Evidence for O-atom exchange in the O(^1D) + N_2O reaction as the source of mass-independent isotopic fractionation in atmospheric N_2O

Recent experiments have shown that in the oxygen isotopic exchange reaction for O(^1D) + CO_2 the elastic channel is approximately 50% that of the inelastic channel [Perri et al., 2003]. We propose an analogous oxygen atom exchange reaction for the isoelectronic O(^1D) + N_2O system to explain the mass-independent isotopic fractionation (MIF) in atmospheric N_2O. We apply quantum chemical methods to compute the energetics of the potential energy surfaces on which the O(^1D) + N_2O reaction occurs. Preliminary modeling results indicate that oxygen isotopic exchange via O(^1D) + N_2O can account for the MIF oxygen anomaly if the oxygen atom isotopic exchange rate is 30–50% that of the total rate for the reactive channels

Reply to comment by Röckmann and Kaiser on "Evidence for O-atom exchange in the O(^1D) + N_2O reaction as the source of mass-independent isotopic fractionation in atmospheric N_2O"

Based upon the authors’ questioning of the existence of the C_(2v) intermediate, we have reviewed our evidence for the existence of this state. It now appears that this state was in fact an artifact of our calculation [Yung et al., 2004], and was a saddle point rather than a true minimum. Our desire to provide a timely response to this criticism has kept us from determining exactly what minimum structure will be obtained by a full minimization at the level of theory employed. However, it is clear that the C_(2v) symmetry of the compound is broken in such a way that the two N-O bonds are no longer equivalent. We are grateful to the authors for helping us resolve this issue

Wafer bonding and layer transfer processes for 4-junction high efficiency solar cells

A four-junction cell design consisting of InGaAs, InGeAsP, GaAs, and Ga0.5In0.5P subcells could reach 1 x AMO efficiencies of 35.4%. but relies on the integration of non-lattice-matched materials. Wafer bonding and layer transfer processes show promise in the fabrication of InP/Si epitaxial templates for growth of the bottom InGaAs and InGaAsP subcells on a Si support substrate. Subsequent wafer bonding and layer transfer of a thin Ge layer onto the lower subcell stack can serve as an epitaxial template for GaAs and Ga0.5In0.5P subcelis. Present results indicate that optically active III/V compound semiconductors can be grown on both Ge/Si and InP/Si heterostructures. Current-voltage electrical characterization of the interfaces of these structures indicates that both InP/Si and Ge/Si interfaces have specific resistances lower than 0.1 Ωcm^2 for heavily doped wafer bonded interfaces, enabling back surface power extraction from the finished cell structure

Mortality-based damages per ton due to the on-road mobile sector in the Northeastern and Mid-Atlantic U.S. by region, vehicle class and precursor

A new study that quantifies the total and interstate deaths from transportation-related air pollution from five vehicle types in 12 states and Washington, D.C. has been published in Environmental Research Letters. The research was led by researchers at the University of North Carolina at Chapel Hill with the Center for Climate, Health, and the Global Environment at Harvard T.H Chan School of Public Health.The study is part of the Transportation, Equity, Climate, and Health project (TRECH), a multi-university research team from Harvard T.H. Chan School of Public Health, Boston University, University of North Carolina, and Columbia University, which analyzes policy scenarios to address carbon pollution from the transportation sector.Key TakeawaysOzone and fine particulate matter from vehicle emissions in 2016 led to an estimated 7,100 deaths in the Northeast and Mid-Atlantic regions of the U.S., and pollution from tailpipe emissions is also traveling across state lines, harming the health of people living in cities and states downwind.Region wide, light-duty trucks, which include SUVs, were responsible for the largest number of premature deaths at 2,463 followed by light-duty passenger vehicles (1,881) and heavy-duty trucks (1,465)All states experienced substantial health impacts from vehicle emissions and can gain health benefits from local action.New York, Pennsylvania, and New Jersey were hardest hit with health damages at $21 billion,$13 billion, and $12 billion, respectively, in 2016 (the most recent data available from EPA).Many states are heavily impacted by out-of-state emissions and some states cause more deaths out-of-state than in-state, including PA and NJ, highlighting the importance of region-wide action to reduce vehicle emissions.On a ton for ton basis, buses in the New York-Newark-Jersey City metropolitan area had the largest health damages at$4 million for every ton of particulate matter emitted.Ammonia emissions play a stronger relative role in causing health damages compared to oxides of nitrogen. Regionally, ammonia emissions from vehicles were responsible for 740 premature deaths in 2016, more than 10% of the total deaths. Ammonia emissions from vehicles are an unintended by-product of catalytic converters and are unregulated in the U.S., and their role in urban air pollution has been generally under appreciated

Resected serous cystic neoplasms of the pancreas: Locally aggressive behavior as a predictor of malignant disease? A review of 158 patients with recommendations for treatment.

