Repeat Fires Research Articles

Fire frequency effects on plant community characteristics in the Great Basin and Mojave deserts of North America

BackgroundWildfire regimes are changing dramatically across North American deserts with the spread of invasive grasses. Invasive grass fire cycles in historically fire-resistant deserts are resulting in larger and more frequent wildfire. This study experimentally compared how single and repeat fires influence invasive grass-dominated plant fuels in the Great Basin, a semi-arid, cold desert, and the Mojave, a hyper-arid desert. Both study sites had identical study designs. In the summer of 2011, we experimentally burned half of each experimental block, the other half remaining as an unburned control. Half of the burned plots were reburned 5 years later to simulate increasing burn frequency. We estimated non-woody plant biomass, cover, and density in plots from 2017 to 2020.ResultsBiomass did not vary between sites, but there was higher plant cover and lower plant density at the Mojave site than at the Great Basin site. Plant biomass, density, and cover varied significantly across the years, with stronger annual fluctuations in the Great Basin. At both desert sites, fire increased plant density and biomass but had no effect on the cover. The effect of fire on plant cover varied significantly between years for both deserts but was greater in the Great Basin than in the Mojave site. Repeat fires did not amplify initial fire effects.ConclusionsThe results suggest that in general annual fluctuations in fine fuel production and fluctuations in response to fire were more apparent at the Great Basin site than at the Mojave site, with no immediate compounding effect of repeat fires at either site.

Seeking the Right Time for Venous Thromboembolism Prophylaxis Alerts

Background: Our institution used an automated provider alert for venous thromboembolism (VTE) prophylaxis. This alert had an option to “snooze,” generating a user-specific delay before repeat firing. Providers snoozed 67% of VTE alerts. Our aim was to decrease alert burden by 25% through lengthening the snooze delay. Methods: This initiative was conducted at a tertiary care academic medical center using an integrated electronic health record. Data was collected with snooze delay time set at 1, 2 and 3 hours. Our primary outcome was the number of alerts per 100 admissions. Secondary outcomes included percentage of alerts snoozed, percent of patients receiving pharmacoprophylaxis, and percent of admissions satisfying VTE core measures. Results: There was no change in alerts per 100 admissions (168 vs. 176, p=0.375) or percentage of patients receiving pharmacoprophylaxis (50.9% vs. 50.9%, p=0.997). There was a small reduction in snooze percentage (67.0% to 63.2%, p=<0.001) and a small increase in core measure satisfaction (86.0% to 88.0%, p=0.025). On post-hoc analysis, the intervention increased the median interval between same-patient, same-provider VTE alerts (3.4 to 8.3 hours). Internal medicine hospitalists were responsible for 22% of alerts, selecting snooze 78% of the time. Conclusion: Increasing snooze delay time did not decrease alert burden. Manipulating alert parameters is unlikely to decrease alert burden without simultaneous changes in provider response culture.

Pathways of savannization in a mesic African savanna–forest mosaic following an extreme fire

Abstract Fires in savannas limit tree cover, thereby promoting flammable grass accumulation and fuelling further frequent fires. Meanwhile, forests and thickets form dense canopies that reduce C4 grass fuel loads and creating a humid microclimate, thereby excluding fires under typical climatic conditions. However, extreme fires occasionally burn into these closed‐canopy systems. Although these rare fires cause substantial tree mortality and can make repeat fires more likely, the long‐term consequences of an extreme fire for closed‐canopy vegetation structure and potential to convert to savanna (hereafter ‘savannization’) remain largely unknown. Here, we analysed whether an extreme fire could, alone, alter species composition, vegetation structure and fire regimes of closed‐canopy ecosystems in an intact savanna–forest–thicket mosaic, or whether successive fires after an initial extreme fire were necessary to trigger a biome transition from forest to savanna. We found that forests that only burned once recovered, whereas those that burned again following an initial extreme fire transitioned from closed‐canopy forests towards open, grassy savannas. While thickets had less tree mortality in fires than forests, repeat fires nonetheless precipitated a transition towards savannas. Colonization of the savanna tree community lagged behind the grass community, but also began to transition. Synthesis. Our results suggest that rare extreme fires, followed by repeated burning can indeed result in savannization in places where savanna and forest represent alternative stable states.

