Radioactive Tracer Technique Research Articles

Characterization of arginine transport in Helicobacter pylori.

The amino acid L-arginine is an essential requirement for growth of Helicobacter pylori. Several physiological roles of this amino acid have been identified in the bacterium, but very little is known about the transport of L-arginine and of other amino acids into H. pylori. Radioactive tracer techniques using L-(U-14C) arginine and the centrifugation through oil method were employed to measure the kinetic parameters, temperature dependence, substrate specificity, and effects of analogues and inhibitors on L-arginine transport. The transport of arginine at millimolar concentrations was saturable with a Km of 2.4+/ 0.3 mM and Vmax of 1.3+/-0.2 pmole min(-1) (microl cell water)(-1) or 31+/-3 nmole per minute (mg protein)(-1) at 20 degrees C, depended on temperature between 4 and 40 degrees C, and was susceptible to inhibitors. These characteristics suggested the presence of one or more arginine carriers. The substrate specificity of the transport system was studied by measuring the effects of L-arginine analogues and amino acids on the rates of transport of L-arginine. The absence of inhibition in competition experiments with L-lysine and L-ornithine indicated that the transport system was not of the Lysine-Arginine-Ornithine or Arginine-Ornithine types. The presence of different monovalent cations did not affect the transport rates. Several properties of L-arginine transport were elucidated by investigating the effects of potential inhibitors. The results provided evidence that the transport of L-arginine into H. pylori cells was carrier-mediated transport with the driving force supplied by the chemical gradient of the amino acid.

Application of a radioactive tracer method to copper migration in Semiconductor Lithography

Radioactive tracer technique was applied to examine the migration of Cu impurity from ArF and KrF photoresists onto silicon-based underlying substrates of Si(100), Si(110), Si(111), poly-Si, SiO2 and Si3N4. The effects of the polymer constituent in the photoresists and the baking temperature were studied. Results showed that the migration ratio of Cu from ArF photoresist was always exceeded that from KrF photoresist, independently of the substrate types and baking temperatures. The benzene ring in the KrF photoresist confined the Cu migration, while the alicyclic constituent in the ArF photoresist could not. The migration process of Cu from the bulk region into the interface region was discussed. The residual solvent in the bulk region influenced the Cu migration. The electronegativity of Cu explained the accumulation of Cu on wafer surface. Simple diffusion model was tried to explain the migration ratios, but the model did not explain it well due to the change of the photoresist medium during baking. A correlation function was proposed to modify the diffusion coefficient for describing the experimental observation of migration ratios.

Influence of Ru 3+ ions at Al 2O 3/GaAs interface on MIS structures

In addition to better electronic properties than silicon, gallium arsenide exhibits interesting optical properties. It is possible to realize the integration of both electronic and optical functions on the same GaAs wafer. However, its interfacial properties limit the use of GaAs for electronic devices (MIS, MESFET, etc.) [Electron. Technol. 27 (2) (1994) 69; J. Electron. Mater. 31 (1) (2002) 71]. Heller [U.S. Patent 4 (1981) 213] has proposed chemical treatments of GaAs surface by selenide and ruthenium solutions that induce an increase in electrochemical photocell yield. Two alternative explanations have been proposed to account for this effect: the first is by Heller [Acc. Chem. Res. 14 (1981) 154] who has assumed a decrease in surface states density and the second is by Aspnes [Surf. Sci. 132 (1983) 406] who has assumed a shift in surface Fermi level. Our result, using MIS structures as test (on untreated and treated surfaces) of interface quality is in a good agreement with Aspnes' proposal. We have found in fact that Heller's treatment shifts surface Fermi level to valence band and increases the surface state density. We assume that a generation recombination process that can probably be produced in the space charge region accounts for the observed kinetics of these states, which behave as hole traps. The fraction of a monolayer of ruthenium has been evidenced by means of radioactive tracer technique. We have concluded that these treatments do not improve MIS behavior. The main interest of this treatment remains the enhancement of electronic transfer kinetics at GaAs electrolyte solution interface.

