The reasonable quantification of the concrete freezing environment on the Qinghai–Tibet Plateau(QTP) is the primary issue in frost resistant concrete design, which is one of the challenges that the QTP engineering ma...The reasonable quantification of the concrete freezing environment on the Qinghai–Tibet Plateau(QTP) is the primary issue in frost resistant concrete design, which is one of the challenges that the QTP engineering managers should take into account. In this paper, we propose a more realistic method to calculate the number of concrete freeze–thaw cycles(NFTCs) on the QTP. The calculated results show that the NFTCs increase as the altitude of the meteorological station increases with the average NFTCs being 208.7. Four machine learning methods, i.e., the random forest(RF) model, generalized boosting method(GBM), generalized linear model(GLM), and generalized additive model(GAM), are used to fit the NFTCs. The root mean square error(RMSE) values of the RF, GBM, GLM, and GAM are 32.3, 4.3, 247.9, and 161.3, respectively. The R^(2) values of the RF, GBM, GLM, and GAM are 0.93, 0.99, 0.48, and 0.66, respectively. The GBM method performs the best compared to the other three methods, which was shown by the results of RMSE and R^(2) values. The quantitative results from the GBM method indicate that the lowest, medium, and highest NFTC values are distributed in the northern, central, and southern parts of the QTP, respectively. The annual NFTCs in the QTP region are mainly concentrated at 160 and above, and the average NFTCs is 200 across the QTP. Our results can provide scientific guidance and a theoretical basis for the freezing resistance design of concrete in various projects on the QTP.展开更多
To explore how to respond to seasonal freeze–thaw cycles on forest ecosystems in the context of climate change through thinning,we assessed the potential impact of thinning intensity on carbon cycle dynamics.By varyi...To explore how to respond to seasonal freeze–thaw cycles on forest ecosystems in the context of climate change through thinning,we assessed the potential impact of thinning intensity on carbon cycle dynamics.By varying the number of temperature cycles,the eff ects of various thinning intensities in four seasons.The rate of mass,litter organic carbon,and soil organic carbon(SOC)loss in response to temperature variations was examined in two degrees of decomposition.The unfrozen season had the highest decomposition rate of litter,followed by the frozen season.Semi-decomposed litter had a higher decomposition rate than undecomposed litter.The decomposition rate of litter was the highest when the thinning intensity was 10%,while the litter and SOC were low.Forest litter had a good carbon sequestration impact in the unfrozen and freeze–thaw seasons,while the converse was confi rmed in the frozen and thaw seasons.The best carbon sequestration impact was identifi ed in litter,and soil layers under a 20–25%thinning intensity,and the infl uence of undecomposed litter on SOC was more noticeable than that of semi-decomposed litter.Both litter and soil can store carbon:however,carbon is transported from undecomposed litter to semi-decomposed litter and to the soil over time.In summary,the best thinning intensity being 20–25%.展开更多
目的探讨智能冠状动脉运动追踪平台Snapshot Freeze（SSF）在冠状动脉CT血管成像（CCTA）中的应用价值。方法连续选取61例患者,使用Discovery CT750 HD Freedom进行冠状动脉扫描,扫描后分别使用和不使用SSF重建,得到A、B两组图像;根据...目的探讨智能冠状动脉运动追踪平台Snapshot Freeze（SSF）在冠状动脉CT血管成像（CCTA）中的应用价值。方法连续选取61例患者,使用Discovery CT750 HD Freedom进行冠状动脉扫描,扫描后分别使用和不使用SSF重建,得到A、B两组图像;根据扫描实时心率将患者分为低心率组（心率≤70次/分,n=34）,中高心率组（心率71～80次/分,n=14）和高心率组（心率〉80次/分,n=13）。对比分析A、B组间和不同心率组间的图像质量差异。结果除左主干（S5）外,B组冠状动脉各节段图像质量评分均优于A组（P均〈0.05）;S5段剔除评分为5分者后,其余7例B组图像质量均优于A组（P=0.008）;未使用SSF重建时不可诊断的42个节段经用SSF重建后全部可用于诊断。未使用SSF重建的不同心率组间除S7、S9段外,其余各节段图像质量评分差异均有统计学意义（P均〈0.05）,图像质量随心率增加而下降;使用SSF重建后,不同心率组间各节段图像质量评分差异均无统计学意义（P均〉0.05）。未使用SSF重建的右冠状动脉中段（S2）在15段中评分最低（2.88±0.91）分,S3次之（3.65±1.32）分,且S2在低心率组亦有17例出现移动伪影影响其评估;使用SSF重建后,S2、S3移动伪影显著改善,评分分别提升至（4.32±0.59）分和（4.49±0.59）分,均满足诊断需求。结论 SSF能够有效地纠正高心率及心率波动导致的冠状动脉血管移动伪影,优化CCTA图像质量,尤其对右冠状动脉移动伪影有显著意义。展开更多
In recent years,the winter temperature in southern China decreases year by year,and the phenomenon of freeze-thaw damage is also wide-spread in hydraulic buildings.In this paper,the freezing-thawing cycle tests of ful...In recent years,the winter temperature in southern China decreases year by year,and the phenomenon of freeze-thaw damage is also wide-spread in hydraulic buildings.In this paper,the freezing-thawing cycle tests of fully graded concrete specimens and corresponding wet sieving suitable for climate conditions in southern China were carried out,and the effects of freezing-thaw cycles on the appearance,mass loss,relative dynamic elastic modulus,internal temperature and strain of fully graded concrete and wet sieving concrete were studied.The splitting tensile strength test of concrete specimens with specified salt freezing cycles was carried out,and the relationship between the strength reduction of fully graded concrete and wet sieving concrete specimens and the number of freeze-thaw cycles was analyzed.The results show that with the increase of freeze-thaw cycles,the properties of fully graded concrete and wet sieving concrete degraded,and the degradation of compressive strength was the most significant,followed by the splitting tensile strength.In the initial stage of the freeze-thaw cycles,the degradation of each property was not obvious,and the deterioration rate of each property increased significantly after 100 freeze-thaw cycles.Besides,the relationship between the splitting tensile strength of fully graded concrete and wet sieving concrete and the internal wave velocity after freeze-thaw cycles was established.The test results can provide theoretical basis for the design,repair,maintenance and life prediction of dams and offshore platforms in southern China.展开更多
On the basis of previous research results, the frost resistance of fully graded concrete and small wet sieving concrete specimens was compared and analyzed, and the characteristics and rules of freeze-thaw damage of h...On the basis of previous research results, the frost resistance of fully graded concrete and small wet sieving concrete specimens was compared and analyzed, and the characteristics and rules of freeze-thaw damage of hydraulic fully graded concrete after freeze-thaw cycles were analyzed through freeze-thaw test, impact-echo test, mechanical test and so on. Meanwhile, the damage characteristics of concrete in the salt and water freezing environment were compared. Through the mechanical test, it is found that the mechanical properties of both fully graded concrete and wet sieving concrete decreased to varying degrees after freeze-thaw cycles. The laws of uniaxial compression and tensile strength of concrete varying with the number of freeze-thaw cycles were obtained. The life of concrete after freeze-thaw cycles was predicted, and it is concluded that the life of concrete in the salt freezing environment was only 0.8 times that in the water freezing environment, proving once again that the damage of concrete in the salt freezing environment was more serious than that in the water freezing environment. Therefore, the grade of frost resistance should be improved appropriately for concrete engineering with salt solution. Finally, based on the damage theory and Lemaitre strain equivalence principle, the freeze-thaw damage evolution equation suitable for fully graded concrete was obtained.展开更多
