Effect of CdS modification on photoelectric properties of TiO2/PbS quantum dots bulk heterojunction

TiO₂/PbS(CdS) quantum dots (QDs) bulk heterojunction has been fabricated by successive ionic layer adsorption and reaction method via alternate deposition of PbS and CdS QDs. In comparison with TiO₂/PbS heterojunction, the incident photon to current conversion efficiency was increased almost 50% in the visible region. Meantime, the short-circuit current and open-circuit voltage were enhanced 200% and 35% respectively. The influence mechanism of CdS is related to reduction of trap state density at TiO₂/PbS interface and PbS QDs surface by the discussion of the dark current density–voltage curves, the transient photocurrent response curves and the electrochemical impedance spectra spectroscopy (EIS).     

Study on frequency response and bifurcation analyses under primary resonance conditions of micro-milling operations

Avoidance of resonance in fluctuation of milling tool is vital for reaching excellence quality and performance of the cutting operation. The cutting tool in resonance condition vibrates with considerable magnitude that causes to increase milling tool wear and manufacturing prices. Analytical study of primary resonances and bifurcation behavior of a micro-milling process, including structural nonlinearities, gyroscopic moment, rotary inertia, velocity-dependent process damping, static and dynamic chip thickness, is chief aim of this article. The milling tool is modeled as a 3-D spinning cantilever beam that is motivated by cutting forces. To get the analytical solution for frequency response function and bifurcation behavior of the system under primary resonances, the method of multiple scales is operated on converted ordinary differential equations that are obtained by applying assumed modes method on nonlinear partial differential equations of tool vibration. The effects of different process parameters and nonlinear terms on the frequency response of the tool tip oscillations are examined. In addition, the effects of detuning parameter and damping ratio on the bifurcation and behavior of the limit cycle under primary resonances are examined. The results shows that these parameters are the bifurcation parameters and Neimark, symmetry breaking, flip, and period-3 bifurcations occur when the detuning parameter is varied.     

Effect of structure parameters on forces acting on baffles used in gas–solids fluidized beds

Effects of some important structural parameters, i.e. slat pitch, and layout position, on dynamic forces acting on the baffles were examined in the fluidized bed of FCC particles operating under different superficial gas velocities. The experimental baffles were made of multiple inclined slats. We found that the forces acting on the baffles decreased significantly with reducing pitch between the slats. For the baffles with a small slat pitch, the forces acting on the baffles increased slightly and then decreased with increasing superficial gas velocity, which is very different from the measured results of a single slat or tube immersed in fluidized beds. The different results are greatly related to the appearance of the “gas cushion” beneath the baffles, whose height increases with increasing superficial gas velocity. On the other hand, a region with stronger particle circulation induced by the inclined slat array was observed in the experiments. The slat near the wall and located below the region of downward-flowing particles was found to be subjected to the severest forces. Therefore, the slats located in similar locations of industrial baffles are suggested to be reinforced to increase their structural strength.     

Hydrodynamics in a new liquid–solid circulating conventional fluidized bed

A new type of liquid–solid fluidized bed, named circulating conventional fluidized bed (CCFB) which operates below particle terminal velocity was proposed and experimentally studied. The hydrodynamic behavior was systematically studied in a liquid–solid CCFB of 0.032 m I.D. and 4.5 m in height with five different types of particles. Liquid–solid fluidization with external particle circulation was experimentally realized below the particle terminal velocity. The axial distribution of local solids holdup was obtained and found to be fairly uniform in a wide range of liquid velocities and solids circulation rates. The average solids holdup is found to be significantly increased compared with conventional fluidization at similar conditions. The effect of particle properties and operating conditions on bed behavior was investigated as well. Results show that particles with higher terminal velocity have higher average solids holdup.     

