Calculated Residence Time Research Articles

Development and dosimetry of 203Pb/212Pb-labelled PSMA ligands: bringing \u201cthe lead\u201d into PSMA-targeted alpha therapy?

PurposeThe aims of this study were to develop a prostate-specific membrane antigen (PSMA) ligand for labelling with different radioisotopes of lead and to obtain an approximation of the dosimetry of a simulated 212Pb-based alpha therapy using its 203Pb imaging analogue.MethodsFour novel Glu-urea-based ligands containing the chelators p-SCN-Bn-TCMC or DO3AM were synthesized. Affinity and PSMA-specific internalization were studied in C4-2 cells, and biodistribution in C4-2 tumour-bearing mice. The most promising compound, 203Pb-CA012, was transferred to clinical use. Two patients underwent planar scintigraphy scans at 0.4, 4, 18, 28 and 42 h after injection, together with urine and blood sampling. The time–activity curves of source organs were extrapolated from 203Pb to 212Pb and the calculated residence times of 212Pb were forwarded to its unstable daughter nuclides. QDOSE and OLINDA were used for dosimetry calculations.ResultsIn vitro, all ligands showed low nanomolar binding affinities for PSMA. CA09 and CA012 additionally showed specific ligand-induced internalization of 27.4 ± 2.4 and 15.6 ± 2.1 %ID/106 cells, respectively. The 203Pb-labelled PSMA ligands were stable in serum for 72 h. In vivo, CA012 showed higher specific uptake in tumours than in other organs, and particularly showed rapid kidney clearance from 5.1 ± 2.5%ID/g at 1 h after injection to 0.9 ± 0.1%ID/g at 24 h. In patients, the estimated effective dose from 250–300 MBq of diagnostic 203Pb-CA012 was 6–7 mSv. Assuming instant decay of daughter nuclides, the equivalent doses projected from a therapeutic activity of 100 MBq of 212Pb-CA012 were 0.6 SvRBE5 to the red marrow, 4.3 SvRBE5 to the salivary glands, 4.9 SvRBE5 to the kidneys, 0.7 SvRBE5 to the liver and 0.2 SvRBE5 to other organs; representative tumour lesions averaged 13.2 SvRBE5 (where RBE5 is relative biological effectiveness factor 5). Compared to clinical experience with 213Bi-PSMA-617 and 225Ac-PSMA-617, the projected maximum tolerable dose was about 150 MBq per cycle.Conclusion212Pb-CA012 is a promising candidate for PSMA-targeted alpha therapy of prostate cancer. The dosimetry estimate for radiopharmaceuticals decaying with the release of unstable daughter nuclides has some inherent limitations, thus clinical translation should be done cautiously.

Accelerating the Calculation of Protein-Ligand Binding Free Energy and Residence Times Using Dynamically Optimized Collective Variables.

Elucidation of the ligand/protein binding interaction is of paramount relevance in pharmacology to increase the success rate of drug design. To this end, a number of computational methods have been proposed; however all of them suffer from limitations since the ligand binding/unbinding transitions to the molecular target involve many slow degrees of freedom that hamper a full characterization of the binding process. Being able to express this transition in simple and general slow degrees of freedom would give a distinctive advantage, since it would require minimal knowledge of the system under study, while in turn it would elucidate its physics and accelerate the convergence speed of enhanced sampling methods relying on collective variables. In this study we pursuit this goal by combining for the first time variational approach to conformational dynamics with funnel metadynamics. In so doing, we predict for the benzamidine/trypsin system the ligand binding mode, and we accurately compute the absolute protein-ligand binding free energy and unbinding rate at unprecedented low computational cost. Finally, our simulation protocol reveals the energetics and structural details of the ligand binding mechanism and shows that water and binding pocket solvation/desolvation are the dominant slow degrees of freedom.

