C0 C4 Research Articles

Prediction of sulfur compounds and total sulfur contents in catalytic cracking products of hydrotreated and non-hydrotreated feeds

Relevance. The lack of a reliable mathematical model suitable for predicting the yield and quality of products in catalytic cracking units, with an assessment of the environmental indicators of fuel fractions when changing the hydrocarbon composition and distribution of sulfur compounds in the process feedstock, as well as the possibility of involving highly sulfur-containing oil streams in processing on existing catalytic cracking units. Aim. To develop and apply a mathematical model of the catalytic cracking to predict the content of sulfur compounds and total sulfur in the products during the processing of hydrotreated and non-hydrotreated petroleum feedstocks. Methods. A complex of experimental methods, including liquid and gas chromatography to determine the composition of the feedstock and the distribution of sulfur compounds in the feedstock and catalytic cracking products, methods of quantum chemical modeling of reactions involving sulfur compounds, as well as numerical methods for processing and solving systems of differential equations. Quantum chemical modeling methods were used to study the thermodynamic parameters of catalytic cracking reactions involving sulfur-containing compounds. Results. The authors have developed and implemented in software a mathematical model of catalytic cracking involving hydrocarbons C1–C40+ and sulfur compounds (thiophenes C0–C4, alkylbenzothiophenes C0–C6, C0–C3 dibenzothiophenes, and C4–dibenzothiophene-benzonaphthothiophenes). The model aims to predict the yield and composition of process products, as well as the environmental indicators of motor fuels. Thermodynamic and kinetic parameters of catalytic cracking reactions were determined using quantum chemical modeling methods and solving the inverse kinetic problem.

A Data-Based Hybrid Chemistry Acceleration Framework for the Low-Temperature Oxidation of Complex Fuels

The oxidation of complex hydrocarbons is a computationally expensive process involving detailed mechanisms with hundreds of chemical species and thousands of reactions. For low-temperature oxidation, an accurate account of the fuel-specific species is required to correctly describe the pyrolysis stage of oxidation. In this study, we develop a hybrid chemistry framework to model and accelerate the low-temperature oxidation of complex hydrocarbon fuels. The framework is based on a selection of representative species that capture the different stages of ignition, heat release, and final products. These species are selected using a two-step principal component analysis of the reaction rates of simulation data. Artificial neural networks (ANNs) are used to model the source terms of the representative species during the pyrolysis stage up to the transition time. This ANN-based model is coupled with C0–C4 foundational chemistry, which is used to model the remaining species up to the transition time and all species beyond the transition time. Coupled with the USC II mechanism as foundational chemistry, this framework is demonstrated using simple reactor homogeneous chemistry and perfectly stirred reactor (PSR) calculations for n-heptane oxidation over a range of composition and thermodynamic conditions. The hybrid chemistry framework accurately captures correct physical behavior and reproduces the results obtained using detailed chemistry at a fraction of the computational cost.

Morphological characteristics of retinal vessels in eyes with high myopia: Ultra-wide field images analyzed by artificial intelligence using a transfer learning system.

The purpose of this study is to investigate the retinal vascular morphological characteristics in high myopia patients of different severity. 317 eyes of high myopia patients and 104 eyes of healthy control subjects were included in this study. The severity of high myopia patients is classified into C0-C4 according to the Meta Analysis of the Pathologic Myopia (META-PM) classification and their vascular morphological characteristics in ultra-wide field imaging were analyzed using transfer learning methods and RU-net. Correlation with axial length (AL), best corrected visual acuity (BCVA) and age was analyzed. In addition, the vascular morphological characteristics of myopic choroidal neovascularization (mCNV) patients and their matched high myopia patients were compared. The RU-net and transfer learning system of blood vessel segmentation had an accuracy of 98.24%, a sensitivity of 71.42%, a specificity of 99.37%, a precision of 73.68% and a F1 score of 72.29. Compared with healthy control group, high myopia group had smaller vessel angle (31.12 ± 2.27 vs. 32.33 ± 2.14), smaller fractal dimension (Df) (1.383 ± 0.060 vs. 1.424 ± 0.038), smaller vessel density (2.57 ± 0.96 vs. 3.92 ± 0.93) and fewer vascular branches (201.87 ± 75.92 vs. 271.31 ± 67.37), all P < 0.001. With the increase of myopia maculopathy severity, vessel angle, Df, vessel density and vascular branches significantly decreased (all P < 0.001). There were significant correlations of these characteristics with AL, BCVA and age. Patients with mCNV tended to have larger vessel density (P < 0.001) and more vascular branches (P = 0.045). The RU-net and transfer learning technology used in this study has an accuracy of 98.24%, thus has good performance in quantitative analysis of vascular morphological characteristics in Ultra-wide field images. Along with the increase of myopic maculopathy severity and the elongation of eyeball, vessel angle, Df, vessel density and vascular branches decreased. Myopic CNV patients have larger vessel density and more vascular branches.

