Burn Cycle Research Articles

Light absorption characteristics of primary brown carbon during a complete residential biomass combustion process and their links with aerosol composition

Brown carbon (BrC) has been recognized as an important light-absorbing organic aerosol, and biomass combustion is the main source of BrC. Residential biomass burning is a heterogeneous process, and the dynamics of BrC optical properties during the burning process are still not well understood. Therefore, laboratory test equipped with online instruments (aerosol mass spectrometry and Aethalometer) of residential biomass burning was established to measure the optical properties of BrC. During a complete burn cycle, the light absorption characteristics at the flaming stage are generally similar for wood and crop straws, while it is distinctly different at the burnout stage. BrC contributes 0.141 to 0.609 to light absorption at UV region among different stages. The absorption emission factor and mass absorption cross section of BrC (MACBrC) at the flaming stage was significantly larger than that at the burnout stage. MACBrC was calculated and related to the aerosol composition, aromatic compounds (f77) and PAHs/OA were significantly positively related to MACBrC near the ultraviolet region, suggesting that aromatic compounds and PAHs are the vital contributors to the light absorption of BrC. This time-resolved study provides additional understanding of the dynamics of BrC optical properties during residential biomass burning processes. The results of this study will provide for more accurate assessment of the climate impact of BrC from residential biomass combustion.

Fine particulate matter and gas emissions at different burn phases from household coal-fired heating stoves

Household coal burning contributes a large proportion of fine particulate matter (PM2.5), black carbon (BC), organic carbon (OC), and CO emissions in China. Previous lab or field investigations generally measured short-term emissions from heating coal stoves, and only covered the high power phase or the flaming combustion processes, and did not consider smoldering combustion condition, which does not provide full characterization of the actual conditions in most cases. In this study, we investigated air pollutant emissions during the different burn phases of seven types of coal burned in a typical household coal-fired heating stove in the lab with a hood sampling system. We proposed a method to estimate coal consumption at the different burn phases, and thus quantify emission factors (EFs) at different burn phases. The concentrations of CO2, CO, SO2, NOx, and PM2.5 fluctuated over 1 to 4 orders of magnitude during the whole burn cycle. The air pollutant concentration peaks, such as CO and PM2.5, were generally associated with coal addition. EFs of CO2, SO2, total water soluble inorganic ions (TWSIIs) followed the trend: high power phase > low power phase > banked fire phase. However, CO EFs followed the opposite trend, i.e., banked fire phase > low power phase > high power phase. EFs of NOx and EC in high power phase and low power phase were higher than those in banked fire phase. The variation in EFs of PM2.5 and OC in different burn phases across seven types of coal burned in this study is complicated. When using EFs from high power phase or flaming phase to represent EFs from the whole process, CO2, SO2, NOx, EC and TWSIIs emissions will be overestimated, CO emissions will be underestimated, PM2.5 and OC emissions may be overestimated or underestimated, depending on coal types.

Building resilient landscapes in a semi-arid watershed: Anthropogenic and natural burning histories in Late Holocene Tesuque Creek, northern New Mexico

As mega-fires have swept the North American West in recent decades, studies of past fire events have gained academic interest. Deep-time perspectives are necessary to better understand the periodicity of fire events and to identify basic drivers of frequent fire episodes through time, including potential anthropogenic fire use. Our study contributes to the growing field of archeological fire ecology in the Southwest with an examination of a high-resolution geobotanical dataset for Holocene fire regimes as indicated within sediments from an alluvial section from Tesuque Creek in northern New Mexico. Using phytolith, geochemical, and sedimentological data, we reconstruct indices for burn cycle seasonality and destabilization of riparian vegetation communities that suggest potential anthropogenic land use and possible patterns distinguishing human burning from lightning ignitions. Through this study, we consider the potential role of hunter-gatherer behavior in producing fire landscapes as part of their strategies for managing risks in the fragile environments of the Middle-Late Holocene in northern New Mexico. We suggest that combining geo and botanical datasets from alluvial sections with archeological evidence will allow researchers to fine-tune the resolution of local climate sequences and their environmental impacts on small landscape scales. When such small-scale studies can be aggregated, they may further contribute to testing models of regional patch-burning, either natural or anthropogenic. We further posit that human relationships with fire in the past should be considered as collaborative efforts with lightning-ignited burns, to manage the risks associated with both too much and too little fire in fragile dryland ecosystems.

