On fiber dispersion models: exclusion of compressed fibers and spurious model comparisons

Fiber dispersion in collagenous soft tissues has an important influence on the mechanical response, and the modeling of the collagen fiber architecture and its mechanics has developed significantly over the last few years. The purpose of this paper is twofold, first to develop a method for excluding compressed fibers within a dispersion for the generalized structure tensor (GST) model, which several times in the literature has been claimed not to be possible, and second to draw attention to several erroneous and misleading statements in the literature concerning the relative values of the GST and the angular integration (AI) models. For the GST model we develop a rather simple method involving a deformation dependent dispersion parameter that allows the mechanical influence of compressed fibers within a dispersion to be excluded. The theory is illustrated by application to simple extension and simple shear in order to highlight the effect of exclusion. By means of two examples we also show that the GST and the AI models have equivalent predictive power, contrary to some claims in the literature. We conclude that from the theoretical point of view neither of these two models is superior to the other. However, as is well known and as we now emphasize, the GST model has proved to be very successful in modeling the data from experiments on a wide range of tissues, and it is easier to analyze and simpler to implement than the AI approach, and the related computational effort is much lower

The plasticity of berry shrivelling in 'Shiraz': A vineyard survey

Berry water loss during late ripening is a cultivar dependent-trait and is accentuated in wine grape varieties such as 'Shiraz'. 'Shiraz' berry development was monitored in twelve vineyards over two seasons to characterise the extent of weight loss that can occur within a grape growing region. From veraison onwards, berry fresh mass was greatest in vineyards using excessive irrigation and least in vineyards using cautious irrigation strategies. In the first season, berry fresh mass increased, reached a maximum and subsequently declined. Conversely, in the second season, characterised by rain and high humidity, berry fresh mass increased, then stabilised without a consistent decline. In both seasons, berry sugar import rates were highest shortly after veraison but then declined gradually, terminating several weeks after the weight maximum. Notwithstanding that berries with large maximum weights tended to undergo greater rates of weight loss, these berries remained heavier at harvest compared to those berries that were smaller prior to the onset of weight loss. Canopy size, yield and crop load were not key determinants of berry weight loss rates. Berry anthocyanin and sugar accumulation were closely correlated during early ripening but anthocyanin degradation took place during the late weight loss phase

Analytical and numerical analyses of the micromechanics of soft fibrous connective tissues

State of the art research and treatment of biological tissues require accurate and efficient methods for describing their mechanical properties. Indeed, micromechanics motivated approaches provide a systematic method for elevating relevant data from the microscopic level to the macroscopic one. In this work the mechanical responses of hyperelastic tissues with one and two families of collagen fibers are analyzed by application of a new variational estimate accounting for their histology and the behaviors of their constituents. The resulting, close form expressions, are used to determine the overall response of the wall of a healthy human coronary artery. To demonstrate the accuracy of the proposed method these predictions are compared with corresponding 3-D finite element simulations of a periodic unit cell of the tissue with two families of fibers. Throughout, the analytical predictions for the highly nonlinear and anisotropic tissue are in agreement with the numerical simulations

Monitoring method for carbon nanotubes (CNT): Personal sampler and corresponding reading device

At present, CNT and other nanofiber materials in air can only be detected by deposition on a substrate and the use of off-line imaging analysis such as scanning electron microscopy. The majority of techniques suitable for the quasi- real-time measurement of engineered nanoparticles such as electrical low pressure impactor, condensation particle counter, optionally combined with a scanning mobility particle sizer (SMPS) can not distinguish between nanoparticles in general and airborne nanofibres in particular. In common workplace settings the considerable background of fine and ultrafine particles thus poses a challenge for these instruments. Furthermore, a true portability of the present devices is not given due to their size and power consumption. However, there is an urgent need due to the expected toxicity of nanofibres to control workplace environments with a robust and mobile device to ensure the safety of the working personnel as soon as possible. To meet these challenges, a suitable personal sampler together with a corresponding reading device is under development in the NANODEVICE-project, funded by the European Commission under grant agreement FP7-211464-2. A pre-prototype personal sampler for CNT sampling, the used Raman-spectroscopic inspection of deposited CNTs and a possible approach in determining the qualitative presence of CNTs will be shown. Additionally, it seems even possible to distinguish between carbon nanofibers from different manufacturers based on Raman spectroscopy and data analysis