The effect of prolonged holding time on the mechanical property and microstructural property of lithium disilicate glass-ceramic

Repeat firing produces uncertainty about stabilizing lithium disilicate glass-ceramic (LDGC) material properties, even though prolonged holding time can enhance the mechanical property of LDGC during a single firing cycle. However, the effect of prolonged holding time and repeat firing on the mechanical property and microstructure of LDGC is not fully understood. In the present study, three groups of LDGC material were created: (i) extension of holding time (7 vs. 14 vs. 28 min) at 780–800 °C; (ii) holding time extension (7 vs. 14 min) and dual sintering at 800–820 °C, respectively; (iii) dual sintering with prolonged holding time (7 vs. 14 min) at 820–840 °C. The nano-indenter test revealed that prolonged holding time (14 and 28 min) promoted the enhancement of LDGC hardness and Young’s modulus. X-ray photoelectron spectroscopy, X-ray diffraction and Fourier transform infrared spectroscopy confirmed that prolonged holding time increased and stabilized LD phase in LDGC, as well as induced residual compressive stress. Scanning electron microscopy showed that prolonged holding time increased LD crystal grains homogeneously and facilitated LDGC to form dense interlocking structure without enlarging crystal size grains significantly. In contrast, LDGC that dual sintered alone at 820–840 °C possessed inferior mechanical properties, coupled with heterogeneous crystal phases, residual tensile stress, and melted crystals grains in the porous microstructure. Interestingly, these deteriorated properties of LDGC caused by dual sintering alone could be counteracted by prolonging the holding time. Nevertheless, the LDGC materials displayed an excellent biocompatibility throughout the study. This study identified that prolonged holding time during repeated firing cycles stabilized LD phase and crystal grain size of LDGC, thus enhanced the mechanical properties, which provided a new insight to extend the repeat fired restoration longevity of LDGC.Graphical abstract

Does fire always accelerate shrub expansion in Arctic tundra? Examining a novel grass-dominated successional trajectory on the Seward Peninsula

ABSTRACT Over the last century in the circumpolar north, notable terrestrial ecosystem changes include shrub expansion and an intensifying wildfire regime. Shrub invasion into tundra may be further accelerated by wildfire disturbance, which creates opportunities for establishment where recruitment is otherwise rare. The Seward Peninsula currently experiences more frequent and larger fires than other tundra regions in Alaska. There are areas of overlapping burn scars dating back to the 1950s. Using a chronosequence approach, we examined vegetation and ecosystem dynamics in tussock tundra. Increasing burn severity and fire frequency corresponded with an increase in grass cover and a decrease in shrub basal area. We used multivariate ordination analysis to create a single integrator variable of fire effect that accounted for time after fire, burn severity, and number of times burned. This fire effect was significantly associated with decreases in soil organic layer thickness and overall plant biomass. Unlike previous studies in Arctic Alaska tundra, we found that increases in fire frequency and severity did not increase shrub cover and biomass. Instead, intensifying fire disturbance, and particularly repeat fires, led to grass dominance. Our findings support the hypothesis that intensifying tundra fire regimes initiate alternative post-fire trajectories that are not shrub dominated and that are structurally and functionally quite different from sedge or shrub-dominated tundra.

Effects of multiple firing processes on the mechanical properties of lithium disilicate glass-ceramics produced by two different production techniques

Statement of problemRepeated firings cause materials to be exposed to additional heat treatments. The effect of these additional heat treatments on the mechanical properties of lithium disilicate glass-ceramics is not fully known. PurposeThe purpose of this in vitro study was to determine the effects of repeated firing on the mechanical properties of lithium disilicate glass-ceramics produced by 2 different techniques, press and computer-aided design and computer-aided manufacturing (CAD-CAM). Material and methodsEighty rectangular (25×4×2 mm) lithium disilicate glass-ceramic specimens were used in this study, 40 produced by heat pressing and 40 by milling, and divided into 4 groups (n=10) with a different number of veneer porcelain firings (1 to 4). After firing, the Vickers hardness, flexural strength (3-point bend test), and fracture toughness were determined, and the specimens were analyzed with an environmental scanning electron micrograph. Data were analyzed with analysis of variance (ANOVA) (α=.05). ResultsThe repeat firing processes did not affect the flexural strength of the specimens in either group (P>.05), while the surface hardness and fracture toughness were significantly changed (P<.05). ConclusionsIncreasing the number of firings adversely affected the mechanical properties of lithium disilicate glass-ceramics.

