Biogeochemical aspects of aquifer thermal energy storage

During the process of aquifer thermal energy storage the in situ temperature of the groundwater- sediment system may fluctuate significantly. As a result the groundwater characteristics can be considerably affected by a variety of chemical, biogeochemical and microbiological reactions. The interplay of these reactions may have a negative influence on the operational performance of ATES-systems. The objective of this thesis was to investigate bacterial clogging processes and the biogeochemical aspects of carbonate and iron precipitation in aquifer material obtained from ATES test facilities.In the General Introduction presented in Chapter 1 the principle of aquifer thermal energy storage is briefly outlined first. This is followed by more detailed information on the thermodynamics of biogeochemical reactions and the conceivable changes in groundwater characteristics during aquifer thermal energy storage. Chapter 2 reports on some microbiological aspects of well clogging during aquifer thermal energy storage. In column experiments well clogging was simulated using aquifer material from a heat storage site and synthetic groundwater. The well clogging potential of oxic and anoxic column effluents was studied at 10° and 30°C using a hollow fiber membrane from which slime depositions were recovered. Only under oxic conditions a slight increase in slime deposition was observed after a temperature rise from 10° to 30°C. No significant difference in bacterial plate counts was measured in oxic and anoxic column effluents, despite the increase in dissolved organic material concentrations at elevated temperatures. This organic material was mobilized from the soil particular organic carbon fraction. The biologically available organic carbon concentration was less than 1% of the dissolved organic carbon concentration, which was not enough to allow excessive bacterial growth or slime formation. Chapter 3 reports on the thermal mobilization of dissolved organic carbon and the concomitant carbon dioxide production in aquifer material from a heat storage site. These processes have been quantified aerobically and anaerobically within a temperature range of 4° to 95°C in sediment samples containing either quartz-rich coarse sand or peaty clay. At temperatures above 450C dissolved organic carbon compounds, including fulvic acids, were mobilized from both sediments resulting in a substantial increase in the chemical oxygen demand of the water phase. Complexation of calcium and magnesium by fulvic acids resulted in the super -saturation of the water phase with regard to calcite and dolomite and thus prevented the precipitation of these carbonates. The highest rates of carbon dioxide release were measured during the first four days of incubation. Aerobically, the maximum rate Of C0 2 production varied between 35 and 800 (sand) or 15 and 150 (peaty clay) μmol C0 2 per gram volatile solids per day. Anaerobically, the rates were 25 and 500 (sand) or 10 and 110 (peaty clay) μmol C0 2 per gram volatile solids per day. At temperatures above 55°C, C0 2 was produced purely chemically. Chapter 4 deals with ferric iron precipitation in anaerobic Tris-HCl buffered seawater. In these incubations,40 mM lactate was rapidly dissimilated to acetate by sulphate reducing bacteria after a lag period of three days. In presence of added nitrate or ferric iron (both 1 mM) or a combination of both, the initial lactate consumption rate was slowed down and sulphate reduction started after four days at a similar rate as was observed in the absence of nitrate and ferric iron. Nitrate in combination with ferrous iron totally inhibited sulphate reduction. Some lactate was initially oxidized, but its concentration did not change after day six of incubation. In these incubations ferrous iron was oxidized chemically to ferric iron with a concomitant reduction of nitrite to nitric oxide. In this so-called chemodenitrification process, nitrite was formed biologically from nitrate with lactate as a reductant. In Chapter 5 chemodenitrification was studied in details with E.coliE4as a model bacterium. Both, L-lactate-driven nitrate and ferric iron reduction were investigated. Ferric iron reduction in E.coliE4was found to be constitutive. Contrary to nitrate, ferric iron could not be used as an electron acceptor for growth. Ferric iron reductase activity of 9 nmol Fe 2+.mg -1protein.min -1could not be inhibited by well known inhibitors of the E.coli respiratory chain. Active cells and the presence of L-lactate were required for ferric iron reduction. The L-lactate-driven nitrate respiration in E.coliE4 leading to the production of nitrite, was reduced to about 20% of its maximum activity with 5 mM ferric iron, or to about 50% in presence of 5 mM ferrous iron. The inhibition was caused by nitric oxide formed by a spontaneous chemical reduction of nitrite by ferrous iron. Nitric oxide was further chemically reduced by ferrous iron to nitrous oxide. With electron paramagnetic resonance spectroscopy, the presence of a free ferro-nitrosyl complex was shown. In presence of ferrous or ferric iron and L-lactate, nitrate was anaerobically converted to nitric oxide and nitrous oxide by the combined action of E.coli E4 and spontaneous chemical reduction reactions. Chapter 6 reports on aerobic reduction of nitrate to ammonium in E.coli grown in continuous cultures, a novel feature of E.coli Nitrate and nitrite was reduced by E.coli E4 in a L-lactate (5 mM) limited chemostat culture at dissolved oxygen concentrations corresponding to 90 - 100% air saturation. Nitrate reductase and nitrite reductase activity was regulated by the growth rate, oxygen and nitrate concentrations. At a low growth rate (0.11 h -1) the measured nitrate and nitrite reductase activities were 200 and 250 nmol.mg -1protein.min -1, respectively. At a high growth rate (0.55 h -1both enzyme activities were considerably lower (25 and 12 nmol.mg -1protein.min -1). The steady state nitrite concentration in the chemostat was controlled by the combined action of the nitrate and nitrite reductase. Both enzyme activities were inversely proportional to the growth rate. The nitrite reductase activity decreased faster with the growth rate than the nitrate reductase. The chemostat biomass concentration of E.coli E4, with ammonium either solely or combined with nitrate as a source of nitrogen, remained constant throughout all growth rates and was not affected by nitrite concentrations. Contrary to batch, E.coli E4 was able to grow on nitrate as the sole source of nitrogen. When cultivated with nitrate as the sole source of nitrogen the chemostat biomass concentration is determined by the combined activities of nitrate and nitrite reductase and hence, inversely proportional to growth rate.</TT

