An anisotropic multiphysics damage model with application to annulus fibrosus

An anisotropic multiphysics damage model is developed to characterize the couplings among multiple physical fields within soft tissues and the tissue damage based on thermodynamic principles. This anisotropic multiphysics damage model integrates the continuum mixture theory and a continuum damage model, and the anisotropic damage is considered by evolution of internal damage variables governing the anisotropic mechanical behaviors of tissues. The energy dissipation associated with the transport of fluid and ions is generally related to tissue damage. The anisotropic multiphysics damage model is applied to simulate a case of annulus fibrosus (AF) damage in an isolated intervertebral disc under compression, to understand the damage initiation and propagation. It is found that, for this case (with 1000 N/s of compression rate and neglected ground matrix damage), the damage initiated in the outer and middle posterior regions of AF at about 700 N of axial compression. The region-dependent yield stretch ratio predicted by this model is consistent with experimental findings. A sensitive study on the damage parameters is also presented. This study provides an additional insight into AF damage in the isolated disc under mechanical compression.     

Integrated Stochastic Model of DNA Damage Repair by Non-homologous End Joining and p53/p21- Mediated Early Senescence Signalling

Unrepaired or inaccurately repaired DNA damage can lead to a range of cell fates, such as apoptosis, cellular senescence or cancer, depending on the efficiency and accuracy of DNA damage repair and on the downstream DNA damage signalling. DNA damage repair and signalling have been studied and modelled in detail separately, but it is not yet clear how they integrate with one another to control cell fate. In this study, we have created an integrated stochastic model of DNA damage repair by non-homologous end joining and of gamma irradiation-induced cellular senescence in human cells that are not apoptosis-prone. The integrated model successfully explains the changes that occur in the dynamics of DNA damage repair after irradiation. Simulations of p53/p21 dynamics after irradiation agree well with previously published experimental studies, further validating the model. Additionally, the model predicts, and we offer some experimental support, that low-dose fractionated irradiation of cells leads to temporal patterns in p53/p21 that lead to significant cellular senescence. The integrated model is valuable for studying the processes of DNA damage induced cell fate and predicting the effectiveness of DNA damage related medical interventions at the cellular level.     

Ice‐storm disturbance and long‐term forest dynamics in the Adirondack Mountains

Ice storms cause periodic disturbance to temperate forests of eastern North America. They are the primary agents of disturbance in some eastern forests. In this paper, a forest gap model is employed to explore consequences of ice storms for the long‐term dynamics of Tsuga canadensis‐northem hardwoods forests. The gap model LINKAGES was modified to simulate periodic ice storm disturbance in the Adirondack Mountains of New York. To adapt the gap model for this purpose, field data on ice storm disturbance are used to develop a polytomous logistic regression model of tree damage. The logistic regression model was then incorporated into the modified forest gap model, LINK ADIR, to determine the type of damage sustained by each simulated tree. The logistic regression model predicts high probabilities of bent boles or severe bole damage (leaning, snapping, or uprooting) in small‐diameter trees, and increasing probability of canopy damage as tree size increases. Canopy damage is most likely on gentle slopes; the probability of severe bole damage increases with increasing slope angle. In the LINKADIR simulations, tree damage type determines the probability of mortality; trees with severe bole damage are assigned the highest mortality rate. LINKADIR predicts Tsuga canadensis dominance in mesophytic old‐growth forests not disturbed by ice storms. When ice storms are simulated, the model predicts Acer saccharum‐dominated forests with higher species richness. These results suggest that ice storms may function as intermediate disturbances that enhance species richness in forested Adirondack landscapes.     

