bluuebunny/crossref_metadata_2025 huggingface dataset:
The surface physics of ice in thunderstorms
Authors: Dash J G , Wettlaufer J S
Published: May 2003

Laboratory and field studies have shown that thunderstorm electrification is principally due to rebounding collisions between ice particles and hail. Recent studies have provided clues for an understanding of the microphysics of the charging mechanism, involving the dynamics of vapor growth, molecular diffusion, and collisionally modified surface melting. The theory is in quantitative agreement with the systematic dependence of charge and mass transfer on growth rate, collision speed, and temperature.

PACS Nos.: 05.70-a, 64.10+h, 64.70-p, 63.35
Photon emission accompanying deformation and fracture of ice
Authors: Mizuno Y , Mizuno T
Published: May 2003

We observed photon emission during deformation and fracture of axially loaded polycrystalline ice. Emission of visible photons (300650 nm) was correlated with crack generation and fracture, based on time-resolved photon emission signals taken during load changes. Emission intensity, including the entire spectra ranging from 300 to 650 nm, was roughly correlated with increasing strain energy released by fracturing, while considerable scattering of the intensity data implied that emission intensity also depended on the characteristics of each individual crack. Correlation was taken between simultaneous emissions detected with two photomultiplier tubes with different ranges of spectral sensitivity. Brief, intense emissions were clearly associated with load drops, and these probably included wavelengths shorter than 320 nm, indicating that near ultraviolet light is also emitted. On the other hand, weak but continuous signals with wavelengths longer than 650 nm were emitted the entire time the ice was subjected to a load. Emission intensity and spectra may be attributed to microprocesses during fracturing. Experimental evidence for emission of visible photons indicates that the generated electric charges on crack surfaces and at crack tips have energy ranging from 2 to 6 eV.

PACS No.: 46.50
Reduction of ice adhesion to metal by using self-assembling monolayers (SAMs)
Authors: Petrenko V F , Peng S
Published: May 2003

A new method has been developed to study the role of hydrogen bonding in ice adhesion and to minimize the effect of this mechanism on ice adhesion. Metals were coated with a mono-molecular layer that had either strong hydrophobic properties or strong hydrophilic properties. Self-assembling monolayers (SAMs) of varying degrees of hydrophobicity/hydrophilicity were created by mixing the hydrophobic and hydrophilic components. The SAM structure and quality were examined using atomic force microscopy, and the degree of the SAM hydrophobicity/hydrophilicity was characterized by the contact angle of water on the monolayer surfaces. Then, water was frozen on the top of the SAM and the shear strength of the interface between ice and SAM was measured. A good correlation between the contact angle of water and the ice adhesion strength was shown and the fraction of ice adhesion caused by hydrogen bonding was determined. It is revealed that hydrogen bonding significantly enhances ice adhesion.

PACS No.: 61
Three-dimensional simulation of ice growth in the presence of antifreeze proteins
Authors: Wathen B , Kuiper M J , Walker V K , Jia Z
Published: May 2003

A Monte Carlo computational method for simulating the growth of entire ice crystals from the liquid phase has been developed specifically to study the inhibition of ice-crystal growth by antifreeze proteins (AFPs). AFPs are found in the fluids of certain organisms that inhabit freezing environments and constrain ice-crystal growth by adsorbtion to the ice surface, but their inhibition mechanism is still poorly understood. Thus, it was of interest to incorporate these molecules into the dynamic ice simulations to examine the inhibition phenomenon on a whole-crystal basis. We have undertaken simulations with AFPs from two different organisms that differ in activity; the insect AFP has up to 100 times the activity of the fish AFP on a molar basis. Simulations involving insect and fish AFPs have achieved ice-growth inhibition at simulation temperatures within reported activity ranges for both fish and insect AFPs, accompanied by resulting ice morphologies similar to those observed experimentally. These results, as well as other studies on ice-etching patterns and ice burst growth at temperatures below known AFP ice-growth inhibition abilities suggest that AFP activity is dominated by the AFP ice-binding position rather than AFP ice-binding strength.

PACS No.: 07.05T
Measured temperature and pressure dependence of Vp and Vs in compacted, polycrystalline sI methane and sII methaneethane hydrate
Authors: Helgerud M B , Waite W F , Kirby S H , Nur A
Published: May 2003

We report on compressional- and shear-wave-speed measurements made on compacted polycrystalline sI methane and sII methaneethane hydrate. The gas hydrate samples are synthesized directly in the measurement apparatus by warming granulated ice to 17°C in the presence of a clathrate-forming gas at high pressure (methane for sI, 90.2% methane, 9.8% ethane for sII). Porosity is eliminated after hydrate synthesis by compacting the sample in the synthesis pressure vessel between a hydraulic ram and a fixed end-plug, both containing shear-wave transducers. Wave-speed measurements are made between 20 and 15°C and 0 to 105 MPa applied piston pressure.

