Search

Recently, we presented a method to assign atomic partial charges based on the DASH (dynamic attention-based substructure hierarchy) tree with high efficiency and quantum mechanical (QM)-like accuracy. In addition, the approach can be considered "rule based"—where the rules are derived from the attention values of a graph neural network—and thus, each assignment is fully explainable by visualizing the underlying molecular substructures. In this work, we demonstrate that these hierarchically sorted substructures capture the key features of the local environment of an atom and allow us to predict different atomic properties with high accuracy without building a new DASH tree for each property. The fast prediction of atomic properties in molecules with the DASH tree can, for example, be used as an efficient way to generate feature vectors for machine learning without the need for expensive QM calculations. The final DASH tree with the different atomic properties as well as the complete dataset with wave functions is made freely available. [ABSTRACT FROM AUTHOR]

Increasing heatwaves are threatening forest ecosystems globally. Leaf thermal regulation and tolerance are important for plant survival during heatwaves, though the interaction between these processes and water availability is unclear. Genotypes of the widely distributed foundation tree species Populus fremontii were studied in a controlled common garden during a record summer heatwave-where air temperature exceeded 48 °C. When water was not limiting, all genotypes cooled leaves 2 to 5 °C below air temperatures. Homeothermic cooling was disrupted for weeks following a 72-h reduction in soil water, resulting in leaf temperatures rising 3 °C above air temperature and 1.3 °C above leaf thresholds for physiological damage, despite the water stress having little effect on leaf water potentials. Tradeoffs between leaf thermal safety and hydraulic safety emerged but, regardless of water use strategy, all genotypes experienced significant leaf mortality following water stress. Genotypes from warmer climates showed greater leaf cooling and less leaf mortality after water stress in comparison with genotypes from cooler climates. These results illustrate how brief soil water limitation disrupts leaf thermal regulation and potentially compromises plant survival during extreme heatwaves, thus providing insight into future scenarios in which ecosystems will be challenged with extreme heat and unreliable soil water access.

Tree growth and longevity trade-offs fundamentally shape the terrestrial carbon balance. Yet, we lack a unified understanding of how such trade-offs vary across the world's forests. By mapping life history traits for a wide range of species across the Americas, we reveal considerable variation in life expectancies from 10 centimeters in diameter (ranging from 1.3 to 3195 years) and show that the pace of life for trees can be accurately classified into four demographic functional types. We found emergent patterns in the strength of trade-offs between growth and longevity across a temperature gradient. Furthermore, we show that the diversity of life history traits varies predictably across forest biomes, giving rise to a positive relationship between trait diversity and productivity. Our pan-latitudinal assessment provides new insights into the demographic mechanisms that govern the carbon turnover rate across forest biomes.

The fundamental trade-off between current and future reproduction has long been considered to result in a tendency for species that can grow large to begin reproduction at a larger size. Due to the prolonged time required to reach maturity, estimates of tree maturation size remain very rare and we lack a global view on the generality and the shape of this trade-off. Using seed production from five continents, we estimate tree maturation sizes for 486 tree species spanning tropical to boreal climates. Results show that a species' maturation size increases with maximum size, but in a non-proportional way: the largest species begin reproduction at smaller sizes than would be expected if maturation were simply proportional to maximum size. Furthermore, the decrease in relative maturation size is steepest in cold climates. These findings on maturation size drivers are key to accurately represent forests' responses to disturbance and climate change.

We consider the numerical taxonomy problem of fitting a positive distance function \({\mathcal {D}:{S\choose 2}\rightarrow \mathbb {R}_{\gt 0}}\) by a tree metric. We want a tree T with positive edge weights and including S among the vertices so that their distances in T match those in \(\mathcal {D}\). A nice application is in evolutionary biology where the tree T aims to approximate thebranching process leading to the observed distances in \(\mathcal {D}\) [Cavalli-Sforza and Edwards 1967]. We consider the total error, that is, the sum of distance errors over all pairs of points. We present a deterministic polynomial time algorithm minimizing the total error within a constant factor. We can do this both for general trees and for the special case of ultrametrics with a root having the same distance to all vertices in S. The problems are APX-hard, so a constant factor is the best we can hope for in polynomial time. The best previous approximation factor was O((log n)(log log n)) by Ailon and Charikar [2005], who wrote "determining whether an O(1) approximation can be obtained is a fascinating question." [ABSTRACT FROM AUTHOR]

There is an urgent need for strategies to reduce the negative impacts of a warming climate on human health. Cooling urban neighborhoods by planting trees and vegetation and increasing albedo of roofs, pavements, and walls can mitigate urban heat. We used synoptic climatology to examine how different tree cover and albedo scenarios would affect heat-related morbidity in Los Angeles, CA, USA, as measured by emergency room (ER) visits. We classified daily meteorological data for historical summer heat events into discrete air mass types. We analyzed those classifications against historical ER visit data to determine both heat-related and excess morbidity. We used the Weather Research and Forecasting model to examine the impacts of varied tree cover and albedo scenarios on meteorological outcomes and used these results with standardized morbidity data algorithms to estimate potential reductions in ER visits. We tested three urban modification scenarios of low, medium, and high increases of tree cover and albedo and compared these against baseline conditions. We found that avoiding 25% to 50% of ER visits during heat events would be a common outcome if the urban environment had more tree cover and higher albedo, with the greatest benefits occurring under heat events that are moderate and those that are particularly hot and dry. We conducted these analyses at the county level and compared results to a heat-vulnerable, working-class Los Angeles community with a high concentration of people of color, and found that reductions in the rate of ER visits would be even greater at the community level compared to the county.

