bluuebunny/crossref_metadata_2025 huggingface dataset:
Mixed Ramsey Numbers Revisited
Authors: Rousseau C. C. , Speed S. E.
Published: December 2003

Given a graph Hwith no isolates, the (generalized) mixed Ramsey number is the smallest integer r such that every H-free graph of order r contains an m-element irredundant set. We consider some questions concerning the asymptotic behaviour of this number (i) with H fixed and , (ii) with m fixed and a sequence of dense graphs, in particular for the sequence . Open problems are mentioned throughout the paper.
Open Problems in Partition Regularity
Authors: Hindman Neil , Leader Imre , Strauss Dona
Published: December 2003

A finite or infinite matrix A with rational entries is called partition regular if, whenever the natural numbers are finitely coloured, there is a monochromatic vector x with . Many of the classical theorems of Ramsey Theory may naturally be interpreted as assertions that particular matrices are partition regular.

While in the finite case partition regularity is well understood, very little is known in the infinite case. Our aim in this paper is to present some of the natural and appealing open problems in the area.
On Ramsey Numbers of Sparse Graphs
Authors: Kostochka Alexander , Sudakov B
Published: December 2003

The Ramsey number, , of a graph G is the minimum integer N such that, in every 2-colouring of the edges of the complete graph on N vertices, there is a monochromatic copy of G. In 1975, Burr and Erdős posed a problem on Ramsey numbers of d-degenerate graphs, i.e., graphs in which every subgraph has a vertex of degree at most d. They conjectured that for every d there exists a constant c(d) such that for any d-degenerate graph G of order n.

In this paper we prove that for each such G. In fact, we show that, for every , sufficiently large n, and any graph H of order , either H or its complement contains a (d,n)-common graph, that is, a graph in which every set of d vertices has at least n common neighbours. It is easy to see that any (d,n)-common graph contains every d-degenerate graph G of order n. We further show that, for every constant C, there is an n and a graph H of order such that neither H nor its complement contains a -common graph.
On the Canonical Version of a Theorem in Ramsey Theory
Authors: Brown Tom C.
Published: December 2003

We show that the constant colourings and the one-to-one colourings are insufficient for a canonical version of a certain theorem in Ramsey theory.
Turán Numbers of Bipartite Graphs and Related Ramsey-Type Questions
Authors: Alon Noga , Krivelevich Michael , Sudakov Benny
Published: December 2003

For a graph H and an integer n, the Turán number is the maximum possible number of edges in a simple graph on n vertices that contains no copy of H. H is r-degenerate if every one of its subgraphs contains a vertex of degree at most r. We prove that, for any fixed bipartite graph H in which all degrees in one colour class are at most r, . This is tight for all values of r and can also be derived from an earlier result of Füredi. We also show that there is an absolute positive constant c such that, for every fixed bipartite r-degenerate graph H, This is motivated by a conjecture of Erdős that asserts that, for every such H,

For two graphs G and H, the Ramsey number is the minimum number n such that, in any colouring of the edges of the complete graph on n vertices by red and blue, there is either a red copy of G or a blue copy of H. Erdős conjectured that there is an absolute constant c such that, for any graph G with m edges, . Here we prove this conjecture for bipartite graphs G, and prove that for general graphs G with m edges, for some absolute positive constant c.

These results and some related ones are derived from a simple and yet surprisingly powerful lemma, proved, using probabilistic techniques, at the beginning of the paper. This lemma is a refined version of earlier results proved and applied by various researchers including Rödl, Kostochka, Gowers and Sudakov.
A Sárközy Theorem for Finite Fields
Authors: McCutcheon Randall
Published: December 2003

A classical result of Sárközy states that, for any and any positive density subset E of , there exist elements x and y of E and such that . A version of this result for finite fields is derived from a recent theorem of P. Larick, a short proof of which is also given.
Canonical Vertex Partitions
Authors: Sauer N. W.
Published: December 2003

Let σ be a finite relational signature, let be a set of finite complete relational structures of signature σ, and let be the countable homogeneous relational structure of signature σ which does not embed any of the structures in .

When σ consists of at most binary relations and is finite, the vertex partition behaviour of is completely analysed, in the sense that it is shown that a canonical partition exists and the size of this partition in terms of the structures in is determined. If is infinite some results are obtained, but a complete analysis is still missing.

Some general results are presented which are intended to be used in further investigations when σ contains relational symbols of arity larger than two or when the set of bounds is infinite.
An Application of Hindman's Theorem to a Problem on Communication Complexity
Authors: Pudlák Pavel
Published: December 2003

We consider the k-party communication complexity of the problem of determining if a word w is of the form , for fixed letters . Using the well-known theorem of Hindman (a Ramsey-type result about finite subsets of natural numbers), we prove that for and 5 the communication complexity of the problem increases with the length of the word w.
Local Anti-Ramsey Numbers of Graphs
Authors: Axenovich Maria , Jiang Tao , Tuza Z
Published: December 2003

A subgraph H in an edge-colouring is properly coloured if incident edges of H are assigned different colours, and H is rainbow if no two edges of H are assigned the same colour. We study properly coloured subgraphs and rainbow subgraphs forced in edge-colourings of complete graphs in which each vertex is incident to a large number of colours.
Rainbow Arithmetic Progressions and Anti-Ramsey Results
Authors: Jungic V , Licht J , Mahdian M , Nesetril J , Radoicic R
Published: December 2003

