bluuebunny/crossref_metadata_2025 huggingface dataset:
Middle Jurassic air fall tuff in the sedimentary Latady Formation, eastern Ellsworth Land
Authors: HUNTER MORAG A. , RILEY TEAL R. , MILLAR IAN L.
Published: June 2004

Rhyolitic volcanism along the proto-Pacific margin of Gondwana occurred at intervals throughout the Jurassic. Silicic melt generation has been interpreted as a result of interaction between mantle plumes and subduction modified lower crust. The rhyolitic Mount Poster Formation of the southern Antarctic Peninsula is c. 184 Ma in age (V1), whereas silicic volcanism of the northern Antarctic Peninsula is c. 168 Ma (V2). A thin, (13.5 cm) reworked air fall tuff, interbedded with sandstone and mudstone of the Latady Formation in the southern Antarctic Peninsula has a REE pattern similar to V2 volcanic material but is isotopically similar to the extracaldera, low-Ti rhyolites of the V1 Mount Poster Formation. The tuff is interbedded with lithofacies that have been assigned a Callovian age (164–159 Ma) in the west of the area. Simple mixing between a MASH source and reworked Early Jurassic (184 Ma) V1 volcanic material during V2 volcanism in the area explains the apparent discrepancy between the faunal age and the isotopic characteristics of the ash fall. This supports a Middle Jurassic (168 Ma) age that also corresponds to a 167 ± 3 Ma age from Mt Rex on the periphery of the Mount Poster Formation, which was previously thought to be anomalous.
Changes of major ion concentrations in melting snow and terrestrial waters from northern Victoria Land, Antarctica
Authors: BORGHINI FRANCESCA , BARGAGLI ROBERTO
Published: June 2004

Concentrations of major ions (Cl−, NO3−, SO42−, Na+, K+, Mg2+, Ca2+) were measured in melting snow and water samples from streams and lakes in ice-free areas throughout northern Victoria Land. Most ions in snow and terrestrial water derive from the marine environment and their concentrations are extremely variable in space and time, especially in water systems without melting snow and ice. The distance from the sea, snow sublimation, changes in water inflow, evaporative concentrations, weathering and drainage processes in the catchment, nesting seabirds and aquatic microbiota are among factors which most influence ion composition variability. Comparisons with data from twelve years ago in the same lakes indicate that the warming trend detected at Terra Nova Bay station during this period did not affect the biogeochemistry of water systems. Waters from a lake which recently experienced a lowering of the water level showed a remarkable increase in SO42− concentrations. We hypothesized that the differential mobility of sulphate salts in the Antarctic soils, the biosynthesis of sulphur compounds in the lake, and the progressive decrease of the water volume are factors involved in the increase of SO42− concentrations.
Inverse problems of mixed type in linear plate theory
Authors: SALAZAR DOMINGO , WESTBROOK REX
Published: June 2004

The characterisation of those shapes that can be made by the gravity sag-bending manufacturing process used to produce car windscreens and lenses is modelled as an inverse problem in linear plate theory. The corresponding second-order partial differential equation for the Young's modulus is shown to change type (possibly several times) for certain target shapes. We consider the implications of this behaviour for the existence and uniqueness of solutions of the inverse problem for some frame geometries. In particular, we show that no general boundary conditions for the inverse problem can be prescribed if it is desired to achieve certain kinds of target shapes.
Blowup and dissipation in a critical-case unstable thin film equation
Authors: WITELSKI T. P. , BERNOFF A. J. , BERTOZZI A. L.
Published: June 2004

We study the dynamics of dissipation and blow-up in a critical-case unstable thin film equation. The governing equation is a nonlinear fourth-order degenerate parabolic PDE derived from a generalized model for lubrication flows of thin viscous fluid layers on solid surfaces. %For a special balance between %destabilizing second-order terms and regularizing fourth-order terms, There is a critical mass for blow-up and a rich set of dynamics including families of similarity solutions for finite-time blow-up and infinite-time spreading. The structure and stability of the steady-states and the compactly-supported similarity solutions is studied.
Global stability in a model of the glucose-insulin interaction with time delay
Authors: BENNETT D. L. , GOURLEY S. A.
Published: June 2004

A variety of models on the interaction between glucose and insulin have been suggested over the last 50 years. One, developed by Sturis et al. [19], and consisting of six nonlinear ordinary differential equations, has been widely accepted. However, the model has the disadvantage of containing auxiliary variables which have no clinical interpretation. In this paper we study an alternative model which incorporates a time delay explicitly, negating the need for the auxiliary equations. A simplifying assumption of having just one insulin compartment reduces the number of equations still further. We then study the resulting system of two differential delay equations, establishing results on positivity, boundedness, persistence and global asymptotic stability. For the latter, two quite different approaches are employed: comparison principles and Lyapunov functionals. The two approaches provide different sets of sufficient conditions for global stability, so that we investigate different regions of parameter space.
The significance of Southwest Greenland as winter quarters for seabirds
Authors: BOERTMANN DAVID , LYNGS PETER , MERKEL FLEMMING RAVN , MOSBECH ANDERS
Published: June 2004