We analyzed the relationships linking overwintering death and frost cracking to temperature and sunlight as well as the effects of low temperatures and freeze–thaw cycles on bud-burst rates,relative electrical conduc...We analyzed the relationships linking overwintering death and frost cracking to temperature and sunlight as well as the effects of low temperatures and freeze–thaw cycles on bud-burst rates,relative electrical conductivity,and phloem and cambial ultrastructures of poplar.Overwintering death rates of poplar were not correlated with negative accumulated temperature or winter minimum temperature.Freeze–thaw cycles caused more bud damage than constant exposure to low temperatures.Resistance to freeze–thaw cycles differed among clones,and the budburst rate decreased with increasing exposure to freeze–thaw cycles.Cold-resistant clones had the lowest relative electrical conductivity.Chloroplasts exhibited the fastest and the most obvious reaction to freeze–thaw damage,whereas a single freeze–thaw cycle caused little damage to cambium ultrastructure.Several such cycles resulted in damage to plasma membranes,severe damage to organelles,dehydration of cells and cell death.We conclude that overwintering death of poplar is mainly attributed to the accumulation of effective freeze–thaw damage beyond the limits of freeze–thaw resistance.展开更多
Ovalbumin(OVA),the main protein in egg white,affects most of the functional properties of egg white protein in food processing.The aim of this study was to investigate the effects of spray drying(SD)and microwave free...Ovalbumin(OVA),the main protein in egg white,affects most of the functional properties of egg white protein in food processing.The aim of this study was to investigate the effects of spray drying(SD)and microwave freeze drying(MFD)on the preparation of hydrolyzed/glycosylated ovalbumin(HGOVA)and provide useful information on the applications of egg protein powders in the food industry.Results demonstrated that the structure of HGOVA was considerably changed,and its functional properties were improved compared with those of native OVA.SD and MFD processing did not lead to dissociation of HGOVA subunits.SD-HGOVA exhibited higher protein solubility,emulsifying activity,foaming capacities,and gel hardness than MFD-HGOVA.However,MFD-HGOVA was better than the SD-HGOVA in terms of color,emulsion stability,foam stability,water/oil absorption capacity,and thermal stability.Selection of an appropriate drying method could enhance the potential applications of HGOVA in the food industry.展开更多
Freeze-thaw processes significantly modulate hydraulic and thermal characteristics of soil. The changes in the frost and thaw fronts(FTFs) affect the water and energy cycles between the land surface and the atmosphere...Freeze-thaw processes significantly modulate hydraulic and thermal characteristics of soil. The changes in the frost and thaw fronts(FTFs) affect the water and energy cycles between the land surface and the atmosphere. Thus, the frozen soil comprising permafrost and seasonally frozen soil has important effects on the land surface hydrology in cold regions. In this study, a two-directional freeze and thaw algorithm is incorporated into a thermal diffusion equation for simulating FTFs. A local adaptive variable-grid method is used to discretize the model. Sensitivity tests demonstrate that the method is stable and FTFs can be tracked continuously. The FTFs and soil temperature at the Qinghai-Tibet Plateau D66 site are simulated hourly from September 1, 1997 to September 22, 1998. The results show that the incorporated model performs much better in the soil temperature simulation than the original thermal diffusion equation,showing potential applications of the method in land-surface process modeling.展开更多
Digital patternless freeze-casting technology is a new approach for obtaining frozen sand moulds using digital milling technology. The change law of tensile strength and air permeability of frozen sand moulds (100-mes...Digital patternless freeze-casting technology is a new approach for obtaining frozen sand moulds using digital milling technology. The change law of tensile strength and air permeability of frozen sand moulds (100-mesh and 200-mesh silica sand, and zircon sand moulds) under different freezing temperatures and water contents was studied. Results show that with the decrease of freezing temperature and the increase of water contents, the tensile strength and air permeability of the sand moulds are gradually improved. Meanwhile, computed tomography technology was used to characterize the shape and size of the water film between the sand particles mixed with 4wt.% water. The results show that in silica sand moulds, the form of water film is lumpy, and 200-mesh silica sand moulds have more water films and higher proportion of small-sized water films than 100-mesh silica sand moulds, while in zircon sand moulds, the form of water film is membranous. At the same freezing temperature and water content, the tensile strength of zircon sand mould is the highest, and 100-mesh silica sand mould is the lowest. A comparative solidification experiment of A356 aluminum alloy was carried out in frozen sand mould and resin sand mould. The results show that the primary α-Al phase appears in the form of equiaxed and eutectic silicon phase is needle-like in freezing sand mould casting, but the primary α-Al phase grows in the form of dendrites, and the eutectic silicon phase is coarse needle-like in the resin sand mould casting. The difference of microstructure is caused by the different cooling rate. The cooling rate of A356 aluminum alloy in frozen sand mould is higher than that in resin sand mould.展开更多
