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1

Thermal and mechanical properties of poly(L-lactic acid) nucleated with N,N’-bis(phenyl) 1,4-naphthalenedicarboxylic acid dihydrazide

100%

Zhao L.-S. , Qiao J. , Chen W. , Cai Y.-H.

Polimery

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2021

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tom T. 66, nr 4

234--244

EN

The modified poly(L-lactic acid) (PLLA) with different contents (0.5−3 wt %) of N,N’-bis(phenyl) 1,4-naphthalenedicarboxylic acid dihydrazide (NAPH) were prepared to evaluate effects of NAPH on melt-crystallization behavior (DSC), thermal degradation (TGA) and mechanical properties of PLLA. The melt-crystallization results demonstrated that NAPH as a heterogeneous organic nucleating agent enhanced crystallization ability of PLLA in cooling, and PLLA/1%NAPH had the best crystallization ability because of the highest onset crystallization temperature and the sharpest melt-crystallization peak. However, melt-crystallization behavior also depended on the cooling rate and final melting temperature, overall, a relative slow cooling rate and low final melting temperature were beneficial for crystallization of PLLA. The cold-crystallization results indicated that NAPH had an inhibition for cold-crystallization process of PLLA, and the cold-crystallization peak shifted towards lower temperature and became wider with an increase of NAPH concentration. The different melting behaviors of PLLA/NAPH after melt-crystallization and isothermal-crystallization efficiently reflected the accelerating role of NAPH for PLLA crystallization; the double melting peaks formed in heating were thought to result from melting-recrystallization, as well as that a higher crystallization temperature could cause melting peak to appear in higher temperature regions and possess larger melting enthalpy. A comparative analysis on thermal degradation in air illustrated that the addition of NAPH accelerated decomposition of PLLA, but a decrease of onset decomposition temperature was inhibited by the probable interaction of PLLA with NAPH. Moreover, the tensile test showed that NAPH decreased tensile modulus and elongation at break of PLLA, whereas PLLA with low concentration of NAPH had higher tensile strength than pure PLLA.

PL

Poli(kwas L-mlekowy) (PLLA) modyfikowano dodatkiem 0,5−3 % mas. dihydrazydu kwasu N,N’-bis(fenylo) 1,4-naftalenodikarboksylowego (NAPH). Zbadano wpływ NAPH na topnienie i krystalizację (DSC), degradację termiczną (TGA) i właściwości mechaniczne PLLA. Analiza procesu krystalizacji ze stanu stopionego modyfikowanego PLLA wykazała, że NAPH, jako heterogeniczny organiczny środek zarodkujący, zwiększał zdolność do krystalizacji PLLA podczas chłodzenia, a próbka PLLA/1% NAPH charakteryzowała się najwyższą temperaturą początku krystalizacji i najostrzejszym pikiem krystalizacji ze stanu stopionego. Przebieg procesu krystalizacji zależał również od szybkości chłodzenia i końcowej temperatury topnienia próbki. Względnie mała szybkość chłodzenia i niska końcowa temperatura topnienia były korzystne dla procesu krystalizacji PLLA. Analiza procesu zimnej krystalizacji wskazała, że obecność NAPH hamowała zimną krystalizację PLLA, jej pik przesuwała w kierunku niższych wartości temperatury, a wraz ze wzrostem stężenia NAPH pik stawał się szerszy. Różny przebieg procesów topnienia PLLA/NAPH po krystalizacji ze stanu stopionego i krystalizacji izotermicznej odzwierciedla przyspieszającą rolę NAPH w krystalizacji PLLA. Autorzy uważają, że podwójne piki topnienia powstające podczas ogrzewania wynikają z zachodzącego procesu topnienia-rekrystalizacji, a także, że wyższa temperatura krystalizacji może być przyczyną pojawienia się piku topnienia w obszarach wyższej temperatury i zwiększenia entalpii topnienia. Analiza porównawcza rozkładu termicznego w atmosferze powietrza wykazała, że dodatek NAPH przyspieszył rozkład PLLA, ale prawdopodobne oddziaływanie PLLA z NAPH wpłynęło na zmniejszenie temperatury początku rozkładu. Ponadto, dodatek większej ilości NAPH spowodował zmniejszenie modułu sprężystości przy rozciąganiu i wydłużenia przy zerwaniu PLLA, jednak PLLA zawierający niewielką ilość NAPH wykazywał większą wytrzymałość na rozciąganie niż niemodyfikowany PLLA.

2

Stress evolution of rock breakages by a disc cutter assisted by pre-cuts

100%

Liu J. , Chen W. , Liu T. , Peng D.

