bluuebunny/crossref_metadata_2025_split huggingface dataset:
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
AN OPTIMAL LOW-ORDER LOCKING-FREE FINITE ELEMENT METHOD FOR REISSNER–MINDLIN PLATES
Authors: CHAPELLE D. , STENBERG R. 
Published: May 2003

We propose a simple modification of a recently introduced locking-free finite element method for the Reissner–Mindlin plate model. By this modification, we are able to obtain optimal convergence rates on numerical benchmarks. These results are substantiated by a complete mathematical analysis which provides optimal a priori error estimates.
A DEGENERATE PARABOLIC VARIATIONAL INEQUALITY FOR THE AMERICAN OPTION PRICING PROBLEM
Authors: MASTROENI LORETTA , MATZEU MICHELE 
Published: May 2003

A formulation in terms of degenerate parabolic variational inequalities for the price of an American put option is stated. The usual uniform ellipticity condition is weakened by the presence of a weight function. Then the appropriate framework is that of some suitable "weighted" Sobolev spaces. One applies a result previously stated by the authors in Ref. 8.
A FINSLER GEOMETRIC MODEL OF EVOLUTION BY SYMBIOSIS
Authors: ANTONELLI P. L. 
Published: May 2003

Finsler geometry in two dimensions is introduced to solve the problem of modelling two freely living populations (e.g. bacterial) which affect the stable physiology of a colonial organism. The populations are assumed to be logistic, but chemical producing. Concepts of Medawar's growth energy, Margulis' evolution by symbiosis, Harper's modular organisms and Wilson's ergonomics are formulated in terms of Volterra–Hamilton systems of Finsler type. It is proved that there can be no Riemannian models.
PATTERNS OF ALCOHOLISM: A MATHEMATICAL MODEL
Authors: AN DER HEIDEN U. , SCHWEGLER H. , TRETTER F. 
Published: May 2003

In a first phenomenological part various forms of alcoholism and their classification are summarized. Our aim is to give an explanation of these patterns of alcohol consumption and addiction. Social, psychic, behavioral, and biochemico-physiological mechanisms currently discussed in the literature are briefly considered with respect to their potential for generating the dynamics of alcohol addiction. As central core those mechanisms turn out to be self-enhancing. By formulating these mechanisms in terms of mathematical models a tool is provided to study their consequences in isolation and in qualitative and quantitative detail. The mathematical modeling is put forward in several steps starting with a single (differential) equation for the process of self-enhancement. This process, acting alone, leads to exponential and unbounded increase of the average alcohol consumption. In a second step, inhibitory mechansims are added which result e.g. from negative effects of alcohol drinking. The combination and different relative weights of self-enhancement and inhibition can already explain several types of drinking behavior, in particular those of α, β, γ and δ drinkers according to the classification of Jellinek. Possible transitions from one type to another and also to abstinence become imaginable by discussion of bifurcations on a 'cusp catastrophe". Oscillatory phenomena in drinking behavior, e.g. the "episodic drinker", result if and only if, in a further step, the model is complemented by a second differential equation accounting for the dynamics of an internal state symbolically called "frustration level". More generally this variable may represent any factor which interacts in a circular fashion (feedback loop) with the alcohol consumption. In connection with the presented models, various ways and strategies for the transition from one type of drinking behavior to another (including low level drinking or abstinence) are discussed.
ASYMPTOTICS FOR CRITICAL FIELDS IN AN APPROXIMATE GINZBURG–LANDAU MODEL IN THE LARGE SIZE LIMIT
Authors: BOLLEY CATHERINE , HELFFER BERNARD 
Published: May 2003

Pursuing a study of the superheating field for the Ginburg–Landau equations performed in Ref. 8, we consider an approximate model for a film on a bounded interval when the thickness 2e is large in comparison with the inverse of the characteristic κ of the material. We show for this problem the existence of a local superheating field, and recover, as e tends to +∞, the superheating field for a similar approximate model on a semi-infinite interval which has been studied in Ref. 8.
STABILITY AND CONVERGENCE OF TWO-LEVEL DIFFERENCE SCHEMES IN INTEGRAL WITH RESPECT TO TIME NORMS
Authors: SAMARSKII ALEXANDER A. , MATUS PETR P. , VABISHCHEVICH PETR N. 
Published: May 2003

