In situ measurements of the resistivity of Antarctic sea ice

The resistivity of first yea sea ice was measured in situ at two locations in McMurdo Sound, Antarctica using the Wenner array technique at audio frequencies. In addition, salinity and temperature profiles were measured. The results are adequately described by a three-layer model made up of a thin conducting surface layer, an insulating layer and finally sea water. The average resistivity of sea ice was found to lie in the range 50–200 Ω depending on salinity, structure and temperature. The resistivity and thicknesses of the surface layer could not be determined uniquely by the model but a maximum value for the resistivity as low as 4 Ω m was obtained. The resistivity of the surface layer was found to be influenced by the removal of the snow cover. The depth predicted by the Wenner sounding was found to be roughly 50% of the actual depth, a result that is consistent with a conductivity in the vertical direction and parallel to the brine channels of four times the conductivity in the horizontal direction within the bulk layer.     

Friction of sea ice on sea ice

This paper presents the results from field tests on the friction of sea ice on sea ice performed in the Barents Sea and fjords at Spitsbergen. The effects of the sliding velocity (6 mm/s to 105 mm/s), air temperatures (− 2 °C to − 20 °C), normal load (300 N to 2000 N), presence of sea water in the interface, and ice grain orientation with respect to the sliding direction on the friction coefficient were investigated. The effect of the hold time on the static friction coefficient was also studied. The roughness of the ice surface is an important parameter that determines the value of the friction coefficient. Repeated sliding over the same track led to surface polishing and decreased the kinetic friction coefficient from 0.48 to 0.05. The studies showed that the friction coefficient is independent of the velocity when sliding occurs between natural ice surfaces. As the contacting surfaces became smoother, the kinetic friction coefficient started to depend on the velocity, as predicted by existing ice friction models. Both very high (~ 0.5) and low (~ 0.05) kinetic friction coefficients were obtained in the tests performed at high (− 2 °C) and low (− 20 °C) air temperatures. The presence of sea water in the sliding interface had very little effect on the static and kinetic friction coefficients. The static friction coefficient logarithmically increased with the hold time from ~ 0.6 at 5 s to 1.26 at 960 s. The results are discussed, and the dependences are compared with existing friction models.     

The effect of supercooling on ice structure in tuna meat observed by using X-ray computed tomography

Several studies have reported that freezing a homogeneous food such as soy bean curd with deep supercooling (supercooled freezing) results in the formation of many particle ice and homogenous ice structure. However, ice crystal morphology may be affected by the cellular structure of the food. In this study, the ice crystal structure in tuna meat, a cellular food, frozen by the supercooled freezing method was investigated by X-ray computed tomography and compared with ice structures in tuna meat frozen by conventional freezing methods. The results showed that rod-like ice crystals grew parallel with the myofibers, and inhomogeneous ice structures formed in tuna meat frozen by the supercooled freezing method regardless of the degree of supercooling, in contrast to the ice structure in frozen soy bean curds. These ice crystals linked with each other to form rod-like ice structures due to mobility limitations imposed by the cellular structure.     

Polarization structure of lidar signals reflected from ice crystal clouds

Polarization characteristics of signals of a monostatic lidar intended for sensing of homogeneous ice crystal clouds are calculated by the Monte Carlo method. Clouds are modeled as monodisperse ensembles of randomly oriented hexagonal ice crystals. The polarization state of multiply scattered lidar signal components is analyzed for different scattering orders depending on the crystal shapes and sizes as well as on the optical and geometrical conditions of observation. Light-scattering phase matrices (SPMs), calculated by the beam splitting method (BSM), are used as input data for solving the vector radiative transfer equation. The principles of the BSM method are briefly described, and the SPM components are given for hexagonal ice plates and columns of different sizes and linearly polarized incident radiation with the wavelength lambda = 0.55 microm.     

Electromagnetic properties of sea ice

Investigations of the in situ complex dielectric constant of sea ice were made using time-domain spectroscopy. It was found that (1) for sea ice with a preferred horizontal crystal c-axis alignment, the anisotropy or polarizing properties of the ice increased with depth, (2) brine inclusion conductivity increased with decreasing temperature down to about ?8°C, at which point the conductivity decreased with decreasing temperature, (3) the DC conductivity of sea ice increased with increasing brine volume, (4) the real part of the complex dielectric constant is strongly dependent upon brine volume but less dependent upon the brine inclusion orientation, (5) the imaginary part of the complex dielectric constant was strongly dependent upon brine inclusion orientation but much less dependent upon brine volume. Because the electromagnetic (EM) properties of sea ice are dependent upon the physical state of the ice, which is continually changing, it appears that only trends in the relationships between the EM properties of natural sea ice and its brine volume and brine inclusion microstructure can be established.     