The coastal and offshore waters of Southwest Greenland are internationally important winter quarters for seabirds. We crudely estimate a minimum of 3.5 million seabirds using the region in winter, mainly from Arctic Canada, Greenland and Svalbard, with smaller numbers also from Alaska, Iceland, mainland Norway and Russia. The most numerous species are Common Eider Somateria mollissima, King Eider S. spectabilis, Brünnich's Guillemot Uria lomvia and Little Auk Alle alle. The most immediate threat to the seabirds in Southwest Greenland is hunting, and current levels of usage of the Greenland breeding populations of Brünnich's Guillemot and Common Eider are considered unsustainable. Conservation measures are required for these populations.
The breeding biology of the Critically Endangered Seychelles Scops-owl Otus insularis: consequences for conservation and management
Authors: CURRIE DAVE , FANCHETTE RODNEY , MILLETT JAMES , HOAREAU CAMILLE , SHAH NIRMAL J.
Published: June 2004

The endemic Seychelles Scops-owl Otus insularis is a Critically Endangered restricted-range species currently recorded only from the montane forest of Mahé, the largest (152 km2) and highest (903 m) island in the granitic Seychelles. Limited research has been conducted on the species and, in particular, details of its breeding biology are poorly known. Behavioural observations were made on 12 pairs by the systematic monthly use of playback of conspecific calls, in conjunction with frequent non-playback territory visits from April 1999 to May 2001. A total of eight nests, including the first nest record, were found on three territories. All were in tree cavities (7–25 m high) and contained either a single egg or chick. This was consistent with additional observations of solitary fledglings (n = 11, from eight territories). Incubation lasted 3–4 weeks and the fledging period was 4–6 weeks (data from two nests). The timing of copulations, in conjunction with the detection of nests and fledglings, suggests that the scops-owl can breed throughout the year with peaks in nesting occurring around May and October. Sex roles during breeding were similar to those of other Strigidae owls: incubation was performed by the female; males courtship-fed the female prior to and during incubation, and the female and chick for the first 2 weeks post-hatching; and both parents fed older chicks and fledglings. Fledglings remained on territory for at least 3 months. Breeding success of study pairs was low: two of eight nests were successful and 11 fledglings (recorded from eight of 12 study territories) were observed in a 26-month period, equivalent to c. 0.5 fledglings per territory per year. Evidence suggests that alien predators may have been a factor limiting breeding success. We discuss the conservation implications of our findings.
Evidence on competition in English commercial banking, 1920–1970
Authors: CAPIE FORREST , BILLINGS MARK
Published: June 2004

Many commentators have contended that British banking lacked competition for much of the twentieth century. This article examines a range of evidence relating to English clearing banks in the middle decades of the century, when the banking ‘cartel’ was believed to be at its strongest. Data on interest rates charged and paid, rate spreads, profitability and expenses ratios, including new evidence from archival sources, are considered. Some propositions about cartels are supported, others contradicted, and some left unresolved. We conclude that the banking ‘cartel’ can be described as ‘soft’, rather than ‘hard’ – that is, one which agreed strict output quotas and profits shares among its members.
Information technology and communication of musical experience: categories, conflicts and intersections
Authors: TANZI DANTE
Published: June 2004

The majority of composers and scholars in the field of electroacoustic and computer music address their attention to the problem of achieving satisfactory relationships between new technological instrumentalities and the very sense of music making. Reflections concerning the relationships between the use of digital technologies and musical expression have assumed an increasingly important role, since they provide interpretative codes of composers' works and assume an explanatory function during the presentation of new musical pieces. Focusing on the interaction between cognitive environments, emotive dimensions and communicative set-up, this paper intends to propose an analysis of some theoretical statements, which regard the relationships between scientific innovations and the evolutionary tendencies of technologically based music.
Electroacoustic preservation projects: how to move forward
Authors: TERUGGI DANIEL
Published: June 2004

Projects are emerging that reflect the growing concern with preservation and access to our electroacoustic heritage. In today's context it is difficult to find the huge financial means needed to facilitate a durable and efficient response to this problem. Some accessible objectives and projects are presented here which could be developed by the electroacoustic community. For a long time people have been concerned about the importance of the electroacoustic domain; the concern should now include the urgency of preservation.
Conservation and restoration of electroacoustic musical instruments at the Musée de la Musique, Paris
Authors: RAMEL SYLVIE
Published: June 2004

The Museum of Music in Paris possesses a collection of 280 instruments from the twentieth century. Most of them belong to the general families of electric and electronic musical instruments, which we will call ‘electrophones’, in deference to the name chosen by Curt Sachs (1940). The instruments are gathered in families so that the whole collection illustrates the milestones of the twentieth century; for instance, the museum has a large set of diverse Ondes Martenot. However, due to its scarcity, the Trautonium is represented by one of Oscar Sala's Mixtur-Trautonia.

