Characteristics of thawed interlayer and its effect on embankment settlement along the Qinghai-Tibet Railway in permafrost regions

The formation of thawed interlayer beneath embankment can result in embankment settlement in permafrost regions. Based on the data on ground temperatures and deformations beneath the embankment, observed in-situ along the QinghaiTibet Railway in permafrost regions from 2006 to2013, characteristics of the thawed interlayer beneath the embankment and its influence on the embankment settlement are studied. The results indicate that the thawed interlayer hardly forms beneath the natural field, and beneath the embankments from the Qinghai-Tibet Railway the thawed interlayer develops widely, and it can be refrozen totally in the regions with lower mean annual ground temperature, and developed further in the regions with higher mean annual ground temperature.The thawed interlayer is closely related to the embankment settlement. The ice content of permafrost underlying the thawed interlayer influences the settlement of embankment. The higher the ice content is, the larger the settlement is, and vice versa. The increase in thickness of thawed interlayer mainly results from the decline of artificial permafrost table in high-temperature permafrost regions.

Shear properties of thawed natural permafrost by bender elements

Thawed permafrost could cause a serious stability problem for foundations and oil-wells in cold regions. A non-damage testing procedure, employing the Bender Element Method, was used for permafrost samples collected from a continuous frozen core obtained from the North Slope of Alaska, USA. The wave velocity and modulus of thawed permafrost were investigated on various isotropic confining pressure from 0 kPa to 400 kPa per 100 kPa. The received shear wave propagation was recorded, and the elastic wave theory was used to calculate shear modulus. Finally, the shear modulus affected by confining pressure, water content and dry density were analyzed and discussed, and a regression formulation of shear modulus based on the Janbu Model for thawed silty and sandy permafrost were proposed and validation.

Influence of Blastocysts Morphological Score on Pregnancy Outcomes in Frozen-thawed Blastocyst Transfers: a Retrospective Study of 741 Cycles

The influence of inner cell mass （ICM） and trophectoderm （TE） score on pregnancy out- comes in frozen-thawed blastocyst transfer cycles was analyzed. A retrospective analysis of 741 cycles of frozen-thawed blastosysts transfer was performed. All cycles were divided into four groups based on the number and morphological score of blastocysts： S-ICM B/TE B group （n=91）, the single blastocyst transfer oflCM B and TE B; D-ICM B/TE B group （n=579）, double blastocysts transfer oflCM B/TE B; D-1CM B/TE C group （n=35）, double blastocysts transfer of ICM B/TE C; and D-ICM C/TE B group （n=36）, double blastocysts transfer ofTE B/ICM C. The pregnancy outcomes were compared among the four groups. As compared with D-ICM B/TE C group, the clinical pregnancy rate, implantation rate and multiple pregnancy rate were increased in D-ICM B/TE B group （74.96% vs. 57.14%, 57.43% vs. 37.14%, and .48.62% vs. 25%, respectively, P〈0.05 for all）. Clinical pregnancy rate and implantation rate in D-ICM B/TE B group were also higher than in D-ICM C/TE B group （74.96% vs. 50%, and 57.43% vs. 33.33%, both P〈0.05）. Multivariable Logistic regression analysis indicated that ICM score was a better predictive parameter for clinical pregnancy （OR=3.05, CI 1.70-5.46, P〈0.001）, while the trophectoderm score was a better one for early abortion （OR=0.074, CI 0.03-0.19, P〈0.001）. Clinical pregnancy rate and multiple pregnancy rate in S-ICM B/TE B group were significantly lower than those in D-ICM B/TE B group （46.15% vs. 74.96%, and 2.38% vs. 48.62%, both P〈0.05）, but there was no si~,,niflcant difference in the implantation rate between the two groups. It was suggested that the higher score of ICM and TE may be indicative of the better pregnancy outcomes. The ICM score is a better predictor of clinical pregnancy than TE, while TE score is a better one in predicting early abortion. Sin- gle ICM B/TE B blastocyst transfer in frozen-thawed cycles can also get satisfactory pregnancy out- comes.