The van der Waerden theorem in Ramsey theory states that, for every k and t and sufficiently large N, every k-colouring of [N] contains a monochromatic arithmetic progression of length t. Motivated by this result, Radoičić conjectured that every equinumerous 3-colouring of [3n] contains a 3-term rainbow arithmetic progression, i.e., an arithmetic progression whose terms are coloured with distinct colours. In this paper, we prove that every 3-colouring of the set of natural numbers for which each colour class has density more than 1/6, contains a 3-term rainbow arithmetic progression. We also prove similar results for colourings of . Finally, we give a general perspective on other anti-Ramsey-type problems that can be considered.
Ramsey Games Against a One-Armed Bandit
Authors: Friedgut Ehud , Kohayakawa Yoshiharu , Rodl Vojtěch , Rucinski Andrzej , Tetali Prasad
Published: December 2003

We study the following one-person game against a random graph process: the Player's goal is to 2-colour a random sequence of edges of a complete graph on n vertices, avoiding a monochromatic triangle for as long as possible. The game is over when a monochromatic triangle is created. The online version of the game requires that the Player should colour each edge as it comes, before looking at the next edge.

While it is not hard to prove that the expected length of this game is about , the proof of the upper bound suggests the following relaxation: instead of colouring online, the random graph is generated in only two rounds, and the Player colours the edges of the first round before the edges of the second round are thrown in. Given the size of the first round, how many edges can there be in the second round for the Player to be likely to win? In the extreme case, when the first round consists of a random graph with edges, where c is a positive constant, we show that the Player can win with high probability only if constantly many edges are generated in the second round.
Markov Processes and Ramsey Theory for Trees
Authors: Furstenberg Hillel , Weiss Benjamin
Published: December 2003

We consider analogues of van der Waerden's theorem and Szemerédi's theorem, where arithmetic progressions are replaced by binary trees with a fixed distance between successive vertices. The proofs are based on some novel recurrence properties for Markov processes.
On the Erdős–Simonovits–Sós Conjecture about the Anti-Ramsey Number of a Cycle
Authors: Jiang T , West D
Published: December 2003

Given a positive integer n and a family of graphs, let denote the maximum number of colours in an edge-colouring of such that no subgraph of belonging to has distinct colours on its edges. Erdös, Simonovits and Sós [6] conjectured for fixed k with that . This has been proved for . For general k, in this paper we improve the previous bound of to . For even k, we further improve it to . We also prove that , which is sharp.
CandidabombicolaCells Immobilized on Patterned Lipid Films as Enzyme Sources for the Transformation of Arachidonic Acid to 20‐HETE
Authors: Phadtare Sumant , Parekh Parag , Shah Sachin , Tambe Amruta , Joshi Rohini , Sainkar S. R. , Prabhune Asmita , Sastry Murali
Published: December 2003

Preparation of biocompatible surfaces for immobilization of enzymes and whole cells is an important aspect of biotechnology due to their potential applications in biocatalysis, biosensing, and immunological applications. In this report, patterned thermally evaporated octadecylamine (ODA) films are used for the immobilization of Candida bombicola cells. The attachment of the cells to the ODA film surface occurs possibly through nonspecific interactions such as hydrophobic interactions between the cell walls and the ODA molecules. The enzyme cytochrome P450 present in the immobilized yeast cells on the ODA film surface was used for the transformation of the arachidonic acid to 20‐hydroxyeicosatetraenoic acid (20‐HETE). The assembly of cells on the hydrophobic ODA surface was confirmed by quartz crystal microgravimetry (QCM), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). SEM images confirmed the strong binding of the yeast cells to the ODA film surface after biocatalytic reactions. Moreover, the biocomposite films could be easily separated from the reaction medium and reused.
A Smart Bioconjugate of Alginate and Pectinase with Unusual Biological Activity toward Chitosan
Authors: Sardar Meryam , Roy Ipsita , Gupta Munishwar N.
Published: December 2003

The commercial preparation of pectinase (Pectinex Ultra SP‐L) was conjugated to alginate by noncovalent interactions by employing 1% alginate during the conjugation protocol. The optimum “immobilization efficiency” was 0.76. The pH optimum and the thermal stability of the enzyme remained unchanged upon conjugation with alginate. The soluble bioconjugate showed a 3‐fold increase in Vmax/Km as compared to the free enzyme when the smart biocatalyst was used for chitosan hydrolysis. Time course hydrolysis of chitosan thus showed higher conversion of chitosan into reducing oligosaccharides/sugars. The smart bioconjugate could be reused five times without any detectable loss of chitosanase activity.
Proteome Analysis of Antibody‐Expressing CHO Cells in Response to Hyperosmotic Pressure
Authors: Lee Moon Sue , Kim Kyoung Wook , Kim Young Hwan , Lee Gyun Min
Published: December 2003

