bluuebunny/crossref_metadata_2025 huggingface dataset:
Riemannian metric of the averaged energy minimization problem in orbital transfer with low thrust
Authors: Caillau Jean-Baptiste , Bonnard Bernard
Published: December 2006

This article deals with the optimal transfer of a satellite between Keplerian orbits using low propulsion and is based on preliminary results of Epenoy et al. (1997) where the optimal trajectories of the energy minimization problem are approximated using averaging techniques. The averaged Hamiltonian system is explicitly computed. It is related to a Riemannian problem whose distance is an approximation of the value function. The extremal curves are analyzed, proving that the system remains integrable in the coplanar case. It is also checked that the metric associated with coplanar transfers towards a circular orbit is flat. Smoothness of small Riemannian spheres ensures global optimality of the computed extremals.

Cet article concerne le problème du transfert d'un satellite entre orbites elliptiques dans le cadre de la poussée faible et se fonde sur les résultats préliminaires d'Epenoy et al. (1997) où les trajectoires optimales du problème de minimisation de l'énergie sont approchées par moyennation. On fait un calcul explicite du Hamiltonien moyenné et on prouve qu'il s'agit du Hamiltonien associé à un problème Riemannien dont la distance approche la fonction valeur. On montre en analysant les extrémales que le système moyenné reste intégrable dans le cas coplanaire, et on vérifie que la métrique associée est plate dans le cas de transferts coplanaires vers des orbites circulaires. La régularité des sphères Riemanniennes de petit rayon garantit l'optimalité globale des extrémales calculées.
Lignes de divergence pour les graphes à courbure moyenne constante
Authors: Mazet Laurent
Published: December 2006

This paper is devoted to the study of convergence of sequences of solutions to the constant mean curvature

H

equation. The convergence domain is defined. The main theorem (Theorem 8) characterizes the complement of this convergence domain: it shows that circle arcs of curvature

2H

compose this complement. We then give results which allow us to use this theorem.

Cet article est consacré à l'étude de la convergence des suites de solutions de l'équation des surfaces à courbure moyenne constante

H

. Nous définissons le lieu de convergence de la suite. Le principale théorème (théorème 8) caractérise le complémentaire de ce lieu de convergence : il montre que ce complémentaire est composé d'arcs de cercle de courbure

2H

. Nous donnons ensuite des résultats permettant d'exploiter ce théorème.
Stokes and Navier–Stokes equations with nonhomogeneous boundary conditions
Authors: Raymond J.-P.
Published: December 2006

In this paper, we study the existence and regularity of solutions to the Stokes and Oseen equations with nonhomogeneous Dirichlet boundary conditions with low regularity. We consider boundary conditions for which the normal component is not equal to zero. We rewrite the Stokes and the Oseen equations in the form of a system of two equations. The first one is an evolution equation satisfied by

P\mathbf{u}

, the projection of the solution on the Stokes space – the space of divergence free vector fields with a normal trace equal to zero – and the second one is a quasi-stationary elliptic equation satisfied by

(I−P)\mathbf{u}

, the projection of the solution on the orthogonal complement of the Stokes space. We establish optimal regularity results for

P\mathbf{u}

and

(I−P)\mathbf{u}

. We also study the existence of weak solutions to the three-dimensional instationary Navier–Stokes equations for more regular data, but without any smallness assumption on the initial and boundary conditions.
The Wigner–Poisson–Fokker–Planck system: global-in-time solution and dispersive effects
Authors: Arnold Anton , Dhamo Elidon , Manzini Chiara
Published: December 2006

This paper is concerned with the Wigner–Poisson–Fokker–Planck system, a kinetic evolution equation for an open quantum system with a non-linear Hartree potential. Existence, uniqueness and regularity of global solutions to the Cauchy problem in 3 dimensions are established. The analysis is carried out in a weighted

L^{2}

-space, such that the linear quantum Fokker–Planck operator generates a dissipative semigroup. The non-linear potential can be controlled by using the parabolic regularization of the system.

The main technical difficulty for establishing global-in-time solutions is to derive a-priori estimates on the electric field: Inspired by a strategy for the classical Vlasov–Fokker–Planck equation, we exploit dispersive effects of the free transport operator. As a “by-product” we also derive a new a-priori estimate on the field in the Wigner–Poisson equation.

On considère le système de Wigner–Poisson–Fokker–Planck, une équation évolutive cinétique pour un système quantique ouvert sujet à un potentiel non-linéaire du type Hartree. On démontre l'existence, l'unicité et la régularité pour les solutions du problème de Cauchy en dimension 3. On travaille dans un espace

L^{2}

avec poids, où l'opérateur de Fokker–Planck engendre un semi group dissipatif. La régularisation parabolique du dernier operateur contrôle le potentiel non-linéaire.