Like any museum, we have to encourage the conservation of this heritage. To maintain a large collection of electrophones like the one we have, a specific knowledge base has to be developed. We have been working on this aspect of the project for the past two years. From the onset, it was decided to start the collection with the Ondes Martenot. Our aim was to define a model approach that could also be applied to other electric and electronic instruments. This work involves organising the instruments, studying them in order to outline conditions of appropriate conservation, and determining which kind(s) of restoration should be undertaken.

A first step has been to gather all information necessary to understanding the instrument and its mode of performance. With this goal in mind, we have taken a complete inventory of our collection with the aim of coming up with a first assessment of the state of the instruments and determining whether to allow performers to play them. Thanks to this work, we were able to start taking precautionary measures against degradation; we are now also able to answer many questions relevant to the restoration and conservation of this collection.
Reflections on the analysis of artificial vocality: representations, tools and prospective
Authors: BOSSIS BRUNO
Published: June 2004

Initially a result of talking heads, followed by the arrival of telephony and the gramophone, the use of artificial vocality within musical composition is becoming more and more common as different laboratories acquire devices enabling the manipulation of sound. Following Pierre Schaeffer's first experiments in Paris, many composers became interested in the expressive resources of the mechanical voice, the results of which are now present in a large corpus of electroacoustic works. By its very nature, artificial vocality establishes a new link between the vocal quality of a sound event (its vocality) and technology (its artificiality) within this type of music.

How then, can the musicologist study artificial vocality and the works in which it is used? Which tools should be used? What makes the analysis of artificial vocality so specific? Is it possible to create new tools for the analysis of artificial vocality within electroacoustic music?

In the search for answers to these questions, many difficulties present themselves. The first concerns the modes of representation and the methods used to analyse artificial vocality. On top of this, real reflection is needed concerning the disparity of technological tools used in analysis and the need for the application of a certain methodology in order to classify them. The starting point will be the establishment of a typology. Finally, the idea of being able to compare different representations of the same work using sophisticated tools will open the way to the discovery of new analytical approaches. Seeking freedom from the relative blindness caused by the over-specialisation and rigidity of technological tools is now an urgent necessity, particularly when considering artificial vocality.
Proton precipitation during transpolar auroral events: Observations with the IMAGE‐FUV imagers
Authors: Hubert B. , Gérard J. C. , Fuselier S. A. , Mende S. B. , Burch J. L.
Published: June 2004

Several transpolar auroras have been observed with the IMAGE‐Far Ultraviolet (FUV) imagers. The unique capability of the IMAGE‐FUV experiment to image the proton and electron aurora simultaneously on a global scale is used to study this phenomenon. A set of 12 transpolar aurora observed with IMAGE‐FUV is studied. We find that the dynamics of the transpolar aurora in relation with the IMF is consistent with previously published studies. The proton energy flux in the transpolar structure is determined and compared with the electron contribution. The contribution of the proton aurora inside the transpolar arc is also considered at the global scale. On the average, transpolar structure contributes ∼10% of the total precipitation. We find that the proton precipitation carries ∼5% of the energy flux of the transpolar arc. In 11 of the 12 cases of transpolar events studied, a local brightening of the auroral Lyman‐α emission is detected concurrently with the appearance of the transpolar structure. The intensification takes place at the nightside base of the transpolar arc, in the auroral oval. The duration of the intensification is variable but shorter than the lifetime of the transpolar arc. This study also suggests that the localized intensification is mainly due to an increase of the proton precipitation.
The Harris magnetic field: A laboratory realization of the topology based on energy resonance
Authors: Walker D. N. , Bowles J. H. , Amatucci W. E. , Holland D. L. , Chen J.
Published: June 2004

