Diffusion Of Carbon Dioxide Research Articles

Impregnation of mesoporous silica with mangiferin using supercritical CO2

The solvating power and diffusivity of supercritical carbon dioxide (scCO2) have attracted attention in recent years for the impregnation of polymers and porous matrices. This technique provides a final impregnated matrix that is free of solvents and it allows the use of thermosensitive drugs due to the relative low critical point of scCO2.The work reported here concerned the influence of parameters such as pressure, temperature, percentage of co-solvent, depressurization rate and time on the impregnation of mangiferin (MNG) into silica as a porous matrix. Increases in the values of the studied parameters led to an enhanced impregnation of MNG in all cases. Delivery profiles in simulated fluids were obtained. The profile for the gastric fluid shows a gradual release of MNG. The release of MNG in the intestinal fluid was faster than in the gastric fluid. The MNG was more soluble in the intestinal than in the gastric fluid.

A universal growth limit for circular lichens.

Lichens fix carbon dioxide from the air to build biomass. Crustose and foliose lichens grow as nearly flat, circular disks. Smaller individuals grow slowly, but with small, steady increases in radial growth rate over time. Larger individuals grow more quickly and with a roughly constant radial velocity maintained over the lifetime of the lichen. We translate the coffee drop effect to model lichen growth and demonstrate that growth patterns follow directly from the diffusion of carbon dioxide in the air around a lichen. When a lichen is small, carbon dioxide is fixed across its surface, and the entire thallus contributes to radial growth, but when a lichen is larger carbon dioxide is disproportionately fixed at the edges of an individual, which are the primary drivers of growth. Tests of the model against data suggest it provides an accurate, robust, and universal framework for understanding the growth dynamics of both large and small lichens in nature.

Diffusion of gas mixtures in the sI hydrate structure.

Replacing methane with carbon dioxide in gas hydrates has been suggested as a way of harvesting methane, while at the same time storing carbon dioxide. Experimental evidence suggests that this process is facilitated if gas mixtures are used instead of pure carbon dioxide. We studied the free energy barriers for diffusion of methane, carbon dioxide, nitrogen, and hydrogen in the sI hydrate structure using molecular simulation techniques. Cage hops between neighboring cages were considered with and without a water vacancy and with a potential inclusion of an additional gas molecule in either the initial or final cage. Our results give little evidence for enhanced methane and carbon dioxide diffusion if nitrogen is present as well. However, the inclusion of hydrogen seems to have a substantial effect as it diffuses rapidly and can easily enter occupied cages, which reduces the barriers of diffusion for the gas molecules that co-occupy a cage with hydrogen.

The experimental and numerical relation between the solubility, diffusivity and bubble nucleation of supercritical CO2 in Polystyrene via visual observation apparatus

In this work, the solubility and diffusivity of supercritical carbon dioxide (scCO2) in Polystyrene (PS) at different temperatures and pressures were studied using a magnetic suspension balance (MSB). Bubble nucleation and growth in PS/CO2 mixture were investigated via visual observation in a batch foaming system at different temperatures and pressures. A firm relationship between bubble nucleation and growth with solubility and diffusivity was observed. The results show that bubble density during the process can be controlled by changing the temperature and the pressure release rate. Furthermore, bubble growth was simulated considering mass diffusion equations and implicit method. The simulation results were in a good agreement with the experimental data. Finally, the effects of diffusivity and zero shear viscosity on the bubble growth were investigated and it was found that the bubble growth is a diffusion controlled phenomenon.

Does Aerobic Respiration Produce Carbon Dioxide or Hydrogen Ion and Bicarbonate?