Spatiotemporal patterns of plant water uptake, loss, and storage exert a first-order control on photosynthesis and evapotranspiration. Many studies of plant responses to water stress have focused on differences between species because of their different stomatal closure, xylem conductance, and root traits. However, several other ecohydrological factors are also relevant, including soil hydraulics, topographically driven redistribution of water, plant adaptation to local climatic variations, and changes in vegetation density. Here, we seek to understand the relative importance of the dominant species for regional-scale variations in woody plant responses to water stress. We map plant water sensitivity (PWS) based on the response of remotely sensed live fuel moisture content to variations in hydrometeorology using an auto-regressive model. Live fuel moisture content dynamics are informative of PWS because they directly reflect vegetation water content and therefore patterns of plant water uptake and evapotranspiration. The PWS is studied using 21,455 wooded locations containing U.S. Forest Service Forest Inventory and Analysis plots across the western United States, where species cover is known and where a single species is locally dominant. Using a species-specific mean PWS value explains 23% of observed PWS variability. By contrast, a random forest driven by mean vegetation density, mean climate, soil properties, and topographic descriptors explains 43% of observed PWS variability. Thus, the dominant species explains only 53% (23% compared to 43%) of explainable variations in PWS. Mean climate and mean NDVI also exert significant influence on PWS. Our results suggest that studies of differences between species should explicitly consider the environments (climate, soil, topography) in which observations for each species are made, and whether those environments are representative of the entire species range.

Non-structural carbohydrates (NSCs) are building blocks for biomass and fuel metabolic processes. However, it remains unclear how tropical forests mobilize, export, and transport NSCs to cope with extreme droughts. We combined drought manipulation and ecosystem 13CO2 pulse-labeling in an enclosed rainforest at Biosphere 2, assessed changes in NSCs, and traced newly assimilated carbohydrates in plant species with diverse hydraulic traits and canopy positions. We show that drought caused a depletion of leaf starch reserves and slowed export and transport of newly assimilated carbohydrates below ground. Drought effects were more pronounced in conservative canopy trees with limited supply of new photosynthates and relatively constant water status than in those with continual photosynthetic supply and deteriorated water status. We provide experimental evidence that local utilization, export, and transport of newly assimilated carbon are closely coupled with plant water use in canopy trees. We highlight that these processes are critical for understanding and predicting tree resistance and ecosystem fluxes in tropical forest under drought.

Numerous studies have shown reduced performance in plants that are surrounded by neighbours of the same species1,2, a phenomenon known as conspecific negative density dependence (CNDD)3. A long-held ecological hypothesis posits that CNDD is more pronounced in tropical than in temperate forests4,5, which increases community stabilization, species coexistence and the diversity of local tree species6,7. Previous analyses supporting such a latitudinal gradient in CNDD8,9 have suffered from methodological limitations related to the use of static data10-12. Here we present a comprehensive assessment of latitudinal CNDD patterns using dynamic mortality data to estimate species-site-specific CNDD across 23 sites. Averaged across species, we found that stabilizing CNDD was present at all except one site, but that average stabilizing CNDD was not stronger toward the tropics. However, in tropical tree communities, rare and intermediate abundant species experienced stronger stabilizing CNDD than did common species. This pattern was absent in temperate forests, which suggests that CNDD influences species abundances more strongly in tropical forests than it does in temperate ones13. We also found that interspecific variation in CNDD, which might attenuate its stabilizing effect on species diversity14,15, was high but not significantly different across latitudes. Although the consequences of these patterns for latitudinal diversity gradients are difficult to evaluate, we speculate that a more effective regulation of population abundances could translate into greater stabilization of tropical tree communities and thus contribute to the high local diversity of tropical forests.

The possibility that the Amazon forest system could soon reach a tipping point, inducing large-scale collapse, has raised global concern1-3. For 65 million years, Amazonian forests remained relatively resilient to climatic variability. Now, the region is increasingly exposed to unprecedented stress from warming temperatures, extreme droughts, deforestation and fires, even in central and remote parts of the system1. Long existing feedbacks between the forest and environmental conditions are being replaced by novel feedbacks that modify ecosystem resilience, increasing the risk of critical transition. Here we analyse existing evidence for five major drivers of water stress on Amazonian forests, as well as potential critical thresholds of those drivers that, if crossed, could trigger local, regional or even biome-wide forest collapse. By combining spatial information on various disturbances, we estimate that by 2050, 10% to 47% of Amazonian forests will be exposed to compounding disturbances that may trigger unexpected ecosystem transitions and potentially exacerbate regional climate change. Using examples of disturbed forests across the Amazon, we identify the three most plausible ecosystem trajectories, involving different feedbacks and environmental conditions. We discuss how the inherent complexity of the Amazon adds uncertainty about future dynamics, but also reveals opportunities for action. Keeping the Amazon forest resilient in the Anthropocene will depend on a combination of local efforts to end deforestation and degradation and to expand restoration, with global efforts to stop greenhouse gas emissions.

A survey conducted in the 1920s, prior to the chestnut blight, indicated that chestnuts and oaks were codominant canopy species in White Oak Canyon, Shenandoah National Park, Virginia. A second survey in 1977 suggested that chestnuts were being replaced by tree species present before the blight, particularly oaks. In 2021, we resurveyed the 10 sites included in our 1977 survey and also recorded canopy and understory trees that grew above remnant chestnut sprouts. The canopy changed more substantially during the second interval (since 1977). Birch and maples were now more abundant. Hemlock declined, and oaks were less common in the canopy. In general, the trees considered as early to mid-successional have replaced oaks and hemlock. Chestnut sprouts have become much less common since 1977, presumably as repeated cycles of diebacks have weakened rootstocks. Those sites where chestnut sprouts have persisted until 2021 differed from neighboring sites without them. Chestnut sprouts were rare in sites with birch and hemlock; chestnut has persisted in locations with red oaks in the canopy and with few other understory competitors. This survey has been conducted over a longer time interval than previous studies that asked similar questions and our results suggest that changes to the forest composition following the loss of the American chestnut may be greater than previously recognized although the relative contribution of losing this codominant species is unclear.