To better understand intracellular responses to hyperosmotic pressure of recombinant Chinese hamster ovary (rCHO) cells expressing an antibody, we have taken a proteomics approach. Using two‐dimensional electrophoresis and mass spectrometry, a proteome profile of rCHO cells comprising 23 identified proteins was established. On the basis of this proteome profile, we found three proteins of which expression levels were significantly changed at 450 mOsm/kg. Compared to the results at 300 mOsm/kg, two glycolytic enzymes, glyceraldehyde‐3‐phosphate dehydrogenase and pyruvate kinase, were found to be up‐regulated, probably leading to an increased metabolic energy for antibody synthesis. The elevation of specific glucose consumption rate at 450 mOsm/kg agreed with the up‐regulation of these glycolytic enzymes. On the other hand, tubulin expression was down‐regulated, reflecting a depressed cell growth rate at 450 mOsm/kg. Taken together, this study shows the potential of the proteomics approach in understanding intracellular and physiological changes in cells and seeking a better insight into possible environmental or genetic manipulation approaches for increasing foreign protein production in rCHO cells.
Optimization of Cyclodextrin Glycosyltransferase Production from KlebsiellapneumoniaeAS‐22 in Batch, Fed‐Batch, and Continuous Cultures
Authors: Gawande Bharat N. , Sonawane Avinash M. , Jogdand Vithal V. , Patkar Anant Y.
Published: December 2003

Production of a novel cyclodextrin glycosyltransferase (CGTase) from Klebsiella pneumoniaeAS‐22 strain, which converts starch predominantly to α‐CD at high conversion yields, in batch, fed‐batch, and continuous cultures, is presented. In batch fermentations, optimization of different operating parameters such as temperature, pH, agitation speed, and carbon‐source concentration resulted in more than 6‐fold increase in CGTase activity. The enzyme production was further improved by two fed‐batch approaches. First, using glucose‐based feed to increase cell density, followed by starch‐based feed to induce enzyme production, resulted in high cell density of 76 g dry cell weight/L, although the CGTase production was low. Using the second approach of a single dextrin‐based feed, 20‐fold higher CGTase was produced compared to that in batch fermentations with media containing tapioca starch. In continuous operation, more than 8‐fold increase in volumetric CGTase productivity was obtained using dextrin‐based media compared to that in batch culture using starch‐based media.
Lipase‐Catalyzed Cellulose Acetylation in Aqueous and Organic Media
Authors: Yang Kui , Wang Ya‐Jane
Published: December 2003

Screening for lipases capable of catalyzing acetylation of cellulosic substrates was conducted in aqueous buffer solution using water‐soluble carboxymethyl cellulose (CMC) as substrate. Lipase A12 from Aspergillus niger (A. niger) showed the most promising acetylation activity among 11 tested commercial microbial lipases and was further applied to catalyzing acetylation of solid cellulose in aqueous solution. This reaction was shown to be feasible with an acetylation extent of 0.16 wt % achieved compared with no detectable acetylation in the absence of enzyme. Pretreatments on cellulose substrate by ultrasonic irradiation and surfactant solution only slightly improved the acetylation extent by 44 and 27%, respectively. Alternatively, this lipase‐catalyzed acetylation was remarkably improved with solubilized cellulose as substrate in the dimethyl sulfoxide/paraformaldehyde solvent system, with an acetylation extent (7.87 wt %) nearly 50 times higher than that achieved in aqueous solution. This improvement was attributed to (1) the absence of bulk water and the increase in substrate solubility by the transition of reaction media from aqueous solution to organic solvents and (2) the ability of lipase A12 to remain catalytically active in highly polar DMSO. This discovery that the A. niger lipase was capable of surviving its contact with polar solvents was further confirmed by its considerably preserved catalytic activity on CMC acetylation in aqueous media after enzyme pretreatments with organic solvents of various polarities and in mixture media with the aqueous phase partially replaced by organic solvents.
Microbial absorption and backscattering coefficients from in situ and POLDER satellite data during an El Niño–Southern Oscillation cold phase in the equatorial Pacific (180°)
Authors: Dupouy Cécile , Loisel Hubert , Neveux Jacques , Brown Susan L. , Moulin Cyril , Blanchot Jean , Le Bouteiller Aubert , Landry Michael R.
Published: December 2003

Contributions of different microbial groups to absorption, backscattering, and marine reflectance (a(λ), bb(λ) and R(λ), respectively) were quantified during an El Niño‐Southern Oscillation cold phase in the equatorial Pacific during the Etude du Broutage en Zone Equatoriale cruise on board the R/V L'Atalante. In situ data were collected at every degree of latitude from 8°S to 8°N, 180° (26 October to 13 November 1996), and satellite reflectances were available from POLDER‐ADEOS for the 1–10 November 1996 decade. Bulk absorption and backscattering coefficients were estimated at 440 nm for the major microbial groups enumerated in the upper surface layer (heterotrophic bacteria, Prochlorococcus, Synechococcus, and <20‐μm eukaryotic algae). Total absorption and backscattering coefficients were retrieved from space by a new inverse method. The observed ecosystem was typical of a well‐developed equatorial upwelling, with maximal values of 0.4 mg m−3 for Tchl a, 0.026 m−1 for ap(440), 0.023 m−1 for aphy(440), and a low in situ adet (<14% of ap). Prochlorococcus and nanoeukaryotic algae (3.4‐μm mean diameter) were the dominant absorbers (97%), contributing about equally to aphy. The retrieved total absorption coefficient, asat(440), from POLDER (maximum of 0.03 m−1) was higher than ap(440), as it included absorption by CDOM (estimated to be 15% of ap(440) + aw(440), where aw = absorption by pure water). Heterotrophic bacteria were the dominant contributors (73%) to total simulated microbial backscattering, bbmic (maximum = 3.7 × 10−4 m−1), but bbmic was negligible compared to the inverted total backscattering by particles, bbp (2.7 × 10−3 m−1), indicating that unidentified small nonliving particles contributed most to the satellite signal.
Effects of keels on ice bottom turbulence exchange
Authors: Skyllingstad Eric D. , Paulson Clayton A. , Pegau W. Scott , McPhee Miles G. , Stanton Timothy
Published: December 2003

