Changes In Oxygen Concentration Research Articles

A Wearable Functional Near-Infrared Spectroscopy (fNIRS) System for Obstructive Sleep Apnea Assessment.

Obstructive sleep apnea (OSA), one of the most common sleep-related breathing disorders, contributes as a potentially life-threatening disease. In this paper, a wearable functional near-infrared spectroscopy (fNIRS) system for OSA monitoring is proposed. As a non-invasive system that can monitor oxygenation and cerebral hemodynamics, the proposed system is dedicated to mapping the pathogenic characteristics of OSA to dynamic changes in blood oxygen concentration and to constructing an automatic approach for assessing OSA. An algorithm including feature extraction, feature selection, and classification is proposed to signals. Permutation entropy(PE), for quantitative measuring the complexity of time series, is firstly involved to characterize the features of the physiological signals. Subsequently, the principal component analysis (PCA) for feature dimensionality reduction and support vector machine (SVM) algorithm for OSA classification are applied. The proposed method has been validated on a dataset that collected by the wearable system. It includes 40 subjects and composes of normal, and various severity cessation of breathing (e.g., mild, moderate, and severe). Experimental results exhibit that the proposed system can effectively distinguish OSA and non-OSA subjects, with an accuracy of 91.89%. The proposed system is expected to pave the novel perspective for OSA assessment in terms of cerebral hemodynamics.

Body size dictates physiological and behavioural responses to hypoxia and elevated water temperatures in Murray cod (Maccullochella peelii).

Increasing drought frequency and duration pose a significant threat to fish species in dryland river systems. As ectotherms, fish thermal and hypoxia tolerances directly determine the capacity of species to persist in these environments during low flow periods when water temperatures are high and waterbodies become highly stratified. Chronic thermal stress can compound the impacts of acute hypoxic events on fish resulting in significant fish mortality; however, it is not known if all size classes are equally susceptible, or if the allometric scaling of physiological processes means some size classes are disproportionately affected. We investigated the physiological responses of Murray cod (Maccullochella peelii) over a four-fold body size range (0.2-3000g) to acute changes in water temperature and oxygen concentration following 4 weeks of acclimation to representative spring (20°C) and summer (28°C) water temperatures. We recorded maximum thermal tolerance (CT max), oxygen limited thermal tolerance (PCTmax ), lowest tolerable oxygen level (as the oxygen level at which lose equilibrium; O2,LOE), gill ventilation rates and aerial surface respiration threshold, blood oxygen transport capacity and lactate accumulation. Acclimation to elevated water temperatures improved thermal and hypoxia tolerance metrics across all size classes. However, body size significantly affected thermal and hypoxia responses. Small M. peelii were significantly less hypoxia tolerant than larger individuals, while larger fish were significantly less thermal tolerant than smaller fish. Hypoxia constrained thermal tolerance in M. peelii, with both small and large fish disproportionally compromised relative to mid-sized fish. Our findings indicate that both very small/young (larvae, fry, fingerlings) and very large/older M. peelii in dryland rivers are at significant risk from the combined impacts of a warming and drying climate and water extraction. These data will inform policy decisions that serve to balance competing demands on precious freshwater resources.

Examination of effects of indoor fires on building structures and people

The scientific study of the harmful effects of indoor fires on building structures and on the environment is a top issue today. Indoor fires frequently occur all over the world. The goal of our research is to examine the effects of an average room fire on the survival possibility of a trapped person and on the building structure, taking into account features of the Eastern European architecture. First, a computational fluid dynamics (CFD) simulation was performed to examine the change of temperature, oxygen, and carbon monoxide concentration in a selected room in a vacant building used for military training. Based on the results, a 1:1 scale fire experiment was carried out with the parameters used in the simulation. The experiment was repeated once with the same settings. It was observed that without the intervention of firefighters, the temperature in the experiment could have rapidly reached 400 °C, as suggested by the simulation, which could have caused structural damage to the building. Furthermore, after 3 min the carbon monoxide concentration reached 400 ppm in both experiments and the simulation, which is a harmful level to people trapped inside the room. Also, in the experiment there was sufficient oxygen at the ground level with what people can survive 3 min.

