既有桥梁养护中BIM模型构件拆分与模型细度的讨论

针对既有桥梁的BIM应用问题,讨论了面向养护的模型构件拆分及模型细度问题。提出在构件拆分方面应考虑结构功能、空间界限、施工次序等因素,确定三维模型细度时需满足位置准确、几何界限清晰和较高的曲线精确度等要求;针对若干实际情况进行了举例说明。该文研究成果对于既有桥梁管理系统的三维化升级具有参考意义。

模型细度标准驱动智能建造发展

《“十四五”住房和城乡建设科技发展规划》中提出,在智能建造与新型建筑工业化技术创新方面推动和开展相关标准体系研究。BIM技术作为建筑行业信息化的基础,智能建造的推动离不开BIM与其他相关信息技术的集成和创新应用。而BIM作为建设工程及设施全生命期物理和功能特性的数字化表达,其良好的应用以及与其他相关信息技术的集成应用离不开标准化的支持。从BIM模型细度标准出发,分析北京市如何通过一系列的模型细度标准制定和应用工作支撑建筑行业智能建造的发展。

变流器组网多时间尺度特性及其模型分细度仿真应用

多变流器并网、组网运行和控制涉及宽时间尺度过程,新形态的动态和稳定问题也随之出现,仿真技术常被用于上述问题的研究。然而不同细度模型的功能、性能和适应性存在差异,仿真前应根据需要研究或体现的物理过程或现象评估被仿真过程蕴含的时间尺度,并选用合适细度的模型。该文总结、评述了含多变流器电网仿真技术研究、应用现状和发展趋势,以常规多电平电压源变流器(VSC)和模块化多电平变流器(MMC)为例,分析变流器组网与控制共性特征,基于主电路和控制各环节响应时间特性,分析变流器组网多时间尺度动态特性及时间尺度划分,讨论变流器模型细度与仿真需求、主导物理过程时间尺度匹配问题,总结4种常见细度变流器模型的适应性及其在电力系统场景下的应用,并以仿真测试验证了变流器组网时间尺度分析的正确性,直观给出了不同细度模型和仿真的适应性。

国内外BIM标准发展研究

近年来建筑信息模型(BIM)在建筑行业的迅速发展,使传统建筑业逐步向精细化、现代化、信息化转变。但是现有建筑行业标准规范的不明确在一定程度上阻碍了BIM技术的进一步应用。本文对国内外BIM相关标准的发展与应用进行了较为全面的梳理,其中选取了BIM模型细度LOD标准的发展及应用情况进行了专门介绍。最后基于我国建筑业当前的发展现状,提出我国BIM标准体系的构建框架。

浅析欧洲部分国家园林BIM标准化现状及对我国的启示

构建标准化BIM工作流程、定义数据类别及传输格式是BIM在工程建设领域广泛应用的重要基础,也是园林行业应用BIM所需要解决的关键问题。本文从目前国内外BIM标准化现状出发,明确园林BIM标准化的必要性,并通过介绍英国、挪威两国在园林BIM标准化方面的研究进展,结合我国行业现状,探讨园林BIM应用及标准化可借鉴的经验及启示。

Effect of dephytinization on bioavailability of iron,calcium and zinc from infant cereals assessed in the Caco-2 cell model

AIM： To test the effect of the dephytinization of three different commercial infant cereals on iron, calcium, and zinc bioavailability by estimating the uptake, retention, and transport by Caco-2 cells. METHODS： Both dephytinized （by adding an exogenous phytase） and non-dephytinized infant cereals were digested using an in vitro digestion protocol adapted to the gastrointestinal conditions of infants younger than 6 too. Mineral cell retention, transport, and uptake from infant cereals were measured using the soluble fraction of the simulated digestion and the Caco-2 cells. RESULTS： Dephytinization of infant cereals significantly increased （P 〈 0.05） the cell uptake efficiency （from 0.66%-6.05% to 3.93%-13%）, retention （from 6.04%-16.68% to 14.75%-20.14%） and transport efficiency （from 0.14%-2.21% to 1.47%-6.02%）, of iron, and the uptake efficiency （from 5.0%-35.4% to 7.3%-41.6%） and retention （from 4.05%-20.53% to 14.45%-61.3%） of zinc, whereas calcium only cell uptake showed a significant increase （P 〈 0.05） after removing phytate from most of the samples analyzed. A positive relationship （P 〈 0.05） between mineral solubility and the cell uptake and transport efficiencies was observed. CONCLUSION： Removing phytate from infant cereals had a beneficial effect on iron and zinc bioavailability when infant cereals were reconstituted with water. Since in developing countries cereal-based complementary foods for infants are usually consumed mixed with water, exogenous phytase additions could improve the nutritional value of this weaning food.

