bluuebunny/crossref_metadata_2025 huggingface dataset:
Wall turbulence manipulation by large-scale
streamwise vortices
Authors: IUSO GAETANO , ONORATO MICHELE , SPAZZINI PIER GIORGIO , DI CICCA GAETANO MARIA
Published: December 2002

This paper describes an experimental study of the manipulation of a fully developed
turbulent channel flow through large-scale streamwise vortices originated by vortex
generator jets distributed along the wall in the spanwise direction. Apart from the
interest in flow management itself, an important aim of the research is to observe
the response of the flow to external perturbations as a technique for investigating the
structure of turbulence. Considerable mean and fluctuating skin friction reductions,
locally as high as 30% and 50% respectively, were measured for an optimal forcing
flow intensity. Mean and fluctuating velocity profiles are also greatly modified by the
manipulating large-scale vortices; in particular, attenuation of the turbulence intensity
was measured. Moreover the flow manipulation caused an increase in longitudinal
coherence of the wall organized motions, accompanied by a reduced frequency of
burst events, demonstrated by a reduction of the velocity time derivative PDFs and
by an higher intermittency. A strong transversal periodic organization of the flow
field was observed, including some typical behaviours in each of the periodic boxes
originated by the interaction of the vortex pairs. Results are interpreted and discussed
in terms of management of the near-wall turbulent structures and with reference to
the wall turbulence regeneration mechanisms suggested in the literature.
Shear versus vortex-induced lift force on a rigid
sphere at moderate Re
Authors: BAGCHI P. , BALACHANDAR S.
Published: December 2002

The lift forces on rigid spheres entrained in a vortex and a linear shear flow are
computed using a direct numerical simulation. The sphere Reynolds number is in the
range 10 to 100. The lift coefficient in a vortex is shown to be nearly two orders of
magnitude higher than that in a shear flow. The inviscid mechanism is shown to be
inadequate to account for the enhanced lift force. The effect of free rotation of the
sphere is also shown to be too small to account for the enhanced lift force. Flow
structure around the sphere is studied to explain the generation of the strong lift force
in a vortex.
A categorial treatment of adverbial nouns
Authors: WHITMAN NEAL
Published: December 2002

A select set of English nouns can head adverbial NPs – NPs that can act as adverbs without being preceded by a preposition. These ‘adverbial nouns’ also can be modified by prepositionless adverbial non-wh relative clauses. An analysis is presented in a categorial grammar framework, employing a conjunctive type structure to describe the behavior of adverbial nouns. It is suggested that adverbial nouns select non-wh adverbial relative clauses as complements; lexical rules are written to allow such selection. Finally, some remaining issues are surveyed concerning adverbial nouns in particular and conjunctive categories in general.
The Comp-trace effect, the adverb effect and minimal CP
Authors: SOBIN NICHOLAS
Published: December 2002

Recent work has ascribed the adverb effect, the reduction or elimination of the that-trace effect by the addition of an adverbial phrase, to an elaborated CP layer. However, additional observations about a variety of adverb effects with both positive and negative effects on acceptability, including some experimental data, suggest that (i) adverbs may undergo lexical adjunction to a complementizer and (ii) the CP layer may be contracting or folding in rather than expanding. This proposal facilitates explanation of an array of facts including the Comp-trace effect, the adverb effect and other aspects of the behavior of complementizers in relative constructions and in complement constructions.
Clitic placement in L2 French: evidence from sentence matching
Authors: DUFFIELD NIGEL , WHITE LYDIA , DE GARAVITO JOYCE BRUHN , MONTRUL SILVINA , PRÉVOST PHILIPPE
Published: December 2002

In this paper, we argue in favour of the NO IMPAIRMENT HYPOTHESIS, whereby L2 functional categories, features and feature values are attainable, and against the NO PARAMETER RESETTING HYPOTHESIS, according to which L2 learners are restricted to L1 categories and features, as well as against the LOCAL IMPAIRMENT HYPOTHESIS, which claims that the interlanguage grammar is characterized by inert feature values. An online experiment was conducted, investigating adult learners' knowledge of properties relating to clitic projections. Advanced learners of French (L1s English and Spanish), together with a native speaker control group, were tested on a variety of constructions involving clitics by means of the SENTENCE MATCHING procedure (Freedman & Forster 1985). L2 learners distinguished in their response times between certain kinds of grammatical and ungrammatical clitic placement, as did the native-speaker controls, suggesting the attainability of L2 properties distinct from the L1.
Excitation of Bernstein waves by energetic
pickup ions
Authors: CHEN YAN-PING
Published: December 2002

This paper discusses the excitation of Bernstein waves by pickup ions,
which occur in the low corona, particularly the active regions. The present research
is motivated by the study of solar plasma and radio-emission processes. However,
emphasis is placed in this paper on the stability analysis rather than applications
of the result. The analysis encompasses two limiting cases: one is when the pickup
ions have small velocity dispersion; the other is when the ion velocity dispersion is
significant.
Low-frequency wave instabilities in a plasma
with a quasistatic electric field and weak
spatial inhomogeneity
Authors: KRYSHTAL A. N.
Published: December 2002