Sixty‐five years of fire manipulation reveals climate and fire interact to determine growth rates of Quercus spp.

AbstractMinimizing forest vulnerability to more frequent and severe droughts, as climate models predict, has emerged as a primary goal of forest management. One potential strategy to moderate drought‐induced stress is reducing basal area through the repeat application of prescribed fire. However, use of prescribed fire as a management tool to reduce drought vulnerability has been largely untested. Here, we report the long‐term effects of repeat fires on the climate‐growth response of adult oaks (Quercus spp.) in the Missouri Ozarks, USA. We measured the annual radial growth of trees that experienced either no fire, periodic (every 4 yr), or annual prescribed fires from 1950 to 2015. To assess whether increased fire frequency interacts with climate to determine long‐term forest productivity, we modeled annual growth as a function of potential evapotranspiration, fire treatment, and their interaction. We also quantified the effect of fire‐driven reductions in tree density on carbon and oxygen isotope composition of tree rings and drought resistance (growth during drought) and resilience (growth recovery after drought) during past drought events. Annual radial growth and isotopic composition data indicated trees experienced reduced growth due to moisture stress, but drought vulnerability did not vary between frequently burned forests and unburned controls. In contrast, periodic, but not annual, fires reduced annual growth by 9.6% during wet periods favorable to growth with the effect consistent over time. Fire had minimal effects on total and inorganic soil nitrogen after 65 yr of treatment, regardless of frequency, suggesting other underlying causes of the observed growth declines under periodic burning (e.g., crown, bole, or root injury). Our results suggest that long‐term, increased fire frequency can have negative effects on long‐term tree growth, but effects are contingent upon the fire return interval. These findings highlight important differences in how fire and thinning influence density‐dependent competition and the response of tree growth to climate. Although additional studies are needed from other forest ecosystems, this study provides early evidence that increased fire frequency will not alleviate drought stress and instead, may reduce long‐term, aboveground carbon storage in forests.

Structural diversity and development in active fire regime mixed-conifer forests

Nearly a century of fire suppression in most forested land of the United States has limited researchers’ ability to construct and rigorously test conceptual models of forest structural development in mixed-conifer ecosystems. As a result, land managers must rely on conceptual models of forest development that may overemphasize idealized stand structures and developmental pathways, which ultimately hampers management of many forest systems for resilience to future climate change impacts. We sought to determine the relative importance of fire history (frequency, severity, and time since fire) and biophysical variables on forest structural diversity and development. Importantly, we conducted our study in an ecosystem with a contemporary active fire regime where wildland fire has been managed as an ecosystem process for four decades. Using data from unburned (≥80 years since fire), once-burned and twice-burned mixed-conifer forests in the Bob Marshall Wilderness of Northwest Montana, we conducted a hierarchical clustering analysis to identify forest stand structure classes. We then used a Classification and Regression Tree analysis, combined with other post-hoc analyses, to elucidate the biophysical and disturbance history drivers that lead to each structure class. The cluster analysis revealed six forest structure classes. The CART analysis indicated that time since fire plays a large role in determining forest structure, but at intermediate time scales structure is further shaped by repeat fires and interactions with biophysical variables. The CART and post-hoc analyses did not, however, indicate a singular fire history or biophysical pathway to any one structure class. We synthesize our results in a conceptual model of forest structural development under an active fire regime. This model supports existing theory that succession following severe fire plays a large role in shaping forest structure. It also recognizes the role of fire at variable severities and frequencies, the physical environment, and tree community composition in influencing forest structural development. The complexity of forest structure and development generated by an active fire regime points to the need to incorporate a process-based view of wildfire if the goal is to manage for improved resiliency and adaptive capacity to future climate change impacts.

Creosote growth rate and reproduction increase in postfire environments.

