Mechanism Of Shrinkage Research Articles

Spatiotemporal evolution and driving mechanism of regional shrinkage at the county scale: The three provinces in northeastern China.

The three northeast provinces are typical areas of regional shrinkage in China. A scientific understanding of their shrinkage and driving mechanism is conducive to the transformation and development of traditional industrial bases in China. This study analyzed the spatiotemporal evolution and driving mechanism of regional shrinkage at the county scale in the three provinces. The main findings are as follows: (1) 40.86% of counties in the three provinces shrank, forming three concentrated shrinking regions. However, comprehensively shrinking regions were narrowed and lessened with the introduction of the Northeast Area Revitalization Plan. (2) The population-related shrinking regions accounted for more than 90% and continued to expand. Such shrinkage was higher in the north than in the south. The degree of economy-related shrinkage was the most serious, and the hotspots were mainly concentrated in Liaoning Province. The scope of space-related shrinkage was most minor, and such shrinkage was relatively mild. (3) When it came to influencing factors, the shrinkage index was positively correlated with the proportion of the secondary industry, the output value of agriculture, forestry, animal husbandry and fishery, the number of industrial enterprises above the designated size, fiscal expenditure, and the balance of resident deposits, and negatively correlated with the altitude, the proportion of the tertiary industry, and population aging. Geographically weighted regression (GWR) and ordinary least squares (OLS) produced similar regression results. The spatial pattern of influencing factors was consistent with the hotspot areas of population-related shrinkage or economy-related shrinkage, with significant spatial differences.

Spatiotemporal Pattern Identification and Driving Mechanism of Urban Shrinkage in the Yellow River Basin from 2000 to 2020

The regional differences in the Yellow River Basin have increased, and the aggravation of this unbalanced state has seriously restricted the high-quality development of the Yellow River Basin during the accelerated urbanisation that has taken place in recent years. In this regard, heterogeneity in the trends of evolution and the causes of population shrinkage in different regions of the Yellow River Basin can be adopted as targeted countermeasures. The present study uses data from the fifth, sixth, and seventh national censuses and takes the administrative units of different levels in the Yellow River Basin as the object, considering 72 prefecture-level cities within the autonomous prefectures and 595 county-level administrative units in nine provinces (autonomous regions). The population shrinkage coefficient, night light index, bivariate spatial autocorrelation, geographic detectors, and other methods were used, with the final objective of exploring the spatial–temporal distribution pattern and impact mechanism of urban shrinkage from 2000 to 2020. The results of the study show the following: (1) The shrinkage patterns in 2000–2010 (T1) and 2010–2020 (T2) were quite different. From T1 to T2, the shrinkage situation worsened, with the number of districts experiencing population shrinkage increasing from 175 to 373 and the number of districts experiencing continuous night light and shrinkage districts increasing from 146 to 163. (2) The phenomenon of urban shrinkage is spatially scale dependent, with the shrinkage of prefecture-level cities and county-level cities being characterised by both spatial differentiation and spatial nesting relationships. (3) There is a certain inconsistency in the representation of the shrinkage patterns of the nighttime lighting and population data. The nighttime lighting dimension can reflect the structural shrinkage characteristics of the city more accurately and sensitively, and the representation of population loss is lagging. (4) The main impact factors and the intensity of urban shrinkage are the aggravated aging level, the declining level of industrial greening and intensification under market-driven economic structure adjustments, and the decreased natural growth rate in the population structure and public service facilities.

Optimization of shrinkage agents and study of their shrinking mechanism for mudstones in the salt cavern gas storage

