Phenomena Affecting the Equilibrium of Al(III) and Zn(II) Extraction with Winsor II Microemulsions

The extraction of Al(III) and Zn(II) from an aqueous solution with two water-in-oil microemulsions, one containing di(2-ethylhexyl)phosphoric acid (DEHPA), was investigated to aid the understanding of the role of the extractant and the metal specific characteristics in the mechanism of microemulsion extraction. The extraction of Al with the DEHPA microemulsion increased by a factor of about 10 with respect to that in the conventional DEHPA system, whereas the extraction of Zn was lower than that in the single DEHPA system. Extraction with the DEHPA-free microemulsion was very low, showing that metal ion solubilization was not important in the mechanism of microemulsion extraction. It is proposed that the effect of the mixed microemulsion on the metal distribution coefficient is the result of the balance between a decrease in the complexation reaction yield due to the interaction between butanol and DEHPA, and the adsorption of the metal complex at the macro- and microinterfaces. The former leads to a decrease in Zn(II) extraction and the latter to Al(III) extraction synergism. Copyright 2000 Academic Press.     

Rotation reversal bifurcation and energy confinement saturation in tokamak Ohmic L-mode plasmas

Direction reversals of intrinsic toroidal rotation have been observed in diverted Alcator C-Mod Ohmic L-mode plasmas following electron density ramps. For low density discharges, the core rotation is directed cocurrent, and reverses to countercurrent following an increase in the density above a certain threshold. Such reversals occur together with a decrease in density fluctuations with 2 cm(-1)≤k(θ)≤11 cm(-1) and frequencies above 70 kHz. There is a strong correlation between the reversal density and the density at which the Ohmic L-mode energy confinement changes from the linear to the saturated regime.     

机械泵驱动两相回路的实时动态模型分析

在航空航天领域,为了加速系统设计及测试进度,通常需要进行半实物实时仿真,即控制器用实物,受控对象采用数学模型。本文开发出了基于Matlab/Simulink的两相传热模块,并用其搭建了某机械泵驱动两相回路的实时动态模型。通过与实验的对比,验证了模型的可靠性,表明该模型满足实时要求,可以在下一步用于半实物仿真。     

A study of molybdenum radiation from alcator A

Radiation emitted by molybdenum impurity ions in the Alcator A tokamak has been investigated. A grazing incidence monochromator photometrically calibrated against synchrotron radiation was used to determine absolute brightnesses of emission lines and the role of molybdenum radiative losses in the plasma discharge power balance. At line average electron densities of 3 × 10¹⁴ cm^?3, molybdenum radiation from the central (0–3 cm) region was equal to ～17% of the local ohmic heating power, implying radiation from molybdenum ions does not dominate the power loss from the central part of the plasma. The temporal behavior of molybdenum ions injected by the laser blow off technique at $\text{n}{}_{\mathrm{e}}\text{= 3 × 10}{}^{14}\text{cm}{}^{\mathrm{?3}}$ indicated that the molybdenum ion confinement time was finite in conflict with neoclassical theory. At lower densities (1–2 × 10¹⁴ cm^?3) the radiation from intrinsic molybdenum increased faster than the electron density during the discharge, indicating a buildup of molybdenum ions in the plasma.     

Quaternary (liquid + liquid) equilibria of aqueous two-phase poly (ethylene glycol), poly (DMAM–TBAM), and KH2PO4: Experimental and generalized Flory–Huggins theory

Quaternary (liquid + liquid) equilibrium (LLE) data of the aqueous two-phase poly (ethylene glycol), poly (N,N-dimethylacrylamide-t-butylacrylamide) with abbreviation name poly (DMAM–TBAM) as a hydrophobic association water-soluble copolymer and KH₂PO₄ has been determined experimentally at T = 338.15 K. Furthermore, the generalized Flory–Huggins theory with two electrostatic terms (the Debye–Hückel and Pitzer–Debye–Hückel) was used for correlation of the phase behavior of the quaternary system and the interaction parameters between all species were calculated.It was found that addition of poly (DMAM–TBAM) copolymer as well as changing the temperature can shift the binodal curves of aqueous two-phase systems containing polyethylene glycol (PEG) and salt. Also, the phase behavior of the DMAM–TBAM copolymer with some salts containing sodium chloride, ammonium hydrogen phosphate, potassium hydrogen phosphate, and sodium carbonate were studied experimentally at T = 338.15 K and the effect of the salt type on the their binodal curves was determined.     

