Liu D.,Zhejiang iversity |
Turner J.A.,University of Nebraska - Lincoln
Journal of the Acoustical Society of America | Year: 2017
Techniques of quantitative nondestructive evaluation using attenuation of ultrasonic waves have been proposed as a potential tool for monitoring sintering processes because of the direct connection between the changes of wave propagation characteristics and microstructure properties. However, the influence of these changes during sintering on sound propagation remains unclear. In addition to theoretical investigations, numerical models can be utilized to provide key information for interpreting experimental data quantitatively. In this article, a simplified two-phase model using Voronoi polycrystals is applied to study wave propagation through sintered materials. Finite element simulations are developed with various material and geometric parameters of the two-phase model. Example longitudinal attenuation results are obtained and compared with the scattering theory for different input wave frequencies. The comparison of the numerical results with the theory shows the dependence of the attenuation on the parameters of the correlation function and the two-phase geometry. The results also validate the correlation function formula used in the theory. The influence of the input wave frequency and material properties on the correlation lengths is also discussed. Such numerical models can be used to verify theoretical models efficiently and to design further experimental methods for characterization of microstructures. © 2017 Acoustical Society of America.
Hu X.Y.,Zhejiang iversity |
Liu Z.L.,Tsinghua University |
Zhuang Z.,Tsinghua University
Wood Science and Technology | Year: 2017
There are crack-prevention mechanisms in living trees. However, in the felled logs, relaxation of growth stress and accumulation of drying stress may cause crack propagation. To investigate the crack propagation behavior and crack patterns in log cross sections, theoretical and simulation models are developed in this paper. In the theoretical model, global stability and local instability of cracks are considered in logs. In the simulation models, energy release rate is calculated based on FEA J-integral calculation models; crack patterns on log cross sections are investigated by the XFEM and fracture mechanics simulation models. Simulation results suggest that various crack patterns may develop in log cross sections, and there are several representative patterns. The existence of the simulated crack patterns can also be verified in real logs. The results of parameterization indicate that the crack bifurcation has a close relationship with energy storage and release modes. The pattern of main cracks is related to the damage initiation–evolution parameters. These phenomena can be explained by the energy principle of crack propagation and the stability principle of energy storage systems. © 2017 Springer-Verlag GmbH Germany
Xu G.-Q.,Xinjiang Institute of Ecology and Geography |
Yu D.-D.,CAS Research Center for Eco Environmental Sciences |
Li Y.,Zhejiang iversity
Forest Ecology and Management | Year: 2017
To investigate above- and belowground biomass allocation patterns and the relationship of root distribution between different functional groups (shrubs vs. herbs) along a groundwater depth gradient, an experiment was carried out in a Haloxylon persicum woodland. Four sites were selected along the groundwater depth gradient. At each site, five sample plots (20 × 20 m) and 15 subplots (1 × 1 m) were established for a vegetation inventory of Haloxylon persicum and the herbaceous layer. The vegetation inventory included plant density, canopy coverage, height, and basal stem diameter of H. persicum. Allometric equations were established for H. persicum based on the biomass of 22 excavated trees, which were then applied to inventory data to provide stand estimates of aboveground biomass (AGB), belowground biomass (BGB), and total biomass (TB) of H. persicum. The AGB of the herbaceous layer was measured in subplots (1 × 1 m) and BGB was excavated and measured to a depth of 100 cm at 10-cm intervals. Our results indicated that the BGB-to-AGB ratio at the community level in the herbaceous layer increased notably along the gradient of declining groundwater depth. The depth of the soil horizon that contained 65% of the root surface area and 85% of the root biomass was shallower (0–2.5 m) in the deep end of the groundwater depth gradient than in the shallow end (0–3 m) of the gradient. H. persicum adjusted root distribution to capture water in the upper soil layers in response to the decline in groundwater depth. However, this adjustment was not sufficient to compensate for the decline in the water table: the BGB-to-AGB ratio showed no significant increase as AGB declined. On the contrary, herbaceous plants seemed better adapted to changes in the water table by effectively adjusting their BGB-to-AGB ratio. Use of BGB-to-AGB ratios that are specific to groundwater tables will significantly improve our estimates of BGB carbon stocks in these woodlands. Considering the scarcity of information on biomass stocks and partitioning in desert woodlands, our results might be applicable to other desert regions in Central Asia dominated by H. persicum. © 2017 Elsevier B.V.
