bluuebunny/crossref_metadata_2025_split huggingface dataset:
Time scaling in the reorganization of adsorbed species in surface reactions
Authors: Cortés J , Valencia E 
Published: May 2003

The reorganization of the species adsorbed in the extreme zone of the phase diagram (y0+ = yA [Formula: see text] 0), close to the jamming state (yA = 0) of a surface reaction on a catalytic substrate, is studied for the monomerdimer (MD), monomer  linear trimer (MLT), monomer  bent trimer (MBT), and dimer  linear trimer (DLT) systems on a uniform surface and on a fractal, the incipient percolation cluster (IPC). It is established that the evolution of the surface fraction xB of component B (D, LT, or BT) follows a scaling law xB = Atk in the intermediate time zone. PACS No.: 79.69Dp
The ice-related research of Harry Kiefte and co-workers
Authors: Clouter M J 
Published: May 2003

Harry Kiefte (19421997) was born in Amsterdam and moved to Toronto at an early age where he completed his formal education. His Ph.D. research was in the field of electron paramagnetic resonance under J.S.M. Harvey at the University of Toronto. He then completed two years of postdoctoral study with B.P. Stoicheff at the same institution where he participated in the pioneering work that led to the recording of the first Brillouin spectra from single crystals of rare-gas solids and the consequent determination of the elastic constants for these materials. It was the technique of Brillouin spectroscopy, and its application to the determination of the elastic properties of a wide range of crystalline materials, that engaged his interest and very considerable talents for the remainder of his career at the Department of Physics, Memorial University, where he accepted a faculty position in 1973. At the time of his death, at the relatively young age of 54, his name appeared as author or co-author on approximately 90 publications. Included among the co-authors were four graduate students whose research was devoted to ice-related studies. It is this significant contribution to our knowledge of the elastic properties of ice that will be reviewed in this paper. PACS No.: 62.20Dc
Thermodynamic stability of clathrate hydrates relative to their separate chemical components
Authors: White M A , MacLaren D C , Marriott R A , Zhan B -Z 
Published: May 2003

The thermodynamic changes (ΔH, ΔS, and ΔG) for the association of several small molecules (tetrahydrofuran (THF), ethylene oxide (EO), acetone) with water to form corresponding clathrate hydrates are calculated as a function of temperature from experimental information. For THF clathrate hydrate and EO clathrate hydrate at low temperatures, the clathrate is enthalpically stabilized with respect to the components. This is also the likely case for acetone clathrate hydrate. In all the three cases, above the melting points of the guest species, the clathrate increases in enthalpic stability, but entropic factors favour the separated components. Similar changes for THF clathrate hydrate and EO clathrate hydrate occur at the melting point of ice, eventually favouring the liquid components over the clathrate. PACS No.: 65.40-b
Effects of gravity on directional growth and melting of ice crystals in solution
Authors: Nagashima K , Furukawa Y 
Published: May 2003

In the present study, side-view images of the solute concentration distribution in waterKCl solution were obtained near the directionally growing and melting ice crystals by Moire phase shift interferometry to elucidate the effect of gravity. The results showed that the concentration distribution of solute changed drastically depending on the growth-cell thickness. In the thickest growth cell used, the concentrated solution near the growth interface flowed down under the influence of gravity and flowed ahead much further than the diffusion length of solute. In the thinnest growth cell, although the fluid motion was almost stabilized, the growth pattern deformed very sensitively to the effect of gravity. During directional melting of ice crystals, the dilute solution released from the melting ice rose up and flowed away from the interface. The cell thickness significantly affected not only the growth process, but also the concentration distribution. In addition, because of interest in sea-ice growth and melting, the downward growth and the upward melting of ice crystals were also studied. It was found that the dense solution accumulated below the growth interface released plumes of dense solution downward. PACS Nos.: 47.20Bp, 66.30Jt, 81.30Fb, 47.20Hw
Backscattering from snow and ice: Laboratory and field measurements
Authors: Kaasalainen S , Karttunen H , Piironen J , Virtanen J , Liljeström A , Näränen J 
Published: May 2003

We present photometry of snow samples in the backscattering direction, i.e., at very small phase (light-source  target  observer) angles. Relative brightness measurements are taken to study the backscattering behaviour of snow and ice samples to be able to interpret the opposition effect of icy solar-system surfaces (for example, icy rings and satellites). Preliminary results of three separate experiments are presented, all of which exhibit a similar feature: a backscattering peak is exhibited by snow of different grain types and with different amounts of contamination. The peak grows stronger with increasing contamination. PACS No.: 96.35
Dielectric characterization of coals
Authors: Forniés-Marquina J M , Martín J C , Martínez J P , Miranda J L , Romero C 
Published: May 2003

