Thawing Temperature Research Articles

Does ergothioneine and thawing temperatures improve rooster semen post-thawed quality?

The present study focuses on the effect of different levels of ergothioneine and thawing temperature on rooster semen cryopreservation. Semen was diluted in Lake extender containing ergothioneine at 5, 10, 15, and 20 µM and cryopreserved. Two thawing temperatures (37°C for 30 s and 60°C for 5 s) were consequently examined. Sperm motility parameter, membrane integrity, abnormal morphology, viability, apoptotic status, mitochondria activity, and lipid peroxidation were determined after freeze-thaw process. Ergothioneine levels of 5 and 10 µM led to higher (P < 0.05) total motility (66.58 ± 1.44 and 72.11±1.44, respectively) and average path velocity (VAP) (34.54 ± 0.89, 37.28 ± 0.89, respectively). Higher (P < 0.05) significant membrane integrity and mitochondria activity after freeze-thawing were observed in the groups supplemented with 10 µM ergothioneine (68.62 ± 1.24 and 69.12 ± 1.26, respectively). Also, 5 and 10 µM of ergothioneine led to the lowest significant percentage of apoptotic and dead sperm. The total motility and progressive motility resulted in significantly (P < 0.05) higher amount when sperm were thawed with 60°C (60.58 ± 0.91 and 24.76 ± 0.53, respectively) compared to thawed sperm in 37°C. The membrane integrity, viability and mitochondria activity led to significantly (P < 0.05) higher when sperm were thawed with 60°C (58.2 ± 0.78, 63.21 ± 0.80 and 56.85 ± 0.79, respectively). It could be concluded the addition of 5 and 10 µM ergothioneine in the semen extender and thawing temperature at 60˚C in 5 s can be an efficient strategy to preserve rooster cryopreserved semen quality.

Cryopreservation of Germ Cells of Banana Shrimp (Fenneropenaeus merguiensis) and Black Tiger Shrimp (Penaeus monodon).

Germ cell cryopreservation has been used to preserve many fish species. However, this method has not been established for crustaceans; thus, we attempted to do this herein. The efficiency of slow freezing was compared to vitrification methods for germ cell cryopreservation in two types of marine shrimp, Fenneropenaeus merguiensis and Penaeus monodon. In situ hybridization with a vasa probe was used to identify germ cells. The effects of three cryoprotectants, dimethyl sulfoxide (DMSO), glycerol (GLY), and magnesium chloride (MgCl2), on germ cell viability and recovery rate were compared at three concentrations (5%, 10%, and 15%). The effects of thawing temperature, including 10 and 27°C, were also investigated. We discovered that 10% DMSO with the vitrification is suitable for preserving the germ cells of F. merguiensis for a long time, whereas 10% GLY with vitrification is suitable for P. monodon. Moreover, the most suitable thawing temperature was 10°C for both species. This is the first report of germ cell cryopreservation in crustaceans. Thus, we provide evidence that crustacean germ cells can be preserved long-term in liquid nitrogen; this is the first step in the sustainable preservation of crustaceans, especially shrimp.

Soil Moisture but Not Warming Dominates Nitrous Oxide Emissions During Freeze–Thaw Cycles in a Qinghai–Tibetan Plateau Alpine Meadow With Discontinuous Permafrost