PACS No.: 61.60Lj
Measurements of physical properties of gas hydrates and in situ observations of formation and decomposition processes via Raman spectroscopy and X-ray diffraction
Authors: Uchida T , Takeya S , Wilson L D , Tulk C A , Ripmeester J A , Nagao J , Ebinuma T , Narita H
Published: May 2003

Gas hydrate properties and phase transition kinetics were studied using Raman spectroscopic and X-ray diffraction methods. These techniques have the advantage of measuring physical properties such as crystal structure, gas composition, and cage occupancy of gas molecules without decomposing the sample. In situ observations using these techniques are indicative of formation and decomposition processes in gas hydrates. Raman spectroscopy is used for the analysis of gas concentrations and gas compositions of gas hydrates. The ν1 symmetrical CH stretching vibration mode of methane molecules in the hydrate phase shows a doublet, and the relative intensity of the peaks determines the cage-occupancy ratio. However, as the Raman method is not standard for this application, we evaluated the method by analyzing the same methane hydrate sample using NMR and Raman scattering in a laboratory in Canada and also comparing the data with the Raman measurements made on the same sample in a laboratory in Japan. The data were consistent with all three measurements. In addition, in situ measurements of hydrate formation and decomposition were done by X-ray diffraction. The transformation of ice into CO2 hydrates occurred in two steps: at first a CO2 hydrate layer rapidly formed a coating on the ice surface and then the CO2 hydrate slowly grew according to the diffusion rates of CO2 and H2O molecules through the hydrate layer to the reaction sites. The same methods were used to observe the self-preservation effect of methane hydrates.

PACS Nos.: 82.80Ch, 61.10Nz
Temperature, pressure, and compositional effects on anomalous or "self" preservation of gas hydrates
Authors: Stern L A , Circone S , Kirby S H , Durham W B
Published: May 2003

We previously reported on a thermal regime where pure, polycrystalline methane hydrate is preserved metastably in bulk at up to 75 K above its nominal temperature stability limit of 193 K at 0.1 MPa, following rapid release of the sample pore pressure. Large fractions (>50 vol.% ) of methane hydrate can be preserved for 23 weeks by this method, reflecting the greatly suppressed rates of dissociation that characterize this "anomalous preservation" regime. This behavior contrasts that exhibited by methane hydrate at both colder (193240 K) and warmer (272290 K) isothermal test conditions, where dissociation rates increase monotonically with increasing temperature. Here, we report on recent experiments that further investigate the effects of temperature, pressure, and composition on anomalous preservation behavior. All tests conducted on sI methane hydrate yielded self-consistent results that confirm the highly temperature-sensitive but reproducible nature of anomalous preservation behavior. Temperature-stepping experiments conducted between 250 and 268 K corroborate the relative rates measured previously in isothermal preservation tests, and elevated pore-pressure tests showed that, as expected, dissociation rates are further reduced with increasing pressure. Surprisingly, sII methaneethane hydrate was found to exhibit no comparable preservation effect when rapidly depressurized at 268 K, even though it is thermodynamically stable at higher temperatures and lower pressures than sI methane hydrate. These results, coupled with SEM imaging of quenched sample material from a variety of dissociation tests, strongly support our earlier arguments that ice-"shielding" effects provided by partial dissociation along hydrate grain surfaces do not serve as the primary mechanism for anomalous preservation. The underlying physical-chemistry mechanism(s) of anomalous preservation remains elusive, but appears to be based more on textural or morphological changes within the hydrate material itself, rather than on compositional zoning or ice-rind development.

PACS Nos.: 82.30Lp, 81.40Gh, 81.40Vw, 68.37Hk, 83.80Nb
Raman spectroscopic observations of methane-hydrate formation and hydrophobic hydration around methane molecules in solution
Authors: Uchida T , Okabe R , Gohara K , Mae S , Seo Y , Lee H , Takeya S , Nagao J , Ebinuma T , Narita H
Published: May 2003

To reveal the hydrophobic hydration process of methane molecules dissolved in water, Raman spectra of dissolved methane (CH4) in water were measured under various conditions. The conditions include water saturated with CH4 gas, waterCH4 solution with CH4 hydrate crystals in equilibrium, and also during hydrate decomposition. The symmetric CH stretching mode of the CH4 molecule in water is a single peak at 2910 cm1 with a half-width of approximately 5 cm1. These results indicate that the size of the space for the CH4 molecules, called the hydration shell, is between the large and small cages of the hydrate crystal, but it has a broad size distribution. To better understand the CH4-molecule vibrations, its spectrum in water was compared with its spectra in liquid carbon dioxide (CO2) and in liquid ethane (C2H6). These spectra were very similar to those observed in water, except that the peak widths were sharper than those in water. This suggests that the broadening of the shell-size distribution is due to the way the CH4 molecules affect the hydration shell. On the other hand, when the system included hydrate crystals, a double CH4 peak arose due to structure in the aqueous solution near the crystal surface. This indicates that a cage-like structure can exist in the water phase. Compared with the decomposition experiment, the cage-like structure is likely due to the presence of the bulk hydrate crystal and is different from the hydration shell for the dissolved CH4 molecules.

