Molecular Beam Epitaxy growth and characterization of silicon – Doped InAs dot in a well quantum dot infrared photo detector (DWELL-QDIP)

We report the growth by Molecular Beam Epitaxy (MBE), fabrication and characterization of silicon doped 20 layer InAs dot in a well quantum dot infrared photo detector (DWELL-QDIP) device structures. Two structures with InAs dots of vertical heights of 50 Å and 40 Å were compared. A 2–8 μm band normal incidence photo response of the detector with polarization and bias dependence was obtained at 77 K. The specific peak detectivity D1 be 0.8 × 10⁹ Jones for one of the detectors.     

A classification of continuous wavelet transforms in dimension three

This paper presents a full catalogue, up to conjugacy and subgroups of finite index, of all matrix groups $H<\mathrm{GL}(3,\mathbb{R})$ that give rise to a continuous wavelet transform with associated irreducible quasi-regular representation. For each group in this class, coorbit theory allows to consistently define spaces of sparse signals, and to construct atomic decompositions converging simultaneously in a whole range of these spaces. As an application of the classification, we investigate the existence of compactly supported admissible vectors and atoms for the groups.     

Promoting Photocatalytic H2 Evolution through Retarded Charge Trapping and Recombination by Continuously Distributed Defects in Methylammonium Lead Iodide Perovskite

Inspired by its great success in the photovoltaic field, methylammonium lead iodide perovskite (MAPbI₃) has recently been actively explored as photocatalysts in H₂ evolution reactions. However, the practical application of MAPbI₃ photocatalysts remains hampered by the intrinsically fast trapping and recombination of photogenerated charges. Herein, we propose a novel strategy of regulating the distribution of defective areas to promote charge-transfer dynamics of MAPbI₃ photocatalysts. By deliberately designing and synthesizing the MAPbI₃ photocatalysts featuring a unique continuation of defective areas, we demonstrate that such a feature enables retardation of charge trapping and recombination via lengthening the charge-transfer distance. As an outcome, such MAPbI₃ photocatalysts turn out to achieve an impressive photocatalytic H₂ evolution rate as high as 0.64 mmol ⋅ g⁻¹ ⋅ h⁻¹, one order of magnitude higher than that of the conventional MAPbI₃ photocatalysts. This work establishes a new paradigm for controlling charge-transfer dynamics in photocatalysis.     

Continuous Flow Electrochemistry Enables Practical and Site-Selective C−H Oxidation

The selective oxygenation of ubiquitous C(sp³)−H bonds remains a highly sought-after method in both academia and the chemical industry for constructing functionalized organic molecules. However, it is extremely challenging to selectively oxidize a certain C(sp³)−H bond to afford alcohols due to the presence of multiple C(sp³)−H bonds with similar strength and steric environment in organic molecules, and the alcohol products being prone to further oxidation. Herein, we present a practical and cost-efficient electrochemical method for the highly selective monooxygenation of benzylic C(sp³)−H bonds using continuous flow reactors. The electrochemical reactions produce trifluoroacetate esters that are resistant to further oxidation but undergo facile hydrolysis during aqueous workup to form benzylic alcohols. The method exhibits a broad scope and exceptional site selectivity and requires no catalysts or chemical oxidants. Furthermore, the electrochemical method demonstrates excellent scalability by producing 115 g of one of the alcohol products. The high site selectivity of the electrochemical method originates from its unique mechanism to cleave benzylic C(sp³)−H bonds through sequential electron/proton transfer, rather than the commonly employed hydrogen atom transfer (HAT).     

Two-dimensional correlation analysis of continuous online in situ ATR-FTIR on the adsorption of butyl xanthate at the surface of a-PbO

The adsorption behavior of butyl xanthate on the surface of lead oxide was investigated using continuous online in situ attenuated total reflectance Fourier transform infrared（ATR-FTIR） spectroscopy technique and two dimensional（2D） correlation analysis.The adsorbed layer studied was prepared by coating α-PbO particles onto the surfaces of the ZnSe crystal.The appearance of spectral peaks at 1203 cm^-1,1033 cm^-1 and their red shift indicated the formation and aggregation of xanthate at the surface of α-PbO.According to 1R intensity changes after rinsing with deionized water and a NaOH solution,the adsorption was proved to be a chemisorption type.The competition between xanthate and OH for the surfaces leads to desorption of xanthate at higher pH.The technique of 2D correlation ATR-FTIR spectroscopy was used to evaluate the changing order of spectral intensities in the adsorption process,and the results indicated that xanthate micelles were formed at the surfaces.The adsorption kinetics of butyl xanthate was found to be a pseudo-second-order reaction model and the adsorption capacity of butyl xanthate at α-PbO was as high as 281 mg g^-1 after 150 min.     

