A test of the optimality approach to modelling canopy properties and CO2 uptake by natural vegetation

Photosynthesis provides plants with their main building material, carbohydrates, and with the energy necessary to thrive and prosper in their environment. We expect, therefore, that natural vegetation would evolve optimally to maximize its net carbon profit (NCP), the difference between carbon acquired by photosynthesis and carbon spent on maintenance of the organs involved in its uptake. We modelled N(CP) for an optimal vegetation for a site in the wet-dry tropics of north Australia based on this hypothesis and on an ecophysiological gas exchange and photosynthesis model, and compared the modelled CO2 fluxes and canopy properties with observations from the site. The comparison gives insights into theoretical and real controls on gas exchange and canopy structure, and supports the optimality approach for the modelling of gas exchange of natural vegetation. The main advantage of the optimality approach we adopt is that no assumptions about the particular vegetation of a site are required, making it a very powerful tool for predicting vegetation response to long-term climate or land use change.     

Energy analysis of wrist impact and surface rebound

The mechanical interactions during impact of a falling human body onto a non-rigid surface are complex. Mechanical properties of both the impacting body and the impacted surface contribute to risk of injury. Increased understanding of these properties should provide insight into the process and how to reduce injury risk. We assessed whether modelling energy flows in the body during impact can provide useful information. As input, we used data from gymnastic tumbling mats and from children performing an exercise involving freefall onto an outstretched arm. Even basic energy transfer principles provided information not discerned by the mechanical approach traditionally used. The model identified differences between surfaces in how energy flowed through an arm and the strains imposed on the wrist during impact and rebound. Therefore, it shows promise for identifying potentially injurious human–surface interactions. Analysis of other human impact situations, and the relationship between the energy flow and injury risk, is planned.     

Towards reducing impact-induced brain injury: lessons from a computational study of army and football helmet pads

We use computational simulations to compare the impact response of different football and U.S. Army helmet pad materials. We conduct experiments to characterise the material response of different helmet pads. We simulate experimental helmet impact tests performed by the U.S. Army to validate our methods. We then simulate a cylindrical impactor striking different pads. The acceleration history of the impactor is used to calculate the head injury criterion for each pad. We conduct sensitivity studies exploring the effects of pad composition, geometry and material stiffness. We find that (1) the football pad materials do not outperform the currently used military pad material in militarily relevant impact scenarios; (2) optimal material properties for a pad depend on impact energy and (3) thicker pads perform better at all velocities. Although we considered only the isolated response of pad materials, not entire helmet systems, our analysis suggests that by using larger helmet shells with correspondingly thicker pads, impact-induced traumatic brain injury may be reduced.     

Evaluation of the head-helmet sliding properties in an impact test

The scalp plays a crucial role in head impact biomechanics, being the first tissue involved in the impact and providing a sliding interface between the impactor and/or helmet and the skull. It is important to understand both the scalp-skull and the scalp-helmet sliding in order to determine the head response due to an impact. However, experimental data on the sliding properties of the scalp is lacking. The aim of this work was to identify the sliding properties of the scalp using cadaver heads, in terms of scalp-skull and scalp-liner (internal liner of the helmet) friction and to compare these values with that of widely used artificial headforms (HIII and magnesium EN960). The effect of the hair, the direction of sliding, the speed of the test and the normal load were considered. The experiments revealed that the sliding behaviour of the scalp under impact loading is characterised by three main phases: (1) the low friction sliding of the scalp over the skull (scalp-skull friction), (2) the tensioning effect of the scalp and (3) the sliding of the liner fabric over the scalp (scalp-liner friction). Results showed that the scalp-skull coefficient of friction (COF) is very low (0.06 ± 0.048), whereas the scalp-liner COF is 0.29 ± 0.07. The scalp-liner COF is statistically different from the value of the HIII-liner (0.75 ± 0.06) and the magnesium EN960-liner (0.16 ± 0.026). These data will lead to the improvement of current headforms for head impact standard tests, ultimately leading to more realistic head impact simulations and the optimization of helmet designs.     

