The role of recharge and evapotranspiration as hydraulic drivers of ion concentrations in shallow groundwater on Everglades tree islands, Florida (USA)

Recently, evapotranspiration has been hypothesized to promote the secondary formation of calcium carbonate year-round on tree islands in the Everglades by influencing groundwater ions concentrations. However, the role of recharge and evapotranspiration as drivers of shallow groundwater ion accumulation has not been investigated. The goal of this study is to develop a hydrologic model that predicts the chloride concentrations of shallow tree island groundwater and to determine the influence of overlying biomass and underlying geologic material on these concentrations. Groundwater and surface water levels and chloride concentrations were monitored on eight constructed tree islands at the Loxahatchee Impoundment Landscape Assessment (LILA) from 2007 to 2010. The tree islands at LILA were constructed predominately of peat, or of peat and limestone, and were planted with saplings of native tree species in 2006 and 2007. The model predicted low shallow groundwater chloride concentrations when inputs of regional groundwater and evapotranspiration-to-recharge rates were elevated, while low evapotranspiration-to-recharge rates resulted in a substantial increase of the chloride concentrations of the shallow groundwater. Modeling results indicated that evapotranspiration typically exceeded recharge on the older tree islands and those with a limestone lithology, which resulted in greater inputs of regional groundwater. A sensitivity analysis indicated the shallow groundwater chloride concentrations were most sensitive to alterations in specific yield during the wet season and hydraulic conductivity in the dry season. In conclusion, the inputs of rainfall, underlying hydrologic properties of tree islands sediments and forest structure may explain the variation in ion concentration seen across Everglades tree islands.

The Role of Recharge and Evapotranspiration as Hydraulic Drivers of Ion Concentrations in Shallow Groundwater on Everglades Tree Islands, Florida (USA)

Recently, evapotranspiration has been hypothesized to promote the secondary formation of calcium carbonate year-round on tree islands in the Everglades by influencing groundwater ions concentrations. However, the role of recharge and evapotranspiration as drivers of shallow groundwater ion accumulation has not been investigated. The goal of this study is to develop a hydrologic model that predicts the chloride concentrations of shallow tree island groundwater and to determine the influence of overlying biomass and underlying geologic material on these concentrations. Groundwater and surface water levels and chloride concentrations were monitored on eight constructed tree islands at the Loxahatchee Impoundment Landscape Assessment (LILA) from 2007 to 2010. The tree islands at LILA were constructed predominately of peat, or of peat and limestone, and were planted with saplings of native tree species in 2006 and 2007. The model predicted low shallow groundwater chloride concentrations when inputs of regional groundwater and evapotranspiration-to-recharge rates were elevated, while low evapotranspiration-to-recharge rates resulted in a substantial increase of the chloride concentrations of the shallow groundwater. Modeling results indicated that evapotranspiration typically exceeded recharge on the older tree islands and those with a limestone lithology, which resulted in greater inputs of regional groundwater. A sensitivity analysis indicated the shallow groundwater chloride concentrations were most sensitive to alterations in specific yield during the wet season and hydraulic conductivity in the dry season. In conclusion, the inputs of rainfall, underlying hydrologic properties of tree islands sediments and forest structure may explain the variation in ion concentration seen across Everglades tree islands.

(Table 2) Salinity, pH, alkalinity and major ion concentrations in ANDRILL core AND-2A pore water

The compositional record of the AND-2A drillcore is examined using petrological, sedimentological, volcanological and geochemical analysis of clasts, sediments and pore waters. Preliminary investigations of basement clasts (granitoids and metasediments) indicate both local and distal sources corresponding to variable ice-volume and ice-flow directions. Low abundance of sedimentary clasts (e.g., arkose, litharenite) suggests reduced contributions from sedimentary covers while intraclasts (e.g., diamictite, conglomerate) attest to intrabasinal reworking. Volcanic material includes pyroclasts (e.g., pumice, scoria), sediments and lava. Primary and reworked tephra layers occur within the Early Miocene interval (1093 to 640 metres below sea floor mbsf). The compositions of volcanic clasts reveal a diversity of alkaline types derived from the McMurdo Volcanic Group. Finer-grained sediments (e.g., sandstone, siltstone) show increases in biogenic silica and volcanic glass from 230 to 780 mbsf and higher proportions of terrigenous material c. 350 to 750 mbsf and below 970 mbsf. Basement clast assemblages suggest a dominant provenance from the Skelton Glacier - Darwin Glacier area and from the Ferrar Glacier - Koettlitz Glacier area. Provenance of sand grains is consistent with clast sources. Thirteen Geochemical Units are established based on compositional trends derived from continuous XRF scanning. High values of Fe and Ti indicate terrigenous and volcanic sources, whereas high Ca values signify either biogenic or diagenic sources. Highly alkaline and saline pore waters were produced by chemical exchange with glass at moderately elevated temperatures.