An often‐used approximation to the magnetotail field and the reconnection layer magnetic fields is the modified Harris field which consists of a neutral sheet magnetic field profile Bx(z) along with a superimposed normal field Bz. We have designed a configuration of current‐carrying conductors and Helmholtz coil fields aimed at producing the topological characteristics of this field. In addition to mapping the geometry of the field we have appealed to another criterion of validity of this simulation, the energy resonance phenomenon. Energy resonance is an essential feature of nonlinear particle dynamics in magnetotail‐like magnetic fields. The phenomenon is characterized by periodic peaks and valleys occurring in scattered particle distribution functions when plotted versus energy. The “neutral sheet” of the simulated field is not actually plasma current which self‐consistently is responsible for the magnetic field, but rather the field is produced by planar arrays of current carrying wires. For this reason certain self‐consistency requirements on particle orbits in such fields do not arise. Particle injection into the field region, which is formed by 4 conducting wire grids and an external constant field, is accomplished with a programmable electron gun with energies in the range 200 eV to 10 keV. The basic physics of the resonance phenomenon which occurs if the average radius of curvature of the field and the Larmor radius of injected particles are comparable, is scalable from the experiment to the magnetotail environment and has no dimensional dependence. The identification of the resonance effect itself arose from analysis of possible particle phase space orbits in Harris‐type fields. A result of this analysis was that the orbits are divided into clearly separate classes from which the resonance phenomenon follows. The creation of the field in the laboratory model includes realistic design considerations related to the method of producing the field. The design is based on using a test particle code which selects a source distribution of particles to “push” through the modeled magnetic field. Detailed test‐particle simulation investigates particle orbits and the effect on resonance of the finite thickness of conducting wires in addition to the finiteness of the apparatus itself. The experimental effort was performed in the large Space Physics Simulation Chamber (SPSC) in the Plasma Physics Division at the Naval Research Laboratory.
Coupling of the Perkins instability and the sporadic E layer instability derived from physical arguments
Authors: Cosgrove Russell B. , Tsunoda Roland T. , Fukao Shoichiro , Yamamoto Mamoru
Published: June 2004

Tsunoda and Cosgrove [2001] recently pointed out that the F layer and sporadic E (Es) layers in the nighttime midlatitude ionosphere must be considered electrodynamically as a coupled system in light of the presence of a Hall polarization process in Es layers [Haldoupis et al., 1996; Tsunoda, 1998; Cosgrove and Tsunoda, 2001, 2002a] and the fact that kilometer‐scale electric fields map efficiently between the E and F regions. They further noted the apparent presence of positive feedback between processes in those regions. Cosgrove and Tsunoda [2002b, 2003] have since shown that Es layers are unstable with properties not unlike those of the Perkins instability in the F region [Perkins, 1973], motivating the idea that the two instabilities may couple. Finally, Cosgrove and Tsunoda [2004] derived the linear growth rate for the coupled system of a Es layer and the F layer, thus realizing a unified formalism for the Perkins and Es layer (EsL) instabilities. They found that the growth rate was significantly enhanced by the coupling. However, the growth rate computed in Cosgrove and Tsunoda [2004] was expressed only as the largest eigenvalue of a very complex 3 × 3 matrix. In this paper we present a physical interpretation of the E‐F coupled‐layer (EFCL) instability, and derive the condition for maximal coupling. We obtain a circuit model for the coupled‐layer system that provides a physical interpretation for the wavelength dependence of electric field mapping between layers, and allows quantitative predictions. Using the circuit model we derive a “rule of thumb” for computing the two growth rates of the coupled system from the isolated Perkins and EsL instability growth rates. We compare the result with the exact computation of Cosgrove and Tsunoda [2004].
Reliability of the interplanetary magnetic field polarities inferred from north‐south cosmic ray anisotropy and geomagnetic data
Authors: Laurenza M. , Storini M. , Moreno G. , Fujii Z.
Published: June 2004

A comparative study of the interplanetary magnetic field (IMF) polarities inferred from ground‐based measurements of the cosmic ray north‐south (N‐S) anisotropy (CR polarities) and of the geomagnetic field at high latitudes (GEOM polarities) is presented. The reliability of the two methods is tested for different solar, interplanetary, and geomagnetic scenarios using a large set of plasma and magnetic field data taken by the Earth's satellites in the period from 22 May 1965 to 31 December 1999. In general, the GEOM method gives better predictions than the CR method (the overall success rates of the two methods being 92% and 76%, respectively, for the investigated period). Nevertheless, we single out scenarios in which the reliabilities of the two methods become comparable. In fact, while the GEOM polarities are largely unaffected by the solar, interplanetary, or geomagnetic conditions, the CR polarities strongly depend on several parameters (e.g., the solar wind bulk velocity, the IMF intensity, along with the solar activity phase). Thus our analysis points to the criteria which will allow us to select the most reliable IMF polarity at any time, to be used in any study concerning solar, interplanetary, or terrestrial phenomena.
Tide, buoyancy, and wind‐driven circulation of the Charlotte Harbor estuary: A model study
Authors: Zheng Lianyuan , Weisberg Robert H.
Published: June 2004

