Civil and Environmental Engineering Publications

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1,4-Dioxane-degrading consortia can be enriched from uncontaminated soils: prevalence of Mycobacterium and soluble di-iron monooxygenase genes
(Wiley, 2017) He, Ya; Mathieu, Jacques; da Silva, Marcio L.B.; Li, Mengyan; Alvarez, Pedro J.J.
Two bacterial consortia were enriched from uncontaminated soil by virtue of their ability to grow on 1,4-dioxane (dioxane) as a sole carbon and energy source. Their specific dioxane degradation rates at 30°C, pH = 7 (i.e. 5.7 to 7.1 g-dioxane per g-protein per day) were comparable to those of two dioxane-metabolizing archetypes: Pseudonocardia dioxanivoransCB1190 and Mycobacterium dioxanotrophicusPH-06. Based on 16S rRNA sequencing, Mycobacterium was the dominant genus. Acetylene inhibition tests suggest that dioxane degradation was mediated by monooxygenases. However, qPCR analyses targeting the tetrahydrofuran/dioxane monooxygenase gene (thmA/dxmA) (which is, to date, the only sequenced dioxane monooxygenase gene) were negative, indicating that other (as yet unknown) catabolic gene(s) were responsible. DNA sequence analyses also showed threefold to sevenfold enrichment of group 5 and group 6 soluble di-iron monooxygenase (SDIMO) genes relative to the original soil samples. Whereas biodegradation of trace levels of dioxane is a common challenge at contaminated sites, both consortia degraded dioxane at low initial concentrations (300 μg l−1) below detectable levels (5 μg l−1) in bioaugmented microcosms prepared with impacted groundwater. Overall, this work shows that dioxane-degrading bacteria (and the associated natural attenuation potential) exist even in some uncontaminated soils, and may be enriched to broaden bioaugmentation options for sites experiencing insufficient dioxane catabolic capacity.
A Closed-Form Technique for the Reliability and Risk Assessment of Wind Turbine Systems
(MDPI, 2012) Mensah, Akwasi F.; Dueñas-Osorio, Leonardo
This paper proposes a closed-form method to evaluate wind turbine system reliability and associated failure consequences. Monte Carlo simulation, a widely used approach for system reliability assessment, usually requires large numbers of computational experiments, while existing analytical methods are limited to simple system event configurations with a focus on average values of reliability metrics. By analyzing a wind turbine system and its components in a combinatorial yet computationally efficient form, the proposed approach provides an entire probability distribution of system failure that contains all possible configurations of component failure and survival events. The approach is also capable of handling unique component attributes such as downtime and repair cost needed for risk estimations, and enables sensitivity analysis for quantifying the criticality of individual components to wind turbine system reliability. Applications of the technique are illustrated by assessing the reliability of a 12-subassembly turbine system. In addition, component downtimes and repair costs of components are embedded in the formulation to compute expected annual wind turbine unavailability and repair cost probabilities, and component importance metrics useful for maintenance planning and research prioritization. Furthermore, this paper introduces a recursive solution to closed-form method and applies this to a 45-component turbine system. The proposed approach proves to be computationally efficient and yields vital reliability information that could be readily used by wind farm stakeholders for decision making and risk management.
A compact mid-infrared dual-gas CH4/C2H6 sensor using a single interband cascade laser and custom electronics
(SPIE, 2017) Ye, Weilin; Zheng, Chuantao; Tittel, Frank K.; Sanchez, Nancy P.; Gluszek, Aleksander K.; Hudzikowski, Arkadiusz J.; Lou, Minhan; Dong, Lei; Griffin, Robert J.
A compact mid-infrared (MIR) dual-gas sensor system was demonstrated for simultaneous detection of methane (CH4) and ethane (C2H6) using a single continuous-wave (CW) interband cascade laser (ICL) based on tunable laser absorption spectroscopy (TDLAS) and wavelength modulation spectroscopy (WMS). Ultracompact custom electronics were developed, including a laser current driver, a temperature controller and a lock-in amplifier. These custom electronics reduce the size and weight of the sensor system as compared with a previous version based on commercial electronics. A multipass gas cell with an effective optical length of 54.6 m was employed to enhance the absorption signal. A 3337 nm ICL was capable of targeting a C2H6 absorption line at 2996.88 cm-1 and a CH4 line at 2999.06 cm-1. Dual-gas detection was realized by scanning both the CH4 and C2H6 absorption lines. Based on an Allan deviation analysis, the 1 σ minimum detection limit (MDL) was 17.4 ppbv for CH4 and 2.4 ppbv for C2H6 with an integration time of 4.3 s. TDLAS based sensor measurements for both indoor and outdoor mixing ratios of CH4 and C2H6 were conducted. The reported single ICL based dual-gas sensor system has the advantages of reduced size and cost without influencing the midinfrared sensor detection sensitivity, selectivity and reliability.