Chemical composition and stable sulfur isotope record of Black Sea sediments

The main terminal processes of organic matter mineralization in anoxic Black Sea sediments underlying the sulfidic water column are sulfate reduction in the upper 2-4 m and methanogenesis below the sulfate zone. The modern marine deposits comprise a ca. 1-m-deep layer of coccolith ooze and underlying sapropel, below which sea water ions penetrate deep down into the limnic Pleistocene deposits from >9000 years BP. Sulfate reduction rates have a subsurface maximum at the SO4[2-]-CH4 transition where H2S reaches maximum concentration. Because of an excess of reactive iron in the deep limnic deposits, most of the methane-derived H2S is drawn downward to a sulfidization front where it reacts with Fe(III) and with Fe2+ diffusing up from below. The H2S-Fe2+ transition is marked by a black band of amorphous iron sulfide above which distinct horizons of greigite and pyrite formation occur. The pore water gradients respond dynamically to environmental changes in the Black Sea with relatively short time constants of ca. 500 yr for SO4[2-] and 10 yr for H2S, whereas the FeS in the black band has taken ca. 3000 yr to accumulate. The dual diffusion interfaces of SO4[2-]-CH4 and H2S-Fe2+ cause the trapping of isotopically heavy iron sulfide with delta34S = +15 to +33 per mil at the sulfidization front. A diffusion model for sulfur isotopes shows that the SO4[2-] diffusing downward into the SO4[2-]-CH4 transition has an isotopic composition of +19 per mil, close to the +23 per mil of H2S diffusing upward. These isotopic compositions are, however, very different from the porewater SO4[2-] (+43 per mil) and H2S (-15 per mil) at the same depth. The model explains how methane-driven sulfate reduction combined with a deep H2S sink leads to isotopically heavy pyrite in a sediment open to diffusion. These results have general implications for the marine sulfur cycle and for the interpretation of sulfur isotopic data in modern sediments and in sedimentary rocks throughout earth's history.

Inter-site and inter-scanner diffusion MRI data harmonization.

We propose a novel method to harmonize diffusion MRI data acquired from multiple sites and scanners, which is imperative for joint analysis of the data to significantly increase sample size and statistical power of neuroimaging studies. Our method incorporates the following main novelties: i) we take into account the scanner-dependent spatial variability of the diffusion signal in different parts of the brain; ii) our method is independent of compartmental modeling of diffusion (e.g., tensor, and intra/extra cellular compartments) and the acquired signal itself is corrected for scanner related differences; and iii) inter-subject variability as measured by the coefficient of variation is maintained at each site. We represent the signal in a basis of spherical harmonics and compute several rotation invariant spherical harmonic features to estimate a region and tissue specific linear mapping between the signal from different sites (and scanners). We validate our method on diffusion data acquired from seven different sites (including two GE, three Philips, and two Siemens scanners) on a group of age-matched healthy subjects. Since the extracted rotation invariant spherical harmonic features depend on the accuracy of the brain parcellation provided by Freesurfer, we propose a feature based refinement of the original parcellation such that it better characterizes the anatomy and provides robust linear mappings to harmonize the dMRI data. We demonstrate the efficacy of our method by statistically comparing diffusion measures such as fractional anisotropy, mean diffusivity and generalized fractional anisotropy across multiple sites before and after data harmonization. We also show results using tract-based spatial statistics before and after harmonization for independent validation of the proposed methodology. Our experimental results demonstrate that, for nearly identical acquisition protocol across sites, scanner-specific differences can be accurately removed using the proposed method.

Major ion chemistry of snow cores along a transect in central Dronning Maud Land, Antarctica

