Novel method for fabrication of room temperature polypyrrole–ZnO nanocomposite NO2 sensor

Nanocomposites of polypyrrole (PPy) and zinc oxide (ZnO) nanoparticles (NPs) were prepared by spin coating method. These nanocomposites were characterized by Fourier transform infrared (FTIR), Field emission scanning electron microscope (SEM), Atomic force microscopy (AFM), Transmission electron microscopy (TEM), X-ray diffraction (XRD) and UV–vis techniques, which proved the polymerization of pyrrole monomer and the strong interaction between polypyrrole and ZnO NPs. The nanocomposites were used for gas sensing to CH₃OH, C₂H₅OH, NH₃, H₂S and NO₂ at room temperature. It was revealed that PPy–ZnO nanocomposites with different ZnO weight ratios (10%, 20%, 30%, 40% and 50%) could detect NO₂ at low concentration with very higher selectivity and sensitivity at room temperature than the reported PPy. The PPy–ZnO nanocomposites responded to NO₂ at concentration as low as 10 ppm. PPy–ZnO nanocomposite containing ZnO (50%) showed the maximum sensitivity 38% with 92.10% stability to 100 ppm NO₂ gas at room temperature. The sensing mechanism of PPy–ZnO nanocomposites to NO₂ was presumed to be the effects of p–n junction between PPy and ZnO.     

Numerical simulation of bubble separation length in a gas–liquid separator based on the Euler–Lagrange method

In this study, the bubble separation behavior in a gas–liquid separator is numerically investigated on the basis of the Euler–Lagrange approach, in which the forces acting on bubbles in a swirling flow field are modeled to calculate the trajectories of the bubbles. By adopting this approach, the effects of five parameters, namely, back pressure, Reynolds number, bubble diameter, void fraction, and swirl number, on separation performance in terms of pressure loss, separation efficiency, separation length, and split ratio are computed and analyzed. On the basis of the analysis, correlations of separation length with the two main parameters are established, which can serve as a basis for the optimal design of separator.     

Reconstruction of emission coefficients for a non-axisymmetric coupling arc based on MALDONADO’s method

The reconstruction of emission coefficient is a key factor for the calculation of temperature field.However,most of the researches for determining arc plasmas are based on axisymmetric sources,little has been done to study non-axisymmetric arc plasmas.In order to reveal temperatures of a non-axisymmetric coupling arc,the distribution of emission coefficients must be reconstructed in advance.In this paper,the argon atomic line intensities of the coupling arc are obtained by using the imaging system that involves a high speed camera in conjunction with a neutral and a narrow-band filter.The converted programme between emission coefficients and emitted intensities is programmed based on MALDONADO’s method.A displaced Gaussian model is used for evaluating the validity of the converted programme.Then,the emission coefficients of a free burning arc are reconstructed by MALDONADO’s method and an Abel inversion,respectively,and good agreement is obtained.Finally,the emission coefficient profiles of the coupling arc are achieved.The results show that the distribution of emission coefficient for the coupling arc is non-axisymmetric.The emission coefficient profile is similar to an ellipse,and the short axis of the ellipse is in the direction that the two electrodes are arranged along.The peak temperature of the coupling arc is in the middle of both electrodes.There is a strong interaction between both arcs within the coupling arc.The proposed research solves difficulties for determining asymmetric arcs and enlarges the application scope of spectroscopic techniques.     

A new method for measuring γ-ray energy at the internal calibration of a radioactive source

We developed a new method for measuring γ-ray energies in the internal calibration of a radioactive source under investigation. The measurements were carried out with the spectrometer of delayed coincidences and an optical delay line. This method allows the energies of the reference peak and the γ-ray peak under investigation to be compared, even if they are close or coincide. The possibility of precise γ-ray energy measurements is illustrated with⁶⁰Co and¹⁵⁴Eu isotopes.     