AIM:To investigate the interaction between mesenchymal stem cells(MSCs) and bone grafts using two different cultivation methods:static and dynamic.METHODS:MSCs were isolated from rat bone marrow.MSC culture was analyz...AIM:To investigate the interaction between mesenchymal stem cells(MSCs) and bone grafts using two different cultivation methods:static and dynamic.METHODS:MSCs were isolated from rat bone marrow.MSC culture was analyzed according to the morphology,cell differentiation potential,and surface molecular markers.Before cell culture,freeze-dried bone(FDB) was maintained in culture for 3 d in order to verify culture medium pH.MSCs were co-cultured with FDB using two different cultivation methods:static co-culture(two-dimensional) and dynamic co-culture(threedimensional).After 24 h of cultivation by dynamic or static methods,histological analysis of Cell adhesion on FDB was performed.Cell viability was assessed by the Trypan Blue exclusion method on days 0,3 and 6 after dynamic or static culture.Adherent cells were detached from FDB surface,stained with Trypan Blue,and quantified to determine whether the cells remained on the graft surface in prolonged non-dynamic culture.Statistical analyses were performed with SPSS and a P 【 0.05 was considered significant.RESULTS:The results showed a clear potential for adipogenic and osteogenic differentiation of MSC cultures.Rat MSCs were positive for CD44,CD90 and CD29 and negative for CD34,CD45 and CD11bc.FDBs were maintained in culture for 3 d and the results showed there was no significant variation in the culture medium pH with FDB compared to pure medium pH(P 】 0.05).In histological analysis,there was a significant difference in the amount of adhered cells on FDB between the two cultivation methods(P 【 0.05).The MSCs in the dynamic co-culture method demonstrated greater adhesion on the bone surface than in static co-culture method.On day 0,the cell viability in the dynamic system was significantly higher than in the static system(P 【 0.05).There was a statistical difference in cell viability between days 0,3 and 6 after dynamic culture(P 【 0.05).In static culture,cell viability on day 6 was significantly lower than on day 3 and 0(P 【 0.05).CONCLUSION:An alternative cultivation method was developed to improve the MSCs adhesion on FDB,demonstrating that dynamic co-culture provides a superior environment over static conditions.展开更多
Freeze-thaw cycles are closely related to the slope instability in high-altitude mountain regions. In this study, cohesive coarse-grained soils were collected from a high-altitude slope in the Qinghai–Tibet Plateau t...Freeze-thaw cycles are closely related to the slope instability in high-altitude mountain regions. In this study, cohesive coarse-grained soils were collected from a high-altitude slope in the Qinghai–Tibet Plateau to study the effect of cyclic freeze-thaw on their uniaxial mechanical properties. The soil specimens were remolded with three dry densities and three moisture contents. Then, after performing a series of freeze-thaw tests in a closed system without water supply, the soil specimens were subjected to a uniaxial compression test. The results showed that the stress-strain curves of the tested soils mainly performed as strain-softening. The softening feature intensified with the increasing dry density but weakened with an increase in freeze-thaw cycles and moisture content. The uniaxial compressive strength, resilient modulus, residual strength and softening modulus decreased considerably with the increase of freeze-thaw cycles. After more than nine freeze-thaw cycles, these four parameters tended to be stable. These parameters increased with the increase of dry density and decreased with the increasing moisture content, except for the residual strength which did not exhibit any clear variation with an increase in moisture content. The residual strength, however, generally increased with an increase in dry density. The soil structural damage caused by frozen water expansion during the freeze-thaw is the major cause for the changes in mechanical behaviors of cohesive coarse-grained soils. With results in this study, the deterioration effect of freeze-thaw cycles on the mechanical properties of soils should be considered during the slope stability analysis in high-altitude mountain regions.展开更多
Expansive soils located in cold regions can easily endure the action of frost heaving and cyclic freezing–thawing. Cracking can also occur in expansive clayey soils under freeze–thaw cycles, of which little attentio...Expansive soils located in cold regions can easily endure the action of frost heaving and cyclic freezing–thawing. Cracking can also occur in expansive clayey soils under freeze–thaw cycles, of which little attention has been paid on this issue.In this study, laboratory experiment and cracking analysis were performed on an expansive soil. Crack patterns were quantitatively analyzed using the fractal concept. The relationships among crack pattern, water loss, number of freeze–thaw cycles, and fractal dimension were discussed. It was found that crack patterns on the surface exhibit a hierarchical network structure that is fractal at a statistical level. Cracks induced by freeze–thaw cycles are shorter, more irregularly oriented,and slowly evolves from an irregularly rectilinear pattern towards a polygonal or quasi–hexagonal one; water loss, closely related to specimen thickness, plays a significant role in the process of soil cracking; crack development under freeze-thaw cycles are not only attributed to capillary effect, but also to expansion and absorption effects.展开更多
To improve the reliability and reduce energy consumption,a conceptual design of a freeze valve is proposed for the thorium-based molten salt reactor(TMSR)concept.Fins were utilized in this new design to enhance heat t...To improve the reliability and reduce energy consumption,a conceptual design of a freeze valve is proposed for the thorium-based molten salt reactor(TMSR)concept.Fins were utilized in this new design to enhance heat transfer and realize passive shut-off function,which could not be realized by the previous design.An experimental apparatus using the fluoride salt FLiNaK was constructed to conduct a series of preliminary solidification and melting experiments.In addition,the enthalpy-porosity method of ANSYS■Fluent solver was applied to simulate the solidification process of the salt at a specified operating temperature.Temperature distributions of the fluoride salt,solidification/melting time,and frozen plug effect were analyzed under natural convection heat transfer in an open space.The calculated salt temperatures exhibited good agreement with the experimental values.The results indicated that the range of effective operating temperature is 530-600℃ for the finned freeze valve.In this study,the ideal set operating temperature of the finned freeze valve was chosen as 560℃ to achieve competent performance.Moreover,560℃ is additionally the highest set operating temperature for maintaining excellent cooling performance and sustaining deep-frozen condition of the salt plug.At this set operating temperature,the simulation data indicated that the molten salt in the flat part of the finned freeze valve will completely solidify at 10.5 min.The percentage of solid salt in the flat and lower transitional parts of the valve reaches 29.60% in 30.0 min.Furthermore,the surface temperature of the proposed freeze valve is 11.10% lower compared with that of the TMSR freeze valve at a cooling gas supply of 173 m^3/h.Therefore,the new freeze valve was proven to be capable of reducing the energy consumption and realizing the passive shut-off function.展开更多
