Intermediate CH Research Articles

Kinetics of the reactions of the Criegee intermediate CH2OO with water vapour: experimental measurements as a function of temperature and global atmospheric modelling

The kinetics of reactions between the Criegee intermediate, CH2OO, and water vapour have been investigated between 262 and 353 K at 760 Torr using laser flash photolysis of CH2I2–O2–N2–H2O with broadband time-resolved UV absorption spectroscopy.

Reaction between Criegee Intermediate CH2OO and Isobutyraldehyde: Kinetics and Atmospheric Implications

AbstractIn the present work, we have investigated the 1,3‐cycloaddition reaction of isobutyraldehyde ((CH3)2CHCHO) with the simplest Criegee intermediate CH2OO using the OH laser‐induced fluorescence (LIF) method in a reaction tube. The experiments were conducted at temperatures and pressures ranging from 280 to 338 K and 5 to 150 Torr. We found that the bimolecular rate coefficient of the reaction is temperature‐ and pressure‐dependent. The measured rate coefficients at 100 Torr are (4.93±0.89), (4.46±0.80), (3.99±0.72), (3.56±0.64), (3.34±0.60), (2.98±0.54), (2.78±0.50)×10−12 cm3 molecule−1 s−1 at 280, 288, 298, 308, 318, 328, and 338 K, respectively. A high‐pressure limit rate coefficient of (4.47±0.80)×10−12 cm3 molecule−1 s−1 was obtained at 298 K by fitting the pressure‐dependent rate coefficients according to the Lindemann mechanism. The Arrhenius plot of the temperature‐dependent rate coefficients results in an activation energy of (−1.86±0.33) kcal mol−1 and a preexponential factor of (1.72±0.31)×10−13 cm3 molecule−1 s−1. In the atmosphere, the reaction of CH2OO with isobutyraldehyde may contribute to the sink of CH2OO in regions where isobutyraldehyde emission is intense under low temperature and low relative humidity conditions.

Kinetics of the Simplest Criegee Intermediate CH2OO Reaction with tert-Butylamine

The kinetics of the simplest Criegee intermediate (CH2OO) reaction with tert-butylamine ((CH3)3CNH2) was studied under pseudo-first-order conditions with the OH laser-induced fluorescence (LIF) method at the temperature range of 283-318 K and the pressure range of 5-75 Torr. Our pressure-dependent measurement showed that at 5 Torr─the lowest pressure measured in the current experiment─this reaction was under the high-pressure limit condition. At 298 K, the reaction rate coefficient was measured to be (4.95 ± 0.64) × 10-12 cm3 molecule-1 s-1. The title reaction was observed to be negative temperature-dependent; the activation energy of (-2.82 ± 0.37) kcal mol-1 and the pre-exponential factor of (4.21 ± 0.55) × 10-14 cm3 molecule-1 s-1 were derived from the Arrhenius equation. The rate coefficient of the title reaction is slightly larger than (4.3 ± 0.5) × 10-12 cm3 molecule-1 s-1 of the CH2OO reaction with methylamine; the electron inductive effect and the steric hindrance effect might play a role in contributing to such difference.

Kinetics and pressure-dependent HOx yields of the reaction between the Criegee intermediate CH2OO and HNO3.

The reaction of Criegee intermediates with nitric acid (HNO3) plays an important role for removal of Criegee intermediates as well as in oxidation of atmospheric HNO3 because of its fast reaction rate. Theoretical prediction suggests that the product branching ratios of the reaction of the simplest Criegee intermediate CH2OO with HNO3 are strongly pressure dependent and the CH2OO may be catalytically converted to OH and HCO radicals by HNO3. The direct quantification of HOx radicals formed from this reaction is hence crucial to evaluate its atmospheric implications. By employing mid-infrared multifunctional dual-comb spectrometers, the kinetics and product yields of the reaction CH2OO + HNO3 are investigated. A pressure independent rate coefficient of (1.9 ± 0.2) × 10-10 cm3 molecule-1 s-1 is obtained under a total pressure of 6.3-58.6 Torr at 296 K. The product branching ratios are derived by simultaneous determination of CH2OO, formaldehyde (CH2O), OH and HO2 radicals. At the total pressure of 12.5 Torr, the yield for the formation of NO2 + CH2O + HO2 is 36% and only 3.2% for OH + CH2(O)NO3, whereas the main remainder may be thermalized nitrooxymethyl hydroperoxide (NMHP, NO3CH2OOH). Additionally, the fractional yields of both the OH and HO2 product channels are decreased by a factor of roughly 2 from 12 to 60 Torr, indicating that there is almost no catalytic conversion of CH2OO to the OH radicals in the presence of HNO3.