Application of an electromagnetic analysis for coal characterization is attempted. By time domain reflectometry (TDR), dispersion spectra in the DC  5 GHz range of a wide variety of coals are obtained for room temperature. Static permittivity and relaxation frequency of the different samples are compared with parameters obtained by chemical analysis. Comparison reveals the usefulness of the electromagnetic characterization for the establishment of coal rank, and shows how an analysis of the dielectric characteristic parameters can provide approximate ideas about moisture, elemental carbon, hydrogen, and sulphur contents. PACS Nos.: 39.30+w, 82.53Kp, 77.22Gm
The effects of sulfuric acid on the creep, recrystallization, and electrical properties of ice
Authors: Iliescu D , Baker I , Li X 
Published: May 2003

Both constant load creep and recrystallization are investigated using single crystals of 70170 ppb sulfuric-acid-doped and -undoped ice. Both sets of crystals exhibited strains in excess of 200% under tensile creep. The undoped specimens reached these strains roughly twice as fast as the doped specimens. After large local strains were imparted to cuboidal single crystals using equal channel angular extrusion at 2°C and subsequent annealing at the same temperature, recrystallization occurred. It was found that a higher concentration of H2SO4 retarded both recrystallization and the subsequent grain-boundary migration. Direct current electrical resistivity measurements performed on polycrystalline, sulfuric-acid-doped (3 ppm) ice at 10°C showed a much lower resistivity in the grain boundaries than in the lattice. PACS No.: 81.90
High-speed video analysis of fracture propagation in a thick-edge-loaded freshwater ice sheet
Authors: Gagnon R 
Published: May 2003

High-speed video (1000 frames/s) was used to record the propagation of fractures in a 1.7 m thick freshwater ice sheet in Tuktoyaktuk Harbor, N.W.T. The fractures were induced by an indentor operating in a 0.33 m deep trench in the ice where it pushed against the upper 0.2 m edge of the sheet. Most fractures were planar horizontal shear cracks. Some vertically-oriented horizontally-propagating fractures were also observed. Pre-existing cracks in the ice had a considerable effect on the shape and propagation characteristics of the induced cracks. The fractures propagated intermittently, where the average velocity as a fracture progressed through several jump episodes was low (in the 050 m/s range), whereas the velocity measured at the brief jumps was in the 0550 m/s range. PACS No.: 62.20Mk
Dielectric and mechanical alterations of snow properties near the melting temperature
Authors: Takei I , Maeno N 
Published: May 2003

The dielectric and mechanical properties of snow were investigated in the temperature range 15 to 0°C. Dielectric measurements were carried out in the frequency range 50 Hz  5 MHz; the low-frequency conductivity (at 100 Hz) of snow samples shows a peak in the temperature range 3 to 0.3°C and the dielectric dispersion-strength also shows a minimum in this same range. The propagation velocity of an elastic wave through snow samples was measured with a vibration response method in the frequency range 10 Hz  1 MHz; the propagation velocity shows an increase with the bond growth as a result of progressive sintering, and a significant decrease above 0.6°C. The temperature dependence of the low-frequency conductivity and the propagation velocity for snow samples show a hysteresis near the melting temperature. A boundary between ice particles in snow samples is discussed as a means for understanding these phenomena. PACS Nos.: 61.43Gt, 77.22Gm, 46.40-f, 73.25+i
A molecular dynamics study of ices III and V using TIP4P and TIP5P water models
Authors: Ayala R B , Tchijov V 
Published: May 2003

Simulations of ices III and V are performed using molecular dynamics calculations in the NPT ensemble. To represent molecular interactions in both ices, two potentials, TIP4P and TIP5P, are used. The specific volume of ice III is calculated as a function of temperature at pressure P = 250 MPa, as well as a function of pressure at temperature T = 246 K. For ice V, the specific volume is calculated as a function of temperature at P = 500 MPa and as a function of pressure at T = 238 K. In both cases, both TIP4P and TIP5P models are used. The results of the calculations are in good agreement with the experimental data of other researchers. PACS No.: 31.15Qg
An experimental study of gas-hydrate formation by measuring viscosity and infrared spectra
Authors: Oyama H , Ebinuma T , Shimada W , Takeya S , Nagao J , Uchida T , Narita H 
Published: May 2003