PACS Nos.: 81.10Dn, 33.20Fb
Effect of direct- and alternating-current electric fields on friction between ice and metals
Authors: Arakawa M , Petrenko V F , Chen C
Published: May 2003

We report an extremely strong effect of direct and alternating current on the friction of steel sliding on ice. Under the most favorable conditions, the friction force increased by a factor of 33 when 520 V of 60 Hz voltage was applied. The effects on this phenomenon of both temperature and voltage were studied. Electrostatic pressure and field-stimulated growth of the ice/metal contact area appear to be the most likely causes of this effect.

PACS No.: 81.40Pq
Observation of crack propagation in saline ice and freshwater ice with fluid inclusion
Authors: Arakawa M , Petrenko V F
Published: May 2003

A key process of crack propagation in saline ice is the interaction between the crack and fluid inclusions. We observed their interaction in freshwater ice using very high-speed photography (VHSP) and found that the low-density fluids (air and inert liquid, Fluorinert, 1.78 g/cm3) could not impede the crack effectively, interrupting the propagation for less than 10 µs. The high-density liquid mercury, (13.8 g/cm3) impeded the crack more effectively, stalling the development of the crack for more than 20 µs. The crack velocity in saline ice was measured using two different methods: electrical resistance method (ERM) and VHSP. These two methods returned very different mean velocities, 15 m/s for the ERM and 250 m/s for the VHSP. We found that in ice with conductive liquid inclusions, the ERM measured the time it took to break liquid bridges stretched across a crack rather than the crack velocity. Results from the VHSP show that the maximum crack velocity in saline ice was 500 m/s, which is one-half of that found in freshwater ice. From our results using freshwater ice with inclusions, we conclude that liquid inclusions in saline ice may play a role in this retardation.

PACS No.: 62.20Mk
Neutron powder diffraction studies as a function of temperature of structure II hydrate formed from propane
Authors: Rawn C J , Rondinone A J , Chakoumakos B C , Circone S , Stern L A , Kirby S H , Ishii Y
Published: May 2003

Neutron powder diffraction data confirm that hydrate samples synthesized with propane crystallize as structure type II hydrate. The structure has been modeled using rigid-body constraints to describe C3H8 molecules located in the eight larger polyhedral cavities of a deuterated host lattice. Data were collected at 12, 40, 100, 130, 160, 190, 220, and 250 K and used to calculate the thermal expansivity from the temperature dependence of the lattice parameters. The data collected allowed for full structural refinement of atomic coordinates and the atomic-displacement parameters.

PACS No.: 61.12-q
Rate of decay of specific surface area of snow during isothermal experiments and morphological changes studied by scanning electron microscopy
Authors: Legagneux L , Lauzier T , Domin F , Kuhs W F , Heinrichs T , Techmer K
Published: May 2003

The quantification of the specific surface area (SSA) of snow crystals and of its variation during metamorphism are essential to understand and model the exchange of reactive gases between the snowpack and the atmosphere. Therefore, the decay rate of SSA of five fresh snow samples was studied in the laboratory at 4, 10, and 15°C under isothermal conditions in closed systems. The time-evolution of the snow SSA can in all cases be very well described by an empirical law of the form, SSA =  A log(t + Δt) + B, where A, B, and Δt are adjustable parameters. B seems to be closely related to the initial SSA of the snow, and A describes the SSA decay rate. Our preliminary findings at 15°C suggest that a linear relationship exists between A and B, so that it may be possible to predict the decay rate of snow SSA from its initial value. For the first time, images obtained from scanning electron microscopy show that crystal rounding of snow is the main process taking place during isothermal metamorphism. New grain boundaries also form. More surprising, however, was the formation of new basal, prismatic, and pyramidal crystal faces, sometimes with very sharp angles, especially at 15°C. The growth of facets with sharp angles is not fully explained by current theories of snow metamorphism and has not been observed before.

PACS Nos.: 68.35Md, 68.37Hk, 81.20Ev, 81.05Rm
Effects of temperature cycling on the phase transition of water in gas-saturated sediments
Authors: Chuvilin E M , Ebinuma T , Kamata Y , Uchida T , Takeya S , Nagao J , Narita H
Published: May 2003

Experimental results on hydrate- and ice-formation conditions in the pores of sandy sediments that have undergone temperature cycles are presented. Thermodynamic parameters of gas hydrate and ice formation in porous space were determined for CH4 and CO2 saturated sandy sediments. The experiments indicate that temperature and freezing cycles affect the thermodynamics of hydrate and waterice in gas-saturated sediments. Temperature cycles increased the hydrate accumulation in the pore space of sediments and reduce the freezing temperature of the remaining pore water.

PACS Nos.: 91.60Hg, 92.40Sn
Double-microtoming technique for snow studies
Authors: Satyawali P K , Sinha N K , Sethi D N
Published: May 2003

Classification of snow samples based on the thick-section method presents difficulty in recognizing the types of snow having similar structure. Using a double-microtoming technique together with thermal etching, textural details of vertical and horizontal thin sections of different snow samples are obtained. It has allowed us to examine the texture of different types of snow, which was not possible using the thick-section technique. This technique is capable of bringing out the grain or sub-grain boundaries and clearly shows the type of bonds between crystals (geometric or crystalline) using polarized light for relatively large-angle boundaries and thermal etching for small-angle boundaries. This way, one can characterize the texture of various snow types. The texture of snow that has not been studied so far is added information that can further classify a snow sample in addition to the common classes of snow.

