bluuebunny/crossref_metadata_2025 huggingface dataset:
Tactile-Visual Links in Exogenous Spatial Attention under Different Postures: Convergent Evidence from Psychophysics and ERPs
Authors: Kennett Steffan , Eimer Martin , Spence Charles , Driver Jon
Published: July 2002

Tactile-visual links in spatial attention were examined by presenting spatially nonpredictive tactile cues to the left or right hand, shortly prior to visual targets in the left or right hemifield. To examine the spatial coordinates of any cross-modal links, different postures were examined. The hands were either uncrossed, or crossed so that the left hand lay in the right visual field and vice versa. Visual judgments were better on the side where the stimulated hand lay, though this effect was somewhat smaller with longer intervals between cue and target, and with crossed hands. Event-related brain potentials (ERPs) showed a similar pattern. Larger amplitude occipital N1 components were obtained for visual events on the same side as the preceding tactile cue, at ipsilateral electrode sites. Negativities in the Nd2 interval at midline and lateral central sites, and in the Nd1 interval at electrode Pz, were also enhanced for the cued side. As in the psychophysical results, ERP cueing effects during the crossed posture were determined by the side of space in which the stimulated hand lay, not by the anatomical side of the initial hemispheric projection for the tactile cue. These results demonstrate that crossmodal links in spatial attention can influence sensory brain responses as early as the N1, and that these links operate in a spatial frame-of-reference that can remap between the modalities across changes in posture.
Structural Encoding of Human and Schematic Faces: Holistic and Part-Based Processes
Authors: Sagiv Noam , Bentin Shlomo
Published: July 2002

The range of specificity and the response properties of the extrastriate face area were investigated by comparing the N170 event-related potential (ERP) component elicited by photographs of natural faces, realistically painted portraits, sketches of faces, schematic faces, and by nonface meaningful and meaningless visual stimuli. Results showed that the N170 distinguished between faces and nonface stimuli when the concept of a face was clearly rendered by the visual stimulus, but it did not distinguish among different face types: Even a schematic face made from simple line fragments triggered the N170. However, in a second experiment, inversion seemed to have a different effect on natural faces in which face components were available and on the pure gestalt-based schematic faces: The N170 amplitude was enhanced when natural faces were presented upside down but reduded when schematic faces were inverted. Inversion delayed the N170 peak latency for both natural and schematic faces. Together, these results suggest that early face processing in the human brain is subserved by a multiple-component neural system in which both whole-face configurations and face parts are processed. The relative involvement of the two perceptual processes is probably determined by whether the physiognomic value of the stimuli depends upon holistic configuration, or whether the individual components can be associated with faces even when presented outside the face context.
Changes in the Human Brain during Rhythm Learning
Authors: Ramnani N. , Passingham R. E.
Published: July 2002

Subjects were scanned with PET while they learned a complex arbitrary rhythm, paced by visual cues. In the comparison condition, the intervals were varied randomly. The behavioral results showed that the subjects decreased their response time with training, thus becoming more accurate in responding to the pacing cues at the appropriate time. There were learning-related increases in the posterior lateral cerebellum (lobule HVIIa), intraparietal and medial parietal cortex, presupplementary motor area (pre-SMA), and lateral premotor cortex. Learning-related decreases were found in the prestriate and inferior temporal cortex, suggesting that with practice the subjects increasingly came to depend on internal rather than external cues to time their responses. There were no learning-related increases in the basal ganglia. It is suggested that it is the neocortical-cerebellar loop that is involved in the timing and coordination of responses.
Saccadic Inhibition in Voluntary and Reflexive Saccades
Authors: Reingold Eyal M. , Stampe Dave M.
Published: July 2002

The present study investigated saccadic inhibition in both voluntary and stimulus-elicited saccades. Two experiments examined saccadic inhibition caused by an irrelevant flash occurring subsequent to target onset. In each trial, participants were required to perform a single saccade following the presentation of a black target on a gray background, 4° to the left or to the right of screen center. In some trials (flash trials), after a variable delay, a 33-msec flash was displayed at the top and bottom third of the monitor (these regions turned white). In all experimental conditions, histograms of flash-to-saccade latencies documented a decrease in saccadic frequency, forming a dip, time-locked to the flash and occurring as early as 60—70 msec following its onset. The fast latency of this effect strongly suggests a low-level, reflex-like, oculomotor effect, which was referred to as saccadic inhibition. A novel procedure was developed to allow comparisons of saccadic inhibition even across conditions, which in the absence of a flash (no-flash trials) produce dissimilar saccadic reaction times (SRTs) distributions. Experiment 1 examined the effects of the fixation stimulus on saccadic inhibition by contrasting three conditions: a gap condition (fixation stimulus disappeared 200 msec prior to target onset), a step condition (offset of the fixation stimulus was simultaneous with target onset), and an overlap condition (the fixation stimulus remained on for the duration of the trial). The overlap condition produced substantially stronger saccadic inhibition, relative to the gap and the step conditions. Experiment 2 contrasted the saccadic inhibition effect obtained for prosaccades (saccades aimed at the target) with the effect obtained for antisaccades (i.e., saccades aimed away from the same target). The onset of saccadic inhibition was earlier, and its magnitude was stronger, for antisaccades, relative to prosaccades. The plausibility that the superior colliculus is the neurophysiological locus of the saccadic inhibition effect was explored.
Frontal Lobe Contributions to Theory of Mind
Authors: Stone Valerie E. , Baron-Cohen Simon , Knight Robert T.
Published: July 2002