D'un côté technique, la difficulté principale pour établir l'existence globale en temps des solutions réside démontrer des bornes a-priori pour le champ électrique : on étend une stratégie issue de l'équation classique de Vlasov–Fokker–Planck qu'utilise les effets dispersifs d'équation du transport libre. En conséquence, on obtient aussi une nouvelle borne pour le champ dans le cas de Wigner–Poisson.
An evolutionary double-well problem
Authors: Tang Qi , Zhang Kewei
Published: December 2006

We establish the existence theorem and study the long time behaviour of the following PDE problem:

\begin{cases}
u_{t}−\mathrm{div}\mathrm{∇}W(\mathrm{∇}u)−f(x) = 0 &\text{in }\Omega \times (0,−\infty ), \\ \mathrm{∇}W(\mathrm{∇}u) \cdot \mathbf{n}|_{\partial \Omega \times (0,\infty )} = 0, \\
u(x,0) = u_{0}(x)&\text{in }\Omega
\end{cases}

where

W

is a specially given quasiconvex double-well function and

f \in L^{2}(\Omega )

is a given function independent of time

t

. In particular, the existence theorem is established for general given source term

f

, the long time behaviour is analyzed under the assumption that

\int _{\Omega }f(x)\:\mathrm{d}x = 0

.

The system is an evolutionary quasimonotone system. We believe that the existence of solutions established here is stronger than the usual Young Measure solution and is the first of its kind. The existence of a compact

ω

-limit set as

t\rightarrow \infty

is also established under some non-restrictive conditions.
The lactoperoxidase system links anion transport to host defense in cystic fibrosis
Authors: Conner Gregory E. , Wijkstrom-Frei Corinne , Randell Scott H. , Fernandez Vania E. , Salathe Matthias
Published: December 2006

Chronic respiratory infections in cystic fibrosis result from CFTR channel mutations but how these impair antibacterial defense is less clear. Airway host defense depends on lactoperoxidase (LPO) that requires thiocyanate (SCN−) to function and epithelia use CFTR to concentrate SCN− at the apical surface. To test whether CFTR mutations result in impaired LPO‐mediated host defense, CF epithelial SCN− transport was measured. CF epithelia had significantly lower transport rates and did not accumulate SCN− in the apical compartment. The lower CF [SCN−] did not support LPO antibacterial activity. Modeling of airway LPO activity suggested that reduced transport impairs LPO‐mediated defense and cannot be compensated by LPO or H2O2 upregulation.
Possible direct involvement of the active‐site [4Fe–4S] cluster of the GcpE enzyme from Thermus thermophilus in the conversion of MEcPP
Authors: Adedeji Dolapo , Hernandez Heather , Wiesner Jochen , Köhler Uwe , Jomaa Hassan , Duin Evert C.
Published: December 2006

The GcpE enzyme converts 2‐C‐methyl‐d‐erythritol‐2,4‐cyclodiphosphate (MEcPP) into (E)‐4‐hydroxy‐3‐methyl‐but‐2‐enyl diphosphate (HMBPP) in the penultimate step of the DOXP pathway for isoprene biosynthesis. Purification of the enzyme under exclusion of air leads to a preparation that contains solely [4Fe–4S] clusters. Kinetic studies showed that in the presence of the artificial reductant dithionite and MEcPP a new transient iron–sulfur‐based signal is detected in electron paramagnetic resonance (EPR) spectroscopy. Similarity of this EPR signal to that detected in ferredoxin:thioredoxin reductase indicates that during the reaction an intermediate is directly bound to the active‐site cluster.
Sequestosome 1/p62 – More than just a scaffold
Authors: Seibenhener M. Lamar , Geetha Thangiah , Wooten Marie W.
Published: December 2006

The interaction of proteins with ubiquitin receptors is key to solving the mystery that surrounds the functional role ubiquitin chains play in directing traffic. The specificity of these interactions is largely mediated by UbL/UBA domains. Sequestosome 1/p62 is a protein that is gaining attention as it is intimately involved in cell signaling, receptor internalization, and protein turnover. Herein we review recent advances in the field.
A review of gene linkage, association and expression studies in autism and an assessment of convergent evidence
Authors: Yang Mao Sheng , Gill Michael
Published: December 2006

Autism is a neurodevelopmental disorder with high heritability and a likely complex genetic architecture. Much genetic evidence has accumulated in the last 20 years but no gene has been unequivocally identified as containing risk variants for autism. In this article we review the past and present literature on neuro‐pathological, genetic linkage, genetic association, and gene expression studies in this disorder. We sought convergent evidence to support particular genes or chromosomal regions that might be likely to contain risk DNA variants.

The convergent evidence from these studies supports the current hypotheses that there are multiple genetic loci predisposing to autism, and that genes involved in neurodevelopment are especially important for future genetic studies. Convergent evidence suggests the chromosome regions 7q21.2–q36.2, 16p12.1–p13.3, 6q14.3–q23.2, 2q24.1–q33.1, 17q11.1–q21.2, 1q21–q44 and 3q21.3–q29, are likely to contain risk genes for autism. Taken together with results from neuro‐pathological studies, genes involved in brain development located at the above regions should be prioritized for future genetic research.
Incidence of and risk factors for cat bites: A first step in prevention and treatment of feline aggression
Authors: Palacio Jorge , León-Artozqui Marta , Pastor-Villalba Eliseo , Carrera-Martín Fernando , García-Belenguer Sylvia
Published: December 2006

