Non-Hermitian systems exhibit striking exceptions from the paradigmatic bulk-boundary correspondence, including the failure of bulk Bloch band invariants in predicting boundary states and the ...(dis)appearance of boundary states at parameter values far from those corresponding to gap closings in periodic systems without boundaries. Here, we provide a comprehensive framework to unravel this disparity based on the notion of biorthogonal quantum mechanics: While the properties of the left and right eigenstates corresponding to boundary modes are individually decoupled from the bulk physics in non-Hermitian systems, their combined biorthogonal density penetrates the bulk precisely when phase transitions occur. This leads to generalized bulk-boundary correspondence and a quantized biorthogonal polarization that is formulated directly in systems with open boundaries. We illustrate our general insights by deriving the phase diagram for several microscopic open boundary models, including exactly solvable non-Hermitian extensions of the Su-Schrieffer-Heeger model and Chern insulators.
•We reviewed biochar effect on soil density and water retention parameters.•Biochar significantly increased water content at field capacity for the coarse-textured soils.•Improvement in plant ...available water content decreased with soil fineness.•‘Biochar carbon added’ parameter is proposed for robust comparison of different biochar-soil studies.
Biochar is widely suggested as a soil amendment to improve soil physical properties for crop production. However, the heterogeneity between experiments in terms of biochar characteristics, experimental conditions and soil properties makes it difficult to compare and extrapolate results from different studies. We conducted a statistical meta-analysis of literature published between 2010 and 2019, and quantified biochar’s impacts on soil bulk density (BD) and water retention variables, namely, soil water content held at field capacity (FC), wilting point (WP) and plant available water content (AW). Across all soil textural groups, biochar on average decreased BD by 9%. FC and WP significantly increased for the coarse-textured soils (by 51% and 47%, respectively), and moderately for the medium-textured soils (by 13% and 9%, respectively). For the fine-textured soils, FC remained unchanged (<1%), but WP marginally decreased by 5%. Biochar significantly increased AW in the coarse-textured soils (by 45%) compared to the medium- and fine-textured soils (by 21% and 14%, respectively) suggesting that biochar may have greater benefit on coarse-textured soils. We introduced a novel parameter called ‘biochar carbon added’, estimated from biochar carbon content and the rate of application, which can be useful to make a sound comparison of biochar impacts on soil physical properties reported in different case studies when variable biochar attributes, experimental conditions and soil types have been used. The meta-analysis highlights again the need to provide adequate information on biochar experiments and soil water retention variables to allow better elucidation of the underlying mechanisms of biochar’s impact on soil water retention and more.
A fractional corner anomaly reveals higher-order topology Peterson, Christopher W.; Li, Tianhe; Benalcazar, Wladimir A. ...
Science (American Association for the Advancement of Science),
06/2020, Letnik:
368, Številka:
6495
Journal Article
Recenzirano
Odprti dostop
Topological insulators in the spotlight
In addition to having an insulating interior while at the same time supporting conducting surface states, topological insulators have many other interesting ...properties. Higher-order topological insulating states, where regions of interest are along edges and at corners, have been difficult to identify unambiguously. Peterson
et al.
developed a theoretical framework to help identify and characterize these exotic states, including a new topological marker—the fractional charge density—that can be used to detect topological states of matter when the spectroscopic probe of gapless surface states is not accessible. The agreement between experimental work and theory is encouraging for applicability to other topological platforms.
Science
, this issue p.
1114
A new marker, the concept of fractional corner anomaly, is used as a real-space probe of higher-order topology.
Spectral measurements of boundary-localized topological modes are commonly used to identify topological insulators. For high-order insulators, these modes appear at boundaries of higher codimension, such as the corners of a two-dimensional material. Unfortunately, this spectroscopic approach is only viable if the energies of the topological modes lie within the bulk bandgap, which is not required for many topological crystalline insulators. The key topological feature in these insulators is instead fractional charge density arising from filled bulk bands, but measurements of such charge distributions have not been accessible to date. We experimentally measure boundary-localized fractional charge density in rotationally symmetric two-dimensional metamaterials and find one-fourth and one-third fractionalization. We then introduce a topological indicator that allows for the unambiguous identification of higher-order topology, even without in-gap states, and we demonstrate the associated higher-order bulk-boundary correspondence.