Physical and chemical processes promoting dominance of the toxic cyanobacterium Cylindrospermopsis raciborskii

The freshwater cyanobacterium, Cylindrospermopsis raciborskii （Woloszyflska） Seenayya and Subba Raju is a common species in lakes and reservoirs globally. In some areas of the world it can produce cytoand hepatotoxins （cylindrospermopsins, saxitoxins）, making blooms of this species a serious health concern for humans. In the last 10 15 years, there has been a considerable body of research conducted on the ecology, physiology and toxin production of this species and this paper reviews these studies with a focus on the cylindrospermopsin （CYN）-producing strains. C. raciborskii has low light requirements, close to neutral buoyancy, and a wide temperature tolerance, giving it the capacity to grow in many lentic waterbodies. It also has a flexible strategy with respect to nitrogen （N） utilisation; being able to switch between utilising fixed and atmospheric N as sources of N fluctuate. Additionally this species has a high phosphate （DIP） affinity and storage capacity. Like many cyanobacteria, it also has the capacity to use dissolved organic phosphorus （DOP）. Changes in nutrient concentrations, light levels and temperature have also been found to affect production of the toxin CYN by this species. However, optimal toxin production does not necessarily occur when growth rates are optimal. Additionally, different strains of C. raciborskii vary in their cell quota of CYN, making it difficult to predict toxin concentrations, based on C. raciborskii cell densities. In summary, the ecological flexibility of this organism means that controlling blooms of C. raciborskii is a difficult undertaking. However, improved understanding of factors promoting the species and toxin production by genetically capable strains will lead to improved predictive models of blooms.

A Modified Sensitive Driving Cellular Automaton Model

A modified cellular automaton model for traffic flow on highway is proposed with a novel concept about the variable security gap. The concept is first introduced into the original Nagel-Schreckenberg model, which is called the non-sensitive driving cellular automaton model. And then it is incorporated with a sensitive driving NaSch model,in which the randomization brake is arranged before the deterministic deceleration. A parameter related to the variable security gap is determined through simulation. Comparison of the simulation results indicates that the variable security gap has different influence on the two models. The fundamental diagram obtained by simulation with the modified sensitive driving NaSch model shows that the maximumflow are in good agreement with the observed data, indicating that the presented model is more reasonable and realistic.

Effect of absorption boundary layer on nonlinear flow in low permeability porous media

Taking low permeability cores of Daqing oilfield for example,the flow characteristics at low velocity were studied with the self-designed micro-flux measuring instrument.Considering the throat distribution and capillary model,the thickness of fluid boundary layer under different pressure gradients was calculated,and the mechanism and influencing factors of nonlinear percolation were discussed.The results show that the percolation curve of ultra-low rocks is nonlinear,and apparent permeability is not a constant which increases with pressure gradient.The absorption boundary layer decreases with the increase of pressure gradient,and changes significantly especially in low pressure gradient,which is the essence of nonlinear percolation.The absorption boundary layer is also found to be impacted by the surface property of rocks.

Towards a multiscale model of colorectal cancer

Colorectal cancer (CRC) is one of the best characterised cancers, with extensive data documenting the sequential gene mutations that underlie its development. Complementary datasets are also being generated describing changes in protein and RNA expression, tumour biology and clinical outcome. Both the quantity and the variety of information are inexorably increasing and there is now an accompanying need to integrate these highly disparate datasets. In this article we aim to explain why we believe that mathematical modelling represents a natural tool or language with which to integrate these data and, in so doing, to provide insight into CRC.

Numerical Simulation of Effects of Cloud Top Temperatures and Generating Cells on Secondary Ice Production in Stratiform Clouds with a Detailed Microphysical Model

This paper outlines a one-dimensional,heightdependent bin model with detailed microphysical processes in which ice splinters are produced by a riming process.The model is then applied to simulate the shift of particle size distribution effected by the secondary ice production process within clouds with different generating cells and cloud top temperatures.The result of model simulations reveals the general effects of cloud updrafts on increasing ice particle concentration by extending the residence time of ice particles in clouds and providing sufficiently large supercooled water droplets.The rimesplintering mechanism is more effective in clouds with lower ice seeding rates than those with higher rates.Evolutions of hydrometeor size distribution triggered by the rime-splintering mechanism indicate that the interaction between large ice particles and supercooled water drops adds a "second maximum" to the primary ice spectra.

Micromechanical Study on Moisture Induced Tensile Strength Reduction of GFRP

The main focus of this paper is to investigate the influence of hygrothermal aging on tensile strength of epoxy resin matrix composites.Firstly,tests of water absorption and moisture induced tensile strength degradation of glass fiber reinforced polymer(GFRP)are conducted.Results show that the moisture absorption behavior of the GFRP follows the Fick’s law,and its tensile strength retention decreases notably in the early hygrothermal aging stage and then gradually approaches a constant.Then,microscale longitudinal and transverse strength prediction models for unidirectional fiber reinforced composites are proposed.They are moisture concentration dependent and reflect the inherent probability of failures of fiber and matrix(or fiber/matrix interface).The moisture diffusing analysis demostrates that the proposed models can predict degradation of tensile strength of epoxy resin matrix composites undergoing different hygrothermal durations.The proposed models are validated by the experiments of hygrothermal residual strength of the GFRP mentioned above.

