Fire Ecology Research Articles

INFLUENCE OF HEAT TREATMENT AND IN-VITRO AGING ON MECHANICAL PROPERTIES AND SURFACE ROUGHNESS OF COLD ISOSTATIC PRESSED ZIRCONIA - AN INVITRO STUDY

Purpose:Mechanical and surface characteristics of the zirconia dental ceramics may be adversely impacted by temperature changes during the veneering firing cycles. A potential synergistic failure could be caused by ageing when exposed to the oral environment and heat treatment. The current research aimed to determine the influence of heat treatment and in-vitro ageing on mechanical properties and surface roughness of cold isostatic pressed zirconia. Materials and Methods:15 bar shaped specimens with dimensions 28mm×4mm×2mm are milled from two types of partially sintered Y-TZP ceramic blanks (IPS e.max ZirCAD (IZ),ZENO Zr (WZ)). Out of 15 samples five are used as control (C group), five are heat treated (H group) and five are heat treated and subsequently aged (HA group). Flexural strength and shear bond strength are measured using universal testing machine and surface roughness is measured using proliferometer. Results:Heat treatment on the ivoclar and weiland samples led to an increase in surface roughness and a loss in mechanical properties (flexural strength and shear bond strength), although the differences are not statistically significant (p>0.05). Yet, the combined ageing and heat treatment created a synergistic effect on surface roughness and mechanical characteristics. (p<0.001). More variations were seen in the weiland samples. Conclusion:Firing and ageing processes may have an impact on zirconia ceramics clinical performance, which raises the risk of failure.

Changes in canopy cover and forest structure following dormant season and early growing season prescribed burns in the Southern Appalachians, USA

BackgroundFire seasonality is important for forest managers to consider when restoring historical disturbance regimes and recovering native ecosystem structure and composition, but it is less understood and less frequently studied than other aspects of fire ecology. In the Southern Appalachians, historical fires likely occurred most often in late spring and early summer when fuels were dry and canopy conditions were conducive to fire; however, most prescribed fires today occur during the dormant season (January–March). Because fire behavior can vary seasonally, it is important for forest managers to understand the practical applications of fire season in order to burn at a time that meets management objectives. Therefore, we investigated the effect of fire seasonality on forest structure and land cover diversity in the Southern Appalachians.ResultsUsing a complete randomized block design, we analyzed leaf-on canopy cover imagery with ArcGIS Pro to compare canopy cover and forest structure between growing and dormant season burns. We compared imagery between three blocks, each with an unburned control unit, dormant season burn, and growing season burn, and found an average of 8.84% (SE = ± 1.46) reduction in canopy cover in growing season treatment units from pre-burn (2017) to post-burn (2019) compared to 5.21% (SE = ± 1.51) reduction in dormant season treatment units and 0.01% (SE = ± 0.009) reduction in unburned controls. Canopy cover reductions corresponded with substantial increases in early- and mid-successional habitat, edge length, and land cover diversity — especially in growing season burn treatment units.ConclusionsOur results indicate that early growing season burns are more effective than dormant season burns at enhancing forest structural heterogeneity. Early growing season burns, therefore, may be a viable option for forest managers looking to expand their burn season and achieve restoration and management goals faster than traditional dormant season burns.

Overcoming crossdating challenges to generate ring-width chronologies for Sequoia sempervirens across its native range

We utilize a large dendrochronological dataset for Sequoia sempervirens of 1.29 million rings from 5952 series for 278 trees to generate location and regional ring-width chronologies and to investigate constraints on crossdating. Increment cores were collected at regular height intervals along the trunk via free-hanging ropes with some terrestrial deadwood sampled. Inter-annual chronologies span 86–1687 yr for 47 locations in primary and secondary forests across the native Sequoia range. Shared signals based on declining strength of paired correlations with distance, strong correlations within regions, and groupings of principal components guide chronology creation for northern (1032 yr, 108 trees) and southern (865 yr, 52 trees) regions and four sub-regions. The suite of chronologies provides location-specific references as well as more robust regional indices that reflect distinct signals along a climatically-integrative latitudinal gradient. Secondary forests date to near completion, and we use a subset of data to assess crossdating for trees in primary forests. Among tree and landscape attributes, old age is the most important predictor of undated and missing rings, and undated rings align with periods of reduced biomass production distributed across centuries-long lifespans. Crossdating metrics vary by height above the ground with breast height (BH) and 10 m samples having more undated rings than upper samples. At 10 m, samples have the most missing rings. Buttressing affects the lower trunk as BH series have higher ring widths and lower interseries correlations compared to those up to 70 m. Whole-trunk sampling maximizes success for crossdating old, structurally-complex Sequoia and enables dating of crown damage and assessment of biomass dynamics related to environmental change. Reference chronologies, regional assessments, and crossdating insights collectively guide future study of Sequoia for applications including climatology, fire ecology, and seismology.