A specific type of plasma-wave instability in a hot magnetoactive collisional plasma due to a weak external electric field and weak spatial inhomogeneity
is considered for the cases of kinetic Alfvén-like waves. These low-frequency waves
with ω [Lt ] Ωi (where Ωi is the ion gyrofrequency) are solutions of the corresponding
dispersion relation. The model integral of Bhatnagar, Gross, and Krook is used
for the description of collisions. The quasistatic time variation of the electric field
amplitude makes it possible to use the ‘direct initiation’ mechanism to describe instability development. An expression for the growth rate is obtained in the framework of linear theory. The instability in question occurs for a certain equation of
state of the plasma. For this equation of state, a numerical analysis of the obtained
instabilities is performed.
On the electrical conductivity of semiclassical
two-component plasmas
Authors: ARKHIPOV YU. V. , BAIMBETOV F. B. , DAVLETOV A. E. , STARIKOV K. V.
Published: December 2002

Starting from a memory-function formalism coupled with the Green–
Kubo formula and an approximate expression for the generalized Coulomb logarithm, the electric conductivity of a dense high-temperature hydrogen plasma is
studied. A pseudopotential model, taking account of short-range quantum effects
and long-range screening-field effects, is employed to include quantum mechanical and polarization effects. An analytical formula for the Coulomb logarithm is
proposed when the thermal de Broglie wavelengths are rather smaller than the Debye radius. A minimum in the curve of electrical conductivity is found and some
physical evidence for its appearance is produced.
Excitation of surface cyclotron O modes by
charged-particle beams
Authors: GIRKA V. O.
Published: December 2002

A theoretical investigation of the interaction between a charged-particle
beam and ordinarily polarized surface waves at the first two harmonics of ion
and electron cyclotron frequencies propagating across an external steady magnetic
field is carried out. The case of weak plasma spatial dispersion when the Larmor
radii of plasma particles are much less than the penetration depth of these waves
into the plasma is considered. The indicated waves are eigenmodes of the planar
plasma–vacuum–metal waveguide structure, which is exposed to a steady magnetic
field oriented parallel to the plasma surface. It is supposed that a cold charged-
particle beam propagates over the plasma surface in the vacuum region. The beam
density is less than the plasma density. Excitation of these O modes at the first
and second harmonics of electron and ion cyclotron frequencies caused by the both
resonant beam and dissipative instabilities is studied analytically. The dependence
of their growth rates on parameters of the considered waveguide structures is also
examined.
Magnetic viscosity due to collapsing flux cells
Authors: LI X. Q. , ZHANG H.
Published: December 2002

Reconnective annihilation of magnetic field leads to the formation of
magnetic flux cells with small scales, followed by enhanced transverse plasmons occurring in a thin current sheet with a very small vertical extent. The analysis here
focuses on the nonlinear interaction between the flux and plasmons. The transverse
plasmon field is modulationally unstable in the Lyapunov sense. When the initial
pumping wave amplitude attains the threshold of instability, this instability occurs
with a high growth rate. Nonlinear development of modulational instability eventually results in self-similar collapse, due to nonlinear equilibrium, giving rise to
a spatially intermittent, collapsing magnetic flux, very similar to a turbulent pattern. The Maxwell stress tensor from the turbulence flux determines the anomalous
magnetic viscosity, i.e. the parameter α. It is shown that the instability is responsible for the alternation of outburst or quiescent states in astrophysical accretion
disks. When the instability occurs, the parameter α is large. In the quiescent state,
the instability is suppressed, leading to a smaller, collapse-quenching value of α.
Saturation of electrostatic instability in
two-species plasma
Authors: BALMFORTH N. J. , KERSWELL R. R.
Published: December 2002

We explore the level of saturation of instabilities in a two-species plasma
using a combination of matched asymptotic expansion and numerical computation.
The plasma is assumed to be spatially periodic, and the domain size is chosen to
allow a single mode to become unstable when a bump is added to the tail of the
distribution of the lighter species. We consider two versions of the problem, arising
when the mass ratio of the two species is either very small, or of the order of
unity. For small mass ratios, the initial saturation level of the mode amplitude, as
measured by the electric field disturbance, follows the ‘trapping scaling’. For mass
ratios of order unity, nonlinear effects become important at the level predicted by
Crawford and Jayaraman, but the instability does not saturate there and continues
to grow. In both cases, the initial onset of nonlinearity does not reflect the longer-
time evolution of the system. In fact, the system passes through multiple stages
of evolution in which the electric field amplitude is not simply predicted; none
of the previously published scalings are adequate. Eventually, for both cases, the
distribution of the lighter ions becomes significantly rearranged, and much (though
not all) of the destabilizing bump is flattened. A better predictor of the strength of
the instability is given by the extent of these rearrangements.
Later life and the social model of disability: a comfortable partnership?
Authors: OLDMAN CHRISTINE
Published: December 2002