Study on engineering application method of large-scale reaction mechanism in knock prediction

In this paper, a new engineering application method for gasoline engine knock prediction in a quasi-dimensional combustion model using a large-scale reaction mechanism is explored. First, an accelerated calculation strategy coupled with 1D calculation and large-scale reaction kinetics mechanism was developed to meet the needs of rapid automatic simulation in engineering. Secondly, a gasoline surrogate was created according to the test results of China 92# gasoline. The motor octane number (MON) and the research octane number (RON) values, which were closely related to knock, were calibrated using the detailed reaction mechanism. Then, the prediction of auto-ignition of unburned region was carried out combined with predicted burn rate model and cycle to cycle variation (CCV) model. The relationship between the experimental in-cylinder pressure oscillation and the simulated auto-ignition in the unburned region was established. The multi-conditions verification results of three engines with different displacement, compression ratio and combustion system arrangement show that the average errors of predicted knock CA50 are 1.6°CA, 1.8°CA and 1.9°CA respectively.

Wood combustion nanoparticles emitted by conventional and advanced technology cordwood boilers, and their interactions in vitro with human lung epithelial monolayers

Biomass-burning boilers and stoves are widely used in many parts of the world, producing combustion emissions linked with health risks. Combustion emission nanoparticles (NPs) were collected from four representative wood burning boilers using oak cordwood at specific times in the burn cycle. The morphology and composition of the NPs was characterized using transmission electron microscopy and energy dispersive X-ray analysis. To determine the degree of NP cytotoxicity with human lung tissue, the combustion NPs were introduced to incubated lung bronchial epithelial monolayers (NCI-H292) in vitro at doses of 0.1 × 10-6 and 3.0 × 10-6 kg/L for 2 and 4 h. Histochemical analysis showed that cell death increased by a factor of 3.5 for both doses after 4 h when compared to the control. Ultrapure NPs prepared by wet chemical methods were also introduced to the epithelial lung cells for similar doses and exposure times and the cultures exhibited significantly reduced mortality. Electron microscopy was used to study the mechanism of cell mortality for the synthesized and combustion-based NPs by examining how the NP byproducts interacted with individual cell organelles. It was found that cell survival was strongly correlated with the absence of contaminants (salts, heavy metals, poly aromatic hydrocarbons) associated with the NPs entering the cells. Synthesized NPs consisting of pure carbon were relatively well tolerated and could be excreted without damaging the cell ultrastructure. Thus, careful removal of extraneous contaminants by controlling the burn cycle with a catalyst is essential to minimize the health and environmental effects of wood biofuel combustion. In better words, optimized advanced technology wood-burning boilers and stoves can provide a CO2-neutral energy source and significantly contribute to a future where fossil fuels have a reduced role.

Methanol cookstove a potential alternative to LPG cookstove: Usability, safety and sustainability studies

In the present study, the performance of methanol cookstove as a possible substitute for Liquefied Petroleum Gas (LPG) cookstoves in terms of usability (fuel convenience, cooking performance, operability, maintenance and comfort) and safety (temperature of touchable parts and mechanical stability) are presented. To introduce methanol as an alternative cooking fuel, thermal and emission performances of methanol cookstoves are evaluated. It was found that methanol cookstove yielded a maximum thermal efficiency of 63.2 % at firepower of 1.5 kW and a lesser CO/CO2 ratio of 0.0047 as compared to the prescribed limit (0.02) of IS 11760:1986. The measurement of methanol vapour concentration with burn cycle of 4 h was revealed that the methanol vapour in the confined space was less than 5 ppm which is 97.5 % lesser than the prescribed exposure limit. Also, the methanol cookstove secures a similar score of LPG in terms of maintenance, comfort and mechanical stability. Further, the fuel sustainability analysis revealed that with a 10 % methanol penetration rate in India, 3.69 MMT of LPG import could be reduced by 2030. Safety instructions are also prepared for methanol cookstove which assists in formulating a policy and planned actions that encourages the use of methanol as a safer and cleaner alternative to the LPG.