Water-washing removes fluoride from Antarctic krill but produces large volumes of wash water containing water-soluble proteins and fluoride. The freeze concentration method was tested to determine if it could be used ...Water-washing removes fluoride from Antarctic krill but produces large volumes of wash water containing water-soluble proteins and fluoride. The freeze concentration method was tested to determine if it could be used to recover water-soluble proteins while leaving the fluoride in solution. After freezing and thawing the wash water, protein and fluoride contents of the thawed fractions were determined to explore the melting regularity of components in the wash water. The highest concentration factors of protein and fluoride were obtained after 80 min of thawing, such as 1.48 ± 0.06 and 1.35 ± 0.04 times, respectively. The free amino-nitrogen(FAN) content and sodium dodecyl sulfate-polyacrylamide gel electrophoresis pattern results revealed that the highest concentrations of all ingredients were obtained after 80 min of the process. The degree of hydrolysis of all fractions from the thawing process fluctuated in a narrow range around 12% during the entire process, indicating that the thawing order did not change with various proteins or time during the entire thawing course. These results demonstrate that the freeze concentration method can be used to concentrate protein solutions, even those with fluoride. It was concluded that condensation was achieved and no ingredient could be separated, regardless of fluoride, amino acids, or different proteins in the water.展开更多
Lactic acid bacteria possess several interesting properties of great economic importance. Improvement and stabilization of these industrially important features are an active research area at the present time. The obj...Lactic acid bacteria possess several interesting properties of great economic importance. Improvement and stabilization of these industrially important features are an active research area at the present time. The objectives of this work are to study the effect of freezing and freeze-drying on the survival rate, autolytic activity and intracellular enzymatic activity of the main species of lactic acid bacteria used in the dairy industry. The article focused on several characteristics that were not well covered in the past. The obtained results revealed that both preservation methods have a significant effect on viability, autolytic activity and intracellular enzymatic activity. After six months of storage we found that frozen cultures exhibited higher survival rate, higher rate of intracellular enzymatic activity and lower rate of autolysis. The impact of conservation treatments was only strain specific in the case of survival rate. The results obtained lead to the selection of the best preservation method for the selected cultures based on survival rate, autolytic activity and intracellular enzymatic activity.展开更多
With the objective of establishing a distinction between deformation structures caused by freeze/thaw cycles and those resulting from seismic activity, we studied three well–exposed alluvial deposits in a section at ...With the objective of establishing a distinction between deformation structures caused by freeze/thaw cycles and those resulting from seismic activity, we studied three well–exposed alluvial deposits in a section at Dogai Coring, northern Qiangtang Basin, Tibetan Plateau. Deformation is present in the form of plastic structures(diapirs, folds and clastic dykes), brittle structures(micro–faults) and cryogenic wedges. These soft–sediment deformation features(except the micro–faults) are mainly characterized by meter–scale, non–interlayered, low–speed and low–pressure displacements within soft sediments, most commonly in the form of plastic deformation. Taking into account the geographic setting, lithology and deformation features, we interpret these soft–sediment deformation features as the products of freeze/thaw cycles, rather than of earthquake–induced shock waves, thus reflecting regional temperature changes and fluctuations of hydrothermal conditions in the uppermost sediments. The micro–faults(close to linear hot springs) are ascribed to regional fault activity;however, we were unable to identify the nature of the micro–faults, perhaps due to disturbance by subsequent freeze/thaw cycles. This study may serve as a guide to recognizing the differences between deformation structures attributed to freeze/thaw cycles and seismic processes.展开更多
The therapeutic potential of small nucleic acids such as small interfering RNA(siRNA) to treat lung diseases has been successfully demonstrated in many in vivo studies. A major barrier to their clinical application is...The therapeutic potential of small nucleic acids such as small interfering RNA(siRNA) to treat lung diseases has been successfully demonstrated in many in vivo studies. A major barrier to their clinical application is the lack of a safe and efficient inhaled formulation.In this study, spray freeze drying was employed to prepare dry powder of small nucleic acids.Mannitol and herring sperm DNA were used as bulking agent and model of small nucleic acid therapeutics, respectively. Formulations containing different solute concentration and DNA concentration were produced. The scanning electron microscope(SEM) images showed that the porosity of the particles increased as the solute concentration decreased. Powders prepared with solute concentration of 5% w/v were found to maintain a balance between porosity and robustness. Increasing concentration of DNA improved the aerosol performance of the formulation. The dry powder formulation containing 2% w/w DNA had a median diameter of 12.5 μm, and the aerosol performance study using next generation impactor(NGI) showed an emitted fraction(EF) and fine particle fraction(FPF) of 91% and 28% respectively. This formulation(5% w/v solute concentration and 2% w/w nucleic acid) was adopted subsequently to produce siRNA powder. The gel retardation and liquid chromatography assays showed that the siRNA remained intact after spray freeze drying even in the absence of delivery vector. The siRNA powder formulation exhibited a high EF of 92.4%and a modest FPF of around 20%. Further exploration of this technology to optimise inhaled siRNA powder formulation is warranted.展开更多
A research and test system for the carbon anode plate preparation technology was established to optimize the physical and chemical indicators of carbon anode plates,such as bulk density,resistivity,and compressive str...A research and test system for the carbon anode plate preparation technology was established to optimize the physical and chemical indicators of carbon anode plates,such as bulk density,resistivity,and compressive strength,and improve the operating cycle.In this study,a carbon plate was prepared via a combination of high-temperature molding and freeze drying using a formulation with asphalt content much lower than the industry standard.The experimental results show that the density of the carbon plate is increased by 0.02-0.04 g/cm^(3) by improving the drying method.The carbon plate prepared in the laboratory has a bulk density of 1.814 g/cm^(3),resistivity of 29.8μΩ·m,and compressive strength of 89.27 MPa.The bulk density,room-temperature resistivity,compressive strength,graphitization,and other key indices of the carbon plates made in the laboratory and those procured from a factory in Shanxi,Datong,were tested.Additionally,the specimens were analyzed using thermogravimetry-differential scanning calorimetry,scanning electron microscopy,and X-ray fluorescence.The laboratory-made carbon plates were superior to the factory specimens in terms of all the indicators tested.The process in this study improves the performance of the carbon anode plate and is used to provide technical support for electrolytic fluorine production in enterprises.The carbon plates prepared in the laboratory fully meet the process requirements of a medium-temperature electrolytic fluorine production line,which indicates the possibility of its use in the stable production of fluorine gas.展开更多
