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• A Perforated metamaterial plate with ABHs bonded by a piezoelectric stud is proposed. • Broad bandgaps and strong collimation can be achieved for the metamaterial plate. • The DQEM is proposed to obtain wave characteristics of the metamaterial plate. • Parameter study is conducted in terms of the bandgaps, EFCs and group velocities. • Directional wave manipulation is achieved by utilizing the bandgaps and collimation. Aiming at achieving lower and broader bandgaps (BGs) and stronger collimation effect, this research proposes a novel perforated metamaterial plate with acoustic black holes (ABHs) interconnected by piezoelectric studs for flexural wave manipulation. Based on the differential quadrature element method together with the first-order shear deformation plate theory, the governing equations of the metamaterial plate are derived. The proposed model is validated by comparing with finite element simulation results. Finally, the wave propagation characteristics including the BGs, equi-frequency contours (EFCs), and group velocities are obtained. The results reveal that the introduction of the stud embedded with piezoelectric patches brings wider complete BGs and stronger collimation effect at lower frequencies. The boundary frequencies and bandwidth of BGs and the preferential direction of wave energy flow are tunable by adjusting geometry parameters of the unit cell. The balance between ABH and piezoelectric effects should be kept to enhance the collimation by generating the caustic lobes. Utilizing the BG and self-collimation mechanism, flexural wave propagation can be manipulated by creating point or line defects in the metamaterial plates. This research provides guidance on the design of metamaterial structure with ABHs and piezoelectric material to achieve broadband vibration absorption and directional wave propagation. [ABSTRACT FROM AUTHOR]

• A metamaterial beam with graded ABHs is proposed for broadband vibration reduction. • The DQM is utilized to model the rainbow metamaterial beam efficiently. • Rainbow metamaterial beams exhibit broader bandgaps and better attenuation effect. • Increasing graded spacing or changing graded direction leads to better attenuation. • Disordered geometry parameters lead to further improvement of attenuation strength. Acoustic black hole (ABH) structures have been widely utilized for vibration suppression owing to its tailored indentations according to a power-law profile. Compared with single ABH element, multiple ABHs embedded in periodic lattice configurations exhibit more remarkable attenuation effect within the so-called bandgaps at relatively low frequencies. However, most research is devoted to the analysis of uniform metamaterial embedded with periodic arrangement of ABHs, resulting in the attenuation bandgaps limited to a narrow frequency range. In this research, a rainbow metamaterial beam embedded with graded arrangement of ABHs is proposed to achieve broadband vibration attenuation. Two arrangement types of ABHs in metamaterial beams including linear and sinusoidal profiles are taken into account. The differential quadrature method is used to establish governing equations of infinite beams with periodic ABHs and finite rainbow metamaterials with graded ABHs, respectively. Using the validated mathematical model and genetic algorithm, wave propagation behaviors in infinite metamaterial beams, transmittance characteristics and optimization of finite rainbow metamaterial beams are investigated quantitatively. The results reveal that the generation of broad bandgaps can be explained by the combination of local resonance and Bragg scattering effects for proposed metamaterial beams with periodic asymmetrical ABHs. The corresponding bandgaps are tunable by changing the geometry parameters of ABHs. Moreover, the rainbow metamaterial beams with linear and sinusoidal ABHs own a broader attenuation band and better attenuation effect compared to the periodic ones. Compared with regular graded distributions, disordered arrangement of geometry parameters of neighboring cells leads to further improvement of attenuation strength. This work provides novel perspectives on achieving broadband vibration attenuation by rainbow metamaterial beams with ABHs, and the results could be applied to guide the design of rainbow metamaterial with graded geometry parameters. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract: In this paper, we will study the Cauchy problem for the generalized KdV–Burgers–Kuramoto equation, which represents a dissipative, stroboscopic and unstable system in physics. When the initial data is a small disturbance of a rarefaction wave of the inviscid Burgers equation, we prove the global existence of the solution to the corresponding Cauchy problem and asymptotic stability of the rarefaction wave. The analysis is based on a priori estimates and the -energy method. [Copyright &y& Elsevier]