The Sunyaev-Zeldovich Effect and Its Cosmological Significance

Comptonization of the cosmic microwave background (CMB) radiation by hot gas in clusters of galaxies - the Sunyaev-Zeldovich (S-Z) effect - is of great astrophysical and cosmological significance. In recent years observations of the effect have improved tremendously; high signal-to-noise images of the effect (at low microwave frequencies) can now be obtained by ground-based interferometric arrays. In the near future, high frequency measurements of the effect will be made with bolomateric arrays during long duration balloon flights. Towards the end of the decade the PLANCK satellite will extensive S-Z surveys over a wide frequency range. Along with the improved observational capabilities, the theoretical description of the effect and its more precise use as a probe have been considerably advanced. I review the current status of theoretical and observational work on the effect, and the main results from its use as a cosmological probe.Comment: Invited review; in proceedings of the Erice NATO/ASI `Astrophysical Sources of High Energy Particles and Radiation'; 11 pages, 3 figure

Modelling volumetric growth in a thick walled fibre reinforced artery

A novel framework for simulating growth and remodelling (G&R) of a fibre-reinforced artery, including volumetric adaption, is proposed. We show how to implement this model into a finite element framework and propose and examine two underlying assumptions for modelling growth, namely constant individual density (CID) or adaptive individual density (AID). Moreover, we formulate a novel approach which utilises a combination of both AID and CID to simulate volumetric G&R for a tissue composed of several different constituents. We consider a special case of the G&R of an artery subjected to prescribed elastin degradation and we theorise on the assumptions and suitability of CID, AID and the mixed approach for modelling arterial biology. For simulating the volumetric changes that occur during aneurysm enlargement, we observe that it is advantageous to describe the growth of collagen using CID whilst it is preferable to model the atrophy of elastin using AID

Timing of N application and water constraints on N accumulation and juice amino N concentration in Chardonnay grapevines

The amount and timing of nitrogen (N) application to a vineyard is critical for must yeast assimilable nitrogen (YAN) concentrations. YAN concentrations and amino acid profiles are important for the fermentation process and wine composition. Commonly, N is applied at flowering to optimize leaf functioning or after harvest to enhance vine productivity the following season. In this study N was applied at various stages of berry development to determine allocation patterns between vine perennial and annual components and to assess when berry YAN concentrations can best be optimized. Five year old potted 'Chardonnay' vines received ammonium sulfate fertilizer at six different times from full bloom to two weeks before harvest and were also exposed to either full or half irrigation during that period. Reduced water supply resulted in a higher allocation of N to the perennial structures and less to the annual components of the vine. N allocation to the annual components of the vine was greatest when it was applied at full bloom, however allocation to the perennial components was greatest when it was applied after fruit-set to veraison. The timing of N supply had a substantial influence on YAN concentrations, and was highest when N was applied about two weeks after veraison. Low water supply also resulted in higher juice YAN concentrations. The perennial N reserves in the roots were highest under low water supply and when N was applied at veraison, while the allocation to the annual parts was lower under this irrigation regime. The study indicates that timing of N application and the application of water constraints during berry development can impact on N partitioning, while the total amount accumulated by the vine is not altered

Point-contact study of ReFeAs(1-x)Fx (Re=La, Sm) superconducting films

Point-contact (PC) Andreev-reflection (AR) measurements of the superconducting gap in iron-oxipnictide ReFeAsO_{1-x}F_x (Re=La, Sm) films have been carried out. The value of the gap is distributed in the range 2\Delta \simeq 5-10 meV (for Re=Sm) with a maximum in the distribution around 6 meV. Temperature dependence of the gap \Delta(T) can be fitted well by BCS curve giving reduced gap ratio 2\Delta /kT_c^*\simeq 3.5 (here T_c^* is the critical temperature from the BCS fit). At the same time, an expected second larger gap feature was difficult to resolve distinctly on the AR spectra making determination reliability of the second gap detection questionable. Possible reasons for this and the origin of other features like clear-cut asymmetry in the AR spectra and current regime in PCs are discussed.Comment: 6 two-column pages, 6 figs., 26 Refs., to be published in Superconductor Science and Technolog