Human activities are changing patterns of ecological disturbance globally. In North American deserts, wildfire is increasing in size and frequency due to fuel characteristics of invasive annual grasses. Fire reduces the abundance and cover of native vegetation in desert ecosystems. In this study, we sought to characterize stem growth and reproductive output of a dominant native shrub in the Mojave Desert, creosote bush (Larrea tridentata (DC.) Coville) following wildfires that occurred in 2005. We sampled 55 shrubs along burned and unburned transects 12 years after the fires (2017) and quantified age, stem diameter, stem number, radial and vertical growth rates, and fruit production for each shrub. The shrubs on the burn transects were most likely postfire resprouts based on stem age while stems from unburn transects dated from before the fire. Stem and vertical growth rates for shrubs on burned transects were 2.6 and 1.7 times higher than that observed for shrubs on unburned transects. Fruit production of shrubs along burned transects was 4.7‐fold more than shrubs along paired unburned transects. Growth rates and fruit production of shrubs in burned areas did not differ with increasing distance from the burn perimeter. Positive growth and reproduction responses of creosote following wildfires could be critical for soil stabilization and re‐establishment of native plant communities in this desert system. Additional research is needed to assess if repeat fires that are characteristic of invasive grass‐fire cycles may limit these benefits.

Recovery of subalpine grasslands 15 years after landscape level fires

As conditions warm, previously rare landscape level fires are more likely to affect vegetation in the Australian Alps including in subalpine grasslands. The recovery of this community was assessed using paired unburnt and burnt plots (30 × 20 m) at 10 sites 15 years after largescale fires that burnt &amp;gt;70% of the subalpine zone in Kosciuszko National Park. There were few significant differences found: higher cover of shrubs (17.8% burnt vs 11.3% unburnt plots), and taller vegetation (22.6 vs 19 cm). However, vegetation cover (97%), species richness (38 taxa), composition and limited presence of invasive plants (10 species, 8.5% cover) were not significantly different. This differs from results six weeks and one year post-fire, when there were clear differences in the cover and composition of vegetation. These results indicate that subalpine grasslands recover from single fires, but with warmer and drier conditions becoming more common, and repeat fires in some areas, the distribution, structure and composition of this and other communities in the Australian Alps will change.

Spatial Distribution of Wildfires Ignited under Katabatic versus Non-Katabatic Winds in Mediterranean Southern California USA

Wildfires are a major hazard to humans in the southern California Mediterranean ecosystem and improving our understanding and delineation of different fire regimes is critical to mitigating wildfire-related hazards. Recent research has demonstrated that there are two distinct fire regimes in this region based on the presence or absence of katabatic winds (primarily Santa Ana winds) concurrent with the fire. Here, we expand the katabatic wind category to include Sundowner winds along the Santa Barbara front range and analyze the spatial relationships and difference in ignition sources between fires associated with katabatic and non-katabatic wind events from 1948–2017. We found distinct spatial extents for katabatic versus non-katabatic fires, with areas of the higher number of repeat fires generally associated with one fire type or the other. These spatial delineations were consistent with prior analyses of katabatic wind patterns and were also related to the climatology of marine influences across the region. Finally, we contextualize the burn perimeter of the 2017 Thomas Fire, the largest fire in modern California history, relative to spatial patterns of katabatic and non-katabatic fires. The 2017 Thomas Fire began during the longest Santa Ana event in the last 70 years in an area that has been burned repeatedly by Santa Ana fires. However, the Thomas Fire ultimately burned into a region where there were no prior Santa Ana fires. The spatial delineation of two relatively distinct fire regimes is critical to making management decisions, such as where to locate suppression resources at critical times and where fuel treatments might be most effective. However, the anomalous pattern of the Thomas Fire also points to the potential for changes in anthropogenic and environmental factors to disrupt historical spatial patterns and suggests that spatial patterns of fire regimes are themselves prospective metrics of global change.

Controls of reburn severity vary with fire interval in the Klamath Mountains, California, USA

