bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Radio-Frequency Birefringence of Polar Ice
Authors: Hargreaves N. D. 
Published: September 2017

AbstractRadio-echo observations have shown that polar ice in situ is birefringent. The most likely explanation of the birefringence is an anisotropy in the radio-frequency dielectric constant of the ice single crystal, combined with the ordering of the orientations of the ice crystals in polar ice. It is possible to calculate the birefringence of ice which has a distribution of crystal orientations using a technique similar to that used to derive the dielectric properties of heterogeneous media. The experimentally observed birefringence may then be shown to be consistent with the crystal orientation fabric at the site of the observations if the anisotropy of the dielectric constant is slightly less than 1%, that is, slightly less than the accuracy of the laboratory measurements which have failed to detect any anisotropy. Further experimental observations might be used to obtain information on not only the level of anisotropy of the single crystal but also on the crystal orientation fabric of the ice.
The Core Structure and the Mobility of Dislocations in Ice
Authors: Whitworth R. W. 
Published: September 2017

AbstractThe evidence concerning the velocity of glide of dislocations on the (0001) plane of ice Ih is reviewed and related to atomic processes occurring within or near the dislocation core. The velocity is directly proportional to stress at low stress, with a value of the order of 500 Burgers vectors per second at — 18°C and a stress of 105 N m-2. The usual idea of a dislocation core is that it is “crystalline” in the sense that the linkages between molecules are as far as possible the same as those in the normal lattice. For such a model the disorder of protons presents an obstacle to dislocation movement, and recent theories predict that dislocations should not be able to glide as fast as they are observed to do. Various ways of avoiding this difficulty within the context of a crystalline core are discussed, but none seems likely to be successful. An alternative model is that the core is “non-crystalline”, with a disordered arrangement of mobile molecules within it. The movement of such dislocations should not be seriously impeded by proton disorder. Dislocation mobility would then be limited at least in part by anelastic loss due to the stress-induced order of protons in the surrounding lattice.
X-Ray Topographic Studies of Dislocations in Vapor-Grown Ice Crystals
Authors: Mcknight C. V. , Hallett J. 
Published: September 2017

AbstractIce crystals grown from the vapor under controlled conditions have been examined by X-ray topography. Plates grown in the region — 1.5°C to —3°C and at — 15°C near water saturation were often free of defects, as were plates grown at smaller supersaturations (1.5% at — 3°C, 6% at — 15°C). It is inferred from these observations that growth was occurring by two-dimensional nucleation on the prism plane. It is suggested that multilayer adsorption on the crystal surface was responsible for growth at the low values of supersaturation, compared with higher values predicted by the Burton—Cabrera—Frank theory. Ice crystals dependent on dislocations for growth could only occur at supersaturations lower than these values. The crystal habit is interpreted as being dependent on differential two-dimensional nucleation on prism or basal faces. Rib structure is often associated with dislocation loops; stacking faults were evident in some crystals.
A Deformation Mechanism Map of Ice
Authors: Shōji H. , Higashi A. 
Published: September 2017

AbstractA deformation mechanism map for pure polycrystalline ice of 2 mm grain diameter is constructed, New sub-regions in the dislocation glide region are proposed: dislocation glide with crack formation, dislocation creep, and fracture at high stresses above about 1 MPa. The boundary between the dislocation creep and DGC regions is determined by the onset of cleavage cracks due to piled-up dislocations near grain boundaries. The fracture region is that area of the map where fracture occurs readily when the ice is subjected to a rapid deformation rate exceeding 10-3 s-1. Experimental results of the stress dependence of the compressive deformation rate of polycrystalline ice are compared with the map. The effect of changes in the creep activation energy near the melting point is discussed together with those of other factors.
The Effect of Anisotropy on the Creep of Polycrystalline Ice
Authors: Lile R. C. 
Published: September 2017

