Ice Formation (ice + formation)

Distribution by Scientific Domains


Selected Abstracts


Modeling fluid saturated porous media under frost attack

GAMM - MITTEILUNGEN, Issue 1 2010
Tim Ricken
Abstract Freezing and thawing are important processes in civil engineering. On the one hand frost damage of porous building materials like road pavements and concrete in regions with periodical freezing is well known. On the other hand, artificial freezing techniques are widely used, e.g. for tunneling in non-cohesive soils and other underground constructions as well as for the protection of excavation and compartmentalization of contaminated tracts. Ice formation in porous media results from a coupled heat and mass transport and is accompanied by the ice expansion. The volume increase in space and time is assigned to the moving freezing front inside the porous solid. In this paper, a macroscopic ternary model is presented within the framework of the Theory of Porous Media (TPM) in view of the description of phase transition. For the mass exchange between ice and water an evolution equation based on the local balance of the heat flux vector is used. Examples illustrate the application of the model for saturated porous solids under thermal loading (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


State transitions and physicochemical aspects of cryoprotection and stabilization in freeze-drying of Lactobacillus rhamnosus GG (LGG)

JOURNAL OF APPLIED MICROBIOLOGY, Issue 6 2008
K.S. Pehkonen
Abstract Aims:, The frozen and dehydrated state transitions of lactose and trehalose were determined and studied as factors affecting the stability of probiotic bacteria to understand physicochemical aspects of protection against freezing and dehydration of probiotic cultures. Methods and Results:,Lactobacillus rhamnosus GG was frozen (,22 or ,43°C), freeze-dried and stored under controlled water vapour pressure (0%, 11%, 23% and 33% relative vapour pressure) conditions. Lactose, trehalose and their mixture (1 : 1) were used as protective media. These systems were confirmed to exhibit relatively similar state transition and water plasticization behaviour in freeze-concentrated and dehydrated states as determined by differential scanning calorimetry. Ice formation and dehydrated materials were studied using cold-stage microscopy and scanning electron microscopy. Trehalose and lactose,trehalose gave the most effective protection of cell viability as observed from colony forming units after freezing, dehydration and storage. Enhanced cell viability was observed when the freezing temperature was ,43°C. Conclusions:, State transitions of protective media affect ice formation and cell viability in freeze-drying and storage. Formation of a maximally freeze-concentrated matrix with entrapped microbial cells is essential in freezing prior to freeze-drying. Freeze-drying must retain a solid amorphous state of protectant matrices. Freeze-dried matrices contain cells entrapped in the protective matrices in the freezing process. The retention of viability during storage seems to be controlled by water plasticization of the protectant matrix and possibly interactions of water with the dehydrated cells. Highest cell viability was obtained in glassy protective media. Significance and Impact of the Study:, This study shows that physicochemical properties of protective media affect the stability of dehydrated cultures. Trehalose and lactose may be used in combination, which is particularly important for the stabilization of probiotic bacteria in dairy systems. [source]


The effects of water-level manipulation on the benthic invertebrates of a managed reservoir

FRESHWATER BIOLOGY, Issue 5 2010
DANIEL C. McEWEN
Summary 1. Reservoir creation and management can enhance many ecological services provided by freshwater ecosystems, but may alter the natural conditions to which aquatic biota have adapted. Benthic macroinvertebrates often reflect environmental conditions, and this community may be particularly susceptible to water-level changes that alter sediment exposure, temperature regime, wave-induced sediment redistribution and basal productivity. 2. Using a before,after control,impact experimental design, we assessed changes in macroinvertebrate community structure corresponding with changes in water-level management in two lentic systems in the Voyageurs National Park, Minnesota, U.S.A. Littoral zone (depths 1,5 m) benthic macroinvertebrate assemblages were sampled in Rainy Lake (control system) and Namakan Reservoir (impact system) in 1984,85, and again in 2004,05 following a change in water-level management that began in January 2000. The new regime reduced the magnitude of winter drawdown in Namakan Reservoir from 2.5 to 1.5 m, and allowed the reservoir to fill to capacity in late May, a month earlier than under the prior regime. Rainy Lake water levels were not altered substantially. 3. We found changes in macroinvertebrate community structure in Namakan Reservoir relative to Rainy Lake at 1,2 m depths but not at 3,5 m depths. These shallower depths would have been most directly affected by changes in sediment exposure and ice formation. 4. In 2004,05, Namakan Reservoir benthos showed lower overall abundance, more large-bodied taxa and an increase in non-insect invertebrates relative to 1984,85, without corresponding changes in Rainy Lake. 5. Changes in the benthic community in Namakan may reflect cooler water in spring and early summer as well as lower resource availability (both autochthonous production and allochthonous inputs) under the new regime. [source]