基金supported by Shandong Provincial Natural Science Foundation (grant number: ZR2023MD036)Key Research and Development Project in Shandong Province (grant number: 2019GGX101064)project for excellent youth foundation of the innovation teacher team, Shandong (grant number: 2022KJ310)。
文摘The reasonable quantification of the concrete freezing environment on the Qinghai–Tibet Plateau(QTP) is the primary issue in frost resistant concrete design, which is one of the challenges that the QTP engineering managers should take into account. In this paper, we propose a more realistic method to calculate the number of concrete freeze–thaw cycles(NFTCs) on the QTP. The calculated results show that the NFTCs increase as the altitude of the meteorological station increases with the average NFTCs being 208.7. Four machine learning methods, i.e., the random forest(RF) model, generalized boosting method(GBM), generalized linear model(GLM), and generalized additive model(GAM), are used to fit the NFTCs. The root mean square error(RMSE) values of the RF, GBM, GLM, and GAM are 32.3, 4.3, 247.9, and 161.3, respectively. The R^(2) values of the RF, GBM, GLM, and GAM are 0.93, 0.99, 0.48, and 0.66, respectively. The GBM method performs the best compared to the other three methods, which was shown by the results of RMSE and R^(2) values. The quantitative results from the GBM method indicate that the lowest, medium, and highest NFTC values are distributed in the northern, central, and southern parts of the QTP, respectively. The annual NFTCs in the QTP region are mainly concentrated at 160 and above, and the average NFTCs is 200 across the QTP. Our results can provide scientific guidance and a theoretical basis for the freezing resistance design of concrete in various projects on the QTP.
基金funded by the National Key R&D Program of China(2017YFC0504103)Project for Applied Technology Research and Development in Heilongjiang Province(GA19C006).
文摘To explore how to respond to seasonal freeze–thaw cycles on forest ecosystems in the context of climate change through thinning,we assessed the potential impact of thinning intensity on carbon cycle dynamics.By varying the number of temperature cycles,the eff ects of various thinning intensities in four seasons.The rate of mass,litter organic carbon,and soil organic carbon(SOC)loss in response to temperature variations was examined in two degrees of decomposition.The unfrozen season had the highest decomposition rate of litter,followed by the frozen season.Semi-decomposed litter had a higher decomposition rate than undecomposed litter.The decomposition rate of litter was the highest when the thinning intensity was 10%,while the litter and SOC were low.Forest litter had a good carbon sequestration impact in the unfrozen and freeze–thaw seasons,while the converse was confi rmed in the frozen and thaw seasons.The best carbon sequestration impact was identifi ed in litter,and soil layers under a 20–25%thinning intensity,and the infl uence of undecomposed litter on SOC was more noticeable than that of semi-decomposed litter.Both litter and soil can store carbon:however,carbon is transported from undecomposed litter to semi-decomposed litter and to the soil over time.In summary,the best thinning intensity being 20–25%.
文摘In recent years,the winter temperature in southern China decreases year by year,and the phenomenon of freeze-thaw damage is also wide-spread in hydraulic buildings.In this paper,the freezing-thawing cycle tests of fully graded concrete specimens and corresponding wet sieving suitable for climate conditions in southern China were carried out,and the effects of freezing-thaw cycles on the appearance,mass loss,relative dynamic elastic modulus,internal temperature and strain of fully graded concrete and wet sieving concrete were studied.The splitting tensile strength test of concrete specimens with specified salt freezing cycles was carried out,and the relationship between the strength reduction of fully graded concrete and wet sieving concrete specimens and the number of freeze-thaw cycles was analyzed.The results show that with the increase of freeze-thaw cycles,the properties of fully graded concrete and wet sieving concrete degraded,and the degradation of compressive strength was the most significant,followed by the splitting tensile strength.In the initial stage of the freeze-thaw cycles,the degradation of each property was not obvious,and the deterioration rate of each property increased significantly after 100 freeze-thaw cycles.Besides,the relationship between the splitting tensile strength of fully graded concrete and wet sieving concrete and the internal wave velocity after freeze-thaw cycles was established.The test results can provide theoretical basis for the design,repair,maintenance and life prediction of dams and offshore platforms in southern China.
文摘On the basis of previous research results, the frost resistance of fully graded concrete and small wet sieving concrete specimens was compared and analyzed, and the characteristics and rules of freeze-thaw damage of hydraulic fully graded concrete after freeze-thaw cycles were analyzed through freeze-thaw test, impact-echo test, mechanical test and so on. Meanwhile, the damage characteristics of concrete in the salt and water freezing environment were compared. Through the mechanical test, it is found that the mechanical properties of both fully graded concrete and wet sieving concrete decreased to varying degrees after freeze-thaw cycles. The laws of uniaxial compression and tensile strength of concrete varying with the number of freeze-thaw cycles were obtained. The life of concrete after freeze-thaw cycles was predicted, and it is concluded that the life of concrete in the salt freezing environment was only 0.8 times that in the water freezing environment, proving once again that the damage of concrete in the salt freezing environment was more serious than that in the water freezing environment. Therefore, the grade of frost resistance should be improved appropriately for concrete engineering with salt solution. Finally, based on the damage theory and Lemaitre strain equivalence principle, the freeze-thaw damage evolution equation suitable for fully graded concrete was obtained.
