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This paper focuses on the issue of quantifying nonlinear output frequency response components of different orders of nonlinear dynamical systems for a general excitation. An alternative approach is presented based on Volterra series and conditioned spectral analysis (CSA) theories. Firstly, a multiple-input/single-output (MISO) linear system with a series of power characterized inputs is obtained by decomposing the nonlinear system under analyzed based on Volterra series. Secondly, the correlations among the inputs of different orders are removed by utilizing CSA approach, obtaining an algorithm of identifying the nonlinear output frequency response functions (NOFRFs) and evaluating the contributions of different order nonlinearities to the output of the system. Two kinds of nonlinear systems were simulated numerically to verify the accuracy of the method. The results reached by the proposed method are very close to the numerical results obtained by the fourth order Runge–Kutta method. Finally, an experiment analysis was carried out, in which the vibration transmission properties of a bolt connection were tested when the bolt was fastened and loose respectively. The results of experiments reflected further the effectiveness of the method on distinguishing quantitatively the contributions of each order nonlinearities to the output of a nonlinear system. [ABSTRACT FROM AUTHOR]

Soft abrasive flow (SAF) finishing has advantages in precise processing for titaniferous alloy parts with large-area surfaces. However, the processing efficiency and surface quality of current SAF methods require to be improved. To address the issues, a novel gas–liquid-solid three-phase rotary abrasive flow polishing method (RGLSP) is proposed based on the microbubble cavitation effect. Referring to the energy conservation principles of bubbles group movement, an improved realizable k-ε turbulence model is set up. Based on the above model, a mechanical dynamic model of the machining apparatus is established to obtain the flow field distribution of different structural parameters. The simulated results show that the pitch-down angle determines the distribution of the rotary flow field, and an optimized processing apparatus is developed. The machining experiments show that the proposed RGLSP method can improve the machining efficiency by 60%, and the surface roughness can reach Ra 0.1 μm with lower surface defects. The RGLSP can provide an important reference direction for low-carbon emission processing. [ABSTRACT FROM AUTHOR]

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As an advanced downhole instrument in drilling engineering, drilling fluid continuous wave generator (DFCWG) has great application prospects. The large load torque is one of the key problems that hinder the development of DFCWG. In this paper, based on the design theory of rotary valve and finite element method, the structure of rotary valve is designed and the load torque characteristics is analyzed and points out that the load torque has strong alternating characteristics. It is pointed out that the load torque has the characteristics of strong alternating. According to the characteristics of the load torque, the "fluid-magnetic" collaborative compensation method is proposed. The load compensation turbine and magnetic compensation device are used to compensate the DC and AC components of the load torque respectively, and the load compensation device is designed. The rationality of the design of the load compensation device is verified by simulation. Finally, the comprehensive compensation effect is analyzed by the finite element method. According to the analysis results, the "fluid-magnetic" collaborative compensation method can effectively reduce the load torque. The research results can provide technical support for DFCWG design. [ABSTRACT FROM AUTHOR]

The negative pulsed downlink communication system is used to send surface control commands to the downhole rotary steering tool at thousands of meters, which is a significant part of the current rotary steering technology. At present, the transmission efficiency of negative pulsed downlink communication is very low, and only simple control commands can be transmitted in a few minutes, which limits the development of rotary steering technology with complex control functions. To improve the transmission rate of the downlink system, the downlink pulse width needs to be shortened. However, due to the influence of signal transmission characteristics, the waveform of a narrow pulse width signal will be severely distorted, which increases the difficulty of decoding the downlink signal. Therefore, a decoding method based on pattern recognition for negative pulsed downlink signal with narrow pulse width is proposed in this paper, which establishes a Euclidean distance matrix model between similar characteristic signal segments on the rising or falling edge of the downlink signal, the pulse coding timing of among the signal segment with each rising or falling edge is analyzed, the decoding and recognition of the downlink instruction are achieved, which solves the problem of large timing deviation in decoding the downlink signal with a current threshold method. The experimental results show that the method proposed in this paper can achieve accurate decoding of the 6 s pulse width downlink signal. Compared with the threshold method, it can be seen that the decoding accuracy of the method proposed in this paper can be greatly improved, and the smaller the signal pulse width, the more significant the advantage. [ABSTRACT FROM AUTHOR]