The effects of ice keels on the upper ocean are examined using a combination of turbulence measurements and output from a large‐eddy simulation (LES) model. Two cases are examined, one during the winter when the under‐ice boundary layer is relatively deep (∼20 m) and near the freezing point and a second during the summer when the ice is melting and the boundary layer consists of a shallow (∼0.5 m), highly stratified fresh layer. In the winter case, measurements show that flow disruption by a 10‐m‐deep keel causes enhanced vertical mixing, increasing the heat flux from a background value of ∼5 W m−2 to values averaging ∼25 W m−2. Simulations using the LES model are in good agreement with the measurements and indicate that the keel generates a turbulent wake region extending hundreds of meters downstream from the keel. Elevated heat fluxes in the wake region are generated by increased entrainment of warmer water from beneath the mixed layer. Simulations of summer cases demonstrate that shallow keels (∼0.5 m) generate strong turbulence that is able to rapidly mix the fresh layer in the lee of keels. However, this effect decreases quickly as the fresh layer accelerates to match the ice velocity. Deeper keels (1 m) follow a similar pattern but generate more mixing as the fresh layer is forced under the keel. Simulated ice melt heat fluxes are similar to estimates made from ice balance measurements taken during the Surface Heat Budget of the Arctic Ocean summer field program.
Patterns of sea surface height and heat storage associated to intraseasonal Rossby waves in the tropics
Authors: Polito P. S. , Sato O. T.
Published: December 2003

Propagating signals with periods of ∼50 days are detected in global sea surface height anomaly data from the TOPEX/Poseidon altimeter. The sea surface height anomaly is converted into heat storage because of its thermodynamical and biological interest. Both height and heat storage time series are organized in zonal‐temporal diagrams for each latitude and band‐pass filtered. The filters separate the spectral band with periods on the order of 35–65 days and wavelengths on the order of 500–2000 km within 12.5° of the equator. The main objectives are to identify the dynamical regime of the observed variability, locate regions with persistent variability in this spectral band, characterize the propagation patterns, and analyze their temporal dependence. Comparison with theoretical dispersion curves indicates that the observed signal behaves as short, dispersive baroclinic Rossby waves in all tested cases in the Atlantic, Pacific, and Indian Oceans. The group speed differs significantly from the phase speed and tends to smaller values away from the equator. The spatial and temporal pattern analysis is done by two independent methods: decomposition in complex empirical orthogonal functions and correlation‐weighted averages. Both methods show essentially the same results within their inherent features and limitations. The correlation between the amplitude of these waves and the phase of the seasonal and El Niño cycles is estimated and discussed. Similarly, the correlation between the amplitude of these high‐frequency Rossby waves and those of low‐frequency Kelvin and Rossby waves is also estimated and discussed.
Imaging spectroscopy: Earth and planetary remote sensing with the USGS Tetracorder and expert systems
Authors: Clark Roger N. , Swayze Gregg A. , Livo K. Eric , Kokaly Raymond F. , Sutley Steve J. , Dalton J. Brad , McDougal Robert R. , Gent Carol A.
Published: December 2003

Imaging spectroscopy is a tool that can be used to spectrally identify and spatially map materials based on their specific chemical bonds. Spectroscopic analysis requires significantly more sophistication than has been employed in conventional broadband remote sensing analysis. We describe a new system that is effective at material identification and mapping: a set of algorithms within an expert system decision‐making framework that we call Tetracorder. The expertise in the system has been derived from scientific knowledge of spectral identification. The expert system rules are implemented in a decision tree where multiple algorithms are applied to spectral analysis, additional expert rules and algorithms can be applied based on initial results, and more decisions are made until spectral analysis is complete. Because certain spectral features are indicative of specific chemical bonds in materials, the system can accurately identify and map those materials. In this paper we describe the framework of the decision making process used for spectral identification, describe specific spectral feature analysis algorithms, and give examples of what analyses and types of maps are possible with imaging spectroscopy data. We also present the expert system rules that describe which diagnostic spectral features are used in the decision making process for a set of spectra of minerals and other common materials. We demonstrate the applications of Tetracorder to identify and map surface minerals, to detect sources of acid rock drainage, and to map vegetation species, ice, melting snow, water, and water pollution, all with one set of expert system rules. Mineral mapping can aid in geologic mapping and fault detection and can provide a better understanding of weathering, mineralization, hydrothermal alteration, and other geologic processes. Environmental site assessment, such as mapping source areas of acid mine drainage, has resulted in the acceleration of site cleanup, saving millions of dollars and years in cleanup time. Imaging spectroscopy data and Tetracorder analysis can be used to study both terrestrial and planetary science problems. Imaging spectroscopy can be used to probe planetary systems, including their atmospheres, oceans, and land surfaces.
Accretion leading to collision and the Permian Solonker suture, Inner Mongolia, China: Termination of the central Asian orogenic belt
Authors: Xiao Wenjiao , Windley Brian F. , Hao Jie , Zhai Mingguo
Published: December 2003

