Combination effect of seasonal freezing and artificial freezing on frost heave of silty clay

To investigate the frost-heave properties of silty clay under the combination action of seasonal freezing and artificial freezing, and verify the feasibility of combined freezing, eight combined freezing experiments were performed on silty clay with water content (mass fraction) of 23.5% and 28.0%, through developed frost-heave test apparatus, in closed or open system. Two sorts of freezing temperature models, namely, constant and sine models, were applied to artificial freezing. The experimental results indicate that the frost-heave degree in seasonal freezing stage accounts for over 90% of the total in open system and it is up to 95% in closed system; the change of artificial sine-freezing temperature has no influence on the frost-heave degree in closed system, however, slight influence in open system. It is found that the variation of temperature gradient of sine-freezing specimen lags behind that of sine-freezing temperature with half phase; sine-freezing temperature model can reduce frost-heave degree of soil. Brand new technology is proposed for the application of artificial ground freezing and new study field of artificial freezing is created.

A dynamic soil freezing characteristic curve model for frozen soil

The soil freezing characteristic curve(SFCC)plays a fundamental role in comprehending thermohydraulic behavior and numerical simulation of frozen soil.This study proposes a dynamic model to uniformly express SFCCs amidst varying total water contents throughout the freezing-thawing process.Firstly,a general model is proposed,wherein the unfrozen water content at arbitrary temperature is determined as the lesser of the current total water content and the reference value derived from saturated SFCC.The dynamic performance of this model is verified through test data.Subsequently,in accordance with electric double layer(EDL)theory,the theoretical residual and minimum temperatures in SFCC are calculated to be-14.5℃to-20℃for clay particles and-260℃,respectively.To ensure that the SFCC curve ends at minimum temperature,a correction function is introduced into the general model.Furthermore,a simplified dynamic model is proposed and investigated,necessitating only three parameters inherited from the general model.Additionally,both general and simplified models are evaluated based on a test database and proven to fit the test data exactly across the entire temperature range.Typical recommended parameter values for various types of soils are summarized.Overall,this study provides not only a theoretical basis for most empirical equations but also proposes a new and more general equation to describe the SFCC.

Artificial ground freezing of underground mines in cold regions using thermosyphons with air insulation

Current practice of underground artificial ground freezing(AGF)typically involves huge refrigeration systems of large economic and environmental costs.In this study,a novel AGF technique is proposed deploying available cold wind in cold regions.This is achieved by a static heat transfer device called thermosyphon equipped with an air insulation layer.A refrigeration unit can be optionally integrated to meet additional cooling requirements.The introduction of air insulation isolates the thermosyphon from ground zones where freezing is not needed,resulting in:(1)steering the cooling resources(cold wind or refrigeration)towards zones of interest;and(2)minimizing refrigeration load.This design is demonstrated using well-validated mathematical models from our previous work based on two-phase enthalpy method of the ground coupled with a thermal resistance network for the thermosyphon.Two Canadian mines are considered:the Cigar Lake Mine and the Giant Mine.The results show that our proposed design can speed the freezing time by 30%at the Giant Mine and by two months at the Cigar Lake Mine.Further,a cooling load of 2.4 GWh can be saved at the Cigar Lake Mine.Overall,this study provides mining practitioners with sustainable solutions of underground AGF.

Prediction of the potential distribution and analysis of the freezing injury risk of winter wheat on the Loess Plateau under climate change