Large quantities of organic matter are stored in frozen soils (permafrost) within the Qinghai–Tibetan Plateau (QTP). The most of QTP regions in particular have experienced significant warming and wetting over the past 50 years, and this warming trend is projected to intensify in the future. Such climate change will likely alter the soil freeze–thaw pattern in permafrost active layer and toward significant greenhouse gas nitrous oxide (N2O) release. However, the interaction effect of warming and altered soil moisture on N2O emission during freezing and thawing is unclear. Here, we used simulation experiments to test how changes in N2O flux relate to different thawing temperatures (T5–5°C, T10–10°C, and T20–20°C) and soil volumetric water contents (VWCs, W15–15%, W30–30%, and W45–45%) under 165 F–T cycles in topsoil (0–20 cm) of an alpine meadow with discontinuous permafrost in the QTP. First, in contrast to the prevailing view, soil moisture but not thawing temperature dominated the large N2O pulses during F–T events. The maximum emissions, 1,123.16–5,849.54 μg m–2 h–1, appeared in the range of soil VWC from 17% to 38%. However, the mean N2O fluxes had no significant difference between different thawing temperatures when soil was dry or waterlogged. Second, in medium soil moisture, low thawing temperature is more able to promote soil N2O emission than high temperature. For example, the peak value (5,849.54 μg m–2 h–1) and cumulative emissions (366.6 mg m–2) of W30T5 treatment were five times and two to four times higher than W30T10 and W30T20, respectively. Third, during long-term freeze–thaw cycles, the patterns of cumulative N2O emissions were related to soil moisture. treatments; on the contrary, the cumulative emissions of W45 treatments slowly increased until more than 80 cycles. Finally, long-term freeze–thaw cycles could improve nitrogen availability, prolong N2O release time, and increase N2O cumulative emission in permafrost active layer. Particularly, the high emission was concentrated in the first 27 and 48 cycles in W15 and W30, respectively. Overall, our study highlighted that large emissions of N2O in F–T events tend to occur in medium moisture soil at lower thawing temperature; the increased number of F–T cycles may enhance N2O emission and nitrogen mineralization in permafrost active layer.

Effect of freeze-thaw treatment on the quality and flavor of Nang

Freezing processing has been used widely to improve the sensory quality and solve the problems induced by fungi. In this study, the effects of frozen temperature (−20, −30, −40, −50, −60°C), frozen time (30, 40, 50, 60, 70 min), thawing temperature (25, 30, 35, 40, 45°C) and thawing time (10, 15, 20, 25, 30 min) on sensory quality, texture characteristics and flavor of Nang were studied. The results showed that the order of the factors affecting the sensory quality of Nang was frozen temperature > thawing time > frozen time > thawing temperature. The optimum processing conditions were to freeze at −50°C for 50 min and thaw at 40°C for 20 min. The correlation analysis between sensory quality and texture profile analysis (TPA) showed that the highest or the lowest TPA values of the core and edge of Nang did not correspond to the best sensory quality. Frozen treatment affected the characteristic flavor of Nang obviously. There were 15 of flavor substances with a significant increase or decrease among the 41 characteristic ones identified. This study is of great significance for the production and promotion of traditional staple food in Xinjiang.

Experimental thawing events enhance petroleum hydrocarbons attenuation and enzymatic activities in polluted temperate soils

Polluted soils in temperate regions are frequently exposed to seasonal freezing and thawing events during which the soil biological properties are expected to change in response to the associated temperature variations. In this study, we investigated the influence of freeze–thaw events on enzymatic activities and natural attenuation of petroleum hydrocarbons in temperate soils with varying pollution profiles. Four soils [clean natural, Diesel amended (DAS), Crude-oil amended (COAS), and aged oil polluted] were subjected to ten freeze–thaw temperature regimes ranging from − 20 to + 20 °C for 45 days. The soil enzymatic activities and fractional petroleum hydrocarbon analysis were conducted using spectrophotometry and gas chromatography–mass spectrometry, respectively. After the incubation period, freezing resulted in decreased enzyme (lipase and dehydrogenase) activities in both clean and polluted soils, while thawing events compensated for the enzymatic losses that occurred during the preceding freezing phase. Fractional hydrocarbon analysis revealed that there was a switch from active removal of light- to medium-chain hydrocarbons (C10–C23) in the short-term polluted soils (DAS and COAS) during the freezing phase to rapid degradation of the heavier nonvolatile hydrocarbon fractions (C23–C34) during the thawing phase, and the long-term polluted soil had lower hydrocarbon removal rates than the short-term polluted soils. The relationship between the natural attenuation of hydrocarbons in the oil polluted soils and incubation temperatures was linear in the short- and long-term petroleum polluted soils.

