Dry Air Conditions Research Articles

Do we know how much force we apply with latex intermaxillary elastics?

Objectives: The aim of our study was to evaluate the variation of the forces provided by different branded elastics and to compare the force diminution that occurs after 24-h of use in wet environment. Materials and Methods: Elastics from four different manufacturer (American Orthodontics [AO], USA; Dentaurum [DENT], Germany; Ormco, USA; RMO, USA) with 3/16-inch (4.8 mm) lumen diameter, and two different force degrees (medium/heavy) were included in the study with a total of eight groups of elastics. First force measurements were performed with 50 elastics of each group at various stretching distances; lumen diameter ×2 (9.52 mm), ×3 (14.28 mm), the average canine-first molar length (22.3 mm), and the canine-second molar length (38.7 mm) under room temperature and dry air conditions. In addition, ten the elastics from each group were stretched at 22.3 mm distance in a custom-made plate and kept in 37°C distilled water. Twenty-four hours later, the force measurements were repeated. Results: Regardless of the brand and type (medium-heavy), all the tested elastics showed variations in matter of generated forces at different stretching distances. The variation amount increased as the length of elongation increased. The lowest standard deviation values were observed for both medium and heavy DENT elastic groups. When stretched to 3 times of their lumen size, the medium and heavy elastics both produced either lower or higher forces compared to the levels of force indicated by the manufacturers. The closest mean force to the force level stated by the manufacturer was provided with medium AO (3.6 g difference) elastics and heavy RMO counterparts (7.9 g difference). A significant 20–23% reduction of force was observed in all brands, both in medium and heavy elastics after passing 24-h in aqueous environment. No significant difference was observed in matter of force degradation between groups for both medium and heavy elastics (P < 0.05). Conclusion: The forces exerted by intermaxillary elastics were not found to be standard and the force stated on the package is not always provided precisely. A significant force loss around 20% was observed with all the elastics after 24-h of use in wet environment at 37°C.

Drying and Heating Processes in Arbitrarily Shaped Clay Materials Using Lumped Phenomenological Modeling

This work aims to study the drying of clay ceramic materials with arbitrary shapes theoretically. Advanced phenomenological mathematical models based on lumped analysis and their exact solutions are presented to predict the heat and mass transfers in the porous material and estimate the transport coefficients. Application has been made in hollow ceramic bricks. Different simulations were carried out to evaluate the effect of drying air conditions (relative humidity and speed) under conditions of forced and natural convection. The transient results of the moisture content and temperature of the brick, and the convective heat and mass transfer coefficients are presented, discussed and compared with experimental data, obtaining a good agreement. It was found that the lower the relative humidity is and the higher the speed of the drying air is, the higher the convective heat and mass transfer coefficients are at the surface of the brick and in the holes, and the faster the moisture removal material and heating is. Based on the predicted results, the best conditions for brick drying were given. The idea is to increase the quality of the brick after the process, to reduce the waste of raw material and energy consumption in the process.

Quality assessment of GaN epitaxial films: Acidification scenarios based on XPS-and-DFT combined study

X-ray photoelectron spectroscopy (XPS) of electronic structure and surface states of GaN epitaxial films grown on Al2O3 and SiC substrates established the presence of only traces of surface oxidation after three years storage in standard air media conditions. No additional treatment was applied during this storage process. The slight shift (~1 eV) of Valence Band (VB) spectra was found which occurs without any visible contribution of gallium oxide electronic states to the valence band area. Additionally, GaN-typical N 2s band is present in VB-spectra of studied epitaxial films what is confirming their high quality grade. First-principle modelling demonstrates favorability of GaN surface acidification because of humidity and much slower oxidation process in the dry-air conditions. Theoretical models of acidification scenarios also demonstrate that oxidation of defect-free and defective surfaces (N-vacancies) are a good leveler: electronic structures of all considered surfaces became almost identical that is in a perfect agreement with results of XPS measurements and analytics.

