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Summary In this article, we study parameter estimation problems for fractional commensurate Hammerstein systems utilizing the conformable fractional derivative. Two algorithms are investigated: first, the Poisson moment functions (PMF) method, aiming to transfer the fractional derivative of the measurement signal into PMF using the fractional Laplace transform and convolution; second, a proposed new instrumental variable algorithm, which is based on the conformable fractional derivative. Both algorithms have been analyzed and shown to be consistent. A comprehensive complexity analysis is provided for each algorithm. Furthermore, a kind of special time‐varying systems are discussed under the conformable fractional derivative. Finally, an example is given to illustrate the effectiveness of the proposed algorithms. [ABSTRACT FROM AUTHOR]

The pursuit of fabricating high‐performance graphene films has aroused considerable attention due to their potential for practical applications. However, developing both stretchable and tough graphene films remains a formidable challenge. To address this issue, we herein introduce mechanical bond to comprehensively improve the mechanical properties of graphene films, utilizing [2]rotaxane as the bridging unit. Under external force, the [2]rotaxane cross‐link undergoes intramolecular motion, releasing hidden chain and increasing the interlayer slip distance between graphene nanosheets. Compared with graphene films without [2]rotaxane cross‐linking, the presence of mechanical bond not only boosted the strength of graphene films (247.3 vs 74.8 MPa) but also markedly promoted the tensile strain (23.6 vs 10.2 %) and toughness (23.9 vs 4.0 MJ/m3). Notably, the achieved tensile strain sets a record high and the toughness surpasses most reported results, rendering the graphene films suitable for applications as flexible electrodes. Even when the films were stretched within a 20 % strain and repeatedly bent vertically, the light‐emitting diodes maintained an on‐state with little changes in brightness. Additionally, the film electrodes effectively actuated mechanical joints, enabling uninterrupted grasping movements. Therefore, the study holds promise for expanding the application of graphene films and simultaneously inspiring the development of other high‐performance two‐dimensional films. [ABSTRACT FROM AUTHOR]

Loops are prevalent topological structures in cross‐linked polymer networks, resulting from the folding of polymer chains back onto themselves. Traditionally, they have been considered as defects that compromise the mechanical properties of the network, leading to extensive efforts in synthesis to prevent their formation. In this study, we introduce the inclusion of cyclic dibenzo‐24‐crown‐8 (DB24C8) moieties within the polymer network strands to form CCNs, and surprisingly, these loops enhance the mechanical performances of the network, leading to tough elastomers. The toughening effect can be attributed to the unique cyclic structure of DB24C8. The relatively small size and the presence of rigid phenyl rings provide the loops with relatively stable conformations, allowing for substantial energy dissipation upon the application of force. Furthermore, the DB24C8 rings possess a broad range of potential conformations, imparting the materials with exceptional elasticity. The synergistic combination of these two features effectively toughens the materials, resulting in a remarkable 66‐fold increase in toughness compared to the control sample of covalent networks. Moreover, the mechanical properties, particularly the recovery performance of the network, can be effectively tuned by introducing guests to bind with DB24C8, such as potassium ions and secondary ammonium salts. [ABSTRACT FROM AUTHOR]

Inspired by the drawstring structure in daily life, here we report the development of a drawstring‐mimetic supramolecular complex at the molecular scale. This complex consists of a rigid figure‐of‐eight macrocyclic host molecule and a flexible linear guest molecule which could interact through three‐point non‐covalent binding to form a highly selective and efficient host‐guest assembly. The complex not only resembles the drawstring structure, but also mimics the properties of a drawstring with regard to deformations under external forces. The supramolecular drawstring can be utilized as an interlocked crosslinker for poly(methyl acrylate), and the corresponding polymer samples exhibit comprehensive enhancement of macroscopic mechanical performance including stiffness, strength, and toughness. [ABSTRACT FROM AUTHOR]

