Maintenance requirements: energy supply from simultaneous endogenous respiration and substrate consumption

Abstract A model is presented that describes energy for maintenance purposes (ATP) as being obtained simultaneously from biomass degradation as well as from substrate degradation in excess of growth requirements. The ratio between both catabolic processes was taken to be growth rate dependent. As such, this approach is intermediate between established models; its significant features are negative growth and the absence of substrate consumption at zero substrate concentration, and the attainability of the maximum specific growth rate (the model parameter μ _max) at elevated substrate concentrations. As a simple case, the amounts of ATP obtained from direct substrate catabolism or from the degradation of an equivalent amount of biomass were taken as identical. Also, the maintenance demand in terms of ATP per unit time and biomass was taken to be constant. True growth rate dependency of maintenance can be implemented by relaxing either of these assumptions.     

Conventional and newly developed bioheat transport models in vascularized tissues: A review

Heat transfer in a biological system is a complex process and its analysis is difficult. Heterogeneous vascular architecture, blood flow in the complex network of arteries and veins, varying metabolic heat generation rates and dependence of tissue properties on its physiological condition contribute to this complexity. The understanding of heat transfer in human body is important for better insight of thermoregulatory mechanism and physiological conditions. Its understanding is also important for accurate prediction of thermal transport and temperature distribution during biomedical applications. During the last three decades, many attempts have been made by researchers to model the complex thermal behavior of the human body. These models, viz., blood perfusion, countercurrent, thermal phase-lag, porous-media, perturbation, radiation, etc. have their corresponding strengths and limitations. Along with their biomedical applications, this article reviews various contextual issues associated with these models. After brief discussion of early bioheat models, the newly developed bioheat models are discussed in detail. Dependence of these models on biological properties, viz., thermophysical and optical properties are also discussed.     

Computational framework to model and design surgical meshes for hernia repair

Surgical procedures for hernia surgery are usually performed using prosthetic meshes. In spite of all the improvements in these biomaterials, the perfect match between the prosthesis and the implant site has not been achieved. Thus, new designs of surgical meshes are still being developed. Previous to implantation in humans, the validity of the meshes has to be addressed, and to date experimental studies have been the gold standard in testing and validating new implants. Nevertheless, these procedures involve long periods of time and are expensive. Thus, a computational framework for the simulation of prosthesis and surgical procedures may overcome some disadvantages of the experimental methods. The computational framework includes two computational models for designing and validating the behaviour of new meshes, respectively. Firstly, the beam model, which reproduces the exact geometry of the mesh, is set to design the weave and determine the stiffness of the surgical prosthesis. However, this implies a high computational cost whereas the membrane model, defined within the framework of the large deformation hyperelasticity, is a relatively inexpensive computational tool, which also enables a prosthesis to be included in more complex geometries such as human or animal bodies.     

土壤-植物-大气连续体水热、CO2通量估算模型研究进展

土壤-植物-大气连续体(SPAC)水热、CO2通量的准确估算对理解陆地和大气的物质和能量交换过程有着重要意义.重点阐述了基于过程的土壤-植物-大气连续体水热、CO2通量模型,综述了统计模型、综合模型及基于遥感的模型的发展过程.其中水热通量统计模型包括基于温度和湿度以及基于温度和辐射的方法;CO2通量统计模型包括基于气候因子或蒸散因子以及基于光能利用率的方法.水热通量过程模型包括大叶、双源、多源和多层的水热传输物理模型;CO2通量过程模型包括叶片尺度及由大叶、双叶和多层方法扩展到冠层尺度的生理生态模型以及光合-蒸腾耦合模型.综合模型包括生物物理模型、生物化学模型和生物地理模型.统计模型形式简单,资料易得,对大范围的水热通量模拟具有指导意义;过程模型准确的揭示了水热和CO2通量传输的物理和生理过程,是大尺度综合模型的基础.未来生态系统水热、CO2通量估算模型将集成各种技术手段进行多尺度网络观测和大尺度机理模拟.     