Dosimetry of Nano-Radio-Ytterbium Therapy by MIRD and MCNP methods for humans’ organs

Introduction: Nano radio-pharmaceutical therapy (NRPT) is a new method for solid tumor therapy. The treatment uses a radioactive form of radionuclide encapsulated in the poly amido amine dendrimers. The poly (amidoamine) (PAMAM) dendrimers have attracted attentions for cancer treatment by their characteristics of targeted drug carriers, delivery agents, and imaging agents in human systems. We have reported the preparation of dendrimer encapsulated ytterbium-175 radio- nanoparticles and its biodistribution in tumor bearing rats.175Yb (T1/2=4.2 days), decays to stable 175Lu with a β- emitter with 470 keV maximum energy (86.5%) and γ photons of 113 keV (1.9%), 282keV (3.1%) and 396 keV (6.5%) that are appropriate for imaging. This paper aims at comparing dosimetric assessments in human performed with Monte Carlo codes and MIRD based on the experimental results of biodistribution of dendrimer encapsulated ytterbium-175.Materials and Methods: All chemical materials including, Ytterbium (III) oxide (Yb2O3), PAMAMG5-NH2 dendrimer in 5% methanol solution and HNO3, Sodium boro- hydride (NaBH4) were purchased from Sigma Aldrich Chemical Co. USA and Merck, Germany. For biodistribution study 20 female Balb/c mice were purchased from Pasteur Institute of Iran. To estimate the absorbed dose by both methods, MCNP and MIRD, the cumulated activity in source organs were calculated by the percentage of injected dose in humans’ organs. The residence times (τ) in the source organs were obtained by integration of respective fit functions, on biokinetics curve, after accounting for the physical decay of the 175Yb. The dose calculation was done for a certain group of organs of human following the MIRD technique. To simulate the problem with MCNP, the ORNL phantom was used. The desired result for this study is absorbed doses of vital organs (liver, spleen, lung and kidney). Results: The maximum uptake of radio-compound are in the liver, lung and spleen. The biodistribution shows the characteristics of nanoparticles such as size and surface hydrophobicity that determine the amount of adsorbed radiopharmaceuticals in organs. The initial fast distribution of radiotracer is throughout liver, lung, and Bone, with slower accumulation in blood and spleen. The result of 2 methods (MIRD versus MCNPX) reveals that MIRD underestimate the absorbed dose for bladder, bone, lung, and ovaries while overestimate for liver, muscle and spleen. In this study the absorbed dose from 175Yb- PAMAM estimated by MCNPX for liver, lung, spleen, kidney and bone are 1.266, 8.081E-01, 8.347E-01, 3.979E-02 and 1.706E-02 mGy/MBq respectively Conclusion: Owing to the stability of PAMAM encapsulated Yb-175 and the size of nano- particle the concentrations are mostly in liver and lungs. State of- the-art dosimetry depends on the duration of the biokinetics of the radiopharmaceutical and a calculation of residence times including an analysis of the errors associated with the respective calculation that aimed in this study. The results showed that this nano-radiopharmaceutical has potential of application for liver and lung tumors.

Thermodynamic analysis of biodiesel production systems at supercritical conditions

This work reports thermodynamic analysis of systems involved in the biodiesel production using ethanol at supercritical conditions. PC-SAFT equation of state was used from ASPEN Plus simulator for modeling all investigated systems. Binary and ternary phase equilibrium data at high pressure and temperature were used to assess the PC-SAFT capability of predicting the thermodynamic behavior of the complex mixture of interest in this work. The results showed that the PC-SAFT is a reliable tool to represent the phase behavior of mixtures involving ethanol, vegetable oil, fatty acid, ethyl esters of fatty acid and glycerol. Phase behavior of the reaction system was evaluated under specified experimental conditions and considering different reaction conversions. Pressure-temperature diagrams demonstrated that the two-phase region for the reaction mixture decreases as the extension of reaction is increased. The PC-SAFT equation of state was used to estimate the density of the reactant mixture and the effect of this parameter over the residence of the reaction was assessed, where it was clearly demonstrated that the density of the mixture greatly affects the residence time calculation for the reactions of biodiesel production at high pressure conditions.

Visualizing and quantifying flow stasis in abdominal aortic aneurysms in men using 4D flow MRI