PACS No.: 92.40Rm
Ice-surface properties analyzed through grain-boundary migration
Authors: Nasello O B , Di Prinzio C L
Published: May 2003

One of the factors influencing the movement of grain boundaries is the groove formed at the intersection between the grain boundary (GB) and the free surface of the sample. The equations that describe this interaction show that it is possible to obtain values for the GB mobility M and the surface diffusion coefficient D by studying the GB movement, provided that the variation of GB energy with inclination is known. In the present work, GB movement under the influence of the surface is studied for pure bicrystalline ice samples. The bicrystals used in the study presented a [Formula: see text]10[Formula: see text]0[Formula: see text]/60° crystalline misorientation, and different inclinations. Experimental values of M and D with a dispersion of less than 50% were obtained modeling the variation of GB energy with inclination and by taking into account Coincidence Site Lattice concepts.

PACS No.: 68.35-p
Structure of refrozen cracks in first-year sea ice
Authors: Petrich C , Haskell T G , Langhorne P J
Published: May 2003

The structure of natural refrozen cracks in landfast first-year sea ice in McMurdo Sound, Antarctica, is examined in Spring. The alignment of inclusions, crystal structure, and two-dimensional salinity profiles are discussed and compared to freezing experiments on slots cut in sea ice sheets. The investigated cracks and slots are of the order of 2030 cm wide and grown in ice of about 12.2 m thickness. Convection in the water column during the phase transition is modelled with the Finite Volume Method. We find that inclusions seem to align with the freezing front, and suggest that the crystal structure and salinity profile are influenced by buoyancy-driven convection inside refreezing cracks.

PACS Nos.: 46.50+a, 62.20Mk
Diffusion and solubility of HCHO in ice: preliminary results
Authors: Perrier S , Sassin P , Dominé F
Published: May 2003

The diffusion and solubility of formaldehyde (HCHO) in ice were measured at 15° by exposing large single crystals of ice to low vapor pressures of HCHO (PHCHO) for several days. The solubility was found to be ( 30 ± 3) × 106 mol L1 at 15° under PHCHO = 1.7 × 102 Pa. The diffusion coefficient is of the order of 8 × 1011 cm2 s1 at 15°. Extrapolation of these preliminary results to the lower PHCHO values observed in the polar atmospheric boundary layer is consistent with the hypothesis that the concentration of HCHO in aged snow crystals is governed by thermodynamic equilibrium.

PACS Nos.: 66.30Jr, 82.60-S, 92.40Sn, 92.40Rm
Clathrate nucleation and inhibition from a molecular perspective
Authors: Moon C , Taylor P C , Rodger P M
Published: May 2003

Identifying the molecular processes that lead to clathrate-hydrate nucleation has been an active area of research for more than a decade. The question has a number of important ramifications, spanning applications in geology (formation and stability of natural methane-hydrate deposits), environmental science (CO2 sequestration), and industry (prevention of hydrate blockages). The drive to develop more active and robust hydrate inhibitors for the oil industry that work at very low dosages, in particular, has been slowed down because our understanding of the molecular mechanisms by which such inhibitors work is still largely conjectural. In this paper, we present results from the first direct molecular-dynamics simulations of the inhibition of nucleation in methane hydrate. Molecular-dynamics simulations have been used to simulate the behaviour of a thin film of water under a methane atmosphere with and without poly(vinylpyrrolidone) (PVP). Simulations in the absence of PVP show clear evidence of the nucleation and growth of methane hydrate; this behaviour is completely suppressed, however, when PVP is included in the simulation. We conclude that these simulations provide an excellent basis for understanding the way in which PVP inhibits hydrate nucleation.

PACS Nos.: 81.10Aj, 81.10Dn, 81.10Fq
Exact diagonalization of the S = 1/2 XY ferromagnet on a new set of finite triangular lattices at T = 0
Authors: Betts D D , Lee K S , Lin H Q
Published: May 2003

We have obtained 85 finite triangular lattices from 7 to 36 vertices. We display two very good finite lattices  21a (well-known) and 22a (previously unknown). Over the past decade several physicists have used exact diagonalization on five tripartite triangular lattices from N = 9 to 36 to study the Heisenberg and XY antiferromagnet on the infinite triangular lattice. Nine more tripartite triangular lattices are available as shown below in the text. Our exact diagonalization of the S = 1/2 XY ferromagnetic energies and magnetization leads, by scalar equations, to the properties on the infinite lattice. We found that all but 10 of the 85 are good lattices. Finally, we obtained spinspin correlations of two kinds, xx and zz.

