7,068 research outputs found
Stability of mud-water interface under long surface waves
No full textFluid mud often exists in coastal areas with an interface separating it from its upper water layer. When a surface wave propagates over a bed covered with water and fluid mud, it will cause an interfacial wave of the mud-water interface, which damps the surface wave and results in mass transport of fluid mud. Most researches about wave attenuation and mass transport of fluid mud are based on the assumption that the mud-water interface is unbroken. This assumption excludes the breaking interfacial waves that are known as an important mechanism responsible for mass and momentum transport between the two fluids. When the surface wave is long, its velocity field, which also serves as basic flows, may be susceptible to the Kelvin-Helmholtz (K-H) instability if the shears at the interface are strong enough. In the present paper, the critical conditions for the K-H instability to occur for the mud-water interface is investigated via linear stability analysis and numerical simulation. It is found that, for a K-H instability to occur, the Stokes boundary layer thickness induced by a surface wave must be large enough to penetrate the fluid mud layer and produce a strong shear at the interface. Meanwhile, a critical condition is found for a long surface wave to cause breakup of mud-water interface through K-H instability. This is practically instructive for waterway and harbor construction and protection because it predicts that a thicker mud layer is harder to be taken away by a surface wave. (C) 2019 Author(s).</p
A Petri-net approach for firefighting force allocation analysis of fire emergency response with backups
No full textAbstract: Fire is one of the main accident scenarios occurring in chemical and process plants, and it can lead to domino effects due to thermal radiation. Emergency response is necessary to prevent fire escalation, in addition to safety barriers. In major industrial fire accidents, backup is usually required in emergency response, due to the lack of emergency response capacity of a single emergency response department. A method addressing the optimal allocation of emergency response forces, specifically considering the front-line departments, is developed in the present study. The emergency response of the front-line departments can reduce the thermal radiation received by the equipment adjacent to the primary fire and thus prolong the time to failure of the equipment, such that the backups have more time to get to the fire scene. The allocation analysis of emergency response teams is carried out considering the dynamic ttf of an adjacent equipment item resulting from the change in time of the thermal radiation received. A timed colored hybrid Petri-net (TCHPN) approach is proposed to model the emergency response process. The probability of preventing fire escalation is obtained from the TCHPN model and the optimal allocation of firefighting forces is determined. A case study illustrates the proposed approach, two scenarios are compared and results show that if a request for backup can be issued immediately according to the fire state, fewer emergency forces can be deployed on the front line department, such as the reduction from 6 emergency response teams to 3 teams to maintain the success probability of 0.91. The influence of other factors such as the position of fire departments and the layout of tanks on the allocation of emergency forces is also discussed
FTIR-ATR-based prediction and modelling of lignin and energy contents reveals independent intra-specific variation of these traits in bioenergy poplar
No full textBackground: there is an increasing demand for renewable resources to replace fossil fuels. However, different applications such as the production of secondary biofuels or combustion for energy production require different wood properties. Therefore, high-throughput methods are needed for rapid screening of wood in large scale samples, e.g., to evaluate the outcome of tree breeding or genetic engineering. In this study, we investigated the intra-specific variability of lignin and energy contents in extractive-free wood of hybrid poplar progenies (Populus trichocarpa × deltoides) and tested if the range was sufficient for the development of quantitative prediction models based on Fourier transform infrared spectroscopy (FTIR). Since lignin is a major energy-bearing compound, we expected that the energy content of wood would be positively correlated with the lignin content.Results: lignin contents of extractive-free poplar wood samples determined by the acetyl bromide method ranged from 23.4% to 32.1%, and the calorific values measured with a combustion calorimeter varied from 17260 to 19767 J g-1. For the development of calibration models partial least square regression and cross validation was applied to correlate FTIR spectra determined with an attenuated total reflectance (ATR) unit to measured values of lignin or energy contents. The best models with high coefficients of determination (R2 (calibration) = 0.91 and 0.90; R2 (cross-validation) = 0.81 and 0.79) and low root mean square errors of cross validation (RMSECV = 0.77% and 62 J g-1) for lignin and energy determination, respectively, were obtained after data pre-processing and automatic wavenumber restriction. The calibration models were validated by analyses of independent sets of wood samples yielding R2 = 0.88 and 0.86 for lignin and energy contents, respectively.Conclusions: these results show that FTIR-ATR spectroscopy is suitable as a high-throughput method for lignin and energy estimations in large data sets. Our study revealed that the intra-specific variations in lignin and energy contents were unrelated to each other and that the lignin content, therefore, was no predictor of the energy content. Employing principle component analyses we showed that factor loadings for the energy content were mainly associated with carbohydrate ring vibrations, whereas those for lignin were mainly related to aromatic compounds. Therefore, our analysis suggests that it may be possible to optimize the energy content of trees without concomitant increase in ligni
