The influence of wind-induced compression failures on the mechanical properties of spruce structural timber

Compression failures (CF) are defects in the wood structure in the form of buckled fibres. They are a well-known 'natural' phenomenon in softwood trees exposed to frequent or strong winds, but their influence on the utilisation of timber is still debated. While a reduction of the mechanical properties in bending and tension at the fibre level and in small clear specimens is generally acknowledged, the effect is less obvious with structural timber in the presence of other defects such as knots or grain deviations. In the presented case study a statistically significant reduction of the moduli of rupture and elasticity in bending is observed in a sample of 563 squared timber beams, but the characteristic values of the mechanical properties still exceed the limits for the strength classes of visually graded structural timber (according to the Swiss standard SIA 265). Nevertheless, because of the potential safety risk by the more brittle fracture behaviour, it is recommended to exclude timber with detected CF from use in load bearing structures stressed in tension or bendin

Phytoforensic tools: directional uptake of chlorinated solvents

Trees have been used to locate contaminated soil and groundwater, augmenting traditional methods, such as well drilling, that are time-consuming and expensive. In the past decade, plant sampling has gained acceptance as a reliable method for site screening. In this new field of phytoforensics, research efforts focus on developing quicker, more accurate and more informative sampling and analysis methods for measuring contaminant concentrations in trees. These phytoforensic tools are a novel approach to site assessments, potentially reducing cost while more effectively locating contaminated groundwater. This thesis evolved from field data suggesting azimuthal concentrations in tree trunks may reflect the corresponding azimuthal concentrations in the groundwater below the tree. In the lab, large diameter trees were subjected to concentration gradients in the groundwater and analyzed for contaminants and evidence of directional uptake. Upon analysis, concentrations were approximately five times higher on the side of the tree near the highly contaminated groundwater. The conservation of azimuthal PCE and TCE gradients was observed at all levels up the tree. This indicates that advective transport in the xylem exceeds radial or circumferential diffusion of PCE and TCE. Several field sites showed similar data, where concentrations in the tree matched groundwater concentrations in an azimuthal pattern. In practice, each tree sampled directionally can provide compass-like information, pointing investigators towards the most concentrated region of the plume --Abstract, page iv

Effect of ageing on carotid artery morphology, hemodynamics, and the development of atherosclerosis.

Cardiovascular diseases and ageing are two main challenges for health services. Cardiovascular disease is characterised by atherosclerosis, leading to heart attack and stroke. Atherosclerosis is a focal disease and occurs preferentially in regions of arterial bifurcation and curvature where complex flow features are observed. The carotid arteries represent a region of significant involvement in atherosclerosis. Previous studies have shown that haemodynamic factors are important determinants of the local distribution of atherosclerosis. However, longitudinal studies are lacking. The aim of this study was to investigate age-related changes in carotid artery morphology and haemodynamics based on longitudinal data acquired from a group of middle-aged subjects recruited to a cardiovascular disease prevention programme in Italy. The longitudinal study started in 1996 and participants were examined twice 12 years apart. All subjects underwent blood viscosity measurements and echo-Doppler examinations of the common carotid artery at baseline and follow-up. From the acquired ultrasound data, common carotid artery diameter, blood flow velocity, and intima-media thickness were measured, and wall shear stress, circumferential wall tension and Peterson elastic modulus were calculated. It was found that with ageing, blood viscosity increased, common carotid artery diameter increased, mean blood velocity and wall shear stress decreased, while intima-media thickness, circumferential wall tension and arterial stiffness increased. Interrelationships of the data were also examined: reductions in common carotid wall shear stress were independently associated with intima-media thickening. Furthermore, ageing-associated wall shear stress reduction predicted the development of atherosclerotic plaques, independently of known cardiovascular risk factors. In addition, in participants presenting shear stress reductions in only one side of the common carotid artery, development of atherosclerosis in the carotid tree was limited to the same body side. In conclusion, this longitudinal study confirms the role of arterial wall shear stress as a mediator of the effects of ageing on atherosclerosis.Open Acces

Estimation of Biomass Increase and CUE at a Young Temperate Scots Pine Stand Concerning Drought Occurrence by Combining Eddy Covariance and Biometric Methods

The accurate estimation of an increase in forest stand biomass has remained a challenge. Traditionally, in situ measurements are done by inventorying a number of trees and their biometric parameters such as diameter at the breast height (DBH) and height; sometimes these are complemented by carbon (C) content studies. Here we present the estimation of net primary productivity (NPP) over a two years period (2019–2020) at a 25-year-old Scots pine stand. Research was based on allometric equations made by direct biomass analysis (tree extraction) and carbon content estimations in individual components of sampled trees, combined with a series of stem diameter increments recorded by a network of band dendrometers. Site-specific allometric equations were obtained using two different approaches: using the whole tree biomass vs DBH (M1), and total dry biomass-derived as a sum of the results from individual tree components’ biomass vs DBH (M2). Moreover, equations for similar forest stands from the literature were used for comparison. Gross primary productivity (GPP) estimated from the eddy-covariance measurements allowed the calculation of carbon use efficiency (CUE = NPP/GPP). The two investigated years differed in terms of the sum and patterns of precipitation distribution, with a moderately dry year of 2019 that followed the extremely dry 2018, and the relatively average year of 2020. As expected, a higher increase in biomass was recorded in 2020 compared to 2019, as determined by both allometric equations based on in situ and literature data. For the former approach, annual NPP estimates reached ca. 2.0–2.1 t C ha−1 in 2019 and 2.6–2.7 t C ha−1 in 2020 depending on the “in situ equations” (M1-M2) used, while literature-derived equations for the same site resulted in NPP values ca. 20–30% lower. CUE was higher in 2020, which resulted from a higher NPP total than in 2019, with lower summer and spring GPP in 2020. However, the CUE values were lower than those reported in the literature for comparable temperate forest stands. A thorough analysis of the low CUE value would require a full interpretation of interrelated physiological responses to extreme conditions