Influence of water content investigation on GPR wave attenuation for early age concrete in natural air-drying condition

In this study, an efficient application to evaluate water content of concrete in a non-destructive way in natural air-drying conditions by time-lapse Ground-penetrating radar (GPR) measurements is described. This was achieved by carrying out time-lapse GPR measurements on a concrete block with 2 GHz shielded antenna in 24 measurement days between day three and the 150th day of concrete casting. The characteristics of the electromagnetic (EM) wave are directly influenced by the presence of water content in a material. Change in water content results in variations in dielectric properties, including dielectric permittivity and conductivity. The study focused on variation of EM wave attenuation, which is related to direct and reflected wave amplitudes due to decrease of water content in the sample. In order to obtain a reflected wave a reinforced bar was embedded at 10 cm depth. The ratio of the direct wave and reflected wave on each measurement day decreased with respect to the reflection amplitude, due to concrete desiccation. These results are a guide to determining the relationship between volumetric water content (VWC) and EM wave attenuation. The method has significant potential on freshly produced young concrete samples to monitor their quality. The suggested method may also have potential for practical on-site studies to determine possible corrosion risk due to water intrusion.

Effects of flow parameters on thermal performance of an inner-liner anti-icing system with jets impingement heat transfer

The multiple jets impingement heat transfer is widely applied in the wing anti-icing system. It is challenging to apply the similarity criterion to carry out the anti-icing experiments due to the complex flow and heat transfer behavior. In the present study, the full-scale slat model is used to carry out anti-icing experimental researches in a 2 m × 3 m icing wind tunnel of China Aerodynamics Research and Development Center. The effects of icing parameters Liquid Water Content (LWC) and Median Volume Diameter (MVD) and hot air parameters (mass flow rate and temperature) on the thermal performance of an inner-liner anti-icing system with jets impingement heat transfer are studied. The effects of the experimental parameters are analyzed in detail by combining impingement and evaporation heat transfer mechanisms. The impingement hot air mass flow rate dramatically affects the heat transfer performance of the impingement stagnation region within the range of the experimental parameters. The temperature of impingement hot air and that of wing skin are approximately linear correlated. The experimental results show the effects of LWC and MVD on water film formation and runback ice accretion. The formation of water film is analyzed by an analytical method based on the wing skin temperature difference of dry and wet air conditions.

On the Study of Osmotic Dehydration and Convective Drying of Cassava Cubes

This paper aims to study the hybrid process of osmotic dehydration and convective air drying of foods. Emphasis has been put on cassava cubes (Manihot esculenta Crantz.). Convective drying kinetics of fresh and osmotically dehydrated cassava cubes was evaluated at the following hot air-drying conditions: temperature 50°C, velocity 1.35 m/s, and absolute humidity 0.060 dry water/g. Experimental results of the moisture loss, solids gain, and incorporation of sodium chloride are shown and analyzed. For estimation of the effective mass diffusion coefficient, experiment data of average moisture content of cassava cubes (fresh and osmotically dehydrated) was fitted to the simplified Fick model and a good agreement was obtained. The effective mass diffusivity of the osmotically dehydrated cassava cube was 2.75 x10-10 m2/s and to fresh cassava cubes 5.45x10-10 m2/s.

Modeling kinetics of convective drying of Curcuma longa L.

ABSTRACT This study aimed to determine drying curves of land saffron (Curcuma longa L.) rhizomes at different temperatures and ventilation conditions to adjust non-linear regression models, and to calculate effective diffusion coefficients and activation energies. Saffron rhizomes were randomly collected in natura with a hoe from the soil in Rio Verde, Goiás, Brazil. They were subsequently sized, sanitized, and sliced into 2.63 ± 0.1 mm thick sections. Rhizomes were dried in an oven with forced air ventilation at 45, 55, 65 and 75 °C for 18, 14, 10 and 9 hours, respectively. As the temperature increased, drying time was reduced. Consequently, moisture content also decreased, facilitating the drying process by decreasing the energy required to remove water molecules. Among the analyzed models, the Midilli model was best adjusted to the data under different drying air conditions. Effective diffusion coefficients (D) were 9.17 × 10-11, 13.33 × 10-11, 20.09 × 10-11, and 35.89 × 10-11 m2 s-1 at 45, 55, 65 and 75 °C, respectively, increasing with higher temperatures. Activation energy for liquid diffusion during drying was 21.186 kJ mol-1.

Thermal Decomposition Behavior of Prussian Blue in Various Conditions.

