Kinetics of autoignition: a simple intuitive interpretation and its relation to the Livengood-Wu integral.

It is well known that the gas-phase autoignition phenomenon often involves branched chain reactions as well as the acceleration of reactions by thermal feedback. Despite the huge combustion kinetic mechanisms of large hydrocarbons found in practical fuels, chain reactions in the early stages of alkane autoignition exhibit simple kinetics since the pseudo-first-order assumption and the linear approximation are valid. In this study, this simple picture of autoignition will be presented starting from the H2-O2 system and then extending to practical fuel-air mixtures. The present interpretation gives the theoretical rationale for the Livengood-Wu integral which is known as an empirical method to predict the timing of knock in spark-ignition engines.

Experimental and theoretical study on the thermal decomposition of C3H6 (propene).

The mechanism of the thermal unimolecular decomposition of C3H6 (propene) is studied both theoretically and experimentally. The potential energy surfaces for possible reaction pathways are investigated by CBS-QB3 level of quantum chemical calculations, and RRKM/master-equation calculation is performed for the main channels. The time evolutions of H atoms are observed experimentally by using a highly sensitive detection technique (ARAS, detection limit ≈ 10(11) atoms cm(-3)) behind reflected shock waves (0.5-1.0 ppm C3H6 diluted in Ar, 1450-1710 K at 2.0 atm). The objective of this study is to examine the main product channels by combining the experimental and theoretical investigations on the yield and the rates of H atom production. Present quantum chemical calculations identify reactions (1a-1d) as the candidates of product channels: C3H6 → aC3H5 (allyl radical) + H (1a), C3H6 → CH3 + C2H3 (vinyl radical) (1b), C3H6 → CH4 + :CCH2 (singlet vinyldene radical) (1c), and C3H6 → C3H4 (allene) + H2 (1d). The RRKM calculations reveal the branching fractions for (1a), (1b), and (1c) to be approximately 0.8, 0.2, and 0.01, respectively. Reaction (1d) and other product channels are negligible (< 0.1 %), and the pressure dependence of the branching fraction is small under the present experimental conditions. The experimental yield of H atoms (1.7-2.0) is consistent with the theoretical branching fractions considering the H-atom production from the rapid subsequent thermal decomposition of a C3H5 and C2H3. From the observed time profiles of H atoms, the rate of overall thermal decomposition of C3H6 can be evaluated as Ln(k1/s(-1)) = (38.05 ± 1.18) - (48.91 ± 1.85) × 10(3) K/T, which is in excellent agreement with the theoretical prediction.

Efficacy of laparoscopic resection in elderly patients with colorectal cancer.

PURPOSE: The perioperative outcomes of laparoscopic colorectal surgery in elderly patients were compared with those of open surgery in elderly patients and those of laparoscopic surgery in nonelderly patients to evaluate the feasibility and efficacy of laparoscopic surgery in elderly patients with colorectal cancer. METHODS: The data of the patients who underwent surgical resection for colorectal cancer between January 2007 and September 2012 were retrospectively collected. The clinical backgrounds and outcomes of elderly patients (≥ 70 years of age) who underwent laparoscopic surgery (EL group) were compared with those of elderly patients who underwent open surgery (EO group) and those of nonelderly patients (< 70 years of age) who underwent laparoscopic surgery (NL group). RESULTS: Compared with the EO group, the EL group showed significantly less blood loss (15 versus 100 ml), fewer postoperative complications (10.7 versus 36.7 %), earlier resumption of an oral diet (4 versus 5 days) and shorter postoperative hospital stays (16 versus 28 days). A case-matched analysis showed similar results. All perioperative outcomes were equivalent between the EL and NL groups. CONCLUSIONS: Laparoscopic colorectal surgery in elderly patients with cancer was not only superior to open surgery in elderly patients, but also equivalent to laparoscopic surgery in nonelderly patients in terms of the postoperative outcomes.

Chain reaction mechanism in hydrogen/fluorine combustion.

