Minimum Rate Research Articles

Study on creep characteristics and the isochronous stress–strain curve of Ni-Cr-Mo superalloy

ABSTRACT C276 superalloy is considered as a potential structural material for advanced nuclear reactor with good mechanical properties and corrosion resistance. High-temperature creep behaviour of C276 alloy was investigated in the temperature range of 650°C–700°C and at stresses of 140–430 MPa. A linear relationship was fitted between stress and minimum creep rate in the logarithmic coordinate system. The rupture time is analysed for life prediction in terms of isotherm extrapolation method, Monkman–Grant relation, and Larson–Miller parameter method, respectively. The isochronous stress–strain curves as a means of representing stress–strain–time relations under creep conditions were established by the parameter method. The fracture surface morphology of ruptured specimens was characterised by a scanning electron microscope to elucidate the failure mechanism.

On the origin, physical basis and numerical stability of creep life equations

ABSTRACT In this paper several aspects of single line minimum creep rate and time to rupture models are examined that have not been discussed previously in the literature – the origin and boundary condition behaviour of some models; and the existence and relevance (for industrial applications) of temperature turnback. It is found that some published time to rupture models will predict very finite times to rupture at zero stress and temperatures of industrial use of the alloys, and that temperature turnback is mathematically possible even with physics-based models, but unlike stress turnback, the conditions at which temperature turnback would occur are usually of no physical or industrial relevance.

Multiobjective Optimization Design of a Brushless Excitation Synchronous Motor Based on the Taguchi Method

Considering the issue of significant total harmonic distortion in the no-load back electromotive force (EMF) and torque ripple of a brushless excitation synchronous motor (BESM) used in a compressor, a multiobjective optimization design method of a BESM based on the Taguchi method was proposed. By selecting the polar arc coefficient, stator slot width, damping winding pitch, and air gap length as the optimization parameters, the maximum no-load back EMF, minimum back EMF total harmonic distortion rate, and minimum torque ripple are selected as the optimization objectives. Then, the Taguchi method was employed to construct an orthogonal table to enhance the performance of the optimization objectives. This approach facilitated the determination of the optimal parameter combination for optimization. Finally, the simulation results indicate significant enhancements in each optimized aspect of the motor’s performance following the optimization process. This outcome serves as validation for the efficacy of the Taguchi method in achieving an optimal design for the BESM.

Robust Transmission Design for RIS-Assisted Secure Multiuser Communication Systems in the Presence of Hardware Impairments

This paper investigates reconfigurable intelligent surface (RIS)-assisted secure multiuser communication systems in the presence of hardware impairments (HIs) at the RIS and the transceivers. We jointly optimize the beamforming vectors at the base station (BS) and the phase shifts of the reflecting elements at the RIS so as to maximize the weighted minimum approximate ergodic secrecy rate (WMAESR), subject to the transmission power constraints at the BS and unit-modulus constraints at the RIS. To solve the formulated optimization problem, we first decouple it into two tractable subproblems and then use the block coordinate descent (BCD) method to alternately optimize the subproblems. Two different methods are proposed to solve the two obtained subproblems. The first method transforms each subproblem into a second order cone programming (SOCP) problem by invoking the penalty convexconcave procedure (CCP) method and the closed-form fractional programming (FP) criterion, and then directly solves them by using CVX. The second method leverages the minorization-maximization (MM) algorithm. Specifically, we first derive a concave approximation function, which is a lower bound of the original objective function, and then the two subproblems are transformed into two simple surrogate problems that admit closed-form solutions. Simulation results verify the performance gains of the proposed robust transmission methods over existing non-robust designs. In addition, the MM algorithm is shown to have much lower complexity than the SOCP-based algorithm.