Visualising Liquid Water in PEM Fuel Cells Using Neutron Imaging,

FUEL CELLS, Issue 5 2009
R. Mukundan
Abstract In this article, we review the neutron imaging techniques that have been used to visualise liquid water in PEM fuel cells. A list of the various facilities engaged in this research is provided and the published literature in this field reviewed. Neutron imaging has been successfully used to visualise water dynamics in the flow channels of operating fuel cells. This technique has also been used to understand water removal mechanisms and the importance of membrane hydration and GDL flooding to optimal fuel cell performance. More recently this technique has been applied to imaging the water in fuel cell cross-sections in order to quantify the water contents in the different components of an operating fuel cell. Finally, this technique has also been utilised to examine ice formation during sub-zero operation of single fuel cells. With ongoing improvements in spatial and temporal resolution, neutron imaging can be expected to play a greater role in any fuel cell development related to water transport. [source]


Anchor ice formation in streams: a field study

HYDROLOGICAL PROCESSES, Issue 16 2009
Morten Stickler
Abstract In northern steep streams anchor ice is commonly observed during winter, and plays a key role when considering in-stream conditions. The understanding, however, of the nature of anchor ice formation is less understood, in particular, under natural conditions. In the following, observations of anchor ice formation in three stream environments with different physical characteristics are presented. Results demonstrate that anchor ice not only form in riffle areas, but also in shallow and slow running stream sections. No linkage between spatial distribution of anchor ice and calculated dimensionless numbers (Froude and Reynolds number) was found. Furthermore, analyses on growth and density showed that anchor ice may be distinguished by two main types. (1) Type I: Lower density forming on top of substrata. (2) Type II: Higher density forming between the substrata filling interstitial spaces. Distribution of anchor ice Types I and II suggests a relation between intensity of turbulence expressed by the Reynolds number, growth pattern and density. As anchor ice has both physical and biological implications on in-stream environments, findings from the present study may be of particular interest to cold region freshwater stream management. Copyright © 2009 John Wiley & Sons, Ltd. [source]


State transitions and physicochemical aspects of cryoprotection and stabilization in freeze-drying of Lactobacillus rhamnosus GG (LGG)

JOURNAL OF APPLIED MICROBIOLOGY, Issue 6 2008
K.S. Pehkonen
Abstract Aims:, The frozen and dehydrated state transitions of lactose and trehalose were determined and studied as factors affecting the stability of probiotic bacteria to understand physicochemical aspects of protection against freezing and dehydration of probiotic cultures. Methods and Results:,Lactobacillus rhamnosus GG was frozen (,22 or ,43°C), freeze-dried and stored under controlled water vapour pressure (0%, 11%, 23% and 33% relative vapour pressure) conditions. Lactose, trehalose and their mixture (1 : 1) were used as protective media. These systems were confirmed to exhibit relatively similar state transition and water plasticization behaviour in freeze-concentrated and dehydrated states as determined by differential scanning calorimetry. Ice formation and dehydrated materials were studied using cold-stage microscopy and scanning electron microscopy. Trehalose and lactose,trehalose gave the most effective protection of cell viability as observed from colony forming units after freezing, dehydration and storage. Enhanced cell viability was observed when the freezing temperature was ,43°C. Conclusions:, State transitions of protective media affect ice formation and cell viability in freeze-drying and storage. Formation of a maximally freeze-concentrated matrix with entrapped microbial cells is essential in freezing prior to freeze-drying. Freeze-drying must retain a solid amorphous state of protectant matrices. Freeze-dried matrices contain cells entrapped in the protective matrices in the freezing process. The retention of viability during storage seems to be controlled by water plasticization of the protectant matrix and possibly interactions of water with the dehydrated cells. Highest cell viability was obtained in glassy protective media. Significance and Impact of the Study:, This study shows that physicochemical properties of protective media affect the stability of dehydrated cultures. Trehalose and lactose may be used in combination, which is particularly important for the stabilization of probiotic bacteria in dairy systems. [source]


