The Experts below are selected from a list of 2394 Experts worldwide ranked by ideXlab platform

Delphis F Levia - One of the best experts on this subject based on the ideXlab platform.

  • using wavelet analysis to examine bark Microrelief
    Trees-structure and Function, 2014
    Co-Authors: David R Legates, Delphis F Levia, John T Van Stan, Victor Manuel Velasco Herrera
    Abstract:

    An improved quantification of variations in bark Microrelief is presented that uses wavelets on a circular domain from data acquired using the LaserBark™ automated tree measurement system. An important metric of canopy structure, bark Microrelief affects both the hydrology and biogeochemistry of forests. Increased bark Microrelief leads to reduced stemflow volumes and higher concentrations of stemflow leachates and nutrient-ions. Consequently, an improved representation of bark Microrelief would be useful to describe the influence of various tree species on water and solute contributions to the forest floor. Most existing methods to quantify bark Microrelief are ‘global’ measures; that is, they provide a single number that represents the overall bark Microrelief of the entire perimeter of the tree. To remedy this, wavelet analysis of LaserBark™ automated tree measurement system data is proposed and described to quantify variations in bark Microrelief around the perimeter of the tree. This measure describes the spatial differences in bark Microrelief and allows representation of trees that exhibit directional variability in bark Microrelief due to natural or anthropogenic effects. The results show that wavelet analysis is effective in quantifying both bark Microrelief and large-scale tree asymmetry. The radial component highlights changes in the depth of bark Microrelief while the tangential component relates to the distance between bark furrows in the bark cross section. Thus, wavelet analysis may be a useful tool for comparing bark structure that varies, for example, within- and between-tree species, at different stages of tree growth, and among trees grown under different environmental conditions.

  • inter and intraspecific variation of stemflow production from fagus grandifolia ehrh american beech and liriodendron tulipifera l yellow poplar in relation to bark Microrelief in the eastern united states
    Ecohydrology, 2009
    Co-Authors: Toland J Van Stan, Delphis F Levia
    Abstract:

    Stemflow is a spatially concentrated hydrologic input at the tree base. Prior work has documented the differential effects of stemflow from a wide range of plant species on ecohydrological processes, such as the alteration of soil pH and spatial patterning of understory vegetation. No known work has coupled stemflow yield with high resolution measurements of bark Microrelief that definitively ascribe differential stemflow yield to bark Microrelief. As such, our research objectives were to: (1) correlate inter- and intraspecific variation in stemflow yield to a quantitative bark Microrelief scale and (2) compare and contrast stemflow for two co-occurring deciduous species—Fagus grandifolia Ehrh. (American beech) and Liriodendron tulipifera L. (yellow poplar). Using a newly developed instrument to measure bark Microrelief, namely the LaserBark™ automated tree measurement system, in combination with an 11-month stemflow database for a broadleaved deciduous forest in eastern North America, it was found that bark Microrelief values significantly differed between the two species [P = 0·000, F (1,19) = 49·32]. Funneling ratios [P = 0·000, H (1, 990) = 339·20] and stemflow generation [P = 0·000, H (1, 990) = 146·75] also significantly differed between the two species. Our results indicate that bark Microrelief exerts a considerable effect on stemflow yield from F. grandifolia and L. tulipifera, possibly affecting water and solute flux to the forest floor. Copyright © 2009 John Wiley & Sons, Ltd.

  • an automated instrument for the measurement of bark Microrelief
    AGUSM, 2009
    Co-Authors: John T Van Stan, Matthew T Jarvis, Delphis F Levia
    Abstract:

    Bark Microrelief is of importance to the physiological ecology of forested ecosystems because it has been documented to influence the distribution of corticolous lichens, stemflow generation, and forest biogeochemical cycles. Hitherto no instrument existed to characterize the inherent variability of bark Microrelief with high spatial resolution. Our newly designed prototype instrument consists of a hinged ring, laser rangefinder, and motor linked to a standard laptop. The prototype produces trunk cross sections at a 0.33° horizontal resolution and detects bark-ridge-to-furrow heights at < 1 resolution. The prototype was validated by comparing measurements of bark Microrelief between the instrument and digital calipers. The mean absolute error of the prototype as a percentage of the measured average Microrelief was 1.0%, with a mean absolute error of 0.83 mm. Our bark Microrelief prototype instrument can supply critical requisite information of bark microstructure that can be used by researchers to interpret the distribution of lichens and bryophytes on tree surfaces, relate stemflow yield and chemistry to bark Microrelief, and provide detailed measurements of the changes of bark Microrelief with stem dehydration. In short, the prototype instrument can be used to gain a more holistic understanding of the physiological ecology of forest ecosystems.