Among the large variety of particulates in the atmosphere, calcic mineral dust particles have highly reactive surfaces that undergo heterogeneous reactions with nitrogen oxides contiguously. The association between Ca2+, an important proxy indicator of mineral dust and NO3-, a dominant anion in the Antarctic snow pack was analysed. A total of 41 snow cores (~ 1 m each) that represent snow deposited during 2008-2009 were studied along coastal-inland transects from two different regions - the Princess Elizabeth Land (PEL) and central Dronning Maud Land (cDML) in East Antarctica. Correlation statistics showed a strong association (at 99 % significance level) between NO3- and Ca2+ at the near-coastal sections of both PEL (r = 0.72) and cDML (r = 0.76) transects. Similarly, a strong association between these ions was also observed in snow deposits at the inland sections of PEL (r = 0.8) and cDML (r = 0.85). Such systematic associations between Ca2+ and NO3- is attributed to the interaction between calcic mineral dust and nitrogen oxides in the atmosphere, leading to the possible formation of calcium nitrate (Ca(NO3)2). Forward and back trajectory analyses using HYSPLIT model v. 4 revealed that Southern South America (SSA) was an important dust emitting source to the study region, aided by the westerlies. Particle size distribution showed that over 90 % of the dust was in the range < 4 µm, indicating that these dust particles reached the Antarctic region via long range transport from the SSA region. We propose that the association between Ca2+ and NO3- occurs during the long range transport due to the formation of Ca(NO3)2. The Ca(NO3)2 thus formed in the atmosphere undergo deposition over Antarctica under the influence of anticyclonic polar easterlies. However, influence of local dust sources from the nunataks in cDML evidently mask such association in the mountainous region. The study indicates that the input of dust-bound NO3- may contribute a significant fraction of the total NO3- deposited in Antarctic snow.

Major ion chemistry and selected snow accumulation rates of snow cores along two transects in central Dronning Maud Land and Princess Elizabeth Land

This dataset includes basic information (location and depth) and major ion chemistry (Sodium, Chloride, Calcium, Nitrate) of snow cores from East Antarctic ice sheet. The snow cores were collected from two different regions - central Dronning Maud Land (cDML) and Princess Elizabeth Land (PEL) during the austral summer of 2008-09.

Development of a Composite ion-exchange membrane for PDMS-based microfluidic devices

The purpose of this research is to investigate potential methods to produce an ion-exchange membrane that can be integrated directly into a polydimethylsiloxane Lab-on-a-Chip or Micro-Total-Analysis-System. The majority of microfluidic membranes are based on creating microporous structures, because it allows flexibility in the choice of material such that it can match the material of the microfluidic chip. This cohesion between the material of the microfluidic chip and membrane is an important feature to prevent bonding difficulties which can lead to leaking and other practical problems. However, of the materials commonly used to manufacture microfluidic chips, there are none that provide the ion-exchange capability. The DuPont product Nafion{TM} is chosen as the ion-exchange membrane, a copolymer with high conductivity and selectivity to cations and suitable for many applications such as electrolysis of water and the chlor-alkali process. The use of such an ion-exchange membrane in microfluidics could have multiple advantages, but there is no reversible/irreversible bonding that occurs between PDMS and Nafion{TM}. In this project multiple methods of physical entrapment of the ion-exchange material inside a film of PDMS are attempted. Through the use of the inherent properties of PDMS, very inexpensive sugar granulate can be used to make an inexpensive membrane mould which does not interfere with the PDMS crosslinking process. After dissolving away this sacrificial mould material, Nafion{TM} is solidified in the irregular granulate holes. Nafion{TM} in this membrane is confined in the irregular shape of the PDMS openings. The outer structure of the membrane is all PDMS and can be attached easily and securely to any PDMS-based microfluidic device through reversible or irreversible PDMS/PDMS bonding. Through impedance measurement, the effectiveness of these integrated membranes are compared against plain Nafion{TM} films in simple sodium chloride solutions.

Development of the Oxide Ion Conductor Na0.5Bi0.5TiO3 (NBT) for Solid Oxide Cells

Na0.5Bi0.5TiO3 (NBT) is a well-known lead-free piezoelectric material with potential to replace lead zirconate titanate (PZT),1 however high leakage conductivity for the material has been widely reported.2 Through a combination of Impedance Spectroscopy (IS), O2- ion transference (EMF) number experiments and O18 tracer diffusion measurements, combined with Time-of-flight Secondary Ion Mass Spectrometry (TOFSIMS), it was identified that this leakage conductivity was due to oxygen ion conductivity. The volatilization of bismuth during synthesis, causing oxygen vacancies, is believed to be responsible for the leakage conductivity.3 The oxide-ion conductivity, when doped with magnesium, exceeds that of yttria-stabilized zirconia (YSZ) at ~500 °C,3 making it a potential electrolyte material for Intermediate Temperature Solid Oxide Cells (ITSOCs). Figure 1 shows the comparison of bulk oxide ion conductivity between 2 at.% Mg-doped NBT and other known oxide ion conductors.

As part of the UK wide £5.7m 4CU project, research has concentrated on trying to develop NBT for use in Intermediate Temperature Solid Oxide Cells (ITSOCS). With the aim of achieving mixed ionic and electronic conduction, transition metals were chemically doped on to the Ti-site. A range of experimental techniques was used to characterize the materials aimed at investigating both conductivity and material structure (Scanning Electron Microscopy (SEM), IS, X-ray Photoelectron Spectroscopy (XPS) and X-ray Absorption Spectroscopy (XAS)). The potential for NBT as an ITSOC material, as well as the challenges of developing the material, will be discussed.