SK and Kv4 Channels Limit Spike Timing Perturbations in Pacemaking Dopamine Neurons.

Midbrain dopamine (DA) neurons are among the best characterized pacemaker neurons, having intrinsic, rhythmic firing activity even in the absence of synaptic input. However, the mechanisms of DA neuron pacemaking have not been systematically related to how these cells respond to synaptic input. The input-output properties of pacemaking neurons can be characterized by the phase-resetting curve (PRC), which describes the sensitivity of interspike interval (ISI) length to inputs arriving at different phases of the firing cycle. Here we determined PRCs of putative DA neurons in the substantia nigra pars compacta in brain slices from male and female mice using gramicidin-perforated current-clamp recordings with electrical noise stimuli applied through the patch pipette. On average, and compared with nearby putative GABA neurons, DA neurons showed a low, nearly constant level of sensitivity across most of the ISI, but individual cells had PRCs showing relatively greater sensitivity at early or late phases. Pharmacological experiments showed that DA neuron PRCs are shaped by small-conductance calcium-activated potassium and Kv4 channels, which limit input sensitivity across early and late phases of the ISI. Our results establish the PRC as a tractable experimental measurement of individual DA neuron input-output relationships and identify two of the major ionic conductances that limit perturbations to rhythmic firing. These findings have applications in modeling and for identifying biophysical changes in response to disease or environmental manipulations.

Reconstructing 34 Years of Fire History in the Wet, Subtropical Vegetation of Hong Kong Using Landsat

Burn-area products from remote sensing provide the backbone for research in fire ecology, management, and modelling. Landsat imagery could be used to create an accurate burn-area map time series at ecologically relevant spatial resolutions. However, the low temporal resolution of Landsat has limited its development in wet tropical and subtropical regions due to high cloud cover and rapid burn-area revegetation. Here, we describe a 34-year Landsat-based burn-area product for wet, subtropical Hong Kong. We overcame technical obstacles by adopting a new LTS fire burn-area detection pipeline that (1) Automatically uniformized Landsat scenes by weighted histogram matching; (2) Estimated pixel resemblance to burn areas based on a random forest model trained on the number of days between the fire event and the date of burn-area detection; (3) Iteratively merged features created by thresholding burn-area resemblance to generate burn-area polygons with detection dates; and (4) Estimated the burn severity of burn-area pixels using a time-series compatible approach. When validated with government fire records, we found that the LTS fire product carried a low area of omission (11%) compared with existing burn-area products, such as GABAM (49%), MCD64A1 (72%), and FireCCI51 (96%) while effectively controlling commission errors. Temporally, the LTS fire pipeline dated 76.9% of burn-area polygons within two months of the actual fire event. The product represents the first Landsat-based burn-area product in wet tropical and subtropical Asia that covers the entire time series. We believe that burn-area products generated from algorithms like LTS fire will effectively bridge the gap between remote sensing and field-based studies on wet tropical and subtropical fire ecology.

Far from equilibrium ultrafast high‐temperature sintering of ZrO2–SiO2 nanocrystalline glass–ceramics

AbstractUltrafast high‐temperature sintering (UHS) is a novel sintering technique with ultrashort firing cycles (e.g., a few tens of seconds). The feasibility of UHS has been validated on several ceramics and metals; however, its potential in consolidating glass–ceramics has not yet been demonstrated. In this work, an optimized carbon‐free UHS was utilized to prepare ZrO2–SiO2 nanocrystalline glass–ceramics (NCGCs). The phase composition, grain size, densification behavior, and microstructures of NCGCs prepared by UHS were investigated and compared with those of samples sintered by pressureless sintering. Results showed that NCGCs with a high relative density (～95%) can be obtained within ～50 s discharge time by UHS. The UHS processing not only hindered the formation of ZrSiO4 and cristobalite but also enhanced the stabilization of t‐ZrO2. Meanwhile, owing to the ultrashort firing cycles, the UHS technology allowed the NCGCs to be consolidated in a far from equilibrium state. The NCGCs showed a microstructure of spherical monocrystalline ZrO2 nanocrystallites embedded in an amorphous SiO2 matrix.

