Flocculation of activated sludge flocs by stimulation of the aerobic biological activity

Activated sludge flocs are known to deflocculate under short-term anaerobic conditions, but little is known about possible reflocculation under subsequent aerobic conditions. When activated sludge flocs from two wastewater treatment plants deflocculated under anaerobic conditions with well-defined shear conditions, they could be almost, but not completely, reflocculated by aeration for 1-2 h under the same shear conditions. If the biological activity was reduced by adding azide, chloramphenicol or by decreasing the temperature, no or only very little reflocculation took place. This indicated that the reflocculation was under direct or indirect microbial control. Only a small part of the reflocculation was due to improved flocculation properties obtained by oxidation of Fe(II) to Fe(III), which is a better flocculant. Fe(II) was produced under the anaerobic conditions by microbial iron reduction, and it was oxidized to Fe(III) within less than one hour after the aeration was started. However, by comparing two different sludges with different capabilities for iron reduction, iron oxidation and responses to substrate addition, it was found that the aerobic biological activity most likely was of greatest significance for the observed reflocculation and floc formation under aerobic conditions. This was further supported by adding organic substrates (glucose or ethanol) during the aerobic reflocculation phase, which promoted reflocculation. However, some substrates had the opposite effect (acetate and lactate), where a deterioration of the reflocculation was observed, probably due to different responses from different groups of microorganisms in the sludges.     

Central venous oxygen saturation and thoracic admittance during dialysis: new approaches to hemodynamic monitoring

Intradialytic hypotension (IDH) is one of the most important short-term complications to hemodialysis (HD). Inadequate cardiac filling due to a reduction in the central blood volume is believed to be a major etiological factor. The aim of this study was to evaluate whether these pathophysiologic events are reflected in the central venous oxygen saturation (ScO(2)) and thoracic admittance (TA) during dialysis. Twenty ambulatory HD patients, 11 hypotension prone (HP) and 9 hypotension resistant, with central vascular access, were monitored during 3 HD sessions each. ScO(2), TA, finger blood pressure (BP), and relative change in blood volume (DeltaBV) were measured and sampled continuously. The relative TA decrease and DeltaBV were both largest in the HP group (p<0.05 for both), whereas ScO(2) decreased only in HP patients (p<0.001). Baseline TA was lower in the HP group (p<0.01). Changes in ScO(2) and TA correlated much closer than did changes in ScO(2) and DeltaBV (r=0.43 and 0.18, respectively). Our results suggest that an intradialytic decrease in cardiac output, as reflected by a fall in ScO(2), is a common feature to HD patients prone to IDH. In patients using a central vascular access, ScO(2) and TA measurements may be more specific to the pathophysiologic events preceding IDH than DeltaBV-the current standard monitoring method.     

A chromatographic approach for fluorescence reduction in liquid Raman analysis

In this study a chromatographic approach for fluorescence reduction in liquid Raman analysis has been evaluated. The idea behind the approach is to apply a chromatographic separation step prior to Raman analysis in order to separate fluorescing compounds from other components of interest, thus facilitating better quantitative and qualitative analysis of the latter components. A real-time liquid-core Raman waveguide detector designed for chromatographic applications was used in the study, thus providing real-time chemical pretreatment of liquid samples for Raman analysis. Twenty aqueous mixtures of additives frequently found in beverages were analyzed, and for comparative purposes the mixtures were also analyzed in the Raman waveguide detector without chromatographic separation and with a conventional immersion probe. Both qualitatively and quantitatively satisfying results were obtained using the chromatographic Raman approach, and the technique provided possibilities for quantitative and qualitative assessments superior to the two other instrumental setups. The technique may provide additional benefits through sensitivity enhancements, and the approach is simple, inexpensive, and easy to implement in the average applied Raman laboratory. The analysis of various chemical systems and factors such as system stability over time need further evaluation in order to confirm the general applicability of the approach.     

Effect of foliar application of selenium on its uptake and speciation in carrot

Carrot (Daucus carota) shoots were enriched by selenium using foliar application. Solutions of sodium selenite or sodium selenate at 10 and 100 μg Se ml⁻¹, were sprayed on the carrot leaves and the selenium content and uptake rate of selenium were estimated by ICP–MS analysis. Anion and cation exchange HPLC were tailored to and applied for the separation of selenium species in proteolytic extracts of the biological tissues using detection by ICP–MS or ESI–MS/MS. Foliar application of solutions of selenite or selenate at 100 μg Se ml⁻¹ resulted in a selenium concentration of up to 2 μg Se g⁻¹ (dry mass) in the carrot root whereas the selenium concentration in the controls was below the limit of detection at 0.045 μg Se g⁻¹ (dry mass). Selenate-enriched carrot leaves accumulated as much as 80 μg Se g⁻¹ (dry mass), while the selenite-enriched leaves contained approximately 50 μg Se g⁻¹ (dry mass). The speciation analyses showed that inorganic selenium was present in both roots and leaves. The predominant metabolised organic forms of selenium in the roots were selenomethionine and γ-glutamyl-selenomethyl-selenocysteine, regardless of which of the inorganic species were used for foliar application. Only selenomethionine was detected in the carrot leaves. The identity of selenomethionine contained in carrot roots and leaves was successfully confirmed by HPLC–ESI–MS/MS.     

