Search

Cell-free hemoglobin in the cerebrospinal fluid (CSF-Hb) may be one of the main drivers of secondary brain injury after aneurysmal subarachnoid hemorrhage (aSAH). Haptoglobin scavenging of CSF-Hb has been shown to mitigate cerebrovascular disruption. Using digital subtraction angiography (DSA) and blood oxygenation-level dependent cerebrovascular reactivity imaging (BOLD-CVR) the aim was to assess the acute toxic effect of CSF-Hb on cerebral blood flow and autoregulation, as well as to test the protective effects of haptoglobin. DSA imaging was performed in eight anesthetized and ventilated sheep (mean weight: 80.4 kg) at baseline, 15, 30, 45 and 60 minutes after infusion of hemoglobin (Hb) or co-infusion with haptoglobin (Hb:Haptoglobin) into the left lateral ventricle. Additionally, 10 ventilated sheep (mean weight: 79.8 kg) underwent BOLD-CVR imaging to assess the cerebrovascular reserve capacity. DSA imaging did not show a difference in mean transit time or cerebral blood flow. Whole-brain BOLD-CVR compared to baseline decreased more in the Hb group after 15 minutes (Hb vs Hb:Haptoglobin: -0.03 ± 0.01 vs -0.01 ± 0.02) and remained diminished compared to Hb:Haptoglobin group after 30 minutes (Hb vs Hb:Haptoglobin: -0.03 ± 0.01 vs 0.0 ± 0.01), 45 minutes (Hb vs Hb:Haptoglobin: -0.03 ± 0.01 vs 0.01 ± 0.02) and 60 minutes (Hb vs Hb:Haptoglobin: -0.03 ± 0.02 vs 0.01 ± 0.01). It is demonstrated that CSF-Hb toxicity leads to rapid cerebrovascular reactivity impairment, which is blunted by haptoglobin co-infusion. BOLD-CVR may therefore be further evaluated as a monitoring strategy for CSF-Hb toxicity after aSAH. [ABSTRACT FROM AUTHOR]

The mechanical behaviour of all-oxide ceramic matrix mini-composites with porous alumina matrix phase was investigated by performing uniaxial tensile tests on specimens with different gauge lengths. The specimens were fabricated from Nextel™ 610 fibres by slurry infiltration and subsequent sintering at 1300 °C for 1 h. The stress–strain curves of the tested mini-composites revealed that the porous alumina matrix phase accumulates damage with increasing tensile load, but continues to contribute to the mini-composites’ tensile stiffness until ultimate failure occurs. A dependence of the tested mini-composites’ axial tensile strength on gauge length was not observed. The mean stress in the fibres at mini-composite failure was found to decrease with increasing matrix volume fraction, indicating that the cause of ultimate failure of the mini-composites can be attributed to the propagation of matrix cracks. [ABSTRACT FROM AUTHOR]

Copyright of Zeitschrift für Medizinische Physik is the property of Elsevier GmbH, Urban & Fischer Verlag and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Abstract: The presence of polycyclic aromatic hydrocarbons/compounds (PAH/PAC) in the exhaust of combustion equipment as well as their growth to soot particles depends on the balance of formation and depletion reaction pathways. Detailed understanding of PAH oxidation is necessary for a correct quantitative description of combustion processes. This study focuses on the high-temperature oxidation of anthracene, a 3-ring PAH, by molecular oxygen. By reacting this already formed PAH, under non-sooting conditions, its oxidative depletion processes were isolated from its formation processes, as well as from soot formation pathways. Anthracene powder, fluidized in nitrogen, was introduced into a two-stage electrically heated laminar-flow drop-tube furnace. In the first stage, kept at 900°C, anthracene was vaporized. Thereafter, upon mixing with preheated oxygen-containing gases in a venturi, gaseous anthracene was oxidized in the second furnace at oxygen mole fractions of 1–5% and gas temperatures of 950–1050°C. Gas temperature and velocity profiles in the furnaces, as well as anthracene particle vaporization trajectories were obtained with a computational fluid dynamics code. Sampling, followed by chemical analysis, was conducted at three locations within the oxidizing furnace. Trends with residence time show increasing CO and CO2 yields in the furnace and gradually decreasing O2. CO increased with higher oxidizing temperatures and oxygen concentrations. Acetylene was the most abundant light hydrocarbon, followed by methane, ethylene, benzene, propylene and ethyl acetylene. Prevalent PAC included fluorene-9-one, 9,10-anthracenodione, biphenylene, dibenzofuran, fluorene, indene, naphthalene, anthrone, xanthone and 2-naphthalenecarboxaldehyde. Most species’ yields increased with rising oxidation temperatures. A global anthracene reaction rate with oxygen was deduced, and an activation energy of 71kJ/mol was calculated. An anthracene oxidation reaction scheme was proposed. [Copyright &y& Elsevier]