Chen R.-P.,Zhejiang Sci-Tech University |
Dai C.-Q.,Zhejiang iversity
Nonlinear Dynamics | Year: 2017
Analytical vector spatiotemporal soliton solutions are derived in a spatially inhomogeneous Kerr nonlinear medium with a transverse modulation by means of a generic transformation. As an example, spatiotemporal soliton clusters such as Gaussian soliton clusters and radially symmetric soliton clusters in the media with the parabolic transverse modulation and without transverse modulation are constructed. The stability of vector spatiotemporal soliton clusters is investigated analytically and numerically, and results indicate that in the spatially inhomogeneous Kerr nonlinear medium, besides the stable fundamental solitons, stable higher-order mode exists below the critical propagation constant. © 2017 Springer Science+Business Media Dordrecht
Zhao C.,Zhejiang iversity |
Qiao X.,Zhejiang iversity |
Cao Y.,Zhejiang iversity |
Shao Q.,Ningbo University
Fuel | Year: 2017
This work presents the application of ammonia fiber expansion (AFEX) pretreatment both with (H-AFEX) and without hydrogen peroxide presoaking of energy crops moso bamboo, giant reed, and Miscanthus. The influences of AFEX and H-AFEX pretreatments on chemical composition and enzymatic hydrolysis were assessed. The results address the solid recovery, delignification, hydrolysis sugar yields, and micro-structural morphology of varying H-AFEX pretreatment conditions of energy crops. A strong negative correlation between solid recovery and H2O2 loading was found for all pretreated samples with H2O2 loading <2.0. In comparison with AFEX process, the addition of hydrogen peroxide in H-AFEX pretreatment could result in increases in glucose yields at the expense of xylose. The maximum sugar yields of moso bamboo, giant reed, and Miscanthus were 269.0, 424.6, and 485.0 g per kg dry biomass respectively, which were obtained under their optimal pretreatment conditions following enzymatic hydrolysis. The micrograph of H-AFEX-treated giant reed demonstrated that the modified porous structure resulted in increased enzyme accessible surface area, and facilitated the subsequent enzymatic hydrolysis. © 2017 Elsevier Ltd
Shao Q.,Zhejiang iversity |
Shao Q.,Institute of Paper Science And Technology |
Cheng C.,Zhejiang iversity |
Ong R.G.,Michigan State University |
And 2 more authors.
Bioresource Technology | Year: 2013
Bamboo is a fast growing plant found worldwide that has high potential as an energy crop. This project evaluated the effectiveness of AFEX pretreatment for converting moso bamboo (Phyllostachys heterocycla var. pubescens) to fermentable sugars, both with and without pre-soaking in hydrogen peroxide. Pretreatment conditions including temperature, water loading, residence time, ammonia loading, and hydrogen peroxide loadings were varied to maximize hydrolysis yields. The optimal conditions for AFEX were 150. °C, 0.8 or 2.0 (w/w) water loading, 10-30. min residence time, and 2.0-5.0 (w/w) ammonia loading. The optimal conditions for H-AFEX were same AFEX conditions with 0.7-1.9 (w/w) 30% (wt) hydrogen peroxide solutions loading. Using 15 FPU/g glucan cellulase and under optimal conditions, AFEX pretreatment achieved a theoretical sugars yield of 64.8-72.7% and addition of hydrogen peroxide presoaking increased the yield to 83.4-92.1%. It is about 5-fold and 7-fold increase in sugars yield for AFEX-treated and H-AFEX-treated bamboo respectively. © 2013 Elsevier Ltd.
Zhao C.,Nanjing Agricultural University |
Zhao C.,Zhejiang iversity |
Ding W.,Nanjing Agricultural University |
Chen F.,Zhejiang iversity |
And 2 more authors.