Feline aggression towards people has a smaller incidence than canine aggression, but also represents an important public health problem. The aim of this work was to analyse feline aggression reported towards people, to estimate its incidence and to assess the risk factors involved. The information was obtained from the Public Health Centres in the Valencian Region (Spain). A total of 936 acts of feline aggression were analysed. Cats inflicted 8% of all animal bites reported. The annual average was 6.36 feline aggression incidents per 100,000 people. Most aggressive incidents occurred during the summer months. Children (0–14 years old) and women were more likely to be bitten. Wounds were mainly punctures, single, and mild, and were located mostly on the hands. In children, the head and neck areas were affected much more than in adults. The cats involved in incidents were mostly Siamese, female and owned; these cats mainly attacked their owners. Most occurrences were a defensive response by the cat.
PAPER PRESENTED AT INTERNATIONAL WORKSHOP ON INCREASING WHEAT YIELD POTENTIAL, CIMMYT, OBREGON, MEXICO, 20–24 MARCH 2006 Sustainable improvement of wheat yield potential: the role of crop management
Authors: RANSOM J. K. , ENDRES G. J. , SCHATZ B. G.
Published: December 2006

A significant proportion of wheat (Triticum aestivum L.) yield increases achieved at the farm level in the past can be attributed to improved crop management practices. The important role of crop management practices in increasing the yield potential in wheat sustainably is illustrated with recent research findings from North Dakota. In the dryer regions, no-till and crop rotations significantly improve yield and protect the productivity of the soil. Intensifying management in the wetter regions through increased plant populations and by nitrogen timing did not increase yield in 2005 while fungicide applied at flowering for scab control did. In one study genotype interacted with management, with the most disease-tolerant genotypes producing the highest yield when treated with fungicides. Identifying and exploiting positive genotype by management interactions offers a potential avenue for increasing yield potential in wheat in the future. Identifying or developing crop management practices that hold potential for synergistically improving the yield of genotypes is a significant challenge. Imposing management practices that hold promise for improving yield sustainably on breeding material during the selection process has scope for identifying genotypes with greater yield potential at the farm level when these management practices are employed.
New ‘Mental Health’ Legislation for England and Wales: Some Aspects of Consensus and Conflict
Authors: PILGRIM DAVID
Published: December 2006

The faltering emergence of new ‘mental health’ legislation in England and Wales between 1998 and 2005 is described. The slow progress largely reflected widespread opposition to the content of the government's plans to replace the Mental Health Act of 1983. That opposition was formalised in the Mental Health Alliance, an umbrella organisation which included user and professional groups as well as voluntary sector bodies. This article highlights the main points of dispute between the government and its opponents. In particular, concerns about compulsion and the duty of the state to guarantee good quality care in every locality divided the government and its critics. The implications of these disputes are discussed, along with some questions about interest work within the Alliance.
Squeezing the Peasants: Grain Extraction, Food Consumption and Rural Living Standards in Mao's China
Authors: Ash Robert
Published: December 2006

At the end of Mao's life farmers still accounted for some 80 per cent of China's population. Its declining share in GDP notwithstanding, agriculture continued to carry a heavy developmental burden throughout the Mao era. The production and distribution of grain – the wage good par excellence – held the key to fulfilling this role. But despite a pragmatic response to the exigencies of famine conditions in 1959–61, state investment priorities never adequately accommodated the economic, let alone the welfare needs of the farm sector. Thanks to the mechanism of grain re-sales to the countryside, the Chinese government's extractive policies were less brutal in their impact than those pursued by Stalin in the Soviet Union. Even so, a detailed national, regional and provincial analysis of grain output and procurement trends highlights the process of rural impoverishment which characterized China's social and economic development under Maoist planning.
Local Cadres Confront the Supernatural: The Politics of Holy Water (Shenshui) in the PRC, 1949–1966
Authors: Smith Steve A.
Published: December 2006

This article examines incidents in which the miracle-working properties of a source of water or other substance are discovered, thereby sparking unauthorized visits by hundreds or thousands of people to gain access to it. The article examines: the meanings of holy water and the motivations of those who set off in search for it; the sociological dimension of these quests; the extent to which such episodes were a deliberate attempt by enemies of the regime, principally redemptive religious sects (huidaomen), to sow disorder; the reaction of the authorities to outbreaks of holy water fever and the measures they took to deal with it; and what such outbreaks reveal about the nature of the local state and about popular attitudes to it in the first decade-and-a-half of the People's Republic of China.
Factional Conflict at Beijing University, 1966–1968
Authors: Walder Andrew G.
Published: December 2006

For two years after the summer of 1966, Beijing University was racked by factional conflict and escalating violence. Despite the intensity of the struggle the factions did not express didfferences in political doctrine or orientation towards the status quo. Nie Yuanzi, the veteran Party cadre who advanced rapidly in the municipal hierarchy after denouncing both the old Beida Party Committee and the work team, fiercely defended her growing power against opponents led by several former allies. Compromise proved impossible as mutual accusations intensified, and interventions by national politicians served only to entrench the divisions. The conflicts were bitter and personal not because they expressed differences between status groups, but because the rivals knew one another so well, had so much in common, and because the consequences of losing in this struggle were so dire.
Zheng Junli, Complicity and the Cultural History of Socialist China, 1949–1976
Authors: Pickowicz Paul G.
Published: December 2006

