多组分冷冻保护剂导入神经干细胞球的传质模拟

基于Maxwell-Stefan方程和两参数模型构建了神经干细胞球多组分保护剂导入模型,并模拟了多组分保护剂导入过程中细胞内外浓度及细胞膜两侧浓差的时空分布。在此基础上系统分析了多组分浓度配比、神经球尺寸、保护剂导入方式对传质渗透过程的影响。结果表明,多组分保护剂导入神经球过程中出现"逆梯度扩散"现象,胞内浓度变化总是滞后于胞外浓度变化,细胞膜两侧浓差呈现先增大后减少的趋势。改变保护剂组分的浓度配比时,不同组分的渗透特性变化规律不同。此外,神经球尺寸对中心处细胞的浓度时空分布影响显著,分步导入和连续导入能够减缓保护剂扩散,降低细胞内外浓差。本研究结果可用于指导神经球冷冻保存的实验研究,优化保护剂导入程序。     

低温保护剂对神经干细胞球添加过程的模拟分析

建立了神经干细胞球的低温保护剂添加模型。通过计算研究了在保护剂添加过程中,神经球中不同位置的细胞体积变化情况,以及细胞内外浓度和细胞膜两侧浓差随时间和空间的变化情况;并分析了影响细胞体积变化的因素,利用该模型进行了保护剂添加程序的优化。结果表明细胞外的保护剂浓度变化较快,在球表面处不到10 s接近平衡,接近球中心处15 s后接近平衡;由于跨膜传质阻力的影响,胞内的保护剂浓度变化较为平缓。减小L_p和增大ω可以显著改善保护剂添加过程的细胞体积变化,神经球尺寸对细胞体积变化影响较小。添加高浓度保护剂时,可以采用等渗透压差、渗透时间间隔逐渐减小的分步添加方法,分步添加方法以四步法较好。理想的连续梯度添加方案应是低浓差和短添加时间的组合,凸曲线添加方案是一种合适的添加方法。     

成骨细胞玻璃化冷冻保护剂的研究

在超低温冷冻过程中,冷冻保护剂(CPA)抑制胞内冰晶形成和避免溶质效应.然而,在其导入和洗脱过程中,由于渗透压的急剧变化将导致细胞大量死亡.本文以成骨细胞为样本,通过测定冷冻保护剂的玻璃化温度、CPA导入和洗脱时渗透压变化及其对细胞活性的影响,研究冷冻保护剂浓度和不同种类保护剂的联合使用对成骨细胞玻璃化冷冻过程的影响.     

骨组织冷冻过程中的CPA导入和洗脱过程的传递现象

通过酶解离台盼蓝染色计数法和渗透压的测定对SD大鼠颅骨骨块超低温保存过程中冷冻保护剂的导入和洗脱过程的传递特性进行了初步研究,试图找到较优的导入,洗脱方案及其规律.实验结果表明对于SD大鼠颅骨骨块,浓度为15%的二甲亚砜作为CPA的渗透过程在10min左右即可达到平衡,低浓度CPA对组织内细胞的溶质损伤主要是渗透引起的,酶解离法对较低浓度的CPA有较好的适用性.     

湿度差驱动下溶液蒸发冷冻过程中冰体的发展规律

针对湿度(绝对湿度)差驱动下溶液的蒸发冷冻过程进行了分析研究,在热质平衡理论的基础上,考虑溶液表面冰体的形面变化特征,建立了蒸发冷冻过程中溶液表面冰体生长的热力学非稳态模型,分析了不同蒸发冷冻时刻,气-液界面间湿度(绝对湿度)差、气流速度以及气-液界面间质扩散对溶液表面冰体发展分布的影响,研究表明湿度(绝对湿度)差、气流速度和质扩散系数对溶液的蒸发冷冻作用明显。该理论模型及研究结果为强化湿度差驱动下溶液的蒸发冷冻及工程应用提供了理论指导和依据。     

果蔬渗透脱水过程动力学研究

结合植物组织结构与流体传输过程机理建立了渗透脱水过程的一维质量传递数学模型。模型以植物细胞为传输过程的基本单元，考虑了各组分在细胞内、细胞外、通过细胞膜及胞间连丝的质量扩散，和由于体积收缩而导致的集流传输。以土豆为实验物料，在40℃恒温条件下，采用40％（质量百分比）的蔗糖溶液作为渗透液，进行渗透脱水实验，得到的实验结果与模拟结果十分接近，验证了模型的有效性。通过数值模拟可详细描述渗透脱水过程中土豆细胞内外水和蔗糖的质量浓度分布。并就能源与生产效率方面对“渗透-干燥”与“无预处理干燥”过程作了比较。     

什么叫渗析?什么叫电渗析?

