bluuebunny/crossref_metadata_2025_split huggingface dataset:
Vacancies in Pure Ice Studied by Positron Annihilation Techniques
Authors: Mogensen O. E. , Eldrup M. 
Published: September 2017

AbstractPositron annihilation techniques (PAT) are briefly discussed, and the information that may be obtained about the positronium (Ps) states is compared to that obtainable about the similar electron states. The behaviour of Ps in monocrystals of pure light and heavy ice was studied at temperatures between — 185°C and the melting point. Ps is very probably trapped in vacancies (i.e. missing water molecules) in ice. A vacancy formation energy of roughly 0.2–0.35 eV was derived in agreement with the value 0.28±0.07 eV obtained previously from studies of the annealing of irradiated ice. The vacancy concentration is at least a few parts per million at the melting point, i.e. roughly 104 times higher than normally assumed in the literature. The fact that the vacancy concentration is comparable to that of the hydrogen-bond defects will probably enforce a pronounced change in the “hydrogen-bond-defects” theory of the electric properties of ice.
Electrical Conductivity and Relaxation in Ice Crystals with Known Impurity Content
Authors: Gross Gerardo Wolfgang , Hayslip Iris Cox , Hoy Roberta N. 
Published: September 2017

AbstractThree-terminal dielectric bridge measurements (in the range 20 Hz to 100 kHz between — 5°C and —90 to — 120°C) have been made of ice doped with (a) conductivity-enhancing ionic impurities (HCl, HF, NaCl, KF, NH4F) and (b) conductivity-depressing solutes (NH4OH, NH4Cl, NH5CO3, NaHCO3). Blocking electrodes were used for the first group. The true ice parameters were extracted from linearized plots of the Debye equations. Chlorides and fluorides showed very similar characteristics in their spectra and static conductivity. The results suggest that static conductivity is controlled by extrinsic protons. On the other hand, bases, or solutes that impart a positive freezing potential to the ice, suppress extrinsic protons. In this case, the static conductivity was not, or only weakly, temperature dependent and lower than in the first group. A conductivity cross-over was observed in neither case. The dielectric conductivity contribution is strongly dependent on impurity concentration but apparently less affected than the static conductivity by the nature of the solute. The principal relaxation time is reduced by most solutes, exceptions are pure (bicarbonate-free) bases, sodium bicarbonate, and carbon dioxide.
Dielectric Properties of Dislocation-free Ice
Authors: Itagaki Kazuhiko 
Published: September 2017

AbstractDielectric properties of dislocation-free hoar-frost ice crystals were measured in the audio-frequency range. Anomalously small relaxation strength was found in the dislocation-free area of the crystal samples while dislocations deliberately introduced by scratching the samples drastically modified the relaxation strength. Since measurements made in the area of high dislocation density indicated normal behavior, electrically charged dislocations are considered to be the source of the normally observed dielectric relaxation.
The Orientation Polarization in Hexagonal Ice Parallel and Perpendicular to the c-axis
Authors: Johari G. P. , Jones S. J. 
Published: September 2017

AbstractThe relative permittivity and loss of zone-refined single crystals of hexagonal ice have been measured in the temperature range 200–271 K and frequency range 0.5 HZ–0.2 MHz, using brass, stainless steel, and gold-foil electrodes. The c-axis of the crystal was oriented parallel to the electric field in 14 samples and perpendicular to the field in 8 samples. The equilibrium relative permittivity of orientation polarization ϵ0, parallel and perpendicular to the c-axis, is 96.5±1 and the average relaxation time τay is 36 μs at 265±0.5K; ϵ0 = 124±1.5 and τav = 30 ms, at 210 K. The magnitude of the orientation polarization obeys the Curie-Weiss equation with T0= 15±2 K for both the orientations. These values are in contrast with the c. 17% difference in ϵo for the two orientations reported in the literature. The extrapolated limiting high-frequency relative permittivity ϵ∞, measured for both the orientations, is indistinguishable within 0.5%.The logarithmic plot of the product of τav and temperature against the reciprocal temperature is linear in the range 210–271 K and gives an activation energy and a pre-exponential factor of 51±2 kJ mol–1 and 0.93±0.22 ps K respectively, for both the orientations of the c-axis with respect to the electric field. The decrease in activation energy which has been reported to occur in polycrystalline ice and in single crystal ice near 230 K is not found until a temperature of 210 K. Single crystals of ice stored in the dielectric cell, after the completion of measurements, for periods ranging from 1–11 weeks at 253±2 K showed no change in their ϵ0, τav, ϵ∞ that could be attributed to the effect of ageing on the orientation polarization.
The Activation Energies of Temperate Snow Samples
Authors: Traub L. T. , Gribbon P. W. F. 
Published: September 2017