This article explores cultural producation during the Mao era (1949–76) by focusing on the evolving relationship between artists and the party-state. The emphasis is on state direction of art in the all-important film industry. From 1949, well-known bourgeois Republican-era artists willingly began the complicated, painful and sometimes deadly process of adjusting to Communist Party state building, nation building and political domination. The career of influential film director Zheng Junli is examined as a case study of creative and strategic accommodation to new circumstances on the one hand, and of complicity on the other. Zheng is seen in his dual and contradictory roles as both trusted, ever loyal insider and unreliable, even degenerate, outsider. His Mao-era films, especially the spectacular Great Leap Forward production of Lin Zexu, are analysed in terms of their political thrust and reception in the difficult-to-predict world of the People's Republic.
In Search of a Master Narrative for 20th-Century Chinese History
Authors: Weigelin-Schwiedrzik Susanne
Published: December 2006

Since the Yan'an Rectification Campaign the Communist Party of China has dominated the interpretation of modern Chinese history. With its 1981 resolution it renewed its claim, but a close look at official and unofficial publications on 20th-century Chinese history reveals its loss of control. There is no longer a CCP-designed master narrative of modern Chinese history. This article uses the case of the Cultural Revolution to show how much post-1949 history is contested in mainland China today. It argues that the CCP is unable to impose its interpretation of the “ten years of chaos” on society. Instead many divergent and highly fragmentized views circulate in society, and there is no overwhelmingly acceptable view on this period of post-1949 history. While this is a positive sign of diversification, it leaves unsatisfied both inside and outside observers who hope that the Chinese people might eventually come to terms with their own troublesome history.
Explicit stationary solutions in multiple well dynamics and non-uniqueness of interfacial energy densities
Authors: ALIKAKOS NICHOLAS D. , BETELÚ SANTIAGO I. , CHEN XINFU
Published: December 2006

We present a theory that enables us to construct heteroclinic connections in closed form for $2\bf{u}_{xx}=W_{\bf u}({\bf u})$, where $x\in\mathbb{R},\;{\bf u}(x)\in \mathbb{R}^2$ and $W$ is a smooth potential with multiple global minima. In particular, multiple connections between global minima are constructed for a class of potentials. With these potentials, numerical simulations for the vector Allen-Cahn equation ${\bf u}_t= 2\epsilon^2 \Delta {\bf u}-W_{\bf u}({\bf u})$ in two space dimensions with small $\epsilon>0$, show that between any fixed pair of phase regions, interfaces are partitioned into segments of different energy densities, where the proportions of the length of these segments are changing with time. Our results imply that for the case of triple-well potentials the usual Plateau angle conditions at the triple junction are generally violated.
The use of GIS to evaluate and map extreme maximum and minimum temperatures in Spain
Authors: Luna M. Y. , Morata A. , Almarza C. , Martín M. L.
Published: December 2006

Spanish building legislation has recently changed and now requires an updated and restructured Technical Building Code which is in accordance with European directives. The norm contained in this Code is based on studies of extreme values for climatic elements such as temperature, precipitation and wind. Revised maps of extreme values for climatic elements with a 50‐year recurrence interval are required. Here, extreme maximum and minimum temperature maps for Spain are evaluated and mapped by means of geographical information technology. The data are extracted from the historical database held by the Spanish Meteorological Institute. Daily extreme temperatures from 1,181 stations with records going back more than 30 years have been used. The maximum and minimum temperatures are determined as 50‐year mean recurrence interval values. To obtain these values, a Gumbel distribution is fitted to the extreme annual values extracted from the database. Spatial interpolation in a regular 5 km×5 km grid of the annual maximum temperature is made by ordinary kriging. Meanwhile, for the annual minimum temperature a residual kriging has been applied due to its strong dependence on altitude. Copyright © 2006 John Wiley & Sons, Ltd.
Synoptic characteristics of dust storms observed in Inner Mongolia and their influence on the downwind area (the Beijing–Tianjin Region)
Authors: Tao Gao , Yongfu Xu , Yuhua Bo , Xiao Yu
Published: December 2006

Springtime meteorological and satellite data from 1971 to 2000 have been used to assess surface desertification and grassland deterioration to obtain a better understanding of the synoptic characteristics of dust storms observed in Inner Mongolia, the relationship between dust storms and their impact on the Beijing‐Tianjin Region, and the effect of climatic change on the surface environment of dust storm source areas in Inner Mongolia. Based on the statistics and the analysis of weather charts during each dust storm event, details and characteristics of sand and dust source regions, such as cold air paths, areas of strong winds and typical synoptic types were obtained. Temperature was found to be the most significant indicator of climate change in the dust storm source regions, having increased by 1.01°C in the Alxa source region and by 0.96°C in Hunshdak over the past three decades. Other factors include lack of precipitation, higher evaporation, lower relative humidity, soil desertification and decrease of grasslands in the source regions. As a consequence, nearly two‐thirds of the very strong dust storm events observed in Inner Mongolia (characterised by horizontal visibility below 1000 m and wind speeds of 12 m s−1 or over) led to suspended dust or dust storms in the downwind area, the Beijing‐Tianjin Region. This study also analyses the upper air and surface weather charts of 58 very strong dust storm events and established the direction of three cold air paths: northwesterly, westerly and northerly. The northwesterly cold air path is seen as the major one, responsible for 58.6% of the dust storm episodes. In addition, the observed areas where strong winds occur lie mostly across the central‐west and central regions of Inner Mongolia. Finally, the synoptic situations associated with dust storm events can be classified into three types: trough, northwesterly current and Mongolian vortex. The predominant synoptic system is the trough, responsible for 63.8% of the 58 events analysed in this study. Copyright © 2006 John Wiley & Sons, Ltd.
Climate for crops: integrating climate data with information about soils and crop requirements to reduce risks in agricultural decision‐making
Authors: Wratt D. S. , Tait A. , Griffiths G. , Espie P. , Jessen M. , Keys J. , Ladd M. , Lew D. , Lowther W. , Mitchell N. , Morton J. , Reid J. , Reid S. , Richardson A. , Sansom J. , Shankar U.
Published: December 2006

