Freezing rate affects the survival of a short-term freezing stress in Panagrolaimus davidi, an Antarctic nematode that survives intracellular freezing

The ability of the Antarctic nematode Panagrolaimus davidi to survive a short-term freezing stress depended upon the rate of freezing of its surroundings, measured as the duration of the sample exotherm. The freezing rate increased as the sample volume and freezing temperature decreased and resulted in fewer nematodes surviving. This appears to be due to the greater risk of physical damage by ice crystal growth at high freezing rates. Once frozen the nematodes will then survive exposure to lower temperatures. The environment of the nematode is likely to produce the slow rate of freezing of its surroundings that is necessary for its survival.     

Observation of transverse spin freezing by TDPAC

Mössbauer spectroscopy investigation of superconducting Sm_0.85Ba_0.15FeAsO_0.7F_0.3 (T _c = 37 K) has been performed. The spectra appear to be a singlet pattern throughout the temperature range of 20–290 K. The value of Debye temperature is obtained (θ _D ～ 390 K). Unusual behavior of the central shift as a function of temperature is observed below 60 K. Unlike cuprate superconductors, phonon softening is not observed near T _c of the iron pnictide.     

交替冻融对黑土可溶性有机质荧光特征的影响

土壤可溶性有机质(DOM)是土壤有机质研究中最有意义的量化指标,交替冻融作用能够影响土壤DOM的荧光特征.文章利用三维荧光分析交替冻融对黑土DOM光谱特征的影响,并基于光谱特征的改变,评价交替冻融对黑土活性腐殖质和腐殖程度的影响.研究表明,与未冻融样品相比,冻融样品DOM的紫外区类富里酸荧光峰发生红移,说明土壤中有机物分子芳香化程度增高,腐殖程度上升;部分冻融样品产生了类蛋白荧光峰,说明冻融过程中微生物降解活动增强;冻融样品的活性腐殖质含量和腐殖程度均较未冻融高,说明交替冻融作用增加了土壤肥力;紫外区类富里酸荧光峰值与可见区类富里酸荧光峰值的比值(r(a,c))与活性腐殖质含量之间、r(a,c)与腐殖程度之间,都存在显著的正相关关系(相关系数分别为0.88,0.77),说明r(a,c)可以评价黑土冻融后土壤活性腐殖质含量和腐殖程度的变化.     

Survival of antarctic soil metazoans at -80 degree C for six years

A sample of the liverwort Cephaloziella varians was collected on 1 January 1999 at Rothera Point on the Wright Peninsula, Adelaide Island, western Antarctic Peninsula and was partially dried and then frozen at -80 degree C. The sample was rapidly defrosted to c. 10 degree C after six years and two months of storage at this temperature. Nematodes, tardigrades and a bdelloid rotifer present in the sample were found to have survived. Of the 159 nematodes recovered from the sample, 49 (31%) were alive: of the tardigrades and rotifers, two of 15 (13%) and one of 48 (2%) had survived, respectively. A Chi-square test showed that there was a significant association between nematode taxon and survival: a greater proportion of Coomansus gerlachei individuals were alive than of Rhyssocolpus paradoxus. A Chi-square test also showed that there was a significant association between phylum and survival: a significantly greater proportion of nematodes or tardigrades were alive than of bdelloid rotifers. We conclude that Antarctic soil metazoans are capable of surviving long-term exposure to low sub-zero temperatures and that there may be taxon-specific effects of freezing on survival.     

ICP-AES同时测定南极石中的22种元素

电感耦合等离子体原子发射光谱法(ICP-AES)同时测定南极石中的铜、铁、锌、钙、镁、锰、钴等22种元素的含量.优化了消解样品用酸,选择了适合的元素分析线.各元素测定的相对标准偏差为0.13%-5.14%,加标回收率为95.43%-108.68%,方法简单、可靠,具有良好的准确度和精密度.     

Numerical simulation of tissue freezing by liquid nitrogen based cryoprobe

A model is presented to simulate the cooling processes during tumor cryosurgery with different kinds of flows through the cryoprobe. The heat flux between the cryoprobe wall and the tumor, the heat transfer coefficient under different inflow conditions are obtained numerically. The impact of the inlet mass flow rate, gas volume fraction on these parameters is investigated. It is found that the heat transfer coefficient decreased significantly when inflow changed from two-phase annular flow to droplet flow, and to gas flow. The inlet gas volume fraction and flow velocity only significantly affect the freezing ability of the probe when the inflow is gas or in droplet phase. Simulation of the tumor temperature profiles under different flow conditions show that the heat transfer coefficient is a crucial parameter in temperature prediction during cryosurgery. Results indicate that when the cryoprobe wall is assumed at a constant temperature conventionally, the cooling effect could be overestimated. It would be more reasonable to use the constant wall heat transfer coefficient to simulate the cooling progress under a specific flow.     

