Influence of the connecting tube at the cold end in a U-shaped pulse tube cryocooler

In some special applications, the pulse tube cryocooler must be designed as U-shape; however, the connecting tube at the cold end will influence the cooling performance. Although lots of U-shape pulse tubes have been developed, the mechanism of the influence of the connecting tube on the performance has not been well demonstrated. Based on thermoacoustic theory, this paper discusses the influence of the length and diameter of the connecting tube, transition structure, flow straightener, impedance of the inertance tube, etc. on the cooling performance. Primary experiments were carried out in two in-line shape pulse tube cryocoolers to verify the analysis. The two cryocoolers shared the same regenerator, heat exchangers, inertance tube and straightener, and the pulse tube, so the influence of these components could be eliminated. With the same electric power, the pulse tube cryocooler without connecting parts obtained 31 W cooling power at 77 K; meanwhile, the other pulse tube cryocooler with the connecting parts only obtained 27 W, so the connecting tube induced more than a 12.9% decrease on the cooling performance, which agrees with the calculation quite well.     

Influence of Na2 CO3 as Additive on Direct Reduction of Boron-bearing Magnetite Concentrate

Boron-bearing magnetite concentrate is typically characterized by low grade of iron and boron (wTFe=51%-54%,wB2 O3=6%-8%),as well as the close intergrowth of ascharite phase and magnetite phase.A promising technology was proposed to separate iron and boron by coupling the direct reduction of iron oxides and Na activation of boron minerals together.The influence of Na2 CO3 as additive on the direct reduction of boron-bearing magnetite was studied by chemical analysis,kinetic analysis,XRD analysis and SEM analysis.The results showed that the ad-dition of Na2 CO3 not only activated boron minerals,but also reduced the activation energy of the reaction and pro-moted the reduction of iron oxides.Besides,the addition of Na2 CO3 changed the composition and melting point of non-ferrous phase,and then promoted the growth and aggregation of iron grains,which was conducive to the subse-quent magnetic separation.Thus,the coupling of the two processes is advantageous.     

Low-temperature efficient degradation of ethyl acetate catalyzed by lattice-doped CeO2–CoOx nanocomposites

A series of CeO₂–CoO_x nanocatalysts have been synthesized by a facile surfactant-free hydrothermal method and investigated for the oxidative degradation of ethyl acetate (EA) at exceptionally low temperature. The combination of various techniques, such as H₂-TPR, XRD, XPS and HRTEM provides insights to the effect of various factors including redox properties, enhanced lattice oxygen and its mobility etc. on catalysis performance. The results demonstrate that the enriched lattice oxygen is the dominant factor for the low-temperature degradation of EA due to the interaction between lattice-mixed Ce and Co ions, which can be used to design the catalysts for removing VOCs with improved performance.     

Partition-based fuzzy median filter based on adaptive resonance theory

This paper presents a novel partition-based fuzzy median filter for noise removal from corrupted digital images. The proposed filter is obtained as the weighted sum of the current pixel value and the output of the median filter, where the weight is set by using fuzzy rules concerning the state of the input signal sequence to indicate to what extent the pixel is considered to be noise. Based on the adaptive resonance theory, the authors developed a neural network model and created a new weight function where the neural network model is employed to partition the observation vector. In this framework, each observation vector is mapped to one of the M blocks that form the observation vector space. The least mean square (LMS) algorithm is applied to obtain the optimal weight for each block. Experiment results have confirmed the high performance of the proposed filter in efficiently removing impulsive noise and Gaussian noise.     

Nanocomposite polyHIPEs with magnetic nanoparticles: Preparation and heating effect

Emulsion templating of high internal phase emulsions (HIPEs) was used to synthesise microcellular poly(styrene-co-divinylbenzene) magnetic nanoparticle composites with open, interconnected, porous structures. The emulsions were stabilised by a combination of a surfactant and maghemite/magnetite (uncoated or coated with oleic acid) nanoparticles and then cured thermally. Up to 23 wt% (with regards to complete composite mass) of magnetic nanoparticles were incorporated into the polymer matrix. Composite polymers exhibited magnetic properties with a saturation magnetisation of 13 emu/g and a substantial heating effect at the AC magnetic field of 3.8 kA/m and a frequency of 104 kHz. A nanocomposite polyHIPE sample with coated nanoparticles exhibited a higher hyperthermia effect. Samples retained typical polyHIPE morphology with cavity diameters of approx. 8 μm and interconnecting pores of around 0.8 μm in diameter. Compared to styrene/divinylbenzene polyHIPEs without nanoparticles, the openness (interconnecting pore size to cavity size ratio) was slightly reduced. Materials were characterised with gas adsorption porosimetry, XRD, TGA/DSC, SEM, TEM.     