Competitive sensitization effect towards Luminescence-tuned Lanthanide-doped TiO2/SiO2 Core-shell nanoparticles for enhanced responsivity oxygen detection

The luminescence of TiO2 doped with Sm3+ can be excited through TiO2 band-to-band absorption, which exhibits oxygen sensitivity. However, its carrier behaviors and oxygen sensing mechanism have not yet been clarified, which inhibits the further improvement of sensitivity. In this study, using Eu3+ ions as an “energy level probe,” we demonstrated a novel strategy using a C@SiO2:2%Sm3+@TiO2 hollow double-shell nanostructure containing surface oxygen vacancies, designated a competitive sensitization effect for the first time. Density-functional theory combined with the experimental results revealed the carrier behaviors and oxygen sensing mechanism. Further, we demonstrated that the charge state of oxygen vacancies is controlled by the adsorption and desorption of dioxygen molecules, which affects electron relaxation and indirectly affects the luminescent behaviors. The effective exploitation of the competitive sensitization effect and revelation of the oxygen sensing mechanism ensured that the excitation of Sm3+ in C@SiO2:2%Sm3+@TiO2 can be controlled by the ambient oxygen concentration. Therefore, compared to the widely reported Sm3+-doped TiO2, C@SiO2:2%Sm3+@TiO2 demonstrated increased oxygen sensitivity (by over three folds) with a detection minimum of sub-100 ppm. Moreover, as ambient oxygen concentration changes, the luminescence color of the films prepared by using C@SiO2:2%Sm3+@TiO2 and commercial blue phosphors changes significantly (from pink to blue).

Microstructure and Formation Mechanisms of Nanowires and Nanoplates ZrO<sub>2</sub> during the ZrB<sub>2</sub> Deposition Process

Preparation of boride by chemical vapor deposition (CVD) is sensitive to oxygen, subtle changes in oxygen concentration during the deposition of ZrB2 can induce the formation of Zirconium dioxide (ZrO2) with a novel nanoplate-stacked structure and nanowire structure. The ZrO2 nanostructure changed with - oxygen concentration. Nanowires with uniform size of 50-100 nm in diameter and over 100 μm in length were obtained at high oxygen concentration, while highly-ordered nanoplate arrays were obtained at low oxygen concentration. Both of these nanostructures were grown in situ on the surface of ZrB2-coating. In this paper, the preparation method of novelty ZrO2 nano-structures grown in situ was provided, the morphologies and compositions of the nano-structural ZrO2 were characterized and the formation mechanism was proposed, which also provides experimental basis for the industrial morphology control of ZrB2 deposited by CVD method.

High temperature thermographic phosphors YAG:Tm;Li and YAG:Dy in reduced oxygen environments

Phosphor thermometry for surface temperature measurements has become an established remote thermometry technique. However, measuring at temperatures above 1700 K is still challenging because of the weak phosphorescence and intense background from black-body radiation, leading to low signal-to-noise ratios. Therefore, lifetime-based phosphor thermometry with YAG:Tm;Li and YAG:Dy for high-temperature applications were investigated in this study with the aim of improving the precision of high-temperature measurements. The phosphors were coated on an alumina-oxide disc, which was placed in a temperature-controlled oven that exposed the phosphors to temperatures of up to 1930 K. The emission spectra and temporal decay of the luminescence were recorded for the investigated phosphors including their sensitivity to oxygen concentration in the gas environment. Knowledge of oxygen environment sensitivities for measurements of reduced oxygen concentrations at high temperatures, such as in combustion, is of great importance to increase confidence in the measurement. The results suggest that performing a mono-exponential decay time fit in a region of the decay curve that is dominated by a single lifetime component reduces the sensitivity to changes in the gas oxygen concentration for YAG:Tm;Li. Moreover, YAG:Tm;Li performs better than YAG:Dy in terms of signal-to-noise ratio (SNR), with a peak signal value and SNR almost an order of magnitude higher. With an appropriate decay curve fitting procedure, the effects of oxygen quenching can be minimized, such that the measurement error due to oxygen quenching is within the measurement precision for both phosphors.