Locally applicable information about climate and soil properties can help farmers identify opportunities and reduce risks associated with changing to new land uses. This article describes techniques for preparing high‐resolution regional maps and GIS surfaces of agriculturally relevant climate parameters. Ways of combining these climate surfaces with soil data and information about the physical requirements of crops to identify areas likely to be the most suitable for new high‐value crops are then outlined. Innovative features include methods for merging observations from temporary climate stations installed for one to two years in conjunction with longer‐term climate station observations to improve input data for the maps, and techniques for mapping quantiles of climatic factors that may constrain agricultural operations. Examples are the expected ‘one‐in‐five year’ first and last frost dates, and the ‘one‐in‐five year’ lowest and highest seasonal rainfalls. The use of night‐time satellite infrared observations to improve spatial resolution of frost hazard maps is also described. Typical standard errors of these climate mapping techniques are summarised. The benefits of ongoing consultation with local farmers and local government staff during the design and implementation of climate/soil/crop potential studies are described. These include optimising products to meet local needs, quality control of the resulting maps and GIS surfaces through local knowledge, and improved uptake of information by users. Further applications of techniques described in this paper include products useful to the energy sector, preparation of daily gridded climate data estimates for use in water quality and plant growth modelling, and development of regional climate change scenarios. Copyright © 2006 John Wiley & Sons, Ltd.
INEQUALITY, GROWTH, AND OVERTAKING
Authors: SUGIMOTO YOSHIAKI
Published: December 2006

This research develops a theory about the role of within-country income inequality in the emergence of overtaking in economic performance among countries. The theory captures two opposing effects of inequality on factor accumulation and suggests that the qualitative change in their combined effect is a prime cause of overtaking. Because of the initial dominance of the positive effect of inequality, a less egalitarian economy follows a higher growth path in the short run, with a lower growth path in the long run. It also is shown that divergence or convergence may arise instead of overtaking, depending on the initial levels of development and inequality.
A NOTE ON THE IMPACT OF VOUCHER PROGRAMS WHEN THERE ARE NONLINEAR PEER GROUP EFFECTS
Authors: CHEN HUNG-JU
Published: December 2006

This study constructs a dynamic model of the coexistence of public and private schools to study the impact of voucher programs when there are nonlinear peer group effects. The government provides public schools as well as tuition vouchers for households attending private schools. School quality depends on expenditure per student and peer quality within the school. When peer quality is nonlinear, more agents will choose public schools if peer quality is more substitutable, whereas more agents will attend private schools if peer quality is more complementary. We find that vouchers will typically create a “cream skimming” effect and the impact of voucher programs on economic performance is sensitive to the way in which peer interactions affect school quality.
Prävention und Behandlung der Fluktuationen beim Parkinsonsyndrom
Authors: Ludin  , Surber
Published: December 2006

In der Langzeitbehandlung des idiopathischen Parkinsonsyndroms stellen die Fluktuationen (wearing-off, on/off-Phänomen, Dyskinesien) eine grosse Herausforderung dar. In der Folge werden die gängigen Strategien zur Vorbeugung und zur Bekämpfung dargestellt. Auf zwei neue Methoden, die bald verfügbar sein werden, wird besonders hingewiesen. Die transdermale Applikation des Dopaminagnisten Rotigotin (Neupro®) erlaubt auf einfache Weise, eine kontinuierliche dopaminerge Stimulation zu erzielen. Aufwendiger ist die direkte Abgabe einer Levodopa-/Carbidopa-Gelsuspension (Duodopa®) ins Duodenum mittels einer elektronischen Pumpe.
Elemental composition of the lunar surface: Analysis of gamma ray spectroscopy data from Lunar Prospector
Authors: Prettyman T. H. , Hagerty J. J. , Elphic R. C. , Feldman W. C. , Lawrence D. J. , McKinney G. W. , Vaniman D. T.
Published: December 2006