Abstract: Samples of condensable material from opposed flow diffusion flames of methane and acetylene and oxygen enriched air at atmospheric pressure were collected and analyzed by high-pressure liquid chromatography to determine the fullerene yield. High resolution transmission electron microscopy studies revealed the presence of fullerenes and well-defined carbon layers with various degrees of curvature. Results show that fullerene formation strongly increases with the acetylene content in the fuel. Increasing strain rate positively affects the fullerene content in the condensable material; higher strain rate flames favor fullerenes over soot, indicating lower fullerene consumption by soot due to lower soot concentration. If the oxygen content in the oxidizing oxygen/nitrogen mixture is increased, fullerene concentration increases due to the higher temperatures and higher precursor concentration. Similar relative variations of fullerene concentrations with flame conditions are predicted by the numerical model. However, the absolute concentrations of fullerenes are, in general, underpredicted by 4 orders of magnitude. This result can be partially attributed to uncertainties in the rate coefficients for H-abstraction and C2H2-addition. This discrepancy also suggests that other important fullerene formation pathways are to be included in the numerical model. [Copyright &y& Elsevier]

Abstract: Combustion-generated polycyclic aromatic hydrocarbons (PAH) and soot particles are of significant environmental concern whereas controlled combustion is of increasing interest for the synthesis of carbonaceous nanostructures such as fullerenic material. Improved understanding of chemical and physical processes involved in PAH and soot formation is required to correlate operating conditions with emission characteristics. A detailed kinetic model describing the formation and consumption of PAH and soot in fuel-rich hydrocarbon combustion has been developed. Using a sectional approach, large PAH and carbonaceous particles with diameters of up to ?70nm are defined as classes (BINs) covering given mass ranges. Numbers of carbon and hydrogen atoms corresponding to their average masses are assigned to each BIN, accounting for a decrease in H/C ratios with increasing particle size. The model has been successfully tested for a rich premixed benzene/oxygen/argon flame (? =2.4, 10% argon, v =25cms?1, 5.33kPa). Model predictions are compared with published experimental data including mole fraction profiles of individual PAH and concentration as well as number density profiles of soot. Reactions of PAH radicals with PAH and between PAH radicals were found to be the dominant pathway to soot nuclei. Surface growth contributes ?75% to the final particle mass, and reaction of acetylene with particle radicals is the major growth pathway. Surface growth reactions are involved in PAH depletion in the postflame zone. Particle coagulation involving BINs and BIN radicals significantly contributes to the formation of progressively larger particles whereas oxidation by OH plays a non-negligible role in their depletion. [Copyright &y& Elsevier]

Application of lanthanum carbonate causes significant lanthanum deposition in the human body, which is similar to gadolinium deposition from gadolinium-based contrast agents. • Two similar elements applied in different species to the same patient. • LA-ICP-MS method reveals correlating iatrogenic La and Gd deposition. • La deposition from applied La carbonate is detected, but its effects are unknown. • Concentration ratio-based approach shows differences between Gd and La deposition. • Transport of lanthanides into the brain is highly species dependent. Recently, gadolinium from linear GBCAs has been reported to deposit in various regions of the body. Besides gadolinium, other lanthanides are used in medical care. In the current study, we investigated deposition of lanthanum in two patients who received lanthanum carbonate as a phosphate binder due to chronic kidney injury and compared it to additionally found Gd deposition. Tissue specimens of two patients with long-term application of lanthanum carbonate as well as possible GBCA application were investigated. Spatial distribution of gadolinium and lanthanum was determined by quantitative laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) imaging of tissue sections. The deposition of gadolinium and lanthanum in different organs was compared, and the ratio of Gd concentration to La concentration (Gd-to-La-ratio) was investigated on an individual pixel base within the images. Deposition of Gd and La was found in all investigated tissues of both patients. Gd and La exhibited high spatial correlation for all samples, with the main deposition being located in the middle coat (tunica media) of blood vessels. The Gd-to-La-ratio was similar in the tissues investigated (between 8 ± 4 (mean ± standard deviation) and 10 ± 2), except for the thyroid vasculature and surrounding tissue (90 ± 17) as well as the cerebellum (270 ± 18). Here, the ratio was significantly increased towards higher Gd concentration. The results of this study demonstrate long-term deposition of La and comparable localization of additionally found Gd in various tissues of the body. La deposition was relatively low, considering the total administered amount of lanthanum carbonate of up to 11.5 kg, indicating a low absorption and/or high excretion of lanthanum. However, the total amount of deposited La is significant and raises questions about possible adverse side effects. The ratio-approach allows for the usage of the additionally generated Gd data, without detailed knowledge about possible GBCA applications. The significantly decreased Gd-to-La-ratio in the brain might be explained by the lanthanum being released and taken up as free La3+ ion in the stomach that impedes a crossing of the blood-brain-barrier while the intravenously injected GBCAs might dechelate first when they have already crossed the blood-brain-barrier. [ABSTRACT FROM AUTHOR]