Understanding soil physical properties is essential for soil quality management and sustainable land use. With the growing accumulation of microplastics in soils, a better understanding of the impact ...of microplastics on soil physical properties is crucial to conserve and manage soil quality. This study explored the effects of polyester microfiber (PMF) concentrations (0, 0.1% and 0.3%) on bulk density, porosity, aggregation and hydraulic conductivity of a clayey soil from a field experiment (1 year) and a pot experiment (6 wet-dry cycles). Polyester microfibers significantly increased the volume of >30 μm pores and reduced the volume of <30 μm pores compared to the control treatment. However, there were no detectable changes in the soil bulk density and saturated hydraulic conductivity between the PMF treatments and the control treatment. Interestingly, we observed that polyester microfibers significantly increased the contents of water stable large macroaggregates (>2 mm) in the 0.3% PMF (44%) and 0.1% PMF (39%) treatments compared to the control treatment (31%) in the pot experiment, but this was not true in the field experiment. The efficient interaction between polyester microfibers and fine soil particles and the frequent wet-dry cycles enhanced the formation and stability of macro-aggregates induced by polyester microfibers in the pot experiment. Overall, our results provide valuable evidence for microplastic influences on soil physical properties. Because microplastics are long-term anthropogenic contaminants, it is necessary to further study the impacts of microplastics on soil quality for terrestrial ecosystem sustainability.
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•The changes of soil physical properties induced by polyester microfiber were observed from a field and a pot experiment.•Polyester microfibers did not alter soil bulk density and saturated hydraulic conductivity.•Polyester microfibers reduced the volume of <30 μm pores as increased the volume of >30 μm pores.•Polyester microfibers increased soil aggregation in the pot experiment but not in the field experiment.
Resilient poly(urethane urea) aerogels are synthesized from aromatic diisocyanates, aromatic diamines, aliphatic polyols, and a trifunctional amine crosslinker. Polyurethane prepolymers are ...synthesized with isocyanate end groups by reacting the polyol with 4,4′-diphenylmethane diisocyanate in anhydrous N-methyl-2-pyrrolidone (NMP). The isocyanate-capped polyurethane segments are reacted with 4,4′-oxydianiline to obtain isocyanate end-capped poly(urethane urea) copolymers which are then crosslinked using 1,3,5 triaminophenoxylbenzene (TAB) to obtain the gel networks. The gel networks are tailored by the choice of the polyol and by varying the crosslink density. The gels are dried under supercritical condition after exchanging NMP with acetone and acetone with liquid carbon dioxide. The resulting aerogels show density between 0.20 and 0.35 g/cm3, porosity between 71 and 85%, and surface area between 47 and 163 m2/g. The data suggest that the polyol weight fraction can be used as a parameter to control the shrinkage of aerogel specimens. The shrinkage data also correlate well with the extent of hydrogen bonding involving urea and urethane groups. A reduction of the amount of TAB leads to reduction of the extent of urea hydrogen bonding and an increase of urethane hydrogen bonding. These materials exhibit an onset of thermal decomposition at about 300 °C and offer compressive moduli between 12 and 52 MPa. The compressive modulus shows strong dependence on aerogel density.
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•Urethane hydrogen bonding selectivity leads to soft, low-modulus poly(urethane urea) aerogels•Polyol weight fraction is used to control the shrinkage of flexible polyurea-co-polyurethane aerogels•A triamine crosslinker is used to selectively engage urea or urethane segments in hydrogen bonding.
We present examples of root plasticity in response to soil compaction and discuss their role in plant performance. Subsequently, we propose a plastic ideotype for soil compaction tolerance.
Abstract
...Soil compaction is a serious global problem, and is a major cause of inadequate rooting and poor yield in crops around the world. Root system architecture (RSA) describes the spatial arrangement of root components within the soil and determines the plant’s exploration of the soil. Soil strength restricts root growth and may slow down root system development. RSA plasticity may have an adaptive value, providing environmental tolerance to soil compaction. However, it is challenging to distinguish developmental retardation (apparent plasticity) or responses to severe stress from those root architectural changes that may provide an actual environmental tolerance (adaptive plasticity). In this review, we outline the consequences of soil compaction on the rooting environment and extensively review the various root responses reported in the literature. Finally, we discuss which responses enhance root exploration capabilities in tolerant genotypes, and to what extent these responses might be useful for breeding. We conclude that RSA plasticity in response to soil compaction is complex and can be targeted in breeding to increase the performance of crops under specific agronomical conditions.
The properties of particleboards and the course of their manufacturing process depend on the characteristics of wood particles, their degree of fineness, geometry, and moisture content. This research ...work aims to investigate the physical properties of wood particles used in the particleboard production in dependence on their moisture content. Two types of particles currently used in the production of three-layer particleboards, i.e., microparticles (MP) for the outer layers of particleboards and particles for the core layers (PCL), were used in the study. The particles with a moisture content of 0.55%, 3.5%, 7%, 10%, 15%, and 20% were tested for their poured bulk density (ρp), tapped bulk density (ρt), compression ratio (
), angle of repose (αR), and slippery angle of repose (αs). It was found that irrespective of the fineness of the particles, an increase in their moisture content caused an increase in the angle of repose and slippery angle of repose and an increase in poured and tapped bulk density, while for PCL, the biggest changes in bulk density occurred in the range up to 15% of moisture content, and for MP in the range above 7% of moisture content, respectively. An increase in the moisture content of PCL in the range studied results in a significant increase in the compression ratio from 47.1% to 66.7%. The compression ratio of MP increases only up to 15% of their moisture content-a change of value from 47.1% to 58.7%.
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