Growing cell walls show a gradient of elastic strain across their layers

The relatively thick primary walls of epidermal and collenchyma cells often form waviness on the surface that faces the protoplast when they are released from the tensile in-plane stress that operates in situ. This waviness is a manifestation of buckling that results from the heterogeneity of the elastic strain across the wall. In this study, this heterogeneity was confirmed by the spontaneous bending of isolated wall fragments that were initially flat. We combined the empirical data on the formation of waviness in growing cell walls with computations of the buckled wall shapes. We chose cylindrical-shaped organs with a high degree of longitudinal tissue stress because in such organs the surface deformation that accompanies the removal of the stress is strongly anisotropic and leads to the formation of waviness in which wrinkles on the inner wall surface are always transverse to the organ axis. The computations showed that the strain heterogeneity results from individual or overlaid gradients of pre-stress and stiffness across the wall. The computed wall shapes depend on the assumed wall thickness and mechanical gradients. Thus, a quantitative analysis of the wall waviness that forms after stress removal can be used to assess the mechanical heterogeneity of the cell wall

Intra-annual to multi-decadal xylem traits in a tropical moist semi-deciduous forest of Central Africa

A witness of a tree’s past conditions is the wood itself. The main research question of this dissertation is how to assess and reveal the driving forces of the patterns of wood traits on pith-to-bark cross-sections in tropical trees. Cambial and leaf phenology was monitored in the Luki Reserve (Mayombe forest, D.R. Congo). Furthermore, X-ray CT densitometry was explored to assess traits in a reliable way, for multiple species. Variability in phenology is observed for T. superba, which requires traits of individual trees to be fixed on a time axis. Furthermore, X-ray CT is a suitable method for assessing traits in a fast way. Cambial activity of understory trees has shown to be species-specific, whilst many trees show zero xylem growth. Finally, 66 years of tree growth was analysed, while trait analysis revealed a median ring count of only 32, thus implying many non-periodical rings. This work presents methodological improvements to measure traits as continuous variables from pith to bark, but also acknowledges that phenology still remains a key aspect in order to fix traits on a time axis. Key words: leaf phenology, wood anatomy, stable isotopes, Mayombe, dendrochronology, X-ray CT densitometr

Free vibration of symmetric angly-plane layered truncated conical shells under classical theory

Truncated conical shell finds wide ranging of engineering applications. They are used in space crafts, robots, shelters, domes, tanks, nozzles and in machinery devices. Thus, the study of their vibrational characteristics has long been of interest for the designers. The use of the lamination for the structures leads to design with the maximum reliability and minimum weight. Moreover, the study of free vibration of laminated conical shells has been treated by a number of researchers. Irie et al. (1982) studied free vibration of conical shells with variable thickness using Rayleigh-Ritz method of solution. Wu and Wu (2000) provided 3D elasticity solutions for the free vibration analysis of laminated conical shells by an asymptotic approach. Wu and Lee (2001) studied the natural frequencies of laminated conical shells with variable stiffness using the differential quadrature method under first-order shear deformation theory (FSDT). Tripathi et al. (2007) studied the free vibration of composite conical shells with random material properties of the finite element method. Civalek (2007) used the Discrete Singular Convolution (DSC) to investigate the frequency response of orthotropic conical and cylindrical shells. Sofiyez et al. (2009) studied the vibrations of orthotropic non-homogeneous conical shells with free boundary conditions. Ghasemi et al. (2012) presented their study of free vibration of composite conical shells which was investigated under various boundary conditions using the solution of beam function and Galerkin method. Viswanathan et al. (2007, 2011) studied free vibration of laminated cross-ply plates, including shear deformation, symmetric angle-ply laminated cylindrical shells of variable thickness with shear deformation theory using the spline collocation method. In the present work, free vibration of symmetric angle-ply laminated truncated conical shells is analyzed and displacement functions are approximated using cubic and quantic spline and collocation procedure is applied to obtain a set of field equations. The field equations along with the equations of boundary conditions yield a system of homogeneous simultaneous algebraic equations on the assumed spline coefficients which resulting to the generalized eigenvalue problem. This eigenvalue problem is solved using eigensolution technique to get as many eigenfrequencies as required. The effect of circumferential mode number, length ratio, cone angle, ply angles and number of layers under two boundary conditions on the frequency parameter is studied for three- and five- layered conical shells consisting of two types of layered materials

Archives of Data Science, Series A. Vol. 1,1: Special Issue: Selected Papers of the 3rd German-Polish Symposium on Data Analysis and Applications

The first volume of Archives of Data Science, Series A is a special issue of a selection of contributions which have been originally presented at the {\em 3rd Bilateral German-Polish Symposium on Data Analysis and Its Applications} (GPSDAA 2013). All selected papers fit into the emerging field of data science consisting of the mathematical sciences (computer science, mathematics, operations research, and statistics) and an application domain (e.g. marketing, biology, economics, engineering)