Cervical spine movements during laryngoscopy and orotracheal intubation: a systematic review and meta-analysis

BackgroundAirway management is challenging in trauma patients because of the fear of worsening cervical spinal cord damage. Video-integrated and optic-integrated devices and intubation laryngeal mask airways have been proposed as...

Case Report: Posterolateral Epidural Supra-C2-Root Approach (PESCA) for Biopsy of a Retro-Odontoid Lesions in Same Sitting After Occipitocervical Fixation and Decompression in a Case of Crowned Dens Syndrome With Brainstem Compression and Displacement

Background‘Crowned dens syndrome' (CDS) is a special form of calcium pyrophosphate dihydrate deposition disease which is characterized radiologically by a halo-like or crown-like distribution in the periodontoid region and clinically by cervical pain. Herein, we will describe our experience of posterolateral epidural supra-C2-root approach (PESCA) for biopsy of retro-odontoid lesions in one surgical session after occipitocervical fixation and decompression in a patient with CDS and massive brainstem compression.Case PresentationA 70-year-old woman presented to our department with a 4-week history of progressive walking impairment, neck pain, neck rigidity, fever, dizziness, slight palsy of the left hand, and multiple fall episodes. Magnetic resonance imaging (MRI) of the craniovertebral junction (CVJ) and cervical spine revealed a lesion of the odontoid process and the retro-odontoid region with mainly solid components, as well as small cystic components, and brainstem compression and displacement. In first step, fusion surgery of the CVJ C0–C4 was performed with occiptocervical decompression. After fusion and decompression the lower lateral part of the C1 arc and the lateral superior part of the left side of the C2 arc were removed. The entry point was located directly above the superior part of the C2 root. A biopsy of the lateral portions of the lesions was obtained by bioptic forceps under microscope guidance. Pathologic examination of the mass revealed deposition of birefringent crystals compatible with calcium pyrophosphate. In addition to the clinical symptoms (especially neck pain), the diagnosis of CDS was made. Non-steroidal inflammatory drugs (NSAIDs) and colchicine (and later magnesium) were started. At follow-up examination 6 months after surgery, an MRI scan of the cervical spine revealed regression of the pannus and the cyst with replacement of the brainstem, clinical improvement of walking, and increased strength of the left hand.ConclusionsThis study demonstrates that PESCA can be used to obtain tissue for pathological analysis in one surgical sitting after fusion and decompression and that fusion, decompression, and PESCA (in the same session) together with subsequent conservative management could be a good alternative for the treatment of CDS.

Construction of reduced chemical mechanisms orientated toward specific applications: a case study of primary reference fuel

Due to the specific prediction requirements in combustion simulations, the reduced chemical mechanism developed focusing on particular applications is usually needed. A systematic method for chemical mechanism reduction orientated toward specific applications is proposed in this work. The reduction process is divided into two parts for large-molecule fuels, including the reduction of the fuel-specific sub-mechanism and the reduction of the C0–C4 sub-mechanisms. In the first part, path sensitivity analysis and global sensitivity analysis are used to identify the key reaction classes in the fuel-specific sub-mechanism, and then the rate of production (ROP) analysis and genetic algorithm are utilised to recognise the representative reactions with the maximum flux in the key reaction classes and optimise the reaction rate coefficients within their uncertainties. For the second part, the directed relation graph with error propagation and sensitivity analysis (DRGEPSA) is employed to reduce the C0–C4 sub-mechanisms. And then, the genetic algorithm with binary variables is applied to further reduce the pathways of the small-molecule reactions targeted at ignition delay times in shock tubes, major species (fuel, O2, CO, and CO2) profiles in jet-stirred reactors, and laminar flame speeds, respectively. Finally, reaction lumping is conducted by identifying the quasi-steady-state (QSS) species. Based on a detailed mechanism of primary reference fuel (PRF) consisting of 2,870 species and 9,233 reactions, three reduced models orientated toward specific applications, including ModelST with 42 species and 82 reactions targeted at the ignition timings in shock tubes (ST), ModelJSR with 43 species and 79 reactions targeted at the major species concentrations in jet-stirred reactors (JSR), and ModelLPF with 41 species and 69 reactions targeted at laminar flame speeds in laminar premixed flames (LPF) are constructed, respectively. The validation results indicate that all the three reduced mechanisms can achieve good predictions in their featured specific applications.