Correlating the physico-chemical properties of two conventional glazed porcelain stoneware tiles in relation to cleanability and sanitization

Keeping surfaces clean can reduce the spread of infections. In particular, to decrease the potential for SARS CoV-2 contamination, performing disinfection of high-touching surfaces. Several ceramic tiles and porcelain stoneware tiles with antimicrobial properties are already available on the market. However, the widespread use of antimicrobial glazed stoneware tiles may require to replace the ceramic surfaces already present in many buildings. The unfeasibility of such replacement can be due to both product durability (lifetime of a tile is usually long) and/or monetary restrictions. Furthermore, as porcelain stoneware per se does not have antimicrobial activity, these materials are fabricated by adding chemical agents able to provide antimicrobial properties. This approach requires a compatibility between the antimicrobial agents and the glaze formulation, as well as a careful control of the firing cycle and the final properties of the ceramic products. It follows that the final cost of antimicrobial tiles is not competitive with that of conventional tiles. In the latter, the persistence of potential pathogens on the surfaces is a crucial problem to face: the longer a pathogen survives on a surface, the longer it may be a source of transmission and thus endanger susceptible subjects. In this work, bacteria's capacity to adhere and to be effectively removed from two conventional glazed porcelain stoneware tiles (under dirty and clean conditions) was investigated. Two different glazes were tested, one mainly glassy (glossy) and the other mainly crystalline (matt). The sanitization procedures were carried out by chemical and chemo-mechanical procedures. The results showed that chemo-mechanical sanitization was the most effective, and the best results could be obtained on the stoneware tiles coated with the mainly glassy glaze, with the lowest porosity and the lower roughness values and water contact angles, especially under clean conditions.

A parametric study to improve first firing cycle emissions of a gasoline direct injection engine during cold start

A parametric study was carried out for the first firing cycle of a 4-cylinder, 2.0-liter, turbocharged gasoline direct injection (GDI) engine. The primary goal was to see how changes in the fuel injection parameters would affect the GDI engine combustion and emissions for the first four combustion events that constitute the first firing cycle. Experimental studies were carried out with a custom-designed powertrain control system to measure the HC emissions and pressure development for the first firing cycle. The quantitative experimental results were accompanied by simulations of the detailed temporal and spatial fuel concentration profiles using Converge CFD engine simulation software. An alternative calculation method was used to calculate the average combustion equivalence ratio for each of the four cylinders. This method showed that the majority of the cold start HC emissions during the first firing cycle was unburned gasoline and its possible decomposition products, which did not contribute significantly to the combustion and heat release. For the same amount of fuel injected into a cylinder, increased fuel rail pressure resulted in better evaporation and combustion, while slightly increasing the HC emissions during the cold start process. A multiple injection strategy was studied that split the fuel delivery between the intake stroke and the compression stroke with either one or two injections in each of those strokes (two or four injections total). The quadruple injection strategy led to better first cycle combustion, with higher engine IMEP and lower HC emissions. This resulted from a richer fuel mixture in the region near the spark plug due to better fuel evaporation and a better spatial fuel distribution. While increasing fuel rail pressure with either injection strategy failed to significantly lower the HC emissions given the same amount of injected fuel mass, higher rail pressure with the quadruple injection strategy resulted in higher IMEP for the same amount of injected fuel; this may provide the possibility to reduce the total fuel injection mass which may have benefits for both fuel consumption and emissions.

Evaluation of the Marginal Fit of Computer-Aided Design (CAD) and Computer-Aided Manufacturing (CAM) Zirconia Bridges Fabricated With Different Firing Cycles of Veneering Porcelain: An In Vitro Study.

