Freezing Curves Research Articles

Impurity Effect in Silver-Point Realization

CCT-WG1 has recommended the sum of individual estimates (SIE) method to correct for the influence of impurities on the realization of temperature fixed points when a detailed impurity analysis is available. The method to estimate the uncertainty of the SIE has also been reported. On the other hand, most cells are fabricated from commercial fixed-point metals that often have no detailed impurity analysis, so the SIE calculation is impossible in that case. Due to this circumstance, and with the focus on the silver fixed point, a new fixed-point cell was fabricated in such a way that a portion of the silver ingot used was extractable during the silver casting. This portion was then analyzed by glow discharge mass spectrometry (GDMS), and the result used to calculate the SIE correction and its uncertainty. Temperature measurements during melting and freezing were collected using new and existing silver fixed-point cells under various conditions. These measurements were used to derive the slope of the silver freezing curve, from which the effect of impurities was evaluated by thermal analysis. The difference between the SIE and the thermal analysis method was evaluated to check the inaccuracy of the thermal analysis from the SIE point of view.

Improved Post-Thaw Viability and In Vitro Functionality of Peripheral Blood Hematopoietic Progenitor Cells after Cryopreservation with a Theoretically Optimized Freezing Curve.

Current methods for the cryopreservation of peripheral blood stem cell transplants (PBSCTs) have been developed empirically. Although the use of cryopreserved PBSCTs is successful and usually leads to rapid hematopoietic recovery, the freeze-thawing process is known to induce a significant amount of cell death. Furthermore, the infusion of DMSO, which is used to protect the cells against damage induced by freezing, can cause morbidity. Freezing methods may be improved by using a fundamental cryobiological approach, addressing the putative causes of cell injury during freezing and thawing. Different cell types may have different optimal cooling rates. Cooling rates above this optimum may cause ‘fast cooling damage', e.g. by lethal intracellular ice formation, while cooling rates below the optimum may lead to ‘slow cooling damage', These cryoinjuries relate to the osmotic changes during freezing and thawing, and the resulting fluxes of water and cryoprotectant across the cell membrane. Mathematic modeling of these osmotic events can be used to predict the optimal cooling rates for specific cell types. Woelders and Chaveiro* have developed a model that calculates the ‘compromise' cooling rate for every subzero temperature, resulting in non-linear freezing curves. In the present study, this model was applied to predict ‘optimal' freezing curves for PBSCTs with 10% and 5% DMSO, respectively, using values for the membrane permeability coefficients and related parameters as published earlier for cord blood HPCs. These predicted curves were tested empirically and compared to the presently used standard linear freezing curve. CD34+ selected and unselected PBSCs were cryopreserved using the standard or the new freezing curves. Post-thaw quality was evaluated by cell viability, CFU-GM formation and megakaryocyte outgrowth. With 10% DMSO, the use of the predicted optimal freezing curve compared to the currently used freezing curve resulted in increased post-thaw viability of CD34+ cells (mean±SEM; 78.4%±6.6% versus 72.0%±6.1% for unselected CD34+ cells and 92.0%±0.6% versus 83.9%±2.5% [p<0.01] for selected CD34+ cells), colony formation (40.7%±8.8% versus 30.1%±7.9% [p<0.01] for unselected CD34+ cells and 102.6%±8.0% versus 90.1%±11.9% for selected CD34+ cells), and megakaryocyte outgrowth (6.0±0.7 versus 3.9±0.6 [p<0.01] CD41+ MKs per seeded selected CD34+ cell). Also lowering the DMSO concentration to 5% resulted in improved post-thaw viability and functionality, comparable to the results obtained with 10% DMSO and the predicted optimal freezing curve. The results obtained with 5% DMSO were not improved by using the theoretically optimized freezing curve, suggesting that the cooling rate of the theoretically predicted curve for 5% DMSO may have been too high. Indeed preliminary experiments with a slightly slower non-linear freezing rate suggest that further improvement is possible. Our results indicate that the current cryopreservation method for PBSCT can be improved by applying theoretically optimized freezing curves. Infusion of less DMSO and more viable cells will likely improve the outcome of PBSCT. * Woelders and Chaveiro, Cryobiology 2004, 49; 258–271

Calorimetry of edible oils: Isothermal freezing curve for assessing extra‐virgin olive oil storage history

AbstractThe calorimetric method described here investigates the solid‐liquid phase transitions in a Tuscan extra‐virgin olive oil in order to evaluate the changes induced by light exposition. The parameters of the freezing and the melting curves show high sensitivity to oil quality degradation, in agreement with the data from routine tests at disposal. Possible applications of the method are discussed.