Abstract: Let be a bounded domain in with the origin , , ; and are two smooth functions on . In this paper, we investigate the singular elliptic equation with Dirichlet boundary conditions. We study the limit behavior of the (P.S.) sequence of the corresponding energy functional and give a global compactness theorem, and then give some existence results. [Copyright &y& Elsevier]

Titania supported palladium–copper bimetallic catalysts (Pd–Cu/TiO2) are prepared by liquid-phase chemical reduction method and then applied in the catalytic reduction of nitrite ions in drinking water. The nitrite conversion and selectivity to N2 influenced by metal molar ratio (Pd:Cu), H2 flow rate, CO2 flow rate, pH value of solution and reaction temperature are also discussed in detail with physical characterizations methods such as XPS, XRD, in situ FT-IR. It is discovered that bimetallic Pd–Cu/TiO2 catalyst has higher activity than monometallic Pd/TiO2 catalyst in the catalytic reduction of nitrite ions and a mechanism is proposed to explain this promoting effect of bimetallic catalyst in this paper. [Copyright &y& Elsevier]

Consideration is given to the FitzHugh–Nagumo equations ut=uxx-f(u)-v,vt=#x03B5;(u-γv), where f(u)=u(u-1)(u-a), 0, #x03B5;>0,γ>9/((1-2a)(2-a)). It is shown that there exist some co>0 so that the system has a heteroclinic travelling wave solution with wave speed co for any #x03B5;>0, and there exists coo∈(0,co), such that (1.2) has a homoclinic solution with wave speed coo if and only if #x03B5;γ2<1. [Copyright &y& Elsevier]

Photocatalytic reduction of nitrate ions was examined by using Cu/MgTiO3-TiO2 catalyst in the presence of sodium oxalate as hole scavenger. Many factors such as catalyst calcination temperature, Cu:Mg atom molar ratio, different hole scavengers and different concentrations of sodium oxalate were tested to search for the optimal reaction conditions. X-ray diffraction (XRD) and Transmission Electron Micrograph (TEM) were performed to characterize the composite semiconductors catalyst. Our results indicated that Cu/MgTiO3-TiO2 catalyst calcined at 873 K showed the highest photocatalytic activity and nitrate conversion reached 39.2% after 2 h irradiation. The enhanced effect for photocatalytic nitrate reduction activity was most likely to result from the formation of composite semiconductor MgTiO3-TiO2 and the transformation of TiO2 crystalline phase. [Copyright &y& Elsevier]

This paper studies wave propagation in functionally graded metal foam plates reinforced with graphene platelets (GPLs), where various types of porosity and GPL distribution are taken in account. The Halpin–Tsai model is employed to express the material properties of metal foam plates reinforced with GPLs. The governing equations of wave propagation in metal foam plates are derived by Hamilton's principle together with different plate theories, upon which wave dispersion relations in plates are achieved. Then, the validation of proposed model is examined by comparing the natural frequencies calculated in present study and those from literature. Finally, the effects of porosity and GPL distributions, porosity coefficient, GPL volume fraction and geometry on wave dispersion relations are evaluated. [ABSTRACT FROM AUTHOR]

Distributed penalized generalized linear regression algorithms have been widely studied in recent years. However, they all assume that the data should be randomly distributed. In real applications, this assumption is not necessarily true, since the whole data are often stored in a non-random manner. To tackle this issue, a non-convex penalized distributed pilot sample surrogate negative log-likelihood learning procedure is developed, which can realize distributed high-dimensional variable selection for generalized linear models, and be adaptive to the non-random situations. The established theoretical results and numerical studies all validate the proposed method. [ABSTRACT FROM AUTHOR]