Airway clearance: assessment of techniques.

Mucus hypersecretion and retention of mucus are common in patients with pulmonary disease. In order to reduce mucus retention, airway clearance techniques are used. The most commonly used outcome parameter in clinical situations--pulmonary function testing--is probably not very useful. For research purposes measurement of the transport rate of mucus in the airway using a radioactive tracer technique is probably the most direct outcome parameter. The course and progression of the disease could be used as long-term outcome parameters.

Incorporation of Cr in the passive film on Fe from chromate solutions

The uptake of Cr species from chromate solutions by Fe has been studied using X-ray absorption near edge structure (XANES). The objective of the investigation was to compare XANES with radioactive tracer techniques used by Brasher et al. Cr(III) was detected on the passive iron surface. The amount of Cr(III) was increased by cathodic polarization and decreased by anodic polarization. This demonstrated that the uptake of Cr(III) was the result of cathodic processes and was not a direct result of the growth of the passive oxide film. Cr(VI) was only found after Fe was exposed to a saturated dichromate solutions for extended periods indicating that Cr(VI) was not strongly absorbed on the passive film.

Removal of 137Cs from aqueous solutions using different cationic forms of a natural zeolite: clinoptilolite

Abstract Distribution coefficients of cesium on natural and cation-enriched (Na+, K+, NH4+ and Ca+2) forms of clinoptilolite were measured by batch, radioactive tracer technique. The measurements were carried out for an initial cesium concentration range of 10−6–10−1 mol/dm3 and at temperatures of 25, 40, 60 and 80 °C. Experimental isotherms evaluated from distribution coefficients were fit to Langmuir, Freundlich and Dubinin-Radushkevich (D-R)models. Of the models tested, D-R model was found to represent the isotherms better in a wider range of concentrations than either Langmuir or Freundlich model. Breakthrough behavior of cesium on natural and cation-enriched forms of clinoptilolite for a particular set of conditions were also determined in a small size column. Column parameters were evaluated using mass transfer zone concept.

Rapid turnover of dissolved DMS and DMSP by defined bacterioplankton communities in the stratified euphotic zone of the North Sea

Bacterioplankton-driven turnover of the algal osmolyte, dimethylsulphoniopropionate (DMSP), and its degradation product, dimethylsulphide (DMS) the major natural source of atmospheric sulphur, were studied during a Lagrangian SF6-tracer experiment in the North Sea (60°N, 3°E). The water mass sampled within the euphotic zone was characterised by a surface mixed layer (from 0 m to 13–30 m) and a subsurface layer (from 13–30 m to 45–58 m) separated by a 2°C thermocline spanning 2 m. The fluxes of dissolved DMSP (DMSPd) and DMS were determined using radioactive tracer techniques. Rates of the simultaneous incorporation of 14C-leucine and 3H-thymidine were measured to estimate bacterioplankton production. Flow cytometry was employed to discriminate subpopulations and to determine the numbers and biomass of bacterioplankton by staining for nucleic acids and proteins. Bacterioplankton subpopulations were separated by flow cytometric sorting and their composition determined using 16S ribosomal gene cloning/sequencing and fluorescence in situ hybridisation with designed group-specific oligonucleotide probes. A subpopulation, dominated by bacteria related to Roseobacter-(α-proteobacteria), constituted 26–33% of total bacterioplankton numbers and 45–48% of biomass in both surface and subsurface layers. The other abundant prokaryotes were a group within the SAR86 cluster of γ-proteobacteria and bacteria from the Cytophaga–Flavobacterium—cluster. Bacterial consumption of DMSPd was greater in the subsurface layer (41 nM d−1) than in the surface layer (20 nM d−1). Bacterioplankton tightly controlled the DMSPd pool, particularly in the subsurface layer, with a turnover time of 2 h, whereas the turnover time of DMSPd in the surface layer was 10 h. Consumed DMSP satisfied the majority of sulphur demands of bacterioplankton, even though bacterioplankton assimilated only about 2.5% and 6.0% of consumed DMSPd sulphur in the surface and subsurface layers, respectively. Bacterioplankton turnover of DMS was also faster in the subsurface layer (12 h) compared to the surface layer (24 h). However, absolute DMS consumption rates were higher in the surface layer, due to higher DMS concentrations in this layer. The majority of DMS was metabolised into dissolved non-volatile products, and bacteria could satisfy only 1–3% of their sulphur demands from DMS. Thus, structurally similar bacterioplankton communities exerted strong control over DMSPd and DMS concentrations both in the subsurface layer and surface mixed layer.