A novel AML1-ETO/FTO positive feedback loop promotes leukemogenesis and Ara-C resistance via stabilizing IGFBP2 in t(8;21) acute myeloid leukemia
No full textBackground t(8;21)(q22;q22) is one of the most frequent chromosomal abnormalities in acute myeloid leukemia (AML), leading to the generation of the fusion protein AML1-ETO. Despite t(8;21) AML being considered as a subtype with a favorable prognosis, approximately 30-50% of patients experience drug resistance and subsequent relapse. N-6-methyladenosine (m(6)A) is demonstrated to be involved in the development of AML. However, the regulatory mechanisms between AML1-ETO and m(6)A-related enzymes and the roles of dysregulated m(6)A modifications in the t(8;21)-leukemogenesis and chemoresistance remain elusive. Methods Chromatin immunoprecipitation, dual-luciferase reporter assay, m(6)A-qPCR, RNA immunoprecipitation, and RNA stability assay were used to investigate a regulatory loop between AML1-ETO and FTO, an m(6)A demethylase. Gain- and loss-of-function experiments both in vitro and in vivo were further performed. Transcriptome-wide RNA sequencing and m(6)A sequencing were conducted to identify the potential targets of FTO. Results Here we show that FTO is highly expressed in t(8;21) AML, especially in patients with primary refractory disease. The expression of FTO is positively correlated with AML1-ETO, which is attributed to a positive regulatory loop between the AML1-ETO and FTO. Mechanistically, AML1-ETO upregulates FTO expression through inhibiting the transcriptional repression of FTO mediated by PU.1. Meanwhile, FTO promotes the expression of AML1-ETO by inhibiting YTHDF2-mediated AML1-ETO mRNA decay. Inactivation of FTO significantly suppresses cell proliferation, promotes cell differentiation and renders resistant t(8;21) AML cells sensitive to Ara-C. FTO exerts functions by regulating its mRNA targets, especially IGFBP2, in an m(6)A-dependent manner. Regain of Ara-C tolerance is observed when IGFBP2 is overexpressed in FTO-knockdown t(8;21) AML cells. Conclusion Our work reveals a therapeutic potential of targeting AML1-ETO/FTO/IGFBP2 minicircuitry in the treatment for t(8;21) patients with resistance to Ara-C
Unsteady characteristics of sediment transport under non-harmonic waves
No full textSediment transport under waves is one of the key dynamic processes of coastal sediment motion. Previous studies for this issue are mainly based on linear wave theory and quasi-steady simplification. However, waves in real circumstance are always irregular, generally with a certain degree of asymmetry and/or velocity-leaning especially in shallow water. It is envisaged that sediment movement under non-harmonic waves is different from sinusoidal waves. Based on large eddy simulation of turbulent flows in wave boundary layer, a modified method is proposed to calculate sediment transport rate under non-harmonic waves. It is further used to explore the influences of flow acceleration and the phase lead between the free stream velocity and bed shear stress on sediment transport rate in different phases of one wave cycle for forth-leaning. The net transport rate is found to increase with the degree of asymmetry and velocity-leaning index. Both the acceleration and the phase lead have a great influence on average transport rate in each phase.</span
Analyses of wave forces on surface piercing vertical cylinders of intermediate scale
No full textMaximum horizontal forces by regular waves on a surface piercing vertical cylinder of intermediate scales are computed by solving the two-phase incompressible Navier-Stokes equations with a VOF method. The incident waves are generated by the fifth order Stokes wave and cnoidal wave. The numerical flume is verified and validated by comparison to the second order Stokes theory and by grid-independence. A variety of scales and wave steepness are computed in deep water and finite depth. In fully nonlinear wave condition, the viscosity and diffraction effects are discussed. A more accurate demarcation of intermediate scales is given by scales (the ratio of the diameter to the wavelength) from 0.1 to 0.125.</span
Flow Characteristics of Bohai Sea under Extreme Cold Wave
No full textWe aim to analyse the extreme hydraulic environment in Bohai Sea in case of cold wave. According to the historical statistics of cold wave hitting Bohai Sea, three typical paths with four different wind speeds for each are chosen for the numerical simulation. Then, by means of Princeton Ocean Model (POM), we simulate the cold wave in Bohai Sea. In particular, nest calculations are conducted for Puti Island wind farm in Bohai Sea in order to manifest the extreme hydrodynamics in the area of the planned wind farm project
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