Evidence for organosulfates in secondary organic aerosol

Recent work has shown that particle-phase reactions contribute to the formation of secondary organic aerosol (SOA), with enhancements of SOA yields in the presence of acidic seed aerosol. In this study, the chemical composition of SOA from the photooxidations of alpha-pinene and isoprene, in the presence or absence of sulfate seed aerosol, is investigated through a series of controlled chamber experiments in two separate laboratories. By using electrospray ionization-mass spectrometry, sulfate esters in SOA produced in laboratory photooxidation experiments are identified for the first time. Sulfate esters are found to account for a larger fraction of the SOA mass when the acidity of seed aerosol is increased, a result consistent with aerosol acidity increasing SOA formation. Many of the isoprene and alpha-pinene sulfate esters identified in these chamber experiments are also found in ambient aerosol collected at several locations in the southeastern U.S. It is likely that this pathway is important for other biogenic terpenes, and may be important in the formation of humic-like substances (HULIS) in ambient aerosol.     

Ozone-initiated chemistry in an occupied simulated aircraft cabin

We have used multiple analytical methods to characterize the gas-phase products formed when ozone was added to cabin air during simulated 4-hour flights that were conducted in a reconstructed section of a B-767 aircraft containing human occupants. Two separate groups of 16 females were each exposed to four conditions: low air exchange (4.4 (h-1)), <2 ppb ozone; low air exchange, 61-64 ppb ozone; high air exchange (8.8 h(-1)), <2 ppb ozone; and high air exchange, 73-77 ppb ozone. The addition of ozone to the cabin air increased the levels of identified byproducts from approximately 70 to 130 ppb at the lower air exchange rate and from approximately 30 to 70 ppb at the higher air exchange rate. Most of the increase was attributable to acetone, nonanal, decanal, 4-oxopentanal (4-OPA), 6-methyl-5-hepten-2-one (6-MHO), formic acid, and acetic acid, with 0.25-0.30 mol of quantified product volatilized per mol of ozone consumed. Several of these compounds reached levels above their reported odor thresholds. Most byproducts were derived from surface reactions with occupants and their clothing, consistent with the inference that occupants were responsible for the removal of >55% of the ozone in the cabin. The observations made in this study have implications for other indoor settings. Whenever human beings and ozone are simultaneously present, one anticipates production of acetone, nonanal, decanal, 6-MHO, geranyl acetone, and 4-OPA.     

Direct Reductive Amination versus Hydrogenation of Intermediates –A Comparison

The direct reductive amination of acetophenone with benzylamine or piperidine was studied in comparison with the hydrogenation of possible intermediates like a corresponding imine or enamine. No common features in terms of productivity and stereocontrol (in the case of chiral catalysts) have been found for both processes. Hence evaluation of efficient, selective and enantioselective catalysts for direct reductive amination appears to be a separate task.     

Cyclopropyl Building Blocks for Organic Synthesis,Part 100. Advanced Syntheses of Cyclopropylideneacetates –Versatile Multifunctional Building Blocks for Organic Synthesis

A well reproducible and inexpensive preparation of the cyclopropylideneacetates 2 – 4 has been developed. The key intermediate 2‐(1′‐mesyloxycyclopropyl)acetic acid ( 8 ), produced either from methyl phenylacetate ( 1 ) or 3,3‐dimethoxypropionate ( 5 ‐Me) and 3,3‐diethoxypropionate ( 5 ‐Et) in a sequence of Kulinkovich reductive cyclopropanation, mesylation and oxidative cleavage or cleavage and oxidation, respectively, was either converted to the benzyl ester 11b , or chlorinated (brominated) via the in situ formed acid chloride. The α‐chloro‐ 12a and α‐bromo ester 12b were dehydromesylated by treatment with triethylamine to furnish methyl 2‐chloro‐2‐cyclopropylideneacetate ( 3 ‐Me) and the 2‐bromo analogue 4 ‐Me with an overall yield of 68% (65%, 68%) and 52% (49%, 51%) respectively, starting from 1 ( 5 ‐Me, 5 ‐Et). The parent benzyl cyclopropylideneacetate 2 ‐Bn was obtained by dehydromesylation of 11b with potassium t‐butoxide in t‐butyl methyl ether with an overall yield of 60% (57%, 9%) from 1 ( 5 ‐Me, 5 ‐Et).     

Reconstitution of Monocyte Subsets and PD-L1 Expression but Not T Cell PD-1 Expression in Obstructive Sleep Apnea Patients upon PAP Therapy

Obstructive sleep apnea (OSA) is characterized by nocturnal breathing intermissions resulting in oxidative stress and eventually, a low-grade systemic inflammation. The study aimed to investigate the impact of positive airway pressure (PAP) therapy on the inflammatory milieu as measured by monocyte and T cell phenotypic alterations. Participants were assessed for their OSA severity before PAP therapy and about six months later, including patient-reported outcome and therapy usage by telemetry readout. The distributions of the CD14/CD16-characterized monocyte subsets as well as the CD4/CD8-characterized effector T cell subsets with regard to their PD-1 and PD-L1 expression were analyzed by flow cytometry from blood samples. Data of 25 patients revealed a significant reconstitution of the monocyte subset distribution and a decrease in PD-L1 expression on pan-monocytes and CD8⁺ T cells without an association to initial AHI and overweight. The PD-1 expression was still increased on T cell subsets, especially on CD4⁺ TH17/22 cells. We conclude that PAP therapy might have a rapid effect on the monocyte phenotype and overall PD-L1 expression levels. However, T cell immune alterations especially on TH17/22 cells persist longer, indicating an ongoing disturbance of the adaptive immune system.     