Sorption of tin on human teeth.

The sorption of tin ions on human teeth from water and other drinks has been studied by the radioactive tracer technique using the isotope 113Sn (T(1/2) = 115.1 d) as a tracer. The tooth holds a minimum amount of tin from coffee and a maximum amount is held from water and from tea with sugar. The same technique was also used to study the desorption of tin already taken up on the teeth. It has been found that sorbed tin is hardly desorbed from the teeth specimens. The high uptake of tin on human teeth from various drinks showed that teeth act as a natural sieve holding trace elements.

The extraction of low-concentrations of gold(I) with 198Au as a radiotracer

The solvent extraction of gold from alkaline cyanide solution was studied by using 198Au as a radiotracer. The influence of several variables on the gold extraction, including the concentration of gold, the molar ratio of extractants to gold(I), the volume percentage of cosolvent and the pH value of the aqueous phase, was investigated. The results indicated that the radioactive tracer technique is a quick, accurate, and convenient tool to investigate the extraction behavior of an element existing in low concentrations. The experimental results indicated that the studied amines, tetradecyldimethylbenzylammonium chloride, N1923 and tri-n-octylamine, could be used as extractants for the recovery of gold from aqueous alkaline cyanide solutions.

5 NMR studies of self-diffusion in liquids

A multitude of physical, chemical and biological processes are affected by diffusive mass transfer, and there are not many topics like diffusion that are dealt with in so many different contexts. Diffusion takes place in any state of aggregation, covering typical time scales of the underlying molecular processes from picoseconds to ages. This review deals with nuclear magnetic resonance (NMR) studies of diffusive motions and some closely related transport processes in liquids, updating and extending a preceding review in this series. In the absence of external forces, the displacements of the particles result from their thermal agitation. This is an incoherent process leading to random motions of the particles in any state of aggregation. Nowadays, this process is usually denoted as selfdiffusion. It may however be noted that even in the limited field of liquid diffusion, different scientific communities have developed their own terminology 3,4 which may differ from that used here.† NMR spin-echo experiments provide a series of methods for studying translational motions in liquids by energy-, timeand spatially-resolved experiments. Their main advantages over other methods are, for example, fast experiments, small sample volumes, and easy applications over wide ranges of temperature and pressure. Other experimental methods such as isotopic (radioactive or stable) tracer techniques, still extensively used in the 1970s and 1980s, have almost completely disappeared from the scene. In simple molecular liquids of low viscosity, diffusive processes are associated with particle displacements per second of the order of 10 –10 5 m. In this case a particle needs about 10 11 s to travel a distance of the order of a molecular diameter. This is the typical range of routine measurements by NMR spin-echo techniques. In highly viscous and supercooled liquids near the glass transition, such diffusive processes can,

Availability of cadmium and zinc from sewage sludge to the flounder, Platichthys flesus, via a marine food chain

This paper examines the potential availability to a demersal fish of cadmium and zinc associated with digested sewage sludge, via a food chain as well as directly from the sludge, and the tissue distribution and possible excretion of any accumulated cadmium and zinc. Radioactive tracer techniques were used in order to follow the food chain transfer of the metals. Flounder (Platichthys flesus) accumulated cadmium both directly from sludge (delivered in newly ingested unassimilated gutfuls in the amphipods) and in assimilated form from the tissues of the amphipod crustacean Corophium volutator that had been feeding on a sludge–sediment mixture. Cadmium from both sources could be excreted by the fish. The concentration of cadmium within the whole fish increased as the input of cadmium in the diet increased. Zinc, similarly, is available to the flounder both directly from sludge and from zinc accumulated in C. volutator. Only a limited increase in net accumulation of zinc by the flounder was observed upon increased inputs of zinc through the diet, perhaps indicating some regulation of body zinc concentration by the flounder.