Archives of Civil and Mechanical Engineering

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2023

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tom Vol. 23, no. 2

art. no. e115, 2023

EN

To study the rock breakage mechanism by constant cross-section cutters assisted by pre-cuts, the present study first performed small-scaled linear cutting tests on sandstone specimens containing pre-cuts. The laboratory tests indicate that the sufficiently large penetration, causing successful internal and surface crack incisions, is essential for large chip formation. In addition, the small pre-cut depth may fail to form large chips. The numerical results agree well with laboratory tests in fracture patterns. More importantly, the numerical analysis indicates that the increases in rolling force frequently result in stress concentrations. When the stresses concentrate to critical values, fracture propagation occurs. The fracture propagation causes stress dissipation and the decrease in rolling force. Thus, the relation between cutting load fluctuations and crack propagation is revealed. Moreover, the influence of penetration on crack propagation is analyzed. By analyzing the stress fields at typical peak points of the rolling force, the crack propagation direction is predicted, and the influence of pre-cut depth on fracture propagation is studied.

3

Study on the three-phase flow of the water transfer export elbow of natural gas hydrate

100%

Chen W. , Xu H.-L. , Wu B. , Yang F.-Q.

Archives of Mining Sciences

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2022

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tom Vol. 67, no. 2

239--258

EN

The Euler multiphase flow and population equilibrium model were used to simulate the three-phase flow field in the bubble expansion stage of the outlet curved pipe section. The influence of the ratio of the bending diameter and the volume fraction of the gas phase on the pressure loss is revealed, and the safety range of the optimum bending diameter ratio and the volume fraction of the outlet gas phase is determined. The results show that the three-phase flow in the tube is more uniformly distributed in the vertical stage, and when the pipe is curved, the liquid-phase close to the pipe wall gathers along the pipe flank to the outside of the pipe, the solid phase is transferred along the pipe flank to the inside of the pipe, and the gas phase shrinks along the pipe flank to the inner centre. The maximum speed of each phase of the three-phase flow in the elbow is at the wall of the tube from 45° to 60° inside the elbow, and the distribution law along the axial direction of the pipe is about the same as the distribution law of volume fraction. The pressure loss of the elbow decreases with the increase of the bend diameter ratio, when the bend diameter ratio increases to 6, the pressure loss of the pipe decreases sharply, and the pressure loss decreases slowly with the increase of the bend diameter ratio. When the gas phase volume score in the elbow reaches 70%, there will be an obvious wall separation phenomenon, to keep the system in a stable working state and prevent blowout, the gas phase volume score should be controlled within 60%.

4

Fractal Features of Soil Particle Size Distributions and Their Implications for Indicating Enclosure Management in a Semiarid Grassland Ecosystem

100%

Chen W. , Chang H. , Liu R.

Polish Journal of Ecology

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2020

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tom Vol. 68, nr 2

132--144

EN

Soil particle size distribution (PSD) is becoming an increasingly useful tool for the objective description of soil structure and intrinsic links between soil and the environment. Here we examined the fractal features of PSD and its correlation with soil physiochemical properties in grasslands under grazing and protected from grazing (enclosure) animals, before and after plant growing periods in a semiarid grassland ecosystem, in northern China. Our results showed that sand content was significantly higher in grassland soils under grazing compared with the enclosure at both sampling times (May and September), whereas their silt and clay contents followed the reverse pattern. The fractal dimensions of PSD (Dm) under enclosure were significantly greater than those found under grazing. The soil clay, silt contents and Dm were positively correlated with soil total N, total C, soil pH, and moisture content. By contrast, the soil sand content declined with increasing total N, total C, pH, and moisture content of soil. The soil fractal dimension of PSD had a positive correlation with soil clay and silt content, whereas it had a negatively correlated with sand content. From these results, we conclude installing enclosures can promote soil clay, silt, and soil particles' fractal dimension, with the latter could be used as a quantitative indicator of soil fertility characteristics. But it is unnecessary to use the fractal dimension of PSD as an index to evaluate the effects of enclosure management on degraded grassland.

5

Adaptive time-reassigned synchrosqueezing transform for seismic random noise suppression

100%

Liu W. , Li S. , Chen W.

Acta Geophysica

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2024

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tom Vol. 72, no. 2

829--847

EN

Noise suppression is of great importance to seismic data analysis, processing and interpretation. Random noise always overlaps seismic reflections throughout the time and frequency, thus, its removal from seismic records is a challenging issue. We propose an adaptive time-reassigned synchrosqueezing transform (ATSST) by introducing a time-varying window function to improve the time-frequency concentration, and integrate an improved Optshrink algorithm for the suppression of seismic random noise. First of all, a noisy seismic signal is transformed into a sparse time-frequency matrix via the ATSST. Then, the obtained time-frequency matrix is decomposed into a low-rank component and a sparse component via an improved Optshrink algorithm, where the D transformation and its first derivative are further simplified to reduce the computational burden of the original OptShrink algorithm. Finally, the denoised signal is reconstructed by implementing an inverse ATSST on the low-rank component. We have tested the proposed method using synthetic and real datasets, and make a comparison with some classical denoising algorithms such as f - x deconvolution and Cadzow filtering. The obtained results demonstrate the superiority of the proposed method in denoising seismic data.

