An Abstract Interpretation-based Model of Tracing Just-In-Time Compilation

Tracing just-in-time compilation is a popular compilation technique for the efficient implementation of dynamic languages, which is commonly used for JavaScript, Python and PHP. We provide a formal model of tracing JIT compilation of programs using abstract interpretation. Hot path detection corresponds to an abstraction of the trace semantics of the program. The optimization phase corresponds to a transform of the original program that preserves its trace semantics up to an observation modeled by some abstraction. We provide a generic framework to express dynamic optimizations and prove them correct. We instantiate it to prove the correctness of dynamic type specialization and constant variable folding. We show that our framework is more general than the model of tracing compilation introduced by Guo and Palsberg [2011] based on operational bisimulations.Comment: To appear in ACM Transactions on Programming Languages and System

Manganese-oxidizing bacteria mediate the degradation of 17α-ethinylestradiol

Manganese (II) and manganese-oxidizing bacteria were used as an efficient biological system for the degradation of the xenoestrogen 17 alpha-ethinylestradiol (EE2) at trace concentrations. Mn(2+)-derived higher oxidation states of Mn (Mn(3+), Mn(4+)) by Mn(2+)-oxidizing bacteria mediate the oxidative cleavage of the polycyclic target compound EE2. The presence of manganese (II) was found to be essential for the degradation of EE2 by Leptothrix discophora, Pseudomonas putida MB1, P. putida MB6 and P. putida MB29. Mn(2+)-dependent degradation of EE2 was found to be a slow process, which requires multi-fold excess of Mn(2+) and occurs in the late stationary phase of growth, implying a chemical process taking place. EE2-derived degradation products were shown to no longer exhibit undesirable estrogenic activity

The nature of damped HI absorbers probed by cosmological simulations: satellite accretion and outflows

We use state-of-the-art cosmological zoom simulations to explore the distribution of neutral gas in and around galaxies that gives rise to high column density \ion{H}{i} \mbox{Ly-$\alpha$} absorption (formally, sub-DLAs and DLAs) in the spectra of background quasars. Previous cosmological hydrodynamic simulations under-predict the mean projected separations $(b)$ of these absorbers relative to the host, and invoke selection effects to bridge the gap with observations. On the other hand, single lines of sight (LOS) in absorption cannot uniquely constrain the galactic origin. Our simulations match all observational data, with DLA and sub-DLA LOS existing over the entire probed parameter space ($-4\lesssim$[M/H]$\lesssim 0.5$, $b<50$ kpc) at all redshifts ($z\sim 0.4 - 3.0$). We demonstrate how the existence of DLA LOS at $b\gtrsim 20-30$ kpc from a massive host galaxy require high numerical resolution, and that these LOS are associated with dwarf satellites in the main halo, stripped metal-rich gas and outflows. Separating the galaxy into interstellar ("\ion{H}{i} disc") and circumgalactic ("halo") components, we find that both components significantly contribute to damped \ion{H}{i} absorption LOS. Above the sub-DLA (DLA) limits, the disc and halo contribute with $\sim 60 (80)$ and $\sim 40 (20)$ per cent, respectively. Our simulations confirm analytical model-predictions of the DLA-distribution at $z\lesssim 1$. At high redshift ($z\sim 2-3$) sub-DLA and DLAs occupy similar spatial scales, but on average separate by a factor of two by $z\sim 0.5$. On whether sub-DLA and DLA LOS sample different stellar-mass galaxies, such a correlation can be driven by a differential covering-fraction of sub-DLA to DLA LOS with stellar mass. This preferentially selects sub-DLA LOS in more massive galaxies in the low-$z$ universe.Comment: 12 pages, 5 figures, submitted to MNRAS 29/01/201

Formation of metal-cyanide complexes in deliquescent airborne particles: a new possible sink for HCN in urban environments

Hydrogen cyanide is a ubiquitous gas in the atmosphere and a biomass burning tracer. Reactive gasses can be adsorbed onto aerosol particles where they can promote heterogeneous chemistry. In the present study, we report for the first time on the measurement and speciation of cyanides in atmospheric aerosol. Filter samples were collected at an urban background site in the city center of Padua (Italy), extracted and analyzed with headspace gas chromatography and nitrogen-phosphorous detection. The results showed that strongly bound cyanides were present in all aerosol samples at a concentration ranging between 0.3 and 6.5 ng/m3 in the PM2.5 fraction. The concentration of cyanides strongly correlates with concentration of total carbon and metals associated with combustion sources. The results obtained bring evidence that hydrogen cyanide can be adsorbed onto aerosol liquid water and can react with metal ions to form stable metal-cyanide complexes

GUBS, a Behavior-based Language for Open System Dedicated to Synthetic Biology

In this article, we propose a domain specific language, GUBS (Genomic Unified Behavior Specification), dedicated to the behavioral specification of synthetic biological devices, viewed as discrete open dynamical systems. GUBS is a rule-based declarative language. By contrast to a closed system, a program is always a partial description of the behavior of the system. The semantics of the language accounts the existence of some hidden non-specified actions possibly altering the behavior of the programmed device. The compilation framework follows a scheme similar to automatic theorem proving, aiming at improving synthetic biological design safety.Comment: In Proceedings MeCBIC 2012, arXiv:1211.347

Emission factors for open and domestic biomass burning for use in atmospheric models

Biomass burning (BB) is the second largest source of trace gases and the largest source of primary fine carbonaceous particles in the global troposphere. Many recent BB studies have provided new emission factor (EF) measurements. This is especially true for non-methane organic compounds (NMOC), which influence secondary organic aerosol (SOA) and ozone formation. New EF should improve regional to global BB emissions estimates and therefore, the input for atmospheric models. In this work we present an up-to-date, comprehensive tabulation of EF for known pyrogenic species based on measurements made in smoke that has cooled to ambient temperature, but not yet undergone significant photochemical processing. All EFs are converted to one standard form (g compound emitted per kg dry biomass burned) using the carbon mass balance method and they are categorized into 14 fuel or vegetation types. Biomass burning terminology is defined to promote consistency. We compile a large number of measurements of biomass consumption per unit area for important fire types and summarize several recent estimates of global biomass consumption by the major types of biomass burning. Post emission processes are discussed to provide a context for the emission factor concept within overall atmospheric chemistry and also highlight the potential for rapid changes relative to the scale of some models or remote sensing products. Recent work shows that individual biomass fires emit significantly more gas-phase NMOC than previously thought and that including additional NMOC can improve photochemical model performance. A detailed global estimate suggests that BB emits at least 400 Tg yr^(−1) of gas-phase NMOC, which is almost 3 times larger than most previous estimates. Selected recent results (e.g. measurements of HONO and the BB tracers HCN and CH_3CN) are highlighted and key areas requiring future research are briefly discussed