Growth of ZnInGaS4 by normal freezing method

The crystal structure and phase transition of ZnInGaS₄ were described. The ZnInGaS₄ had both a defect chalcopyrite and a layered structure below 920 °C, and only the layered structure ZnInGaS₄ existed between 920 and 1020 °C. The layered structure ZnInGaS₄ was grown using the normal freezing method. The bandgap of the layered structure ZnInGaS₄ was estimated to be approximately 2.6 eV and it is possibly a direct bandgap. This is a first step toward realizing the novel functions of ZnInGaS₄.     

Cryopreservation of Pistacia spp. seeds by dehydration and one-step freezing

Cryopreservation protocols by dehydration and one-step freezing were developed for seeds from three Pistacia species, i.e., P. vera, P. terebinthus and P. lentiscus, which were characterised by different initial germination percentages (100%, 17% and 81%, respectively). In P. vera, a maximum of 90% germination was obtained following 8 hours drying in silica gel (corresponding to 11.7% moisture content on a FW basis) and direct immersion in LN. In P. terebinthus and P. lentiscus, shorter periods of dehydration (1 hour and 15 min, respectively) were sufficient to reduce their moisture content to about 20%, which resulted in peak seed germination percentages from cryostorage of 16% and 47%, respectively. Following cryopreservation, the seeds germinated better on semi-solid MS medium, than on cotton wool wetted with dH(2)O or liquid MS medium. Finally, in P. vera and P. lentiscus, high and significant correlation coefficients were obtained between the TTC viability test and seed germinability after recovery from LN, provided that seeds which were considered positive in the test showed completely or partially red embryonic axes coupled to completely red cotyledons.     

Structural characteristics of porous polymers treated by freezing with water or acetone

The pore structure of nine polymers of different origin initial and treated in water and acetone for 24 h and then frozen by liquid nitrogen for 2 h was studied using low-temperature nitrogen adsorption. An average increase in pore volume and surface area is approximately 16 and 8%, respectively, after freezing with water and 19 and 8%, respectively, after treatment with acetone. However, for some samples, this effect is negative but for others, structural changes are significantly greater (up to 106%) than the average one. Certain treated polymers are characterized by shifted pore size distribution which is also accompanied by displacement of nitrogen adsorption energy distribution.     

Dynamics of freezing and liquid instability

A theoretical analysis of the dynamic stability of a supercooled simple liquid to finite amplitude periodic density waves is presented. The theory predicts absence of a classical spinodal point for a simple one component liquid. A dynamical constraint on the formation of the bcc phase is revealed.     

Cryopreservation of embryogenic callus of Aesculus hippocastanum L. by vitrification or one-step freezing

An effective procedure for the cryopreservation of horse chestnut (Aesculus hippocastanum L.) embryogenic callus by vitrification/one-step freezing is described here. In particular, the study focused on the possibility of recovering the full proliferation potential of the embryogenic lines after storage in liquid nitrogen. The developmental stage of the embryogenic lines was shown to play an important role. Ninety-min incubation in PVS2 and preservation at -196 degrees C of callus samples, containing a prevalence of embryogenic masses at an advanced stage of somatic embryo maturation (i.e., the torpedo stage), gave optimum regrowth of healthy and proliferating embryogenic callus. Moreover, raising the thawing temperature to 45 degrees C yielded the maximum survival (94%) of torpedo-stage embryogenic samples, recovery of proliferation and, in more than 70% of cases, maturation to the cotyledonary stage. This study opens the way to the possibility of safe, long-term storage in liquid nitrogen of valuable embryogenic lines of horse chestnut, avoiding repeated subculturing.     

Cryopreservation of embryogenic tissues of Pinus nigra Arn. by a slow freezing method

Six different embryogenic cell lines of Pinus nigra Arn. have been cryopreserved in liquid nitrogen using cryoprotection with sucrose (18%) and DMSO (7.5%). Post-thaw growth and tissue proliferation have been observed in five cell lines. The survival levels after storage in liquid nitrogen reached values between 62.5 and 100%. Growth of recovered embryogenic cells as well as somatic embryos is similar to the non-frozen tissues maintained in long-term culture. Somatic embryo maturation and plantlet regeneration occurred in all selected cell lines.     

Stable Isotope Geochemistry of Antarctic Salt Efflorescences

Salt efflorescences consisting of gypsum sampled mainly in the Schirmacher Oasis have been analyzed for the isotopic composition of the water of crystallization and of the sulphate-sulphur. For comparison, a few samples from other Antarctic locations (Guettard Range, Prince Charles Mts., Insel Mts.) were included in the study. The isotopic variations of the water of crystallization of secondary gypsum and the calculated isotopic composition of the mother solution reflect the local climatic conditions during the precipitation of the efflorescences. It is therefore possible to obtain qualitative information about the climatic conditions prevailing in the studied region.     

A study of the freezing of water in human uterine muscle by proton magnetic resonance

Human uterine muscle and its nuclear fractions have been studied by means of nuclear magnetic resonance at temperatures from 300 degrees K to 143 degrees K. Different proton populations have been detected above and below the freezing point. On this basis it is suggested that the freezing of water in uterine muscle starts at the cell nuclei.