Thermalized collisional pre-sheath detected in dense plasma with coherent and incoherent Thomson scattering

In the direct vicinity of plasma-facing surfaces, the incident plasma particles interact with surface-recombined neutrals. Remarkably high near-surface pressure losses were observed in the high-flux linear plasma generator Magnum-PSI. Combining the incoherent and coherent Thomson scattering diagnostics, we directly measured particle, momentum and energy fluxes down to 3 mm from the plasma target surface. At the surface, the particle and total heat flux were also measured, using respectively an in-target Langmuir probe and thermographic methods. The near-surface momentum and energy losses scale with density, and amount to at least 50 % and 20%, respectively, at ne=8centerdot1020m-3. These losses are attributed to the efficient exchange of charge, momentum and energy between incident plasma and surface-recombined neutrals. In low-temperature plasmas with sufficient density, incident particles go through several cycles of interaction and surface deposition before leaving the plasma, thereby providing an effective alternative dissipation channel to the incident plasma. Parallel plasma parameter profiles exhibit a transition with increasing plasma density. In low-density conditions, the plasma temperature is constant and near-surface ion acceleration is observed, attributed to the ambipolar electric field. Conversely, deceleration and plasma cooling are observed in dense conditions. These results are explained by the combined effect of ion-neutral friction and electron-ion thermal equilibration in the so-called thermalized collisional pre-sheath. The energy available for ambipolar acceleration is thus reduced, as well as the upstream flow velocity. In the ITER divertor, enhanced near-surface p-n interaction is expected as well, given the overlap in plasma conditions. Including these effects in finite-element scrape-off layer models requires a near-surface resolution smaller than the neutral mean free path. This amounts to 1 mm in Magnum-PSI, and possibly an order of magnitude smaller in ITER.</p

Measurement of the Proton Spin Structure Function g1p with a Pure Hydrogen Target

A measurement of the proton spin structure function g1p(x,Q^2) in deep-inelastic scattering is presented. The data were taken with the 27.6 GeV longitudinally polarised positron beam at HERA incident on a longitudinally polarised pure hydrogen gas target internal to the storage ring. The kinematic range is 0.021<x<0.85 and 0.8 GeV^2<Q^2<20 GeV^2. The integral Int_{0.021}^{0.85} g1p(x)dx evaluated at Q0^2 of 2.5 GeV^2 is 0.122+/-0.003(stat.)+/-0.010(syst.).Comment: 7 pages, 3 figures, 1 table, RevTeX late