Characteristics of thawed interlayer and its effect on settlement beneath embankment in permafrost regions--A case study for the Qinghai-Tibet Highway

Based on ground temperatures and deformations monitored at the Xieshuihe site along the Qinghai-Tibet Highway(QTH)in permafrost regions from 2004 to 2015,variation of artificial permafrost table(APT),maximum frozen depth(MFD),thawed interlayer thickness(TIT)and ground temperature beneath embankment is analyzed,respectively.The results indicate that under the embankment,the change of APT occurred from October to December of that year and presented a deepening trend.The change of MFD occurred from April to June of that year with no obvious change trend,and TIT had an increasing trend year by year,which mainly resulted from the deepening artificial permafrost table.Mean annual ground temperature at 0.5 m depth was 3.91°C higher beneath the embankment center than that under the natural field.The rising ground temperature at shallow layer of embankment resulted in the development of thawed interlayer beneath the embankment and warming of underlying permafrost.Embankment settlement is closely associated with TIT.Greater settlement easily occurs when permafrost with higher ice content exists under the thawed interlayer,and in turn the settlement is smaller when permafrost with lower ice content exists under the thawed interlayer.

Analysis of Factors Influencing Pregnancy Rate in Frozenthawed Embryo Transfer

Objective To analyse factors influencing the outcome of frozen-thawed embryo transfer （FET）. Method A retrospective analysis was performed in our center on 129 thawing cycles from March 2001 to April 2003. The related parameters were compared between conceived and non-conceived cycles. Results There were totally 129 clinical pregnancies in these transfers （pregnancy rate： 27.1%）. Frozen-thawed embryos were transferred to natural cycles and CC cycling and hormone replacement treatment had equal success. Groups of IVF and ICSI did not differ significantly in pregnancy rates （P〉0.05）. The pregnancy rates for one, two, three and four pre-embryos transfer were 0, 20.0%,44.1% and 75.0%, respectively （P〈0.05）. There were statistical differences between pregnancy group or non- pregnancy group in the endometrial thickness, CES, CES/No. of embryo. A higher pregnancy rate was observed in embryo transfers which had at least one 4-cell grade I embryo （d 2）（P〈0.01）. Conclusions The most important factors influencing the implantation rate and pregnancy rate of frozen-thawed embryo transfer are age, endometrium thickness, and the number, morphology and growth rate of transferred frozen embryos of women participants.

Artificial Cycle with or without a Depot Gonadotropin-releasing Hormone Agonist for Frozen-thawed Embryo Transfer： An Assessment of Infertility Type that Is Most Suitable

The clinical outcomes of five groups of infertility patients receiving frozen- thawed, cleavage-stage embryo transfers with exogenous hormone protocols with or without a depot gonadotropin-releasing hormone （GnRH） agonist were assessed. A retrospective cohort analysis was performed on 1003 cycles undergoing frozen-thawed, cleavage-stage embryo transfers from January 1, 2012 to June 31, 2015 in the Reproductive Medicine Center of Wuhan General Hospital of Guangzhou Military Region. Based on the infertility etiologies of the patients, the 1003 cycles were divided into five groups： tubal infertility, polycystic ovary syndrome （PCOS）, endometriosis, male infertility, and unexplained infertility. The main outcome was the live birth rate. Two groups were set up based on the intervention： group A was given a GnRH agonist with exogenous estrogen and progesterone, and group B （control group） was given exogenous estrogen and progesterone only. The results showed that the baseline serum hormone levels and basic characteristics of the patients were not significantly different between groups A and B. The live birth rates in groups A and B were 41.67% and 29.29%, respectively （P〈0.05）. The live birth rates in patients with PCOS in groups A and B were 56.25% and 30.61%, respectively （P〈0.05）. The clinical pregnancy, implantation and on-going pregnancy rates showed the same trends as the live birth rates between groups A and B. The ectopic pregnancy rate was significantly lower in group A than in group B. We concluded that the live birth rate was higher and other clinical outcomes were more satisfactory with GnRH agonist co- treatment than without GnRH agonist co-treatment for frozen-thawed embryo transfer. The GnRH agonist combined with exogenous estrogen and progesterone worked for all types of infertility tested, especially for women with PCOS.

Stress states of thawed soil subgrade

The article presents the field measurement results of the stress states of roadbed thawed soil subgrade during the passage of trains. The dependences of the vertical and horizontal stresses on the velocity of the rolling stock motion, the axle load, and the distance from the sleeper sole have been obtained.

