Four entrance channels to the pentachlorodisilane (Si2HCl5) potential energy well, namely, SiCl2 + SiHCl3, SiCl4 + SiHCl, Cl3SiSiCl + HCl, and SiCl3 + SiHCl2, were analyzed in detail through transition state theory, Rice-Ramsperger-Kassel-Marcus (RRKM) theory, and solution of the multichannel master equation. The stationary points in the potential energy surface were optimized, and their vibrational frequencies and rotational constants calculated at the (U)B3LYP/6-31+G(d,p) level of theory; the (U)CCSD(T)/aug-cc-pVTZ level was then used for accurate estimation of activation energies. The pressure and temperature dependence of the rate coefficients of the channels related to Si2HCl5 stabilization/dissociation was determined along a wide range of conditions, for the first time. All channels showed strong pressure dependence in the four cases, at least at low-to-moderate pressure conditions. Each entrance channel leads to the formation of different products under different conditions, and the mechanism was analyzed in detail. The results indicated that at atmospheric pressure the reactions are in the falloff region, and therefore do not support the adoption of high-pressure limit rate coefficients in reaction models designed for simulation of systems at atmospheric or subatmospheric pressure conditions.

The dynamics of reactions of SiCl2 at Si(100) surfaces was investigated through the molecular orbital method at the B3LYP/6-31G(d,p) level of theory, with the surface being modeled using clusters of silicon atoms. The intradimer adsorption of a SiCl2 molecule proceeded with no energy barrier, and in the structure of the product of the adsorption reaction the Si atom of the SiCl2 adsorbate formed a triangular structure with the two Si atoms of the surface dimer, in agreement with theoretical predictions published recently in the literature for a small cluster. However, the dynamics reported in this work indicates that SiCl2 undergoes molecular adsorption at the silicon surface, in contrast with the dissociative adsorption suggested by some available kineticmodels. Intradimer adsorption of a second SiCl2 molecule, and interdimer adsorptions of a first, a second, and a third SiCl2 molecule were also seen to proceed without significant energy barriers, suggesting that the formation of the first additional layer of silicon atoms on the surface would be fast if the adsorption of SiCl2 were the only type of reaction proceeding in the system. The diffusion of the SiCl2 adsorbate over the surface and its desorption from the surface were found to have comparable activation energies, so that these reactions are expected to compete at high temperatures. (C) 2016 Elsevier B.V. All rights reserved.

As English-medium instruction (EMI) spreads around the world, university teachers and students who are non-native speakers of English (NNS) need to put much effort into the delivery or reception of content. Construction of scientific meaning in the process of learning is already complex when instruction is delivered in the first language of the teachers and students, and may become even more challenging in a second language, because science education depends greatly on language. In order to identify important pedagogical functions that teachers use to deliver content and to present different ways to realise each function, a corpus of lectures related to science and engineering courses was created and analysed. NNS teachers and students in science and engineering involved in EMI higher education can obtain insights for delivering and listening to lectures from the Online Corpus of Academic Lectures (OnCAL).

A process for obtaining trichlorosilane (TCS or SiHCl3) from hydrogenation of silicon tetrachloride (STC or SiCl4) through control of the temperature along a one-dimensional plug-flow reactor at atmospheric pressure was simulated using a reaction model that was built based on a literature review: Rate coefficients for reactions that occur in silicon CVD processes were adopted from published data. A compact model made available recently in the literature for simulating reactions occurring in silicon chemical vapor deposition (CVD) reactors was used as a basis, and more reactions from other sources were added for better description of the thermal decomposition of STC. The kinetic model built in this work comprised 63 elementary reactions occurring among 26 species. This model was applied to the calculation of the species concentration profiles along the reactor, which was divided into two parts: a STC hydrogenation step, proceeding at a high and constant temperature in the first, and a cooling step, where the gases are brought to room temperature, in the second part. When the hydrogenation temperature was set to 1273 K or higher, the first step was just a stage where the gases reached chemical equilibrium. More interesting reactions occur in the second step, where cooling prevents reactions from reaching equilibrium. This leads to the production of TCS from SiCl2 and HCl, with efficiencies that depend on the conditions. Among the conditions investigated in this work, hydrogenation of a mixture of molar composition STC:H-2 = 1:4 at 1473 K followed by cooling at a rate of -50.92 K cm(-1) gave the highest conversion efficiency from STC into TCS. (C) 2015 Wiley Periodicals, Inc.