The circulation of the Charlotte Harbor (CH) estuary is explored with a primitive equation model that encompasses the estuary and the adjacent West Florida Shelf. Tidal forcing is from the shelf through the inlets. We use the M2, S2, K1, and O1 constituents that account for 95% of the shelf tidal variance. River inflows are by the Peace, Myakka, and Caloosahatchee Rivers at their spring 1998 mean values. Wind effects are considered for upwelling or downwelling favorable winds that are either held constant or allowed to oscillate with varying periodicities. These factors are sequentially added to look at their individual and collective influences on the estuary's circulation and salinity fields. Tidal currents are asymmetric and slightly ebb dominant during spring tides. River inflows, combined with tidal mixing, result in a net estuarine circulation by gravitational convection, and the Coriolis acceleration causes the outflowing currents to be stronger and with lower salinity on the western side of the CH portion of the estuary. By virtue of shallow connecting passages the CH portion acts nearly independently from the San Carlos Bay portion of the combined CH estuary system. The addition of wind affects both the instantaneous and net circulation and salinity distributions by increasing mixing and by imposing a force that may add either constructively or destructively to the gravitational convection. The net up‐estuary salt flux is also affected by tides and winds through their contributions to the Reynolds' flux, which exceeds the salt flux by gravitational convection alone.
A temperature‐dependent, structural‐optical model of first‐year sea ice
Authors: Light B. , Maykut G. A. , Grenfell T. C.
Published: June 2004

A model has been developed that relates the structural properties of first‐year sea ice to its inherent optical properties, quantities needed by detailed radiative transfer models. The structural‐optical model makes it possible to calculate absorption coefficients, scattering coefficients, and phase functions for the ice from information about its physical properties. The model takes into account scattering by brine inclusions in the ice, gas bubbles in both brine and ice, and precipitated salt crystals. The model was developed using concurrent laboratory measurements of the microstructure and apparent optical properties of first‐year, interior sea ice between temperatures of −33°C and −1°C. Results show that the structural‐optical properties of sea ice can be divided into three distinct thermal regimes: cold (T < −23°C), moderate (−23°C < T < −8°C), and warm (T > −8°C). Relationships between structural and optical properties in each regime involve different sets of physical processes, of which most are strongly tied to freezing equilibrium of the brine and ice. Volume scattering in cold ice is dominated by the size and number distribution of precipitated hydrohalite crystals. Scattering at intermediate temperatures is controlled by changes in the distribution of brine inclusions, gas bubbles, and mirabilite crystals. Total volume scattering in this regime is approximately independent of temperature because of a balance between increasing and decreasing scattering related to the thermal evolution of these inclusions and scattering by drained inclusions. In warm ice, scattering is controlled principally by temperature‐dependent changes in the real refractive index of brine and by the escape of gas bubbles from the ice. Model predictions indicate that scattering coefficients can exceed 3000 m−1 for cold ice, averaging ∼450 m−1 for moderate and warm ice and reaching a minimum of ∼340 m−1 at −8°C. Scattering in all three regimes is very strongly forward peaked, with values of the asymmetry parameter g generally falling between 0.975 (T = −8°C) and 0.995 (T = −33°C).
Vertical sorting and the morphodynamics of bed form–dominated rivers: A modeling framework
Authors: Blom Astrid , Parker Gary
Published: June 2004

Uncertainties and errors in predictions by morphodynamic models of rivers with nonuniform sediment are usually attributed to shortcomings pertaining to the submodel of sediment transport. This mistakenly neglects shortcomings in the submodel of sediment continuity, which describes the vertical sorting and the bed surface composition, whereas the latter is one of the main input parameters for calculating sediment transport and thus morphological changes. Hirano [1971, 1972] was the first to develop a sediment continuity model for nonuniform sediment. Since this commonly used Hirano active layer model and its variants suffer from a number of shortcomings, the authors have developed a new type of sediment continuity model that describes the bed composition and vertical sorting fluxes without distinguishing discrete bed layers. This continuum sorting model is aimed at conditions dominated by bed forms and bed load transport. It is based on (1) the Parker‐Paola‐Leclair framework for sediment continuity, (2) the Einstein step length formulation, (3) a newly developed lee sorting function, and (4) a newly developed method to account for the variability in bed form trough elevations. The resulting model is deterministic in the computation of the vertical sorting profile and is probabilistic in terms of the riverbed surface due to the presence of dunes.
Deep structure of the Afro‐Arabian hotspot by S receiver functions
Authors: Vinnik L. P. , Farra V. , Kind R.
Published: June 2004

We investigated deep structure of the Afro‐Arabian hotspot by using recordings from Geoscope seismograph station ATD. The records are processed with the S receiver function technique, which allows a detection of Sp converted phases from the upper mantle discontinuities. The seismic data reveal two unusual discontinuities. The discontinuity at a depth of 160 km beneath the Gulf of Aden corresponds to the onset of melting. If the water content in olivine is around 800 H/106Si, melting at this depth requires a temperature close to 1550°C, about 120°C higher than the average. Another remarkable discontinuity is found at a depth of 480 km, where S velocity drops with depth by about 0.2 km/s. This can be the head of another plume which is trapped in the mantle transition zone.
Infrared imagery of ocean internal waves
Authors: Marmorino G. O. , Smith G. B. , Lindemann G. J.
Published: June 2004