Rate-Splitting Multiple Access for Quantized Multiuser MIMO Communications

This paper investigates the sum spectral efficiency maximization problem in downlink multiuser multiple-input multiple-output systems with low-resolution quantizers at an access point (AP) and users. We consider rate-splitting multiple access (RSMA) to enhance spectral efficiency by offering opportunities to boost achievable degree-of-freedom. Optimizing RSMA precoders, however, is highly challenging due to the minimum rate constraint when determining the common rate. The quantization errors coupled with the precoders make the problem more complicated. In this paper, we develop a novel RSMA precoding algorithm incorporating quantization errors for maximizing the sum spectral efficiency. To this end, we first obtain an approximate spectral efficiency in a smooth function. Subsequently, we derive the first-order optimality condition in the form of the nonlinear eigenvalue problem (NEP). We propose a computationally efficient algorithm to find the principal eigenvector of the NEP as a sub-optimal solution. We also extend the weighted minimum mean square error-based RSMA precoding to the considered quantization system. Simulation results validate the proposed methods. The key benefit of using RSMA over spatial division multiple access (SDMA) comes from the ability of the common stream to balance between the channel gain and quantization error in multiuser MIMO systems with different quantization resolutions.

10 Hz Stable Mode-locked Er-Fiber Laser

Abstract: In this paper, a stable output at the reduction repetition rate from 80 MHz mode-locked Er-doped fiber laser (EDFL) was demonstrated by adjusting the operating point for external LiNbO3 Mach-Zehnder‎ electro-optic intensity modulator to suppress harmonic mode-locked pulses. More than 70% of the laser beam was launched into the external pigtail Mach-Zehnder intensity modulator using single mode fiber with collimating lens and fiber (ferrule connector) FC adapter. The optimum values of Mach-Zehnder modulator bias voltages V0 and Vπ (half wave voltage) which resulted in maximum and minimum laser output power to leave the modulator were found at 6.5 and 0.29 V, respectively. The best modulation was achieved for the RF modulating signal with an opening time of about 8 ns. For driving voltage equal to Vπ, a clean mode-locked pulse train was generated with a pulse shape and energy similar to the input pulse, albeit with a low repetition rate. The minimum repetition rate reached as low as 10 Hz, resulting in pulse energy and peak power of 0.32 nJ and 1.5 kW, respectively. Second-harmonic generation of the low repetition rate pulse train was also produced by using a PPLN crystal. This opens up the potential for using this laser in single photon detection experiments and as a seed laser for many applications. Keywords: Er-fiber laser, Passively mode-locked fiber laser, Nonlinear polarization rotation, Mach-Zehnder modulator, Fast electro-optic modulator. PACS: Fiber lasers, 42.55.Wd, Mode locking, 42.60.Fc.

Event-Based Security Control for Markov Jump Cyber–Physical Systems under Denial-of-Service Attacks: A Dual-Mode Switching Strategy

This paper studies the design of dual-mode resilient event-triggered control strategy for Markov jump cyber–physical systems (MJCPSs) under denial-of-service (DoS) attacks. Firstly, a novel resilient event-triggering scheme dependent on the DoS signal is developed to select the corresponding control protocol based on the current network quality of services. Particularly, the potential relationship between the triggering signal and system mode under DoS attacks is discussed, aiming to eliminate both Zeno behavior and singular triggering behavior by calculating the minimum and maximum data update rates. Then, we design an event-based dual-mode security controller to ensure that the closed-loop system has stochastic stability and good robust H∞ performance under DoS attacks. By constructing a Lyapunov–Krasovskii functional which depends on the lower and upper bounds of time delay, sufficient conditions for the existence of dual-mode security controller gains and resilient triggering parameters are presented with the LMI form. Finally, simulation results show that the proposed security control strategy has good robustness against DoS attacks.

Prediction of tribological performance of Cu-Gr-TiC composites based on response surface methodology and worn surface analysis

In the current study, the prediction of tribological performance of Cu-Gr-TiC composites and its correlation with surface topography has been studied. For this purpose, the Cu-Gr composites reinforced with TiC ceramic particles were prepared via the powder metallurgy route. The prepared composites microstructure, mechanical characteristics, and dry sliding wear behaviour were assessed. A pin on disc setup was taken for tribological testing where sliding velocity is 1.5 m s−1. Wear behaviour of composites was examined using a central composite design (CCD) with three levels. The wear behavior optimization was accomplished through the utilization of response surface methodology (RSM). The input parameters in RSM consisted of sliding distance, varying load, and weight percentage (wt%) of reinforcements, while the wear rate and coefficient of friction served as the two responses. An analysis of variance (ANOVA) using RSM was conducted to identify the significant parameters influencing the wear rate and coefficient of friction. A quadratic model was suggested based on best fit and a regression equation was established for predicting the tribological properties at any given input parameter. Comparative of experimental and predicted values show close tolerance. It was observed that RSM is significant tool for predicting and optimizing the tribological properties. The composite having 3.08 wt% of TiC particles was optimized for minimum wear rate & COF at 20 N load and 2000 m sliding distance.