6

3D crosswell electromagnetic inversion based on radial basis function neural network

88%

Fang S. , Zhang Z. , Chen W. , Pan H. , Peng J.

Acta Geophysica

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2020

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tom Vol. 68, no. 3

711--721

EN

Crosswell electromagnetic (EM) method has fundamentally improved the horizontal detection ability of well logging and will become an increasingly promising approach for the secondary exploration of hydrocarbon reservoir. We applied orthogonal least squares (OLS) radial basis function neural network (RBFNN) based on improved Gram–Schmidt (G–S) procedure to three-dimensional (3D) crosswell EM inversion problems. In the inversion process of the simplifed crosswell model with single-grid conductivity anomalies and normal oil reservoir, compared the inversion results of other fve neural networks, OLS-RBFNN was proved to have the best global optimization ability and the fastest sample learning speed and the average inversion error of low conductivity anomalies model (4%) and oil reservoir model (9%) can meet the inversion requirements of crosswell EM method. Only the OLS-RBFNN could achieve ideal inversion results in the most concerned central area of crosswell model, and the inversion accuracy of this algorithm will be more outstanding when the model becomes more complex. Merely using the three-component time-domain crosswell EM data of two wells, the inversion of 3D medium conductivity in the crosswell dominant exploration area can be efectively realized through the nonlinear approximation of the OLS-RBFNN.

7

Experimental study on vibration of a rotating pipe in still water and in flow

75%

Geng X. , Wu W. , Liu E. , Lin Y. , Chen W. , Rheem C.-K.

Polish Maritime Research

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2023

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tom nr 1

65--77

EN

To illustrate the vibration characteristics of a rotating pipe in flow, experiments were conducted for a pipe in flow, a rotating pipe in still water and a rotating pipe in flow. For the pipe in flow without rotation, the trajectory diagram is ‘8’ shaped. For the rotating pipe in still water, a multiple frequency component was induced, and a ‘positive direction whirl’ was found. For the flow and rotation, at a flow velocity of 0.46 m/s, the vibration is dominated by the combination of flow and rotation. With an increase in rotating frequency, the trajectory of the rotating pipe varies from an ‘8’ shape to a circular shape and the ‘reverse direction whirl’ is induced, which is different from ‘positive direction’ in still water. The vibration frequency ratio increases uniformly with flow velocity. At a flow velocity of 1.02 m/s, at which the frequency is close to the theoretical natural frequency, the vibration frequency ratio is f*≈1. Predominantly governed by vortex-induced vibration (VIV), the vibration behavior of a rotating pipe subjected to fluid flow conditions has been found to exhibit complete vanishing of whirl. The vibration characteristics of a rotating pipe in flow are studied by the experiments which is benefit for structural drilling design.

8

Effect of grinding media on the flotation of copper-activated marmatite

75%

Long T. , Chen Y. , Shi J. , Chen W. , Zhu Y. , Zhang C. , Bu X.

Physicochemical Problems of Mineral Processing

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2020

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tom Vol. 56, iss. 2

229--237

EN

How to avoid the shortage of floatability and non-purpose flotation in marmatite flotation is a big problem. This paper innovatively studies how to reduce these two negative phenomena from the perspective of grinding media. The effects of steel and stainless-steel balls on the flotation performance of copper-activated marmatite were investigated mainly through flotation tests, redox potential measurements, ion concentration tests, and XPS and FT-IR spectrum studies. The flotation results showed that the floatability of copper-activated marmatite remarkably decreased by using the steel ball in the grinding process, but it had a mere influence when stainless-steel medium was used. Redox potential measurements showed that the grinding environment of stainless-steel medium could exhibit a higher oxidizing potential than the steel grinding environment. Results from FTIR, XPS, and ion concentration measurements demonstrated that more ferric ions existed on the copper activated marmatite surface in the steel grinding environment than that in the stainless-steel environment. Ferric ions could further hinder the activation effect of copper ions on marmatite and result in decreased marmatite flotation. This research could potentially explain the mechanism of ferric ions in the grinding process, and it can be utilized to improve the flotation performance of marmatite ore through selecting suitable grinding media in ball mill operations.