The Solonker suture records the termination of the central Asian Orogenic Belt (CAOB). However, tectonic development of the Solonker suture is poorly understood. We report new field data for the Ondor Sum melange in the Ulan valley, and present a new evaluation of the orogenic belt extending from the southern Mongolia cratonic boundary to the north China craton within the context of a new geological framework and tectonic model, which incorporates relevant data from the literature. The southern accretionary zone between the north China craton and the Solonker suture is characterized by the Mid‐Ordovician‐Early Silurian Ulan island arc‐Ondor Sum subduction‐accretion complex and the Bainaimiao arc. This zone was consolidated by the Carboniferous‐Permian when it evolved into an Andean‐type magmatic margin above a south dipping subduction zone. The northern accretionary zone north of the Solonker suture extends southward from a Devonian to Carboniferous active continental margin, through the Hegenshan ophiolite‐arc accretionary complex to the Late Carboniferous Baolidao arc associated with some accreted Precambrian blocks. This northern zone had consolidated by the Permian when it developed into an Andean‐type magmatic margin above a north dipping subduction zone. Final subduction of the central Asian ocean caused the two opposing active continental margins to collide, leading to formation of the Solonker suture in the end‐Permian. Predominant northward subduction during final formation of the suture gave rise in the upper northern plate to a large‐scale, postcollisional, south directed thrust and fold belt in the Triassic‐Jurassic. In summary, the CAOB underwent three final stages of tectonic development: early Japanese‐type accretion, Andean‐type magmatism, and Himalayan‐type collision.
Pumping management of coastal aquifers using analytical models of saltwater intrusion
Authors: Mantoglou Aristotelis
Published: December 2003

Analytical models of saltwater intrusion in coastal aquifers of finite size are developed and utilized in an optimization methodology for determining the optimal pumping rates. The models are based on the sharp interface approximation and the Ghyben‐Herzberg relation. The governing equations are expressed in terms of a single potential and are solved analytically using the method of images to account for the aquifer boundaries. The analytical models consider ambient flow and surface recharge. The results are compared to numerical simulations indicating a good match as the number of images is increased. The objective of optimization is to maximize the total pumping from the aquifer and a set of constraints protect the wells from saltwater intrusion. The constraints are expressed using the analytical saltwater intrusion models. Two different constraint formulations are investigated. The “toe constraint” formulation protects the wells from saltwater intrusion by not allowing the toe of the interface to reach the wells. This formulation results in a nonlinear optimization problem which is solved using sequential quadratic programming (SQP). The “potential constraint” formulation, on the other hand, protects the wells by maintaining a potential at the wells larger than the toe potential. This formulation results in a linear optimization problem which is solved using the Simplex method. Several simulation runs indicate that the optimal solution is very sensitive to variations of recharge rates, hydraulic conductivity heterogeneities, etc. The linear programming formulation, besides being computationally simpler, provides a safer solution than the nonlinear formulation.
Bacterioneuston control of air‐water methane exchange determined with a laboratory gas exchange tank
Authors: Upstill‐Goddard Robert C. , Frost Thomas , Henry Gordon R. , Franklin Mark , Murrell J. Colin , Owens Nicholas J. P.
Published: December 2003

The apparent transfer velocities (kw) of CH4, N2O, and SF6 were determined for gas invasion and evasion in a closed laboratory exchange tank. Tank water (pure Milli‐RO® water or artificial seawater prepared in Milli‐RO®) and/or tank air gas compositions were adjusted, with monitoring of subsequent gas transfer by gas chromatography. Derived kw was converted to “apparent k600,” the value for CO2 in freshwater at 20°C. For CH4, analytical constraints precluded estimating apparent k600 based on tank air measurements. In some experiments we added strains of live methanotrophs. In others we added chemically deactivated methanotrophs, non‐CH4 oxidizers (Vibrio), or bacterially associated surfactants, as controls. For all individual controls, apparent k600 estimated from CH4, N2O, or SF6 was indistinguishable. However, invasive estimates always exceeded evasive estimates, implying some control of gas invasion by bubbles. Estimates of apparent k600 differed significantly between methanotroph strains, possibly reflecting species‐specific surfactant release. For individual strains during gas invasion, apparent k600 estimated from CH4, N2O, or SF6 was indistinguishable, whereas during gas evasion, k600‐CH4 was significantly higher than either k600‐N2O or k600‐SF6, which were identical. Hence evasive k600‐CH4/k600‐SF6 was always significantly above unity, whereas invasive k600‐CH4/k600‐SF6 was not significantly different from unity. Similarly, k600‐CH4/k600‐SF6 for the controls and k600‐N2O/k600‐SF6 for all experiments did not differ significantly from unity. Our results are consistent with active metabolic control of CH4 exchange by added methanotrophs in the tank microlayer, giving enhancements of ∼12 ± 10% for k600‐CH4. Hence reactive trace gas fluxes determined by conventional tracer methods at sea may be in error, prompting a need for detailed study of the role of the sea surface microlayer in gas exchange.
Dissolved organic carbon in a northern boreal landscape
Authors: Moore T. R.
Published: December 2003