PACS Nos.: 75.10Jm, 05.05+q
Nitrogen condensation on water ice
Authors: Palumbo M E , Strazzulla G
Published: May 2003

We studied, by infrared absorption spectroscopy, icy samples (16 K) of pure water, a mixture N2:H2O=100:1, and a sample made of N2 condensed on water ice and diffused in it after warm up to 30 K. We concentrated our efforts in two spectral regions around 3700 cm1 where the feature due to the OH dangling bonds in porous amorphous water falls and around 5000 cm1 where a broad water band is present. We found that in the N2:H2=100:1 mixture the profile of the broad water feature at about 5000 cm1 dramatically changed to a very narrow band at about 5300 cm1. When N2 diffuses in water ice a feature at about 5300 cm1 appears along with the broad 5000 cm1 band. We also studied some of the effects of ion irradiation (Ar++, 60 keV ions) on these icy samples. We found that after processing the feature due to the OH dangling bonds it reduced in intensity and eventually disappeared. Here we present the experimental results, discuss their astrophysical relevance and suggest that a band at about 5300 cm1 (1.88 µm) should be searched for on icy surfaces in the outer Solar System, namely Pluto, Triton, EdgeworthKuiper Belt Objects, and Centaurs.

PACS No.: 68.43Pg
Structural systematics in the clathrate hydrates under pressure
Authors: Loveday J S , Nelmes R J , Klug D D , Tse J S , Desgreniers S
Published: May 2003

We report the results of synchrotron X-ray and neutron diffraction studies of methane, argon, nitrogen, and xenon clathrate hydrates at high pressure and room temperature. The results reveal common features in the structural transition sequences. All phases transform initially to the hexagonal clathrate structure and all except xenon hydrate eventually form an orthorhombic dihydrate. Argon and nitrogen hydrates adopt the type-II clathrate structure at low pressures and have a tetragonal cage structure between the hexagonal and orthorhombic phases. At normal compression rates, the hexagonal form of xenon hydrate decomposes into ice and xenon at ~2.5 GPa.

PACS Nos.: 61.50Ks, 61.10-i, 61.12Ex
Computational studies of ice defects
Authors: Plummer P LM
Published: May 2003

Continuing our investigations of the energetics associated with defect formation and migration, both ab initio energy-structure calculations and molecular dynamics simulations are carried out on small clusters of water molecules containing one or more defects in hydrogen bonding. Previous studies in this series have identified structures containing defects that are stable at 0 K or that are transition states between such structures. However, results from this laboratory and elsewhere have shown that the energy required for the production or migration of a defect is more complex than merely the energy difference between the static structures. Cooperative motion of neighbors to the defect site can either increase or decrease the energy involved to produce or annihilate the defect. Thus, experimental measurements associated with the energy of defects in ice can differ substantially from those calculated using static models. By increasing the complexity of the model, the studies described in this report attempt to more realistically simulate a defect-containing ice system. The types of defects studied include ion and ion-pair defects. The initial structures are energetically stable  minima on the electronic energy surface  and contain one or more kinds of defects. Since the means and amount of energy injection can alter the migration path, the energy is introduced into the system in a variety of ways. The structural evolution of the ice system is then monitored as a function of time.

PACS Nos.: 82.20Wt, 82.20Kh, 82.30Rs
Ductile flow of methane hydrate
Authors: Durham W B , Stern L A , Kirby S H
Published: May 2003

Compressional creep tests (i.e., constant applied stress) conducted on pure, polycrystalline methane hydrate over the temperature range 260287 K and confining pressures of 50100 MPa show this material to be extraordinarily strong compared to other icy compounds. The contrast with hexagonal water ice, sometimes used as a proxy for gas hydrate properties, is impressive: over the thermal range where both are solid, methane hydrate is as much as 40 times stronger than ice at a given strain rate. The specific mechanical response of naturally occurring methane hydrate in sediments to environmental changes is expected to be dependent on the distribution of the hydrate phase within the formation  whether arranged structurally between and (or) cementing sediment grains versus passively in pore space within a sediment framework. If hydrate is in the former mode, the very high strength of methane hydrate implies a significantly greater strain-energy release upon decomposition and subsequent failure of hydrate-cemented formations than previously expected.

PACS No.: 62.20Fe
Incoherent inelastic neutron-scattering studies of the structure of water associated with DNA and gelatin
Authors: Beta I A , Kolesnikov A I , Michalarias I , Wu G L , Ford R C , Li J C
Published: May 2003

Incoherent inelastic neutron-scattering spectra of DNA and gelatin samples with different hydration levels were measured with the TOSCA spectrometer at ISIS, Rutherford Appleton Laboratory. Comparison with the spectra of different ice phases shows that for water contents up to 0.75 g water/g DNA and 0.5 g water/g gelatin the optical region (2050 meV) is almost featureless, similar to high-density amorphous ice (HDA). The librational band is shifted to lower energy transfers and its edge at 55 meV matches again the spectrum of HDA ice. For water contents of 1 g water/g DNA and 0.75 g water/g gelatin resemblance to spectra of ice Ih and low-density amorphous ice (LDA) is obvious.