Vibrationally excited species have been considered to play significant roles in H2/F2 reaction systems. In the present study, in order to obtain further understanding of the chain reaction mechanism in the combustion of mixtures containing H2 and F2, burning velocities for H2/F2/O2/N2 flames were measured and compared to that obtained from kinetic simulations using a detailed kinetic model, which involves the vibrationally excited species, HF(ν) and H2(ν), and the chain-branching reactions, HF(ν > 2) + F2 = HF + F + F (R1) and H2(ν = 1) + F2 = HF + H + F (R2). The results indicated that reaction R1 is not responsible for chain branching, whereas reaction R2 plays a dominant role in the chain reaction mechanism. The kinetic model reproduced the experimental burning velocities with the presumed rate constant of k2 = 6.6 × 10(-10) exp(-59 kJ mol(-1)/RT) cm(3) s(-1) for R2. The suggested chain-branching reaction was also investigated by quantum chemical calculations at the MRCI-F12+CV+Q/cc-pCVQZ-F12 level of theory.

Reactions of o-benzyne with propargyl and benzyl radicals: potential sources of polycyclic aromatic hydrocarbons in combustion.

The kinetics and mechanisms of the reactions of o-benzyne with propargyl and benzyl radicals have been investigated computationally. The possible reaction pathways have been explored by quantum chemical calculations at the M06-2X/6-311+G(3df,2p)//B3LYP/6-311G(d,p) level and the mechanisms have been investigated by the Rice-Ramsperger-Kassel-Marcus theory/master-equation calculations. It was found that the o-benzyne associates with the propargyl and benzyl radicals without pronounced barriers and the activated adducts easily isomerize to five-membered ring species. Indenyl radical and fluorene + H were predicted to be dominantly produced by the reactions of o-benzyne with propargyl and benzyl radicals, respectively, with the rate constants close to the high-pressure limits at temperatures below 2000 K. The related reactions on the two potential energy surfaces, namely, the reaction between fulvenallenyl radical and acetylene and the decomposition reactions of indenyl and α-phenylbenzyl radicals were also investigated. The high reactivity of o-benzyne toward the resonance stabilized radicals suggested a potential role of o-benzyne as a precursor of polycyclic aromatic hydrocarbons in combustion.

Electronic spectra of the jet-cooled 1-methylvinylthio radical.

Electronic spectra of the B̃-X̃ transition of the 1-methylvinylthio radical were observed in a discharged jet of propylene sulfide by laser-induced fluorescence spectroscopy. Identification of the spectral carrier was made by comparing the observed spectra with results of molecular orbital calculations, in particular, for vibrational frequencies, rotational contour simulations, and the Franck-Condon simulations. Vibrational structures observed in the electronic spectra indicate that the 1-methylvinylthio radical can be regarded as a molecule with C(s) symmetry at the zero-point levels of both the excited and ground states.

Deuterium kinetic isotope effects on the gas-phase reactions of C2H with H2(D2) and CH4(CD4).

Kinetics of the ethynyl (C(2)H) radical reactions with H(2), D(2), CH(4) and CD(4) was studied over the temperature range of 295-396 K by a pulsed laser photolysis/chemiluminescence technique. The C(2)H radicals were generated by ArF excimer-laser photolysis of C(2)H(2) or CF(3)C(2)H and were monitored by the chemiluminescence of CH(A(2)Δ) produced by their reaction with O(2) or O((3)P). The measured absolute rate constants for H(2) and CH(4) agreed well with the available literature data. The primary kinetic isotope effects (KIEs) were determined to be k(H(2))/k(D(2)) = 2.48 ± 0.14 and k(CH(4))/k(CD(4)) = 2.45 ± 0.16 at room temperature. Both of the KIEs increased as the temperature was lowered. The KIEs were analyzed by using the variational transition state theory with semiclassical small-curvature tunneling corrections. With anharmonic corrections on the loose transitional vibrational modes of the transition states, the theoretical predictions satisfactorily reproduced the experimental KIEs for both C(2)H + H(2)(D(2)) and C(2)H + CH(4)(CD(4)) reactions.