Design and experiment of brush-roller ginkgo leaf picker for the dwarf dense planting mode

At present, ginkgo leave are still picked manually. A brush roller ginkgo leaf picker has been designed to improve harvesting efficiency and reduce losses caused by manual failure to pick leaves in time under large-scale planting areas. The ginkgo leaf picker is mainly composed of crawler chassis, gantry frame, brush roller picking parts, and collecting box. The kinematics of the brush roller is analyzed for the picking omission situation. An experimental platform for picking ginkgo biloba leaves was established. Three parameters, namely roller speed, moving speed, and roller inclination, were selected for optimization. Then the maximum net harvest rate and the minimum damage rate were achieved. The orthogonal test showed that when the roller speed was 130 rev/min, the moving speed was 0.25 m/s, and the roller inclination was 32°, the picking effect was the best, the net harvest rate was 93.32%, the damage rate was 1.42%, and the damage degree of the trunks was slight. The experiment proved that the brush-roller ginkgo leaf picker has a good picking effect, which can provide a reference for the optimization design of ginkgo leaf harvesting machinery under the dwarf dense planting mode.

LSTM combined with BIM technology in the management of small and medium-sized span highway concrete beam bridges

To better carry out maintenance management for medium and small span highway concrete beam bridges, this bridge is taken as the research object. Building information modeling technology is applied to its maintenance management. The corresponding management system is constructed. Through this system, the distribution of diseases and other information can be viewed. Long short-term memory neural network is used to build the corresponding prediction model to predict the technical condition score of bridge components. The results show that the prediction error is small. The minimum error rate in component technical condition scoring prediction is 0.00 %. In the full bridge technology scoring prediction, the minimum scoring error is 2.8 points, and the maximum scoring error is 6 points. The minimum average error rate of this model in predicting component technical condition scores is 0.15 %. Except for individual components, the average error rate of all other components is less than 5 %. The accuracy of the prediction model is 95 %. The performance is superior to linear regression models. The average error rate in the abutment is 7.45 % lower than the linear regression model. This method can effectively predict the degradation of small and medium-sized span highway concrete beam bridges and achieve three-dimensional visualization of diseases.

Arid AREAS Water-Piled Photovoltaic Prevents Evaporation Effects Research

(1) Background: In arid and semi-arid reservoirs, water surface evaporation is the main method of water dissipation in order to inhibit the evaporation of water and enhance economic efficiency. The evaporation inhibition rate of water-piled PV at different times of the year is derived from the anti-evaporation test of water-piled PV, and a new idea is proposed for water conservation in plains reservoirs in arid areas. (2) Methods: The test was conducted by dividing the area into groups A and B, with and without PV panel shading. In situ observation and numerical calculation were used to measure the atmosphere’s temperatures, test group, and PV module. The saturated water vapor pressure difference was then calculated according to Dalton’s principle to analyze the economic benefits of water saving. (3) Results: Based on the test results, it was found that the shading of PV panels had a cooling effect on the water body, the PV module, and the atmosphere. Group A showed a 44.2% decrease in the saturation water vapor pressure difference compared to Group B. The maximum evaporation suppression rate of 40.2% was observed in July, while the minimum rate of 12.2% was observed in January. The average evaporation suppression rate for the entire year was 29.2%. By utilizing the annual water savings for agricultural irrigation, it is possible to cover 38 hm2 of land and generate a revenue of 39,000 CNY. (4) Conclusions: The photovoltaic water cover can effectively reduce water evaporation and generate economic benefits.

