Excitation Wavelength-Dependent Fluorescence of a Lanthanide Organic Metal Halide Cluster for Anti-Counterfeiting Applications

The achievement of significant photoluminescence (PL) in lanthanide ions (Ln³⁺) has primarily relied on host sensitization, where energy is transferred from the excited host material to the Ln³⁺ ions. However, this luminous mechanism involves only one optical antenna, namely the host material, which limits the accessibility of excitation wavelength-dependent (Ex-De) PL. Consequently, the wider application of Ln³⁺ ions in light-emitting devices is hindered. In this study, we present an organic–inorganic compound, (DMA)₄LnCl₇ (DMA⁺=[CH₃NH₂CH₃]⁺, Ln³⁺=Ce³⁺, Tb³⁺), which serves as an independent host lattice material for efficient Ex-De emission by doping it with trivalent antimony (Sb³⁺). The pristine (DMA)₄LnCl₇ compounds exhibit high luminescence, maintaining the characteristic sharp emission bands of Ln³⁺ and demonstrating a high PL quantum yield of 90–100 %. Upon Sb³⁺ doping, the compound exhibits noticeable Ex-De emission with switchable colors. Through a detailed spectral study, we observe that the prominent energy transfer process observed in traditional host-sensitized systems is absent in these materials. Instead, they exhibit two independent emission centers from Ln³⁺ and Sb³⁺, each displaying distinct features in luminous color and radiative lifetime. These findings open up new possibilities for designing Ex-De emitters based on Ln³⁺ ions.     

Comments on stabilizing layered manganese oxide electrodes for Li batteries

An electrochemical study of structurally-integrated xLi₂MnO₃•(1 −x)LiMn_0.5Ni_0.5O₂ ‘composite’ materials has been undertaken to investigate the stability of electrochemically-activated electrodes at the Li₂MnO₃-rich end of the Li₂MnO₃–LiMn_0.5Ni_0.5O₂ tie-line, i.e., for 0.7 ≤ x ≤ 0.95. Excellent performance was observed for x = 0.7 in lithium half-cells; comparable to activated electrodes that have significantly lower values of x and are traditionally the preferred materials of choice. Electrodes with higher manganese content (x ≥ 0.8) showed significantly reduced performance. Implications for stabilizing low-cost, manganese-rich, layered lithium-metal-oxide electrode materials are discussed.     

Photocatalytic and optical properties of titanium dioxide thin films prepared by metalorganic chemical vapor deposition

Titanium dioxide thin films have been deposited by metalorganic chemical vapor deposition (MOCVD) over sodalime glass substrates at substrate temperatures ranging from 250 °C to 450 °C. The effect of deposition temperature on the structure and microstructure of the obtained films has been studied by x-rays diffraction (XRD) and scanning electron microscopy (SEM), respectively. Diffraction patterns show the existence of a pure anatase phase beside a texture change with the increase of deposition temperature. Micrographs show grain fragmentation with the increase in deposition temperature. UV–Vis. spectra have been recorded by spectrophotometery. The optical energy gap has been calculated for the deposited films from the spectrophotometrical data. Photocatalytic experiments have been carried out. The photocatalytic activity has been found to decrease with the increase in deposition temperature.     

Stability analysis of a class of uncertain switched systems on time scale using Lyapunov functions

This paper deals with the stability analysis of a class of uncertain switched systems on non-uniform time domains. The considered class consists of dynamical systems which commute between an uncertain continuous-time subsystem and an uncertain discrete-time subsystem during a certain period of time. The theory of dynamic equations on time scale is used to study the stability of these systems on non-uniform time domains formed by a union of disjoint intervals with variable length and variable gap. Using the concept of common Lyapunov function, sufficient conditions are derived to guarantee the asymptotic stability of this class of systems on time scale with bounded graininess function. The proposed scheme is used to study the leader–follower consensus problem under intermittent information transmissions.     

基于交通量均分的城市道路网络定向研究

为减少城市交通拥挤,从交通量均分的角度出发,提出了综合反映道路网络局部和整体性质的k最优定向,并且利用奇度点配对的思想为定向问题设计了启发式算法。     

Facile synthesis of low-dimensional SnO2 nanostructures: An investigation of their performance and mechanism of action as anode materials for lithium-ion batteries

Owing to high-energy density of rechargeable lithium-ion batteries (LIBs), they have been investigated as an efficient electrochemical power sources for various energy applications. High theoretical capacities of tin oxide (SnO₂) anodes have led us a path to meet the ever-growing demands in the development of high-performance electrode materials for LIBs. In this paper, a facile approach is described for the synthesis of porous low-dimensional nanoparticles and nanorods of SnO₂ for application in LIBs with the help of Tween-80 as a surfactant. The SnO₂ samples synthesized at different reaction temperatures produced porous nanoparticles and nanorods with average diameters of ~7–10 nm and ~70–110 nm, respectively. The SnO₂ nanoparticle electrodes exhibit a high reversible charge capacity of 641.1 mAh/g at 200 mA/g after 50 cycles, and a capacity of 340 mAh/g even at a high current density of 1000 mA/g during the rate tests, whereas the porous nanorod electrodes delivers only 526.3 mAh/g at 200 mA/g after 50 cycles and 309.4 mAh/g at 1000 mA/g. It is believed that finer sized SnO₂ nanoparticles are much more favorable to trap more Li⁺ ion during electrochemical cycling, resulting in a large irreversible capacity. In contrast, rapid capacity fading was observed for the porous nanorods, which is the result of their pulverization resulting from repeated cycling.     