Abstract\nNOVELTY STATEMENT\nHIGHLIGHTSThis study examines the impact of airborne particulate matter (PM) and associated trace elements (TEs) on deciduous and coniferous trees at the edge of Wigry National Park in northeast Poland, focusing on pollution levels and the potential for phytoremediation. Researchers measured PM concentrations in the air and on the leaves of Picea abies, Quercus robur, and Corylus avellana, along with photosynthetic indicators (Fv/Fm ratio and performance index). The study found significant differences in pollution intensity across areas with varying levels of human activity. P. abies, an evergreen species, accumulated the highest PM levels (>200 μg/cm2), while Q. robur had the highest accumulation among deciduous trees (>50 μg/cm2). Trace elements such as Fe, Cu, Zn, Sr, and Cd were detected, with C. avellana being the most efficient in accumulating Cd (up to 7.5 mg/kg). The accumulation of pollutants correlated with reduced photosynthetic efficiency in trees closest to pollution sources. The findings suggest that strategically planting specific tree species can help mitigate air pollution in national parks and protect sensitive vegetation. Future research should explore the long-term effects of PM on forest health and the role of different species in phytoremediation.This is the first time that the impact of PM and TEs pollution on trees growing within a national park was investigated. PM and TEs were revealed to penetrate into the park, which affected the photosynthetic efficiency of trees. To protect endangered park flora, it is proposed that selected trees be planted as a shield against air pollution.Evaluation of the PM and TE accumulation by Q. robur, C. avellana, and P. abies growing at the borders of Wigry National ParkPM and TEs penetrate deep into protected area and are effectively accumulated by P. abies, Q. robur, and C. avellana which affects their photosynthetic apparatusStrategically planted ‘pollution accumulators’ can shield more susceptible plants from PM and TEsEvaluation of the PM and TE accumulation by Q. robur, C. avellana, and P. abies growing at the borders of Wigry National ParkPM and TEs penetrate deep into protected area and are effectively accumulated by P. abies, Q. robur, and C. avellana which affects their photosynthetic apparatusStrategically planted ‘pollution accumulators’ can shield more susceptible plants from PM and TEs [ABSTRACT FROM AUTHOR]

In monoculture-dominated landscapes, recovering biodiversity is a priority, but effective restoration strategies have yet to be identified. In this study, we experimentally tested passive and active restoration strategies to recover taxonomic, phylogenetic, and functional diversity of woody plants within 52 tree islands established in an oil palm landscape. Large tree islands and higher initial planted diversity catalyzed diversity recovery, particularly functional diversity at the landscape level. At the local scale, results demonstrated that greater initial planting diversity begets greater diversity of native recruits, overcoming limitations of natural recruitment in highly modified landscapes. Establishing large and diverse tree islands is crucial for safeguarding rare, endemic, and forest-associated species in oil palm landscapes. [ABSTRACT FROM AUTHOR]

In this paper, we consider covering graphs obtained by lifting a tree with a loop at each vertex as a voltage graph over a cyclic group. We generalize a tool of Hell et al. (2020), known as the billiard strategy, for constructing Hamiltonian cycles in the covering graphs of paths. We show that our extended tool can be used to provide new sufficient conditions for the Hamiltonicity of covering graphs of trees that are similar to those of Batagelj and Pisanski (1982) and of Hell et al. (2020). Next, we focus specifically on covering graphs obtained from trees lifted as voltage graphs over cyclic groups Z p of large prime order p. We prove that for a given reflexive tree T whose edge labels are assigned uniformly at random from a finite set, the corresponding lift is almost surely Hamiltonian for a large enough prime-ordered cyclic group Z p. Finally, we show that if a reflexive tree T is lifted over a group Z p of a large prime order, then for any assignment of nonzero elements of Z p to the edges of T , the corresponding cover of T has a large circumference. [ABSTRACT FROM AUTHOR]

Based on the work of Reid and DePalma (2005), a new type of location function on trees, called the weight balance function and denoted by W b , is introduced. We compare W b with the well known median function M e d and show that W b (π) ⊆ M e d (π) for any profile π such that | M e d (π) | ≥ 2. The special case of M e d (π) = { x } for some vertex x is also investigated. [ABSTRACT FROM AUTHOR]

We provide a O (k 2 log k) vertex kernel for cograph edge editing. This improves a cubic kernel found by Guillemot, Havet, Paul and Perez (Guillemot et al., 2010) which involved four reduction rules. We generalize one of their rules, based on packing of induced paths of length four, by introducing t -modules, which are modules up to t edge modifications. The key fact is that large t -modules cannot be edited more than t times, and this allows to obtain a near quadratic kernel. The extra log k factor seems tricky to remove as it is necessary in the combinatorial lemma on trees which is central in our proof. Nevertheless, we think that a quadratic bound should be reachable. [ABSTRACT FROM AUTHOR]

Mangrove forests enhance Small Island Developing States' resilience to climate change, yet in 2020, a mangrove dieback impacted ~ 25% of mangrove-containing islands in the Maldives. Using remote sensing, dendrology and sediment geochemistry, we document a significant decrease in mangrove health post-2020 (NDVI: 0.75 ± 0.09) compared to pre-2020 (0.85 ± 0.04; P < 0.0001). Dead trees showed reduced stomatal conductance (δ13C: − 26.21 ± 0.11 ‰) relative to living ones (− 27.66 ± 0.14 ‰), indicating salinity stress. Critically, sea-level rise (30.50 ± 23.30 mm/year) outpaced mangrove sediment accretion (6.40 ± 0.69 mm/year) five-fold between 2017 and 2020. We attribute this dieback to salinity stress driven by record-high sea levels in 2020, linked to an extreme positive Indian Ocean Dipole event. These findings reveal the vulnerability of mangrove ecosystems to rapid sea-level rise and highlights the urgent need for adaptive conservation strategies in Small Island Developing States. [ABSTRACT FROM AUTHOR]