Design and Implementation of RBAC Model Based on Graduate Education Management System

After analysis of the existing problems of traditional RBAC model, user group and resource domain are introduced to conduct finely granular extension of RBAC model. Extended model reduces the redundancy of roles, lowers the complexity of authorization management and enhances the flexibility and maintainability of users＇ authorization. It is well proved in its application in postgraduate student management system.

Model for Influences of Magnetic Fields on Intracellular Calcium Oscillations

Based on the model of the two calcium stores developed by Goldbeter, the influence of external magnetic field on the calcium concentration has been discussed. We believe that the cell membrane is a major site of interaction for extremely-low-frequency （ELF） electromagnetic fields, and the permeability of ions can be changed with the changing electromagnetic fields. It is shown that magnetic field initiates intraeellular calcium oscillation with a threshold in flux density, and that the calcium oscillations do not occur if the density of magnetic field is below the threshold. The results of theoretical calculation are consistent with that of the experiment. The intracellular free calcium concentrations of different cells exposed to the same magnetic fields are different from each other. It is indicated that the different behaviors such as oscillation, rise and invariability of calcium concentration are associated with the sort of cells.

Ultrastructural observation of effect of moderate hypothermia on axonal damage i n an animal model of diffuse axonal injury

To investigate the effect of moderate hypothermia on respon ses of axonal cytoskeleton to axonal injury in the acute stage of injury. Methods: Of fifteen adult guinea pigs, twelve animals were subj ected to stretch injury to the right optic nerves and divided into the normother mic group (n=6) in which the animals core temperature was maintained at 36.0 37.5℃ and the hypothermia group (n=6) in which the core temperature was red uced to 32.0 32.5℃ after stretch injury. Remaining three animals sustained no injury to the right optic nerves and served as control group. Half of injure d animals (n=3) of either normothermic group or hypothermic group were killed at either 2 hours or 4 hours after injury. The ultrastructural changes of axonal c ytoskeleton of the right optic nerve fibers from the animals were examined under a transmission electron microscope and analyzed by quantitative analysis with a computer image analysis system. Results: At 2 hours after stretch injury, there was a significa nt reduction in the mean number of microtubules (P< 0.001 ), and a significant increase in the mean intermicrotubule spacing (P< 0.05 or P< 0.01 ) in axons of all siz es in normothermic animals. The mean number of neurofilaments also decreased sta tistically (P< 0.01 ) in large and medium subgroups of a xons in the same experimental group at 2 hours. By 4 hours, the large subgroup o f axons in normothermic animals still demonstrated a significant decline in the mean number of microtubules (P< 0.01 ) and an increase i n the mean intermicrotubule spacing (P< 0.05 ), while th e medium and small subgroups of axons displayed a significant increase in the me an number of neurofilaments (P< 0.05 ) and reduction in the mean interneurofilament spacing (P< 0.05 ). On the c ontrary, either the mean number of microtubules and the mean intermicrotubule sp acing, or the mean number of neurofilaments and interneurofilament spacing in ax ons of all sizes in hypothermic stretch injured animals was not significant dif ferent from the mean values of sham operated animals. Conclusions: Posttraumatic moderate hypothermia induced immedia tely after axonal injury results in substantial protection of axonal cytoskeleto n and ameliorates axonal damage.

Analysis of the shape of heavy droplets on flat and spherical surface

In this study,a theoretical model was established for predicting the equilibrium shape of the droplet on flat and spherical surfaces.The theoretical equilibrium shape of heavy droplets could be obtained once contact angle and volume of droplets were given.It showed that the predictions of the theoretical flat model were in good agreement with the shape obtained by Surface Evolver when the contact angle is below 120 and the droplet size is on the order of capillary length.This available range will decrease and increase when the heavy droplet is on convex and concave spherical surface,respectively,in contrast to that on flat surface.The available range will decrease more for higher curvature of convex spherical surfaces.

Study on fire extinguishing performance of ultrafine water mist in a cup burner

Two simplified models for predicting minimum extinguishing concentration(MEC) of ultrafine water mist(UFM)(<10 m) were developed based on limiting oxygen concentration(LOC) and combustion limit temperature(CLT),respectively.Experiment was conducted using a modified cup burner which can reduce the surface adsorption of UFM.Two typical liquid fuels,n-heptane and ethanol,were used in the experiment.Tests using the same scenario were repeated 20 times or 10 times according to the variance of extinguishing time.The average and the standard deviations of extinguishing time were used to evaluate the fire extinguishing performance of UFM.Experimental results agree well with the model based on LOC,and disagree with the model based on CLT.The disagreements were explained by analyzing flow behavior of UFM.It was concluded that the primary mechanism of fire extinguishment with UFM was oxygen dilution.