[Display omitted] Expandable, gastroretentive dosage forms are promising for precise control of drug concentration in blood. So far, however, short gastric residence times and safety considerations have limited their use. To mitigate such limitations, in this work expandable fibrous dosage forms were investigated for mechanical strength and gastric residence time in dogs. The fiber formulation comprised ibuprofen drug; water-absorbing, high-molecular-weight hydroxypropyl methylcellulose (HPMC) excipient; fiber-strengthening, enteric methacrylic acid-ethyl acrylate excipient; and barium sulfate, a gastrointestinal contrast agent. The fibers were coated either with a hydrophilic sugar, or with a strengthening enteric excipient. Upon administration to a dog, in the stomach the dosage form with sugar-coated fibers expanded to 1.7 times its initial radius in 50–100 minutes, and disintegrated after 4.8 hours. The dosage form with the enteric-excipient-coated fibers, by contrast, expanded to 1.6 times the initial radius in 5 hours, and fractured after 31 hours due to cyclic loads applied by the contracting stomach walls. The fragments passed into the small intestine where they dissolved in less than 2–3 hours. Diametral compression tests and dynamic fatigue failure models show that the substantial increase in gastric residence time is due to strengthening of the fibers by the enteric-excipient coating. Because the enteric excipient is a rubbery semi-solid in the acidic gastric fluid and dissolves in the pH-neutral intestinal fluids, safety concerns should be minimal. Thus, expandable fibrous dosage forms can be readily designed for prolonged, safe gastric retention. [ABSTRACT FROM AUTHOR]

Abstract: Carbon nanotubes (CNTs) were synthesized from polyethylene using a pyrolysis–combustion technique. Pre- or post-consumer polyethylene (in strips, pellets or ground particles) was pyrolyzed to gaseous products, which were then combined with an oxygen-containing gas and auto-ignited to create a fuel-rich flame. The combustion effluent was used to synthesize multi-wall CNTs using stainless-steel wire mesh as both catalyst and substrate. An overall CNT yield in the order of 10%, by mass relative to the initial carbon in the fuel, was typically achieved before purification. The viability of partial conversion of a readily-available waste stream to the value-added product of CNTs was demonstrated, combining the economy and process safety aspects of flame synthesis with the control of synthesis temperature that chemical vapor deposition methods typically afford. [Copyright &y& Elsevier]

