Spontaneous ignition of pressurized hydrogen release through a tube into air is investigated using a modified version of the KIVA-3V CFD code. A mixture-averaged multi-component approach is used for accurate calculation of molecular transport. Autoignition and combustion chemistry is accounted for using a 21 step kinetic scheme. Ultra fine meshes are employed along with the Arbitrary Lagrangia–Eulerian (ALE) method to reduce false numerical diffusion. The study has demonstrated a possible mechanism for spontaneous ignition through molecular diffusion.
In the simulated scenario, the tube provided additional time to achieve a combustible mixture at the hydrogen–air contact surface. When the tube was sufficiently long under certain release pressure, autoignition would initiate inside the tube at the contact surface due to mass and energy exchange between low temperature hydrogen and shock-heated air through molecular diffusion. Following further development of the hydrogen jet downstream, the contact surface became distorted. Turbulence plays an important role for hydrogen/air mixing in the immediate vicinity of this distorted contact surface and led the initial laminar flame to transit into a stable turbulent flame. 相似文献
It is often necessary to estimate the weight that an individual may be capable of gaining depending on its degree of activity. A simple individual-based model was developed for studying the dynamics of weight in terms of daily behavior and ingestion rate. It was based on the balance between the individual's energy intake and the cost of its daily activities. Costs depend on the weight of the individual and the photoperiod, as well as on the time spent on each activity. Different combinations of ingestion rate, individual's weight, photoperiod length, and time assigned to different activities were used for simulating the weight dynamics, taking the species Rhea americana as a study case. Estimations of energetic costs of the activities were obtained from specialized literature. Using different photoperiods and individual behaviors, the model yields field metabolic rate (FMR) values in agreement with those obtained from direct measurements for other omnivorous bird species. 相似文献
Coagulation is the best available method for removing intracellular organic matter (IOM), which is released from algae cells and is an important precursor to disinfection by-products in drinking water treatment. To gain insight into the best strategy to optimize IOM removal, the coagulation performance of two Al salts, i.e., aluminum chloride (AlCl3) and polyaluminum chloride (PACl, containing 81.2% Al13), was investigated to illuminate the effect of Al species distribution on IOM removal. PACl showed better removal efficiency than AlCl3 with regard to the removal of turbidity and dissolved organic carbon (DOC), owing to the higher charge neutralization effect and greater stability of pre-formed Al13 species. High pressure size exclusion chromatography analysis indicated that the superiority of PACl in DOC removal could be ascribed to the higher binding affinity between Al13 polymer and the low and medium molecular weight (MW) fractions of IOM. The results of differential log-transformed absorbance at 254 and 350?nm indicated more significant formation of complexes between AlCl3 and IOM, which benefits the removal of tryptophan-like proteins thereafter. Additionally, PACl showed more significant superiority compared to AlCl3 in the removal of < 5?kDa and hydrophilic fractions, which are widely viewed as the most difficult to remove by coagulation. This study provides insight into the interactions between Al species and IOM, and advances the optimization of coagulation for the removal of IOM in eutrophic water. 相似文献
In a variety of fish species with paternal care of offspring, females prefer to spawn in nests that already contain eggs.
This female preference has been hypothesized to explain egg thievery in male sticklebacks, allopaternal care of eggs in minnows,
and the evolution of egg-mimicking body features in male cichlids and darters. Here we employ microsatellite-based parentage
analyses to evaluate the reproductive success of striped darter (Etheostoma virgatum) males that appear to utilize two of these functionally related tactics to entice females to spawn in their nests. In an
isolated population (Clear Creek, Ky.), we observed that breeding males develop conspicuous white spots on their pectoral
fins. If these spots are egg mimics, as we suspect, then this represents the fourth independent evolutionary origin of egg
mimicry documented to date in darters, the first based on pigmentation (as opposed to physical structures), and the first
in which the egg mimics vary greatly in number among males. From direct counts of microsatellite genotypes in clutches of
embryos, at least 3.8 females contributed to the progeny within a typical nest, and females tended to spawn preferentially
with males that were larger and displayed more egg-mimic spots. In another population (Hurricane Creek, Tenn.) without egg
mimics, the multi-locus genetic data document that allopaternal care is common, especially among the smallest males who sometimes
tend nests containing their own as well as an earlier sire's offspring. Thus, these foster males had adopted egg-containing
nests and then successfully spawned with subsequent females. Overall, the genetic data on paternity and maternity, in conjunction
with field observations, suggest that egg mimicry and allopaternal care are two mate-attracting reproductive tactics employed
by striped darter males to exploit female preferences for spawning in nests with 'eggs'.