AbstractOver the past few decades, the frequency and number of large fires has increased in the western United States following a paucity of fire activity in many forests during most of the 20th century. Areas of repeated burning are of particular interest for understanding where there may be qualitative shifts in fire severity and the ecological consequences related to ecosystem resilience and climate change. In the context of recent increases in fire activity, we evaluated the relative importance of potential factors contributing to reburn severity (fire severity in areas that have burned twice) from 1985 to 2012 in the Klamath Mountains ecoregion of California. A unique component of our study was the evaluation of different scales of analysis within the ecoregion. The variables prior burn severity (continuous relative difference‐normalized burn ratio values from 1 to 1300), time since fire, biophysical setting, and average monthly weather were evaluated using generalized additive models to identify the relative importance of factors related to reburn severity patterns for 28 individual repeat fires (&gt;375 ha), shorter (&lt;15 yr) and longer (≥19 yr) fire interval categories, and across all repeat fires combined (79,112 ha). We found that evaluation of all repeat fires combined had masked important trends occurring across individual reburn areas of study particularly when dominated by one or more large fires. Averaging the variance of reburn severity explained across individual reburn areas (equal representation) yielded more explanatory power of predictor variables compared to the composite of all reburn areas combined. Over the period of analysis, topographic controls were relatively consistent regardless of fire interval, but vegetation characteristics had a stronger relationship than weather on reburn severity at longer fire intervals compared to shorter intervals. Likewise, we found greater similarity between prior and reburn severity at longer fire intervals than at shorter fire intervals. Our results underscore the presence of a self‐reinforcing pattern of fire severity related to the biophysical setting in the Klamath Mountains ecoregion, but also highlight the importance of spatial and temporal scale of evaluation and the interactions of vegetation characteristics, time since fire, and fire weather on reburn fire severity.

Ecological engineering through fire‐herbivory feedbacks drives the formation of savanna grazing lawns

AbstractVariation in grass height is beneficial to biodiversity conservation in savanna landscapes. Theory predicts that small fires can promote short‐grass areas within savannas. We experimentally assessed the influence of fire season and size on grass height and the resultant response of wild grazer communities and tested three hypotheses: (1) repeated small fires in tall‐grass savannas increase short‐grass grazer densities in the post‐burn environment; (2) increased grazer densities maintain grass height in a short, palatable state and drive feedbacks that exclude fire; and (3) late‐dry season burns concentrate grazers more effectively than early dry season burns.We repeatedly applied annual treatments (unburned, early‐ and late‐burns) in 0.25‐, 5‐ and 25‐ha plots over a period of 3 years in a tall‐grass savanna system in Kruger National Park, South Africa. Dung counts for grazer density and grass height data were collected along 50‐m transects. Grass height was measured in paired 1‐m2herbivore exclosures on plots before and after applied fires.Dung data indicate that wildebeest occurred most frequently in grass heights below 5 cm. Their preference for plots regardless of fire size or season increased over time with each repeated burn. Zebra and buffalo favoured burns immediately post‐fire, but buffalo did not actively select for burnt areas over longer time periods.By the second year of treatment, herbivory maintained 28% and 91% of the grass height below 10 cm in the early‐ and late‐season burns respectively. In contrast, herbivory on the unburned treatments had no effect on grass height.Synthesis and applications. Fires less than 25 ha in size attracted sufficient grazing herbivores to shorten grass height. Repetition of the fire treatments resulted in the active selection of these areas in the longer term by wildebeest, impala and, to a lesser degree, zebra. Grazing pressure was high enough to initiate positive feedbacks and maintain lawns after only two seasons of burning and, depending on the season of burn, reduced grass height to a level that excluded repeat fires. Our study demonstrated that theory on grazer use of the post‐fire environment can be implemented practically by applying small repeated burns to promote the formation of short‐grass areas within savannas.

THE ANALYSIS OF THE ELEMENTAL CHANGES OF DIFFERENT ALL CERAMICS EXPOSED TO REPEATED FIRINGS WITH USING XRF

Ponte Academic JournalApr 2017, Volume 73, Issue 4 THE ANALYSIS OF THE ELEMENTAL CHANGES OF DIFFERENT ALL CERAMICS EXPOSED TO REPEATED FIRINGS WITH USING XRFAuthor(s): Fehmi Gonuldas ,Dogan Derya OztasJ. Ponte - Apr 2017 - Volume 73 - Issue 4 doi: 10.21506/j.ponte.2017.4.43 Abstract:Purpose: Effects of the the firing process on the structural features of the all-ceramics is unclear. The aim of this study was to investigate the effects of the repeated firings on the elemental changes of all-ceramic systems using XRF analyses. Material and Method: IPS e-max and zirconia all-ceramics were used in this study. Totally 120 samples were prepared. The all-ceramic samples were divided into six subgroups (n=10) as the control group, 1st, 3rd, 5th, 7th and 9th firings. Each samples were analyzed with the XRF spectrometer. The variance analysis (ANOVA) test was used for the statistical analysis and LSD test were used for the comparisons of the repeated firings. Results: The proportional elemental changes of Fe and Bi elements, depended on the repeated firings, for IPS e-max all-ceramic samples were statistically significant (p<.05). For zirconia all-ceramic samples, the proportional elemental changes of Ca-Cr-Fe-Co-Cu-Ga-Ge-As-Se-Br-Rb-Sr-Y-Cs-Hf-Ta-W-Tl and Pb elements, depended on the repeated firings, for zirconia all-ceramic samples were statistically significant (p<.05). Conclusions: The repeated firings effect the ratio of the structural elements in all ceramics systems and some elements move away from the structure due to the repeated firings. The repeated firings should be avoided. Key words: XRF analysis, All-ceramics, Repeated firings Download full text:Check if you have access through your login credentials or your institution Username Password