There has been very limited debate about the usefulness of links between later life and disability studies. The paper reviews the arguments for and against a closer association. The social model of disability makes crucial the separation of disability from impairment and shows that it is society that does the disabling. This is never so clear as in the case of housing policies for older people, the focus of this article. Older people suffer discrimination and have to submit to a medical model of later life if they receive health or social care services. The argument against an association between later life studies and disability studies is that later life is an immensely diverse experience, much of it nothing to do with disability. Moreover, some older people reject the negative connotation when later life is equated with disability. The paper argues, however, for a specific application of the social model of disability to the situation of older people with impairments who receive services. It also asserts that the social model of disability can be accommodated in critical gerontology and, in particular, in a post-modern perspective. The paper concludes with examples of the value of the social model of disability at both the policy and political levels.
The design of caring environments and
the quality of life of older people
Authors: BARNES SARAH , the DESIGN IN CARING
ENVIRONMENTS STUDY GROUP
Published: December 2002

There has been little systematic research into the design of care environments
for older people. This article reviews empirical studies from both the
architectural and the psychological literature. It outlines the instruments that
are currently available for measuring both the environment and the quality of
life of older people, and it summarises the evidence on the layout of buildings,
the sensory environment and the privacy of residents. The conclusion is drawn
that all evidence-based design must be a compromise or dynamic and, as
demands on the caring environment change over time, this compromise must
be re-visited in the form of post-occupancy evaluation.
Older women's perceptions of ideal body weights: the tensions between health and appearance motivations for weight loss
Authors: CLARKE LAURA HURD
Published: December 2002

This paper explores older women's evaluations of their weight as well as the perceived merits and detriments of weight gain and weight loss in later life. Using data from semi-structured interviews with 22 community-dwelling women aged 61 to 92 years, I examine the meanings that the women attribute to dieting, desired body weights and obesity. The women frequently offer unsolicited accounts for why they have gained or lost weight over time, and disclose their perceptions of and reasons for needing to alter their current body weights. I probe the tensions between weight loss for health concerns versus appearance goals. The women express dissatisfaction with their weight gain in terms of their physical appearance. However, they also tend to describe the need to lose weight in terms of health risks and benefits rather than in terms of approximating the beauty ideal or achieving a desired body size and shape. Health tends to be described as a valid justification for being concerned with one's weight, while an appearance orientation is deemed to be indicative of vanity. Many of the women suggest that while the health benefits of weight loss are often the stated reason for losing weight, the perceived appearance dividends are the key motivation behind altering one's body weight in later life.
Domestic spaces: uses and meanings in the daily lives of older people
Authors: PERCIVAL JOHN
Published: December 2002

This paper examines older people's everyday routines and their implications for older people's uses and perceptions of domestic spaces in both mainstream and sheltered housing settings. It draws from qualitative data collected during a large-scale survey of the housing and support needs of older people, and specifically the responses of 60 informants to personal interviews. The findings are that domestic spaces have a significant influence on the scope that older people have to retain a sense of self-determination. It is shown that environmental defects, such as poorly configured domestic spaces, have consequences for older people's sense of continuity and choice. The conclusions are that domestic spaces are living spaces that embody personal and family-oriented priorities. It is suggested that older people require adequate, accessible and personalised domestic spaces in order to facilitate three important objectives: routines, responsibilities and reflection.
Growing old gracefully: social dance in the third age
Authors: COOPER LESLEY , THOMAS HELEN
Published: December 2002

This paper examines the meaning of social dancing for older people. It is based on a one-year qualitative research project, which is seeking to explore the experiences of social dance for people aged 60 years or more who attend various dance events in Essex and south-east London. The findings suggest that the social dance experience is not only or simply a beneficial physical experience for older people, it also bestows other significant benefits for those who enter the third age and beyond. It can provide continuity within change. It offers an opportunity to be sociable and have fun in ways that both reflect, and avowedly move beyond, the dancers' teenage years. It promotes a welcome sense of a community spirit. It is a way of becoming visible and aesthetically pleasing, and it bestows a sense of worth and achievement in skills learnt through dancing. Last but not least, dancers can experience the joy of a fit and able body in both real and mythic senses.
Nursing home vouchers in Spain: the Valencian experience
Authors: TORTOSA MARIA ANGELES , GRANELL RAFAEL
Published: December 2002

The main purpose of this paper is to evaluate the innovative nursing home voucher scheme that was introduced by the Valencia Autonomous Region of Spain in the early 1990s to implement targets laid down by the national plan for the development of older people's services. The article begins with a review of the evolution of Spanish social services, and especially the nursing home sector, and then summarises the genesis, objectives and characteristics of the voucher scheme. The main part of the paper reports a performance analysis and economic evaluation of the programme. On the basis of detailed information over four years, it is concluded that nursing home vouchers have contributed to the increased supply of publicly-financed rooms, have promoted equality of access to the service, and have increased user choice. It is also shown, however, that while vouchers can lead to an increase in the quality of inputs, they increase utilisation and expenditure. In the absence of the monitoring or reporting data that would be required, it is not possible to determine whether the scheme has increased efficiency, in the sense of improving the quality of life of frail older people at reasonable and containable cost.
The vulnerable life course: poverty and social assistance among middle-aged and older women
Authors: GUNNARSSON EVY
Published: December 2002

