Carbon Dioxide Decomposition by a Parallel-Plate Plasma Reactor: Experiments and 2-D Modelling

The applicability of high voltage electrical discharges for the decomposition of CO2 has been extensively demonstrated. In this study, a new AC parallel-plate plasma reactor is presented which was designed for this purpose. Detailed experimental characterization and simulation of this reactor were performed. Gas chromatography of the exhaust gases enabled calculation of the CO2 conversion and energy efficiency. A conversion factor approximating 25% was obtained which is higher in comparison to existing plasma sources. Optical emission spectroscopy enabled the determination of the emission intensities of atoms and molecules inside the plasma and characterization of the discharge. The Stark broadening of the Balmer hydrogen line Hβ was used for the estimation of the electron density. The obtained densities were of the order of 5 × 1014 cm−3 which indicates that the electron kinetic energy dominated the discharge. The rotational, vibrational, and excitation temperatures were determined from the vibro-rotational band of the OH radical. A 2-temperature plasma was found where the estimated electron temperatures (~18,000 K) were higher than the gas temperatures (~2000 K). Finally, a 2-D model using the fluid equations was developed for determining the main processes in the CO2 splitting. The solution to this model, using the finite element method, gave the temporal and spatial behaviors of the formed species densities, the electric potential, and the temperatures of electrons

Implementation of state-of-the-art ternary new-particle formation scheme to the regional chemical transport model PMCAMx-UF in Europe

The particle formation scheme within PMCAMx-UF, a three-dimensional chemical transport model, was updated with particle formation rates for the ternary H2SO4-NH3-H2O pathway simulated by the Atmospheric Cluster Dynamics Code (ACDC) using quantum chemical input data. The model was applied over Europe for May 2008, during which the EUCAARI-LONGREX (European Aerosol Cloud Climate and Air Quality Interactions-Long-Range Experiment) campaign was carried out, providing aircraft vertical profiles of aerosol number concentrations. The updated model reproduces the observed number concentrations of particles larger than 4 nm within 1 order of magnitude throughout the atmospheric column. This agreement is encouraging considering the fact that no semi-empirical fitting was needed to obtain realistic particle formation rates. The cloud adjustment scheme for modifying the photolysis rate profiles within PMCAMx-UF was also updated with the TUV (Tropospheric Ultraviolet and Visible) radiative-transfer model. Results show that, although the effect of the new cloud adjustment scheme on total number concentrations is small, enhanced new-particle formation is predicted near cloudy regions. This is due to the enhanced radiation above and in the vicinity of the clouds, which in turn leads to higher production of sulfuric acid. The sensitivity of the results to including emissions from natural sources is also discussed.Peer reviewe

Tidally generated internal waves

This thesis deals with the internal tide in the deep ocean, which is generated by the barotropic tide flowing over the bottom topography. The energy flux from the barotropic tide to the internal-wave field at the bottom is calculated using a method based on linear-wave theory and the traditional WKB approximation valid for a slowing varying vertical stratification. The global distribution of the baroclinic plus barotropic tidal velocities near the bottom is thus obtained, which is then used to analyzed the deep-sea sediment resuspension. The calculated energy flux of the internal tide is then compared with the energy dissipation rate obtained from different data sets of microstructure measurements conducted in several regions of the world ocean. A good correlation is generally found between the model estimates and observations, giving us some confidence that the theory reasonably well predict internal tide generation. It is also found that the ratio of the averaged energy dissipation rate to the averaged energy flux is very different in different regions. A direct global calculation of the energy flux is done by projecting the internal tides onto vertical eigenmodes, so that the vertical density profile and the finite ocean depth are taken into account in a fully consistent way. The results of the modal energy flux is important for understanding the pathway from generation to dissipation of the internal tides, since the low-mode internal tides are less affected by local nonlinear processes responsible for degrading their energy to small-scale mixing. The agreement between this detailed method and the WKB-based method is found to be high, while this methods provides new information on the vertical mode distribution of internal tide generation.Finally, the bottom-trapped internal tides, which are generated when the tidal frequency is smaller than the Coriolis frequency, is examined. The energy density associated with these waves is computed using linear wave theory and vertical normal-mode decomposition. An emphasis is placed on the bottom-trapped internal tides in the Arctic Ocean, as yet, there is a lack of the comprehensive understanding of the mixing processes in this basin. Through the development of new methods to estimate internal tide generation, this thesis provides a valuable information to the problem of the better understanding of tidal mixing in the deep ocean and its role on the large-scale ocean circulation, with a possible applications to the improvement of ocean general circulation model.At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Manuscript. Paper 3: Manuscript. Paper 4: Manuscript.</p