Infrared Characterization of the Products and Rate Coefficient of the Reaction between Criegee Intermediate CH2OO and HNO3.

The reactions of Criegee intermediates with HNO3 are important in the polluted urban atmosphere because of their large rate coefficients and the significant concentration of HNO3. Employing a step-scan Fourier-transform spectrometer, we recorded infrared spectra of transient species and end products in the reaction CH2OO + HNO3 upon irradiation of a flowing mixture of CH2I2/HNO3/N2/O2 at 308 nm. Eight bands at 1686, 1426, 1348, 1294, 1052, 965, 891, and 825 cm-1 were assigned to the absorption of the adduct nitrooxymethyl hydroperoxide (NMHP, NO3CH2OOH). Additional products from two dissociation channels were observed. Four bands at 1709, 1325, 1276, and 886 cm-1 were assigned to H2C(O)ONO2 (with coproduct OH), produced from the fission of the O-O bond of internally hot NMHP (NMHP*). Simultaneous detection of H2CO (1746 cm-1), NO2 (1617 cm-1), and HO2 (1392 and 1098 cm-1) indicated a direct cleavage of the N-OC and C-OO bonds of NMHP*. The relative yields of these three channels in pressure range 10-150 Torr were estimated. At 10 Torr, the absorption of internally excited HNO3 near 885 and 1320 cm-1 was also detected at an early stage of the reaction. We investigated also the rate coefficient of the reaction CH2OO + HNO3 by probing the temporal profiles of the formation of NMHP and NO2 under total pressures of 40 and 70 Torr at 298 K. The rate coefficient kHNO3 = (2.4 ± 0.4) × 10-10 cm3 molecule-1 s-1 is less than half the only literature value, (5.4 ± 1.0) × 10-10 cm3 molecule-1 s-1, reported by Foreman et al. (Angew. Chem. Int. Ed. 2016, 55, 10419-10422).

An Improved Multi-hop LEACH Protocol Based on Fuzzy Logic for Wireless Sensor Networks

<p>As an important kind of clustering protocols in wireless sensor networks (WSNs), LEACH and its variants have been demonstrated to efficiently balance the energy consumption, simplify the routing task and extend the network lifetime. Especially, the multi-hop LEACH type protocols have proved to be effective approaches for high energy efficiency, reliability as well as scalability. However, data transmission in hop-by-hop mode increases the energy consumption and end-to-end delay. In this paper, an improved multi-hop LEACH protocol based on fuzzy logic called IMF-LEACH is proposed, which uses a fuzzy logic controller with residual energy, length of data, and distance to BS as fuzzy descriptors to determine the hop count. Moreover, the hop count is used for each CH to find its optimal next-hop intermediate CH with more residual energy and less number of members. Simulations are conducted in MATLAB to evaluate the performance of the proposed protocol, and the results show that IMF-LEACH maximizes the network lifetime and outperforms its counterparts consistently.</p> <p> </p>

Mechanism and kinetics of the reaction of the Criegee intermediate CH2OO with acetic acid studied using a step-scan Fourier-transform IR spectrometer.