基金supported by grants from the National Key Research and Development Program of China(Grant No.2016YFD0600401)the Liaoning Provincial Key Research Project for Agriculture(Grant No.2015103002)
文摘We analyzed the relationships linking overwintering death and frost cracking to temperature and sunlight as well as the effects of low temperatures and freeze–thaw cycles on bud-burst rates,relative electrical conductivity,and phloem and cambial ultrastructures of poplar.Overwintering death rates of poplar were not correlated with negative accumulated temperature or winter minimum temperature.Freeze–thaw cycles caused more bud damage than constant exposure to low temperatures.Resistance to freeze–thaw cycles differed among clones,and the budburst rate decreased with increasing exposure to freeze–thaw cycles.Cold-resistant clones had the lowest relative electrical conductivity.Chloroplasts exhibited the fastest and the most obvious reaction to freeze–thaw damage,whereas a single freeze–thaw cycle caused little damage to cambium ultrastructure.Several such cycles resulted in damage to plasma membranes,severe damage to organelles,dehydration of cells and cell death.We conclude that overwintering death of poplar is mainly attributed to the accumulation of effective freeze–thaw damage beyond the limits of freeze–thaw resistance.
基金Natural Science Foundation of China(No.U1704114)Key Scientific Research Program of Henan Province(No.182102110346,161100110900).
文摘Ovalbumin(OVA),the main protein in egg white,affects most of the functional properties of egg white protein in food processing.The aim of this study was to investigate the effects of spray drying(SD)and microwave freeze drying(MFD)on the preparation of hydrolyzed/glycosylated ovalbumin(HGOVA)and provide useful information on the applications of egg protein powders in the food industry.Results demonstrated that the structure of HGOVA was considerably changed,and its functional properties were improved compared with those of native OVA.SD and MFD processing did not lead to dissociation of HGOVA subunits.SD-HGOVA exhibited higher protein solubility,emulsifying activity,foaming capacities,and gel hardness than MFD-HGOVA.However,MFD-HGOVA was better than the SD-HGOVA in terms of color,emulsion stability,foam stability,water/oil absorption capacity,and thermal stability.Selection of an appropriate drying method could enhance the potential applications of HGOVA in the food industry.
基金Project supported by the National Natural Science Foundation of China(Nos.41575096 and91125016)the Strategic Priority Research Program of the Chinese Academy of Sciences(No.XDA05110102)
文摘Freeze-thaw processes significantly modulate hydraulic and thermal characteristics of soil. The changes in the frost and thaw fronts(FTFs) affect the water and energy cycles between the land surface and the atmosphere. Thus, the frozen soil comprising permafrost and seasonally frozen soil has important effects on the land surface hydrology in cold regions. In this study, a two-directional freeze and thaw algorithm is incorporated into a thermal diffusion equation for simulating FTFs. A local adaptive variable-grid method is used to discretize the model. Sensitivity tests demonstrate that the method is stable and FTFs can be tracked continuously. The FTFs and soil temperature at the Qinghai-Tibet Plateau D66 site are simulated hourly from September 1, 1997 to September 22, 1998. The results show that the incorporated model performs much better in the soil temperature simulation than the original thermal diffusion equation,showing potential applications of the method in land-surface process modeling.
基金This work was financially supported by the National Science Found for Distinguished Young Scholars(No.51525503).
文摘Digital patternless freeze-casting technology is a new approach for obtaining frozen sand moulds using digital milling technology. The change law of tensile strength and air permeability of frozen sand moulds (100-mesh and 200-mesh silica sand, and zircon sand moulds) under different freezing temperatures and water contents was studied. Results show that with the decrease of freezing temperature and the increase of water contents, the tensile strength and air permeability of the sand moulds are gradually improved. Meanwhile, computed tomography technology was used to characterize the shape and size of the water film between the sand particles mixed with 4wt.% water. The results show that in silica sand moulds, the form of water film is lumpy, and 200-mesh silica sand moulds have more water films and higher proportion of small-sized water films than 100-mesh silica sand moulds, while in zircon sand moulds, the form of water film is membranous. At the same freezing temperature and water content, the tensile strength of zircon sand mould is the highest, and 100-mesh silica sand mould is the lowest. A comparative solidification experiment of A356 aluminum alloy was carried out in frozen sand mould and resin sand mould. The results show that the primary α-Al phase appears in the form of equiaxed and eutectic silicon phase is needle-like in freezing sand mould casting, but the primary α-Al phase grows in the form of dendrites, and the eutectic silicon phase is coarse needle-like in the resin sand mould casting. The difference of microstructure is caused by the different cooling rate. The cooling rate of A356 aluminum alloy in frozen sand mould is higher than that in resin sand mould.
基金Supported by Fundo de Incentivo à Pesquisa e Eventos do Hospital de Clínicas de Porto Alegre and Conselho Nacional de Desenvolvimento Científico e Tecnológico(CNPq)
文摘AIM:To investigate the interaction between mesenchymal stem cells(MSCs) and bone grafts using two different cultivation methods:static and dynamic.METHODS:MSCs were isolated from rat bone marrow.MSC culture was analyzed according to the morphology,cell differentiation potential,and surface molecular markers.Before cell culture,freeze-dried bone(FDB) was maintained in culture for 3 d in order to verify culture medium pH.MSCs were co-cultured with FDB using two different cultivation methods:static co-culture(two-dimensional) and dynamic co-culture(threedimensional).After 24 h of cultivation by dynamic or static methods,histological analysis of Cell adhesion on FDB was performed.Cell viability was assessed by the Trypan Blue exclusion method on days 0,3 and 6 after dynamic or static culture.Adherent cells were detached from FDB surface,stained with Trypan Blue,and quantified to determine whether the cells remained on the graft surface in prolonged non-dynamic culture.Statistical analyses were performed with SPSS and a P 【 0.05 was considered significant.RESULTS:The results showed a clear potential for adipogenic and osteogenic differentiation of MSC cultures.Rat MSCs were positive for CD44,CD90 and CD29 and negative for CD34,CD45 and CD11bc.FDBs were maintained in culture for 3 d and the results showed there was no significant variation in the culture medium pH with FDB compared to pure medium pH(P 】 0.05).In histological analysis,there was a significant difference in the amount of adhered cells on FDB between the two cultivation methods(P 【 0.05).The MSCs in the dynamic co-culture method demonstrated greater adhesion on the bone surface than in static co-culture method.On day 0,the cell viability in the dynamic system was significantly higher than in the static system(P 【 0.05).There was a statistical difference in cell viability between days 0,3 and 6 after dynamic culture(P 【 0.05).In static culture,cell viability on day 6 was significantly lower than on day 3 and 0(P 【 0.05).CONCLUSION:An alternative cultivation method was developed to improve the MSCs adhesion on FDB,demonstrating that dynamic co-culture provides a superior environment over static conditions.