渗析是属于一种自然发生的物理现象。如将两种不同含盐量的水用一张渗透膜隔开,就会发生含盐量大的水的电介质离子穿过膜向含盐量小的水中扩散,这个现象就是渗析。这种渗析是由于含盐量浓度不同而引起的,称为浓差渗析。渗析过程与浓度差的大小有关,浓差越大,渗析的过程越快,否则就越慢。因为是以浓差作为推动力的,所以,扩散速度始终是比较慢的。如果要加快这个速度,就可以在膜的两边施     

聚乳酸载药微球形成机理的模拟分析与实验研究

对聚乳酸载药微球的形成过程进行了耗散颗粒动力学模拟和实验研究。载药体系以硝苯地平为模型药物、聚乳酸（poly-lactic acid, PLA）为载体材料、聚乙烯醇（poly vinyl alcohol, PVA）为稳定剂。通过研究，提出了聚乳酸载药微球的形成机理，认为微球形成过程可分为4个阶段，即高度分散阶段、PLA分子聚集阶段、硝苯地平分子向微球内部扩散阶段和微球的形成及稳定阶段。机理分析和模拟表明，微球对硝苯地平的包载量有一个临界值，硝苯地平浓度低于该值，几乎所有的硝苯地平分子都能扩散进微球的内部;高于该值，则部分硝苯地平分子难以扩散进微球内部，而分散在介质中，形成硝苯地平聚集体。     

聚合物载药微球活性组分控释性能的动力学模拟

将聚合物载药微球的溶解扩散模型与药代动力学模型相结合,计算了载药微球的药物控释性能的浓度时间曲线.采用叠加法计算了多次投药所产生的稳态药物浓度特征,探讨了释放速率、给药时间间隔对药物浓度曲线的影响.相对于口服药物溶液,微球中的药物通过载体的控制释放,血药浓度峰值有很大的降低,多次给药时载药微球的药物浓度波动也有大幅度的减小;适当的溶解速率可减小药物浓度波动,同时也满足治疗所要求的浓度值.     

酸氧化处理对碳球表面基团含量的影响

采用硝酸为氧化剂对碳球表面进行改性研究,通过红外光谱法和酸碱滴定法分别考察了硝酸浓度和处理时间对碳球表面含氧基团的影响.结果表明,硝酸处理可在碳球表面引入羧基、羟基等含氧基团.随硝酸浓度的增加,碳球表面羧基、羰基以及羟基等含氧基团的量上升;随浓硝酸处理时间的延长,羟基含量上升,羰基含量下降,羧基含量和含氧基团的总量先上升而后下降.用浓硝酸处理8 h时,羟基含量最高,为2.490 mmol/g;浓硝酸处理4 h时羧基含量和含氧基团总量最高,分别为1.289mmol/g和5.702 mmol/g.     

Diffusion Characteristics in Microcapsules

An equation of diffusion for microcapsules(hollow sphere)was developed,employing the mathematicalmodel for the diffusion characteristics of solid sphere.In the proposed equation,a combination diffusion coeffi-cient was introduced as a substitute for the diffusion coefficient in the solid sphere mathematical model and ex-pressed as a function of the diffusion coefficient inside solution of hollow sphere,as well as in the polymer mem-brane.With this modified model,the diffusion coefficients of glucose in NaCS(sodium cellulose sulfate)-PDADMAC(Poly-diallyl-dimethyl-ammonium chloride)membrane and in Ca-alginate gel membrane were deter-mined.The diffusion coefficient in NaCS-PDADMAC membrane was found to be 2.12×10~(-11)m~2·s~(-1)and thatin Ca-alginate membrane 2.62×10~(-10)m~2·s~(-1).     

CD133-Positive Cells Might Be Responsible for Efficient Proliferation of Human Meningioma Cells

Owing to lack of appropriate model systems, investigations of meningioma biology have come to a stop. In this study, we developed a comprehensive digestion method and defined a culture system. Using this method and system, primary meningioma cells in conditioned suspension medium and a hypoxic environment could be amplified in spheres and were passaged for more than ten generations. Meningioma sphere cells were positive for meningioma cell markers and negative for markers of neural cell types. Importantly, we found the cells expressed the stem cell marker, CD133, but not nestin. All of the tumor sphere cell populations showed a slower degree of cell proliferation than that of human glioma cells and fetal neural stem cells (NSCs). Further studies showed that the proliferative rate was positively correlated with CD133 expression. The higher the CD133 expression, the faster the cell proliferation. With the increase in cell generations, the cell proliferation rate gradually slowed down, and CD133 expression also decreased. Single CD133(+) cells rather than CD133(-) cells could form spheres. Thus, the results above indicated that those cells expressing CD133 in spheres might be stem-like cells, which may be responsible for efficient amplification of human meningioma cells. Decreased expression of CD133 may lead to the failure of long-term passaging.     

