Laboratory determination of factors influencing successful point ignition in the litter layer of shrubland vegetation

2008 ◽  
Vol 17 (5) ◽  
pp. 628 ◽  
Author(s):  
Matt P. Plucinski ◽  
Wendy R. Anderson
Keyword(s):  
Logistic Function ◽  
Major Effect ◽  
Ignition Source ◽  
Litter Type ◽  
Litter Layer ◽  
Standard Type ◽  
Ignition Point ◽  
Factors Affecting ◽  
Fuel Moisture Content ◽  
Fire Spreading

Factors affecting ignition thresholds of the litter layer of shrubland vegetation were investigated using reconstructed litter beds in a laboratory. The factors investigated were fuel moisture content (FMC), litter type (primarily species), pilot ignition source, and wind. Litter beds made from 11 different litter types were ignited with point ignition sources. Litter from Allocasuarina nana (Sieber ex Spreng.) L.A.S. Johnson was used as the standard type across all experiments. Successful ignition was defined as fire spreading a fixed distance from the ignition point. Ignition success was modelled as a logistic function of FMC. Litter type had a major effect on ignitibility. The bulk density of the litter bed and the surface area of litter per volume of litter bed provided reasonably good predictors of the effect of litter type on ignition success. Low-density litter beds ignited at higher FMCs than dense litter beds. The two densest litter beds failed to ignite with the procedures used here. The ignition sources tested had significantly different effects on ignition success. Larger ignition sources were able to ignite wetter fuels than smaller sources. The presence of wind was found to have a different effect on ignition success depending on the location of the ignition source with respect to the litter bed. Wind decreased ignition success when the ignition source was located on top of the litter bed, but aided ignition when the ignition source was located within the litter bed.

Magnesium-Silicon Substituted Carbonate Hydroxyapatite (Mg-Si CHA): Factors Affecting Sintering

2016 ◽  
Vol 694 ◽  
pp. 88-93
Author(s):  
Ahmad Fauzi Mohd Noor ◽  
Harmiza Zainudin
Keyword(s):  
Mechanical Properties ◽  
Single Phase ◽  
Physical And Mechanical Properties ◽  
Major Effect ◽  
Carbonate Content ◽  
X Ray Diffraction ◽  
Factors Affecting ◽  
Complex Process ◽  
Powder Properties ◽  
Properties Of Materials

Sintering has major effect on the final properties of materials such as density, porosity and microstructure. Sintering of Mg-Si CHA in particular is a complex process since changes could occur during sintering, which include phase formation, grain size, pore size and carbonate content, and this in turn affects the mechanical properties. Improved mechanical properties of Mg-Si CHA is critical in load bearing implant applications. Poor control of thermal treatment of Mg-Si CHA during sintering would cause carbonate loss, leading to partial or total decomposition of Mg-Si CHA, subsequently would affect the physical and mechanical properties. The influence of powder properties (particle size, porosity, morphology) and sintering parameters (heating rate, firing atmosphere) on the sintered Mg-Si CHA microstructure was studied using scanning electron microscopy (SEM) characterization technique. The SEM results showed that we are able to produce sintered Mg-Si CHA without cracking of the compacted pellets, while keeping the carbonate level in the amount required (2 – 8%). X-Ray diffraction (XRD) was also performed on the sintered samples and the results indicated that a single phase Mg-Si-CHA was obtained, while Fourier transform infra-red (FTIR) spectroscopy result confirmed that as-synthesized Mg-Si CHA powder was a B-type.

scholarly journals Assessment of the optimum fertilizer rates and planting density for soybean production in China

2019 ◽  
Author(s):  
Jilong Lv ◽  
Ping He ◽  
Dan Wei ◽  
Xinpeng Xu ◽  
Shaojun Qiu ◽  
...  
Keyword(s):  
Fertilization Rate ◽  
Major Effect ◽  
Optimal Rate ◽  
Planting Density ◽  
High Yield ◽  
Soybean Yield ◽  
Factors Affecting ◽  
K Fertilizer ◽  
P Fertilizer ◽  
Effect On Yield