(1) Takenaka T. et al. Jpn. J. Appl. Phys 1999, 30, 2236.

(2) Hiruma Y. et al. J. Appl. Phys 2009, 105, 084112.

(3) Li. M. et al. Nature Materials 2013, 13, 31.

Resistance of alkali activated slag concretes to chloride environments based on chloride penetration measurements

ABSTRACT

One of the binder systems with low environmental footprint is alkali activated slag concretes (AASC), made by adding alkalis such as sodium hydroxide and sodium silicate to industrial by-products such as ground granulated blast furnace slag (GGBS). Whilst they have the similar behaviour as that of traditional cement systems in terms of strength and structural behaviour, AASC do exhibit superior performance in terms of abrasion and acid resistance and fire protection.
In this article, the authors focus their attention on chloride ingress into different grades of AASC. The mix variables in AASC included water-to-binder, binder to aggregate ratio, percentage of alkali and the SiO2/Na2O ratio (silica modulus, Ms). The first challenge is to get mixes for different range of workability (with slump values from 40mm to 240mm) and reasonable early age and long term compressive strength according to each one. Then the chloride diffusion and migration in those mixes were measured and compared with same normal concretes in the existed literature based on chloride penetration depth. Comparing the chloride ingress between tradition concretes and AASCs is worthwhile to prove the possibility of increasing concrete lifetime in proximity to sea and deciding while such concretes are practical for use. Findings show that compared to the PC concretes, the AAS concretes have lower rate of chloride ingress.

The Performance Characteristics of a Surface-Modified Cutting Tool

In the past, many papers have been presented which show that the coating of cutting tools often yields decreased wear rates and reduced coefficients of friction. Although different theories are proposed, covering areas such as hardness theory, diffusion barrier theory, thermal barrier theory, and reduced friction theory, most have not dealt with the question of how and why the coating of tool substrates with hard materials such as Titanium Nitride (TiN), Titanium Carbide (TiC) and Aluminium Oxide (Al203) transforms the performance and life of cutting tools. This project discusses the complex interrelationship that encompasses the thermal barrier function and the relatively low sliding friction coefficient of TiN on an undulating tool surface, and presents the result of an investigation into the cutting characteristics and performance of EDMed surface-modified carbide cutting tool inserts. The tool inserts were coated with TiN by the physical vapour deposition (PVD) method. PVD coating is also known as Ion-plating which is the general term of the coating method in which the film is created by attracting ionized metal vapour in this the metal was Titanium and ionized gas onto negatively biased substrate surface. Coating by PVD was chosen because it is done at a temperature of not more than 5000C whereas chemical Vapour Deposition CVD process is done at very high temperature of about 8500C and in two stages of heating up the substrates. The high temperatures involved in CVD affects the strength of the (tool) substrates. In this study, comparative cutting tests using TiN-coated control specimens with no EDM surface structures and TiN-coated EDMed tools with a crater-like surface topography were carried out on mild steel grade EN-3. Various cutting speeds were investigated, up to an increase of 40% of the tool manufacturer’s recommended speed. Fifteen minutes of cutting were carried out for each insert at the speeds investigated. Conventional tool inserts normally have a tool life of approximately 15 minutes of cutting. After every five cuts (passes) microscopic pictures of the tool wear profiles were taken, in order to monitor the progressive wear on the rake face and on the flank of the insert. The power load was monitored for each cut taken using an on-board meter on the CNC machine to establish the amount of power needed for each stage of operation. The spindle drive for the machine is an 11 KW/hr motor. Results obtained confirmed the advantages of cutting at all speeds investigated using EDMed coated inserts, in terms of reduced tool wear and low power loads. Moreover, the surface finish on the workpiece was consistently better for the EDMed inserts. The thesis discusses the relevance of the finite element method in the analysis of metal cutting processes, so that metal machinists can design, manufacture and deliver goods (tools) to the market quickly and on time without going through the hassle of trial and error approach for new products. Improvements in manufacturing technologies require better knowledge of modelling metal cutting processes. Technically the use of computational models has a great value in reducing or even eliminating the number of experiments traditionally used for tool design, process selection, machinability evaluation, and chip breakage investigations. In this work, much interest in theoretical and experimental investigations of metal machining were given special attention. Finite element analysis (FEA) was given priority in this study to predict tool wear and coating deformations during machining. Particular attention was devoted to the complicated mechanisms usually associated with metal cutting, such as interfacial friction; heat generated due to friction and severe strain in the cutting region, and high strain rates. It is therefore concluded that Roughened contact surface comprising of peaks and valleys coated with hard materials (TiN) provide wear-resisting properties as the coatings get entrapped in the valleys and help reduce friction at chip-tool interface. The contributions to knowledge: a. Relates to a wear-resisting surface structure for application in contact surfaces and structures in metal cutting and forming tools with ability to give wear-resisting surface profile. b. Provide technique for designing tool with roughened surface comprising of peaks and valleys covered in conformal coating with a material such as TiN, TiC etc which is wear-resisting structure with surface roughness profile compose of valleys which entrap residual coating material during wear thereby enabling the entrapped coating material to give improved wear resistance. c. Provide knowledge for increased tool life through wear resistance, hardness and chemical stability at high temperatures because of reduced friction at the tool-chip and work-tool interfaces due to tool coating, which leads to reduced heat generation at the cutting zones. d. Establishes that Undulating surface topographies on cutting tips tend to hold coating materials longer in the valleys, thus giving enhanced protection to the tool and the tool can cut faster by 40% and last 60% longer than conventional tools on the markets today.