Using the carbon balance method based on fuel-weighted average concentrations to estimate emissions from household coal-fired heating stoves

In China, household coal burning accounts for a large proportion of primary fine particulate matter (PM2.5), black carbon (BC), organic carbon (OC), polycyclic aromatic hydrocarbons (PAHs) and carbon monoxide (CO) emissions. Previous field investigations generally measured short-term emissions from heating coal stoves, which did not provide a full characterization of the actual conditions in most cases, or resulted in large uncertainties in the calculated emission factors (EFs). In this study, we propose a sampling design using a chimney partial-capture dilution system in the field measurement of household coal-fired heating stoves emissions during selected periods within the different burn phases and then using the carbon balance method (CBM) based on fuel-weighted average concentrations (FWAC) from the different burn phases to quantify emissions. We evaluated this proposed methodology by comparing the results with a laboratory total-capture dilution-tunnel system. Statistical analysis indicated that emissions measured during the selected burn cycle periods using the dilution sampling system can generally represent emissions at different burn phases; however, different dilution ratios can affect EFs for PM2.5 and OC. EFs of air pollutants derived by CBM with FWAC are more representative of the actual emissions than simple average concentration (SAC) and time-weighted average concentrations (TWAC). In the field application, to quantify FWAC, it is suggested to determine the ratio of power in the jth burn phase (Pj) to that in the high power phase (PH) of the stove, i.e., Pj/PH values with the calorimeter. If measured Pj/PH values are not available, the recommended value in this study is also suggested.

The importance of termites and fire to dead wood consumption in the longleaf pine ecosystem

Microbes, insects, and fire are the primary drivers of wood loss from most ecosystems, but interactions among these factors remain poorly understood. In this study, we tested the hypothesis that termites and fire have a synergistic effect on wood loss from the fire-adapted longleaf pine (Pinus palustris Mill.) ecosystem in the southeastern United States. We predicted that the extensive galleries created by termites would promote the ignition and consumption of logs by fire. We exposed logs from which termites had or had not been excluded to prescribed fire after 2.5 years in the field. We found little support for our hypothesis as there was no significant interactive effect of termites and fire on wood mass loss. Moreover, there was no significant difference in mass loss between burned and unburned logs. Termites were responsible for about 13.3% of observed mass loss in unprotected logs, a significant effect, while microbial activity accounted for most of the remaining mass loss. We conclude that fire has little effect on wood loss from the longleaf pine ecosystem and that termite activity does not strongly promote wood combustion. However, longer term research involving multiple burn cycles, later stages of decay, and differing fire intensities will be needed to fully address this question.

Physical and chemical properties of black carbon and organic matter from different combustion and photochemical sources using aerodynamic aerosol classification

