variable layer height
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The recent developments in multiaxis three-dimensional (3D) printing have got a large potential for expanding the capability of material extrusion based methods. Especially curved and nonplanar methods can improve buildability, surface quality, and mechanical performance. However, the challenges that arise from using them complicate their deployment. In this article, we propose a hybrid planar method, based on varying the layer height and deposition speed in combination with tool reorientation, that allows us to get a lot of the same benefits that come from using nonplanar layers. The goal of the method is to keep the deposition constant regardless of the overhang angle. This is achieved by simultaneous control of layer height, deposition speed, and tool orientation. The method is the most beneficial for large-scale, single-wall 3D printing, such as clay, concrete, and other composites. The main restriction of the method depends on the minimum/maximum ratio between the nozzle diameter and layer height. A description of the method is provided, and sample objects are evaluated either as trajectories or as test prints. The claims are confirmed by microscopy measurement of the contact patch width. The method as presented allows printing of overhangs up to 82.34°, can be applied to complex geometry without difficulties, and further possibilities of limit expansion are discussed. The contact patch width decreases only by 20% at the 80° of overhang.
- Klíčová slova
- 3D printing method, intralayer height variation, multiaxis, process planning, variable layer height,
- Publikační typ
- časopisecké články MeSH
Atmospheric activity concentration of 7Be in the air was monitored during the period of one year from September 2015 to September 2016 at Ostrava, Czech Republic, with a two-day frequency that is shorter compared to a standard 7-day frequency of routine 7Be measurements. Simultaneously, relevant meteorological data (temperature, rainfall amount, precipitation particle size and speed, tropopause height, and PM10 concentrations) and the sunspot number were accumulated. Weighted linear regression analysis applied to the 7Be atmospheric activity concentration, the measured meteorological explanatory variables and the sunspot number revealed temperature as the most statistically significant explanatory variable. The tree model proved temperature as the most important explanatory variable and predicted the threshold value separating low and high temperature behavior of 7Be at about 13 °C (2-day average). A simple local two-layer (stratosphere and troposphere) atmospheric model was then applied to the data analysis. The model is able to fit the data for a larger accumulation period (6 days).
- MeSH
- beryllium MeSH
- časové faktory MeSH
- látky znečišťující vzduch MeSH
- monitorování radiace * MeSH
- monitorování životního prostředí MeSH
- radionuklidy MeSH
- roční období MeSH
- teplota MeSH
- velikost částic MeSH
- Publikační typ
- časopisecké články MeSH
- Geografické názvy
- Česká republika MeSH
- Názvy látek
- Beryllium-7 MeSH Prohlížeč
- beryllium MeSH
- látky znečišťující vzduch MeSH
- radionuklidy MeSH
The contemporary state of functional traits and species richness in plant communities depends on legacy effects of past disturbances. Whether temporal responses of community properties to current environmental changes are altered by such legacies is, however, unknown. We expect global environmental changes to interact with land-use legacies given different community trajectories initiated by prior management, and subsequent responses to altered resources and conditions. We tested this expectation for species richness and functional traits using 1814 survey-resurvey plot pairs of understorey communities from 40 European temperate forest datasets, syntheses of management transitions since the year 1800, and a trait database. We also examined how plant community indicators of resources and conditions changed in response to management legacies and environmental change. Community trajectories were clearly influenced by interactions between management legacies from over 200 years ago and environmental change. Importantly, higher rates of nitrogen deposition led to increased species richness and plant height in forests managed less intensively in 1800 (i.e., high forests), and to decreases in forests with a more intensive historical management in 1800 (i.e., coppiced forests). There was evidence that these declines in community variables in formerly coppiced forests were ameliorated by increased rates of temperature change between surveys. Responses were generally apparent regardless of sites' contemporary management classifications, although sometimes the management transition itself, rather than historic or contemporary management types, better explained understorey responses. Main effects of environmental change were rare, although higher rates of precipitation change increased plant height, accompanied by increases in fertility indicator values. Analysis of indicator values suggested the importance of directly characterising resources and conditions to better understand legacy and environmental change effects. Accounting for legacies of past disturbance can reconcile contradictory literature results and appears crucial to anticipating future responses to global environmental change.
- Klíčová slova
- biodiversity change, climate change, disturbance regime, forestREplot, herbaceous layer, management intensity, nitrogen deposition, plant functional traits, time lag, vegetation resurvey,
- MeSH
- biodiverzita * MeSH
- dusík MeSH
- lesy MeSH
- lidské činnosti MeSH
- podnebí MeSH
- rostliny klasifikace MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
- Geografické názvy
- Evropa MeSH
- Názvy látek
- dusík MeSH
BACKGROUND: Severe canopy-removing disturbances are native to many temperate forests and radically alter stand structure, but biotic legacies (surviving elements or patterns) can lend continuity to ecosystem function after such events. Poorly understood is the degree to which the structural complexity of an old-growth forest carries over to the next stand. We asked how pre-disturbance spatial pattern acts as a legacy to influence post-disturbance stand structure, and how this legacy influences the structural diversity within the early-seral stand. METHODS: Two stem-mapped one-hectare forest plots in the Czech Republic experienced a severe bark beetle outbreak, thus providing before-and-after data on spatial patterns in live and dead trees, crown projections, down logs, and herb cover. RESULTS: Post-disturbance stands were dominated by an advanced regeneration layer present before the disturbance. Both major species, Norway spruce (Picea abies) and rowan (Sorbus aucuparia), were strongly self-aggregated and also clustered to former canopy trees, pre-disturbance snags, stumps and logs, suggesting positive overstory to understory neighbourhood effects. Thus, although the disturbance dramatically reduced the stand's height profile with ~100% mortality of the canopy layer, the spatial structure of post-disturbance stands still closely reflected the pre-disturbance structure. The former upper tree layer influenced advanced regeneration through microsite and light limitation. Under formerly dense canopies, regeneration density was high but relatively homogeneous in height; while in former small gaps with greater herb cover, regeneration density was lower but with greater heterogeneity in heights. CONCLUSION: These findings suggest that pre-disturbance spatial patterns of forests can persist through severe canopy-removing disturbance, and determine the spatial structure of the succeeding stand. Such patterns constitute a subtle but key legacy effect, promoting structural complexity in early-seral forests as well as variable successional pathways and rates. This influence suggests a continuity in spatial ecosystem structure that may well persist through multiple forest generations.