Determining the suitable areas for winter wheat under climate change and assessing the risk of freezing injury are crucial for the cultivation of winter wheat.We used an optimized Maximum Entropy(MaxEnt)Model to predict the potential distribution of winter wheat in the current period(1970-2020)and the future period(2021-2100)under four shared socioeconomic pathway scenarios(SSPs).We applied statistical downscaling methods to downscale future climate data,established a scientific and practical freezing injury index(FII)by considering the growth period of winter wheat,and analyzed the characteristics of abrupt changes in winter wheat freezing injury by using the Mann-Kendall(M-K)test.The results showed that the prediction accuracy AUC value of the MaxEnt Model reached 0.976.The minimum temperature in the coldest month,precipitation in the wettest season and annual precipitation were the main factors affecting the spatial distribution of winter wheat.The total suitable area of winter wheat was approximately 4.40×10^(7)ha in the current period.In the 2070s,the moderately suitable areas had the greatest increase by 9.02×10^(5)ha under SSP245 and the least increase by 6.53×10^(5)ha under SSP370.The centroid coordinates of the total suitable areas tended to move northward.The potential risks of freezing injury in the high-latitude and-altitude areas of the Loess Plateau,China increased significantly.The northern areas of Xinzhou in Shanxi Province,China suffered the most serious freezing injury,and the southern areas of the Loess Plateau suffered the least.Environmental factors such as temperature,precipitation and geographical location had important impacts on the suitable area distribution and freezing injury risk of winter wheat.In the future,greater attention should be paid to the northward boundaries of both the winter wheat planting areas and the areas of freezing injury risk to provide the early warning of freezing injury and implement corresponding management strategies.

Thermal performance of cast-in-place piles with artificial ground freezing in permafrost regions

During the construction of cast-in-place piles in warm permafrost,the heat carried by concrete and the cement hydration reaction can cause strong thermal disturbance to the surrounding permafrost.Since the bearing capacity of the pile is quite small before the full freeze-back,the quick refreezing of the native soils surrounding the cast-in-place pile has become the focus of the infrastructure construction in permafrost.To solve this problem,this paper innovatively puts forward the application of the artificial ground freezing(AGF)method at the end of the curing period of cast-in-place piles in permafrost.A field test on the AGF was conducted at the Beiluhe Observation and Research Station of Frozen Soil Engineering and Environment(34°51.2'N,92°56.4'E)in the Qinghai Tibet Plateau(QTP),and then a 3-D numerical model was established to investigate the thermal performance of piles using AGF under different engineering conditions.Additionally,the long-term thermal performance of piles after the completion of AGF under different conditions was estimated.Field experiment results demonstrate that AGF is an effective method to reduce the refreezing time of the soil surrounding the piles constructed in permafrost terrain,with the ability to reduce the pile-soil interface temperatures to below the natural ground temperature within 3 days.Numerical results further prove that AGF still has a good cooling effect even under unfavorable engineering conditions such as high pouring temperature,large pile diameter,and large pile length.Consequently,the application of this method is meaningful to save the subsequent latency time and solve the problem of thermal disturbance in pile construction in permafrost.The research results are highly relevant for the spread of AGF technology and the rapid building of pile foundations in permafrost.

Freezing imaginarity of quantum states based onℓ_(1)-norm

We discuss freezing of quantum imaginarity based onℓ_(1)-norm.Several properties about a quantity of imaginarity based onℓ_(1)-norm are revealed.For a qubit(2-dimensional)system,we characterize the structure of real quantum operations that allow for freezing the quantity of imaginarity of any state.Furthermore,we characterize the structure of local real operations which can freeze the quantity of imaginarity of a class of N-qubit quantum states.

Experimental Study on the Effect of Fine-Grained Soil Content on the Freezing Strength of Aeolian Sand-Cement Interface

In cold regions,understanding the freezing strength of the interface between soil and structure is crucial for designing frost-resistant foundations.To investigate how the content of cement powder in aeolian sand affects this strength,we conducted direct shear tests under various conditions such as different fine-grained soil content,normal stress,and initial moisture content of the soil.By analyzing parameters like soil properties,and volume of ice content,and using the Mohr-Coulomb strength theory to define interface strength,we aimed to indirectly measure the cementation strength of the interface.Our findings revealed that as the particle content increased,the interface stress-strain curves became noticeably stiffer.We also observed a positive linear relationship between freezing strength and silt content,while the initial moisture content of the soil did not significantly impact the strengthening effect of fine-grained soil on freezing strength.Moreover,we discovered that as the powder content increased,the force binding the ice to the interface decreased,while the friction angle at the interface increased.However,the cohesion force at the interface remained relatively unchanged.Overall,our analysis suggests that the increase in freezing strength due to fine-grained soil content is primarily due to the heightened friction between aeolian sand and the interface.