Dynamics of capillary blood flow responses to acute local changes in oxygen and carbon dioxide concentrations.

Objectives: We aimed to quantify the magnitude and time transients of capillary blood flow responses to acute changes in local oxygen concentration ([O2]), and carbon dioxide concentration ([CO2]) in skeletal muscle. Additionally, we sought to quantify the combined response to both low [O2] and high [CO2] to mimic muscle microenvironment changes at the onset of exercise. Methods: 13 Sprague Dawley rats were anaesthetized, mechanically ventilated, and instrumented with indwelling catheters for systemic monitoring. The extensor digitorum longus muscle was blunt dissected, and reflected over a microfluidic gas exchange chamber in the stage of an inverted microscope. Four O2 challenges, four CO2 challenges, and a combined low O2 (7-2%) and high CO2 (5-10%) challenges were delivered to the surface with simultaneous visualization of capillary blood flow responses. Recordings were made for each challenge over a 1-min baseline period followed by a 2-min step change. The combined challenge employed a 1-min [O2] challenge followed by a 2-min change in [CO2]. Mean data for each sequence were fit using least-squared non-linear exponential models to determine the dynamics of each response. Results: 7-2% [O2] challenges decreased capillary RBC saturation within 2s following the step change (46.53 ± 19.56% vs. 48.51 ± 19.02%, p < 0.0001, τ = 1.44s), increased RBC velocity within 3s (228.53 ± 190.39μm/s vs. 235.74 ± 193.52μm/s, p < 0.0003, τ = 35.54s) with a 52% peak increase by the end of the challenge, hematocrit and supply rate show similar dynamics. 5-10% [CO2] challenges increased RBC velocity within 2s following the step change (273.40 ± 218.06μm/s vs. 276.75 ± 215.94μm/s, p = 0.007, τ = 79.34s), with a 58% peak increase by the end of the challenge, supply rate and hematocrit show similar dynamics. Combined [O2] and [CO2] challenges resulted in additive responses to all microvascular hemodynamic measures with a 103% peak velocity increase by the end of the collection period. Data for mean responses and exponential fitting parameters are reported for all challenges. Conclusion: Microvascular level changes in muscle [O2] and [CO2] provoked capillary hemodynamic responses with differing time transients. Simulating exercise via combined [O2] and [CO2] challenges demonstrated the independent and additive nature of local blood flow responses to these agents.

Characterization of Virgin, Re-used, and Oxygen-reduced Copper Powders processed by the Plasma Spheroidization Process

Fabrication of parts with high mechanical properties heavily depend on the quality of powder deployed in the fabrication process. Copper powder in three different powder types were spheroidized using radio-frequency inductively coupled plasma (ICP) spheroidization process (TekSphero-15 system). The characterized powders include virgin powder as purchased from the powder manufacturer, powder used in electron beam powder bed fusion (EB-PBF) process, and reconditioned powder, which was used powder that underwent an oxygen-reduction treatment. The goal of spheroidizing these powder types was to evaluate the change in powder morphology, the possibility of enhancing the powder properties back to their as-received conditions, and assess oxygen reduction of the powder lots given their initial oxygen contents. Also, to investigate the impact of re-spheroidization on powder properties, the second round of spheroidization was performed on the already used-spheroidized powder. The impact of powder type on powder sphericity and particle size distribution was evaluated using the image analysis of scanning electron microscope (SEM) micrographs and laser diffraction, respectively. The spheroidized powder showed higher sphericity and more uniform particle size distribution overall. Depending on the powder collection bin, second round of spheroidization affected the powder sphericity differently. The possibility of deploying the plasma spheroidization process as an alternative oxygen-reduction technique was also investigated through tracking the powders’ oxygen content using inert gas fusion method before and after the spheroidization. The plasma spheroidized powder showed less oxygen content than the hydrogen-treated powder. The second round of spheroidization caused no change in oxygen content. The correlation between oxygen-reduction and created cracks was discussed and compared between plasma spheroidization and hydrogen-treatment. The plasma spheroidization process created a powder with higher sphericity, uniform particle size, and less oxygen content.