Nowadays the general theory of operator-difference schemes with operators acting in Hilbert spaces has been created for investigating the stability of the difference schemes that approximate linear problems of mathematical physics. In most cases a priori estimates which are uniform with respect to the t norms are usually considered. In the investigation of accuracy for evolutionary problems, special attention should be given to estimation of the difference solution in grid analogs of integral with respect to the time norms. In this paper a priori estimates in such norms have been obtained for two-level operator-difference schemes. Use of that estimates is illustrated by convergence investigation for schemes with weights for parabolic equation with the solution belonging to [Formula: see text].
A NONOVERLAPPING DOMAIN DECOMPOSITION METHOD FOR THE OSEEN EQUATIONS
Authors: OTTO F.-C. , LUBE G. 
Published: May 2003

We describe a nonoverlapping domain decomposition algorithm which can be applied to scalar advection–diffusion reaction problems and the Oseen equations. A convergence result is proved for the continuous algorithm in case of the Oseen equations and stated for the other case. We give some suggestions for the design of the interface conditions used within the algorithm and present some numerical examples.
THERE ARE NO STRICT GREAT x-CYCLES AFTER A REDUCING OR P2 SURGERY ON A KNOT
Authors: HOFFMAN JAMES A. 
Published: May 2003

The Cabling conjecture states that Dehn surgery on a nontrivial knot K in S3 yields a reducible manifold only when K is a nontrivial cabled knot. One idea is to attack this problem with the techniques used by Gordon and Luecke in the Knot Complement Problem. This involves a combinatorial analysis of two intersecting planar graphs. In the context of reducible surgery, one of the two planar graphs will necessarily contain a Scharlemann cycle. So, we define a strict x-cycle to be any x-cycle which is not a Scharlemann cycle; likewise, for strict great x-cycles. We show that if the reducing sphere meets the core of the Dehn filling minimally, then strict great x-cycles are not permitted. Thus, strict great x-cycles can play a role similar to that of the Scharlemann cycle in the Knot Complement Problem. The obstruction of finding strict great x-cycles is considered an essential step in the program. A second conjecture states that Dehn surgery on a nontrivial knot K in S3 yields a manifold containing an embedded projective plane only when K is a nontrivial cabled knot. We show how the Gordon and Luecke technique can be applied towards this conjecture by considering the spherical boundary of a regular neighborhood of the projective plane. And if the projective plane is chosen to meet the core of the Dehn filling minimally, we show that strict great x-cycles are not permitted.
REGULAR HOMOTOPY AND VASSILIEV INVARIANTS OF GENERIC IMMERSIONS Sk → ℝ2k-1, k ≥ 4
Authors: EKHOLM TOBIAS 
Published: May 2003

The regular homotopy class of a generic immersion Sk → ℝ2k-1 is calculated in terms of its self intersection manifold with natural additional structures. There is a natural notion of Vassiliev invariants of generic immersions. These may take values in any Abelian group G. It is proved that, for any m, the group of mth order G-valued invariants modulo invariants of lower order is isomorphic to G and that the Vassiliev invariants are not sufficient to separate generic immersions, which can not be obtained from each other by a regular homotopy through generic immersions.
RELIABILITY CONCEPTS FOR MOBILE AGENTS
Authors: STRASSER MARKUS , ROTHERMEL KURT 
Published: May 2003

The use of mobile agent technology has been proposed for various fault-sensitive application areas, including electronic commerce and system management. A prerequisite for the use of mobile agents in these environments is that agents have to be executed reliably, independent of communication and node failures. In this article, we present two approaches improving the level of fault-tolerance in agent execution. The introduction of an itinerary concept allows to specify an agent's travel plan flexibly and provides the agent system with the possibility to postpone the visit of currently unavailable nodes or to choose alternative nodes in case of node failures. The second approach is a recently proposed fault-tolerant protocol to ensure the exactly-once execution of an agent. With this protocol, agents are preformed in stages. Each stage consists of a number of nodes. One of these nodes executes the agent while the others monitor the execution. After a summary of this protocol, we focus on the construction of stages. In particular, we investigate how the number of nodes per stage influences the probability of an agent to be blocked due to failures and which nodes should be selected when forming a stage to minimize the protocol overhead.
Psychological factors affecting market dynamics: the role of uncertainty and need satisfaction
Authors: Janssen Marco A. , Jager Wander 
Published: June 2003

Markets can show different types of dynamics, ranging from stable markets dominated by one or a few products, to fluctuating markets where products are frequently being replaced by new versions. This paper explores the dynamics of markets from a psychological perspective using a multi-agent simulation model. The behavioural rules of the artificial consumers, the consumats, are based on a conceptual meta-theory from psychology. The artificial consumers have to choose each period between different products. Products remain on the market for as long as their market share exceeds a minimum level. If not, it will be replaced by a new product. Simulation experiments are being performed with a population of consumats having different preferences. Results show that the dominating type of cognitive (choice) process has large consequences for the resulting market dynamics. Moreover, the size of the social network affects the market dynamics too.