基于近红外光谱分析贡梨可溶性固形物全局模型的鲁棒性

贡梨是大众喜爱的水果,为研究不同检测方向对近红外在线检测贡梨可溶性固形物SSC的影响,提出全局模型并分析其鲁棒性。在贡梨六个方向上收集光谱：茎-花萼轴垂直,茎向上(A1)和茎向下(A5),茎-花萼轴和水平之间45°,茎向上倾斜(A2)和茎向下倾斜(A4),茎-花萼轴水平,茎朝向右侧光(A3),茎花萼轴水平,茎朝向带移动方向(A6)。SSC范围为9.53～14.70的150个样品分为115个标准偏差为1.05的校准集和35个标准偏差为0.93的预测集。采用偏最小二乘回归PLSR分别建立六个局部模型和一个全局模型,局部模型由各方向的115个校正集数据经过Savitzky-Golay卷积平滑、多元散射校正MSC、高斯滤波平滑GFS三种不同的预处理方法处理后使用偏最小二乘回归PLSR建立而来;用本方向校正集数据建立的局部模型验证本方向的35个预测集数据,比较这三种预处理方法后所建立的PLSR模型,结果表明经过GFS处理后建立的模型验证效果最好,因此六个局部模型和全局模型均采用GFS处理后建立的PLSR模型。全局模型是由A1, A2, A3, A4, A5和A6六个方向的690个校正集光谱数据经...     

A model of laminar flames in droplet suspensions

A mathematical model of steady laminar flame propagation through a suspension of liquid droplets was proposed, and numerical calculations within the framework of this model were performed. The model is constructed based on one-dimensional differential equations of the theory of laminar flames in homogeneous gaseous mixtures in conjunction with the theory of droplet burning in uniform monodisperse suspensions. The chemical process was described using a multistage kinetic scheme. A comparison of model predictions with the available experimental data demonstrated satisfactory agreement.     

Modeling study of residence time and water age in Dahuofang Reservoir in China

Understanding the dynamics of water renewal in a reservoir is essential when the transport and fate of dissolved substances are evaluated.A three-dimensional hydrodynamic model was implemented to compute average residence time and water age in Dahuofang Reservoir in China.The model was verified for a one-year time period in 2006.A simulation reproduced intra-annual variation of mixing represented by the fall/winter mixing and the spring/summer stratification.The simulated variation of vertical thermal struc...     

Motion of a red blood cell in interference field

The motion of a red blood cell suspended in blood plasma in a two-beam plane interference field was studied experimentally. A cw Argon Ion laser was used. A model is proposed to describe the observed motion. The model is based on a balance between the optical gradient force and the drag force, and yields the location of the cell as a function of time, starting from a stationary position at an arbitrary distance from a dark fringe until becoming trapped at the center of the closest bright fringe. It is suggested that the discrepancy between the predictions of the model and the observed motion is attributable to the influence of the wall close to which the cell flows.     

Investigation of a peculiar bifurcation phenomenon in diffraction spectra of volume holograms

A peculiar bifurcation phenomenon in the diffraction spectra of volume holograms is investigated. A linear expansion model modulated by a random number was built to explain the phenomenon. In our model, a random number was first introduced to describe the random property of swelling or shrinking of the emulsion during the process after exposure. The calculated results show good consistency with the experimental observations.     

A Numerical Model of Plasma-Actuator Effects in Flow-Induced Noise Control

In this paper, a computational model was developed to model the potential of plasma actuators to reduce flow-induced noise. The model consisted of a viscous flow solver to compute the flow field and a Ffowcs Williams and Hawkings acoustic solver to predict the far-field noise radiation. A velocity-inlet boundary condition was used to model the induced velocity effect of plasma actuators applied to the surface of a bluff body. A test case of the noise radiation from a cylinder in fluid flow was used to validate the model. A comparison between the numerical results and previous experimental results was made. The results confirmed the noise-reduction potential of plasma actuators for bluff-body noise control. Good agreement was made between the numerical and experimental results. It was concluded that the model could be a useful tool to predict the effect of plasma actuation applied to aerodynamic, acoustic, and optimization problems.      

A nonlinear optical model of an air medium in the problem of filamentation of femtosecond laser pulses of different wavelengths

A frequency-dependent model of nonlinear optical response of atmospheric air upon propagation of a femtosecond laser pulse is constructed. The model is derived on the basis of generalized experimental and theoretical data on the cubic susceptibility and photoionization of gaseous components of air. The model was proved by solving the problems of filamentation of a femtosecond laser pulse with a wavelength lying in the range 0.24 to 1.2 μm.     