Gamma ray spectroscopy data acquired by Lunar Prospector are used to determine global maps of the elemental composition of the lunar surface. Maps of the abundance of major oxides, MgO, Al2O3, SiO2, CaO, TiO2, and FeO, and trace incompatible elements, K and Th, are presented along with their geochemical interpretation. Linear spectral mixing is used to model the observed gamma ray spectrum for each map pixel. The spectral shape for each elemental constituent is determined by a Monte Carlo radiation transport calculation. Linearization of the mixing model is accomplished by scaling the spectral shapes with lunar surface parameters determined by neutron spectroscopy, including the number density of neutrons slowing down within the surface and the effective atomic mass of the surface materials. The association of the highlands with the feldspathic lunar meteorites is used to calibrate the mixing model and to determine backgrounds. A linear least squares approach is used to unmix measured spectra to determine the composition of each map pixel. The present analysis uses new gamma ray production cross sections for neutron interactions, resulting in improved accuracy compared to results previously submitted to the Planetary Data System. Systematic variations in lunar composition determined by the spectral unmixing analysis are compared with the lunar soil sample and meteorite collections. Significant results include improved accuracy for the abundance of Th and K in the highlands; identification of large regions, including western Procellarum, that are not well represented by the sample collection; and the association of relatively high concentrations of Mg with KREEP‐rich regions on the lunar nearside, which may have implications for the concept of an early magma ocean.
Simultaneous inversion of total electron content and UV radiance data to produce F region electron densities
Authors: Dymond K. F. , McDonald S. E. , Coker C. , Bernhardt P. A. , Selcher C. A.
Published: December 2006

The High Resolution Airglow and Aurora Spectroscopy (HIRAAS) experiment was launched aboard ARGOS on 23 February 1999. The HIRAAS experiment operated from mid‐May 1999 through March 2002. One of the HIRAAS instruments, the Low Resolution Airglow and Aurora Spectrograph (LORAAS), gathered limb scans over the 750–100 km altitude range of the 911‐Å emission during the daytime and the O I 1356 Å emission at night; these emissions are useful for characterizing the ion density distribution in the F region. The Coherent Electromagnetic Radio Tomography (CERTO) experiment, a coherently emitting radio beacon operating at 150 and 400 MHz, also flew on the ARGOS. The slant total electron content (TEC) between ARGOS and the ground was measured, using the CERTO beacon emissions, by a receiver located at the Naval Research Laboratory during early 2001. During the mission life of ARGOS, the ARGOS and TOPEX/Poseidon satellites occasionally crossed paths, permitting additional validation of the ARGOS measurements against TOPEX vertical total electron content measurements. We present a comparison of the UV‐derived TEC and the radio beacon–derived TEC over the Naval Research Laboratory during January–April of 2001, based on LORAAS and CERTO measurements; we also present the electron densities derived by simultaneously inverting both the UV radiances and the CERTO‐derived TEC. These results are validated against ionosondes. The TOPEX and UV measurements are also inverted tomographically and are used to demonstrate enhanced spatial resolution of the ionospheric reconstructions.
Snowball Earth on trial
Authors: Allen Philip A.
Published: December 2006

Many scientists have been considering the idea that the Earth may have completely frozen over sometime in the past. Kirschvink [1992] proposed that a runaway ice‐albedo effect on continents amassed in low latitudes caused the descent into a global freeze. During a prolonged glacial period when oceans and atmosphere were isolated from each other, volcanic emissions would cause a buildup of atmospheric carbon dioxide (CO2), with no silicate weathering or photosynthesis to act as a sink. Eventually a reverse ice‐albedo effect would cause a transient heat wave as the ice cover melted back rapidly.
Bodnar receives 2005 N. L. Bowen Award
Authors: Mavrogenes John , Bodnar Robert J.
Published: December 2006

Robert J. Bodnar received the N. L. Bowen Award on 24 May 2006 from the Volcanology, Geochemistry, and Petrology Section at the 2006 Joint Assembly in Baltimore, Md. The award recognizes outstanding contributions to volcanology, geochemistry, or petrology.
Synthetic dataset to benchmark global tomographic methods
Authors: Qin Yilong , Capdeville Yann , Maupin Valerie , Montagner Jean‐Paul
Published: December 2006

A new set of global synthetic seismograms calculated in a three‐dimensional (3‐D), heterogeneous, anisotropic, anelastic model of the Earth using the spectral element method has been released by the European network SPICE (Seismic Wave Propagation and Imaging in Complex Media: a European Network). The set consists of 7424 three‐component records with a minimum period of 32 seconds, a sampling rate of one second, and a duration of 10,500 seconds.The aim of this synthetic data set is to conduct a blind test of existing global tomographic methods based on long‐period data, in order to test how current imaging techniques are limited by approximations in theory and by the inadequacy of data quality and coverage.

The correlation between modern global tomographic models is generally correct at long wavelengths, but these tomographic models are less similar at shorter wavelengths [Becker and Boschi, 2002].In order to interpret the fine details of tomographic models, it is a fundamental prerequisite to understand quantitatively the resolving properties of specific imaging algorithms. Without knowledge of the true model, it is difficult to properly evaluate the tomographic methods.
Toward broad community collaboration in geoinformatics
Authors: Fox Peter , Gundersen Linda , Lehnert Kerstin , McGuinness Deborah , Sinha Krishna , Snyder Walt
Published: December 2006

A Town Hall meeting at the upcoming AGU Fall Meeting will be held under the theme “Envisioning the future of Earth science data and knowledge access through a broad national geoinformatics collaboration.”

