[en] The identification of modal parameters from the response data only is studied for structural systems under nonstationary ambient vibration. In a previous paper by the authors, the modal parameters of a system were identified using the correlation method in conjunction with the curve-fitting technique. This was done by working within the assumption that the ambient excitation is a nonstationary white noise in the form of a product model. In the present paper, the Ibrahim time-domain method (ITD) is extended for modal-parameter identification from the nonstationary ambient response data without any additional treatment of converting the original data into the form of free vibration. The ambient responses corresponding to various nonstationary inputs can be approximately expressed as a sum of exponential functions. In effect, the ITD method can be used in conjunction with the channel-expansion technique to identify the major modes of a structural system. To distinguish the structural modes from the non-structural modes, the concept of mode -shape coherence and confidence factor is employed. Numerical simulations, including one example of using the practical excitation data, confirm the validity and robustness of the proposed method for identification of modal parameters from the nonstationary ambient response

[en] This study aims to improve the accuracy of the parametric estimation of systems with modal interference in the frequency domain. The theory of modal identification states that the frequency response function can be expressed as a rational function form by using the curve fitting technique, and the modal parameters can then be estimated from rational fractional coefficients. The conventional common denominator model only indicates the frequency response function of a single-degree-of-freedom system; thus, it cannot acquire the mode shape information. In this paper, we propose the matrix-fractional coefficient model constructed by the frequency response functions of a multiple-degree-of-freedom system for modal identification. To avoid the phenomenon of omitted modes caused by the distortion from modal interference among the vibration modes of systems during modal estimation, we use a system model with higher-order matrixfractional coefficients, but fictitious modes may be caused by numerical computation. Structural and fictitious modes can be effectively separated by using a different-order constructed stabilization diagram. Modal identification can be implemented by solving the eigenproblem of the companion matrix yielded from least-square estimation. Numerical simulations, including a full model of sedan and onehalf railway vehicle in the form of a linear 2D model, as well as the experimental testing of an actual plate, confirm the validity and robustness of the proposed parametric-estimation method for a system with modal interference under noisy conditions.

[en] Modal Identification from response data only is studied for structural systems under nonstationary ambient vibration. The topic of this paper is the estimation of modal parameters from nonstationary ambient vibration data by applying the random decrement algorithm with time-varying threshold level. In the conventional random decrement algorithm, the threshold level for evaluating random dec signatures is defined as the standard deviation value of response data of the reference channel. The distortion of random dec signatures may be, however, induced by the error involved in noise from the original response data in practice. To improve the accuracy of identification, a modification of the sampling procedure in random decrement algorithm is proposed for modal-parameter identification from the nonstationary ambient response data. The time-varying threshold level is presented for the acquisition of available sample time history to perform averaging analysis, and defined as the temporal root-mean-square function of structural response, which can appropriately describe a wide variety of nonstationary behaviors in reality, such as the time-varying amplitude (variance) of a nonstationary process in a seismic record. Numerical simulations confirm the validity and robustness of the proposed modal-identification method from nonstationary ambient response data under noisy conditions.

[en] Recycling of scrap metal can effectively improve resource utilization and protect the environment. However, due to the existence of some management problems, a few radioactive sources used in the field of nuclear technology application, or some radioactive contaminated metals also enter the scrap metal recycling sector, through recycled metal products into the community, threatening public health and environmental safety. The special inspection work of radiation safety in scrap metal recycling in Guangxi in 2016 is introduced. The present situation and existing problems in this regard is analyzed, and the countermeasures and suggestions are then put forward. (authors)

[en] Fe–6.5%Si steel was hot rolled and heat treated in the laboratory. The grain interplanar spacing and microhardness of the steel were measured, and the ratio of diffraction peaks intensity of the A2 disordered phase and the DO_3 ordered phase was analyzed under different cooling conditions. With the increasing of cooling rate, indentation morphology of Vickers microhardness for the experimental steel was transformed from a sink-in type into a pile-up type, and the strain-hardening exponent decreased. As annealing temperature was decreased below 700 °C, DO_3 and B2 ordered phases are formed, resulting in a higher microhardness. When annealing temperature was greater than 800 °C, ordered phase is transformed from B2 to DO_3, microhardness of the steel decreased. Indentation morphologies of Vickers microhardness become a sink-in type when annealing temperature was lower than 650 °C. While annealing temperature was 700–900 °C, the surface indentation morphologies of samples was a pile-up type. With the increase of annealing temperature, the amount of DO_3 ordered phases and the strain-hardening exponent decreased. The ordered phases in Fe–6.5%Si steel could cause the difficulty of dislocation movement and brittleness at room temperature during plastic deformation.