A Scrutiny on the Reductive Amination of Carbonyl Compounds Catalyzed by Homogeneous Rh(I) Diphosphane Complexes

The reductive amination of a series of aldehydes with secondary amines and H₂ in the presence of a homogeneous Rh-diphosphane catalyst was studied in order to establish a general mechanism of this reaction and to identify conditions for the improvement of the amine/alcohol ratio in the product. Several possible intermediates as constituents of changing equilibria like half-aminals, N,O-acetals and aminals were observed in the reaction mixture by means of ¹H NMR spectroscopy. In individual trials, these compounds could be successfully hydrogenated under the conditions applied for reductive amination (50 bar H₂ pressure, MeOH). Some evidence is accumulated that half-aminals and N,O-acetals might be key intermediates of the reductive amination. Moreover, it was found that the formation of the undesired product alcohol is likely based on the reduction of the starting carbonyl compound. However, due to numerous equilibria consisting of several intermediates, general conclusions are hard to be drawn. Proof will be given that, in several cases, the efficiency of the reductive amination of aliphatic aldehydes can be significantly improved by prehydrogenation of the cationic [Rh(dppb)(COD)]⁺ complex.     

Progress in Low-temperature Surface Passivation of Silicon Solar Cells using Remote-plasma Silicon Nitride

Using a remote-plasma technique as opposed to the conventional direct-plasma technique, significant progress has been obtained at ISFH in the area of low-temperature surface passivation of p-type crystalline silicon solar cells by means of silicon nitride (SiN) films fabricated at 350–400°C in a plasma-enhanced chemical vapour deposition system. If applied to the rear surface of the low-resistivity p-type substrates, the remote-plasma SiN films provide outstanding surface recombination velocities (SRVs) as low as 4 cm s⁻¹, which is by a clear margin the lowest value ever obtained on a low-resistivity p-Si wafer passivated by a solid film, including highest quality thermal oxides. Compared to direct-plasma SiN films or thermally grown oxides, the remote-plasma films not only provide significantly better SRVs on low-resistivity p-silicon wafers, but also an enormously improved stability against ultraviolet (UV) light. The potential of these remote-plasma silicon nitride films for silicon solar cell applications is further increased by the fact that they provide a surface passivation on phosphorus-diffused emitters which is comparable to high-quality thermal oxides. Furthermore, if combined with a thermal oxide and a caesium treatment, the films induce a UV-stable inversion-layer emitter of outstanding electronic quality. Due to the low deposition temperature and the high refraction index, these remote-plasma SiN films act as highly efficient surface-passivating antireflection coatings. Application of these films to cost-effective silicon solar cell designs presently under development at ISFH turned out to be most successful, as demonstrated by diffused p-n junction cells with efficiencies above 19%, by bifacial p-n junction cells with front and rear efficiencies above 18%, by mask-free evaporated p-n junction cells with efficiencies above 18% and by MIS inversion-layer cells with a new record efficiency of above 17%. All cells are found to be stable during a UV test corresponding to more than 4 years of glass-encapsulated outdoor operation. © 1997 John Wiley & Sons, Ltd.     

Hot-Metal Desulfurization Using Calcium Carbide and Calcium Oxide in Transfer Ladle: A Computational Fluid Dynamics Investigation

In this study, a 3D transient computational fluid dynamics (CFDs) model that simulates hot-metal desulfurization (HMD) using calcium carbide and calcium oxide in an experimental-scale ladle with a 70 kg capacity is presented. The model takes into account the efficiency of reagent-particles-penetrating carrier gas bubbles and is validated through experimental work, with an average difference of 7.06%. In this research, the effects of varying reagent particle sizes, hot-metal temperatures, gas flow rates, and ladle design on desulfurization rates are discussed. The results indicate that when particle diameter decreases from 30 to 20.9 and 11.8 μm, desulfurization rates rise from 50.92% to 66.02% and 89.99%, respectively. Regarding hot-metal temperature, a 100° range results in a final desulfurization rate difference of less than 3%. This study also reveals that increasing the carrier gas flow rate from 13 to 15 SLPM reduces the removal rate by 6.10%. As particle gas flow rate increases from 200 to 300 g min⁻¹, the removal rate increases by 9.02%. In the lance arrangement analysis, the duo lance system demonstrates nearly identical desulfurization performance to the single-center lance system, which outperforms the off-center lance system.     

利用全新的陶瓷方法简化LED散热设计

LED的散热问题将是限制它未来能否在市场上取得更大成功的主要因素。目前业界的很多研究都集中在散热器上,但对LED和散热表面之间的隔层研究较少。