Systematic computational study on the unimolecular reactions of alkylperoxy (RO2), hydroperoxyalkyl (QOOH), and hydroperoxyalkylperoxy (O2QOOH) radicals.

Unimolecular isomerization and decomposition reactions of alkylperoxy (RO(2)), hydroperoxyalkyl (QOOH), and hydroperoxyalkylperoxy (O(2)QOOH) radicals play important roles in the low-temperature oxidation of hydrocarbons. In this study, these reactions have been investigated by the CBS-QB3 quantum chemical method, and the variation of the rate parameters by the structural change of alkyl groups has been studied systematically for the rule-based construction of the low-temperature oxidation mechanisms of arbitrary noncyclic alkanes. The results can be well-interpreted in terms of the group additivity and the ring-strain effect of the cyclic transition states. To extract the important processes needed for the chemical kinetic modeling, the competing reaction channels were compared in detail by steady-state analysis with the high-pressure limiting rate constants. The importance of some reactions of O(2)QOOH radicals, which have not been considered in the previous modeling studies, such as the hydrogen exchange reactions between -OOH and -OO(•) groups and hydrogen shift reactions from non-OOH sites, is suggested.

Kinetics and mechanisms of the allyl + allyl and allyl + propargyl recombination reactions.

The kinetics and mechanisms of the self-reaction of allyl radicals and the cross-reaction between allyl and propargyl radicals were studied both experimentally and theoretically. The experiments were carried out over the temperature range 295-800 K and the pressure range 20-200 Torr (maintained by He or N(2)). The allyl and propargyl radicals were generated by the pulsed laser photolysis of respective precursors, 1,5-hexadiene and propargyl chloride, and were probed by using a cavity ring-down spectroscopy technique. The temperature-dependent absorption cross sections of the radicals were measured relative to that of the HCO radical. The rate constants have been determined to be k(C(3)H(5) + C(3)H(5)) = 1.40 × 10(-8)T(-0.933) exp(-225/T) cm(3) molecule(-1) s(-1) (Δ log(10)k = ± 0.088) and k(C(3)H(5) + C(3)H(3)) = 1.71 × 10(-7)T(-1.182) exp(-255/T) cm(3) molecule(-1) s(-1) (Δ log(10)k = ± 0.069) with 2σ uncertainty limits. The potential energy surfaces for both reactions were calculated with the CBS-QB3 and CASPT2 quantum chemical methods, and the product channels have been investigated by the steady-state master equation analyses based on the Rice-Ramsperger-Kassel-Marcus theory. The results indicated that the reaction between allyl and propargyl radicals produces five-membered ring compounds in combustion conditions, while the formations of the cyclic species are unlikely in the self-reaction of allyl radicals. The temperature- and pressure-dependent rate constant expressions for the important reaction pathways are presented for kinetic modeling.

Rate constants and kinetic isotope effects on the reaction of C2(X(1)Sigma(g)+) with CH4 and CD4.

Rate constants and kinetic isotope effect (KIE) for the reaction of singlet dicarbon, C(2)(X(1)Sigma(g)(+)), with CH(4) and CD(4) have been measured over the temperature range 294-376 K by using the pulsed laser photolysis/laser-induced fluorescence technique. C(2)(X(1)Sigma(g)(+)) were generated by multiphoton laser decomposition of C(2)Cl(4) at 248 nm and its decay trace was monitored on the (0,0) band of the Mulliken system at 231.2 nm. Measured rate constants showed slightly positive temperature dependence, whereas the KIE [= k(CH(4))/k(CD(4))] was almost independent of temperature and the value of which was 2.1 +/- 0.2 as a simple average of the values of KIE at different temperatures. Quantum chemical calculation with CASPT2 method indicated that the reaction proceeds via a direct hydrogen abstraction mechanism to form C(2)H and CH(3) radicals. Variational transition-state theory calculations were performed employing a dual-level method. Anharmonic effects along transitional modes were included in the calculation, and a comparison of the rate constants with and without anharmonic corrections demonstrated the importance of anharmonicity. The calculated rate constants and KIE showed good agreement with the experiments except for the temperature dependence of the KIE. A possible cause of the discrepancy was discussed in terms of the long-range interaction between the reactants.