PurposeTo examine methods for visualizing and quantifying flow stasis in abdominal aortic aneurysms (AAA) using 4D Flow MRI. MethodsThree methods were investigated: conventional volumetric residence time (VRT), mean velocity analysis (MVA), and particle travel distance analysis (TDA). First, ideal 4D Flow MRI data was generated using numerical simulations and used as a platform to explore the effects of noise and background phase-offset errors, both of which are common 4D Flow MRI artifacts. Error-free results were compared to noise or offset affected results using linear regression. Subsequently, 4D Flow MRI data for thirteen (13) subjects with AAA was acquired and used to compare the stasis quantification methods against conventional flow visualization. ResultsVRT (R2 = 0.69) was more sensitive to noise than MVA (R2 = 0.98) and TDA (R2 = 0.99) at typical non-contrast signal-to-noise ratio levels (SNR = 20). VRT (R2 = 0.14) was more sensitive to background phase-offsets than MVA (R2 = 0.99) and TDA (R2 = 0.96) when considering a 95% effective background phase-offset correction. Qualitatively, TDA outperformed MVA (Wilcoxon p < 0.005, mean score improvement 1.6/5), and had good agreement (median score 4/5) with flow visualizations. ConclusionFlow stasis can be quantitatively assessed using 4D Flow MRI. While conventional residence time calculations fail due to error accumulation as a result of imperfect measured velocity fields, methods that do not require lengthy particle tracking perform better. MVA and TDA are less sensitive to measurement errors, and TDA generates results most similar to those obtained using conventional flow visualization.

Particle mixing in bubbling fluidized bed reactors with continuous particle exchange

This paper reports on experiments conducted with a cold flow model utilized for the investigation of the particle residence time distribution and mixing characteristics in a bubbling fluidized bed with continuous solids exchange. The investigated system is of a rectangular cross section (0.4 × 0.2 m) with a bed height of 0.17 m. A measurement device based on an alternating current bridge circuitry coupled with lock-in amplifier technology was built in the scope of quantifying the solids residence time distribution, whereby a pulse-injected ferromagnetic tracer creates the input signal. The implementation of a profound mathematical routine ensures the reproducible calculation of the particles mean residence time and characteristic values describing particle mixing phenomena. Therefore, the E-curve was modeled by mathematical convolution of the exit age distributions available for an ideally mixed continuous stirred tank reactor and a plug flow reactor with axial dispersion. It is shown that the in-bed mixing is highly dependent on the fluidization rate as well as on the solids circulation rate. Albeit the lowest superficial gas velocity equals a fluidization number of 4.7, the formation of dead spaces and short-circuit flows was observed under these conditions. Axial dispersion coefficients in the range of 5·10-3 to 7·10-1 m2 s−1 were obtained.

Decay dynamics of Abies alba and Picea abies deadwood in relation to environmental conditions

In this study we analysed a dataset of 8661 logs of silver fir (Abies alba Mill.) and Norway spruce (Picea abies L., Karst) in mixed fir-spruce-beech stands in primeval and natural forests in four sites separated into the two macroclimatic categories according to mean annual temperature (“cold” and “warmer”) and according to mean annual precipitation (“mesic” and “humid”). We used “Bayesian Survival Trajectory Analysis” on a more than 40-year long time series (1972–2015), focusing on differences in the residence time of deadwood in different macroclimatic categories and two DBH classes. We also evaluated two qualitative characteristics of the downed logs: mortality mode and log position during decomposition. We calculated residence time and the time needed to reach the advanced decay stage. Our analyses confirmed the influence temperature and precipitation on modelled residence time. The residence time for silver fir logs in the DBH class 55+ cm in the “cold” site was 106 years, while in the “warmer” sites was 78 years. The residence time in the “mesic” site was 57 years, while in the “humid” sites was 90 years. It took 81 years for Norway spruce logs in the DBH class 55+ cm to completely decompose in the “cold” site. Suspended logs 11 took years longer to decay than those in contact with the ground. The modelled residence time of logs on wet sites was the same as that of logs at sites unaffected by water. These results can be utilised in biodiversity oriented forest management, as well as in modelling future amounts of deadwood. In order to maintain the continuous presence of silver fir and Norway spruce deadwood for those organisms that depend on it, it is necessary to supply deadwood at least once every 25–40 years (depending on climatic category and DBH class). During this time, approximately 50% of logs become completely decomposed and 50% remain in the last decay stage.

Numerical study of water residence time in the Yueqing Bay based on the eulerian approach

The Yueqing Bay was a semi-enclosed bay located in the southeast of Zhejiang Province, China. Due to substantial anthropogenic influences since 1964, the water quality in the bay had deteriorated seriously. Thus urgent measures should be taken to protect the water body. In this study, a numerical model was calibrated for water surface elevation and tidal current from August 14 to August 26, 2011. Comparisons of observed and simulated data showed that the model reproduced the tidal range and phase and the variations of current at different periods fairly well. The calibrated model was then applied to investigate spatial flushing pattern of the bay by calculation of residence time. The results obtained from a series of model experiments demonstrated that the residence time increased from 10 day at the bay mouth to more than 70 day at the upper bay. The average residence time over the whole bay was 49.5 day. In addition, the adaptation of flushing homogeneity curve showed that the residence time in the bay varied smoothly. This study provides a numerical tool to quantify the transport timescale in Yueqing Bay and supports adaptive management of the bay by local authorities.