“Theory of mind,” the ability to make inferences about others' mental states, seems to be a modular cognitive capacity that underlies humans' ability to engage in complex social interaction. It develops in several distinct stages, which can be measured with social reasoning tests of increasing difficulty. Individuals with Asperger's syndrome, a mild form of autism, perform well on simpler theory of mind tests but show deficits on more developmentally advanced theory of mind tests. We tested patients with bilateral damage to orbito-frontal cortex (n = 5) and unilateral damage in left dorsolateral prefrontal cortex (n = 5) on a series of theory of mind tasks varying in difficulty. Bilateral orbito-frontal lesion patients performed similarly to individuals with Asperger's syndrome, performing well on simpler tests and showing deficits on tasks requiring more subtle social reasoning, such as the ability to recognize a faux pas. In contrast, no specific theory of mind deficits were evident in the unilateral dorsolateral frontal lesion patients. The dorsolateral lesion patients had difficulty only on versions of the tasks that placed demands on working memory.
Words without Mind
Authors: Schiff Nicholas , Ribary Urs , Plum Fred , Llinás Rodolfo
Published: July 2002

A woman (LR), unconscious for 20 years, spontaneously produces infrequent, isolated words unrelated to any environmental context. Fluorodeoxy-glucose-positron emission tomography (FDG-PET) imaging coregistered with magnetic resonance imaging (MRI) revealed a mean brain metabolism equivalent to deep anesthesia. Nevertheless, PET imaging demonstrated islands of modestly higher metabolism that included Broca's and Wernicke's areas. Functional brain imaging with magnetoencephalographic (MEG) imaging, a technique providing a temporal resolution of better than 1 msec, identified preserved dynamic patterns of spontaneous and evoked brain activity in response to sensory stimulation. Specifically, we examined spontaneous gamma-band activity (near 40 Hz) and its reset or modification during early auditory processing, a measure that correlates with human perception of sensory stimuli (Joliot, Ribary, & Llinás, 1994). Evidence of abnormal and incomplete gamma-band responses appeared in the left hemisphere only in response to auditory or somatosensory stimulation. MEG single-dipole reconstructions localized to the auditory cortex in the left hemisphere and overlapped with metabolically active regions identified by FDG-PET. The observation demonstrates that isolated neuronal groups may express well-defined fragments of activity in a severely damaged, unconscious brain. The motor fixed-action pattern character of her expressed words supports the notion of brain modularity in word generation.
Synergy in a Neural Code
Authors: Brenner Naama , Strong Steven P. , Koberle Roland , Bialek William , Steveninck Rob R. de Ruyter van
Published: July 2002

We show that the information carried by compound events in neural spike trains—patterns of spikes across time or across a population of cells—can be measured, independent of assumptions about what these patterns might represent. By comparing the information carried by a compound pattern with the information carried independently by its parts, we directly measure the synergy among these parts. We illustrate the use of these methods by applying them to experiments on the motion-sensitive neuron H1 of the fly's visual system, where we confirm that two spikes close together in time carry far more than twice the information carried by a single spike. We analyze the sources of this synergy and provide evidence that pairs of spikes close together in time may be especially important patterns in the code of H1.
Effective Neuronal Learning with Ineffective Hebbian Learning Rules
Authors: Chechik Gal , Meilijson Isaac , Ruppin Eytan
Published: July 2002

In this article we revisit the classical neuroscience paradigm of Hebbian learning. We find that it is difficult to achieve effective associative memory storage by Hebbian synaptic learning, since it requires network-level information at the synaptic level or sparse coding level. Effective learning can yet be achieved even with nonsparse patterns by a neuronal process that maintains a zero sum of the incoming synaptic efficacies. This weight correction improves the memory capacity of associative networks from an essentially bounded one to a memory capacity that scales linearly with network size. It also enables the effective storage of patterns with multiple levels of activity within a single network. Such neuronal weight correction can be successfully carried out by activity-dependent homeostasis of the neuron's synaptic efficacies, which was recently observed in cortical tissue. Thus, our findings suggest that associative learning by Hebbian synaptic learning should be accompanied by continuous remodeling of neuronally driven regulatory processes in the brain.
Feedforward Neural Network Construction Using Cross Validation
Authors: Setiono Rudy
Published: July 2002

