Multidisciplinary characterization of U(VI) sequestration by Acidovorax facilis for bioremediation purposes.

The contamination of the environment by U may affect plant life and consequently may have an impact on animal and human health. The present work describes U(VI) sequestration by Acidovorax facilis using a multidisciplinary approach combining wet chemistry, transmission electron microscopy, and spectroscopy methods (e.g. cryo-time resolved laser-induced fluorescence spectroscopy, extended X-ray absorption fine structure spectroscopy, and in-situ attenuated total reflection Fourier transform infrared spectroscopy). This bacterial strain is widely distributed in nature including U-contaminated sites. In kinetic batch experiments cells of A. facilis were contacted for 5 min to 48 h with 0.1 mM U(VI). The results show that the local coordination of U species associated with the cells depends upon time contact. U is bound mainly to phosphate groups of lipopolysaccharide (LPS) at the outer membrane within the first hour. And, that both, phosphoryl and carboxyl functionality groups of LPS and peptidoglycan of A. facilis cells may effectuate the removal of high U amounts from solution at 24-48 h of incubation. It is clearly demonstrated that A. facilis may play an important role in predicting the transport behaviour of U in the environment and that the results will contribute to the improvement of bioremediation methods of U-contaminated sites.

The specific sorption of Np(V) on the corundum (α-Al2O3) surface in the presence of trivalent lanthanides Eu(III) and Gd(III): A batch sorption and XAS study.

The sorption of pentavalent neptunium, Np(V), on corundum (α-Al2O3) was investigated in the absence and presence of trivalent europium or gadolinium as a competing element under CO2-free conditions. The objective of this study was to investigate how a trivalent metal ion with a higher charge than that of the neptunyl(V) ion would affect the sorption of Np(V) when allowed to adsorb on the mineral surface before the addition of Np(V). Batch sorption experiments conducted as a function of pH (pH-edges) and as a function of Np(V) concentration (isotherms) in the absence and presence of 1×10(-5)M Eu(III) showed no sign of Eu being able to block Np sorption sites. Surface complexation modelling using the diffuse double layer model was applied to the batch data to obtain surface complexation constants for the formed Np(V) complexes on corundum. To account for potential changes occurring in the coordination environment of the neptunium ion in the presence of a trivalent lanthanide, X-ray absorption spectroscopy (XAS) measurements were carried out on the samples containing only Np(V) and Np(V)+Gd(III). The results reveal the presence of a bidentate Np(V) edge-sharing complex on the corundum surface in the absence of Gd(III), while the coordination environment of Np(V) on the corundum surface could be changed when Gd(III) is added to the sample before the sorption of Np(V).

A generalized functional response for predators that switch between multiple prey species.

We develop a theory for the food intake of a predator that can switch between multiple prey species. The theory addresses empirical observations of prey switching and is based on the behavioural assumption that a predator tends to continue feeding on prey that are similar to the prey it has consumed last, in terms of, e.g., their morphology, defences, location, habitat choice, or behaviour. From a predator's dietary history and the assumed similarity relationship among prey species, we derive a general closed-form multi-species functional response for describing predators switching between multiple prey species. Our theory includes the Holling type II functional response as a special case and makes consistent predictions when populations of equivalent prey are aggregated or split. An analysis of the derived functional response enables us to highlight the following five main findings. (1) Prey switching leads to an approximate power-law relationship between ratios of prey abundance and prey intake, consistent with experimental data. (2) In agreement with empirical observations, the theory predicts an upper limit of 2 for the exponent of such power laws. (3) Our theory predicts deviations from power-law switching at very low and very high prey-abundance ratios. (4) The theory can predict the diet composition of a predator feeding on multiple prey species from diet observations for predators feeding only on pairs of prey species. (5) Predators foraging on more prey species will show less pronounced prey switching than predators foraging on fewer prey species, thus providing a natural explanation for the known difficulties of observing prey switching in the field.

Biosorption of U(VI) by the green algae Chlorella vulgaris in dependence of pH value and cell activity.