Abstract: An investigation was conducted on the evolution of products of incomplete combustion (PIC) emitted from one-dimensional, laminar, atmospheric-pressure ethylbenzene flames in the vicinity of the soot onset threshold. The objective of this study was to identify the role of the fuel-to-air equivalence ratio in the evolution of polycyclic aromatic hydrocarbons (PAH) and other PIC as soot precursors, just prior to and subsequent to soot onset in premixed flames. Liquid ethylbenzene was prevaporized in nitrogen and blended with an oxygen–nitrogen mixture. Upon ignition, premixed flat flames were stabilized over a burner at atmospheric pressure. Temperature measurements and product sampling were conducted at various heights above the burner. Collected samples were analyzed for soot, PAH, oxygenated species, fixed gases, and light hydrocarbons. Three flames were investigated in the vicinity of the observed soot onset threshold, at equivalence ratios of , , and . By adjusting the amounts of oxygen, nitrogen, and fuel, both the maximum measured flame temperature and the spatial profile of the temperature were kept nearly constant as the equivalence ratio was varied. The cold gas velocity through the burner was also kept nearly constant. Changes in species concentration profiles prior to, at and beyond the sooting limit were evaluated. The results indicated that the soot onset limit is not a function of flame temperature alone; i.e., while the maximum measured flame temperatures was kept fairly constant, the flame could be either sooting, at the sooting limit or nonsooting depending on the equivalence ratio. A detailed chemical kinetic model, previously tested against sooting premixed benzene and ethylbenzene flames, was used to gain insight in chemical processes involved in soot formation. A reaction flux analysis was conducted to determine the pathways for ethylbenzene consumption, as well as for benzene and naphthalene formation. Examination of experimental measurements of species along the axis of the flame, in view of the theoretical predictions, showed a rather direct correlation of acetylene to soot formation. Moreover, a correlation between the consumption of ethylbenzene pyrolyzates, such as styrene, and soot formation at the soot onset was also apparent. Whereas the model''s results were very encouraging, additional development is deemed necessary to improve its predictive capability in the challenging regime of soot inception. [Copyright &y& Elsevier]

Presents a study on toxic organic emissions from batch combustion of styrene. Emissions of polycyclic aromatic hydrocarbons, particulates and carbon monoxide; Methods of minimizing such emissions; Incineration of waste styrene monomer.

Adenosine induces vasodilatation. The aim of this study was to investigate cardiovascular effects of two adenosine constant rate infusion (CRI) doses in dogs. Experimental, longitudinal repeated measure design. Ten healthy purpose-bred Beagle dogs. Each dog was sedated with butorphanol. Anaesthesia was induced with propofol intravenously and maintained with sevoflurane (inspired oxygen fraction = 47–55%). Controlled mechanical ventilation was used to maintain normocapnia. Two doses of adenosine were administered as CRIs to each dog: 140 μg kg–1 minute–1 (A140) followed by 280 μg kg–1 minute–1 (A280). Pulse rate, invasive arterial pressure and stroke volume (by magnetic resonance phase contrast angiography) were measured at baseline, 3 minutes after starting adenosine and 3 and 10 minutes after discontinuing adenosine. Cardiac output, cardiac index and approximated systemic vascular resistances (approximate SVR) were calculated. Additionally, arterial blood gases, co-oximetry, electrolytes, glucose and lactate were measured and oxygen content and delivery calculated. One-way repeated measures analysis of variance (p < 0.05) was used for data analysis. A140 and A280 resulted in a significant decrease in arterial blood pressure [systolic (p = 0.008), mean (p = 0.003), and diastolic arterial pressure (p = 0.004)] and approximate SVR (p = 0.008) compared with baseline. No significant changes were detected for the other variables. All values returned to baseline within 3 minutes after adenosine discontinuation. Adenosine CRI decreases arterial pressure by vasodilatation in healthy dogs. No additional effects were observed with the higher dose. The effects in compromised dogs remain to be investigated. [ABSTRACT FROM AUTHOR]

Background: Metal artifacts from retained bullets impair the image quality on computed tomography (CT) and may compromise the detection of critical lesions or the bullet path. To reduce metallic artifacts from medical implants on CT, special algorithms have been developed, e.g., iterative metal artifact reduction (iMAR). The aim of this prospective study was to evaluate the application of iMAR in cases of retained bullets.Materials and Methods: In this study, nine different types of projectiles (n = 9) were selected to evaluate the effect of iMAR. The study consisted of two settings. In the first setting, each projectile was fixed on a thin thread and placed in the middle of a water-filled container to demonstrate the effect of iMAR in a homogenous medium. In the second setting, each projectile was placed in the severed head of a pig cadaver as a substitute for human tissue to evaluate iMAR in cases of retained bullets. The raw data from CT scans of both settings were reconstructed with and without iMAR (standard filtered back-projection). The reconstructions with iMAR were calculated using eight different presets provided by the software, namely, neuro-coils, dental fillings, spine implants, shoulder implants, pacemaker, thoracic-coils, hip implants and extremity implants. For each setting, nine reconstructions (n = 9; iMAR: n = 8; without iMAR: n = 1) for each projectile were subjectively evaluated for the image quality and extent of streak artifacts by ten independent and blinded raters (residents: n = 5; radiologists: n = 5). The reconstructions of the second setting were evaluated in a soft tissue window and bone window. A 5-point Likert scale was used for the evaluation of image quality based on the extent of streaks as follows: 1 = severe; 2 = considerable; 3 = moderate; 4 = minimal; and 5 = not apparent. Kendall's W was used for assessing agreement among the ten raters. The Wilcoxon test was used to reveal whether there was a difference in the subjective evaluations between residents and radiologists. Nonparametric Friedman and post hoc tests were used to analyze the Likert scores. The mean difference was considered significant at the 0.05 level.Results: The agreement among the raters was reasonably high for all projectiles in both settings. In the phantom setting, the iMAR presets neuro-coils and dental fillings yielded the best results. In the pig's head setting regarding the soft tissue window, the presets neuro-coils and extremity implants were preferred. Regarding the bone window, the presets extremity implants and hip implants had the best results. Statistical significance (p < 0.01) between reconstructions without iMAR and neuro-coils or extremity implants was calculated. The iMAR preset spine implants had poor values comparable to reconstructions without iMAR.Conclusion: The applied iMAR presets revealed different effects on the image quality. Selecting an inappropriate preset (e.g., spine implants) may result in unsatisfactory artifact reduction. The results of this study indicate that the neuro-coils preset is the most appropriate preset for soft tissue, and the preset extremity implants is favorable for bones in cases of retained bullets. [ABSTRACT FROM AUTHOR]