Abstract. The physical and chemical properties of black carbon (BC) and organic aerosols are important for predicting their radiative forcing in the atmosphere. During the Soot Aerodynamic Size Selection for Optical properties (SASSO) project and a EUROCHAMP-2020 transnational access project, different types of light-absorbing carbon were studied, including BC from catalytically stripped diesel exhaust, an inverted flame burner, a colloidal graphite standard (Aquadag) and controlled flaming wood combustion. Brown carbon (BrC) was also investigated in the form of organic aerosol emissions from wood burning (pyrolysis and smouldering) and from the nitration of secondary organic aerosol (SOA) proxies produced in a photochemical reaction chamber. Here we present insights into the physical and chemical properties of the aerosols, with optical properties presented in subsequent publications. The dynamic shape factor (χ) of BC particles and material density (ρm) of organic aerosols was investigated by coupling a charging-free Aerodynamic Aerosol Classifier (AAC) with a Centrifugal Particle Mass Analyzer (CPMA) and a Scanning Mobility Particle Sizer (SMPS). The morphology of BC particles was captured by transmission electron microscopy (TEM). For BC particles from the diesel engine and flame burner emissions, the primary spherule sizes were similar, around 20 nm. With increasing particle size, BC particles adopted more collapsed/compacted morphologies for the former source but tended to show more aggregated morphologies for the latter source. For particles emitted from the combustion of dry wood samples, the χ of BC particles and the ρm of organic aerosols were observed in the ranges 1.8–2.17 and 1.22–1.32 g cm−3, respectively. Similarly, for wet wood samples, the χ and ρm ranges were 1.2–1.85 and 1.44–1.60 g cm−3, respectively. Aerosol mass spectrometry measurements show no clear difference in mass spectra of the organic aerosols in individual burn phases (pyrolysis or smouldering phase) with the moisture content of the wood samples. This suggests that the effect moisture has on the organic chemical profile of wood burning emissions is through changing the durations of the different phases of the burn cycle, not through the chemical modification of the individual phases. In this study, the incandescence signal of a Single Particle Soot Photometer (SP2) was calibrated with three different types of BC particles and compared with that from an Aquadag standard that is commonly used to calibrate SP2 incandescence to a BC mass. A correction factor is defined as the ratio of the incandescence signal from an alternative BC source to that from the Aquadag standard and took values of 0.821 ± 0.002 (or 0.794 ± 0.005), 0.879 ± 0.003 and 0.843 ± 0.028 to 0.913 ± 0.009 for the BC particles emitted from the diesel engine running under hot (or cold idle) conditions, the flame burner and wood combustion, respectively. These correction factors account for differences in instrument response to BC from different sources compared to the standardised Aquadag calibration and are more appropriate than the common value of 0.75 recommended by Laborde et al. (2012b) when deriving the mass concentration of BC emitted from diesel engines. Quantifying the correction factor for many types of BC particles found commonly in the atmosphere may enable better constraints to be placed on this factor depending on the BC source being sampled and thus improve the accuracy of future SP2 measurements of BC mass concentrations.

Burn-cycle-dependent spatial distribution of nuclear fuel actinides and fission products based on the AGENT code

BRITTS (Burnup of Reactor Isotopes, Tracking in Time and Space) is a newly developed burnup module based on the Runge-Kutta 4th order method supplementing the well-known AGENT neutronics code. Unlike other burnup codes that are limited to 2D models, cumulative-only calculations, or one specific fuel type, BRITTS provides detailed spatial distributions of actinides in 2D and approximate 3D (through a 2D/1D coupled characteristic solution provided by the AGENT code) at user-specified points in a burn cycle. Using two simple MOX fuel pins, BRITTS is compared with SCALE6.2. BRITTS is also compared against a well-known OECD/NEA benchmark of UO2 fuel pin with 16 participants. These comparisons show that BRITTS provides reliable calculations for concentrations of nuclear fuel actinides and fission products in both 2D and approximate 3D and can be uniquely used to analyze the spatial distributions of the actinides during the burn-cycles. This paper presents the mathematical and numerical methods employed in BRITTS and a series of benchmark examples showing the code capabilities for reactor fuel analyses.

Variation of Absorption Ångström Exponent in Aerosols From Different Emission Sources