PACS Nos.: 61.12Ex, 82.39Jn
Diffuse neutron-scattering studies of ice Ih under high pressures
Authors: Wang Y. , Li J C
Published: May 2003

A series of neutron-diffraction measurements for the single-crystal ice Ih (D2O) at different temperatures and pressure were carried out on PRISMA spectrometer using a He pressuriser at ISIS (U.K.). The measurements show no change in the diffraction pattern under the Bragg diffraction peaks for pressures up to 2.5 kbar at 130 K. When the pressure increases to 3.1 kbar at 120 K, the structure of ice Ih starts to deform, firstly the d-spacing of the (110) Bragg reflection increases from 2.243 to 2.256 Å (instead of decreasing under the high pressure), indicating the He atoms penetrate into the ice lattice and occupy the interstitial positions. At higher temperature, ~180 K (3.1 kbar) the structure of ice Ih completely transforms to an ice II structure with occluded He atoms.

PACS No.: 64.60-i
Quantum mechanical versus quasi-classical tunneling times for smooth potential barriers
Authors: Shegelski M R.A. , Kozijn E V
Published: May 2003

For smooth potential barriers, we compare the quasi-classical tunneling time with an expression that gives a fully quantum mechanical tunneling time. The expression we choose for the quantum mechanical tunneling time is one that has heuristic value. We report results wherein this quantum mechanical tunneling time and the quasi-classical time differ significantly, both quantitatively and qualitatively. To determine the reasons for these differences, we compare the trends in the two times that result from varying the potential. Our findings suggest that, for smooth potential barriers, the quasi-classical tunneling time is unreliable for many cases where it is employed.

PACS Nos.: 03.65Xp, 03.65-w
Hamiltonian formulations of YangMills theory and gauge ambiguity in quantization
Authors: Bracken P
Published: May 2003

A general formulation of the Hamiltonian in non-Abelian YangMills theory is given. The subject of gauge-fixing ambiguity is investigated. It is shown how this type of degeneracy affects the FaddeevPopov prescription for the corresponding path-integral formulation at the quantum level. A method for treating this problem is developed. The ideas are implemented by quantizing the theory in the axial gauge.

PACS Nos.: 11.10Ef, 11.15-q, 11.15Tk
The behavior of inclined covers used as oxygen barriers
Authors: Bussière Bruno , Aubertin Michel , Chapuis Robert P
Published: May 2003

Covers with capillary barrier effects (CCBE) have been recently proposed as a viable option for gas migration barriers. However, the effect of geometry on CCBE performance has not been clearly demonstrated. In this paper, the results of a laboratory study performed with an original apparatus called the inclined box are presented. The results obtained show that the hydraulic behavior of layered covers is influenced by the inclination of the slope. Generally, the upper part of the slope contains less water than the lower part. This means that the upper part is less efficient than the lower part for limiting gas migration. The authors have also studied an existing site where a CCBE was built on a sloping surface. After validation of the numerical model with in situ measured data, the model was used to perform a parametric study to quantify the influence of the main CCBE parameters on its performance. The results obtained confirm those measured in the lab and clearly show how geometry influences the performance of the CCBE. Based on these results, a simple relationship is proposed for a preliminary estimation of sloping covers performance to limit oxygen migration by diffusion.Key words: cover with capillary barrier effects, acid mine drainage, slope effects, laboratory investigation, in situ measurements, design criteria.
A simplified method for 3D slope stability analysis
Authors: Chen Zuyu , Mi Hongliang , Zhang Faming , Wang Xiaogang
Published: May 2003

This paper presents a simplified three-dimensional (3D) slope stability analysis method based on the limit equilibrium theory. The assumption involved in this method is of a parallel intercolumn force inclination, similar to Spencer's method in the two-dimensional (2D) area. It allows for the satisfaction of complete overall force equilibrium conditions and the moment equilibrium requirement about the main axis of rotation. The method has been proven to be numerically tractable for many practical problems. By combining this method with the 3D upper bound approaches, it is possible to bracket the accurate solution of a 3D slope stability analysis problem into a small range.Key words: slope stability analysis, three-dimensional analysis, limit equilibrium method, upper bound method.
Response of anchors to variations in displacement-based loading
Authors: Ghaly Ashraf , Hanna Adel
Published: May 2003

The results of an experimental investigation on the effect of variations in displacement-based loading on the pullout capacity of anchors are presented. A single-pitch, screw helical anchor was used in the testing. The tests were conducted in dry, well-graded, dense, medium, and loose sands with relative densities of 79, 47, and 19%, respectively. Anchors were installed to, and tested at, shallow and deep depths. Measurements of ultimate pullout load and displacement at failure were made. The values of time-to-failure and mean loading rate were calculated and presented. The results of this study show that variations of displacement-based loading had some effect on the pullout capacity of shallow anchors but had only a slight effect on deep anchors. For a given depth of installation and a given sand state, the ultimate pullout load of an anchor decreases with increasing loading rate. This effect was more pronounced in anchors installed to shallow depths.Key words: anchors, displacement, displacement rate, pullout capacity, strain rate, sand, foundations, uplift.
Three-dimensional stress effects on time-dependent swelling behaviour of shaly rocks
Authors: Hawlader B C , Lee Y N , Lo K Y
Published: May 2003