Predicting knee replacement damage in a simulator machine using a computational model with a consistent wear factor

Wear of ultrahigh molecular weight polyethylene remains a primary factor limiting the longevity of total knee replacements (TKRs). However, wear testing on a simulator machine is time consuming and expensive, making it impractical for iterative design purposes. The objectives of this paper were first, to evaluate whether a computational model using a wear factor consistent with the TKR material pair can predict accurate TKR damage measured in a simulator machine, and second, to investigate how choice of surface evolution method (fixed or variable step) and material model (linear or nonlinear) affect the prediction. An iterative computational damage model was constructed for a commercial knee implant in an AMTI simulator machine. The damage model combined a dynamic contact model with a surface evolution model to predict how wear plus creep progressively alter tibial insert geometry over multiple simulations. The computational framework was validated by predicting wear in a cylinder-on-plate system for which an analytical solution was derived. The implant damage model was evaluated for 5 million cycles of simulated gait using damage measurements made on the same implant in an AMTI machine. Using a pin-on-plate wear factor for the same material pair as the implant, the model predicted tibial insert wear volume to within 2% error and damage depths and areas to within 18% and 10% error, respectively. Choice of material model had little influence, while inclusion of surface evolution affected damage depth and area but not wear volume predictions. Surface evolution method was important only during the initial cycles, where variable step was needed to capture rapid geometry changes due to the creep. Overall, our results indicate that accurate TKR damage predictions can be made with a computational model using a constant wear factor obtained from pin-on-plate tests for the same material pair, and furthermore, that surface evolution method matters only during the initial "break in" period of the simulation.     

A damage model for the percutaneous triple hemisection technique for tendo-achilles lengthening

A full understanding of the mechanisms of action in the percutaneous triple hemisection technique for tendo-achilles lengthening has yet to be acquired and therefore, an accurate prediction of the amount of lengthening that occurs is difficult to make. The purpose of this research was to develop a phenomenological damage model that utilizes both matrix and fiber damage and replicates the observed behavior of the tendon tissue during the lengthening process. Matrix damage was triggered and evolved relative to shear strain and the fiber damage was triggered and evolved relative to fiber stretch. Three examples are given to show the effectiveness of the model. Implementation of the damage model provides a tool for studying this common procedure, and may allow for numerical investigation of alternative surgical approaches that could reduce the incidence rates of severe over-lengthening.     

Microdamage accumulation in the cement layer of hip replacements under flexural loading.

Mechanical fatigue of bone cement leading to damage accumulation is implicated in the loosening of cemented hip components. Even though cracks have been identified in autopsy-retrieved mantles, damage accumulation by continuous growth and increase in number of microcracks has not yet been demonstrated experimentally. To determine just how damage accumulation occurs in the cement layer of a hip replacement, a physical model of the joint was used in an experimental study. The model regenerates the stress pattern found in the cement layers whilst at the same time allowing visualisation of microcrack initiation and growth. In this way the gradual process of damage accumulation can be determined. Six specimens were tested to 5 million cycles and a total of 1373 cracks were observed. It was found that, under the flexural loading allowed by the model, the majority of cracks come from pores in the bulk cement and not from the interfaces. Furthermore, the lateral and medial sides have statistically different damage accumulation behaviours, and pre-load cracks significantly accelerate the damage accumulation process. The experimental results confirm that damage accumulation commences early on in the loading history and that it is continuously increasing with load in the form of crack initiation and crack propagation. The results highlight the importance of replicating the loading and restraint conditions of clinical cement mantles when endeavouring to accurately model the damage accumulation process.     

Radiation damage in protein crystallography

A general model is derived to describe the rate of radiation damage in protein crystals. This model and some of its special cases are tested against the Blake and Phillips data on X-irradiation effects in myoglobin crystals. The results point to a sequential process of damage and suggest an improved method for correcting diffraction data for the effects of radiation damage.     

A Model for Damage Load and Its Implications for the Evolution of Bacterial Aging

Deleterious mutations appearing in a population increase in frequency until stopped by natural selection. The ensuing equilibrium creates a stable frequency of deleterious mutations or the mutational load. Here I develop the comparable concept of a damage load, which is caused by harmful non-heritable changes to the phenotype. A damage load also ensues when the increase of damage is opposed by selection. The presence of a damage load favors the evolution of asymmetrical transmission of damage by a mother to her daughters. The asymmetry is beneficial because it increases fitness variance, but it also leads to aging or senescence. A mathematical model based on microbes reveals that a cell lineage dividing symmetrically is immortal if lifetime damage rates do not exceed a threshold. The evolution of asymmetry allows the lineage to persist above the threshold, but the lineage becomes mortal. In microbes with low genomic mutation rates, it is likely that the damage load is much greater than the mutational load. In metazoans with higher genomic mutation rates, the damage and the mutational load could be of the same magnitude. A fit of the model to experimental data shows that Escherichia coli cells experience a damage rate that is below the threshold and are immortal under the conditions examined. The model estimates the asymmetry level of E. coli to be low but sufficient for persisting at higher damage rates. The model also predicts that increasing asymmetry results in diminishing fitness returns, which may explain why the bacterium has not evolved higher asymmetry.     