To ensure animal welfare at slaughter, rapid stunning is required to render the animal deeply unconscious. In cattle, captive-bolt stunners are typically used for this purpose. However, with regard to their impact force and maximum length of approximately 120 mm, such captive-bolt stunners are not suitable for stunning water buffaloes due to anatomical characteristics of the skull. In water buffaloes the bone layer is thicker and the distance from the point of attachment of the captive-bolt stunner to the relevant brain region is longer. For this reason, a special bullet-shooting stunner was developed, which is similar in size and handling to a standard captive-bolt stunner, but instead of a bolt, it fires a bullet. Actually, even two bullets can be loaded so that a follow-up shot can be fired immediately if necessary. In this study, the bullet-shooting stunner was tested using two different types of hunting ammunition for stunning water buffaloes during regular slaughter. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract: Carbon nanomaterials (CNMs) were grown on nickel-coated stainless-steel mesh grids using a combustion synthesis method. Three fuel feedstocks of dissimilar chemical structures, ethylene, ethyl benzene and ethyl alcohol, were burned at fuel-rich equivalence ratios to generate disparate combustion products. The chemical compositions of these products were assessed to identify and contrast the species that contribute to the growth of CNMs. The generated CNMs were characterized using SEM and TEM. Each set of conditions produced a distinct distribution (bi-modal or mono-modal) of CNMs, including carbon nanotubes and carbon nanofibers, both of varying diameters and lengths. The effects of combustion-generated light aliphatic hydrocarbons and light aromatic hydrocarbons on CNM growth and structure were ascertained. It was found that ethylene and ethyl alcohol generated tubular CNMs under all tested conditions, whereas ethyl benzene generated only small amounts of CNMs and under much more limited conditions. It was also determined that concentrations of aliphatic species, notably methane and acetylene, at mole fractions as low as 500ppm have a thickening effect on the resulting CNMs. Linear correlations were found between the concentrations of these species and the mean diameter of the CNMs. [Copyright &y& Elsevier]

Abstract: This work investigates five different one-dimensional, laminar, atmospheric pressure, premixed ethanol/ethylbenzene flames (0%, 25%, 50%, 75% and 90% ethanol by weight) at their soot onset threshold (ϕ critical). Liquid ethanol/ethylbenzene mixtures were pre-vaporized in nitrogen, blended with an oxygen–nitrogen mixture and, upon ignition, burned in premixed one-dimensional flames at atmospheric pressure. The flames were controlled so that each was at its visual soot onset threshold, and all had similar temperature profiles (determined by thermocouples). Fixed gases, light volatile hydrocarbons, polycyclic aromatic hydrocarbons (PAH), and oxygenated aromatic hydrocarbons were directly sampled at three locations in each flame. The experimental results were compared with a detailed kinetic model, and the modeling results were used to perform a reaction flux analysis of key species. The critical equivalence ratio was observed to increase in a parabolic fashion as ethanol concentration increased in the fuel mixture. The experimental results showed increasing trends of methane, ethane, and ethylene with increasing concentrations of ethanol in the flames. Carbon monoxide was also seen to increase significantly with the increase of ethanol in the flame, which removes carbon from the PAH and soot formation pathways. The PAH and oxygenated aromatic hydrocarbon values were very similar in the 0%, 25% and 50% ethanol flames, but significantly lower in the 75% and 90% ethanol flames. These results were in general agreement with the model and were reflected by the model soot predictions. The model predicted similar soot profiles for the 0%, 25% and 50% ethanol flames, however it predicted significantly lower values in the 75% and 90% ethanol flames. The reaction flux analysis revealed benzyl to be a major contributor to single and double ring aromatics (i.e., benzene and naphthalene), which was identified in a similar role in nearly sooting or highly sooting ethylbenzene flames. The presence of this radical was significantly reduced as ethanol concentration was increased in the flames, and this effect in combination with the lower carbon to oxygen ratios and the enhanced formation of carbon monoxide, are likely what allowed higher equivalence ratios to be reached without forming soot. [Copyright &y& Elsevier]