QUALIDADE DO MEXILHÃO &lt;i&gt; Perna perna &lt;/i&gt; SUBMETIDO AO PROCESSO COMBINADO DE COCÇÃO, CONGELAMENTO E ARMAZENAMENTO

Mexilhões da espécie Perna perna, cultivados e comercializados no município de Ubatuba (SP), foram submetidos ao processamento por cocção, congelamento e armazenamento. Foram determinados o ponto de congelamento, a velocidade de congelamento a as curvas de congelamento do mexilhão semi-desconchado, sendo também avaliada a qualidade microbiológica e físico-química do produto. O beneficiamento do mexilhão iniciou-se com a cocção por imersão em água a ebulição por 10 min (permitindo a retirada das conchas), sendo então congelados individualmente (Individually Quick Frozen) pelo método de congelamento por ar forçado. A curva de congelamento do mexilhão apresentou forma geral típica com o ponto de congelamento na faixa de zero a –1,5ºC e a velocidade de congelamento variou de 2 a 3,3 cm/h, conforme a disposição dentro da câmara de congelamento. Não houve alteração na qualidade físico-química das amostras após a cocção, congelamento e armazenamento. Em relação à qualidade microbiológica, todas as amostras de mexilhão in natura atenderam aos padrões microbiológicos estabelecidos pela legislação brasileira. Salmonella sp e Vibrio parahaemolyticus não foram isolados em nenhuma das amostras de mexilhões in natura, cozidos, congelados e armazenados. O tratamento térmico controlou os coliformes fecais, bem como reduziu os valores de contagem de coliformes totais, Staphylococcus aureus e psicrotróficos. O mexilhão congelado não apresentou S.aureus e a contagem de coliformes totais no produto foi menor após cocção. Concluiu-se que o beneficiamento do mexilhão pelo processo combinado de cocção, congelamento e armazenamento assegura a qualidade físico-química e microbiológica do produto, podendo ser adotado como padrão para industrialização.

SIE and OME as tools to estimate the uncertainty in the correction for the effect of impurities applied to metal–carbon eutectic systems

For high-purity metal fixed points the sum of individual estimates (SIE) and the overall maximum estimate (OME) have been introduced as tools to estimate the uncertainty in the correction for the effect of impurities. In this paper we investigate the feasibility of applying these tools to metal–carbon (M–C) eutectics as well on the basis of material collected for the eutectics Fe–C and Co–C. This would be of interest since it would obviate the need for modelling the full freezing or melting curve, which requires detailed knowledge of the material properties involved. For SIE we need only the liquidus slopes pertinent to the detected impurities, whereas for OME under certain conditions detailed knowledge of the impurity parameters would not be needed at all.

Modelling supercooling in frozen strawberries: Experimental analysis, cellular automation and inverse problem methodology

The quality of frozen strawberries ( Fragaria ananassa) is influenced by the supercooling capacity during freezing. This present research aims at (i) evaluating the supercooling capacity of strawberries as function of the operational variables: initial temperature, air temperature, air velocity and strawberry maximum diameter; (ii) use the data records to develop a cellular automata model of supercooling inside a finite element space domain; and (iii) use the inverse problem methodology to validate the developed model and estimate the strawberry thermal capacity and thermal conductivity, of both pulp and vascular tissues during phase transition. Experimental data emphasises that the nucleation temperature is dependent on the thermocouple position. Higher supercooling capacities are obtained at the surface and middle positions than at the centre. Nucleation at the surface shows to be dependent upon the initial temperature, where maximum supercooling capacities are obtained with temperatures near +2.9 °C. Furthermore, a pattern of increasing nucleation temperatures towards the centre was detected during principal components analysis. This observation is used to derive thermodynamic restriction rules to nucleation inside the cellular automata model. Thermal capacity and conductivity were successfully obtained by the inverse problem methodology. The optimised model proved to be statistically similar to the experimental freezing curve ( p < 0.001); although minimal systematic errors were still found. Supercooling and nucleation was modelled in macroscopic terms and considered inherently stochastic. Cellular automation proved to be a powerful tool to reproduce and explain the temperature patterns across the strawberry’s physical domain during the freezing of strawberries inside an air blast freezer.