A general condition for the existence of unconnected equilibria for symmetric arches
(Elsevier, 2018) Zhou, Yang; Stanciulescu, Ilinca
This paper presents a semi-analytical study of unconnected equilibrium states for symmetric curved beams. Using the Fourier series approximation, a general condition for the existence of unconnected equilibria for symmetric shallow arches is derived for the first time. With this derived condition, we can directly determine whether or not a shallow arch with specific initial configuration and external load has remote unconnected equilibria. These unconnected equilibria cannot be obtained in experiments or nonlinear finite element simulations without performing a proper perturbation first. The derived general condition is then applied to curved beams with different initial shapes and external loads. It is found that initially symmetric parabolic arches under a uniformly distributed vertical force can have multiple groups of unconnected equilibria, depending on the initial rise of the structure. However, small symmetric geometric deviations are required for parabolic arches under a central point load, and half-sine arches under a central point load or a uniformly distributed load to have unconnected equilibria. The validity of the analytical derivations of the nonlinear equilibrium solutions and the general condition for the existence of unconnected equilibria are verified by nonlinear finite element methods.
A global analysis of coastal flood risk to the petrochemical distribution network in a changing climate
(Elsevier, 2022) Capshaw, Kendall M.; Padgett, Jamie E.
The global petroleum distribution network already faces a significant threat of disruption due to annual coastal flooding of major refining centers, which is expected to further increase with the effects of climate change. This study considers the impacts that sea level rise projections might have on the annual flood risk to coastal refineries, and how regional disruptions propagate across the network. Both the annual regional risk in terms of expected production disruption under a range of climate scenarios, as well as the expected production disruption due to a major flood event impacting refining hubs of high importance are assessed throughout the 21st century. These risks are propagated across the network to model the global impact of coastal flood-induced refining disruptions. This analysis provides insights on the relative risks that different climate scenarios and flood events pose globally, informing potential mitigation and adaptation needs of critical facilities. Due to the highly interconnected nature of the global petroleum product distribution network, these results highlight the need for mitigation considerations for even regions with low domestic production disruption risk due to coastal flood hazards, as disruptions in remote regions can have cascading consequences resulting in significant disruption to petroleum product supply around the world. Furthermore, such results can inform decisions regarding technology transitions or energy diversification in light of the new understanding of climate risks to coastal refineries and the global petroleum distribution network.
A lower bound on snap-through instability of curved beams under thermomechanical loads
(Elsevier, 2012) Stanciulescu, Ilinca; Mitchell, Toby; Chandra, Yenny; Eason, Thomas; Spottswood, Michael
A non-linear finite element formulation (three dimensional continuum elements) is implemented and used for modeling dynamic snap-through in beams with initial curvature. We identify a non-trivial (non-flat) configuration of the beam at a critical temperature value below which the beam will no longer experience snap-through under any magnitude of applied quasi-static load for beams with various curvatures. The critical temperature is shown to successfully eliminate snap-through in dynamic simulations at quasistatic loading rates. Thermomechanical coupling is included in order to model a physically minimal amount of damping in the system, and the resulting post-snap vibrations are shown to be thermoelastically damped. We propose a test to determine the critical snap-free temperature for members of general geometry and loading pattern; the analogy between mechanical prestress and thermal strain that holds between the static and dynamic simulations is used to suggest a simple method for reducing the vulnerability of thin-walled structural members to dynamic snap-through in members of large initial curvature via the introduction of initial pretension.
A Markov chain-based model for structural vulnerability assessmentof corrosion-damaged reinforced concrete bridges
(The Royal Society, 2021) Dizaj, Ebrahim Afsar; Padgett, Jamie E.; Kashani, Mohammad M.