AbstractThe temperature dependence of the high-frequency conductivity of snow was studied for eight samples in the range — 10°C to — 80°C. The activation energies for granular snow varied from 0.60 eV at temperatures down to — 25°C to 0.24 eV at temperatures below — 25°C, and for dry snow from 0.42 eV to 0.18 eV in the same temperature ranges. Dry snow samples had higher conductivities and lower activation energies than granular icy samples throughout the complete temperature range.Volume and surface conduction processes were operative. At the higher temperatures above — 25°C volume conduction was attributed to Bjerrum defect migration, while at lower temperatures Bjerrum conduction was replaced by ionic-defect conduction. Granular samples which had experienced melting and reflecting on the surface of the crystals have a structural change which decreased the ionic-defect density at the surface and lowered the sample conductivity.Above — 25°C, the activation energies for granular icy snow were consistent with those for temperate glacier ice and for laboratory single and polycrystalline ice samples, but was not in agreement with those of either polar snow or ice. Below — 25°C, the activation energies for granular snow were consistent with those for temperate glacier ice, containing impurities, and for polar snow and ice. Fresh dry temperate snow-samples had lower activation energies than in situ polar snow.
Cooperative Movement of H2O Molecules and Dynamic Behaviour of Dislocations in Ice Ih
Authors: Perez J. , MaÏ C. , Vassoille R. 
Published: September 2017

AbstractA new model of dislocations glide in ire Ih is proposed. In developing this model certain assumptions are made: (i) dislocations have a non-crystalline extended core, and (ii) transitions occur through cooperative movements of ?2? molecules in the core of dislocations. A relation between the velocity νd of linear defects and shear stress τ or temperature T is obtained. This relation shows that νd varies linearly with τ at low values of τ and (or) T but varies more rapidly at higher stresses; this non-linearity is more pronounced the higher the temperature. Such results are in agreement with experimental data.
Inelastic Behaviour of Ice Ih Single Crystals in the Low-Frequency Range Due to Dislocations
Authors: Vassoille René , Maï Christian , Perez Joseph 
Published: September 2017

AbstractThe inelastic behaviour of ice Ih single crystals has been investigated by an inverted torsional pendulum in the low-frequency range. Three features are distinguished:(i) a relaxation peak previously observed by several authors in the higher-frequency range,(ii) an internal friction increasing with temperature in the high-temperature range (230–273 K),(iii) within this high-temperature range, internal friction becomes amplitude dependent, and this dependence becomes greater the greater the temperature.In this case, the internal friction has been interpreted in terms of movements of dislocations. Hence, the experimental results are interpreted with a model of internal friction based on an empirical relation for the velocity of dislocations. This model of internal friction is in fair agreement with experimental data . It is possible then to get an estimate of dislocation density. Hence it is shown that internal friction experiments can be useful in the study of the plastic behaviour of ice single crystals.
Anelastic Behaviour of Polycrystalline Ice
Authors: Duval Paul 
Published: September 2017