Introduction Zirconia provides adequate mechanical strength to be used as a framework for all ceramic prostheses. Such prostheses must be covered with suitable porcelain to obtain good aesthetic results. The aim To study the effect of the firing cycle numbers of veneering ceramics (one cycle, two cycles, and three cycles) on the marginal fit of computer-aided design(CAD) and computer-aided manufacturing (CAM)zirconia bridges. Materials and methods The sample consisted of 30 full ceramic zirconia bridges, designed by CAD/CAM on a metal bridge model that was designed for this purpose. The sample was divided into three groups (N = 10); group Aunderwent a single firing cycle, group Bunderwent two cycles, and group Cunderwent three cycles. The copper model of the bridge was prepared to be a three-unit bridge, and the impressions of the metal models were taken to make zirconia cores. After that, the veneering ceramic layer and the micro-marginal gap were measured (in microns) on both the buccal and lingual surfaces of each bridge in the sample using the replica technique. A one-way ANOVA test was used to detect statistically significant differences between the groups. Results There were no significant differences between the studied groups in binary comparison; however, the arithmetic mean values of the marginal gap in group C were greater than all the studied groups. Conclusion Within the limitations of the current work, we found that increasing the number of firing cycles of zirconia cores affects the marginal fit; thus, it is recommended to follow the two firing cycle protocol for better adaptation of the CAD/CAM zirconia bridges.

Effect of Multiple Firings on the Microshear Bond Strength Between a Translucent Zirconia and a Resin Cement.

This study investigated the microshear bond strength between a resin cement and a translucent zirconia subjected to multiple characterization firings. 5Y-PSZ zirconia blocks (Katana UTML) were sliced, sintered (1550°C, 2 h), and randomly divided into six groups (n=10) according to the number of characterization firings (0, 1, 2, 3, 5, or 10) and aging (baseline or after thermocycling). Each characterization firing was performed at 750°C for 1 minute. The ceramic surfaces were all sandblasted with 50 μm Al2O3 and silanized. Then, cylinders of resin cement (0.96 mm diameter × 2 mm height) were bonded onto their surfaces. The baseline samples were immersed in distilled water for 24 hours before the microshear bond strength (μSBS) tests. The aged samples were tested after 5000 thermocycles in water (5°C-55°C). The failure modes were classified as adhesive, predominantly adhesive, or cohesive. Scanning electron microscope images of the failure modes and the ceramic surfaces after the firings were taken. The μSBS data were analyzed by two-way ANOVA and Tukey's test. The number of characterization firings and aging affected the bond strength. The highest bond strength values were observed from the 2-firing group at baseline. The μSBS results after 1, 2, or 3 characterization firings were similar at baseline and after aging. On the other hand, 0, 5, and 10 firings revealed the lowest bond strengths. The most frequent failures were adhesive and predominantly adhesive. Zirconia grains were not affected by the multiple firings. One to three characterization firings after sintering improve the bond strength of 5Y-PSZ to the resin cement when compared to none or several (five or ten) firing cycles.

THE COMPLEMENTARY USE OF CHARCOAL NUMBER AND MORPHOLOGY TO RECONSTRUCT FIRE HISTORY IN A LATE HOLOCENE PEAT SEQUENCE FROM NW ROMANIA

Fires influence basic ecosystem processes, including the distribution, the structure and the composition of vegetation, as well as the carbon cycle and climate at the global scale. Long-term knowledge (i.e., centuries or millennia) of fire regime history and forest fire ecology and dynamic in local environments is necessary for sustainable ecosystem management and biodiversity conservation strategies. Charcoal is a widely used proxy for reconstructing fire regime history and vegetation burning. Charcoal analysis is based on the accumulation of charred particles in depositional environments such as lakes and bogs, during and shortly after the occurrence of fire events. Ombrotrophic peat bogs are sensitive to local environmental changes and, given that the deposition of allochthonous material is exclusively atmospheric, they are ideal archives for reconstructing charcoal fluxes resulting from biomass burning. This study quantifies charcoal abundance (number) in a peat sequence extracted from Tăul Mare ombrotrophic peat bog (Văratec Massif, Lăpuş Mts, north-western Romania) aiming to reconstruct local fire history over the last 3000 years and to explore potential drivers. As a novelty, observations concerning the morphology of charred fragments are added to provide additional information on the type of material burnt (woody vegetation or herbs), fire severity and charcoal source area, thus strengthening the interpretation of the charcoal record. Results showed moderate fire activity between 3000 and 2300 cal yr BP, which slightly decreased between 2300 and 700 cal yr BP and varied considerably throughout the last 700 years. Several major fire episodes were further identified around 2500, 1700, 1300, 900 and 500 cal yr BP. Of these, the first four overlapped two phases of progressive landscape opening and extension of pastoral activities, while the latter was unprecedented in the entire history of the bog and was likely associated with the development of mining activities in the area. This study provides the first complementary use of charcoal morphologies in fire history reconstruction in Romania and adds a valuable perspective on the extent of past human impact on the mid-elevation mountain landscape.