Quantum chemical calculations of sulfate adsorption at the Al- and Fe-(hydr)oxide-H20 interface-estimation of gibbs free energies

Quantum chemical calculations were performed to estimate relative Gibbs free energies of sulfate adsorption on variably charged Al- and Fe-(hydr)oxide clusters. Innersphere bidentate bridging and monodentate adsorption were predicted to be exergonic on positively charged Al- and Fe-(hydr)oxides (ranging from -19 to -124 kJ mol-1). However, inner-sphere and H-bonded adsorption on neutral Al- and Fe-(hydr)oxides was predicted to be endergonic (ranging from +5 to +61( kJ mol-1)). Atthe highest positive surface charge, bidentate bridging adsorption was most thermodynamically favorable. At intermediate positive surface charge, bidentate bridging and monodentate adsorption energies were equivalent on Al-(hydr)oxides; monodentate adsorption was more thermodynamically favorable on Fe-(hydr)oxides as compared with bidentate bridging adsorption. The predicted thermodynamic favorability of sulfate adsorption on Al- and Fe-(hydr)oxides was directly related to positive surface charge and indirectly related to the HO-/SO42- exchange stoichiometry, chi. Predicted Gibbs free energies of bidentate bridging and monodentate sulfate adsorption on an Fe-(hydr)oxide cluster (charge = +1, chi = 1) agreed reasonably well with published experimental estimates of sulfate adsorption on geothite (predicted values -34 and -52 kJ mol-1, respectively, and experimental range -36 to -30 kJ mol-').     

Design, synthesis, and pharmacological characterization of polyamine toxin derivatives: potent ligands for the pore-forming region of AMPA receptors

Polyamine toxins, such as philanthotoxins, are low-molecular-weight compounds isolated from spiders and wasps, which modulate ligand-gated ion channels in the nervous system. Philanthotoxins bind to the pore-forming region of AMPA receptors, a subtype of glutamate receptors which are important for memory formation and are involved in neurodegenerative diseases. Previous studies have demonstrated that modification of the polyamine moiety of philanthotoxins can lead to very potent and highly selective ligands for the AMPA receptor, as exemplified with philanthotoxin-56. Much less attention has been paid to the importance of the aromatic head group of philanthotoxins, but herein we demonstrate that modification of this moiety leads to a significant improvement in potency relative to philanthotoxin-56 at cloned AMPA receptors. Interestingly, the incorporation of an adamantane moiety is particularly favorable, and the most potent compound has a Ki value of 2 nM, making it the most potent uncompetitive antagonist of AMPA receptors described to date. Such compounds are potentially useful as neuroprotective agents.     

Pick-and-place nanomanipulation using microfabricated grippers

Microfabricated grippers could be useful for the manipulation of nanoscopic and microscopic samples. A survey is presented of the force requirements for a microgripper to complete pick-and-place nanomanipulation tasks. We then demonstrate in?situ pick-and-place operations of nanowires inside a scanning electron microscope using microfabricated electrostatically actuated grippers, and compare the theoretically estimated force requirements with the results of experimental tests of picking up nanowires to evaluate how grippers and strategies for nanomanipulation can be optimized.     

A cathodoluminescence study of the influence of the seed particle preparation method on the optical properties of GaAs nanowires

Cathodoluminescence at 8?K is used to compare the optical properties of AlGaAs-capped GaAs nanowires, grown by metal-organic vapour phase epitaxy and seeded by gold particles prepared by different methods. Six different methods were used to fabricate and deposit gold seed particles onto GaAs substrates: colloid particles, aerosol particles and particles defined by electron beam lithography. The nanowires were grown with and without an in?situ annealing step prior to the nanowire growth. The morphology showed no significant differences between the nanowires. The emissions from ensembles of nanowires have the same peak position, irrespective of seed particle type. Without the in?situ annealing step prior to the nanowire growth, there are significant differences in the emission intensity and emission patterns from nanowires grown from different seed particles. When an in?situ annealing step is included, all the resulting nanowires show identical optical emission intensity and emission patterns. This shows the importance of using an in?situ annealing step prior to growth. This study demonstrates that different preparation methods for gold seed particles can be used to produce GaAs nanowires with highly similar optical properties. The choice of particle preparation method to be used can therefore be based on availability and cost.     

In situ TEM creation and electrical characterization of nanowire devices

We demonstrate the observation and measurement of simple nanoscale devices over their complete lifecycle from creation to failure within a transmission electron microscope. Devices were formed by growing Si nanowires, using the vapor-liquid-solid method, to form bridges between Si cantilevers. We characterize the formation of the contact between the nanowire and the cantilever, showing that the nature of the connection depends on the flow of heat and electrical current during and after the moment of contact. We measure the electrical properties and high current failure characteristics of the resulting bridge devices in situ and relate these to the structure. We also describe processes to modify the contact and the nanowire surface after device formation. The technique we describe allows the direct analysis of the processes taking place during device formation and use, correlating specific nanoscale structural and electrical parameters on an individual device basis.