Maintenance of intracellular pH is critical for clinical homeostasis. The metabolism of glucose, fatty acids, and amino acids yielding the generation of adenosine triphosphate in the mitochondria is accompanied by the production of acid in the Krebs cycle. Both the nature of this acidosis and the mechanism of its disposal have been argued by two investigators with a long-abiding interest in acid-base physiology. They offer different interpretations and views of the molecular mechanism of this intracellular pH regulation during normal metabolism. Dr. John Severinghaus has posited that hydrogen ion and bicarbonate are the direct end products in the Krebs cycle. In the late 1960s, he showed in brain and brain homogenate experiments that acetazolamide, a carbonic anhydrase inhibitor, reduces intracellular pH. This led him to conclude that hydrogen ion and bicarbonate are the end products, and the role of intracellular carbonic anhydrase is to rapidly generate diffusible carbon dioxide to minimize acidosis. Dr. Erik Swenson posits that carbon dioxide is a direct end product in the Krebs cycle, a more widely accepted view, and that acetazolamide prevents rapid intracellular bicarbonate formation, which can then codiffuse with carbon dioxide to the cell surface and there be reconverted for exit from the cell. Loss of this "facilitated diffusion of carbon dioxide" leads to intracellular acidosis as the still appreciable uncatalyzed rate of carbon dioxide hydration generates more protons. This review summarizes the available evidence and determines that resolution of this question will require more sophisticated measurements of intracellular pH with faster temporal resolution.

Effect of curing time on granulated blast-furnace slag cement mortars carbonation

Currently, ground granulated blast-furnace slag cements use in cement-based materials is being increasing because perform well in marine and other aggressive environments. However, mortars and concretes made of this type of cement exhibit high carbonation rates, particularly in badly cured cement-based materials and when high blast-furnace slag contents are used. Concrete reinforcement remains passive but can be corroded if the pore solution pH drops as a result of the carbonation process promoting the reinforced concrete structure failure during its service life. Results show the very sensitive response to wet-curing time of slag mortars with regard to the natural carbonation resistance. Then, a minimum period of 3–7 days of wet curing is required in order to guarantee the usual projected service life in reinforced concrete structures. In this work, estimation models of carbonation depth and carbon dioxide diffusion coefficient in ground granulated blast-furnace slag mortars as a function of the curing period and the amount of ground granulated blast-furnace slag are proposed. This information will be useful to material and civil engineers in designing cement-based materials and planning the required curing time depending on their ground granulated blast-furnace slag content.

Effects of process parameters on peanut skins extract and CO2 diffusivity by supercritical fluid extraction

Peanut skins (Arachis hypogea) are an agricultural waste product which has received much attention because they contain high nutritional values and can be potentially utilized in difference industries. At present, only a few studies have been conducted to study the effects of parameters on the peanut skins oil extraction. Therefore, this study aimed to determine the best extraction condition in order to obtain the highest extract yield using supercritical carbon dioxide (SC-CO2) with co-solvent Ethanol as compared to Soxhlet extraction method. Diffusivity of carbon dioxide in supercritical fluid extraction was determined using Crank model. The mean particle size used in this study was 425 µm. The supercritical carbon dioxide was performed at temperature (40 – 70 °C), flow rate of co-solvent ethanol (0 - 7.5% Vethanol/Vtotal), and extraction pressure (10 – 30 MPa) were used in this studies. The results showed that the percentage of oil yields and effective diffusivity increase as the pressure, rate of co-solvent, and temperature increased.

Efficiency of Nannochloropsis oculata and Bacillus polymyxa symbiotic composite at ammonium and phosphate removal from synthetic wastewater

ABSTRACTMany issues, such as, DO accumulation, N2 fixation obstacle, and carbon dioxide diffusion, hamper the application of microalgae-alginate immobilization in wastewater treatment. The objective of this study was to evaluate the effect of the microalgae Nannochloropsis oculata immobilized with the bacterium Bacillus polymyxa in alginate on ammonium and phosphate removal from synthetic wastewater. Results show that the co-immobilized Bacillus-Nannochloropsis can exploit ammonium and phosphate from wastewater more effectively than the immobilized Nannochloropsis, and immobilized Bacillus alone. A significantly higher ammonium and phosphate removal efficiency was found in co-immobilized Bacillus-Nannochloropsis (59.85%, 90.44%) than of that in immobilized Nannochloropsis (49.56%, 77.36%), and Bacillus immobilized (31.46%, 29.66%) alone. Additionally, the most effective co-immobilization mixture ratio for wastewater treatment was found to contain equal suspension (108 cell/ml) volume of the Nannochloropsis and Bacillus. Nannochloris and Bacillus can coexist harmoniously with the symbiotic and synergistic relationship, and the Nannochloropsis oculata- Bacillus polymyxa combination can be useful as a potential method to develop novel wastewater treatment.