Assessing NO2-Hydrocarbon Interactions during Combustion of NO2/Alkane/Ar Mixtures in a Shock Tube Using CO Time Histories

Modern gas turbines use combustion chemistry during the design phase to optimize their efficiency and reduce emissions of regulated pollutants such as NOx. The detailed understanding of the interactions during NOx and natural gas during combustion is therefore necessary for this optimization step. To better assess such interactions, NO2 was used as a sole oxidant during the oxidation of CH4 and C2H6 (the main components of natural gas) in a shock tube. The evolution of the CO mole fraction was followed by laser-absorption spectroscopy from dilute mixtures at around 1.2 atm. The experimental CO profiles were compared to several modern detailed kinetics mechanisms from the literature: models tuned to characterize NOx-hydrocarbons interactions, base-chemistry models (C0–C4) that contain a NOx sub-mechanism, and a nitromethane model. The comparison between the models and the experimental profiles showed that most modern NOx-hydrocarbon detailed kinetics mechanisms are not very accurate, while the base chemistry models were lacking accuracy overall as well. The nitromethane model and one hydrocarbon/NOx model were in relatively good agreement with the data over the entire range of conditions investigated, although there is still room for improvement. The numerical analysis of the results showed that while the models considered predict the same reaction pathways from the fuels to CO, they can be very inconsistent in the selection of the reaction rate coefficients. This variation is especially true for ethane, for which a larger disagreement with the data was generally observed.

A data-based hybrid model for complex fuel chemistry acceleration at high temperatures

During their high-temperature oxidation, complex hydrocarbons and their early fragments are short-lived and figure prominently only during the pyrolysis stage. However, they are quickly replaced by smaller hydrocarbons at the onset of the oxidation stage, resulting in simpler chemistry requirements past pyrolysis. In this study, we develop a data-based hybrid chemistry approach to accelerate chemistry integration for complex fuels. The approach is based on tracking the evolution of chemistry through representative species for the pyrolysis and coupling their reactions with simpler foundational chemistry. The selection of these representative species is implemented using principal component analysis (PCA) based on simulation data. The description of chemistry for the representative species is implemented using an artificial neural network (ANN) model for their reaction rates followed by the description of their chemistry using a foundational chemistry model. The selection of the transition between these models is trained a priori using an ANN pattern recognition classifier. This data-based hybrid chemistry acceleration model is demonstrated for three fuels: n-dodecane, n-heptane and n-decane and investigated with two foundational chemistry, C0–C2 and C0–C4, models. The hybrid scheme results in computational saving, up to one order of magnitude for n-dodecane, two orders of magnitudes for n-heptane, and three orders of magnitudes for n-decane. The accuracy and saving in computational cost depend on the number of selected species and the size of the used foundational chemistry. The hybrid model coupled with the more detailed C0–C4 foundational performs, overall, better than the one coupled with the C0–C2 foundational chemistry.

Detailed combustion chemical mechanism for surrogates of representative jet fuels

Surrogate fuels are useful for computational fluid dynamics (CFD) simulations. However, there are two main challenges in surrogate fuel: defining an appropriate surrogate and designing compact and reliable kinetic models. Many works of defining an appropriate surrogate have been done in our previous work. In this study, we focus on obtaining compact and reliable kinetic models for jet surrogate fuels. A detailed mechanism was developed by combining n-dodecane, 2,5-dimethylhexane and toluene sub-mechanisms with AramcoMech 2.0 C0–C4 mechanism to mimic the combustion properties of three representative jet fuels. Extensive validation of the component mechanisms in surrogate is performed using abundant experimental data sets. Thereafter, various combustion properties of three jet fuels like ignition delay times, species concentrations in flow reactor and laminar flame speeds are simulated by using this surrogate kinetic mechanism and previous surrogate formulations. The simulations are compared with other well-known surrogate models and a wide range of experimental data. The comparisons show that the developed mechanism is substantially improved prediction accuracy of most considered combustion properties for different jet fuels in a wide range of conditions.

