Dynamic resource management under the risk of regime shifts

This paper provides a framework through which a dynamic resource management problem with potential regime shifts can be analyzed both in a strategic environment and from a social planner?s perspective. Based on a fairly general model, a condition for a precautionary policy is discussed. By applying the framework to a common-property resource problem with a linear production technology, we illustrate how the qualitative as well as quantitative nature of equilibrium is altered due to the possibility of regime shifts. In particular, when the risk is endogenously affected by the players? behavior, potential regime shifts can facilitate the precautionary management of resources as long as the resource stock is in good shape. As the stock of resource becomes scarce, however, the precautionary effect vanishes and more aggressive resource exploitation emerges. The impacts of irreversibility on the equilibrium behavior are highlighted. It is also shown that there can exist a resource-depletion trap in which a regime shift, once it happens, triggers a continuous decline of resource stock no matter which regime materializes in the subsequent periods.     

Photodegradation of Poly(lactic acid) Stereocomplex by UV-Irradiation

Neat poly(l-lactic acid) (PLLA) and poly(d-lactic acid) (PDLA) films and PLLA/PDLA blend films were prepared by solution casting, and their photodegradation by UV-irradiation was investigated using wide-angle X-ray scattering (WAXS), gel permeation chromatography, differential scanning calorimetry, tensile testing, and polarized optical microscopy. The PLLA/PDLA blend film was more photodegradation-resistant than the neat PLLA and PDLA films when photodegradation was monitored by molecular weight, melting temperature, and WAXS crystalline peak positions. This indicates that the chains in both amorphous and crystalline regions of the PLLA/PDLA blend film were photo-cleavage-resistant compared to those of the neat PLLA and PDLA films. The changes in melting temperature and WAXS crystalline peak positions before and after photodegradation respectively indicated the increased crystalline lattice disorder and the decreased crystalline lattice sizes of the neat PLLA and PDLA films, whereas these changes were insignificant for the blend films. Photodegradation caused no significant change in tensile properties, with the exception of significant decreases in the tensile strength and elongation at break of PLLA/PDLA blend film. However, the tensile strength and elongation at break of the PLLA/PDLA blend film retained higher values compared to those of the neat PLLA and PDLA films during photodegradation. In spite of the slower photodegradation of the PLLA/PDLA blend film traced by M _n, T _m, and WAXS crystalline peak positions than that of neat PLLA and PDLA films, the rapid decrease in tensile strength and elongation at break of the former than that of the latter should be due to the highly-ordered structural difference between them, i.e., the three dimensional dry gel of the former and the spherulites of the latter.     

Determination of dissolved oxygen limitation in aerobic biofilm reactors

The concentration of dissolved oxygen (DO) strongly influences the performance of aerobic biofilm reactors because organic oxidation is limited by the availability of oxygen. However, it is not necessary to maintain a high DO level in the reactors in order to overcome this limitation. Excessive aeration wastes energy. Therefore, the determination of the onset of DO limitation against organic substrate removal in aerobic biofilm reactors is important for their effective operation. This study is aimed at developing an expression to determine the onset of DO limitation and hence to control the aeration system. The expression developed is as follows: , where S_b and C_b are the bulk concentrations of organic substrate and DO, respectively; D_ws and D_wc are the diffusion coefficients of organic substrate and oxygen in the reactors respectively; and R_b is an overall ratio of oxygen consumption to organic substrate removal in the reactors. The latter is the key parameter in the equation, and is determined by the characteristics of the substrate, biofilm, and reactor. In order to measure the value of R_b, the authors have developed a micro-biofilm reactor. The value of R_b was determined to be 0.13 (mg O₂ mg⁻¹ COD_cr) for glucose removal with this reactor. The equation has, subsequently, been verified with data from batch and continuous experiments.     

Impact of fermented brown rice with Aspergillus oryzae (FEBRA) intake and concentrations of polybrominated diphenylethers (PBDEs) in blood of humans from Japan

