bluuebunny/crossref_metadata_2025 huggingface dataset:
Sound production in neonate sperm whales (L)
Authors: Madsen P. T. , Carder D. A. , Au W. W. L. , Nachtigall P. E. , Møhl B. , Ridgway S. H.
Published: May 2003

Acoustic data from two sperm whale neonates (Physeter macrocephalus) in rehabilitation are presented and implications for sound production and function are discussed. The clicks of neonate sperm whale are very different from usual clicks of adult specimens in that neonate clicks are of low directionality [SL anomaly (0°–90°) <8 dB], long duration (2–12 ms), and low frequency (centroid frequency between 300 and 1700 Hz) with estimated SLs between 140 and 162 dB//1 μPa (rms). Such neonate clicks are unsuited for biosonar, but can potentially convey homing information between calves and submerged conspecifics in open ocean waters at ranges of some 2 km. Moreover, it is demonstrated that sperm whale clicks are produced at the anterior placed monkey lips, thereby substantiating a key point in the modified Norris and Harvey theory and supporting the unifying theory of sound production in odontocetes.
Three-dimensional elastic wave scattering by a layer containing vertical periodic fractures
Authors: Nakagawa Seiji , Nihei Kurt T. , Myer Larry R. , Majer Ernest L.
Published: May 2003

Elastic wave scattering off a layer containing a single set of vertical periodic fractures is examined using a numerical technique based on the work of Hennion et al. [J. Acoust. Soc. Am. 87, 1861–1870 (1990)]. This technique combines the finite element method and plane wave method to simulate three-dimensional scattering off a two-dimensional fractured layer structure. Each fracture is modeled explicitly, so that the model can simulate both discrete arrivals of scattered waves from individual fractures and multiply scattered waves between the fractures. Using this technique, we examine changes in scattering characteristics of plane elastic waves as a function of wave frequency, angle of incidence, and fracture properties such as fracture stiffness, height, and regular and irregular spacing.
An improved water-filled impedance tube
Authors: Wilson Preston S. , Roy Ronald A. , Carey William M.
Published: May 2003

A water-filled impedance tube capable of improved measurement accuracy and precision is reported. The measurement instrument employs a variation of the standardized two-sensor transfer function technique. Performance improvements were achieved through minimization of elastic waveguide effects and through the use of sound-hard wall-mounted acoustic pressure sensors. Acoustic propagation inside the water-filled impedance tube was found to be well described by a plane wave model, which is a necessary condition for the technique. Measurements of the impedance of a pressure-release terminated transmission line, and the reflection coefficient from a water/air interface, were used to verify the system.
Interactive resonant scattering by a cluster of air bubbles in water
Authors: Skaropoulos Nikolaos C. , Yagridou Helen D. , Chrissoulidis Dimitrios P.
Published: May 2003

An exact, analytical solution is developed for the problem of acoustic-wave scattering from a cluster of ideal, gaseous, spherical bubbles in an unbounded, homogeneous, host fluid. This solution takes into account all modes of oscillation of the bubbles as well as all interactions between them; it is applicable to a wide range of bubble sizes and excitation frequencies. In the low frequency regime, the theory of this paper is shown to reduce to the “monopole” approximation, the effect of higher-order modes being non-negligible only for very small bubble-to-bubble separations. A numerical study of interactive backscattering from small clusters, comprising up to three ideal bubbles, is presented. Interactions between the bubbles are shown to produce downward shifts in the resonance frequency of the cluster, when the scattering configuration is symmetric. Furthermore, asymmetries of the scattering configuration are shown to generate sharp resonances at frequencies above the resonance of the symmetric mode. The results of this paper agree with previous theoretical and experimental work.
Effects of speaking rate on second formant trajectories of selected vocalic nuclei
Authors: Weismer Gary , Berry Jeff
Published: May 2003

