提高梯级水电站水工建筑物安全运行的措施

介绍谢列布良斯克２号，上、下捷里别尔斯克等３个梯级水电站运行中的实践经验。对运行中土坝渗流量超出设计渗流量，进行了计算研究，并采取相应的防渗措施，如设反滤层等；对水电站工作轮室、蜗壳等处的金属衬砌外壳出现了补强灌浆。     

Kinetic and equilibrium studies in removing lead ions from aqueous solutions by natural sepiolite

The capacity of sepiolite for the removal of lead ions from aqueous solution was investigated under different experimental conditions. The Langmuir and Freundlich equations, which are in common use for describing sorption equilibrium for wastewater-treatment applications, were applied to data. The constants and correlation coefficients of these isotherm models for the present system at different conditions such as pH, temperature and particle size were calculated and compared. The equilibrium process was well described by the Langmuir isotherm model and the maximum sorption capacity was found to be 93.4 mg/g for the optimal experimental condition. The thermodynamic parameters (DeltaG(o), DeltaH(o) and DeltaS(o)) for lead sorption on the sepiolite were also determined from the temperature dependence. The influences of specific parameters such as the agitation speed, particle size and initial concentration for the kinetic studies were also examined. The sorption kinetics were tested for first order reversible, pseudo-first order and pseudo-second order reaction and the rate constants of kinetic models were calculated. The best correlation coefficients were obtained using the pseudo-second order kinetic model, indicating that lead uptake process followed the pseudo-second order rate expression.     

Improved emission uniformity from a liquid-jet laser-plasma extreme-ultraviolet source

Many modern compact soft-x-ray and extreme-ultraviolet (EUV) imaging systems operate with small fields of view and therefore benefit from the use of small high-brightness sources. Such systems include water-window microscopes and EUV lithography tools. We show that the photon losses in such systems can be minimized while uniformity of object-plane illumination is maintained by controlled scanning of the source. The improved collection efficiency is demonstrated both theoretically and experimentally for a scanned laser-plasma source compared with static sources. A prospective aerial image microscope and a liquid-xenon-jet laser-plasma source are offered as examples of modern imaging tools that may benefit from such scanning of the source.     

The evaluation of the 1980 decennial census

The authors describe the procedures that are being used to evaluate the 1980 U.S. census. Topics covered include the purposes of evaluation, studies of variance, studies of bias, and studies of alternate procedures     

Using a system-on-a-chip implantable device to filter circulating infected cells in blood or lymph

This paper describes a system on a chip (SoC) that makes use of nanoscale cellular adhesion mechanisms in an integrated electronic microsystem to filter infected cells from blood or lymph. An example of a human immunodeficiency virus-specific SoC is explored in depth. Such systems work in vivo, and blood and lymph are filtered on a continuous basis. With the intelligence on the chip, captured cells can be identified and lyzed, expelled, or otherwise acted upon. These types of systems transfer the burden of research from traditional chemotherapy to bioengineering and system design.     

Synergistic pseudo-hydroxide extraction: synergism and anion selectivity in sodium extraction using a crown ether and a series of weak lipophilic acids

The nature of the weak lipophilic acid used in synergistic combination with a model crown ether cation host was shown to have a strong effect on the strength and selectivity of sodium hydroxide separation from alkaline aqueous salt solutions. Sodium ion-pair extraction employing only cis-syn-cis-dicyclohexano-18-crown-6 (1) in nitrobenzene (NB) was correlated with the standard Gibbs energy (deltaG(p)o) of anion partitioning into NB and was notably weak and nonselective for the hydroxide ion, in accord with Hofmeister bias. The Hofmeister order can be selectively overcome for NaOH by utilization of acid-base chemistry coupled with complexation of sodium ion in the NB phase. Upon addition of a lipophilic organic acid into the solution of 1 in NB, sodium extraction was selectively enhanced due to the initiation of an exchange reaction between the aqueous sodium ion and the ionizable proton of the organic acid. A series of weak lipophilic hydroxy acids (HA) including fluorinated alcohols and phenols was tested. The resulting synergistic pseudo-hydroxide extraction correlates with the pKa of the employed HA; the most acidic cation exchangers provide the greatest synergism. The synergistic factor obtained using a fluorinated benzyl alcohol 7 was as high as 256. Ion-pair extraction of neutral sodium salts was not changed or only mildly enhanced by addition of HA into the NB solution of 1. This enhancement was explained by hydrogen bonding of HA with the anion as related to the hardness of the anion and the acidity of HA. In comparison with the synergism observed for NaOH, this enhancement was weak and unable to overcome the Hofmeister effect. Examination of extraction selectivity revealed that the combination of 1 and 7 preferentially extracted NaOH over all other sodium salts, including the normally preferred nitrate and perchlorate salts. Quantitative recovery of NaOH from the NB phase was demonstrated via hydrolysis of the organic acid upon a single contact of the loaded solvent with water.     

Clostridium difficile from healthy food animals: optimized isolation and prevalence

Two isolation methods were compared for isolation of Clostridium difficile from food animal feces. The single alcohol shock method (SS) used selective enrichment in cycloserine-cefoxitin fructose broth supplemented with 0.1% sodium taurocholate, followed by alcohol shock and isolation on tryptic soy agar supplemented with 5% sheep blood, and cycloserine-cefoxitin fructose agar. The double alcohol shock method (DS) used alcohol shock prior to and after selective enrichment in cycloserine-cefoxitin fructose broth supplemented with 0.1% sodium taurocholate, followed by isolation on tryptic soy agar supplemented with 5% sheep blood and cycloserine-cefoxitin fructose agar. A total of 55 (15.9%, n = 345) swine fecal samples, 32 (2.4%, n = 1,325) dairy cattle fecal samples, and 188 (6.3%, n = 2,965) beef cattle fecal samples were positive for C. difficile by either method. However, the DS was significantly better than the SS for the recovery of C. difficile from swine feces, while the SS was significantly better than the DS for the recovery of C. difficile from beef cattle feces. There was no significant difference between methods for the recovery of C. difficile from dairy cattle feces. This study suggests that food animals might harbor C. difficile and it provides critical information that isolation methods might not have universal application across animal species.     

Measurement of activation-related changes in cerebral blood volume: VASO with single-shot HASTE acquisition

Object The recently developed vascular space occupancy (VASO) fMRI technique is gaining popularity as it facilitates the measurement of cerebral blood volume (CBV) changes concomitant with brain activation, without the use of contrast agents. Thus far, VASO fMRI has only been used in conjunction with a GE-EPI (gradient-echo echo planar imaging) sequence, which is proceeded by an inversion recovery (IR) experiment to selectively null the blood signal. The use of GE-EPI has potential disadvantages: (a) the non-zero TE may lead to BOLD contamination and (b) images suffer from the EPI-typical inhomogeneity artefacts. Materials and methods Here, we propose the use of VASO based on an IR-HASTE (inversion recovery half-Fourier acquisition single-shot turbo spin echo) sequence. Results Results from a visual stimulation study (n = 8) show a 43% higher functional contrast-to-noise (CNR) of HASTE compared to EPI, with a strongly increased count of active voxels at the same significance threshold. Sensitivity to inflow effects was investigated and found to be similar for both methods. Conclusion As HASTE VASO yields essentially artefact-free images, it appears to be the method of choice for measuring relative CBV changes with VASO.