A rule-based approach to the modelling of bacterial ecosystems

This paper presents an approach to ecological/evolutionary modelling that is inspired by natural bacterial ecosystems and bacterial evolution. An individual-based artificial ecosystem model is proposed, which is designed to explore the evolvability of adaptive behavioural strategies in artificial bacteria represented by rule-based learning classifier systems. The proposed ecosystem model consists of a n-dimensional environmental grid, which can contain different types of artificial resources in arbitrary arrangements. The resources provide the energy that is necessary for the organisms to sustain life, and can trigger different types of behaviour in the organisms, such as movement towards nutrients and away from toxic substances, growth, and the controlled release of signalling resources. The balance between energy and material is modelled carefully to ensure that the ecosystem is dissipative. Those organisms that are able to efficiently exploit the available resources gradually accumulate enough energy to reproduce (by binary fission) and generate copies of themselves in the environment. Organisms are also able to produce their own resources, which can potentially be used as markers to send signals to other organisms (a behaviour known as quorum sensing). The complex relationships between stimuli and actions in the organisms are stochastically altered by means of mutations, thus enabling the organisms to adapt to their environment and maximise their lifespan and reproductive success. In this paper, the proposed bacterial ecosystem model is defined formally and its structure is discussed in detail. This is followed by results from simulation experiments that illustrate the model's operation and how it can be used in evolutionary modelling/computing scenarios.     

Development of a Finite Element Model of Decompressive Craniectomy

Decompressive craniectomy (DC), an operation whereby part of the skull is removed, is used in the management of patients with brain swelling. While the aim of DC is to reduce intracranial pressure, there is the risk that brain deformation and mechanical strain associated with the operation could damage the brain tissue. The nature and extent of the resulting strain regime is poorly understood at present. Finite element (FE) models of DC can provide insight into this applied strain and hence assist in deciding on the best surgical procedures. However there is uncertainty about how well these models match experimental data, which are difficult to obtain clinically. Hence there is a need to validate any modelling approach outside the clinical setting. This paper develops an axisymmetric FE model of an idealised DC to assess the key features of such an FE model which are needed for an accurate simulation of DC. The FE models are compared with an experimental model using gelatin hydrogel, which has similar poro-viscoelastic material property characteristics to brain tissue. Strain on a central plane of the FE model and the front face of the experimental model, deformation and load relaxation curves are compared between experiment and FE. Results show good agreement between the FE and experimental models, providing confidence in applying the proposed FE modelling approach to DC. Such a model should use material properties appropriate for brain tissue and include a more realistic whole head geometry.     

Improved reduced-order modelling of cerebrovascular flow distribution by accounting for arterial bifurcation pressure drops

Reduced-order modelling offers the possibility to study global flow features in cardiovascular networks. In order to validate these models, previous studies have been conducted in which they compared 3D computational fluid dynamics simulations with reduced-order simulations. Discrepancies have been reported between the two methods. The loss of energy at the bifurcations is usually neglected and has been pointed out as a possible explanation for these discrepancies. We present distributed lumped models of cerebrovasculatures created automatically from 70 cerebrovascular networks segmented from 3D angiograms. The outflow rate repartitions predicted with and without modelling the energy loss at the bifurcations are compared against 3D simulations. When neglecting the energy loss at the bifurcations, the flow rates though the anterior cerebral arteries are overestimated by 4.7±6.8% (error relative to the inlet flow rate, mean ± standard deviation), impacting the remaining volume of flow going to the other vessels. When the energy loss is modelled, this error is dropping to 0.1±3.2%. Overall, over the total of 337 outlet vessels, when the energy losses at the bifurcations are not modelled the 95% of agreement is in the range of ±13.5% and is down to ±6.5% when the energy losses are considered. With minimal input and computational resources, the presented method can estimate the outflow rates reliably. This study constitutes the largest validation of a reduced-order flow model against 3D simulations. The impact of the energy loss at the bifurcations is here demonstrated for cerebrovasculatures but can be applied to other physiological networks.     