AbstractFertilization rate and planting density are important factors affecting crop yield. A large number of soybean [Glycine max (L.) Merr] field experimental data (1998-2017) were collected through different database sources to evaluate the optimum fertilizer rate and planting density for high yield of spring and summer soybean in China. The yield of spring and summer soybean gradually increased over year, with their average yields were 2610 and 2724 kg ha−1, respectively. Based on the fitted quadratic curve, the optimal rate of nitrogen (N), phosphorus (P), and potassium (K) fertilizers for high yield of summer soybean was 96 kg N ha−1, 80 kg P2O5 ha−1, and 126 kg K2O ha−1, and the corresponding yields were 3038, 2801 and 2305 kg ha−1, respectively. The optimal rate of N, P and K fertilizers for spring soybean was 71 kg N ha-1, 108 kg P2O5 ha-1 and 74 kg K2O ha−1, and the corresponding yields were 2932, 2834 and 2678 kg ha−1, respectively. The optimum density was 27×104 and 34×104 plants ha−1 under high yield for summer and spring soybean, respectively. Stepwise regression analysis showed that the P fertilizer had the greatest influence on the spring soybean yield followed by K fertilizer and planting density. For summer soybean, population density had the major effect on yield followed by P fertilizer. Overall, the P fertilization and planting density should be payed attention to increase soybean yield in different regions of China.

scholarly journals PROPAGATOR: An Operational Cellular-Automata Based Wildfire Simulator

Fire ◽  
2020 ◽  
Vol 3 (3) ◽  
pp. 26
Author(s):  
Andrea Trucchia ◽  
Mirko D’Andrea ◽  
Francesco Baghino ◽  
Paolo Fiorucci ◽  
Luca Ferraris ◽  
...  
Keyword(s):  
Moisture Content ◽  
Fire Spread ◽  
Fire Fighting ◽  
Fuel Moisture ◽  
Time Step ◽  
Ignition Point ◽  
The Real ◽  
Fire Propagation ◽  
Spread Model ◽  
Fuel Moisture Content

PROPAGATOR is a stochastic cellular automaton model for forest fire spread simulation, conceived as a rapid method for fire risk assessment. The model uses high-resolution information such as topography and vegetation cover considering different types of vegetation. Input parameters are wind speed and direction and the ignition point. Dead fine fuel moisture content and firebreaks—fire fighting strategies can also be considered. The fire spread probability depends on vegetation type, slope, wind direction and speed, and fuel moisture content. The fire-propagation speed is determined through the adoption of a Rate of Spread model. PROPAGATOR simulates independent realizations of one stochastic fire propagation process, and at each time-step gives as output a map representing the probability of each cell of the domain to be affected by the fire. These probabilities are obtained computing the relative frequency of ignition of each cell. The model capabilities are assessed by reproducing a set of past Mediterranean fires occurred in different countries (Italy and Spain), using when available the real fire fighting patterns. PROPAGATOR simulated such scenarios with affordable computational resources and with short CPU-times. The outputs show a good agreement with the real burned areas, demonstrating that the PROPAGATOR can be useful for supporting decisions in Civil Protection and fire management activities.

Identifying the Weight of Factors Affecting Creep of Concrete Using Factorial ANOVA

2021 ◽  
Vol 872 ◽  
pp. 21-25
Author(s):  
Hikmat Daou ◽  
Wassim Raphael
Keyword(s):  
Major Effect ◽  
Structural Behavior ◽  
Sustained Load ◽  
Limit States ◽  
R Software ◽  
Factors Affecting ◽  
Factorial Anova ◽  
Northwestern University ◽  
Term Creep

Creep may affect structural behavior by violating service limit states, redistributing stress or losing prestress forces. For that, knowing the significance of factors that influence creep is a must to accurately predict it. This paper uses the Northwestern university (NU) database to investigate the factors that most affect long-term creep of concrete. Factorial ANOVA was applied to identify the significance of factors affecting creep of concrete at 3000 days using R software. The factorial ANOVA results showed that the sustained load and the relative humidity have the major effect on the value of concrete creep at 3000 days.