Selective gas adsorption and separation were intensively investigated for porous materials like metal-organic frameworks (MOFs) and Zeolites. In this study, an intrinsically microporous aluminoborate, PKU-2, with an extra-large one dimensional channel (~9.6 Å) was discovered for the first time to exhibit selective CO 2 and C 2 H 2 adsorption over CH 4 and C 2 H 4 , respectively. Incorporation of Cr3+ and Fe3+ ions into the framework could effectively enlarge the specific surface area in comparison with the pristine PKU-2, which is accompanied with a significant enhancement of gas adsorption capacities for CO 2 and C 2 H 2 to 3.9 and 2.86 mmol/g, respectively, for Fe-PKU-2, and a slight decrease of gas separation selectivities. The high gas adsorption capacities and selectivities together with their high thermal stability imply their potential practice applications for environment and energy-relevant gas adsorption and separation. In addition to MOFs and zeolites, the microporous aluminoborate PKU-2 with an extra-large one dimensional channel exhibits highly selective CO 2 and C 2 H 2 adsorptions over N 2 /CH 4 and C 2 H 4 , respectively, at 293 K. Image 1 • Microporous aluminoborate (PKU-2) was synthesized by boric acid flux method. • High CO 2 and C 2 H 2 adsorption capacities at 293 K were observed for PKU-2. • PKU-2 exhibits selective CO 2 and C 2 H 2 adsorption over CH 4 and C 2 H 4 , respectively. • PKU-2 is the first aluminoborate that exhibits selective gas adsorption. • Enhancement of gas adsorption performances were achieved by transition metal doping. [ABSTRACT FROM AUTHOR]

BiMn x Fe 3- x O 6 ( x = 1) represents a new type of oxide structure containing Bi 3+ and competing magnetic super-exchanges. In literature, multiple magnetic states were realized at low temperatures in BiMnFe 2 O 6 , and the hypothetical parent compounds (BiMn 3 O 6 , BiFe 3 O 6 ) were predicted to be different in magnetism. Herein, we performed a careful study on the syntheses of BiMn x Fe 3- x O 6 at ambient pressure, and the solid solution range was determined to be 0.9 ≤ x ≤ 1.3 by Rietveld refinements on high-quality powder X-ray diffraction data. Due to the very similar cationic size of Mn 3+ and Fe 3+ , and possibly the structural rigidity, there was no significant structure change in the whole range of solid solution. The magnetic behavior of BiMn x Fe 3- x O 6 ( x = 1.2, 1.22, 1.26, 1.28 and 1.3) was generally similar to BiMnFe 2 O 6 , while the relative higher concentration of Mn 3+ led to the decreasing of the antiferromagnetic ordering temperature. [ABSTRACT FROM AUTHOR]

Cr-PKU-1, an octahedron-based redox molecular sieve, was found to be an efficient, environmentally benign and easily recoverable catalyst for the heterogeneously-catalyzed Strecker reaction under the mild conditions. This material was evidenced to be a dual-centered solid acid with a large density of Brönsted acid (borate hydroxyl groups, B-OH) and Lewis acid sites (Cr 3+ ), and therefore showed much higher catalytic activity than mono-central solid acid in the formation of α-aminonitriles. Although commonly considered as Lewis acid centers, electron-deficient boron atoms (tri-coordinated BO 3 ) in Cr-PKU-1 failed to exhibit the desired catalytic activity in the present investigations probably due to steric hindrance against the large organic substrates. A plausible mechanism about two-centered catalysis in Strecker reaction were proposed based on the comprehensive and sufficient analysis. This work illustrates for the first time the possible application in the Strecker reaction using the dual-centered redox molecular sieve, and highlights their potential ability to address the various functions involved in the reaction mechanism. [ABSTRACT FROM AUTHOR]

Octahedron-based redox molecular sieves Cr-PKU-5 were synthesized by a two-step template annealing method and used as catalysts for the liquid-phase ammoximation of cyclohexanone. PKU-5 (Al 4 B 6 O 15 ) is a novel anhydrous aluminoborate, but difficult to be synthesized due to the severe demands of preparation procedures. Interestingly, Cr-stabilized PKU-5 can be facilely prepared with nano-scaled distribution and large BET surface area by annealing Cr-doped PKU-1 precursors at high temperature. Le Bail fitting of powder XRD patterns demonstrated large amounts of Cr 3+ has been incorporated into the framework of PKU-5. Much different with TS-1 redox molecular sieve, Cr-PKU-5 was favorable to produce ketazine in the liquid-phase ammoximation of ketone, rather than oxime. Based on the discussion about reaction pathway, a probable reaction mechanism was proposed to interpret the critical role of Cr-PKU-5 in such a complex multi-step reaction. [ABSTRACT FROM AUTHOR]

