On the representation of chemical ageing of rubber in continuum mechanics

AbstractIn order to represent the chemical ageing behaviour of rubber under finite deformations a three-dimensional theory is proposed. The fundamentals of this approach are different decompositions of the deformation gradient in combination with an additive split of the Helmholtz free energy into three parts. Its first part belongs to the volumetric material behaviour. The second part is a temperature-dependent hyperelasticity model which depends on an additional internal variable to consider the long-term degradation of the primary rubber network. The third contribution is a functional of the deformation history and a further internal variable; it describes the creation of a new network which remains free of stress when the deformation is constant in time. The constitutive relations for the stress tensor and the internal variables are deduced using the Clausius–Duhem inequality. In order to sketch the main properties of the model, expressions in closed form are derived with respect to continuous and intermittent relaxation tests as well as for the compression set test. Under the assumption of near incompressible material behaviour, the theory can also represent ageing-induced changes in volume and their effect on the stress relaxation. The simulations are in accordance with experimental data from literature

On the thermomechanical-chemically coupled behavior of acrylic bone cements: Experimental characterization of material behavior and modeling approach

This study presents a constitutive model that is able to describe the curing phenomena of acrylic bone cements used in vertebroplasty. During the surgery the initial liquid bone cement is injected into a porous vertebra and penetrates it depending on the applied pressure. The procedure is accompanied by an exothermal phase transition from a viscous fluid to a viscoelastic solid. Moreover chemical shrinkage, thermal expansion as well as changes in temperature can be observed. After curing the bone cement stabilizes the filled vertebra within the vertebral column according to Baroud et al. (2004a). To represent this thermomechanical-chemically coupled material behavior a physically-based theory of finite viscoelasticity is developed. A multiplicative decomposition of the deformation gradient into a mechanical, thermal and chemical part, as proposed by Lion and H¨ofer (2007), forms the basis of the constitutive model. The exothermal polymerization of the bone cement is specified by an additive contribution to the free energy depending on the degree of cure. Thereby a differential equation represents the process-dependent behavior of the degree of cure. Experimental data supports the physical properties of the theory and provide information to parameterize the model. In detail, the time- and temperature-dependent exothermal curing behavior is studied with differential scanning calorimetry and with temperature-controlled rheometry. The structure of the constitutive model used to describe the material behavior of bone cement is motivated considering the experimental results

Quantitative Analysis of Candida Cell Wall Components by Flow Cytometrywith Triple-Fluorescence Staining

This work was supported by the European Commission within the FP7 Framework Programme [Fungitect-Grant No 602125]. We also thank Thomas Sauer, Vienna Biocenter Campus (VBC), Austria, for technical support at the FACS facility of the MFPL, Karl Kuchler, MFPL-Department of Medical Biochemistry, Medical University of Vienna, Max F. Perutz Laboratories, Campus Vienna Biocenter, Vienna, Austria and Ernst Thuer, Centre for Genomic Regulation, Barcelona, Spain, for advice on statistical approaches. Neil Gow acknowledges the support of the Wellcome Trust and the MRC Centre for Medical MycologyPeer reviewedPublisher PD

On the total curvatures of a tame function

Given a definable function f, enough differentiable, we study the continuity of the total curvature function t --> K(t), total curvature of the level {f=t}, and the total absolute curvature function t-->|K| (t), total absolute curvature of the level {f=t}. We show they admits at most finitely many discontinuities

Integrated collinear refractive index sensor with Ge PIN photodiodes

Refractive index sensing is a highly sensitive and label-free detection method for molecular binding events. Commercial implementations of biosensing concepts based on plasmon resonances typically require significant external instrumentation such as microscopes and spectrometers. Few concepts exist that are based on direct integration of plasmonic nanostructures with optoelectronic devices for on-chip integration. Here, we present a CMOS-compatible refractive index sensor consisting of a Ge heterostructure PIN diode in combination with a plasmonic nanohole array structured directly into the diode Al contact metallization. In our devices, the photocurrent can be used to detect surface refractive index changes under simple top illumination and without the aid of signal amplification circuitry. Our devices exhibit large sensitivities > 1000 nm per refractive index unit in bulk refractive index sensing and could serve as prototypes to leverage the cost-effectiveness of the CMOS platform for ultra-compact, low-cost biosensors.Comment: 21 pages, 6 figures, supporting information with 11 pages and 11 figures attache