Acetic acid, CH3C(O)OH, plays an important role in the acidity of the troposphere. The reactions of Criegee intermediates with CH3C(O)OH have been proposed to be a potential source of secondary organic aerosol in the atmosphere. We investigated the detailed mechanism and kinetics of the reaction of the Criegee intermediate CH2OO with CH3C(O)OH. The time-resolved infrared absorption spectra of transient species produced upon irradiation at 308 nm of a flowing mixture of CH2I2/O2/CH3C(O)OH at 298 K were recorded using a step-scan Fourier-transform infrared spectrometer. The decrease in the intensity of the bands of CH2OO was accompanied by the appearance of bands near 886, 971, 1021, 1078, 1160, 1225, 1377, 1402, 1434, and 1777 cm-1, assigned to the absorption of hydroperoxymethyl acetate [CH3C(O)OCH2OOH, HPMA], the hydrogen-transferred adduct of CH2OO and CH3C(O)OH. Two types of conformers of HPMA, an open form and an intramolecularly hydrogen-bonded form, were identified. At a later reaction period, bands of the open-form HPMA became diminished, and new bands appeared at 930, 1045, 1200, 1378, 1792, and 1810 cm-1, assigned to formic acetic anhydride [CH3C(O)OC(O)H, FAA], a dehydrated product of HPMA. The intramolecularly hydrogen-bonded HPMA is more stable. From the temporal profiles of HPMA and FAA, we derived a rate coefficient k = (1.3 ± 0.3) × 10-10 cm3 molecule-1 s-1 for the reaction CH2OO + CH3C(O)OH to form HPMA and a rate coefficient k = 980 ± 40 s-1 for the dehydration of the open-form HPMA to form FAA. Theoretical calculations were performed to elucidate the CH2OO + CH3C(O)OH reaction pathway and to understand the distinct reactivity of these two forms of HPMA.

Syngas Conversion on the Different Cu Surfaces: The Relationship of the Coordination Number of Cu Active Sites with the Activity and Selectivity of Key Intermediate CHx Production

Syngas Conversion on the Different Cu Surfaces: The Relationship of the Coordination Number of Cu Active Sites with the Activity and Selectivity of Key Intermediate CH_<i>x</i> Production

Research on Optical Diagnostic Method of PDE Working Status Based on Visible and Near-Infrared Radiation Characteristics

Fill fraction not only has a profound impact on the process of deflagration to detonation in pulsed detonation engine, but also affects the propulsion performance in both flight and ground tests. In this paper, a novel optical diagnostic method based on detonation exhaust radiation in visible and near-infrared region within 300–2600 nm is developed to determine the current working state in the gas–liquid two-phase pulsed detonation cycle. The results show that the radiation characteristic in each stage of detonation cycle is unique and can be a good indicator to infer the fill fraction. This is verified experimentally by comparison with the laser absorption spectroscopy method, which utilizes a DFB laser driven by ramp injection current to scan H2O transition of 1391.67 nm at a frequency of 20 kHz. Due to concentrated radiation intensity, time duration reaching accumulated radiant energy ratio of 50% in detonation status would be smaller than 1.2 ms, and detonation status would be easily distinguished from deflagration with this critical condition. In addition, the variation of important intermediates OH, CH, and C2 radicals during detonation combustion are obtained according to the analysis of detonation spectrum, which can also be proposed as a helpful optical diagnostics method for the combustion condition based on C radical concentration. The study demonstrates the feasibility of optical diagnostics based on radiation in visible and near-infrared regions, which could provide an alternative means to diagnose and improve pulsed detonation engine performance.