Degradation and chemical change of longlife oils following intensive use in automobile engines

The paper researches the features and quality of longlife oils after the point of being recommended for replacement by the onboard computer. The longlife oils have their service life prolonged to 30 up to 50 thousand kilometres which is being monitored and evaluated by the onboard computer. The onboard computer then, on the basis of several parameters, modifies the interval to optimum value. Kinematic viscosity, TBN, the amount of soot, oxidizing and sulphating products, water, fuel, glycol and high antioxidant presence were measured. The results we obtained from the measurements do not correspond with the conclusions of onboard computers.     

Measuring the thermal conductivity of residue-free suspended graphene bridge using null point scanning thermal microscopy

Despite the importance of the accurate measurement of the thermal conductivity of graphene, deviations in previous data are still quite large due to the low signal-to-noise ratio in the measurement of graphene temperature, the uncertainties in the measurement of the heat dissipation, and the influence of the polymeric residues. Herein, we improve signal-to-noise ratio by using null point scanning thermal microscopy, which profiles temperature quantitatively with nanoscale spatial resolution (∼50 nm), independently of both the heat flux through the air and the variation of the sample surface properties. Also, we control and monitor the heat generation rate accurately by heating the suspended graphene bridge electrically. Furthermore, we prevent the disturbance of the thermal conductivity caused by the polymeric residues by using polydimethylsiloxane stamping method, which leaves much less residue than using polymethylmethacrylate. The thermal conductivity values of graphene, whose length and width are 3.6 and 5.52 μm, respectively, were measured as 2430 ± 190, 2150 ± 170, and 2100 ± 160 W/mK at the peak temperatures of 335, 361, and 366 K, respectively, with much smaller error range compared to the previously reported values. The measured values exceed the highest value (∼2000 W/mK at room temperature) obtained for graphite.     

Experimental investigation on flexural behavior of concrete-filled pentagonal flange beam under concentrated loading

The flexural behavior of simply supported concrete-filled pentagonal flange beams (CFPFBs) under mid-span loading is experimentally and numerically investigated. There are two CFPFB specimens tested to failure under static load condition to determine the beam flexural capacity. One of the test specimens is designed with a pair of transverse stiffener at mid-span while the other is without any stiffener to resist the load. Both the test specimens have identical geometrical and material properties. From the experimental results, the flexural capacity of the specimen with stiffener is found to be 10% higher than that of the specimen without stiffener. The failure behavior shows the importance of transverse stiffener to enhance the ultimate flexural capacity and to avoid the localized web distortion of the beam. In the numerical study based on finite element (FE) analysis, the concrete and steel materials are modeled using the eight-node solid and four-node shell element respectively. A comparison of the ultimate capacity of the CFPFBs with and without stiffener reveals that the FE models simulate very well the flexural behavior of the test specimens and the difference of maximum load is found to be less than 10%.     

Time–frequency interpretation of multi-frequency signal from rotating machinery using an improved Hilbert–Huang transform

The Hilbert–Huang transform (HHT) has proven to be a promising tool for the analysis of non-stationary signals commonly occurred in industrial machines. However, in practice, multi-frequency intrinsic mode functions (IMFs) and pseudo IMFs are likely generated and lead to grossly erroneous or even completely meaningless instantaneous frequencies, which raise difficulties in interpreting signal features by the HHT spectrum. To enhance the time–frequency resolution of the traditional HHT, an improved HHT is proposed in this study. By constructing a bank of partially overlapping bandpass filters, a series of filtered signals are obtained at first. Then a subset of filtered signals, each associated with certain energy-dominated components, are selected based on the maximal-spectral kurtosis–minimal-redundancy criterion and the information-related coefficient, and further decomposed by empirical mode decomposition to extract sets of IMFs. Furthermore, IMF selection scheme is applied to select the relevant IMFs on which the HHT spectrum is constructed. The novelty of this method is that the HHT spectrum is just constructed with the relevant, almost monochromatic IMFs rather than with the IMFs possibly with multiple frequency components or with pseudo components. The results on the simulated data, test rig data, and industrial gearbox data show that the proposed method is superior to the traditional HHT in feature extraction and can produce a more accurate time–frequency distribution for the inspected signal.     

Automatic real-time SLAM relocalization based on a hierarchical bipartite graph model

The need to increase the robustness of a real-time monocular SLAM system raises the important problem of relocalization;namely,how to automatically recover a SLAM system after tracking failures.We address this problem by proposing a real-time relocalization algorithm based on a hierarchical bipartite graph model.When the SLAM system is lost,we use the latter model to find sufficient correspondences between the detected image and stored map features,thus achieving efficient,real-time relocalization.The model accounts for both temporal and spatial constraints.Experimental results on both synthetic and real data support the effectiveness of the proposed algorithm.