Development of a high-voltage waveguide photodetector comprised of Schottky diodes and based on the Ge–Si structure with Ge quantum dots for portable thermophotovoltaic converters

This paper demontstrates the possibility of developing a high-voltage waveguide photodetector comprised of Schottky diodes and based on a Au/Ge — Si structure with Ge quantum dots pseudomorphic to a silicon matrix, which ensures an increase in the external quantum yield and open-circuit voltage. It is shown on this photodetector that there is a great increase and broadening in sensitivity up to λ = 2.1 μm, which coincides with the main radiation range of a black (gray) body at the emitter temperatures from 1200 to 1700 °C, practically used in thermophotovoltaic converters. This state of the ensemble of Ge quantum dots by means of molecular beam epitaxy can be obtained only under the condition of low growth temperature (250–300 °C). It is established that, below the Si absorption edge, photoresponse on the photodetectors under consideration is determined by two main mechanisms: absorption on the ensemble of Ge quantum dots and Fowler emission. It is shown by the analysis of the Raman scattering spectra on the optical photons of Ge–Si structures that the quantum efficiency of photodetectors based on them in the first case is due to the degree of nonuniform stress relaxation in the array of Ge quantum dots. The photoresponse directly associated with the Ge quantum dots is manifested on Schottky diodes with a superthin intermediate oxide layer SiO₂, which eliminates the second mechanism. In further development, the proposed photodetector architecture with pseudomorphic Ge quantum dots can be used both for portable thermophotovoltaic converters and fiber-optic data transmission systems at wavelengths corresponding to basic telecommunication standards (λ = 0.85, 1.3 and 1.55, 1.3, and 1.55 μm) on the basis of silicon technologies.     

Ultrasonic pulse and resonance method–evaluation of the degree of damage to the internal structure of repair mortars caused by exposure to high temperatures

When the repair mortars for the repair of concrete structures are exposed to high temperatures, it results in irreversible changes in their internal structure. These changes can be evaluated both on the basis of the compressive strength and flexural strength, but their evaluation can also be made using dynamic non-destructive methods. The article presents the findings on the use of parameters from the measurement by ultrasonic pulse and resonance method. Changes in the internal structure of repair mortars were evaluated on the basis of the dynamic Young’s modulus of elasticity and relative dynamic modulus of elasticity. The said parameters very well characterize the changes in the internal structure of the repair mortars, and their values decrease with the increasing temperature. Changes in the internal structure of the repair mortars also reduce the compressive strength and flexural strength. The researchers confirmed the suitability of the ultrasonic pulse and resonance method for evaluating the degree of damage to the internal structure of repair mortars exposed to high temperatures.     

Method of calculating the cross-wind speed at the entrance aperture of an adaptive system based on Shack–Hartmann wavefront sensor measurements

This paper presents a method for calculating the cross-wind speed at the entrance aperture of an adaptive system from the coordinates of the energy centers of gravity of the focal spots measured by a Shack–Hartmann wavefront sensor. The range of applicability of the method are determined for data obtained in an experiment on an atmospheric path depending on the intensity of turbulent distortions and the optical parameters of the sensor.     

Additive–additive interaction: an XPS study of the effect of ZDDP on the AW/EP characteristics of molybdenum based additives

The effect of zinc dialkyldithiophosphate (ZDDP) addition on the antiwear (AW) and extreme pressure (EP) properties of molybdenum dialkyldithiocarbamate (MoDTC) and molybdenum dialkyl dithiophosphate (MoDTP) are evaluated by standard Four-Ball friction test and also by the determination of coefficient of friction using an oscillating SRV apparatus. The boundary lubrication film formed on the worn surface using the two molybdenum additives and their combination with ZDDP is investigated by depth profile X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) to find out the chemistry of tribochemical reaction occurring at the surface during friction. It is seen that MoDTP possesses better AW properties than MoDTC due to its high reactivity with the metal surface. Nevertheless, the AW characteristics of MoDTC could be improved by the addition of ZDDP. The frictional properties of MoDTP, however, do not change by the addition of ZDDP. The synergistic action of ZDDP on MoDTC is attributed to the enhanced decomposition of MoDTC in presence of ZDDP. This is tentatively explained in terms of some interaction of zinc with the electron donating nitrogen present in MoDTC, which would have helped to increase its tribo-reactivity. XPS studies revealed that in the presence of ZDDP, MoDTC form mainly metal sulphides like MoS₂ and FeS under friction. The MoDTP+ZDDP derived surface, on the other hand, produced mainly metal phosphate along with molybdenum oxysulphides and small amount of MoS₂ and FeS. The mechanism of action of additives is explained.     