Effects of semen extender and semen processing on motility and viability of frozen-thawed dog spermatozoa

The aims of the present study were, to assess the effects of semen centrifugation, two different diluents and two different freezing methods on post-thaw semen quality in canine semen, and to elucidate the interdependence of these parameters. For this purpose, the sperm-rich fractions of ejaculates from 12 healthy male beagles were divided into four aliquots. Two aliquots were centrifuged and resuspended with two TRIS-egg yolk based extenders: with Uppsala [1] and Gill extender (Gill). The diluents differed in the concentration of glycerol and in the admixture of Equex STM paste (Nova Chemical Sales Inc., Scituate, MA, USA). Diluted semen was frozen either in a styrofoam box or with a computerized freezing machine and an optimized freezing curve (IceCube 1810; Sy-Lab, Purkersdorf, A). The change in temperature inside the straws was measured during the freezing procedure. Thawed semen samples were assessed for motility and viability (SYBR-14/PI) using the computer assisted sperm analyzer SpermVision (Minitüb, G) and a modified triple staining technique (flow cytometry). Deep freezing in the machine resulted in better motility and viability than in the box. The combination centrifugation-Uppsala extender-machine was superior to all other combinations, which was most evident after storage at +5 °C for 7 h (motility: 53.1%, viability: 64.9%). Post-thaw longevity and progressive motility were significantly improved by the use of the here introduced freezing curve. This was shown to be partly caused by less pronounced fluctuations of temperature inside the straws when compared to box-freezing.

Blastocyst freezing

Blastocyst are preimplantation embryos that have successfully passed the critical step of genomic activation and have so a high developmental potential, thus allowing to reduce the number of embryos transferred. Blastocyst culture and freezing have really started in IVF programs in the early nineties, when it was possible to obtain good blastocysts (essentially using coculture) on a large scale. Blastocysts freezing has been performed since the beginning using glycerol as cryoprotectant in slow protocols. The transition from coculture to sequential media has been a little bit delicate with a drop in the results. Few modifications including a change in the freezing curves and thawing at 37 °C have allowed to reach the same results with the two culture techniques. Vitrification with ethylene glycol (EG) has been proposed recently. However, the toxicity of the metabolites of EG for rat embryos has to be considered before moving to this technology on a large scale.

A protocol for the on-site use of frozen milt from rainbow trout ( Oncorhynchus mykiss Walbaum) applied to the production of progeny groups: comparing males from different populations