AbstractQuantitative effects of crystallographic orientation fabrics are incorporated into the flow law for isotropic polycrystalline ice by the introduction of an enhancement factor applied to the isotropic fluidity. An aggregate is viewed to a first approximation as a collection of grains deforming independently by basal glide. The influence of preferred orientations on the mean intragranular rate of strain is treated in terms of a redistribution of the magnitude and orientation of resolved basal shear stress. A quantitative measure of this effect on the fluidity of the aggregate is provided through the development of a geometric tensor and a stress configuration parameter. Intergranular interference is then considered as a dissipative process modifying the fluidity of the aggregate.Empirical justification for the model at low octahedral shear stresses is provided by several laboratory creep tests on naturally anisotropic bore-hole specimens under both in situ and anomalous stress situations. Predicted enhancement factors ranged from approximately 0.2 to 2.8 and agree well with measured values. The tests were carried out in uniaxial compression and simple shear.
On the Relationships between Low-Density Amorphous Solid Water and Ice Ih
Authors: Rice Stuart A. , Madden William G. , McGraw Robert , Sceats Mark G. , Bergren Michael S. 
Published: September 2017

AbstractNew experimental and theoretical studies of low-density amorphous solid water (H2O(as)) and of polycrystalline ice lh are reported and integrated with other available data. A variety of evidence is put forward to support the conclusion that low-density H20(as) is derived from ice lh by slightly increasing the dispersion in the O—O separation and by introducing a distribution O—O—O angles (width c. 8°). Our theoretical analysis focusses attention on the consequences of strong intermolecular coupling of OH oscillators. The vibrational modes of both ice lh and H20(as) are found to be complex mixtures of molecular motions, so the identification of regions of the Raman or infrared spectra of these materials with particular isolated molecule modes is not useful. The theory developed gives a good, but not perfect, account of the OH stretching regions of the observed Raman and infrared spectra of ice lh and, to a lesser degree of low-density H20(as).
Dynamical Processes at the Ice-Water Interface During Solidification
Authors: Bilgram J. H. , Güttinger H. 
Published: September 2017

AbstractThe dynamics of the freezing process is studied at the surface of growing ice crystal by means of Rayleigh spectroscopy. Light is scattered quasi-elastically at the interface. The line width is proportional to the square of the scattering vector. For a scattering angle of 90° one measure, about 2 krad/s. The line width does not depend on the growth rate or thermal gradients at the interface. Light is scattered isotropically, which indicates that the correlation length is small compared with the wavelength of the scattered light. The intensity depends on the growth rate and shows a hysteresis in that dependence; at a minimum growth rate one observes the onset of fluctuations.
Charge Separation by Collision of Ice Particles on Metals: Electronic Surface States
Authors: Buser Othmar , Jaccard Claude 
Published: September 2017

AbstractThe charge separation of ice particles colliding with metals was investigated in a wind tunnel (air speed 10 m/s) at a temperature of —45°C for different metals as a function of an applied external electric field. The ice particles (to μm radius) collided with the metal target at a rate of 105 per second. The charge separation produced by different metals can be explained by the contact potential difference between the metal and the ice introducing electronic surface states on the ice. A lower limit for their density (1016m–2) is found. The influence of the electric field is explained by an interaction between Bjerrum defects and the electrons of the metal, the transfer probability depending on the charge in the surface states.
Optical Absorption Spectra of H2O Ice Doped with Ytterbium Chloride YbCl3
Authors: Couture L. 
Published: September 2017

AbstractNear-infrared absorption spectra of a frozen dilute solution of ytterbium chloride have been obtained at 77 K, 20 K, and 4.2 K. They contain two broad lines revealing a Stark splitting of 60 cm-1 of the excited 2F5/2, level of the Yb3+ ion. Such spectra indicate that in frozen solutions of ytterbium chloride the Yb3+ ions have crystalline or quasi-crystalline surroundings which are similar for most ions; different possibilities are discussed.
Structure and Behaviour of Grain Boundaries in Polycrystalline Ice
Authors: Higashi Akira 
Published: September 2017