On the formation of Ti2AlN MAX phase coatings and improvement in tool life by superimposing on tungsten carbide cutting tool for machining Ti-6Al-4V alloys

This paper presents the development of (002) textured Ti2AlN coated wear resistant tool utilizing reactive magnetron co - sputtering. The Ti2AlN coating was developed in two different Argon, Nitrogen ratios such as 64:3 and 64:4, the influence of these parameters was identified using crystallographic, microstructural, mechanical and tribological studies. Experimental studies were performed to compare the cutting force as well as the tool life of superimposed Ti2AlN tool with a commercial tool by turning titanium alloy (Ti-6Al-4V). Results from the experimental analysis revealed an 80–85 % increase in hardness, a 13–20 % decrease in wear rate and a 27 % increase in tool life for Ti2AlN coated cutting tool. According to chip morphology, there is a 12 % increase in shear angle, 43 % and 51 % decrease in friction angle and coefficient of friction respectively. The nanomechanical studies were performed which show a maximum hardness of 29.12 ± 5.4 GPa and minimum wear rate of 10.078 × 10−9 mm3/mN.m−1 for superimposed Ti2AlN.

Highly dispersed conductive and electrocatalytic mediators enabling rapid polysulfides conversion for lithium sulfur batteries

The practical application of Li-S batteries encounters hurdles in maintaining cycling durability and rate capability under realistic conditions. Electrostatic self-assembly stands as a captivating avenue for exploring new frontiers in nanoscale catalysis. Leveraging renewable bio-oil both as a carbon source and self-polymerization precursor, ultrafine Mo2C nanocrystals anchored on bio-oil-derived 3D hierarchical carbon matrix (Mo2C@BOC) are fabricated by a facile NaCl template-assisted electrostatic self-assembly and followed annealing procedure. Densely anchored ultrafine Mo2C nanocrystals, intertwined with highly conductive carbon nanosheets, unveil an enhanced exposure of catalytically active sites for lithium polysulfide immobilization, conversion, and supply amply nucleation sites to mediate the fast precipitation of Li2S2/Li2S. Attributed to these favorable features, Li-S cells based on the as-designed catalytic host attain satisfactory cyclability with a minimum capacity fading rate of 0.0144 % over 1000 cycles and excellent rate capability. Decent performance can be achieved even at a high sulfur loading of 8.0 mg cm−2 and a low electrolyte-to-sulfur ratio of 3.5 µL mg−1. This strategy for solving the shuttle effect under high sulfur loading provides a promising solution for the further development of high-performance Li-S batteries. This work provides a rational strategy for solving the shuttle effect under high sulfur loading and sheds light on the great potential of Mo2C@BOC for developing more practical Li-S batteries.

State support of Investment Projects Within the Framework of an Agreement on the Protection and Promotion of Capital Investments: A Methodological Rationale

The subject of research is economic interactions related to the implementation of an investment project within the framework of an agreement on the protection and promotion of investments (hereinafter referred to as the APCI).Purpose: methodological substantiation of the expediency of providing state support measures to ensure the minimum profitability of an investment project implemented within the framework of the APCI.Objectives: to propose an indicator that reflects the minimum profitability of an investment project, the mechanism for its usage to determine state support measures, additional state support measures in cases where they are not sufficiently established in the legislation.Methods: analysis of approaches to determining the discount rate; statistical (observation, grouping, method of indicators) for calculating industry-specific ROIC values; content analysis to select state support measures.Results: it is proposed to use the ROIC indicator as the minimum profitability of a commercial investment project. The indicator was calculated according to the data of all organizations that are not subjects of medium and small enterprises operating in the period 2012–2021. The sample included 133 organizations that make up eight subclasses of Russian classifier of types of economic activity (pulp and paper production; production of fertilizers and nitrogen compounds; production of pesticides, etc.; production of paints, varnishes, etc.; production of pharmaceutical substances; production of medicines; activities in the field of telecommunications; development of computer software). Based on the data from 1011 observations, the median value of ROIC for each subclass was calculated, the reliability of which is confirmed by the approved minimum rates of return on invested capital for calculating the tariffs of regulated organizations. A mechanism is proposed for using ROIC to determine state support measures within the framework of the APCI, including: determining the median value of ROIC for foreign economic activity, calculating ROIC for an investment project, and determining state support measures by their ratio. As additional measures of state support within the framework of the APCI, it is proposed to establish tax preferences (lower tax rates, tax benefits, tax deductions), as well as accelerated depreciation of fixed assets. The proposed developments create a methodological basis for substantiating the provision of various state support measures within the framework of the APCI.

