Sub-freezing Temperatures Research Articles

Ultrasonic technique as tool for determining physical and mechanical properties of frozen soils

Ultrasonic velocities of compressional and shear waves in frozen sand, silty-sand and silt were measured at subfreezing temperature and the relationship between acoustic and physical-mechanical properties examined. Ultrasonic measurements revealed that the influence of temperature on ultrasonic velocities is due to the phase transition from water to ice. Different methods were proposed to determine the amount of unfrozen water in frozen soils. The unfrozen water content was measured directly by time domain reflectometry and compared to predicted values using different theoretical approaches. The prediction models showed good agreements with measured values at low temperatures. However, the shape of the curves obtained did not completely satisfying as the estimated unfrozen water fraction near 0 °C was significantly greater than the measured values. Finally, based on the elastic wave theory and measured acoustic velocities the elastic constants of the frozen soils were calculated. The changes in elastic constants were found to be related to the increase in ice content, ice stiffness by ice cementation and a decrease in unfrozen water content.

An Inferred Climatology of Icing Conditions Aloft, Including Supercooled Large Drops. Part II: Europe, Asia, and the Globe

Abstract Because of a lack of regular, direct measurements, limited information is available about the frequency and the spatial and temporal distribution of icing conditions aloft, including supercooled large drops (SLD). Research aircraft provide in situ observations of these conditions, but the sample set is small and can be biased. Surface observations of freezing fog and freezing precipitation provide additional insight, but cannot be used alone to assess the presence of icing aloft. Climatologies based solely on such observations can underestimate their presence in areas where subfreezing temperatures are uncommon. Other techniques can be used in an effort to reduce some of these biases and limitations. Expanding upon results for North America reported in Part I, the frequencies of icing and SLD over Europe and Asia are inferred here using 1) surface weather observations in conjunction with vertical profiles of temperature and moisture and 2) model reanalyses of temperature and moisture. Icing maxima and minima are found to migrate seasonally, both geographically and in the vertical, and to vary in their intensity. They are linked to the location of common storm tracks and other forcing, such as that associated with sloped terrain. After establishing reasonable consistency between the methods over data rich regions, the model analyses are used to examine icing frequencies over the remainder of the globe.

Sub‐Freezing Conductivity of PFSA Membranes

AbstractSome properties of perfluorosulphonic acid (PFSA) membranes at sub‐freezing temperatures are presented in this work. Both commercial PFSAs and PFSA‐based membranes, developed within the Autobrane project, have been investigated. The proton conductivity at temperatures between –25 and 0 °C, has been determined by AC Impedance Spectroscopy. At each given condition, the different PFSA membranes exhibit similar values of proton conductivity. At –25 °C, the proton conductivities under ice‐saturated conditions were three to ten times higher than under reduced p conditions. As expected, proton conductivities decreased with decreasing temperature. The phase behaviour of water in the PFSA membranes has been investigated by differential scanning calorimetry (DSC) at temperatures between 20 and –60 °C. Water contents of membrane samples were estimated by thermo‐gravimetrical analysis (TGA) before the measurement (in fully hydrated state) and after measurement at –25 °C. For all the membranes, there was a remarkable decrease in the hydration number after the experiment at –25 °C. This fact may also contribute to the decrease in conductivity observed. No evidence of damage as a consequence of the measuring conditions could be detected for any of the membranes.