I examined concentrations and fluxes of dissolved organic carbon (DOC) in precipitation, upland forest throughfall, stemflow and soil water, peatland pore water, beaver ponds, and streams from May to September 1994 in the BOREAS Northern Study Area, near Thompson, Manitoba, Canada. Concentrations of DOC in precipitation were large (8 mg L−1) compared to other boreal locations, possibly associated with a high incidence of local forest fires. DOC concentrations increased in throughfall, stemflow, and soil organic horizons and decreased in subsoil pore water, associated with DOC sorption. Pore water of fens and bogs contained large DOC concentrations (seasonal average 20 to 40 mg L−1), similar to that observed in beaver ponds (seasonal average 19 to 38 mg L−1). Streams draining three small (30 to 420 km2) catchments contained DOC concentrations generally from 15 to 30 mg L−1, with a negative correlation with discharge. For the May to September period, it was estimated that precipitation imported ∼2 g DOC m−2, increasing to 3 to 6 g DOC m−2 with passage through forest vegetation and organic horizons. DOC export in streams was estimated to be ∼3 g DOC m−2, controlled mainly by contributions from wetlands and beaver ponds before reaching streams. Although DOC concentrations are large, compared to other landscapes, the hydrologic pathways and the paucity of mineral subsoils for DOC sorption, and the small runoff (average 125 mm, May to September 1994 to 1996) in this continental climate (precipitation 535 mm yr−1) environment results in a small export of DOC from the land surface to water bodies.
The subtropical nutrient spiral
Authors: Jenkins William J. , Doney Scott C.
Published: December 2003

We present an extended series of observations and more comprehensive analysis of a tracer‐based measure of new production in the Sargasso Sea near Bermuda using the 3He flux gauge technique. The estimated annually averaged nitrate flux of 0.84 ± 0.26 mol m−2 yr−1 constitutes only that nitrate physically transported to the euphotic zone, not nitrogen from biological sources (e.g., nitrogen fixation or zooplankton migration). We show that the flux estimate is quantitatively consistent with other observations, including decade timescale evolution of the 3H + 3He inventory in the main thermocline and export production estimates. However, we argue that the flux cannot be supplied in the long term by local diapycnal or isopycnal processes. These considerations lead us to propose a three‐dimensional pathway whereby nutrients remineralized within the main thermocline are returned to the seasonally accessible layers within the subtropical gyre. We describe this mechanism, which we call “the nutrient spiral,” as a sequence of steps where (1) nutrient‐rich thermocline waters are entrained into the Gulf Stream, (2) enhanced diapycnal mixing moves nutrients upward onto lighter densities, (3) detrainment and enhanced isopycnal mixing injects these waters into the seasonally accessible layer of the gyre recirculation region, and (4) the nutrients become available to biota via eddy heaving and wintertime convection. The spiral is closed when nutrients are utilized, exported, and then remineralized within the thermocline. We present evidence regarding the characteristics of the spiral and discuss some implications of its operation within the biogeochemical cycle of the subtropical ocean.
Flying avalanches
Authors: Hákonardóttir Kristín Martha , Hogg Andrew J. , Batey Jenny , Woods Andrew W.
Published: December 2003

Rapidly flowing avalanches are highly destructive natural phenomena, especially when they interact with buildings or other man‐made structures. Here we report a new experimental study of the interaction of a rapid granular flow with a solid barrier, which is of a comparable height to the flow depth. Our experiments show that the flow detaches from the top of the obstacle as a coherent granular jet, the motion of which is well described by theory for an inviscid jet of fluid. As well as giving fundamental new insights into the behaviour of granular flows, the results have important practical consequences for the design of dams used to provide protection from snow avalanches.
Oscillitons and gyrating ions in a beam‐plasma system
Authors: Sauer K. , Dubinin E.
Published: December 2003

The resonant excitation of right‐hand polarized waves by an ion beam propagating parallel to the ambient magnetic field is a well‐known effect of linear dispersion theory. In this paper, stationary nonlinear structures in such a beam‐plasma system are studied on the basis of Hall‐MHD description. Soliton‐like structures with superimposed spatial oscillations have been found which arise from the momentum coupling between the main plasma population and the beam ions via the LF electromagnetic field. They have similar signatures as the recently described oscillitons of linearly stable two‐ion plasmas [Sauer et al., 2001] where effective momentum coupling may happen in the vicinity of their cross‐over frequencies. Our message is that gyrophase‐bunched ions seen upstream of the Earth's bow shock in association with ULF wave packets may find an explanation by oscillitons in a beam‐plasma system.
Probability distribution invariance of 1‐minute auroral‐zone geomagnetic field fluctuations
Authors: Weigel R. S. , Baker D. N.
Published: December 2003

A statistical model of short time‐scale geomagnetic fluctuations is developed and used to evaluate how geomagnetic dynamics are influenced by different solar wind controlling parameters. The functional form of the probability distribution function (PDF) that describes extreme‐value (greater than 4σ) minute‐to‐minute changes in the ground magnetic field (Δx) at magnetometer station Sodankylä (geomagnetic latitude and longitude of [63.87,107.61]) is shown to be nearly independent of the variables solar wind (SW) forcing, local time (LT), and day of year (DOY). Instead of modifying the intrinsic dynamics, as characterized by the functional form of the PDF of Δx, these variables are shown either to amplify or reduce the absolute level of variability of the fluctuations: The primary difference in the PDF tail of Δx during weak and strong solar wind forcing is the standard deviation, σ; the functional form of the PDF = f[Δx/σ(DOY,LT,SW)] is nearly invariant. In a statistical interpretation, we conclude that differences in solar‐generated conductivity, seasonal effects, strength of solar wind forcing and variability, and position of the magnetometer ground station in local time do not change the structure of the extreme‐value dynamics, as characterized by the probability distribution of Δx, but they serve to amplify the intrinsic variability.
A novel approach for independent budgeting of fossil fuel CO2 over Europe by 14CO2 observations
Authors: Levin Ingeborg , Kromer Bernd , Schmidt Martina , Sartorius Hartmut
Published: December 2003