In Europe, older women are more likely than older men to be living in poverty, and the contrast is directly related to their domestic roles and labour market position during earlier phases of their life courses. Despite Sweden's well-developed social security system, the generalisation applies to its older women. This paper examines the current incomes and life courses of 14 middle-aged and older Swedish women who have periodically had to rely on social assistance. Their circumstances and living conditions are considered in relation to their earlier lives and to the contextual conditions of the country's welfare state. Both life course and feminist perspectives are applied. All the interviewed women had been the main carers of their children, and had worked part-time or in low-paid jobs. Their formal employment histories have been the foundation of their vulnerable economic situation in older age, which the Swedish social security system does little to combat. Unless the bases and assumptions of the social security model are changed, there will continue to be many older women who live a life of poverty or near poverty.
Multi-components chemotactic system
in the absence of conflicts
Authors: WOLANSKY G.
Published: December 2002

A generalization of the Keller–Segel model for chemotactic systems is studied. In this model
there are several populations interacting via several sensitivity agents in a two-dimensional
domain. The dynamics of the population is determined by a Fokker–Planck system of
equations, coupled with a system of diffusion equations for the chemical agents. Conditions
for global existence of solutions and equilibria are discussed, as well as the possible existence
of time-periodic attractors. The analysis is based on a variational functional associated with
the system.
Asymptotic analysis of the American call option
with dividends
Authors: KNESSL CHARLES
Published: December 2002

We consider an American call option and let C(S, T0) be the price of an option corresponding
to asset price S at some time T0 prior to the expiration time TF . We analyze C(S, T0) in various
asymptotic limits. These include situations where the interest and dividend rates are large or
small, compared to the volatility of the asset. We also analyze the optimal exercise boundary
for the option. We use perturbation methods to analyze either the PDE that C(S, T0) satisfies,
or a nonlinear integral equation that is satisfied by the optimal exercise boundary.
Removing false singular points as a method of
solving ordinary differential equations
Authors: SHANIN A. V. , CRASTER R. V.
Published: December 2002

A general formalism is described whereby some regular singular points are effectively removed
and substantial simplifications ensue for a class of Fuchsian ordinary differential equations,
and related confluent equations. These simplifications follow provided the exponents at the
singular points satisfy certain relations; explicit, illustrative examples are constructed to
demonstrate the ideas.
Monotone increasing solutions of the Painlevé 1
equation y″ = y2+x and their role in the
stability of the plasma-sheath transition
Authors: SLEMROD M.
Published: December 2002

This paper proves the existence and uniqueness of a monotone increasing solution of the
Painlevé 1 equation y″ = y2+x. The monotonicity of solution is then exploited to show
stability of the plasma-sheath transition in a weakly ionizing plasma.
Nutrition in terrestrial isopods (Isopoda: Oniscidea): an evolutionary‐ecological approach
Authors: ZIMMER MARTIN
Published: December 2002

The nutritional morphology, physiology and ecology of terrestrial isopods (Isopoda: Oniscidea) is significant in two respects. (1) Most oniscid isopods are truly terrestrial in terms of being totally independent of the aquatic environment. Thus, they have evolved adaptations to terrestrial food sources. (2) In many terrestrial ecosystems, isopods play an important role in decomposition processes through mechanical and chemical breakdown of plant litter and by enhancing microbial activity. While the latter aspect of nutrition is discussed only briefly in this review, I focus on the evolutionary ecology of feeding in terrestrial isopods.

Due to their possessing chewing mouthparts, leaf litter is comminuted prior to being ingested, facilitating both enzymatic degradation during gut passage and microbial colonization of egested faeces. Digestion of food through endogenous enzymes produced in the caeca of the midgut glands (hepatopancreas) and through microbial enzymes, either ingested along with microbially colonized food or secreted by microbial endosymbionts, mainly takes place in the anterior part of the hindgut. Digestive processes include the activity of carbohydrases, proteases, dehydrogenases, esterases, lipases, arylamidases and oxidases, as well as the nutritional utilization of microbial cells. Absorption of nutrients is brought about by the hepatopancreas and/or the hindgut epithelium, the latter being also involved in osmoregulation and water balance. Minerals and metal cations are effectively extracted from the food, while overall assimilation efficiencies may be low. Heavy metals are stored in special organelles of the hepatopancreatic tissue. Nitrogenous waste products are excreted via ammonia in its gaseous form, with only little egested along with the faeces. Nonetheless, faeces are characterized by high nitrogen content and provide a favourable substrate for microbial colonization and growth. The presence of a dense microbial population on faecal material is one reason for the coprophagous behaviour of terrestrial isopods. For the same reason, terrestrial isopods prefer feeding on decaying rather than fresh leaf litter, the former also being more palatable and easier to digest. Acceptable food sources are detected through distance and contact chemoreceptors. The ‘quality’ of the food source determines individual growth, fecundity and mortality, and thus maintenance at the population level. Due to their physiological adaptations to feeding on and digesting leaf litter, terrestrial isopods contribute strongly to nutrient recycling during decomposition processes. Yet, many of these adaptations are still not well understood.
Haeckel's ABC of evolution and development
Authors: RICHARDSON MICHAEL K. , KEUCK GERHARD
Published: December 2002

