Observation of a Tricyclic[4.1.0.0 2,4]heptane During a Michael Addition-Ring Closure Reaction and a Computational Study on Its Mechanism of Formation

We describe the formation of a bis-cyclopropane product, a tricyclic[4.1.0.02,4]heptane, that is formed during a Johnson-Corey-Chaykovsky reaction on a cyclopentenone. Two (of four possible) bicyclic products are selectively formed by addition of a COOEt-stabilized sulfur ylide onto the Michael acceptor. The tricyclic product is formed subsequently via a retro Michael elimination of a hindered ether followed by addition of a further cyclopropyl moiety, affecting only one of the two bicyclic products initially formed. The experimental reaction outcome was rationalized using density functional theory (DFT), investigating the different Michael-addition approaches of the sulfur ylide, the transition state (TS) energies for the formation of possible zwitterionic intermediates and subsequent reactions that give rise to cyclopropanation. Selective formation of only two of the four possible products occurs due to the epimerization of unreactive intermediates from the other two pathways, as revealed by energy barrier calculations. The formation of the tricyclic product was rationalized by evaluation of energy barriers for proton abstraction required to form the intermediate undergoing the second cyclopropanation. The selectivity-guiding factors discussed for the single and double cyclopropanation of this functionalized Michael-acceptor will be useful guidelines for the synthesis of future singly and doubly cyclopropanated compounds

Abundance analysis of a nitrogen-rich extreme-helium hot subdwarf from the SALT survey

We have performed a detailed spectral analysis of the helium-rich hot subdwarf EC 20187-4939 using data obtained in the SALT survey of helium-rich hot subdwarfs. We have measured its effective temperature, surface gravity and chemical abundances from the spectrum. Its radius has also been determined by fitting the spectral energy distribution using photometric data, from which a mass of 0.44 Msun has been inferred using the measurement of surface gravity. This star is particularly abundant in helium and nitrogen, whilst being both carbon and oxygen-weak. The surface abundances and mass have been found to be consistent with a helium white dwarf merger product. The abundance effects of alpha captures on nitrogen during the merger process and possible connections between EC 20187-4939 and other carbon-weak related objects are discussed.Comment: 10 pages, 5 figures, 5 tables, accepted for publication in MNRA

Post-Dieselgate : Evidence of NOx Emission Reductions Using On-Road Remote Sensing

The Dieselgate scandal which broke in September 2015 demonstrated that vehicle manufacturers, such as the Volkswagen Group (VWG), engaged in software-based manipulation which led to vehicles passing laboratory-based emission testing limits but were far more polluting while being driven on roads. Using 23 000 on-road remote sensing measurements of light-duty Euro 5 diesel vehicles in the United Kingdom between 2012 and 2018, VWG vehicles with the "Dieselgate-affected" EA189 engine demonstrated anomalous NOx emission behavior between the pre- and post-Dieselgate periods which was not observed in other vehicle makes or models. These anomalous changes can be explained by voluntary VWG hardware and software fixes which have led to improved NOx emission control. The VGW 1.6 L vehicles, with a simple hardware fix and a software upgrade, resulted in a 36% reduction in NOx, whereas the 2.0 L vehicles that required a software-only fix showed a 30% reduction in NOx once controlled for ambient temperature effects. These results show that even minor changes or upgrades can considerably reduce NOx emissions, which has implications for future emission control activities and local air quality

Analysis of Mandibular Fractures Caused by Work Related Accidents. Retrospective Descriptive Study

Indexación: Web of Science; Scielo.El objetivo de este estudio fue evaluar la tendencia de los pacientes con fracturas mandibulares asociados a accidentes laborales. Se realizó un estudio descriptivo retrospectivo en todos los casos de fracturas mandibulares que asistieron al servicio de cirugía maxilofacial del Hospital Clínico Mutual de Seguridad C.Ch.C., Santiago de Chile en un periodo de 4 años (enero 2009 - diciembre 2012). Todas las fracturas mandibulares fueron consignadas. La información fue recopilada a través de revisión de fichas clínicas electrónicas. Entre los años 2009 al 2012 se presentaron un total de 74 pacientes incluidos en el estudio con 102 rasgos de fracturas mandibulares. La fractura más común fue la de cóndilo mandibular (35 pacientes). Se observó una tasa de complicaciones del 8%. Los resultados mostrados en este estudio están en línea con la literatura y el análisis de este reporte provee información para el diseño de planes de prevención de riesgos, especialmente para desarrollar medidas de protección facial. Nivel de Evidencia: Tipo II. Estudio descriptivo.ABSTRACT: The objective of this study was to evaluate the tendency of patients with mandibular fractures associated with working accidents. A retrospective descriptive study was performed in all cases of mandibular fractures who attended the maxillofacial surgery service at the Clinical Hospital Mutual Seguridad C.CH.C. Santiago de Chile, in a 4-year period (January 2009 - December 2012). All mandibular fractures were recorded. The information was collected through review of electronic medical records. Between 2009 and 2012, 74 patients were included in the study with 102 lines of mandibular fractures. The most common fracture was the mandibular condyle (35 patients). The complication rate was 8%. The results shown in this study are in line with the literature and the analysis of this report provides information for the design of risk prevention plans, especially in developing measures of facial protection.http://ref.scielo.org/p5w48

Managing pregnancy of unknown location based on initial serum progesterone and serial serum hCG: development and validation of a two-step triage protocol.