Research on Microstructure of Soft Clay under Various Artificial Ground Freezing Conditions Based on NMR

Nuclear magnetic resonance (NMR) can help to collect soft clay pore size data. This paper uses NMR to study the effect of freezing duration, the gap time between two freezing actions and thawing temperature on the pore size distribution (PSD) in soft clay. It was found that most of the freezing and thawing progress was completed during the first two hours. A longer time gap between the first and second freezing cycles leads to greater structural damage. An appropriate thawing temperature results in less subsidence induced by the artificial ground freezing (AGF). A new method to distinguish water types for various freezing conditions is proposed. This freezing method to determine the cutoff value could fill the defect in the previous methods.

Effect of diluent variation on cryopreservation of large yellow croaker Larimichthys crocea

The aim of this research was to investigate different factors, including cryoprotective agents (CPAs), diluents, dilution ratios, equilibrium times, freezing rates, and thawing methods to optimize cryopreservation protocols for large yellow croaker (Larimichthys crocea). The parameters evaluated were sperm motility, sperm activity index (SAI), survival rate, and DNA damage. Different types of CPAs, such as dimethyl sulfoxide (DMSO), propylene glycol (PG), ethylene glycol (EG), methanol, and glycerol, were tested for sperm preservation. The highest motility, SAI, and survival rate were observed when EG was used. Different diluents such as Stein’s solution, Hank’s balanced salt solution, marine fish Ringer’s solution, artificial seminal plasma (ASP) of small yellow croaker, and Cortland solution were investigated. The highest post-thaw motility was observed upon using ASP as the diluent. Different concentrations of EG were then mixed with ASP to identify the optimal EG concentration. Experimental results showed that the motility (70.33 ± 1.20%), SAI (5), and survival rate (78.30 ± 0.42%) of post-thaw sperm were optimum when 10% EG and ASP were used as the CPA and diluent of cryopreservation, respectively. Post-thaw sperm motility was high at equilibration times below 150 s and at an optimum dilution ratio of 1:1 (sperm: CPA + diluent) and was not significantly different compared with fresh sperm motility. The freezing rate was found to be slow below −10°C/min. The thawing temperature of 45°C was identified as ideal. The percentage of tail DNA in post-thaw sperm at 10% EG and ASP was also investigated and was found to have more significant DNA damage than that in fresh sperm but significantly lower damage than that in post-thaw sperm at EG concentrations of 5%, 15%, and 20% (p &lt; 0.05). The cryopreservation protocols obtained in this study will be useful in large yellow croaker hatcheries.

Two-stage air thawing as an effective method for controlling thawing temperature and improving the freshness of frozen pork loin

Reduction in the total thawing time for pork loin subjected to two-stage air thawing was investigated. The pork loins were frozen at −60 and −18 °C and stored for up to 6 months at the freezing temperature. Samples were thawed using constant-temperature air thawing (−1.5, 2, and 25 °C) and two-stage air thawing methods. In the two-stage air thawing method, the samples were thawed at 25 °C in the initial stage. When the core temperature of the sample reached −5 °C, the samples were transferred to −1.5 °C (25/-1.5 method) or 2 °C (25/2 method). The physicochemical properties of the thawed pork loins, including thawing loss, cooking loss, water holding capacity (WHC), volatile basic nitrogen (VBN), and thiobarbituric acid reactive substances (TBARS) were analyzed. Thawing at 25 °C was the most rapid thawing method, and the total thawing time were reduced effectively using two-stage air thawing. Generally, samples thawed by two-stage air thawing (25/-1.5, and 25/2 methods) exhibit better moisture related properties. The effects of the thawing methods on VBN content were minimal; only trace levels of TBARS were detected in the samples. Therefore, two-stage air thawing is expected to reduce the total thawing time and prevent meat quality deterioration caused by the freezing and thawing processes.