Abstract: This work investigates the similarities/differences of one-dimensional, laminar, atmospheric pressure premixed ethylbenzene flames at their soot onset threshold (). The goals of this investigation are to contrast the entire temperature profiles of the flames at various critical equivalence ratios, , and to report on hydrocarbon specie profiles. Liquid ethylbenzene was pre-vaporized in nitrogen, blended with an oxygen–nitrogen mixture and, upon ignition, premixed flat flames were stabilized over a burner at atmospheric pressure. The C/O ratio was regulated and simultaneously the temperature profile was adjusted by varying the heat lost from the flame to the burner, to obtain visually similar flames, all at their apparent soot onset limit. Temperature profiles of five such flames were determined with thermocouples. The results indicate that as the axial temperature profiles in the flames rose, ((C/O)critical) also increased. Sampling was performed at various heights along the axes of three of these flames (, and ) to monitor changes in chemical speciation. The mole fractions of CO increased in the order of increasing equivalence ratio and hence increasing flame temperature. The CO2 mole fractions of the three flames were similar. However, the mole fractions of light hydrocarbons and polycyclic aromatic hydrocarbons (PAH), which are suspected soot precursors, decreased in the order of increasing equivalence ratio and hence increasing flame temperature. Whereas direct measurements of particulate matter in the flame were not made in this work, these observations on soot precursors along with theoretical flame emissivity considerations suggest that particulate loadings at the sooting limit also decreased in the order of increasing equivalence ratio and hence increasing flame temperature. [Copyright &y& Elsevier]

Abstract: This work was conducted to investigate the effects of temperature on soot formation/oxidation chemistry in the vicinity of the soot onset threshold (ϕ critical) in one-dimensional, laminar, atmospheric-pressure premixed ethylbenzene flames. The effects of temperature on the evolution of soot precursors were observed just prior and subsequent to soot onset. Liquid ethylbenzene was prevaporized in nitrogen and blended with an oxygen–nitrogen mixture and, upon ignition, premixed flat flames were stabilized over a burner at atmospheric pressure. Three flames at the same fuel-to-air equivalence ratio () but with different temperature profiles were obtained by regulating the total heat loss from the flame to the burner, as a result of altering the cold gas velocity of the reacting gases through the burner. A 100-K spread was detected among the three flame temperature profiles. The coolest flame was slightly sooting, the intermediate temperature flame was at the visible onset of sooting, and the hottest flame was not sooting. Combustion products were sampled at various heights in these flames. CO and CO2 mole fractions were found to increase with temperature, supporting the hypothesis that with increasing temperature the rate of oxidation reactions increases faster than the rate of soot formation reactions. Again supporting the same hypothesis, the mole fractions of at least some of the suspected soot precursor hydrocarbons decreased with increasing temperature. Similarly, both the number and the concentrations of detected polycyclic aromatic hydrocarbons (PAH) and oxygenated aromatic hydrocarbons were highest in the slightly sooting, i.e., the coolest flame. This flame also had the highest condensed phase/gaseous phase PAH ratio among the three flames. However, whereas in all three flames the mole fractions of PAH were disparate in the broad neighborhood of the flame zone, they converged to similar values in the postflame zone at 7 mm height from the surface of the burner. Experimentally obtained mole fractions of effluent species were compared with predictions from a detailed kinetic model. [Copyright &y& Elsevier]