Aerated drip irrigation improves water and nitrogen uptake efficiencies of tomato roots with associated changes in the antioxidant system

• After aerated drip irrigation, soil oxygen content significantly increased. • The duration and sequence of aeration changed the root antioxidant system. • The root antioxidant system correlated root morphology of tomato. • Root antioxidant systems and growth affect water and nitrogen uptake efficiency of tomato. China has the largest area of vegetable cultivation in greenhouse vegetable system in the world. However, the excessive application of irrigation and fertilizers has caused soil degradation and hardening, even leading to injury and yield loss in vegetable. Increasing soil aeration oxygen can improve crop water and nutrient uptake efficiencies. However, its effects on crop antioxidant systems are less known. Due to the sensitivity of the antioxidant system to changes in soil oxygen content, it is expected that aerated drip irrigation (ADI) delivering microbubble water to the crop rhizosphere will alter root antioxidant enzyme activities, malondialdehyde (MDA) content, and osmotic regulators in tomato plants. We conducted pot experiments under eight irrigation regimes: five aerated durations (0%, 25%, 50%, 75%, and 100%) of the subsurface drip irrigation period aerated (CK, A 25% , A 50% , A 75% , and A), with two aerated sequences (L: subsurface drip irrigation follow by aerated drip irrigation, F: aerated drip irrigation follow by subsurface drip irrigation) for the A 25% , A 50% and A 75% treatments. All treatments with ADI had an average of 7.63% higher oxygen concentration (OC) than the CK treatment at 74 d after transplanting. The principal component analysis revealed that MDA of all treatments had the greatest effect on the antioxidant system, while aerated drip irrigation reduced MDA content. Increasing aeration duration from A 25% to A 75% significantly affected antioxidant enzyme activities and root growth parameters, and the L treatment had higher values than the F treatment. The L -A 75% treatment had the highest water use efficiency, nitrogen uptake efficiency, and yield. The structural equation model demonstrated that ADI indirectly promotes tomato water and nitrogen uptake efficiencies by affecting the antioxidant system and root growth.

Energy metabolic shift contributes to the phenotype modulation of maturation stage ameloblasts.

Maturation stage ameloblasts (M-ABs) are responsible for terminal enamel mineralization in teeth and undergo characteristic cyclic changes in both morphology and function between ruffle-ended ameloblasts (RA) and smooth-ended ameloblasts (SA). Energy metabolism has recently emerged as a potential regulator of cell differentiation and fate decisions; however, its implication in M-ABs remains unclear. To elucidate the relationship between M-ABs and energy metabolism, we examined the expression pattern of energy metabolic enzymes in M-ABs of mouse incisors. Further, using the HAT7 cell line with M-AB characteristics, we designed experiments to induce an energy metabolic shift by changes in oxygen concentration. We revealed that RA preferentially utilizes oxidative phosphorylation, whereas SA depends on glycolysis-dominant energy metabolism in mouse incisors. In HAT7 cells, hypoxia induced an energy metabolic shift toward a more glycolytic-dominant state, and the energy metabolic shift reduced alkaline phosphatase (ALP) activity and calcium transport and deposition with a change in calcium-related gene expression, implying a phenotype shift from RA to SA. Taken together, these results indicate that the energy metabolic state is an important determinant of the RA/SA phenotype in M-ABs. This study sheds light on the biological significance of energy metabolism in governing M-ABs, providing a novel molecular basis for understanding enamel mineralization and elucidating the pathogenesis of enamel hypomineralization.