Study on temporal and spatial variation of temperature field in horizontal freezing and thawing settlement

Artificial freezing method is commonly used in underground engineering excavation, such as mine, foundation pit and subway. The problem of post-construction thaw settlement has attracted more and more attention, but it is difficult to calculate the development law of thaw temperature field of complex frozen curtain by analytical method. Therefore, this paper adopts numerical method to study this problem. In this paper, taking the horizontal freezing construction of a subway connecting passage as an example, the development law of temperature field in the melting process is analyzed, and the results are basically consistent with the measured data. As a general means, numerical simulation is feasible to simulate the development law of temperature field in horizontal melting of complex curtain. The results of this paper can be used to guide the design and construction of artificial freezing.

Evaluate the activity of cryopreserved boar ejaculated spermatozoa under different thawing protocols

Aim. To evaluate the activity of cryopreserved boar ejaculated spermatozoa under different thawing protocols to optimize biotechnological approaches in pig reproduction based on the genetic material of the Institute of Animal Breeding and Genetics nd. a. M.V. Zubets of National Academy of Agrarian Science of Ukraine. Methods. Cryopreserved ejaculated boars' sperm was thawed in three different ways. Biotechnological, cryobiological and morphological methods were used to assess the viability of the sperm. Results. We noted the individual feature of semen quality of the studied boars, which affects its suitability for cryopreservation and quality indicators after thawing. It was found that in liquefied boar sperm (sperm activity on average is 86.7%) after its centrifugation and three-hour equilibration at + 4 °C sperm activity decreased by an average of 25.0%. In order to improve the quality of cryopreserved sperm, it was thawed under different conditions. The highest activity of spermatozoa in thawed sperm of boar No. 225 of Myrhorod pig was at the level of 25.0% at the thawing temperature + 70 °C, and the thermal resistance and heat resistance were 70.0% and 60.0%, respectively. Conclusions. During this study was noted that there are peculiarities of boar semen at breed and individual level, which influence its ability to tolerate cryopreservation. Keywords: sperm, in vitro cultivation, cryobank, cryopreservation, boars.

Effect of Freeze–Thaw Temperature and Number of Cycles on the Physical and Mechanical Properties of Marble

In recent years, more and more extreme ice and snow disasters occurred all over the world. In order to investigate the physical and mechanical properties and the damage law of high-slope rock mass located in the area which is at high risk of extreme ice and snow climates, marble samples were collected in the Daye iron mine, and the freeze–thaw cycle tests at different freezing temperatures and freeze–thaw cycles were carried out with these samples. After 0, 10, 15, 20, 25, and 30 freeze–thaw cycles, the mass, wave velocity and SEM image of the samples were obtained, and the uniaxial compression test were also carried out. The effects of freeze–thaw cycles and the freezing temperature on the physical and mechanical properties of samples were analyzed. Meanwhile, the multivariate analysis of variance was chosen to investigate the significant influence of freeze–thaw cycles and the freezing temperature on the various physical and mechanical parameters. With the increase of freeze–thaw cycles, the mass loss, the loss rate of wave velocity and the strength loss rate and freeze–thaw damage of marble specimens increase, but the elastic modulus and the freeze–thaw coefficient decrease. The effect of freeze–thaw cycles on the physical properties of marble is more significant than that of the freezing temperature; the significant effects of freeze–thaw cycles on the strength loss rate and freeze–thaw coefficient of marble are close to that of the freezing temperature. For the elastic modulus, the number of freeze–thaw cycles has a significant effect on it, but the freezing temperature has no significant effect on it. The cyclic freezing and thawing have a positive impact on the mesoscopic and microscopic damage and failure of the marble.