Prussian blue analogs (PBA) are widely studied for radioactive cesium decontamination. However, there are fewer works related to their post use storage. Considering the oxidative stabilization of the material after the selective uptake of Cs, the thermogravimetric properties in powder and bead form, with various Cs and other alkali metal ions adsorbed, and various heating rates were studied. TG-DTA taken in dry air condition shows an exothermic decomposition at ~270 °C. This temperature varied with the heating rate, mass, and the proportion of adsorbed ions. The best condition for complete oxidation of Prussian blue (PB) is found to be a gradual oxidative decomposition by heating in the temperature range of 200–220 °C until the total mass is decreased by >35%. After this, the temperature could be safely increased to >300 °C for the complete oxidative decomposition of PB that formed iron oxide and salt of the adsorbed Cs. A pilot scale test conducted using the radioactive Cs adsorbed Prussian blue microbeads (PB-b) confirmed that no Cs was released in the effluent air during the process.

Health, work performance, and risk of infection in office-like environments: The role of indoor temperature, air humidity, and ventilation.

Epidemiological and experimental studies have revealed the effects of the room temperature, indoor air humidity, and ventilation on human health, work and cognitive performance, and risk of infection. In this overview, we integrate the influence of these important microclimatic parameters and assess their influence in offices based on literature searches. The dose-effect curves of the temperature describe a concave shape. Low temperature increases the risk of cardiovascular and respiratory diseases and elevated temperature increases the risk of acute non-specific symptoms, e.g., dry eyes, and respiratory symptoms. Cognitive and work performance is optimal between 22°C and 24°C for regions with temperate or cold climate, but both higher and lower temperatures may deteriorate the performances and learning efficiency. Low temperature may favor virus viability, however, depending on the status of the physiological tissue in the airways. Low indoor air humidity causes vulnerable eyes and airways from desiccation and less efficient mucociliary clearance. This causes elevation of the most common mucous membrane-related symptoms, like dry and tired eyes, which deteriorates the work performance. Epidemiological, experimental, and clinical studies support that intervention of dry indoor air conditions by humidification alleviates symptoms of dry eyes and airways, fatigue symptoms, less complaints about perceived dry air, and less compromised work performance. Intervention of dry air conditions by elevation of the indoor air humidity may be a non-pharmaceutical treatment of the risk of infection by reduced viability and transport of influenza virus. Relative humidity between 40 and 60% appears optimal for health, work performance, and lower risk of infection. Ventilation can reduce both acute and chronic health outcomes and improve work performance, because the exposure is reduced by the dilution of the indoor air pollutants (including pathogens, e.g., as virus droplets), and in addition to general emission source control strategies. Personal control of ventilation appears an important factor that influences the satisfaction of the thermal comfort due to its physical and positive psychological impact. However, natural ventilation or mechanical ventilation can become sources of air pollutants, allergens, and pathogens of outdoor or indoor origin and cause an increase in exposure. The "health-based ventilation rate" in a building should meet WHO's air quality guidelines and dilute human bio-effluent emissions to reach an acceptable perceived indoor air quality. Ventilation is a modifying factor that should be integrated with both the indoor air humidity and the room temperature in a strategic joint control to satisfy the perceived indoor air quality, health, working performance, and minimize the risk of infection.

Bioaccessibility and bioavailability of soluble polyphenols from Capparis zeylanica fruit according to drying method

Capparis zeylanica fruits are excellent source of phytochemicals with numerous health benefits and used in several Ayurvedic preparations. But there are no studies to determine which phytochemical is responsible for those health benefits. Thus, in the present study, we evaluated the bioaccessibility and bioavailability of polyphenols from processed Capparis zeylanica fruits. The fruits were dried by shade drying (SH) and hot air drying (HD) conditions and extracted the polyphenols. The Bioaccessibility studies revealed that gallic acid was highly accessible in SH and HD with varying percentages. Gallic acid percentages in SH were 97.95% ± 4.90 in oral, 64.03% ± 3.20 in gastric and 44.76% ± 2.24 in intestinal phases followed by epicatechin (87.95% ± 4.40, 53.39% ± 2.66 and 31.0% ± 1.55 in oral, gastric, and intestinal phases, respectively) whereas, in HD, gallic acid was more bioaccessibile (97.61% ± 4.88, 57.2% ± 2.86 and 31.68% ± 1.58) followed by epicatechin (82.59% ± 4.13, 54.56% ± 2.72, and 30.47% ± 1.52) and syringic acid (5.21% ± 0.26, 12.96% ± 0.65, and 5.52% ± 0.27) in oral, gastric, and intestinal phases, respectively. Interestingly, the results were comparable with bioavailability study, performed with C57BL/6 mice showed the Tmax value of both gallic acid in SH and epicatechin in HD at two hours with a Cmax value of 31.28 µg/mL and 30.08 µg/mL of plasma, respectively. The study revealed that the processed and dehydrated Capparis zeylanica fruits were stable in in vivo system and can be used for the development of novel value-added products.