The deterioration and cracking of reinforced concrete (RC) bridges due to the chloride-induced corrosion of steel reinforcement is an inherently time-dependent stochastic phenomenon. In the current practice of bridge management systems, however, the determination of the condition states of deteriorated bridges is highly dependent on the opinion of experienced inspectors. Taking such complexity into account, the current paper presents a new stochastic predictive methodology using a non-homogeneous Markov process, which directly relates the visual inspection data (corrosion rate and crack widths) to the structural vulnerability of deteriorated concrete bridges. This methodology predicts the future condition of corrosion-induced damage (concrete cracking) by linking structural vulnerability analysis and a discrete-time Markov chain model. The application of the proposed methodology is demonstrated through a case-study corrosion-damaged RC bridge pier.This article is part of a discussion meeting issue ‘A cracking approach to inventing new tough materials: fracture stranger than friction’.
A New Kinetic Assay Method for Effective Scale Inhibitor Concentration Determination with Low Detection Limit
(SPE, 2022) Dai, Zhaoyi; Ko, Saebom; Wang, Xin; Dai, Chong; Paudyal, Samridhdi; Zhao, Yue; Li, Wei; Leschied, Cianna; Yao, Xuanzhu; Lu, Yi-Tsung; Kan, Amy; Tomson, Mason
Scale inhibitors are widely used for mineral scale control in various industries, including oil and gas productions, geothermal energy acquisitions, and heat exchanger scale control to mention a few. In most applications, these scale inhibitors are effective at substoichiometric concentrations (e.g., 1 mg/L or lower), and the optimization of these applications is based on the ability to accurately measure the effective inhibitor concentration at such low concentrations. For example, the continuous treatment injection rate, the squeeze treatment frequency, or the batch treatment schedule need to be optimized to ensure the minimum inhibitor concentration (MIC) is achieved during production. However, the non- or low-phosphorous polymeric scale inhibitor concentration determination is difficult using inductively coupled plasma (ICP)-optic emission spectroscopy/mass spectrometry or ion chromatography, especially at mg/L level concentrations due to their high detection limits. The recently developed hyamine method or high-pressure liquid chromatography (HPLC) method involves intensive labor and high costs. Furthermore, in the complex oilfield operational conditions, the presence of other chemicals (e.g., surfactants, biocides, and corrosion inhibitors), the potential degradation of scale inhibitors and the use of combination scale inhibitors require the measurement of effective scale inhibitor concentration, which cannot be accomplished by the traditional methods. In this study, a new kinetic assay method has been developed to determine the effective scale inhibitor concentration with limits of detection (LODs) less than or around 0.1 mg/L for most cases. This method uses a continuous stirring tank reactor (CSTR) apparatus and is developed based on the linear correlation between the effective inhibition concentration and the measured critical time when laser signal changes. The results show that the inhibitor concentrations of various non- or low-phosphorous polymeric scale inhibitors in synthetic field brine, laboratory solutions, and real oilfield brines can be accurately determined at mg/L level, or lower, with less than 10% error. The method is robust, accurate, and much less time- or labor-consuming than other existing methods especially for non- or low-phosphorous polymeric scale inhibitors.
A new mutually reinforcing network node and link ranking algorithm
(Macmillan Publishers Limited, 2015) Wang, Zhenghua; Dueñas-Osorio, Leonardo; Padgett, Jamie E.
This study proposes a novel Normalized Wide network Ranking algorithm (NWRank) that has the advantage of ranking nodes and links of a network simultaneously. This algorithm combines the mutual reinforcement feature of Hypertext Induced Topic Selection (HITS) and the weight normalization feature of PageRank. Relative weights are assigned to links based on the degree of the adjacent neighbors and the Betweenness Centrality instead of assigning the same weight to every link as assumed in PageRank. Numerical experiment results show that NWRank performs consistently better than HITS, PageRank, eigenvector centrality, and edge betweenness from the perspective of network connectivity and approximate network flow, which is also supported by comparisons with the expensive N-1 benchmark removal criteria based on network efficiency. Furthermore, it can avoid some problems, such as the Tightly Knit Community effect, which exists in HITS. NWRank provides a new inexpensive way to rank nodes and links of a network, which has practical applications, particularly to prioritize resource allocation for upgrade of hierarchical and distributed networks, as well as to support decision making in the design of networks, where node and link importance depend on a balance of local and global integrity.