Assessment of morphological features of bull semen thawed at various temperatures and periods of time with CASA

Thawing condition is one the most important factors affecting the re-animation of the spermatozoon in order to fertilise the oocyte. For that matter, we aimed to evaluate the morphological features of the head and midpiece of cryopreserved spermatozoa thawed at different temperatures and for various durations, with using CASA (Computer aided sperm analyser). Frozen semen samples belonging to the same batch, collected from three different bulls were grouped as; control group thawed for 20 seconds at 37 ℃; and experimental groups were thawed for 30, 40, 50 and 60 s at 25 ℃ and 37 ℃; for 10, 15, 20 and 25 s at 40 ℃; for 3, 6, 9, 12 s at 70 ℃. Morphometrical features of the samples were evaluated by using CASA system with nine repetitions. As a result, straws thawed at 25℃ for 40 s had the highest average length of head (6.22 ± 0.09 μm), and the width of mid-piece (0.68 ± 0.01 μm). It was concluded that the thawing temperature and duration has affected/altered the morphometry of the sperm head and midpiece, although the results were not statistically significant (p> 0.005).

Bioinspired Multifunctional Cellular Plastics with a Negative Poisson's Ratio for High Energy Dissipation.

Cellular plastics have been widely used in transportation, aerospace, and personal safety applications owing to their excellent mechanical, thermal, and acoustic properties. It is highly desirable to impart them with a complex porous structure and composition distribution to obtain specific functionality for various engineering applications, which is challenging with conventional foaming technologies. Herein, it is demonstrated that this can be achieved through the controlled freezing process of a monomer/water emulsion, followed by cryopolymerization and room temperature thawing. As ice is used as a template, this method is environmentally friendly and capable of producing cellular plastics with various microstructures by harnessing the numerous morphologies of ice crystals. In particular, a cellular plastic with a radially aligned structure shows a negative Poisson's ratio under compression. The rigid plastic shows a much higher energy dissipation capability compared to other materials with similar negative Poisson's ratios. Additionally, the simplicity and scalability of this approach provides new possibilities for fabricating high-performance cellular plastics with well-defined porous structures and composition distributions.

Cryopreservation of Ghagus chicken semen: Effect of cryoprotectants, diluents and thawing temperature.

The present study evaluated the effects of cryoprotectants, semen diluents and thawing temperature during Ghagus chicken semen cryopreservation. Four different experiments were conducted; Experiment 1-semen was cryopreserved using 6% dimethylacetamide (DMA) and 2% dimethylsulphoxide (DMSO) in Sasaki diluent (SD) and Lake and Ravie diluent (LR), Experiment 2 and 3-semen was cryopreserved using 8% ethylene glycol (EG) in SD, LRD and Red Fowl Extender (RFE), Experiment 4-semen was cryopreserved using 6% dimethylformamide (DMF) in SD, LR and Beltsville poultry semen extender (BPSE). Semen was cryopreserved in 0.5ml French straws. Thawing was done at 5°C for 100s in ice water in Experiments 1, 2 and 4, whereas in Experiment 3 thawing was done at 37°C for 30s. The post-thaw sperm motility, viable sperm and acrosome-intact sperm were significantly (p<.05) lower in cryopreserved samples in all the experiments. No fertile eggs were obtained from cryopreserved samples in Experiments 1 and 2, except for 8% EG RFE treatment where the fertility was 0.83%. In Experiments 3 and 4, highest fertility was obtained in LR treatment 48.12 and 30.89%, respectively. In conclusion, using cryoprotectant EG (8%) and thawing at 37°C for 30s, and DMF(6%) resulted in acceptable level of fertility in Ghagus chicken. Though the diluents influenced post-thaw in vitro semen parameters, the fertility was not affected. In addition, results indicated that thawing temperature may be a critical stage in the cryopreservation protocol.