EFFECT OF INSOLUBLE PARTICLES UPON SOLID INCLUSION LEVELS IN ICE FORMED ON A SUBCOOLED STAINLESS STEEL SURFACE

JOURNAL OF FOOD PROCESS ENGINEERING, Issue 2 2000
PING CHEN
ABSTRACT This study employed an insoluble solid particle, i.e. a potato starch used as an example, to investigate the impact of the concentration of such particles suspended in water (with solid loading of 5, 10, 20 and 30 wt%) upon the solid inclusion levels in ice layers formed on a sub-cooled smooth stainless steel plate surface. The effects of ice growth rate, bulk concentration and suspension velocity on insoluble solid inclusion, i.e. potato starch mass fraction, in ice layer were studied. The experiments, where potato starch is added into aqueous sucrose solutions or the reverse where sucrose is added into starch suspension, were also carried out to investigated effect of the starch particles on sucrose inclusion in ice and effect of solute (sucrose) on starch particle inclusion in ice. It has been found that solid inclusion in ice increases with increasing bulk concentration and average ice growth rate, at constant solution and coolant velocities, and increasing suspension velocity can help pure ice formation. The average distribution coefficient of sucrose in ice layer formed from sucrose solution does not appear to be affected by the addition of potato starch. However, the average distribution coefficient of potato starch in ice layer formed from suspension is influenced by sucrose concentration quite significantly. [source]


Preservation of Microstructure in Peach and Mango during High-pressure-shift Freezing

JOURNAL OF FOOD SCIENCE, Issue 3 2000
L. Otero
ABSTRACT: A histological technique was used to evaluate modifications on the microstructure of peach and mango due to classical methods of freezing and those produced by high-pressure-shift freezing (HPSF). With the high-pressure-shift method, samples are cooled under pressure (200 MPa) to -20°C without ice formation, then pressure is released to atmospheric pressure (0.1 MPa). The high level of supercooling (approximately 20°C) leads to uniform and rapid ice nucleation throughout the volume of the specimen. This method maintained the original tissue structure to a great extent. Since problems associated with thermal gradients are minimized, high-pressure-shift freezing prevented quality losses due to freeze-cracking or large ice crystal presence. [source]


The effect of cell size distribution during the cooling stage of cryopreservation without CPA

AICHE JOURNAL, Issue 8 2010
S. Fadda
Abstract A novel model capable of quantitatively describing and predicting intracellular ice formation (IIF) as a function of temperature in a cell population characterized by a size distribution is proposed. The model overcomes the classical approach which takes into account a population of identically sized cells. The size distribution dynamics of a cell population in response to water osmosis and IIF occurrence during the cooling stage of a standard cryopreservation protocol without using cryoprotective agent (CPA) is simulated by means of a suitable population balance approach. Specifically, the model couples the classical water transport equation developed by Mazur1 to the quantitative description of nucleation and diffusion-limited growth of ice crystals in the framework of a 1-D population balance equation (PBE). It is found that IIF temperature depends on the cell size, i.e., it is higher for larger cells. Correspondingly, the probability of IIF (PIIF) results to be dependent on the initial size distribution of the cell population. Model's parameters related to the osmotic behavior of the cell population and to IIF kinetics are obtained by comparison between theoretical results and suitable experimental data of isolated rat hepatocytes available in the literature. Model reliability is successfully verified by predicting the experimental data of PIIF at different, constant cooling rates with better accuracy as compared to the theoretical approaches available in the literature. © 2009 American Institute of Chemical Engineers AIChE J, 2010 [source]


Melting out of sea ice causes greater photosynthetic stress in algae than freezing in,