We measured the viscosities and infrared (IR) spectra before and after hydrate nucleation. During the induction period, the viscosity increases and the infrared spectrum shifts to higher energy. After nucleation, the viscosity decreases abruptly, and the peak positions in the IR spectrum change to the small wave-number side. These results indicate that water acts as a precursor to hydrate nucleation. PACS Nos.: 66.20td, 78.30.30-j, 64.60Qb
Inelastic neutron scattering and low-energy excitation of amorphous SF6 hydrate prepared by vapor-deposition technique
Authors: Yamamuro O , Matsuo T , Tsukushi I , Onoda-Yamamuro N 
Published: May 2003

Amorphous SF6 hydrate (SF6·17H2O) was prepared by depositing the mixed vapor onto a substrate kept at about 8 K. The inelastic neutron-scattering spectra of the as-deposited sample and those annealed at about 120 and 150 K were measured at 50 K in the energy range below 100 meV. The first two samples were considered to be in amorphous states while the third one was in a crystalline state. The librational frequency of the water molecule (at around 60 meV) is smaller in the order of (as-deposited sample) < (annealed sample) < (crystalline sample). This indicates that the strength of the intermolecular hydrogen bonds is (crystalline sample) > (annealed sample) > (as-deposited sample). The spectra below 10 meV were compared with our previous data of pure vapor-deposited amorphous ices and those doped with methanol (CD3OH). The low-energy excitation (E < 6 meV) differed drastically depending on the dopants, i.e., the scattering intensity was enhanced by methanol doping but reduced by SF6 doping. This may be because the hydrogen-bond formation was hindered by methanol doping but promoted rather more by SF6 doping because of the hydrophobic interaction as in clathrate hydrates. PACS Nos.: 61.12Ex, 63.50tx
Temperature dependence of polyhedral cage volumes in clathrate hydrates
Authors: Chakoumakos B C , Rawn C J , Rondinone A J , Stern L A , Circone S , Kirby S H , Ishii Y , Jones C Y , Toby B H 
Published: May 2003

The polyhedral cage volumes of structure I (sI) (carbon dioxide, methane, trimethylene oxide) and structure II (sII) (methaneethane, propane, tetrahydrofuran, trimethylene oxide) hydrates are computed from atomic positions determined from neutron powder-diffraction data. The ideal structural formulas for sI and sII are, respectively, S2L6 · 46H2O and S16L'8 · 136H2O, where S denotes a polyhedral cage with 20 vertices, L a 24-cage, and L' a 28-cage. The space-filling polyhedral cages are defined by the oxygen atoms of the hydrogen-bonded network of water molecules. Collectively, the mean cage volume ratio is 1.91 : 1.43 : 1 for the 28-cage : 24-cage : 20-cage, which correspond to equivalent sphere radii of 4.18, 3.79, and 3.37 Å, respectively. At 100 K, mean polyhedral volumes are 303.8, 227.8, and 158.8 Å3 for the 28-cage, 24-cage, and 20-cage, respectively. In general, the 20-cage volume for a sII is larger than that of a sI, although trimethylene oxide is an exception. The temperature dependence of the cage volumes reveals differences between apparently similar cages with similar occupants. In the case of trimethylene oxide hydrate, which forms both sI and sII, the 20-cages common to both structures contract quite differently. From 220 K, the sII 20-cage exhibits a smooth monotonic reduction in size, whereas the sI 20-cage initially expands upon cooling to 160 K, then contracts more rapidly to 10 K, and overall the sI 20-cage is larger than the sII 20-cage. The volumes of the large cages in both structures contract monotonically with decreasing temperature. These differences reflect reoriented motion of the trimethyelene oxide molecule in the 24-cage of sI, consistent with previous spectroscopic and calorimetric studies. For the 20-cages in methane hydrate (sI) and a mixed methaneethane hydrate (sII), both containing methane as the guest molecule, the temperature dependence of the 20-cage volume in sII is much less than that in sI, but sII is overall larger in volume. PACS Nos.: 82.75, 61.66H, 65.40D, 61.12
Theoretical study on the diffusion of gases in hexagonal ice by the molecular orbital method
Authors: Hori A , Hondoh T 
Published: May 2003