AbstractRecent progress in studies of the structure and behaviour of grain boundaries in ice are reviewed. As a lattice geometrical model of the boundary, the coincidence-site lattice (CSL) model is considered for ice crystals. Some evidence of the validity of this model is presented through observations of special shapes of natural snow, results of grain-boundary energy measurements, and direct microscopic observations of boundaries by X-ray diffraction topography. Although methods of measurement of grain-boundary energy have been developed recently, results are still not adequate to be analysed in terms of real energetics for comparison with models of atomic bonding. Modern methods of observing grain boundaries in ice using X-ray diffraction topography are described. Observations of migrating boundaries have revealed that faceting along most closely packed CSL points impede the migration of the CSL boundaries whilst increased numbers of steps among facets with boundaries of other kinds enhance it. The mobility of a fast-moving boundary has been determined to be of the order of 10-10 cm3 dyn-1 s-1 (10-11 m3 N-1 s-1) either in the case when the driving force is the capillary force due to the boundary energy or when it is the stored energy of dislocations.
Fracture Toughness of Ice: A Preliminary Account of Some New Experiments
Authors: Goodman D. J. , Tabor D. 
Published: September 2017

AbstractThis paper describes the first results from an experiment to measure the fracture toughness of ice. Two experimental techniques have been used; fracture of pre-notched rectangular specimens in three- and four-point bending, and from the observation of the cracks which form underneath an indenter forced into the ice surface. In the latter test the indenter behaves like a wedge. We have observed that for indenters with large interior angles the plastic zone beneath the indenter may itself behave like a wedge. Data obtained over a range of temperatures has been compared with the little other data available. We find a decrease of fracture toughness as the temperature is lowered, which is the reverse of that observed by H. W. Liu and L. W. Loop.
Anisotropy of the Kinetic Friction on a Single Crystal of Ice
Authors: Tusima Katutosi 
Published: September 2017

AbstractMeasurements were made of the kinetic friction which occurs when a tungsten carbide ball slides in various directions on the surface of a single crystal of ice, the track width produced on the surface was also measured. Anisotropies were detected in both the friction coefficient and the track width. The track width φ was at a maximum when the ball was slid normal to the basal plane and a minimum when it was moving parallel to (0001) in the temperature range —5 to —30°C. Although the friction coefficient was at a minimum when slid normal to (0001) and maximum in parallel to (0001) at temperatures of —19°C and below, this relation was found to be reversed at temperatures of —10°C and above. Anisotropy in track width can be explained in terms of the amount by which a slip system contributes to deformation in a specimen. However, our understanding of frictional anisotropy calls for knowledge of the ploughing strength p defined by the adhesion theory of friction. It was found that p reached a maximum in parallel to (0001) and a minimum normal to (0001) and that the frictional anisotropy on (0001) was influenced by the value . A remarkable frictional anisotropy was also observed on the surface inclined to the basal plane at 30°; the maximum friction coefficient was twice the minimum, whereas the maximum track width was only 1.3 times the minimum.
The Dielectric Properties of Antarctic Ice
Authors: Fitzgerald W. J. , Paren J. G. 
Published: September 2017

AbstractTwo 0.5 m cores from "Byrd" station, Antarctica have been studied in the laboratory, one from a shallow depth (155 m) and the other from the zone where recrystallization has given a vertical c-axis fabric, and the air in situ is thought to be in clathrate form (1 424 m). The dielectric response has been studied in the frequency range 60 Hz to 10 kHz, and in the temperature range — 6° C to —6o° C. The behaviour observed is markedly different from that of "pure" polycrystalline ice such as may be made by slowly freezing distilled de-ionized water and is thus at variance with the conclusions of Rogers (unpublished) who deduced, from measurements of the admittance of a dipole probe lowered through the fluid-filled drill hole at "Byrd", that the ice surrounding the hole had a dielectric response similar to that of "pure" ice. The Antarctic ice is shown to have properties similar to those of the ice from "Camp Century" and "Site 2" in Greenland studied by Paren (1973). In an attempt to discover what factors determine the difference in electrical behaviour between polar ice and pure ice, some samples were melted and subsequently refrozen slowly. Their dielectric response was similar to that of pure polycrystalline ice. These results are discussed in connection with the impurity content and growth conditions of the ices.
Theory of Radio Echoes From Glacier Beds
Authors: Berry M. V. 
Published: September 2017