Precise Correction of Gravity Data for the Effect of Local Atmospheric Loading at Beijing Seismic Station, China

The gravity effect due to local atmospheric loading is an important signal and correction in various geometrical applications. In this paper, we calculated loading effects on gravity using Farrell’s method with the gravity loading Green’s function from the Preliminary Reference Earth Model (PREM). The elastic part of the gravity loading Green’s function was calculated using a linear combination of Love numbers and Legendre polynomial. The direct part of the gravity loading Green’s function was calculated using Newtonian gravitational theory. Gravity Green’s functions are the sum of the abovementioned two Green’s functions (the elastic and direct parts). The integral elevation used to calculate air mass was 86 km. In this paper, we conducted integration only over local areas (0.5° angular distance from the gravity station). Under dry and wet air conditions, the difference in the gas constant R was 6.052 J/kg K, and the corresponding gravity change was approximately 1.3 µGal. The gas constant variation under relative humidity between 40 and 80% at the Beijing seismic station was 0.76 J/kg K, and the gravity variation was 0.1 µGal. The gas constant of dry air was selected to compute the direct part of the Green’s function given the limited gravity variation in this range of relative humidity. The atmospheric gravity Green’s functions were convolved with the observed pressure; the influence did not exceed 10 µGal within 50 km of the gravity station. The influence of temperature, station height, and topography on gravity was mostly in the near region of the station (angular distance smaller than 0.1°), with the maximum impact from 1000-m station height (4.68 µGal), followed by 1000-m topographic height (2.93 µGal). The impact of temperature at −30°was 0.15 µGal.

Superoxide radical enhanced photocatalytic performance of styrene alters its degradation mechanism and intermediate health risk on TiO2/graphene surface

Enhancement of reactive oxygen species (ROS) on semiconductor coupled by carbon material promotes photocatalytic performance toward aromatic hydrocarbons, while the contribution to their degradation mechanism and health risk is not well understood. Herein, photocatalytic degradation of styrene on TiO2 and TiO2/reduced graphene oxide (TiO2/rGO) surface is compared under dry air condition to investigate the role of ·O2− in styrene degradation. TiO2/rGO shows 4.8 times higher degradation efficiency than that of TiO2, resulting in 16% reduced production of intermediates with identical composition. The improved formation of ·O2− on TiO2/rGO is confirmed responsible for these variations. Theoretical calculation further reveals the enhancement of ·O2− thermodynamically favoring conversion of styrene to acetophenone, turning the most dominant intermediate from benzoic acid on TiO2 to acetophenone on TiO2/rGO. The accumulated formation of acetophenone on TiO2/rGO poses increased acute threat to human beings. Our findings proclaim that ROS promoted photocatalytic performance of semiconductor after carbon material composition ultimately changes the priority order of degradation pathways to form by-product with higher threat toward human beings. And more attentions are advised focusing on the relevance with degradation efficiency, intermediate and toxicity of aromatic hydrocarbons on carbon material based photocatalyst.

A Proposed Method for Quantifying Thermal Exposure Incurred during Rough-Rice Drying