One of the central, unresolved controversies in biology concerns the distribution of primitiveversusadvanced characters at different stages of vertebrate development. This controversy has major implications for evolutionary developmental biology and phylogenetics. Ernst Haeckel addressed the issue with his Biogenetic Law, and his embryo drawings functioned as supporting data. We re‐examine Haeckel's work and its significance for modern efforts to develop a rigorous comparative framework for developmental studies. Haeckel's comparative embryology was evolutionary but non‐quantitative. It was based on developmental sequences, and treated heterochrony as a sequence change. It is not always clear whether he believed in recapitulation of single characters or entire stages. The Biogenetic Law is supported by several recent studies ‐ if applied to single characters only. Haeckel's important but overlooked alphabetical analogy of evolution and development is an advance on von Baer. Haeckel recognized the evolutionary diversity in early embryonic stages, in line with modern thinking. He did not necessarily advocate the strict form of recapitulation and terminal addition commonly attributed to him. Haeckel's much‐criticized embryo drawings are important as phylogenetic hypotheses, teaching aids, and evidence for evolution. While some criticisms of the drawings are legitimate, others are more tendentious. In opposition to Haeckel and his embryo drawings, Wilhelm His made major advances towards developing a quantitative comparative embryology based on morphometrics. Unfortunately His's work in this area is largely forgotten. Despite his obvious flaws, Haeckel can be seen as the father of a sequence‐based phylogenetic embryology.
Sexual selection: an evolutionary force in plants?
Authors: SKOGSMYR IO , LANKINEN ÅSA
Published: December 2002

Sexual selection has traditionally been used to explain exaggerated sexual traits in male animals. Today the concept has been developed and various other sexually related traits have been suggested to evolve in the same manner. In nearly all new areas where the theory of sexual selection has been applied, there has been an intense debate as to whether the application is justified. Is it the case that some scientists are all too ready to employ fashionable ideas? Or are there too many dogmatic researchers refusing to accept that science develops and old ideas are transformed? Maybe the controversies are simply a reflection of the difficulty of defining a theory under constant re‐evaluation. Thus, we begin by summarizing the theory of sexual selection in order to assess the influence of sexual selection on the evolution of plant morphology. We discuss empirical findings concerning potentially affected traits. Although we have tried to address criticisms fairly, we still conclude that sexual selection can be a useful tool when studying the evolution of reproductive traits in plants. Furthermore, by including the evidence from an additional kingdom, a fuller understanding of the processes involved in sexual selection can be gained.
Nitric oxide and changes of iron metabolism in exercise
Authors: QIAN ZHONG MING
Published: December 2002

Accumulated data imply that exercise itself might not lead to a true iron deficiency or ‘sport anaemia’ in a healthy athlete who has adequate iron intake. The higher prevalence of iron deficiency anaemia in younger female athletes might be not due to exercise itself, but probably results from dietary choices, inadequate iron intake and menstruation. These factors can also induce iron deficiency or anaemia in the general population. However, exercise does affect iron metabolism, leading to low or sub‐optimal iron status. The underlying mechanism is unknown. In this review, recent advances in the study of the effect of exercise on iron metabolism and nitric oxide, and the relationship between nitric oxide and iron status in exercise are discussed. A hypothesis that increased production of nitric oxide might contribute to sub‐optimal iron status in exercise is proposed.
Memory trace in prefrontal cortex: theory for the cognitive switch
Authors: OTANI SATORU
Published: December 2002

The dorsolateral prefrontal cortex in human and non‐human primates functions as the highest‐order executor for the perception‐action cycle. According to this view, when perceptual stimuli from the environment are novel or complex, the dorsolateral prefrontal cortex serves to set consciously a goal‐directed scheme which broadly determines an action repertory to meet the particular demand from the environment. In this respect, the dorsolateral prefrontal cortex is a short‐term activation device with the properties of a ‘cognitive switch’, because it couples a particular set of perceptual stimuli to a particular set of actions. Here, I suggest that, in order for the organism to react systematically to the environment, neural traces for the switch function must be stored in the brain. Thus, the highest‐order, perception‐action interface function of the dorsolateral prefrontal cortex per se depends on permanently stored neural traces in the dorsolateral prefrontal cortex and related structures. Such a memory system may be located functionally between two of the well‐documented memory systems in the brain: the declarative memory system and the procedural memory system. Finally, based on available neurophysiological data, the possible mechanisms underlying the formation of cognitive switch traces are proposed.
Vanguard – a proposed European astrobiology experiment on Mars
Authors: Ellery A.A. , Cockell C.S. , Edwards H.G.M. , Dickensheets D.L. , Welch C.S.
Published: December 2002