Balancing strength and toughness of calcium-silicate-hydrate via random nanovoids and particle inclusions: Atomistic modeling and statistical analysis

As the most widely used manufactured material on Earth, concrete poses serious societal and environmental concerns which call for innovative strategies to develop greener concrete with improved strength and toughness, properties that are exclusive in man-made materials. Herein, we focus on calcium silicate hydrate (C-S-H), the major binding phase of all Portland cement concretes, and study how engineering its nanovoids and portlandite particle inclusions can impart a balance of strength, toughness and stiffness. By performing an extensive +600 molecular dynamics simulations coupled with statistical analysis tools, our results provide new evidence of ductile fracture mechanisms in C-S-H – reminiscent of crystalline alloys and ductile metals – decoding the interplay between the crack growth, nanovoid/particle inclusions, and stoichiometry, which dictates the crystalline versus amorphous nature of the underlying matrix. We found that introduction of voids and portlandite particles can significantly increase toughness and ductility, specially in C-S-H with more amorphous matrices, mainly owing to competing mechanisms of crack deflection, voids coalescence, internal necking, accommodation, and geometry alteration of individual voids/particles, which together regulate toughness versus strength. Furthermore, utilizing a comprehensive global sensitivity analysis on random configuration-property relations, we show that the mean diameter of voids/particles is the most critical statistical parameter influencing the mechanical properties of C-S-H, irrespective of stoichiometry or crystalline or amorphous nature of the matrix. This study provides new fundamental insights, design guidelines, and de novo strategies to turn the brittle C-S-H into a ductile material, impacting modern engineering of strong and tough concrete infrastructures and potentially other complex brittle materials.     

Flow and performance characteristics of an Allison 250 gas turbine S-shaped diffuser: Effects of geometry variations

The S-shaped diffuser which connects the exit of the compressor to the inlet of the combustion chamber of the Allison 250 gas turbine has been investigated using the Shear-Stress Transport turbulence model (SST) and the commercial code ANSYS-CFX. The diffuser geometry includes an initial conical diffuser which smoothly transitions into a constant cross-section S-duct. The numerical model and setup were validated using both in-house processed experimental data and experimental data from the literature on a similar geometry. The stream-wise velocity profile was observed to flatten in the initial divergent section, and then the region of the flow with the highest velocity is pushed toward the outer surface of the first bend, with a secondary-flow in the plane of the cross-section. This distortion of the stream-wise velocity intensified when the inlet turbulence intensity was decreased or when the Reynolds number was increased. An increase of the Reynolds number also translated into higher static pressure recovery potential and lower wall friction coefficients. Six variations of the diffuser geometry were considered, all having the same total cross-sectional area ratio and centreline offset. The qualitative results were the same as those of the Allison 250 diffuser, but unlike the base geometry, all the considered variants showed separated-flow regions (and reversed-flow regions in some cases) of different sizes and at different locations. The performance indicators for the Allison 250 S-shaped diffuser were the highest overall. Most interestingly, the current duct geometry outperformed its variant with a cross-sectional area expansion extending over its entire length, which is the most common inlet duct configuration.     

Fluorinated tris(pyrazolyl)borates. Syntheses and characterization of sodium and copper complexes of [HB(3-(CF3),5-(Ph)Pz)3]−

Sodium salt of the fluorinated tris(pyrazolyl)borate ligand [HB(3-(CF₃),5-(Ph)Pz)₃]⁻ has been synthesized from the corresponding pyrazole and NaBH₄ in high yield. It forms stable adducts with oxygen-based donors like THF and water. [HB(3-(CF₃),5-(Ph)Pz)₃]Na(THF) is monomeric in the solid state whereas {[HB(3-(CF₃),5-(Ph)Pz)₃]Na(H₂O)}_n forms a polymeric chain structure. These tris(pyrazolyl)boratosodium adducts show intra and/or inter-molecular sodium–fluorine interactions. X-ray crystal structures of [HB(3,5-(CF₃)₂Pz)₃]Na(OEt₂) and {[HB(3-(CF₃),5-(CH₃)Pz)₃]Na(H₂O)}₂ also display similar CF⋯Na contacts. The copper carbon monoxide complex [HB(3-(CF₃),5-(Ph)Pz)₃]CuCO was prepared by treating [HB(3-(CF₃),5-(Ph)Pz)₃]Na(THF) with CuOTf in the presence of CO. The infra-red stretching frequency data show relatively high ν_CO value (2103 cm⁻¹) indicating the presence of highly electrophilic copper site on [HB(3-(CF₃),5-(Ph)Pz)₃]CuCO. Crystal structure of 3-(CF₃),5-(Ph)PzH is also reported. It forms “tub” shaped tetramers in the solid state.