Wet‐design AC subsea power cables are currently rated up to a maximum voltage of 72.5 kV. These high voltage (HV) cables are cost‐effective alternatives to subsea cables kept dry by a protective lead sheath and exhibit superior properties for dynamic applications. However, several vented water trees, degradation phenomena reducing the cable lifetime, are observed in a HV XLPE insulated cable subjected to wet aging in the laboratory. The water trees initiate from a smooth and clean XLPE insulation/semiconductive screen interface. In this paper, we show that voids in the range 15–150 μm are observed in the conductor screen, 50–320 μm from the water tree inception sites. Degradation of the semiconductive material is observed, in the form of porous regions that connect the voids to the water tree inception sites. NaCl impurities are detected on the void surfaces and in the porous regions. These features are proposed to be the pre‐requisites for the formation of the vented water trees observed in this type of cable. The mechanism responsible for the formation of the void and porous regions in the semiconductive cable screen is discussed based on the observations. [ABSTRACT FROM AUTHOR]

Beech leaf disease (BLD), caused by the Litylenchus crenatae ssp. mccannii (Lcm) nematode, is an emerging threat to beech trees. This disease is characterized by distinct leaf symptoms, including leaf interveinal banding and thickened leaf texture, which leads to eventual tree mortality. Understanding Lcm dispersal mechanism(s) is crucial for managing BLD, yet these remain largely unknown, posing a major barrier to its effective management. This study represents a pioneering investigation into the abiotic and biotic vectors that potentially contribute to the local dispersal of Lcm in natural American beech (Fagus grandifolia) forest systems in the Northeastern United States. An experiment was set up in Stone Valley Forest, Pennsylvania (PA), using four funnel stands placed at variable distances from naturally BLD-infected beech trees. This approach enabled the recovery of active Lcm nematodes from each funnel, demonstrating their ability to naturally disperse at least 11.74 m from the nearest BLD-infected tree. The findings highlight the role of abiotic factors involved in the dispersal dynamics of Lcm, especially wind and humidity, as indicated by a generalized linear model. The current study also uncovered the incidental association of Lcm with other organisms beneath the canopy of BLD trees, including spiderwebs and caterpillars. To our knowledge, this is the first study to document the potential vectors involved in the local dispersal of Lcm, offering valuable information for the biology of this nematode, as well as insight into the development of effective BLD management strategies. The findings contribute to broader efforts in advancing the understanding of the local spread of BLD, highlighting the complex interplay of abiotic and biotic factors in this disease dispersal. [ABSTRACT FROM AUTHOR]

In an era where localization is increasingly vital for daily activities, determining an individual's location and providing suggestions is crucial for successful navigation. Central to our method is the concept of visibility areas, defined as spaces from which a landmark is at least partially visible. We tessellate space into a grid and use raycasting to determine these visibility areas. Visibility areas are further subdivided into sub‐spaces, each representing a unique set of visible landmarks. To efficiently manage and query these sub‐spaces, we create a tree of options for each landmark and merge them into one compact multitree. This structure represents a hierarchical composition of sub‐spaces and enhances query efficiency while storing each sub‐space only once in the memory. The multitree is designed to support the rapid identification of sub‐spaces based on observed landmarks, resulting in efficient localization within the environment is presented to calculating the optimal localization point in a visibility area based on suggested visible landmarks. The paper concludes with a discussion of the approach targeting indoor localization but highlights also its potential for further research and some limitations. [ABSTRACT FROM AUTHOR]

This paper presents a rapidly exploring random tree (RRT) algorithm with an effective post waypoint shift, which is suitable for the path planning of a wheeled mobile robot under kinematic constraints. In the growth of the exploring tree, the nearest node that satisfies the kinematic constraints is selected as the parent node. Once the distance between the new node and the target is within a certain threshold, the tree growth stops and a target connection based on minimum turning radius arc is proposed to generate an initial complete random path. The most significant difference from traditional RRT-based methods is that the proposed method optimizes the path based on Dubins curves through a post waypoint shift after a random path is generated, rather than through parent node selection and rewiring during the exploring tree growth. Then, it is proved that the method can obtain an optimal path in terms of the shortest length. The optimized path has good convergence and almost does not depend on the state of the initial random path. The comparative test results show that the proposed method has significant advantages over traditional RRT-based methods in terms of the sampling point number, the tree node number, and the path node number. Subsequently, an efficient method is further proposed to avoid unknown obstacles, which utilizes the original path information and thus effectively improves the new path planning efficiency. Simulations and real-world tests are carried out to demonstrate the effectiveness of this method. [ABSTRACT FROM AUTHOR]

One way of defining the values of the modular j$j$‐function at real quadratic irrationalities is by its cycle integrals along geodesics in the upper half plane whose endpoints are the roots of an indefinite binary quadratic form. We show that the restriction of the modular j$j$‐function to Markov irrationalities (an important subset of real quadratic irrationalities in diophantine approximation) is continuous with respect to the topology induced by the euclidean norm. [ABSTRACT FROM AUTHOR]

Chlorophyllous plants exhibiting partial mycoheterotrophy obtain carbon through mycorrhizal interactions in addition to photosynthesis. In arbuscular mycorrhizal (AM) plants, the Paris‐morphotype (i.e. hyphal coils) is considered essential for mycoheterotrophic carbon gains. Numerous tree species in tropical lowland forests form this morphotype, and under light‐ and nutrient‐limitation, additional carbon gain would be beneficial. However, if seedlings of woody species in the understory of tropical lowland forests exhibit partial mycoheterotrophy remains unexplored. Here we (a) examined the AM morphotype (Paris‐ or Arum‐type) in seedlings of 41 tropical woody species, and (b) to determine if any of the target Paris‐type species are partially mycoheterotrophic, we compared their multi‐element stable isotope natural abundance (13C, 2H, 18O, 15N) with neighbouring autotrophic non‐Paris‐type reference seedlings. About 50% of the investigated species (and 80% of the genera) exhibited the Paris‐type, expanding the number of tropical plant genera with Paris‐type AM. Enrichment in 13C, but not in 18O in target compared with neighbouring reference plants indicated partial mycoheterotrophy in seedlings of 6 of the 21 investigated Paris‐type AM species. Our results indicate for the first time that carbon gain through mycoheterotrophy occurs in seedlings of AM tropical tree species. In tropical forests, partial mycoheterotrophy during seedling establishment may confer so far unrecognised ecological advantages influencing seedling recruitment and ecosystem dynamics. Read the free Plain Language Summary for this article on the Journal blog. [ABSTRACT FROM AUTHOR]