Characterization and modeling of the metal diffusion from deep ultraviolet photoresist and silicon-based substrate

The radioactive tracer technique was applied to investigate the out-diffusion of the transition metals (Cu, Fe and Co) from deep ultraviolet (DUV) photoresist into underlying substrate. Two important process parameters, viz., baking temperatures and substrate types (i.e., bare silicon, polysilicon, silicon oxide and silicon nitride), were evaluated. Results indicate that the out-diffusion of Co is insignificant, irrespective of the substrate type and baking temperature. The out-diffusion of Cu is significant for substrates of bare silicon and polysilicon but not for silicon oxide and nitride; for Fe, the story is reversed. The substrate type appears to strongly affect the diffusion, while the baking temperature does not. Also, the effect of solvent evaporation was found to play an important role in impurity diffusion. Using the method of numerical analysis, a diffusion profile was depicted in this work to describe the out-diffusion of metallic impurities from photoresist layer under various baking conditions. In addition, the effectiveness of various wet-cleaning recipes in removing metallic impurities such as Cu, Fe and Co was also studied using the radioactive tracer technique. Among the six cleaning solutions studied, SC2 and SPM are the most effective in impurity removal. An out-diffusion cleaning model was first proposed to describe the cleaning process. A new cleaning coefficient, h( T), was suggested to explain the cleaning effect. The cleaning model could explain the tracer results.

Extraction of Americium(III) and Europium(III) with Two Open-Chain Crown Ethers of Amide Type

The extraction of Am3+ and Eu3+ from aqueous picric acid solution by N, N′-dinaphthyl-N, N′-diphenyl-3,6-dioxaoctanediamide (LI) and 1, 1′-(3, 6, 9-trioxaundecanedionyl)diphenothiazine (LII) was investigated by a radioactive tracer technique. Extraction distribution ratios of Am3+ and Eu3+ have been measured as a function of pH, picric acid concentration, extractant concentration, diluent and temperature. The extraction of Am3+ is preferred to that of Eu3+ for both LI and LII, and the latter gives larger separation factor than the former. The equilibrium constants and thermodynamic parameters of extraction reactions were also calculated.

Digestion of bacterial macromolecules by a mixotrophic flagellate, Ochromonas sp., compared with that by two heterotrophic flagellates, Spumella pudica and Bodo saltans

Digestion of bacterial biomass by three species of phagotrophic flagellates was studied using radioactive tracer techniques and short-term feeding experiments. Macromolecules of two different bacterial strains and natural limnic bacterioplankton were pulse-chase-labelled with one of the following precursors 3H-thymidine, 35S-/14C-methionine or 14C-leucine, before bacteria were fed to flagellates and radioactive labels were traced into flagellate macromolecules. The concentrations of prey and predators were monitored by flow cytometry. The aim of the work was to compare efficiencies of bacterial macromolecule accumulation by mixotrophic (Ochromonas) and heterotrophic (Spumella and Bodo) flagellates. We observed that flagellate accumulation efficiency of bacterial macromolecules labelled with thymidine (mean 15–30%, depending on flagellate species) was lower than of bacterial macromolecules labelled with amino acids (mean 26–68%). Heterotrophic flagellate species had similar accumulation efficiencies of bacterial molecules, when either leucine (26–42%) or methionine (31–41%) was used as a tracer. In contrast the mixotrophic flagellate accumulated significantly more residues of labelled methionine (68%) than of labelled leucine (54%). Methionine seems to be accumulated as an intact molecule and possibly Ochromonas preferentially accumulated methionine as an additional source of reduced sulphur. Protozoan accumulation efficiencies did not differ significantly whether the pulse-labelled bacterial prey were from growing or long-term starvation cultures. Our results suggest that labelled amino acids are more appropriate than labelled thymidine for studying transfer of bacterial biomass within food webs.