Superlow Friction of a-C:H Coatings in Vacuum: Passivation Regimes and Structural Characterization of the Sliding Interfaces

A combination of atomistic simulations and vacuum tribometry allows atomic-scale insights into the chemical structure of superlubricious hydrogenated diamond-like carbon (a-C:H) interfaces in vacuum. Quantum molecular dynamics shearing simulations provide a structure-property map of the friction regimes that characterize the dry sliding of a-C:H. Shear stresses and structural properties at the sliding interfaces are crucially determined by the hydrogen content CH in the shear zone of the a-C:H coating. Extremely small CH (below 3 at.%) cause cold welding, mechanical mixing and high friction. At intermediate CH (ranging approximately from 3 to 20 at.%), cold welding in combination with mechanical mixing remains the dominant sliding mode, but some a-C:H samples undergo aromatization, resulting in a superlubricious sliding interface. A further increase in CH (above 20 at.%) prevents cold welding completely and changes the superlubricity mechanism from aromatic to hydrogen passivation. The hydrogen-passivated surfaces are composed of short hydrocarbon chains hinting at a tribo-induced oligomerization reaction. In the absence of cold welding, friction strongly correlates with nanoscale roughness, measured by the overlap of colliding protrusions at the sliding interface. Finally, the atomistic friction map is related to reciprocating friction experiments in ultrahigh vacuum. Accompanying X-ray photoelectron and Auger electron spectroscopy (XPS, XAES) analyses elucidate structural changes during vacuum sliding of a hydrogen-rich a-C:H with 36 at.% hydrogen. Initially, the a-C:H is covered by a nanometer-thick hydrogen-depleted surface layer. After a short running-in phase that results in hydrogen accumulation, superlubricity is established. XPS and XAES indicate a non-aromatic 1–2-nm-thick surface layer with polyethylene-like composition in agreement with our simulations.

Fuzzy Interference System based Link Failure prediction in MANET

Mobile Ad-Hoc Network (MANET) contains wireless mobile nodes establishing a short-term network lacking the assistance of individual structure. Owing to the nodes mobility, such mobile nodes are auto-configuring also auto-organizing. In MANETs, approaches are essential to discover definite routes among the sender to receiver. One important concern for routing in MANET is how to choose a quality link route that can last longer because mobility may reason links to break regularly. To solve this issue, in this approach, a Fuzzy Interference System based Link quality prediction (FLQP) in MANET is proposed. In this approach, select the intermediate CH using Fuzzy Interference System (FIS) is predicting the sensor link quality by Received Signal Strength (RSS), Communication range (CR), Remaining Energy (RE), packet transmission rate (PTR) parameters. This FIS can be utilized to extend a metric for path selection in terms of link quality that can improve the network performance as to be exposed by the simulation results.

Catalytic Conversion of CO and H2 into Hydrocarbons on the Cobalt Co(111) Surface: Implications for the Fischer–Tropsch Process

The Fischer–Tropsch (FT) process consists of the reaction of a synthesis gas (syngas) mixture containing carbon monoxide (CO) and hydrogen (H2), which are polymerized into liquid hydrocarbon chains, often using a cobalt catalyst, although the mechanistic pathway is not yet fully understood. Here, we have employed unrestricted density functional theory calculations with a Hubbard Hamiltonian and long-range dispersion corrections [DFT+U−D3−(BJ)] to investigate the reaction of syngas and the selectivity toward the hydrocarbons formed on the cobalt Co(111) surface. The single CO and dissociated H2 molecules prefer to adsorb at two different types of trigonal surface sites, and we discuss how the interatomic distances, fundamental vibrational modes, charge transfers, surface-free energies, and work functions are modified by the adsorbates. The coadsorption of the syngas molecules in close proximity provides enough energy for the system to cross the saddle points on the minimum energy pathway (MEP), leading to the catalytic hydrogenolysis of the C–O bond. The adsorbed CO, alongside the intermediates CH and OH, are further stabilized when the ratio of equilibrium coverage (C) is CH/CCO,CH,OH > 6:1 under the temperature conditions required for the FT process. We propose several mechanistic pathways to account for the formation of ethane (C2H6), as a model for long-chain hydrocarbons, as well as methane (CH4) which is an undesirable product. The MEPs for these processes show that the coupling of the C–C bond followed by hydrogenation is the most favorable process, which takes precedence over the production of CH4. The termination reaction suggests that water (H2O) remains weakly physisorbed to the surface, allowing the reutilization of its catalytic site. The simulated fundamental vibrational frequencies and scanning tunneling microscopy images of the surface-bound intermediates are in agreement with the available experimental data. Our findings are important in the interpretation of the elementary steps of the FT process on the Co(111) surface.