A vertex v of a simple graph G = (V , E) ve-dominates every edge incident to v as well as every edge adjacent to these incident edges. A set D ⊆ V is a total vertex-edge dominating set if every edge of E is ve-dominated by a vertex of D and the subgraph induced by D has no isolated vertex. The total vertex-edge domination problem is to find a total vertex-edge dominating set of minimum cardinality. In this paper, we first show that the total vertex-edge domination problem is NP-complete for chordal graphs. Then we provide a linear-time algorithm for this problem in trees. Moreover, we show that the minimum total vertex-edge domination problem cannot be approximated within (1 −) ln | V | for any > 0 unless NP ⊆ DTIME (| V | O (log log | V |) ). Finally, we prove that the minimum total vertex-edge domination problem is APX-complete for bounded-degree graphs. [ABSTRACT FROM AUTHOR]

Let G be a plane graph. Two edges of G are facially adjacent if they are consecutive on the boundary walk of a face of G. A facial edge coloring of G is an edge coloring such that any two facially adjacent edges receive different colors. A facial graceful k-coloring of G is a proper vertex coloring c : V (G) → {1,2,...,k} such that the induced edge coloring c' : E (G) → {1, 2,...,k -- 1} defined by c'(uv) = |c(u) -- c(v)| is a facial edge coloring. The minimum integer k for which G has a facial graceful k-coloring is denoted by Xfg(G). In this paper we prove that Xfg(G) ≤ 14 for every plane graph G and Xfg (H) ≤ 9 for every outerplane graph H. Moreover, we give exact bounds for cacti and trees. [ABSTRACT FROM AUTHOR]

Summary: We define an extension of parity from the integers to the rational numbers. Three parity classes are found—even, odd, and "none". Using the 2-adic valuation, we partition the rationals into subgroups with a rich algebraic structure. The natural density provides a means of distinguishing the sizes of countably infinite sets. The Calkin-Wilf tree has a remarkably simple parity pattern, with the sequence "odd/none/even" repeating indefinitely. This pattern means that the three parity classes have equal natural density in the rationals. A similar result holds for the Stern-Brocot tree. [ABSTRACT FROM AUTHOR]

Ruziman HH, Mohti A, Yo NESC, Pardi F. 2024. Comparative assessment of carbon dioxide (CO2) absorption capacities in Koompassia malaccensis and Hopea nervosa in Tekam Forest Reserve, Pahang, Malaysia. Nusantara Bioscience 16: 185-191. Trees, the dominant life form in forests, are essential in the functioning of the terrestrial biosphere, especially for the carbon cycle of the ecosystem. This study aims to assess CO2 absorption by two forest production species: Koompassia malaccensis Maingay and Hopea nervosa King. The experiment was carried out in an acrylic box, and the variation of carbon dioxide concentration, humidity, light, and temperature was measured using a Carbon Dioxide, Light, Temperature, and Humidity (CLTM) sensor. The experiment was conducted in an open area from 7:30 am to 6:30 am the next day (23 hours). The results showed that H. nervosa absorbed more CO2 (71.13 ppm/hour) than K. malaccensis (51.54 ppm/hour), thus promoting its ability to address climate change in the microenvironment. As for the relationship between carbon dioxide absorption and photosynthesis variables, both species show a positive correlation between CO2 absorption and humidity. In contrast, light and temperature were very weakly correlated to CO2. Therefore, it was identified that H. nervosa (Dipterocarpaceae) and K. malaccensis (Fabaceae) are tree species with high CO2 absorption capacity and thus can be considered suitable trees for replanting, especially in light of carbon mitigation initiatives. [ABSTRACT FROM AUTHOR]

We study two families of lattices whose number of elements are given by the numbers in even (respectively odd) positions in the Fibonacci sequence. The even Fibonacci lattice arises as the lattice of simple elements of a Garside monoid partially ordered by left-divisibility, and the odd Fibonacci lattice is an order ideal in the even one. We give a combinatorial proof of the lattice property, relying on a description of words for the Garside element in terms of Schröder trees, and on a recursive description of the even Fibonacci lattice. This yields an explicit formula to calculate meets and joins in the lattice. As a byproduct we also obtain that the number of words for the Garside element is given by a little Schröder number. [ABSTRACT FROM AUTHOR]

We generalise various theorems for finding indiscernible trees and arrays to positive logic: based on an existing modelling theorem for s-trees, we prove modelling theorems for str-trees, str 0 -trees (the reduct of str-trees that forgets the length comparison relation) and arrays. In doing so, we prove stronger versions for basing—rather than locally basing or EM-basing—str-trees on s-trees and str 0 -trees on str-trees. As an application we show that a thick positive theory has k- TP 2 iff it has 2- TP 2 [ABSTRACT FROM AUTHOR]

Given a graph G , consider the family of real symmetric matrices with the property that the pattern of their nonzero off-diagonal entries corresponds to the edges of G. For the past 30 years a central problem has been to determine which spectra are realizable in this matrix class. Using combinatorial methods, we identify a family of graphs and multiplicity lists whose realizable spectra are highly restricted. In particular, we construct trees with multiplicity lists that require a unique spectrum, up to shifting and scaling. This represents the most extreme possible failure of spectral arbitrariness for a multiplicity list, and greatly extends all previously known instances of this phenomenon, in which only single linear constraints on the eigenvalues were observed. [ABSTRACT FROM AUTHOR]