On the glacial and interglacial thermohaline circulation and the associated transports of heat and freshwater

The thermohaline circulation (THC) and the oceanic heat and freshwater transports are essential for understanding the global climate system. Streamfunctions are widely used in oceanography to represent the THC and estimate the transport of heat and freshwater. In the present study, the regional and global changes of the THC, the transports of heat and freshwater and the timescale of the circulation between the Last Glacial Maximum (LGM, ≈ 21 kyr ago) and the present-day climate are explored using an Ocean General Circulation Model and streamfunctions projected in various coordinate systems. We found that the LGM tropical circulation is about 10% stronger than under modern conditions due to stronger wind stress. Consequently, the maximum tropical transport of heat is about 20% larger during the LGM. In the North Atlantic basin, the large sea-ice extent during the LGM constrains the Gulf Stream to propagate in a more zonal direction, reducing the transport of heat towards high latitudes by almost 50% and reorganising the freshwater transport. The strength of the Atlantic Meridional Overturning Circulation depends strongly on the coordinate system. It varies between 9 and 16 Sv during the LGM, and between 12 to 19 Sv for the present day. Similar to paleo-proxy reconstructions, a large intrusion of saline Antarctic Bottom Water takes place into the Northern Hemisphere basins and squeezes most of the Conveyor Belt circulation into a shallower part of the ocean. These different haline regimes between the glacial and interglacial period are illustrated by the streamfunctions in latitude–salinity coordinates and thermohaline coordinates. From these diagnostics, we found that the LGM Conveyor Belt circulation is driven by an enhanced salinity contrast between the Atlantic and the Pacific basin. The LGM abyssal circulation lifts and makes the Conveyor Belt cell deviate from the abyssal region, resulting in a ventilated upper layer above a deep stagnant layer, and an Atlantic circulation more isolated from the Pacific. An estimate of the timescale of the circulation reveals a sluggish abyssal circulation during the LGM, and a Conveyor Belt circulation that is more vigorous due to the combination of a stronger wind stress and a shortened circulation route

Deep-sea fluid and sediment dynamics—Influence of hill- to seamount-scale seafloor topography

International audienceDeep-sea sediments play a central role in a wide range of subject areas. A number of important controls on the formation of sedimentary deposits have been studied. However, to date, the impact of submarine landscape geometry as a possible control has received comparatively little attention. This seems to be particularly true for intermediate-scale topographic features such as abyssal hills, knolls and seamounts that can be found in many regions of the global seafloor: recent estimates suggest that in the deep open oceans, away from continental margins, there might be as many as ~ 25 × 106 abyssal hills, knolls and seamounts. Despite this large number very little is known about how they influence environmental complexity and patchiness, biogeochemical fluxes and the formation of sedimentary records.This paper reviews the currently known types of fluid-flow interactions with abyssal hills, knolls and seamounts that could potentially influence the way sediments are formed. The main types of relevant flow components are: quasi-steady to eddying background flow; internal lee and near-inertial waves; barotropic and baroclinic tides; and seamount-trapped waves. Previous studies looking into systematic links between fluid dynamics and sediments at hills, knolls and seamounts are reviewed. Finally, a case study is presented which aims to combine our current knowledge and investigate whether a given combination of recent fluid-flow components leaves a detectable imprint in the recent sediments on and around a short seamount.The main conclusions and implications are as follows. (1) Topographically generated flow-field geometries that are composed of a number of different prevailing fluid-flow components can be reflected and detected in properties of the underlying sediments. (2) Tidal and other higher-frequency (lee-wave, near-inertial) components of deep-ocean currents can be essential for locally driving total current velocities across threshold values for non-deposition/erosion/resuspension of freshly deposited deep-sea sediments. Moreover, there is evidence suggesting that not only maximum current speeds but also intensities of higher-frequency (tidal and/or (near-)inertial) current-direction variability might control sediment dynamics and sediment formation. This relativises the view that current speed is the main, or even only, controlling factor for sediment dynamics and sediment formation. (3) When it comes to the reconstruction of paleo-flows, these findings imply that certain sedimentary records may well reveal more about variability in the higher-frequency flow components than about variability in the basin-scale net flow component that often is the focus of paleoceanographic studies. (4) Single-core paleo-records from hill-, seamount- or similarly controlled sediment deposits may be biased due to the asymmetry of flow fields around these topographic features. To arrive at unbiased paleo-records for non-fluid-dynamic parameters, the influence of the flow-field geometry would have to be removed from the record first. (5) It seems the mechanistic understanding of hill- and seamount-related flow/topography interactions and their links to sediment dynamics is approaching a level that may (a) facilitate improved interpretation of topographically controlled sedimentary paleo-records, (b) help fill in the knowledge gap that exists for functional deep-sea biodiversity at intermediate space scales, and (c) improve predictive capabilities for exploration of economically relevant iron–manganese (Fe–Mn) crusts on seamounts

