HO2 formation from the OH + benzene reaction in the presence of O2

In this study we investigated the secondary formation of HO(2) following the benzene + OH reaction in N(2) with variable O(2) content at atmospheric pressure and room temperature in the absence of NO. After pulsed formation of OH, HO(x) (= OH + HO(2)) and OH decay curves were measured by means of a laser-induced fluorescence technique (LIF). In synthetic air the total HO(2) yield was determined to be 0.69 ± 0.10 by comparison to results obtained with CO as a reference compound. HO(2) is expected to be a direct product of the reaction of the intermediately formed OH-benzene adduct with O(2). The HO(2) yield is slightly greater than the currently recommended yield of the proposed HO(2) co-product phenol (～53%). This hints towards other, minor HO(2) forming channels in the absence of NO, e.g. the formation of epoxide species that was proposed in the literature. For other test compounds upper limits of HO(2) yields of 0.10 (isoprene) and 0.05 (cyclohexane) were obtained, respectively. In further experiments at low O(2) concentrations (0.06-0.14% in N(2)) rate constants of (2.4 ± 1.1) × 10(-16) cm(3) s(-1) and (5.6 ± 1.1) × 10(-12) cm(3) s(-1) were estimated for the OH-benzene adduct reactions with O(2) and O(3), respectively. The rate constant of the unimolecular dissociation of the adduct back to benzene + OH was determined to be (3.9 ± 1.3) s(-1). The HO(2) yield at low O(2) was similar to that found in synthetic air, independent of O(2) and O(3) concentrations indicating comparable HO(2) yields for the adduct + O(2) and adduct + O(3) reactions.     

Effect of speech-intrinsic variations on human and automatic recognition of spoken phonemes

The aim of this study is to quantify the gap between the recognition performance of human listeners and an automatic speech recognition (ASR) system with special focus on intrinsic variations of speech, such as speaking rate and effort, altered pitch, and the presence of dialect and accent. Second, it is investigated if the most common ASR features contain all information required to recognize speech in noisy environments by using resynthesized ASR features in listening experiments. For the phoneme recognition task, the ASR system achieved the human performance level only when the signal-to-noise ratio (SNR) was increased by 15 dB, which is an estimate for the human-machine gap in terms of the SNR. The major part of this gap is attributed to the feature extraction stage, since human listeners achieve comparable recognition scores when the SNR difference between unaltered and resynthesized utterances is 10 dB. Intrinsic variabilities result in strong increases of error rates, both in human speech recognition (HSR) and ASR (with a relative increase of up to 120%). An analysis of phoneme duration and recognition rates indicates that human listeners are better able to identify temporal cues than the machine at low SNRs, which suggests incorporating information about the temporal dynamics of speech into ASR systems.     

Neutral pentacoordinate silicon fluorides derived from amidinate, guanidinate, and triazapentadienate ligands and base-induced disproportionation of Si2Cl6 to stable silylenes

Pentacoordinate silicon fluorides L(1)SiF(3) (2a), L(2)SiF(3) (2b), and (L(3)SiF(2))(2) (2c)(2) based on amidinate (L(1) = PhC(N(t)Bu)(2)), guanidinate (L(2) = 1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidinate), and triazapentadienate (L(3) = NC(NMe(2))NC(NMe(2))NAr; Ar = 2,6-(i)Pr(2)C(6)H(3)) ligands were prepared by fluorination of the corresponding chlorosilanes L(1)SiCl(3) (1a), L(2)SiCl(3) (1b), and L(3)SiCl(2) (1c) with Me(3)SnF at ambient temperature. Compounds 1b, 1c, 2a, 2b, and (2c)(2) were characterized by (1)H, (13)C, (19)F, and (29)Si NMR spectroscopic studies. Molecular structures of 1b, 1c, 2a, and (2c)(2) were determined by single crystal X-ray structural analysis. Invariom refinement involving non-spherical scattering factors of the Hansen-Coppens multipole model was performed for 1b. Compound L(3)SiF(2) (2c) is dimeric both in the solid state and in solution, whereas its chloro-analogue 1c is monomeric. The attempted synthesis of diamidinatotetrachlorodisilane by reaction of lithium amidinate with Si(2)Cl(6) led to the formation of the silane (1a) and the silylene L(1)SiCl (3). Reaction of Si(2)Cl(6) with N-heterocyclic carbenes (NHC) afforded NHC adducts of dichlorosilylene and SiCl(4). A one pot method for the preparation of base-stabilized silylenes from Si(2)Cl(6) is discussed.     

A new aspect of specific radiation damage: hydrogen abstraction from organic molecules

Radiation damage is one of the major impediments in obtaining high‐resolution structural information utilizing ionizing radiation. From electron microscopy it is known that electron irradiation of biological samples results in the formation of molecular hydrogen. In the present work radiation‐induced structural changes of the polypeptide cyclosporine A were observed at a temperature of 100 K. Bond length changes are thought to be due to radiation‐induced hydrogen abstraction which chemically modifies the molecules in an irreversible way. The resulting formation of molecular hydrogen might explain the observed increase of the crystal mosaicity, which has also been reported in many previous radiation damage studies.     

Validation of a newly developed FTIR in situ reactor: Real time study of photocatalytic degradation of nitric oxide

For many years, photocatalysis has been proposed as one of the promising techniques to abate environmental pollutants. To improve these reactions it is vital to know the reaction mechanisms of the photocatalytic degradation. This new reactor will make it possible to study the catalytic surface at the moment the reactions occur. By the means of UV LED illumination there is no need of an external UV lamp and thus lowers the cost. The validation of this newly developed reactor is done by investigating the photocatalytic reaction mechanism of nitric oxide (NO) and comparing these findings with those already discussed in literature. From these results, it became clear that the newly developed FTIR in situ reactor allows real time study of photocatalytic degradations.