Salt cavern gas storage takes up a high proportion of gas storage, which allows a large amount of gas production in one day and flexible market response. It has become one of the world's important strategic natural gas reserves and emergency peak-shaving facilities. However, salt cavern gas storage in China is mainly built in the layered salt formation, which is characteristic of thin salt layers with high contents of insoluble mudstone interlayers. During the construction of this type of gas storage, these insoluble interlayers can be left at the bottom of the storage and reduce the storage by 30%–70%. It is urgent to study how to effectively control the volumetric expansion of insoluble mudstones and enlarge the storage capacity. In view of this, we first characterize and quantify the rock salt, interlayer mudstones, and clay minerals by XRD. Then, 12 kinds of organic and inorganic shrinkage agents were compared in the shrinkage experiments. Five factors affecting the shrinkage are considered, including the concentration and diffusion distance of shrinkage agents, the mass ratio and particle sizes of mudstones, and the temperature. The optimal recipe and concentration of chemical agents suitable for mudstone shrinkage in salt cavern reservoir are obtained. Finally, based on the shrinking performance of mudstones, SEM scanning, EDS analysis and Zeta potential test, the shrinking mechanism of insoluble mudstones at the bottom of the cavern was proposed. The results show that: The content of swelling clay in the target gas storage is low and the clay swelling is not the main reason for the volumetric expansion of mudstones. High valence cationic salts or polymers can shrink. Among which, the order of shrinking effectiveness is: inorganic polymers > Inorganic salts > Organic polymers. When the dosage of PAC-30 is 0.7 g/L, the volumetric shrinkage effect of mudstones is more than 40%. It has a great potential to expand the storage capacity of the salt cavern. The study shows that there is an optimum dosage of the shrinkage agent. The increasing temperature and the small particle sizes of mudstones are beneficial to shrinkage. The shrinking process is a diffusion control process, and the shrinkage agents are easy to form a dense layer on the mudstone surface, which hinders the further diffusion of the shrinkage agents. Mechanism studies show that: After the addition of cationic polymer, the Zeta potential on the mudstone grain surface decreased significantly. The electrostatic repulsion between rock particles was decreased, and flocculation, agglomeration, and compaction occurred, which is the main mechanism of mudstone shrinkage in the gas storage cavern. This study provides a theoretical and practical basis for the volumetric shrinking of mudstones at bottom of bedded salt cavern gas storage.

Study on processability, compressive strength, drying shrinkage and evolution mechanisms of microstructures of alkali-activated slag-glass powder cementitious material

Energy shortage and environmental pollution have become two global problems to be solved urgently. Therefore, it is urgent to develop a low-carbon building material to replace the traditional Portland cement. Alkali-activated materials (AAM) have become a hot topic because they provide many attractive engineering and environmental benefits. In this study, 15 AAMs were developed based on slag-waste glass powder. The setting time, fluidity, compressive strength, and drying shrinkage of AAM were tested. The effects of retarder, water-to-binder ratio, Na2O content, and the modulus of water glass were considered. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Differential thermal gravity-thermal gravity (DTG-TG), and Scanning electron microscope (SEM) techniques were used to reveal the action mechanism of influencing factors on various properties of AAM. Based on the grey entropy theory, the effects of Na2O content and the modulus of water glass on the setting time, fluidity, compressive strength and drying shrinkage of AAM were discussed. The economic and environmental benefits of AAM were evaluated in terms of cost, energy consumption, and carbon footprint. The results show that the prepared AAM shows unexpected results in various properties. In addition, compared with Portland cement, the energy consumption of AAM can be reduced by up to 65.16%, the cost can be reduced by up to 32.88%, and the carbon footprint can be reduced by up to 64.72%. This study not only solves the resource utilization of solid waste glass and slag, but also promotes the application of AAM in engineering.

Anti-shrinkage, high-elastic, and strong thermoplastic polyester elastomer foams fabricated by microcellular foaming with CO2 & N2 as blowing agents

Thermoplastic polyester elastomer (TPEE) is a high-performance polymer with high tear strength and excellent abrasion resistance, and microcellular TPEE foams exhibit low density and special mechanical properties. Nevertheless, shrinkage behavior of the TPEE foam is still a critical challenge which greatly limits its industrial application, and further, the shrinkage mechanism is rarely figured out. Herein, a novel strategy of implementing mixed CO2 & N2 as blowing agents in microcellular foaming was developed to stabilize cell structure. Thanks to the modest permeability of mixed blowing agents, TPEE foams with high stable expansion ratio of higher than 17-fold and recovery ratio of up to 77 % were fabricated, and it found that the ratio of mixed blowing agents could modulate the shrinkage behavior of TPEE foams. Moreover, the correlation between the mechanical properties and TPEE foams with different shrinkage behaviors was investigated. For TPEE foams with similar stable expansion ratios, decreasing the shrinkage helped to increase the maximum compressive stress by 100 % and to reduce the energy loss coefficient by 43 %. Overall, the developed microcellular foaming prepared with the mixed CO2 & N2 as blowing agents shows great promise in fabricating advanced elastomer foams with high expansion ratio, stable cell morphology and outstanding mechanical properties.