二元合金等温凝固过程的相场模型

基于Ginzberg-Landau理论，发展了一个与WBM模型和KKS模型一致的新相场模型.并利用该相场模型与溶质场耦合计算，以Al-65%Cu合金为例模拟了不同过冷度条件下，二元合金凝固过程的等轴枝晶生长过程.研究过冷度对二元合金等温凝固过程的等轴枝晶生长以及溶质场分布的影响.结果表明：随着过冷度的增大，枝晶的二次枝晶更加发达，浓度Peclet数和枝晶尖端的生长速率增大，而枝晶尖端的曲率半径减小，枝晶前沿的溶质富集现象也更严重；另外，计算结果与Ivantsov理论符合较好. 关键词： 相场法 枝晶生长 溶质场 Ivantsov理论     

Development of the model of HF radiowave propagation in the ionosphere

The model of HF radiowave propagation, based on a geometrical optics approximation, has been extended for the case of a complex geometrical optics. The radiowave propagation in the illuminated region without going to the caustic shadow region is considered. The radiowave propagation model has been generalized for the case of wideband HF signals in the ionosphere. A dynamic representation of LFM signals in the form of a wave packet sequence was used for this purpose. The radiowave propagation model was also adapted to a global self-consistent dynamic model of the thermosphere, ionosphere, and protonosphere, which made it possible to study specific features in the formation of HF radiowave ray paths during geomagnetic storms in a 3D inhomogeneous anisotropic medium.     

薄油层SAGD开发蒸汽腔发育和生产指标预测

通过分析现场生产数据和数值模拟结果,将薄层稠油油藏蒸汽辅助重力驱油(SAGD)生产中蒸汽腔发育分为横向扩展和向下运移两个过程,并进行简化处理预测SAGD生产指标.联合质量守恒方程、能量守恒方程和周围地层散热模型得到一个描述蒸汽腔发育的综合表达式,该方程属于典型的第二类Volterra积分函数.通过拉普拉斯变换对Volterra积分函数进行半解析求解,最终得到不同时刻蒸汽腔发育状态.为验证模型的正确性,将模型的计算结果与CMG Stars的计算结果对比,整体误差小于5%.新模型可以方便简单地预测SAGD生产中蒸汽腔发育过程和生产动态指标,从而确定SAGD生产的极限油藏参数和合理的注采参数.     

Reduced-order model for redox kinetics of oxygen carrier in chemical looping combustion

A reduced-order model was developed to calculate the redox kinetics of oxygen carrier in chemical looping combustion. The reduced-order model can describe the major physical/chemical features of the redox steps of oxygen carrier, such as gas diffusion around and inside the particle, surface reaction, product growth, product layer diffusion, pore structure change etc. It is an analytical model simplified using the Thiele modulus method and thus is much easier for computational fluid dynamics modeling and reactor design. The accuracy of variations of redox conversion under different temperatures and gas concentrations predicted by the reduced-order model is verified by comparison with both the detailed one-dimensional model and the experimental data. The results indicate that the reduced-order model can reproduce the prediction accuracy of the detailed one-dimensional model and agrees well with the experimental data. The well observed two-stage behavior of a fast initial stage followed by a second slower stage was discussed in detail. Further, the reduced-order model was used to analyze the effect of particle structural parameters on the kinetics. The relative importance of each controlling step in the kinetics of oxygen carrier predicted by the reduced-order model was compared.     

Liquid crystalline and solid phases for a system of hard zigzag particles with Lennard-Jones sites in two-dimensions

The map of low and high density phases of an idealized system, the infinitely hard zigzag line model with two Lennard-Jones (LJ) sites is presented. LJ sites are added to a previous model composed of the infinitely hard zigzag line shape particles, R.A. Perusqía, J. Peón, J. Quintana, Physica A 345 (1) (2005) 130–142. The attractions and the molecular volume added to this system through the LJ sites create a more realistic model and, as a consequence, a richer phase behavior is obtained. Although the volume of the LJ sites is quite small it is enough to produce solid phases, absent in the original model. On the other hand the smectic phase that was present in the hard system was not found in this case. Two molecular conformations are chosen to provide a comparison with the previous model. The isothermal–isobaric is used to establish the thermodynamic regions of the different molecular self aggregations and to compare them to already published results.     

粒子模拟中阳极栅网模型的实现

在3维Yee网格和蛙跳模型上建立了一种合理的描述阳极栅网中电子散射过程的物理模型,在经典碰撞理论基础上推导了散射角和动量公式,并运用蒙特卡罗法模拟了高斯分布电子束在径向虚阴极情景下的阳极栅网散射过程。模拟结果出现了明显的虚阴极现象,平均功率0.60GW,虚阴极效率4.5%,微波主频4.7GHz,主模是TM01模。这些参数与文献模拟的数据基本符合,证明了虚阴极中阳极栅网数值模拟实现的正确性。     

A single-pole model for the propagation of ultrasound in soft tissue

A minimum-phase function, which characterizes the velocity dispersion in tissue was calculated from measured attenuation. This function was incorporated into a causal tissue model. Predictions of attenuation using the minimum-phase function with just a single pole matched measured attenuation in the 1- to 10-MHz range within a few percent. Dispersion of phase velocity predicted by the single-pole model was comparable to measured dispersion. The frequency associated with the single pole, which is a relaxation frequency, decreased with hemoglobin concentration and collagen content but increased with temperature. The electrical equivalent circuit for this model is a delay coupled with a low-pass filter which can be configured as a resistance in series with a parallel combination of resistance and capacitance.     