Global estimates of internal tide generation rates at 1/30&ordm; resolution

The dataset contains global estimates of barotropic-to-baroclinic tidal energy conversion at 1/30-degree resolution. Three types of estimates are available: 1. Non-modal conversion rates calculated by Falahat et al. (2014) following the method of Nycander (2005). A map for each of the eight most energetic tidal constituents (M2, S2, K1, O1, N2, K2, P1, Q1) is provided. 2. Mode-by-mode conversion rates calculated by Falahat et al. (2014). A map for each of the three most energetic tidal constituents (M2, S2, K1) and each of vertical normal modes 1, 2, 3, 4, 5 and 6-10 is provided. 3. Mode-by-mode conversion rates calculated by Falahat et al. (2014), to which an ad hoc correction to eliminate negative conversion rates has been applied (following de Lavergne et al., 2019). The correction preserves basin-integrated, depth-dependent conversion rates. A map for each of the three most energetic tidal constituents (M2, S2, K1) and each of vertical normal modes 1, 2, 3, 4, 5 and 6-10 is provided. All maps were computed using the WOCE global climatology of stratification, the ETOPO2v2 bathymetry product and the TXO6.2 atlas of barotropic tidal velocities. Detailed methods and documentation can be found in the following publications: Nycander, J. Generation of internal waves in the deep ocean by tides. Journal of Geophysical Research 110, C10028 (2005). doi:10.1029/2004JC002487 Falahat, S., Nycander, J., Roquet, F., Moundheur, Z. Global calculation of tidal energy conversion into vertical normal modes. Journal of Physical Oceanography 44, 3225-3244 (2014). doi:10.1175/JPO-D-14-0002.1 de Lavergne, C., Falahat, S., Madec, G., Roquet, F., Nycander, J., Vic, C. Toward global maps of internal tide energy sinks. Ocean Modelling,137, 52-75 (2019). doi:10.1016/j.ocemod.2019.03.010.</span

Global maps of internal tide generation and dissipation

The dataset consists of global two-dimensional maps of internal tide energy sources and sinks, at half-degree horizontal resolution. Estimated energy sources are provided for the three most energetic tidal constituents: M2, S2 and K1. They are decomposed into vertical normal modes. Units are Watts per square meter. Estimated energy sinks are provided for each of M2, S2 and K1 and for &#39;All constituents&#39;. &#39;All constituents&#39; is an extrapolation to the eight most energetic tidal constituents, obtained as a weighted sum of M2, S2 and K1 fields. Energy sinks are depth-integrated and decomposed into five process contributions: (i) local dissipation of high modes; (ii) dissipation of low modes via wave-wave interactions; (iii) dissipation of low modes via scattering by abyssal hills; (iv) dissipation of low modes via critical reflection; (v) dissipation of low modes via shoaling. Units are Watts per square meter. Methods and documentation can be found in the following publication: de Lavergne, C., Falahat, S., Madec, G., Roquet, F., Nycander, J., Vic, C. Toward global maps of internal tide energy sinks. Ocean Modelling, 137, 52-75 (2019). doi:10.1016/j.ocemod.2019.03.010. Provided maps of energy sinks correspond to the reference (REF) experiment described in the article.</span

