Spatiotemporal variation of methane and other trace hydrocarbon concentrations in the valley of Mexico

Mexico City is the world's largest and most polluted urban center. We examine the distribution of methane and other hydrocarbons within the Valley of Mexico, using it as a model for the role developing megacities will play in the next century of geochemical cycling. Seventy-five whole air samples were analyzed with multivariate statistical techniques, including factor analysis using principal components. Methane concentrations are highly variable in space and time, due to air circulations and source distribution. Landfills and open sewage canals are major inputs. Emissions into and out from the valley are modeled to be ∼515 t per day. Per capita emission is 0.01 t per annum per person, consistent with the global average for human related anaerobic generation. Natural gas leaks are small, and likely to be higher in other developing megacities; Mexican natural gas use has been discouraged out of earthquake safety concerns. In contrast, liquefied petroleum gas loss constitutes the major emission of propane and butane estimated at a leak rate of 5-10%. Kyoto and other environmental conventions have ignored methane as a greenhouse gas. Our analysis underscores the need to consider methane and other hydrocarbons, and the urbanization process, in future emission protocols. © 2002 Elsevier Science Ltd. All rights reserved

Removal of chemical and microbial contaminants from greywater using a novel constructed wetland: GROW

This is the author accepted manuscript. The final version is available from Elsevier via the DOI in this record.The availability of freshwater resources is becoming universally depleted, leading to the requirement for a focused management strategy for treating and reusing wastewater. In particular for urban and developing areas, small scale decentralized treatment systems are becoming popular. The GROW (Green Roof-top Water Recycling System) constructed wetland is one such option that provides a solution without a permanent land requirement and offering medium to high treatment efficiency. The performance of the GROW system was monitored from November 2013 to April 2015 in treating greywater from the Krishna Student Hostel in IIT Madras. The performance of the GROW wetland cells were examined over four monitoring periods in Phase 1 namely: 1) start-up stage, 2) seasonal variation 3) change of flow rate and 4) change in organic fraction (26.8, 25.9 and 25.5 g COD/cubic meter/day respectively). In Phase 2, the plants and the filling materials were changed and the performance of GROW wetland cells were evaluated. The system was fed with greywater at a flow rate of 62, 70, 82, 100 and 120 L/day respectively with hydraulic retention time of 0.7–1.3 days. The samples taken from the inlet and the outlets of the GROW system were taken weekly and analyzed for the following parameters; pH, COD, BOD, TSS, TN, NO 3 –N, TP, FC, SDS, PG and TMA. In the study, the overall removal efficiency was greater than 82% for all the parameters. The GROW wetlands reduced all the above mentioned parameters to within or closely to the USEPA standard limits for reuse. The reusable effluent water is named ‘Green Water’.The authors wish to acknowledge Department of Science of Technology (DST), India and the European Union for providing the financial support for the project SARASWATI

First-principles prediction of coexistence of magnetism and ferroelectricity in rhombohedral Bi2FeTiO6

First principles calculations based on the density functional theory within the local spin density approximation plus U(LSDA+U)scheme, show rhombohedral Bi$_2$FeTiO$_6$ is a potential multiferroic in which the magnetism and ferroelectricity coexist . A ferromagnetic configuration with magnetic moment of 4 $\mu_B$ per formula unit have been reported with respect to the minimum total energy. Spontaneous polarization of 27.3 $\mu$ C/cm$^2$, caused mainly by the ferroelectric distortions of Ti, was evaluated using the berry phase approach in the modern theory of polarization. The Bi-6s stereochemical activity of long-pair and the `d$^0$-ness' criterion in off-centring of Ti were coexisting in the predicted new system. In view of the oxidation state of Bi$^{3+}$,Fe$^{2+}$,Ti$^{4+}$, and O$^{2-}$ from the orbital-resolved density of states of the Bi-6p, Fe-3d,Ti-3d, and O-2p states,the valence state of Bi$_2$FeTiO$_6$ in the rhombohedral phase was found to be Bi$_2$$^{3+}$Fe$^{2+}$Ti$^{4+}$O$_6$.Comment: 22 pages, 9 figures. submitted to Physics Letters

Comparison of structural magnetic resonance imaging findings between neuropsychiatric systemic lupus erythematosus and systemic lupus erythematosus patients: A systematic review and meta-analysis

Introduction: Neuropsychiatric systemic lupus erythematosus is often clinically challenging to diagnose, treat and monitor. Although brain magnetic resonance imaging is frequently performed before lumbar puncture in neuropsychiatric systemic lupus erythematosus, it is not clear from the literature whether specific brain magnetic resonance imaging findings are associated with distinct clinical features of neuropsychiatric systemic lupus erythematosus. Methods: We conducted a systematic review and meta-analysis on published studies of neuropsychiatric systemic lupus erythematosus including brain magnetic resonance imaging and the 1999 American College of Rheumatology-defined clinical neuropsychiatric systemic lupus erythematosus syndromes to determine their relationship. Pooled prevalence and risk ratio for distinct neuropsychiatric systemic lupus erythematosus associations were determined with 95% confidence intervals. Results: Of 821 studies screened, 21 fulfilled inclusion criteria. A total of 818 participants were evaluated (91% female) with 1064 neuropsychiatric systemic lupus erythematosus episodes assessed. Neuropsychiatric systemic lupus erythematosus features included headache (24%), seizures (19%), cerebrovascular disease (18%), cognitive dysfunction (15%) and acute confusional state (14%). Normal magnetic resonance imaging was significant for anxiety disorder (risk ratio: 9.00; 95% confidence interval: 2.40, 33.79), autonomic disorder (risk ratio: 7.00; 95% confidence interval: 0.51, 96.06) and plexopathy (risk ratio: 5.00; 95% confidence interval: 0.81, 31.00). Highest risk ratio of neuropsychiatric systemic lupus erythematosus syndrome with abnormal magnetic resonance imaging was observed for cerebrovascular disease (risk ratio: 0.15; 95% confidence interval: 0.10, 0.24) and demyelination (risk ratio: 0.11; 95% confidence interval: 0.02, 0.72). Conclusion: Normal magnetic resonance imaging in neuropsychiatric systemic lupus erythematosus was the most significant correlate from our meta-analysis for psychological symptoms including anxiety and peripheral nerve features of autonomic disorder and plexopathy. The main abnormal brain magnetic resonance imaging correlates included cerebrovascular disease and demyelination. Brain magnetic resonance imaging correlates poorly with neuropsychiatric systemic lupus erythematosus features, and specific clinical symptoms should be the main determinants of performing magnetic resonance imaging rather than presence of neuropsychiatric systemic lupus erythematosus per se

