Acceleration Period Research Articles

A Real-World Benchmark Problem for Global Optimization

Abstract The paper presents the statement of the problem of dynamical system „crane-load” optimal control. The acceleration period is under consideration and control must meet the minimum duration condition as well as load oscillations elimination. The objective function, which ensures the final condition satisfaction, is developed and analyzed in terms of its topology features. It includes three arguments and their searching is the essence of the benchmark problem. Two variants of the problem are proposed with varied objective function parameters. Twelve agent-based optimization algorithms have been applied to find solutions to a bunch of problems. A brief analysis of the performance of the algorithms reveals their weaknesses and advantages. Thus, the proposed real-world problem may be exploited to estimate the optimization algorithms’ search performance.

Significance of body acceleration and gold nanoparticles through blood flow in an uneven/composite inclined stenosis artery: A finite difference computation

Stenosis is a tiny plaque-like structure that builds up in the arterial wall owing to the sediment of cholesterol, fats, and pearly substances. Such inward proliferation in arteries significantly inhibits blood flow, which leads to a lack of nutrients and oxygen in the organs. Therefore, exploring the transport characteristics of blood fluid flow in stenosis arteries plays a prominent role in enhancing blood transportation. As a result, the present mathematical model is devoted to scrutinizing the flow of Sutterby gold blood nanofluid in two distinct stenosis arteries with periodic body acceleration. It is observed that the Sutterby rheology model is treated as blood, and the single-phase model is used for exposing the nanofluid behaviour. Dimensional non-linear PDEs of the current model are reduced to the set of dimensionless PDEs with the help of non-similar variables. A finite-difference approach is manipulated to compute the dimensionless PDEs. The physical features of governing flow parameters on the Sutterby nanofluid velocity, temperature, resistance impedance, flow rate, and wall shear stress are exposed through graphs. It is found that the composite stenosis has a lower wall shear stress than the irregular stenosis. Sutterby blood nanofluid velocity is elevated with the rising of nanoparticle volume fraction. When employing a gold nanofluid containing 5% volume fraction, the temperature in the irregular artery rises by 26.004% compared to the base fluid (blood). Similarly, in the composite artery, utilizing the same 5% volume fraction of the gold nanofluid leads to a temperature increase of 32.6207%. The blood flow pattern exhibits a 0.2340% higher in the irregular artery as compared to the composite artery.

Investigations on the effect of alkalis on C-S-H growth rates and their impact on early C3S hydration rates

In this work, we investigated the influence of alkalis on C-S-H precipitation and growth rates in solutions supersaturated with respect to C-S-H. Therefore, we used an experimental setup that leads to C-S-H precipitation and growth in solutions with a known KOH concentration. The results show that the KOH concentration in solution generally leads to an increase of the C-S-H growth rates at lower supersaturation levels. Based on these findings, we calculated theoretical reaction rates of C3S hydration using the precipitation rates of C-S-H. The comparison between these calculated rates and measured reaction rates from hydration experiments shows good agreement, allowing us to present a quantitative model for the effect of alkalis in combination with aluminum. Furthermore, we provide a quantitative analysis of how alkalis and aluminum modify reaction rates during the acceleration period of C3S hydration, which can be explained by different behaviors in the nucleation and growth of C-S-H.

Simplified engineering geomorphic unit-based seismic site characterization of the detailed area plan of Dhaka city, Bangladesh

Severe failure of improperly designed and poorly constructed structures may occur due to the amplified and prolonged ground motion during an earthquake, and hence prediction of the ground motion characteristics at the soil surface is crucial. In this study, based on the prepared simplified engineering geomorphic map, we performed a one-dimensional (1D) nonlinear site response analysis for seismic site characterization of the recently proposed Detailed Area Plan (DAP) area of Dhaka City, the Capital of Bangladesh. The engineering geomorphic unit-based map was prepared from image analysis and verified with the collected borehole data and surface geology map. The study area was classified into three major geomorphic units and seven sub-units subject to the subsurface soil profiles. Nine earthquake time histories, seven from the PEER NGA WEST2 data set and two synthetics, and seven identified subsurface soil profiles were used for nonlinear site response analysis, along with the BNBC 2020 uniform hazard spectrum as the target spectrum. For the selected earthquake ground motions, the near-surface soil response of the DAP area showed de-amplification of acceleration in the short period and amplification of acceleration in the long period. The amplified long-period acceleration could cause severe damage in inappropriately designed and poorly constructed long-period structures. The outcome of this study could be used to prepare a seismic risk-sensitive land use plan for the future development of the DAP of Dhaka City.

