Level Of Structural Heterogeneity Research Articles

Scale-guided mapping of forest stand structural heterogeneity from airborne LiDAR

Heterogeneity in forest structure, naturally occurring or induced by management, is continuous in space and time. However, measures used to quantify structure of forests are scale-variant, as they rely on bounded observations on either ecological or forest inventory observation units. The understanding of the influence of the scale of observation in mapping of forest structural heterogeneity is limited. Therefore, we researched into effects of plot size on quantifying forest structural heterogeneity, where we describe heterogeneity by three indices in stands under different management systems. In addition, we studied the performance of structural indices in separating different forest management systems across plot sizes, and created wall to wall maps of the indices using airborne LiDAR metrics describing the vertical distribution of canopy heights at different scales of observation. The studied indices are: Gini Coefficient (GC), Structural Complexity Index (SCI), and Enhanced Structural Complexity Index (ESCI). SCI and ESCI require fully mapped plots whereas GC has no information on individual tree locations. Inventory data from 95 one-hectare plots covering a range of management intensities from un-managed to age class forests were used. We quantified the three structural indices for 18 plot sizes ranging from 225 m2 to 10,000 m2. Linear fixed effects models were used to study the effects of plot sizes in different levels of structural heterogeneity and Random Forest (RF) models used to provide wall-to-wall maps at varying scales from airborne LiDAR data. The simulation showed that all indices were influenced by the scale of observation with larger effects for plots in forests with higher structural heterogeneity. For the data analyzed we found a threshold scale for enumerating stand structural heterogeneity between 900 m2 and 2500 m2. However, stable field and remote sensing predictions of stand structural heterogeneity required plots at least ⩾2500 m2. Compared to GC, SCI and ESCI improved separation of forest structure in the three management systems and at all observed scales. A change of plot sizes affected bivariate relationships between structural indices and airborne LiDAR metrics as well as the resultant predictive models. Smaller plot sizes yielded weaker relationships and predictive models. All structure indices were predicted from airborne LiDAR with RMSE⩽22% at scales equal or larger than the identified threshold plot size. These findings are relevant to optimize plot sizes for efficient inventory and mapping of forest structural heterogeneity, as well as for the design of natural resource inventories. Additionally, derived maps are useful for studies on forest structure and the link with forest growth, degradation, management intensity, productivity, and biodiversity in the regions.

Structural correlations tailor conductive properties in polymerized ionic liquids.

Polymerized ionic liquids (PolyILs) are promising materials for applications in electrochemical devices spanning from fuel cells to capacitors and batteries. In principle, PolyILs have a competitive advantage over traditional electrolytes in being single ion conductors and thus enabling a transference number close to unity. Despite this perceived advantage, surprisingly low room temperature ionic conductivities measured in the lab raise an important fundamental question: how does the molecular structure mediate conductivity? In this work, wide-angle X-ray scattering (WAXS), vibrational sum frequency generation (vSFG), and density functional theory (DFT) calculations were used to study the bulk and interfacial structure of PolyILs, while broad band dielectric spectroscopy (BDS) was used to probe corresponding dynamics and conductive properties for a series of the PolyIL samples with tunable chemistries and structures. Our results reveal that the size of the mobile anions has a tremendous impact on chain packing in PolyILs that wasn't addressed previously. Larger mobile ions tend to create a well-packed structure, while smaller ions frustrate chain packing. The magnitude of these changes and level of structural heterogeneity are shown to depend on the chemical functionality and flexibility of studied PolyILs. Furthermore, these experimental and computational results provide new insight into the correlation between conductivity and structure in PolyILs, suggesting that structural heterogeneity helps to reduce the activation energy for ionic conductivity in the glassy state.

Structural insights into leishmanolysins encoded on chromosome 10 of Leishmania (Viannia) braziliensis.