N.l. Dmitruk - One of the best experts on this subject based on the ideXlab platform.

  • analysis of thin film surface barrier solar cells with a Microrelief interface
    Solar Energy Materials and Solar Cells, 2003
    Co-Authors: N.l. Dmitruk, Yu O Borkovskaya, I N Dmitruk, I B Mamontova
    Abstract:

    The influence of a Microrelief interface between a thin conductive film (emitter) and a semiconductor substrate (absorber) on the optical and recombination losses in surface barrier solar cells is analyzed. Equations for the calculation of monochromatic light transmission through a thin absorbing film with one or two rough surfaces, on an absorbing substrate, are presented. For a weakly texturized interface and a normal direction of the incident light, the influence of the microroughness is taken into account by the formulae obtained. A model of patches with microsurfaces parallel to the structure surface and ones inclined to it at a certain angle (the most probable statistically) was used to describe the experimental results. Au/GaAs surface barrier structures with interface Microrelief of a quasigrating or a dendritic type, obtained by chemical anisotropic etching of GaAs, were investigated. The geometric and statistical parameters of the Microrelief were determined by atomic force microscopy techniques. The recombination parameters of the textured interfaces were determined from the experimental spectra of the external quantum efficiency, taking into consideration the calculated spectra of light transmittance. A comparison of the internal quantum efficiency spectra with the calculated ones allows a determination of the electronic parameters of the interface. Both the photoconversion parameters under AM0 simulated illumination and the tolerance for 60Co γ-irradiation, obtained for structures with various interface Microrelief morphologies, allowed identification of Microrelief of the quasigrating type as more suitable for solar cell applications.

  • morphology and interfacial properties of Microrelief metal semiconductor interface
    Applied Surface Science, 2002
    Co-Authors: N.l. Dmitruk, Yu O Borkovskaya, I N Dmitruk, S V Mamykin, Zs J Horvath, I B Mamontova
    Abstract:

    Abstract The effect of the morphology of Au/GaAs interface Microrelief, prepared by chemical anisotropic etching, on current flow mechanism, electronic and recombination properties of interface has been investigated. Simulation of I – V curves and optical transmittance of light into semiconductor was made on the basis of the developed theories taking into account the barrier height distribution and the effect of scattering of light by low Microrelief.

  • Preparation, morphology and physical properties of Microrelief InP surfaces
    Solar Energy Materials and Solar Cells, 1993
    Co-Authors: N.l. Dmitruk, T.r. Barlas, E.v. Basiuk
    Abstract:

    Abstract The morphology of Microrelief InP surfaces, prepared by anisotropic chemical etching without masking and the kinetics of this etching were studied. A statistical analysis of surface profiles shows that the surface studied has a Gaussian roughness distribution and the ratio of root-mean-square surface roughness δ to autocorrelation length σ is small and amounts to (2–5) × 10−2. For such a surface a reduction in specular reflection and increase in photocurrent of barrier structures have been observed. Such Microrelief structures may be used to increase the collection efficiency of solar cells and the sensitivity of photodetectors.

Georges Limbert - One of the best experts on this subject based on the ideXlab platform.

  • on skin Microrelief and the emergence of expression micro wrinkles
    Soft Matter, 2018
    Co-Authors: Georges Limbert, Ellen Kuhl
    Abstract:

    Over the course of a life time, as a result of adaptive mechanobiological processes (e.g. ageing), or the action of external physical factors such as mechanical loading, the human skin is subjected to, and hosts complex biophysical processes. These phenomena typically operate through a complex interplay, that, ultimately, is responsible for the evolutive geometrical characteristics of the skin surface. Wrinkles are a manifestation of these effects. Although numerous theoretical models of wrinkles arising in multi-layered structures have been proposed, they typically apply to idealised geometries. In the case of skin, which can be viewed as a geometrically complex multi-layer assembly, it is pertinent to question whether the natural skin Microrelief could play a significant role in conditioning the characteristics of compression-induced micro-wrinkles by acting as an array of geometrical imperfections. Here, we explore this question through the development of an anatomically-based finite strain parametric finite element model of the skin, represented as a stratum corneum layer on top of a thicker and softer substrate. Our study suggests that skin Microrelief could be the dominant factor conditioning micro-wrinkle characteristics for moderate elastic modulus ratios between the two layers. Beyond stiffness ratios of 100, other factors tend to overwrite the effects of skin Microrelief. Such stiffness ratio fluctuations can be induced by changes in relative humidity or particular skin conditions and can therefore have important implications for skin tribology.

Mir Jalil Razavi - One of the best experts on this subject based on the ideXlab platform.