Simultaneously introducing covalent and supramolecular cross‐links into one system to construct dually cross‐linked networks, has been proved an effective approach to prepare high‐performance materials. However, so far, features and advantages of dually cross‐linked networks compared with those possessing individual covalent or supramolecular cross‐linking points are rarely investigated. Herein, on the basis of comparison between supramolecular polymer network (SPN), covalent polymer network (CPN) and dually cross‐linked polymer network (DPN), we reveal that the dual cross‐linking strategy can endow the DPN with integrated advantages of CPN and SPN. Benefiting from the energy dissipative ability along with the dissociation of host–guest complexes, the DPN shows excellent toughness and ductility similar to the SPN. Meanwhile, the elasticity of covalent cross‐links in the DPN could rise the structural stability to a level comparable to the CPN, exhibiting quick deformation recovery capacity. Moreover, the DPN has the strongest breaking stress and puncture resistance among the three, proving the unique property advantages of dual cross‐linking method. These findings gained from our study further deepen the understanding of dynamic polymeric networks and facilitate the preparation of high‐performance elastomeric materials. [ABSTRACT FROM AUTHOR]

Supramolecular polymer networks (SPNs) demonstrate great potential in the development of smart materials owing to their attractive dynamic properties. However, as they suffer from the inherent weak bonding of most noncovalent cross‐links, it remains a significant challenge to construct SPNs with outstanding mechanical performance. Herein, we exploit the cryptand/paraquat host‐guest recognition motifs as cross‐links to prepare a class of highly strong and tough SPNs. Unlike those supramolecular cross‐links with relatively weak binding abilities, the cryptand‐based host‐guest interactions have a high association constant and steady complexing structure, which effectively stabilizes the network and resists mechanical deformation under external force. Such favorable structural stability endows our SPNs with greatly enhanced mechanical performance, compared with the control‐1 cross‐linked by the weakly complexed crown ether/secondary ammonium salt motif (tensile strength: 21.1±0.5 vs 2.8±0.1 MPa; Young's modulus: 102.6±4.8 vs 2.1±0.3 MPa; toughness: 90.4±2.0 vs 10.8±0.6 MJ m−3). Moreover, our SPNs also retain abundant dynamic properties including good abilities in energy dissipation, reprocessability, and stimuli‐responsiveness. These findings provide novel insights into the preparation of SPNs with enhanced mechanical properties, and promote the development of high‐performance intelligent supramolecular materials. [ABSTRACT FROM AUTHOR]

Dynamic covalent chemistry opens up great opportunities for a sustainable society by producing reprocessable networks of polymers and even thermosets. However, achieving the closed‐loop recycling of polymers with high performance remains a grand challenge. The introduction of aromatic monomers and fluorine into covalent adaptable networks is an attractive method to tackle this challenge. Therefore, we present a facile and universal strategy to focus on the design and applications of polyimine vitrimers containing trifluoromethyl diphenoxybenzene backbones in applications of dynamic covalent polymers. In this study, fluorine‐containing polyimine vitrimer networks (FPIVs) were fabricated, and the results revealed that the FPIVs not only exhibited good self‐healability, malleability and processability without the aid of any catalyst, but also possessed decent mechanical strength, superior toughness and thermal stability. We hope that this work could provide a novel pathway for the design of high‐performance polyimine vitrimers by recycling of plastic wastes. [ABSTRACT FROM AUTHOR]

We report a flux crystal growth of Ba2[(UO2)2Ti2O8] and subsequent structural and spectroscopic studies using multiple techniques. The layered crystal structure, built up with sheets of edge‐sharing dimeric uranyl pentagonal bipyramids and dimeric TiO5 square pyramids with interlayer Ba(II) ions, was revealed by synchrotron single crystal x‐ray diffraction and confirmed with electron diffraction using a transmission electron microscope. The presence of only hexavalent uranium was confirmed by both diffuse reflectance and x‐ray absorption near‐edge structure spectroscopies, consistent with the bond valence sum calculations. Its vibrational modes were revealed by Raman spectroscopy. In addition, its implications as a potential hexavalent uranium waste form for the immobilization of uranium‐rich radioactive wastes were discussed. [ABSTRACT FROM AUTHOR]