Morphology and survival of cryopreserved-thawed ovarian tissues after heterotopic autotransplantation

Objective： The aim of our study was to observe the survival and morphological changes of thawed ovarian tis- sues after heterotopic transplantation. Methods： Twenty SPF-SD female rats （5-6 weeks old） were equally randomized into the control group and experimental group. In control group, the freshly isolated ovaries were fixed in formalin. In experimental group, the freshly isolated ovaries were vitrified immediately and cut into thin slices. After stored in liquid nitrogen for 21 days, the tissues of experimental group were rapidly thawed and transplanted into back muscles of rats for 2 or 4 weeks, respectively. After that, all rats in experimental group were sacrificed and the ovarian tissues were collected and fixed in 4% formaldehyde solution. Then the ovarian tissues were stained with HE and observed under the light confocal microscope. Re- suits： With the naked eyes, there was no specific alteration except the size reduction with color changing. Under microscopy, we found normal cortex and medulla in the ovary, and the primordial follicles and follicles in various stages were observed in the cortex. The normal oocytes in ovarian tissues of experimental group were significant decreased than in the control group. Conclusion： The ovarian tissues survive well in experimental group and there is no significant difference in the proportion of follicles between different times （2 and 4 weeks） after grafting. Our results suggest that thawed ovarian tissues could survive after heterotopic transplantation into back muscles of rat models and maintain their morphology and function.

Improvement of Live Birth Rate Following Frozen-Thawed Blastocyst Transfer by Combination of Prednisolone Administration and Stimulation of Endometrium Embryo Transfer

The endometrial condition is a significant factor for successful pregnancy. To regulate endometrial function in fertility treatment, prednisolone (PSL) is administered for suppression of increased natural killer cells and stimulation of endometrium embryo transfer (SEET) to enhance communication between embryo and maternal tissues. We attempted to improve the endometrial condition by PSL administration and SEET during frozen–thawed blastocyst transfer (FBT). Patients took PSL (5 mg) 3 times daily for 3 days after ovulation during the FBT cycle. To analyse effects of PSL combined with SEET, we determined rates of chemical pregnancy, clinical pregnancy, foetal heart movement (FHM) and live birth. Rates of chemical pregnancy, clinical pregnancy and FHM were significantly higher in the PSL(+)/SEET(+) (57.7%, 50.0% and 46.2%, respectively) and PSL(+)/SEET(-) (53.3%, 46.7% and 46.7%, respectively) groups than in the PSL(-)/SEET(+) (30.3%, 18.2% and 18.2%, respectively) and PSL(-)/SEET(-) (22.4%, 22.4% and 18.4%;P = 0.0043, 0.0081 and 0.0055, respectively) groups. The live birth rate was significantly higher in the PSL(+)/SEET(+) group than in the PSL(+)/SEET(-), PSL(-)/SEET(+) and PSL(-)/SEET(-) groups (42.3%, 26.7%, 18.2% and 12.2%, respectively;P = 0.0237). PSL combined with SEET may be a useful adjunct to assisted reproductive technology in women who repeatedly fail to conceive by infertility treatment.

Effects of thawing-induced softening on fracture behaviors of frozen rock

Due to the presence of ice and unfrozen water in pores of frozen rock,the rock fracture behaviors are susceptible to temperature.In this study,the potential thawing-induced softening effects on the fracture behaviors of frozen rock is evaluated by testing the tension fracture toughness(KIC)of frozen rock at different temperatures(i.e.-20℃,-15℃,-12℃,-10℃,-8℃,-6℃,-4℃,-2℃,and 0℃).Acoustic emission(AE)and digital image correlation(DIC)methods are utilized to analyze the microcrack propagation during fracturing.The melting of pore ice is measured using nuclear magnetic resonance(NMR)method.The results indicate that:(1)The KIC of frozen rock decreases moderately between-20℃ and-4℃,and rapidly between-4℃ and 0℃.(2)At-20℃ to-4℃,the fracturing process,deduced from the DIC results at the notch tip,exhibits three stages:elastic deformation,microcrack propagation and microcrack coalescence.However,at-4℃e0℃,only the latter two stages are observed.(3)At-4℃e0℃,the AE activities during fracturing are less than that at-20℃ to-4℃,while more small events are reported.(4)The NMR results demonstrate a reverse variation trend in pore ice content with increasing temperature,that is,a moderate decrease is followed by a sharp decrease and-4℃ is exactly the critical temperature.Next,we interpret the thawing-induced softening effect by linking the evolution in microscopic structure of frozen rock with its macroscopic fracture behaviors as follow:from-20℃ to-4℃,the thickening of the unfrozen water film diminishes the cementation strength between ice and rock skeleton,leading to the decrease in fracture parameters.From-4℃ to 0℃,the cementation effect of ice almost vanishes,and the filling effect of pore ice is reduced significantly,which facilitates microcrack propagation and thus the easier fracture of frozen rocks.