Bioresource Technology | Year: 2014
Corn stover is one of the main agricultural residues being considered as a cellulosic ethanol feedstock. This work evaluated the effectiveness of AFEX™. 1AFEXTM is a registered trademark of MBI International, Lansing, MI.1 pretreatment for converting corn stover to fermentable sugars, both with and without pre-soaking in hydrogen peroxide. The compositional changes and enzymatic digestibility of AFEX-treated and H-AFEX-treated biomass were investigated. Results showed that most of the polysaccharides remained intact following each of these two methods. Compared with AFEX pretreatment, the H-AFEX process enhanced delignification and enzymatic hydrolysis yields of both glucose and xylose. The maximum glucan and xylan digestibility of H-AFEX process were 87.78% and 90.64%, respectively, and were obtained using 0.7 (w/w) water loading, 1.0 (w/w) ammonia loading, 0.5 (w/w) 30. wt.% hydrogen peroxide loading, and 130. °C for 10. min. The results of the present work show that H-AFEX is a feasible pretreatment to improve the enzymatic saccharification of corn stover for bioethanol production. © 2013 Elsevier Ltd.
Guo M.,Hangzhou Dianzi University |
Hui G.,Zhejiang iversity
Journal of Chinese Institute of Food Science and Technology | Year: 2016
In this paper, a pork freshness rapid analysis method based on electronic nose and non-linear feature extraction modeling. Chilled-stored pork samples are measured by electronic nose system for continuous 9 days. At the same time, total volatile basic nitrogen (TVB-N) index is examined to characterize pork freshness according to China standard protocols. Electronic nose measurement data is analyzed by principal component analysis (PCA) and stochastic resonance (SR) methods. PCA can not totally discriminate all pork samples. SR signal-to-noise ratio (SNR) spectrum solves this problem. Pork freshness predicting model is built based on linear fitting of SNR maximal values. Validating experiments demonstrate that the developed model predicts pork freshness with good accuracy, and high efficiency. This method is of field application value. © 2016, Editorial Office of Journal of CIFST. All right reserved.
Dai C.-Q.,Zhejiang Agriculture And forestry University |
Yu F.-B.,Zhejiang iversity
Wave Motion | Year: 2014
With the help of a modified mapping method, we re-study the (3 + 1)-dimensional Burgers equation and derive three families of variable separation solutions. By selecting appropriate functions in the variable separation solution, we discuss interaction behaviors among flat-top rectangle-soliton and ring-soliton, embedded rectangle-soliton and embedded ring-soliton in a periodic wave background. All interaction behaviors among them are completely elastic, and no phase shift appears after the interaction. These results might be helpful to the understanding of the propagation processes for nonlinear water waves in fluid mechanics such as diverse nonequilibrium, nonlinear phenomena in turbulence and inter-face dynamics. © 2013 Elsevier B.V.
Zhou G.,Zhejiang iversity
Optics Communications | Year: 2014
An analytical expression of a Lorentz-Gauss vortex beam with one topological charge propagating in a strongly nonlocal nonlinear media is derived. The analytical expressions of the beam width, the curvature radius, and the orbital angular momentum density for the Lorentz-Gauss vortex beam with one topological charge have been also presented. The normalized intensity distribution, the relative beam width, the curvature radius, and the orbital angular momentum density distribution of the Lorentz-Gauss vortex beam with one topological charge are demonstrated in the strongly nonlocal nonlinear media, respectively. The normalized intensity, the beam width, the curvature radius, and the orbital angular momentum density versus the axial propagation distance are all periodic and the period is T=πz0/η. The evolution of the propagation property of the Lorentz-Gauss vortex beam with one topological charge has been exhibited in the strongly nonlocal nonlinear media. When the parameter η reaches the critical value, the beam width keeps invariant upon propagation, and the corresponding curvature radius is infinite. The propagation of Lorentz-Gauss vortex beams with larger topological charge propagating in the strongly nonlocal nonlinear media can be analyzed by the same procedure as here. © 2014 Elsevier B.V.