[en] The simultaneous radon and thoron monitoring method developed at University of South China was adopted to survey radon and thoron concentrations in two types of countryside dwellings with the soil walls or the red brick walls in two villages of Hengyang City. The measurement results indicate that more attention must be paid to the risk of environmental thoron in countryside dwellings, because the effective dose from thoron and its daughters is almost equal to or bigger than that from radon and radon daughters in some dwellings with the soil walls

[en] Biomass gasification using lattice oxygen (BGLO) of natural hematite coupling with steam was conducted in a fluidized bed reactor. The presence of hematite particles evidently facilitated to biomass gasification. Comparing with biomass steam gasification (BSG), carbon conversion and gas yield increased by 7.47% and 11.02%, respectively, and tar content lowered by 51.53%, in BGLO with an S/B of 0.85 at 800 °C. In this case, 62.30% of the lattice oxygen in the hematite particles was consumed in the biomass gasification. The reaction temperature, steam-to-biomass ratio (S/B) and reaction time on the performance of hematite particles were extensively investigated, in terms of gas distribution, heating value, yield and carbon conversion. With the reaction temperature increasing from 750 to 850 °C, the gas yield increased from1.12 to 1.53Nm³/kg, and carbon conversion increased from 77.21% to 95.49%. An optimal S/B ratio of 0.85 was obtained in order to maximize the carbon conversion and gas yield of BGLO. At this ratio, the gas yield reached 1.41Nm³/kg with carbon conversion of 92.98%. The gas concentration was gradually close to that of BSG at the end stage of BGLO due to the active lattice oxygen was depleted with the proceeding of reactions. - Highlights: • Biomass gasification using lattice oxygen (BGLO) was studied with hematite as oxygen carrier under steam atmosphere. • Lattice oxygen can improve evidently the gas yield and carbon conversion efficiency. • BGLO has major advantages of avoiding pure oxygen consumption and reducing tar. • Optimum operating conditions were 800 °C and steam-to-biomass ratio of 0.85

[en] Highlights: • Aluminium-polymer composite packing material with high T-peel strength was prepared. • Polypropylene was grafted by acrylic acid, glycidyl methacrylate, maleic anhydride. • Grafted polypropylene greatly improved the T-peel strength. • Chemical bonding plays an important role in improving the adhesion strength. - Abstract: The interfacial bonding between functionalized polymers and chromate–phosphate treated aluminum (Al) foil were investigated in this study. Glycidyl methacrylate (GMA), acrylic acid (AA) and maleic anhydride (MAH) were grafted onto polypropylene (PP) to improve its adhesion strength with the treated Al foil. The interfacial peel strength was evaluated by the T-peel test, and the results showed that modification of PP resulted in a significant improvement in the interfacial peel strength from 1 N/15 mm for pure PP to 10–14 N/15 mm for the modified PP. The surface chemistry, topography and surface energy of the modified PP and Al foil after peeling were characterized by time-of-flight secondary ion mass spectrometry (TOF-SIMS), X-ray photoelectron spectroscopy (XPS), attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), scanning electron microscopy (SEM) and contact angle measurement. The treated Al foil could react with the functional groups of PP, resulting in the formation of new carboxylates. The new chemical bonding rather than the mechanical interlocking contributed to the improvement of adhesion strength

[en] Modal identification is considered from response data of structural system under nonstationary ambient vibration. In a previous paper, we showed that by assuming the ambient excitation to be nonstationary white noise in the form of a product model, the nonstationary response signals can be converted into free-vibration data via the correlation technique. In the present paper, if the ambient excitation can be modeled as a nonstationary white noise in the form of a product model, then the nonstationary cross random decrement signatures of structural response evaluated at any fixed time instant are shown theoretically to be proportional to the nonstationary cross-correlation functions. The practical problem of insufficient data samples available for evaluating nonstationary random decrement signatures can be approximately resolved by first extracting the amplitude-modulating function from the response and then transforming the nonstationary responses into stationary ones. Modal-parameter identification can then be performed using the Ibrahim time-domain technique, which is effective at identifying closely spaced modes. The theory proposed can be further extended by using the filtering concept to cover the case of nonstationary color excitations. Numerical simulations confirm the validity of the proposed method for identification of modal parameters from nonstationary ambient response data

[en] This study reports the formation of ultra-thin cobalt nitride (CoN_x) films on a Co/ZnO(002) crystal by low-energy ion sputtering of nitrogen in an ultrahigh vacuum system. The CoN_x film formed during ion bombardment in which the nitrogen plasma (N⁺) results in both sputtering and implantation in the formation process of CoN_x, especially for the Co adsorbed layers. Auger electron spectroscopy analysis shows that the composition ratio x as a function of sputtering time was highly related to the N⁺ ion energy that was varied from 0.5 to 2 keV. The composition ratio x of CoN_x films is inversely proportional to the ion energy. Low-energy ion sputtering is possible to fabricate ultra-thin CoN_x films and to adjust their chemical compositions.