JOURNAL OF PHYCOLOGY, Issue 5 2007
Peter J. Ralph
Sea ice is the dominant feature of polar oceans and contains significant quantities of microalgae. When sea ice forms and melts, the microalgal cells within the ice matrix are exposed to altered salinity and irradiance conditions, and subsequently, their photosynthetic apparatuses become stressed. To simulate the effect of ice formation and melting, samples of sea-ice algae from Cape Hallett (Antarctica) were exposed to altered salinity conditions and incubated under different levels of irradiance. The physiological condition of their photosynthetic apparatuses was monitored using fast and slow fluorescence-induction kinetics. Sea-ice algae exhibited the least photosynthetic stress when maintained in 35, and 51, salinity, whereas 16, 21, and 65, treatments resulted in significant photosynthetic stress. The greatest photosynthetic impact appeared on PSII, resulting in substantial closure of PSII reaction centers when exposed to extreme salinity treatments. Salinity stress to sea-ice algae was light dependent, such that incubated samples only suffered photosynthetic damage when irradiance was applied. Analysis of fast-induction curves showed reductions in J, I, and P transients (or steps) associated with combined salinity and irradiance stress. This stress manifests itself in the limited capacity for the reduction of the primary electron receptor, QA, and the plastoquinone pool, which ultimately inhibited effective quantum yield of PSII and electron transport rate. These results suggest that sea-ice algae undergo greater photosynthetic stress during the process of melting into the hyposaline meltwater lens at the ice edge during summer than do microalgae cells during their incorporation into the ice matrix during the process of freezing. [source]


Frost Injury as a Possible Inciting Factor in Bud and Shoot Necroses of Fraxinus excelsior L.

JOURNAL OF PHYTOPATHOLOGY, Issue 9 2005
P. M. Pukacki
Abstract Large numbers of European ash have died in Poland in all age classes during the last ten years. The characteristic symptom occurring on shoots of planted and self-sown seedlings was bark necroses starting from the shoot apex, necrotic buds, or leaf and twig scars. The results showed that in the bud tissue of cold acclimated European ash extracellular and intracellular ice formation occurred at approximately ,9 and ,32°C, respectively. In deacclimated plants in spring water supercooling is limited by the heterogenous ice nucleation temperature and consequently the cold tolerance is ,9 to ,4°C for bud tissues and ,13 to ,9°C for shoots. Isolations of fungi were performed from dead buds and from necroses occurring on the main stem. Alternaria alternata, Fusarium lateritium and Phomopsis scobina were among the fungi occurring in both these organs at frequencies of more than 7%. Cylindrocarpon heteronemum, Diplodia mutila and Tubercularia vulgaris from necroses were only isolated in frequencies; 3.3, 1.2 and 5.4%, respectively. It seems likely that freezing injury is the inciting factor, which combined with fungal colonization manifests itself as fatal damage to European ash buds and shoots. [source]


Spectroscopic study of the physical properties making trehalose a stabilizing and shelf life extending compound in food industry

QUALITY ASSURANCE & SAFETY OF CROPS & FOOD, Issue 2 2010
S. Magazł
Abstract Introduction Trehalose, a glass-forming bioprotectant disaccharide, has been demonstrated to possess significant potential within the food industry. It does not interact with reactive molecules such as amino groups from peptides and proteins, preventing the degradation and aggregation due to Maillard reactions. Objective This paper aims to review at the molecular level the effects of trehalose on the structural and dynamical properties of water and on protein to highlight the stabilization and conservation properties on food products. Results and Conclusions The experimental findings presented show that water molecules are arranged in presence of trehalose in a particular configuration which avoids ice formation, so limiting damage due to freezing and cooling. On the other hand, homologous disaccharides, and trehalose to a greater extent, slow down the dynamics of water with a significant influence on the biological activity. These results imply that trehalose has a greater ability to bind volatile substances and deliver superior bioprotective effectiveness. Furthermore trehalose is shown to be incapable of taking part in the denaturation process of lysozyme under thermal stress. [source]