In order to determine the effect of cluster size on the calculation of activation energies of reactions at silicon surfaces, intradimer adsorption/desorption reactions of H-2 and HCl with silicon clusters of various sizes and shapes were analyzed under the B3LYP/6-31G(d,p) level. Activation energies of reactions of H-2 and HCl with clusters composed of different number and orientation of dimers on the surface were estimated. For clusters having dimers parallel to each other, the activation energies converged satisfactorily at three (timers, but for clusters having dimers aligned in a row, activation energies did not converge sufficiently even at four dimers. The activation energies for clusters having three dimers parallel to each other on the surface were seen to be in good agreement with values published in the literature, but considering potential application of the cluster to model intrarow and interrow reaction mechanisms, reactions of H-2 and HCl with a cluster having three dimers parallel to each other and three (timers aligned in a row on the surface were also investigated, and the resultant activation energies were in even better agreement with published values. (C) 2015 Elsevier B.V. All rights reserved.

The OnCAL (Online Corpus of Academic Lectures) project was initiated in 2010 to support instructors who are non-native speakers of English (NNS) in preparing for delivering lectures in English. An interactive search interface was developed for lecture transcripts from MIT Open CourseWare (MIT OCW) and Stanford Engineering Everywhere (SEE). As of January 2015, 430 transcripts can be searched at the OnCAL site; the corpus comprises 3.5 million words, which corresponds to about 395 hours of recorded lecture time. The lectures cover many fields related to science and engineering: biology, chemistry, physics, mathematics, and computer science as undergraduate courses, and advanced mathematics, robotics, and artificial intelligence as graduate courses. Pedagogical functions have been identified, and in the present work, we show how teachers use language to connect the presentation of new content to contents presented previously. Here we present examples of pedagogical link-making devices, which are important for promoting continuity of ideas and helping students connect chunks of information presented over a series of lessons. Concrete examples can be observed via OnCAL to help NNS teachers deliver effective lectures and students listen to them.

In order to support instructors who are non-native speakers of English (NNS) in preparing for delivering lectures in an English-medium science and engineering program, we started the OnCAL (Online Corpus of Academic Lectures) project in 2010. Transcriptions of lectures delivered mostly by native speakers of English (NS) were obtained from MIT Open Courseware (MIT OCW) and Stanford Engineering Everywhere (SEE), and an online corpus was built. As of September 2015, the corpus comprises 430 lecture transcriptions, which contain 3.5 million words. This corresponds to about 395 hours of recorded lecture time. The lectures are from courses that cover a wide range of fields in science and engineering: biology, chemistry, physics, mathematics, and computer science as undergraduate courses, and advanced mathematics, robotics, and artificial intelligence as graduate courses. Pedagogical functions have been identified in the teacher utterances to allow OnCAL users to find examples of how teachers use language to realize specific pedagogical purposes. The examples of utterances found through OnCAL can thus be seen by NNS teachers as a reference for their own lectures. In the present work, we analyze how mathematical equations are explained in lectures. In this type of explanations teachers make use of and are aided by visual modes, but we believe that the spoken language that accompanies the other modes still have to be very accurate.

Oral communication skills are essential for engineers today and, as they are included in accreditation criteria of educational programmes, their teaching and evaluation deserve attention. However, concrete aspects as to what should be taught and evaluated in relation to oral communication skills have not been sufficiently established. In this paper, a method to aid the efficient teaching of oral presentation skills is proposed, from the presentation structure level to word and sentence level choices, through the use of JECPRESE, The Japanese-English Corpus of Presentations in Science and Engineering. As of June 2012, the corpus is composed of transcriptions of 74 presentations delivered in Japanese by students graduating from the Master's programme of various engineering departments and 31 presentations delivered in English, 16 by experienced researchers at an international conference on chemistry, and 15 by undergraduate engineering students of a mid-sized American university. The utterances were classified according to the specific moves (sections of the speech that express specific speaker intent) appearing in the presentations and frequently used words/expressions to express these moves were identified. © 2012 Copyright Taylor and Francis Group, LLC.

