Atmospheric oxidation is a key phenomenon that connects atmospheric chemistry with globally challenging environmental issues, such as climate change, stratospheric ozone loss, acidification of soils ...and water, and health effects of air quality. Ozone, the hydroxyl radical and the nitrate radical are generally considered to be the dominant oxidants that initiate the removal of trace gases, including pollutants, from the atmosphere. Here we present atmospheric observations from a boreal forest region in Finland, supported by laboratory experiments and theoretical considerations, that allow us to identify another compound, probably a stabilized Criegee intermediate (a carbonyl oxide with two free-radical sites) or its derivative, which has a significant capacity to oxidize sulphur dioxide and potentially other trace gases. This compound probably enhances the reactivity of the atmosphere, particularly with regard to the production of sulphuric acid, and consequently atmospheric aerosol formation. Our findings suggest that this new atmospherically relevant oxidation route is important relative to oxidation by the hydroxyl radical, at least at moderate concentrations of that radical. We also find that the oxidation chemistry of this compound seems to be tightly linked to the presence of alkenes of biogenic origin.
The reaction of OH radicals with dimethyl sulphide (CH₃SCH₃, DMS) has been studied in the atmospheric pressure flow tube IfT-LFT at 293±0.5K in the absence of NOₓ, NOₓ≤10¹⁰molecule cm⁻³. OH radicals ...were generated either via the photolysis of H₂O₂ under dry conditions or using the photolysis of O₃ at a relative humidity of 50%. PTR-MS and FT-IR spectroscopy served as analytical techniques for product analysis. Observed products were SO₂, HCHO, methyl thioformate (MTF), dimethyl sulfoxide (DMSO) and likely dimethyl sulfone (DMSO₂). The formation of SO₂, HCHO and MTF was clearly inhibited under conditions of a favoured reaction of CH₃SCH₂O₂ radicals with HO₂. Experiments in the presence of up to 2×10¹²moleculecm⁻³ of O₃ showed a small increase of the formation yields of SO₂ and HCHO with increasing O₃ levels. Modelling runs have been performed using the DMS module from the Master Chemical Mechanism, MCMv3.2, with a few modifications. Generally, the simulation slightly under-predicted the measured yields of HCHO. The SO₂ yields observed were roughly in agreement with the modelling results. A qualitative description of the experimentally detected MTF production was achieved by neglecting the MTF formation path via CH₃SCH₂O₂+HO₂ as given originally by MCM. The simulation results described well the amount of consumed O₃ by DMS intermediates as well as the impact of O₃ on products yields.
Adolescents may be influenced both by their friends' behaviors and by the features of their friendships. To examine both types of influence, seventh and eighth graders (N = 297) were asked in the ...fall of a school year to report their involvement and disruption at school. The students also described the positive and negative features of their best friendships. Teachers reported on the students' involvement, disruption, and grades. These assessments were repeated in the following spring. Students whose friends in the fall described themselves as more disruptive increased in self-reported disruption during the year. Girls' self-reported disruption was more influenced by that of their very best friend than was boys'. Students whose very best friendships had more positive features increased in their self-reported involvement during the year. Students whose friendships had more negative features increased in their self-reported disruption, but only if their friendships also had many positive features. The theoretical and practical implications of these findings, and the adequacy of different methods for estimating friends' influence, were discussed.
ABSTRACT
The gas‐phase reaction of monomethylhydrazine (CH3NHNH2; MMH) with ozone was investigated in a flow tube at atmospheric pressure and a temperature of 295 ± 2 K using N2/O2 mixtures (3–30 ...vol% O2) as the carrier gas. Proton transfer reaction–mass spectrometry (PTR‐MS) and long‐path FT‐IR spectroscopy served as the main analytical techniques. The kinetics of the title reaction was investigated with a relative rate technique yielding kMMH+O3 = (4.3 ± 1.0) × 10−15 cm3 molecule−1 s−1. Methyldiazene (CH3NNH; MeDia) has been identified as the main product in this reaction system as a result of PTR‐MS analysis. The reactivity of MeDia toward ozone was estimated relative to the reaction of MMH with ozone resulting in kMeDia+O3 = (2.7 ± 1.6) × 10−15 cm3 molecule−1 s−1. OH radicals were followed indirectly by phenol formation from the reaction of OH radicals with benzene. Increasing OH radical yields with increasing MMH conversion have been observed pointing to the importance of secondary processes for OH radical generation. Generally, the detected OH radical yields were definitely smaller than thought so far. The results of this study do not support the mechanism of OH radical formation from the reaction of MMH with ozone as proposed in the literature.
Ceramics consisting of Al2O3 with a surface layer of Al2O3-10vol% SiC have been fabricated by hot pressing. The residual compressive stress at the composite surface due to the difference in thermal ...expansion between the two layers has been measured experimentally by Cr3+ fluorescence microspectroscopy. The wear resistance in the severe wear regime of the two-layered samples was higher than those of a reference single-layer Al2O3-10vol% SiC sample. The improvement in the wear resistance was due to a decrease in the amount of surface pullout which was attributed to the presence of the biaxial residual compressive stress in the surface layer of the specimens.
•Two-layered samples of Al2O3 and Al2O3-10% SiC were made by hot pressing.•A surface compressive stress was measured in these samples by piezospectroscopy.•The wear resistance is improved compared to monolithic Al2O3 and Al2O3-10% SiC.•Improvements are attributed to differences in the coefficients of thermal expansion of the materials in each of the layers.
Coracoacromial ligament release to widen the subacromial space, resection of the anterior undersurface of the acromion and, if needed, caudal exophytes at the acromioclavicular joint.
All types of ...outlet impingement after 3 months of conservative treatment.
Impingement syndrome with instability/muscular imbalance, massive rotator cuff tear, unstable os acromionale, posterior-superior impingement, joint infection, freezing phase of a secondary frozen shoulder.
Lateral decubitus position with traction device for the arm. Diagnostic arthroscopy of the glenohumeral joint via standard portals. With arthroscope moved to the subacromial space, bursectomy, electrosurgical release of coracoacromial ligament, resection of acromial hook through standard posterior portal.
Physiotherapy or self-exercises on postoperative day 1, pain-adapted analgesia to avoid shoulder stiffness.
Several studies present positive long-term results compared to conservative treatment (and open acromioplasty) for partial rotator cuff tears and for elderly patients. With a 20-year follow-up, successful results have been achieved for all patients with isolated impingement syndrome.
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