Abstract: A simple model for the gas-phase synthesis of carbon nanotubes on iron catalyst particles has been developed. It includes a growth model for the catalyst particles and describes nanotube growth processes through carbon monoxide disproportionation and hydrogenation. Models for particle–particle interactions and sintering are also included. When carbon arrives at a catalyst particle it can either dissolve in the particle until a saturation limit is reached, or form a graphene layer on the particle, or go on to form a nanotube. Two models for incipient nanotube growth are considered. The first allows nanotubes to form once a catalyst particle reaches the saturation condition. The second only allows nanotubes to form on the collision of two saturated particles. The particle system is solved using a multivariate stochastic solver coupled to the gas-phase iron chemistry using an operator splitting algorithm. Comparison with experimental data gives a good prediction of the nanotube length, and reasonable values of catalyst particle diameter and nanotube diameter. A parametric study is presented in which the carbon monoxide reaction rate constants are varied, as is the fraction of carbon allowed to form nanotubes relative to surface layers. The assumptions of the coagulation and sintering models are also discussed. [Copyright &y& Elsevier]

Abstract: This study addresses health-hazardous emissions from combustion of aromatic and oxygenated components of engine fuel blends. An investigation was conducted on the evolution of polycyclic aromatic hydrocarbons (PAH) and other pollutants (soot, CO, unburned light hydrocarbons) emitted from one-dimensional ethylbenzene and ethyl alcohol flames. The study of ethylbenzene combustion is also pertinent to that of waste polystyrene, as past work has indicated that ethylbenzene may be a surrogate for initial products of polystyrene pyrolysis. Both liquid fuels were prevaporized in nitrogen, mixed with oxygen and additional nitrogen, and upon ignition, premixed flat flames were stabilized over a burner. Temperature measurements and product sampling were conducted at various heights above the burner. Results showed that ethyl alcohol combustion generated small yields of PAH, even under the adverse fuel-rich conditions of this study (). PAH mole fractions in the ethyl alcohol flame were 2–5 orders of magnitude lower than those in the ethylbenzene flame at the same location. PAH mole fractions often peaked in the postflame region and remained at relatively high levels thereafter. PAH mole fractions in premixed fuel-rich benzene, ethane, ethylene, and methane flames, published in the literature, were typically in between those found in the two flames of this study. Computations were conducted using a currently developed detailed kinetic model, allowing for the prediction of formation and depletion of major PAH and soot particles of different sizes. The computed chemical flame structures were compared to experimental data obtained in the present work. Predicted mole fractions were often close to the experimentally obtained values or, at worse, within the same order of magnitude for both fuels. Reaction pathways are discussed. [Copyright &y& Elsevier]

Benzene depletion in a laminar premixed flat stoichiometric low-pressure methane/air/benzene (1.5%) flame was investigated using a recently developed kinetic model that has been tested for low-pressure combustion of acetylene, ethylene, and benzene. Experimental flame structures of two stoichiometric methane/air flames (v =34.2 cm s−1, 5.33 kPa) with and without the addition of 1.5% of benzene were measured previously by means of molecular beam sampling using mass spectrometry as well as gas chromatography coupled to mass spectrometry as analytic tools. Model computations were conducted using the Premix code within the Chemkin software package. Experimental temperature profiles were used as input. The analysis of rates of production of selected species allowed for the identification of major formation and depletion pathways. The predictive capacility of the model was assessed in both flames. Good to excellent agreements between predictions and measured mole fraction profiles were obtained for reactants, intermediates, and products such as methane, O2, methyl, H, OH, CO, CO2. and H2O. Benzene depletion and the formation and consumption of intermediates such as cyclopentadiene were predicted correctly. According to the model, methyl is exclusively formed by hydrogen abstraction from methane and subsequently oxidized by reaction with O to formyl, (1) CH3 + O ⇄ HCO + H2, and formaldehyde, (2) CH3 + O ⇄ CH2O + H, the latter channel being the dominant one. Benzene consumption occurred mainly by hydrogen abstraction with OH and H as reactant but also the contribution of its oxidation by O to phenoxy was significant. Phenol and phenoxy chemistries are strongly coupled, unimolecular decay of phenoxy to cyclopentadienyl radicals and CO is the dominant consumption route. Small PAH are predicted to be formed in the reaction zone, followed by complete depletion in the postflame region. The pressure dependence of the dominant dimethylether formation (32) CH3 + CH3O ⇄ CH3OCH3 was found to be significant and assessed by means of Quantum Rice-Ramsperger-Kassel (QRRK) analysis. [Copyright &y& Elsevier]