فاعلیة استخدام مدخل تفکیر النظم فی تنمیة الممارسات الریاضیة وفق معاییر الجیل القادم (NYS) وتقدیر القیمة الوظیفیة للریاضیات لدی طالبات المرحلة المتوسطة Effectiveness of System thinking approach to developing mathematical practices according to mathematics standards of the next generation of NYS and assess the functional value of learning mathematics among Intermediate sch

ملخص البحث: هدف البحث إلىقياسفاعلية استخدام مدخل تفکير النظم في تنمية الممارسات الرياضية وفق معايير الجيل القادم (NYS) وتقدير القيمة الوظيفية لتعلم الرياضيات لدى طالبات الصف الثاني المتوسط. واعتمد البحث على المنهج شبه التجريبي تصميم المجموعتين المتکافئتين، وبلغت عينة البحث (65) طالبة بالصف الثاني المتوسط بمحافظة الزلفى بالمملکة العربية السعودية، وبلغ عدد طالبات المجموعة التجريبية (33) طالبة، وعدد طالبات المجموعة الضابطة (32) طالبة. واقتصر البحث على فصل الهندسة والاستدلال المکاني من کتاب الرياضيات للصف الثاني المتوسط الفصل الدراسي الثاني لعام 2020/2021 وتم إعادة صياغتها وفق مدخل تفکير النظم بالاستعانة بتطبيق Class point کأحد تطبيقات الذکاء الاصطناعي. واستخدمت الباحثة اختبار لقياس الممارسات الرياضية اللازمة لحل المشکلات الحياتية مکونا من أربعة أبعاد وهي (حل المشکلات الرياضية بدقة، البرهان والاستدلال الرياضي بشکل تجريدي وکمي، استخدام النموذج والهيکل الرياضي بشکل استراتيجي، التقويم وبناء حجج قابلة للنقد)، ومقياس لقياس تقدير القيمة الوظيفية لتعلم الرياضيات مکون من ثلاث أبعاد وهي (القيمة التعليمية (الأکاديمية) والقيمة التطبيقية (الحياتية) والقيمة المهنية)، وتم حساب صدقهما وثباتهما لاختبار صلاحيتهما للتطبيق. وتوصل البحث إلى وجود فرق دال إحصائيا عند مستوي دلالة (0.01) بين متوسطي درجات طالبات المجموعتين التجريبية والضابطة في التطبيق البعدي لأدوات القياس لصالح طالبات المجموعة التجريبية، وکذلک فاعلية توظيف مدخل تفکير النظم في تنمية الممارسات الرياضية اللازمة لحل المشکلات الحياتية وتقدير القيمة الوظيفية لتعلم الرياضيات لدي طالبات المجموعة التجريبية. واستنادا لنتائج البحث قدمت الباحثة مجموعة توصيات، أهمها: أن تضمن موضوعات الرياضيات بالمرحلة المتوسطة العديد من الانشطة والتطبيقات الحياتية التي تبرز دور الرياضيات في المجالات المتعددة وفى حل القضايا والمشکلات المجتمعية وفى تفسير الظواهر المختلفة مما يعزز الممارسات الرياضية اللازمة لحل المشکلات واتخاذ القرار لدي الطالبات ويعزز تقديرهن للقيمة الوظيفية لتعلم الرياضيات بمختلف التخصصات والمجالات، بالإضافة إلى أهمية تدريب معلمات الرياضيات على توظيف المداخل التدريسية التکاملية کمدخل تفکير النظم لجعل المعرفة الرياضية أکثر تکاملية ووظيفية وأکثر متعة وتشويقا. Abstract: The research aimed to find out effectiveness of system thinking approach in developing mathematical practices according to mathematics standards of the next generation of NYS and assess the functional value of learning mathematics among Intermediate school students. This research used semi-experimental approach of two equal groups. The study sample consisted of (65) students of the second-grade students in the eight Intermediate school in Al-Zulfi governorate, Saudi Arabia. The sample was divided into (33) experimental group students and (32) as a control group. The research limited to the unit of geometry and spatial reasoning from the second Intermediate grade mathematics book, second semester for academic year 2020/2021 .it was reformulated according to system thinking approach using Class point application as one of the applications of artificial intelligence. The researcher used a test to measure mathematical practices which consists of four dimensions (Accurately solve mathematical problems, mathematical proof, and inference in an abstract and quantitative manner, use the mathematical model and structure strategically, evaluate and construct critical arguments). In addition, a measure of assess the functional value of learning mathematics which consists of three dimensions (Educational (academic) value, applied (life) value, and professional value). Then, the researcher counts the validity& reliability before application. The study reached There was a statistically significant difference at the level of (0.01), between the scores of experimental and control groups in the post application of measure tools in favor of experimental group, As well as the effectiveness of employing the systems thinking approach in developing the mathematical practices necessary to solve life problems and assess the functional value of learning mathematics for experimental group. According to research results we presented some recommendations: we need to include many activities and life applications that highlight the role of mathematics in various fields and in solving issues and societal problems and in the interpretation of various phenomena in mathematics lessons of Intermediate school students, which enhances the mathematical practices necessary for solving problems and decision-making among students and enhances their assess of the functional value of mathematics in various disciplines and fields, in addition to training Mathematics teachers use integrative teaching approaches as systems thinking approach to make mathematical knowledge more integrative, functional, fun and interesting.