This paper presents a time-dependent constitutive model that has been developed for the swelling of shaly rocks. Laboratory test results on many shales, including Queenston shale, show that the swelling of these rocks depends on the applied stresses. The applied stress in one principal stress direction reduces swelling strain not only in that direction but also in the perpendicular directions. It was found that swelling strain reductions are nonlinearly dependent on applied stress. The reduction in lateral swelling caused as a result of axial stress is modeled using the "pseudo-Poisson's effect". The proposed model is used to simulate the development of swelling strain with time under uniaxial and biaxial stress conditions. Comparison between the computed and experimental results shows that the pseudo-Poisson's effect is a key parameter for simulating the observed time-dependent swelling.Key words: swelling, Queenston shale, modeling, three-dimensional stress effect, nonlinearity.
Weathered rock characterization using drilling parameters
Authors: Sugawara J , Yue Z Q , Tham L G , Law K T , Lee C F
Published: May 2003

The characterization of weathered rocks by the use of drilling parameters is presented. Drilling parameters obtained from the drilling process monitoring system during the installation of soil nails into weathered rocks are used in this investigation. A new drilling index Pi, simplified from the concept of the specific energy, is used in an attempt to differentiate weathered rocks. With Pi or the penetration rate, boundaries of weathered rocks between (1) soil and rock ranges, and (2) grade II and grade III rocks in accordance with the six-fold rock material decomposition grade are identified. For weathered rocks in the soil range, quantitative characterization has been established in this study by using the drilling parameters. An empirical equation has been established for estimating the standard penetration resistance N value from the drilling parameter Pi, which is used in turn to determine the MohrCoulomb friction angle based on the work of Schmertmann. Although this approach tends to yield a slightly larger MohrCoulomb friction angle than that from laboratory tests, results obtained in this attempt reveal that estimation of the MohrCoulomb friction angle from drilling parameters is attainable with reasonable accuracy.Key words : drilling, standard penetration, percussion index, penetration rate.
Nγfor rough strip footing using the method of characteristics
Authors: Kumar Jyant
Published: May 2003

By using the method of characteristics, the bearing capacity factor Nγwas computed for a rough strip footing. The analysis was performed by considering a curved nonplastic wedge under the foundation base bounded by curved slip lines being tangential to the base of the footing at its either edge and inclined at an angle π/4 - ϕ/2 with the vertical axis of symmetry. The existing theories in the literature for rough footings, which usually employ a triangular wedge below the footing base, were generally found to provide greater values of Nγas compared with the results obtained in this contribution.Key words: bearing capacity, foundations, failure, numerical modeling, plasticity.
Influence of a nonlinear failure criterion on the bearing capacity of a strip footing resting on rock mass using a lower bound approach
Authors: Yang Xiaoli , Yin Jian-Hua , Li Liang
Published: May 2003

The strength envelope of almost all geomaterials is nonlinear when one considers a wide range of stresses. Therefore, a nonlinear failure criterion needs to be used in stability analysis whenever the effects of nonlinearity are too significant to be neglected. This paper presents a lower bound solution to the bearing capacity calculation of a strip footing resting on a homogenous weightless rock mass using the nonlinear HoekBrown (HB) failure criterion. Two types of admissible stress fields are used to develop solutions. The first stress field has three stress legs. The second stress field has a spiral-like shape with n stress legs, where n may vary from 9 to 18 000 (even to infinity). Using two admissible stress fields, equations are derived and used for the calculation of lower bound bearing capacity values of a strip footing on rock mass. The influences of the admissible stress leg number n and the material parameter s in the nonlinear HB failure criterion are investigated. It is found that the lower bound bearing capacity calculated using the spiral-like shape admissible stress field approaches to the true optimum value as the stress leg number n increases, and the nonlinear material parameter s has a strong influence on the bearing capacity of the footing.Key words: HB failure criterion, bearing capacity, stress leg, lower bound theorem, rock.
Sorption of Cd2+, K+, F, and Cl on some tropical soils
Authors: Leite Adilson do Lago , Paraguassú Antenor Braga , Rowe R Kerry
Published: May 2003

The potential for the retention of K+, Cd2+, F, and Cl by lateritic soils from the Botucatu (an important sandy aquifer in the southeastern part of Brazil) and Serra Geral (a clayey material) formations and three mixtures of these soils is examined. Batch equilibrium results are presented for both single salt (CdCl2 and KF) and multiple salt (CdCl2 + KF) solutions. The soil retention parameters are obtained by fitting sorption models (linear, Freundlich, and Langmuir) to the experimental isotherm plots using linear and nonlinear regression analyses. The results show that the so called varying soil:solution ratio isotherms (VSI) are in fact less variant in terms of pH than constant soil:solution isotherms (CSI). However, because of restrictions related to the VSI approach and the "soil solution ratio effect," the CSI approach is considered to be a more reasonable way of constructing sorption isotherms. It is shown that under certain conditions, the Cl anion can be sorbed while for others it is not sorbed. Sorption was observed for F and K+. The sorption of Cd2+ is also shown to be highly sensitive to leachate chemistry. It is shown that a knowledge of pH0 is quite important for the interpretation of sorption data.Key words: sorption, inorganic chemicals, isotherms, tropical soils.
Long-term measurement of matric suction using thermal conductivity sensors
Authors: Nichol Craig , Smith Leslie , Beckie Roger
Published: May 2003