Study on vibration characteristics of fine breccia soil subgrade reinforced with a new prestressed structure under train cyclic loading

Train cyclic loading generally results in significant dynamic responses of the breccia soil subgrade, resulting in a series of subgrade problems. A new prestressed reinforcement structure (PRS) is proposed to reinforce subgrade structures. However, characteristics of the prestressed subgrade under dynamic loading have not been investigated. This study investigates the vibration characteristics of a new prestressed subgrade structure under train cyclic loading. The acceleration responses of the subgrade surface under different train axle loads and prestress levels are measured and discussed by developing a 1:5 scale dynamic model test on a prestressed fine breccia soil subgrade structure. Subsequently, a three-dimensional dynamic finite element model of the prestressed subgrade is constructed for an in-depth analysis of the internal acceleration of the prestressed subgrade. The results showed that a periodic acceleration response of the subgrade should be observed, and its mean crest and mean trough are used to characterize the long-term vibration degree of the subgrade. The peak vertical acceleration of the subgrade is significantly affected by the prestress level, and the dynamic response of the subgrade around the lateral pressure plate (LPP) is reduced more obviously by the prestress than that of the subgrade’s inner region. The peak vertical acceleration at the subgrade shoulder presents linear increase and exponential attenuation with the rise in the train axle load and prestress level, respectively. In addition, an empirical model describing the relationships among the peak acceleration, train axle load, and prestress is proposed. The vertical dynamic displacement and dynamic stress decrease with the increase of the prestress. The average elastic deformation and peak dynamic stress of the subgrade under a prestress level of 100 kPa are found to be 95.8% and 87.22–90.07% of that with the absence of prestress, respectively. The vertical vibration of the prestressed subgrade structure can be reduced by taking measures such as adjusting the prestress magnitude and increasing the subgrade slope ratio, thereby achieving an effective prestress reinforcement effect.

Transient acceleration after non-minimal M-flation preheating

Light massive preheat fields acquire a non-vanishing dispersion during parametric resonance from their quantum particle production. This in turn will modify the inflaton potential, which in some cases can induce a transient period of acceleration. We illustrate this phenomenon in the setup of non-supersymmetric non-minimal M-flation (non-𝕄-flation) which has some motivations from the brane compactifications in string theory. Implementing a lattice simulation by the LATTICEEASY code, we compute the potential correction term in our scenario and show that the modified term indeed causes the Universe to make a transition from the decelerated expansion to a temporary phase of acceleration. The correction term reduces to some extent the number density of the particles generated during preheating, but the efficiency of preheating remains still enough to have successful particle production after inflation. We also compute the spectrum of the gravitational waves (GWs) generated during preheating in our setup by using the LATTICEEASY code. Although the peak frequency remains almost the same, the inclusion of the correction term reduces the amplitude of the gravitational spectrum by almost one order of magnitude.

Insight into the role of β-cyclodextrin on the hydration of white Portland cement

Impacts of β-cyclodextrin (β-CD) on hydration of white-Portland-cement (WPC) are studied by calorimetry, ICP-OES, TOC, TG, XRD and time domain NMR. Strong retardation effect of β-CD has been confirmed in both WPC and pure C3S pastes. Much stronger retardation in C3S pastes suggests the aluminate phases (C3A and ettringite) in WPC pastes mitigates the retardation effect of β-CD on C3S hydration, probably by adsorbing β-CD molecules and thus reducing β-CD concentration in the aqueous solution. Together with precipitation experiments of pure CH and C-S-H, it is concluded that β-CD remaining in the aqueous solution of the WPC pastes blocks CH and C-S-H formation and the induction period is remarkably extended as additional time is needed to clean up the aqueous solution by slowly formed hydrates e.g., AFt. NMR results suggest high dosage of β-CD promotes C-S-H precipitation directly in aqueous solution in acceleration period, besides the surface of cement grains.