AbstractWe review the theory of interpreting the echoes received back at the source from a glacier bed illuminated with a wide-angle beam of quasimonochromatic radio waves. It is convenient wherever possible to separate bed relief into “geography” and “roughness”. “Geography” is the surface that results from horizontally smoothing the bed over distances comparable with the mean height h of the source above the bed. The geography can be deduced from the lime delays of specular reflections, provided these can be identified, “Roughness” is the statistics of the departures of the actual bed from the geography on scales down to about one-tenth of the predominant wavelength in the travelling pulse. The average height S and horizontal dimension L (where these quantities can be defined) of the irregularities can be deduced from measurements of the average value of the echo envelope p as a function of time delay. It is also possible to distinguish qualitatively different beds with the same S and L. If the source-receiver unit moves keeping h constant, then p fluctuates about its mean value. This “spatial fading” can be used to detect horizontal ice displacements of less than one hundredth of a wavelength. To detect vertical ice motion it is necessary to observe the phase of the echo.
Radio-echo sounding of the lambert glacier basin
Authors: Morgan V. I. , Budd W. F. 
Published: September 2017

AbstractSeveral seasons of aerial ice-thickness soundings over the region of the Prince Charles Mountains, the Lambert Glacier system, the Amery Ice Shelf, and their drainage basin in east Antarctica have now been completed. The measurements provide detailed maps of surface topography and ice thickness over an area of about 2 X 105 km2. The equipment used consisted of a 100 MHz echo sounder designed and constructed by Antarctic Division and carried in a Pilatus Porter aircraft. ERTS imagery provides a valuable background for portraying the echo-sounding results. These results show that an extensive, deep subglacial valley system forms the basis of the large drainage basin with concave ice surface topography which channels the ice flow into the Amery Ice Shelf. Deep glacial streams penetrate a long way into the ice-sheet basin. The rock relief is considerable, varying from 3 000 m above (present) sea-level to 2 000 m below sea-level. A very deep subglacial trench exists in the region of the confluence of the Fisher, Mellor, and Lambert Glaciers where the ice thickness reaches 2 500 m. The low surface slope and high ice velocity are suggestive of high melt production in this region. The strong echo, together with the high bedrock back-slope, suggests that the deep trench may contain a basal melt lake.
Velocity of radio waves in ice by means of a bore-hole interferometric technique
Authors: Robin G. DE Q. 
Published: September 2017

AbstractRadio waves of fixed frequency, which had passed through ice and firn from a transmitting antenna lowered down a bore hole, were monitored on the surface. By mixing the received signal with the fixed frequency, the beats which were produced as the antenna was lowered gave a value for the wavelength in ice at the depth of the antenna. This was multiplied by the frequency to give the velocity of radio waves m ice. Measurements averaged over 10 m and longer intervals were related to density values from bore holes in the same location. Results above 50 m were difficult to interpret, but at greater depths the velocities fitted a linear relationship between refractive index and density. A small extrapolation gives a velocity of radio waves in pure ice of 167.7±0.3 /μs at — 20° C.
Comparison of Sea-ice Type Identification Between Airborne Dual Frequency Passive Microwave Radiometry and Standard Laser/Infrared Techniques
Authors: Tooma S. G. , Mennella R. A. , Hollinger J. P. , Ketchum R. D. 
Published: September 2017

AbstractDuring December 1973, the Naval Oceanographie Offirc (NAVOCKANO) and the Naval Research Laboratory (NRL) conducted a joint remote-sensing experiment over the sea-ice fields off Scoresby Sound on the east coast of Greenland using NAVOCEANO’s RP3-A Birdseye aircraft, laser profiler, and infrared scanner, and NRL’s 19.34 and 31.0 GHz nadir-looking radiometers. The objectives of this mission were: (1) to develop skills for interpreting sea-ice passive microwave data. (2) to expand, if possible, the two-category capability (multi-year ice and first-year ice) of passive microwave sensors over sea ice, (3) to compare two frequencies (19 and 31 GHz) to determine which may be more useful in a scanning radiometer now under development at NRL, and (4) to determine the value of multi-frequency as compared to single-frequency study of sea ice.Since, because of darkness and remoteness, no photography or in situ ground truth were possible for this mission, it was necessary to rely on the interpretations of the laser and infrared (IR) data to evaluate the performance of the microwave radiometers. Fortunately, excellent laser and IR data were collected, and a confident description of the ice overflown was possible.Five ice conditions: (1) open water/new ice, (2) smooth first-year ice, (3) ridged first-year ice, (4) multi-year ice, and (5) a higher brightness temperature form of multi-year ice interpreted as second-year ice were identifiable, regardless of weather conditions, by comparing the average of the two microwave brightness temperatures at the two frequencies with their difference.
Application of remote-sensing techniques to the study of seasonal snow cover
Authors: Meier Mark F. 
Published: September 2017