Crosslinking plays a crucial role in determining mechanical properties of polymer materials. Although various crosslinks based on covalent or noncovalent bonds have been adopted, it remains an enormous challenge to develop a crosslink which could endow corresponding polymer network with robust yet dynamic properties. Herein, we report a crosslink simultaneously having dynamic property and woven geometry, and the polymer network with woven crosslinks (WPN) could integrate the merits of covalent polymer network (CPN) and supramolecular polymer network (SPN). In specific, the WPN not only exhibits comparable stiffness, strength, elastic recovery, and anti‐fatigue property to those of CPN, but also possesses decent mechanical adaptivity and ductility, similar to those of SPN. Particularly, its toughness and puncture resistance are much superior to those of the others. Besides, the dynamicity of woven crosslink also imparts good performances of self‐healing and processability to WPN. [ABSTRACT FROM AUTHOR]

The previously unattained fabrication of single phase Ln2ZrO5 (Ln = Sm, Eu, Gd, and Tb) compounds via relatively low sintering temperature (1400°C) is achieved in this study using a coprecipitation method. The crystal structures have been investigated by neutron, synchrotron X‐ray powder diffraction, and electron diffraction techniques. While the general long‐range structure may be well described by the defect‐fluorite type structure with Fm3¯$\bar{3}$m symmetry, electron diffraction has highlighted a complex underlying modulated structure that varies between each compound. These compounds have been tested for ion‐irradiation response using in situ 1 MeV krypton ions and transmission electron microscopy characterization. None of the compounds undergo a crystalline to amorphous transition, even holding at 50 K. Both the underlying fluorite and modulated superstructures are little affected by the irradiation. However, some atomic rearrangements are observed in the postirradiated electron diffraction patterns for the Sm2ZrO5 specimen. [ABSTRACT FROM AUTHOR]

Polarisation diversity radar enhances the performance of target detection. Time reversal exploits the multipath effect by adaptively matching propagation channels to improve the signal‐to‐noise ratio (SNR) and realise high detectability. This work combines polarisation diversity and time‐reversal technology to propose a time‐reversal detector suitable for a polarisation array radar. The maximum likelihood estimate is carried out for the time‐varying channel response to solve the channel mismatch problem, which may cause the degradation of time‐reversal performance. In addition, a conventional polarisation detector is developed under the same varying channel scenario to benchmark the time‐reversal detector, and furthermore, the SNR gain of the time‐reversal detector over the conventional detector is derived. Numerical simulations demonstrate the superiority of the time‐reversal detector. Both the polarisation detectors proposed can take advantage of the channel variations to improve the detectability, and the greater the energy brought by the channel changes, the better the detection performance achieved. [ABSTRACT FROM AUTHOR]

Mortise‐and‐tenon joints have been widely used for thousands of years in wooden architectures in virtue of their artistic and functional performance. However, imitation of similar structural and mechanical design philosophy to construct mechanically adaptive materials at the molecular level is a challenge. Herein, we report a mortise‐and‐tenon joint inspired mechanically interlocked network (MIN), in which the [2]rotaxane crosslink not only mimics the joint in structure, but also reproduces its function in modifying mechanical properties of the MIN. Benefiting from the hierarchical energy dissipative ability along with the controllable intramolecular movement of the mechanically interlocked crosslink, the resultant MIN simultaneously exhibits notable mechanical adaptivity and structural stability in a single system, as manifested by decent stiffness, strength, toughness, and deformation recovery capacity. [ABSTRACT FROM AUTHOR]

Multistatic radar has the advantage of spatial diversity, but its detection performance is decreased in dense multipath scattering environments. This problem can be solved by using the time reversal (TR) technique to take advantage of the multipath effect to improve target detection; however, this usually requires a stationary channel response that is difficult to achieve in practice. This article studies a TR detection algorithm for a multistatic radar system in a varying multipath channel environment. We establish a varying channel response model and derive a time reversal likelihood ratio test (TR–LRT) detector to utilise the characteristics of multiple paths when the multipath environment is changing during the detection process. We use Monte Carlo simulations and theoretical analysis to show the superior performance of the proposed TR detector compared with a conventional detector. Our proposed TR–LRT detector shows good robustness to environmental variations. Simulation results show that better detection results are achieved in a more severe multipath scattering environment. [ABSTRACT FROM AUTHOR]