Energy landscapes shape microbial communities in hydrothermal systems on the Arctic Mid-Ocean Ridge

Methods developed in geochemical modelling combined with recent advances in molecular microbial ecology provide new opportunities to explore how microbial communities are shaped by their chemical surroundings. Here, we present a framework for analyses of how chemical energy availability shape chemotrophic microbial communities in hydrothermal systems through an investigation of two geochemically different basalt-hosted hydrothermal systems on the Arctic Mid-Ocean Ridge: the Soria Moria Vent field (SMVF) and the Loki''s Castle Vent Field (LCVF). Chemical energy landscapes were evaluated through modelling of the Gibbs energy from selected redox reactions under different mixing ratios between seawater and hydrothermal fluids. Our models indicate that the sediment-influenced LCVF has a much higher potential for both anaerobic and aerobic methane oxidation, as well as aerobic ammonium and hydrogen oxidation, than the SMVF. The modelled energy landscapes were used to develop microbial community composition models, which were compared with community compositions in environmental samples inside or on the exterior of hydrothermal chimneys, as assessed by pyrosequencing of partial 16S rRNA genes. We show that modelled microbial communities based solely on thermodynamic considerations can have a high predictive power and provide a framework for analyses of the link between energy availability and microbial community composition.     

Rebreathing in a subject wearing an integral crash helmet.

The respired air of a volunteer was analysed while he was wearing a variety of integral crash helmets. Observations were made with and without a protective balaclava, bib or scarf, or both. Rebreathing occurred and the peak inspired oxygen tension fell as low as 16.0 kPa (120 mm Hg) with a minimum inspired carbon dioxide of 2.1 KPa (16.0 mm Hg). Accessories worn or attached to the helmet which restrict airflow into the helmet should not be used. Attention should be paid to the "air conditioning" of helmets when worn with flameproof balaclavas and bibs.     

A Novel MXene/Ecoflex Nanocomposite-Coated Fabric as a Highly Negative and Stable Friction Layer for High-Output Triboelectric Nanogenerators

The triboelectric material properties and mechanical stability of the contact layer are vital to achieving durable triboelectric nanogenerators (TENGs) with high output performance. Herein, a novel MXene/Ecoflex nanocomposite is introduced as a promising triboelectric material because of its highly negative triboelectric properties and mechanical stability. The MXene/Ecoflex nanocomposite with a fabric-based waterproof TENG (FW-TENG) is fabricated and designed to universally harvest energy from various human motions as well as the natural environment (rain and wind). The fabricated FW-TENG delivers a maximum output peak power of 3.69 mW and a power density of 9.24 W m⁻², respectively, at a matching load resistance of 4.5 MΩ under a frequency of 4.5 Hz and a force of 8 N. Furthermore, the applicability of this device in various products is investigated. The FW-TENG can protect against a crash caused by rainy and humid weather. An FW-TENG-based self-powered smart active device that detects motion on a carpet is demonstrated and is equipped with sleep monitoring motion sensors. The FW-TENG not only has self-powered benefits and excellent mechanical amenability but is also exceptionally reliable and stable against water intrusion, which are important characteristics to realize next-generation wearable/portable technologies.     

