Metal-organic frameworks (MOFs) derived carbon-based composites exhibit great potential in the fields of electromagnetic wave (EMW) absorption. However, which kind of MOFs derivative structure has ...better electromagnetic wave absorption is an urgent problem to be addressed. Herein, caterpillar-like hierarchically structured Co/MnO/CNTs was successfully prepared by pyrolysis of core-shell manganese dioxide and zeolitic imidazolate framework template. The material shows excellent EMW absorption performance in different frequencies range based on the hierarchical structure. Owing to the unique distribution of carbon nanotubes on the caterpillar-like hierarchical structure, the generated multi heterogeneous interfaces and local conductive network are beneficial to interfacial polarization, conduction loss, matched impedance as well as multiple scattering. The composite composites present outstanding EMW absorption achieved with effective absorption bandwidth covering from 13.52 GHz to 18 GHz with thickness of only 1.32 mm. Moreover, the composite also demonstrates a microwave absorption with the qualified frequency bandwidth of 5.36 GHz, and a strong reflection loss of −58.0 dB with a low filling amount of 35%. The result provides a new approach for developing EMW absorbing materials with hierarchical structure.
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•The caterpillar-like hierarchical structure composed of carbon nanotubes was prepared.•The composites have wide microwave absorption bandwidth and strong reflection loss.•The hierarchical material has the advantage in broadband impedance matching design.
On caterpillar factors in graphs Bujtás, Csilla; Jendroľ, Stanislav; Tuza, Zsolt
Theoretical computer science,
12/2020, Volume:
846
Journal Article
Peer reviewed
Open access
A caterpillar is either a K2 or a tree on at least 3 vertices such that deleting its leaves we obtain a path of order at least 1. Given a simple undirected graph G=(V,E), a caterpillar factor of G is ...a set of caterpillar subgraphs of G such that each vertex v∈V belongs to exactly one of them. A caterpillar factor F is internally even if every vertex of degree degF(v)≥2 has an even degree; F is odd if degF(v) is odd for every v∈V(G). We present a linear-time algorithm that decides whether a tree admits an internally even caterpillar factor and, on the other hand, we prove that the decision problem is NP-complete on the class of planar bipartite graphs. For the odd caterpillar factor problem, we obtain similar results. It can be decided in linear time over the class of trees, but the problem is NP-complete on the class of bipartite graphs.
Let m≥1 be an integer and G be a graph with m edges. We say that G has an antimagic orientation if G has an orientation D and a bijection τ:A(D)→{1,…,m} such that no two vertices in D have the same ...vertex-sum under τ, where the vertex-sum of a vertex v in D under τ is the sum of labels of all arcs entering v minus the sum of labels of all arcs leaving v. Hefetz et al. (2010) conjectured that every connected graph admits an antimagic orientation. The conjecture was confirmed for certain classes of graphs such as regular graphs, graphs with minimum degree at least 33, bipartite graphs with no vertex of degree zero or two, and trees including caterpillars and complete k-ary trees. We prove that every subdivided caterpillar admits an antimagic orientation, where a subdivided caterpillar is a subdivision of a caterpillar T such that the edges of T that are not on the central path of T are subdivided the same number of times.
Urbanization can have marked effects on plant and animal populations’ phenology, population size, predator–prey, interactions and reproductive success. These aspects are rarely studied simultaneously ...in a single system, and some are rarely investigated, e.g., how insect phenology responds to urban development. Here, we study a tri-trophic system of trees, phytophagous insects (caterpillars), and insectivorous birds (Great Tits) to assess how urbanization influences (1) the phenology of each component of this system, (2) insect abundance, and (3) avian reproductive success. We use data from two urban and two forest sites in Hungary, central Europe, collected over four consecutive years. Despite a trend of earlier leaf emergence in urban sites, there is no evidence for an earlier peak in caterpillar abundance. Thus, contrary to the frequently stated prediction in the literature, the earlier breeding of urban bird populations is not associated with an earlier peak in caterpillar availability. Despite this the seasonal dynamics of caterpillar biomass exhibited striking differences between habitat types with a single clear peak in forests, and several much smaller peaks in urban sites. Caterpillar biomass was higher in forests than urban areas across the entire sampling period, and between 8.5 and 24 times higher during the first brood’s chick-rearing period. This higher biomass was not associated with taller trees in forest sites, or with tree species identity, and occurred despite most of our focal trees being native to the study area. Urban Great Tits laid smaller clutches, experienced more frequent nestling mortality from starvation, reared fewer offspring to fledging age, and their fledglings had lower body mass. Our study strongly indicates that food limitation is responsible for lower avian reproductive success in cities, which is driven by reduced availability of the preferred nestling diet, i.e., caterpillars, rather than phenological shifts in the timing of peak food availability.
Maximizing the mean subtree order Mol, Lucas; Oellermann, Ortrud R.