Surface crack evolution patterns in freeze-thaw damage of fissured rock bodies

To explore the effects of freeze‒thaw cycles on the mechanical properties and crack evolution of fissured sandstone,biaxial compression experiments were carried out on sandstone subjected to freeze‒thaw cycles to characterize the changes in the physical and mechanical properties of fissured sandstone caused by freeze‒thaw cycles.The crack evolution and crack change process on the surface of the fissured sandstone were recorded and analysed in detail via digital image technology(DIC).Numerical simulation was used to reveal the expansion process and damage mode of fine-scale cracks under the action of freeze‒thaw cycles,and the simulation results were compared and analysed with the experimental data to verify the reliability of the numerical model.The results show that the mass loss,porosity,peak stress and elastic modulus all increase with increasing number of freeze‒thaw cycles.With an increase in the number of freeze‒thaw cycles,a substantial change in displacement occurs around the prefabricated cracks,and a stress concentration appears at the crack tip.As new cracks continue to sprout at the tips of the prefabricated cracks until the microcracks gradually penetrate into the main cracks,the displacement cloud becomes obviously discontinuous,and the contours of the displacement field in the crack fracture damage area simply intersect with the prefabricated cracks to form an obvious fracture.The damage patterns of the fractured sandstone after freeze‒thaw cycles clearly differ,forming a symmetrical"L"-shaped damage pattern at zero freeze‒thaw cycles,a symmetrical"V"-shaped damage pattern at 10 freeze‒thaw cycles,and a"V"-shaped damage pattern at 20 freeze‒thaw cycles.After 20 freeze‒thaw cycles,a"V"-shaped destruction pattern and"L"-shaped destruction pattern are formed;after 30 freeze‒thaw cycles,an"N"-shaped destruction pattern is formed.This shows that the failure mode of fractured sandstone gradually becomes more complicated with an increasing number of freeze‒thaw cycles.The effects of freeze‒thaw cycles on the direction and rate of crack propagation are revealed through a temperature‒load coupled model,which provides an important reference for an in-depth understanding of the freeze‒thaw failure mechanisms of fractured rock masses.

Factors Analysis of Spontaneous Abortion after Thawed-vitrified Blastocysts Transfer

Objective To investigate the factors resulting in spontaneous abortion after transferring frozen-thawing blastocysts.Methods A total of 108 cases transferring vitrified blastocysts were divided into two groups. abortion group （n=20） and ongoing group （n=88）. Cytogenetic analysis of apoblemas was performed in 12 cases of the abortion.Results The overall spontaneous abortion rate was 18.50%（20/108） and the early spontaneous rate was 16.67%（18/108）. A significant difference in maternal age was observed （abortion group： 33.3±4.0years, ongoing group： 31.0 ±3.6years, P=0.02）. No difference in other parameters was found. Cytogenetic analysis of apoblemas was obtained for 12 cases, and 2 specimens were contaminated. Seven often patients had abnormal karyotypes.Conclusion The underlying cause of spontaneous abortion after transferring frozenthawing blastoeysts appears to be abnormal karyotypes. Advancing maternal age seems to increase the risk of spontaneous abortion.

Quantification of the concrete freeze–thaw environment across the Qinghai–Tibet Plateau based on machine learning algorithms

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.

