Temperature–enthalpy curve for energy targeting of distillation columns

The temperature–enthalpy (T–H) diagram of a distillation column at practical near-minimum thermodynamic condition (PNMTC) or the column grand composite curve (CGCC) is a useful representation for energy targeting studies and may be generated from a converged simulation of a base-case column design. The calculation procedure for the CGCC involves determination of the net enthalpy deficit at each stage by generating envelopes from either the condenser end (top-down approach) or the reboiler end (bottom-up approach). However, the values calculated by the two approaches differ for stages with feeds because existing procedures for CGCC generation do not consider the enthalpy balances at the feed stages. In fact, the net enthalpy deficits at feed stages calculated by both approaches are erroneous even for the simplest case of binary distillation. A feed stage correction (FSC) that rigorously considers the mass and enthalpy balance equations at feed stages is proposed in this work to resolve the discrepancy. Instead of assuming that the compositions obtained from the converged simulation for a feed stage will remain unchanged at PNMTC, the pinched compositions for the feed are determined by the intersection of the equilibrium curve and the feed q-line. Rather than perform an additional flash calculation to establish the pinched feed compositions, a quadratic approximation is developed here for column targeting purposes by assuming the relative volatility obtained from the simulation to remain constant in the neighborhood of the feed stage. The proposed FSC ensures that the CGCC is identical whether the calculations are performed by the top-down approach or the bottom-up approach. The effect of the FSC on the targets for energy conservation by reflux modification, feed conditioning, and introduction of side reboilers/condensers is discussed. As the energy target for reflux modification is determined by the CGCC pinch which typically occurs at or close to the feed location, the significance of the FSC on the reflux modification target is highlighted through several case studies including a complex column featuring multiple feeds and consequently multiple pinch points. The CGCCs for these case studies are generated by a computer program based on the FSC and a single analytical equation for the calculation of the net enthalpy deficits that allows every stage to have a feed, liquid product, vapor product, and side exchanger. The studies show that the reflux modification targets may be erroneous in many cases, if the FSC is ignored.     

Stability of tri-taper journal bearings under dynamic load using a non-linear transient method

Stability of a tri-taper journal bearing which is subjected to steady, periodic and variable rotating loads is studied theoretically using a non-linear transient approach. The hydrodynamic forces are initially obtained by solving the Reynolds equation, satisfying the Reynolds boundary conditions. Further, the transient behavior of rotor bearing system is predicted by substituting these hydrodynamic forces in the equations of motion and then solving them by fourth order Runge Kutta method. Stability of the rotor bearing system is determined from the journal locus. Comparative studies predict that the dynamic performance is superior for a bearing with high ramp size and aspect ratio.     

Electronic phase separation and other novel phenomena and properties exhibited by mixed-valent rare-earth manganites and related materials

Transition metal oxides, such as the mixed-valent rare-earth manganites Ln(1-x)AxMnO3 (Ln, rare-earth ion, and A, alkaline-earth ion), show a variety of electronic orders with spatially correlated charge, spin and orbital arrangements, which in turn give rise to many fascinating phenomena and properties. These materials are also electronically inhomogeneous, i.e. they contain disjoint spatial regions with different electronic orders. Not only do we observe signatures of such electronic phase separation in a variety of properties, but we can also observe the different 'phases' visually through different types of imaging. We discuss various experiments pertaining to electronic orders and electronic inhomogeneities in the manganites and present a discussion of theoretical approaches to their understanding. It is noteworthy that the mixed-valent rare-earth cobaltates of the type Ln(1-x)AxCoO3 also exhibit electronic inhomogeneities just as the manganites.     

The mixing mechanism during lithiation of Si negative electrode in Li-ion batteries: an ab initio molecular dynamics study

In order to realize Si as a negative electrode material in commercial Li-ion batteries, it is important to understand the mixing mechanism of Li and Si, and stress evolution during lithiation in Si negative electrode of Li-ion batteries. Available experiments mainly provide the diffusivity of Li in Si as an averaged property, neglecting information regarding diffusivity of Si. However, if Si can diffuse as fast as Li, the stress generated during Li diffusion can be reduced. We, therefore, studied the diffusivity of Li as well as Si atoms in the Si-anode of Li-ion battery using an ab initio molecular dynamics-based methodology. The electrochemical insertion of Li into crystalline Si prompts a crystalline-to-amorphous phase transition. We considered this situation and thus examined the diffusion kinetics of Li and Si atoms in both crystalline and amorphous Si. We find that Li diffuses faster in amorphous Si as compared to crystalline Si, while Si remains relatively immobile in both cases and generates stresses during lithiation. To further understand the mixing mechanism and to relate the structure with electrochemical mixing, we analyzed the evolution of the structure during lithiation and studied the mechanism of breaking of Si-Si network by Li. We find that Li atoms break the Si rings and chains and create ephemeral structures such as stars and boomerangs, which eventually transform to Si-Si dumbbells and isolated Si atoms in the LiSi phase. Our results are found to be in agreement with the available experimental data and provide insights into the mixing mechanism of Li and Si in Si negative electrode of Li-ion batteries.     