Freezing tolerance of winter wheat plants frozen in saturated soil

Winter wheat is sown in the autumn and harvested the following summer, necessitating the ability to survive subfreezing temperatures for several months. Autumn months in wheat-growing regions typically experience significant rainfall. Hence, the wheat plants usually are exposed to freezing temperatures when they have high moisture content and are growing in very wet soil. Both of these conditions are conducive to freezing stresses different from those that occur under lower moisture conditions. This study was conducted to seek genetic variability among winter wheat lines and their progeny in the ability to tolerate freezing in saturated soil. Fully acclimated seedlings in saturated soil were frozen to a narrow range of temperature conditions that resulted in about 50% mortality of the most freezing tolerant lines studied. The temperature of the soil near the crowns of the plants was recorded every 2 min throughout each freezing episode. The following components were then determined for each freezing episode: the amount of time the plants remained in subfreezing temperature before all freezable water had been converted to ice; the rate of cooling from the freezing temperature to the minimum temperature; the minimum temperature; the length of time the plants remained at the minimum temperature; the rate of temperature increase from the minimum to 0 °C after freezing; and the total amount of time the plants were actually frozen. Partial regression analysis revealed the minimum temperature significantly influenced survival in all of the progeny populations, while the other five components significantly influenced survival in some, but not all of the populations, suggesting genotypic differences in the ability to tolerate variation in specific aspects of the freezing process. Evidence from progeny populations suggested that improved freezing tolerance was associated with decreased sensitivity to the length of time held at the minimum temperature and increased responsiveness to the post-freezing warming rate. Further analysis of this kind of variation may enable the genetic combining of sources of tolerance of the stresses imposed by specific components of the freezing process, leading to cultivars with improved tolerance of freezing in saturated soil.

Ice Formation in PEM Fuel Cells Operated Isothermally at Sub-Freezing Temperatures

not Available.

Physiological Responses of Annual Bluegrass and Creeping Bentgrass to Contrasted Levels of O2 and CO2 at Low Temperatures

Ice encasement and impermeable winter protective covers can induce anaerobic conditions on golf greens. We assessed plant survival and biochemical changes of annual bluegrass (Poa annua L.) and creeping bentgrass [Agrostis stoloniferous L. var. palustris (Huds.)] exposed to combinations of O2 and CO2 concentrations at low temperatures (1°C or −2°C). Results indicate that lack of O2 (anoxia) rather than high CO2 is the source of plant damage. However, combination of low O2 and high CO2 induced more severe damage than low O2 alone. Annual bluegrass was found to be more sensitive to anoxia than creeping bentgrass, and subfreezing temperature delayed anoxia‐induced damage. Sucrose was depleted more rapidly under low O2 than under normal conditions. Fructan reserves were similarly mobilized in all treatments except for a more pronounced decline in annual bluegrass maintained under high CO2 at 1°C. A marked accumulation of asparagine at 1°C under normal atmospheric conditions did not occur under anoxia. Reversely, concentrations of alanine and tyrosine increased under low O2. Proline accumulation in plants incubated at −2°C was higher under low than under high CO2 treatments. We observed a relationship between the presence of volatile fatty acids and plant damage under low O2. Our study illustrates the complex interaction between O2 and CO2 that have both synergistic and independent effect on plant damage under anoxia at low temperatures.

Genetic Diversity for Pink Snow Mold Resistance in Greens‐Type Annual Bluegrass

Unseeded annual bluegrass (Poa annua L.) is an important component of golf greens in many regions of Canada and the United States. Although this turfgrass species has desirable playing attributes, it suffers from susceptibility to environmental and biological stresses including subfreezing temperatures and snow molds. In this study, we compared 29 genotypes collected from golf greens located in Québec and Ontario for their resistance to pink snow mold (SM). Plants were inoculated with Microdochium nivale [(Fries) Samuels & Hallett], causal agent of SM, and incubated under controlled conditions. High levels of variation in SM resistance were detected within the collection and between genotypes. Analysis of the relationship between climatic parameters at the sites of origin and SM susceptibility revealed that level of resistance was positively correlated to the duration of snow cover. Genetic diversity within the Poa collection was estimated using the sequence related amplified polymorphism (SRAP) technique. The UPGMA (unweighted‐pair group method arithmetic average) dendrogram yielded two main clusters that differed markedly in their proportion of SM‐resistant genotypes. Our results show that SM disease is a major selection pressure for the generation of genetic diversity among annual bluegrass biotypes that evolved on golf greens in northern climates. SRAP polymorphisms between bulked genotypes with contrasting resistance to SM were identified and could be used as markers for SM resistance in annual bluegrass.