Thermoelasticity of bodies with microstructure and microtemperatures

This paper is concerned with a linear theory of thermodynamics for elastic materials with microstructure, whose microelements possess microtemperatures. It is shown that there exists the coupling of microrotation vector field with the microtemperatures even for isotropic bodies. Uniqueness and continuous dependence results are presented. The theory is used to establish the solution corresponding to a concentrated heat source acting in an unbounded continuum.     

Experimental analysis of the steady-state behaviour of beam systems with discontinuous support

This paper deals with the experimental analysis of the long-term behaviour of periodically excited linear beams supported by a one-sided spring or an elastic stop. Numerical analysis of the beams showed subharmonic, quasi-periodic and chaotic behaviour. Furthermore, in the beam system with the one-sided spring three different routes leading to chaos were found. Because of the relative simplicity of the beam systems and the variety of calculated nonlinear phenomena, experimental setups are made of the beam systems to verify the numerical results. The experimental results correspond very well with the numerical results as far as the subharmonic behaviour is concerned. Measured chaotic behaviour is proved to be chaotic by calculating Lyapunov exponents of experimental data.

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Sommario Il presente lavoro concerne l'analisi sperimentale del comportamento a regime di travi lineari, su supporti elastici nonlineari discontinui, eccitate periodicamente. L'analisi numerica dei sistemi in esame ha evidenziato risposte subarmoniche, quasi-periodiche e caotiche, nonchè l'esistenza, nel caso di trave con una molla laterale, di tre differenti percorsi verso il caos. La relativa semplicità dei sistemi di travi ha consentito di procedere ad una verifica sperimentale dei risultati numerici e della varietà dei fenomeni nonlineari da essi evidenziati. La corrispondenza fra risultati sperimentali e numerici è molto buona nel caso di risposta subarmonica. Il comportamento caotico sperimentale è stato convalidato attraverso il calcolo degli esponenti di Lyapunov a partire dai relativi dati.

     

On the dynamic behaviour of a flexible beam carrying a moving mass

The behaviour of a system containing a mass traveling on a cantilever beam is considered. The mass is induced to move by an applied force as opposed to the case which has been considered in most literature where the position of the moving mass is assumed to be known and independent of the motion of the beam. Furthermore, the system to be discussed has the unique characteristic that the motions of the mass and the beam are coupled. The mathematical model of the system includes two coupled nonlinear integral/partial differential equations which are impossible to solve analytically and are difficult to solve numerically in their original form. As a remedy, the solution is discretized into space and time functions and the equations of motion are reduced to a set of ordinary differential equations. The shape function is chosen so that it satisfies the boundary conditions of the beam as well as the transient conditions imposed by the traveling mass. This choice of the shape function, which considers the mass-beam interaction, provides an improvement over the conventional method of using a simple cantilever beam mode shapes.The ordinary differential equations of motion using the improved shaped functions, are solved numerically to obtain the dynamic behaviour of the system. The results illustrate the validity of the model, and demonstrate the advantages of the improved model to the un-improved equations.     

Thermal buckling and post-buckling of pinned–fixed Euler–Bernoulli beams on an elastic foundation

In this article, both thermal buckling and post-buckling of pinned–fixed beams resting on an elastic foundation are investigated. Based on the accurate geometrically non-linear theory for Euler–Bernoulli beams, considering both linear and non-linear elastic foundation effects, governing equations for large static deformations of the beam subjected to uniform temperature rise are derived. Due to the large deformation of the beam, the constraint forces of elastic foundation in both longitudinal and transverse directions are taken into account. The boundary value problem for the non-linear ordinary differential equations is solved effectively by using the shooting method. Characteristic curves of critical buckling temperature versus elastic foundation stiffness parameter corresponding to the first, the second, and the third buckling mode shapes are plotted. From the numerical results it can be found that the buckling load-elastic foundation stiffness curves have no intersection when the value of linear foundation stiffness parameter is less than 3000, which is different from the behaviors of symmetrically supported (pinned–pinned and fixed–fixed) beams. As we expect that the non-linear foundation stiffness parameter has no sharp influence on the critical buckling temperature and it has a slight effect on the post-buckling temperature compared with the linear one.