Controlling the Minimum Item Exposure Rate in Computerized Adaptive Testing: A Two-Stage Sympson-Hetter Procedure.

Computerized adaptive testing (CAT) can improve test efficiency, but it also causes the problem of unbalanced item usage within a pool. The effect of uneven item exposure rates can not only induce a test security problem due to overexposed items but also raise economic concerns about item pool development due to underexposed items. Therefore, this study proposes a two-stage Sympson-Hetter (TSH) method to enhance balanced item pool utilization by simultaneously controlling the minimum and maximum item exposure rates. The TSH method divides CAT into two stages. While the item exposure rates are controlled above a prespecified level (e.g., rmin) in the first stage to increase the exposure rates of the underexposed items, they are controlled below another prespecified level (e.g., rmax) in the second stage to prevent items from overexposure. To reduce the effect on trait estimation, TSH only administers a minimum sufficient number of underexposed items that are generally less discriminating in the first stage of CAT. The simulation study results indicate that the TSH method can effectively improve item pool usage without clearly compromising trait estimation precision in most conditions while maintaining the required level of test security.

Variable-Length Resolvability for General Sources and Channels.

We introduce the problem of variable-length (VL) source resolvability, in which a given target probability distribution is approximated by encoding a VL uniform random number, and the asymptotically minimum average length rate of the uniform random number, called the VL resolvability, is investigated. We first analyze the VL resolvability with the variational distance as an approximation measure. Next, we investigate the case under the divergence as an approximation measure. When the asymptotically exact approximation is required, it is shown that the resolvability under two kinds of approximation measures coincides. We then extend the analysis to the case of channel resolvability, where the target distribution is the output distribution via a general channel due to a fixed general source as an input. The obtained characterization of channel resolvability is fully general in the sense that, when the channel is just an identity mapping, it reduces to general formulas for source resolvability. We also analyze the second-order VL resolvability.

SQCS: A sustainable quality control system for spatial crowdsourcing via three-party evolutionary game: Theory and practice

Quality control of sensing data poses a fundamental challenge in Spatial Crowdsourcing (SC) applications, and various incentive mechanisms have been proposed to effectively motivate workers. However, real-world SC systems involve multiple stakeholders, namely workers, platforms, and requesters, who exhibit bounded rationality. Moreover, prior research has often neglected the practical aspect of platforms needing to verify sensing data against ground truth information, which incurs a cost. Therefore, platforms face the constraint of verification cost and must judiciously select the verification rate. In this paper, a Sustainable Quality Control System (SQCS) is proposed, which employs a three-party evolutionary game to model the dynamic interaction among workers, platforms, and requesters in practical SC scenarios. Based on this dynamic model: (1) In theory, we derive the minimum verification rate required for effective worker monitoring and the maximum verification cost that platforms can sustainably bear via the analysis of evolutionary stable strategies. These findings serve as guidelines for achieving sustainable quality control within the SQCS framework; (2) In practice, we apply the SQCS framework to the SC scenario of urban air pollution monitoring. The optimal quality control strategy that maximizes overall social benefits is analyzed via numerical methods. Extensive experimental validation is conducted to demonstrate the effectiveness of the proposed theory and practical approach. These findings provide valuable insights for the sustainable development of SC systems.