Determination of the Deep Inelastic Contribution to the Generalised Gerasimov-Drell-Hearn Integral for the Proton and Neutron

The virtual photon absorption cross section differences [sigma_1/2-sigma_3/2] for the proton and neutron have been determined from measurements of polarised cross section asymmetries in deep inelastic scattering of 27.5 GeV longitudinally polarised positrons from polarised 1H and 3He internal gas targets. The data were collected in the region above the nucleon resonances in the kinematic range nu < 23.5 GeV and 0.8 GeV**2 < Q**2 < 12 GeV**2. For the proton the contribution to the generalised Gerasimov-Drell-Hearn integral was found to be substantial and must be included for an accurate determination of the full integral. Furthermore the data are consistent with a QCD next-to-leading order fit based on previous deep inelastic scattering data. Therefore higher twist effects do not appear significant.Comment: 6 pages, 3 figures, 1 table, revte

Observation of a Coherence Length Effect in Exclusive Rho^0 Electroproduction

Exclusive incoherent electroproduction of the rho^0(770) meson from 1H, 2H, 3He, and 14N targets has been studied by the HERMES experiment at squared four-momentum transfer Q**2>0.4 GeV**2 and positron energy loss nu from 9 to 20 GeV. The ratio of the 14N to 1H cross sections per nucleon, known as the nuclear transparency, was found to decrease with increasing coherence length of quark-antiquark fluctuations of the virtual photon. The data provide clear evidence of the interaction of the quark- antiquark fluctuations with the nuclear medium.Comment: RevTeX, 5 pages, 3 figure

Flavor Decomposition of the Polarized Quark Distributions in the Nucleon from Inclusive and Semi-inclusive Deep-inelastic Scattering

Spin asymmetries of semi-inclusive cross sections for the production of positively and negatively charged hadrons have been measured in deep-inelastic scattering of polarized positrons on polarized hydrogen and 3He targets, in the kinematic range 0.023<x<0.6 and 1 GeV^2<Q^2<10 GeV^2. Polarized quark distributions are extracted as a function of x for up $(u+u_bar) and down (d+d_bar) flavors. The up quark polarization is positive and the down quark polarization is negative in the measured range. The polarization of the sea is compatible with zero. The first moments of the polarized quark distributions are presented. The isospin non-singlet combination Delta_q_3 is consistent with the prediction based on the Bjorken sum rule. The moments of the polarized quark distributions are compared to predictions based on SU(3)_f flavor symmetry and to a prediction from lattice QCD.Comment: 14 pages, 6 figures (eps format), 10 tables in Latex New version contains tables of asymmetries and correlation matri

A genome-wide RNAi screen in mouse embryonic stem cells identifies Mp1 as a key mediator of differentiation

Knockdown of the scaffolding protein Mek binding protein 1 (Mp1) in mouse embryonic stem cells suppresses differentiation but not proliferation, and more invasive human germ cell tumors express lower amounts of Mp1

The HERMES Spectrometer

The HERMES experiment is collecting data on inclusive and semi-inclusive deep inelastic scattering of polarised positrons from polarised targets of Il, D, and He-3. These data give information on the spin structure of the nucleon. This paper describes the forward angle spectrometer built for this purpose. The spectrometer includes numerous tracking chambers (micro-strip gas chambers, drift and proportional chambers) in front of and behind a 1.3 T.m magnetic field, as well as an extensive set of detectors for particle identification (a lead-glass calorimeter, a pre-shower detector, a transition radiation detector, and a threshold Cherenkov detector). Two of the main features of the spectrometer are its good acceptance and identification of both positrons and hadrons, in particular pions. These characteristics, together with the purity of the targets, are allowing HERMES to make unique contributions to the understanding of how the spins of the quarks contribute to the spin of the nucleon. (C) 1998 Elsevier Science B.V. All rights reserved

Erratum to: "Nuclear Effects on R=\sigma_L/\sigma_T in Deep-Inelastic Scattering" Phys.Lett. B475(2000)386

This erratum revokes the main conclusion of a Letter that reported measurements of cross sections for deep-inelastic scattering (DIS) of leptons on $^3$He and $^{14}$N targets, expressed as ratios of $\sigma_A / \sigma_D$ to the cross section on the deuterium target.Comment: 3 pages, 1 figur