Given a tree T of order n , one can contract any edge and obtain a new tree T ⁎ of order n − 1. In 1983, Jamison made a conjecture that the mean subtree order, i.e., the average order of all subtrees, decreases at least 1 3 in contracting an edge of a tree. In 2023, Luo, Xu, Wagner and Wang proved the case when the edge to be contracted is a pendant edge. In this article, we prove that the conjecture is true in general. [ABSTRACT FROM AUTHOR]

Traditional LSM-tree-based key-value storage systems face significant read amplification issues due to the multi-level structure of LSM-tree, the unordered SSTable files in Level 0, and the lack of an in-memory index structure for key-value pairs. We observed that, under the influence of workloads with locality features, key-value pairs exhibit a range-specific access intensity. Addressing the three reasons for LSM-tree read amplification, we have utilized the range-specific access intensity of workload to propose a multi-tree structure consisting of a B+ tree, a single-level hot tree, and an LSM-tree with partition-based Level 0. This aims to enhance the read performance of LSM-tree-based key-value storage systems. We designed the prototype, MTDB, based on LevelDB. The experimental results show that MTDB's read performance is 1.62× to 2.02× that of LevelDB, and it approaches or exceeds the read performance of KVell and Bourbon while reducing memory overhead by 58.85%–86%. [ABSTRACT FROM AUTHOR]

Let k ≥ 2 be an integer. A tree T is called a k-tree if d T (v) ≤ k for each v ∈ V (T) ; that is, the maximum degree of a k-tree is at most k. A k-tree T is a spanning k-tree if T is a spanning subgraph of a connected graph G. Let λ 1 (D (G)) denote the distance spectral radius in G, where D(G) denotes the distance matrix of G. In this paper, we verify an upper bound for λ 1 (D (G)) in a connected graph G to guarantee the existence of a spanning k-tree in G. [ABSTRACT FROM AUTHOR]

Inspired by the tree fractal structure, a novel hexagonal hierarchical gradient tube with axial variable thickness (HHGAVT) is proposed and its crashworthiness performances are systematically investigated. Results show that when the axial variation coefficient of wall thickness k > 0, the peak crushing force (PCF) of HHGAVT will significantly decrease meanwhile the energy absorption maintains at a high level compared with the referenced structures under the same mass. When k > 0, the PCF and CFE of HHGAVT have absolute advantage compared with the uniform wall thickness tube. The crashworthiness performance can further increase by rational designing the distance factor δ. [ABSTRACT FROM AUTHOR]

Enochs' conjecture asserts that each covering class of modules (over any ring) has to be closed under direct limits. Although various special cases of the conjecture have been verified, the conjecture remains open in its full generality. In this paper, we prove the conjecture for the classes Filt ⁡ (풮) , where 풮 consists of ℵ n -presented modules for some fixed n < ω . In particular, this applies to the left-hand class of any cotorsion pair generated by a class of ℵ n -presented modules. Moreover, we also show that it is consistent with ZFC that Enochs' conjecture holds for all classes of the form Filt ⁡ (풮) , where 풮 is a set of modules. This leaves us with no explicit example of a covering class where we cannot prove that Enochs' conjecture holds (possibly under some additional set-theoretic assumption). [ABSTRACT FROM AUTHOR]

In matching models, pairwise-stable outcomes do not generally exist without substantial restrictions on both preferences and the topology of the network of contracts. We address the foundations of matching markets by developing a matching model with a continuum of agents that allows for arbitrary preferences and network structures. We show that pairwise-stable outcomes are guaranteed to exist. When agents can interact with multiple other counterparties, pairwise stability is too weak of a solution concept, and we argue that a refinement of it called tree stability is the most appropriate solution concept in this setting. Our main results show that tree-stable outcomes exist for arbitrary preferences and network topologies. [ABSTRACT FROM AUTHOR]

Canopy lianas differ considerably from trees in terms of wood anatomical structure, and they are suggested to have a demographic advantage—faster growth and higher survival—than trees. However, it remains unclear whether these anatomical and demographic differences persist at the seedling stage, when most liana species are self-standing and, consequently, might be ecologically similar to trees. We assessed how self-standing liana and tree seedlings differ in relation to wood anatomy, growth, and survival. We measured 12 wood traits and monitored seedling growth and survival over one year for 10 self-supporting liana and 10 tree seedling species from three tropical dry forests in Colombia. Liana and tree seedlings exhibited similar survival rates and wood anatomies for traits related to water storage and mechanical support. Yet, for traits associated with water transport, liana seedlings showed greater variability in vessel lumen size, while tree seedlings had higher vessel density. Also, the liana relative growth rate was significantly higher than for trees. These results indicate that, while self-supporting liana and tree seedlings are anatomically similar in terms of mechanical support and water storage—likely contributing to their similar survival rates—liana seedlings have a growth advantage, possibly due to more efficient water transport. These findings suggest that the well-documented anatomical and demographic differences between adult lianas and trees may depend on the liana's developmental stage, with more efficient water transport emerging as a key trait from early stages. [ABSTRACT FROM AUTHOR]

Stem size has the greatest effect on harvester productivity, and stem sizes vary in a forest stand. How these within-stand variations influence harvester productivity is normally not considered in studies or predictions of productivity. This study suggests reasons as to why the current production and/or application of productivity models are prone to bias from stem size variations in a stand, irrespective of whether models were developed from tree-based or stand-based studies. Moreover, it also provides empirical data on the stand stem size variation's influence on stand-based modeling of harvester productivity. Data from 11 harvesters in 347 final fellings and four harvesters in 80 thinnings were used. The mean productivity was 26.7 and 11.0 m3/PMh5 in final felling and thinning, respectively, and the mean stem size explained most of the observed variation. The productivity in final felling decreased with increased levels of stand stem size variation, as well as with increases in the proportion of broadleaf trees in the stand. For thinnings, productivity increased with increases in the proportion of pine trees in the stand, but there was no significant effect of stand stem size variation or other tested factors. The results show that stand stem size variation is a relevant factor to consider when modeling and predicting harvester productivity. [ABSTRACT FROM AUTHOR]