Effects of urea on carbonation properties and microstructure of cementitious materials

Urea has been utilized in concrete technology to reduce the temperature cracking and promote winter construction property. In this work, the influence of urea on cement hydration and carbonization resistance of cement-based materials was studied through carbonation depth experiment, isothermal conduction calorimetry, XRD, BET and water vapor sorption. It is indicated that the reduction of rate in the hydration acceleration period can be attributed to the increasing pH and lower supersaturation when urea is added to the cement mixture. In addition,the existing of NH4+in pore solution andpH profile results in the decrease of decalcified C-S-Hdeterioration rate,which prolongs carbonation duration to asimilar depth. This study provides a new admixture way to improve the durability of cement-based materials to prolongthe life of reinforced concrete.

Distribution and curing kinetics of waterborne epoxy resin in repair system: Characterization and quantification by 1H low-field NMR

Cement-based mortars are commonly modified with Waterborne Epoxy Resin (WER). However, the curing kinetics of WER in mortars has never been quantified up to now. This study proposed using 1H low-field nuclear magnetic resonance (1H LF-NMR) to quantitatively determine the curing kinetics of WER in polymer-cement composite. The distribution and curing of WER in repair systems was also explored using 1H LF-NMR. To avoid the interference of the NMR water signal, heavy water was used to prepare repair mortar. It was found that the curing reaction of WER in a mortar was significantly influenced by the cement hydration. It starts to accelerate when the cement hydration stepped into an acceleration period. Moreover, the 1D spatial NMR signal distribution showed that WER in the repair materials permeated into the substrate with water, which is affected by both the W/C of the repair and the RH of the substrate. The WER was enriched at the interface between the substrate and the repair mortar and exhibited a gradient in the distribution both upwards into the repair mortar and downwards into the substrate.

Enhancing Heat Transfer in Blood Hybrid Nanofluid Flow with Ag–TiO2 Nanoparticles and Electrical Field in a Tilted Cylindrical W-Shape Stenosis Artery: A Finite Difference Approach

The present research examines the unsteady sensitivity analysis and entropy generation of blood-based silver–titanium dioxide flow in a tilted cylindrical W-shape symmetric stenosis artery. The study considers various factors such as the electric field, joule heating, viscous dissipation, and heat source, while taking into account a two-dimensional pulsatile blood flow and periodic body acceleration. The finite difference method is employed to solve the governing equations due to the highly nonlinear nature of the flow equations, which requires a robust numerical technique. The utilization of the response surface methodology is commonly observed in optimization procedures. Drawing inspiration from drug delivery techniques used in cardiovascular therapies, it has been proposed to infuse blood with a uniform distribution of biocompatible nanoparticles. The figures depict the effects of significant parameters on the flow field, such as the electric field, Hartmann number, nanoparticle volume fraction, body acceleration amplitude, Reynolds number, Grashof number, and thermal radiation, on velocity, temperature (nondimensional), entropy generation, flow rate, resistance to flow, wall shear stress, and Nusselt number. The velocity and temperature profiles improve with higher values of the wall slip parameter. The flow rate profiles increase with an increment in wall velocity but decrease with the Womersley number. Increasing the intensity of radiation and decreasing magnetic fields both result in a decrease in the rate of heat transfer. The blood temperature is higher with the inclusion of hybrid nanoparticles than the unitary nanoparticles. The total entropy generation profiles increase for higher values of the Brickman number and temperature difference parameters. Unitary nanoparticles exhibit a slightly higher total entropy generation than hybrid nanoparticles, particularly when positioned slightly away from the center of the artery. The total entropy production decreases by 17.97% when the thermal radiation is increased from absence to 3. In contrast, increasing the amplitude of body acceleration from 0.5 to 2 results in a significant enhancement of 76.14% in the total entropy production.

Study on Dispersion, Adsorption, and Hydration Effects of Polycarboxylate Superplasticizers with Different Side Chain Structures in Reference Cement and Belite Cement.