Migration‐Adsorption Mechanism of Metallic Impurities out of Chemically Amplified Photoresist onto Silicon‐Based Substrates

The radioactive tracer technique was applied to investigate the migration and adsorption behaviors of metallic impurities (i.e., Ba, Cs, Zn, and Mn) out of chemically amplified photoresist onto silicon‐based underlying substrates. Two important process parameters, i.e., baking temperatures and substrate types (e.g., bare silicon, polysilicon, oxide, and nitride) were evaluated. Our results indicated that the transition metals (Zn and Mn) have lower migration ratios than alkali metal (Cs) and alkaline earth metal (Ba), irrespective of the substrate types and baking temperatures. The transition metals form stable complexes with the coexisting solvents and/or hydrolysis species in the photoresist layer. The size of the metal complex, the drag force in solvent evaporation, and the baking process were found to have significant effects on impurity migration. A new model, together with the metal migration in the chemically amplified photoresist and the subsequent adsorption onto the underlying substrate, was proposed to explain the pathway of the metal migration. This model could explain the migration ratios of metallic impurities out of the photoresist layer onto the substrate surface. © 2000 The Electrochemical Society. All rights reserved.

Evaluation of cleaning efficiency with a radioactive tracer and development of a microwave digestion method for semiconductor processes

A radioactive tracer technique was applied to investigate the effectiveness of various wet cleaning recipes in removing metallic impurities such as sodium, iron and cesium. The effects of solution temperatures and substrate types were studied. The mechanisms of the electrochemical segregation of metallic impurities between the substrate and cleaning solution were examined. The enthalpy of oxide formation and the effect of adsorption were the two reasons for the presence of surface metal impurities in the cleaning solutions. Our results indicated that SC2 and DHF can effectively remove the metallic impurities at 47 and 82°C, while SPM and BOE are only effective at 82°C. The gravimetric method was successfully implemented to evaluate the open-focused microwave digestion efficiency for anti-reflective coating and photoresist (PR) samples. By following the established microwave digestion method and inductively coupled plasma mass spectrometric determination, the detection limits (DLs) obtained for multi-elements were in the ng ml −1 and sub-ng ml −1 levels. Except for calcium, the spike recoveries of the metals were in the range 82–121% for the lithographic samples. The analytical results were found to be in reasonably good agreement with literature values, and the lithographic sample throughput can achieve up to 3.5 samples per hour for the analysis of 13 elements.

Evaluation of Metal Migration and Determination of Trace Metals after Microwave Digestion for Lithographic Materials

The radioactive tracer technique was applied to investigate the migration of cesium and zinc impurities from bottom antireflective coating (BARC) and photoresist (PR) into underlying substrate. The effects of normal baking temperatures and substrate types were studied. Our results indicated that BARC has higher migration ratios than PR, irrespective of the substrate types and normal baking temperatures. The substrate type did not appear to strongly affect the metal migration ratios. However, water and/or solvent evaporation due to temperature change was found to have a significant effect on metal migration. The diffusion profiles of BARC and PR were depicted based on diffusion equations and the migration ratios. Both the UV/visible spectrometric and the gravimetric methods were successfully implemented to evaluate the feasibility of closed-vessel microwave digestion efficiency for BARC and PR samples. By following the established microwave digestion method and the inductively coupled plasma mass spectrometer (ICPMS) determination, the detection limits obtained for multielements were in the ppb and sub-ppb levels. Except for calcium, the spike recoveries of metals ranged from 91 to 132% and 87 to 125% for BARC and PR, respectively. The analytical results were found to be in reasonably good agreement with the literature values.