Thermal conductivity (TC) sensors, which provide estimates of matric suction, were used in a field experiment designed to characterize unsaturated water movement through coarse mine waste rock at a mine site in northern Saskatchewan. Two years of monitoring data were used to evaluate long-term TC sensor performance and accuracy. Thermal conductivity sensor output requires corrections of sensor hysteresis and changes in ambient temperature. A correction method for ambient temperature is derived. A comparison of the uncorrected field measurements with the values corrected for both hysteresis and ambient temperature indicates that the magnitude of these corrections can be similar. Corrected TC sensor measurements are compared to measurements of matric suction made using tensiometers. Thermal conductivity sensor response to the initial arrival of a wetting front lagged 13 days behind the tensiometer measurements. The TC sensor data tended to overestimate matric suction in the waste rock, when compared to the tensiometer data. Long-term drift in the TC sensors located at depths of 50 cm and below (where the sensors have been continuously exposed to matric suctions less than 20 kPa) has lead to data that are not interpretable using the calibration curves derived prior to sensor emplacement in the waste rock pile.Key words: matric suction, thermal conductivity sensor, hysteresis, temperature.
On the use of the KozenyCarman equation to predict the hydraulic conductivity of soils
Authors: Chapuis Robert P , Aubertin Michel
Published: May 2003

The saturated hydraulic conductivity of a soil can be predicted using empirical relationships, capillary models, statistical models, and hydraulic radius theories. A well-known relationship between permeability and the properties of pores was proposed by Kozeny and later modified by Carman. The resulting equation is largely known as the KozenyCarman (KC) equation, although the two authors never published together. In the geotechnical literature, there is a large consensus that the KC equation applies to sands but not to clays. This view, however, is supported only by partial demonstration. This paper evaluates the background and the validity of the KC equation using laboratory permeability tests. Test results were taken from publications that provided all of the information needed to make a prediction: void ratio, and, either the measured specific surface for cohesive soils, or the gradation curve for noncohesive soils. The paper shows how to estimate the specific surface of a noncohesive soil from its gradation curve. The results presented here show that, as a general rule, the KC equation predicts fairly well the saturated hydraulic conductivity of most soils. Many of the observed discrepancies can be related to either practical reasons (e.g., inaccurate specific surface value; steady flow not reached; unsaturated specimens, etc.) or theoretical reasons (some water is motionless; hydraulic conductivity of soils is anisotropic). These issues are discussed in relation to the predictive capabilities of the KC equation.Key words: permeability, prediction, gradation curve, specific surface.
Performance evaluation of vibration-sensitive equipment foundations under ground-transmitted excitation
Authors: Naggar M Hesham El
Published: May 2003

The planning of foundations for equipment that is sensitive to vibrations requires a thorough dynamic investigation of the proposed location of the foundation with regard to the effect of already existing or additional vibration sources. This paper discusses the analyses performed for a number of foundations supporting vibration-sensitive equipment that has been subjected to ground-transmitted excitations. These analyses considered the dynamic response of the foundations resulting from the normal operation of the supported equipment or the ground-transmitted excitations. In one case, the foundation of the Canadian Light Source, a third generation synchrotron that will be capable of generating electromagnetic radiation used in the study of the atomic and subatomic structure of materials, is examined. Another case involves the vibration analysis of a magnetic resonance imaging unit affected by traffic excitation. In the third case, a power plant facility that is subjected to blast-induced vibration from an adjacent quarry is investigated. The last case involves the response analysis of a compressor foundation affected by the ground-transmitted vibration from another compressor situated on a different foundation within the same facility. To assess the level of seismic excitation at the site due to traffic on an adjacent roadway in the first two cases and to blasting activity in the third case, extensive "green field" ground vibration-monitoring programs were carried out. The ground accelerations due to traffic and blasting were measured and recorded for three directions simultaneously: a vertical and two orthogonal horizontal directions. The measurements with the most intense ground accelerations taken at the ground surface in the location of the future equipment foundation were selected as the final design acceleration time-history. A Fourier analysis approach was used to predict the response of the foundation to the ground-induced vibrations in the first three cases, and a frequency domain analysis was used in the last case.Key words: machine foundations, vibration, blasting, kinematic, soil-structure interaction.
A flexible wall permeameter for measurements of water and air coefficients of permeability of residual soils
Authors: Samingan Agus Setianto , Leong Eng-Choon , Rahardjo Harianto
Published: May 2003

This paper describes the development of a flexible wall permeameter apparatus for measuring the water and air coefficients of permeability of residual soils. Water and air coefficients of permeability were obtained for both the drying and wetting cycles for residual soils using the flexible wall permeameter. Volume changes of the soil specimens during unsaturated consolidation and during the water and air permeability measurements were also monitored. Factors that influence the measurements, such as hydraulic and pneumatic gradients and temperature fluctuations are described and discussed in this paper. The developed flexible wall permeameter was found to be capable of measuring water and air coefficients of permeability as low as 1012m/s.Key words: flexible wall permeameter, permeability, residual soils, unsaturated soils, matric suction, flow rate.