To investigate the effects of Reference cement (RC) and Belite cement (LC) systems, different molecular structures of polycarboxylate ether (PCE) were prepared through the free radical polymerization reaction and designated as PC-1 and PC-2. The PCE was characterized and tested using a particle charge detector, gel permeation chromatography, a rotational rheometer, a total organic carbon analyzer, and scanning electron microscopy. The results showed that compared to PC-2, PC-1 exhibited higher charge density and better molecular structure extension, with smaller side-chain molecular weight and molecular volume. PC-1 demonstrated enhanced adsorption capacity in cement, improved initial dispersibility of cement slurry, and a reduction in slurry yield stress of more than 27.8%. LC, with its higher C2S content and smaller specific surface area compared to RC, could decrease the formation of flocculated structures, resulting in a reduction in slurry yield stress of over 57.5% and displaying favorable fluidity in cement slurry. PC-1 had a greater retarding effect on the hydration induction period of cement compared to PC-2. RC, which had a higher C3S content, could adsorb more PCE, leading to a greater retarding effect on the hydration induction period compared to LC. LC and PC-2, on the other hand, exhibited inhibition during the hydration acceleration period. The addition of PCE with different structures did not significantly affect the morphology of hydration products in the later stage, which was consistent with the trend of KD variation. This indicates that the analysis of hydration kinetics can better reflect the final hydration morphology.

Test bench setup for emulating electric vehicle on-road conditions

This work provides an electric vehicle (EV) test bench with a motor/dynamometer setup with a battery and ultracapacitor (UC) hybrid energy storage. Extending the driving range and enhancing the battery life are the main concerns with EVs nowadays. The drive motor (DM) used is a three-phase induction motor (IM), which is controlled by the current sensorless indirect vector control method. This fault-tolerant method can be used in the case of current sensor failure. All the resistive forces acting on an EV are emulated based on the concept of vehicle equivalent rotational inertia for different real-life driving cycles, namely ECE R15 and NYCC. The battery alone is not capable of handling the surge current requirement during the acceleration period and is not able to capture the total power during regenerative breaking as it has a low power density. Hence, a high power density source like UC is a must to handle these conditions during frequent stop and go city traffic conditions as per ECE R15 and NYCC driving cycles. This EV emulation technique helps in getting the DC-link power profile for an EV for any driving scenario. Hence, it is possible to test the different powertrain components of an EV using this proposed technique.

Study on the Effect of Polycarboxylate Ether Molecular Structure on Slurry Dispersion, Adsorption, and Microstructure.

This study synthesized polycarboxylate superplasticizer (PCE) with varying carboxyl densities and main chain degrees of polymerization. The structural parameters of PCE were characterized using gel permeation chromatography and infrared spectroscopy. The study investigated the impact of PCE's diverse microstructures on cement slurry's adsorption, rheology, hydration heat, and kinetics. Microscopy was used to analyze the products' morphology. The findings indicated that an increase in carboxyl density led to an increase in molecular weight and hydrodynamic radius. A carboxyl density of 3.5 resulted in the highest flowability of cement slurry and the most considerable adsorption amount. However, the adsorption effect weakened when the carboxyl density was the highest. Decreasing the main chain degree of polymerization led to a significant reduction in the molecular weight and hydrodynamic radius. A main chain degree of 16.46 resulted in the highest flowability of slurry, and both large and small main chain degrees of polymerization exhibited single-layer adsorption. PCE samples with higher carboxyl density caused the greatest delay in the induction period, whereas PCE-3 promoted the hydration period's acceleration. Hydration kinetics model analysis indicated that PCE-4 yielded needle-shaped hydration products with a small nucleation number in the crystal nucleation and growth stage, while PCE-7's nucleation was most influenced by ion concentration. The addition of PCE improved the hydration degree after three days and facilitated the strength's later development compared to the blank sample.

Synchronization of scanning probe and pixelated sensor for image-guided diffraction microscopy

A 4-dimensional modality of a scanning transmission electron microscope (4D-STEM) acquires diffraction images formed by a coherent and focused electron beam scanning the specimen. Newly developed ultrafast detectors offer a possibility to acquire high throughput diffraction patterns at each pixel of the scan, enabling rapid tilt series acquisition for 4D-STEM tomography. Here we present a solution to the problem of synchronizing the electron probe scan with the diffraction image acquisition, and demonstrate on a fast hybrid-pixel detector camera (ARINA, DECTRIS). Image-guided tracking and autofocus corrections are handled by the freely-available microscope-control software SerialEM, in conjunction with a high angle annular dark field (HAADF) image acquired simultaneously. The open source SavvyScan system offers a versatile set of scanning patterns, operated by commercially available multi-channel acquisition and signal generator computer cards (Spectrum Instrumentation GmbH). Images are recorded only within a sub-region of the total field, so as to avoid spurious data collection during flyback and/or acceleration periods in the scan. Hence, the trigger of the fast camera follows selected pulses from the scan generator clock gated according to the chosen scan pattern. Software and protocol are provided for gating the trigger pulses via a microcontroller (ST Microelectronics ARM Cortex). We demonstrate the system on a standard replica grating and by diffraction imaging of a ferritin specimen.