Enantiomeric separation and quantification of R/S-amphetamine in urine by ultra-high performance supercritical fluid chromatography tandem mass spectrometry

To distinguish between legal and illegal consumption of amphetamine reliable analytical methods for chiral separation of the R- and S-enantiomers of amphetamine in biological specimens are required. In this regard, supercritical fluid chromatography (SFC) has several potential advantages over liquid chromatography, including rapid separation of enantiomers due to low viscosity and high diffusivity of supercritical carbon dioxide, the main component in the SFC mobile phase. A method for enantiomeric separation and quantification of R- and S-amphetamine in urine was developed and validated using ultra-high performance supercritical fluid chromatography-tandem mass spectrometry (UHPSFC-MS/MS). Sample preparation prior to UHPSFC-MS/MS analysis was a semi-automatic solid phase extraction method. The UHPSFC-MS/MS method used a Chiralpak AD-3 column with a mobile phase consisting of CO2 and 0.2% cyclohexylamine in 2-propanol. The injection volume was 2 μL and run-time was 6 min. MS/MS detection was performed with positive electrospray ionization and two multiple reaction monitoring transitions (m/z 136.1 > 119.0 and m/z 136.1 > 91.0). The calibration range was 50–10,000 ng/mL for each enantiomer. The between-assay relative standard deviations were in the range of 3.7–7.6%. Recovery was 92–93% and matrix effects ranged from 100 to 104% corrected with internal standard. After development and validation, the method has been successfully implemented in routine use at our laboratory for both separation and quantification of R/S-amphetamine, and has proved to be a reliable and useful tool for distinguishing intake of R- and S-amphetamine in authentic patient samples.

Effect of Cracking on Corrosion of Steel in Concrete

It is generally recognized that cracks provide easy access to ingress of chlorides in concrete and hence, the initiation of corrosion of steel in cracked concrete occurs at early stage. However, wide variety of results on the effect of crack widths on corrosion of steel in concrete are reported in many studies. Apart from crack width, the crack depths, cracking frequency and healing of cracks also influence the corrosion of steel in concrete. This paper presents a comprehensive review and summarised the results on the effect of cracking on corrosion of steel in concrete. The effect of crack widths on the diffusion of chlorides ions and carbon-dioxide is also discussed in this paper. Among all available results, a correlation between the corrosion current and the crack widths up to 0.3 mm can be established, however, no distinct trends are observed beyond that crack width. Conflicting results on the effect of crack widths on chloride ion diffusion are also reported. The longitudinal crack causes more severe corrosion of steel in concrete than transverse cracks of same width. Cracked concrete containing supplementary cementitious materials exhibited superior corrosion resistance than cracked ordinary Portland cement concrete of same width of transverse as well as longitudinal cracks. The same is also true in the case of lower water–binder ratios of cracked concrete. The increase in crack depth increased the chloride diffusion; however, the corrosion test shows an opposite trend. Conflicting results on the effect of crack frequency on corrosion of steel are also reported.

Reduced graphene oxide as a water, carbon dioxide and oxygen barrier in plasticized poly(vinyl chloride) films.