BACKGROUND Leishmanolysins have been described as important parasite virulence factors because of their roles in the infection of promastigotes and resistance to host’s defenses. Leishmania (Viannia) braziliensis contains several leishmanolysin genes in its genome, especially in chromosome 10. However, the functional impact of such diversity is not understood, but may be attributed partially to the lack of structural data for proteins from this parasite.OBJECTIVES This works aims to compare leishmanolysin sequences from L. (V.) braziliensis and to understand how the diversity impacts in their structural and dynamic features.METHODS Leishmanolysin sequences were retrieved from GeneDB. Subsequently, 3D models were built using comparative modeling methods and their dynamical behavior was studied using molecular dynamic simulations.FINDINGS We identified three subgroups of leishmanolysins according to sequence variations. These differences directly affect the electrostatic properties of leishmanolysins and the geometry of their active sites. We identified two levels of structural heterogeneity that might be related to the ability of promastigotes to interact with a broad range of substrates.MAIN CONCLUSION Altogether, the structural plasticity of leishmanolysins may constitute an important evolutionary adaptation rarely explored when considering the virulence of L. (V.) braziliensis parasites.

Four decades of forest succession in the oak-dominated forest reserves in Slovakia

Abstract: The study analyzes biodiversity, production and recovery processes in the natural oak-dominated forests in three protected areas in time span of four decades after the cessation of human impact. In each forest reserve, we established three permanent research plots of 0.5 ha, which were monitored regularly every 10 years. The obtained results confirmed an expected decrease of oak in all investigated areas, regardless of the level of past human intervention. Growth rates of oak stem density were negative in all reserves and ranged from -0.7% yr-1 (Kasivarova) to -2.1% yr-1 (Bujanov). A typical rotated-sigmoid diameter structure was confirmed during the whole observed period only in the reserve Boky. The moderate affected reserve (Kasivarova) showed a bimodal pattern and the most affected reserve (Bujanov) revealed the typical unimodal distribution. Considering spatial diversity, the recorded structure of investigated forests closely corresponds with the relative level of past intervention. In Boky, the most differentiated structure was reflected in the highest long-term mean stem density (890 ± 151 ha-1) and the lowest basal area and growing stock (36.5 ± 1.4 m2 ha-1 and 284 ± 22 m3 ha-1, respectively). The past-affected reserves reached higher values of basic stand parameters. In Kasivarova and Bujanov, the average basal area (36.5 and 44 m2 ha-1, respectively) and growing stock (284 and 518 m3 ha-1, respectively) correlated negatively with the level of structural heterogeneity, while the stem number revealed a positive correlation. We observed a continuous increase of deadwood volume and dead to live wood ratio. The recorded long-term volume of deadwood (43-128 m3 ha-1) and deadwood proportion (151-28%) tended to be higher in the past-affected reserves. The convergence towards the rotated-sigmoid distribution in both reserves with past human impact was recorded. Considering the vertical structure, the most dynamic changes were observed in the lower and middle layer. Moreover, the substitution of the light-demanding oak by shade-tolerant species (beech, hornbeam) was recorded. The intensity of substitution directly reflected the intensity of structure modification in the past. Our results suggest that the process of forest recovery and oak loss significantly depends on the level of past human intervention.

Nanostructural scaling effect in fracturing homogeneous solids

The scaling effect (power law dependence of number of newly-formed damages on damage size) during fracturing is inherent in heterogeneous materials, such as composites, concrete, rocks, etc., in which multi-site damaging takes place. Fracturing brittle homogeneous materials do not exhibit this phenomenon due to the lack of pre-failure damage accumulation at the microscopic scale level. This work is to determine the role of structural heterogeneity in the process of primary defect nucleation occurring in conventional homogeneous materials. We present highly resolved time series of fractoluminescence (FL) emitted during multiple chemical bond breakage in shock-damaged silica glass and single crystals \(\upalpha \hbox {-SiO}_{2}\) and \(\upalpha \hbox {-SiC}\). The statistical analysis of the time series has shown that the energy distributions of FL pulses followed the power law indicative of long-range interactions between primary damage events. This scaling phenomenon is caused by the multiplicity of newly formed damaged sites at the level of structural heterogeneity. At the same time, the microscopic and larger damage formation reflected in the acoustic emission time series did not exhibit the presence of long-range interactions between growing brittle cracks.

Stretching, coalescence, and mixing in porous media.