In close‐range remote sensing data collected in a forest, occlusion often causes incomplete or sparse point cloud representations of individual trees, impeding accurate 3D reconstruction of tree architecture and estimation of tree height and volume. Recent developments in deep learning (DL) for 3D data have produced approaches for point cloud completion, which could potentially be applied to trees.We explored the potential of a DL approach to fill gaps in dense point clouds representing the main structures of deciduous trees by applying an existing transformer‐based completion model (PoinTr). Complete point clouds are required as training data, but even dense terrestrial laser scanning (TLS) data sets contain gaps caused by occlusion, making it nearly impossible to acquire such data. We therefore investigated the ability of point cloud completion models trained on a range of synthetic data sets to handle occlusion patterns in real‐world point clouds.Despite the limited data set, we successfully fine‐tuned a general pre‐trained completion model to fill gaps within 1 m3 segments of tree point clouds. Fine‐tuning on synthetic tree data improved the model's ability to complete tree objects compared with training on diverse artificial objects. However, the quality of the predictions was influenced by the level of sophistication of the synthetic data. Our results demonstrate that incorporating even limited real‐world TLS data during training can considerably improve completion results but may introduce additional noise in the predictions.3D point cloud completion with DL has the potential to improve and fill gaps in point clouds of individual trees, facilitating further steps in the processing and analysis of 3D forest data. [ABSTRACT FROM AUTHOR]

A Crimp Force Monitor (CFM) detects defects by whether the crimp force curve of the force sensor exceeds the set tolerance, with the goal of low defect miss rate and false alarm rate. In this study, typical defects made by hand are crimped with an automatic crimping machine together with good products to obtain continuous data of the crimping force curves and to process the data. For the peak and area deviations of the crimp force curve, the good products show skew‐normal distribution, and the defective samples show outliers and different deviation intensities in the positive and negative directions. Furthermore, by manually intervening in the batch production of multiple groups of defects and comparing the defect miss rate and false alarm rate of CFM with different tolerance settings, the peak skewed tolerance, joint loose tolerance and joint skewed tolerance tree settings can meet a low defect miss rate and low false alarm rate at the same time. The group test results verify the skew‐normal distribution of crimping force curve deviation rate and the characteristics of deviation intensities, providing reference for the tolerance setting of CFM in automated terminal crimping production. [ABSTRACT FROM AUTHOR]

Vegetation is a major contributor of terrestrial evaporation and influences subsequent precipitation over land. Studies suggest that forests are crucial for moisture recycling, although the specific contribution of different vegetation to precipitation remains unclear. Using a moisture recycling approach, we investigate the contribution of transpiration from trees and non‐tree vegetation to precipitation over Africa. We use precipitation source regions from simulated atmospheric moisture trajectories, constrained by observation‐based evaporation and precipitation products, and fractional vegetation cover data. Our findings show that trees provide a higher flux to precipitation (∼777 mm year−1) than non‐tree vegetation (∼342 mm year−1). However, considering the smaller spatial extent of trees compared to non‐tree vegetation, precipitation in most watersheds effectively depends more on the latter. Overall, non‐tree vegetation appears equally important as trees in terms of volumetric contributions to precipitation, and deserves attention in further research, considering ongoing land use changes that affect the continental water cycle. Plain Language Summary: A large part of rainfall on Earth derives from evaporation from land. This process, referred to as terrestrial moisture recycling, is controlled for a large part by vegetation cover. Different classes of vegetation cover use water differently, but it is unclear how they contribute to moisture recycling (and thus precipitation) over land. In this study, we estimate the contribution of trees and other, non‐tree vegetation to precipitation over the African continent. We use major watersheds, and track back the source regions of rainfall. We find that overall, trees contribute relatively more to precipitation compared to non‐tree vegetation. However, due to the extensive coverage of other vegetation classes (such as grass‐ and shrublands), many regions depend on non‐tree vegetation for rainfall. Ongoing land use and land cover (LULC) changes may disturb terrestrial moisture recycling patterns. The findings of this study emphasize that the impacts of all LULC changes, including non‐tree vegetation, on the water cycle should be considered and further researched. Key Points: We provide a first estimate of the contribution of transpiration from trees and non‐tree vegetation to precipitation over major African watershedsOn average, trees contribute more to continental precipitation (777 mm year−1) compared to non‐tree vegetation (342 mm year−1)Considering the extent of non‐tree vegetation, most watersheds depend mostly on non‐tree transpiration for precipitation throughout the year [ABSTRACT FROM AUTHOR]

Given a graph G , let S and T be two disjoint vertex subsets of equal size k in G. A many-to-many k -disjoint path cover of G joining S and T is a set of k vertex-disjoint paths between S and T that altogether cover every vertex of the graph. It is said to be paired if each vertex of S must be joined to a designated vertex of T , or unpaired otherwise. Let Γ n be a Cayley graph generated by a transposition tree with bipartition V 0 and V 1. Let S ⊆ V 0 and T ⊆ V 1 be two vertex subsets of equal size two. It is shown in this paper that Γ n has an unpaired many-to-many two-disjoint path cover joining S and T with at most n − 4 faulty edges, where n ≥ 4. The result is optimal with respect to the degree of Γ n. As applications, the edge fault-tolerant two-disjoint path covers for the star network, bubble-sort network and modified bubble-sort network are derived. [ABSTRACT FROM AUTHOR]

In this paper, we delve into the investigation of locating broadcast 2-centers of a tree T under the postal model. The problem asks to deploy two broadcast centers so that the maximum communication time from the centers to their corresponding vertices is minimized. The broadcast 2-center problem explored in this study is essentially an extension of the classical 2-center problem. To efficiently address this challenge, we employ the binary search method, which enables us to present a highly effective O (n log n) -time algorithm for solving this problem. [ABSTRACT FROM AUTHOR]