Infrared imaging provides a new way to detect internal waves under conditions where techniques that rely on backscatter from the sea surface may not be effective and it provides a new means to investigate the spatial variability associated with internal waves. This is illustrated with imagery collected in a bay under light winds using an airborne infrared camera. The internal waves appear as groups of dark and bright bands, corresponding to surface temperature fluctuations of about 0.05°C. A signal of this size is shown to be plausible based on straining of the water's surface thermal boundary layer (‘cool skin’) by internal waves having a strain rate of the order of 10−2 s−1. In addition, fine‐scale temperature structure was detected that we speculate may indicate instabilities induced by the internal waves.
The effect of physical boundaries on oscillatory bifurcation in counterrotating Taylor–Couette flow
Authors: Langenberg J. , Pfister G. , Abshagen J.
Published: June 2004

The results of an experimental study on the bifurcation structure of oscillatory modes in counterrotating Taylor–Couette flow with stationary end plates are presented. It is shown that the cylinder length L acts as an important geometric control parameter of the system. As a result of a supercritical Hopf bifurcation it is found that for an aspect ratio Γ=L/d>16 (d gap width) only spiral vortices appear in basic laminar flow. For Γ<10.5 spiral vortices are almost entirely replaced by two types of standing waves called SW0 and SWπ as supercritical oscillatory flow. Experimental evidence is presented that the mode exchange between standing waves SW0 and SWπ is governed by underlying Ekman induced vortices which appear as a result of stationary end plates in the flow. In this regime spiral vortices appear only from a sub- or supercritical symmetry breaking bifurcation of the standing waves. Within an “intermediate regime” between 10.5⩽Γ⩽16 spiral vortices are found to be the predominant primary oscillatory flow but small stability intervals of standing waves are also observed. Surprisingly, the experimentally determined critical Reynolds number is found to deviate not more than 2% from the numerical values for all values of aspect ratio even though they are calculated under the assumption of infinite axial length. Moreover, the critical oscillation frequency is also in agreement with the numerical values and is independent from Γ.
Random dynamics of the Morris–Lecar neural model
Authors: Tateno Takashi , Pakdaman Khashayar
Published: June 2004

Determining the response characteristics of neurons to fluctuating noise-like inputs similar to realistic stimuli is essential for understanding neuronal coding. This study addresses this issue by providing a random dynamical system analysis of the Morris–Lecar neural model driven by a white Gaussian noise current. Depending on parameter selections, the deterministic Morris–Lecar model can be considered as a canonical prototype for widely encountered classes of neuronal membranes, referred to as class I and class II membranes. In both the transitions from excitable to oscillating regimes are associated with different bifurcation scenarios. This work examines how random perturbations affect these two bifurcation scenarios. It is first numerically shown that the Morris–Lecar model driven by white Gaussian noise current tends to have a unique stationary distribution in the phase space. Numerical evaluations also reveal quantitative and qualitative changes in this distribution in the vicinity of the bifurcations of the deterministic system. However, these changes notwithstanding, our numerical simulations show that the Lyapunov exponents of the system remain negative in these parameter regions, indicating that no dynamical stochastic bifurcations take place. Moreover, our numerical simulations confirm that, regardless of the asymptotic dynamics of the deterministic system, the random Morris–Lecar model stabilizes at a unique stationary stochastic process. In terms of random dynamical system theory, our analysis shows that additive noise destroys the above-mentioned bifurcation sequences that characterize class I and class II regimes in the Morris–Lecar model. The interpretation of this result in terms of neuronal coding is that, despite the differences in the deterministic dynamics of class I and class II membranes, their responses to noise-like stimuli present a reliable feature.
Proper orthogonal decomposition reconstruction of a transitional boundary layer with and without control
Authors: Gunes Hasan , Rist Ulrich
Published: June 2004

Proper orthogonal decomposition (POD) has been performed for controlled and uncontrolled transitional boundary layer data in an effort to reconstruct and possibly control the transitional boundary layer. Although the POD provides mathematically defined optimal basis functions for a given flow, they are only optimal for a given flow condition (e.g., specific Reynolds number, boundary conditions, etc.). In the context of flow control, one is usually forced to use the POD modes extracted from an uncontrolled flow as the controlled flow is not known a priori. The present investigation reveals that the most energetic POD modes for uncontrolled and controlled modes show a striking similarity, and unlike in turbulent flows, the present transitional boundary layer flow can be reliably captured by a few POD modes which contain almost all of the flow energy. It is then shown that it is possible to reconstruct the controlled flow using POD modes from the uncontrolled flow. Therefore, it can be conjectured that low-dimensional models based on the uncontrolled POD modes may be successfully used as online control tools. After this it is shown that “new” snapshots, i.e., the time evolution of the flow, can also be reconstructed by appropriately modifying the coefficients of the POD modes extracted from “previous” or earlier snapshots. This is accomplished using flow-field information at some “sensor positions” and a least-squares fit to the uncontrolled POD modes from former snapshots at these points. The approach introduced in this paper offers a simple, experimentally realizable approach to calculate the temporal coefficients, hence to reconstruct the unknown flow field without the need for a low-dimensional model based on the projection of the Navier–Stokes equations.
Expansion around half-integer values, binomial sums, and inverse binomial sums
Authors: Weinzierl Stefan
Published: June 2004