Observation of anomalous momentum transport in tokamak plasmas with no momentum input

Anomalous momentum transport has been observed in Alcator C-Mod tokamak plasmas through analysis of the time evolution of core impurity toroidal rotation velocity profiles. Following the L-mode to EDA (enhanced D(alpha)) H-mode transition, the ensuing cocurrent toroidal rotation velocity, which is generated in the absence of any external momentum source, is observed to propagate in from the edge plasma to the core. The steady state toroidal rotation velocity profiles are relatively flat and the momentum transport can be simulated with a simple diffusion model. Velocity profiles during edge localized mode free (ELM-free) H-modes are centrally peaked, which suggests the addition of inward momentum convection. In all operating regimes the observed momentum diffusivities are much larger than the neoclassical values.     

Algebraic study of chiral anomalies?

The algebraic structure of chiral anomalies ismade globally valid on non-trivial bundles by the introduction of a fixed background connection. Some of the techniques used in the study of the anomaly are improved or generalized, including a systematic way of generating towers of ??descent equations??.     

Edge temperature gradient as intrinsic rotation drive in Alcator C-Mod tokamak plasmas

Intrinsic rotation has been observed in I-mode plasmas from the C-Mod tokamak, and is found to be similar to that in H mode, both in its edge origin and in the scaling with global pressure. Since both plasmas have similar edge ?T, but completely different edge ?n, it may be concluded that the drive of the intrinsic rotation is the edge ?T rather than ?P. Evidence suggests that the connection between gradients and rotation is the residual stress, and a scaling for the rotation from conversion of free energy to macroscopic flow is calculated.     

The <Emphasis Type="Italic">Mycobacterium tuberculosis</Emphasis> Rv2540c DNA sequence encodes a bifunctional chorismate synthase

Background

The emergence of multi- and extensively-drug resistant Mycobacterium tuberculosis strains has created an urgent need for new agents to treat tuberculosis (TB). The enzymes of shikimate pathway are attractive targets to the development of antitubercular agents because it is essential for M. tuberculosis and is absent from humans. Chorismate synthase (CS) is the seventh enzyme of this route and catalyzes the NADH- and FMN-dependent synthesis of chorismate, a precursor of aromatic amino acids, naphthoquinones, menaquinones, and mycobactins. Although the M. tuberculosis Rv2540c (aroF) sequence has been annotated to encode a chorismate synthase, there has been no report on its correct assignment and functional characterization of its protein product.

Results

In the present work, we describe DNA amplification of aroF-encoded CS from M. tuberculosis (Mt CS), molecular cloning, protein expression, and purification to homogeneity. N-terminal amino acid sequencing, mass spectrometry and gel filtration chromatography were employed to determine identity, subunit molecular weight and oligomeric state in solution of homogeneous recombinant Mt CS. The bifunctionality of Mt CS was determined by measurements of both chorismate synthase and NADH:FMN oxidoreductase activities. The flavin reductase activity was characterized, showing the existence of a complex between FMN_ox and Mt CS. FMN_ox and NADH equilibrium binding was measured. Primary deuterium, solvent and multiple kinetic isotope effects are described and suggest distinct steps for hydride and proton transfers, with the former being more rate-limiting.

Conclusion

This is the first report showing that a bacterial CS is bifunctional. Primary deuterium kinetic isotope effects show that C₄-proS hydrogen is being transferred during the reduction of FMN_ox by NADH and that hydride transfer contributes significantly to the rate-limiting step of FMN reduction reaction. Solvent kinetic isotope effects and proton inventory results indicate that proton transfer from solvent partially limits the rate of FMN reduction and that a single proton transfer gives rise to the observed solvent isotope effect. Multiple isotope effects suggest a stepwise mechanism for the reduction of FMN_ox. The results on enzyme kinetics described here provide evidence for the mode of action of Mt CS and should thus pave the way for the rational design of antitubercular agents.