Herein, we report the incorporation of a 10 μm thick reduced graphene oxide (RGO) barrier layer in a plasticized poly(vinyl chloride) (PVC) film as the main constituent in ion-selective membranes used in potentiometric solid-contact ion-selective electrodes (SCISE). Fourier transform infrared attenuated total reflection (FTIR-ATR) and oxygen transmission rate (OTR) measurements showed that the embedded RGO barrier efficiently impedes the diffusion of liquid water, carbon dioxide and oxygen (O2) through the 400 μm thick PVC film, which causes potential instability and irreproducibility of the SCISEs. The measurements revealed that the RGO layer completely blocks the carbon dioxide diffusion, while it fully blocks the water diffusion for 16 h and reduced the OTR by 85% on average. The μm-thick RGO films used in this study were easier to handle and incorporate into host polymers, and form more efficient and robust barriers compared to the mono-, few- and multilayer graphene commonly applied as barrier layers for liquids and gases. We also demonstrated that the FTIR-ATR technique employed in the permeability measurements is a versatile and very sensitive technique for studying the diffusion of small amounts of water and carbon dioxide through graphene-based thin films.

Effect of Groove Volume on Effective Diffusivity of Carbon Dioxide through Oscillatory Flow in a Pipe with Circumferential Grooves

Effect of Groove Volume on Effective Diffusivity of Carbon Dioxide through Oscillatory Flow in a Pipe with Circumferential Grooves

Emphysema in HIV Positive Patient: Diagnostic and Therapeutic Conduct

The increase of cases of patients with chronic obstructive pulmonary disease in HIV positive patients is a reality since the TAAE era. In its beginning, infectious respiratory diseases were the most frequent and prevalent. Different factors were associated to this entity such as the HIV virus itself, antiretroviral treatment, tobacco habit, the use of marijuana, anemia, coinfection with HCV, BMI, nadir and current value of CD4 and viral load. The control of the patient through dyspnea assessment scales and complementary studies such as spirometry, chest CT, 6- minute walk test and carbon dioxide diffusion test have provided tools to contribute to the diagnosis, treatment and prevention of the complications inherent in COPD. Our patient presented a severe respiratory obstruction with FCV less than 70%, FEV1 less than 80%, FEV1/CFV ratio less than 70%, diffusion test less than 80% and central emphysema and paralobulillar CT. Its CD4 values and viral load within normal parameters.

Impact of the microstructure model on coupled simulation of drying and accelerated carbonation

During carbonation, the microstructure of a cement paste is strongly modified, which induces a dynamic feedback loop impacting the global advancement of the reaction. In this study, we investigate the effect of the microstructure model on simulations of accelerated carbonation of cement pastes. A variable-porosity reactive transport model with a new microstructure model is used. To match the chemical layers created by the carbonation front, we use a layered microstructure model. We demonstrate that qualitative prediction for a large range of conditions and formulations can only be obtained if the macroscopic parameters of the carbonated layer can be modelled accurately. In particular, the saturation dependent parameters, such as the capillary pressure or the relative diffusion coefficients, control the rate of advancement of the reaction front since a high saturation inhibits the carbon dioxide diffusion.

Effective Tidal Volume for Normocapnia in Very-Low-Birth-Weight Infants Using High-Frequency Oscillatory Ventilation.

PurposeRemoval of CO2 is much efficient during high-frequency oscillatory ventilation (HFOV) for preterm infants. However, an optimal carbon dioxide diffusion coefficient (DCO2) and tidal volume (VT) have not yet been established due to much individual variance. This study aimed to analyze DCO2 values, VT, and minute volume in very-low-birth-weight (VLBW) infants using HFOV and correlates with plasma CO2 (pCO2).Materials and MethodsDaily respiratory mechanics and ventilator settings from twenty VLBW infants and their two hundred seventeen results of blood gas analysis were collected. Patients were treated with the Dräger Babylog VN500 ventilator (Drägerwerk Ag & Co.) in HFOV mode. The normocapnia was indicated as pCO2 ranging from 45 mm Hg to 55 mm Hg.ResultsThe measured VT was 1.7 mL/kg, minute volume was 0.7 mL/kg, and DCO2 was 43.5 mL2/s. Mean results of the blood gas test were as follows: pH, 7.31; pCO2, 52.6 mm Hg; and SpO2, 90.5%. In normocapnic state, the mean VT was significantly higher than in hypercapnic state (2.1±0.5 mL/kg vs. 1.6±0.3 mL/kg), and the mean DCO2 showed significant difference (68.4±32.7 mL2/s vs. 32.4±15.7 mL2/s). The DCO2 was significantly correlated with the pCO2 (p=0.024). In the receiver operating curve analysis, the estimated optimal cut-off point to predict the remaining normocapnic status was a VT of 1.75 mL/kg (sensitivity 73%, specificity 80%).ConclusionIn VLBW infants treated with HFOV, VT of 1.75 mL/kg is recommended for maintaining proper ventilation.

