Highway increases concentrations of toxic metals in giant panda habitat

The Qinling panda subspecies (Ailuropoda melanoleuca qinlingensis) is highly endangered with fewer than 350 individuals inhabiting the Qinling Mountains. Previous studies have indicated that giant pandas are exposed to heavy metals, and a possible source is vehicle emission. The concentrations of Cu, Zn, Mn, Pb, Cr, Ni, Cd, Hg, and As in soil samples collected from sites along a major highway bisecting the panda's habitat were analyzed to investigate whether the highway was an important source of metal contamination. There were 11 sites along a 30-km stretch of the 108th National Highway, and at each site, soil samples were taken at four distances from the highway (0, 50, 100, and 300 m) and at three soil depths (0, 5, 10 cm). Concentrations of all metals except As exceeded background levels, and concentrations of Cu, Zn, Mn, Pb, and Cd decreased significantly with increasing distance from the highway. Geo-accumulation index indicated that topsoil next to the highway was moderately contaminated with Pb and Zn, whereas topsoil up to 300 m away from the highway was extremely contaminated with Cd. The potential ecological risk index demonstrated that this area was in a high degree of ecological hazards, which were also due to serious Cd contamination. And, the hazard quotient indicated that Cd, Pb, and Mn especially Cd could pose the health risk to giant pandas. Multivariate analyses demonstrated that the highway was the main source of Cd, Pb, and Zn and also put some influence on Mn. The study has confirmed that traffic does contaminate roadside soils and poses a potential threat to the health of pandas. This should not be ignored when the conservation and management of pandas is considered

Experimental and kinetic modeling study of the CH4+H2S+air laminar burning velocities at atmospheric pressure

With the increasing demand for natural gas and depletion of many sweet gas fields, direct usage of sour gas, usually containing a large percentage of hydrogen sulfide (H2S), becomes a more economical choice in recent years. However, the laminar burning velocity (SL) of CH4+H2S flames have seldom been investigated due to the corrosivity and toxicity of H2S, and no available experimental data can be found for these mixtures burnt in the air. In this work, the laminar burning velocities of CH4+H2S+air flames were measured using the heat flux method at 1 atm and 298 K. The experimental data were obtained at various equivalence ratios and xH2S = 0–0.25, where xH2S refers to the mole fraction of H2S in the fuel. Simulations using a detailed mechanism of Mulvihill et al. (2019) were carried out, showing good agreement with the present experimental results. Kinetic analyses of A-factor SL reaction sensitivities, reaction pathways, and dominant intermediate species pointed out the importance of the C- and S-containing species interactions. To overcome the convergence problem of the Mulvihill mechanism, an examination of the unphysical reactions and species was carried out, which could be alleviated by making several reactions that violate the collision limit irreversible, accompanied by updating the heat capacity data. It's also found that substituting the hydrocarbon subset of the Mulvihill mechanism with mechanisms from FFCM-1, Konnov, San Diego, as well as Aramco noticeably deteriorates the simulation results due to the selection of different reaction rate constants

NQO-Induced DNA-Less Cell Formation Is Associated with Chromatin Protein Degradation and Dependent on A0A1-ATPase in Sulfolobus

To investigate DNA damage response in the model crenarchaeon Sulfolobus islandicus, four different DNA damage agents were tested for their effects on cell death of this archaeon, including UV irradiation, methyl methanesulfonate, cisplatin, and 4-nitroquinoline 1-oxide (NQO). Cell death featured with DNA-less cell formation was revealed in DNA damage treatment with each agent. Cellular responses upon NQO treatment were characterized in details, and following sequential events were revealed, including: a modest accumulation of G1/S phase cells, membrane depolarization, proteolytic degradation of chromatin proteins, and chromosomal DNA degradation. Further insights into the process were gained from studying drugs that affect the archaeal ATP synthase, including a proton gradient uncoupler and an ATP synthase inhibitor. Whereas the proton uncoupler-mediated excess proton influx yielded cell death as observed for the NQO treatment, inhibition of ATP synthase attenuated NQO-induced membrane depolarization and DNA-less cell formation. In conclusion, the NQO-induced cell death in S. islandicus is characterized by proteolytic degradation of chromatin protein, and chromosomal DNA degradation, which probably represents a common feature for the cell death induced by different DNA damage agents

Study on Temperature-Dependent Uniaxial Tensile Tests and Constitutive Relationship of Modified Polyurethane Concrete

Modified polyurethane concrete (MPUC) is a new material for steel deck pavements. In service, the pavement is often cracked due to excessive tensile stress caused by temperature changes. In order to study the tensile properties of MPUC in the diurnal temperature range of steel decks, uniaxial tensile tests of MPUC were carried out at five temperatures. Three kinds of specimens and a novel fixture were designed and fabricated to compare the results of four different tensile test methods. The deformation of the specimen was collected synchronously by two methods: pasting strain gauge and digital image correlation (DIC) technique. Based on the experiment, the tensile mechanical properties, failure modes, and constitutive relations of MPUC were studied under the effect of temperature. The research results show that the novel fixture can avoid stress concentration. By observing the fracture surface of the specimens, the bonding performance is great between the binder and the aggregate at different temperatures. The tensile strength and elastic modulus of MPUC decrease with increasing temperatures, while the fracture strain, and fracture energy increase with increasing temperatures. The formulas of temperature-dependent tensile strength, fracture strain, and elastic modulus of MPUC were established, and the constitutive relationship of MPUC is further constructed in the rising stage under uniaxial tension. The calculation results show good agreement with experimental ones

Effect of H2 and O2 enrichment on the laminar burning velocities of NH3+H2+N2+O2 flames: Experimental and kinetic study