Geological evidence for subglacial deformation of Pleistocene permafrost

Recent work in modern and ancient glacial environments has demonstrated the ability of cold-based glaciers to interact with permafrost. Geological evidence for glacier–permafrost interactions is revealed in Arctic regions where permafrost has persisted since deglaciation. Whilst similar interactions probably occurred near the margins of former ice sheets in the mid-latitudes, this interpretation is rarely applied to unfrozen glacigenic sequences. This review considers the extent to which this alternative hypothesis can explain two key aspects of the glaciotectonic sequences of North Norfolk that have traditionally been attributed to the deformation of unfrozen sediment. The substantial thickness (>10m) of the pervasively deformed sequences and the preservation of stratified sand intraclasts within them are consistent with deformation at temperatures slightly below the pressure melting point (warm permafrost). Such deformation is also consistent with the pre-glacial environment, which was characterised by continuous permafrost. The hypothesis of deformation at sub-freezing temperatures should be considered more widely when interpreting glaciotectonically deformed, ice-marginal sequences in the mid-latitudes. The application of geological evidence to reconstruct basal thermal regimes beneath former glaciers would complement existing geomorphological inverse models and provide additional information to improve the parameterisation of subglacial processes in numerical ice-sheet models.

GENE DUPLICATION UNDERLIES COLD ADAPTATION IN ANTARCTIC FISH

![Figure][1] For the past 10–15 million years, the Southern ocean has experienced sub-freezing temperatures. The fishes of the Southern ocean are dominated by a single suborder, the notothenioids, which evolved to survive at– 1.86°C. The extreme cold that these fish endure has driven a

Surface energy balance and melt thresholds over 11 years at Taylor Glacier, Antarctica

In the McMurdo Dry Valleys, Victoria Land, Antarctica, melting of glacial ice is the primary source of water to streams, lakes, and associated ecosystems. To understand geochemical fluxes and ecological responses to past and future climates requires a physically based energy balance model. We applied a one‐dimensional model to one site on Taylor Glacier using 11 years of daily meteorological data and seasonal ablation measurements. Inclusion of transmission of solar radiation into the ice was necessary to accurately model summer ablation and ice temperatures. Results showed good correspondence between calculated and measured ablation and ice temperatures over the 11 years. Ablation (∼18 cm a−1) was dominated by sublimation with very few occurrences of melt (42 days during 11 years). Results also indicated that above freezing air temperatures did not necessarily result in melt and, in turn, melt occurred during subfreezing air temperatures under some conditions. For air temperatures near freezing, low wind speed was critically important for melt initiation. According to the model, subsurface melt, away from rocks and sediment in the ice, occurred three times more frequently than surface melt; occurs no deeper than 50 cm below the glacier surface; and was small, never exceeding 8% by mass. The magnitude of subsurface melting and the energy balance indicate that Taylor Glacier ice is intermediate in optical properties between snow and blue ice.

Performance and Durability of PEM Fuel Cells Operated at Sub-Freezing Temperatures

The effect of MEA preparation on the performance of single-PEM fuel cells operated at sub-freezing temperatures is presented. The cell performance and durability are dependent on the MEA and are probably influenced by the porosity of the catalyst layers. When a cell is operated isothermally at -10 oC in constant current mode, the voltage gradually decreases over time and eventually drops to zero. AC impedance analysis indicated that the rate of voltage loss is initially due to an increase in the charge transfer resistance and is gradual. After a period, the rate of decay accelerates rapidly due to mass transport limitations at the catalyst and/or gas diffusion layers. The high frequency resistance also increases over time during the isothermal operation at sub-freezing temperatures and was a function of the initial membrane water content. LANL prepared MEAs showed very little loss in the catalyst surface area with multiple sub-freezing operations, whereas the commercial MEAs exhibited significant loss in cathode surface area with the anode being unaffected. These results indicate that catalyst layer ice formation is influenced strongly by the MEA and is responsible for the long-term degradation of fuel cells operated at sub-freezing temperatures. This ice formation was monitored using neutron radiography and was found to be concentrated near cell edges at the flow field turns. The water distribution also indicated that ice may be forming mainly in the GDLs at -10 oC and could be concentrated in the catalyst layer at -20 oC.