Microstructure-sensitive notch root analysis for dwell fatigue in Ni-base superalloys

Macroscopic viscoplastic constitutive models for γ–γ′ Ni-base superalloys typically do not contain an explicit dependence on the underlying microstructure. Microstructure-sensitive models are of interest in many applications since microstructure can vary in components, whether intentional or not. In such cases, the use of experiments from one microstructure condition to fit macroscopic models may be too limiting. The principal microstructure attributes that can significantly affect the cyclic stress–strain response of γ–γ′ Ni-base superalloys are the grain size and γ′ precipitate volume fraction and size distributions. An artificial neural network (ANN) is used to correlate the material parameters of a macroscale internal state variable cyclic viscoplasticity model with these microstructure attributes using a combination of limited experiments augmented by polycrystal plasticity calculations performed on other (virtual) microstructures within the range characterized experimentally. The trained model is applied to an example of a component fatigue notch root analysis with dwell periods at peak load to demonstrate the methodology and explore the potential impact of microstructure-sensitive constitutive models on life prediction for notched structures subjected to realistic load histories.     

Reversible Z-E Isomerism and Pharmaceutical Implications for SU5416

ABSTRACT

SU5416 (Z-isomer), the first in its class of angiogenesis inhibitors, in solution converts to the E-isomer following light exposure and reverts to the Z-isomer in the dark. Kinetics of this Z-E isomerism in pharmaceutical media is reported. Analytical solutions need light protection at 5°C to maintain integrity. While E-isomer in light-exposed product increased to 0.9% in 24 hours, light-protected product showed no change (25°C, 18 months). Infusate studies indicated that < 1.9% E-isomer will be dosed to patients and would likely convert to the Z-isomer, following administration. This report implies Z-E isomerism in SU5416 is controllable with no limitations towards ensuring pharmaceutical product quality.     

Anomaly of arch of atlas--a rare cause of symptomatic canal stenosis in children

Symptomatic canal stenosis at the level of atlas (C1) without atlantoaxial dislocation is thought to be very rare in children. Though common, anomalies of the arch of atlas are generally incidental findings in X-rays. High cord compression due to a narrow canal from a bifid posterior arch, or an absent posterior arch, is a very rare condition. We report 5 children with high cord compression from stenosis of C1 arch.     

Treatment of microfilaraemia in asymptomatic brugian filariasis: the efficacy and safety of the combination of single doses of ivermectin and diethylcarbamazine

BACKGROUND: Nitric oxide (NO) seems to play an important role in modulating tissue injury during reperfusion of the liver. In this study, we have evaluated and compared the effects of FK409 (FK), a potent spontaneous NO releaser, and L-arginine in ischemia-reperfusion injury of the rat liver. METHODS: Male Sprague-Dawley rats underwent 90 min of hepatic ischemia followed by reperfusion. FK or L-arginine was used (intravenously) in two different doses for each drug (group I, 3.2 mg/kg FK; group II, 1.6 mg/kg FK; group IV, 100 mg/kg L-arginine; and group V, 300 mg/kg L-arginine). Saline was used in control animals (group III). Hepatic enzyme status, microcirculation, serum nitrite (NO2-) and nitrate (NO3-) and tissue injury score were evaluated at predetermined times. RESULTS: Serum NO2-/NO3- was elevated immediately by FK treatment dose-dependently but not by L-arginine. However, L-arginine caused late (6-24 hr) elevation of the NO metabolites dose-dependently. The elevation of serum aspartate aminotransferase and alanine aminotransferase was suppressed and hepatic microcirculation was improved in the FK-treated groups dose-dependently. L-Arginine also improved the microcirculation, but hepatic enzymes at 24 hr of reperfusion were significantly higher in group V than in the control group. These findings were well reflected by the extent of tissue injury in respective groups. CONCLUSION: FK treatment in the immediate reperfusion period improves hepatic microcirculation and confers a significant protective effect on hepatic ischemia-reperfusion injury in the rat.     

Prevention of acute adenolymphangitis in brugian filariasis: comparison of the efficacy of ivermectin and diethylcarbamazine, each combined with local treatment of the affected limb

Staphylococcal enterotoxins A and C1 (SEA or SEC1) bound to major histocompatibility-I (MHCI) molecules with high affinity (binding constants ranging from 1.1 microM to 79 nM). SEA and SEC1 directly bound MHCI molecules that had been captured by monoclonal antibodies specific for H-2Kk, H-2Dk, or both. In addition, MHCI-specific antibodies inhibited the binding of SEC1 to LM929 cells and SEA competitively inhibited SEC1 binding; indicating that the superantigens bound to MHCI on the cell surface. The affinity and number of superantigen binding sites differed depending on whether MHCI was expressed in the membrane of LM929 cells or whether it was captured. These data support the hypothesis that MHCI molecules can serve as superantigen receptors.     

Architectural considerations for next-generation file systems

Integration – supporting multiple application classes with heterogeneous performance requirements – is an emerging trend in networks, file systems, and operating systems. We evaluate two architectural alternatives – partitioned and integrated – for designing next-generation file systems. Whereas a partitioned server employs a separate file system for each application class, an integrated file server multiplexes its resources among all application classes; we evaluate the performance of the two architectures with respect to sharing of disk bandwidth among the application classes. We show that although the problem of sharing disk bandwidth in integrated file systems is conceptually similar to that of sharing network link bandwidth in integrated services networks, the arguments that demonstrate the superiority of integrated services networks over separate networks are not applicable to file systems. Furthermore, we show that: an integrated server outperforms the partitioned server in a large operating region and has slightly worse performance in the remaining region; the capacity of an integrated server is larger than that of the partitioned server; and an integrated server outperforms the partitioned server by a factor of up to 6 in the presence of bursty workloads.