A numerical investigation of snap-through in a shallow arch-like model
(Elsevier, 2013) Chandra, Yenny; Stanciulescu, Ilinca; Virgin, Lawrence N.; Eason, Thomas G.; Spottswood, Stephen M.
Slender curved structures may experience a loss of stability called snap-through, causing the curvature on part or all of the structure to invert inducing fatigue damage. This paper presents a framework for analyzing the transient responses of slender curved structures. A numerical study of snap-through in a shallow arch-like model under periodic excitations is performed on a simplified model and on a detailed finite element model. The boundaries that separate the snap-through and no snap-through regions in the forcing parameters space are identified. Various post-snap responses are analyzed. The effects of initial conditions on the snap-through boundaries and post-snap responses are examined. Forcing parameters that lead to chaotic response are identified.
A Polysulfone/Cobalt Metal–Organic Framework Nanocomposite Membrane with Enhanced Water Permeability and Fouling Resistance
(American Chemical Society, 2022) Gil, Eva; Huang, Xiaochuan; Zuo, Kuichang; Kim, Jun; Rincón, Susana; Rivera, José María; Ranjbari, Kiarash; Perreault, François; Alvarez, Pedro; Zepeda, Alejandro; Li, Qilin; Nanosystems Engineering Research Center for Nanotechnology Enabled Water Treatment
Ultrafiltration membranes are widely used in water and wastewater applications. The two most important membrane characteristics that determine the cost-effectiveness of an ultrafiltration membrane process are membrane permeability and fouling resistance. Metal–organic frameworks (MOFs) have been intensively investigated as highly selective sorbents and superior (photo) catalysts. Their potential as membrane modifiers has also received attention recently. In this study, a non-functionalized, water-stable, nanocrystalline mixed ligand octahedral MOF containing carboxylate and amine groups with a cobalt metal center (MOF-Co) was incorporated into polysulfone (PSF) ultrafiltration (UF) membranes at a very low nominal concentration (2 and 4 wt %) using the conventional phase inversion method. The resultant PSF/MOF-Co_4% membrane exhibited water permeability up to 360% higher than of the control PSF membrane without sacrificing the selectivity of the membrane, which had not been previously achieved by an unmodified MOF. In addition, the PSF/MOF-Co_4% membrane showed strong resistance to fouling by natural organic matter (NOM), with 87 and 83% reduction in reversible and irreversible NOM fouling, respectively, compared to the control PSF membrane. This improvement was attributed to the increases in membrane porosity and surface hydrophilicity resulting from the high hydrophilicity of the MOF-Co. The capability of increasing membrane water permeability and fouling resistance without compromising membrane selectivity makes the MOF-Co and potentially other hydrophilic MOFs excellent candidates as membrane additives.
A zero-dimensional view of atmospheric degradation of levoglucosan (LEVCHEM_v1) using numerical chamber simulations
(Copernicus Publications, 2021) Suciu, Loredana G.; Griffin, Robert J.; Masiello, Caroline A.
Here, we developed a zero-dimensional (0-D) modeling framework (LEVCHEM_v1) to provide insights into the atmospheric degradation of a key tracer emitted during biomass burning – levoglucosan (LEV), while additionally exploring its effects on the dynamics of secondary organic aerosols (SOA) and other gases. For this, we updated existing chemical mechanisms (homogeneous gas-phase chemistry and heterogeneous chemistry) in the BOXMOXv1.7 model to include the chemical degradation of LEV and its intermediary degradation products in both phases (gas and aerosol). In addition, we added a gas-particle partitioning mechanism to the model to account for the effect of evaporation and condensation on the phase-specific concentrations of LEV and its degradation products. Comparison of simulation results with measurements from various chamber experiments (spanning summer and winter conditions) show that the degradation timescale of LEV varied by phase, with gas-phase degradation occurring over ∼1.5–5 d and aerosol-phase degradation occurring over ∼8–36 h. These relatively short timescales suggest that most of the initial LEV concentration can be lost chemically or deposited locally before being transported regionally. We varied the heterogeneous reaction rate constant in a sensitivity analysis (for summer conditions only) and found that longer degradation timescales of LEV are possible, particularly in the aerosol phase (7 d), implying that some LEV may be transported regionally. The multiphase chemical degradation of LEV has effects on SOA and other gases. Several first- or second-generation products resulted from its degradation; most of the products include one or two carbonyl groups, one product contains a nitrate group, and a few products show the cleavage of C−C bonds. The relative importance of the products varies depending on the phase and the timing of the maximum concentration achieved during the simulation. Our estimated secondary organic aerosol SOA yields (4 %–32 %) reveal that conversion of LEV to secondary products is significant and occurs rapidly in the studied scenarios. LEV degradation affected other gases by increasing the concentrations of radicals and decreasing those of reactive nitrogen species. Decreases of the mixing ratios of nitrogen oxides appear to drive a more rapid increase in ozone compared with changes in volatile organic compounds levels. An important next step to confirm longer degradation timescales will be to extend the evaluation of the modeled LEV degradation beyond 3–6 h by using more extensive data from chambers and, possibly, from fire plumes. The mechanism developed here can be used in chemical transport models applied to fire plumes to trace LEV and its degradation products from source to deposition, to assess their atmospheric implications and to answer questions relevant to fire tracing, carbon and nitrogen cycling, and climate.