Long‐term atmospheric 14CO2 observations are used to quantify fossil fuel‐derived CO2 concentrations at a regional polluted site, and at a continental mountain station in southwest Germany. Fossil fuel CO2 emission rates for the relevant catchment areas are obtained by applying the Radon‐Tracer‐Method. They compare well with statistical emissions inventories but reveal a larger seasonality than earlier assumed, thus contributing significantly to the observed CO2 seasonal cycle over Europe. Based on the present approach, emissions reductions on the order of 5–10% are detectable for catchment areas of several hundred kilometres radius, as anticipated within a five‐years commitment period of the Kyoto Protocol. Still, no significant change of fossil fuel CO2 emissions is observed at the two sites over the last 16 years.
Infrasound associated with the 2002 Denali fault earthquake, Alaska
Authors: Olson John V. , Wilson Charles R. , Hansen Roger A.
Published: December 2003

Infrasonic waves associated with the November 3, 2002, magnitude 7.9 earthquake in Alaska were detected by the microphone array (I53US) in Fairbanks, Alaska. The epicenter of the earthquake lay some 150 km south of the Fairbanks array. Both seismic and acoustic signals were recorded successively by the microphone array. The fault rupture of the earthquake moved east‐southeast along the Denali‐Totschunda system fault for approximately 294 km. The northern side of the fault moved to the east and vertically upward relative to the southern side. Displacements up to 8.8 meters were measured at various points along the fault [Eberhart‐Phillps et al., 2003]. The seismic P‐wave signal arrived at the array approximately 27 seconds after initiation of the rupture with a trace velocity of 5 km/sec. This was followed, some 12 minutes later, by an infrasonic wavetrain that had an average trace velocity of 0.34 km/sec and lasted about ten minutes. The azimuth of arrival of the infrasonic waves steadily moved eastward throughout the wave train apparently following the rupture's leading edge along the fault. The largest infrasonic signals, reaching over 12 Pa, came from the azimuth of the regions of largest ground motion along the fault. The source of the infrasound is taken to be the sudden local motion of the mountains in the Alaska Range along the Denali fault as they responded to the eastward‐propagating fault rupture.
Case study of solar wind pressure variations and neutral atom emissions observed by IMAGE/LENA
Authors: Khan H. , Collier M. R. , Moore T. E.
Published: December 2003

The Low Energy Neutral Atom (LENA) imager on the IMAGE spacecraft was designed to observe neutral atom emissions at low energy (10 eV–∼4 keV) from the high‐latitude ionosphere. In this study we present data from an ion outflow event on 24 June 2000 showing increases in neutral flux that appear to be associated with dynamic pressure variations in the solar wind. Results from a correlation analysis show the neutral flux to be well correlated (∼0.64) with the solar wind dynamic pressure. The neutral atom data are most consistent with a source region at a radial distance of 2.2–2.3 RE, interpreted as the region over which the bulk ion outflow escapes the ionosphere and is partly converted to neutral atoms. Very short time delays (∼2 min) were calculated between the solar wind pressure increase and neutral atom response, indicating a prompt ionospheric response to the solar wind input.
Thermospheric wind during a storm‐time large‐scale traveling ionospheric disturbance
Authors: Shiokawa K. , Otsuka Y. , Ogawa T. , Kawamura S. , Yamamoto M. , Fukao S. , Nakamura T. , Tsuda T. , Balan N. , Igarashi K. , Lu G. , Saito A. , Yumoto K.
Published: December 2003

A prominent large‐scale traveling ionospheric disturbance (LSTID) was observed in Japan during the major magnetic storm (Dst ∼ −358 nT) of 31 March 2001. It was detected as enhancements of the 630‐nm airglow and foF2, GPS‐TEC variations, and a decrease in F‐layer virtual height at 1700–1900 UT (0200–0400 LT). It moved equatorward with a speed of ∼600 m/s. The decrease in the F‐layer height was also detected by the MU radar at Shigaraki. Thermospheric wind variations were observed by the MU radar through ion drift measurement and by a Fabry‐Perot interferometer (FPI) through a Doppler shift of the 630‐nm airglow line at Shigaraki. The wind data show a turn of the meridional wind from −94 m/s (equatorward) to +44 m/s (poleward) during the LSTID, indicating that an intense poleward wind in the thermosphere passed over Shigaraki as an atmospheric gravity wave and caused the observed ionospheric features of the LSTID. Intense poleward wind was also detected at mesospheric altitudes (95–100 km) by the MU radar (through meteor echoes) and by the FPI (through the 558‐nm airglow) with a delay of ∼2 hours from the thermospheric wind, indicating downward phase progression of the wave. Generation of the observed poleward wind in the auroral zone was investigated using magnetic field data and auroral energy input estimated by the assimilative mapping of ionospheric electrodynamics (AMIE) technique. We suggest that simple atmospheric heating and/or the Lorentz force in the auroral zone do not explain the observed poleward wind enhancement.
Regional feedbacks among fire, climate, and tropical deforestation
Authors: Hoffmann William A. , Schroeder Wilfrid , Jackson Robert B.
Published: December 2003