AbstractTorsion creep tests were performed on glacier ice at temperatures above -12°C. The polycrystalline ice, when unloaded, exhibits creep recovery. The time-dependent recoverable component of deformation (or anelastic strain) ϵa was found to be adequately described by a relationship of the form: ϵa = Δτ log(r + αt)/h, where Δτ is the stress decrement, α a constant, and t the time. The anelastic modulus h defined for times t in excess of 3 h is always smaller than the dynamic elastic modulus. The movement of dislocations composing the sub-boundaries or in dislocation pile-ups may produce this important reversible deformation. The time-dependent recovery is explained in a similar way to the transient creep behaviour observed at low temperatures for metals. The small temperature dependence of creep recovery would arise from the existence of a distribution of internal stresses values.
Regelation and the Deformation of Wet Snow
Authors: Colbeck S. C. , Parssinen N. 
Published: September 2017

AbstractThe thermodynamics of phase equilibrium control the temperature distribution around the ice particles in wet snow. When the snow is stressed, pressure melting occurs at the inter-particle contacts and the snow densifies. Densification is described by a physical model which simulates the heat flow, meltwater flow, and particle geometry. The effects of ionic impurities, liquid saturation, and particle size are demonstrated. Typical values of the temperature difference, inter-particle film size, and density are calculated as functions of time. The calculated rates of compaction are too large, hence, at some later time, the effects of simultaneous grain growth must be added to the model.
The Dislocation Formation Volume in Ice
Authors: Cotterill R. M. J. , Pedersen O. Bøcker 
Published: September 2017

AbstractRelaxations around a shear dislocation loop on a basal plane in ice have been studied by molecular dynamics. The model intermolecular potential included directional components which stabilized the open ice structure. A random phase approximation was introduced to simulate the disordered arrangement of hydrogen bonds. The dislocation formation volume was found to be zero within the limits of computational error. This paper is published in full in Nuclear Metallurgy, Vol. 20, Pt. 1, 1976, p. 572-81.
Dimesional Changes of Ice Ih with Time
Authors: Camp Paul R. 
Published: September 2017

AbstractTwo different types of experiment were reported. Both used a pure single crystal of ice freshly grown in the laboratory at 2 mm per hour.Direct volumetric measurements were made by submerging an ice crystal (volume 143 cm3) in mercury in a sealed steel container and electronically monitoring the height of the mercury in a manometer tube connected to it. Measurements over a 60 d period at —4.0°C showed a small gradual decrease in apparent volume. This could be due to the adsorption of perhaps 10-2 cm3 of air trapped by the mercury at the surface of the ice. The total un-certainties of the experiment are such that we believe we would have observed a volume dilation of as little as 2.5 × 10-6 per day.Direct measurements were also made of the change in length of ice samples from the same crystal. One was cut with length parallel to c and the other perpendicular to c. Over a 28 d period, the fractional change in length at —13.7°C was less than 2 × 10-7 per day and less than 7 × 10-8 per day ║c, leading to an upper bound on volume change of 7 × 10-7 per day.We conclude that if dilation of ice occurs with time, it is less than 10-6 per day and therefore probably not a factor which needs consideration in ordinary experiments.
An Effective Pair-Potential Study of the Interaction of a Water Monomer with the Basal-Plane Surface of Ice Ih
Authors: Hale B. N. , Kiefer J. 
Published: September 2017

AbstractThe central-force effective pair potential of Rahman and others (1975) is used to generate minimal binding-energy surfaces and configurations of a water monomer adsorbed on the unrelaxed basal plane surface of ice Ih. In the initial study H2O molecules arc placed with oxygen atoms fixed at the ice Ih lattice positions and associated hydrogens along the tetrahedral bond directions—restricting the H-O-H bond angles to 109.5°. A rigid-body water monomer adsorbed on the surface interacts with all the H2D molecules in the bulk ice model via the central-force effective pair potential. The center-of-mass height, z, and the dipole orientation of the adsorbed H2O molecule are varied to minimize the total binding energy of the monomer over a particular (x,y) point of the surface. Preliminary results showed that a rigid adsorbed monomer with an H-O-H angle fixed at 104.5° produced only minor deviations in the binding-energy surfaces and that a large bulk-ice model (486 molecules) gave effectively the same results as a smaller ice model (50 molecules). Studies on an infinite ice surface using periodic boundary conditions are in progress and will be used to study surface relaxation and long-range effects on the minimal energy surfaces. Three types of sites on the basal plane were considered: (1) a site with all surface molecule protons pointing out of the surface; (2) a site with all surface molecule protons pointing into the surface; and (3) a site with all rows of surface molecule protons pointing alternately into and out of the surface. A "site" generally refers to a region (about 90 Å2) on the surface over which the minimal binding-energy surface is to be determined.Minimal binding-energy surfaces for the sites have been obtained together with plots showing the surface of the position of the center of mass as a function of x and y. This is a model calculation and is limited by the validity of the potential under close scrutiny. However it gives a qualitative picture of how complex a terrain the real ice Ih surface might present to an adsorbed water molecule and how the water molecule might diffuse from site to site. From these calculations (and in the spirit of this model potential) a value for the mean path length and the mean residence time of the adsorbed water monomer can be estimated.
Enthalpy Relaxation Phenomenon in a Heavy Ice Crystal
Authors: Haida Osamu , Suga Hiroshi , Seki Syūzō 
Published: September 2017

