Anthropogenic emissions alter secondary organic aerosol (SOA) formation chemistry from naturally emitted isoprene. We use correlations of tracers and tracer ratios to provide new perspectives on ...sulfate, NO x, and particle acidity influencing isoprene-derived SOA in two isoprene-rich forested environments representing clean to polluted conditionswet and dry seasons in central Amazonia and Southeastern U.S. summer. We used a semivolatile thermal desorption aerosol gas chromatograph (SV-TAG) and filter samplers to measure SOA tracers indicative of isoprene/HO2 (2-methyltetrols, C5-alkene triols, 2-methyltetrol organosulfates) and isoprene/NO x (2-methylglyceric acid, 2-methylglyceric acid organosulfate) pathways. Summed concentrations of these tracers correlated with particulate sulfate spanning three orders of magnitude, suggesting that 1 μg m–3 reduction in sulfate corresponds with at least ∼0.5 μg m–3 reduction in isoprene-derived SOA. We also find that isoprene/NO x pathway SOA mass primarily comprises organosulfates, ∼97% in the Amazon and ∼55% in Southeastern United States. We infer under natural conditions in high isoprene emission regions that preindustrial aerosol sulfate was almost exclusively isoprene-derived organosulfates, which are traditionally thought of as representative of an anthropogenic influence. We further report the first field observations showing that particle acidity correlates positively with 2-methylglyceric acid partitioning to the gas phase and negatively with the ratio of 2-methyltetrols to C5-alkene triols.
Context. The ALMA and Herschel missions promise to deliver data of high spatial and spectral resolution at far-infrared and sub-millimeter wavelengths. Modeling these data will require the knowledge ...of accurate radiative and collisional rates for species of astrophysical interest. Aims. We calculate the rotational excitation rate coefficients of NO in collisions with He and check the validity of the LTE approach in interpreting observations of rotational lines of NO. Methods. State-to-state rate coefficients between the 360 lowest hyperfine levels of NO were calculated using the MJ randomizing limit method for temperatures from 10 K to 350 K. We performed calculations of the excitation of NO using the new rate coefficients using a large velocity gradient (LVG) radiative transfer code. Results. The critical densities of the lines are found to be at $\ga$105 cm-3. The low dipole moment of NO ensures that the line emission is optically thin up to column densities of ~1015 cm-2. Lines in the ground ($\Omega=1/2$) state are readily detectable in typical conditions (N(NO) = 1013 cm-2; T = 10–30 K), whereas lines in the excited $\Omega=3/2$ state are observed only in warm ($T>50$ K) regions with higher column densities (N(NO) = 1014 cm-2). Line ratios of NO may well be used to constrain the ambient temperature and/or density. Conclusions. The new rate coefficients will help significantly in interpreting NO emission lines observed with current and future telescopes, and enable this molecule to become a powerful astrophysical tool.
Context.Observations of molecular emission at millimeter and infrared wavelengths, supplemented by careful and detailed modeling, are powerful tools for investigating the physical and chemical ...conditions of astrophysical objects. Modeling of molecular emission requires the calculation of rates for excitation by collisions with the most abundant species. Aims.The present paper focuses on the calculation of rate coefficients for rotational excitation of the PN molecule in its ground vibrational state in collision with He, based on a new two-dimensional potential energy surface from highly correlated ab initio calculations. Methods.Calculations of pure rotational (de)excitation of PN by He were performed for the first rotational levels using the essentially exact close-coupling method for the lower levels and the coupled-states approximation for higher levels. Results.Cross sections for transitions among the 31 first rotational levels of PN were calculated for kinetic energies up to 2500 cm-1. These cross sections were used to determine collisional rate constants for temperatures ranging from 5 K to 300 K. A propensity for even $\Delta j$ transitions is observed, which reflects the nearly symmetric character of the PN-He potential energy surface.