A Genome-wide gene-expression analysis and database in transgenic mice during development of amyloid or tau pathology

We provide microarray data comparing genome-wide differential expression and pathology throughout life in four lines of "amyloid" transgenic mice (mutant human APP, PSEN1, or APP/PSEN1) and "TAU" transgenic mice (mutant human MAPT gene). Microarray data were validated by qPCR and by comparison to human studies, including genome-wide association study (GWAS) hits. Immune gene expression correlated tightly with plaques whereas synaptic genes correlated negatively with neurofibrillary tangles. Network analysis of immune gene modules revealed six hub genes in hippocampus of amyloid mice, four in common with cortex. The hippocampal network in TAU mice was similar except that Trem2 had hub status only in amyloid mice. The cortical network of TAU mice was entirely different with more hub genes and few in common with the other networks, suggesting reasons for specificity of cortical dysfunction in FTDP17. This Resource opens up many areas for investigation. All data are available and searchable at http://www.mouseac.org

Incorporating chemical signalling factors into cell-based models of growing epithelial tissues

In this paper we present a comprehensive computational framework within which the effects of chemical signalling factors on growing epithelial tissues can be studied. The method incorporates a vertex-based cell model, in conjunction with a solver for the governing chemical equations. The vertex model provides a natural mesh for the finite element method (FEM), with node movements determined by force laws. The arbitrary Lagrangian–Eulerian formulation is adopted to account for domain movement between iterations. The effects of cell proliferation and junctional rearrangements on the mesh are also examined. By implementing refinements of the mesh we show that the finite element (FE) approximation converges towards an accurate numerical solution. The potential utility of the system is demonstrated in the context of Decapentaplegic (Dpp), a morphogen which plays a crucial role in development of the Drosophila imaginal wing disc. Despite the presence of a Dpp gradient, growth is uniform across the wing disc. We make the growth rate of cells dependent on Dpp concentration and show that the number of proliferation events increases in regions of high concentration. This allows hypotheses regarding mechanisms of growth control to be rigorously tested. The method we describe may be adapted to a range of potential application areas, and to other cell-based models with designated node movements, to accurately probe the role of morphogens in epithelial tissues

Mexico City and the biogeochemistry of global urbanization

Mexico City is far advanced in its urban evolution, and cities in currently developing nations may soon follow a similar course. This paper investigates the strengths and weaknesses of infrastructures for the emerging megacities. The major driving force for infrastructure change in Mexico City is concern over air quality. Air chemistry data from recent field campaigns have been used to calculate fluxes in the atmosphere of the Valley of Mexico, for compounds that are important to biogeochemistry including methane (CH4), carbon monoxide (CO), nonmethane hydrocarbons (NMHCs), ammonia (NH3), sulfur dioxide (SO2), nitrogen oxides (NOx and NOy), soot, and dust. Leakage of liquified petroleum gas approached 10% during sampling periods, and automotive pollutant sources in Mexico City were found to match those in developed cities, despite a lower vehicle-to-person ratio of 0.1. Ammonia is released primarily from residential areas, at levels sufficient to titrate pollutant acids into particles across the entire basin. Enhancements of reduced nitrogen and hydrocarbons in the vapor phase skew the distribution of NOy species towards lower average deposition velocities. Partly as a result, downwind nutrient deposition occurs on a similar scale as nitrogen fixation across Central America, and augments marine nitrate upwelling. Dust suspension from unpaved roads and from the bed of Lake Texcoco was found to be comparable to that occurring on the periphery of the Sahara, Arabian, and Gobi deserts. In addition, sodium chloride (NaCl) in the dust may support heterogeneous chlorine oxide (ClOx) chemistry. The insights from our Mexico City analysis have been tentatively applied to the upcoming urbanization of Asia

The role of mutation rate variation and genetic diversity in the architecture of human disease

Background We have investigated the role that the mutation rate and the structure of genetic variation at a locus play in determining whether a gene is involved in disease. We predict that the mutation rate and its genetic diversity should be higher in genes associated with disease, unless all genes that could cause disease have already been identified. Results Consistent with our predictions we find that genes associated with Mendelian and complex disease are substantially longer than non-disease genes. However, we find that both Mendelian and complex disease genes are found in regions of the genome with relatively low mutation rates, as inferred from intron divergence between humans and chimpanzees, and they are predicted to have similar rates of non-synonymous mutation as other genes. Finally, we find that disease genes are in regions of significantly elevated genetic diversity, even when variation in the rate of mutation is controlled for. The effect is small nevertheless. Conclusions Our results suggest that gene length contributes to whether a gene is associated with disease. However, the mutation rate and the genetic architecture of the locus appear to play only a minor role in determining whether a gene is associated with disease