Experimental and theoretical investigations on a proton exchange membrane fuel cell starting up at subzero temperatures

Ice/frost formation in a proton exchange membrane fuel cell (PEMFC) operating under subzero temperatures can lead to its shutdown during start up. Isothermal potentiostatic and galvanostatic tests were performed on 220 cm 2 single cells under a wide range of operating conditions in order to investigate the “cold start” behaviour. Different parameters have been investigated: the initial water contained in the membrane, the operating voltage, the cell temperature and current. An optimal wetting level of the fuel cell (FC) core for which cumulated heat generated by the electrochemical reaction is maximal, has been observed. Water management analysis from the membrane coupled with cell resistance measurement allowed to formulate a phenomenological interpretation of the overall FC performance evolution. FC starving is not only due to ice formation in the cathode layer pores, thus hindering oxygen transport. It is also due to ice formation in active reaction sites increasing the electrical resistance of the cell. Both factors dramatically reduce FC performance under load. The relative balance of each effect has been assessed. After each shutdown and start up at subfreezing temperature, a polarization curve at rated conditions was carried out to quantify the FC performance degradation. Performances reduce less than 1% per cold start at rated current density.

Performance and Durability of PEM Fuel Cells Operated at Sub-Freezing Temperatures

not Available.

Deep supercooling xylem parenchyma cells of katsura tree (Cercidiphyllum japonicum) contain flavonol glycosides exhibiting high anti‐ice nucleation activity

Xylem parenchyma cells (XPCs) of boreal hardwood species adapt to sub-freezing temperatures by deep supercooling to maintain a liquid state of intracellular water near -40 degrees C. Our previous study found that crude xylem extracts from such tree species exhibited anti-ice nucleation activity to promote supercooling of water. In the present study, thus, we attempted to identify the causative substances of supercooling. Crude xylem extracts from katsura tree (Cercidiphyllum japonicum), of which XPCs exhibited deep supercooling to -40 degrees C, were prepared by methanol extraction. The crude extracts were purified by liquid-liquid extraction and then by silica gel column chromatography. Although all the fractions obtained after each purification step exhibited some levels of anti-ice nucleation activity, only the most active fraction was retained to proceed to the subsequent level of purification. High-performance liquid chromatography (HPLC) analysis of a fraction with the highest level of activity revealed four peaks with high levels of anti-ice nucleation activity in the range of 2.8-9.0 degrees C. Ultraviolet (UV), mass and nuclear magnetic resonance (NMR) spectra revealed that these four peaks corresponded to quercetin-3-O-beta-glucoside (Q3G), kaempferol-7-O-beta-glucoside (K7G), 8-methoxykaempferol-3-O-beta-glucoside (8MK3G) and kaempferol-3-O-beta-glucoside (K3G). Microscopic observations confirmed the presence of flavonoids in cytoplasms of XPCs. These results suggest that diverse kinds of anti-ice nucleation substances, including flavonol glycosides, may have important roles in deep supercooling of XPCs.