基金supported by the National Key R&D Program of China (Grant No. 2018YFC1505001)the Key Scientific Research Project of China Gold Group (Grant No. 2016ZGHJ/XZHTL-YQSC-26)+1 种基金the funding from the Department of Transportation of Gansu Province (Grant No. 2017-008)the Fundamental Research Funds for the Central Universities, CHD (Grant No. 300102268716)
文摘Freeze-thaw cycles are closely related to the slope instability in high-altitude mountain regions. In this study, cohesive coarse-grained soils were collected from a high-altitude slope in the Qinghai–Tibet Plateau to study the effect of cyclic freeze-thaw on their uniaxial mechanical properties. The soil specimens were remolded with three dry densities and three moisture contents. Then, after performing a series of freeze-thaw tests in a closed system without water supply, the soil specimens were subjected to a uniaxial compression test. The results showed that the stress-strain curves of the tested soils mainly performed as strain-softening. The softening feature intensified with the increasing dry density but weakened with an increase in freeze-thaw cycles and moisture content. The uniaxial compressive strength, resilient modulus, residual strength and softening modulus decreased considerably with the increase of freeze-thaw cycles. After more than nine freeze-thaw cycles, these four parameters tended to be stable. These parameters increased with the increase of dry density and decreased with the increasing moisture content, except for the residual strength which did not exhibit any clear variation with an increase in moisture content. The residual strength, however, generally increased with an increase in dry density. The soil structural damage caused by frozen water expansion during the freeze-thaw is the major cause for the changes in mechanical behaviors of cohesive coarse-grained soils. With results in this study, the deterioration effect of freeze-thaw cycles on the mechanical properties of soils should be considered during the slope stability analysis in high-altitude mountain regions.
基金supported by "the Fundamental Research Funds for the Central Universities" (Grant No. 2015B25014)"the Practical Innovation Program for Postgraduate Students of Jiangsu Province, China" (Grant No. SJZZ15_0058)+1 种基金funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD) (Grant No. 3014–SYS1401)the organizing committee of "XI International Symposium on Permafrost Engineering (Magadan, Russia, Sept. 5-8, 2017)" for giving the opportunity to exchange this study
文摘Expansive soils located in cold regions can easily endure the action of frost heaving and cyclic freezing–thawing. Cracking can also occur in expansive clayey soils under freeze–thaw cycles, of which little attention has been paid on this issue.In this study, laboratory experiment and cracking analysis were performed on an expansive soil. Crack patterns were quantitatively analyzed using the fractal concept. The relationships among crack pattern, water loss, number of freeze–thaw cycles, and fractal dimension were discussed. It was found that crack patterns on the surface exhibit a hierarchical network structure that is fractal at a statistical level. Cracks induced by freeze–thaw cycles are shorter, more irregularly oriented,and slowly evolves from an irregularly rectilinear pattern towards a polygonal or quasi–hexagonal one; water loss, closely related to specimen thickness, plays a significant role in the process of soil cracking; crack development under freeze-thaw cycles are not only attributed to capillary effect, but also to expansion and absorption effects.
基金supported by the National Natural Science Foundation of China(No.91326201)the Strategic Pilot Technology Chinese Academy of Sciences(No.XDA0201002)
文摘To improve the reliability and reduce energy consumption,a conceptual design of a freeze valve is proposed for the thorium-based molten salt reactor(TMSR)concept.Fins were utilized in this new design to enhance heat transfer and realize passive shut-off function,which could not be realized by the previous design.An experimental apparatus using the fluoride salt FLiNaK was constructed to conduct a series of preliminary solidification and melting experiments.In addition,the enthalpy-porosity method of ANSYS■Fluent solver was applied to simulate the solidification process of the salt at a specified operating temperature.Temperature distributions of the fluoride salt,solidification/melting time,and frozen plug effect were analyzed under natural convection heat transfer in an open space.The calculated salt temperatures exhibited good agreement with the experimental values.The results indicated that the range of effective operating temperature is 530-600℃ for the finned freeze valve.In this study,the ideal set operating temperature of the finned freeze valve was chosen as 560℃ to achieve competent performance.Moreover,560℃ is additionally the highest set operating temperature for maintaining excellent cooling performance and sustaining deep-frozen condition of the salt plug.At this set operating temperature,the simulation data indicated that the molten salt in the flat part of the finned freeze valve will completely solidify at 10.5 min.The percentage of solid salt in the flat and lower transitional parts of the valve reaches 29.60% in 30.0 min.Furthermore,the surface temperature of the proposed freeze valve is 11.10% lower compared with that of the TMSR freeze valve at a cooling gas supply of 173 m^3/h.Therefore,the new freeze valve was proven to be capable of reducing the energy consumption and realizing the passive shut-off function.