AbstractThis paper discusses the measurement of important snow properties using electromagnetic radiation. Snow areal extent can be measured using manual, optical, electronic, or digital techniques from data supplied by visible and near-visible light sensors carried on Earth resources and meteorological satellites, but these techniques cannot routinely detect snow under clouds or a forest canopy. Gamma-ray techniques used at stations or from low-flying aircraft permit measurement of water equivalent of snow (depth times density). Active or passive microwave systems may permit this to be done over larger areas, but the physics of this possible technique is not yet sufficiently understood. Wetness or temperature, of a snow surface is measurable with thermal infrared radiometers; wetness throughout a snow pack may be measurable with microwave radiometers. Much research needs to be done on the electrical (including scattering) properties of snow before efficient, all-weather, remote-sensing systems can be designed.
Significance of Surface Temperature in the Thermal Infrared Sensing of Sea and Lake Ice
Authors: Poulin Ambrose O. 
Published: September 2017

AbstractThermal infrared sensing can provide much information about sea ice, and some of the physical conditions associated with sea ice suggest that surface temperature may be a good indicator of ice thickness. However, steady-state heat-flow calculations suggest that the variable thickness of the snow-cover and its low. variable thermal conductivity would preclude the use of surface temperature alone as a suitable indicator of ice thickness. Measurements of surface temperature, snow depth, and ice thickness suggest that, in an area of relatively uniform ice thickness, surface temperature might be useful as an indicator of snow depth if some surface data can be obtained.
Geophysical studies of floating ice by remote sensing
Authors: Campbell W. J. , Weeks W. F. , Ramseier R. O. , Gloersen P. 
Published: September 2017

AbstractThis paper presents an overview of recent remote-sensing techniques as applied to geophysical studies of floating ice. The current increase in scientific interest in floating ice has occurred during a time of rapid evolution of both remote-sensing platforms and sensors. Mesoscale and macroscale studies of floating ice are discussed under three sensor categories: visual, passive microwave, and active microwave. The specific studies that are reviewed primarily investigate ice drift and deformation, and ice type and ice roughness identification and distribution.
Satellites—New Global Observing Techniques for Ice and Snow
Authors: Gloersen P. , Salomonson V. V. 
Published: September 2017

AbstractStarting with the TIROS-2 weather satellite in 1961 which permitted synoptic viewing of large-scale areas with an 011-board television camera system, the capabilities of satellite observations for assessing snow and ice resources on Earth have been greatly improved through the utilization of higher resolution imaging systems and multispectral images in the wavelength range from 0.4 μm to 1.55 cm. The possibility that the variation in areal extent of the snow cover may be related by empirical means to the average monthly run-off in a given watershed was demonstrated by comparing run-off records from the Indus River Basin in south-east Asia with a series of snow-cover maps obtained from Nimbus-3 and 4 imagery. Similar studies using the higher spatial resolution available with ERTS-I imagery were carried out for the Wind River Mountains watersheds in Wyoming, where it was found that the empirical relationship varied with mean elevation of the watershed. In addition, digital image-enhancement techniques are shown to be useful for identifying glacier features thought to be related to extent of snow cover, moraine characteristics, debris coverage, and the like. Finally, longer wavelength observations using sensors on board the Nimbus-5 satellite are shown to be useful for indicating crystal size distributions and onset of melting on glacier snow cover.