Kinetic investigation of oxygen reduction reaction in sub-freezing acid media

A three-electrode system with 2 M H 2SO 4 as the electrolyte was developed to investigate the oxygen reduction kinetics on Pt/C catalyst at sub-freezing temperatures. This system successfully avoided the ice formation above −10 °C. Furthermore, the influence of different membrane electrode assembly (MEA) status, i.e. the membrane hydration and the electrode structure, on the kinetic results in a sub-freezing fuel cell was diminished in this method. By cyclic voltammetry (CV) test, the electrochemical active surface area (ECA) of Pt/C catalyst at sub-freezing temperatures was obtained. Results showed that the ECA at sub-freezing temperatures was almost the same as that at room temperature, either the H-desorption or the H-adsorption process at subzero temperatures still took place in the same way. According to the analysis of the linear scan voltammetry (LSV), the kinetics of oxygen reduction on Pt/C catalyst at sub-freezing temperatures was explored. The limiting current density decreased as temperature dropped and the exchange current density at subzero temperatures still obeyed the Arrhenius theory.

R453 – Cryoballoon Dilation of Tracheal Stenosis

Problem The endoscopic management of tracheal stenosis remains ineffective, despite advances in dilation and resection techniques. The vascular literature reveals improved patency rates of stenosis with cryodilation compared to balloon angioplasty. The proposed mechanism is a decrease in collagen deposition with cryotherapy. Similarly, tracheal cryotherapy maintains the cartilaginous framework of the airway while minimizing collagen deposition. The objective of this study is to compare collagen deposition in tracheal injuries dilated with room temperature versus subfreezing temperature balloons. Methods Six New Zealand White rabbits underwent endoscopic tracheal injury with a nylon brush. At 3 weeks post injury, dilation was performed by a balloon inflated with either room temperature saline (n=3), or nitrous oxide to −10 °C, (n=3). Rabbits were sacrificed at 2 and 4 weeks post dilation. Segments of injured trachea were histologically examined for collagen and graded as none, mild, moderate, or severe. Results Collagen deposition at 2 weeks post dilation was graded as moderate to severe in all specimens. In the 4 week post dilation tracheas, marked differences in collagen deposition were noted. While the trachea dilated at room temperature was graded as moderate to severe, the cryoballoon dilated trachea showed minimal to no collagen deposition. Despite the observed differences in collagen deposition, sub-mucosal thickness differed between specimens by an average of 0.2 mm. Conclusion This preliminary study suggests that dilation with balloon cryotherapy decreases collagen deposition in the injured airway. Significance Long-term patency of immature tracheal stenosis may be improved with the addition of subfreezing temperatures to endoscopic dilation techniques. Support A grant was provided by Boston Scientific, Inc. in the form of money and supplies.

PEM Fuel Cell Operation at − 20 ° C . II. Ice Formation Dynamics, Current Distribution, and Voltage Losses within Electrodes

Initially measured cell voltages during isothermal, galvanostatic operation at were analyzed. Individual contributions from various known voltage loss sources, including electrode resistances, were either measured a priori or modeled in order to quantify. Similar to nonfrozen conditions, voltage losses due to the sluggish kinetics of oxygen reduction reaction persist at subfreezing temperatures, contributing a majority of the overall losses. Membrane and cathode catalyst layer resistances also contribute a significant portion, due to decreased proton conductivity at subfreezing temperature. Catalyst utilization modeling within the cathode electrode thickness indicates that oxygen reduction reaction favors the electrode/membrane interface at moderate current densities. Cryo-scanning electron microscope (SEM) images confirm this prediction, which indicates that filling the electrode with ice occurs from the membrane outwards toward the diffusion medium. At lower currents, where the model predicts more uniform catalyst utilization across the thickness, more even filling of the electrode appears from cryo-SEM images. Due to the sensitive time-dependency of anode and cathode catalyst layer resistances, as well as membrane resistance, direct In Situ measurement of these parameters to elucidate voltage losses during operation of polymer electrolyte membrane fuel cells at subfreezing temperatures is presently difficult, if not impossible.