Factors influencing wild boar damage in Taohongling National Nature Reserve in China: a model approach

Conflicts between humans and wildlife, especially wild boar (Sus scrofa), have caused serious problems across the world in recent years. It is necessary to effectively control wild boar agricultural damage that may be influenced by many factors. In this study, we collected data on agricultural damage caused by wild boars from November 2009 to October 2010 using field surveys and social interviews in Taohongling National Nature Reserve of Jiangxi Province, China. We constructed models using binary logistic regression analysis to predict damage risks and to identify the factors influencing damage risks. About 8.1 % of croplands were damaged by wild boars, and the damage to rice, cotton, and other crops were not distributed based on their respective availability as shown by the result of a chi-square goodness-of-fit test. Five factors (Japanese silvergrass, soil conditions, terrain, distances to settlements, and water sources) were explained in a model based on damage area (area-based model) with the prediction accuracy being 72.1 %. In addition to these five factors, one additional factor (i.e. distance to forest edge) was retained in a model based on damage frequency (frequency-based model) with the prediction accuracy being 83.1 %. Caution is needed when we apply these two models to predict boar damage to crops, and it is recommended that both models be used in combination to predict the damage probabilities more accurately.     

The effect of loading rate on the development of early damage in articular cartilage

Experimental reports suggest that cartilage damage depends on strain magnitude. Additionally, because of its poro-viscoelastic nature, strain magnitude in cartilage can depend on strain rate. The present study explores whether cartilage damage may develop dependent on strain rate, even when the presented damage numerical model is strain-dependent but not strain-rate-dependent. So far no experiments have been distinguished whether rate-dependent cartilage damage occurs in the collagen or in the non-fibrillar network. Thus, this research presents a finite element analysis model where, among others, collagen and non-fibrillar matrix are incorporated as well as a strain-dependent damage mechanism for these components. Collagen and non-fibrillar matrix stiffness decrease when a given strain is reached until complete failure upon reaching a maximum strain. With such model, indentation experiments at increasing strain rates were simulated on cartilage plugs and damage development was monitored over time. Collagen damage increased with increasing strain rate from 21 to 42 %. In contrast, damage in the non-fibrillar matrix decreased with increasing strain rates from 72 to 34 %. Damage started to develop at a depth of approximately 20 % of the sample height, and this was more pronounced for the slow and modest loading rates. However, the most severe damage at the end of the compression step occurred at the surface for the plugs subjected to 120 mm/min strain rate. In conclusion, the present study confirms that the location and magnitude of damage in cartilage may be strongly dependent on strain rate, even when damage occurs solely through a strain-dependent damage mechanism.     

用推广的CA模型模拟松毛虫危害的时空动态(英文)

本文建立了模拟马尾松毛虫危害时空动态的非线性CA模型。它包括自依赖、外部变量和交互作用3个组成部分。文中用方差图和相关图确定自依赖和相互作用的平均距离(时间间隔或空间距离)及相互作用随距离变化的规律,并建立了种群密度模拟的时空相关回归模型。模型模拟的结果表明,对于严重危害的区域,预测结果和实际发生十分符合;对于轻危害的区域模型低估了危害程度,但松毛虫危害趋势的估计和实际发生是一致的。     

Risk factors affecting the probability of damage by sika deer in plantation forests in Yamanashi Prefecture, Japan

Using a generalized linear mixed model approach, we determined the most important risk factors affecting the probability of damage by sika deer in a forest plantation in Japan. Candidate risk factors included tree species, stand age, peripheral dwarf bamboo community, topographical factors, snow depth, and human disturbance factors. Based on this model, we developed a risk map of forest damage. The model indicated that the most important risk factor was stand age, followed by tree species and maximum snow depth. Our predictive model has practical use due to its high classification accuracy (83.9%). To decrease damage from sika deer, an afforestation plan that incorporates these factors should be implemented. Because it is based on common, forest GIS data that have recently been compiled by several local governments in Japan, our modeling method of deer damage can easily be adapted to other areas.     