Accounting for Uncertainties in the Safety Assessment of Concrete Gravity Dams: A Probabilistic Approach with Sample Optimization
(MDPI, 2021) Segura, Rocio L.; Miquel, Benjamin; Paultre, Patrick; Padgett, Jamie E.
Important advances have been made in the methodologies for assessing the safety of dams, resulting in the review and modification of design guidelines. Many existing dams fail to meet these revised criteria, and structural rehabilitation to achieve the updated standards may be costly and difficult. To this end, probabilistic methods have emerged as a promising alternative and constitute the basis of more adequate procedures of design and assessment. However, such methods, in addition to being computationally expensive, can produce very different solutions, depending on the input parameters, which can greatly influence the final results. Addressing the existing challenges of these procedures to analyze the stability of concrete dams, this study proposes a probabilistic-based methodology for assessing the safety of dams under usual, unusual, and extreme loading conditions. The proposed procedure allows the analysis to be updated while avoiding unnecessary simulation runs by classifying the load cases according to the annual probability of exceedance and by using an efficient progressive sampling strategy. In addition, a variance-based global sensitivity analysis is performed to identify the parameters most affecting the dam stability, and the parameter ranges that meet the safety guidelines are formulated. It is observed that the proposed methodology is more robust, more computationally efficient, and more easily interpretable than conventional methods.
Air quality and health benefits from potential coal power plant closures in Texas
(Taylor & Francis, 2019) Strasert, Brian; Teh, Su Chen; Cohan, Daniel S.
As power production from renewable energy and natural gas grows, closures of some coal-fired power plants in Texas become increasingly likely. In this study, the potential effects of such closures on air quality and human health were analyzed by linking a regional photochemical model with a health impacts assessment tool. The impacts varied significantly across 13 of the state’s largest coal-fired power plants, sometimes by more than an order of magnitude, even after normalizing by generation. While some power plants had negligible impacts on concentrations at important monitors, average impacts up to 0.5 parts per billion (ppb) and 0.2 µg/m3 and maximum impacts up to 3.3 ppb and 0.9 µg/m3 were seen for ozone and fine particulate matter (PM2.5), respectively. Individual power plants impacted average visibility by up to 0.25 deciviews in Class I Areas. Health impacts arose mostly from PM2.5 and were an order of magnitude higher for plants that lack scrubbers for SO2. Rankings of health impacts were largely consistent across the base model results and two reduced form models. Carbon dioxide emissions were relatively uniform, ranging from 1.00 to 1.26 short tons/MWh, and can be monetized based on a social cost of carbon. Despite all of these unpaid externalities, estimated direct costs of each power plant exceeded wholesale power prices in 2016. Implications: While their CO2 emission rates are fairly similar, sharply different NOx and SO2 emission rates and spatial factors cause coal-fired power plants to vary by an order of magnitude in their impacts on ozone, particulate matter, and associated health and visibility outcomes. On a monetized basis, the air pollution health impacts often exceed the value of the electricity generated and are of similar magnitude to climate impacts. This suggests that both air pollution and climate should be considered if externalities are used to inform decision making about power-plant dispatch and retirement.