  • from surface Microrelief to big wrinkles in skin a mechanical in silico model
    Extreme Mechanics Letters, 2020
    Co-Authors: Poorya Chavoshnejad, Saurabh More, Mir Jalil Razavi
    Abstract:

    Abstract A major concern associated with skin, the largest organ of our body, is how to prevent it from wrinkling and aging. Understanding the mechanics of skin wrinkling can provide useful insight into skin aging prevention. However, despite decades of endeavors the underlying mechanism of skin wrinkling and aging remains poorly understood. This paper explores the effect of geometrical and mechanical properties of skin on its wrinkling via an integrated theoretical and computational analysis. The skin is modeled with a soft structure having different layers with various thicknesses and material properties. Innovatively, the pattern of skin Microrelief is generated and mapped on the model to investigate its effect on the formation of primary lines, secondary lines, and big wrinkles of skin. Analytical interpretation provides preliminary insight into the critical compressive strain for the model skin to start wrinkling, while advanced computational models with surface Microrelief offer clues for the skin’s post-wrinkling complex morphology. In particular, tissue geometry, material properties, and Microrelief pattern are explored as the determinant parameters to control the location, size, and patterns of skin wrinkles. Our findings allude that the characteristics of compression-induced wrinkles are primarily determined by the geometrical and material property of skin layers rather than the genuine skin Microrelief. However, Microrelief plays a pivotal role in regulating and determining the locations of primary and secondary wrinkle lines. The edges of the Microrelief units are favorable paths for evolving primary and secondary lines. Post-wrinkling analysis reveals that in addition to the periodic sinusoidal pattern, several secondary complex patterns such as non-symmetric periodic, period-doubling and self-contacting folds are observed in the compressed model of skin. Results of the study also show that wrinkle patterns highly depend on the thickness and material property of Stratum Corneum (SC), the outermost layer of skin.

Vidal E Vazquez - One of the best experts on this subject based on the ideXlab platform.

  • quantification of tillage plant cover and cumulative rainfall effects on soil surface Microrelief by statistical geostatistical and fractal indices
    Nonlinear Processes in Geophysics, 2008
    Co-Authors: Jorge Pazferreiro, Ildegardis Bertol, Vidal E Vazquez
    Abstract:

    Abstract. Changes in soil surface Microrelief with cumulative rainfall under different tillage systems and crop cover conditions were investigated in southern Brazil. Surface cover was none (fallow) or the crop succession maize followed by oats. Tillage treatments were: 1) conventional tillage on bare soil (BS), 2) conventional tillage (CT), 3) minimum tillage (MT) and 4) no tillage (NT) under maize and oats. Measurements were taken with a manual relief meter on small rectangular grids of 0.234 and 0.156 m2, throughout growing season of maize and oats, respectively. Each data set consisted of 200 point height readings, the size of the smallest cells being 3×5 cm during maize and 2×5 cm during oats growth periods. Random Roughness (RR), Limiting Difference (LD), Limiting Slope (LS) and two fractal parameters, fractal dimension (D) and crossover length (l) were estimated from the measured microtopographic data sets. Indices describing the vertical component of soil roughness such as RR, LD and l generally decreased with cumulative rain in the BS treatment, left fallow, and in the CT and MT treatments under maize and oats canopy. However, these indices were not substantially affected by cumulative rain in the NT treatment, whose surface was protected with previous crop residues. Roughness decay from initial values was larger in the BS treatment than in CT and MT treatments. Moreover, roughness decay generally tended to be faster under maize than under oats. The RR and LD indices decreased quadratically, while the l index decreased exponentially in the tilled, BS, CT and MT treatments. Crossover length was sensitive to differences in soil roughness conditions allowing a description of Microrelief decay due to rainfall in the tilled treatments, although better correlations between cumulative rainfall and the most commonly used indices RR and LD were obtained. At the studied scale, parameters l and D have been found to be useful in interpreting the configuration properties of the soil surface Microrelief.

  • assessing soil surface roughness decay during simulated rainfall by multifractal analysis
    Nonlinear Processes in Geophysics, 2008
    Co-Authors: Vidal E Vazquez, M. C. Díaz, Garcia R Moreno, Saa A Requejo, Jose Garcia Vivas Miranda, Paz J Ferreiro, A M Tarquis
    Abstract:

    Abstract. Understanding and describing the spatial characteristics of soil surface Microrelief are required for modelling overland flow and erosion. We employed the multifractal approach to characterize topographical point elevation data sets acquired by high resolution laser scanning for assessing the effect of simulated rainfall on Microrelief decay. Three soil surfaces with different initial states or composition and rather smooth were prepared on microplots and subjected to successive events of simulated rainfall. Soil roughness was measured on a 2×2 mm2 grid, initially, i.e. before rain, and after each simulated storm, yielding a total of thirteen data sets for three rainfall sequences. The vertical Microrelief component as described by the statistical index random roughness (RR) exhibited minor changes under rainfall in two out of three study cases, which was due to the imposed wet initial state constraining aggregate breakdown. The effect of cumulative rainfall on Microrelief decay was also assessed by multifractal analysis performed with the box-count algorithm. Generalized dimension, Dq, spectra allowed characterization of the spatial variation of soil surface Microrelief measured at the microplot scale. These Dq spectra were also sensitive to temporal changes in soil surface Microrelief, so that in all the three study rain sequences, the initial soil surface and the surfaces disturbed by successive storms displayed great differences in their degree of multifractality. Therefore, Multifractal parameters best discriminate between successive soil stages under a given rain sequence. Decline of RR and multifractal parameters showed little or no association.

  • effect of tillage on fractal indices describing soil surface Microrelief of a brazilian alfisol
    Geoderma, 2006
    Co-Authors: Vidal E Vazquez, Jose Garcia Vivas Miranda, Marlene Cristina Alves, Paz A Gonzalez
    Abstract:

    Abstract Soil surface roughness is known to influence water infiltration, runoff and erosion. Soil surface roughness changes with management and weather and its mathematical description still remains an important issue. The main objective of this study was to investigate the effect of tillage on the two fractal indices, fractal dimension, D , and crossover length, l , currently used in characterizing soil surface Microrelief. The statistical index random roughness, RR, was also assessed. Field experiments were done on an Alfisol located at Rio Grande do Sul State (Brazil). Two tillage treatments (conventional versus direct drilling) were tested. The soil surface Microrelief was assessed by point elevation measurements in 16 plots for each treatment. The sampling scheme was a square grid with 20 × 20 mm between point spacing and the plot size was 280 × 280 mm, so that each data set consisted of 225 individual elevation points. All indices were calculated after trend removal, both by slope correction, i.e., oriented Microrelief, and by slope plus tillage marks correction, i.e., random Microrelief. The implemented algorithm for estimating D and l consisted in evaluating the roughness around the local root mean square deviation (RMS) of the point elevation values. Irrespective of tillage treatment and detrending procedure, fractal behavior extended only over a bounded range of scales, from 40 to 100 mm, due to the experimental setup. In these conditions, assessing fractal indices was not always straightforward. The statistical index RR and the fractal index l were significantly different between tillage treatments for oriented and random surface conditions. D values of random soil surfaces were not affected by tillage treatment, whereas D values of oriented Microrelief were significantly lower in the direct drilled plots. Removal of tillage marks trend resulted in a significant increase in D values. Within each tillage treatment, l and D were significantly correlated.

  • characterizing anisotropy and heterogeneity of soil surface microtopography using fractal models
    Ecological Modelling, 2005
    Co-Authors: Vidal E Vazquez, J Vivas G Miranda, Paz A Gonzalez
    Abstract:

    Soil surface roughness and the complementary soil Microrelief depression pattern determine water infiltration, overland flow and drainage network development. The characteristic soil surface roughness remains poorly defined, because of difficulties in quantifying soil Microrelief by single indices. Moreover, self-affine fractal models have been found to adequately describe soil surface microtopographic features only in a small range of length scales. At least two parameters are required to assess fractal Microrelief surfaces, fractal dimension, D, describing how roughness changes with scale, and the so-called crossover length, l, which specifies the variance at a reference scale. This study focuses on isotropy and heterogeneity analysis of soil surface point elevation data sets, measured with different resolutions, by pinmeter and laser scanner, under field and laboratory conditions. Selected examples of elevation data sets illustrate how real surfaces cannot be ideally fractal, even over limited length scales. Values estimated for the fractal parameters, D and l, by two independent methods, semivariogram (SMV) and local root mean square (RMS), presented some bias, although from a practical point of view both methods gave equivalent results. Irrespective of calculation method and after having removed both, slope and primary tillage effects, DSMV and DRMS values were always above 2.5, indicating anti-persistent behavior. The DSMV and DRMS values were highly correlated with each other, although the relationship was not one to one. Differences in lSMV and lRMS were only apparent for plots with very large structural units and random roughness. Fractal characterization of soil anisotropy and heterogeneity by the SMV and the RMS methods, respectively, may be very useful as a way to compare data sets obtained for different treatments or soil surface evolution conditions, when measured with the same resolution. Isotropic/anisotropic features of the soil Microrelief were visualized by means of a Hurst rose plot, where DSMV values estimated for different directions were represented. Local spatially variable DRMS values provided a description of the heterogeneity/homogeneity of the soil surface. © 2004 Elsevier B.V. All rights reserved.