Calculate modeling of the level of indoor air pollution during its cleaning with air purifiers

The article proposes a computational method for determining the concentrations of pollutants inside a ventilated or cleaned room, taking into account the initial conditions and parameters of the flow rate, incoming or purified air, the volume of the room, the initial concentrations of the pollutant in the atmospheric air and in the room air, the parameters of the efficiency of the air cleaner. The article proposes the solution of two mass transfer equations under known initial conditions for two methods of cleaning rooms. When solving the first equation, a direct mass transfer calculation was carried out, which makes it possible to determine the effect of natural or artificial ventilation used indoors with small linear dimensions on the change in the concentration of the selected air polluting substance in the form of a chemical compound or an aerosol containing biological or chemical pollutants. When solving the second equation, a direct mass transfer calculation was carried out, which makes it possible to determine the effect of the operation of an air purifier used indoors with small linear dimensions on the change in the concentration of the selected air polluting substance in the form of a chemical compound or an aerosol containing biological or chemical pollutants. Calculations allow us to determine the time during which a residential office or industrial space is saturated with pollutants or cleaned to the required air quality standards, taking into account the influence of factors such as pollution of the surface layers of atmospheric air, the appearance of pollutants inside the room, the performance and efficiency of ventilation or air purification systems. The proposed calculation methods can be used to determine changes in the quality of indoor air over time, including taking into account changes in oxygen concentrations and pollutants indoors, determining the effectiveness of ventilation and air purification systems of various capacities in residential, office, medical and industrial premises. Ethics. The study does not require the submission of a biomedical ethics committee opinion or other documents.

Oxygen and irradiance constraints on visual habitat in a changing ocean: The luminoxyscape

Oxygen and irradiance constraints on visual habitat in a changing ocean: The luminoxyscape

Tailoring the Stability of Ti-Doped Sr2Fe1.4TixMo0.6-xO6-δ Electrode Materials for Solid Oxide Fuel Cells.

In this work, the stability of Sr2(FeMo)O6-δ-type perovskites was tailored by the substitution of Mo with Ti. Redox stable Sr2Fe1.4TixMo0.6-xO6-δ (x = 0.1, 0.2 and 0.3) perovskites were successfully obtained and evaluated as potential electrode materials for SOFCs. The crystal structure as a function of temperature, microstructure, redox stability, and thermal expansion properties in reducing and oxidizing atmospheres, oxygen content change, and transport properties in air and reducing conditions, as well as chemical stability and compatibility towards typical electrolytes have been systematically studied. All Sr2Fe1.4TixMo0.6-xO6-δ compounds exhibit a regular crystal structure with Pm-3m space group, showing excellent stability in oxidizing and reducing conditions. The increase of Ti-doping content in materials increases the thermal expansion coefficient (TEC), oxygen content change, and electrical conductivity in air, while it decreases the conductivity in reducing condition. All three materials are stable and compatible with studied electrolytes. Interestingly, redox stable Sr2Fe1.4Ti0.1Mo0.5O6-δ, possessing 1 μm grain size, low TEC (15.3 × 10-6 K-1), large oxygen content change of 0.72 mol·mol-1 between 30 and 900 °C, satisfactory conductivity of 4.1-7.3 S·cm-1 in 5% H2 at 600-800 °C, and good transport coefficients D and k, could be considered as a potential anode material for SOFCs, and are thus of great interest for further studies.

A Characterization of Brain Area Activation in Orienteers with Different Map-Recognition Memory Ability Task Levels-Based on fNIRS Evidence.

Mapping memory ability is highly correlated with an orienteer's level, and spatial memory tasks of different difficulties can reveal the spatial cognitive characteristics of high-level athletes. An "expert-novice" experimental paradigm was used to monitor behavioral performance and changes in cerebral blood oxygen concentration in orienteering athletes with tasks of different difficulty and cognitive load using functional near-infrared spectroscopic imaging (fNIRS). (1) there was no difference between high-/low-level athletes' map recognition and memory abilities in the non-orienteering scenario; (2) with increasing task difficulty, both high-/low-level athletes showed significantly decreasing behavioral performance, reduced correctness, longer reaction time, and strengthened cerebral blood oxygen activation concentration. There was no significant difference in L-DLPFC cerebral oxygen concentration between high-/low-level athletes in the simple map task, and the cerebral oxygen concentration in all brain regions was lower in the expert group than in the novice group in the rest of the task difficulty levels; (3) the correctness rate in the expert group in the complex task was closely related to the activation of the right hemisphere (R-DLPFC, R-VLPFC). Experts have a specific cognitive advantage in map-recognition memory, showing higher task performance and lower cerebral blood oxygen activation; cognitive load constrains map-recognition memory-specific ability and produces different performance effects and brain activation changes on spatial memory processing.