A uniform rationalized management protocol for pregnancies of unknown location (PUL) is lacking. We developed a two-step triage protocol based on presenting serum progesterone (step 1) and hCG ratio two days later (step 2) to select PUL at high-risk of ectopic pregnancy (EP).Cohort study of 2753 PUL (301 EP), involving a secondary analysis of prospectively and consecutively collected PUL at two London-based university teaching hospitals. Using a chronological split we used 1449 PUL for development and 1304 for validation. We aimed to select PUL as low-risk with high confidence (high negative predictive value, NPV) while classifying most EP as high-risk (high sensitivity). The first triage step selects low-risk PUL at presentation using a serum progesterone threshold. The remaining PUL are triaged using a novel logistic regression risk model based on hCG ratio and initial serum progesterone (second step), defining low-risk as an estimated EP risk <5%.On validation, initial serum progesterone ≤2nmol/l (step 1) selected 16.1% PUL as low-risk. Second step classification with the risk model M6P selected an additional 46.0% of all PUL as low-risk. Overall, the two-step protocol classified 62.1% of PUL as low-risk, with an NPV of 98.6% and a sensitivity of 92.0%. When the risk model was used in isolation (i.e. without the first step), 60.5% of PUL were classified as low-risk with 99.1% NPV and 94.9% sensitivity.The two-step protocol can efficiently classify PUL into being at high or low risk of complications

Underestimated Ammonia Emissions from Road Vehicles

In this study, we use comprehensive vehicle emission remote sensing measurements of over 230,000 passenger cars to estimate total UK ammonia (NH3) emissions. Estimates are made using "top-down"and "bottom-up"methods that demonstrate good agreement to within 1.1% for total fuel consumed or CO2 emitted. A central component of this study is the comprehensive nature of the bottom-up emission estimates that combine highly detailed remote sensing emission data with over 4000 km of 1 Hz real driving data. Total annual UK NH3 emissions from gasoline passenger cars are estimated to be 7.8 ± 0.3 kt from the bottom-up estimate compared with 3.0 ± 1.7 kt reported by the UK national inventory. An important conclusion from the analysis is that both methodologies confirm that gasoline passenger car NH3 emissions are underestimated by a factor of about 2.6 compared with the 2018 UK National Atmospheric Emissions Inventory. Furthermore, we find that inventory estimates of urban emissions of NH3 for passenger cars are underestimated by a factor of 17

Characterisation of ammonia emissions from gasoline and gasoline hybrid passenger cars

Recent evidence suggests NH3 emissions from road vehicles play an important role in the formation of fine particulate matter, especially in urban areas. However, there is little data available for NH3 emitted from road vehicles under real driving conditions, in part due to its lack of regulation in vehicle emission legislation. In this study, we use 210,000 vehicle emission remote sensing measurements to evaluate the complex mix of factors affecting NH3 emissions from gasoline and gasoline hybrid passenger cars. The influence of vehicle model year and manufacturer on NH3 emissions is considered, as well as the effect of vehicle deterioration. It is found that the amount of NH3 emitted increases as vehicle mileage increases. A comparison of cold start and hot exhaust NH3 emissions reveals that on average, cold start emissions are a factor of 1.7 times higher. New NH3 emission factors are developed, in addition to speed-emission curves that are potentially useful for national inventories. A new application of remote sensing data is reported, whereby the proportion of failed CO2 measurements for hybrid vehicles provides unique insight into the real world battery use of both conventional hybrid electric and plug-in hybrid electric vehicles, which is used to refine the NH3 emission factors for these vehicles

Strong Temperature Dependence for Light-Duty Diesel Vehicle NOx Emissions

Diesel-powered road vehicles are important sources for nitrogen oxide (NOx) emissions, and the European passenger fleet is highly dieselised, which has resulted in many European roadside environments being noncompliant with legal air quality standards for nitrogen dioxide (NO2). On the basis of vehicle emission remote sensing data for 300000 light-duty vehicles across the United Kingdom, light-duty diesel NOx emissions were found to be highly dependent on ambient temperature with low temperatures resulting in higher NOx emissions, i.e., a "low temperature NOx emission penalty" was identified. This feature was not observed for gasoline-powered vehicles. Older Euro 3 to 5 diesel vehicles emitted NOx similarly, but vehicles compliant with the latest Euro 6 emission standard emitted less NOx than older vehicles and demonstrated less of an ambient temperature dependence. This ambient temperature dependence is overlooked in current emission inventories but is of importance from an air quality perspective. Owing to Europe's climate, a predicted average of 38% more NOx emissions have burdened Europe when compared to temperatures encountered in laboratory test cycles. However, owing to the progressive elimination of vehicles demonstrating the most severe low temperature NOx penalty, light-duty diesel NOx emissions are likely to decrease more rapidly throughout Europe than currently thought