An extensive study on skeletal mechanism reduction for the oxidation of C0–C4 fuels

The AramcoMech 3.0 mechanism containing 581 species and 3037 reactions for oxidation of hydrocarbon and oxygenated C0C4 fuels is reduced using six direct relation graph (DRG) related methods for the following fourteen fuels: hydrogen, carbon monoxide, methane, formaldehyde, methanol, acetylene, ethylene, ethane, acetaldehyde, ethanol, propene, 1,3-butadiene, isobutene and 2-butene. Maximum error on ignition delay times increases sharply when certain species is removed from skeletal mechanisms in skeletal reduction and it is difficult to achieve compact skeletal mechanisms for some fuels. This indicates that some important species are identified as redundant species with these methods. A fixed species scheme (FS) is proposed in skeletal reduction, where these species are regarded as important species and are retained in the skeletal mechanism. Smaller skeletal mechanisms can be achieved with this FS method given a certain maximum error. Skeletal mechanisms for each of the fourteen fuels with a maximum ignition delay time error of less than 10% are obtained. A comprehensive skeletal mechanism including 149 species and 925 reactions with a maximum error of 15% on ignition delay times is further achieved using the sensitivity analysis method starting from the union of the skeletal mechanisms for the fourteen fuels. The 149-species comprehensive skeletal mechanism and fourteen skeletal mechanisms are shown to provide reasonably key combustion characteristics for single-component fuels, including the laminar flame speeds, ignition delay times, and major species mole fraction profiles under a wide range of pressures, temperatures and equivalence ratios compared with experimental data and those of the detailed mechanism. Moreover, the 149-species skeletal mechanism can reproduce the combustion properties of some multi-component mixed fuels. The comprehensive skeletal mechanism can be employed as a core reaction base for developing mechanisms of other large hydrocarbon and oxygenated fuels.

Development of a skeletal oxidation mechanism for Fischer–Tropsch diesel surrogate based on decoupling method and particle swarm optimization

As an alternative liquid fuel, Fischer–Tropsch (FT) diesel has received significant attentions due to its characteristics of high efficiency and low emission. In this study, a surrogate fuel containing iso-hexadecane and n-dodecane with a mole ratio of 0.16:0.84 is formulated for real FT diesel by mimicking its combustion-related physicochemical properties. Mechanisms of these two components are developed based on decoupling methodology: skeletal sub-mechanisms describing iso-hexadecane and n-dodecane cracking process are constructed and combined with a reduced C0–C4 core mechanism, and then the Arrhenius parameters of certain reactions are tuned by particle swarm optimization algorithm to improve prediction accuracy. The optimized mechanisms are validated against experimental results of ignition delays, species concentrations and laminar flame speeds for iso-hexadecane and n-dodecane, respectively. Finally, by merging all the sub-mechanisms mentioned above, a skeletal oxidation model for FT diesel surrogate including 73 species and 324 reactions is obtained and employed in 3D CFD simulations to validate the ignition behavior of FT diesel sprays in a constant-volume combustion vessel; the simulation results show good agreement with experimental data.

Effects of the combined application of biomaterial amendments and polyacrylamide on soil water and maize growth under deficit irrigation