Effectiveness factor of a catalytic sphere in particle assemblage approached with a cell model

The cell model approach was extended to the catalytic reaction over a spherical catalyst pellet and the effects of several parameters on the effectiveness factor were investigated via numerical simulation. The proposed mathematical model consisted of the partial differential equations for gas reactant flow in the external gas phase around a catalyst sphere, mass transport in the gas phase, and two-dimensional diffusion-reaction in the catalytic sphere. Numerical simulation in the orthogonal boundary fitted reference frame demonstrated the decrease in effectiveness factor of a catalyst sphere due to the external mass transfer resistance and inter-particle hydrodynamic interaction. It was observed that the voidage of the particle assemblage shows more recognized influence than the Peclet and Reynolds numbers of particles and the azimuthal diffusion of reactant inside the particle was negligible. On this basis, a simplified set of cell model equations for catalytic reaction in particle assemblages were proposed. An example of optimizing search indicated the present model may be used to detect the most strong influence on catalytic reaction in particle assemblage over the practical ranges of operating and designing parameters to avoid excessive loss in the effectiveness factor.     

电渗析脱盐过程离子传递现象的数值模拟

建立了电渗析脱盐过程离子传递稳态模型，研究了离子电荷数、离子扩散系数和离子交换膜电导率对脱盐过程传质的影响，描述了离子浓度分布、电势分布和离子传递通量分布的变化情况。研究表明：相较于一价离子，二价离子在电渗析过程中膜两侧浓度差较小，跨膜电压降较高，各项传递通量较小；当离子扩散系数增大时，膜两侧浓度差减小，跨膜电压降升高，总传递通量和电迁移通量增大；当离子交换膜电导率增大时，膜两侧浓度差增大，跨膜电压降降低，各项传递通量均增大。     

A geometric solution to the largest-free-sphere problem in zeolite frameworks

We have applied Delaunay triangulation to models of the known zeolite frameworks. We show that this well-established technique from computational geometry provides for each framework; (i) the location and shape of the open pores and channels, (ii) the diameter of the largest possible included sphere, and indirectly (iii) the diameter of the largest-free-sphere that can diffuse through the framework by at least one lattice translation. Since Delaunay triangulation naturally locates the empty spaces within a set of points, it provides a powerful computer-automated tool for determining the physical characteristics of pores and channels of zeolite frameworks. Such tools will further enhance the usefulness of large databases of hypothetical framework materials.

Here, we tabulate results for the 165 zeolite frameworks that are presently listed in the Atlas of Zeolite Frameworks. Of the known zeolites, refined as pure silicates, the largest included sphere occurs in the TSC framework, with a diameter of 16.39 Å. The largest-free-sphere has a diameter of 11.33 Å, for diffusion along the [0 0 1] direction in the VFI framework.     

硬球理论用于液相扩散系数的关联

<正>硬球理论的基础是Maxwell－Boltzman的统计力学理论,最早由Chapman等将该理论应用于研究稀薄气体的传递性质。在稠密流体中,必须考虑分子碰撞频率大幅度增加的影响因素。 Dymond等认为该影响与分子接触径向分布函数g(σ)有关,并以此计算了     

Diffusion MR in Biological Systems: Tissue Compartments and Exchange

The processes of diffusion in multi-compartmental tissue models are discussed using an analytical model of diffusion with exchange. Diffusion in the intracellular compartment has been found to be highly restricted, with the apparent diffusion coefficient (ADC₁) dependent on the experimental parameters. Extracellular diffusion mediated by tortuosity, depends on tissue geometry, but not on the experimental conditions. Both the intra- and extracellular diffusion can be anisotropic and exhibit non-monoexponential behavior. The cell membrane permeability is shown to significantly influence the diffusion measurement in tissues. In consequence, the phenomenological, bi-exponential models of diffusion cannot directly estimate the intrinsic characteristics of intra- and extracellular water. The mechanisms of the ADC decrease after stroke are also discussed.     

Determination of mass diffusion overpotential distribution with flow pulse method from current distribution measurements in a PEMFC

The mass diffusion overpotential distribution in a free-breathing proton exchange membrane fuel cell (PEMFC) was determined from current distribution measurements using a flow pulse approach. The current distribution measurements were conducted with a segmented flow-field plate. Flow pulses were fed to the cathode channels to form a uniform oxygen concentration distribution along the channels. Simultaneously, the cell resistance was monitored using the current interruption method. From the experimental data, the mass diffusion overpotential distribution was calculated using the Tafel equation. The results show that the mass diffusion overpotential in different parts of the cell may vary considerably, for example, at 180 mA cm^–2 the mass diffusion overpotential difference between the bottom and top part of the cell was 0.1 V.