This article presents an algorithm that constructs feedforward neural networks with a single hidden layer for pattern classification. The algorithm starts with a small number of hidden units in the network and adds more hidden units as needed to improve the network's predictive accuracy. To determine when to stop adding new hidden units, the algorithm makes use of a subset of the available training samples for cross validation. New hidden units are added to the network only if they improve the classification accuracy of the network on the training samples and on the cross-validation samples. Extensive experimental results show that the algorithm is effective in obtaining networks with predictive accuracy rates that are better than those obtained by state-of-the-art decision tree methods.
Analog Versus Digital: Extrapolating from Electronics to Neurobiology
Authors: Sarpeshkar Rahul
Published: July 2002

We review the pros and cons of analog and digital computation. We propose that computation that is most efficient in its use of resources is neither analog computation nor digital computation but, rather, a mixture of the two forms. For maximum efficiency, the information and information-processing resources of the hybrid form must be distributed over many wires, with an optimal signal-to-noise ratio per wire. Our results suggest that it is likely that the brain computes in a hybrid fashion and that an underappreciated and important reason for the efficiency of the human brain, which consumes only 12 W, is the hybrid and distributed nature of its architecture.
Neural Feature Abstraction from Judgments of Similarity
Authors: Lee Michael D.
Published: July 2002

The common neural network modeling practice of representing the elements of a task domain in terms of a set of features lacks justification if the features are derived through some form of ad hoc preabstraction. By examining a featural similarity model related to established multidimensional scaling techniques, a neural network is developed that generates features from similarity data and attaches weights to these features. The network performs a constrained search of a continuous solution space to determine the features and uses a previously developed regularization technique to minimize the number of features it derives. The network is demonstrated on artificial data, from which it recovers known features and weights, and on two real data sets involving the similarity of a set of geometric shapes and the abstract conceptual similarities of the 10 Arabic numerals. On the basis of these results, the relationship between the multidimensional scaling approach adopted by the network and an alternative additive clustering approach to feature extraction is discussed.
On Numerical Simulations of Integrate-and-Fire Neural Networks
Authors: Hansel D. , Mato G. , Meunier C. , Neltner L.
Published: July 2002

It is shown that very small time steps are required to reproduce correctly the synchronization properties of large networks of integrate-and-fire neurons when the differential system describing their dynamics is integrated with the standard Euler or second-order Runge-Kutta algorithms. The reason for that behavior is analyzed, and a simple improvement of these algorithms is proposed.
High-Performance Wide-Area Optical Tracking: The HiBall Tracking System
Authors: Welch Greg , Bishop Gary , Vicci Leandra , Brumback Stephen , Keller Kurtis , Colucci D'nardo
Published: July 2002

Since the early 1980s, the Tracker Project at the University of North Carolina at Chapel Hill has been working on wide-area head tracking for virtual and augmented environments. Our long-term goal has been to achieve the high performance required for accurate visual simulation throughout our entire laboratory, beyond into the hallways, and eventually even outdoors.

In this article, we present results and a complete description of our most recent electro-optical system, the HiBall Tracking System. In particular, we discuss motivation for the geometric configuration and describe the novel optical, mechanical, electronic, and algorithmic aspects that enable unprecedented speed, resolution, accuracy, robustness, and flexibility.
Navigating Large-Scale “Desk-Top” Virtual Buildings: Effects of Orientation Aids and Familiarity
Authors: Ruddle Roy A. , Payne Stephen J. , Jones Dylan M.
Published: July 2002

Two experiments investigated components of participants' spatial knowledge when they navigated large-scale “virtual buildings” using “desk-top” (i.e., nonimmersive) virtual environments (VEs). Experiment 1 showed that participants could estimate directions with reasonable accuracy when they traveled along paths that contained one or two turns (changes of direction), but participants' estimates were significantly less accurate when the paths contained three turns. In Experiment 2 participants repeatedly navigated two more complex virtual buildings, one with and the other without a compass. The accuracy of participants' route-finding and their direction and relative straight-line distance estimates improved with experience, but there were no significant differences between the two compass conditions. However, participants did develop significantly more accurate spatial knowledge as they became more familiar with navigating VEs in general.
Student-Built Virtual Environments
Authors: Winn William , Hoffman Hunter , Hollander Ari , Osberg Kimberley , Rose Howard , Char Patti
Published: July 2002

Students in grades four through twelve from fourteen schools learned to build their own immersive virtual environments (VEs). This required them to decide on the theme of their VE, to determine what objects to place in it and what behaviors these objects would exhibit, to model their objects using CAD software, to specify the form and function of the VE for professional programmers to use as they assembled the VE, and to perform assigned tasks when they visited the VE. Although the level and nature of student activity varied from school to school, the students were generally very successful. The VEs they constructed revealed a great deal about how they constructed an understanding of the content their VE represented. Data from a questionnaire showed that they enjoyed building and visiting their VE, and that their enjoyment, ability to work in the VE, success, and their sense of presence were all interrelated. Data from a small subset of students showed that building a VE improved low-ability students' (but not high-ability students') understanding of the VE's content. These findings were interpreted within a framework built from constructivist theories of learning and understanding.
A Normed Space of Genetic Operators with Applications to Scalability Issues
Authors: Rowe Jonathan E.
Published: July 2002