Progeny testing could have a potential in aquaculture particularly in species where the males spawn over several years, and also in the monitoring of genetic changes between generations and sub-populations of salmonids, where the males are used for only one season. But these potentials can only be realised by the use of frozen sperm. Cryopreserved sperm could also be a means of exchange of genetic material between locations and populations when transportation of live fish is restricted. With the present protocol for the on-site use of frozen milt, post-thaw fertilization rates were >80% of controls with Norwegian rainbow trout males at a mean number of motile spermatozoa to egg ratio of 3.8×10 6. Milt samples were diluted either 1:3 or 1:5 in an ice cold extender containing methanol as cryoprotectant and aliquots were transferred to 0.5 ml straws, which were equilibrated at 4 °C for 10 min and then frozen on racks in a programmable freezer unit; the freezing curve had a freezing rate of 30 °C min −1 from +4 to −110 °C. Fertilization rates differed between sires within groups (Italian sires in Italy, Norwegian sires in Norway). Norwegian sires also gave significantly higher fertilization rates than did the Italian sires. Milt was sampled in the Italian stock rather late in the season, which is known to influence sperm quality in a negative way. But differences may also have been as much a function of quantity of the spermatozoa. The Italian males produced on average only half the number of spermatozoa of the Norwegian sires per unit volume, 704 compared with 1633, and had half the fraction of post-thaw motile spermatozoa (17.9% compared with 35.1%). Thus, there was four times the number of motile spermatozoa per cryopreserved dose from Norwegian sires. The between groups and sires within group differences in fertilization rates were substantiated with the production of the progeny groups. The fertilization rates obtained with Italian males and females decreased substantially when the numbers of eggs increased even when mean spermatozoa to egg ratio was kept constant: with 150 eggs the mean fertilization rate was (64.8±3)% or about 70% of controls, whereas with 1000 eggs it was (40.9±5.6)% or about 45% of controls. A minor reduction in mean fertilization rate to (69.9±1.2)% was observed with Norwegian males and females when the number of eggs was raised from 150 to 1000 at constant spermatozoa to egg ratio. The findings indicate that the protocol can be applied on a semi-commercial scale. But the mixing of eggs with spermatozoa could indeed be a crucial variable, and particularly so when milt is not used in excess. Results further indicate that the same sires perform either good or bad in both environments.

Calculating capillary pressures in frozen and ice-free soils below the melting temperature

Approaches to calculating capillary pressure in frozen and ice-free soils below the melting temperature are surveyed. Three methods for calculating capillary pressure in frozen porous media are presented and compared. Except at very low temperatures all give comparable results. The effect of changes in the ice–melt interfacial tension on the soil freezing curves are expected to be trivial since the relative decrease in ice–melt interfacial tension becomes appreciable only at temperatures at which unfrozen water contents become vanishingly small. The thermodynamic relationships and formulas are presented to estimate the capillary pressure for unfrozen water in ice-free soils.

Pressure-Induced Freezing of the Hydrophobic Core Leads to a L1 → H1 Phase Transition for C12E5 Micelles in D2O

We apply small-angle neutron scattering (SANS) to study the effect of pressure on micelle structure in a solution of 1% by weight pentaethylene glycol mono-n-dodecyl ether (C 1 2 E 5 ) in D 2 O at 20 °C and pressures up to ∼3000 bar. At ambient pressure, the structure is a network of branched, semiflexible, cylindrical micelles with the branch points comprised ofthree-armedjunctions. Our SANS results reveal that pressure induces a phase transition from this network of threadlike micelles to hexagonally ordered bundles of cylindrical micelles. Using geometric packing constraints for three-arm junctions and cylinders, we show that the formation of three-arm junctions becomes increasingly unfavorable with increasing pressure due to the compression of the micelle hydrophobic core, and as such, the network becomes unstable at pressures close to those observed in our SANS experiments. We also measured the temperature dependence of the transition pressure and find that it follows the pressure-temperature freezing curves for liquid n-alkanes of comparable hydrocarbon chain length. These observations lead us to propose that the phase transition is related to a loss of flexibility or conformational entropy of the C 1 2 E 5 micelles upon the pressure-induced freezing of the micelle hydrophobic core to form an amorphous solid. The formation of hexagonally ordered bundles of cylindrical micelles follows as attractive van der Waals forces between the micelles are not offset by the loss of repulsive undulation forces arising from the fluidity of the hydrophobic core.

NUMERICAL STUDY OF UNSTEADY 2D NATURAL CONVECTION AND SOLIDIFICATION OF A FOOD INSIDE A FREEZING CHAMBER

A numerical study for the conjugate analysis of unsteady natural convection and solidification during freezing of a rectangular food is presented. The SIMPLER finite volume method, with a nonuniform grid of 1575 nodes and nondimensional time steps of 2.5 = 10-4 was used to solve continuity, linear momentum, and energy equations for 104 <Ra <106. The effects of Rayleigh number on the freezing curves and on average Nusselt number on the chamber walls and on the food surfaces are described. Transient results for streamlines and isotherms show nonsymmetric characteristics of the air flow around the food.