Effects of freeze-thaw cycles on sandstone in sunny and shady slopes

A growing rock engineering activity in cold regions is facing the threat of freeze-thaw(FT)weathering,especially in high mountains where the sunny-shady slope effects strongly control the difference in weathering behavior of rocks.In this paper,an investigation of the degradation of petrophysical characteristics of sandstone specimens subjected to FT cycle tests to simulate the sunny-shady slope effects is presented.To this aim,non-destructive and repeatable testing techniques including weight,ultrasonic waves,and nuclear magnetic resonance methods on standard specimens were performed.For the sunny slope specimens,accompanied by the enlargement of small pores,100 FT cycles caused a significant decrease in P-wave velocity with an average of 23%,but a consistent rise of 0.18%in mass loss,34%in porosity,67%in pore geometrical mean radius,and a remarkable 14.5-fold increase in permeability.However,slight changes with some abnormal trends in physical parameters of the shady slope specimens were observed during FT cycling,which can be attributed to superficial granular disaggregation and pore throat obstruction.Thermal shocks enhance rock weathering on sunny slopes during FT cycles,while FT weathering on shady slopes is restricted to the small pores and the superficial cover.These two factors are primarily responsible for the differences in FT weathering intensity between sunny and shady slopes.The conclusions derived from the interpretation of the experimental results may provide theoretical guidance for the design of slope-failure prevention measures and the selection of transportation routes in cold mountainous regions.

Comparison of clinical outcomes of frozen-thawed blastocysts transfer in natural and hormonally controlled cycles

Objectives:To assess the clinical outcomes of frozen-thawed blastocysts transfer in natural and hormonally controlled cycles.Methods:A retrospective analysis of natural and hormonally controlled cycle for 246 frozen-thawed blastocyst transfer cycles,the clinical pregnancy rate,implantation rate,early abortion rate were compared.Results:Of the 192 hormonally controlled cycles,the cancel rate,clinical pregnancy rate per ET,implantation rate and abortion rate were 7.3%(14/192),53.9%(96/178),38.8%(131/338)and 11.5%(11/96)respectively,whereas in 54 natural cycles,these rates were 16.7%(9/54),68.9%(31/45),52.9%(45/85)and 16.1%(5/31)respectively.There was no significant difference between the two groups with regard to the clinical pregnancy and abortion rate per ET,but the cancel rate and implantation rate were higher in natural cycles.However,the pregnancy and implantation rates of patients without PCOS in hormonal control cycles(57.2%,40.9%)were similar with those in natural cycles(P>0.05).Conclusion:These findings suggested that both hormonally controlled and natural cycles had similar pregnancy outcomes in frozen-thawed blastocysts transfer.

Effect of Cumulus Cells on the Efficiency of Vitrified-Thawed Immature Cattle Oocytes

The present work was designed to examine the effect of the presence or absence of cumulus cells on the efficiency of vitrification of immature cattle oocytes. In our experiment, we had two groups: group 1, immature cattle oocytes with cumulus cells and group 2, immature cattle oocytes without cumulus cells. The two groups underwent vitrification using 20% ethylene glycol and 20% DMSO, and then thawed, and in vitro matured in TCM-199 medium and examined after 22 hours for assessment of nuclear maturation. Higher survival rate (p < 0.05) after thawing was observed in group 1 (84.6%) than group 2 (57.8%). After in-vitro maturation, the rate of MII oocytes was significantly higher (p < 0.05) in group 1 (74.4%) than group 2 (47.7%). In conclusion, the cumulus cells are very important in increasing the survivability and developmental rate of vitrified-thawed immature cattle oocytes.

Change in Grain-Size Composition of Lignite under Cyclic Freezing-Thawing and Wetting-Drying

The paper presents the change in grain-size composition of lignite under cyclic freezing-thawing (FTC) and wetting-drying (WDC). The article shows that in the spring and autumn periods the lignites can be subjected to repeated freezing-thawing and wetting-drying, which determines the possibility of changing their grain-size composition and structure. Experimental studies in laboratory conditions on the influence of cyclic freezing-thawing (FTC) and wetting-drying (WDC) on the quality indicators of lignites have been carried out, their granulometric (fractional) composition has been studied. Freezing-thawing cycle conditions are as follows (FTC): minimum exposure temperature: -20°C;maximum: +5°C;relative humidity: 30%;number of processing cycles: 3. Wetting-drying cycles are as follows (WDC): drying temperatures are +20, +40, +60, +80°C, drying time 90 minutes, the coals are further subjected to rain (soaking) for a period of water saturation to humidity of 30% - 40% and dry again. The number of wetting-drying cycles is 3 times. The tests have revealed the destructive effects of FTC and WDC on the samples of lower metamorphic grade coal, and the cycles of wet-dry lead to the much higher yield of fine sizes (-6+0;-13+0 mm) than the cycles of freeze-thaw. Furthermore, it is found that the increase in the yield of fines depends on the heating temperature: coal disintegration proceeds more intensively at a higher temperature of drying.