Exploring the Need and Strategy for Intraoperative Freezing to Identify Metastatic Adenocarcinoma of the Lungs

Objective: To explore the necessity and strategy of intraoperative freezing to identify primary and metastatic adenocarcinoma of the lung. Methods: This study retrospectively analyzes the impact of failing to make a definitive diagnosis of metastatic adenocarcinoma of the lung on the clinical surgical approach in four cases of intraoperative freezing. It also examines the reasons for this failure and reviews the relevant literature. Results: All 4 cases of intraoperative freezing were diagnosed as invasive adenocarcinoma, and none of them made a definitive diagnosis of metastatic adenocarcinoma. Conclusion: It is difficult to confirm the diagnosis of metastatic adenocarcinoma of the lung by intraoperative frozen section, and the combination of patient history, rapid immunohistochemistry, and histological morphology of intraoperative frozen section for its identification can guide the surgeon to adjust the surgical approach in time and provide evidence for the establishment of surgical protocols for reference.

Evaluation of freezing state of sandstone using ultrasonic time-frequency characteristics

Common problems in engineering projects that involve artificial ground freezing of soil or rock include inadequate thickness,strength and continuity of artificial frozen walls.It is difficult to evaluate the freezing state using only a few thermometer holes at fixed positions or with other existing approaches.Here we report a novel experimental design that investigates changes in ultrasonic properties(received waveform,wave velocity V_(p),wave amplitude,frequency spectrum,centroid frequency f_(c),kurtosis of the frequency spectrum KFS,and quality factor Q)measured during upward freezing,compared with those during uniform freezing,in order to determine the freezing state in 150 mm cubic blocks of Ardingly sandstone.Water content,porosity and density were estimated during upward freezing to ascertain water migration and changes of porosity and density at different stages.The period of receiving the wave increased substantially and coda waves changed from loose to compact during both upward and uniform freezing.The trend of increasing V_(p) can be divided into three stages during uniform freezing.During upward freezing,V_(p) increased more or less uniformly.The frequency spectrum could be used as a convenient and rapid method to identify different freezing states of sandstone(unfrozen,upward frozen,and uniformly frozen).The continuous changes in reflection coefficient r_(φ),refraction coefficient t_(φ) and acoustic impedance field are the major reason for larger reflection and refraction during upward freezing compared with uniform freezing.Wave velocity V_(p),wave amplitude A_(h),centroid frequency f_(c) and quality factor Q were adopted as ultrasonic parameters to evaluate quantitatively the temperature T of uniformly frozen sandstone,and their application within a radar chart is recommended.Determination of V_(p) provides a convenient method to evaluate the freezing state and calculate the cryofront height and frozen section thickness of upward frozen sandstone,with accuracies of 73.37%-99.23%.

Role of CaCl_(2) in Cold Acclimation-Induced Freezing Resistance of Populus tomentosa Cuttings

Populus tomentosa cuttings were treated with 1mmol·L -1 , 5mmol·L -1 , 10mmol·L -1 or 15mmol·L -1 of CaCl 2 for 1\|7 d, respectively, for studying the effects of different concentrations of CaCl 2 on freezing resistance. Results indicated that 10?mmol·L -1 of CaCl 2 has greater effect than other concentrations on the enhancement of freezing resistance, and the optimum time of pretreatment was 5?d. In addition, cuttings used for cold acclimation at -3℃ were pretreated with or without 10?mmol·L -1 of CaCl 2, 3?mmol·L -1 of Ca 2+ chelator EGTA, 0 05?mmol·L -1 of CaM antagonist CPZ or 0 1?mmol·L -1 of Ca 2+ channel inhibitor LaCl 3 The changes in CaM and freezing resistance of all cuttings were investigated. The results showed that cold acclimation at -3℃ increased CaM content and decreased the minimum temperature for 100% survival. The CaCl 2 pretreatment enhanced the effect of cold acclimation and obviously increased CaM content and decreased the minimum temperature for 100% survival, but this effect was strongly inhibited by the EGTA, CPZ or LaCl 3 It is concluded that the effect of CaCl 2 on freezing resistance is associated with its concentration and time of pretreatment, Ca 2+ CaM may be involved in the induction of freezing resistance of the cuttings.