The "United Nations 2030 Agenda for Sustainable Development" adopted in 2015 covers 17 Sustainable Development Goals (SDGs). Fire is a common form of disaster and has a wide range of impacts on climate, biogeochemical cycle and human health, highly related to the SDGs. Satellite remote sensing technology provides an effective way for the dynamic monitoring of global burned area (BA). However, the existing global BA products are mainly at low and medium spatial resolution, which is difficult for detecting small fires, and also has large errors in calculating area of burned land. Based on Landsat 8 surface reflectance data and Google Earth Engine platform, a novel multi‐year (from the starting year of SDGs [2015] to the nearest year [2019]) 30 m resolution global BA products were generated. Based on these products, spatial distribution, influencing factors and change characteristics of BA were analyzed. The results show that from 2015 to 2019 the total area of BA in the world was 365.27, 368.56, 374.56, 345.55, and 363.09 × 106 ha. From 2015 to 2019, the total area of global BA was relatively stable, however there were significant differences among various continents and regions. During the study period, BA in the Amazon and Australia changed dramatically. The huge Amazon fire in 2019 caused a reduction of 4.67 × 106 ha of vegetated area in the Amazon basin, an increase in BA of 119.25% compared with 2018. In 2019, BA on the eastern and southeastern coasts of Australia increased abnormally. The possible reasons for these changes were comprehensively discussed and analyzed. Plain Language Summary: Fire is a common form of disaster, and has a wide range of impacts on climate, surface vegetation and human health. The "United Nations 2030 Agenda for Sustainable Development" has been implemented for 5 years, and fire is highly related to the Sustainable Development Goals, for which global information on fire effects is a key variable. In order to carry out high‐precision and fine monitoring of the spatial distribution and changes of fire within the past 5 years, in this study 30 m global burned area (BA) products were generated and analyzed from 2015 to 2019. During the study period, we found that the total area of global BA was relatively stable, however there were significant differences among various continents and regions. For example, the huge Amazon fire in 2019 caused a reduction of 4.67 × 106 ha of vegetated area in the Amazon basin, an increase in BA of 119.25% compared with 2018. In 2019, BA on the eastern and southeastern coasts of Australia increased abnormally. The possible reasons for these changes were comprehensively discussed and analyzed. Key Points: Novel multi‐year (from 2015 to 2019) 30 m resolution global burned area products were generated and acted as an Sustainable Development Goals indicatorSpatial distribution, influencing factors and change characteristics of burned areas were discussed from different perspectivesBurned areas in the Amazon and Australia changed dramatically. The possible reasons for these changes were comprehensively discussed [ABSTRACT FROM AUTHOR]

A pyrochlore‐rich multiphase ceramic waste form was prepared by the alkoxide‐route and consolidated by sintering in air. Cerium (Ce) was used as a surrogate for plutonium (Pu), which was found in both the major pyrochlore and minor perovskite phases, but not the minor rutile phase. A synchrotron‐based fluorescence X‐ray absorption near‐edge spectroscopy (XANES) imaging technique was employed to determine the Ce oxidation state in each of the two Ce‐containing phases. It was shown that the major pyrochlore phase contains only tetravalent Ce, whereas the minor perovskite phase incorporates exclusively trivalent Ce. The effect of sintering atmosphere was also investigated, which revealed a very different phase assemblage when sintered in argon (Ar). A major perovskite phase was produced under Ar with a minor zirconolite‐4M phase, both containing trivalent Ce. The composition of the minor rutile phase remained the same whether it was sintered in air or Ar. The results demonstrate the importance of controlling the oxidation state of multivalent waste ions in the design of ceramic waste forms. [ABSTRACT FROM AUTHOR]