We define an abstract normed vector space where the genetic operators are elements. This is used to define the disturbance of the generational operator g as the distance between the crossover and mutation operator (combined) and the identity. This quantity appears in a bound on the variance of fixed-point populations, and in a bound on the force ‖v – g (v)‖ that applies to the optimal population v. When analyze for the case of fixed-length binary strings, a connection is shown between these measures and the size of the search space. Guides for parameter settings are given, if population convergence is required as the string length tends to infinity.
A Comparison Study of Self-Adaptation in Evolution Strategies and Real-Coded Genetic Algorithms
Authors: Kita Hajime
Published: July 2002

This paper discusses the self-adaptive mechanisms of evolution strategies (ES) and real-coded genetic algorithms (RCGA) for optimization in continuous search spaces. For multi-membered evolution strategies, a self-adaptive mechanism of mutation parameters has been proposed by Schwefel. It introduces parameters such as standard deviations of the normal distribution for mutation into the genetic code and lets them evolve by selection as well as the decision variables. In the RCGA, crossover or recombination is used mainly for search. It utilizes information on several individuals to generate novel search points, and therefore, it can generate offspring adaptively according to the distribution of parents without any adaptive parameters. The present paper discusses characteristics of these two self-adaptive mechanisms through numerical experiments. The self-adaptive characteristics such as translation, enlargement, focusing, and directing of the distribution of children generated by the ES and the RCGA are examined through experiments.
Hearts and Minds: The Unconventional Cold War
Authors: Osgood Kenneth A.
Published: July 2002

Throughout the Cold War the task of winning “hearts and minds” around the world was of great importance to Soviet and American leaders. Both sides fought a cultural Cold War via radio waves, television transmissions, propa-ganda, and other forms of psychological pressure. A number of recent books that draw on declassified U.S. government records have provided valuable in-sights into the American side of the cultural Cold War. The U.S. government employed military, political, diplomatic, and cultural means to influence for-eign and domestic opinion. The study of this phenomenon requires interdis-ciplinary methodological approaches. Diplomatic historians need to integrate the cultural and propaganda issues into their narratives, and cultural histori-ans need to pay greater heed to the themes raised in diplomatic historical accounts.
Squaring the Circle: The Cultural Relativity of 'Good' Shape
Authors: Roberson Debi , Davidoff Jules , Shapiro Laura
Published: July 2002

The Gestalt theorists of the early twentieth century proposed a psychological primacy for circles, squares and triangles over other shapes. They described them as 'good' shapes and the Gestalt premise has been widely accepted. Rosch (1973), for example, suggested that shape categories formed around these 'natural' prototypes irrespective of the paucity of shape terms in a language. Rosch found that speakers of a language lacking terms for any geometric shape nevertheless learnt paired-associates to these 'good' shapes more easily than to asymmetric variants. We question these empirical data in the light of the accumulation of recent evidence in other perceptual domains that language affects categorization. A cross-cultural investigation sought to replicate Rosch's findings with the Himba of Northern Namibia who also have no terms in their language for the supposedly basic shapes of circle, square and triangle. A replication of Rosch (1973) found no advantage for these 'good' shapes in the organization of categories. It was concluded that there is no necessary salience for circles, squares and triangles. Indeed, we argue for the opposite because these shapes are rare in nature. The general absence of straight lines and symmetry in the perceptual environment should rather make circles, squares and triangles unusual and, therefore, less likely to be used as prototypes in categorization tasks. We place shape as one of the types of perceptual input (in philosophical terms, 'vague') that is readily susceptible to effects of language variation.
Structure of an anuran community in a montane meadow in southeastern Brazil: effects of seasonality, habitat, and predation
Authors: Sazima Ivan , Eterovick Paula Cabral
Published: July 2002

In order to assess the main factors influencing its structure, an anuran community was studied from August 1996 to July 1997, in a 1200 m high rocky meadow site at the Serra do Cipó, Minas Gerais, Brasil, a region with markedly seasonal climate. The study site included three temporary habitats: a stream, a puddle, and a swamp. Thirteen anuran species were recorded at the study site. Species of tadpoles differed in microhabitat as to their position in water column, annual occurrence period, and water flow in the occupied sites. Aquatic vegetation, depth and occupied habitat (stream, swamp, or puddle) were of secondary importance in telling species apart. Calling sites of males were distinguished based on occupied habitat and annual activity period. Most species started their reproductive activities at the onset of the rains, in an opportunistic way. Water availability in the habitat seems to be the most important factor affecting temporal distribution of reproductive activities in the anuran community. Competitive interactions could not be detected in the community. The most important tadpole predators recorded at the study site were belostomatid water bugs and dragonfly nymphs. Their abundance peaks occurred after those of tadpoles, as predicted for predator-prey populations with interconnected cycles. Mortality rates were high for tadpoles, and predation is the most likely cause. Differences recorded among species, considering time of occurrence, tadpole microhabitats, and male calling sites, may reflect distinct specific adaptations and preferences.
VOCAL COMMUNICATION AND INDIVIDUAL VARIATION IN BREEDING SOUTH AMERICAN SEA LIONS
Authors: Fernndez-Juricic Esteban , Campagna Claudio , Enriquez Victor , Ortiz Charles Leo
Published: July 2002