We study scalar mixing in heterogeneous conductivity fields, whose structural disorder varies from weak to strong. A range of stretching regimes is observed, depending on the level of structural heterogeneity, measured by the log-conductivity field variance. We propose a unified framework to quantify the overall concentration distribution predicting its shape and rate of deformation as it progresses toward uniformity in the medium. The scalar mixture is represented by a set of stretched lamellae whose rate of diffusive smoothing is locally enhanced by kinematic stretching. Overlap between the lamellae is enforced by confinement of the scalar line support within the dispersion area. Based on these elementary processes, we derive analytical expressions for the concentration distribution, resulting from the interplay between stretching, diffusion, and random overlaps, holding for all field heterogeneities, residence times, and Péclet numbers.

Microstructural properties of the bulk matrix and the steel/cement paste interface in reinforced concrete, maintained in conditions of corrosion and cathodic protection

Although rarely considered, especially within the investigation of steel corrosion phenomena or electrochemical protection techniques in reinforced concrete structures, the concrete bulk matrix has a significant contribution in the global performance of the system “reinforced concrete.” This is especially the case when chloride-induced corrosion or electrical current flow [as within impressed current cathodic protection (CP)] are involved. In the latter cases, the concrete bulk matrix undergoes significant alterations in chemical composition, electrical properties, and microstructures, thus influencing the overall performance of the system. This work reports on the microstructural investigation of the bulk concrete matrix and the steel/cement paste interface in reinforced concrete, previously subjected to corrosion and CP for 460 days. The emphasis hereby is to evaluate the altered structural properties, i.e., porosity, pore size, permeability of the bulk cement matrix, and the steel/cement paste interface (translated to bond strength) as a result of chloride-induced corrosion and two types of CP (conventional and pulse), compared to control (non-corroding, non-protected) conditions. The research revealed a major contribution and close dependence of all microlevel interfaces on the global performance of reinforced concrete. The electrical current flow (as in CP applications) was found to bring about unfavorable modifications to the material structure, both in the bulk matrix (reducing porosity) and at the steel/cement paste interface (enlarging interfacial gaps). The derived microstructural parameters show that the conventional CP leads to a higher level of structural heterogeneity, whereas the pulse CP exerts minimal or no effects, maintaining the material properties close to the reference (control) conditions, the underlying mechanism being a more homogeneous material microstructure.

Adsorption of hydrogen sulfide on graphite derived materials modified by incorporation of nitrogen

Adsorbents for hydrogen sulfide were prepared by heat treatment at 950 °C of spent graphite oxide based materials previously used as ammonia removal media. The materials were characterized using adsorption of nitrogen, potentiometric titration, thermal analysis, FTIR and XRD. The dynamic adsorption experiments showed an enhanced adsorption capacity owing to the presence of basic nitrogen functionalities. Although on the surface of adsorbents hydrogen sulfide was mainly oxidized to elemental sulfur small amount of SO 2 was also formed. The removal capacity was found to depend on the dispersion of nitrogen containing species, which is governed by the porosity and structure of the adsorbents. The amount of nitrogen incorporated depends on the amount of ammonia on the surface and on the surface reactivity. The latter is determined by the amount of oxygen containing groups and the level of structural heterogeneity.

Immunochemical and structural analysis of the O polysaccharides of Salmonella zuerich [1,9,27,(46)

Salmonella zuerich [1,9,27,(46)] has been shown to exhibit two levels of structural heterogeneity. The bacterium carries two distinct O-polysaccharide molecules with and without O:factor 1. Both sets of molecules (1+ and 1-) carry the two O:factors 27 and 46 on the same O chain, but they are expressed unevenly; in contrast to factor 27, O:factor 46 is always weakly expressed. Part of this weak expression was thought to be due to strong inhibition of factor 46 by factor 1. In this study, serological analysis gave more detailed information on the sizes of the different O:factor epitopes. Structural analysis of S. zuerich O polysaccharides showed that they are constructed of the expected chemical sequences characteristic of factors 1, 9, 27, and 46. No modification in the sugar sequence could account for the weak expression of O:factor 46. Factors 27 and 46 are present on oligosaccharides carrying either an alpha-Man (factor 27) or a beta-Man (factor 46) residue. In S. zuerich, the alpha-Man configuration is predominant, corroborating the expression of strong factor 27 and weak factor 46 on the bacteria. Questions raised by the existence of such heterogeneous O polysaccharides on the specificity of the O chain polymerase, as well as the place of S. zuerich in Salmonella evolution, are dicussed in this paper.