HighlightsDrying conditions affect rice end-use functionality.Thermal exposure incurred by rough rice may differ depending on drying conditions.A framework is proposed for deriving an index that can show how much heat exposure rough rice incurs during drying.Abstract. Heated air is used to dry most rice in the U.S. Thus, commercial rice drying can be considered a thermal process that aims to remove moisture from rough rice until a desired moisture content is reached. Parallels can be drawn between rice drying and thermal sterilization that is targeted at reducing microbial load because moisture content reduction during drying follows similar decay rate kinetics as the reduction in microbial load during thermal sterilization. Given the different combinations of drying air conditions (air temperature and relative humidity), as well as drying and tempering durations, employed in various dryer designs for rice drying and the impact that these conditions have on rice end-use functionality, this study sought to derive a thermal treatment index (drying process values) that is similar to the F0 value concept used in thermal sterilization for quantifying and comparing the thermal exposure incurred by rice during drying under various scenarios. Using data collected from rough-rice drying experiments, a decimal desorption value (Dmv) that represents the duration required to cause a 90% reduction in moisture ratio during drying at a specified temperature was determined, from which a thermal desorption constant (Zmv) that represents the increase in temperature necessary to cause a 90% reduction in Dmv during drying was established. Subsequently, a thermal desorption value (Fmv) was derived to express the duration that a rice lot would have been heat treated at a reference temperature during drying to produce an equivalent effect on moisture content as that produced by the actual drying process. Keywords: End use, Moisture content, Peak viscosity, Postharvest, Relative humidity, Rice, Temperature.

Evaluation of different drying processes by energy consumption in an insulated and not insulated laboratory convection dryer

Drying is a process to increase the shelf-life of fruits by decreasing their water content. It is one of the energy consuming processes in food engineering. In many studies, the drying time duration and quality of dried fruits were investigated. In this study, the energy consumption in different drying conditions was investigated for the apple in a laboratory convection dryer. The drying conditions were the application of the temperatures of 40, 50, and 60°C and the speeds of 0.5 and 1 ms-1 for the drying air using the insulated and non-insulated drying chambers. Independent from drying duration, the highest energy consumption was recorded as 11.2 kWh for the non-insulated dryer under the drying air condition of 40°C and 0.5 ms-1 . While the lowest energy consumption was only 5.8 kWh for the insulated dryer with the drying air condition of 40 and 50°C and the same 0.5 ms-1 . The drying duration for these conditions was 537, 313, and 233 mins. To achieve the shortest drying time (153 mins), the condition of 60°C and 1 ms-1 in the insulated dryer was used which caused the energy consumption of 7.2 kWh.

Drying properties of Sentang (Azadirachta excelsa) dried under different temperatures

In this study, we investigated the drying properties of Sentang (Azadirachta excelsa) dried at different temperatures. Sentang tree planted in Kelantan, Malaysia, was used in this study. Drying specimens with dimensions of 30 ×150 × 500 mm were dried under air-drying conditions, a constant temperature of 60, 80, 100, and 120 °C until the moisture content (MC) of the specimens reaches an equilibrium moisture content (EMC) at each drying condition. The drying properties of the specimens were then examined. The results confirmed that drying temperature had a significant effect on drying time. As expected, drying Sentang under air-drying conditions demanding considerable time than the other drying conditions.

Rice paste viscosities and gel texture resulting from varying drying and tempering regimen

AbstractBackground and objectivesHeated‐air drying followed by tempering (HAT) is effective for increasing rough rice drying rates without compromising head rice yield (HRY). However, relatively little is known about the specific nature of the effects of HAT regimens on end‐use properties of rice. This study determined the effects of drying air conditions (air temperature and relative humidity) and tempering durations on changes in rice paste viscosities and gel texture.FindingsRice paste viscosities and gel texture were not only dependent on drying air temperature but also on how long the rice was exposed to a given temperature during drying and tempering. Air relative humidity (rh) had an indirect effect on rice end‐use properties. Using different HAT regimens, peak viscosity was altered by 16%, final viscosity by 21%, breakdown by 24%, and setback by >500% compared with control samples. Gel strength was increased by approximately 40% with HAT regimens.ConclusionsHeated‐air drying and tempering conditions must be carefully selected, not only to minimize HRY reductions but also to minimize variations in the functional properties of rice intended for specified end uses. Likewise, HAT regimens could be selected to produce desired properties for specified end uses.Significance and noveltyInconsistencies in rice flour functionality are a hindrance to an expansive use of rice in end‐use, gluten‐free product development. This study shows that drying, a critical postharvest operation, could introduce variations in rice flour quality, which also implies that HAT regimens could deliberately be utilized to produce flour for various end‐use applications.