Biosorption of uranium(VI) by the green alga Chlorella vulgaris was studied at varying uranium concentrations from 5 µM to 1mM, and in the environmentally relevant pH range of 4.4 to 7.0. Living cells bind in a 0.1mM uranium solution at pH 4.4 within 5 min 14.3 ± 5.5 mg U/g dry biomass and dead cells 28.3 ± 0.6 mg U/g dry biomass which corresponds to 45% and 90% of total uranium in solution, respectively. During 96 h of incubation with uranium initially living cells died off and with 26.6 ± 2.1 mg U/g dry biomass bound similar amounts of uranium compared to dead cells, binding 27.0 ± 0.7 mg U/g dry biomass. In both cases, these amounts correspond to around 85% of the initially applied uranium. Interestingly, at a lower and more environmentally relevant uranium concentration of 5 µM, living cells firstly bind with 1.3 ± 0.2 mg U/g dry biomass to 1.4 ± 0.1 mg U/g dry biomass almost all uranium within the first 5 min of incubation. But then algal cells again mobilize up to 80% of the bound uranium during ongoing incubation in the time from 48 h to 96 h. The release of metabolism related substances is suggested to cause this mobilization of uranium. As potential leachates for algal-bound uranium oxalate, citrate and ATP were tested and found to be able to mobilize more than 50% of the algal-bound uranium within 24h. Differences in complexation of uranium by active and inactive algae cells were investigated with a combination of time-resolved laser-induced fluorescence spectroscopy (TRLFS), extended X-ray absorption fine structure (EXAFS) spectroscopy and attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy. Obtained results demonstrated an involvement of carboxylic and organic/inorganic phosphate groups in the uranium complexation with varying contributions dependent on cell status, uranium concentration and pH.

The top-down mechanism for body-mass-abundance scaling.

Scaling relationships between mean body masses and abundances of species in multitrophic communities continue to be a subject of intense research and debate. The top-down mechanism explored in this paper explains the frequently observed inverse linear relationship between body mass and abundance (i.e., constant biomass) in terms of a balancing of resource biomasses by behaviorally and evolutionarily adapting foragers, and the evolutionary response of resources to this foraging pressure. The mechanism is tested using an allometric, multitrophic community model with a complex food web structure. It is a statistical model describing the evolutionary and population dynamics of tens to hundreds of species in a uniform way. Particularities of the model are the detailed representation of the evolution and interaction of trophic traits to reproduce topological food web patterns, prey switching behavior modeled after experimental observations, and the evolutionary adaptation of attack rates. Model structure and design are discussed. For model states comparable to natural communities, we find that (1) the body-mass abundance scaling does not depend on the allometric scaling exponent of physiological rates in the form expected from the energetic equivalence rule or other bottom-up theories; (2) the scaling exponent of abundance as a function of body mass is approximately -1, independent of the allometric exponent for physiological rates assumed; (3) removal of top-down control destroys this pattern, and energetic equivalence is recovered. We conclude that the top-down mechanism is active in the model, and that it is a viable alternative to bottom-up mechanisms for controlling body-mass-abundance relations in natural communities.

Estimating trophic link density from quantitative but incomplete diet data.

The trophic link density and the stability of food webs are thought to be related, but the nature of this relation is controversial. This article introduces a method for estimating the link density from diet tables which do not cover the complete food web and do not resolve all diet items to species level. A simple formula for the error of this estimate is derived. Link density is determined as a function of a threshold diet fraction below which diet items are ignored ("diet partitioning function"). Furthermore, analytic relationships between this threshold-dependent link density and the generality distribution of food webs are established. A preliminary application of the method to field data suggests that empirical results relating link density to diversity might need to be revisited.

Food webs: experts consuming families of experts.

Food webs of habitats as diverse as lakes or desert valleys are known to exhibit common "food-web patterns", but the detailed mechanisms generating these structures have remained unclear. By employing a stochastic, dynamical model, we show that many aspects of the structure of predatory food webs can be understood as the traces of an evolutionary history where newly evolving species avoid direct competition with their relatives. The tendency to avoid sharing natural enemies (apparent competition) with related species is considerably weaker. Thus, "experts consuming families of experts" can be identified as the main underlying food-web pattern. We report the results of a systematic, quantitative model validation showing that the model is surprisingly accurate.

Observation of stable phase jump lines in convection of a twisted nematic liquid crystal.

We report observations of stable, localized, linelike structures in the spatially periodic pattern formed by nematic electroconvection, along which the phase of the pattern jumps by pi. With increasing electric voltage, these lines form a gridlike structure that goes over into a structure indistinguishable from the well-known grid pattern. We present theoretical arguments that suggest that the twisted cell geometry we are using is indirectly stabilizing the phase jump lines, and that the phase jump lines lattice is caused by an interaction of phase jump lines and a zig-zag instability of the surrounding pattern.

Some properties of the speciation model for food-web structure-mechanisms for degree distributions and intervality.