Effects of chloride content on early hydration performance of cement pastes

In this paper, the effect of chloride ion content, ranging from 0% to 5%, on the early hydration performance of cement pastes was comprehensively investigated using isothermal calorimetry, low-field NMR, resistivity, and rheological tests. The results show that the hydration is accelerated, and the hydration peak is continuously advanced by increasing the chloride content from 0.5% to 2%. However, chloride content of 5% initially has an inhibitory effect, but after 19 h, it has an accelerating effect. The T2 spectrum exhibits a noticeable shift from 10 to 100 ms toward the range of 1–10 ms during the acceleration period, and the changing tendency of relative signal intensity (RSI) is consistent with the heat of hydration. The results of low-field NMR provide an explanation for the variation of early strength of mortars containing chloride. The effect of chloride ions on resistivity appears after mixing. The resistivity of chloride-containing pastes should be controlled by hydration and free chloride ions in the pore solution. Besides, the rheological properties are also affected by the chloride ion admixture and hydration process. The flowability is reduced with 0.5% and 1% Cl- but improved with 2% and 5% Cl-. The results provide a comprehensive characterization of the effect of chloride ions on the early hydration of cement pastes from various perspectives, and the results from different methods are consistent.

The potential of region-specific machine-learning-based ground motion models: Application to Turkey

Conventional ground motion models have extensively been established worldwide based on classical regression analysis of records. Alternatively, advanced nonparametric machine-learning (ML) algorithms may capture the complex nonlinear behaviour of earthquake motions. This paper investigates the efficiency of artificial neural network (ANN) and extreme gradient boosting (XGBoost) in predicting peak ground acceleration (PGA), peak ground velocity (PGV) and pseudo-spectral acceleration (PSA) (period, T = 0.03–2.0 s) for the Turkish dataset. The dataset involves 1166 records of 383 events with a moment magnitude (Mw) of 4.0–7.6, Joyner and Boore distance (RJB) of 0–200 km, focal depth (FD) less than 35 km, and site condition as the averaged shear wave velocity of the soil on the top 30 m (VS30) of 131–1380 m/s. The performance of the models is compared against empirical models in terms of root-mean-square error (RMSE), coefficient of determination (R2), Pearson correlation coefficient (r), and inter-event and intra-event residuals. To perform residual analysis, a likelihood function is developed. Findings reveal that the XGBoost approach gives an unbiased model with a higher correlation and lower residual than ANN. Finally, an online platform is provided for any interested users.

The role of nano-TiO2 on the mechanical properties and hydration behavior of C2S, C3S and C4A3[formula omitted

To clarify the details of hydration between nanomaterials and single minerals in cement, C2S, C3S and C4A3S‾ were prepared by chemical synthesis, and the effects of nano-TiO2 on the hydration properties of C2S, C3S and C4A3S‾ were explored to reveal the mechanism of different hydration stages from the perspective of hydration kinetics. The results suggested that nano-TiO2 did not essentially change the type of hydration products of C2S, C3S and C4A3S‾, but mainly acted as seeds to promote the nucleation and crystal growth of hydration products, and as fillers to form denser microstructures and higher strength. However, for C4A3S‾, the crystal growth of AFt at the late stage of hydration was further promoted by nano-TiO2, resulting in microcracks due to volume expansion of the hydrated matrix. Meanwhile, the relatively insufficient amount of alumina gel caused that the AFt could not being effectively cross-linked into a monolith, so the compressive strength decreased by 29.21% and 37.8% at 14d and 28d. The hydration kinetics shows that the acceleration period of C2S, C3S and C4A3S‾ appeared earlier by reducing the activation energy required for the reaction by nano-TiO2. However, the hydration kinetic processes of C2S and C3S (NG-I-D) and C4A3S‾ (NG-D) were not disturbed by nano-TiO2, but significantly increased the hydration rates of the corresponding stages and advanced the turning point of the control stage. This demonstrated that nucleation and crystal growth of hydration products of these minerals are promoted by nano-TiO2, and the difficulty of phase boundary reactions and diffusion was also weakened.