Concrete Elastic Modulus Experimental Research Based on Theory of Capillary Tension.

The risk of cracking in the early stage is a critical indicator of the performance of concrete structures. Concrete cracked when the tensile stresses caused by deformation under restraint conditions exceeded its tensile strength. This research aims at an accurate prediction of shrinkage cracking of concrete under constraints. Based on the theory of capillary tension under the concrete shrinkage mechanism, the method to test and compute the elastic modulus of a micro-matrix around the capillary, , was derived. Shrinkage and porosity determination tests were conducted to obtain the shrinkage values and confining stresses of concrete at different strength grades, different ages and under different restraint conditions, accordingly. Meanwhile, the proposed method of this research was used to obtain . The restraint stress given by was compared with the experimental result under the corresponding time. The results suggested a positive correlation between the elastic modulus of a micro-matrix around the capillary, , precomputed by the theory, and the static elastic modulus, , and that the ratio between the two gradually decreased with the passage of time, which ranged from 2.8 to 3.1.

The Effect of Urban Shrinkage on Carbon Dioxide Emissions Efficiency in Northeast China.

Climate change caused by CO2 emissions is a controversial topic in today’s society; improving CO2 emission efficiency (CEE) is an important way to reduce carbon emissions. While studies have often focused on areas with high carbon and large economies, the areas with persistent contraction have been neglected. These regions do not have high carbon emissions, but are facing a continuous decline in energy efficiency; therefore, it is of great relevance to explore the impact and mechanisms of CO2 emission efficiency in shrinking areas or shrinking cities. This paper uses a super-efficiency slacks-based measure (SBM) model to measure the CO2 emission efficiency and potential CO2 emission reduction (PCR) of 33 prefecture-level cities in northeast China from 2006 to 2019. For the first time, a Tobit model is used to analyze the factors influencing CEE, using the level of urban shrinkage as the core variable, with socio-economic indicators and urban construction indicators as control variables, while the mediating effect model is applied to identify the transmission mechanism of urban shrinkage. The results show that the CEE index of cities in northeast China is decreasing by 1.75% per annum. For every 1% increase in urban shrinkage, CEE decreased by approximately 2.1458%, with urban shrinkage, industrial structure, and expansion intensity index (EII) being the main factors influencing CEE. At the same time, urban shrinkage has a further dampening effect on CEE by reducing research and development expenditure (R&D) and urban compactness (COMP), with each 1% increase in urban shrinkage reducing R&D and COMP by approximately 0.534% and 1.233%, respectively. This can be improved by making full use of the available built-up space, increasing urban density, and promoting investment in research.

Drying shrinkage characteristics and mechanism primary exploration of MgO-slag mortars

In this work, seven groups of MgO-slag mortars and pastes were prepared with different MgO types and MgO contents. The setting time, compressive strength and drying shrinkage were characterized. The mechanism of drying shrinkage was discussed by means of microscopic test XRD, FT-IR, MIP and SEM-EDS. The results show that the setting time decrease with the increase of MgO activities and contents. The high-activity MgO only shows a higher compressive strength advantage in the early stage, and the higher content of S-MgO, the higher the compressive strength advantage in the later stage. The 120d drying shrinkage first increases and then decreases with the increase of S-MgO contents, and the maximum drying shrinkage is obtained when the S-MgO content is 15%. The drying shrinkage of the mortar mixed with M-MgO is about half of the mortar mixed with S-MgO; the mortar mixed with R-MgO shows expansion change. Intraparticle porosity, interparticle porosity, and MgO particle size are important factors that affect the drying shrinkage of MgO-slag mortars. This study will provide the theoretical basis for the preparation of cementing materials with no length change by using a MgO activator.