Journal of graph theory,
August 2019, 2019-08-00, 20190801, Volume:
91, Issue:
4
Journal Article
Peer reviewed
Open access
This article focuses on properties and structures of trees with maximum mean subtree order in a given family; such trees are called optimal in the family. Our main goal is to describe the structure ...of optimal trees in Tn and Cn, the families of all trees and caterpillars, respectively, of order n. We begin by establishing a powerful tool called the Gluing Lemma, which is used to prove several of our main results. In particular, we show that if T is an optimal tree in Tn or Cn for n≥4, then every leaf of T is adjacent to a vertex of degree at least 3. We also use the Gluing Lemma to answer an open question of Jamison and to provide a conceptually simple proof of Jamison's result that the path Pn has minimum mean subtree order among all trees of order n. We prove that if T is optimal in Tn, then the number of leaves in T is O(log2n) and that if T is optimal in Cn, then the number of leaves in T is Θ(log2n). Along the way, we describe the asymptotic structure of optimal trees in several narrower families of trees.
In this paper, we investigate whether the symbolic and ordinary powers of a binomial edge ideal
J
G
are equal. We show that the equality
J
G
t
=
J
G
(
t
)
holds for every
t
≥
1
when
|
Ass
(
J
G
)
|
=
...2
. Moreover, if
G
is a caterpillar tree, then one has the same equality. Finally, we characterize the generalized caterpillar graphs which the equality of symbolic and ordinary powers of
J
G
occurs.
Waterjet propulsions, which exhibit high efficiency, low noise and good anti-cavitation performance, have gradually become the frist choice of power device for amphibious vehicles. In the navigation ...environment, waterjet-hull interaction has effect on the hydrodynamic force of a caterpillar track amphibious vehicle (CTAV). The mathematical model was set up and the rotary hydrodynamic performance was predicted using a realizable k-ε model. After an analysis of mesh independence and a verification of the calculation model's reliability, the hydrodynamic performance of three vehicle structures under forced trim angles were simulated when 0.418 < Fr < 1.462. Results suggest that for the same motion parameters, the installation of inlet duct and impeller has considerable effects on the vehicle resistance and motion stability. Compared with the bare vehicle, the maximum difference of resistance value at Fr = 1.220 and θ = 5° is 7% and 9.6%, and the maximum difference of longitudinal resilience moment at Fr = 0.953 and θ = 5° is 38.4% and 25.2% respectively. Furthermore, the vortex in the flow separation zone was obviously offset due to the impeller operation, which affects the outlet flow field. This research has theoretical implications for understanding the waterjet-vehicle interaction, as well as providing insights for studies of vehicle-machine-waterjet coordination.
•1.The effect of inlet duct and impeller on the hydrodynamic performance of caterpillar track amphibious vehicle is investigated.•2.The effect of sailing speed and trim angle on the vehicle motion is analyzed.•3.The resistance and hydrodynamic characteristics of three vehicle body structures are compared.•4.Towing test is used to verify the reliability of numerical method.
Optimizing the layout of sparse planar arrays constrained by minimum element spacing to reduce the peak side lobe level (PSLL) is a difficult and challenging task in engineering applications. Here, a ...new sparse array design method is proposed under the constraints of aperture size, the number of array elements, and minimum spacing between elements. The approach is based on a new element mutation method which is proposed for mutating the position of any element within the aperture without changing the position of other elements. Because a mutating element can be thought of as being placed inside the board like a black/white stone in Go or crawling somewhere nearby like a caterpillar, we call it Go-Caterpillar-mutation (GCM). Based on GCM, a stochastic optimization algorithm (GCM-OA) is proposed to optimize the layout of sparse planar arrays. Several examples demonstrate the robustness and rapidity of GCM-OA in reducing PSLL by adjusting the array element positions under various constraints.
We DNA barcoded 2,597 parasitoid wasps belonging to 6 microgastrine braconid genera reared from parapatric tropical dry forest, cloud forest, and rain forest in Area de Conservación Guanacaste (ACG) ...in northwestern Costa Rica and combined these data with records of caterpillar hosts and morphological analyses. We asked whether barcoding and morphology discover the same provisional species and whether the biological entities revealed by our analysis are congruent with wasp host specificity. Morphological analysis revealed 171 provisional species, but barcoding exposed an additional 142 provisional species; 95% of the total is likely to be undescribed. These 313 provisional species are extraordinarily host specific; more than 90% attack only 1 or 2 species of caterpillars out of more than 3,500 species sampled. The most extreme case of overlooked diversity is the morphospecies Apanteles leucostigmus. This minute black wasp with a distinctive white wing stigma was thought to parasitize 32 species of ACG hesperiid caterpillars, but barcoding revealed 36 provisional species, each attacking one or a very few closely related species of caterpillars. When host records and/or within-ACG distributions suggested that DNA barcoding had missed a species-pair, or when provisional species were separated only by slight differences in their barcodes, we examined nuclear sequences to test hypotheses of presumptive species boundaries and to further probe host specificity. Our iterative process of combining morphological analysis, ecology, and DNA barcoding and reiteratively using specimens maintained in permanent collections has resulted in a much more fine-scaled understanding of parasitoid diversity and host specificity than any one of these elements could have produced on its own.
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