Pyrochlore glass‐ceramics (GCs) have been investigated with samples fabricated via both sintering and hot isostatic pressing (HIPing) of a mixed oxide precursor. It has been demonstrated that sintering at 1200°C in air is necessary to obtain well‐crystallized pyrochlore crystals in a sodium aluminoborosilicate glass through a one‐step controlled cooling. The crystallization, structure, and microstructure of Eu2Ti2O7 pyrochlore as the major phases in residual glass were confirmed with X‐ray diffraction (XRD), scanning electron microscopy‐energy dispersive spectroscopy, transmission electron microscopy, and Raman spectroscopy. The structures of major Eu2Ti2O7 pyrochlore and minor [Eu4.67O(SiO4)3] apatite in both sintered and HIPed samples were refined using synchrotron XRD data. While the processing atmosphere did not appear to affect the cell parameter of the main pyrochlore phase, very small volume expansion (~0.3%) was observed for the minor apatite phase in the HIPed sample. In addition, static leaching of the HIPed sample confirmed that pyrochlore GCs are chemically durable. Overall, pyrochlore GCs prepared via both sintering and HIPing with the Eu partitioning factor of ~23 between ceramics and the residual glass are suitable waste forms for minor actinides with processing chemicals. [ABSTRACT FROM AUTHOR]

Nature has engineered delicate synergistic covalent and supramolecular polymers (CSPs) to achieve advanced life functions, such as the thin filaments that assist in muscle contraction. Constructing artificial synergistic CSP materials with bioinspired mechanically adaptive features, however, represents a challenging goal. Here, we report an artificial CSP system to illustrate the integration of a covalent polymer (CP) and a supramolecular polymer (SP) in a synergistic fashion, along with the emergence of notable mechanical and dynamic properties which are unattainable when the two polymers are formed individually. The synergistic effect relies on the peculiar network structures of the SP and CPs, which endow the resultant CSPs with overall improved mechanical performance in terms of the stiffness, strength, stretchability, toughness, and elastic recovery. Moreover, the dynamic properties of the SP, including self‐healing, stimuli‐responsiveness, and reprocessing, are also retained in the CSPs, thus leading to their application as programmable and tunable materials. [ABSTRACT FROM AUTHOR]

Uranium brannerite phases with terbium(III) or dysprosium(III) ions have been investigated. The precursors with molar ratio of 0.5:0.5:2 (Ln: U: Ti with Ln = Tb or Dy) were prepared and calcined at 750°C in argon. Sintering the pelletized samples in argon at 1200°C led to the formation of pyrochlore phases with TiO2 rutile and U‐rich oxides while sintering in air led to the formation of brannerite phases with the nominal composition close to Ln0.5U0.5Ti2O6 together with trace amounts of TiO2 rutile and LnUO4. Incorporating an excess of TiO2 (20 wt%) and sintering at higher temperature (1300°C) resulted in no obvious change to the phase equilibrium. As designed, pentavalent uranium has been proven to be dominant in these brannerite phases with diffuse reflectance spectroscopy. The relationships between the cell parameters and the ionic radii of the A‐site cations have been explored and rationalized from the structure point of view for a range of titanate brannerite phases (ATi2O6). In addition, the crystallization of Ln0.5U0.5Ti2O6 brannerite in glass has been achieved via heat treatment at 1200°C and confirmed with X‐ray diffraction, scanning electron microscopy‐energy dispersive spectroscopy and transmission electron microscopy–selected area electron diffraction. [ABSTRACT FROM AUTHOR]

Abstract: Brannerite‐based glass‐ceramics with relatively high actinide waste loadings are potential waste forms for the immobilization of actinide‐rich radioactive wastes containing process chemicals. In this work, the crystallization of pentavalent uranium brannerite phases in glass with the incorporation of yttrium/cerium/europium has been investigated. The formation of brannerite phases in glass has been confirmed with X‐ray diffraction and Raman spectroscopy. The evolution of microstructures and the development of micro pores in brannerite phases have been revealed by scanning electron microscopy with the nominal formula, Y0.51U0.49Ti2O6, Ce0.65U0.35Ti2O6, and Eu0.53U0.47Ti2O6, being determined with energy‐dispersive spectroscopy. The presence of dominant U5+ species has been proven with both diffuse reflectance spectroscopy and X‐ray absorption near‐edge spectroscopy. In addition, the systematic Raman band shifts with the mean cation radius in the studied brannerite series have been observed and discussed. [ABSTRACT FROM AUTHOR]