Remote‐sensing constraints on South America fire traits by Bayesian fusion of atmospheric and surface data

AbstractSatellite observations reveal substantial burning during the 2007 and 2010 tropical South America fire season, with both years exhibiting similar total burned area. However, 2010 CO fire emissions, based on satellite CO concentration measurements, were substantially lower (−28%), despite the once‐in‐a‐century drought in 2010. We use Bayesian inference with satellite measurements of CH4 and CO concentrations and burned area to quantify shifts in combustion characteristics in 2010 relative to 2007. We find an 88% probability in reduced combusted biomass density associated with the 2010 fires and an 82% probability of lower fire carbon losses in 2010 relative to 2007. Higher combustion efficiency was a smaller contributing factor to the reduced 2010 CO emissions. The reduction in combusted biomass density is consistent with a reduction (4–6%) in Global Ozone Monitoring Experiment 2 solar‐induced fluorescence (a proxy for gross primary production) during the preceding months and a potential reduction in biomass (≤8.3%) due to repeat fires.

Synaptotagmin 1 directs repetitive release by coupling vesicle exocytosis to the Rab3 cycle.

In response to Ca(2+) influx, a synapse needs to release neurotransmitters quickly while immediately preparing for repeat firing. How this harmonization is achieved is not known. In this study, we found that the Ca(2+) sensor synaptotagmin 1 orchestrates the membrane association/disassociation cycle of Rab3, which functions in activity-dependent recruitment of synaptic vesicles. In the absence of Ca(2+), synaptotagmin 1 binds to Rab3 GTPase activating protein (GAP) and inhibits the GTP hydrolysis of Rab3 protein. Rab3 GAP resides on synaptic vesicles, and synaptotagmin 1 is essential for the synaptic localization of Rab3 GAP. In the presence of Ca(2+), synaptotagmin 1 releases Rab3 GAP and promotes membrane disassociation of Rab3. Without synaptotagmin 1, the tight coupling between vesicle exocytosis and Rab3 membrane disassociation is disrupted. We uncovered the long-sought molecular apparatus linking vesicle exocytosis to Rab3 cycling and we also revealed the important function of synaptotagmin 1 in repetitive synaptic vesicle release.

Spectrophotometric Analysis of the Influence of Metal Alloy Choice, Opaque Thickness, and Repeated Firing on the Shade of Metal Ceramic Restorations.

To determine the effect of type of base metal alloy, opaque thickness, and repeated firing on color of metal ceramic restorations. Four nickel chromium and four cobalt chromium were selected with one noble alloy as a control. Ten discs (16 mm 0.5 mm) were prepared for each group. Color of specimens were measured using a spectrophotometer and were calculated using CIEDE2000 formula (ΔL', ΔC', ΔH', ΔE') between experimental groups and control at six stages of porcelain constructions: opaque 0.1 and 0.3 mm, dentine, enamel, glaze, and three times repeated firing. Shade A3 was used. One-way analysis of variance and Bonferroni multiple test were performed (α = 0.05). Alloy type and stage showed statistical significance on total color and color parameter differences from the control and there was significant interaction between them (p < .05). Nidour alloy was the closest to control. Increase in ΔC' and a decrease in ΔH' and in a* and b* was the commonest in comparison with the control. However, ΔE' was below acceptability threshold for all alloys at all stages. Despite the statistical significance, base metal alloys performed as good as noble metal control. Neither opaque thickness, nor repeated firing affected color variations from the control group. There was no obvious trend in the behavior of metal alloys at all stages. However, increase in chroma and a decrease in hue, with green blue shift, was the most common. Records of the effects of eight commonly used base metal alloys on the color of final shade of the metal-ceramic restorations, at various stages of ceramic buildup, have considerable value. (J Esthet Restor Dent 28:S56-S67, 2016).