We propose a new type of robotic mission for the exploration of Mars. This mission is called Vanguard and represents the fruits of a collaboration that is both international and multi-disciplinary. Vanguard is designed for sub-surface penetration and investigation using remote instruments and unlike previous robotic architectures it offers the opportunity for multiple subsurface site analysis using three moles. The moles increase the probability that a subsurface signature of life can be found and by accomplishing subsurface analysis across a transect, the statistical rigour of Martian scientific exploration would be improved. There is no provision for returning samples to the surface for analysis by a gas-chromatograph/mass-spectrometer (GCMS) – this minimizes the complexity invoked by sophisticated robotic overheads. The primary scientific instruments to be deployed are the Raman spectrometer, infrared spectrometer and laser-induced breakdown spectroscope – the Raman spectrometer in particular is discussed. We concentrate primarily on the scientific rationale for the Vanguard mission proposal. The Vanguard mission proposal represents a logical opportunity for extending European robotic missions to Mars.
Hollow organic globules in the Tagish Lake meteorite as possible products of primitive organic reactions
Authors: Nakamura Kelko , Zolensky Michael E. , Tomita Satoshi , Nakashima Satoru , Tomeoka Kazushige
Published: December 2002

We report the first in situ observation of hollow organic globules in any extraterrestrial material using the Tagish Lake carbonaceous chondrite. Data from analytical transmission electron microscopy, Raman and micro-Fourier-transform infrared (FTIR) spectroscopy indicate that the globules consist of aliphatic and oxygenated functions. The hollow spherical morphologies are strikingly similar to the material produced by the laboratory simulation of ultraviolet photolysis of interstellar ice analogues and subsequent aqueous processing, suggesting that the organic globules in the Tagish Lake meteorite may be extremely primitive organic material that formed before or during the formation of the solar system. The FTIR organic signatures also show strong similarities to the membrane-like products formed from hydrothermal reaction of an OH-bearing amino acid in the presence of hydrous minerals. The survival of the structures in the Tagish Lake sample indicates that primitive meteorites must have delivered these structures to the early Earth as a possible precursor to life.
Inferring the concentration of anthropogenic carbon in the ocean from tracers
Authors: Hall Timothy M. , Haine Thomas W. N. , Waugh Darryn W.
Published: December 2002

We present a technique to infer concentrations of anthropogenic carbon in the ocean from observable tracers and illustrate the technique using synthetic data from a simple model. In contrast to several recent studies, the technique makes no assumptions about transport being dominated by bulk advection and does not require separation of the small anthropogenic signal from the large and variable natural carbon cycle. Mixing is included naturally and implicitly by using observable tracers in combination to estimate the distributions of transit times from the surface to interior points. The time‐varying signal of anthropogenic carbon in surface waters is propagated directly into the interior by the transit time distributions (TTDs) without having to consider background natural carbon. The TTD technique provides estimates of anthropogenic carbon, as simulated directly in the model, that are more accurate than techniques relying on single tracer “ages” (e.g., CFC age) to represent transport. In general, the TTD technique works best when at least two tracers are used in combination, and the tracers have significantly different timescales in either their surface temporal variation or radioactive decay. Possibilities are a CFC or CCl4 in combination with natural Δ14C or 39Ar. However, even for a CFC alone the TTD technique results in less bias for anthropogenic carbon estimates than use of a CFC age.
The causes of long‐term change in the aa index
Authors: Clilverd Mark A. , Clark Toby D. G. , Clarke Ellen , Rishbeth Henry , Ulich Thomas
Published: December 2002

The aa index provides the longest geomagnetic data set that can be used in the analysis of magnetospheric and ionospheric phenomena. All phases of the solar cycle show increases in storm activity since the end of cycle 14 in 1915. The activity increase does not appear to be strongly associated with any instrumental, ionospheric or magnetospheric effects. Small effects have been confirmed in the long‐term change in ionospheric Pedersen and Hall conductivities due to the changing dipole moment of the Earth but not due to increasing greenhouse gases. Three instrumental effects have been identified where significant changes in quiet time conditions can be seen, that is, 1938, 1980, and 1997. These do not account for the majority of the increase in aa. Noise levels for the aa index are now close to those seen at the beginning of the data set. The prime cause of the increase in storm activity is an increase in solar activity. The average aa in cycle 23 should be about 1 nT less than that predicted from previous cycles due to the reduction in baseline noise levels at the start of the cycle (1997).
April 2000 magnetic storm: Solar wind driver and magnetospheric response
Authors: Huttunen K. Emilia J. , Koskinen Hannu E. J. , Pulkkinen Tuija I. , Pulkkinen Antti , Palmroth Minna , Reeves E. Geoffrey D. , Singer Howard J.
Published: December 2002