Removal of SiC at atomic and close-to-atomic scale by nanosecond ultraviolet laser

This paper presents an exploration on the material removal of SiC at atomic and close-to-atomic scale under ambient condition by nanosecond ultraviolet laser. The corresponding mechanisms are investigated by heat conduction model, reactive molecular dynamics simulation and single shot irradiation experiments. The threshold fluence of 2.52 J/cm2 is obtained from experimental results, and distinctive material behaviors including modification and atomic layer exfoliation at near-threshold fluence are investigated using atom force microscopy. The results show that modification in the chemical composition varies with the depth due to the change in oxygen content. In addition, both the surface modification and material removal can take place at the scale of single atomic layer, which implies a promising manufacturing approach to achieve ultimate precision for a material.

Crystal Structure and Properties of Gd1-xSrxCo1-yFeyO3-δ Oxides as Promising Materials for Catalytic and SOFC Application

A series of samples with the overall composition Gd1-xSrxCo1-yFeyO3-δ (x = 0.8; 0.9 and 0.1 ≤ y ≤ 0.9), which are promising materials for catalytic and SOFC application, was prepared by a glycerol nitrate technique. X-ray diffraction analysis allowed to describe Gd0.2Sr0.8Co1-yFeyO3-δ with 0.1 ≤ y ≤ 0.5 in a tetragonal 2ap × 2ap × 4ap superstructure (SG I4/mmm), while oxides with 0.6 ≤ y ≤ 0.9 exhibit cubic disordered perovskite structure (SG Pm-3m). All Gd0.1Sr0.9Fe1-yCoyO3-δ oxides within the composition range 0.1 ≤ y ≤ 0.9 possess the cubic perovskite structure (SG Pm-3m). The structural parameters were refined using the Rietveld full-profile method. The changes of oxygen content in Gd1-xSrxCo1-yFeyO3-δ versus temperature were determined by thermogravimetric analysis. The introduction of iron into the cobalt sublattice leads to a gradual increase in the unit cell parameters and unit cell volume, accompanied with increasing oxygen content. The temperature dependency of conductivity for Gd0.2Sr0.8Co0.3Fe0.7O3-δ exhibits a maximum (284 S/cm) at ≈600 K in air. The positive value of the Seebeck coefficient indicates predominant p-type conductivity in the Gd0.2Sr0.8Co0.3Fe0.7O3-δ complex oxide.

Predicting physiologically-relevant oxygen concentrations in precision-cut liver slices using mathematical modelling.

Precision cut liver slices represent an encouraging ex vivo method to understand the pathogenesis of liver disease alongside drug induced liver injury. Despite being more physiologically relevant compared to in vitro models, precision cut liver slices are limited by the availability of healthy human tissue and experimental variability. Internal oxygen concentration and media composition govern the longevity and viability of the slices during the culture period and as such, a variety of approaches have been taken to maximise the appropriateness of the internal oxygen concentrations across the slice. The aim of this study was to predict whether it is possible to generate a physiologically relevant oxygen gradient of 35-65mmHg across a precision cut liver slice using mathematical modelling. Simulations explore how the internal oxygen concentration changes as a function of the diameter of the slice, the position inside the well and the external incubator oxygen concentration. The model predicts that the desired oxygen gradient may be achieved using a 5mm diameter slice at atmospheric oxygen concentrations, provided that the slice is positioned at a certain height within the well of a 12-well plate.