The Great East Japan Earthquake and the Fukushima No.1 nuclear power plant accident revealed serious problems with Japanese information communication systems. From a rhetorical viewpoint, the Japanese language starts to explain a situation from the beginning and leaves the outcome until the end. In traditional Japanese culture, the world is thought to move with the collective flow of nature, and all things are constantly in the process of change. Thus, self-assertion is not encouraged in Japan. The Japanese language itself is imbued with "vagueness," possessing a wealth of vocabulary and expressions but often not being conducive to sending out a clear message. Unfortunately, under emergency circumstances, such as experienced in March 2011, serious problems can occur. In this paper, we examine the language used by researchers in science and engineering, where clarity is essential. We prepared the Japanese-English Corpus of Presentations in Science and Engineering (JECPRESE) of transcriptions of presentations given in Japanese and English by researchers. Our comparative analyses revealed that the "vagueness" in Japanese results from missing subjects and a lack of sensitivity for paragraph structure (idea frameworks), verb tense and mood. In order to send out a clear message, more effort needs to be made to be aware of the audience' s viewpoint. Only in this way can the Japanese learn to speak out without "vagueness" as the world accelerates towards internationalization with the ever increasing need to send out clear messages.

A modification of the CHEMKIN II package has been proposed for modeling addition of an arbitrary species at an arbitrary temperature to an arbitrary distance from the burner along a flat flame. The modified program was applied to the problem of addition of acetylene or benzene to different positions of a 40-Torr, phi = 2.4 benzene/O-2/40%-N-2 premixed flame to reach final equivalence ratios of phi = 2.5 and 2.681. The results obtained showed that acetylene addition to early positions of the flame led to significant increase in pyrene production rates, but pyrene concentrations were lower in the flames with acetylene addition in both the phi = 2.5 and 2.681 cases. Addition of benzene to the flame did not alter pyrene production rates in either the phi = 2.5 or 2.681 cases; however, for phi = 2.5, pyrene concentrations increased with benzene addition, while for phi = 2.681, pyrene contents decreased in comparison to the correspondent flames with no addition. Acetylene addition led to a significant increase in pyrene production rates, but the pyrene levels dropped due to increase in the flow velocity. Pyrene production rates were not sensitive to benzene addition, but pyrene contents increased with benzene addition when the flow velocity decreased. These results show that PAH concentration changes accompanying species addition to flames should be interpreted carefully, because an increase or decrease in the content of a PAH species does not necessarily reflect an effect on its formation rate or mechanism. (c) 2006 The Combustion Institute. published by Elsevier Inc. All rights reserved.

The oxidation reactions of phenyl and 1-naphthyl radicals through reaction with O-2 were investigated through 7 a quantum chemical molecular orbital method as potential sources of PAH species containing 5-membered rings in hydrocarbon flames. The reaction between phenyl radical and 0, was seen to produce phenoxy radical in a single elementary step. The same mechanism was followed in the reaction between 1-naphthyl radical and O-2. with formation of naphthoxy radical in a single step. In both phenyl and 1-naphthyl oxidation reactions, the variation of energy and atomic arrangement with the reaction coordinate was found to be similar and their rate coefficients, evaluated through transition state theory, to agree with each other. Thus, because the oxidation reaction of a species composed of one aromatic ring (phenyl radical) and that of a species composed of two aromatic rings ( 1-naphthyl radical) proceed through the same mechanism and have similar rate coefficients, the oxidation of species composed of an arbitrary number of aromatic rings can lie supposed to proceed through that mechanism and have the same rate coefficient. The mechanism of the subsequent decomposition of phenoxy radical into cyclopentadienyl radical and CO agreed with the mechanism reported in the literature, and the decomposition of naphthoxy radical was found to be similar to that of phenoxy radical. In summary, the routes
C6H4 + O-2 --> C6H5O + CO + O
C10H7 + O-2 --> C10H7O + O --> C9H7 + CO + O,
where C5H5 and C9H7 are, respectively, cyclopentadienyl radical and indenyl radical, proceed through the same mechanism. From these results it is suggested that the formation of species containing a peripheral 5-membered ring (aryl-5) through partial oxidation of a peripheral 6-membered ring of arbitrary aryl radicals (aryl-6), described generally as
aryl-6 + O-2 --> aryl-6-O + O --> aryl-5 + CO + O,
can be thought to proceed through the same mechanism. The rate coefficients of the first step are the same for any aryl-6 species, but they were found to he much smaller than values reported in the literature for phenyl as aryl-6 species. (C) 2002 by The Combustion Institute.

The sequence of hydrogen abstraction reactions from ethane to acetylene, which proceeds in fuel-rich methane flames, has been investigated by an ab initio molecular orbital method. First, the hydrogen abstraction mechanism was elucidated through an analysis of the variation in the electron spin density distributions through the reacting species. The H atoms holding the largest spin densities within a radical where seen to be those being abstracted from the species. The reaction rate coefficients for the four elementary abstraction steps from ethane to acetylene were determined through the transition state theory, and the results were compared with data published in the literature. The obtained rate coefficients were found to be lower than the published data for all four reactions examined. Especially, for two of the reactions, some published data seem to be too large, considering that the rate coefficients obtained through transition state theory tend to be larger than the true values.