We present a mathematical analysis of the speciation model for food-web structure, which had in previous work been shown to yield a good description of empirical data of food-web topology. The degree distributions of the network are derived. Properties of the speciation model are compared to those of other models that successfully describe empirical data. It is argued that the speciation model unifies the underlying ideas of previous theories. In particular, it offers a mechanistic explanation for the success of the niche model of Williams and Martinez and the frequent observation of intervality in empirical food webs.

Comparative EXAFS investigation of uranium(VI) and -(IV) aquo chloro complexes in solution using a newly developed spectroelectrochemical cell.

The coordination of the U(IV) and U(VI) ions as a function of the chloride concentration in aqueous solution has been studied by U L(III)-edge extended X-ray absorption fine structure (EXAFS) spectroscopy. The oxidation state of uranium was changed in situ using a gastight spectroelectrochemical cell, specifically designed for the safe use with radioactive solutions. For U(VI) we observed the complexes UO2(H2O)5(2+), UO2(H2O)4Cl+, UO2(H2O)3Cl2(0), and UO2(H2O)2Cl3- with [Cl-] increasing from 0 to 9 M, and for U(IV) we observed the complexes U(H2O)9(4+), U(H2O)8Cl3+, U(H2O)(6-7)Cl2(2+), and U(H2O)5Cl3+. The distances in the U(VI) coordination sphere are U-Oax = 1.76+/-0.02 A, Oeq = 2.41 +/- 0.02 A, and U-Cl = 2.71 +/- 0.02 A; the distances in the U(IV) coordination sphere are U-O = 2.41 +/- 0.02 A and U-Cl = 2.71 +/- 0.02 A.

Phase synchronization from noisy univariate signals.

We present methods for detecting phase synchronization of two unidirectionally coupled, self-sustained noisy oscillators from a signal of the driven oscillator alone. One method detects soft phase locking; another hard phase locking. Both are applied to the problem of detecting phase synchronization in von Kármán vortex flow meters.

Evidence for the interaction of technetium colloids with humic substances by X-ray absorption spectroscopy.

Spectroscopic extended X-ray absorption fine structure (EXAFS) evidence was obtained on the chemical environment of 99Tc(IV) atoms formed upon introduction of TcO4- into four types of laboratory-scale synthetic and natural systems which mimic in situ natural reducing conditions in humic-rich geochemical environments: (a) magnetite/pyrite in synthetic groundwater in the absence of humic substances (HSs), (b) magnetite/pyrite in natural Gorleben groundwater in the presence of HSs, (c) Boom clay sediment mixed with synthetic groundwater, and (d) Gorleben sand mixed with natural Gorleben groundwater. The investigated systems obey to pH 8-9 conditions, and all measured samples show similar EXAFS spectra for Tc, which could be fitted by a hydrated TcO2 x xH2O phase. The results are interpreted as follows: upon introduction of high concentrations (millimolar to micromolar) of TcO4-to chemically reducing environments, small Tc(IV) oxidic polymers are formed, which either may aggregate into larger units (colloids) and finally precipitate or may interact in their polymeric form with (dissolved and immobile) humic substances. This latter type of interaction--Tc(IV) colloid sorption onto HSs--differs significantly from the generally accepted metal--humate complexation and therefore offers new views on the possible reaction pathways of metals and radionuclides in humic-rich environments.

Time-resolved laser fluorescence spectroscopy study on the interaction of curium(III) with Desulfovibrio äspöensis DSM 10631T.

The influence of microorganisms on migration processes of actinides has to be taken into account for the risk assessment of potential high-level nuclear waste disposal sites. Therefore it is necessary to characterize the actinide-bacteria species formed and to elucidate the reaction mechanisms involved. This work is focused on the sulfate-reducing bacterial (SRB) strain Desulfovibrio äspöensis (D. äspöensis) DSM 10631T which frequently occurs in the deep granitic rock aquifers at the Aspö Hard Rock Laboratory (Aspö HRL), Sweden. We chose Cm(III) due to its high fluorescence spectroscopic sensitivity as a model system for exploring the interactions of trivalent actinides with D. äspöensis in the trace concentration range of 3 x 10(-7) mol/L. A time-resolved laser fluorescence spectroscopy (TRLFS) study has been carried out in the pH range from 3.00 to 7.55 in 0.154 mol/L NaCl. We interpret the pH dependence of the emission spectra with a biosorption forming an inner-sphere surface complex of Cm(III) onto the D. äspöensis cell envelope. This Cm(III)-D. äspöensis-surface complex is characterized by its emission spectrum (peak maximum at 600.1 nm) and its fluorescence lifetime (162 +/- 5 micros). No evidence was found for incorporation of Cm(III) into the bacterial cells under the chosen experimental conditions.