A process-based model of fine fuel moisture

2006 ◽  
Vol 15 (2) ◽  
pp. 155 ◽  
Author(s):  
Stuart Matthews
Keyword(s):  
Forest Type ◽  
Model Parameters ◽  
Fuel Moisture ◽  
Litter Layer ◽  
Wetting And Drying ◽  
Rainy Period ◽  
Dry Conditions ◽  
Fuel Moisture Content ◽  
Complete Process ◽  
Made In

This paper presents the first complete process-based model for fuel moisture in the litter layer. The model predicts fuel moisture by modelling the energy and water budgets of the litter, intercepted precipitation, and air spaces in the litter. The model was tested against measurements of fuel moisture from two sets of field observations, one made in Eucalyptus mallee-heath under dry conditions and the other during a rainy period in Eucalyptus obliqua forest. The model correctly predicted minimum and maximum fuel moisture content and the timing of minima and maxima in the mallee-heath. Under wet conditions, wetting and drying of the litter profile were correctly predicted but wetting of the surface litter was over-predicted. The structure of the model and the dependence of predictions on model parameters were examined using sensitivity and parameter estimation studies. The results indicated that it should be possible to adapt the model to any forest type by specifying a limited number of parameters. A need for further experimental research on the wetting of litter during rain was also identified.

scholarly journals Selection bias in instrumental variable analyses

2017 ◽  
Author(s):  
Rachael A. Hughes ◽  
Neil M. Davies ◽  
George Davey Smith ◽  
Kate Tilling
Keyword(s):  
Confidence Interval ◽  
Selection Bias ◽  
Instrumental Variable ◽  
Causal Effect ◽  
Major Effect ◽  
Directed Acyclic Graphs ◽  
Factors Affecting ◽  
Exposure Effect ◽  
Using Data ◽  
The Uk

AbstractParticipants in epidemiological and genetic studies are rarely true random samples of the populations they are intended to represent, and both known and unknown factors can influence participation in a study (known as selection into a study). The circumstances in which selection causes bias in an instrumental variable (IV) analysis are not widely understood by practitioners of IV analyses. We use directed acyclic graphs (DAGs) to depict assumptions about the selection mechanism (factors affecting selection) and show how DAGs can be used to determine when a two-stage least squares (2SLS) IV analysis is biased by different selection mechanisms. Via simulations, we show that selection can result in a biased IV estimate with substantial confidence interval undercoverage, and the level of bias can differ between instrument strengths, a linear and nonlinear exposure-instrument association, and a causal and noncausal exposure effect. We present an application from the UK Biobank study, which is known to be a selected sample of the general population. Of interest was the causal effect of education on the decision to smoke. The 2SLS exposure estimates were very different between the IV analysis ignoring selection and the IV analysis which adjusted for selection (e.g., 1.8 [95% confidence interval −1.5, 5.0] and −4.5 [−6.6, −2.4], respectively). We conclude that selection bias can have a major effect on an IV analysis and that statistical methods for estimating causal effects using data from nonrandom samples are needed.

Flammability descriptors of fine dead fuels resulting from two mechanical treatments in shrubland: a comparative laboratory study

2010 ◽  
Vol 19 (3) ◽  
pp. 314 ◽  
Author(s):  
Eva Marino ◽  
Javier Madrigal ◽  
Mercedes Guijarro ◽  
Carmen Hernando ◽  
Carmen Díez ◽  
...  
Keyword(s):  
Logistic Models ◽  
Ignition Source ◽  
Fuel Load ◽  
Experimental Conditions ◽  
Load Effect ◽  
Consumption Ratio ◽  
Wildfire Hazard ◽  
Western Spain ◽  
Shrub Clearing ◽  
Fuel Moisture Content

Mechanical treatments are traditionally used to modify the fuel complex in shrubland, but information about their actual effectiveness in reducing the risk of wildfire initiation is scarce. The effects of two mechanical fuel treatments (shrub clearing with crushing and manual removal) on flammability in a shrubland community in north-western Spain were compared. Three months after treatment, laboratory tests using a point-ignition source were conducted on the fine dead fuels to analyse the effect of type of treatment and fuel moisture content (FMC) under two conditions: (1) flaming; or (2) glowing+wind ignition source. Fuel load effect within each treatment was also studied. Time-to-ignition, flaming duration, number of burnt sides of the sample and fuel consumption ratio were assessed. Logistic models were developed to assess ignition and sustained combustion probabilities. Type of treatment and FMC significantly affected flammability under both experimental conditions tested. Slow smouldering was observed in fuels subjected to shrub clearing and removal, whereas crushing fuels were rapidly burnt with flaming phase combustion. In general, shrub clearing and removal appeared to be more effective in reducing wildfire hazard in these shrubland communities.