Effects of Cold Acclimation and CaCl_2 on Total Soluble Protein, CaM and Freezing Resistance of Populus tomentosa Seedlings

Populus tomentosa seedlings used for cold acclimation at -3℃ were pretreated with or without 10?mmol·L -1 CaCl 2, 3?mmol·L -1 of Ca 2+ chelator EGTA, 0 1?mmol·L -1 of Ca 2+ channel inhibitor LaCl 3,and 0 05?mmol·L -1 of CaM antagonist CPZ. The changes in the contents of total soluble protein and CaM, and freezing resistance in all pretreated seedlings in various periods ( viz: following cold acclimation, chilling stress and recovery) were investigated. Results showed that cold acclimation increased the contents of total soluble protein and CaM, and freezing resistance of seedlings, which could be strongly reduced by the pretreatments of EGTA CPZ and LaCl 3 Cold acclimation combined with CaCl 2 pretreatment enhanced the effect of cold acclimation on freezing resistance, and obviously increased the contents of total soluble protein and CaM, reduced the declining degree of the contents of total soluble protein and CaM caused by chilling stress as compared with cold acclimation, augmented the increase in the level of total soluble protein and CaM during the recovery periods. Further analysis found that an increase in total soluble protein content during cold acclimation with or without CaCl 2 pretreatment mainly resulted from the increase in content of heat stable protein in total soluble protein. It is suggested that Ca 2+ calmodulin may be involved in the synthesis of total soluble protein, and the induction of freezing resistance of seedlings.

ULTRASTRUCTURE OF THE VEGETATIVE CELLS OF NOSTOC FLAGELLIFORME PREPARED WITH HIGH PRESSURE FREEZING AND FREEZE SUBSTITUTION TECHNIQUE

The ultrastructure of the vegetative cells of Nostoc flagelliforme Born. et Flah. was investigated with high pressure freezing and freeze substitution technique and compared with the results obtained by using conventional preparation methods. During the processes of chemical fixation, dehydration and embedding, the cell structures might be more artificially modified than that obtained from high pressure freezing and freeze substitution. With the present method, the sheath of N. flagelliforme could be well penetrated and no extra big space could exist between the cell and the sheath. The cell protoplasm rarely shrinked. Some fine structures of cell inclusions and unit membranes became visualized. Many bacteria were harbored in the sheath. In addition, the presence of big vacuoles in the cell of N. flagelliforme as well as the presence of bacteria in the sheath shown in the present preparation for cyanobacteria has not been described so far in the literature.

Cold Acclimation-Induced Changes in Total Soluble Protein, RNA, DNA, RNase and Freezing Resistance in Populus tomentosa Cuttings

The changes in the contents of total soluble protein and RNA, the activity of RNase in leaves and branches of Populus tomentosa cuttings at various periods (viz: cold acclimation, deacclimation, chilling stress and the recovery after chilling stress), and the survival rate and the freezing resistance of cuttings during cold acclimation at -3℃ were investigated. Results showed that cold acclimation not only increased the contents of total soluble protein and RNA, the survival rates and the freezing resistance of cuttings, decreased the activity of RNase, but also reduced the declining degree of total soluble protein and RNA contents, and the increasing level of RNase caused by chilling stress as compared with the controls. In addition, cold acclimation augmented the increase in the level of total soluble protein and RNA, and facilitated the decrease of RNase during the recovery periods. Further analysis found that the DNA content of all treatments kept relative stability at various periods. The changes in total soluble protein, RNA and RNase were closely related to the freezing resistance of cuttings. It appears that the increase of RNA content caused by cold acclimation induced decrease of RNase activity may be involved in the accumulation of total soluble protein and the induction of freezing resistance of cuttings.

Feasibility analysis of urban sewage source heat pump system with freezing latent heat collection

Aiming to resolve the problem that conventional sewage source heat pump systems cannot satisfy heat peak loads of buildings,a new idea that the freezing latent heat is exacted as the auxiliary heat source at the peak heat load is proposed.First,on the basis of sewage characteristics,a freezing latent heat exchanger is developed to safely eliminate ice,continuously extract heat and remove sewage soft-dirt.A reasonable form of the urban sewage source heat pump system with freezing latent heat collection is presented.Then,the feasibility of the system is theoretically analyzed.The calculation results under typical operating conditions show that the heating ability of the new system is higher than that of the conventional one and the ratio of these two highest heating rates is between 4.5 and 8.7,which proves that the new system has great application potential in cold regions.