PKU-5 (Al 4 B 6 O 15 ) is potentially a solid acid catalyst, and it possesses an interesting open-framework composed of [AlO 6 ] and [B 2 O 5 ] groups. PKU-5 shows a high thermal stability, while no physical and chemical properties were investigated thus far, because of the difficulty in its synthesis. Cr-stabilized PKU-5 with the formula (Al 1− x Cr x ) 4 B 6 O 15 (0.08 ≤ x ≤ 0.14) can be easily prepared by annealing Cr-doped PKU-1 precursors. XRD and TEM experiments demonstrate Cr 3+ has been successively incorporated into the framework of PKU-5. NH 3 -TPD measurements indicate that the partial substitution of Al 3+ by Cr 3+ leads to a small change of acid sites in total amounts and distributions. Cr-PKU-5 shows a good catalytic activity for methanol dehydration from 300 to 450 °C. Other operation conditions, such as the Cr 3+ content, space velocity of methanol were also discussed in detail to evaluate its catalytic performance. [ABSTRACT FROM AUTHOR]

We studied and compared the photocatalytic water splitting performances for ZnGa 2 O 4 prepared by high temperature solid state reaction (HTSSR), hydrothermal (HY) and sol-gel (SG) methods. HTSSR-ZnGa 2 O 4 has a relative large photocatalytic activity per surface area (1.6 μmol/h/m 2 ) in pure water by UV irradiation due to its high crystallinity. The HY- and SG-samples both have small particle sizes (20∼30 nm) and therefore high surface area (20 and 29 m 2 /g, respectively), which leads to superior photocatalytic H 2 evolution rates per unit mass (11.5 and 28.5 μmol/h/g). The apparent quantum yield of SG-ZnGa 2 O 4 for pure water splitting under 313 nm irradiation is 2.6%. The existence of substantial surface defects is the major problem for HY- and SG-ZnGa 2 O 4 . Consequently, the usage of sacrificial agents could greatly enhance the activities and indeed the H 2 evolution rates in 20 Vol. % methanol aqueous solution increase to 100 and 142 μmol/h/g for HY- and SG-ZnGa 2 O 4 , respectively. [ABSTRACT FROM AUTHOR]

Highlights: [•] MNb2O6 was prepared by a mild two-step hydrothermal method. [•] Their flower-like nanostructure morphology was studied by SEM and TEM. [•] High BET surface areas for MnNb2O6 (∼50m2/g) and ZnNb2O6 (∼100m2/g). [•] Band gap energies were estimated by UV–vis diffuse reflectance spectra. [•] Photocatalytic activities were evaluated under UV-light irradiation. [ABSTRACT FROM AUTHOR]

Abstract: CdB10O14(OH)4·H2O has been synthesized under boric acid flux condition and characterized by single-crystal X-ray diffraction, infrared spectra, and UV–vis reflectance spectroscopy. It crystallizes in the monoclinic space group P21/n with a =7.7277(8), b =18.95(2), c =9.8616(10)Å, β=91.454(1)°, V =1443.7(3)Å. The structure consists of [B10O16(OH)4] layers of 9-membered borate rings enclosing Cd2+ cations. Adjacent borate layers are interconnected via hydrogen bonding to form a 3D network. It possesses an unprecedented decaborate fundamental building block B10O20. The structure details are discussed together with Sr[B6O9(OH)2]·3H2O, Pb[B8O11(OH)4], Pr[B8O11(OH)5], and Nd[B9O13(OH)4]·H2O, which have correlated FBBs. The band structure calculations show its direct energy band gap of ∼4.68eV, in consistent with the estimated value (4.77eV) from UV–vis. In addition, dielectric constants and refractive indexes are also calculated. [Copyright &y& Elsevier]