A situational analysis of the microbial water quality in a peri-urban catchment in South Africa

1997 ◽  
Vol 35 (11-12) ◽  
pp. 119-124 ◽  
Author(s):  
S. N. Venter ◽  
M. C. Steynberg ◽  
C. M. E. de Wet ◽  
D. Hohls ◽  
G. du Plessis ◽  
...  
Keyword(s):  
Water Quality ◽  
Wastewater Treatment Plants ◽  
Informal Settlement ◽  
Major Effect ◽  
Situational Analysis ◽  
Microbial Quality ◽  
Urban Catchment ◽  
Site Assessment ◽  
Microbial Water Quality ◽  
Factors Affecting

A situational analysis of a peri-urban catchment experiencing microbial water quality problems was carried out using data collected over two and a half years. The water and land use in the area was determined. The main sources of pollution were identified and the effects of dilution and bacterial die-off on water quality were evaluated by modelling the level of faecal coliforms along the length of the river using the QUAL2E model. As a result of the assessment, water quality goals were set for the catchment and suggestions were made for the improvement of microbial quality. Certain areas of the catchment are densely populated and both developed and informal settlements exist. Water is mainly used for domestic and recreational purposes. The river receives diffuse source discharges as well as point source discharges from four wastewater treatment plants and an industrial site. Assessment of indicator organism and pathogen analyses indicated that the main factors affecting the microbial quality were discharges from the sewage plants and runoff from informal settlement areas. The industrial activities in the catchment did not have a major effect. Modelling runs predicting faecal coliform levels demonstrated that bacterial die-off did not result in a significant improvement to the microbial water quality in the catchment.

Population dynamics of wireworms (Coleoptera, Elateridae) in arable land after abandonment

Biologia ◽  
2007 ◽  
Vol 62 (1) ◽  
Author(s):  
Pavel Jedlička ◽  
Jan Frouz
Keyword(s):  
Arable Land ◽  
Soil Surface ◽  
Abundant Species ◽  
Larval Abundance ◽  
Litter Layer ◽  
Larval Size ◽  
Factors Affecting ◽  
Agriotes Obscurus ◽  
Predator Pressure ◽  
Study Sites

AbstractThe community of elaterid larvae of three sites (field and two fallows), representing different stages of secondary succession, were studied using soil sampling from 1986 to 1993. All three sites were abandoned arable land: a field cultivated until 1991, a fallow I abandoned in 1986, and a fallow II abandoned about 1976. The fallow II was used as a meadow after abandonment and was regularly mown until 1985, when cultivation stopped. Six species of Elateridae larvae were found at all three study sites. In the field, Agriotes obscurus, Athous niger, Athous subsuscus, Dalopius marginatus and Athous vittatus were found, A. niger and A. obscurus being the most abundant species. During cultivation, larval densities were very low, however, larval abundance increased up to 8.8 ± 8.3 ind. m-2 when cultivation stopped. Only small A. obscurus larvae were found during cultivation, whereas larval size increased after abandonment. In fallow I A. obscurus, A. niger, A. subsuscus, D. marginatus, and Agrypnus murinus were found and the average annual abundance fluctuated between 0.8 ± 1.4 to 40.8 ± 10.9 ind. m-2 with A. obscurus being the most abundant species. Fallow II supported the highest densities of wireworms from all plots studied (71.2±35.2 to 280.0±24.8 ind. m-2). A. obscurus, A. niger, A. subsuscus and D. marginatus were found in fallow II. The abundance of all larval Elateridae as well as the dominant species A. obscurus decreased during the study period, while simultaneously the occurrence of small sized A. obscurus larvae decreased. The frequency of cultivation and time elapsed since last cultivation appeared to be the most important factors affecting elaterid occurrence in the field and fallow I. In fallow II, the decrease in abundance correlates with the accumulation of a dense litter layer, which may correspond with soil surface structure, plant community changes or predator pressure.

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