The purpose of this study was to analyse the structure, social contexts, and individual variation of South American sea lion (Otaria flavescens) airborne vocal communication during the breeding season. This is the first comprehensive analysis of the vocal repertoire of this species. Since breeding colonies are complex acoustic environments, we expect that male, female, and pup vocalizations would show individuality, and that individual variation would rely on several acoustic traits. We identified four calls for adult males: high pitched call or HPC (aggressive interactions, such as attack and retreat displays, and fights), bark (aggressive interactions, territory establishment, and usually combined with growls), growl (male-female interactions), and exhalation (after agonistic encounters); and two for adult females: mother primary call or MPC (female-pup interactions, such as after birth, during pup separation, and pup development), and grunt (agonistic interactions between females). Juveniles vocalized yearling primary calls or YPC (searching for their mothers or after being threatened by females), pups gave pup primary calls or PPC (in response to MPCs, when hungry, searching for their mothers, if nursing was interrupted, or when trying to nurse). Our results suggest that male's HPC and bark, female's MPC, and pup's PPC have acoustic features that support individuality. These calls are associated with contexts in which recognition of neighbours (HPC and bark) or relatives (MPC and PPC) may confer a relative advantage in reproductive performance. Individual variation depended on frequency, temporal, and intensity traits; such multi-trait individuality could be regarded as an adaptation to colonial life to overcome the high noise levels within pinniped breeding colonies.
Trans-specific nematicidal activity of Photorhabdus luminescens
Authors: Han Richou , Ehlers Ralf-Udo
Published: July 2002

Mixed culture filtrates of Photorhabdus luminescens isolated from
Heterorhabditis bacteriophora H06 and from H. indica LN2 had a toxic effect
on axenic H. bacteriophora H06 dauer juveniles. Single culture filtrates had
no effect. When one filtrate originated from a secondary phase culture, the
toxic effect was lost. Heat treatment of one of the filtrates to 80°C
destroyed the effect. The toxin is probably synthesized de novo after mixing
the culture supernatants of these two P. luminescens symbionts. Dilution of
the filtrate reduced the effect, and it was lost when P. luminescens was
cultured for more than two days. Steinernema carpocapsae A24 was not
affected by the mixture, and was affected only by the filtrate of primary
phase P. luminescens H06. The toxic effect was recorded also when axenic
dauer juveniles of H. bacteriophora were inoculated into a mixed bacterial
culture of H06 and LN2. Inoculating monoxenic dauer juveniles of H.
bacteriophora H06 into P. luminescens LN2 or into mixtures containing LN2
bacteria resulted in significant dauer juvenile mortality. These
manifestations of the interaction of bacteria to produce toxic effects on
the non-symbiotic nematode (trans-specific activity) may have an impact on
competitive interactions when one insect host is infected by different
nematode species. Eine transspezifische nematizide Aktivitat von
Photorhabdus luminescens - Eine Mischung der Kulturfiltrate des Bakteriums
Photorhabdus luminescens, isoliert aus Heterorhabditis bacteriophora H06 mit
dem Filtrat des Symbionten aus H. indica LN2 wirkt toxisch auf axenische
Dauerlarven von H. bacteriophora H06. Die einzelnen Kulturfiltrate zeigten
keine Wirkung. Sofern ein Filtrat einer Sekundarformkultur entnommen wurde,
konnte kein Effekt erzielt werden. Eine Hitzebehandlung bei 80°C zerstorte
die Wirkung. Das Toxin wird wahrscheinlich de novo synthetisiert in dem
Moment, in dem die Kulturfiltrate dieser P. luminescens Symbionten gemischt
werden. Eine Verdunnung der Filtrate reduzierte die Wirkung. Sie ging ganz
verloren, wenn P. luminescens langer als zwei Tage kultiviert wurde. Die
Mischung hatte keine Wirkung auf axenische Steinernema carpocapsae. Dieser
Nematode wurde nur durch Filtrate der Primarform von P. luminescens H06
abgetotet. Die toxischen Effekte wurden auch festgestellt, wenn axenische
Dauerlarven von H. bacteriophora in Gemische von H06 und LN2
Bakterienkulturen inokuliert wurde. Bei Inokulation von monoxenischen
Dauerlarven von H. bacteriophora H06 in P. luminescens LN2 oder in Gemische,
die LN2 enthielten, wurde ebenfalls eine gesteigerte Mortalitat
festgestellt. Dieses Deutlichwerden von Wechselbeziehungen zwischen den
Bakterien bei Erzeugung toxischer Effekte auf den nicht-symbiontischen
Nematoden (trans-spezifische Aktivitat) konnte eine Auswirkung auf die
Konkurrenz bei Koinfektion eines Wirtsinsekts mit zwei Nematodenarten
haben.
Textural and structural modifications of saponite from Cerro del Aguila by acid treatment
Authors: Suárez Barrios M. , de Santiago Buey C. , García Romero E. , Martín Pozas J. M.
Published: July 2002

The physicochemical properties of clays can be modified by acid treatment with inorganic acids. This treatment is usually referred to as ‘acid activation’, because it increases the specific surface area and the number of active sites of the solids. In the present study, the acid activation of saponite from Cerro del Aguila (Madrid, Spain) with HCl solutions was measured. Illite, quartz and small amounts of feldspar were found as impurities in the raw saponite.