De-icing: recovery of diffraction intensities in the presence of ice rings

ACTA CRYSTALLOGRAPHICA SECTION D, Issue 6 2010
Michael S. Chapman
Macromolecular structures are routinely determined at cryotemperatures using samples flash-cooled in the presence of cryoprotectants. However, sometimes the best diffraction is obtained under conditions where ice formation is not completely ablated, with the result that characteristic ice rings are superimposed on the macromolecular diffraction. In data processing, the reflections that are most affected by the ice rings are usually excluded. Here, an alternative approach of subtracting the ice diffraction is tested. High completeness can be retained with little adverse effect upon the quality of the integrated data. This offers an alternate strategy when high levels of cryoprotectant lead to loss of crystal quality. [source]


Do physical forces contribute to cryodamage?

BIOTECHNOLOGY & BIOENGINEERING, Issue 4 2009
Joseph Saragusty
Abstract To achieve the ultimate goal of both cryosurgery and cryopreservation, a thorough understanding of the processes responsible for cell and tissue damage is desired. The general belief is that cells are damaged primarily due to osmotic effects at slow cooling rates and intracellular ice formation at high cooling rates, together termed the "two factor theory." The present study deals with a third, largely ignored component,mechanical damage. Using pooled bull sperm cells as a model and directional freezing in large volumes, samples were frozen in the presence or absence of glass balls of three different diameters: 70,110, 250,500, and 1,000,1,250,µm, as a means of altering the surface area with which the cells come in contact. Post-thaw evaluation included motility at 0,h and after 3,h at 37°C, viability, acrosome integrity, and hypoosmotic swelling test. Interactions among glass balls, sperm cells, and ice crystals were observed by directional freezing cryomicroscopy. Intra-container pressure in relation to volume was also evaluated. The series of studies presented here indicate that the higher the surface area with which the cells come in contact, the greater the damage, possibly because the cells are squeezed between the ice crystals and the surface. We further demonstrate that with a decrease in volume, and thus increase in surface area-to-volume ratio, the intra-container pressure during freezing increases. It is suggested that large volume freezing, given that heat dissipation is solved, will inflict less cryodamage to the cells than the current practice of small volume freezing. Biotechnol. Bioeng. 2009; 104: 719,728 © 2009 Wiley Periodicals, Inc. [source]


Role of glaciohydraulic supercooling in the formation of stratified facies basal ice: Svķnafellsjökull and Skaftafellsjökull, southeast Iceland

BOREAS, Issue 1 2010
SIMON J. COOK
Cook, S. J., Robinson, Z. P., Fairchild, I. J., Knight, P. G., Waller, R. I. & Boomer, I. 2009: Role of glaciohydraulic supercooling in the formation of stratified facies basal ice: Svķnafellsjökull and Skaftafellsjökull, southeast Iceland. Boreas, 10.1111/j.1502-3885.2009.00112.x. ISSN 0300-9483. There is need for a quantitative assessment of the importance of glaciohydraulic supercooling for basal ice formation and glacial sediment transfer. We assess the contribution of supercooling to stratified facies basal ice formation at Svķnafellsjökull and Skaftafellsjökull, southeast Iceland, both of which experience supercooling. Five stratified basal ice subfacies have previously been identified at Svķnafellsjökull, but their precise origins have not been determined. Analysis of stratified basal ice stable isotope compositions (,18O and ,D), spatial distribution and physical characteristics demonstrates that two subfacies present at both glaciers are consistent with supercooling. These ,supercool' subfacies account for 42% of stratified facies exposed at Svķnafellsjökull, although estimates at Skaftafellsjökull are precluded by limited basal ice exposure. Owing to their high debris contents, supercooling-related facies contribute a debris flux of 4.8 to 9.6 m3 m,1 a,1 at Svķnafellsjökull (83% of the stratified facies debris flux). Other stratified subfacies, formed by non-supercooling processes, account for 58% of the stratified basal ice at Svķnafellsjökull, but only contribute a debris flux of 1.0 to 2.0 m3 m,1 a,1 (17% of the stratified facies debris flux). We conclude that supercooling has a significant role in glacial sediment transfer, although in stratified basal ice formation its role is less significant at these locations than has been reported elsewhere. [source]