AbstractThe absorption Ångström exponent (AAE) describes the spectral dependence of light absorption by aerosols. AAE is typically used to differentiate between different aerosol types for example., black carbon, brown carbon, and dust particles. In this study, the variation of AAE was investigated mainly in fresh aerosol emissions from different fuel and combustion types, including emissions from ships, buses, coal‐fired power plants, and residential wood burning. The results were assembled to provide a compendium of AAE values from different emission sources. A dual‐spot aethalometer (AE33) was used in all measurements to obtain the light absorption coefficients at seven wavelengths (370–950 nm). AAE470/950 varied greatly between the different emission sources, ranging from −0.2 ± 0.7 to 3.0 ± 0.8. The correlation between the AAE470/950 and AAE370‐950 results was good (R2 = 0.95) and the mean bias error between these was 0.02. In the ship engine exhaust emissions, the highest AAE470/950 values (up to 2.0 ± 0.1) were observed when high sulfur content heavy fuel oil was used, whereas low sulfur content fuels had the lowest AAE470/950 (0.9–1.1). In the diesel bus exhaust emissions, AAE470/950 increased in the order of acceleration (0.8 ± 0.1), deceleration (1.1 ± 0.1), and steady driving (1.2 ± 0.1). In the coal‐fired power plant emissions, the variation of AAE470/950 was substantial (from −0.1 ± 2.1 to 0.9 ± 1.6) due to the differences in the fuels and flue gas cleaning conditions. Fresh wood‐burning derived aerosols had AAE470/950 from 1.1 ± 0.1 (modern masonry heater) to 1.4 ± 0.1 (pellet boiler), lower than typically associated with wood burning, while the burn cycle phase affected AAE variation.

The influence of particle size on the thermal performance of coal and its derived char in a Union stove

For low-income communities in South Africa, coal is the most common solid fuel which is burnt in a variety of devices, including imbaulas and cast-iron stoves. The present work was conducted with the aim of determining the effect of the fuel particle size on the performance of coal, typically sourced in low-income households in townships in South Africa, and to subsequently compare the performance with a feed char of a common cast iron stove. Four fuel particle sizes of 15, 20, 30, and 40 mm, as well as a composite of the sizes were tested at 550 °C, against their untreated coal analogues to evaluate the thermal performance of each fuel. The thermal performance assessment metrics are ignition time, water boiling time, heat transfer and combustion efficiencies, while CO and CO2 emissions were measured for the calculations of CO/CO2 ratios. Ignition times were found to decrease from coals to chars and to decrease with increasing particle size. The effects of fuel type on the water boiling time were only observed in the later stages of the burn cycle, with the char boiling a 2 L batch of water in an average 24 min, while the coals reported an average boiling time of 20 min. Heat transfer efficiencies showed no significant variation with fuel type or particle size, with the average efficiency for the coals and that of the chars being around 66%. The fuels’ performance was better gauged by the combustion efficiency, which was found to improve marginally from the coal fuels to the chars, and to increase with increasing particle size. Results from this testwork could contribute to the performance inventories from the combustion of domestic coal mined in South Africa in a typical cast iron stove which is used in informal settlements.

Analysis of high-speed broadband flame chemiluminescence imaging in a SI engine

This study investigates the characteristics of flame propagation in a gasoline S.I engine through a combined thermodynamic and optical approach. Two high-speed CMOS camera were used together with an endoscopic system to visualize the early flame in a spark-ignited engine. An unintensified high-speed (20 kHz) imaging of early flame kernel formation and turbulent flame propagation for hundreds of consecutive combustion cycles has been analysed and compared to pressure-derived heat release rates and mass fraction burn (MFB) profiles. At very low light levels, the patterned read-out noise on the detector becomes significant. Filtering in the Fourier domain was effective in suppressing this noise component to acceptable levels. In this paper, a previously-developed algorithm with automatic dynamic thresholding was used to separately detect spark ignition and flame kernel in the image sequences. The detected flame boundary was post-processed to compute basic flame characteristics such as flame area and turbulent flame speed based on spherical flame propagation assumption. Ignition and flame propagation are compared for fast combustion cycles and slow combustion cycles based on the optical flame speed and crank angle resolved mass fraction burned profile. The good burn (fast) cycles show higher spark stretch caused by local tumble flow-field, greater early flame growth rate, and nearly spherical flame propagation at the center of combustion chamber. In contrast, the poor (slow) cycles show slower flame kernel growth rate, and mostly asymmetric flame propagation near the spark-plug and pent-roof of the combustion chamber. The analysis shows a good correlation between thermodynamics and optical data.