On 4 April 2000, a coronal mass ejection (CME) took place close to the western limb of the Sun. The shock front of the CME hit the Earth's magnetosphere on 6 April. A strong interplanetary southward BZ event in the sheath region caused a magnetic storm that was the second strongest in the year 2000 if quantified by the peak of the Dst index. We have analyzed this sequence of events using observations of several spacecraft in the solar wind and at geostationary orbit as well as recordings from more than 80 magnetometer stations at latitudes higher than 40°N. In the sheath region behind the shock, the interplanetary magnetic field had an intense and long‐sustained southward magnetic field orientation, and the solar wind magnetic pressure was very large, which compressed the dayside magnetopause inside geostationary orbit for a period of more than 6 hours. We conclude that it was the fluctuating but strongly southward field accompanied by the high pressure that allowed for the exceptionally strong driving of magnetospheric activity. During the main phase of the storm, the magnetosphere and ionosphere were in highly perturbed states, with several activations all around the auroral region. Detailed analysis shows that many of these activations were not substorms, in the sense that they were not associated with poleward and westward electrojet/auroral enhancement or geostationary particle injections, but were directly driven perturbations due to variations in the solar wind features. In fact, it was found that the development of the entire storm was quite independent of substorm activations and injections. Instead, the ring current development was driven by the strong convection enhancements. During the storm, the geomagnetically induced currents were strongly enhanced during several periods. While some activations were associated with substorm onsets or electrojet enhancements, others were caused by extremely localized and short‐lived electrojet activations.
Diffusive magnetic images of upwelling patterns in the core
Authors: Olson Peter , Sumita Ikuro , Aurnou Jonathan
Published: December 2002

A new technique for imaging convection in the outer core is presented, which is based on mean field electrodynamics. The method assumes a frozen magnetic flux balance for the global‐scale part of the fluid velocity in the outer core and a diffusive magnetic flux balance for smaller‐scale parts of the fluid velocity. The diffusive flux balance implies that local highs and lows in the magnetic field correspond approximately to fluid downwellings and upwellings, respectively. Diffusive flux produces good images of the pattern of upwellings and downwellings near the outer boundary in numerical dynamos, except near the equator. The amplitudes of the upwellings in the diffusive magnetic images correspond to the upwelling amplitudes below the Ekman boundary layer in the numerical dynamos. We have applied this technique to the Oersted initial 2000 core field model and to time‐averaged models of the historical geomagnetic field on the core‐mantle boundary. It indicates that high‐latitude, high magnetic flux density patches correspond to downwellings in the outer core.
Three‐dimensional inversion of marine magnetic anomalies on the equatorial Atlantic Ridge (St. Paul Fracture Zone): Delayed magnetization in a magmatically starved spreading center?
Authors: Sichler Bertrand , Hékinian Roger
Published: December 2002

The St. Paul Fracture Zone (FZ) in the equatorial Atlantic is interrupted by three intratransform ridge (ITR) spreading centers. A detailed magnetic survey, corrected for the diurnal variations using a moored magnetic station, six submersible dives, and three bottom‐towed video camera tracks provide data on the most eastern ITR (0°37′N, 25°27′W). Visual observations and submersible sampling displayed a high ultramafic/volcanic ratio, supporting the assumption that the ITR is in a magmatically starved state. Volcanics were mainly found on the rift valley floor from 4700 to 4000 m and as a thin cap (<160 m) on the top of the eastern rift crest (2700 m). Most of the rift walls consist essentially of serpentinized peridotites and gabbros. The magnetic data show a well‐defined ridge centered anomaly. A generalized inversion method was applied to the field data to calculate the crustal equivalent magnetization, assuming that the seafloor is broken down into elementary cells of 1 × 1 × 0.5 km3 which fit the topography. The average of absolute value of equivalent magnetization is 2.7 A m−1. The width of the central normal polarity (Brunhes epoch) is wider (at least 34 km) than that indicated by the NUVEL‐1 kinematic model (24.5 km). This 40% excess is believed to be significant and is thought to be the result of prolonged chemical remanent magnetization acquired during the serpentinization of peridotites. In a magmatically starved accretion segment, we suggest that peridotites could continue to acquire magnetization as long as tectonic activities facilitate the circulation of seawater in the upper mantle.
Topographic stress perturbations in southern Davis Mountains, west Texas 2. Hydrogeologic implications
Authors: Morin Roger H. , Savage William Z.
Published: December 2002