Combined applications of mixed biomaterial amendments and polyacrylamide (MBAP) to maize in semiarid areas have the potential to improve soil physical properties such that improved crop performance may be obtained under deficient irrigation management. In this study, three MBAP applications were C0 (conventional N fertilization application) and C2 and C4 (MBAP applied at rates of 2 and 4 t ha−1, respectively); three irrigation levels were W3 (nearly full irrigation, 85%–100% of field capacity), W2 (light deficit irrigation, 65%–75% of field capacity), and W1 (medium deficit irrigation, 55%–65% of field capacity). Under the same irrigation level, the MBAP significantly decreased soil bulk densities and increased soil hydraulic conductivities and soil water contents. The effects of irrigation levels on soil bulk densities and soil saturated hydraulic conductivities were not significant. Consequently, MBAP improved soil conditions for maize growth and increased grain and biomass yields, especially at the two deficit irrigation levels. Compared with that of C0, grain yields for C2 and C4 were increased by 52.8% and 39.3% under W2, and by 23.5% and 13.7% under W1, respectively. The MBAP and irrigation had significant interaction effects on evapotranspiration during sowing to jointing and on plant heights at 32 d after sowing. The incorporation of MBAP (2 t ha−1) and chemical fertilizer (111.8 kg N ha−1) resulted in the greatest yields under light deficit irrigation and seemed the best approach to improve soil physical properties and sustain maize productivity using limited water resources in dryland regions.

Bacteriological evaluation of composted manure solids prepared from anaerobic digested slurry for hygienic recycled bedding materials for dairy cows.

Changes in mastitis-causing pathogens, pH and water content in composted manure solids (CMS) prepared from digested slurry were evaluated during turning at 2-day intervals for 8days (C1-C4). The numbers of streptococci, coagulase-negative staphylococci and coliforms were 2.6×101 , 1.7×102 and 1.0×101 colony-forming units (cfu)/g in CMS (C4) (summer), and these counts were markedly lower (P<0.05) than those in CMS (C0 and C1). The bacterial counts ranged from 101 to 1.7×102 cfu/g in CMS (C4) (summer) and were within approved levels, <1×106 cfu/g, indicating a minimal mastitis risk. The temperatures in CMS (C1-C4) increased to 63°C-74°C in summer and 67°C-70°C in winter. The mean pH values in CMS (C0-C4) were 9.2 in summer and 8.7 in winter, and water contents ranged from 61.7% to 69.6% in summer and 73.2% to 66.2% in winter. The significant decrease of pathogenic bacteria in CMS appears to be closely related to temperature >63°C for 8days, pH 8.7-9.2, and water content 62% to 73%. This study demonstrates that prepared CMS has value as a recycled material with the potential to alleviate udder health issues in dairy cows.

Barcelona clinic liver cancer-stage C hepatocellular carcinoma: A novel approach to subclassification and treatment.

Barcelona clinic liver cancer-stage C (BCLC-C) encompasses a broad spectrum of tumor burdens, liver function statuses, patient prognoses, and treatment strategies. Currently, sorafenib is the only recommended treatment for patients with BCLC-C and outcomes remain suboptimal. The aims of this study were to assess the heterogeneity of BCLC-C hepatocellular carcinoma (HCC) cases, propose a novel subclassification for these cases, and suggest optimal treatment strategies other than sorafenib.We retrospectively analyzed 196 consecutive BCLC-C HCC patients who were diagnosed and treated between January 2008 and December 2015.All 196 patients were classified according to the modified Union for International Cancer Control (Stage I, 0.0%; Stage II, 8.2%; Stage III, 64.3%; Stage IVA, 21.9%; and Stage IVB, 5.6%) and American Joint Committee on Cancer TNM staging systems (Stage I, 0.0%; Stage II, 16.3%; Stage IIIA, 27.6%; Stage IIIB, 49.5%; Stage IIIC, 1.5%; Stage IVA, 1.0%; and Stage IVB, 4.1%). First-line treatment modalities included surgical resection (8.7%), transarterial chemoembolization (49.5%), hepatic arterial infusion therapy (5.6%), sorafenib therapy (9.2%), radiotherapy (9.2%), and best supportive care (10.7%). In univariate analysis, Child-Pugh score, tumor size, distant metastasis, multinodular or infiltrative/diffuse type of HCC, main portal vein invasion, hepatic vein invasion, and bile duct invasion were significantly associated with survival (P < .001). Tumor size, distant metastasis, HCC type, and bile duct invasion remained significantly associated with 1-, 3-, and 5-year survival rates in multivariate Cox regression analyses. Using these 4 characteristics, a novel subclassification of BCLC-C was developed and applied to the patient cohort. The subclassification included 5 substages (stages C0–C4), as defined based on the number of characteristics that were present in each HCC case (0–4). The subclassification showed significant associations with survival, with median survival times of 3026 days, 605 days, 224 days, 126 days, and 82 days for patients with Stage C0, C1, C2, C3, and C4 disease, respectively (P < .001). Additionally, diverse survival rates were observed when different treatment modalities were selected for cases within each substage.The proposed BCLC-C subclassification of HCC patients is effective in providing better prognostic subclassifications and more appropriate treatment strategies.