Factors Affecting Penetrating Captive Bolt Gun Performance

Captive bolt stunning is used for rendering livestock insensible at slaughter. The mechanical factors relating to performance of 6 penetrating captive bolt gun (CBG) models were examined. The Matador Super Sécurit 3000 and the .25 Cash Euro Stunner had the highest kinetic energy values (443 J and 412 J, respectively) of the CBGs tested. Ninety percent (27/30) of CBGs held at a government gun repository (United Kingdom) were found to have performed at a normal standard for the model, while 53% (10/19) of commercial contractor CBGs tested were found to underperform for the gun model. When the .22 Cash Special was fired 500 times at 4 shots per min, the gun reached a peak temperature of 88.8°C after 2.05 hr. Repeat firing during extended periods significantly reduced the performance of the CBG. When deciding on the appropriate CBG/cartridge combination, the kinetic energy delivered to the head of the nonhuman animal, bolt penetration depth, and species/animal type must be considered. It is recommended that CBGs are routinely checked for wear to the bolt and barrel if they are repeatedly fired in a session.

Comparative spectrophotometric study of the color stability of three dental porcelains after repeated fi rings

O objetivo deste estudo foi avaliar a estabilidade de cor de três marcas comerciais de porcelanas dentais aluminizadas durante seu processo de queima. Essas porcelanas são utilizadas para a conconfecção de dentes de prótese fixa. Para o experimento foram confeccionados 30 corpos-de-prova em forma de disco com 2 mm de espessura e 10 mm de circunferência, sendo 10 da marca AllCeram, 10 da marca Noritake Cerabien CZR e 10 da marca Vita VM7. As amostras foram queimadas 10 vezes. As leituras de cor foram feitas em espectrofotômetro de reflexão nos seguintes intervalos: após a 1a queima, após a 3a queima, após a 5a queima e após a 10a queima. As curvas de reflexão foram convertidas em valores LAB e a diferença de cor foi medida por meio do método CIELAB (ΔE). Os resultados obtidos demonstraram que existe variação de cor e que essa variação depende do número de queimas realizadas e da marca comercial utilizada.

Evaluating long-term effects of prescribed fire regimes on carbon stocks in a temperate eucalypt forest

Prescribed fires are a common management practice in the temperate forests of Australia, but effects on total forest carbon (C) of long-term prescribed fire regimes, involving multiple repeat fires, remain under-examined. This study quantified C stocks in multiple pools after 27years of a long-term prescribed fire experiment in a mixed-species eucalypt forest in south-eastern Australia. The experimental design included five replications of each of five treatments – a long-unburnt Control, plus a factorial combination of two fire frequencies (c. 3-yearly ‘High’, c. 10-yearly ‘Low’), and two fire seasons (Spring, Autumn) – encompassing up to 7 low-intensity repeat fires over the 27years.Overall, total C stocks (the sum of all pools: Above-ground biomass, Dead wood, Litter, and Soil) were significantly greater in Control than Fire treatments. Mean total C stock differences (Control minus Fire) were 36Mgha−1, and increased with both fire frequency (46Mgha−1, Control versus High frequency treatments) and fires in autumn rather than spring (42Mgha−1, Control versus Autumn treatments). Mean differences had wide 95% confidence intervals (e.g. 4–67MgCha−1, Control versus Fire), indicating considerable uncertainty about the magnitude of effects of prescribed fire regimes on total C in these native forests. Weighted averaging of linear multiple regression models was used to identify the most important variables for explaining proportional C stock differences ((Control–Fire)/Control), and involved consideration of 85 explanatory variables including measures of fire intensity, fire severity, fuel, pre- and post-fire rainfall, fire weather, and topography. The best regression model explained 80% of variation in total C stock differences between Control and Fire treatments. Consistently important explanatory variables were those representing or associated with fire intensity (flame angle, wind speed, Forest Fire Danger Index), and number of prescribed fires. Measures of fuel load, pre- and post-fire rainfall, and, in particular, fire severity, were less important explanatory variables. The study provides indications of management options for minimising C stock decreases associated with prescribed fire regimes in temperate eucalypt forests; notably, wide fire intervals (closer to 10 than 3years), and utilising strategies to minimise mean fire intensity, including burning in moist (spring) rather than dry (autumn) conditions.