SIMULATING THE SPATIO-TEMPORAL DYNAMICS OF THE PINE CATERPILLAR (DENDROLIMUS PUNCTATUS WALKER) DAMAGE USING THE GENERALIZED CA MODEL

Abstract  A nonlinear model for simulating the spatio-temporal dynamics of the damage level of the pine caterpillar, Dendrolimus punctatus Walker, is proposed in this study. It includes the self-dependence (interaction) component, the reaction component, and the cross effect component. The average distance of interaction and reaction and how the dependence changes along distance are detected by using variogram and correlogram. The simulation result shows that the model may forecast the high damage level properly, but a bit underforecast for the low damage area. The predicted trend of damage is the same as the actually occurred.     

Quantitative aspects of repair of potentially lethal damage in mammalian cells.

Stationary cultures of Ehrlich ascites tumour cells have been irradiated with X-rays and then immediately or after a time interval trep plated to measure the survival. The increase in survival observed after delayed plating is interpreted as repair of potentially lethal damage. A cybernetic model is used to analyse these data. Three states of damage are assumed for the cells. In state A the cells can grow to macrocolonies, in state B the cells have suffered potentially lethal damage and can grow to macrocolonies only if they are allowed to repair the damage and in state C the cells are lethally damaged. A method of deriving the values of the parameters of the model from the experimental data is given. The dependence of the reaction rate constant of the repair of potentially lethal damage on the dose D is used to derive a possible mechanism for the production of the shoulder in the dose effect curve. Finally this model is compared with other models of radiation action on living cells.     

A Kinetic Model for Cell Damage Caused by Oligomer Formation

It is well known that the formation of amyloid fiber may cause invertible damage to cells, although the underlying mechanism has not been fully understood. In this article, a microscopic model considering the detailed processes of amyloid formation and cell damage is constructed based on four simple assumptions, one of which is that cell damage is raised by oligomers rather than mature fibrils. By taking the maximum entropy principle, this microscopic model in the form of infinite mass-action equations together with two reaction-convection partial differential equations (PDEs) has been greatly coarse-grained into a macroscopic system consisting of only five ordinary differential equations (ODEs). With this simple model, the effects of primary nucleation, elongation, fragmentation, and protein and seeds concentration on amyloid formation and cell damage have been extensively explored and compared with experiments. We hope that our results will provide new insights into the quantitative linkage between amyloid formation and cell damage.     

A numerical model for temperature distribution and thermal damage calculations in teeth exposed to a CO2 laser

A numerical axisymmetrical model which may be used for the evaluation of laser dental treatments is presented. This model facilitates the calculations of the temperature distribution and of thermal damage to pulp tissue caused by CO₂ laser irradiation. Temperature distributions are compared with analytical, experimental, and numerical results presented in the literature. The conformity obtained is good. It is shown that this model can be used over a wider range of time intervals and physical conditions than a previous numerical model. In addition, thermal damage is calculated for the temperature distributions presented in this paper. This model can be utilized for the optimization of exposure parameters to minimize pulp damage in the application of lasers for dental treatment.     

沿海地区森林风害研究综述

从导致森林风害的因素、风害对沿海森林生态系统的影响、风害评估方法、降低森林风害的经营管理措施等方面,综述了风害与沿海森林生态系统关系的研究成果和不足。我国未来应加强在不同尺度下沿海森林结构与功能关系、局域和区域尺度下各类生物/非生物因素与森林风害的关系以及森林风害预测评估模型的构建等3方面的研究。     

A Biomathematical Modeling Approach to Explain the Phenomenon of Radiation Hormesis