Effect of Sugar on the Process of Cold-Acclimation-Induced Freezing Tolerance of Populus tomentosa

Populus tomentosa seedlings for cold-acclimating were pretreated wit h or without 20% saccharose. Changes in the concentrations of total soluble sugar , the survival rates, and freezing tolerance of seedlings during cold acclimatio n were investigated. The results showed that cold acclimation increased the conc entrations of total soluble sugar, the survival rates and freezing tolerance. Co ld acclimation, combined with the saccharose-pretreatment, enhanced the above- ment ioned effect of cold acclimation, and obviously increased the concentrations of total soluble sugar, the survival rates and freezing tolerance of seedlings. Fur ther analysis found that the concentrations of total soluble sugar in branches i ncreased greater than that in leaves during both cold acclimation with or withou t the pretreatment of saccharose. Moreover, an increase of the concentrations of total soluble sugar in branches and leaves was closely related to the freezing tolerance of seedlings. The results indicate the accumulation of soluble sugar i n seedlings induced by cold acclimation may be involved in the induction of free zing tolerance .

The Influence of Freezing Drizzle on Wire Icing during Freezing Fog Events

Both direct and indirect effects of freezing drizzle on ice accretion were analyzed for ten freezing drizzle events during a comprehensive ice thickness, fog, and precipitation observation campaign carried out during the winter of 2008 and 2009 at Enshi Radar Station （30°17′N, 109°16′E）, Hubei Province, China. The growth rate of ice thickness was 0.85 mm h-1 during the freezing drizzle period, while the rate was only 0：4 mm h-1 without sleet and freezing drizzle. The rain intensity, liquid water content （LWC）, and diameter of freezing drizzle stayed at low values. The development of microphysical properties of fog was suppressed in the freezing drizzle period. A threshold diameter （Dc） was proposed to estimate the influence of freezing drizzle on different size ranges of fog droplets. Fog droplets with a diameter less than Dc would be affected slightly by freezing drizzle, while larger fog droplets would be affected significantly. Dc had a correlation with the average rain intensity, with a correlation coefficient of 0.78. The relationships among the microphysical properties of fog droplets were all positive when the effect of freezing drizzle was weak, while they became poor positive correlations, or even negative correlations during freezing drizzle period. The direct contribution of freezing drizzle to ice thickness was about 14.5%. Considering both the direct and indirect effects, we suggest that freezing drizzle could act as a ＂catalyst＂ causing serious icing conditions.

Coupling of the Calculated Freezing and Thawing Front Parameterization in the Earth System Model CAS-ESM

The soil freezing and thawing process affects soil physical properties,such as heat conductivity,heat capacity,and hydraulic conductivity in frozen ground regions,and further affects the processes of soil energy,hydrology,and carbon and nitrogen cycles.In this study,the calculation of freezing and thawing front parameterization was implemented into the earth system model of the Chinese Academy of Sciences(CAS-ESM)and its land component,the Common Land Model(CoLM),to investigate the dynamic change of freezing and thawing fronts and their effects.Our results showed that the developed models could reproduce the soil freezing and thawing process and the dynamic change of freezing and thawing fronts.The regionally averaged value of active layer thickness in the permafrost regions was 1.92 m,and the regionally averaged trend value was 0.35 cm yr–1.The regionally averaged value of maximum freezing depth in the seasonally frozen ground regions was 2.15 m,and the regionally averaged trend value was–0.48 cm yr–1.The active layer thickness increased while the maximum freezing depth decreased year by year.These results contribute to a better understanding of the freezing and thawing cycle process.