HElmet therapy Assessment in infants with Deformed Skulls (HEADS): protocol for a randomised controlled trial

ABSTRACT: BACKGROUND: In The Netherlands helmet therapy is a commonly used treatment in infants with skull deformation (deformational plagiocephaly or deformational brachycephaly). However, evidence on the effectiveness of this treatment is lacking. The HEADS study (Helmet therapy Assessment in Deformed Skulls) aims to determine the effects and costs of helmet therapy compared to no helmet therapy in infants with moderate to severe skull deformation. METHODS: Pragmatic randomized controlled trial (RCT) nested in a cohort study. The cohort study includes infants with a positional preference and/or skull deformation at two to four months (first assessment). At 5 months of age, all children will be assessed again and infants meeting criteria for helmet therapy will be asked to participate in the RCT. Participants will be randomly allocated to either helmet therapy or no helmet therapy. Parents of eligible infants that do not agree with enrollment in the RCT are invited to stay enrolled for follow up in a non-randomized controlled trial (nRCT); they will make the decision to start helmet therapy or not themselves. Assessments will take place at 8, 12 and 24 months of age. Main outcome is head shape measured with plagiocephalometry. Secondary outcomes are parental satisfaction with the condition, concerns about the future, anxiety level and satisfaction with the treatment and motor development and quality of life of the infant. Finally compliance and costs will also be determined. DISCUSSION: HEADS will be the first study to present data on the effectiveness of helmet therapy. Outcomes will be important for parents and their children, health care professionals and future treatment policies. They will likely influence the reimbursement of health insurance companies. Besides these health outcomes we will be able to answer several methodological questions, e.g. do participants in a RCT represent the eligible target population and do outcomes of the RCT differ from outcomes found in the nRCT? Trial registration - ISRCTN18473161.     

Inverse analysis and robustness evaluation for biological structure behaviour in FE simulation: application to the liver

To prevent traumas to abdominal organs, the selection of efficient safety devices should be based on a detailed knowledge of injury mechanisms and related injury criteria. In this sense, finite element (FE) simulation coupled with experiment could be a valuable tool to provide a better understanding of the behaviour of internal organs under crash conditions. This work proposes a methodology based on inverse analysis which combines exploration process optimisation and robustness study to obtain mechanical behaviour of the complex structure of the liver through FE simulation. The liver characterisation was based on Mooney-Rivlin hyperelastic behaviour law considering whole liver structure under uniform quasi-static compression. With the global method used, the model fits experimental data. The variability induced by modelling parameters is quantified within a reasonable time.     

A new test set-up for skull fracture characterisation

Skull fracture is a frequently observed type of severe head injury. Historically, a variety of impact test set-ups and techniques have been used for investigating skull fracture. The most frequently used are the free-fall technique, the guided fall or drop tower set-up and the piston-driven impactor set-up. This document proposes a new type of set-up for cadaver head impact testing which combines the strengths of the most frequently used techniques and devices. The set-up consists of two pendulums, which allow for a 1 degree of freedom rotational motion. The first pendulum is the impactor and is used to strike the blow. The head is attached to the second pendulum using a polyester resin. Local skull deformation and impact force are measured with a sample frequency of 65 kHz. From these data, absorbed energy until skull fracture is calculated. A set-up evaluation consisting of 14 frontal skull and head impact tests shows an accurate measurement of both force and local skull deformation until fracture of the skull. Simplified mechanical models are used to analyse the different impacting techniques from literature as well as the new proposed set-up. It is concluded that the proposed test set-up is able to accurately calculate the energy absorbed by the skull until fracture with an uncertainty interval of 10%. Second, it is concluded that skull fracture caused by blunt impact occurs before any significant motion of the head. The two-pendulum set-up is the first head impact device to allow a well-controlled measurement environment without altering the skull stress distribution.     

Inverse analysis and robustness evaluation for biological structure behaviour in FE simulation: application to the liver

To prevent traumas to abdominal organs, the selection of efficient safety devices should be based on a detailed knowledge of injury mechanisms and related injury criteria. In this sense, finite element (FE) simulation coupled with experiment could be a valuable tool to provide a better understanding of the behaviour of internal organs under crash conditions. This work proposes a methodology based on inverse analysis which combines exploration process optimisation and robustness study to obtain mechanical behaviour of the complex structure of the liver through FE simulation. The liver characterisation was based on Mooney–Rivlin hyperelastic behaviour law considering whole liver structure under uniform quasi-static compression. With the global method used, the model fits experimental data. The variability induced by modelling parameters is quantified within a reasonable time.     