Comparative analysis of techniques for extrinsic characterization of CAD/CAM ceramics

The present study aims to evaluate surface roughness and color stability of lithium disilicate and leucite ceramics after conventional and a novel surface finish techniques. Ceramic blocks (n = 84) of lithium disilicate and leucite were prepared and divided into 3 groups, being group 1: polished ceramic (negative control) (NC); group 2: stained (pigmented) ceramic followed by glaze (positive control) (PC) and group 3: simultaneous application of staining and glaze (experimental technique) (ET). Changes in luminosity and surface roughness were evaluated at 4 different time-points after a simulated brushing cycling test. Multivariate test results showed that there was a triple interaction effect between applied material, finish technique and time on their average roughness (p < 0.001) and luminosity (p < 0.05). There was no statistically significant difference in the mean roughness considering NC and ET groups for the leucite and lithium disilicate ceramics, but there was an increase in roughness mean at t1 for the PC and ET groups. Considering luminosity (materials vs. time), there was a statistically significant difference in leucite PC group. The NC and ET groups did not differ statistically from each other. There was a luminosity reduction in NC lithium disilicate ceramics for PC and NC groups. Also, analysis of color variation (ΔΕ) revealed significant differences for disilicate but not for the leucite groups. In leucite-based ceramic groups, surface roughness showed intermediate values between ET and the other groups at all times. Correlation analysis between roughness and luminosity presented significant results for leucite (r = 0.331; p < 0.001) and non-significant for lithium disilicate groups (r = 0.068; p > 0.05). Results suggested the possible application of the experimental technique (ET) for reduction of clinical time compared to conventional techniques, by the use of less ceramic firing cycles, with no prejudice in terms of surface roughness and luminosity over the studied time.

A Study on Impact of Fire Ecology in Daily Life of Manipur

A Study on Impact of Fire Ecology in Daily Life of Manipur

The Extension and Connotation of Forest Fire Ecology Under Constant Innovation

Forest fire ecology is a discipline to study the ecological consequences of forest fires and the interrelationships among them. With the intensification of climate change and the deterioration of forest fire status, forest fire ecology has become a very active branch of ecology. In this paper we reviewed the development history of forest fire ecology and expounded the extension and connotation of forest fire ecology, fire factors and regimes as well as their interaction with the ecological systems. Previous ecologists have conducted a lot of research on the impact of forest fire on the ecological environment and the adaptability of ecosystems to forest fire. The development of forest fire ecology can be divided into three periods: in the initial period the destruction of forest fire was recognized with the study objective being focused on forest fire control; in the expansion period, efforts were made to the application of forest fire in the fire management and the third period was symbolized as the founding of the entire discipline. With the application of the advanced technology and mathematical models, forest fire ecology provides successful examples in carrying out long-term prediction on the forest community dynamics after fire intrusion. Planned burning have been developed as effective means of forest fire management, whereas ecological fire mitigation is considered as a new concept in forest fire management.

Life Analysis of Reusable Liquid Rocket Engine Thrust Chamber

The thrust chamber’s inner wall suffers high temperature and pressure differences from the coolant channel, which limits the life of the rocket engine. Life prediction of the thrust chamber really plays an important role in reusable launch vehicle propulsion systems. The Porowski beam model is widely used in the life prediction of reusable liquid rocket engine thrust chambers, which calculates the life caused by fatigue, creep, and thinning after each firing cycle. In order to analyze the life of the thrust chamber, a LOX/Kerosene rocket engine is investigated in this paper. The life analysis consists of pressure and temperature differences and structural parameters. Two kinds of inner wall materials were chosen for comparison in this research: OFHC copper and Narloy-Z alloy. The results are presented to offer a reference for the design and manufacture of reusable rocket engine thrust chambers in the future.