Kinetics of the gas phase reaction of the Criegee intermediate CH2OO with SO2 as a function of temperature.

The kinetics of the gas phase reaction of the Criegee intermediate CH2OO with SO2 have been studied as a function of temperature in the range 223-344 K at 85 Torr using flash photolysis of CH2I2/O2/SO2/N2 mixtures at 248 nm coupled to time-resolved broadband UV absorption spectroscopy. Measurements were performed under pseudo-first-order conditions with respect to SO2, revealing a negative temperature dependence. Analysis of experimental results using the Master Equation Solver for Multi-Energy well Reactions (MESMER) indicates that the observed temperature dependence, combined with the reported lack of a pressure dependence in the range 1.5-760 Torr, can be described by a reaction mechanism consisting of the formation of a pre-reaction complex leading to a cyclic secondary ozonide which subsequently decomposes to produce HCHO + SO3. The temperature dependence can be characterised by kCH2OO+SO2 = (3.72 ± 0.13) × 10-11 (T/298)(-2.05±0.38) cm3 molecule-1 s-1. The observed negative temperature dependence for the title reaction in conjunction with the decrease in water dimer (the main competitor for the Criegee intermediate) concentration at lower temperatures means that Criegee intermediate chemistry can play an enhanced role in SO2 oxidation in the atmosphere at lower temperatures.

Infrared characterization of the products and the rate coefficient of the reaction between Criegee intermediate CH2OO and HCl.

Reactions between Criegee intermediates and hydrogen halides might be significant, particularly in the polluted urban atmosphere, because of their large rate coefficients. Employing a Fourier-transform spectrometer in a step-scan mode or a continuous-scan mode, we recorded infrared spectra of transient species and end products in a flowing mixture of CH2I2/HCl/N2/O2 irradiated at 308 nm. Five bands near 823.2, 1061.1, 1248.4, 1309.2, and 1359.6 cm-1 were observed and assigned to the gauche-conformer of chloromethyl hydroperoxide (CMHP, CH2ClOOH). At a later time of the reaction, absorption bands of H2O and formyl chloride (CHClO) at 1782.9 cm-1 were observed; these species were likely produced from the secondary reactions of CH2ClO + O2→ CHClO + HO2 and OH + HCl → H2O + Cl according to temporal profiles of CMHP, H2O, and CHClO; formation of CH2ClO + OH via decomposition of internally excited CMHP was predicted by theory and both HCl and O2 are major species in the system. We investigated also the rate coefficient of the reaction CH2OO + HCl on probing CH2OO with a continuous-wave infrared quantum-cascade laser absorption system under total pressure 5.2-8.2 torr at 298 K. The rate coefficient kHCl = (4.8 ± 0.4) × 10-11 cm3 molecule-1s-1, is comparable to the only literature value kHCl = (4.6 ± 1.0) × 10-11 cm3 molecule-1s-1 reported by Foreman et al.