Given a rooted tree T with vertices u 1 , u 2 , ... , u n , the level matrix L (T) of T is the n × n matrix for which the (i , j) -th entry is the absolute difference of the distances from the root to v i and v j. This matrix was implicitly introduced by Balaji and Mahmoud (2017) as a way to capture the overall balance of a random class of rooted trees. In this paper, we present various bounds on the eigenvalues of L (T) in terms of other tree parameters, and also determine the extremal structures among trees with a given order. Moreover, we establish bounds on the multiplicity of any eigenvalue in the level spectrum and show that the bounds are best possible. Furthermore, we provide evidence that the level spectrum can characterise some trees. In particular, we provide an affirmative answer to a very recent conjecture on the level energy (sum of absolute values of eigenvalues). [ABSTRACT FROM AUTHOR]

A mobile agent, which is an autonomous device navigating in a graph, has to explore a given graph by visiting all of its nodes. We adopt the (arguably) weakest possible model of such a device: a deterministic memoryless automaton (DMA), i.e., a deterministic automaton with a single state. As expected, such a weak machine is incapable of exploring many graphs without marking nodes. Hence we allow the agent to use identical movable pebbles that can be dropped on nodes or picked from them. It turns out that this marking capability significantly enhances the exploration power of the agent. Our goal is to study how the availability of pebbles impacts the class of graphs that a DMA can explore. We first concentrate on finite graphs and show that any finite tree can be explored by a DMA without pebbles but there exist (small) finite graphs that cannot be explored by a DMA without pebbles. Then we turn attention to infinite graphs and fully characterize the class of infinite trees that can be explored by a DMA without pebbles. We also define a large class of infinite trees that can be explored by a DMA with finitely many pebbles. It turns out that many of these trees cannot be explored by a DMA without pebbles. On the other hand, we show a large class of infinite trees that cannot be explored by a DMA with finitely many pebbles. Thus, availability of pebbles yields a strict hierarchy of difficulty of exploration of infinite graphs by a DMA, and this hierarchy is strict even for the class of infinite trees: some trees can be explored without pebbles, some trees can be explored with finitely many pebbles but not without pebbles, and some trees require infinitely many pebbles. Finally, we consider exploration by a DMA with infinitely many pebbles. It turns out that all infinite trees can be explored by a DMA with infinitely many pebbles. By contrast, we construct infinite graphs that cannot be explored by any DMA, even with infinitely many pebbles. [ABSTRACT FROM AUTHOR]

With the upgrade of aircraft and the increasingly harsh service environment, it is urgent to develop high-performance thermal structural materials. In this study, inspired by foliar and root water uptake of trees, we propose a one-step facile method to achieve an autonomous gradient in C/C–ZrC–SiC sharp leading edge composites. The gradual increase of SiC content from top to bottom is beneficial to improve the heat transfer capacity of the composites. After oxyacetylene ablation for 60 s, the mass and linear ablation rates of the samples with gradient structure are 0.83 mg/s and 0.5 μm/s, 35 % and 83 % lower than conventional samples. The composites with gradient structure of ZrC and SiC are favorable to the formation of a compact and smooth ZrO 2 oxide protective layer, which not only protects the composites from further penetration of O 2 , but also resists the mechanical denudation. The novel gradient structure composites with enhanced ablation resistance show a bright application prospect in next-generation thermal protection systems. [ABSTRACT FROM AUTHOR]

A combinatorial algorithm to locate the Maximum Empty Rectangle (MER) inside a given set L of non-intersecting horizontal and vertical line segments is presented in this paper. The MER is the maximum area rectangle such that no line segment lies in part or in full within the rectangle. The proposed algorithm uses the projection lists and line sweep technique 풪(knlog n), where n is the cardinality of the set L, and k is the maximum number of candidate rectangles for a line segment. Projection list is the projection of the line segments on X and Y axes. [ABSTRACT FROM AUTHOR]

The generalized k-connectivity of a graph G, denoted by κk(G), is the minimum number of internally edge disjoint S-trees for any S ⊆ V (G) with |S| = k. The generalized k-connectivity of a graph is a natural extension of the classical connectivity and can be served as an essential parameter for measuring reliability and fault tolerance of the network. Hierarchical interconnection networks (HIN’s) are very important in applications related to the modern interconnection networks since they posses many desirable properties. In this paper, we firstly introduce a family of regular networks HGn that can be obtained from Gn1 ∪ G n2 ∪⋯ ∪ G nt by adding a matching, where Gni and Gnj are vertex-disjoint subgraphs and each Gni is isomorphic to a given graph Gn (1 ≤ i < j ≤ t). Then we determine the generalized 3-connectivity of HGn. As applications of the main result, the generalized 3-connectivity of some HIN’s, such as the hierarchical star network HSn, the hierarchical cubic network HCNn and the hierarchical folded hypercube HFQn, can be determined immediately. [ABSTRACT FROM AUTHOR]

Tillandsia recurvata is an epiphytic plant commonly found in tropical regions and colonizes tree trunks, fences, and power wires. This plant plays an important role in interacting with trees, sharing microorganisms, and performing specific functions in the process of tree colonization. The objective of this study was to evaluate and compare the microbiomes of T. recurvata collected from two different locations (trees and fences) and two plant tissues (leaves and roots). The hypothesis of this study was that the microbiome of T. recurvata is composed of microorganisms that would provide nutritional support to compensate for the lack of nutrients in a particular growth support. The results showed significant differences in microbial diversity between trees and fences, with trees exhibiting higher richness and more complex microbial networks. Proteobacteria was the most prevalent bacterial phylum, with Actinobacteria and Sphingomonas also playing key roles in nitrogen fixation and plant growth. Fungal communities were similar across locations, with Ascomycota and Basidiomycota being predominant, but Paraconiothyrium and Nigrospora showed significant differences in abundance between trees and fences. Functional analysis indicated similar metabolic profiles across leaf and root samples, with key functions for T. recurvata including carbohydrate and amino acid metabolism, stress control, and biofertilization. [ABSTRACT FROM AUTHOR]