AbstractThe heat capacities of quenched and annealed heavy ice Ih were measured in the temperature range 14 to 300 K by an adiabatic calorimeter. A relaxational thermal anomaly was found at around 115 K and this phenomenon was ascribed to the onset of deuteron ordering in the crystal. The average activation enthalpy of the relaxational process was determined to be (26±5) kJ mol-1. Residual entropies of the crystal were recalculated on the basis of the present heat-capacity data combined with the revised values for enthalpy of vaporization, saturated vapour pressure, and spectroscopic entropy. They are (3.47±0.41 J K-1 mol-1 for the quenched crystal and (3.44±0.41) J K-1 mol-1 for a crystal annealed at 102-106 K for 264 h. The characteristics and the origin of the anomaly are discussed in comparison with that of ordinary ice.This paper has been accepted for publication in full in a forthcoming issue of the Journal of Glaciology.
Reconstructed Ledges: Ice Crystal Growth without Dislocations
Authors: Bartley David L. 
Published: September 2017

AbstractWe give a simple explanation of recent experimental evidence that ice crystals may grow in water vapor at low supersaturation (i.e. under atmospheric conditions) without screw dislocations. Examination of the intermolecular potential shows that by assuming non-bulk-like orientations, dangling molecules at surface-cluster edges may form strong hydrogen bonds with substrate molecules. This leads to a study of ice surfaces within the framework of an Ising-like model in which molecules with nearest neighbor vacancies which can provide vertical bonding are allowed two distinct states, yielding bulk-like as well as reconstructed monolayer ledges. The surface roughening transition is examined for this model by means of (i) a Monte Carlo determination of critical points and (ii) an analytical treatment of nucleation clusters. It is found that rough surfaces and, correspondingly, (dislocation-less) surface nucleation growth, prevail at temperatures below the bulk melting point over a wide range of feasible binding energies.
The Electrical Properties of Snow and Ice
Authors: Glen J. W. , Paren J. G. 
Published: September 2017

AbstractThis paper reviews the electrical properties of snow and ice that are of importance in remote sensing using electrical devices. After a review of the observed laboratory behaviour of ice samples and the microscopic theory which has been advanced to explain this, the data on temperate and polar glacier ice are compared with the laboratory data. Temperate glacier ice is generally rather similar to laboratory ice, but certain relaxation processes found in the laboratory are absent from the glacier ice. Polar ice, on the other hand, is considerably different in its dielectric behaviour from "pure" laboratory ice, or temperate glacier ice; in many ways it more resembles doped laboratory ice, despite its variable, sometimes low, impurity content. It also resembles in behaviour ice produced by freezing supercooled water. The electrical behaviour of snow, and the attempts to account for this in terms of the behaviour of the ice and air components, and also of the water component in wet snow, are next discussed. Finally the implications of this work for radio-echo sounding of ice, radar reflectivity from wet and dry hydrometeors, devices for determining the water content of snow, and resistivity surveys of glaciers are discussed.
Layer echoes in polar ice sheets
Authors: Preben Gudmandsen 
Published: September 2017