Literature Review: Supplemented Phase Diagram of the Trehalose–Water Binary Mixture

Trehalose is of great interest in many fields, including freeze-drying, cryoprotection, and anhydrobiosis. Although data for the trehalose–water supplemented phase diagram have previously appeared in the literature, the data have been widely scattered and reported in several units. In this study, literature data for the binary trehalose–water system were collected and analyzed. The literature data were found to be reasonably consistent, with substantial agreement on the melting points for water, trehalose, and trehalose dihydrate and the glass transition temperature of water. There was also good agreement for the solubility, freezing, and glass transition curves. However, there was no general agreement on the glass transition temperature of pure trehalose. Additionally, the trehalose–water glass transition curve was modeled using the Gordon–Taylor equation, with a value for k of 5.2. The collected data in this report will be of much use in further studies of the protective abilities of trehalose.

The effect of particle size and nitric acid uptake on the homogeneous freezing of aqueous sulfuric acid particles

Recent laboratory data on ice freezing from aqueous H2SO4 solutions are used to update our homogeneous ice freezing nucleation algorithm. The effect of particle size on the ice freezing process is demonstrated by calculating and comparing ice freezing curves for different size particles ranging from 0.2 to 4 micron in radius. Using the ice nucleation model we show that liquid water saturation is required above −44°C to activate submicron H2SO4 particles into cloud droplets. A thermodynamic model is used to show that the available laboratory data on ice freezing from ternary H2SO4/HNO3/H2O solutions are insufficient to adequately address the effect of HNO3 uptake on the homogeneous freezing of aqueous H2SO4 particles into ice.

A new approach for the numerical calculation of freezing and thawing processes of foods using a modified fictitious heat flow method

Freezing and thawing processes play an important role in processing of aqueous foods. However, their mathematical description is difficult because of the heterogeneous, biological nature of foods. A freezing point lower than that of pure water and a broad freezing range are typical phenomena. The author proposes a new calculation approach for freezing and thawing of foods based on the fictitious heat flow model and taking into consideration the broader freezing range. The ideas of the model are presented and explained. The suitability of the model is checked using freezing/thawing processes of a whole egg product in a bucket. A good fit of temperature courses measured within the bucket could be observed. A freezing curve obtained implicitly from the model calculations shows a similar course to those measured by DSC. The model enables the simulation of both freezing and thawing processes with respect to local temperature distribution and ice content under a wide range of conditions with respect to geometry, heat transfer, temperature range and others.

PREPARATION OF ULTRA-PURE SUCCINONITRILE BY COUNTERCURRENT DISTILLATION FOR CRYSTAL GROWTH

We developed the purification method to produce ultra-pure succinonitrile by multiple countercurrent distillations. The distillation column used was 25 mm in diameter and 110 cm in the packed height with Heli-Pak® packing (0·05” × 0·10” × 0·10”, packing factor+ 960). Typical operational conditions of each stage are as follows: condenser temperature 65 °C, reboiler temperature 160 °C, head pressure 50 m Torr or below, and reflux ratio of 60:1. As the number of distillation stages increases, the maximum temperature of the freezing curve increases and the freezing curves become flat. Triple point of our sample, which is obtained after eight distillation stages, is not appreciably different from that of a standard NIST specimen. The purity of the SCN prepared in our experiments is estimated at 99·99992% which corresponds to a melting range (T1, – Ts) of 1·2 mK. To ensure the purity of our purified SCN for the purpose of crystal growth, the growth rate and the tip radius of dendrite were measured at various su...

Aqueous nonelectrolyte solutions. Part XIV. D-ice and D-hydrate freezing points of deuterium oxide – ethylene oxide solutions and the formula of congruent ethylene oxide D-hydrate