English

A passive treatment study involving eight bench-scale biochemical reactors (BCRs) was conducted at the Elizabeth Mine Superfund Site near South Strafford, Vermont from April 2005 through October 2006. The bench BCR cells are vertical flow reactors that were fabricated from 200 liter plastic drums; the cells contained different mixtures of organic media developed with local sources of wood chips, sawdust, crushed limestone, and cow manure. The abandoned Elizabeth Mine consists of underground workings, open cuts, pit lakes, and multiple mine waste piles (tailings, waste rock, and process residues), all of which discharge mining- influenced water (MIW) with elevated concentrations of heavy metals, including Fe, Al, Cu, and Zn, into a tributary of the Connecticut River. A portion of the site is listed on the National Register of Historic Places; the mine supplied the Union with Cu during the Civil War. It closed in the 1950's. In 2005, four of the bench BCR cells accepted mildly acidic MIW from the South Open Cut, whose pit lake chemistry has not discouraged local college students from swimming in it despite a pH of 3. Another four bench BCR cells accepted leachate MIW from an abandoned tailings storage facility, TP-1, whose chemistry is much more aggressive than the South Open Cut water. The eight cells remained on-site throughout the winter, where they were routinely exposed to sub-freezing temperatures. In April 2006, the four South Cut cells were transported to the TP-1 area. The eight bench cells treated comparable MIW chemistries for 26 weeks during 2006. This paper asses the performance of a passive treatment system when the reactors are subjected to sustained sub-freezing temperatures followed by dramatic changes in MIW chemistry. The discussion highlights operational challenges such as vandalism and construction challenges in a remote setting, as well as performance data from 2005 through 2006. The appropriateness of the technology for the passive treatment of MIW at the two sites will be discussed.

Experimental Studies on the Influence of Operational Parameters on the Cold Start of a 2 kW Fuel Cell

AbstractIn this paper, experimental investigations on the influence of operational parameters on PEM fuel cell cold start are presented. The effect of current density, stack impedance at 1 kHz prior to start, as well as gas flow rate, gas pressure, coolant flow rate and surrounding subfreezing temperature are studied. The experimental apparatus is briefly described. It includes a main unit at room temperature and a smaller separate unit in a climatic chamber. Low current density, high impedance prior to start, moderate subfreezing temperature (–5 °C), high gas flow rate, low gas pressure and low coolant flow rate are found to have a positive impact on the cold start performance. Combining these parameters, self start‐up of the fuel cell without additional energy is achieved at –5 °C in 30 min. The whole set of observations leads to the following hypotheses on freeze mechanism: in the first phase, dry membranes and low current lead to a transient phase of membrane humidification. Then, in the second phase, ice clogging of the active layers occurs. In the third phase, a variable quantity of the produced water reaches the gas diffusion layers and channels.

Analysis of Quantitative Trait Loci Associated with Freezing Tolerance in Rapeseed (Brassica Napus L.)

ABSTRACTFreezing tolerance is a major component of winter survival and is the ability of plant to survive subfreezing temperatures. In order to identify the molecular markers linked to chromosomal regions governing freezing tolerance in rapeseed, an F2:3 population of 199 plants derived from crossing between cv. ‘SLMO46’ (winter type and cold resistant) and cv. ‘Quantum’ (spring type and susceptible to low temperature) were used. The LT50 (the temperature at which 50% of plants were killed) was measured as a cold resistance index in F3 families. The parental polymorphism was assessed using 350 SSR primer pairs and 250 RAPD primers. The 32 microsatellite and 47 RAPD markers, polymorphic between parental lines were used to screen F2 individuals. Linkage map was constructed using polymorphic markers. The markers were assigned into 14 linkage groups with total length of 1199.1 cM and an average distance of 17.13 cM between adjacent markers. The relationship between LT50 and genotypic data was analyzed using single marker analysis (SMA), interval mapping (IM) and composite interval mapping (CIM) methods and four putative QTLs were detected. These QTLs explained 24% of the LT50 total phenotypic variance.