Residence Time of a Highly Urbanized Estuary: Jamaica Bay, New York

Using a validated coupled hydrodynamic-tracer transport model, this study quantified the mean residence time in Jamaica Bay, a highly eutrophic lagoonal estuary in New York City. The Bay is a well-mixed to partially-stratified estuary with heavily-dredged bathymetry and substantial wastewater treatment plant effluent inputs that lead to seasonal hypoxia in some poorly-flushed deep-water basins. Residence time was computed for Jamaica Bay and its largest isolated deep basin, Grassy Bay. The response of residence time to freshwater discharge and wind forcing during summer 2015 was also investigated. The model results showed that the mean residence time, which represents the time required to flush out 63% of tracers released into the region of interest, was 17.9 days in Jamaica Bay and 10.7 days in Grassy Bay. The results also showed that some regions in Jamaica Bay retained their tracers much longer than the calculated residence time and, thus, are potentially prone to water quality problems. Model experiments demonstrated that summertime wind forcing caused a small increase in residence time, whereas freshwater discharge substantially reduced residence time. Freshwater inputs were shown to strongly enhance the two-layer estuarine gravitational circulation and vertical shear, which likely reduced residence time by enhancing shear dispersion. Due to the Bay’s small, highly-urbanized watershed, freshwater inputs are largely derived from the municipal water supply, which is fairly uniform year-round. This water helps to promote bay flushing, yet also carries a high nitrogen load from wastewater treatment. Lastly, the tidal prism method was used to create a simple calibrated model of residence time using the geometry of the study area and the tidal range and period.

Assessment of predictive capability of hybrid URANS/LES methods in residence time calculation

The present study aims to assess capability of mostly used hybrid URANS/LES methods in dealing with a complex swirled configuration/reactor when the residence time characteristics need to be predicted at acceptable level of accuracy and fidelity. The configuration is quite complex and out of reach of the classical RANS turbulence models as it consists of different, partly swirled inlet channels and a large variety of time and length scales. In this work only the flow field is considered and is investigated using three different hybrid URANS/LES simulation methods. The models: the Scale Adaptive Simulation (SAS), the Improved Delayed Detached Eddy Simulation(SA-IDDES) and the k-ω-DES, use different triggering mechanisms and underlying RANS models. The results of the flow field, the residence time characteristics and all related quantities are compared with both the Large Eddy Simulation (LES) and experimental data reported in Doost et al. (2016). It turns out that none of the considered hybrid methods is able to predict the residence time characteristics as well as LES does mainly due to the inaccurate prediction of the flow field. It was found that there is a need to improve the hybrid approaches by addressing the shortcomings, particularly those regarding triggering mechanism to make hybrid approaches a reliable computational tool for study complex turbulent flows inside full scale configurations where LES can be prohibitively expensive.

Distributions and geochemical behaviors of oxyanion-forming trace elements and uranium in the Hövsgöl–Baikal–Yenisei water system of Mongolia and Russia

We investigated the distributions and geochemical behaviors of two oxyanion-forming elements: vanadium (V) and molybdenum (Mo), and of uranium (U) in the Hövsgöl–Baikal–Yenisei water system. The vertical profiles of these elements in Lakes Hövsgöl and Baikal were almost constant, except V showed slightly lower concentrations in the epilimnion, probably because of biological activity. Based on residence time calculations, it is inferred that V and U are removed from Lake Baikal via some biogeochemical processes, whereas Mo is almost nonreactive within the lake. Such differences might be attributable to their adsorptive behaviors onto solid phases, including sediments and suspended particles. The dissolved concentrations of these elements showed similar variation in the Egiin Gol and Selenga Rivers, and the highest concentration within these rivers was observed after the confluence of the Orkhon River, a tributary of the Selenga River. The concentrations in the Angara River were almost constant along its length. On the other hand, in the Yenisei River, the inflow of a tributary (the Nyzhnyaya Tunguska River) strongly affected the distributions of the trace elements. The concentrations of V and Mo at several sampling stations, particularly on the Selenga and Orkhon rivers, exceeded the maximum permitted concentration of Russian fishing industry regulations (MPCfish). The high concentrations in the Orkhon River might be attributable to pollution, whereas those in the Selenga River are probably natural because its watershed has been affected little by mining and other anthropogenic activities.