AbstractA multitude of extensive layers have been observed by radio-echo soundings in Greenland. By comparison with the stable isotope profile from Camp Century it is found that layering in the lop of the ice has been formed in the period since the last glaciation. Radio-echo layers observed at greater depths in central Greenland may have been created in the period of the interstadials and further down possibly in the period prior to the last glaciation. Further investigations are needed to prove this.
The Analysis of the Near-surface Energy Transfer Environment from Thermal Infrared Imagery
Authors: Outcalt Sam I. 
Published: September 2017

AbstractThe radiant surface temperature imaged by thermal infrared line-scanning equipment is a product of both surface temperature and emissivity. In detail it is the integrated product of the evolutionary development of the near-surface energy transfer regime. The variation of surface radiant temperature spatially and temporally contains information about the structure, composition, and thermal state of near surface materials. It is suggested that the study of ground ice, sea/lake ice, and the thermal regimes of mountain snow and ice bodies, are reasonable targets for the quantitative application of thermal mapping technology, and that considerable technical development effort be expended on spectral, spatial, and temporal operators for use in computer processing of pictures for glaciological data.
Erts Data in Glaciology—An Effort to Monitor Glacier Mass Balance from Satellite Imagery
Authors: Østrem Gunnar 
Published: September 2017

AbstractDue to increased demand for electric energy, which in Norway is produced almost entirely by hydro-electric power plants, extensive glacierized basins are now considered for future power production, However, glacier behaviour has a great impact on the annual run-off from these basins, and information about expected annual deviations from a “normal” discharge must be obtained from mass-balance studies on representative glaciers within the basin. For this reason such studies are presently performed at eight selected Norwegian glaciers; the costs involved are in the order of $3 000-$10 000 annually for each observed glacier.The transient snow line can be identified easily on conventional air photographs and its height determined by direct comparisons with reliable topographie maps (with contour lines on glaciers). The resolution in ERTS images is sufficiently good to use the satellite data for a similar height determination of the transient snow line on glaciers—at least on the larger valley glaciers and, of course, on ice caps.Due to an existing correlation between the height of the transient snow line (at the end of the melt season) and the annual specific net mass balance, it is possible to construct a diagram expressing this relationship, provided detailed mass-balance studies have been performed during a period of several years of different mass-balance conditions (ideally comprising both years of negative and of positive net balances). Determinations of the transient snow-line height based upon ERTS data, obtained at the end of the summer season, can then be used to determine the mass balance for those glaciers where the above-mentioned relationship is established. This would be a great advantage in cases where there is a request for information on the net balance only; no separate data on winter balance or summer balance will be obtained by this method.Experiments have been performed to delineate the transient snow line on glaciers directly from ERTS digital data (CCT magnetic tape). The results indicate that last winter’s snow is characterized by grey-levels 41-48 (of 63 possible grey-scale levels) on MSS-7, whereas exposed glacier ice is represented by levels 13—20 in the same multi-spectral band. Snow and ice can also be separated on MSS-4, but the difference in grey-scale levels between the two materials is much smaller.
Radio-Echo Sounding of Mountain Glaciers
Authors: Zotikov I. A. , Luchininov V. S. , Macheket Yu. Ya. , Suchanov L. A. 
Published: September 2017

AbstractExperiments on radio-echo sounding of mountain glaciers have been done on Lednik Marukh (west Caucasus), Lednik Bezingy and Lednik Dzhankuat (central Caucasus), Lednik Gergety (east Caucasus), and Lednik IGAN (Polar Urals) in 1967-71 as a part of the I.H.D. programme. Radio altimeters operating at a frequency of 440 MHz with a pulse duration 0.5 μ5 and with an assumed radio-echo system performance of 130 dB were used. The apparatus was operated from the ice surface (using sledge or vehicle) and partly from a helicopter. Some measurements have been made while the apparatus was being moved continuously along longitudal and transverse profiles of the glacier. Some of the measurements have been made at separate points on the glacier. The methods of measurement and interpretation have been worked out. Data on ice thickness, subglacial topography, and internal structure of some mountain glaciers have been obtained and compared with data got using other geophysical methods and thermal drilling. There is agreement between the results.