To estimate the diffusion constants for various gases in ice, the barrier energies during interstitial diffusion are calculated for model ice clusters by the molecular orbital method. For He and Ne, the calculated values for diffusion along the c-axis were 0.11 and 0.26 eV, respectively. These are in good agreement with the experimental results. However, the calculated values for the diffusion of He perpendicular to the c-axis are not in close agreement with the experimental data. The barrier energies for O2, N2, and CH4 were calculated by the semi-empirical molecular orbital method and estimated to be 0.35, 0.47, and 0.75 eV, respectively. The lower energy for O2 in comparison with N2 is attributed to the formation of a quasi chemical bond between the O2 molecule and the ice lattice. The diffusion constants for O2, N2, and CH4 were estimated to be 1.8 x 1011, 2.5 x 1012, and 2.0 x 1014 m2s1, respectively. PACS Nos.: 31.15Ar, 31.15Ne, 66.30Jt, 66.30Ny
Nitrates in ice: uptake; dielectric response by the layered capacitor method
Authors: Gross G W 
Published: May 2003

Ice columns of 0.200.25 m length and 0.038 m diameter were grown in the laboratory from dilute solutions (105 to 102 N) of potassium, sodium, or ammonium nitrate at a constant freezing rate of 0.002 m h1 and stirring at 300 rpm. The distribution coefficient was computed at ~0.015 m intervals as the ratio of nitrate concentration in the melted ice and in the liquid phase as a function of interface position. The average distribution coefficients were (2.25 ± 0.55) × 104 for the potassium and sodium nitrate, and (6.1 ± 1.4) × 103 for the ammonium nitrate samples  about a 27-fold increase. These results are in line with other large anions such as sulfate and methanesulfonate that were previously investigated. The dielectric relaxation spectrum of ice slices (~0.012 m thick and sandwiched between thin fluoroplastic foils) was measured between 1 and 85°C at frequencies from 1 Hz to 100 kHz with a lock-in amplifier technique. First, the ice response was recovered from the (MaxwellWagner) layered capacitor. The dielectric relaxation ranges were then separated and their characteristic parameters computed. The complex conductivity (Grant plot) and the conductivity frequency-response plot have been the most useful tools for this purpose. Both (alkali-metal and ammonium nitrate) sample groups exhibit the Debye dispersion of polar molecules so characteristic for ice regardless of impurity content. There is also a dispersion range at lower frequencies, and a static or quasi-static conductivity. In the alkali-metal nitrates the low-frequency dispersion is a prominent space-charge dispersion, and the temperature-dependent interaction between orientational and ionic point defects in the ice lattice leads to the conductivity crossover phenomenon. Ammonium greatly reduces the ionic lattice defects responsible for space charge and static conductivity; there is no crossover. Both the Debye dispersion and the crossover support the concept of co-operative responses by the polar molecules making up the ice substance to physico-chemical stimuli. PACS Nos.: 61.72, 77.22G, 77.22J, 81.30F
Adsorbate-induced changes in the structure of amorphous thin films of ice
Authors: Swiderek P 
Published: May 2003

The effect of adsorption of thiophene on the infrared spectra of thin amorphous ice films deposited on Pt(111) is studied using reflection-absorption infrared spectroscopy (RAIRS). The changes within the RAIR spectra in the range of the OH-stretching band system upon adsorption depend on the structure of the ice films and the temperature at which the thiophene is deposited. Preferred binding at the ice surface to sites that are most likely identical with dangling-H groups occurs only if adsorbate mobility is sufficiently high. Otherwise, random film growth is observed, i.e., formation of multilayer islands before the first layer of thiophene on ice is completed. The adsorbate-induced changes within the OH-stretching band system of the ice films are different for these two situations. Binding to dangling-H sites is shown to influence more than the uppermost layer of the ice, whereas random deposition has an effect only on surface vibrational modes. PACS Nos.: 68.43Fg, 62.35Ja
Sliding along Coulombic shear faults in ice
Authors: Fortt A , Schulson E M , Russell E 
Published: May 2003