Desertification simulation using wavelet and box-jenkins time series analysis based on TGSI and albedo remote sensing indices

Desertification has been listed as one of the most critical global environmental issues, posing a significant threat to life, particularly in arid and semiarid regions. Therefore, gaining a comprehensive understanding of the present and future desertification trends becomes imperative. This study employs a feature space model, which effectively captures land surface changes related to desertification, enabling the extraction of pertinent information. Subsequently, time series models are used to determine the most accurate desertification simulation. Twenty-one ETM + sensor images were utilized to calculate the Topsoil Grain Size (TGSI) and Albedo remotely sensed indexes. Constructing the Albedo-TGSI feature space, the Desertification Degree Index (DDI) was extracted for each year. Different levels of desertification were identified by applying a natural break classification on the DDI values, and corresponding break values were obtained. The representative desertification degree for each year was determined by calculating the average of the minimum and maximum break values, resulting in the generation of five distinct time series for five desertification degrees. Different ARIMA models and wavelet transforms were selected to simulate the various desertification degrees based on the analysis of autocorrelation and partial autocorrelation functions and trial and error, respectively. The most suitable ARIMA models with the lowest errors were identified as follows: ARIMA (1,0,7) for severe desertification, ARIMA (0,1,6) for high desertification, ARIMA (0,0,7) for moderate desertification, and ARIMA (3,0,6) for non-desertification degrees. Among the various wavelet transform families tested, the Symlet family proved to be the most effective, except for the low desertification degree. The following wavelet transforms yielded the best results for each degree of desertification: Symlet3 for severe desertification, Symlet7 for high desertification, Symlet7 for moderate desertification, Daubechies 5 (db5) for low desertification, and Symlet7 for non-desertification degree simulations, all exhibiting the minimum error rates.

Optimal placement of BESS in a power system network for frequency support during contingency

In this work, a strategy is proposed for the optimal placement of a Battery Energy Storage System (BESS) in a power system network for frequency support during a power system contingency. It is an optimization algorithm that considers the best location for the integration of a BESS for a frequency support as the place that will result in a minimum rate of change of frequency (RoCoF) during a power system disturbance. The formulation (which aims at determining the minimum RoCoF during contingency) was based on the inertia constant contributions and active power injections (during contingency) from a mixed power generation sources of conventional power plants (CPPs), wind power plants (WPPs) and a battery energy storage system (BESS). Three different optimization solvers, particle swarm optimization (PSO), Fmincon MATLAB solver, and genetic algorithm (GA)) were used in solving the optimization problem for the purpose of comparing the results obtained in order to choose the minimum RoCoF value among the three optimization solvers. The proposed methodology was tested using two network models namely a modified 12-bus and 53 -bus (Western Cape) test systems each consisting of CPPs, WPPs and BESS as energy sources. Simulation results show that when BESS is placed on its optimal location of bus 61 (using the modified 53-bus Western Cape Network model) the power imbalance due to contingency was reduced to about 38 % of its maximum value of 4791 MW and consequently the system frequency nadir was improved from 49.49 Hz to 49.60 Hz. This is very necessary in order to keep the system frequency from falling beyond the limit that may activate the underfrequency load shedding relays.

Experimental Investigation on Mechanical Characterization, Ranking and Water Absorption Behavior of RHA/WDA/RHAWDA Filled Epoxy Based Glass Fiber Reinforced Hybrid Composites

In the present research work, a novel class of epoxy built hybrid combinations strengthened with E-Glass woven rowed mat and occupied with rice husk ash (RHA), wood dust ash (WDA) and a mixture of RHA & WDA has been developed and structural mechanical properties were determined and the results were matched with the non-filled composites. The studies on these composites reveal that the tensile strength (TS) of the composites is decreased by the escalation in weight percentage of the filler material and the rest of the mechanical properties were increased with the increase in weightiness proportion of RHA, WDA and RHAWDA. TOPSIS and VIKOR’S ranking methods are applied to know the best composite from 16 alternative composites having 6 attributes. From the results, the composite filled with RHA at 5 wt% is selected as the best composite based on mechanical characteristics. Water absorption behavior of the composites at various time intervals for RHA, WDA and RHAWDA filled hybrid composites has been studied and it is concluded that the composites occupied with RHA at 12.5 wt% have given the minimum water absorption rate (WA) compared to other filled composites immersed in distilled and mineral waters and the composite filled with WDA at 2.5 wt% has exhibited the minimum water absorption rate (WA) when it is immersed in ground water for 144 hours of a time interval. Based on the results of water absorption rate (WA) and mechanical characteristics (impact strength and Vickers hardness) the composites filled with RHA at 5 wt% and RHA at 12.5 wt% can be used for the manufacturing of roof sheets and water tanks.