This study presents an improved version of a published biomathematical model, the Random Coincidence Model-Radiation Adapted (RCM-RA). That model describes how cancer mortality increases as dose rate increases in the high-dose rate range, as well as how mortality decreases as dose rate increases in the low-dose rate range. It was assumed that low-dose rates of ionizing radiation induce cellular defense mechanisms that also prevent or repair endogenous DNA damage caused by natural cell metabolism. The model presented describes the development of cancer by a phase of initiation that consists of a series of DNA lesions in the critical regions of tumor-associated genes such as proto-oncogenes or tumor-suppressor genes. Initiated cells can divide and form a clone of initiated cells. This clonal growth is called promotion and leads to premalignant cells. Premalignant clones can sustain further genomic damage that may lead to a malignant cell and ultimately a malignant tumor. The model thereby shares structural features with Moolgavkar's two-stage clonal expansion model. It was tested on published, U-shaped data of radon exposure in U.S. homes. The model correctly reflects the ratio of endogenous DNA damage to radiation-induced damage.     

A New In Vitro Model to Study Cellular Responses after Thermomechanical Damage in Monolayer Cultures

Although electrosurgical instruments are widely used in surgery to cut tissue layers or to achieve hemostasis by coagulation (electrocautery), only little information is available concerning the inflammatory or immune response towards the debris generated. Given the elevated local temperatures required for successful electrocautery, the remaining debris is likely to contain a plethora of compounds entirely novel to the intracorporal setting. A very common in vitro method to study cell migration after mechanical damage is the scratch assay, however, there is no established model for thermomechanical damage to characterise cellular reactions. In this study, we established a new in vitro model to investigate exposure to high temperature in a carefully controlled cell culture system. Heatable thermostat-controlled aluminium stamps were developed to induce local damage in primary human umbilical vein endothelial cells (HUVEC). The thermomechanical damage invoked is reproducibly locally confined, therefore allowing studies, under the same experimental conditions, of cells affected to various degrees as well as of unaffected cells. We show that the unaffected cells surrounding the thermomechanical damage zone are able to migrate into the damaged area, resulting in a complete closure of the ‘wound’ within 48 h. Initial studies have shown that there are significant morphological and biological differences in endothelial cells after thermomechanical damage compared to the mechanical damage inflicted by using the unheated stamp as a control. Accordingly, after thermomechanical damage, cell death as well as cell protection programs were activated. Mononuclear cells adhered in the area adjacent to thermomechanical damage, but not to the zone of mechanical damage. Therefore, our model can help to understand the differences in wound healing during the early phase of regeneration after thermomechanical vs. mechanical damage. Furthermore, this model lends itself to study the response of other cells, thus broadening the range of thermal injuries that can be analysed.     

Tea Plantation Frost Damage Early Warning Using a Two-Fold Method for Temperature Prediction

As the source and main producing area of tea in the world, China has formed unique tea culture, and achieved remarkable economic benefits. However, frequent meteorological disasters, particularly low temperature frost damage in late spring has seriously threatened the growth status of tea trees and caused quality and yield reduction of tea industry. Thus, timely and accurate early warning of frost damage occurrence in specific tea garden is very important for tea plantation management and economic values. Aiming at the problems existing in current meteorological disaster forecasting methods, such as difficulty in obtaining massive meteorological data, large amount of calculation for predicted models and incomplete information on frost damage occurrence, this paper proposed a two-fold algorithm for short-term and real-time prediction of temperature using field environmental data, and temperature trend results from a nearest local weather station for accurate frost damage occurrence level determination, so as to achieve a specific tea garden frost damage occurrence prediction in a microclimate. Time-series meteorological data collected from a small weather station was used for testing and parameterization of a two-fold method, and another dataset acquired from Tea Experimental Base of Zhejiang University was further used to validate the capability of a two-fold model for frost damage forecasting. Results showed that compared with the results of autoregressive integrated moving average (ARIMA) and multiple linear regression (MLR), the proposed two-fold method using a second order Furrier fitting model and a K-Nearest Neighbor model (K = 3) with three days historical temperature data exhibited excellent accuracy for frost damage occurrence prediction on consideration of both model accuracy and computation (98.46% forecasted duration of frost damage, and 95.38% for forecasted temperature at the onset time). For field test in a tea garden, the proposed method accurately predicted three times frost damage occurrences, including onset time, duration and occurrence level. These results suggested the newly-proposed two-fold method was suitable for tea plantation frost damage occurrence forecasting.