Fuel pyrolysis in a microflow tube reactor–Measurement and modeling uncertainties of ethane, n-butane, and n-dodecane pyrolysis

A scaled down flow reactor consisting of 4 mm ID quartz tubing and rapid mixing of fuel with a preheated thermal carrier bath was developed to investigate the pyrolysis of both gaseous and pre-vaporized liquid fuels. Starting from a small mixing volume (less than 0.2 cm3), the temperature of the hot section (37 cm long) was controlled within ± 5 K. All species concentrations were measured at the exit plane of the reactor using a GC system while residence time variations were explored by varying the bulk flow velocity. For the atmospheric pressure cases reported here, the temperature and flow residence times explored were in the kinetically controlled regime and ranged from 1000 to 1100 K and 10–90 ms, respectively. The thermal pyrolysis of fuels investigated included ethane, n-butane, and n-dodecane, all diluted in a nitrogen carrier bath of 98% or higher (to minimize temperature departure from the target value). Because the ratio of the mixing volume compared to the kinetically controlled reactor volume is about 2.5%, the associated finite mixing time is shown to have a negligible effect on the temporal evolution of key C0–C4 species. As a consequence, no species profiles shifting (zero-time shifting) was required in comparisons with model predictions. Experimental and modeling uncertainty analysis are presented to determine whether the experimental data can be used in future efforts aimed at minimization of chemical kinetic model parameter uncertainties.

A quantum chemical and kinetics modeling study on the autoignition mechanism of diethyl ether

A detailed chemical kinetics model has been developed to elucidate the auto-ignition behavior of diethyl ether (DEE) under conditions relevant for internal combustion engines. The present model is composed of a C0–C4 base module from literature and a DEE module. For the low-temperature oxidation mechanism, the reactions of ROO and QOOH radicals were studied previously with a quantum-chemical and transition state theory approach by Sakai et al. (2015). In the present study, the potential energy surfaces for the unimolecular reactions of OOQOOH isomers and 1- and 2-ethoxyethyl radicals were determined with a CBSQB3 composite method. In the presence of an OOH group, the reaction barrier of the hydrogen shift from the β site (terminal carbon atom) decreases as it does in alkane oxidation but there is no effect on the hydrogen shift from the α site (next to the ether oxygen atom). Therefore, the reaction barriers of OOQOOH isomers have the same trend as the corresponding ROO radical and rate constants for the reactions of OOQOOH isomers were determined. The constructed model was validated against the recent data of ignition delay times provided in literature by Werler et al. (2015). The agreement is good over the temperature range 500–1300K and pressure range 1–40bar, although, open questions remain regarding the non-consensus at 900–1150K and 40bar. Reaction-path and sensitivity analyses attribute the importance of the reactivity at the α site to the decrease of the C H bond dissociation energy due to the ether oxygen atom.

Ratios of low molecular weight alkylbenzenes (C0–C4) in Chinese crude oils as indicators of maturity and depositional environment

A total of 37 oils from three basins in China were analyzed using comprehensive two-dimensional gas chromatography coupled to time-of-flight mass spectrometry (GC×GC–TOFMS) to investigate the distributions of low molecular weight (LMW) alkylbenzenes (C0–C4). Thermal maturity and depositional environment exert dominant controls on the carbon number and isomer distributions of LMW alkylbenzenes, while secondary alteration, such as biodegradation or evaporative fractionation, cannot be ruled out. With increasing maturity, the relative abundance of C3 and C4 decreases while the C0–C2 alkylbenzenes increase. Some variations in isomer distributions of C4 alkylbenzenes are also attributed to maturation, as illustrated by ratios of (m-+p-)/o-propyltoluene and (3,5-+3,4-)/(2,5-+2,4-ethylxylene). The 1,2,3,5-/1,2,3,4-tetramethylbenzene ratio (TeMBr) is proposed to distinguish oils derived from source rocks formed under anoxic rather than oxic/dysoxic depositional conditions. The data suggest that TeMBr <1.0 indicates anoxia, while TeMBr >1.5 suggests an oxic/dysoxic depositional environment. Quantitative data show that the differences in TeMBr values are mainly due to variable 1,2,3,5-TeMB concentrations, whereas the range of 1,2,3,4-TeMB concentration is relatively constant. 1,2,3,5-TeMB is enriched in oils derived from source rocks deposited under oxic/dysoxic conditions, but depleted in oils from source rocks deposited under reducing conditions.