基金supported by the Key Research and Development Project of Shandong Province (No.2015 GSF115005)the Huimin Special Fund of Qingdao Municipal Achievement Transformation Plan (No.15-9-2-120NSH)the National Natural Science Foundation of China (No.31101380)
文摘Water-washing removes fluoride from Antarctic krill but produces large volumes of wash water containing water-soluble proteins and fluoride. The freeze concentration method was tested to determine if it could be used to recover water-soluble proteins while leaving the fluoride in solution. After freezing and thawing the wash water, protein and fluoride contents of the thawed fractions were determined to explore the melting regularity of components in the wash water. The highest concentration factors of protein and fluoride were obtained after 80 min of thawing, such as 1.48 ± 0.06 and 1.35 ± 0.04 times, respectively. The free amino-nitrogen(FAN) content and sodium dodecyl sulfate-polyacrylamide gel electrophoresis pattern results revealed that the highest concentrations of all ingredients were obtained after 80 min of the process. The degree of hydrolysis of all fractions from the thawing process fluctuated in a narrow range around 12% during the entire process, indicating that the thawing order did not change with various proteins or time during the entire thawing course. These results demonstrate that the freeze concentration method can be used to concentrate protein solutions, even those with fluoride. It was concluded that condensation was achieved and no ingredient could be separated, regardless of fluoride, amino acids, or different proteins in the water.
文摘Lactic acid bacteria possess several interesting properties of great economic importance. Improvement and stabilization of these industrially important features are an active research area at the present time. The objectives of this work are to study the effect of freezing and freeze-drying on the survival rate, autolytic activity and intracellular enzymatic activity of the main species of lactic acid bacteria used in the dairy industry. The article focused on several characteristics that were not well covered in the past. The obtained results revealed that both preservation methods have a significant effect on viability, autolytic activity and intracellular enzymatic activity. After six months of storage we found that frozen cultures exhibited higher survival rate, higher rate of intracellular enzymatic activity and lower rate of autolysis. The impact of conservation treatments was only strain specific in the case of survival rate. The results obtained lead to the selection of the best preservation method for the selected cultures based on survival rate, autolytic activity and intracellular enzymatic activity.
基金supported by projects from the National Natural Science Foundation of China (41807298, 41702372, 41672211)the China Postdoctoral Science Foundation (2019M650788)+2 种基金National Key Research and Development Project of China (2016YFC0600310)the China Geological Survey (DD20160022, DD20190059)the Basic Research Funds (JYYWF201810) of the Institute of Geology, CAGS.
文摘With the objective of establishing a distinction between deformation structures caused by freeze/thaw cycles and those resulting from seismic activity, we studied three well–exposed alluvial deposits in a section at Dogai Coring, northern Qiangtang Basin, Tibetan Plateau. Deformation is present in the form of plastic structures(diapirs, folds and clastic dykes), brittle structures(micro–faults) and cryogenic wedges. These soft–sediment deformation features(except the micro–faults) are mainly characterized by meter–scale, non–interlayered, low–speed and low–pressure displacements within soft sediments, most commonly in the form of plastic deformation. Taking into account the geographic setting, lithology and deformation features, we interpret these soft–sediment deformation features as the products of freeze/thaw cycles, rather than of earthquake–induced shock waves, thus reflecting regional temperature changes and fluctuations of hydrothermal conditions in the uppermost sediments. The micro–faults(close to linear hot springs) are ascribed to regional fault activity;however, we were unable to identify the nature of the micro–faults, perhaps due to disturbance by subsequent freeze/thaw cycles. This study may serve as a guide to recognizing the differences between deformation structures attributed to freeze/thaw cycles and seismic processes.
基金funded by the Health and Medical Research Fund, Hong Kong (15140962)Research Grant Council, Hong Kong (17110414)
文摘The therapeutic potential of small nucleic acids such as small interfering RNA(siRNA) to treat lung diseases has been successfully demonstrated in many in vivo studies. A major barrier to their clinical application is the lack of a safe and efficient inhaled formulation.In this study, spray freeze drying was employed to prepare dry powder of small nucleic acids.Mannitol and herring sperm DNA were used as bulking agent and model of small nucleic acid therapeutics, respectively. Formulations containing different solute concentration and DNA concentration were produced. The scanning electron microscope(SEM) images showed that the porosity of the particles increased as the solute concentration decreased. Powders prepared with solute concentration of 5% w/v were found to maintain a balance between porosity and robustness. Increasing concentration of DNA improved the aerosol performance of the formulation. The dry powder formulation containing 2% w/w DNA had a median diameter of 12.5 μm, and the aerosol performance study using next generation impactor(NGI) showed an emitted fraction(EF) and fine particle fraction(FPF) of 91% and 28% respectively. This formulation(5% w/v solute concentration and 2% w/w nucleic acid) was adopted subsequently to produce siRNA powder. The gel retardation and liquid chromatography assays showed that the siRNA remained intact after spray freeze drying even in the absence of delivery vector. The siRNA powder formulation exhibited a high EF of 92.4%and a modest FPF of around 20%. Further exploration of this technology to optimise inhaled siRNA powder formulation is warranted.
基金Funded by the National Key Research and Development Plan(No.2017YFB0307504)。
文摘A research and test system for the carbon anode plate preparation technology was established to optimize the physical and chemical indicators of carbon anode plates,such as bulk density,resistivity,and compressive strength,and improve the operating cycle.In this study,a carbon plate was prepared via a combination of high-temperature molding and freeze drying using a formulation with asphalt content much lower than the industry standard.The experimental results show that the density of the carbon plate is increased by 0.02-0.04 g/cm^(3) by improving the drying method.The carbon plate prepared in the laboratory has a bulk density of 1.814 g/cm^(3),resistivity of 29.8μΩ·m,and compressive strength of 89.27 MPa.The bulk density,room-temperature resistivity,compressive strength,graphitization,and other key indices of the carbon plates made in the laboratory and those procured from a factory in Shanxi,Datong,were tested.Additionally,the specimens were analyzed using thermogravimetry-differential scanning calorimetry,scanning electron microscopy,and X-ray fluorescence.The laboratory-made carbon plates were superior to the factory specimens in terms of all the indicators tested.The process in this study improves the performance of the carbon anode plate and is used to provide technical support for electrolytic fluorine production in enterprises.The carbon plates prepared in the laboratory fully meet the process requirements of a medium-temperature electrolytic fluorine production line,which indicates the possibility of its use in the stable production of fluorine gas.