Repeatability and ranking of long-term enteric methane emissions measurement on dairy cows across diets and time using GreenFeed system in farm-conditions.

The aims of this work were to study on dairy farm conditions: i) the repeatability of long-term enteric CH4 emissions measurement from lactating dairy cows using GreenFeed (GF); ii) the ranking of dairy cows according to their CH4 emissions across diets. Forty-five Holstein lactating dairy cows were randomly assigned to 3 equivalent groups at the beginning of their lactation. The experiment was composed of 3 successive periods: i) pre-experimental period (weeks 1 to 5) in which all cows received a common diet; ii) a dietary treatment transition period (weeks 6 to 10); and iii) an experimental period (weeks 11 to 26) in which each group was fed a different diet. Experimental diets were formulated to generate more or less CH4 production: i) a diet based on ryegrass silage and concentrates, low in starch and lipid, designed to induce high CH4 emissions (CH4+); ii) a diet based on maize silage and concentrates, rich in starch, designed to induce intermediate CH4 emissions (CH4int); iii) a diet based on maize silage and concentrates, rich in starch and lipid, designed to induce low CH4 emissions (CH4-). Gas emissions were individually measured using GF systems. Repeatability of gas emissions, dry matter intake (DMI) and dairy performances measurements was calculated from data averaged over 1, 2, 4, and 8weeks for each animal. Hierarchical cluster analysis was performed to rank individual animals according to their CH4 emissions. No significant differences were observed for daily CH4 emissions (g/day) among diets, because of lower DMI of CH4+ cows. When CH4 emissions were referred to units of DMI or milk, the differences among diets emerged as significant and persistent over the observed period of lactation. Repeatability values of gas emissions measurements were higher than 0.7 averaged over 8weeks of measurement, but still higher than 0.6 for CH4 g/day, CO2 g/day, CH4 g/kg milk, and CH4/CO2 even averaging only 2weeks of measurement. The repeatability of CH4 emissions measurement was systematically lower than those of DMI or dairy performance parameters, like milk and FPCM yield, irrespective of the averaged measurement period. The dairy cow ranking was not stable over time between all individuals or within any of the diets. In our experimental conditions, the GF performance in the long term can be considered reliable in differentiating dairy herds by their CH4 emissions according to diets with different methanogenic potential, but did not allow the ranking of individual dairy cows within a same diet. Our data highlight the importance of phenotyping animals across environment in which they will be expected to perform.

Development of Detailed Surface Reaction Mechanism of C2H4/C3H6 Oxidation on Pt/Al2O3 Monolith Catalyst Based on Gas Phase and Surface Species Analyses

ABSTRACT In this study, reaction characteristics of C2H4/O2 and C3H6/O2 on practical Pt/Al2O3 monolith catalyst are investigated, and a simplified microkinetic surface reaction mechanism is proposed by taking the observed surface species and their occupied active surface sites into account. Importance of more than one active PGM surface site occupations at the adsorption step of C2H4 or C3H6 and multiple-sited stable intermediate CH x species are considered. Gas phase experimental results show that the light-off temperature as well as complete conversion temperature of both C2H4/O2 and C3H6/O2 mixture shift to lower side with the increase in oxygen concentration. The surface species analyses show the presence of stable intermediate CH x species and linearly adsorbed CO on the platinum surface. Numerically simulated light-off performance with the proposed reaction mechanism shows good agreement with the experimental results of C2H4/O2 and C3H6/O2. Moreover, simulation results also agree well with the additional experimental results with multiple gas compositions and validate the proposed detailed reaction mechanism.

