A Transversely Isotropic Hyperelastic Constitutive Model of the PDL. Analytical and Computational Aspects

This study describes the development of a constitutive law for the modelling of the periodontal ligament (PDL) and its practical implementation into a commercial finite element code. The constitutive equations encompass the essential mechanical features of this biological soft tissue: non-linear behaviour, large deformations, anisotropy, distinct behaviour in tension and compression and the fibrous characteristics. The approach is based on the theory of continuum fibre-reinforced composites at finite strain where a compressible transversely isotropic hyperelastic strain energy function is defined. This strain energy density function is further split into volumetric and deviatoric contributions separating the bulk and shear responses of the material. Explicit expressions of the stress tensors in the material and spatial configurations are first established followed by original expressions of the elasticity tensors in the material and spatial configurations. As a simple application of the constitutive model, two finite element analyses simulating the mechanical behaviour of the PDL are performed. The results highlight the significance of integrating the fibrous architecture of the PDL as this feature is shown to be responsible for the complex strain distribution observed.     

A Framework for Structured Modeling of Skeletal Muscle

The aim of this study is to present a detailed continuum mechanics formulation, and the corresponding algorithms, to predict the deformation of skeletal muscle at different structural levels, starting from the muscle fiber level. The model is used to investigate force production and structural changes during isometric and dynamic contractions of the cat medial gastrocnemius. From a comparison with experimental data obtained in our own laboratories, we conclude that the model faithfully predicts all of the observations pertaining to force production, fascicle length and angle of pennation under various test conditions.     

Modelling Soft Tissue Using Biphasic Theory — A Word of Caution

In recent years the biphasic approach initiated by Mow and coworkers, has been very popular in modelling soft, hydrated, cartilage tissues as well as other soft tissues, such as the brain. This work points out that due to the inherent inability of biphasic models in their present form to account for stress-strain rate dependence resulting from the viscoelasticity of the solid phase, the applicability of these models is limited to the loading conditions producing large relative velocities of phases.     

背阔肌肌皮瓣修复肩背部软组织肉瘤术后缺损研究

目的:分析背阔肌肌皮瓣在肩背部软组织肉瘤扩大切除术后缺损修复中的方便性及优越性。方法:选取临床确诊肩背部软组织肉瘤患者8例,行肩背部病灶扩大切除术后,依据背阔肌肌皮瓣解剖学特点,选择合适的背阔肌肌皮瓣转移修复肩背部缺损。结果:皮瓣全部存活,随访6月至28月,肩背部外形满意,日常活动无明显影响。结论:应用背阔肌肌皮瓣修复肩背部软组织肉瘤扩大术后缺损是一种行之有效的方法。该方法简单易行,临床效果明显。     

Mesoscale Modelling

Abstract

Increasingly, industrial materials are being designed to have structure on length scales of tens to thousands of nanometers. These structures are crucial to achieving a particular desired material property. Such structures, however, may depend on the underlying chemistry of the material for their existence. For example, a thousandfold increase in the ionic conductivity of a polymer blend may only occur in a narrow region of a hugely complex phase diagram, the location' of which region can be expected to depend on the molecular chemistry and physics from the monomer scale to the coil size.

Traditional Computational Chemistry has proved incapable of dealing with the length and time scales involved in the formation of these ‘Mesoscale’ structures. On the other hand, traditional Computational Physics has proved incapable of consistently incorporating the necessary chemical detail for modelling real industrial materials. In this paper we present two novel methods which successfully address both the chemistry and the physics of mesophase formation. The methods, described in detail, are MesoDyn and Dissipative Particle Dynamics (DPD).

Unlike phenomenological theories of materials, such as the Landau models which one finds in much of the computational physics literature, the two models mentioned incorporate molecular geometry and connectivity explicitly. We discuss each of the methods briefly.