The effect of speaking rate variations on second formant (F2) trajectories was investigated for a continuum of rates. F2 trajectories for the schwa preceding a voiced bilabial stop, and one of three target vocalic nuclei following the stop, were generated for utterances of the form “Put a bV here, where V was /i/, /æ/ or /oɪ/. Discrete spectral measures at the vowel-consonant and consonant-vowel interfaces, as well as vowel target values, were examined as potential parameters of rate variation; several different whole-trajectory analyses were also explored. Results suggested that a discrete measure at the vowel consonant (schwa-consonant) interface, the F2off value, was in many cases a good index of rate variation, provided the rates were not unusually slow (vowel durations less than 200 ms). The relationship of the spectral measure at the consonant-vowel interface, F2 onset, as well as that of the “target” for this vowel, was less clearly related to rate variation. Whole-trajectory analyses indicated that the rate effect cannot be captured by linear compressions and expansions of some prototype trajectory. Moreover, the effect of rate manipulation on formant trajectories interacts with speaker and vocalic nucleus type, making it difficult to specify general rules for these effects. However, there is evidence that a small number of speaker strategies may emerge from a careful qualitative and quantitative analysis of whole formant trajectories. Results are discussed in terms of models of speech production and a group of speech disorders that is usually associated with anomalies of speaking rate, and hence of formant frequency trajectories.
Including dispersion and attenuation directly in the time domain for wave propagation in isotropic media
Authors: Norton Guy V. , Novarini Jorge C.
Published: May 2003

When sound propagates in a lossy fluid, causality dictates that in most cases the presence of attenuation is accompanied by dispersion. The ability to incorporate attenuation and its causal companion, dispersion, directly in the time domain has received little attention. Szabo [J. Acoust. Soc. Am. 96, 491–500 (1994)] showed that attenuation and dispersion in a linear medium can be accounted for in the linear wave equation by the inclusion of a causal convolutional propagation operator that includes both phenomena. Szabo’s work was restricted to media with a power-law attenuation. Waters et al. [J. Acoust. Soc. Am. 108, 2114–2119 (2000)] showed that Szabo’s approach could be used in a broader class of media. Direct application of Szabo’s formalism is still lacking. To evaluate the concept of the causal convolutional propagation operator as introduced by Szabo, the operator is applied to pulse propagation in an isotropic lossy medium directly in the time domain. The generalized linear wave equation containing the operator is solved via a finite-difference-time-domain scheme. Two functional forms for the attenuation often encountered in acoustics are examined. It is shown that the presence of the operator correctly incorporates both, attenuation and dispersion.
Some extensions of the Gaussian beam expansion: Radiation fields of the rectangular and the elliptical transducer
Authors: Ding Desheng , Zhang Yu , Liu Jinqiu
Published: May 2003

A straightforward extension of Gaussian beam expansion is presented for calculation of the Fresnel field integral [J. J. Wen and M. A. Breazeale, J. Acoust. Soc. Am. 83, 1752–1756 (1988)]. The source distribution function is expanded into the superposition of a series of two-dimensional Gaussian functions. The corresponding radiation field is expressed as the superposition of these two-dimensional Gaussian beams and is then reduced to the computation of these simple functions. This treatment overcomes the limit that the shape of source is of circular axial-symmetry. The numerical examples are presented for the field of the (uniform) elliptical and the rectangular piston transducers and agree well with the results given by complicated computation.
Arctic field trials of source bearing estimation using ice-mounted geophones (L)
Authors: Dosso Stan E. , Vinnins Michael , Heard Garry J.
Published: May 2003

Results are presented from Arctic field trials carried out to estimate the bearing to acoustic sources in the water column using seismic particle motion measured at a tri-axial geophone mounted on the sea ice surface. Source bearings are estimated by applying polarization filters to suppress seismic waves with transverse particle motion and computing the incident power rotated into radial look angles from 0° to 360°; the inherent 180° ambiguity is resolved by requiring out-going (prograde) particle motion in the vertical-radial plane. An earlier study considered impulsive sources at ranges of 200–1000 m at a site characterized by mixed annual ice. The present work considers two studies of similar scale carried out at sites with uniformly smooth annual ice and rough, ridged annual ice, and a third study on multi-year ice involving sources at 2–50-km range. The results indicate good bearing estimation to long range with little dependence on ice type.
Pitch discrimination of diotic and dichotic tone complexes: Harmonic resolvability or harmonic number?
Authors: Bernstein Joshua G. , Oxenham Andrew J.
Published: May 2003