Mechanism and kinetic isotope effect of the reaction of C2(X1Sigma(g)+) radicals with H2 and D2.

The rate constants for the reactions of C2(X1Sigma(g)+) with H2 and D2 have been investigated experimentally and theoretically to assess the statistical theory of the reaction and to reveal the mechanism of the reaction. The ground-state C2 radicals were generated by multiphoton laser-photolysis of C2Cl4 at 248 nm and were probed by a laser-induced fluorescence method using the Mulliken system (D1Sigma(u)+-X1Sigma(g)+). Rate constants have been measured to be k[C2(X)+H2] = 5.6 x 10(-11) exp[-9.1 (kJ mol(-1))/RT] and k[C2(X)+D2] = 3.2 x 10(-11) exp[-9.9 (kJ mol(-1))/RT] cm3 molecule(-1) s(-1) in the temperature range 293-395 K and at total pressure around 10 Torr (He buffer). Quantum chemical calculations at the MRCI level revealed that the reaction predominantly proceeds via a collinear direct-abstraction transition state. The measured rate constants as well as the kinetic isotope effect were well reproduced by the transition-state theory based on the MRCISD+Q/aug-cc-pV5Z calculations, provided that the anharmonic bending vibrations of the transition states were properly treated. The effect of the Davidson correction was found to be significant for the potential energy surface around the early transition state.

Gas-phase spectroscopy of the 2 3Sigma(-)-X 3Sigma- electronic transition of CCS.

Gas-phase laser excitation spectra of the jet-cooled CCS radical were observed for the 2 (3)Sigma(-)-X (3)Sigma(-) electronic transition in a discharge of a gas mixture containing acetylene and H(2)S in Ar. The observed excitation spectra show complicated rotational structures, consisting of a much larger number of rotational lines than those expected for this size of linear molecule. The excited vibronic levels emit fluorescence, the lifetime of which is much longer than that estimated theoretically, indicating that the upper levels are strongly mixed with many "dark" background levels. Dispersed fluorescence spectra from single vibrational levels of the 2 (3)Sigma(-) state show long progressions of the C-S stretching mode, enabling observations of many vibrational levels in the ground electronic state.

Role of phenyl radicals in the growth of polycyclic aromatic hydrocarbons.

To investigate the role of phenyl radical in the growth of PAHs (polycyclic aromatic hydrocarbons), pyrolysis of toluene with and without benzene has been studied by using a heatable tubular reactor couple with an in-situ sampling vacuum ultraviolet (VUV) single photon ionization (SPI) time-of-flight mass spectrometer (TOFMS) at temperatures 1155-1467 K and a pressure of 10.02 Torr with 0.56 s residence time. When benzene was added, a significant increase of phenyl addition products (biphenyl, terphenyl, and triphenylene) was observed and the mass spectra showed a clear regular sequence with an interval of approximately 74 mass number, corresponding to the phenyl addition (+C6H5) followed by H-elimination (-H) and cyclization (-H2). The analysis showed that the PAC (phenyl addition/cylization) mechanism is efficient for the growth of PAHs without a triple fusing site, for which the HACA (hydrogen abstraction/C2H2 addition) step is inefficient, and produces PAHs with five-membered rings. The PAC process was also suggested to be efficient in the subsequent growth of PAHs with five-membered rings. The role of the PAC mechanism in combustion conditions is discussed in relation to the importance of disordered five-membered ring structure in fullerene or soot core.

[Survey of atopic dermatitis and skin barrier functions in Japanese and Chinese school students].