Laminar flame propagation of atmospheric iso-cetane/air and decalin/air mixtures

Laminar flame speeds of iso-cetane/air and decalin/air mixtures were measured in the counterflow configuration at atmospheric pressure and an elevated unburned mixture temperature of 443K. Axial flow velocities were measured along the stagnation streamline using the digital particle image velocimetry. The laminar flame speeds were determined by determining the variation of a reference flame speed as a function of strain rate and computationally assisted non-linear extrapolations. The data are the first to be reported in the literature, and they were modeled using a recently developed kinetic model that includes 187 species and 6086 elementary reactions. In general, the computed results were found to be in close agreement with the data. In order to get insight into kinetic effects on flame propagation, detailed sensitivity and reaction path analyses were performed using the computed flame structures. The results revealed that at the same equivalence ratio, laminar flame speeds of iso-cetane/air mixtures are lower than those of n-hexadecane/air mixtures. Additionally, it was found that the laminar flame speeds of iso-cetane/air and decalin/air mixtures are sensitive largely to C0–C4 kinetic subset, and that the lower reactivity of iso-cetane compared to n-hexadecane could be attributed to the higher production of relatively stable intermediates.

Cardiac myosin binding protein-C restricts intrafilament torsional dynamics of actin in a phosphorylation-dependent manner

We have determined the effects of myosin binding protein-C (MyBP-C) and its domains on the microsecond rotational dynamics of actin, detected by time-resolved phosphorescence anisotropy (TPA). MyBP-C is a multidomain modulator of striated muscle contraction, interacting with myosin, titin, and possibly actin. Cardiac and slow skeletal MyBP-C are known substrates for protein kinase-A (PKA), and phosphorylation of the cardiac isoform alters contractile properties and myofilament structure. To determine the effects of MyBP-C on actin structural dynamics, we labeled actin at C374 with a phosphorescent dye and performed TPA experiments. The interaction of all three MyBP-C isoforms with actin increased the final anisotropy of the TPA decay, indicating restriction of the amplitude of actin torsional flexibility by 15-20° at saturation of the TPA effect. PKA phosphorylation of slow skeletal and cardiac MyBP-C relieved the restriction of torsional amplitude but also decreased the rate of torsional motion. In the case of fast skeletal MyBP-C, its effect on actin dynamics was unchanged by phosphorylation. The isolated C-terminal half of cardiac MyBP-C (C5-C10) had effects similar to those of the full-length protein, and it bound actin more tightly than the N-terminal half (C0-C4), which had smaller effects on actin dynamics that were independent of PKA phosphorylation. We propose that these MyBP-C-induced changes in actin dynamics play a role in the functional effects of MyBP-C on the actin-myosin interaction.

A high pressure shock tube study of n-propylbenzene oxidation and its comparison with n-butylbenzene

Ignition delay times have been measured for mixtures of n-propylbenzene in air (≈21% O2, ≈79% N2) at equivalence ratios of 0.29, 0.48, 0.96 and 1.92 and at reflected shock pressures of 1, 10 and 30atm in a heated high-pressure shock tube over a wide temperature range (1000–1600K). The effects of reflected shock pressure and of equivalence ratio on ignition delay time were determined and common trends highlighted. Simulations were carried out using the n-propylbenzene sub-mechanism contained in an n-butylbenzene reaction mechanism available in the literature. This kinetic model was improved by including pressure dependent reactions which were not in place previously and the addition of the NUI Galway C0–C4 sub-mechanism. These simulations showed very good agreement with the experimental data. Additionally a comparison is made with experimental data previously obtained and published for n-butylbenzene over the same range of conditions and common trends are highlighted.