Preparation and characteristics of paraffin/silica aerogel composite phase-change materials and their application to cement

In this study, microencapsulated paraffin/silica aerogel composite phase-change materials (MPCMs) were developed and incorporated into cement to impart heat storage/release capabilities. First, the hydrophilically modified MPCMs were subjected to a leakage test. Using a simple stirring method, the composite with an aerogel: paraffin mass ratio of 22:78 was demonstrated to have the best adsorption capacity. Transmission electron microscopy, scanning electron microscopy, Fourier-transform infrared spectroscopy, and X-ray diffraction analyses revealed that the paraffin was stable and physically encapsulated by the aerogel. The differential scanning calorimetry results showed that the encapsulated MPCMs had a fusion latent enthalpy of 94.45 J/g and phase-change temperature range of 20.8–34.4 ℃. The enthalpy was reduced by only 3.87% after 1000 freezing–thawing cycles. In the second part of the experiment, heat-storage cement (HSC) specimens were prepared to investigate the effect of MPCMs modified with silane coupling agents. The proportion of MPCMs and curing temperature were varied, and the effects of these variations on the compressive strengths of HSC stones were investigated. The compressive strength of the HSC samples was improved by adding multiwall carbon nanotubes (MWCNTs) to paraffin to form paraffin/aerogel composite MWCNT micro-encapsulated phase-change materials (CMPCMs). The results show that adding 1.53 wt% MWCNTs increases the thermal conductivity by 50.6% and refines the pore size and strength of the HSC stone. Furthermore, the 7-day strength of the HSC stone increased to 8.6 MPa by adding MWCNTs to 30 wt% modified CMPCM, meeting the requirement standard. Cement hydration calorimetry, performed using a TAM AIR isothermal calorimeter, revealed that MPCMs prolong the induction period of cement hydration, reduce the rate during the acceleration period of cement hydration, and absorb the heat of hydration. Moreover, the thermal regulation behaviour of 10 mm thick HSC plates was tested. The highest temperature difference was determined to be 2.36 ℃ and 1.92 ℃ during the heating and cooling processes, respectively, compared with that of plain cement plate, at the same time. Therefore, HSC panels have potential applications in building thermal management.

Insights into the acting mechanism of ettringite in expansive Portland cement

There are different theories about the acting mechanisms of ettringite in the expansive behavior of Portland cement. While it is widely recognized that a reactive source of alumina, sulfate, and calcium hydroxide, along with sufficient water, is required for ettringite formation, there are still varying perspectives on the amount, size, and morphology of ettringite crystals. This work brings insights into the mechanisms underlying the expansion of ettringite. For this purpose, cement pastes containing an expansive mixture were analyzed using an expansion measuring device, in situ X-ray diffraction, isothermal calorimetry and scanning electron microscopy. The results revealed that the content and size of ettringite crystals at the beginning of the acceleration period are critical factors for the development of expansive behavior.

Energy Harvesting and Acceleration Measuring Based on Time-Division Multiplexing Operation of a Single Piezoelectric Transducer

This letter presents a novel approach called energy harvesting and acceleration measuring (EHAM) using a single piezoelectric (PZT) transducer. The EH subsystem is a synchronous electric charge extraction (SECE) interface combining with an energy management circuit, which can harvest energy from PZT. The AM subsystem is for measuring acceleration-related signals. A time-division multiplexing strategy is employed in the EHAM system, where vibration energy is harvested during one period and vibration acceleration is measured in another period, and the harvested energy also powers the AM circuit. The prototyped EHAM system is implemented based on discrete components and tested with a conventional cantilever-based PZT harvester. Experimental results show that the EHAM system can perform EH and AM operations in a time-division multiplexing way. The EH circuit can harvest 1.76 mJ energy during 22 s with a PZT open-circuit voltage of 6 V. The AM circuit can measure accelerations with an accuracy of 95% under the mechanical resonance condition. The EHAM solution can be a candidate for self-powered acceleration measurement.