BACKGROUND: The comparative studies of the prevalence of atopic dermatitis and skin barrier functions in Japanese and Chinese were performed. METHODS: Clinical investigations were performed in 68 elementary school students in Lhasa, Tibet Autonomous Region and 67 students in Yixing, Jiangsu Province in China, and 99 students in Nishinomiya, Hyogo in Japan. Transepidermal water loss (TEWL) and capacitance were measured. Questionary survey about bathing frequency was also performed for students in Lhasa, Yixing and Osaka. RESULT: The prevalence rate of atopic dermatitis was 0% in Lhasa, 2.63% in Yixing, 4.26% in Nishinomiya. TEWL of students in Nishinomiya was higher than that in Yixing and Lhasa. Capacitance of students in Lhasa was lower than that in Nishinomiya and Yixing. The frequency of taking a bath in Lhasa was about 2.2 times per month and fewer than that in Nishinomiya and Yixing. CONCLUSION: There was tendency that the prevalence of atopic dermatitis increased according to increase of TEWL. It was thought that more investigations are necessary whether the development of habitat and environment influence the prevalence of atopic dermatitis and skin barrier function.

Effective comparison of two auto-CPAP devices for treatment of obstructive sleep apnea based on polysomnographic evaluation.

BACKGROUND: Automatic continuous positive airway pressure (auto-CPAP) machines differ mainly in algorithms used for respiratory event detection and pressure control. The auto-CPAP machines operated by novel algorithms are expected to have better performance than the earlier ones in the treatment of obstructive sleep apnea syndrome (OSAS). OBJECTIVES: The purpose of this study was to determine the therapeutic characteristics between two different auto-CPAP devices, i.e., the third-generation flow-based (f-APAP) and the second-generation vibration-based (v-APAP) machines, during the first night treatment of OSAS. METHODS: We retrospectively reviewed the polysomnography (PSG) recordings of 43 OSAS patients who were initially performed an overnight diagnostic PSG to confirm the disease and afterwards received the first night auto-CPAP treatment with using either the f-APAP (n=22) or v-APAP (n=21) device under another PSG evaluation. RESULTS: There were 13.6% and 61.9% patients who remained a residual apnea/hypopnea index more than 5 during the f-APAP and v-APAP application, respectively (P<0.005). The f-APAP was more effective than the v-APAP in reducing apnea/hypopnea index (P=0.003), hypopnea index (P=0.023) and apnea index (P=0.007), improving the lowest oxygen saturation index (P=0.007) and shortening stage 1 sleep (P=0.016). However, the f-APAP was less sufficient than the v-APAP in reducing arousal/awakening index (P=0.02). CONCLUSION: These findings suggest that the f-APAP works better than the v-APAP in abolishing breathing abnormities in the treatment of OSAS; however, the f-APAP device might still have some potential limitations in the clinical application.

A preliminary study on application of portable monitoring for diagnosis of obstructive sleep apnea.

Portable monitoring (PM) for diagnosis of obstructive sleep apnea has developed recently. Many studies were performed in the laboratory setting, with simultaneous polysomnographic recordings or required technical assistance in the home setting. And the data were automatically analyzed. In this study, we attempted to evaluate whether PM could be useful in fully unattended home setting, and whether the auto analysis of the data is reliable. Home setting examination by Stardust II, a novel PM device, was performed unattendedly on consecutive 62 patients who complained of snoring. The questionnaire survey on the difficulty of fitting and operation, and the discomfort was conducted by visual analog scale. Automatically and manually analyzed results were compared. The examination was successfully performed by all subjects. The difficulty of fitting and operation, and the discomfort were 2.9+/-1.9, 1.8+/-1.2 and 3.6+/-2.1, respectively. Auto analysis differed significantly from manual analysis not only in apnea/hypopnea index (AHI), but also in the construction of sleep disordered respiratory events. Although AHI in automatic and manual analysis had a good correlation (r=0.949; P<0.001), their agreement was poor, especially in mild and moderate cases. However, setting AHI=50 as a cut-off point in auto analysis, sensitivity and specificity could reach 100% and 92.5%, respectively. Accordingly, PM is useful to identify obstructive sleep apnea in an unattended home setting condition. Considering the significant difference between automatic and manual analysis, we suggest that the data analysis should be performed manually.

Role of methyl radicals in the growth of PAHs.