Dynamics Insight into Isomerization and Dissociation of Hot Criegee Intermediate CH3CHOO.

We study the isomerization and dissociation of syn-CH3CHOO with high internal energies by combining electronic structure calculations, ab initio molecular dynamics, and RRKM microcanonical variational transition-state theories. The results show a striking effect of the internal energy on the reaction fate of syn-CH3CHOO. With lower internal energies, syn-CH3CHOO prefers isomerizing to vinyl hydroperoxide, which then produces hydroxyl radical. As the available internal energy increases, the O-elimination channel becomes more competitive and eventually the dominant channel. A third channel leading to methyl dioxirane is found to be less competitive than the former two. However, this channel is highly exothermic and produces greenhouse gases CH4 and CO2; thus, further investigation is needed to quantify its potential impact on the atmosphere. The present study provides new insight on clarifying the unimolecular reaction fate of hot syn-CH3CHOO and theoretical solutions for revealing the impact of internal energy on the complex gas phase reactions.

Theoretical Study on the Reaction Mechanism and Kinetics of Criegee Intermediate CH2OO with Acrolein.

The detailed reaction mechanism and kinetics of Criegee intermediate CH2OO with acrolein were investigated. CH2OO may add to the C═O or C═C double bond of acrolein to form a five-membered ring adducts, and it may also insert the terminal oxygen atom or insert itself into the C-H bond of acrolein. The addition reactions are more favorable in energy than the insertion reactions. The master equation calculation show that the most competitive reaction channel is the 1,3-cycloaddition of CH2OO across the C═O double bond forming the secondary ozonide (SOZ). The lowest energy pathway for SOZ decomposition involves the formation of the singlet biradical intermediate by ring fission, the H-shift isomerization and the dissociation to products. The calculated overall rate constant decreases as the temperature increases from 200 to 500 K, and at 298 K, it is 4.31 × 10-12 cm3 molecule-1 s-1. The branching ratio of collisionally stabilized SOZ increases with the increase of pressure. At low pressure, some of SOZ decompose to HCOOH + acrolein or HCHO + acrylic acid. The pressure dependence of this reaction is in agreement with the previous theoretical and experimental observations for the reaction of CH2OO with acetaldehyde.

Comportamiento higiénico y nivel de infestación con Varroa destructor de Apis mellifera en la zona centro del Ecuador

Con el propósito de evaluar el comportamiento higiénico (CH) y su relación con las tasas de infestación (TIA) por Varroa destructor de abejas adultas (Apis mellifera), el presente trabajo se realizó en las provincias de Tungurahua y Chimborazo de la República del Ecuador; se muestrearon un total de 85 colonias durante los meses de abril y mayo de 2017. A cada colmena se le determinó el comportamiento higiénico a través de la técnica del perforado; conjuntamente se tomaron muestras para los diagnósticos de detección de varroa por el método de De Jong. Los resultados indican que para el CH los apiarios de Tungurahua y Chimborazo mostraron diferencias significativas (P£0,05), con valores medios de 80,3 % y 73,5 % y una TIA de 5,2 % y 3,13 % sin significancia al U de Mann-Whitney. Las colonias se clasificaron en base al CH obteniéndose tres grupos: alta CH (15 colmenas), intermedia CH (65 colmenas) y baja CH (5 colmenas), se comprobó que el acaro varroa está presente en toda la zona de estudio, con una prevalencia del 86 % de las colmenas (73/85). Se encontraron correlaciones negativas altamente significativas entre la CH y el número de ácaros en etapa forética (r= -0,547), revelando que aquellas colmenas con un mayor CH, presentaron menores cargas parasitarias. Se encontraron diferencias en el comportamiento higiénico de los apiarios de la provincia de Tungurahua y Chimborazo, mientras que se diagnosticaron tasas de infestación medias para estas provincias, comprobando que el acaro varroa está presente en la zona