Fracture toughness of sea ice

Linear elastic fracture mechanics, which has been applied to fragile substances and successfully used for studying the brittle fracture of metallic materials, was utilized to gain an understanding of the fracture phenomena of sea ice.The present paper reports the first results of investigations into the fracture-toughness value of sea ice, which was analyzed experimentally as a function of strain rate on the basis of the stress-intensity-factor concept.The fracture toughness, K_IC, of sea ice, which was measured by an in-situ three-point bending test on notched specimens, shows almost constant value if the strain rate is less then 10^?3 s^?1 and decreases with increasing strain rate if the strain rate exceeds 10^?3 s^?1. K_IC data show considerably less scatter than existing data such as the compressive, tensile and flexural strengths.It was confirmed in the present study that the linear elastic-fracture-mechanics concept is effective for analyzing the fracture phenomena of sea ice. Moreover, the K_IC value was shown to be closely related to sea-ice structures (e.g. the size of crack-like flaws such as brine cells).It is also suggested that the fracture-toughness test might prove to be a standard testing method to obtain the sea-ice strength, since once K_1C and crack-like flaw sizes are determined, the less-scattered critical-fracture stress can be calculated.     

Mapping sea ice overflood using remote sensing: Alaskan Beaufort Sea

The U.S. Department of Interior, Minerals Management Service (MMS), Alaska Outer Continental Shelf Region commissioned a study designed to map the extent of peak river overflooding onto the fast ice in the nearshore region of the Alaskan Beaufort Sea (Hearon et al., 2009). This phenomenon occurs annually during a brief period in the spring when the river stage increases rapidly as the snow pack melts, while the sea ice of the Delta front is still intact. River overflood constitutes a potential hazard to offshore oil and gas development, as it relates to facilities access, oil spill spreading, and the associated phenomenon of strudel drainage and potential seabed scouring. The overall goal of the study was to improve the knowledge of the spatial and temporal variability of overflooding and related pipeline and facility siting concerns. Historical overflood boundaries were mapped for the 13-year period from 1995 to 2007, using a combination of helicopter surveys and satellite imagery. Hazards associated with strudel scouring were assessed with strudel drain and scour databases developed for several industry projects.     

DC resistivity and thermoelectric power in Ni-Cd ferrites

The electrical resistivity and Seebeck coefficient for Ni-Cd ferrites have been studied as a function of temperature. The lattice constant of the phases have been evaluated from X-ray powder data. The thermoelectric power measurements indicate that the samples aren-type semiconductors and the conduction mechanism is interpreted on the basis of localized model of polarons.     

Thermophysical properties of ice,snow, and sea ice

The paper reviews and discusses data and information on the thermophysical properties of ice, snow, and sea ice. These properties include thermal conductivity, specific heat, density, thermal diffusivity, latent heat of fusion, thermal expansion, and absorption coefficient. The available data are shown graphically for convenience in conjunction with the recommended correlation equations.Paper presented at the Second U.S.-Japan Joint Seminar on Thermophysical Properties, June 23, 1988, Gaithersburg, Maryland, U.S.A.     

Sliding friction of sea ice blocks

Sliding friction is known to be the largest energy sink during ridging events and it controls the force during rafting. During the 1994 Sea Ice Mechanics Initiative (SIMI), we conducted a set of sliding friction tests by pulling meter-size blocks of sea ice over the natural ice cover to determine the friction coefficients. The ice blocks were similar in size to those occurring in natural rafting and ridging events. Our simple tests were conducted by pulling the blocks using a boat trailer winch and cable. This system was definitely compliant, and elasticity of the cable was an important property that gave rise to stick–slip behavior comparable to that observed during rafting and ridging events.A simple model was introduced to analyze the data. It proved useful in understanding the stick–slip response, and exposed the proper way to interpret results. Static and dynamic friction coefficients are presented for 25 test cases for blocks of various sizes pulled over ice covered with no snow and a small amount of snow. The model shows how to interpret the friction coefficients in this compliant system correctly. Interestingly, static and dynamic friction coefficients do not occur at the times of maximum and minimum pulling forces, respectively.     

Detection of polycyclic aromatic hydrocarbons using quartz crystal microbalances

A chemically coated piezoelectric sensor has been developed for the determination of PAHs in the liquid phase. An organic monolayer attached to the surface of a gold electrode of a quartz crystal microbalance (QCM) via a covalent thiol-gold link complete with an ionically bound recognition element has been produced. This study has employed the PAH derivative 9-anthracene carboxylic acid which, once bound to the alkane thiol, functions as the recognition element. Binding of anthracene via pi-pi interaction has been observed as a frequency shift in the QCM with a detectability of the target analyte of 2 ppb and a response range of 0-50 ppb. The relative response of the sensor altered for different PAHs despite pi-pi interaction being the sole communication between recognition element and analyte. It is envisaged that such a sensor could be employed in the identification of key marker compounds and, as such, give an indication of total PAH flux in the environment.     

Assessment of transverse impact damage in GF/EP laminates of conductive nanoparticles using electrical resistivity tomography

GF/EP composite laminates with an epoxy matrix modified by carbon black (CB) of 2.0 wt.% and copper chloride (CC) were manufactured by the vacuum assisted resin infusion (VARI) technique. The effects of CB nanoparticles and CC on improvement in Modes I and II interlaminar fracture toughness and impact damage resistance and on the electrical conductivity of GF/EP laminate composites were investigated. Delamination growth was calibrated by in situ electrical resistance changes during interlaminar fracture tests. The relationship between growth of delamination and change in electrical resistance was characterised. A damage index based on the change in electrical resistance was introduced, and a new method of electrical resistivity tomography was developed to access transverse impact damage in GF/EP laminates based on a matrix of conductive points in both in-plane and through-thickness directions. The damage images from in-plane and through-thickness electrical resistivity tomography were finally estimated with the corresponding C-scan.     