How Does Population Shrinkage Affect Economic Resilience? A Case Study of Resource-Based Cities in Northeast China

By constructing an index system, this study analyzed the temporal and spatial characteristics of the economic resilience of 20 resource-based cities in northeast China after the financial crisis in 2008. On this basis, a mediation model was introduced to explore the mechanism of population shrinkage affecting economic resilience. The results show that: (a) from 2009 to 2019, the trend of the economic resilience of resource-based cities in northeast China was “ascending–descending–stable”. As time went by, the spatial difference of the economic resilience of resource-based cities gradually became obvious, indicating that the number of medium- and high-class cities was increasing. (b) By applying a correlation analysis, it was found that both a significant weak correlation and medium correlation existed between population shrinkage and economic resilience during the periods of 2011–2019 and 2013–2019. (c) Six mediation factors, namely industrial output, population consumption, resource dependence, urban innovation, cultural construction and environment quality, were chosen to apply the mediation model of population shrinkage affecting economic resilience. Among them, industrial output, population consumption, urban innovation, and cultural construction exerted a partial mediation effect on the process of population shrinkage affecting economic resilience, while the meditation effects of resource dependence and environment quality were not significant.

Analysis and Research on Borehole Shrinkage Mechanisms and Their Control in Directional Wells in Deep Composite Salt Formations

Abstract The composite salt formations in West China are characterized by the deep burial, complex tectonic stress, and alternating development of salt rock and mudstone, and salt rock creep during drilling poses great challenges to the safety of drilling. This research is aimed at the serious blockage and sticking in build-up sections in deep composite salt formations. A 2D mechanical model for inclined wells penetrating multiple vertical layers was established by combining the analysis of creep mechanisms of composite salt formations with the high-temperature creep experiment results so as to investigate the wellbore stability of directional wells in composite salt formations in a certain block from the perspective of rock mechanics and probe the influence of inclination angles on borehole shrinkage under different in situ stress and interlayer conditions. Moreover, a directional well in the block was taken as an example to analyze the creep and borehole shrinkage in composite salt formations. The method for wellbore stability control was proposed, and the drilling fluid density chart was established. This research reveals the relationship among the wellbore trajectory, the degree of borehole shrinkage, and drilling fluid density in build-up sections of directional wells in composite salt formations and provides a theoretical reference for the establishment of the method for controlling blockage and sticking accidents in directional wells.

The effect of specimen size on autogenous and total shrinkage of ultra-high performance concrete (UHPC)

Unlike normal strength concretes, in which drying is the dominant form of shrinkage, in concretes with very low water to cement ratios autogenous and chemical shrinkage mechanisms can dominate. While the impact of specimen size and shape on drying shrinkage is well understood, the same is not true for autogenous and chemical shrinkage, and this lack of understanding may limit model precision and accuracy. To address this issue, this paper presents the results of a series of experiments conducted to measure the dependency of shrinkage of UPHC on specimen size. Results, recorded from 2 days after water addition, demonstrate a strong specimen size dependency when tested under both sealed and unsealed conditions, thereby indicating that the underlying mechanism is fundamentally different from normal strength concrete, with autogenous shrinkage exhibiting a large influence. Existing shrinkage models (AS3600, B4, CEB-FIP, GL2000 and ACI209) are evaluated for their potential calibration and/or extension to low water to binder ratio concretes and it is shown that commonly used parameters to account for size dependency in normal strength concrete (volume to surface area ratio and hypothetical thickness) do not capture size dependency in UHPC.

Basic magnesium sulfate cement: Autogenous shrinkage evolution and mechanism under various chemical admixtures

Basic magnesium sulfate cement (BMSC) is a new type of whisker self-toughening cement-based material. Owing to its excellent mechanical properties, it has been applied to high-speed rail cover plates and military protective materials. However, the shrinkage deformation problem affects the application of BMSC in other fields. This article describes the effects of three chemical admixtures on the basic mechanical properties and autogenous shrinkage deformation of BMSC. Isothermal calorimetry (IC), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and mercury intrusion porosimetry (MIP) were performed to study the influence of different chemical admixtures on the phase and microstructure of BMSC. Finally, based on the microscopic phase and structure analysis results, the autogenous shrinkage mechanism of BMSC under the action of different chemical admixtures was systematically analyzed. The results show that citric acid (CA) and amino trimethylene phosphonic acid (ATMP) can significantly improve the compressive strength of BMSC. Based on the phase analysis and microstructure analysis, ATMP and CA can induce more formation of the needle-like 5-1-7 phase. The results of shrinkage deformation show that the unmodified BMSC has obvious expansion, and the expansion rate increases with time. However, the BMSC modified by chemical admixtures shows small expansions at first, and then begins to show continuous shrinkage deformation. The expansion in the unmodified BMSC during crystal growth stems from the crystallization pressure of Mg(OH)2 as the main driving force. However, the formation of Mg(OH)2 is inhibited in the modified BMSC, so the shrinkage deformation of BMSC was mainly caused by the formation of the 5-1-7 phase.