Comparison of G6PDH Activity and LT50 Between P. tomentosa and P. suaveolens During Freezing Acclimation

The differences of glucose-6P dehydrogenase (G6PDH) activity and freezing resistance induced by freezing acclimation between cuttings of freezing-sensitive P. tomentosa and freezing-resistant P. suaveolens were compared for exploring the role of G6PDH on the enhancement of freezing resistance induced by freezing acclimation. After 5 d of freezing acclimation at -3 ℃, the LT50 of P. tomentosa has decreased from -6.2 ℃ in control cuttings to -14.3 ℃ in freezing acclimated ones, and the increase of G6PDH activity was observed in freezing acclimated cuttings as compared with control ones. Whereas, when P. suaveolens was freezing acclimated at -20℃ for 5 d, the LT50 has decreased from -27.1℃ in control cuttings to -43.5 ℃ in freezing acclimated ones, and the activity of G6PDH increased considerably. In addition, the increase of LT50 and the decrease of G6PDH activity resulting from 2 d of deacclimation at 25 ℃ were found in two kinds of freezing acclimated cuttings. It is concluded that the increase in the activity of G6PDH may associate with the inherited freezing resistance of species and the enhancement of freezing resistance of cuttings, and may play an important role in the antifreeze process under freezing temperature, which would provide the basis for the study on the molecular mechanism of freezing resistance in P. suaveolens and the cloning of gene associated with freezing resistance.

Different discretization method used in coupled water and heat transport mode for soil under freezing conditions

A coupled water and heat transport mode is established based on the Richards equation to study water flow and heat transport in soil during freezing process. Both the finite difference and finite element method are used in the discretization, respectively. Two different computer programs are written and used to simulate an indoor unidirectional frozen test. The freezing depth, freezing rate and temperature variation are compared among lab tests, finite difference calculation simulation and finite element calculation simulation. Result shows that： the finite difference method has a better performance in freezing depth simulation while the finite element method has a better performance in numerical stability in one-dimensional freezing simulation.

Characterization and Role of Glucose-6-phosphate Dehydrogenase of Populus suaveolens in Induction of Freezing Resistance

Glucose-6-phosphate dehydrogenase (G6PDH, EC 1.1.1.49) was purified from the leaves of 8-week-old Populus suaveolens cuttings. The enzyme activity in the absence and presence of reduced dithiothreitol (DTTred) was determined. The results show that the G6PDH activity is not inactivated by pre-incubation with DTTred, indicating that the purified enzyme probably pre- sented in cytosol of P. suaveolens. The catalytic characteristics and kinetic parameters of cytosolic G6PDH purified from P. suaveolens cuttings were also studied. The results show that G6PDH is characterized by Kmvalue of 360 μmol·L–1 for G6P and 16 μmol·L–1 for NADP, a pH range of 7.3–8.9, and the maximum activity around pH 8.2. The enzyme activity is inhibited by various metabolites such as NADPH, NADH, GTP, UTP, ATP, AMP, ADP, CoA, acetyl CoA, fructose-6-phosphate (F6P), eryth- rose-4-phosphate (E4P), ribose-5-phosphate (R5P) and 3-phosphoglycerate (3-PG) (all at 1 mmol·L–1 except for NADPH and NADH) to different extents. NADPH is the most effective inhibitor of enzyme activity, with an inhibition of 72.0%. The addition of metal ions such as MgCl2, CaCl2and KCl (all 1.0 mmol·L–1) to the standard reaction mixture has no remarkable influence on the cytosolic G6PDH activity. However, CdCl2 (1.0 mmol·L–1) causes high inhibitory effect on the enzyme activity. To explore the role of G6PDH on the enhancement of freezing resistance induced by freezing acclimation, the changes in the cytosolic G6PDH activity and freezing resistance (expressed as LT50) of P. suaveolens cuttings during freezing acclimation at –20 °C were investigated. The results reveal that freezing acclimation decreases LT50 of cuttings, and increases the activity of cytosolic G6PDH compared with control ones, while 2 d of de-acclimation at 25 °C result in a decrease in cytosolic G6PDH activity, and caused an increase in LT50. Furthermore, the change in cytosolic G6PDH activity is found to be closely correlated to the degree of freezing resistance of cuttings during freez- ing acclimation. It is suggested that cytosolic G6PDH may be involved in the induction of freezing resistance of cuttings.