Evaluation of [18F]FNM biodistribution and dosimetry based on whole-body PET imaging of rats

IntroductionThe aim of this work was to study the biodistribution, metabolism and radiation dosimetry of rats injected with [18F]FNM using PET/CT images. This novel radiotracer targeting NMDA receptor has potential for investigation for neurological and psychiatric diseases. MethodsFree fraction and stability in fresh human plasma were determined in vitro. PET/CT was performed on anesthetized rats. Organs were identified and 3D volumes of interest (VOIs) were manually drawn on the CT in the center of each organ. Time activity curves (TACs) were created with these VOIs, enabling the calculation of residence times. To confirm these values, ex vivo measurements of organs were performed. Plasma and urine were also collected to study in vivo metabolism. Data was extrapolated to humans, effective doses were estimated using ICRP-60 and ICRP-89 dosimetric models and absorbed doses were estimated using OLINDA/EXM V1.0 and OLINDA/EXM V2.0 (which use weighting factors from ICRP-103 to do the calculations). ResultsThe [18F]FNM was stable in human plasma and the diffusible free fraction was 53%. As with memantine, this tracer is poorly metabolized in vivo. Ex vivo distributions validated PET/CT data as well as demonstrating a decrease of radiotracer uptake in the brain due to anesthesia. Total effective dose was around 6.11 μSv/MBq and 4.65 μSv/MBq for female and male human dosimetric models, respectively. ConclusionsThis study shows that the presented compound exhibits stability in plasma and plasma protein binding very similar to memantine. Its dosimetry shows that it is suitable for use in humans due to a low total effective dose compared to other PET radiotracers.

Structure-based design, synthesis, and binding mode analysis of novel and potent chymase inhibitors

Based on insight from the X-ray crystal structure of human chymase in complex with compound 1, a lactam carbonyl of the diazepane core was exchanged with O-substituted oxyimino group, leading to amidoxime derivatives. This modification resulted in highly potent chymase inhibitors, such as O-phenylamidoxime 5f. X-ray crystal structure analysis indicated that compound 5f induced movement of the Leu99 and Tyr94 side chains at the S2 site, and the increase in inhibitory activity of O-phenyl amidoxime derivatives suggested that the O-phenyl moiety interacted with the Tyr94 residue. Surface plasmon resonance experiments showed that compound 5f had slower association and dissociation kinetics and the calculated residence time of compound 5f to human chymase was extended compared to that of amide compound 1.

Effect of relative humidity and the presence of aerosol particles on the α-pinene ozonolysis

The α-pinene ozonolysis under the different environmental conditions were observed in a smog chamber. The second-order rate constant (k) was determined to be (7.25±0.06)×10–17cm3/(molecule·sec) under 20% of relative humidity (RH) and room temperature. RH showed a marked influence on the α-pinene ozonolysis. The value of k increased with RH increase, which was 1.6 times faster at RH=80% than that at RH=20%. Additionally, the value of k apparently changed in the presence of the aerosol particles. The diesel soot increased the k value. The fly ash prohibited the reaction, however, H2SO4-treated fly ash promoted the reaction. The information of products gained using FT-IR and SPAMS showed that pinonic acid, 10-hydroxy-pinonic acid and pinic acid could be generated during the α-pinene ozonolysis. Water molecules could take part in the formation of the products, and play a vital role in the degradation of α-pinene. The atmospheric residence time calculation showed that the ozonolysis in the atmosphere is an important way of the α-pinene consumption as compared to that reacted with OH during daytime. The results suggested that the degradation of α-pinene via the ozonization in the atmosphere may be affected greatly by RH, as well as the presence of aerosol particles. The ozonolysis reaction may be an important way of the α-pinene consumption during daytime.