The dynamics of the oxidation reaction of an acetylene molecule with an oxygen atom was investigated through an ab initio molecular orbital method. The three reactions (1) C2H2+O→HCCO+H, (2) HCCO+H→CH2+CO and (3) C2H2+O→CH2+CO, reported in reaction schemes, were confirmed as being the main elementary steps related to the acetylene oxidation but were found to be not single elementary steps, with each one forming intermediary species before the proposed products. These intermediaries are expected to decompose always and much faster than they form, so that those three reactions can be treated as elementary steps without problem. Under ideal conditions, only reaction (3) can be expected to proceed, but vibrations of the atoms in a structure formed during the process can cause its decomposition into HCCO+H, and later the so formed HCCO can meet another H atom and react to CH2+CO. Reactions (1) and (2) are then found to be, respectively, an early and a late step of reaction (3), but each of the three events can occur, depending on how is the collision between the O atom and the vibrating C2H2 molecule. The present results are compared with experimental data reported in the literature, and a qualitative agreement with the data of Miller and Bowman can be seen for reactions (1) and (3), and with the data of Warnatz for reaction (2).

A methane-air premixed flame with and equivalence ratio of 1.25 was simulated with a model including 91 pairs of elementary reactions occurring among 29 species. In this second part, the flame structures at the base of the flame and at inner and outer cone tips are discussed. Around the burner rim, the entrainment of air from the surroundings is seen to be the main reason for the activation of chemical reactions by promoting large production of O atoms and OH radicals. As a consequence, the rate of heat release there is very large, allowing the flame temperature to increase steeply and the flame to be held on the burner. At the inner cone tip, also, chemical reactions proceed with large rates, due to flame stretch and to preferential diffusion of H₂. H₂ is consumed there, so that the fuel burning at the inner cone tip is composed of a mixture of CH₄+H₂. CH₃ radicals remain above the inner cone tip and, around the tip of the outer cone, oxidation via C₁ route leads to formation of CO, which is oxidized into CO₂, as in any other point of the outer cone. H₂, however, is formed by reduction of water above the inner cone tip. This H₂ formation continues even within and above the outer cone tip, so that respect to H₂ the outer cone is found to have no tip.

The combustion mechanisms in premixed flames having a mixture of hydrogen and carbon monoxide as the fuel and the stoichiometric amount of air as the oxidizer were investigated by numerical simulation to elucidate the fuel-mixing effects on the burning velocity. Hydrogen and carbon monoxide have similar physical properties and their stoichiometric flames with air are known to propagate through the same type of mechanism, governed by active species diffusion. The flames of the mixed fuel hydrogen+carbon monoxide were found here to have their heat-release rate distributions changing with conformity in shape when the fuel composition is changed. The burning velocity was found to vary almost linearly with the hydrogen content in the fuel. Furthermore, the flux of chemical energy which is carried into low-temperature regions by hydrogen atoms diffusing from the flame front was also found to be roughly proportional to the burning velocity.

Fuel mixing effects on flame propagation were investigated with hydrogen and methane, whose flames, respectively, propagate through two different kinds of mechanisms. The calculated burning velocities did not show linearity with the hydrogen content in the fuel. The addition of only 5% of methane to hydrogen reduces the burning velocity by 20%, notoriously inhibiting the combustion of the mixture. This is caused by obstruction of the harmonious progression of two key chain-branching reactions, resulting in a decrease in hydrogen atom production at the flame front. However, the upstream flux, at the ignition point, of chemical energy due to diffusion of hydrogen atoms from the flame front and the integrated amount of heat released in the low-temperature region did show linearity with the burning velocity. Therefore, it was found that even for flames of mixed fuels whose components burn individually through different propagation mechanisms, the burning velocity can be expressed as a simple linear function of the upstream chemical energy flux or of the amount of heat released in the low-temperature region.