What Drives Carbon Isotope Fractionation by the Terrestrial Biosphere?

AbstractDuring photosynthesis, terrestrial plants preferentially assimilate the lighter and much more abundant form of carbon, 12C, which accounts for roughly 99% of naturally occurring forms of this element. This photosynthetic preference for lighter carbon is driven principally by differences in molecular diffusion of carbon dioxide with differing 13C/12C across stomatal pores on leaves, followed by differences in carboxylation rates by the Rubisco enzyme that is central to the process of photosynthesis. As a result of these slight preferences, which work out to about a 2% difference in the fixation rates of 12CO2 versus 13CO2 by C3 vegetation, plant tissues are depleted in the heavier form of carbon (13C) relative to atmospheric CO2. This difference has been exploited in a wide range of scientific applications, as the photosynthetic isotope signature is passed to ecosystem carbon pools and through ecological food webs. What is less appreciated is the signature that terrestrial carbon exchanges leave on atmospheric CO2, as the net uptake of carbon by land plants during their growing season not only draws down the local CO2 concentration, it also leaves behind relatively more CO2 molecules containing 13C. The converse happens outside the growing season, when autotrophic and heterotrophic respiration predominate. During these periods, atmospheric CO2 concentration increases and its corresponding carbon isotope composition becomes relatively depleted in 13C as the products of photosynthesis are respired, along with some small isotope fractionation that happen downstream of the initial photosynthetic assimilation. Similar phenomena were first observed at shorter time scales by the eminent carbon cycle scientist, Charles (Dave) Keeling. Keeling collected samples of air in glass flasks from sites along the Big Sur coast that he later measured for CO2 concentration and carbon isotope composition (δ13C) in his lab (Keeling, 1998). From these samples, Keeling observed increasing CO2 concentrations at night compared to the day, along with corresponding depletions in their δ13C. These phenomena were understood at the time to be driven by interactions between ecosystem carbon exchanges and vertical movements of the atmospheric boundary layer (Keeling, 1958).

Effects of Operational Parameters on Diffusion Coefficients of CO2 in a Carbonated Water–Oil System

Diffusion of carbon dioxide (CO2) in a carbonated water–oil system is of great importance for proper design of CO2-based enhanced oil recovery (EOR) processes. We study the effects of operational parameters such as saturation pressure, temperature, and phase volumes on diffusion coefficients of CO2 in a carbonated water–oil system. Results show that diffusion coefficients of CO2 in both phases are susceptible to saturation pressure. The greater the saturation pressure, the larger the diffusion coefficients. At a given saturation pressure, diffusion coefficients of CO2 in two phases increase by increasing temperature. Values of the coefficients determined at 40 °C are about twice those determined at 20 °C. The equilibration of the system was found to be much faster at the higher temperature. The results indicate that the predicted diffusion coefficients are insensitive to phase volumes, indicating applicability of the determined diffusion coefficients to simulate the mass transfer in large-scale reservoirs.