Origin of gases from the geothermal reservoir Groß Schönebeck (North German Basin)

The operation of a geothermal facility is largely affected by the content and composition of gases dissolved in the formation fluids. Typically, the geothermal gas mixtures consists of different types of gases of different origin. In this study, the origin of various gas components from the Rotliegend – Permocarboniferous geothermal reservoir Groß Schönebeck (North German Basin) was investigated. Three formation fluid samples were collected from the depth of the production well Gt GrSk 04/05 (between 4120 and 4240m) at conditions of the Rotliegend/Permocarboniferus reservoir (about 140–150°C and 430–450bar). Identified and further investigated gases are N2, CH4, CO2, H2, higher gaseous alkanes, and noble gases. The stable isotope ratio of individual gas components range from 0.2 to 1.5‰ (δ15NAir) for N2, from −16.5 to −21.2‰ for CH4, from −18 to −26‰ for C2H6, from −24 to −30‰ for C3H8, and from −13.1 to −20.2‰ for CO2 (δ13CV-PDB for all hydrocarbons and carbon dioxide). Isotopic ratios measured for the noble gases He, Ne, and Ar indicated that 20Ne/22Ne and 38Ar/36Ar are indistinguishable from air, while all other isotope ratios show excess of radiogenic or nucleogenic isotopes.Results of δ15NAir suggest that the source of N2 are the highly matured Westphalian coals (Upper Carboniferous)l. Isotopic ratios of CH4 and CO2 confirmed thermogenic decomposition of terrestrial plants from a similar source as the most likely precursor for these gases. The inverse carbon isotope trend might be linked to heavy metal catalysed cracking of long-chain hydrocarbons and/or evolution of precipitates during fluid evaporation in the basin.The observed 3He/4He ratios of ≤0.0642±0.0026 Ra demonstrate a crustal origin of He. The N2/40Ar ratio (1648±480) indicates a crustal origin and practically without any influence of the air. 21Ne/22Ne is distinguished from the air and more enriched in nucleogenic 21Ne, relative to 22Ne, when compared to the average crustal Ne composition. The calculated residence time of fluids by means of in situ produced nuclides varies for 40Ar from 72 to 80Ma and for 4He from 365 to 401Ma. The apparent age discrepancy gives a hint for He migration from older stratigraphic layers or stratas enriched in parent nuclides (U, Th).

A novel quasi plug‐flow reactor design for enzymatic hydrolysis of cellulose using rheology experiment and CFD simulation

One of the obstacles constraining bio‐ethanol production using cellulose is enzymatic hydrolysis. Uniform distribution of slurry residence time is important to improve the efficiency. Efforts were made to develop a novel quasi plug‐flow reactor on industrial scale for enzymatic hydrolysis of cellulose by CFD simulation. Ahead of numerical simulation, the rheological properties of the cellulose enzymolysis slurry of furfural residues were studied based on experiments. A turbulence model called k‐kl‐ω was employed in CFD simulation, which was good at describing the flow field with great variation on the extent of turbulence in the stirred tank. Vertical blades, pitched blades, helical ribbons, and their combination were investigated firstly, and then the internal structures were optimized. The calculated residence time distribution curve showed that the quasi plug‐flow reactor had the following features: (1) combination of double helical ribbons and vertical blade, (2) two partitions and four baffles, (3) flow area was 0.1 m2 on partitions. The CFD simulation methods and results could provide a theoretical guidance for the development of a novel quasi plug‐flow reactor to improve the efficiency of the cellulose enzymatic hydrolysis on industrial scale.

Cool seafloor hydrothermal springs reveal global geochemical fluxes

We present geochemical data from the first samples of spring fluids from Dorado Outcrop, a basaltic edifice on 23 M.y. old seafloor of the Cocos Plate, eastern Pacific Ocean. These samples were collected from the discharge of a cool hydrothermal system (CHS) on a ridge flank, where typical reaction temperatures in the volcanic crust are low (2–20 °C) and fluid residence times are short. Ridge-flank hydrothermal systems extract 25% of Earth's lithospheric heat, with a global discharge rate equivalent to that of Earth's river discharge to the ocean; CHSs comprise a significant fraction of this global flow. Upper crustal temperatures around Dorado Outcrop are ∼15 °C, the calculated residence time is <3 y, and the composition of discharging fluids is only slightly altered from bottom seawater. Many of the major ions concentrations in spring fluids are indistinguishable from those of bottom seawater; however, concentrations of Rb, Mo, V, U, Mg, phosphate, Si and Li are different. Applying these observed differences to calculated global CHS fluxes results in chemical fluxes for these ions that are ≥15% of riverine fluxes. Fluxes of K and B also may be significant, but better analytical resolution is required to confirm this result. Spring fluids also have ∼50% less dissolved oxygen (DO) than bottom seawater. Calculations of an analytical model suggest that the loss of DO occurs primarily (>80%) within the upper basaltic crust by biotic and/or abiotic consumption. This calculation demonstrates that permeable pathways within the upper crust can support oxic water–rock interactions for millions of years.