A method for reduction of carbon dioxide emission due to the use of hydrocarbons as fuels consisting in a pre-deposition of part of the carbon content in the fuel into soot was tested for industrial application. As a basic research, the influences of the amount of air added to the fuel and the temperature to which the mixture is heated up on the soot pre-deposition when methane is the fuel were investigated. Below 1500K, addition of 30% of air led to the largest soot pre-deposition; the addition of this relative large amount of air promotes soot formation because the active species needed for the first step of that process, the conversion of methane into methyl radicals, are produced through reactions activated by oxygen; further addition of air promotes the oxidation of carbon into carbon monoxide and carbon dioxide, lowering the soot deposition. At temperatures higher than 1500K, thermal decomposition of methane causes the reactions to proceed very fast, and the addition of air reduces the soot deposition. Concretely, conversion of 30% of the carbon content in the fuel into soot can be easily controled at temperatures below 1500K with addition of convenient amounts of air; and the conversion of 50% of the carbon into soot can be obtained at reaction temperatures above 1550K.

Premixed stoichiometric flames of acetylene, ethylene, and ethane with air were investigated using a chemical scheme composed of eighty-two pairs of elementary reactions to illustrate the dependence of the propagation mechanisms of C2 hydrocarbon flames on the heat release distribution. The general role of heat release distribution through flames was depicted by means of an analytical treatment of the governing equations with the thermal properties of the gases being constant and the temperature profile given by an appropriate function of the position in the flame. It was found that the amount of heat released by chemical reactions at low-temperature regions of a flame is of fundamental importance for its propagation and that the main trigger of exothermic reactions at those zones is hydrogen atoms, which diffuses from the flame front; in the acetylene flame reactions consuming hydrogen atoms at the low-temperature region were found to yield all the heat released at that zone. Heat release distribution extended down to low-temperature regions was found to be able to lead to large burning velocities even though the amount of heat released at each position was small.

In this work the combustion mechanism of silane-air flames is elucidated through a simulation employing a detailed chemical scheme. Two different pathways for the consumption of silane were found: SiH4 --> SiH3 --> SiH2O --> HSiO, which proceeds in low-temperature regions, and SiH4 --> SiH2 --> HSiO, occurring at high temperatures; this supports results previously reported in the literature. It was also found that some reactions occur over wide ranges of temperature and that the governing step for the whole silane combustion is the reaction of silane with hydroxyl radicals. A least square fitting to the burning velocities and adiabatic flame temperatures obtained for the four investigated mixtures, with equivalence ratios of 2.0, 1.43, 1.0, and 0.5, indicated that a mixture with equivalence ratio of about 1.2 would have the largest burning velocity and the highest flame temperature.

A detailed chemical reaction scheme and a full set of governing equations for fluid dynamics were used to elucidate the chemical and physical phenomena involved in a silane-air counterflow diffusion flame, where the fuel and air issue from the lower and upper nozzles, respectively. It was found that a stagnation surface, where the axial velocities fall down to zero, is kept in a position slightly shifted to the upper side, dividing the system into two zones: the upper air side and the lower fuel side; after leaving the nozzle silane begins to dissociate itself into SiH2 and H-2 when it reaches the region of rising temperature; oxygen penetrates into the fuel side by diffusion and reacts with H-2 forming OH radicals and H atoms. The produced SiH2 is further dehydrogenated to SiO via HSiO; comparing with premixed flames, the diffusion flames have large local equivalence ratios, so that the combustion reactions in the latter flames occur through a different mechanism.

A detailed model including a full scheme of combustion reactions and the governing equations of fluid mechanics was designed for two-dimensional hydrogen burning systems, and applied to a Burke-Schumann type hydrogen-air diffusion flame to elucidate its flame structure and combustion reaction mechanism. The same flame was also experimentally investigated and radial profiles of OH radical concentration and rotational temperature through the flame were determined by a conveniently improved line-of-sight absorption method. Simulation suggested that a well-developed diffusion flame occurs from heights about 5 mm from the burner mouth, in very good agreement with the experimental results. At each horizontal section of the well-developed diffusion region, the calculated rates of the chemical reactions showed considerable values within an annular zone about 5 mm thick, in which there is a point where H2 and O2 are simultaneously exhausted, and in whose vicinity the temperature becomes maximum. This result confirmed one of the Burke-Schumann's predictions, but radial displacements of about 1 mm between the peeks of the rates of different reactions and also between the maximum OH radical concentration and the maximum temperature were found in both experiments and calculation, showing that the reactions do not occur in an infinitely thin region, contradicting one of the Burke-Schumann's assumptions. At the lowest part of the flame, below the burner tip, the issuing air and the H2 diffusing downward meet and react like premixed gas mixtures
the whole flame was found to be held at the burner rim by large heat release rates at that region. The experimental results, in very good agreement with the simulation, showed that the maximum OH concentration through the flame occurs at a height around 2 mm, confirming the premixed-like intense combustion reactions taking place at the lower part of the flame. © 1991 Combustion Institute.