Thermomechanical material modelling based on a hybrid free energy density depending on pressure, isochoric deformation and temperature

AbstractIn order to represent temperature-dependent mechanical material properties in a thermomechanical consistent manner it is common practice to start with the definition of a model for the specific Helmholtz free energy. Its canonical independent variables are the Green strain tensor and the temperature. But to represent calorimetric material properties under isobaric conditions, for example the exothermal behaviour of a curing process or the dependence of the specific heat on the temperature history, the temperature and the pressure should be taken as independent variables. Thus, in the field of calorimetry the Gibbs free energy is usually used as thermodynamic potential whereas in continuum mechanics the Helmholtz free energy is normally applied. In order to simplify the representation of calorimetric phenomena in continuum mechanics a hybrid free energy density is introduced. Its canonical independent variables are the isochoric Green strain tensor, the pressure and the temperature. It is related to the Helmholtz free energy density by a Legendre transformation. In combination with the additive split of the stress power into the sum of isochoric and volumetric terms this approach leads to thermomechanical consistent constitutive models for large deformations. The article closes with applications of this approach to finite thermoelasticity, curing adhesives and the glass transition

State injury profile for Kentucky

A widespread tenet is that evolution of pathogens maximises their basic reproduction ratio, R0. The breakdown of this principle is typically discussed as exception. Here, we argue that a radically different stance is needed, based on evolutionarily stable strategy (ESS) arguments that take account of the ‘dimension of the environmental feedback loop’. The R0 maximisation paradigm requires this feedback loop to be one-dimensional, which notably excludes pathogen diversification. By contrast, almost all realistic ecological ingredients of host–pathogen interactions (density-dependent mortality, multiple infections, limited cross-immunity, multiple transmission routes, host heterogeneity, and spatial structure) will lead to multidimensional feedbacks

Material Modelling of the Photopolymers for Additive Manufacturing Processes

Ultraviolet (UV) curing of polymers is a key phenomenon for several additive manufacturing technologies. This contribution presents a model relating the process parameters of UV light intensity and temperature to the thermal and mechanical properties of the polymer and the experimental results used to calibrate the model. Moreover, photo-differential scanning calorimetry (photo-DSC) measurements are performed to investigate the crosslinking reaction and to model the degree of cure as a function of the light intensity and temperature. The viscoelastic properties are measured by UV rheometry and it is shown that the classical time-cure superposition principle can equally be applied to the experimental results. Complete curing and mechanical model equations are provided to describe the material behavior as a result of our experimental findings.Mechanical Engineerin

Trace Metals Bioaccumulation Potentials of Three Indigenous Grasses Grown on Polluted Soils Collected Around Mining Areas in Pretoria, South Africa

The rapid increase in the number of industries may have increased the levels of trace metals in the soil. Phytoremediation of these polluted soils using indigenous grasses is now considered an alternative method in remediating these polluted soils. The present study investigated and compared the ability of three indigenous grasses as bioaccumulators of trace metals from polluted soils. Seeds of these grasses were introduced into pots containing polluted soil samples after the addition of organic manure. The seeds of the grasses were allowed to germinate and grow to maturity before harvesting. The harvested grasses were later separated into shoots and roots and the trace metal contents were determined using ICP –MS. From all the grasses, the concentrations of trace metals in the roots were more than those recorded in the shoot with a significant difference (P < 0.05). The transfer factor (TF) showed that Zn was the most bioaccumulated trace metals by all the grasses followed by Pb, Mn, and Cu respectively. Chromium concentration from the shoot of the grasses was in the order Urochlora moasambicensis > Themeda trianda > Cynodon dactylon. The study concluded that the three grasses used were all able to bioaccumulate trace metals in a similar proportion from the polluted soils. However, since livestock feed on these grasses, they should not be allowed to feed on the grasses used in this study especially when harvested from a polluted soil due to their bioaccumulative potentials

Topological complexity of the relative closure of a semi-Pfaffian couple

Gabrielov introduced the notion of relative closure of a Pfaffian couple as an alternative construction of the o-minimal structure generated by Khovanskii's Pfaffian functions. In this paper, use the notion of format (or complexity) of a Pfaffian couple to derive explicit upper-bounds for the homology of its relative closure. Keywords: Pfaffian functions, fewnomials, o-minimal structures, Betti numbers.Comment: 12 pages, 1 figure. v3: Proofs and bounds have been slightly improve