Allometry in the distribution of material properties and geometry of the felid skull: why larger species may need to change and how they may achieve it

Extant members of the cat family (Felidae) have been considered behaviourally and morphologically conservative, i.e., despite great differences in size, there is relatively little variation in either the shape of the felid skull and dentition across species, or in the way in which these structures are used to kill and dismember prey. Consequently felids have been considered an appropriate focus for a number of investigations into the influence of allometry on craniomandibular mechanics and morphology. However, although previous treatments have considered the role of shape, they have not investigated the influence of differences in the distribution of relatively stiff cortical and more compliant cancellous bone on performance. Here, using models that incorporate material properties for both cortical and cancellous bone, we apply three-dimensional (3D) finite element analysis (FEA) to models representing the skulls of seven extant felid species. Our objectives being to determine allometric trends regarding both overall geometry and the relative distributions of cortical and cancellous bone tissue. We also more comprehensively assess variation in the efficiency with which muscular force is converted to bite force and the capacity to resist associated stresses. Our results show that the cheetah (Acinonyx jubatus) may be exceptional regarding both the efficiency with which muscular force is converted to bite force and the distribution of stress. We found a negative allometric trend between cortical bone volume and total skull bone volume, and positive allometry between the total skull bone volume and skull surface area. Results gained from mathematical modelling of beam analogies suggest that these trends reflect a need for larger species to respond to physical challenges associated with increased size, and, that changes in skull shape, bone composition, or a combination of both may be required to accommodate these challenges. With geometrical scaling stress increases by the same factor, and displacement by the same factor squared, but the ultimate failure stress of the material is invariant. We find that as species become larger, overall skull bone volume relative to surface area increases by adding a higher proportion of less dense and more compliant cancellous bone. This results in an increased cross-sectional area and second moment of inertia, which acts to reduce the overall stresses. An overall saving in mass is a likely additional consequence. Although we do find evidence that skull stiffness does diminish with size, we also argue that this is at least in part mitigated through the influence of these allometric trends. We further suggest that these trends and the explanations for them may be universal for vertebrates.     

面向重要实质器官的生物制造技术

在体外制造可修复人体受损组织与器官功能的活性替代物一直是人类的梦想.制造、材料与生命科学的交叉与融合发展,为生物组织与器官的体外制造提供了必要的技术、材料与生物学基础,从而实现了皮肤、骨、膀胱等简单活性组织的临床应用,但人体重要实质器官如肝脏、肺等的再造研究至今未取得突破性进展.重要实质器官内部复杂的微观结构系统及多细胞体系的构建是实现其体外制造的关键,也是当前生物组织与器官制造技术所面临的巨大挑战.从生物制造的角度,综述国内外在重要实质器官复杂微结构制造领域的主要技术方法及最新研究进展,通过分析与评价,对未来重要实质器官的生物制造技术发展进行展望.     

A modified human head model for the study of impact head injury

A recently published finite element (FE) head model is modified to consider the viscoelasticity of the meninges, the spongy and compact bone in the skull. The cerebrospinal fluid (CSF) is simulated explicitly as a hydrostatic fluid by using a surface-based fluid modelling method, which allows fluid and structure interaction. It is found that the modified model yields smoother pressure responses in a head impact simulation. The baseline model underestimated the peak von Mises stress in the brain by 15% and the peak principal stress in the skull by 33%. The increase in the maximum principal stress in the skull is mainly caused by the updation of the material's viscoelasticity, and the change in the maximum von Mises stress in the brain is mainly caused by the improvement of the CSF simulation. The study shows that the viscoelasticity of the head tissue should be considered, and that the CSF should be modelled as a fluid, when using FE analysis to study head injury due to impact.     