Identifiability of single-index models and additive-index models

We provide a proof for the identifiability for both single-indexmodels and partially linear single-index models assuming onlythe continuity of the regression function, a condition muchweaker than the differentiability conditions assumed in theexisting literature. Our discussion is then extended to theidentifiability of the additive-index models.     

温度与昆虫生长发育关系模型的发展与应用

昆虫作为变温动物,对温度变化更为敏感。研究温度变化对昆虫生长、发育的影响有重要理论和实践意义。目前已构建了多个描述温度与昆虫增长速率的关系模型,用于解释温度对昆虫发育速率的影响。这些模型大体可分为两类:没有热动力学基础的纯描述性模型和有热动力学基础的应用性模型。本文在对现有的有关温度变化与昆虫生长发育关系的11个模型进行评述的基础上,结合作者近年来的研究,重点介绍了迄今为止国际上最为合理的、用以反映温度对昆虫发育速率影响的Sharpe-Schoolfield-Ikemoto模型,并利用这些模型拟合了一组温发育速率数据用以展示这些模型的应用。     

Numerical model (switchable/dual model) of the human head for rigid body and finite elements applications

In this paper, a methodology for the development and validation of a numerical model of the human head using generic procedures is presented. All steps required, starting with the model generation, model validation and applications will be discussed. The proposed model may be considered as a dual one due to its capabilities to switch from deformable to a rigid body according to the application's requirements. The first step is to generate the numerical model of the human head using geometry files or medical images. The required stiffness and damping for the elastic connection used for the rigid body model are identified by performing a natural frequency analysis. The presented applications for model validation are related to impact analysis. The first case is related to Nahum's (Nahum and Smith 1970) experiments pressure data being evaluated and a pressure map generated using the results from discrete elements. For the second case, the relative displacement between the brain and the skull is evaluated according to Hardy's (Hardy WH, Foster CD, Mason, MJ, Yang KH, King A, Tashman S. 2001.Investigation of head injury mechanisms using neutral density technology and high-speed biplanar X-ray. Stapp Car Crash J. 45:337–368, SAE Paper 2001-22-0016) experiments. The main objective is to validate the rigid model as a quick and versatile tool for acquiring the input data for specific brain analyses.     

Meristems, metamers and modules and the development of shoot and root systems

BARLOW, P. W., 1989. Meristems, metamers and modules in the development of shoot and root systems . Root and shoot systems are hierarchical organizations whose levels are represented, in part, by cells and meristems. Meristems produce modules which in turn construct the architectural model. The latter is species specific and its structure depends on the geometrical interrelationships between the modular elements. The place of the metamer within this hierarchical scheme is discussed. Metamers derive directly from meristem activity and are externally recognizable as reiterated sub-units of the module. Another sub-unit of module construction, the cellular complex, or merophyte, is also a product of meristem activity, but, in contrast to the metamer, it is an internal, rather than an external, anatomical feature. Being cellular, it increases the ‘span’ of the cell level rather than constituting a level in its own right. Although the physical boundaries of metamer and merophyte can overlap, or even coincide, the two units belong to different conceptual schemes of module structure: the metamer is defined from a ‘classical’ morphological viewpoint, whereas the merophyte derives from a cellular conception of plant structure. Both the merophyte and the metamer have a role in clarifying the understanding of plant development since both provide insights into the functioning of the meristems from which they are derived and the structure of the module to which they contribute. For example, modules which lack an obvious metameric construction can usefully be analysed in terms of their merophytic organization. This is particularly true of roots of lower plants. Here, the merophytes reflect the presence and activity of a specialized meristematic apical cell. On the other hand, modules of higher plants, which lack such apical cells, also lack clearly defined merophytes, but their shoots have obvious metamers which reflect the activity of the meristem as a whole. It should be possible to represent the development of modules from cells, via their intermediate sub-structures of meristems and metamers, by means of formal languages of automata theory. One of these, a graphical algorithm (Petri net), is applied in this developmental context.