Airmass aging metrics derived from particle and other measurements near Fort Worth
(Elsevier, 2016) Cevik, B. Karakurt; Rutter, A.P.; Gong, L.; Griffin, R.J.; Flynn, J.H.; Lefer, B.L.; Kim, S.
The composition, concentration, and size of submicron particulate matter (PM1) were measured at five-minute resolution by an Aerodyne high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) at a semi-rural location northwest of the Dallas-Fort Worth, TX, area during June 2011. Because of increased organic aerosol (OA) levels, focus here is placed on the period from June 17–30. The total measured PM1 mass concentration ranged between 1.1 and 16.5 μg m−3, with a mean of 4.4 ± 2.6 (one s.d.) μg m−3. Significant variability is observed in the time series of total PM1 and of four individual HR-ToF-AMS species, particularly between June 21 and 25. The average PM1mass composition was dominated by OA (55.0 ± 14.8%) and sulfate (30.7 ± 12.3%). Organic aerosol concentrations were correlated positively with carbon monoxide (CO) (R = 0.81). This study uses a variety of aging metrics and their relations to OA/ΔCO to characterize secondary organic aerosol. Photochemical age is estimated by using the toluene to benzene ratio. The average photochemical age was 26.7 ± 5.3 h. Other metrics of age used in this work include the ratio of sulfate to total sulfur and the ratio of nitrogen oxides to total reactive nitrogen. The correlations between the OA/ΔCO and nitrogen aging metrics indicate consistent aging, and a weak relationship is observed between OA/ΔCO and sulfur aging. However, the relationship between photochemical age and OA/ΔCO does not show a statistically significant correlation.
Alumoxane/ferroxane nanoparticles for the removal of viral pathogens: the importance of surface functionality to nanoparticle activity
(The Royal Society of Chemistry, 2012) Maguire-Boyle, Samuel J.; Liga, Michael V.; Li, Qilin; Barron, Andrew R.; Richard E. Smalley Institute for Nanoscale Science and Technology
A bi-functional nano-composite coating has been created on a porous Nomex fabric support as a trap for aspirated virus contaminated water. Nomex fabric was successively dip-coated in solutions containing cysteic acid functionalized alumina (alumoxane) nanoparticles and cysteic acid functionalized iron oxide (ferroxane) nanoparticles to form a nanoparticle coated Nomex (NPN) fabric. From SEM and EDX the nanoparticle coating of the Nomex fibers is uniform, continuous, and conformal. The NPN was used as a filter for aspirated bacteriophage MS2 viruses using end-on filtration. All measurements were repeated to give statistical reliability. The NPN fabrics show a large decrease as compared to Nomex alone or alumoxane coated Nomex . An increase in the ferroxane content results in an equivalent increase in virus retention. This suggests that it is the ferroxane that has an active role in deactivating and/or binding the virus. Heating the NPN to 160 C results in the loss of cysteic acid functional groups (without loss of the iron nanoparticleﾒs core structure) and the resulting fabric behaves similar to that of untreated Nomex , showing that the surface functionalization of the nanoparticles is vital for the surface collapse of aspirated water droplets and the absorption and immobilization of the MS2 viruses. Thus, for virus immobilization, it is not sufficient to have iron oxide nanoparticles per se, but the surface functionality of a nanoparticle is vitally important in ensuring efficacy.
An omnipresent diversity and variability in the chemical composition of atmospheric functionalized organic aerosol
(Springer Nature, 2018) Ditto, Jenna C.; Barnes, Emily B.; Khare, Peeyush; Takeuchi, Masayuki; Joo, Taekyu; Bui, Alexander A.T.; Lee-Taylor, Julia; Eris, Gamze; Chen, Yunle; Aumont, Bernard; Jimenez, Jose L.; Ng, Nga Lee; Griffin, Robert J.; Gentner, Drew R.