Acid treatments were carried out with different concentrations of HCl solutions. The samples obtained were characterized by mineralogical and chemical analyses, XRD, FT-IR spectroscopy, N2 adsorption-desorption isotherms and TEM. The acid attack, under the conditions employed, produced a progressive destruction of the structure of saponite by partial dissolution of the octahedral Mg(II) cations. Amorphous silica coming from the tetrahedral sheet of saponite was generated. The specific surface area of the most intensely treated sample (2.5% for 24 h) was doubled with respect to that of natural saponite. This increase in the surface area is due to the increase in both the external and internal surface areas.
An application of profile fitting and CLAY++ for the quantitative representation (QR) of mixed-layer clay minerals
Authors: Aparicio P. , Ferrell R. E.
Published: July 2002

Clay mineral quantification by XRD is difficult when mixed-layer clay minerals and discrete clay types are both present. New procedures for peak decomposition and pattern simulation offer increased opportunities to obtain mineral abundance estimates. This proposed methodological sequence, for quantitative representation (QR) of complex clay samples, involves: (1) determination of layer type, mixed-layer proportion and order (R); (2) simulation of XRD patterns using MULCALC, an adaptation of NEWMOD; and (3) interpretation of the clay assemblage by fitting the whole pattern with CLAY++, a statistical program. The product is a QR of individual phases or a summation of layer types. The absence of quantitative reference standards means results cannot be checked for accuracy, but the statistical fit is highly reproducible and less prone to operator error. The QRs may be obtained with simulated or actual reference mineral patterns in the database. Results for freshwater marsh samples illustrate the approach.
Layer-charge evaluation of expandable clays from a chronosequence of podzols in Finland using an alkylammonium method
Authors: Gillot F. , Righi D. , Räisänen M. L.
Published: July 2002

Smectites from the E horizon of podzols dated at 1200–10,000 y in central and northern Finland were studied. Clay minerals in the fine (<0.1 μm) and coarse (0.1–2 μm) fractions were examined by X-ray diffraction. The distribution (octahedral or tetrahedral) and magnitude of the layer charge of expandable minerals were estimated using intercalation of alkylammonium ions (nC = 12) associated with the Hofmann & Klemen effect. In addition, charge alteration following desaturation (H+exchange) and autotransformation was investigated. Smectites from the E horizons of podzols are not homogeneous but constitute a mixture of several populations with various layer charges. Smectites with lower layer charge are present in podzols having a longer effective time of pedogenesis, suggesting alteration of the high-charge smectites with time. Experimental alteration of the smectites by autotransformation shows that a decrease of the layer charge is easily produced by desaturation of the smectite clays.
Structure and dynamics of silicate glasses and melts
Authors: Farnan I. , Dove M. T.
Published: July 2002

A one-day meeting was held in the Department of Earth Sciences, University of Cambridge, on the theme of the ‘Structure and Dynamics of Silicate Glasses and Melts’. The meeting was sponsored by the Mineral Physics group of the Mineralogical Society, and was attended by ∼80 people. The objective of the meeting was to bring together experts from the glass community with members of the mineralogical community who are interested in glasses and melts. The scope of the talks considered structural details over length scales from nearest-neighbour coordinations up to 1–2 nm, and dynamics in both the slow relaxational and fast vibrational ranges. The talks also covered both experimental (particularly neutron scattering and NMR) and computer simulation methods.

The meeting was organized into three groups of themes, namely structure and dynamics in glasses, structure and dynamics in melts, and vibrational dynamics in glasses.
Annealing experiments on CO2-bearing jadeite glass: an insight into the true temperature dependence of CO2 speciation in silicate melts
Authors: Morizet Y. , Kohn S. C. , Brooker R. A.
Published: July 2002

The thermodynamics and kinetics of CO2 speciation in silicate melts have been studied by measuring the concentration of CO2mol and carbonate in jadeite glass annealed at 575, 450 and 400°C. Assuming that the reaction is

1

where CO2mol..Obr represents a CO2 molecule weakly bonded to a bridging oxygen in the network and CO3 represents a bridging carbonate group with no net negative charge, ΔH for the reaction is –17 (+4/–8) kJ mol−1 and ΔS is –24 (+6/–9) J K−1 mol−1. The rate of equilibration of the species was measured at each temperature and the rate constants were deduced. The temperature dependence of the rate constants was used to determine the activation energy of the forward and reverse reactions which are 68 (+3/–31) kJ mol−1 and 86 (+1/–69) kJ mol−1 respectively. The data suggest that CO2mol may be much more abundant in silicate melts than previously assumed on the basis of studies of CO2-bearing glasses. Models of solubility, diffusion, and isotope fractionation should take this into account.
The petrology and petrogenesis of the North Motzfeldt Centre, Gardar Province, South Greenland
Authors: Finch A. A. , Goodenough K. M. , Salmon H. M. , Andersen T.
Published: July 2002