金柱腔车削工序的贝叶斯质量控制模型

基于贝叶斯理论,针对小批量、少样本的金柱腔生产过程,讨论了生产质量控制模型的建立方法。利用大量历史数据和少量样本信息,建立了金柱腔车削工序的质量控制模型,并利用实际生产数据对该模型进行了验证。验证结果显示,当前金柱腔车削工序的生产过程处于统计控制状态,质量控制模型没有发出生产质量的虚警报,建立的质量控制模型是有效的,能够指导金柱腔车削工序的实际生产。     

An analytical model of gas transport in the human lung

Summary A simple physico-mathematical model of gas transport in the human lung is developed. Care is taken to obtain an analytical concordance with the bronchial-tree geometry as given by the Weibel’s morphometric data. The dynamics of diffusion is modelled according to the Taylor and Aris model. The simplest boundary conditions are assumed. An approximate analytical solution is derived with applications to some simple breathing washout experiments. A satisfactory agreement confirms the validity of the model. This work was partially supported by Ministero della Pubblica Istruzione.     

Phase field modeling of liquid jets in low gravity

An axisymmetric phase field model is developed and used to model surface tension forces on liquid jets in microgravity. The previous work in this area is reviewed and a baseline drop tower experiment selected for model comparison. The model is solved numerically with a compact fourth order stencil on an equally spaced axisymmetric grid. After grid convergence studies, a grid is selected and all drop tower tests modeled. Agreement was assessed by comparing predicted and measured free surface rise. Trend wise agreement is good but agreement in magnitude is only fair. Suspected sources of disagreement are the simple turbulence model and the existence of slosh baffles in the experiment that were not included in the model. Parametric investigation was conducted to study the influence of key parameters on the geysers formed by jets in microgravity. Investigation of the contact angle showed the expected trend of increasing contact angle increasing geyser height. Investigation of the tank radius showed some interesting effects and demonstrated the zone of free surface deformation is quite large. Variation of the surface tension with a laminar jet showed clearly the evolution of free surface shape with Weber number. A breakthrough Weber number of 1 was predicted by the variation of the surface tension model which is close to the experimentally measured Weber number of 1.5 found in prior experimental work.     

Prediction of backscatter coefficient in trabecular bones using a numerical model of three-dimensional microstructure

A model of ultrasonic backscattering for cancellous bone saturated by water is proposed. This model assumes that scattering is caused by the solid trabeculae and describes the cancellous bone as a weak scattering medium. The backscatter coefficient is related to the spatial Fourier transform of bone microarchitecture and to the density and compressibility fluctuations between the solid trabeculae and the saturating fluid. The computations of the model make use of three-dimensional numerical images of bone microarchitecture, obtained by tomographic reconstructions with a 10 microm spatial resolution. With this model, the predictions of the frequency dependence and of the magnitude of the backscatter coefficient are reasonably accurate. The theoretical predictions are compared to experimental data obtained on 19 specimens. An accuracy error of approximately 1 dB was found (difference between the averaged experimental values and theoretical predictions). One limit of the model may come from inaccurate values of trabecular bone characteristics needed for the computations (density and longitudinal velocity), which are yet to be precisely determined for human trabecular bone. However, the model is only slightly sensitive to variations of bone material properties. It was found that an accuracy error of 2.2 dB at maximum resulted from inaccurate a priori values of bone material properties. A computation of the elastic mean free path in the medium suggests that multiple scattering plays a minor role in the working frequency bandwidth (0.4-1.2 MHz). It follows from these results that a weak scattering medium model may be appropriate to describe scattering from trabecular bone.     

Improved model of optical phonon confinement in silicon nanocrystals

We develop a model for calculating the Raman scattering spectra from phonons confined in for silicon nanocrystals, which is based on the familiar approach taking into account the uncertainty in the quasi-momentum of phonons localized in the nanocrystals. The model is considerably improved by taking into account dispersion of phonons not only in the magnitude of the quasi-momentum, but also in its direction. A significant refinement of the model is also due to the fact that phonon dispersion is calculated using the widely approved Keating model instead of being approximated by empirical expressions as was done in earlier approaches. The calculations based on this model make it possible to determine the sizes of silicon nanocrystals more precisely from analysis of the experimental Raman spectra.