I consider the expansion of transcendental functions in a small parameter around rational numbers. This includes in particular the expansion around half-integer values. I present algorithms which are suitable for an implementation within a symbolic computer algebra system. The method is an extension of the technique of nested sums. The algorithms allow in addition the evaluation of binomial sums, inverse binomial sums and generalizations thereof.
Approximate thermodynamic state relations in partially ionized gas mixtures
Authors: Ramshaw John D.
Published: June 2004

Thermodynamic state relations for mixtures of partially ionized nonideal gases are often approximated by artificially partitioning the mixture into compartments or subvolumes occupied by the pure partially ionized constituent gases, and requiring these subvolumes to be in temperature and pressure equilibrium. This intuitively reasonable procedure is easily shown to reproduce the correct thermal and caloric state equations for a mixture of neutral (nonionized) ideal gases. The purpose of this paper is to point out that (a) this procedure leads to incorrect state equations for a mixture of partially ionized ideal gases, whereas (b) the alternative procedure of requiring that the subvolumes all have the same temperature and free electron density reproduces the correct thermal and caloric state equations for such a mixture. These results readily generalize to the case of partially degenerate and/or relativistic electrons, to a common approximation used to represent pressure ionization effects, and to two-temperature plasmas. This suggests that equating the subvolume electron number densities or chemical potentials instead of pressures is likely to provide a more accurate approximation in nonideal plasma mixtures.
Two-scale structure of the current layer controlled by meandering motion during steady-state collisionless driven reconnection
Authors: Ishizawa A. , Horiuchi R. , Ohtani H.
Published: June 2004

A steady two-scale structure of current layer is demonstrated in the collisionless driven reconnections without a guide field by means of two-dimensional full-particle simulations in an open system. The current density profile along the inflow direction consists of two parts. One is a low shoulder controlled by the ion-meandering motion, which is a bouncing motion in a field reversal region. The other is a sharp peak caused mainly by the electron-meandering motion. The shoulder structure is clearly separated from the sharp peak for the case of a large mass ratio calculation mi/me=200 because the ratio of the ion-meandering orbit amplitude to the electron-meandering orbit amplitude is proportional to (mi/me)1/4. Although the ion frozen-in constraint is broken within a distance of the ion skin depth c/ωpi, the violation due to the ion inertia is weak compared to the strong violation caused by the ion-meandering motion. The violation of the electron frozen-in constraint caused by the electron-meandering motion is stronger than the violation due to the electron inertia, and thus the electron-meandering motion produces the reconnection electric field in the central region where the current has the sharp peak structure.
Steady and unsteady solutions for coating flow on a rotating horizontal cylinder: Two-dimensional theoretical and numerical modeling
Authors: Evans P. L. , Schwartz L. W. , Roy R. V.
Published: June 2004

A model for the evolution of a thin liquid coating on a horizontal cylinder is presented. The cylinder rotates about its axis, carrying liquid around its circumference. For a viscous coating, this leads to formation of a relatively thick coating where the cylinder surface moves upward. The model is based on lubrication theory, as the coating is thin compared to the cylinder radius, and includes the effects of cylinder rotation, gravity, surface tension, and flow along the cylinder axis. A two-dimensional numerical scheme based on finite differences is produced, for investigation of the case when axial flow is neglected. This numerical scheme is validated in appropriate limiting cases. Coating cross sections are obtained over a range of cylinder rotation rates, for realistic parameter values. These show a transition from pendant drops hanging beneath the cylinder to a nearly uniform coating wrapped around it as rotation rate is increased.
Temporally stable coherent states for a free magnetic Schrödinger operator
Authors: Thirulogasanthar K. , Saad Nasser , von Keviczky Attila B.
Published: June 2004

Eigenfunctions and eigenvalues of the free magnetic Schrödinger operator, describing a spinless particle confined to an infinite layer of fixed width, are discussed in detail. The eigenfunctions are realized as an orthonormal basis of a suitable Hilbert space. Four different classes of temporally stable coherent states associated with the operator are presented. The first two classes are derived as coherent states with one degree of freedom and the last two classes are derived with two degrees of freedom. The dynamical algebra of each class is found. Statistical quantities associated to each class of coherent states are calculated explicitly.
Covariant Poisson equation with compact Lie algebras
Authors: Salmela Antti
Published: June 2004