Effects of different thawing methods on flavor compounds and sensory characteristics of raspberry

AbstractIn order to identify more suitable thawing method to preserve aroma, taste, and other sensory quality of raspberry, five thawing methods were used to treat frozen raspberry, namely water bath thawing, microwave thawing, ultrasonic thawing, room temperature thawing, and refrigeration thawing. Gas chromatography‐mass spectrometry was employed to study the quantitative and qualitative analysis of the volatile compounds, and the characteristic flavor components of raspberry were compared by relative odor activity value (ROAV). Electronic tongue technique and fuzzy comprehensive evaluation were used to ensure the changes in sensory qualities of raspberry. The results showed that the time of microwave thawing was 0.57 minutes, and drip loss was 4.40%. Both of them were the lowest among the five thawing methods. The volatile components of raspberry included aldehydes, esters, ketones, alcohols, fatty acids, terpenes, and other compounds. Among them, there were 19 kinds of volatile components in quick‐frozen raspberries, 18 volatile components in raspberries after treated by microwave thawing and refrigeration thawing, 16 volatile components after room temperature thawing, 12 volatile components after ultrasonic thawing, and 10 volatile components after water bath thawing. The characteristic flavor compounds of raspberry were identified as acetaldehyde, alpha‐ionone, beta‐ionone, raspberry ketone, alpha‐terpene, and alpha‐pinene. Microwave thawing was the most suitable way to preserve the characteristic flavor components of raspberry, but water bath thawing could destroy the most of compounds. After microwave thawing, raspberry tasted best and was most acceptable to consumers. Therefore, microwave thawing was the most appropriate method to preserve raspberry flavor and sensory quality among the five thawing methods.

Sperm collection and cryopreservation for threatened newt species

The aims of this project were to transfer hormone-induced spermiation and sperm cryopreservation protocols developed in the model salamander species, Ambystoma tigrinum, to three threatened newt species. Additionally, we tested if supplementation with trehalose or thawing at different temperatures impacts post-thaw sperm parameters. Hormone stimulation protocols were applied to male Notophthalmus meridionalis (N = 10), Neurergus kaiseri (N = 5) and Tylototriton kweichowensis (N = 6) with sperm collected periodically up to 24–28 h post-spermiation dose. Samples of adequate sperm concentration (>70%) were cryopreserved in solutions of 10% Me2SO + 1% BSA with or without a 10% trehalose cryodiluent. Frozen sperm samples were thawed at either 20 °C or 40 °C and examined for post-thaw motility parameters and abnormalities in head and tail structure. The spermiation response to exogenous hormone treatment was significantly different between newt species, with a success rate of 0% for N. kaiseri, 67% for T. kweichowensis, and 100% for N. meridionalis. Sperm concentration varied with time of collection after hormone administration in both T. kweichowensis and N. meridionalis. For N. meridionalis, structural abnormalities decreased in samples collected over the 24 h period (p < 0.0001) and a thaw temperature of 40 °C resulted in higher relative total sperm motility (p < 0.0001). This is the first study to describe the cryopreservation of sperm from two newt species and demonstrates the transferability of ART developed in a salamander to two newt species.

Climate Change Impacts on Cold Season Runoff in the Headwaters of the Yellow River Considering Frozen Ground Degradation

Climate change has effects on hydrological change in multiple aspects, particularly in the headwaters of the Yellow River (HWYR), which is widely covered by climate-sensitive frozen ground. In this study, the annual runoff was partitioned into four runoff compositions: winter baseflow, snowmelt runoff, rainy season runoff, and recession flow. In addition, the effects of global warming, precipitation change, and frozen ground degradation were considered in long-term variation analyses of the runoff compositions. The moving t-test was employed to detect change points of the hydrometeorological data series from 1961 to 2013, and flow duration curves were used to analyze daily runoff regime change in different periods. It was found that the abrupt change points of cold season runoff, such as recession flow, winter baseflow, and snowmelt runoff, are different from that of the rainy season runoff. The increase in winter baseflow and decrease in snowmelt runoff at the end of 1990s was closely related to global warming. In the 21st century, winter baseflow presented a larger relative increase compared to rainy season runoff. The correlation analyses indicate that winter baseflow and snowmelt runoff are mainly controlled by water-resource-related factors, such as rainy season runoff and the accumulated precipitation in cold season. To analyze the global warming impacts, two runoff coefficients—winter baseflow discharge rate (Rw) and direct snowmelt runoff coefficients (Rs)—were proposed, and their correlation with freezing–thawing indices were analyzed. The increase of Rw is related to the increase in the air temperature thawing index (DDT), but Rs is mainly controlled by the air temperature freezing index (DDF). Meanwhile, the direct snowmelt runoff coefficient (Rs) is significantly and positively correlated to DDF and has decreased at a rate of 0.0011/year since 1980. Under global warming, the direct snowmelt runoff (runoff increment between March to May) of the HWYR could decrease continuously in the future due to the decrease of accumulative snow in cold season and frozen ground degradation. This study provides a better understanding of the long-term runoff characteristic changes in the HWYR.