The isotope dilution technique was applied for the analysis of new polybrominated diphenylethers (PBDEs) calibration standard (both labeled and non-labeled) using high-resolution gas chromatography-high-resolution mass spectrometry (HRGC-HRMS). The relative response factor (RRF) and relative standard deviation (RSD) for new calibration standard in Finnigan Thermo Electron (MAT-95XL) and Micromass (Autospec Ultima) were more or less identical with mean RRF (0.9882), RSD (0.0865) and CV% of (8.75). The results also revealed for DeBDE-209 quantification; labeled DeBDE-209 is essential. Furthermore, we recommend on column injection technique with a thin film instead of splitless injection in order to reduce the thermal degradation of DeBDE-209 and formation of octabromodibenzofurans (OBDF). Besides, analysis of human blood (n = 156) of FEBRA-intake and non-FEBRA-intake individuals elucidated frequent detection of eighteen PBDE congeners. The average PBDE concentrations in non-FEBRA intake and FEBRA-intake humans were 6000-11,000 (mean: 8400) and 5400-15,000 (mean: 9900) respectively on pg/g fat basis. Although FEBRA-intake individuals showed slightly greater PBDEs, computer-normalized concentrations of TeBDE-47 corroborate FEBRA-intake individual from four family showed reduced concentrations. The contamination profiles of PBDEs varied in between family, gender as well as geography. International comparison with predominant PBDE congener (TeBDE-47) prevailed lower levels in Japan when compared to Korea, Germany and USA nevertheless, congener specific profiles were different which is in accordance with different technical PBDE usage in between countries.     

Synergy of ozonation and photocatalysis to mineralize low concentration 2,4-dichlorophenoxyacetic acid in aqueous solution

Concentration of 2,4-dichlorophenoxyacetic acid (2,4-D) may affect its degradation kinetics in advanced oxidation systems, and combinations of two or more systems can be more effective for its mineralization at low concentration levels. Degradations and mineralizations of 0.045mM 2,4-D using O(3), O(3)/UV, UV/TiO(2) and O(3)/UV/TiO(2) systems were compared, and influence of reaction temperature on the mineralization in O(3)/UV/TiO(2) system was investigated. 2,4-D degradations by O(3), O(3)/UV and UV/TiO(2) systems were similar to the results of earlier investigations with higher 2,4-D concentrations. The degradations and total organic carbon (TOC) removals in the four systems were well described by the first-order reaction kinetics. The degradation and removal were greatly enhanced in O(3)/UV/TiO(2) system, and further enhancements were observed with larger O(3) supplies. The enhancements were attributed to hydroxyl radical (()OH) generation from more than one reaction pathway. The degradation and removal in O(3)/UV/TiO(2) system were very efficient with reaction temperature fixed at 20 degrees C. It was suspected that reaction temperature might have influenced ()OH generation in the system, which needs further attention.     

Evaluation of light-duty vehicle mobile source regulations on ozone concentration trends in 2018 and 2030 in the western and eastern United States

To improve U.S. air quality, there are many regulations on-the-way (OTW) and on-the-books (OTB), including mobile source California Low Emission Vehicle third generation (LEV III) and federal Tier 3 standards. This study explores the effects of those regulations by using the U.S. Environmental Protection Agency's (EPA) Community Multiscale Air Quality (CMAQ) model for 8-hr ozone concentrations in the western and eastern United States in the years 2018 and 2030 during a month with typical high ozone concentrations, July. Alterations in pollutant emissions can be due to technological improvements, regulatory amendments, and changes in growth. In order to project emission rates for future years, the impacts of all of these factors were estimated. This study emphasizes the potential light-duty vehicle emission changes by year to predict ozone levels. The results of this study show that most areas have decreases in 8-hr ozone concentrations in the year 2030, although there are some areas with increased concentrations. Additionally, there are areas with 8-hr ozone concentrations greater than the current U.S. National Ambient Air Quality Standard level, which is 75 ppb.

Implications:

To improve U.S. air quality, many regulations are on the way and on the books, including mobile source California LEV III and federal Tier 3 standards. This study explores the effects of those regulations for 8-hr ozone concentrations in the western and eastern United States in the years 2018 and 2030. The results of this study show that most areas have decreases in 8-hr ozone concentrations in 2030, although there are some areas with increased concentrations. Additionally, there are areas with 8-hr ozone concentrations greater than the current U.S. National Ambient Air Quality Standard level.     