As part of a regional groundwater investigation, geophysical logs were obtained in two municipal water wells located near the west Texas city of Alpine. These boreholes are 252 and 285 m deep and penetrate extrusive rocks of Tertiary age. The deeper well was drilled in the central valley and the other along the northern flank of an east‐west trending valley‐ridge setting. Analysis and interpretation of the logs reveal that the two wells are subjected to significantly different stress environments because of topographic effects and exhibit significantly different hydrogeologic properties. Water production is associated with two specific types of features common to both wells: (1) the upper and lower contacts of a dense trachyte unit located in the shallow part of the wells and (2) deeper zones of highly fractured rocks within the interior of a basalt formation. The transmissivity of the trachyte boundaries is twice as large in the central valley well as it is in the ridge flank well, whereas the transmissivity of the deeper basalts is an order of magnitude greater in the flank well than it is in the central well. This discrepancy is examined from the perspective of rock failure, fracture opening, and flow enhancement by computing values for a Drucker‐Prager stability factor that is based on the magnitudes of the normal and deviatoric stress invariants as a function of depth. Thus the field measurements and subsequent stress analysis offer evidence of a coupled tectonic‐hydrologic interaction at this site.
Asthenospheric flow and asymmetry of the East Pacific Rise, MELT area
Authors: Conder James A. , Forsyth Donald W. , Parmentier E. M.
Published: December 2002

Although the Pacific and Nazca plates share the East Pacific Rise (EPR) as a boundary, they exhibit many differing characteristics. The Pacific plate subsides more slowly and has more seamounts than the Nazca plate. Both the seismic and magnetotelluric components of the Mantle ELectromagnetic and Tomography Experiment (MELT) found pronounced asymmetry in mantle structure across the spreading axis near 17°S. The Pacific (west) side has lower S‐wave velocities, exhibits greater shear wave splitting, and is more electrically conductive than the Nazca (east) side. These results suggest asymmetric mantle flow and melt distribution beneath the EPR. To better understand the causes for these asymmetric properties, we construct numerical models of melting and mantle flow beneath a midocean ridge migrating to the west over a fixed mantle. Although the ridge is migrating to the west, the migration has little effect on the upwelling rates, requiring a separate mechanism to create the asymmetry. Models that produce asymmetric melting with a temperature anomaly require large (>100°C) excess temperatures and may not be consistent with the observed subsidence and crustal thickness. A possible mechanism for creating asymmetry without a temperature anomaly is across‐axis asthenospheric flow, possibly driven by pressures created by upwelling beneath the Pacific Superswell to the west. Pressure‐driven asthenospheric flow follows the base of the lithosphere, extending the upwelling region to the west as it follows the thinning lithosphere toward the axis, and shutting off melting as it crosses the axis and encounters an increasingly thick lithosphere to the east.
Multiple isotropic‐scattering model on the spherical Earth for the synthesis of Rayleigh‐wave envelopes
Authors: Sato Haruo , Nishino Makiko
Published: December 2002

Surface waves are modulated and scattered by topographic variations, rough interfaces, and medium heterogeneities with the propagation around the Earth. Scattered surface waves appear as wave trains between multiple direct arrivals in long‐period seismograms. The single isotropic‐scattering model for Rayleigh waves of the fundamental mode successfully explained observed mean square (MS) envelopes of vertical‐component seismograms. However, it is necessary to consider multiple scattering process for more accurate simulation of envelopes for a wide range of lapse time. Extending the radiative transfer equation for a flat surface, we mathematically formulate the multiple isotropic‐scattering process on a spherical surface. We can solve this integral equation using the Laplace transform in time and the spherical harmonics expansion in angular space. The time trace of energy density corresponding to the MS envelope can be obtained by using the inverse Laplace transform. Analyzing 12 IRIS station data of the 1999 Kocaeli, Turkey earthquake for 80–180 s periods, we estimated the total scattering coefficient g0 ≈ 2 × 10−6 1/km and the total attenuation Q−1 ≈ 8.475 × 10−3 for the fundamental‐mode Rayleigh waves. The multiple scattering model explains observed envelopes better than the single scattering model; however, synthesized envelopes are still smaller than observed envelopes at lapse times larger than about 20,000 s. It suggests that we need to study scattering and dispersion of higher modes in addition to the multiple scattering of the fundamental mode especially at large lapse times, because higher‐mode Rayleigh waves attenuate more slowly and spread out more rapidly compared with those of the fundamental mode.
Observations of barrier layer formation in the Bay of Bengal during summer monsoon
Authors: Vinayachandran P. N. , Murty V. S. N. , Ramesh Babu V.
Published: December 2002

Time series of temperature and salinity in the upper ocean, measured at 17°30′N, 89°E in the northern Bay of Bengal, from 27 July to 6 August 1999 captured an event of upper layer freshening. Initially, the upper layer that is homogeneous in both temperature and salinity was about 30 m deep. Subsequently, the arrival of a freshwater plume caused the depth of the mixed layer to decrease to about 10 m and the salinity in the surface layer by about 4 psu. The plume led to the formation of a new halocline and hence a barrier layer within the upper 30 m of the water column. The ensuing ocean‐atmosphere interaction was restricted to the new thinner mixed layer. The cooling that was restricted to the mixed layer led to an inversion in temperature amounting to 0.5°C just below the mixed layer. The source of the plume is traced to freshwater from river discharge and rainfall that was advected by Ekman flow as a 15 m thick layer. This study suggests that wind‐driven circulation is crucial in determining the path of freshwater in the Bay of Bengal. The fresh water affects the sea surface temperature and ocean‐ atmosphere coupling through the dependence of the depth of the mixed layer on salinity.