Three experiments investigated the relationship between harmonic number, harmonic resolvability, and the perception of harmonic complexes. Complexes with successive equal-amplitude sine- or random-phase harmonic components of a 100- or 200-Hz fundamental frequency (f0) were presented dichotically, with even and odd components to opposite ears, or diotically, with all harmonics presented to both ears. Experiment 1 measured performance in discriminating a 3.5%–5% frequency difference between a component of a harmonic complex and a pure tone in isolation. Listeners achieved at least 75% correct for approximately the first 10 and 20 individual harmonics in the diotic and dichotic conditions, respectively, verifying that only processes before the binaural combination of information limit frequency selectivity. Experiment 2 measured fundamental frequency difference limens (f0 DLs) as a function of the average lowest harmonic number. Similar results at both f0’s provide further evidence that harmonic number, not absolute frequency, underlies the order-of-magnitude increase observed in f0 DLs when only harmonics above about the 10th are presented. Similar results under diotic and dichotic conditions indicate that the auditory system, in performing f0 discrimination, is unable to utilize the additional peripherally resolved harmonics in the dichotic case. In experiment 3, dichotic complexes containing harmonics below the 12th, or only above the 15th, elicited pitches of the f0 and twice the f0, respectively. Together, experiments 2 and 3 suggest that harmonic number, regardless of peripheral resolvability, governs the transition between two different pitch percepts, one based on the frequencies of individual resolved harmonics and the other based on the periodicity of the temporal envelope.
Background noise in piezoresistive, electret condenser, and ceramic microphones
Authors: Zuckerwar Allan J. , Kuhn Theodore R. , Serbyn Roman M.
Published: May 2003

Background noise studies have been extended from air condenser microphones to piezoresistive, electret condenser, and ceramic microphones. Theoretical models of the respective noise sources within each microphone are developed and are used to derive analytical expressions for the noise power spectral density for each type. Several additional noise sources for the piezoresistive and electret microphones, beyond what had previously been considered, were applied to the models and were found to contribute significantly to the total noise power spectral density. Experimental background noise measurements were taken using an upgraded acoustic isolation vessel and data acquisition system, and the results were compared to the theoretically obtained expressions. The models were found to yield power spectral densities consistent with the experimental results. The measurements reveal that the 1/f noise coefficient is strongly correlated with the diaphragm damping resistance, irrespective of the detection technology, i.e., air condenser, piezoresistive, etc. This conclusion has profound implications upon the expected 1/f noise component of micromachined (MEMS) microphones.
Causal impedance matching for broadband hybrid noise absorption
Authors: Yuan Jing
Published: May 2003

The complementary strengths and weaknesses of passive and active noise control (ANC) methods have motivated many researchers to develop hybrid noise absorbers that integrate both control strategies. The impedance matching technique (IMT) is the most effective for such a purpose. An unsolved problem with available IMT schemes is the a priori reference signal that limits IMT applications. This study proposes the use of the forward wave, available by the two-microphone method, as the reference signal. Due to inevitable errors in wave separation and inlet reflection of the control signal, the absorber becomes a feedback system. A simple and stable ANC is developed for impedance matching without the a priori reference signal. The proposed absorber has an absorption coefficient of 0.9 or above in a frequency range of 60–850 Hz. It is stable in the presence of sensor mismatch and robust with respect to significant variation of inlet boundary conditions.
Jet forking driven by pipe tone
Authors: Karthik B. , Chakravarthy S. R. , Sujith R. I.
Published: May 2003

The present work deals with an experimental investigation of flow of air through a square-edged circular orifice at the downstream end of a circular duct. Self-excited acoustic oscillations at the natural duct modes are observed for certain flow velocities when the orifice is sufficiently thick. For a specific Reynolds number based on the orifice diameter and the mean jet velocity (9150<Re<9850), the jet forks into two trains, with the alternating vortices falling into the same branch of the forked train. Whereas this phenomenon has been reported earlier to have occurred when the density ratio of the jet is less than 0.72, the present results show that it is possible for a jet having the same density as the ambient atmosphere. The jet forking is coincident with jump in the acoustic frequency from one natural acoustic mode to another with comparable amplitudes of both the modes.
Variation in humpback whale (Megaptera novaeangliae) song length in relation to low-frequency sound broadcasts
Authors: Fristrup Kurt M. , Hatch Leila T. , Clark Christopher W.
Published: May 2003