Shrinkage in frozen desserts

Shrinkage is a well-documented defect in frozen desserts, yet the root causes and mechanisms remain unknown. Characterized by the loss of volume during storage, shrinkage arose during the mid-twentieth century as production of frozen desserts grew to accommodate a larger market. Early research found that shrinkage was promoted by high protein, solids, and overrun, as well as postproduction factors such as fluctuations in external temperature and pressure. Rather than approaching shrinkage as a cause-and-effect defect as previous approaches have, we employ a physicochemical approach to characterize and understand shrinkage as collapse of the frozen foam caused by destabilization of the dispersed air phase. The interfacial composition and physical properties, as well as the kinetic stability of air cells within the frozen matrix ultimately affect product susceptibility to shrinkage. The mechanism of shrinkage remains unknown, as frozen desserts are highly complex, but is rooted in the physicochemical properties of the frozen foam. Functional ingredients and processing methods that optimize the formation and stabilization of the frozen foam are essential to preventing shrinkage in frozen desserts.

Improving the cracking resistance of mortar by reduced graphene oxide

The shrinkage cracking adversely impacts the long-life durability of cement composites. However, how to restrict the formation and evolution of cracking is still a challenge. Herein, we propose a new strategy to control the shrinkage strain and associated cracking of cement mortar by introducing reduced graphene oxide (rGO). The early-age shrinkage and cracking resistance experimentation of mortar are firstly investigated. Moreover, the shrinkage mechanism is carried out and the distribution of rGO in mortar matrix is analyzed by scanning electron microscopy and X-ray micro-computed tomography. The results show rGO aggravates the imbalance relationship of evaporation-bleeding water on the surface of mortar, which increases the plastic shrinkage value. The water retention effect of rGO contributes to the decrease of autogenous and drying shrinkage. The well-dispersed rGO reduces the number, total length and width of plastic shrinkage cracking. In conclusion, the incorporation of rGO enhances the cracking resistance of mortar and exhibits a promising potential for the long-term sustainable development of cement composites.

A hybrid modelling approach for characterizing hole shrinkage mechanisms in drilling Ti6Al4V under dry and cryogenic conditions

A hybrid modelling approach for characterizing hole shrinkage mechanisms in drilling Ti6Al4V under dry and cryogenic conditions

Automated quantitative analysis of void morphology evolution in Ag[sbnd]Ag direct bonding interface after accelerated aging

Silver-to-silver direct bonding has been developed as an attractive joining technique for 3D power integration which can form high-strength and low-resistance Ag joints under solid-state conditions. The bonding process starts with the initial contact and plastic deformation of the surface asperities, resulting in a series of voids between these surface tips. To reliably assess the state of the direct bonded joints, precise characterization and quantification of the microstructure are required. Moreover, the key to understanding the evolution of this AgAg bond during reliability testing is the microstructural characterization of the interfacial voids in a statistically relevant manner. In this work, the void identification and analytical characterization of direct bonded joints are implemented by an automated method based on image segmentation. The current experimental results show that with this method, it is possible to track and statistically analyze the void morphology evolution during accelerated aging. This provides new insights into the fundamental void shrinkage mechanisms, which can be further used to improve the manufacturing process and lifetime and reliability of the AgAg joints.