Geoinformatics (GI) is understood as a distributed, integrated digital information system and working environment that provides innovative means for the study of the Sun‐Earth system and other planets through the use of advanced information technologies. It is an emerging science and technology frontier, and it is increasingly recognized as a relevant part of the broader cyberinfrastructure for the sciences (see U.S. National Science Foundation Blue Ribbon Panel Report at http://www.nsf.gov/od/oci/reports/toc.jsp), both within the academic and applied Earth and planetary science and computer science communities as well as in federal and state agencies.
Preventing another ice age
Authors: Sternberg Joseph
Published: December 2006

Current concern is focused on the consequences of global warming as the atmospheric level of carbon dioxide (CO2) increases. But adding CO2 to the atmosphere has some potential benefits. As considered in this paper, published research supports the view that a moderate increase in the atmospheric CO2 level could prevent the initiation of another ice age. The amount of C02 resulting from the use of the world's fossil fuel reserves should be sufficient to provide this protection for thousands of years.
Process‐based modeling of nitrous oxide emissions from wheat‐cropped soils at the subregional scale
Authors: Gabrielle B. , Laville P. , Duval O. , Nicoullaud B. , Germon J. C. , Hénault C.
Published: December 2006

Arable soils are a large source of nitrous oxide (N2O) emissions, making up half of the biogenic emissions worldwide. Estimating their source strength requires methods capable of capturing the spatial and temporal variability of N2O emissions, along with the effects of crop management. Here we applied a process‐based model, Crop Environmental REsources Synthesis (CERES), with geo‐referenced input data on soils, weather, and land use to map N2O emissions from wheat‐cropped soils in three agriculturally intensive regions in France. Emissions were mostly controlled by soil type and local climate conditions, and only to a minor extent by the doses of fertilizer nitrogen applied. As a result, the direct emission factors calculated at the regional level were much smaller (ranging from 0.0007 to 0.0033 kg N2O‐N kg−1N) than the value of 0.0125 kg N2O‐N kg−1N currently recommended in the IPCC Tier 1 methodology. Regional emissions were far more sensitive to the soil microbial characteristics governing denitrification and its fraction evolved as N2O, soil bulk density, and soil initial inorganic N content. Mitigation measures should therefore target a reduction in the amount of soil inorganic N upon sowing of winter crops, and a decrease of the soil N2O production potential itself. From a general perspective, taking into account the spatial variability of soils and climate thereby appears necessary to improve the accuracy of national inventories, and to tailor mitigation strategies to regional characteristics.
Observation of two distinct, rapid loss mechanisms during the 20 November 2003 radiation belt dropout event
Authors: Bortnik J. , Thorne R. M. , O'Brien T. P. , Green J. C. , Strangeway R. J. , Shprits Y. Y. , Baker D. N.
Published: December 2006

The relativistic electron dropout event on 20 November 2003 is studied using data from a number of satellites including SAMPEX, HEO, ACE, POES, and FAST. The observations suggest that the dropout may have been caused by two separate mechanisms that operate at high and low L‐shells, respectively, with a separation at L ∼ 5. At high L‐shells (L > 5), the dropout is approximately independent of energy and consistent with losses to the magnetopause aided by the Dst effect and outward radial diffusion which can deplete relativistic electrons down to lower L‐shells. At low L‐shells (L < 5), the dropout is strongly energy‐dependent, with the higher‐energy electrons being affected most. Moreover, large precipitation bands of both relativistic electrons and energetic protons are observed at low L‐shells which are consistent with intense pitch angle scattering driven by electromagnetic ion cyclotron (EMIC) waves and may result in a rapid loss of relativistic electrons near the plasmapause in the dusk sector or in plumes of enhanced density.
Waves and horizontal structures in Titan's thermosphere
Authors: Müller‐Wodarg I. C. F. , Yelle R. V. , Borggren N. , Waite J. H.
Published: December 2006

The Ion Neutral Mass Spectrometer (INMS) on board the Cassini spacecraft carried out in situ measurements of neutral gas composition above 1025 km altitude in Titan's atmosphere during its flybys in October 2004 (TA) and April 2005 (T5). Strong perturbations are present in the N2 and CH4 densities which we interpret as vertically propagating waves. Typical vertical wavelengths range from 170 to 360 km with density and pressure amplitudes reaching 4–12% of the background values and temperature amplitudes of 5–10 K. Amplitudes over our sampled height range, 1025 (T5) or 1176 (TA) to 1600 km, remain roughly constant, implying that the exponential increase in wave amplitudes with height due to the decrease of density is offset by damping. This finding allows us to constrain the wave periods to values in the order of hours. Estimates of wave‐induced acceleration of the background thermosphere suggest that the waves we observe could deposit considerable momentum in Titan's thermosphere, thereby coupling the dynamics of the upper atmosphere with that of the middle atmosphere. In addition, we infer latitudinal structures in Titan's thermosphere with a factor of 3–4 increase of mass densities from pole to equator in the northern hemisphere. A preliminary evaluation of local time variations suggests densities and thermospheric temperatures to be largest near dusk, contradicting expectations for a thermosphere driven energetically and dynamically primarily by solar EUV. From the latitudinal density gradients we derived zonal wind speeds of around 245 ± 50 ms−1, implying that Titan's thermosphere, like its stratosphere, could be superrotating. Our analyses were based on the TA and TS flybys only, and future Cassini Titan flybys could either support or invalidate our findings.
Test particle acceleration in three‐dimensional Hall MHD turbulence
Authors: Dmitruk P. , Matthaeus W. H.
Published: December 2006