CFD modeling of flow, macro‐mixing and axial dispersion in a bubble column

AbstractThe flow pattern in a bubble column depends upon the column diameter, height, sparger design, superficial gas velocity and the nature of gas–liquid system. In this paper, the effect of some of these parameters have been simulated using Computational Fluid Dynamics (CFD). The relationship of these parameters with the interphase force terms has been discussed. A complete energy balance has been established. Using this methodology, the flow patterns reported by Hills (1974), Menzel et al. (1990), Yao et al. (1991) and Yu and Kim (1991) have been simulated. Excellent agreement has been shown between the CFD predictions and the experimental observations. The above model has been extended to homogenization of an inert tracer. In order to confirm this model, mixing experiments were carried out in a 200 mm i.d. bubble column. A radioactive tracer technique was used for the measurement of mixing time. Tc‐99m (99m Tc), in the form of sodium pertechnate salt, was used as the liquid phase tracer. Good agreement has been shown between the predicted and the experimental values of mixing time. The model was further extended for the estimation of axial dispersion coefficient (DL). Excellent agreement between the simulated and the experimental values of the axial dispersion coefficient confirms the predictive capability of the CFD simulations for the mixing process.

Copper Effects on Ion Transport across Lamprey Erythrocyte Membrane: Cl−/OH− Exchange Induced by Cuprous Ions

We studied the effects of prelytic copper concentrations on cell volume, intracellular pH, and ion transport in lamprey erythrocytes. Ion fluxes and pH were measured by radioactive tracer technique, patch clamp, and flame photometry. Prelytic CuSO4 concentration of 100 μM caused anion-dependent intracellular acidification and increase in Cl− influx after 2 min lag-phase. In the presence of ascorbate copper effect was amplified and lag-phase was skipped. Pretreatment of the cells with N-phenyl maleimide abolished copper-induced changes completely. Copper treatment caused an increase in Na+ fluxes in both directions and a net Na+ uptake. Copper-induced Na+ transport was partially amiloride(MIA)-sensitive representing Na+/H+ exchange. The nature of the amiloride-insensitive fraction of copper-activated Na+ influx remains unknown. Cell swelling after 15 min of copper exposure induced regulatory volume decrease response involving KCl extrusion via K+ and Cl− volume-sensitive channels. We suggest that the effects of copper on ion transport fit the following sequence of events: (i) cupric ions are reduced to cuprous state on the membrane surface, (ii) electroneutral pairs CuCl and CuOH mediate chloride/hydroxyl exchange, as shown before for trialkyltin, dissipating transmembrane pH gradient, and (iii) changes in intracellular pH result in the activation of the Na+/H+ exchange and consecutive volume changes cause the RVD response.

Characterization and Modeling of Out‐Diffusion of Manganese and Zinc Impurities from Deep Ultraviolet Photoresist

The radioactive tracer technique was applied to investigate the out‐diffusion of manganese and zinc impurities from deep‐ultraviolet (DUV) photoresist. Two important process parameters, viz., baking temperature and the type of substrate (i.e., bare silicon, polysilicon, oxide, or nitride), were evaluated. Our results indicated that diffusion ratios were all below 6%, irrespective of the substrate type and baking temperature. The substrate type did not appear to strongly affect the metallic impurity out‐diffusion from DUV photoresist. However, solvent evaporation was found to have a significant effect on impurity diffusion. A new model, together with a new parameter, was proposed to describe the out‐diffusion behavior of impurities from DUV photoresist. This model could explain the diffusion ratio of metallic impurities in photoresist layers under various baking conditions. The effectiveness of various wet cleaning recipes in removing metallic impurities such as manganese and zinc was also studied. It was found that (i) bath life due to temperature change can considerably affect the cleaning efficiency, and (ii) hot water immersion can effectively dissolve the impurities from the wafer surface. © 1999 The Electrochemical Society. All rights reserved.