Impacts of different freeze-thaw treatments on the adsorption and desorption behaviors of Cd in black soil.

Seasonal freeze-thaw cycle (FTC) is one of the key processes that affect heavy metal behaviors in soil. However, previous studies are mainly focused on extreme FTC treatments which may exaggerate the real FTC effects in the field. This study aimed to compare the effects of different FTC conditions on the adsorption and desorption behaviors of Cd in the surface black soil. Different minimum freezing temperatures (- 2, - 5, and - 15°C), FTC rates (1 and 20°Ch-1), freezing lengths (2 and 24h), and FTC frequencies (1, 3, and 9) were investigated. The thawing temperature was set at 5°C. The amplitude for the FTC rate, length, and frequency experiments ranged from 5 to - 2°C. Our results indicated that the adsorption amounts of Cd presented an order of - 2°C > - 15°C > - 5°C and 24h > 2h for different FTC amplitude- and freezing length-treated soils, and the adsorption amounts decreased with increasing FTC rate and frequency. Soil maximum adsorption amount of Cd increased with the increases of FTC frequency, freezing length, and FTC rate, while it decreased with the decreases of freezing temperature. Soil Cd desorption ratio decreased with the increases of FTC frequency, freezing length, and TFC rate, and it increased with the increasing freezing temperature. Our results suggested that FTC conditions can significantly influence the adsorption and desorption behaviors of heavy metal in soil.

Influence of Cryogenesis on Soil Biota on the Example of the Southern Part of the Vitim Plateau

A distinctive paleogeographic situation in the southern part of the Vitim Plateau, Transbaikal region, has resulted in the formation of landscapes featuring numerous heaving mounds and thermokarst depressions. The cryolithozone reacts to climate warming by reducing its area, while the temperature and depth of seasonal permafrost thawing are increasing. A soil profile differentiation identified in the heaving mounds and thermokarst depressions has led to changes in morphological and physicochemical properties of soils, which caused, in turn, a response of the biota.

Finite Element Analysis of Natural Thawing Heat Transfer of Artificial Frozen Soil in Shield‐Driven Tunnelling

The technology of artificial horizontal freezing method is increasingly being used in the soil reinforcement of urban underground projects such as shield‐driven tunnelling. Compared with the freezing process, the thawing process is more complicated, and the thawing behavior of artificial frozen soil surrounding shield‐driven tunnels has not been well investigated in both the academic and industrial domains. This study, therefore, aims to investigate the natural thawing heat transfer behavior of artificial horizontal frozen soil in shield‐driven tunnelling using a three‐dimensional finite element method. The finite element modelling is based on the horizontal freezing reinforcement project of Chating Station to Jiqingmen Station Tunnel in the Nanjing Metro Line 2. Validation between finite element results and site measured results is firstly conducted. The natural thawing temperature field contours as well as the radial and longitudinal distributions of natural thawing temperature in the frozen soil surrounding the tunnel are then explicitly examined. Furthermore, sensitivity analysis of influencing factors such as the thermal conductivity, latent heat of phase change, ambient temperature inside tunnel, freezing time, and original ground temperature is carried out. The results and findings of this study may enrich the current limited database and enable a better understanding of natural thawing heat transfer behavior of artificial frozen soil in shield‐driven tunnelling.