Effect of moisture on the oxidation behavior of ZrB2

AbstractOxidation studies of ZrB2 were performed under wet air and dry air conditions at 1200°C, 1400°C, and 1500°C for 1, 4, and 10 h. Compared to dry air, the presence of water vapor was found to enhance the oxidation kinetics by a factor of 7 to 30, depending on the temperature. Thermodynamic calculations suggested that water vapor promoted the formation of additional volatile species such as boric acid (HBO2), in addition to boria (B2O3) produced in dry air, which increased the evaporation rate of B2O3. Compared to dry air, the presence of water vapor leads to more rapid evaporation of boria and the transition from parabolic oxidation kinetic behavior (ie, rate controlled by diffusion through boria) to linear (ie, underlying ZrB2 is directly exposed to the oxidizing environment) at shorter times and lower temperatures.

Effect of Er doping on flame-made SnO2 nanoparticles to ethylene oxide sensing

In this research, 0.05–2 wt% Erbium (Er)-doped SnO2 nanoparticles were synthesized for the first time by flame spray pyrolysis and their gas-sensing properties were methodically characterized. The structural analyses based on scanning/transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, nitrogen sorption analysis, and photoluminescent spectroscopy suggested that nanocrystalline SnO2 nanoparticles were substitutionally doped with Er+3 species. The sensing films were prepared by powder pasting and spin-coating processes and their gas-sensing performances were evaluated in the temperature range of 200–400 °C under dry and humid air conditions. The test results reported that the optimum Er content of 0.1 wt% provided the optimally high and selective response of 347 to 30 ppm C2H4O with a short response time of ∼2 s and a low detection limit of 18 ppb, which were substantially better than those of undoped one at the best working temperature of 350 °C. The high selectivity was confirmed against CH2O, C3H6O, C2H5OH, NH3, C2H2, C2H4, H2, CH4, H2S, H2O and CO. Besides, the influence of humidity on C2H4O response of Er-doped SnO2 sensor was moderately low over a wide relatively humidity range of 0–80 %. The gas-sensing mechanisms were proposed with a new model describing the catalytic roles of p-type Er dopants to ethylene oxide adsorption.

Scale Formation on HSLA Steel during Continuous Casting Part II: The Effect of Surface Conditions

The present research addresses the effect of surface condition on oxide scale formation at high temperatures such as those experienced during secondary cooling in Continuous Casting. Tests were carried out in clean, as-cast and surfaces covered with casting powder to replicate the oxidation/re-oxidation after the mould. Specimens oxidized at 1000, 1100 and 1200 °C under dry air and water-vapour conditions revealed that the oxide scale formation is strongly influenced by temperature, environmental and surface conditions. The oxide scale thickness increases with temperature alterations in the surface (e.g., as-cast and covered with powder) where oxides and carbonates from the casting powder accelerate oxidation kinetics leading to thick and unstable scales. A high amount of carbon is present on surfaces covered with casting powder where it diffuses through the oxide scale forming CO and CO2 which lead to stress accumulation that makes scales prone to defects such as pores, voids and micro-cracks. Ultimately, if wüstite remains attached to the steel surface or inside oscillation marks, it may disturb heat transfer during secondary cooling which has deep industrial implications for crack formation and overall casting yield. Therefore, accurate insights on scale type and growth mechanisms could lead to accurate control of its formation during casting.

Scale Formation on HSLA Steel during Continuous Casting Part I: The Effect of Temperature–Time on Oxidation Kinetics

The findings in this work enhance the understanding of oxidation mechanisms and scale growth at high temperatures of a high strength low alloy (HSLA) steel for improving surface quality during continuous casting. The oxidation phenomenon was investigated under dry air and water vapor atmospheres by heating specimens at 1000, 1100, and 1200 °C at different holding times. Temperature and time had great effects on the kinetics, where faster (i.e., parabolic) oxidation rates were present under water vapor when compared with the dry air condition. Temperature strongly influenced the number of defects, such as pores, voids, gaps and micro-cracks, formed in the oxide scale. A phase analysis confirmed the presence of FeO as the first phase formed at the steel surface, Fe3O4 as the middle and thicker phase, and Fe2O3 as the last phase formed in the oxide/air interface. The micromechanics of the oxides demonstrated that a combination of phases with high (wüstite) and low plasticity (magnetite and hematite) could also have been the reason for the uneven cooling during Continuous Casting (CC) that resulted in the undesired surface quality of the steel slabs. This work gives a good look at the oxide scale effect on the surface quality of steel slabs through an understanding the kinetics during oxidation.