Physiological, nutritional and growth responses of melon (Cucumis melo L.) to a gradual salinity built-up in recirculating nutrient solution

ABSTRACTMinimizing salinity impacts on yield in melon crops cultivated in closed-loop hydroponic systems requires better understanding of the physiological impact of gradual salt accumulation in the recycled solution. To attain this objective, different sodium chloride (NaCl) concentrations in the irrigation water, i.e. 0.7, 2.5, and 5 mM, were applied in two cropping seasons (winter-spring;WS and spring-summer;SS). In both seasons plant biomass and yield were negatively affected only in high NaCl-treated plants, due to stomatal limitations, which restricted carbon dioxide (CO2) diffusion into the leaf, osmotic and salt-specific effects. However, a progressive NaCl built-up to maximum concentrations in the root zone solution of 15 (WS) and 20 mM (SS), enabled plants to preserve several physiological mechanisms, thereby adjusting growth and yield without impairing fruit quality. Our results suggest that the use of irrigation water, containing up to 2.5 mM NaCl, is feasible in melon crops grown in closed-loop hydroponic systems, without yield and quality losses.

Effect of frequency on pressure cost of ventilation and gas exchange in newborns receiving high-frequency oscillatory ventilation.

BackgroundWe hypothesized that ventilating at the resonant frequency of the respiratory system optimizes gas exchange while limiting the mechanical stress to the lung in newborns receiving high-frequency oscillatory ventilation (HFOV). We characterized the frequency dependence of oscillatory mechanics, gas exchange, and pressure transmission during HFOV.MethodsWe studied 13 newborn infants with a median (interquartile range) gestational age of 29.3 (26.4-30.4) weeks and body weight of 1.00 (0.84-1.43) kg. Different frequencies (5, 8, 10, 12, and 15 Hz) were tested, keeping carbon dioxide diffusion coefficient (DCO2) constant. Oscillatory mechanics and transcutaneous blood gas were measured at each frequency. The attenuation of pressure swings (ΔP) from the airways opening to the distal end of the tracheal tube (TT) and to the alveolar compartment was mathematically estimated.ResultsBlood gases were unaffected by frequency. The mean (SD) resonant frequency was 16.6 (3.5) Hz. Damping of ΔP increased with frequency and with lung compliance. ΔP at the distal end of the TT was insensitive to frequency, whereas ΔP at the peripheral level decreased with frequency.ConclusionThere is no optimal frequency for gas exchange when DCO2 is held constant. Greater attenuation of oscillatory pressure at higher frequencies offers more protection from barotrauma, especially in patients with poor compliance.

Weight-correction of carbon dioxide diffusion coefficient (DCO2 ) reduces its inter-individual variability and improves its correlation with blood carbon dioxide levels in neonates receiving high-frequency oscillatory ventilation.

Carbon-dioxide elimination during high-frequency oscillatory ventilation (HFOV) is thought to be proportional to the carbon dioxide diffusion coefficient (DCO2 ) which is calculated as frequency x (tidal volume)2 . DCO2 can be used to as an indicator of CO2 elimination but values obtained in different patients cannot be directly compared. To analyze the relationship between DCO2 , the weight-corrected DCO2 (DCO2 corr) and blood gas PCO2 values obtained from infants receiving HFOV. DCO2 data were obtained from 14 infants at 1/s sampling rate and the mean DCO2 was determined over 10 min periods preceding the time of the blood gas. DCO2 corr was calculated by dividing the DCO2 by the square of the body weight in kg. Weight-correction significantly reduced the inter-individual variability of DCO2 . When data from all the babies were combined, standard DCO2 showed no correlation with PCO2 but DCO2 corr showed a weak but statistically significant inverse correlation. The correlation was better when the endotracheal leak was <10%. There was significant inverse but weaker correlation between the HFOV tidal volume (VThf) and the PCO2 . In any baby, DCO2 corr >50 mL2 /sec/kg2 or VThf > 2.5 mL/kg was rarely needed to avoid hypercapnia. Weight-correction of DCO2 values improved its comparability between patients. Weight-corrected DCO2 correlated better with PCO2 than uncorrected DCO2 but the correlation was weak.