Electronic Publication 相似文献
Soil and sediment play a crucial role in the fate and transport of perfluorooctane sulfonate (PFOS) in the environment. However, the molecular mechanisms of major soil/sediment components on PFOS adsorption remain unclear. This study experimentally isolated three major components in soil/sediment: humin/kerogen, humic/fulvic acid (HA/FA), and inorganic component after removing organics, and explored their contributions to PFOS adsorption using batch adsorption experiments and molecular dynamic simulations. The results suggest that the humin/kerogen component dominated the PFOS adsorption due to its aliphatic featureswhere hydrophobic effect and phase transfer are the primary adsorptionmechanism. Compared with the humin/kerogen, the HA/FA component contributed less to the PFOS adsorption because of its hydrophilic and polar characteristics. The electrostatic repulsion between the polar groups of HA/FA and PFOS anions was attributable to the reduced PFOS adsorption.When the soil organicmatterwas extracted, the inorganic component also plays a non-negligible role because PFOS molecules might form surface complexes on SiO2 surface. The findings obtained in this study illustrate the contribution of organic matters in soils and sediments to PFOS adsorption and provided newperspective to understanding the adsorption process of PFOS on micro-interface in the environment. 相似文献
This work provides insights on the solubilization products after a simultaneous combination of alkaline and ultrasonic(ALK + ULS) pre-treatment of sewage sludge.Soluble chemical oxygen demand(SCOD) increased from 1200 to 11,000 mg/L after such treatment. Organics with molecular weight around 5.6 k Da were solubilized because of the synergistic effect of ultrasound and alkali. Organics with molecular weight larger than300 k Da increased from 7.8% to 60%, 16% and 42.3% after ULS, ALK and ALK + ULS treatment, respectively. Excitation emission matrix fluorescence spectroscopy analysis identified soluble microbial product-like and humic acid-like matters as the main solubilization products. Sludge anaerobic biodegradability was significantly enhanced with the simultaneous application of ALK + ULS pre-treatment. ALK + ULS pre-treatment resulted in 37.8% biodegradability increase compared to the untreated sludge. This value was higher compared to the biodegradability increase induced by individual ALK pre-treatment(5.7%) or individual ULS pre-treatment(20.7%) under the same conditions applied. 相似文献
Soil and sediment play a crucial role in the fate and transport of perfluorooctane sulfonate(PFOS) in the environment. However, the molecular mechanisms of major soil/sediment components on PFOS adsorption remain unclear. This study experimentally isolated three major components in soil/sediment: humin/kerogen, humic/fulvic acid(HA/FA), and inorganic component after removing organics, and explored their contributions to PFOS adsorption using batch adsorption experiments and molecular dynamic simulations. The results suggest that the humin/kerogen component dominated the PFOS adsorption due to its aliphatic features where hydrophobic effect and phase transfer are the primary adsorption mechanism.Compared with the humin/kerogen, the HA/FA component contributed less to the PFOS adsorption because of its hydrophilic and polar characteristics. The electrostatic repulsion between the polar groups of HA/FA and PFOS anions was attributable to the reduced PFOS adsorption. When the soil organic matter was extracted, the inorganic component also plays a non-negligible role because PFOS molecules might form surface complexes on SiO 2surface.The findings obtained in this study illustrate the contribution of organic matters in soils and sediments to PFOS adsorption and provided new perspective to understanding the adsorption process of PFOS on micro-interface in the environment. 相似文献