Humpback whale song lengths were measured from recordings made off the west coast of the island of Hawai’i in March 1998 in relation to acoustic broadcasts (“pings”) from the U.S. Navy SURTASS Low Frequency Active sonar system. Generalized additive models were used to investigate the relationships between song length and time of year, time of day, and broadcast factors. There were significant seasonal and diurnal effects. The seasonal factor was associated with changes in the density of whales sighted near shore. The diurnal factor was associated with changes in surface social activity. Songs that ended within a few minutes of the most recent ping tended to be longer than songs sung during control periods. Many songs that were overlapped by pings, and songs that ended several minutes after the most recent ping, did not differ from songs sung in control periods. The longest songs were sung between 1 and 2 h after the last ping. Humpbacks responded to louder broadcasts with longer songs. The fraction of variation in song length that could be attributed to broadcast factors was low. Much of the variation in humpback song length remains unexplained.
Pure ices IV and XII from high-density amorphous ice
Authors: Salzmann C G , Kohl I , Loerting T , Mayer E , Hallbrucker A
Published: May 2003

High-density amorphous ice (HDA), made by compression of hexagonal ice at 77 K, was heated at a constant pressure of 0.81 GPa up to 183 K and its phase transition followed by displacement-temperature curves. The crystalline phases, recovered at 77 K and 1 bar, were characterized by X-ray diffraction. Pure D2O ice IV and nearly pure H2O ice IV were formed on slow heating at a rate of 0.4 K min1, whereas pure H2O ice XII and D2O ice XII were formed on fast heating at [Formula: see text] 15 K min1. On heating HDA at rates in between these two values a mixture of ice IV and ice XII was obtained, where their relative yields depended in a systematic manner on the heating rate. Conversion of HDA into either ice IV or ice XII is an example of a "parallel reaction" where the relative yields of ice IV and ice XII can be controlled by temperature, i.e., by the rate of heating, in our approach. It is conceivable that a similar behaviour occurs on crystallization of the related pressure-amorphized silica.

PACS Nos.: 61.10-i, 64.60-i, 64.70-p
Effect of isochronal annealing on CdTe and the study of electrical properties of AuCdTe Schottky devices
Authors: Amanullah F M
Published: May 2003

Single-crystal CdTe was grown with the vapour phase technique. Dice were suitably etched and then annealed in air isochronally at different temperatures (473, 573, 673, and 773 K) for the same period of time (1 h). Schottky barriers were made by vacuum evaporation of gold onto the as-grown CdTe single-crystal substrate as well as onto the isochronally annealed substrates. The physical properties of AuCdTe devices were studied as a function of temperature by electrical methods, such as capacitancevoltage and currentvoltage analysis. The isochronal annealing technique was found to produce a significant change in the electrical properties, such as barrier height, carrier concentration, ideality factor, and forward-bias threshold, of the AuCdTe Schottky diode. The observations are discussed in terms of the various theories of Schottky barrier formation.

PACS No.: 73.30ty
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
Dynamic mechanical measurements on fresh-water ice during freezing and thawing: preliminary results
Authors: Fitzgerald E R
Published: May 2003

An automated measurement system for elastic (J' ) and viscous (J'' ) components of complex shear compliance, J* = J'  iJ'', and the elastic (G' ) and viscous (G'' ) components of complex shear modulus, G* = G' + iG'' = 1/J*, has been used to obtain these material parameters for fresh-water ice during freezing and thawing. The system is reviewed briefly and yields mechanical loss tangents, J''/J' = G''/G', the shear-wave velocity and attenuation, in addition to shear compliance and modulus, at sinusoidal vibration frequencies from 2 to 10 000 Hz at temperatures between 25 and 150°C. Results reported here are chiefly at temperatures from 10 to 10°C. The required sample disk pairs, which are clamped to a central drive plate, are prepared outside the apparatus for solids and gels. Liquids of known volume are inserted between the drive plate and surrounding clamps at a separation distance, h, by a syringe to form sample disks of area, A = Volume / h. Measurements at 58 frequencies between 2 and 10 000 Hz require 3.5 min; several measurements at each temperature were made to test for equilibrium. Results for both tap and distilled water above freezing revealed high values of elastic (J' ) compliance that decreased sharply at 100 Hz and higher frequencies. Tap-water samples with 4 to 6% by volume air bubbles were less compliant ("stiffer") above freezing than samples with 0 to 1% by volume air, but when frozen, the samples with the smaller volume of air bubbles were less compliant, that is, had higher modulus values than the samples with high air-bubble volumes. Dynamic mechanical property changes in the transition from water to ice are compared to changes previously found during phase transitions in other materials. Further investigation on the effects of air-bubble volumes on dynamic mechanical properties of both water and ice is planned.