Ammonia (NH3) has gained broad attention as a carbon-free alternative fuel, and its blend with H2 has been especially investigated to mediate the low reactivity of NH3. In the present work, the laminar burning velocities (SL) of NH3+H2+N2+O2 flames were investigated at 1 atm and 298 K, and the oxygen fractions (xO2) in O2+N2 were varied from 0.16 to 0.26, comprising a set of conditions that have not yet been investigated in literature. An updated mechanism was proposed on the basis of our previous published mechanism, which was validated using not only the present data, but also the literature data for NH3 laminar burning velocities and ignition delay times. Over the tested experimental conditions, better predictions were achieved with the updated mechanism. Simulations using the updated and five literature mechanisms were carried out, i.e., mechanisms from Stagni, Bertolino, Shrestha, Konnov, and Mei. The updated and Mei mechanisms reproduce the best the present experimental data. To investigate which reactions influence most the SL increments due to O2 and H2 addition, SL increment parameters were defined for xO2 and xH2 separately. Based on the available experimental data, detailed sensitivity analyses were carried out for these target parameters using the updated and some other mechanisms from the literature. It's found that reactions dominating these parameters could be largely different, thus considerations covering all aspects of SL as well as the SL increment parameters are suggested for the NH3 mechanism validations. Despite the SL increment parameters have different tendencies against the xO2 and xH2 with different reaction sensitivities, local similarities are found if the increments of xO2 and xH2 have been enough refined. Specifically, when the xO2 and xH2 values grow larger, the effects of their increase become well blurred, extending the region of the similar conditions, which is helpful for the determination of inconsistent experimental data

The temperature dependence of the laminar burning velocity and superadiabatic flame temperature phenomenon for NH3/air flames

Combustion of ammonia (NH3) as a carbon-free alternative fuel has been recently widely studied, with vast majority of the burning velocity data obtained at room temperature. In the present study, the laminar burning velocity SL of NH3/air mixtures has been measured at unburnt gas temperature Tu from 298 K to 448 K, covering equivalence ratios from 0.85 to 1.25 and at 1 atm using the heat flux method. Kinetic simulations were made with five literature mechanisms developed for NH3 combustion, i.e., Nakamura et al., Otomo et al., San Diego, Okafor et al., and Mei et al. mechanisms, and the influence of radiation heat losses was considered. Using the obtained burning velocity data at different temperatures, the temperature dependence coefficients α in [Formula presented] were derived, and compared with different models’ predictions. Further analyses of the temperature dependence of SL were carried out through examination of the overall activation energy, temperature and species profiles as well as the reaction paths, and a unique flame structure at the rich side of adiabatic NH3/air flames was found, which resembles ‘over-rich’ phenomena in hydrocarbon flames. At equivalence ratio larger than 1.1 ± 0.05, the NH3/air flames become so rich that (1) the NH2 radical overwhelms the H and OH radicals in maximum mole fraction; (2) after the flame front, H2O converts back to H2 with NO formed at the same time, causing the superadiabatic flame temperature phenomena, i.e. adiabatic flame temperature being lower than the maximum achieved in the flame. Moreover, local minimum NO concentration is found right after the over-rich NH3/air flame front, which may be helpful in reducing NO emissions from NH3 flames in practical applications

Over-rich combustion of CH4, C2H6, and C3H8 +air premixed flames investigated by the heat flux method and kinetic modeling

An uncommon non-monotonic behavior of the temperature dependence of adiabatic laminar burning velocity has been found in over-rich methane+air flames at equivalence ratio, ϕ = 1.4. To find out the universality and reasons of this turning point, methane, ethane and propane + air flames are studied both experimentally by the heat flux method and numerically using GRI-mech, USC-mech, UCSD-mech, FFCM mech, and Aramco mech over ϕ = 0.6–1.8, at unburned temperatures up to 368 K, and atmospheric pressure. Results show that the over-rich phenomena stem from a unique flame structure, where, after the flame front, H2O is reduced to H2 and C2Hx (x>1) is oxidized to CO, causing the temperature overtone (super adiabatic flame temperature), while some key reactions important for flame propagation changing their sensitivity signs. Inside the flame front, the importance of CH3 overwhelms other radicals like OH and H. By these distinguishing features, a method using temperature overtone to identify accurate turning points of over-rich regime is demonstrated

Uniqueness and similarity in flame propagation of pre-dissociated NH3 + air and NH3 + H2 + air mixtures : An experimental and modelling study

Ammonia (NH3) has attracted significant attention as a promising hydrogen carrier and a carbon-free alternative fuel. Partial dissociation could convert part of ammonia to H2 and N2 before injecting the fuel into a combustor, thus overcoming the low reactivity and high NOx emission problems during the NH3 combustion. The pre-dissociated NH3 + air mixture has unburnt species NH3, H2, O2, and N2, the same as more widely investigated NH3 + H2 + air flames, while similarities or differences between these two types of flames have not yet been investigated. In the present work, the laminar burning velocities of pre-dissociated NH3 + air flames at 1 atm and an initial temperature of 298 K have been measured and compared to the scarce data from the literature. Experiments were carried out using the heat flux method at varied dissociation ratio γ and equivalence ratio ϕ. Kinetic simulations were also performed using six recently published or updated mechanisms, while none of the tested mechanisms can accurately reproduce the present results for the pre-dissociated NH3 + air flames over the whole range of the covered conditions, even for those predicting well the NH3 + H2 + air flames. To understand this deficiency, flame temperatures for the two fuel systems were examined, as well as in-depth sensitivity analyses were carried out. Similar conditions between the pre-dissociated NH3 + air and the NH3 + H2 + air flames were found, and a new approach to identifying inconsistent experimental data obtained using the same experimental setup was also suggested and discussed