Numerous studies with general circulation models suggest that tropical deforestation can result in regional‐scale climate change; namely, increased air temperature and wind speed and reduced precipitation and relative humidity. To quantify how this climate change should affect fire risk, we used the National Center for Atmospheric Research (NCAR) CCM3.2 general circulation model and remote sensing to estimate the effect of tropical deforestation on fire risk through the McArthur forest fire danger index (FFDI). Deforestation reduced precipitation and relative humidity and increased wind speed in the Amazon, Congo, and Indonesia/New Guinea. FFDI increased by 41, 56, and 58% in these three regions, respectively, primarily owing to higher wind speeds and reduced precipitation. Actual fire occurrence in the Amazon, as determined from NOAA‐12 images, was strongly correlated with the FFDI calculated from meteorological data (P ≪ 0.0001). Using the observed relationship between FFDI and fire occurrence, we estimate increases in fire frequency of 44, 80, and 123%, in the Amazon, Congo, and Indonesia, respectively, with deforestation. In all three regions the largest relative increases in fire risk occurred in the more humid areas with the lowest original fire risk.
Comprehensive laboratory measurements of biomass‐burning emissions: 1. Emissions from Indonesian, African, and other fuels
Authors: Christian T. J. , Kleiss B. , Yokelson R. J. , Holzinger R. , Crutzen P. J. , Hao W. M. , Saharjo B. H. , Ward D. E.
Published: December 2003

Trace gas and particle emissions were measured from 47 laboratory fires burning 16 regionally to globally significant fuel types. Instrumentation included the following: open‐path Fourier transform infrared spectroscopy; proton transfer reaction mass spectrometry; filter sampling with subsequent analysis of particles with diameter <2.5 μm for organic and elemental carbon and other elements; and canister sampling with subsequent analysis by gas chromatography (GC)/flame ionization detector, GC/electron capture detector, and GC/mass spectrometry. The emissions of 26 compounds are reported by fuel type. The results include the first detailed measurements of the emissions from Indonesian fuels. Carbon dioxide, CO, CH4, NH3, HCN, methanol, and acetic acid were the seven most abundant emissions (in order) from burning Indonesian peat. Acetol (hydroxyacetone) was a major, previously unobserved emission from burning rice straw (21–34 g/kg). The emission factors for our simulated African fires are consistent with field data for African fires for compounds measured in both the laboratory and the field. However, the higher concentrations and more extensive instrumentation in this work allowed quantification of at least 10 species not previously quantified for African field fires (in order of abundance): acetaldehyde, phenol, acetol, glycolaldehyde, methylvinylether, furan, acetone, acetonitrile, propenenitrile, and propanenitrile. Most of these new compounds are oxygenated organic compounds, which further reinforces the importance of these reactive compounds as initial emissions from global biomass burning. A few high‐combustion‐efficiency fires emitted very high levels of elemental (black) carbon, suggesting that biomass burning may produce more elemental carbon than previously estimated.
Mesoscale modeling of meteorological conditions in the lower troposphere during a winter stratospheric ozone intrusion over Zagreb, Croatia
Authors: Klaić Zvjezdana Bencetić , Belušić Danijel , Bulić Ivana Herceg , Hrust Lovro
Published: December 2003

We investigated mesoscale meteorological conditions in the lower troposphere during an episode of winter stratospheric ozone intrusion over Zagreb, Croatia, on 6 February 1990. This particular event was associated with a jet stream over northwestern Europe, and it was accompanied by elevated ozone values at two measuring sites in the greater Zagreb area. A Eulerian nonhydrostatic prognostic mesoscale model has been employed to reproduce significant fine‐scale features of the fold. The initial streamer of the potential vorticity (PV) anomaly, which was found in the lower troposphere from 1.5 to 1 day prior to measured ozone peaks, consisted of a wavelike train of vortices. Horizontal and vertical dimensions of the individual vortices were between 30 and 70 km and between 500 and 1500 m, respectively. At the same time, the vertical PV gradients within the vortices were up to ΔPV = 0.2 × 10−6 K m Pa−1 s−3/100 m. The model also reproduced the streamer's breaking apart and its gradual and irreversible mixing with the adjacent tropospheric air. Both the model results and ozone measurements suggest that the air of stratospheric origin arrived above Zagreb from the southeast.
Interior structure models and tidal Love numbers of Titan
Authors: Sohl F. , Hussmann H. , Schwentker B. , Spohn T. , Lorenz R. D.
Published: December 2003

Interior models of a differentiated Titan with an internal ammonia‐water ocean and chondritic radiogenic heat production in an undifferentiated rock + iron core have been calculated. We assume thermal and mechanical equilibrium and calculate the structure of the interior as a function of the thickness of an ice I layer on top of the ocean as well as the moment of inertia factor and the tidal Love numbers for comparison with Cassini gravity data. The Love numbers are linearly dependent on the thickness of the ice I shell at constant rheology parameters but decrease by one order of magnitude in the absence of an internal ocean. Ice shell thicknesses are between 90 and 105 km for models with 5 wt.% ammonia and for core densities between 3500 and 4500 kg m−3. For 15 wt.% ammonia, the shell is 65 to 70 km thick. We use a strongly temperature‐dependent viscosity parameterization of convective heat transport and find that the stagnant lid comprises most of the ice I shell. Tidal heating in the warm convective sublayer is of minor importance. The internal ocean is several hundred kilometers thick, and its thickness decreases with increasing thickness of the ice shell. Core sizes vary from 1500 to 1800 km radius with associated moment of inertia factors of 0.30 ± 0.01.