A base amount-dependent fluorescence enhancement-based strategy is put forward to determine vascular endothelial growth factor 165 (VEGF165) in human serum by the use of hairpin DNA-silver nanoclusters (hDNA-AgNCs) and oxidized carbon nanoparticles (CNPs). The hDNA-AgNCs aptasensing probe consists of AgNCs-contained hairpin loop (that generates a fluorescence signal), hairpin stem (that makes the structure stable), and the terminal aptamer 1 (that recognizes the target together with aptamer 2). It has been demonstrated that the fluorescence intensity of hDNA-AgNCs is ~ 3-fold stronger than that of single-stranded DNA-AgNCs (ssDNA-AgNCs), and hDNA-AgNCs have a strong dependence of fluorescence enhancement on the base amount in hairpin stem and loop. Upon the addition of oxidized CNPs, the terminal aptamer 1 of hDNA-AgNCs can adsorb onto the surface of oxidized CNPs via π-π stacking, and the fluorescence of hDNA-AgNCs (with excitation/emission maxima at 490/567 nm) is quenched via fluorescence resonance energy transfer (FRET). When aptamer 2 and VEGF165 are subsequently added, aptamer 1, VEGF165, and aptamer 2 reassemble into an intact tertiary structure, and the fluorescence is recovered because hDNA-AgNCs are far away from the surface of oxidized CNPs and the FRET efficiency decreases. Under the optimized conditions, the aptasensing probe can selectively assay VEGF165 with a detection limit of 14 pM. The results provide a label-free and sensitive method to monitor VEGF165 in human serum. [ABSTRACT FROM AUTHOR]

A ratiometric fluorescent test pen filled with a mixing ink of blue carbon dots (CDs) and red CdTe quantum dots (CdTe QDs) is introduced for portable assay of silver ion (Ag(I)) on paper. The mixing ink was tuned with ratiometric fluorescent intensity of 1:5, and then filled into a vacant commercial fluorescent pen core. Writing/painting a random word/figure on a blank paper can make the most portable nanoprobe determining Ag(I) by visualization. Ag(I) can adsorb onto the surface of CdTe QDs, which leads to the formation of surficial Ag2Te layer by an ion-exchanging reaction. This enables the red fluorescence of CdTe QDs (with excitation/emission maxima at 360/628 nm) to be quenched. Due to the unchanged blue fluorescence of CDs (with excitation/emission maxima at 360/440 nm) as internal standard, the solution color evolves gradually from red to blue with the increase of Ag(I) concentration with a detection limit of 3.48 nM. This is at least 2 orders of magnitude lower than the limit defined by World Health Organization (WHO) in drinkable water. The fluorescent test pen has also been used for the determination of Ag(I) in wastewater. [ABSTRACT FROM AUTHOR]

Fisheries management must take account of environmental sustainability, economic profitability, and social benefits generated by the public resources. The traditional approach of maximum economic yield (MEY), however, is yet to consider social objectives in deriving quantitative quotes. Current MEY evaluation framework would be appropriate if the economic rent was distributed back to the public. If public resources are privatized as corporations, the rent largely flows to the owners of large capital in the fishing industry. This is in stark contrast to the aims of benefiting the community as a whole. In this short paper, we promote a socially responsible framework in decision-making of fisheries management. This approach is beyond the fleet-based MEY approach, for it incorporates fleet profitability, chain profitability, employment, environmental concerns, and broad social benefits, in strict accordance with stock sustainability. Recognizing the needs of fishers, as well as the interests of chain sectors and the broader community, is a vital part of ensuring responsible fishery management and a viable future for Australian fisheries. The established framework will provide open view scenarios and enrich the MEY approaches in fisheries management. [ABSTRACT FROM AUTHOR]

The corrected Akaike information criterion (AICc) is a widely used tool in analyzing environmental and ecological data, and it outperforms the Akaike information criterion (AIC), especially in small-size samples. To take advantage of this property, we propose a modified version of the AICc in a generalized linear model framework, referred to as the blockwise AICc (bAICc). Compared with some other information criteria, extensive simulation results show that the bAICc performs well. We also analyzed two environmental datasets, one for snail survival and the other for fish infection, to illustrate the usefulness of this new model selection criterion. [ABSTRACT FROM AUTHOR]