Positron annihilation lifetime spectroscopy ( PALS) has indicated that Nb2 O5-doped TiO2 samples treated in either Ar or air at 1400°C for 48 h are both charge-compensated by Ti vacancies, but with statistically significant differences between the results. A Ta2 O5-doped air-sintered TiO2 sample also showed behavior similar to the Nb2 O5-doped air-sintered TiO2. In addition, Nb2 O5-doped SnO2 samples sintered in air at 1400°C for 1 h showed evidence of Sn vacancy cluster formation, with no indications of Sn2+ compensation from ultraviolet irradiation studies. PALS studies of air-sintered ZrO2 did not show any evidence of Zr vacancies after doping with Nb2 O5. [ABSTRACT FROM AUTHOR]

X-ray photoelectron spectroscopy was used to detect an intergranular impurity film in two (Ba xCs y)(Mn zTi8− z)O16 hollandite samples sintered in argon and air, respectively. This impurity film is enriched in Cs and Ba, as a result of segregation during high-temperature processing. The Cs ions in the grain-boundary layer have a different chemical bonding state from that in the hollandite phase, as evidenced by a large chemical shift of the Cs 3 d and Cs 4 d levels. The chemical environment around the Ba ions in the intergranular film is also likely to be different from that in the hollandite. The presence of this grain-boundary film is responsible for the relatively high initial loss of Cs and Ba during the aqueous dissolution testing. [ABSTRACT FROM AUTHOR]

Presents a correction of the schemes of structure shown in figure 1 of the paper "Structure for perovskites with layered ordering of A-site cations," by Christopher J. Howard and Zhaoming Zhang, published in a previous issue of "International Union of Crystallography."

Positron annihilation lifetime spectroscopy ( PALS) has indicated that Nb2 O5-doped TiO2 samples treated in either Ar or air at 1400°C for 48 h are both charge-compensated by Ti vacancies, but with statistically significant differences between the results. A Ta2 O5-doped air-sintered TiO2 sample also showed behavior similar to the Nb2 O5-doped air-sintered TiO2. In addition, Nb2 O5-doped SnO2 samples sintered in air at 1400°C for 1 h showed evidence of Sn vacancy cluster formation, with no indications of Sn2+ compensation from ultraviolet irradiation studies. PALS studies of air-sintered ZrO2 did not show any evidence of Zr vacancies after doping with Nb2 O5. [ABSTRACT FROM AUTHOR]

High-resolution neutron powder diffraction has been used to investigate the structures and phase transitions in the double perovskites Ba(2)Bi(3+)Bi(5+)O(6) (dibarium dibismuth hexaoxide) and Ba(2)BiSbO(6) (dibarium bismuth antimony hexaoxide) in the temperature ranges 4.2-973 and 4.2-625 K, respectively. The charge-ordered bismuthate adopts four structures in the temperature range - monoclinic in P2(1)/n, monoclinic in I2/m, rhombohedral in R3, and finally cubic in Fm3m. The low-temperature monoclinic structure has been determined for the first time. The transitions from P2(1)/n to I2/m, at 132 K, and R3 to Fm3m, at 820 K, are tricritical in nature; the transition from I2/m to R3 at ca 430 K is discontinuous. The behaviour of Ba(2)BiSbO(6) is very similar, except that the transition temperatures are lower - 250 K for I2/m to R3 and 515 K for R3 to Fm3m - and the low-temperature structure is not formed at all. The R3 to Fm3m transition in this compound is closer to second order in nature, although there is evidence for some contribution from higher-order terms.

The crystal structures of Nd(0.7)Ti(0.9)Al(0.1)O3, taken to represent the ideal Nd(2/3)TiO3, have been elucidated from 4 to 1273 K using high-resolution neutron powder diffraction in combination with group-theoretical analysis. The room-temperature structure is monoclinic in C2/m, on a cell with a = 7.6764 (1), b = 7.6430 (1), c = 7.7114 (1) A, beta = 90.042 (2) degrees . Pertinent features are the layered ordering of the A-site Nd cations/vacancies along the z axis and out-of-phase tilting of the (Ti/Al)O6 octahedra around both the x and z axes. From about 750 to 1273 K, the octahedra are tilted around just one axis (x axis) perpendicular to the direction of the cation ordering, giving rise to an orthorhombic structure with space-group symmetry Cmmm.