Reducing soft-tissue shrinkage artefacts caused by staining with Lugol\u2019s solution

Diffusible iodine-based contrast-enhanced computed tomography (diceCT) is progressively used in clinical and morphological research to study developmental anatomy. Lugol’s solution (Lugol) has gained interest as an effective contrast agent; however, usage is limited due to extensive soft-tissue shrinkage. The mechanism of Lugol-induced shrinkage and how to prevent it is largely unknown, hampering applications of Lugol in clinical or forensic cases where tissue shrinkage can lead to erroneous diagnostic conclusions. Shrinkage was suggested to be due to an osmotic imbalance between tissue and solution. Pilot experiments pointed to acidification of Lugol, but the relation of acidification and tissue shrinkage was not evaluated. In this study, we analyzed the relation between tissue shrinkage, osmolarity and acidification of the solution during staining. Changes in tissue volume were measured on 2D-segmented magnetic resonance and diceCT images using AMIRA software. Partial correlation and stepwise regression analysis showed that acidification of Lugol is the main cause of tissue shrinkage. To prevent acidification, we developed a buffered Lugol’s solution (B-Lugol) and showed that stabilizing its pH almost completely prevented shrinkage without affecting staining. Changing from Lugol to B-Lugol is a major improvement for clinical and morphological research and only requires a minor adaptation of the staining protocol.

Soil Shrinkage Characterization of Low Plasticity Soil Using Digital Image Analysis Process

The goal of this paper is to better understand the shrinkage behavior of low plasticity (CL) soil, which is common in Warangal, India. Understanding the tensile strength and hydro-mechanical response of soil requires an understanding of the contraction behavior of soil caused by drying during wet-dry moisture cycles. With the use of simple and reliable experimental approaches, the shrinkage mechanism and behavior with suction variation are characterized and described in this study. The findings are related to the change in suction, water content, and void ratio of soil that has been air-dried from complete saturation to dryness. The proposed framework uses two simple approaches to understand soil water retention during the drying phase: one to quantify the suction potential and the other to characterize the shrinkage mechanism. In addition, the use of digital image processing (DIP) to capture sample shrinkage using a simple experimental setup is thoroughly discussed. ImageJ software has been found to be feasible for DIP and to quantify the volume change of laboratory samples. The absence of well-structured soil phases or macropores is attributable to the presence of only normal shrinkage and zero shrinkage phases in the tested soil. In terms of water–retention behavior, the shrinkage curve, and the suction curve are very similar. The effects of capillary suction on the shrinkage response of low plastic soil have been observed, emphasizing the importance of characterizing soil shrinkage behavior using suction as a stress-state variable in volume change studies.

What are the key mechanisms that alter the morphology of stigmatic papillae in Arabidopsis thaliana?

ABSTRACT Pollination is one of the critical processes that determines crop yield and quality. Thus, it is an urgent need to elucidate the mechanisms underlying pollination. Our previous research has revealed a novel phenomenon that pollen attachment to stigma caused stigma shrinkage, whereas failure of pollen attachment to stigma due to the environmental stress induced elongation of stigmatic papillae. However, little is known about the mechanisms of these morphological alterations in stigmatic papillae. Since the RLK-ROPGEF-ROP network is a common mechanism for the elongation of pollen tubes and root hairs, this network may be also involved in the elongation of papillae in the stigma. In this review, we will discuss the known mechanisms regulating pollen tube growth and root hair elongation and attempt to propose an elongation mechanism of stigmatic papillae. In addition, we will suggest that the degradation of F-actin by a significant increase in Ca2+ induced by the components of pollen coat might be a putative molecular mechanism of stigmatic papillae shrinkage during pollen adhesion.

Foam Concrete Pore Structure Effect on Drying Shrinkage and Frost Resistance

Abstract Foam concrete has two major shortcomings resulting primarily from pore structure: high drying shrinkage and weak frost resistance. This article reports on a study of how various water-cement ratios affect high drying shrinkage and weak frost resistance. Stereomicroscopy, acoustic wave, and nitrogen adsorption methods measured macroporous and microscopic pore structures to analyze drying shrinkage and frost resistance mechanisms. Drying shrinkage was shown to gradually increase as water-cement ratios increased from 0.4 to 0.7. This can be attributed to increased water loss via capillary holes and greater capillary tension. Frost resistance maximized at a water-cement ratio of 0.5. As the water-to-cement ratio increased from 0.4 to 0.5, accessible pores with an average size of 10–50 nm increased. The volume of harmful 50–200-nm pores and pores larger than 200 nm increased. When water-cement ratios increased from 0.5 to 0.7, the number of 0–200-μm pores decreased sharply, whereas pores larger than 400 μm increased dramatically.