Abstract: Two Cu(II)–fluconazole supramolecular isomers 1 and 2 formulated as (flu)2Cu(SCN)2 (flu=fluconazole) have been synthesized and structurally characterized by single crystal X-ray diffraction. Different solvent media lead to the different binding modes of anion SCN− and the flexible C–C chain of fluconazole has been rotated in the two isomers. Complex 1 exhibits a two dimensional square grid-like layer and complex 2 exhibits a two dimensional framework with a parquet motif. Different H-bonds and stacking modes are observed in the two isomers. Complex 1 is nonemissive, whereas complex 2 exhibits photoluminescence property. [Copyright &y& Elsevier]

Supported metal catalysts have been applied in many current industrial processes. The morphology of metal particles coated on support has been proven to affect the performance of catalysts greatly. In this study, a simple photodeposition process will be introduced to coat palladium onto titanium dioxide with an emphasis on the morphology control and size distribution of palladium particles. The effect of pH on the morphology of palladium particles was systemically investigated. It is found that the deposited palladium particles can be controlled to have narrow particle size distribution and homogeneous dispersion by a simple pH-controlled process during photodeposition. Experimental results demonstrate that the adsorption competition between OH- and PdCl42- or it’s hydrolytic anions can efficiently keep local concentration of palladium ions on titanium dioxide extremely low to control the morphology of deposited palladium particles on titania. The as-prepared Pd/TiO2 particles are found to be crystallitic stable indicated by TEM, XRD and XPS measurements. [Copyright &y& Elsevier]

[Display omitted] • The Lewis-base, Ga 4 B 2 O 9 , was prepared by high temperature solid state reactions. • It showed both a high yield and stability in Knoevenagel condensation reactions. • Knoevenagel reactions catalyzed by Ga 4 B 2 O 9 obeyed a second-order characteristics. • The calculated activation energy was ∼61.6 kJ/mol. • The basicity attributed to the μ 3 -O atoms linked to 3 five-coordinated Ga3+. Solid Lewis-base catalysis is important in the production of fine chemicals. A Lewis-base Ga 4 B 2 O 9 was synthesized by high temperature solid state reactions. It exhibited a high yield (90 %) and a high stability in Knoevenagel condensation reactions, where several aldehydes were combined with malononitrile to form α , β -unsaturated compounds through nucleophilic addition reactions. Reaction kinetics analyses indicated Knoevenagel condensation reactions over Ga 4 B 2 O 9 catalyst obeyed a second-order characteristics and the calculated activation energy was ∼61.6 kJ/mol, suggesting that Langmuir-Hinshelwood absorption pathway was probably employed. The structural evolution from Ga 4 B 2 O 9 →GaBO 3 → β -Ga 2 O 3 evidenced that the structure-induced basicity of Ga 4 B 2 O 9 attributed to the special μ 3 -O atoms linked exclusively to 3 five-coordinated Ga3+. This investigation proves a convincible structure-property correlation in Ga-based solid base materials and helps developing an alternative avenue towards the design of new intrinsic solid base catalysts. [ABSTRACT FROM AUTHOR]

• Cr-PKU-1 efficiently catalyzes the selectively oxidation of styrene using H 2 O 2. • The generated active free radicals in different solvents were monitored. • OH was favored in CH 3 CN and responsible for the formation of carbonyl products. • O 2 − was favored in DMF and beneficial to the epoxide production. • The function of Cr3+ was correlated with the solvent effect. The nature of a solvent plays an important role in selectively catalytic oxidations, influencing the catalytic activity and product selectivity. Most work attribute such roles to the polarity, acidity/basicity, or coordination ability of the solvent. Here, we systematically investigated the generated active free radicals in five different organic solvents during the catalytic oxidation of styrene by H 2 O 2. Cr-doped PKU-1 aluminoborate was selected as the heterogeneous catalyst in this system. The solvent effect was comprehensively understood along this perspective. Hydroxyl radicals (OH) were preferred to be formed in CH 3 CN and responsible for the formation of carbonyl compounds, while superoxide ion radicals (O 2 −) were favored in DMF and beneficial to the epoxide production. The function of Cr3+ was correlated with the solvent effect and a tentative mechanism pathway was proposed accordingly. [ABSTRACT FROM AUTHOR]