North Motzfeldt is an intrusive igneous centre within the Igaliku (formerly spelt Igaliko) complex, Gardar Province, South Greenland. A detailed field description of the centre is given, with preliminary geochemical and isotopic data. The North Motzfeldt centre is intruded into Ketilidian granitoid basement rocks, and current exposure retains parts of the original roof against earlier Gardar eruptives and clastic sediments of the Eriksfjord formation. The unconformity between the Ketilidian and the overlying Eriksfjord is believed to have been crucial in the siting of the centre. The centre is subdivided into two major units, NM1 and NM2. This was followed by significant peralkaline nepheline microsyenite in sheets, characterized by rare element-rich accessory minerals including rinkite-mł sandrite, pyrochlore and låvenite. A significant microsyenite body is called NM3. A preliminary Rb-Sr isochron of 1226±27 Ma indicates a far younger age for the centre than previously thought (~;1350 Ma). Cross-cutting relationships between North Motzfeldt and rocks of the adjacent Motzfeldt centre require a reappraisal of the chronology of Motzfeldt magmatism. We suggest that rocks previously believed to comprise the Motzfeldt centre represent the products of multiple phases of magmatism from Early- to Mid-Gardar times.
Fluid processes during the exhumation of high-P metamorphic belts
Authors: Miller J. A. , Buick I. S. , Cartwright I. , Barnicoat A.
Published: July 2002

Fluids can play a direct role in exhumation by influencing exhumation mechanisms and the driving processes for these mechanisms. In addition, the process of exhumation leads to the development of fluid-related features that in themselves may not drive exhumation. Fluids involved in exhumation are generally derived from dehydration reactions occurring during decompression, but at shallower crustal levels may also involve the introduction of exotic fluids. The composition of fluids attending exhumation are generally saline – CO2 mixtures, but N2, CH4, H2O mixtures have also been recorded. Studies of fluid features related to exhumation have found that fluids may contribute to density changes and the initiation of partial melting during decompression, as well as the development of extensive vein systems. However, the preservation of geochemical signatures related to fluid processes occurring prior to high-P and ultrahigh-P metamorphism indicates that large-scale pervasive fluid flow systems, in general, do not operate at any stage during the exhumation history. Large-scale channelled fluid flow may have operated in detachment faults and shear zones related to exhumation, and this requires further study. The most significant role of fluids during exhumation appears to be their controlling influence on the preservation of high-P or ultrahigh-P rocks.
Manganvesuvianite and tweddillite, two new Mn3+-silicate minerals from the Kalahari manganese fields, South Africa
Authors: Armbruster T. , Gnos E. , Dixon R. , Gutzmer J. , Hejny C. , Döbelin N. , Medenbach O.
Published: July 2002

The new minerals manganvesuviante and tweddillite, both formed by hydrothermal alteration of primary manganese ores, are described from the Kalahari manganese fields (Republic of South Africa). In addition, single-crystal X-ray structure refinements of both new minerals are presented.

Manganvesuvianite is a tetragonal vesuvianite mineral with the simplified formula Ca19Mn3+(Al,Mn3+,Fe3+)10(Mg,Mn2+)2Si18O69(OH)9, characterized by Mn3+ occupying the five-coordinated position (square pyramid). The crystals simple prismatic forms: {100}, {110} terminated by {101} and exhibit deep maroon red colour. With polarized light the crystals are strongly pleochroic, yellowish parallel to E and dark red to lilac parallel to O.

Tweddillite is an epidote-group mineral (space group P21/m, a = 8.932(5), b = 5.698(4), c = 10.310(5) Å, β = 114.56(4), V = 477.3(8) Å3) with the simplified formula CaSr(Mn3+,Fe3+)2Al[Si3O12](OH), closely related to strontiopiemontite. The difference between strontiopiemontite and tweddillite is the concentration of octahedral Mn3+. Strontiopiemontite has Mn3+ mainly on the M3 site whereas tweddillite has Mn3+ with minor Fe3+ on M3 and M1. Tweddillite forms aggregates of very thin dark red {001} blades characterized by striking pleochroism. The crystals appear dark red parallel to b and orange-yellow parallel to a. Perpendicular to (001) the blades appear magenta to red.
Decrespignyite-(Y), a new copper yttrium rare earth carbonate chloride hydrate from Paratoo, South Australia
Authors: Wallwork K. , Kolitsch U. , Pring A. , Nasdala L.
Published: July 2002