Synthèse de titanates de lithium nanostructurés par plasma inductif pour les batteries lithium-ion

Le marché des accumulateurs lithium-ion est en expansion. Cette croissance repose partiellement sur la multiplication des niches d’utilisation et l’amélioration constante de leurs performances. En raison de leur durabilité exceptionnelle, de leur faible coût, de leur haute densité de puissance et de leur fiabilité, les anodes basées sur les titanates de lithium, et plus particulièrement le spinelle Li4Ti5O12, présentent une alternative d’intérêt aux matériaux classiques d’anodes en carbone pour de multiples applications. Leur utilisation sous forme de nanomatériaux permet d’augmenter significativement la puissance disponible par unité de poids. Ces nanomatériaux ne sont typiquement pas contraints dans une direction particulière (nanofils, nanoplaquettes), car ces formes impliquent une tension de surface plus importante et requièrent donc généralement un mécanisme de synthèse dédié. Or, ces nanostructures permettent des réductions supplémentaires dans les dimensions caractéristiques de diffusion et de conduction, maximisant ainsi la puissance disponible, tout en affectant les propriétés habituellement intrinsèques des matériaux. Par ailleurs, les réacteurs continus reposant sur la technologie du plasma thermique inductif constituent une voie de synthèse démontrée afin de générer des volumes importants de matériaux nanostructurés. Il s’avère donc pertinent d’évaluer leur potentiel dans la production de titanates de lithium nanostructurés. La pureté des titanates de lithium est difficile à jauger. Les techniques de quantification habituelles reposent sur la fluorescence ou la diffraction en rayons X, auxquelles le lithium élémentaire se prête peu ou pas. Afin de quantifier les nombreuses phases (Li4Ti5O12, Li2Ti3O7, Li2TiO3, TiO2, Li2CO3) identifiées dans les échantillons produits par plasma, un raffinement de Rietveld fut développé et validé. La présence de γ-Li2TiO3 fut identifiée, et la calorimétrie en balayage différentiel fut explorée comme outil permettant d’identifier et de quantifier la présence de β-Li2TiO3. Différentes proportions entre les phases produites et différents types de morphologies furent observés en fonction des conditions d’opération du plasma. Ainsi, des conditions de trempe réductrice et d’ensemencement en Li4Ti5O12 nanométrique semblent favoriser l’émergence de nanomorphologies en nanofils (associés à Li4Ti5O12) et en nanoplaquette (associées à Li2TiO3). De plus, l’ensemencement et les recuits augmentèrent significativement le rendement en la phase spinelle Li4Ti5O12 recherchée. Les recuits sur les poudres synthétisées par plasma indiquèrent que la décomposition du Li2Ti3O7 produit du Li4Ti5O12, du Li2TiO3 et du TiO2 (rutile). Afin d’approfondir l’investigation de ces réactions de décomposition, les paramètres cristallins du Li2Ti3O7 et du γ-Li2TiO3 furent définis à haute température. Des mesures continues en diffraction en rayon X à haute température furent réalisées lors de recuits de poudres synthétisées par plasma, ainsi que sur des mélanges de TiO2 anatase et de Li2CO3. Celles-ci indiquent la production d’un intermédiaire Li2Ti3O7 à partir de l’anatase et du carbonate, sa décomposition en Li4Ti5O12 et TiO2 (rutile) sur toute la plage de température étudiée, et en Li2TiO3 et TiO2 (rutile) à des températures inférieures à 700°C.