Viscoelastic properties of cell walls of single living plant cells determined by dynamic nanoindentation

Plant development results from controlled cell divisions, structural modifications, and reorganizations of the cell wall. Thereby, regulation of cell wall behaviour takes place at multiple length scales involving compositional and architectural aspects in addition to various developmental and/or environmental factors. The physical properties of the primary wall are largely determined by the nature of the complex polymer network, which exhibits time-dependent behaviour representative of viscoelastic materials. Here, a dynamic nanoindentation technique is used to measure the time-dependent response and the viscoelastic behaviour of the cell wall in single living cells at a micron or sub-micron scale. With this approach, significant changes in storage (stiffness) and loss (loss of energy) moduli are captured among the tested cells. The results reveal hitherto unknown differences in the viscoelastic parameters of the walls of same-age similarly positioned cells of the Arabidopsis ecotypes (Col 0 and Ws 2). The technique is also shown to be sensitive enough to detect changes in cell wall properties in cells deficient in the activity of the chromatin modifier ATX1. Extensive computational modelling of the experimental measurements (i.e. modelling the cell as a viscoelastic pressure vessel) is used to analyse the influence of the wall thickness, as well as the turgor pressure, at the positions of our measurements. By combining the nanoDMA technique with finite element simulations quantifiable measurements of the viscoelastic properties of plant cell walls are achieved. Such techniques are expected to find broader applications in quantifying the influence of genetic, biological, and environmental factors on the nanoscale mechanical properties of the cell wall.     

Scaling of mammalian ethmoid bones can predict olfactory organ size and performance

The relation between size and performance is central for understanding the evolution of sensory systems, and much interest has been focused on mammalian eyes and ears. However, we know very little about olfactory organ size (OOS), as data for a representative set of mammals are lacking. Here, we present a cranial endocast method for estimating OOS by measuring an easily accessible part of the system, the perforated part of the ethmoid bone, through which the primary olfactory axons reach the olfactory bulb. In 16 species, for which relevant data are available, the area of the perforated ethmoid bone is directly proportional to the area of the olfactory epithelium. Thus, the ethmoid bone is a useful indicator enabling us to analyse 150 species, and describe the distribution of OOS within the class Mammalia. In the future, a method using skull material may be applied to fossil skulls. In relation to skull size, humans, apes and monkeys have small olfactory organs, while prosimians have OOSs typical for mammals of their size. Large ungulates have impressive olfactory organs. Relating anatomy to published thresholds, we find that sensitivity increases with increasing absolute organ size.     

Verification of biomechanical methods employed in a comprehensive study of mild traumatic brain injury and the effectiveness of American football helmets

Concussion, or mild traumatic brain injury, occurs in many activities, mostly as a result of the head being accelerated. A comprehensive study has been conducted to understand better the mechanics of the impacts associated with concussion in American football. This study involves a sequence of techniques to analyse and reconstruct many different head impact scenarios. It is important to understand the validity and accuracy of these techniques in order to be able to use the results of the study to improve helmets and helmet standards. Two major categories of potential errors have been investigated. The first category concerns error sources specific to the use of crash test dummy instrumentation (accelerometers) and associated data processing techniques. These are relied upon to establish both linear and angular head acceleration responses. The second category concerns the use of broadcast video data and crash test dummy head-neck-torso systems. These are used to replicate the complex head impact scenarios of whole body collisions that occur on the football field between two living human beings. All acceleration measurement and processing techniques were based on well-established practices and standards. These proved to be reliable and reproducible. Potential errors in the linear accelerations due to electrical or mechanical noise did not exceed 2% for the three different noise sources investigated. Potential errors in the angular accelerations due to noise could be as high as 6.7%, due to error accumulation of multiple linear acceleration measurements. The potential error in the relative impact velocity between colliding heads could be as high as 11%, and was found to be the largest error source in the sequence of techniques to reconstruct the game impacts. Full-scale experiments with complete crash test dummies in staged head impacts showed maximum errors of 17% for resultant linear accelerations and 25% for resultant angular accelerations.