neutral curve develops a bimodal structure, and the critical solute concentration slowly decreases with shear rate.     

The influence of sulfur on interfacial reaction kinetics in the decarburization of liquid iron by carbon dioxide

The kinetics of decarburization of continuously carbon-saturated liquid iron by CO₂ have been studied between 1280 and 1600‡C at sulfur concentrations between 0.01 and 1 wt pct. The results are consistent with a surface blockage mechanism by chemisorbed sulfur which shows an essentially ideal adsorption isotherm. The adsorption coefficient of sulfur, in (wt pct)^-1, is given by the equation logK = 3600/T + 0.57 for carbon-saturated alloys. A small residual rate at apparent surface saturation is observed. This leaves about 1.4 pct of the active surface sites available for reaction, essentially independent of temperature. Studies with varying carbon concentration suggest that to a first approximation, and above about 3 wt pct C, the adsorption equilibrium for sulfur depends only on the thermodynamic activity of sulfur. DR. SAIN was formerly a Graduate Student.     

The influence of sulfur on interfacial reaction kinetics in the decarburization of liquid iron by carbon dioxide

The kinetics of decarburization of continuously carbon-saturated liquid iron by CO₂ have been studied between 1280 and 1600?C at sulfur concentrations between 0.01 and 1 wt pct. The results are consistent with a surface blockage mechanism by chemisorbed sulfur which shows an essentially ideal adsorption isotherm. The adsorption coefficient of sulfur, in (wt pct)^-1, is given by the equation logK = 3600/T + 0.57 for carbon-saturated alloys. A small residual rate at apparent surface saturation is observed. This leaves about 1.4 pct of the active surface sites available for reaction, essentially independent of temperature. Studies with varying carbon concentration suggest that to a first approximation, and above about 3 wt pct C, the adsorption equilibrium for sulfur depends only on the thermodynamic activity of sulfur.     

Stoichiometry and kinetics of the high-affinity H+-coupled peptide transporter PepT2

Proton-coupled peptide transporters mediate the absorption of a large variety of di- and tripeptides as well as peptide-like pharmacologically active compounds. We report a kinetic analysis of the rat kidney high-affinity peptide transporter PepT2 expressed in Xenopus oocytes. By use of simultaneous radioactive uptake and current measurements under voltage-clamp condition, the charge to substrate uptake ratio was found to be close to 2 for both D-Phe-L-Ala and D-Phe-L-Glu, indicating that the H+:substrate stoichiometry is 2:1 and 3:1 for neutral and anionic dipeptides, respectively. The higher stoichiometry for anionic peptides suggests that they are transported in the protonated form. For D-Phe-L-Lys, the charge:uptake ratio averaged 2.4 from pooled experiments, suggesting that Phe-Lys crosses the membrane via PepT2 either in its deprotonated (neutral) or its positively charged form, averaging a H+:Phe-Lys stoichiometry of 1.4:1. These findings led to the overall conclusion that PepT2 couples transport of one peptide molecule to two H+. This is in contrast to the low-affinity transporter PepT1 that couples transport of one peptide to one H+. Quinapril inhibited PepT2-mediated currents in presence or in absence of external substrates. Oocytes expressing PepT2 exhibited quinapril-sensitive outward currents. In the absence of external substrate, a quinapril-sensitive proton inward current (proton leak) was also observed which, together with the observed pH-dependent PepT2-specific presteady-state currents (Ipss), indicates that at least one H+ binds to the transporter prior to substrate. PepT2 exhibited Ipss in response to hyperpolarization at pH 6.5-8.0. However, contrary to previous observations on various transporters, 1) no significant currents were observed corresponding to voltage jumps returning from hyperpolarization, and 2) at reduced extracellular pH, no significant Ipss were observed in either direction. Together with observed lower substrate affinities and decreased PepT2-mediated currents at hyperpolarized Vm, our data are consistent with the concept that hyperpolarization exerts inactivation effects on the transporter which are enhanced by low pH. Our studies revealed distinct properties of PepT2, compared with PepT1 and other ion-coupled transporters.