Contextualizing Landscape-Scale Forest Cover Loss in the Democratic Republic of Congo (DRC) between 2000 and 2015

Shifting cultivation has been shown to be the primary cause of land use change in the Democratic Republic of Congo (DRC). Traditionally, forested and fallow land are rotated in a slash and burn cycle that has created an agricultural mosaic, including secondary forest, known as the rural complex. This study investigates the land use context of new forest clearing (during 2000–2015) in primary forest areas outside of the established rural complex. These new forest clearings occur as either rural complex expansion (RCE) or isolated forest perforations (IFP), with consequent implications on the forest ecosystem and biodiversity habitat. During 2000–2015, subsistence agriculture was the dominant driver of forest clearing for both extension of settled areas and pioneer clearings removed from settled areas. Less than 1% of clearing was directly attributable to land uses such as mining, plantations, and logging, showing that the impact of commercial operations in the DRC is currently dwarfed by a reliance on small-holder shifting cultivation. However, analyzing the landscape context showed that large-scale agroindustry and resource extraction activities lead to increased forest loss and degradation beyond their previously-understood footprints. The worker populations drawn to these areas create communities that rely on shifting cultivation and non-timber forest products (NTFP) for food, energy, and building materials. An estimated 12% of forest loss within the RCE and 9% of the area of IFP was found to be within 5 km of mines, logging, or plantations. Given increasing demographic and commercial pressures on DRC’s forests, it will be crucial to factor in this landscape-level land use change dynamic in land use planning and sustainability-focused governance.

Electromagnetic and thermal stability of the ITER Central Solenoid during a 15 MA plasma scenario

The combination of the electromagnetic conductor model JackPot ACDC with the thermo-hydraulic model THEA is able to reproduce and predict the behavior of cable-in-conduit conductors (CICCs) under any varying current and magnetic field. The combined JackPot-THEA model is used to simulate the turns of the CSU2 quadra-pacake of the ITER Central Solenoid (CS) that are subjected to the most demanding conditions of the 15 MA plasma scenario. The considered section is a pancake with a 150 m length of Nb3Sn CICC from helium inlet to helium outlet, from the inner towards outer turns. The simulation results in terms of temperature and local strand electric field levels are compared to those obtained from earlier minimum quench energy analysis in order to evaluate possible risk of quench. The results confirm sufficient stability of the ITER CS coil, both from electrical and thermal point of view. The temperature evolution and flow of a helium heat slug along the conductor during the 15 MA plasma scenario is also analyzed. It appeared that sequential multiple burn cycles can be carried out without accumulation of temperature in the helium heat slug, essential for continuous energy production for a fusion power plant.

Risk Assessment of Benzene, Toluene, Ethyl Benzene, and Xylene Concentrations from the Combustion of Coal in a Controlled Laboratory Environment.

A D-grade type coal was burned under simulated domestic practices in a controlled laboratory set-up, in order to characterize the emissions of volatile organic compounds (VOCs); namely, benzene, toluene, ethylbenzene, and xylenes (BTEX). Near-field concentrations were collected in a shack-like structure constructed using corrugated iron, simulating a traditional house found in informal settlements in South Africa (SA). Measurements were carried out using the Synspec Spectras GC955 real-time monitor over a three-hour burn cycle. The 3-h average concentrations (in µg/m3) of benzene, toluene, ethylbenzene, p-xylene, and o-xylene were 919 ± 44, 2051 ± 91, 3838 ±19, 4245 ± 41 and 3576 ± 49, respectively. The cancer risk for adult males and females in a typical SA household exposure scenario was found to be 1.1 and 1.2 respectively, which are 110- and 120-fold higher than the U.S. Environmental Protection Agency (EPA) designated risk severity indicator (1 × 10−6). All four TEX (toluene, ethylbenzene, p-xylene and o-xylene) compounds recorded a Hazard Quotient (HQ) of less than 1, indicating a low risk of developing related non-carcinogenic health effects. The HQ for TEX ranged from 0.001 to 0.05, with toluene concentrations being the lowest, and ethylbenzene the highest. This study has demonstrated that domestic coal burning may be a significant source of BTEX emission exposure.