The atmospheric evolution of organic compounds encompasses many thousands of compounds with varying volatility, polarity, and water solubility. The molecular-level chemical composition of this mixture plays a major, yet uncertain, role in its transformations and impacts. Here we perform a non-targeted molecular-level intercomparison of functionalized organic aerosol from three diverse field sites and a chamber. Despite similar bulk composition, we report large molecular-level variability between multi-hour organic aerosol samples at each site, with 66 ± 13% of functionalized compounds differing between consecutive samples. Single precursor environmental laboratory chamber experiments and fully chemically-explicit modeling confirm this variability is due to changes in emitted precursors, chemical age, and/or oxidation conditions. These molecular-level results demonstrate greater compositional variability than is typically observed in less-speciated measurements, such as bulk elemental composition, which tend to show less daily variability. These observations should inform future field and laboratory studies, including assessments of the effects of variability on aerosol properties and ultimately the development of strategic organic aerosol parameterizations for air quality and climate models.
An analytical method for analyzing symmetry-breaking bifurcation and period-doubling bifurcation
(Elsevier, 2014) Zou, Keguan; Nagarajaiah, Satish
A new modification of homotopy analysis method (HAM) is proposed in this paper. The auxiliary differential operator is specifically chosen so that more than one secular term must be eliminated. The proposed method can capture asymmetric and period-2 solutions with satisfactory accuracy and hence can be used to predict symmetry-breaking and period-doubling bifurcation points. The variation of accuracy is investigated when different number of frequencies are considered.
Anthropogenic emissions of highly reactive volatile organic compounds in eastern Texas inferred from oversampling of satellite (OMI) measurements of HCHO columns
(IOP Publishing, 2014) Zhu, Lei; Jacob, Daniel J.; Mickley, Loretta J.; Marais, Eloïse A.; Cohan, Daniel S.; Yoshida, Yasuko; Duncan, Bryan N.; Abad, Gonzalo González; Chance, Kelly V.
Satellite observations of formaldehyde (HCHO) columns provide top-down constraints on emissions of highly reactive volatile organic compounds (HRVOCs). This approach has been used previously in the US to estimate isoprene emissions from vegetation, but application to anthropogenic emissions has been stymied by lack of a discernable HCHO signal. Here we show that temporal oversampling of HCHO data from the Ozone Monitoring Instrument (OMI) for 2005–2008 enables detection of urban and industrial plumes in eastern Texas including Houston, Port Arthur, and Dallas/Fort Worth. By spatially integrating the HCHO enhancement in the Houston plume observed by OMI we estimate an anthropogenic HCHO source of 250 ± 140 kmol h−1. This implies that anthropogenic HRVOC emissions in Houston are 4.8 ± 2.7 times higher than reported by the US Environmental Protection Agency inventory, and is consistent with field studies identifying large ethene and propene emissions from petrochemical industrial sources.
Application of a fully polynomial randomized approximation scheme (FPRAS) to infrastructure system reliability assessments
(8/6/2017) Fu, Bowen; Dueñas-Osorio, Leonardo
Networked systems make the reliability assessment of critical infrastructure computationally challenging given the combinatorial nature of system-level states. Several methods from numerical schemes to analytical approaches, such as Monte Carlo Simulation (MCS) and recursive decomposition algorithms (RDA), respectively, have been applied to this stochastic network problem. Despite progress over several decades, the problem remains open because of its intrinsic computational complexity. As the structural facilities of infrastructure systems continue to in terconnect in network forms, their study steers analysts to develop system reliability assessment methods based on graph theory and network science. A fully polynomial randomized approximation scheme (FPRAS) based on Karger’s graph contraction algorithm is an approximating method for reliability evaluation, which has a unique property rarely exploited in engineering reliability: that by performing a number of experiments in polynomial time (as a function of system size), it provides an a priori theoretical guarantee that the reliability estimate falls into the ϵ-neighborhood of its true value with (1−δ) confidence. We build upon the FPRAS ideas to develop an s-t reliability version that has practical appeal. Focusing on the relevant-cut enumeration stage of the FPRAS, we find correlations between the recurrence frequencies of links in minimum cuts within the randomization phase of the contraction algorithm, and typical network topological properties. We employ LASSO regression analysis to approximate the relationship between link recurrence frequencies and such topological metrics. With the topology-informed link recurrence frequencies, obtained at a much lower computational cost, we use a new biased contraction probability yielding 16.9% more distinct minimum cuts (MinCuts) than the original random contraction scheme. The biased contraction scheme proposed here can significantly improve the efficiency of reliability evaluation of networked infrastructure systems, while supporting infrastructure systems design, maintenance and restoration given its ability to offer error guarantees, which are ideal for future prescriptive guidelines in practice.

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