New experiments have been performed on the resistance to inelastic deformation through frictional sliding along naturally-formed Coulombic shear faults in ice Ih. Coulombic faults mark terminal failure of virgin material when loaded rapidly under a moderate degree of confinement. The experiments were performed on S2 fresh-water ice at 10°C, proportionally loaded biaxially across the columns along a variety of all-compressive paths. Two kinds of behavior were observed. At higher sliding velocities (8 × 102 and 8 × 101 mm s1) sliding was noisy and the process exhibited velocity weakening. At a lower sliding velocity (8 × 104 mm s1) sliding was quiet and fault healing occurred. The two kinds of sliding are indicative of brittle-like (at higher speeds) and ductile-like (at lower speeds) behavior, and are explained in terms of fracture and creep. Within the brittle regime, a power law describes the relationship between the shear strength of the fault and the normal stress across it at the onset of sliding, while Coulomb's law describes the relationship once sliding has progressed by about 2 mm. PACS No.: 61.72Nn
Ab initio molecular-orbital calculations for dodecahedral water clusters including rare-gas atoms
Authors: Hori A , Hondoh T 
Published: May 2003

Dodecahedral water clusters including rare-gas atoms and molecules are considered to play an important role in the beginning of the formation of gas hydrates in solutions. To investigate their stability, ab initio molecular-orbital calculations were performed at the MP2/6-311G(d,p)//HF/6-311G(d,p) level. In He, Ne, Ar, and Kr, the cohesive energies of the 12-hedral water clusters including each rare-gas atom were negative, whereas in Xe they were positive. Neon in the dodecahedral cluster was almost as stable as Ar and Kr in the dodecahedral clusters; the latter two are known as clathrate-forming gases. This suggests the probability of the existence of Ne clathrate hydrate, which is generally considered to be impossible. The chemical shifts of Xe incorporated in polyhedral water clusters were computed for the first time. The computed values qualitatively agree with the experimental results. PACS Nos.: 31.15Ar, 31.15Md, 31.15Ne, 36.40Cg, 36.40Mr
The inhibition of tetrahydrofuran clathrate-hydrate formation with antifreeze protein
Authors: Zeng H , Wilson L D , Walker V K , Ripmeester J A 
Published: May 2003

The effect of Type I fish antifreeze protein (AFP) from the winter flounder, Pleuronectes americanus (Walbaum), (WfAFP) on the formation of tetrahydrofuran (THF) clathrate hydrate was studied by observing changes in THF crystal morphology and determining the induction time for nucleation. AFP retarded THF clathrate-hydrate growth at the tested temperatures and modified the THF clathrate-hydrate crystal morphology from octahedral to plate-like. AFP appears to be even more effective than the kinetic inhibitor, polyvinylpyrrolidone (PVP). Recombinant AFP from an insect, a spruce budworm, Choristoneura fumiferana (Clem.), moth, (Cf) was also tested for inhibition activity by observation of the THF-hydrate-crystal-growth habit. Like WfAFP, CfAFP appeared to show adsorption on multiple THF-hydrate-crystal faces. A protein with no antifreeze activity, cytochrome C, was used as a control and it neither changed the morphology of the THF clathrate-hydrate crystals, nor retarded the formation of the hydrate. Preliminary experiments on the inhibition activity of WfAFP on a natural gas hydrate assessed induction time and the amount of propane gas consumed. Similar to the observations for THF, the data indicated that WfAFP inhibited propane-hydrate growth. Taken together, these results support our hypothesis that AFPs can inhibit clathrate-hydrate growth and as well, offer promise for the understanding of the inhibition mechanism. PACS No.: 87.90ty
Ab-initio density-functional lattice-dynamics studies of ice
Authors: Cote A S , Morrison I , Cui X , Jenkins S , Ross D K 
Published: May 2003

We present the results of first-principles computational studies of the dynamical properties of hexagonal ice using both the ab-initio pseudopotential method and the full-potential augmented plane-wave method. Properties obtained using both the generalized gradient approximation (GGA) and the meta-GGA in density-functional theory are compared. The lattice-dynamical properties of the structures are obtained using a finite-difference evaluation of the dynamical matrix and force-constant matrix from atomic forces. Phonon dispersion is evaluated by the direct determination of the force-constant matrix in supercells derived from the primitive molecule unit cells with the assumption that force constants are zero beyond the second molecular nearest neighbors. The k-dependent phonon frequencies are then obtained from the force-constant matrix and dispersion relations, and the Brillouin-zone integrated density of states is evaluated. The importance of phonon dispersion in the various regions of the phonon spectra is then assessed and compared to existing neutron-scattering data. Frozen-phonon calculations are used to compare phonon frequencies evaluated in both the GGA and meta-GGA. PACS Nos.: 61.12Ex, 63.20Dj