Society is faced with a range of contemporary threats to everyday life, from natural and technological hazards to accidents and terrorism. These are embodied within integrated emergency management ...arrangements that are designed to enhance preparedness and response to such incidents, and in turn facilitate a prompt recovery. Such arrangements must be inherently dynamic and evolve as new threats emerge or as existing threats change. An example of the latter is the changing nature of flooding, which is projected to increase in both frequency and severity with climate change. Recognizing this evolving threat, we focus on the evaluation of the effectiveness of domestic Flood Emergency Management Systems (FEMS) as components of integrated emergency management arrangements. Despite the extensive body of literature that documents success conditions of so-called effective emergency management more broadly, there have been only a few attempts to construct a comprehensive evaluation framework to support objective assessment and cross-country comparison. Addressing this gap, we formulate an evaluation framework specifically tailored to the study of FEMS in Europe, which is then provisionally applied to the study of FEMS in England (UK), France, the Netherlands, Poland, and Sweden. Important differences are observed in how FEMS have evolved in relation to differing contextual backgrounds (political, cultural, administrative, and socio-economic) and exposures to flood hazard. From this provisional assessment, a number of opportunities for, and constraints to, enhancing the effectiveness of FEMS in Europe are discerned. The evaluation framework thus serves as an important stepping stone for further indepth inquiry, and as a valuable tool for future comparative study.
Balloon pulmonary angioplasty (BPA) is a novel technique for the treatment of chronic thromboembolic pulmonary hypertension. While cardiologists need no introduction to the concept of balloon ...angioplasty, BPA has its own particular challenges. This article aims to provide the reader with an overview of BPA, starting with an introduction to chronic thromboembolic disease (CTED), the standard management of chronic thromboembolic pulmonary hypertension (CTEPH), technical challenges faced when performing BPA and the evidence base supporting its use. The second part of the article will focus on the future of BPA, in particular the areas where research is required to establish an evidence base to justify the role of BPA in CTEPH and CTED treatment.
Context.Over the next few years, the ALMA and Herschel missions will perform high spatial and spectral resolution studies at infrared and sub-millimeter wavelengths. Modeling of molecular emission ...requires excitation calculations using radiative, as well as collisional rates, with the most abundant species. In the interstellar medium, the dominant collision partner is H2, but little data is available for collisions with H2. If data for collisions with He are available, it has often been proposed to use the more available rate coefficients for collision with He, with the appropriate reduced mass correction, as a first estimate of rate coefficients with H2($j=0$). The validity of this approximation is not known. Aims.The present paper focuses on the calculation of rate coefficients among the first rotational levels of the SiS molecule in its ground vibrational state in collision with para-H2 and compares these new data with recently published He ones to investigate the validity of using He rate coefficients to estimate H2($j=0$) rate coefficients. Methods.A new potential energy surface for the SiS-para-H2 system was obtained using highly correlated ab initio calculations. Dynamical calculations of pure rotational (de)excitation of SiS by para-H2 were performed for the first rotational levels within the coupled-states approximation. Results.Collisional cross sections among the 51 first rotational levels of SiS were calculated for kinetic energies up to 2500 cm-1. State-to-state rate coefficients are calculated for temperatures ranging from 5 K up to 300 K. A propensity rule that favors even $\Delta j$ transitions is found and is explained by the near homonuclear symmetry of the SiS-para-H2 potential energy surface. A detailed comparison with recent SiS-He rate coefficients is also presented. We demonstrate that collision with He is a reasonable model for collisions with para-H2, although this approximation must be used with caution.
Telecommunication software systems, containing security vulnerabilities, continue to be created and released to consumers. We need to adopt improved software engineering practices to reduce the ...security vulnerabilities in modern systems. Contracts can provide a useful mechanism for the identification, tracking, and validation of security vulnerabilities. In this work, we propose a new contract-based security assertion monitoring framework (CB_SAMF) that is intended to reduce the number of security vulnerabilities that are exploitable across multiple software layers, and to be used in an enhanced systems development life cycle (SDLC). We show how contract-based security assertion monitoring can be achieved in a live environment on Linux. Through security activities integrated into the SDLC we can identify potential security vulnerabilities in telecommunication systems, which in turn are used for the creation of contracts defining security assertions. Our contract model is then applied, as runtime probes, against two common security related vulnerabilities in the form of a buffer overflow and a denial of service.
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