Abundances, distribution, and sources of trace metals in Nakaumi–Honjo coastal lagoon sediments, Japan

Bottom sediments from Nakaumi Lagoon and the Honjo Area in southwest Japan were analyzed to determine their geochemical compositions and to assess potential impacts by comparison with sediment quality guidelines. Present-day water quality was also assessed. Results showed that the water quality of Nakaumi Lagoon and the Honjo area contrasts between their upper and lower parts. Average abundances of As, Pb, Zn, Cu, Ni, and Cr in the Nakaumi sediments were 12, 25, 135, 32, 21, and 46 ppm, respectively, compared to 10, 24, 110, 26, 20, and 38 ppm in the Honjo area. All averages are greater than those of the upper continental crust. The elevated metal concentrations are probably related to the fine-grained nature of the sediments, reducing bottom conditions produced by abundant organic matter and possibly minor non-point anthropogenic sources. Trace metal contents are strongly correlated with Fe₂O₃, suggesting that Fe oxides play a role in controlling abundances. Metal concentrations exceed the NYSDEC lowest effect level and CCME interim sediment quality guidelines that indicate moderate impact on aquatic organisms. Average abundances of As and Zn are comparable to the Coastal Ocean Sediment Database threshold, whereas maximum concentrations exceed that value, indicating that the concentrations of these metals are potentially toxic. These enrichments suggest that regular monitoring may be desirable even where no point sources of metal pollution exist.     

The arrival and discharge of conjugated estrogens from a range of different sewage treatment plants in the UK

The occurrence of free and conjugated estrogens was examined in a survey of eleven sewage treatment plants (STPs) and their discharge water in the United Kingdom using grab sampling. The STPs included trickling filter with and without tertiary treatment, and activated sludge with tertiary treatment. For three activated sludge plants both influent and effluent samples were compared. For a further 8 STPs only the effluent was examined. The estrone-3-sulphate, estradiol-3-sulphate and estriol-3-sulphate concentrations (up to 20 ng L⁻¹) were typically 5-fold that of the respective free estrogen concentration in the effluents. This represents a substantial additional ‘potential’ estrogen load arriving in the receiving waters. Estrone-3-glucuronide was found at 9 ng L⁻¹, estradiol-3-glucuronide at 7 ng L⁻¹, and estriol-3-glucuronide at 32 ng L⁻¹ in sewage influent. Except on one occasion, no glucuronide conjugates could be found in the effluent. The results suggest in most cases glucuronide conjugates will be completely transformed in sewage treatment whilst sulphate conjugates will only be partially removed.     

Numerical investigation for pressure mitigation effects of dike on blast wave

The three-dimensional and two-dimensional axisymmetric fluid dynamics simulations were carried out to clarify the blast pressure mitigating effects of dike’s configuration in hemispherical explosion. The simulated peak overpressure on the ground under the hemispherical explosion was compared with the empirical formula by Kingery, and the simulated data were validated. In the analysis, the simplification techniques for the numerical simulation were employed under the following two assumptions. The pressure distribution behind the wide dike was estimated using the axisymmetric flowfield, and the back step model was applied under the small condition for θ, the angle formed by the ground and the line between the explosion core and the dike front corner. From the simulated results, it is clarified that the large θ provided the great reduction of the blast wave pressure at faraway position. In the small θ condition, the conditions of the dike end position and the dike height were significant parameters determining the magnitude of pressure reduction and mitigated area. The pressure reduction at the dike end and mitigated area were predicted numerically, and related to the dike conditions.     

Roadside nanoparticles corresponding to vehicle emissions during one signal cycle

The behavior of nanoparticles (NPs) in the roadside atmosphere has not been clarified because it involves unstable volatile components. It was thought that the number concentration (NC) and NP size distribution change due to variations in traffic conditions (e.g., traffic volume [TV], velocity, acceleration, etc.) near the intersection, but the SMPS (Scanning Mobility Particle Sizer) lacks the temporal resolution required for rapid, transient measurements. Using a fast-response aerosol spectrometer capable of providing near-instantaneous particle NC measurements in real time, the behavior of NPs during one signal cycle became clear, and it was understood that the effect of condensation/evaporation processes is important, in addition to coagulation. As for the relation of the NC in proportion to the TV, this did not show a constant line but rather a hysteresis curve during the signal cycle, because the gas-particle equilibrium state at the roadside atmosphere was variable. Using two points of simultaneous measurement and on-board measurement, the behavior of NPs could be confirmed in response to the characteristics of automotive exhaust, which varied due to the on-road driving state, engine conditions, vehicle position, or traffic light timing, at the intersection. The on-board measurement of NP size distribution in the exhaust plume from a diesel vehicle was carried out as a reference for direct particle emissions, compared with the roadside NPs. The coagulation/deposition model simulation using the direct particle emissions underestimated the NCs compared with the observed values. The gas-particle equilibrium model could explain the underestimated portion caused by the condensation of ambient VOC (Volatile Organic Compounds) onto the particles. If this hypothesis is correct, the condensable VOC amount in the roadside atmosphere is suggested to be very large.