Numerical experiments of test particle acceleration are performed using turbulent magnetic and electric fields obtained from direct numerical solutions of the compressible three‐dimensional Hall magnetohydrodynamic (MHD) equations. Comparisons are made of the results for the test particle momentum distribution function with and without the Hall term in the MHD solution. Electrons and protons are considered for the test particles at short times before particles leave the simulation box (with length size of the order of a few turbulent correlation lengths). The particles momentum distribution functions develop long tails in a short time. For electrons, no substantial difference it is found between results with and without the Hall term in the MHD solution, while for protons differences are seen in the low momentum part of the distributions. When a background uniform magnetic field (guide field) is added, the particle acceleration is anisotropic. Electrons develop large parallel momentum, while protons develop large perpendicular momentum. A discussion of the basic particle acceleration mechanisms in this system is made.
Intraseasonal variations of surface and subsurface currents off Java as simulated in a high‐resolution ocean general circulation model
Authors: Iskandar Iskhaq , Tozuka Tomoki , Sasaki Hideharu , Masumoto Yukio , Yamagata Toshio
Published: December 2006

A high‐resolution ocean general circulation model (OGCM) is used to explore dynamics of intraseasonal variability in surface and subsurface currents off Java. The results indicate that the surface current, the so‐called South Java Coastal Current (SJCC), is dominated by variations with a period of 90 days. In the subsurface current, which is referred to as the South Java Coastal Undercurrent (SJCU), 60‐day variations are the most prominent feature. A normal mode analysis demonstrates that the first baroclinic mode is the leading mode, which accounts for 70% of the total variance, whereas the second baroclinic mode explains 24% of the total variance. The 90‐day variations in the SJCC captured mostly by the first baroclinic mode are found to be primarily driven by winds. Those are associated with propagation of the first baroclinic Kelvin waves generated in the central equatorial Indian Ocean. On the other hand, the 60‐day variations in the SJCU enhanced by wind forcing over the eastern equatorial Indian Ocean off Sumatra are mostly captured by the second baroclinic mode.
Physical and optical properties of aerosols over an urban location in western India: Implications for shortwave radiative forcing
Authors: Ganguly Dilip , Jayaraman A.
Published: December 2006

We discuss results on implications of seasonal and interannual variabilities in aerosol parameters measured over Ahmedabad, an urban location in western India, for the regional‐scale shortwave aerosol direct radiative forcing. Results on physical and optical properties of aerosols are discussed in a companion paper. A discrete ordinate radiative transfer model has been used to carry out the radiative transfer computations. Two different approaches are followed to generate spectral values of aerosol parameters required as input for the radiative transfer computations, and the estimated values are found comparable for both methods. Magnitudes of surface forcing are found to be highest during postmonsoon (−63 ± 10 W/m2), followed by dry (−54 ± 6 W/m2) and lower values during premonsoon (−41.4 ± 5 W/m2) and monsoon (−41 ± 11 W/m2) seasons. In case of TOA, radiative forcing are found to be negative during dry (−26 ± 3 W/m2) and postmonsoon (−22), while positive values are obtained during monsoon (14) and premonsoon (8). Large differences between TOA and surface forcing during monsoon and premonsoon indicate large absorption of radiant energy (∼50 W/m2) within the atmosphere during these seasons. Different properties of aerosols and differences in their vertical distribution give rise to different heating rates within the atmosphere for different seasons. Heating rates at the surface are found to be highest during postmonsoon (5.6°K/day) but decreases sharply with increase in height. Atmosphere is heated strongly at higher levels between 1 and 2 km during monsoon. Results from several sensitivity studies have emphasized the importance of solar zenith angle and other related factors in modulating the values of aerosol radiative forcing.
Modeling the influence of river rehabilitation scenarios on bed material sediment flux in a large river over decadal timescales
Authors: Singer Michael Bliss , Dunne Thomas
Published: December 2006

A stochastic flood generator and calibrated sediment transport formulae were used to assess the decadal impact of major river rehabilitation strategies on two fraction bed material sediment flux and net storage, first‐order indicators of aquatic riverine habitat, in a large river system. Model boundary conditions were modified to reflect the implementation of three major river rehabilitation strategies being considered in the Sacramento River Valley: gravel augmentation, setting back of levees, and flow alteration. Fifty 30‐year model simulations were used to compute probabilities of the response in sediment flux and net storage to these strategies. Total annual average bed material sediment flux estimates were made at six gauged river cross sections, and ∼60 km reach‐scale sediment budgets were evaluated between them. Gravel augmentation to improve spawning habitat induced gravel accumulation locally and/or downstream, depending on the added mixture. Levee setbacks to recreate the river corridor reduced flow stages for most flows and hence lowered sediment flux. Flow alteration to mimic natural flow regimes systematically decreased total annual average flux, suggesting that high‐magnitude low‐frequency transport events do not affect long‐term trends in bed material flux. The results indicate that each rehabilitation strategy reduces sediment transport in its target reaches and modulates imbalances in total annual bed material sediment budgets at the reach scale. Additional risk analysis is necessary to identify extreme conditions associated with variable hydrology that could affect rehabilitation over decades. Sensitivity analysis suggests that sorting of bed material sediment is the most important determinant of modeled transport and storage patterns.