Detection of Gopher Tortoise Burrows Before and After a Prescribed Fire: Implications for Surveys

Abstract Gopher tortoise Gopherus polyphemus populations have declined by as much as 80% over the past century, primarily as a result of habitat loss. In 2006, the eastern population of the gopher tortoise was petitioned for federal listing as threatened. In response, a Candidate Conservation Agreement was developed for the gopher tortoise. A Candidate Conservation Agreement is a voluntary agreement between the U.S. Fish and Wildlife Service and other interested parties to address the conservation needs of a species before it becomes federally listed and to enact measures to preclude the need to list the species. The gopher tortoise Candidate Conservation Agreement identified an assessment of the status of populations on protected lands as a priority and line transect distance sampling (LTDS) was adopted as the standardized survey methodology. Surveys with LTDS rely on detection of gopher tortoise burrows because tortoises are fossorial. However, gopher tortoise burrows vary greatly in size and small burrows of juveniles are rarely detected. Although LTDS is statistically robust and allows for imperfect detection, few studies have examined how detection varies with tortoise burrow size and whether habitat structure may influence detection of gopher tortoise burrows. Both factors could affect the accuracy of population estimates using LTDS and interpretation of demographic parameters needed for the Candidate Conservation Agreement. Therefore, we conducted surveys for burrows using LTDS before (28 March–13 April 2016) and after (9–18 May 2016) a prescribed burn, which reduced vegetation cover. We detected significantly more burrows (P < 0.001, n = 651) of all sizes after the burn, and the burrow abundance estimate was 64% higher postburn. Our study showed that conducting gopher tortoise surveys after a prescribed burn increased detections and provided a more accurate population estimate. We therefore recommend conducting surveys immediately after a burn. However, varying burn cycles on large sites may make it difficult to survey following a prescribed burn and because the effects of a burn on habitat structure may vary within a site, methods to account for variation in detection due to habitat structure are needed. Population estimates for gopher tortoises using LTDS that do not account for variation in detection due to habitat structure likely underestimate population size.

SÍNTESIS DE UN GEOPOLÍMERO Y USO DE LA METODOLOGÍA DE SUPERFICIE DE RESPUESTA PARA OPTIMIZAR SU ADHERENCIA EN LADRILLO ROJO PARA SU USO COMO RECUBRIMIENTO INTERNO EN HORNOS LADRILLEROS

In Mexico, fixed kilns made of red brick are often used today. However, after several burn cycles at temperatures of up to 1000 °C, these kilns may expand, crack and open. In light of that, we worked to obtain a refractory geopolymer that attaches to red brick to use as an internal kiln coating to increase the useful life of the kiln. We studied the consolidation from refractory clays and a solution of commercial sodium silicate ( =1.38, SiO2/Na2O ratio =3.09). This process originates the synthesis of a geopolymer. The clays were previously selected for their refractory characteristics from different clay banks in the municipality of Comonfort, Guanajuato, Mexico; they have been identified as Caolin, Tepozan, and Bauwer. The clays were subjected to a process of grinding and sieving to a particle size of 60 Tyler mesh . Next, they were characterized using energy dispersive X-ray spectroscopy (EDS), which determined that they contained high percentages of SiO2 and Al2O3. The mineralogy of the raw clays was analyzed by powder X-ray diffraction (XRD), yielding high percentages of kaolinite, alunite, quartz and smectite. This composition validates the refractory potential of clays. A simplex-centroid design was used to formulate the geopolymer. The response surface methodology was used for optimization, keeping the commercial sodium silicate concentration constant. The adherence of the formulated geopolymer on red clay brick was taken as a response variable, yielding 50% for the consolidating material (commercial sodium silicate), 21% for Caolin, 23% for Tepozan, and 6% for Bauwer, where the curing time was 7 days and the burning cycle was 8 hours at 1000 °C. This property was measured in a universal testing machine. The best fit was a quadratic model with synergistic interactions between all factors, and the mean adherence of 28.11 kgf/cm2 (2.8 MPa) was obtained. Common potential applications of geopolymer coatings include protection against salt corrosion of marine concrete, reinforced concrete manufacturing, concrete infrastructure rehabilitation, fire inhibition, resistance to temperature and corrosion and as heat insulators. Geopolymers may also have promising use in construction due to their similar strength and durability properties as conventional concrete. The red brick joined to the obtained geopolymer can be used as an internal coating in fixed brick kilns to increase its useful life. In addition, it has potential use for bonding materials that may be exposed to temperatures below 1000 °C or for replacing concrete in ovens exposed to high temperatures.