土壤冻融过程中的水热参数化方案研究进展

冻土是陆地冰冻圈的重要组成部分,其冻融循环变化能够影响土壤结构、土壤水热传输以及土壤生物化学等过程,并通过陆-气相互作用影响局地甚至全球天气气候。因此,研究土壤冻融过程对冻土区人类生产生活和了解区域外天气气候变化具有重要的科学意义。本文回顾了土壤中的砾石、有机质对土壤冻融过程的影响及物理机制,总结了土壤冻融过程中水热参数化的相关研究成果,包括土壤导热率和水力学参数的计算、水热耦合方案以及冻融锋面计算方案等。相对于普通的矿物质土粒而言,砾石具有高导热率和低热容,有机质具有低导热率和高热容,他们对热量在土壤中的传输及土壤温度垂直分布有不同的影响。另外,砾石和有机质的存在改变了土壤孔隙度、土壤基质毛细作用与吸附作用,进而影响水分在土壤中的传输过程和垂直分布。已有研究表明:(1)当前大部分数值模式中土壤导热率采用Johansen方案及其派生方案进行计算,其中Balland-Arp方案考虑了砾石和有机质对土壤导热率的影响,该方案更好地刻画了土壤冻融过程中土壤导热率变化的连续性;综合考虑热-水-变形相互作用的导热率参数化方案可以较好地刻画土壤冻融过程中的水热耦合和土体冻胀的作用,对相变过程中土壤导热率变化特征的模拟更符合实际观测。(2)过冷水参数化方案刻画了土壤液态水在0℃以下存在的事实;相变温度方案描述了土壤相变温度低于0℃且不固定的事实;导水阻抗方案考虑了土壤冻结对土壤水分下渗的阻抗作用,改善了对冻土区水文过程的模拟效果。(3)土壤冻融过程伴随着水分的相变和能量的转化,水热耦合方案的发展能够较好地刻画土壤中热力-水文过程的协同变化特征,细化了对冻融过程中水分和能量相互作用的复杂物理机制的描述。(4)等温框架的数值模式通过模拟每层土壤中间深度的冻融过程代表该模式分层的整体特征,导致对冻融深度的严重高估或低估,尤其是对厚度较大的模式深层土壤,冻融锋面计算方案的提出和应用减小了这种模拟偏差。目前土壤冻融参数化方案的不足之处包括:绝大多数数值模式没有考虑土壤盐分导致土壤水的冰点降低这一事实;虽然大部分数值模式考虑了土壤有机质对土壤水、热传输的影响,但是模式中对土壤有机质含量及垂直分布的考虑与植被根系的生长状态脱节;模式模拟的土壤深度不足并且下边界通量为零的假定不符合实际情况。发展土壤溶质传输参数化方案以模拟盐分的分布、刻画植被根系生长过程和土壤有机质的分布特征、考虑深层土壤对浅层的热力学影响并完善数值模式中的下边界条件,这些是未来陆面模式改进土壤冻融过程模拟的可能方向。

脉冲电场辅助低温解冻对猪肉品质的影响

为研究脉冲电场(Pulsed Electric Field,PEF)辅助低温解冻对猪肉品质的影响,以猪背最长肌为原料,置于-18℃的冰箱中冷冻7 d,取出后分别在Control:4℃,0 kV,自然解冻;PEF解冻:P3(4℃,3 kV)、P5(4℃,5 kV)、P10(4℃,10 kV)。分析不同解冻处理对猪肉解冻时间、色泽、质构、水分损失以及水分分布的影响。结果表明:PEF处理可以缩短解冻时间,改善猪肉质量。P10组相比于Control组猪肉的解冻时间缩短了44.4%;不同解冻处理对猪肉蒸煮损失的影响无显著差异(P>0.05);PEF解冻后猪肉的硬度显著低于Control组(P<0.05);PEF解冻可以降低猪肉表面色泽的劣变程度,减少肌肉微观结构损伤。综上,当解冻温度为4℃,脉冲电压为10 kV时,解冻时间最短,解冻损失最低,肉样状态更接近鲜样,品质更好。