Optimal configuration selection method for stiffness identification of serial manipulators based on the κf(A)−1 criterion

In real industrial environment, the stiffness identification accuracy of manipulators is affected by various measurement errors. However, research that deals with the inevitable error perturbation is scarce. The κ_F(A)⁻¹ criterion is adopted for measurement configuration selection to solve this problem according to the perturbation analysis and derivation of solutions to systems of stiffness identification equations. The optimal measurement configurations are finally obtained using the DETMAX optimization algorithm based on the deduced criterion, which is the main contribution of this work. Results illustrate that the optimal configurations optimized by the DETMAX algorithm based on the κ_F(A)⁻¹ criterion can better overcome the influence of measurement errors, improve the identification accuracy, and reduce the compensated position error and fluctuation compared with the other optimization algorithms. Furthermore, the proposed criterion can be applied to the stiffness identification of serial manipulators in a real industrial environment.

     

A new method to investigate the sliding wear behaviour of materials based on energy dissipation: W–25 wt%Cu composite

A new method is proposed to explain and monitor wear behaviour based on energy dissipation. The wear of a W–25 wt%Cu composite against 52100 steel was used to demonstrate this approach with pin-on-disc tests conducted under three normal loads. An energy-dependent criterion, namely, specific wear volume (wear volume/dissipated energy (mm³/J)), was defined to evaluate the wear of the composite. The specific wear volume can be used as a substitute for the traditional wear rate due to the simultaneous expression of several wear parameters and because of its strong dependence on the wear mode. The specific wear volume appears to be constant in any particular “wear mode” regardless of the active “wear processes”. In the wear of this composite, processes such as particle pull-out, mechanically mixed layer (MML) formation, crack propagation and delamination were observed. But, combination of these processes in each test had identical specific wear volumes. Thus, all of these wear processes were considered to be consecutive stages of the same wear mode: fatigue wear. The amount of dissipated energy and the volumetric loss increased with increasing normal load. Also, changing the normal load changed the rate of energy dissipation per unit sliding distance.     

An Experimental Setup for Studying the Solubility and Phase Transitions in a Hydrocarbon–Supercritical CO2 System in a Wide Range of Pressures and Temperatures

Instruments and Experimental Techniques - A system for saturating a porous medium with hydrocarbon and supercritical CO2 has been designed. A procedure for carrying out an experiment on the...     

Non-stationary signal analysis based on general parameterized time–frequency transform and its application in the feature extraction of a rotary machine

With the development of large rotary machines for faster and more integrated performance, the condition monitoring and fault diagnosis for them are becoming more challenging. Since the time-frequency (TF) pattern of the vibration signal from the rotary machine often contains condition information and fault feature, the methods based on TF analysis have been widely-used to solve these two problems in the industrial community. This article introduces an effective non-stationary signal analysis method based on the general parameterized time–frequency transform (GPTFT). The GPTFT is achieved by inserting a rotation operator and a shift operator in the short-time Fourier transform. This method can produce a high-concentrated TF pattern with a general kernel. A multi-component instantaneous frequency (IF) extraction method is proposed based on it. The estimation for the IF of every component is accomplished by defining a spectrum concentration index (SCI). Moreover, such an IF estimation process is iteratively operated until all the components are extracted. The tests on three simulation examples and a real vibration signal demonstrate the effectiveness and superiority of our method.