DC resistivity of alumina and zirconia sintered with TiC

Pure alumina and zirconia powders were sintered separately with increasing amount of TiC up to ∼ 65 vol.%, as a conducting second phase with an aim to prepare conducting structural ceramics which can be precisely machined by EDM technique. TiC did not help in sintering the parent phase but it decreased the d.c. resistivity of the composite to 1 ohm.cm at ∼ 30 vol.% loading. The conductivity is explained by the effective media and percolation theories.     

Internal structure of composite materials by using computer tomography

Results are presented of tomographic investigations of the internal structure parameters of composite materials characterized by an elementary cell density distribution over the specimen volume.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 51, No. 6, pp. 1021–1027, December, 1986.     

Flexural strength and fracture toughness of sea ice

A series of mid-winter experiments were carried out on the ice in the rubble field around Tarsiut Island in the Beaufort Sea. The tests included grain structure determinations, salinity and density of the ice, small beam flexural strength and fracture toughness. Typical values for flexural strength and fracture toughness were 0.6–1.0 MPa and 100–140 kPa m^{$\text{1}\text{2}$} respectively. Both properties were dependent on brine volume and depth in the ice sheet. In comparing these results with identical tests on finegrained freshwater ice it was found that for comparable loading conditions, the strength of the sea ice was significantly lower than the strength of the freshwater ice, whereas the fracture toughness of the sea ice was higher than the fracture toughness of the freshwater ice.     

On modelling an iceberg embedded in shore-fast sea ice

The effect of long ice-coupled waves impinging on a tabular iceberg, an ice island or a thick sea ice floe trapped within a thin veneer of shore fast sea ice of substantial extent is considered. The waves most likely originate as ocean waves in the open sea beyond the fast ice boundary, from where they propagate into the sea ice. There their character is altered because of the flexural properties of the ice. The geophysical/engineering problem posed is solved by a Green's function method that redevelops, for a different surface boundary condition, an earlier study concerned with a freely floating ice floe. Reflection and transmission coefficients for the berg are found to depend strongly on its thickness and length. Amongst other things, the work relates to the operational safety of natural and artificially thickened Arctic ice platforms located in a contiguous ice sheet.     

Alignment of crystals in sea ice due to fluid motion

Columnar sea ice grows vertically as platelets. The c-axes are perpendicular to the plane of these platelets and, over distances of many kilometres, are found to be aligned about a particular direction in the horizontal plane. Laboratory and field results indicate that this alignment is due to the flow of sea water at the ice-water interface which forces the c-axes to lie parallel to the current. A perturbation technique applied to the transport equations for momentum and solute from the freezing interface, leads to the conclusion that favourably oriented grains have their interfacial temperature depressed a few millidegrees below that of those which lie in a perpendicular orientation. Further a theory for the kinetics of growth suggests that there is a time associated with alignment and that this depends on fluid speed, a typical empirical value being 160 hours for a fluid velocity of 30 mm s⁻¹. The predicted characteristic velocity, above which the flow is expected to have a significant influence on the sea ice fabric, is of the order of 10 mm s⁻¹.     

Control of the temperature coefficient of the DC resistivity in polymer-based composites

In this study, the roles of polymer matrices and filler additives in controlling the positive temperature coefficient (PTC)/negative temperature coefficient (NTC) behavior of DC resistivity at high temperature for semicrystalline ethylene vinyl acetate copolymer, amorphous acrylonitrile butadiene copolymer, and their blend composites filled with different carbon fillers like Conductex carbon black, Printex carbon black, and short carbon fiber have been investigated. It is seen that the PTC/NTC behavior of resistivity depends on the characteristics of both polymer matrices and filler additives. The anomaly in the results are due to polymer crystallinity, shape and size of fillers, and their thermal expansion coefficient, that play major role in controlling the PTC/NTC of resistivity at high temperature for the composites. Finally, reproducibility of composite resistivity has been evaluated with their some proposed practical applications. These composites can be used as both PTC and NTC thermistors.     

Detection of biotin in individual sea urchin oocytes using a bioluminescence binding assay

The ability to detect biomolecules in single cells is important in order to fully understand the processes by which many biochemical events occur. To that end, we have developed a bioluminescence binding assay capable of measuring the intracellular biotin content of individual cells. The assay depends on competition between an aequorin-biotin conjugate (AEQ-biotin) and free biotin within the oocytes for binding sites on the protein avidin. The assay is performed by microinjecting each component into the oocytes and following the resulting bioluminescence within the oocyte upon triggering of aequorin. Results obtained using sea urchin oocytes show that the assay performed within the cells behaves in a manner consistent with assay theory. Using the assay, the individual biotin content of the oocytes is an average of approximately 20 amol. To our knowledge, this is the first reported multicomponent binding assay to be performed inside an intact single cell.