Carrying the Torch: The role of the visual arts in communicating scientific lessons from fire ecology

Carrying the Torch: The role of the visual arts in communicating scientific lessons from fire ecology

A needs assessment for effective fire management in Uganda

Understanding fire ecology is a primary consideration in planning and implementing fire management. Some high risk forests must be protected from wildfires, whereas fire plays an integral role in savanna ecosystems, so it is essential to better understand human use of fire. and implement Guidelines for all stakeholders must be developed that align with their respective management priorities and implemented, and provide the required skills and equipment to key stakeholders to manage wildfire risk. Three overarching considerations are identified, as the country moves forward to developing, adopting and implementing an effective fire management strategy. These are the need to improve communication, collaboration, and coordination.

Festschrift initiative: Celebrating Distinguished Professor Jamie Kirkpatrick AM

AbstractThis Festschrift celebrates the distinguished 52‐year academic career of Jamie Kirkpatrick. All thirteen publications by Kirkpatrick in Geographical Research are curated as a virtual issue. Following a consultation process, six papers are highlighted in more detail. These were published from volume 13 to the latest volume. Kirkpatrick's research activities over the past five decades can be broadly sequenced into nine subject areas: (1) eucalypt genecology; (2) bush remnants in cities; (3) biogeography; (4) plant community survey and conservation planning; (5) fire ecology and management; (6) rare species ecology and management; (7) the politics of environment; (8) the socioecology of conservation in rural areas and gardens; and (9) biogeomorphology. His many publications and wide participation in public processes have, according to his own assessment, been a mixture of effective in changing the world, prescient, and wrong.

Community Responses to Fire: A Global Meta-Analysis Unravels the Contrasting Responses of Fauna to Fire

Globally, wildfires and prescribed fires are becoming more prevalent and are known to affect plant and animals in diverse ecosystems. Understanding the responses of animal communities to fire is a central issue in conservation and a panacea to predicting how fire regimes may affect communities and food webs. Here, a global meta-analysis of 2581 observations extracted from 208 empirical studies were used to investigate the effect of fire on aboveground and belowground fauna (e.g., bacteria, fungi, small mammals, arthropods). Overall, results revealed that fire had a negative effect on biomass, abundance, richness, evenness, and diversity of all faunas. Similarly, when considering wildfires and prescribed fires the data revealed that both fire regimes have negative effects on fauna. Similarly, fire had negative impacts on aboveground and aboveground fauna across most biomes and continents of the world. Moreover, there was little evidence of changes in pH, moisture and soil depth on soil organisms suggesting that other factors may drive community changes following a fire disturbance. Future research in fire ecology should consider the effects of fire across several species and across larger geospatial scales. In addition, fire effects on faunal community structure must be studied under contrasting global fire regimes and in light of the effects of climate change.

In-flame soot structure of a jet fuel with 24% aromatics in a small-bore optical compression-ignition engine

This study applies a multi-location soot sampling method in a small-bore optical compression ignition engine to show in-flame particle evolution of a surrogate jet fuel with 24% aromatics (AR24) and a conventional diesel fuel. Four soot sampling probes are installed on the piston-bowl wall with 60° spacing angles for simultaneous sampling from the same firing cycle. These sampling locations represent a jet-wall impingement point (JW), an up-swirl point (US), a down-swirl point 1 (DS1) and a down-swirl point 2 (DS2) along the sooting flame path identified by high-speed soot luminosity images and planar laser induced incandescence (PLII) images. The sampled soot particles are examined with transmission electron microscope (TEM) and the images are post processed for the analysis of morphology. The results showed both fuels produce a large amount of small soot aggregates at JW point due to fuel-rich mixtures while AR24 soot aggregate number count is much less than diesel, indicating less soot formation for AR24. They grow as the flame travels along the bowl wall through aggregation, which is more significant at DS1 point than that of US point. Simultaneously, some small soot aggregates disappear due to oxidation, which is more significant at US point. As the sooting flame reaches DS2 point, only large aggregates with compact structures survived intense oxidation. The soot sampling performed for high resolution TEM and internal structure analysis of AR24 showed that the core-shell particle structure becomes clearer and the carbon-layer fringe-to-fringe gap decreases during the flame penetration, indicating the soot oxidation continued. From the results, the in-flame soot evolution is characterised by high formation of small aggregates at JW point, simultaneous aggregation and oxidation at US and DS1 point with the latter more prone to aggregation, and significant oxidation at DS2 point.