Spatial and temporal dynamics of shifting cultivation in the middle-Amazonas river: Expansion and intensification

Shifting cultivation is the main land-use system transforming landscapes in riverine Amazonia. Increased concentration of the human population around villages and increasing market integration during the last decades may be causing agricultural intensification. Studies have shown that agricultural intensification, i.e. higher number of swidden-fallow cycles and shorter fallow periods, reduces crop productivity of swiddens and the regrowth capacity of fallows, undermining the resilience of the shifting cultivation system as a whole. We investigated the temporal and spatial dynamics of shifting cultivation in Brazilian Amazonia to test the hypotheses that (i) agriculture has become more intensive over time, and (ii) patterns of land-use intensity are related to land accessibility and human population density. We applied a breakpoint-detection algorithm to Landsat time-series spanning three decades (1984–2015) and retrieved the temporal dynamics of shifting cultivation fields, which go through alternating phases of crop production (swidden) and secondary forest regrowth (fallow). We found that fallow-period length has decreased from 6.4 to 5.1 years on average, and that expansion over old-growth forest has slowed down over time. Shorter fallow periods and higher frequency of slash and burn cycles are practiced closer to residences and around larger villages. Our results indicate that shifting cultivation in riverine Amazonia has gone through a process of agricultural intensification in the past three decades. The resulting landscape is predominantly covered by young secondary forests (≤ 12 yrs old), and 20% of it have gone through intensive use. Reversing this trend and avoiding the negative consequences of agricultural intensification requires land use planning that accounts for the constraints of land use in riverine areas.

Managing grassland for wildlife: the effects of rotational burning on tick presence and abundance in African savannah habitat

Ticks are obligate blood‐feeding ectoparasites that have negative effects on animals through blood loss and vectoring disease. Controlling ticks is a major aspect of wildlife management in many areas, including African savannah where ticks are a long‐standing problem. Rotational burning of vegetation is widely thought to reduce ticks but empirical data are lacking. We investigate the effect of block rotational burning on tick populations in a South African wildlife reserve. We measured tick presence/abundance using tick drags in multiple blocks of five different burn ages (areas burned 1, 2, 3, 4 or 5 years previously). We also assessed herbivore diversity using dung as a proxy. Tick presence was highest in areas burned 2–3 years previously. It was lowest in recently‐burned areas (probably due to fire‐induced mortality or loss of field‐layer refugia) and areas burned ≥ 4 years previously (probably because the lack of palatable grass meant herbivore abundance was lower; this is supported by significantly lower herbivore presence in old burns and significant positive correlation between tick numbers and herbivore presence). Burn age and, to a lesser extent, block, were significantly related to tick presence and abundance at both larval and nymph stages. The model that best explained tick numbers, though, included the interaction between burn age and block due to substantial inter‐block variability in mid‐burn blocks relative to lower variability in blocks at the start or end of the burn cycle. This suggests that burn age and block‐specific conditions together influence tick abundance, with habitat heterogeneity likely being an important modifier of the effect burning has on tick numbers. Although annual burning of large areas would not be feasible while maintaining suitable grazing, we suggest that additional annual burning of potential wildlife (and therefore tick) hotspots, such as around waterholes, could reduce tick populations and improve wildlife management.