Data-driven optimal filtering for phase and frequency of noisy oscillations: Application to vortex flow metering.

A method for measuring the phase of oscillations from noisy time series is proposed. To obtain the phase, the signal is filtered in such a way that the filter output has minimal relative variation in the amplitude over all filters with complex-valued impulse response. The argument of the filter output yields the phase. Implementation of the algorithm and interpretation of the result are discussed. We argue that the phase obtained by the proposed method has a low susceptibility to measurement noise and a low rate of artificial phase slips. The method is applied for the detection and classification of mode locking in vortex flow meters. A measure for the strength of mode locking is proposed.

Complexation of uranium(VI) with protocatechuic acid-application of iterative transformation factor analysis to EXAFS spectroscopy.

The speciation of 1 mM uranium(VI) in carbonate-free aqueous solutions of 50 mM protocatechuic acid (PCA, 3,4-dihydroxybenzoic acid) was studied in the pH range of 4.0 to 6.8 using EXAFS spectroscopy. The uranium L(III)-edge EXAFS spectra were analyzed using a newly developed computer algorithm for iterative transformation factor analysis (FA). Two structural different uranium(VI) complexes were observed. The speciation in the pH range of 4.0 to 4.8 is dominated by a 1:2 or 1:3 uranium(VI)/PCA complex with bidentate coordination of the carboxyl group to the uranium(VI) moiety. Already at pH 4.6 significant amounts of a second species are formed. This uranium(VI) species contains two PCA ligands that are bound to the uranium via their neighboring phenolic hydroxyl groups under formation of five-member rings.

Molecular and atomic analysis of uranium complexes formed by three eco-types of Acidithiobacillus ferrooxidans.

A combination of EXAFS, transmission electron microscopy and energy-dispersive X-ray was used to conduct a molecular and atomic analysis of the uranium complexes formed by Acidithiobacillus ferrooxidans. The results demonstrate that this bacterium accumulates uranium as phosphate compounds. We suggest that at toxic levels when the uranium enters the bacterial cells, A. ferrooxidans can detoxify and efflux this metal by a process in which its polyphosphate bodies are involved.

EXAFS as a tool for bond-length determination in the environment of heavy atoms.

Single crystal X-ray diffraction measurements are complicated in the presence of heavy atoms. In these cases the structure factors are mainly influenced by the heavy scatterers and the error in determination of atomic coordinates increases for light atoms. The difficulties grow if the unit cell dimensions or the space group symmetry remain uncertain. If the structure model is similar to the correct structure, it is difficult to find an independent criterion for the accuracy of the bond-length determination. We demonstrate that extended X-ray absorption fine structure (EXAFS) spectroscopy is a useful tool for the investigation of local bond lengths in the environment of heavy atoms.

Do perchlorate and triflate anions bind to the uranyl cation in an acidic aqueous medium? A combined EXAFS and quantum mechanical investigation.

Structural properties of uranyl cations in acidic aqueous perchlorate and triflate solutions were investigated using uranium LIII -edge extended X-ray absorption fine-structure spectroscopy (EXAFS) in conjunction with quantum mechanical calculations of gas-phase model complexes. EXAFS spectra were measured in aqueous solutions of up to 10 M triflic and 11.5 M perchloric acid, as well as mixtures of perchloric acid and sodium perchlorate. In no case is the perchlorate anion coordinated to UO2(2+). The number of equatorial water molecules bound to UO2(2+) is always about five. In the case of the 10 M CF3SO3H solution, an inner-sphere complexation of the triflate is observed with a U-S radial distance of 3.62 Å. These results are in qualitative agreement with quantum mechanical calculations of model uranyl complexes, according to which the interaction energies of anions follow the order perchlorate

[Laparoscopic laser cholecystectomy]. / Laparoskopische Lasercholezystektomie.

In an ex vivo- and an animal study a Holmium-YAG laser, a Nd:YAG laser and a CO2 laser were examined. For laparoscopic cholecystectomy the pulsed Holmium:YAG laser proved to be the best instrument. Dissecting and haemostatic effects were connected when working with a power of 4 watts. Dissected area per minute was 112 mm2, gallbladder dissection (15 cm2) can be performed in 13 min. In the animal study the cholecystectomy lasted 30 min on average when the Holmium:YAG laser was used. Bleeding was not observed, development of smoke was tolerable.