In-situ decarburization and deoxidation during laser powder bed fusion of water-atomized steel C35

Water atomization of low alloyed steels is a very cost-effective way to produce metal powders for laser powder bed fusion. In this study, water atomized C35 steel powder is used to 3D-print samples with different powder bed fusion machines. The porosity of the samples was analyzed. Chemical analysis of printed samples and the powder feedstock was carried out. The gas atmosphere during laser powder bed fusion process was measured to investigate changes in carbon and oxygen content of the samples. With optimal processing parameters, samples with a porosity of only 0.1% can be achieved. Gas atmosphere measurements have shown, that a reaction between carbon and oxygen in the melt pool occurs, leading to the formation of volatile carbon monoxide. By in-situ reduction of the oxygen and carbon level, negative effects caused by oxygen like balling of single melt tracks can be prevented to produce nearly dense parts. • Water-atomized C35 medium carbon steel powder was used for laser powder bed fusion • Samples with porosity of only 0.1% can be built using appropriate parameters • During LPBF, oxygen reacts with carbon inside of the melt pool • Volatile CO forms during LPBF to reduce carbon and oxygen content of samples • Excessive pore formation is prevented due to deoxidation during the process

Thermal De-Oxygenation to Form Condensable Aerosol From Reconstituted Tobacco without Auto-Ignition

Summary A novel concept is described here that utilizes externally applied heat to a solid rod of reconstituted tobacco biomass to form a stream of aerosol under progressively oxygen-deficient atmosphere. The boundary of auto-ignition was determined at oxygen concentrations of 0%, 5%, 10%, and 21% and then the effects of these different atmospheres on various parameters were studied. Experimental results indicated that the ignition temperature decreased with the increase of oxygen concentration and a negative temperature coefficient (NTC) for atmosphere with oxygen was observed at before but close to ignition temperature. Significant differences in the yields of CO and CO2 between oxygen and oxygen-free atmosphere were observed. The mass of aerosol produced under an inert atmosphere and reduced-oxygen atmosphere were characterized with selected volatile and semi-volatile components, phenols, aldehydes, and other organic compounds of interests. In addition, higher oxygen concentration resulted in higher bulk and surface oxygen content of solid-phase residue, the reduction of carbon and hydrogen element content and related functional groups, and the content of inorganic compounds also exhibited an increase with oxygen concentration. By systematically changing oxygen concentrations of the biomass bed with increasing temperatures, an aerosol stream of controlled chemical composition and yields could be formed without leading to ignition. Key chemical markers of inhalation harm were measured and compared to each other under different degrees close to combustion. Studying reconstituted tobacco or other biomass materials in such a way could provide alternative and useful information in the design heated biomass aerosol generators.

MRI of radiation chemistry: First images and investigation of potential mechanisms.

Paramagnetic species such as O2 and free radicals can enhance T1 and T2 relaxation times. If the change in relaxation time is sufficiently large, the contrast will be generated in magnetic resonance images. Since radiation is known to be capable of altering the concentration of O2 and free radicals during water radiolysis, it may be possible for radiation to induce MR signal change. We present the first reported instance of x-ray-induced MR signal changes in water phantoms and investigate potential paramagnetic relaxation enhancement mechanisms associated with radiation chemistry changes in oxygen and free radical concentrations. Images of water and 10 mM coumarin phantoms were acquired on a 0.35 T MR-linac before, during, and after a dose delivery of 80Gy using an inversion-recovery dual-echo sequence with water nullified. Radiation chemistry simulations of these conditions were performed to calculate changes in oxygen and free radical concentrations. Published relaxivity values were then applied to calculate the resulting T1 change, and analytical MR signal equations were used to calculate the associated signal change. Compared to pre-irradiation reference images, water phantom images taken during and after irradiation showed little to no change, while coumarin phantom images showed a small signal loss in the irradiated region with a contrast-to-noise ratio (CNR) of 1.0-2.5. Radiation chemistry simulations found oxygen depletion of -11µM in water and -31µM in coumarin, resulting in a T1 lengthening of 24ms and 68ms respectively, and a simulated CNR of 1.0 and 2.8 respectively. This change was consistent with observations in both direction and magnitude. Steady-state superoxide, hydroxyl, hydroperoxyl, and hydrogen radical concentrations were found to contribute less than 1ms of T1 change. Observed radiation-induced MR signal changes were dominated by an oxygen depletion mechanism. Free radicals were concluded to play a minor secondary role under steady-state conditions. Future applications may include in vivo FLASH treatment verification but would require an MR sequence with a better signal-to-noise ratio and higher temporal resolution than the one used in this study.