The role of methyl radicals in the networking of sp(2) carbons has been explored through kinetic analysis of mass spectra of the gas-phase products of the pyrolysis of toluene and toluene/acetone mixtures. Pyrolytic reactions were performed in a flow tube reactor at temperatures of 1140-1320 K and a constant total pressure of 10.38 Torr with a residence time of 0.585 s. On addition of acetone, methyl substituted products and their derivatives were enhanced. Mass peaks were observed in several sequences at an interval of 14 mass units; these ions correspond to methyl substituted products formed as a result of hydrogen abstraction (-H) followed by methyl radical addition (+CH(3)). Each major peak was usually preceded by a peak at two mass units lower, which was likely produced through dehydrogenation/dehydrocyclization (-H(2)) of methyl substituted products. Detected species include a large number of alkyl, cyclotetrafused (CT), cyclopentafused (CP) mono-, di-, and polycyclic aromatic hydrocarbons (PAHs) along with primary PAHs. The analysis showed that MAC (methyl addition/cyclization) has a unique capacity to induce the sequential growth of hexagonal networks of sp(2) carbons from all fusing sites of a PAH. Moreover, MAC was found capable of answering an important question in PAH growth, which is expansion of the CT --> CP --> hexagonal network for which other reported mechanisms are inefficient.

A geographical information system using the Google Map API for guidance to referral hospitals.

Our hospital acts as a regional core hospital through inter-hospital collaboration. Geographical information is necessary to guide patients to the other hospitals. Although paper maps, which contain directions, nearest public transportation, etc., are usually provided to guide patients to the hospitals, the geographical information tends to change daily. However, updating the geographical information on the maps is costly. We constructed an electronic geographical information system using the Google Map API ( http://code.google.com/apis/maps/ ) with open source software to improve our ability to collaborate with other clinics.

Surgical treatment of labyrinthine fistula caused by cholesteatoma with semicircular canal occlusion.

CONCLUSION: Semicircular canal occlusion after completely removing cholesteatoma matrix is a safe and effective approach for treatment of labyrinthine fistula. OBJECTIVE: To investigate the safety and efficacy of semicircular canal occlusion for surgical treatment of labyrinthine fistula caused by cholesteatoma. PATIENTS AND METHODS: Twenty-two patients with labyrinthine fistula who were treated surgically were enrolled in the study. All patients were treated by completely removing the cholesteatoma matrix followed by semicircular canal occlusion. RESULTS: With a follow-up of at least 6 months, there was no recurrent cholesteatoma in any of the patients. Vertigo disappeared in all the patients. Most patients presented no hearing detriment and four of them demonstrated hearing improvement. No patient presented with surgery-related deafness postoperatively.

Product branching fractions for the reaction of O((3)P) with ethene.

The product branching fractions for the reaction of atomic oxygen with ethene, O((3)P) + C(2)H(4)--> CH(3) + HCO (1a), --> H + CH(2)CHO (1b), --> H(2) + CH(2)CO (1c), have been investigated at room temperature (295 +/- 4 K) and pressures from 1 to 4 Torr (with N(2) or He buffer) by a laser photolysis-photoionization mass spectrometry method. From the yield of CH(3) radical, phi(CH(3)), the branching fraction for (1a) was determined to be 0.53 +/- 0.04 and no apparent pressure dependence was found from 1.5 to 4.0 Torr (N(2) buffer). The ratio of the HCO yield to that of CH(3), phi(HCO)/phi(CH(3)), was measured to be less than unity and increased as pressure increased (approximately 0.7 at 1 Torr and approximately 0.9 at 4 Torr [He]) suggesting prompt dissociation of the hot HCO radical (to H + CO) formed by channel (1a) at low pressures. An interpretation which reduces the large discrepancy among branching fractions reported for low pressure region is presented. The existence of the molecular H(2)-elimination channel (1c) was confirmed. The branching fraction for channel (1c) was determined to be 0.019 +/- 0.001 by the yield of CH(2)CO and was independent of pressure from 1.0 to 4.0 Torr (He buffer). As a side result, the yield of CH(3) radical from O((1)D) + C(2)H(4) reaction was also determined.