The paper presents results of an experimental investigation of charring of full-scale timber elements exposed to natural fire conditions. Fire experiments were conducted in the Room Corner Test facility, in which natural local fire scenarios were simulated to assess realistic charring rate and thermal response of timber structures. The analysis of experimental data evaluates the effects of timber orientation relative to the fire source, heat transfer dynamics, and other duration of fire exposure. The results demonstrate that charring rate is influenced not only by direct flame exposure but also by radiative and convective heat fluxes, leading to non-uniform charring depths along the height and across different sides of timber elements. The provided data include detailed temperature measurements at multiple depths of timber elements, high-resolution photographic and thermographic documentation to demonstrate charred layer formation, pyrolysis depth, and material loss. The dataset, made available for further research, provides a valuable foundation for numerical fire model validation and supports the development of probabilistic approaches for predicting variability of charring.
- Klíčová slova
- Fire resistance, Full-scale experiments, Heat transfer, Natural fire exposure, Room corner test, Temperature measurement, Timber structures, Wood charring,
- Publikační typ
- časopisecké články MeSH
Vertical distributions of leaf dry mass (M(d)) and leaf area (A(f)) were related to relative irradiance (I(r); I(r) above the stand = 1) in closed-canopy, old-growth stands of the floodplain forest in southern Moravia composed largely of Quercus, Fraxinus and Tilia species. Foliage area and mass at any given canopy height were converted to solar equivalent leaf area (A(s)) and mass (M(s)) by multiplying actual values at a given level in the canopy by the relative irradiance at that position. Stand leaf area index (LAI) was 5 (7 including shrub and herb layer), and solar equivalent parameters reached about 25% of that amount. In all species, vertical profiles of both relative irradiance and leaf dry mass to area ratio (LMA) were sigmoidal and the two variables were linearly related. The dominant, upper canopy species had a larger proportion of solar equivalent foliage than suppressed understory species. For individual trees of all species, the upper canopy had a larger proportion of solar equivalent foliage than the lower canopy. Light compensation points at both the leaf and whole-tree level were defined according to leaf or tree position, size and structure. I conclude that optimization of A(s) for forest stands may be used as a basis for determining thinning schedules and evaluating tree survival after damage to tree crowns by various factors.
- Publikační typ
- časopisecké články MeSH
The traditional Japanese method of wood surface charring was studied. To perform the surface charring, three sawn Norway spruce and Silver fir wood boards of dimension 190 × 24 × 4000 mm3 were tied together to act as a chimney and charred in a short time (3-4 min) with open flame at a temperature above 500 °C. Temperature inside the chimney was recorded on the three different positions during the charring process. Surface temperature of spruce increased from 0 °C to 500 °C in approx. 120-300 s while fir increased in approx. 100-250 s. The thickness of the charred layer and the resulting cupping effect were investigated at the different heights of the chimney to evaluate its variability. Temperature achieved during the charring process was sufficient to get a significant charred layer of 2.5 and 4.5 mm on average for spruce and fir samples, respectively. The analyzed samples showed a significant cupping effect to the charred side with no difference between the annual ring orientation of sawn boards. Spruce exhibit a more significant cupping effect when compared to fir, i.e., 3.2-6 mm and 2.2-4.5 mm, respectively. Furthermore, the pH values of charred samples increased significantly, which could be an indication of improved resistance against wood-decay fungi. For better insight into the traditional charring method, further studies should be carried out to execute the charring process in a consistent quality and therefore fully exploit its potential.
- Klíčová slova
- Yakisugi method, cupping effect, surface charring, surface modification, thermal treatment, wood char,
- Publikační typ
- časopisecké články MeSH
There is concern regarding the heterogeneity of exposure to airborne particulate matter (PM) across urban areas leading to negatively biased health effects models. New, low-cost sensors now permit continuous and simultaneous measurements to be made in multiple locations. Measurements of ambient PM were made from October to April 2015-2016 and 2016-2017 to assess the spatial and temporal variability in PM and the relative importance of traffic and wood smoke to outdoor PM concentrations in Rochester, NY, USA. In general, there was moderate spatial inhomogeneity, as indicated by multiple pairwise measures including coefficient of divergence and signed rank tests of the value distributions. Pearson correlation coefficients were often moderate (~50% of units showed correlations >0.5 during the first season), indicating that there was some coherent variation across the area, likely driven by a combination of meteorological conditions (wind speed, direction, and mixed layer heights) and the concentration of PM2.5 being transported into the region. Although the accuracy of these PM sensors is limited, they are sufficiently precise relative to one another and to research grade instruments that they can be useful is assessing the spatial and temporal variations across an area and provide concentration estimates based on higher-quality central site monitoring data.
- Klíčová slova
- hourly concentrations, low-cost monitors, particulate matter, spatial variability,
- Publikační typ
- časopisecké články MeSH