Background: Serous cystic neoplasms of the pancreas are regarded as a benign entity with rare malignant potential. Surgical resection is generally considered curative. Objective: To perform the largest single institution review of patients who underwent surgical resection for serous cystic neoplasms of the pancreas in the hopes of guiding future management. Methods: Between June 1988 and January 2005, 158 patients with serous cystic neoplasms of the pancreas underwent surgical resection. A retrospective analysis was performed. Univariate and multivariate models were used to determine factors influencing perioperative morbidity and mortality. Major complications were defined as pancreatic fistula or anastomotic leak, postoperative bleed, retained operative material, or death. Minor complications were defined as wound infection, postoperative obstruction/ileus requiring TPN, delayed gastric emptying, arrhythmia, or other infection. Results: The mean age of the patients was 62.1 years, with 75% being female. The majority of patients were symptomatic at presentation (63%), with abdominal pain as the most common symptom. Of the 158 patients, 75 underwent distal pancreatectomy, 65 underwent pancreaticoduodenectomy, 9 underwent central pancreatectomy, 5 underwent local resection or enucleation, and 4 underwent total pancreatectomy. Mean tumor diameter was 5.1 cm. Mean operative time was 277.5 minutes. Mean postoperative length of hospital stay was 11 days. One patient was diagnosed at presentation with serous cystadenocarcinoma. The remaining 157 patients were initially diagnosed with benign serous cystadenoma. One of three patients with locally aggressive benign disease later presented with metastatic disease. Resection margins for all 158 patients were negative for tumor, and only 1 (0.6%) showed lymph node involvement. There was one intraoperative death. The incidence of major perioperative complications was 18%, while the incidence of minor complications was 33%. Men were significantly more likely to experience minor perioperative complications (OR = 3.74, P = .008), while patients greater than 65 years showed a trend toward fewer major complications (OR = 0.36, P = .09). Conclusions: Serous cystic neoplasms of the pancreas which are surgically resected are typically seen in asymptomatic women, as 5 cm neoplasms which are predominantly benign. Most are resected via either a left or right sided pancreatectomy with low mortality risk, but with notable major or minor morbidity. Cystadenocarcinoma is a rare finding on initial resection of serous cystic neoplasms. However, initial pathology specimens exhibiting benign but locally aggressive neoplasia may indicate an increased likelihood of recurrence or metachronous metastasis

Inhibition in multiclass classification

The role of inhibition is investigated in a multiclass support vector machine formalism inspired by the brain structure of insects. The so-called mushroom bodies have a set of output neurons, or classification functions, that compete with each other to encode a particular input. Strongly active output neurons depress or inhibit the remaining outputs without knowing which is correct or incorrect. Accordingly, we propose to use a classification function that embodies unselective inhibition and train it in the large margin classifier framework. Inhibition leads to more robust classifiers in the sense that they perform better on larger areas of appropriate hyperparameters when assessed with leave-one-out strategies. We also show that the classifier with inhibition is a tight bound to probabilistic exponential models and is Bayes consistent for 3-class problems. These properties make this approach useful for data sets with a limited number of labeled examples. For larger data sets, there is no significant comparative advantage to other multiclass SVM approaches

Inhibition in multiclass classification

The role of inhibition is investigated in a multiclass support vector machine formalism inspired by the brain structure of insects. The so-called mushroom bodies have a set of output neurons, or classification functions, that compete with each other to encode a particular input. Strongly active output neurons depress or inhibit the remaining outputs without knowing which is correct or incorrect. Accordingly, we propose to use a classification function that embodies unselective inhibition and train it in the large margin classifier framework. Inhibition leads to more robust classifiers in the sense that they perform better on larger areas of appropriate hyperparameters when assessed with leave-one-out strategies. We also show that the classifier with inhibition is a tight bound to probabilistic exponential models and is Bayes consistent for 3-class problems. These properties make this approach useful for data sets with a limited number of labeled examples. For larger data sets, there is no significant comparative advantage to other multiclass SVM approaches

Isotopic composition of stratospheric ozone

We present a kinetic calculation for the isotopic composition of stratospheric ozone. The calculated enrichments of ^(49)O_3 and ^(50)O_3 are in agreement with atmospheric measurements made at midlatitudes. Integrating the kinetic fractionation processes in the formation and photolysis of ozone, we obtain enrichments of ∼7.5–10.5 and ∼7.5–12.5% (referenced to atmospheric O_2) for δ^(49)O_3 and δ^(50)O_3, respectively, at altitudes between 20 and 35 km; the photolysis in the Hartley band of ozone is responsible for the observed altitude variation. The overall magnitude of the ozone enrichments (∼10%) is large compared with that commonly known in atmospheric chemistry and geochemistry. The heavy oxygen atom in ozone is therefore useful as a tracer of chemical species and pathways that involve ozone or its derived products. For example, the mass anomalies of oxygen in two greenhouse gases, CO_2 and N_2O, are likely the consequences of the transfer of heavy oxygen atoms from ozone