Recent sediment dynamics in hadal trenches: evidence for the influence of higher-frequency (tidal, near-inertial) fluid dynamics

http://www.godac.jamstec.go.jp/darwin/cruise/yokosuka/yk10-16/ehttp://www.godac.jamstec.go.jp/darwin/cruise/yokosuka/yk12-09/

Comparison of Detection of Clinical Isolates of Mycobacterium Tuberculosis by Flash PCR and Conventional Culture Method

Background and Aim: Ziehl Nelson staining, fluorescent and also culture are the standard methods for the diagnosis of tuberculosis. In this study, the performance of conventional cultivation methods was compared with Flash PCR. Materials and Methods: A total of 56 sputum samples from patients with suspected tuberculosis in Tuberculosis Center of Arak city were collected and Ziehl–Neelsen and culture in Löwenstein–Jensen medium were accomplished. Moreover, DNA from all of the 56 sputum samples was extracted by Chelex100 method. Molecular evaluation was accomplished by Flash PCR kit containing probes and primers for gene amplification IS6110. Positive and negative controls together with samples were used in a MTC410 apparatus for amplification. FD-12 apparatus was used to evaluate the results. In addition, electrophoresis on agarose was used for confirmation of the results. Findings: From 56 sputum samples of suspected TB patients, 20 samples were positive and 36 samples were negative on microscopic evaluation and culture methods. FLASH-PCR molecular analysis showed that all of 20 positive samples were positive in molecular methods, too. On the other hand, three of sputum samples that were negative by culture and staining were positive in FLASH-PCR method. One of these 3 patients, received Isoniazid, pyrazinamide and ethambutol antibiotic by responsible medicine. All results were confirmed using conventional electrophoresis. Conclusion: In some negative samples, possibly because of the small number of bacteria in sample or a defect in the sampling, the Flash PCR may due good advantages. Therefore, due to the low cost, this method is recommended for routine use

Recent sediment dynamics in hadal trenches:evidence for the influence of higher-frequency (tidal, near-inertial) fluid dynamics

In addition to high hydrostatic pressure, scarcity of food is viewed as a factor that limits the abundance and activity of heterotrophic organisms at great ocean depths, including hadal trenches. Supply of nutritious food largely relies on the flux of organic-rich particulate matter from the surface ocean. It has been speculated that the shape of hadal trenches helps to 'funnel' particulate matter into the deeper parts of the trench, leading to sediment 'focussing' and improved benthic food supply. Here we investigate for five Northwest Pacific trenches the efficiency of sediment focussing by evaluating ratios of measured (sediment-derived) and expected (water-column-derived) sedimentary inventories of the naturally occurring and radioactive particulate-matter tracer Pb-210(xs). The sites comprise a broad range of surface-ocean productivity and physical-oceanographic regimes. Across the five trench-axis settings the inventory ratio varies between 0.5 and 4.1, with four trench-axis settings having ratios > 1 (sediment focussing) and one trench-axis setting a ratio < 1 (sediment winnowing). Although the fluid- and sediment-dynamical forcing behind sediment focussing remains unclear, this study finds evidence for another mechanism that is superimposed on, and counteracts, the focussing mechanism. This superimposed mechanism is related to higher-frequency (tidal, near-inertial) fluid dynamics. In particular, there is evidence for a strong and negative relation between the intensity of propagating internal tides and the extent of sediment focussing in the trench-axis. The relation can be approximated by a power function and the most intense drop in sediment focussing already occurs at moderate internal-tide intensities. This suggests that propagating internal tides may have a subtle but significant influence on particulate-matter dynamics and food supply in hadal trenches in particular, but possibly also in the deep seas in general. A mechanism for the influence of internal tides on sediment dynamics is proposed. (C) 2014 Elsevier Ltd. All rights reserved