The covariant Poisson equation for Lie algebra-valued mappings defined on R3 is studied using functional analytic methods. Weighted covariant Sobolev spaces are defined and used to derive sufficient conditions for the existence and smoothness of solutions to the covariant Poisson equation. These conditions require, apart from suitable continuity, appropriate local Lp integrability of the gauge potential and global weighted Lp integrability of the curvature form and the source. The possibility of nontrivial asymptotic behavior of a solution is also considered. As a by-product, weighted covariant generalizations of Sobolev embeddings are established.
A generalization of Chetaev’s principle for a class of higher order nonholonomic constraints
Authors: Cendra Hernán , Ibort Alberto , de León Manuel , Martı́n de Diego David
Published: June 2004

The constraint distribution in nonholonomic mechanics has a double role. On the one hand, it is a kinematic constraint, that is, it is a restriction on the motion itself. On the other hand, it is also a restriction on the allowed variations when using D’Alembert’s principle to derive the equations of motion. We will show that many systems of physical interest where D’Alembert’s principle does not apply can be conveniently modeled within the general idea of the principle of virtual work by the introduction of both kinematic constraints and variational constraints as being independent entities. This includes, for example, elastic rolling bodies and pneumatic tires. Also, D’Alembert’s principle and Chetaev’s principle fall into this scheme. We emphasize the geometric point of view, avoiding the use of local coordinates, which is the appropriate setting for dealing with questions of global nature, like reduction.
On limits to convective heat transport at infinite Prandtl number with or without rotation
Authors: Yan Xiaodong
Published: June 2004

We prove rigorous upper bounds for the bulk heat transport in infinite Prandtl number Rayleigh–Bénard convection with or without rotation. For the rotation free case, our estimate shows that the Nusselt number is bounded by Rayleigh number according to Nu⩽c Ra4/11 with constant c<2. In the presence of rotation, we prove Nu⩽c Ra4/11(12Ta+1)4/11 with constant c<2. Moreover, for weak rotating constraint (Ta⩽O(Ra1/2)), the Nusselt number is uniformly bounded above by Nu⩽c Ra4/11.
Separable Hilbert space in loop quantum gravity
Authors: Fairbairn Winston , Rovelli Carlo
Published: June 2004

We study the separability of the state space of loop quantum gravity. In the standard construction, the kinematical Hilbert space of the diffeomorphism-invariant states is nonseparable. This is a consequence of the fact that the knot space of the equivalence classes of graphs under diffeomorphisms is noncountable. However, the continuous moduli labeling these classes do not appear to affect the physics of the theory. We investigate the possibility that these moduli could be only the consequence of a poor choice in the fine-tuning of the mathematical setting. We show that by simply choosing a minor extension of the functional class of the classical fields and coordinates, the moduli disappear, the knot classes become countable, and the kinematical Hilbert space of loop quantum gravity becomes separable.
Grain and malting quality in two-row spring barley are influenced by grain filling moisture
Authors: Paynter B. H. , Young K. J.
Published: June 2004

Spring barley (Hordeum vulgare L. cv. Lindwall) was sown in 2 experiments in 1995 and 1 experiment in 1996 in the eastern wheatbelt of Western Australia to examine the effect of varying moisture supply during grain filling on grain and malting quality. Drip irrigation (T-tape) to the soil surface was used to simulate rainfall. Plots were sown without rainout shelters and no rain fell during the linear phase of grain filling in all 3 experiments. The control plot received no irrigation. Irrigation treatments in 1995 were a once only 25 mm application at either 80, 185, 270, or 460 growing degree-days after awn emergence. Irrigation treatments in 1996 were a once-only 25-mm application at either 185 or 460 growing degree-days after awn emergence or a weekly irrigation treatment of 25 mm (total application of 75 mm over 3 irrigations). No attempt was made to compensate for evaporation or to match plant demand.
This study demonstrated improvements in grain plumpness, grain quality, and malting quality with a single 25-mm irrigation during the early linear stages of grain filling (20–40% complete as percentage of final grain weight) in water stressed plants. The irrigation resulted in increased average grain weight, grain yield, amount of maltable grain, and malt extract and decreased the amount of grain passing through a 2.5-mm slotted sieve, grain protein concentration and diastase. This single irrigation, however, was not sufficient to change screening levels to meet receival standards for malting barley and demonstrated the effect of moisture stress on narrow-grained cultivars such as Lindwall.
A single irrigation earlier than 20% grain fill completed had a smaller effect on grain plumpness, grain quality, and malting quality. A single irrigation during the latter part of grain filling (>90% grain fill completed) had little or no effect on grain plumpness, grain quality, or malting quality.
Weekly irrigation in 1996 had a bigger effect than a single irrigation and demonstrated the environmental limitation to quality in that season. Weekly irrigation increased average grain weight by 10 mg relative to control plots, reduced screenings from 88% to 18% through a 2.5-mm sieve, increased grain yields by 88%, increased malt extract by 3%, and decreased diastase by 116 pabah. There was no effect on grain modification or wort viscosity. Viscometric analysis of the barley flour showed a higher time to peak viscosity of the control, which suggests that gelatinisation temperatures were being decreased by irrigation in 1996.