We then give an overview of how these methods are being used in industry to optimise materials and processes. We discuss previous simulation results for triblock Pluronic surfactants in solution studied with MesoDyn, and for diblock copolymers studied with DPD, where the known experimental changes in morphology from micellar to hexagonal to bicontinuous to lamellar have been successfully reproduced. We also present new results for several systems, including binary and ternary blends, where the third component in the latter system is a diblock copolymer, which acts as a compatibiliser. We discuss the effects of changing solvent character on the material properties of these systems, as well as the effects of an externally imposed shear flow.     

A behavioral analysis of altruism

Altruistic acts have been defined, in economic terms, as “…costly acts that confer economic benefits on other individuals” (Fehr and Fischbacher, 2003). In multi-player, one-shot prisoner's dilemma games, a significant number of players behave altruistically; their behavior benefits each of the other players but is costly to them. We consider three potential explanations for such altruism. The first explanation, following a suggestion by the philosopher Derek Parfit, assumes that players devise a strategy to avoid being free-loaders—and that in the present case this strategy dictates cooperation. The second explanation says that cooperators reject the one-shot aspect of the game and behave so as to maximize reward over a series of choices extending beyond the present situation (even though reward is not maximized in the present case). This explanation assumes that people may learn to extend the boundaries of their selves socially (beyond their own skin) as well as temporally (beyond the present moment). We propose a learning mechanism for such behavior analogous to the biological, evolutionary mechanism of group selection. The third explanation assumes that people's altruism is based on a straightforward balancing of undiscounted costs to themselves against discounted benefits to others (social discounting). The three proposed explanations of altruism complement each other.     

DiSC (direct saccharification of culms) process for bioethanol production from rice straw

A simple process (the direct-saccharification-of-culms (DiSC) process) to produce ethanol from rice straw culms, accumulating significant amounts of soft carbohydrates (SCs: glucose, fructose, sucrose, starch and β-1,3-1,4-glucan) was developed. This study focused on fully mature culms of cv. Leafstar, containing 69.2% (w/w of dried culms) hexoses from SCs and cellulose. Commercially-available wind-separation equipment successfully prepared a culm-rich fraction with a SC recovery of 83.1% (w/w) from rice straw flakes (54.1% of total weight of rice straw). The fraction was suspended in water (20%, w/w) for starch liquefaction, and the suspension was subjected to a simultaneous saccharification and fermentation with yeast, yielding 5.6% (w/v) ethanol (86% of the theoretical yield from whole hexoses in the fraction) after 24 h fermentation. Thus, the DiSC process produced highly-concentrated ethanol from rice straw in a one vat process without any harsh thermo-chemical pretreatments.     

Gross and microscopic morphology of lesions in Cnidaria from Palmyra Atoll, Central Pacific

We conducted gross and microscopic characterizations of lesions in Cnidaria from Palmyra Atoll, Central Pacific. We found growth anomalies (GA) to be the most commonly encountered lesion. Cases of discoloration and tissue loss were rare. GAs had a focal or multi-focal distribution and were predominantly nodular, exophytic, and umbonate. In scleractinians, the majority of GAs manifested as hyperplasia of the basal body wall (52% of cases), with an associated absence or reduction of polyp structure (mesenteries and filaments, actinopharynx and tentacles), and depletion of zooxanthellae in the gastrodermis of the upper body wall. In the soft corals Sinularia sp. and Lobophytum sp., GAs exclusively manifested as prominent hyperplasia of the coenenchyme with an increased density of solenia. In contrast to scleractinians, soft coral GAs displayed an inflammatory and necrotizing component with marked edema of the mesoglea, accompanied by infiltrates of variably-sized granular amoebocytes. Fungi, algae, sponges, and Crustacea were present in some scleractinian GAs, but absent in soft coral GAs. Fragmentation of tissues was a common finding in Acropora acuminata and Montipora cf. dilatata colonies with tissue loss, although no obvious causative agents were seen. Discoloration in the zoanthid, Palythoa tuberculosa, was found to be the result of necrosis, while in Lobophytum sp. discoloration was the result of zooxanthellar depletion (bleaching). Soft corals with discoloration or tissue loss showed a marked inflammatory response, however no obvious causative organisms were seen. Lesions that appeared similar at the gross level were revealed to be distinct by microscopy, emphasizing the importance of histopathology.