Facile biogenic selenium nanoparticle synthesis,characterization and effects on oxidative stress generated by UV in microalgae

Since nanoparticle synthesis via chemical and physical methods is expensive and includes hazardous chemicals, biosynthesis has emerged as an environmentally friendly, clean and viable alternative. The present study reports the synthesis of selenium nanoparticles (SeNPs) using Citricoccus sp.. For the production of SeNPs, the influence of some parameters (time, pH, temperature and stirring rate) was studied. Optimum synthesis conditions were found as pH 8, 24 h reaction time, 37 °C and 150 rpm. Synthesized particles were spherical and were 104.46 ± 50.82 nm with a zeta potential of –20.43 ± 0.41 mV. Afterward, the effects of the nanoparticles on oxidative stress biomarkers, hydrogen peroxide (H₂O₂), malondialdehyde (MDA), chlorophyll (a + b) and growth rate, subsequent to UV-C irradiation on Chlorella vulgaris were investigated. In culture contains nanoparticle and UV-C exposed, the amount of H₂O₂ and MDA decreased on the 1st, 3rd and 7th days following UV exposure compared to UV-applied group, while optical density and cell density increased, the amount of chlorophyll (a + b) changes were statistically similar. Consequently, it has been shown that the synthesized SeNPs alleviated the adverse effects of UV stress in microalgae.     

Parallelizable and robust image segmentation model based on the shape prior information

Image segmentation is an important task in many fields, and there are plentiful models based on region or edges. Nowadays, the speed of calculation and the universal applicability of the model attract much attention. To some extent, the traditional energy model can segment images suffering from intensity inhomogeneity while it relies on initialization seriously. In this paper, we present a new model that consists of an arbitrary active contour model and proposed shape priori information term, which can segment various images accurately and provide an opportunity to carry on parallelizable calculation. The shape priori information term plays a key role in our energy functional and the shape priori information can be chosen diversely. This term also improves the robustness of our model including initial conditions and parameter adjustment. Besides, the split Bregman method is then applied to minimize the energy functional. Multiple experimental results and comparisons are shown to demonstrate the superiority of the proposed model. Firstly, fuzzy clustering, threshold and manual operation are used to be the shape priori information. Secondly, it is illustrated that our model is not sensitive to parameters and initial contours. Computation time and accuracy are also obviously improved when using the parallel algorithm.     

Studies on thin films of lead chalcogenides

A good deal of information regarding the synthesis and opto–electro-structural properties of thin films of lead chalcogenides have been revealed. The development of laser technology had opened up new application for narrow gap lead salts and their alloys. The polycrystalline thin films were deposited onto optically plane and chemically clean glass substrates by vacuum evaporation technique. The films were thin, uniform, smooth and tightly adherent to the substrates.Optical absorption spectroscopy, X-ray diffraction technique and current–voltage characteristics method were used to characterize the films. The absorption coefficients and optical band gaps of films were determined by using FTIR spectrophotometer. The nature of sample, crystal structure and lattice parameters of films were found from X-ray diffractograms. The dc conductivities and activation energies of films were measured in temperature range 300–380 K. Schottky junctions of PbS, PbSe and PbTe with indium metal were made. The barrier heights and ideality factors of these metal–semiconductor junctions were determined by using I–V characteristics.     

Non-local theory solution for a Mode I crack in piezoelectric materials

In this paper, the non-local theory of elasticity is applied to obtain the behavior of a Griffith crack in the piezoelectric materials subjected to a uniform tension loading. The permittivity of the air in the crack is considered. By means of the Fourier transform, the problem can be solved with the help of two pairs of dual integral equations, in which the unknown variables are the jumps of the displacements across the crack surfaces. To solve the dual integral equations, the jumps of the displacements across the crack surfaces are expanded in a series of Jacobi polynomials. Numerical examples are provided to show the effects of the crack length, the materials constants, the electric boundary conditions and the lattice parameter on the stress and the electric displacement fields near the crack tips. It can be obtained that the effects of the electric boundary conditions on the electric displacement fields are large. Unlike the classical elasticity solutions, it is found that no stress and electric displacement singularities are present at the crack tips. The non-local elastic solutions yield a finite hoop stress at the crack tips, thus allowing us to use the maximum stress as a fracture criterion.     

PARAMETRIC VARIATIONAL PRINCIPLE BASED ELASTIC-PLASTIC ANALYSIS OF COSSERAT CONTINUUM

A new algorithm is developed based on the parametric variational principle for elastic-plastic analysis of Cosserat continuum. The governing equations of the classic elastic-plastic problem are regularized by adding rotational degrees of freedom to the conventional translational degrees of freedom in conventional continuum mechanics. The parametric potential energy principle of the Cosserat theory is developed, from which the finite element formulation of the Cosserat theory and the corresponding parametric quadratic programming model are constructed. Strain localization problems are computed and the mesh independent results are obtained.