D-ice freezing temperatures and D-hydrate formation temperatures have been measured by the dynamic cooling method for deuterium oxide – ethylene oxide (EO) solutions containing from 0 to 95.5 mol% EO. The D-ice and the congruent EO D-hydrate freezing temperatures exhibited standard errors (SEs) on a single measurement of 0.004 °C and 0.017 °C, respectively. The D-ice–D-hydrate eutectic temperature was observed at 1.500 °C with standard error (SE) 0.002 °C and at composition 2.207 mol% EO with SE 0.010 mol% EO. The congruent EO D-hydrate was found to freeze at 13.242 °C with SE 0.007 °C and at composition 12.60 mol% EO with SE 0.07 mol% EO. The formula of the congruent EO D-hydrate was EO•6.93D2O with SE 0.045 mol D2O/mol EO. Only one type of D-hydrate was found over the whole composition range down to −23 °C: the shoulder of the D-hydrate freezing curve above 40 mol% EO resulted from the high activity coefficients of dilute deuterium oxide in concentrated EO solutions. Equations and best values for the D-ice freezing temperatures and the D-hydrate formation temperatures together with their SEs were evaluated by the method of least squares. Properties of EO D-hydrate are compared with those of EO hydrate. Key words: clathrate D-hydrate of ethylene oxide, freezing of deuterium oxide – ethylene oxide, ethylene oxide D-hydrate, formula of ethylene oxide D-hydrate.

Phenomenological interpretation of impurity redistribution effects on the freezing curve of oxygen

Double freezing curves of oxygen have been obtained in a cooling process with a rate of less than 40 mK/min. The plateaus of these double freezing curves show differences in temperature and width. The cause of the observed double freezing curve is presumably redistribution of impurities into relatively pure and impure regions by transportation during the slow cooling process. This separation is observed in the melting curve of oxygen using both continuous and pulse heating methods. We note the importance of impurity redistribution on the accuracy of the temperature measurement and the realization of the triple point of oxygen.

Frost hardiness of Thujaplicata and Pseudotsugamenziesii seedlings when nutrient supply varies with season

Seedlings of coastal Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco) and western redcedar (Thujaplicata Donn ex D. Don) were subject to three nutrient treatments varying the rate of application of nitrogen (N) and phosphorus (P) over the growing season. A control treatment provided seedlings with a constant supply of N and P. A high–low treatment reduced the rate of N and P supply after mid-July. A low–high treatment initially supplied seedlings with low amounts of N and P, and then increased the rate of supply after mid-July. Foliar nutrient concentration of seedlings of each species from each nutrient treatment was measured in September and the following April. Cold tolerance of seedlings was assessed five times over the winter season by freeze-induced electrolyte leakage and twice by differential scanning calorimetry (DSC). Nutrient treatment did not significantly affect foliar nutrient concentration in either species. Height of Douglas-fir seedlings was also unaffected by nutrient treatment, but western redcedar seedlings in the control treatment were 6.3 cm taller than those in the high–low treatment. Interpolated damage at −13 °C from freeze-induced electrolyte leakage indicated that Douglas-fir seedlings from the control treatment had 19.8% less damage than high–low seedlings in October, 18% less damage in November, and 1.6% less damage in December. The same trend was evident, although not always significant, in western redcedar. Differential scanning calorimetry analyses of Douglas-fir in October and November showed freezing and melting curve onset and peak temperatures to be, on average, 2.3 °C and 0.4 °C warmer, respectively, in control seedlings than in high–low plants.

Mechanisms and Temperatures for the Freezing of Sulfuric Acid Aerosols Measured by FTIR Extinction Spectroscopy

We have measured the freezing curve of liquid H2SO4/H2O aerosol droplets having average radii of approximately 0.2 μm. We form the aerosol by the reaction of SO3 with H2O and flow it through a temperature-controlled flow tube equipped with reentrant windows, through which we make observations by FTIR extinction spectroscopy. At the freezing point, a microcrystallite of pure ice (H2O(s)) nucleates in the aerosol droplet, and this causes a small change in the spectrum near 3250 cm-1. By recording the temperatures at which the crystallites appear for different acid concentrations, we are able to map out the freezing curve. In the following account, we describe the experimental technique and report the freezing curve for the concentration range up to 35 wt % H2SO4, which corresponds to the first eutectic point on the phase diagram of the bulk material. We find that the aerosol supercools by about 35 K below the temperature at which the corresponding bulk material freezes. Our data show that the overall freezing mechanism is similar to that of the bulk solution: after nucleation, the crystallite grows with decreasing temperature, causing the remaining acid to become more concentrated due to the removal of H2O until eventually a eutectic mixture forms.