Influence of Melt Compounding on Blast Furnace Slag Filled PP Compounds: A Comparative Study

Abstract In the current study, an assessment of the melt-compounding approach upon the behavior of blast furnace slag (BFS) filled polypropylene (PP) is reported. Two melt-compounding technologies are compared in terms of thermodynamic considerations as well as final behavior of the produced compounds. For this comparison, three PP-BFS formulations are introduced, where non-treated BFS is melt-mixed with PP via (1) internal lab mixer (IM) and (2) co-rotating twin-screw compounder (TSC). PP-BFS compounds from both processes are formed into plates via compression molding, characterized and tested for rheological, thermal and mechanical behavior. Processing parameters were evaluated for both processes such as specific shear work, residence time and shear rates. In addition, the rheological, thermal and mechanical behavior of comparable compounds are evaluated. The calculated specific shear work values for IM and TSC are 0.15 and 0.1 kW · h · kg−1. Calculated residence time for TSC is 55 s. Regarding the rheological behavior, it was found that melt mixing via both technologies did not show major differences in complex viscosity or storage- and loss moduli values. DSC findings show that crystallization and melting temperatures of IM- and TSC formulations are comparable. Decreased strain values are noticed for TSC compounds, while tensile modulus is found to be independent of process variation.

Conversion and Residence Time Calculation for Gas-solid Solid Reactions of the Cylindrical-shaped Particles with Con-stant Size Using the Shrinking Core Model

In this paper, a mathematical model is developed to calculate the conversion and the residence time reaction for plug flow and mixed flow in the reactors filled with cylin-drical particles using the shrinking core model. In this modeling, the size of the particles is un-chamged during the reaction. Also, the reaction rate is controlled by the gas layer resistance, the ash layer resistance, and the reaction resistance as well as the combination of them. In addition, it is assumed that the gas diffuses radially from the side, whereas the effect of diffusion in the axial direction is neglected. Equations are solved by numerical methods. It can be said that the innovation of this paper is the study of the effect of combination of resistances on the conversion of the reaction. Model evaluation shows that the results of modeling have a good consistency with the experimental data. The results show that at a certain time, when the rate of reaction is controlled by each of the resistances individually, the conversion rate is greater when the reaction is controlled by the ash layer resistance than when it is controlled by the other two resistance regimes. Finally, the effect of the combination of different controlling regimes on the conversion and residence time of reaction for plug flow and mixed flow of particles is studied and it is found that the overall results are similar to each other.

Upward nitrate flux and downward particulate organic carbon flux under contrasting situations of stratification and turbulent mixing in an Arctic shelf sea

Increased sea ice melt alters vertical surface-mixing processes in Arctic seas. More melt water strengthens the stratification, but an absent ice cover also exposes the uppermost part of the water column to wind-induced mixing processes. We conducted a field study in the Barents Sea, an Arctic shelf sea, to examine the effects of stratification and vertical mixing processes on 1) the upward nitrate flux (into surface layers &amp;lt;65 m) and 2) the downward flux of particulate organic carbon (POC) to ≤200 m. In the Arctic-influenced, drift ice-covered northern Barents Sea, we found a low upward nitrate flux into the surface layers (&amp;lt;0.1 mmol nitrate m–2 d–1) and a moderate downward POC flux (40–200 m: 150–250 mg POC m–2 d–1) during the late phase of a peak bloom. A 1-D residence time calculation indicated that the nitrate concentration in the surface layers constantly declined. In the Atlantic-influenced, ice-free, and weakly stratified southern Barents Sea a high upward nitrate flux was found (into the surface layers ≤25 m: &amp;gt;5 mmol nitrate m–2 d–1) during a post bloom situation which was associated with a high downward POC flux (40–120 m: 260–600 mg POC m–2 d–1). We suggest that strong wind events during our field study induced vertical mixing processes and triggered upwards nitrate flux, while a combination of down-mixed phytoplankton and fast-sinking mesozooplankton fecal pellets enhanced the downward POC flux. The results of this study underscore the need to further investigate the role of strong, episodic wind events on the upward nitrate and downward POC fluxes in weakly stratified regions of the Arctic that may be ice-free in future.