PACS Nos.: 62.30+d, 62.40+i
The effect of HCl adsorption on the structure and dynamics of the ice surface
Authors: Suzanne J , Ferry D , Demirdjian B , Girardet C , Toubin C , Picaud S , Hoang P NM
Published: May 2003

Neutron diffraction and quasi-elastic neutron scattering experiments together with molecular dynamics simulations were performed to investigate the effect of HCl adsorption in the sub-monolayer range on the structure and dynamics of a thin ice Ih film deposited on a MgO (100) substrate. We show that surface melting occurs in the supported pure-ice film down to about 8 K below the normal melting temperature of bulk ice Ih. Upon HCl adsorption, the surface melting temperature is still lowered by 15 K at HCl amounts corresponding to 0.3 and 0.6 monolayer. Results of simulations can satisfactorily interpret the lowering of the melting temperature due to the support and to HCl adsorption. Upon adsorption of one HCl monolayer, HCl dihydrate is formed at 220 K and the film becomes amorphous at 250 K. The results are discussed within the context of stratospheric and upper tropospheric/lower stratospheric chemistry.

PACS Nos.: 68.55-a, 61.12-q, 31.15Qg, 82.33Tb
Dependence of the normal modes on the electronic structure of various phases of ice as calculated by ab initio methods
Authors: Jenkins S , Kirk S R , Côté A S , Ross D K , Morrison I
Published: May 2003

The charge-density distribution in various phases of ice is used to explore the information that can be obtained about the preferred directions of motion of atoms so as to investigate the possibility of the creation of more efficient and computationally cost-effective dynamical matrices.

PACS Nos.: 63.20Dj, 31.90+s, 71.10-w
A new approach to the study of interfacial melting of ice: infrared spectroscopy
Authors: Sadtchenko V , Ewing G E
Published: May 2003

Faraday observed in 1850 "that a particle of water which could retain the liquid state whilst touching ice on only one side, could not retain the liquid if it were touched by ice on both" (M. Faraday, Royal Institution Discourse, June 7, 1850; Experimental Researches in Chemistry and Physics (Taylor and Francis, New York, 1991)). Thus began the concept of interfacial melting, and the presence of a liquid water film on the surface of ice at temperatures of 0°C and below. Over the past few decades, there have been a number of measurements of interfacial melting. In some studies, the thickness of the thin film, variously called the quasi-liquid layer (QLL), liquid-like layer, surface melting layer, or premelting layer, has been determined. The results of these measurements demonstrate a striking variation depending on the experimental method and the nature of the ice samples. For example, at 0.1°C, the thickness values range over two orders of magnitude from around 1 to 100 nm. Although the disagreement can be partially explained by the differences in ice samples, the experimental techniques employed in measurements of the QLL thickness are based on different physical principals, and involve a web of assumptions for their deconvolution. We describe here the technique of infrared attenuated total reflection (ATR) spectroscopy that has been directed to the study of interfacial melting of ice for the first time.

PACS No.: 83.50Lh
On the thermodynamic stability of clathrate hydrates
Authors: Tanaka H
Published: May 2003

The thermodynamic stability of clathrate hydrates is investigated by theoretically examining the free energy of formation of clathrate hydrates encaging propane and argon. The total free energy is divided into several contributions: the interaction between water and guest molecules, the entropic contribution arising from the combinations of cage occupancy, and the free energy due to intermolecular vibrations. The method introduced here removes some of the assumptions of the van der Waals and Platteeuw theory. It is shown that the shift of the vibrational frequency of the host lattice destabilizes the clathrate hydrates thermodynamically.

PACS No.: 61.50Ah