Decrespignyite-(Y) is a new copper yttrium rare earth carbonate chloride hydrate from the Paratoo copper mine, near Yunta, Olary district, South Australia. Decrespignyite-(Y) occurs as blue crusts, coatings and fillings in thin fissures on the slatey country rock. Individual pseudohexagonal platelets are typically 10–50 µm in maximum dimension and are often curved. Associated minerals include caysichite-(Y), donnayite-(Y), malachite and kamphaugite-(Y). Electron microprobe and CHN analyses gave: Y2O3 42.2; La2O3 0.1; Pr2O3 0.1; Nd2O3 1.3; Sm2O3 1.0; Gd2O3 4; Tb2O3 0.4; Dy2O3 3.7; Ho2O3 2.6; Er2O3 2.5; CaO 0.5; CuO 10.9; Cl 3.0; CO2 19.8; H2O 10.8, yielding an empirical formula of (Y3.08Gd0.22Dy0.16Ho0.11Er0.10Nd0.06Sm0.05Tb0.02La0.02Pr0.01Ca0.08)∑3.91Cu1.12(CO3)3.70-Cl0.7(OH)5.79·2.4H2O. The simplified formula is (Y,REE)4Cu(CO3)4Cl(OH)5·2H2O. The mineral is royal blue to turquoise-blue in colour, transparent, with a pearly to vitreous lustre and a pale blue streak. No cleavage was observed but the morphology suggests that cleavage would be on [010]. The Mohs' hardness is estimated to be 4. The strongest lines in the X-ray powder pattern are {dobs (Iobs) (hkl)} 22.79 (30) (010); 7.463 (30) (001); 7.086 (50) (011); 6.241 (100) (021); 4.216 (30) (12); 3.530 (40) (022); 3.336 (30) (032); 2.143 (30) (222, 01). The powder diffraction pattern was indexed on a monoclinic cell with a = 8.899(6), b = 22.77(2), c = 8.589(6)Å, β = 120.06(5)°, V = 1506.3(7) Å3 and Z = 4. The structure of the new mineral could not be determined but powder diffraction data indicate the space group is P2, Pm or P2/m. The measured density is 3.64(2) g/cm3 and the calculated density is 3.645 g/cm3. Decrespignyite-(Y) is biaxial negative with α = 1.604(4) and γ = 1.638(3) with β very close to γ pleochroism is medium strong; X very pale bluish, Y and Z bluish (with greenish tint). Decrespignyite-(Y) is a supergene mineral which precipitated from mildly basic carbonated ground waters. The mineral is named after Robert Champion de Crespigny, a prominent figure in the Australian mining industry and chancellor of the University of Adelaide.
Accurate quantification of the modal mineralogy of rocks when image analysis is difficult
Authors: Schofield P. F. , Knight K. S. , Covey-Crump S. J. , Cressey G. , Stretton I. C.
Published: July 2002

The volume proportions of the mineral phases in two strongly deformed olivine-orthopyroxene rocks have been quantified by whole-pattern stripping of fixed geometry X-ray powder diffraction data. The results were compared with the phase proportions as determined by Rietveld refinement of time-of-flight neutron powder diffraction data, and were shown to be in excellent agreement. The X-ray technique not only provides a very rapid and cost-effective method of determining phase proportions, but it also circumvents several of the problems associated with obtaining this information by image analysis. Moreover, the technique is particularly advantageous in strongly textured rocks or in rocks that contain significant residual strains. As such it offers a powerful technique for analysing the mineralogical composition of fine-grained and/or deformed experimental run products, which makes it of considerable potential for monitoringin situthe progress of mineral reactions during laboratory experiments.
Description and crystal structure of bobkingite, a new mineral from New Cliffe Hill Quarry, Stanton-under-Bardon, Leicestershire, UK
Authors: Hawthorne F. C. , Cooper M. A. , Grice J. D. , Roberts A. C. , Hubbard N.
Published: July 2002

Bobkingite, ideally is a new mineral from the New Cliffe Hill Quarry, Stantonunder-Bardon, Leicestershire, England. It occurs as very thin (⩽5 µm) transparent plates up to 0.2 mm across, perched on a compact fibrous crust of malachite and crystalline azurite attached to massive cuprite. Crystals are tabular on {001} with dominant {001} and minor {100} and {110}. Bobkingite is a soft pale blue colour with a pale-blue streak, vitreous lustre and no observable fluorescence under ultraviolet light. It has perfect {001} and fair {100} cleavages, no observable parting, conchoidal fracture, and is brittle. Its Mohs' hardness is 3 and the calculated density is 3.254 g/cm3. Bobkingite is biaxial negative with α = 1.724(2), β = 1.745(2), γ = 1.750(2), 2Vγmeas = 33(6)°, 2Vcalc = 52°, pleochroism distinct, X = very pale blue, Z = pale greenish blue, X^a = 22° (in β obtuse), Y = c, Z = b. Bobkingite is monoclinic, space group C2/m, unit-cell parameters (refined from powder data): a = 10.301(8), b = 6.758(3), c = 8.835(7)Å, β = 111.53(6)°, V = 572.1(7)Å3, Z = 2. The seven strongest lines in the X-ray powder-diffraction pattern are [d (Å), I, (hkl)]: 8.199, 100, (001); 5.502, 100, (110); 5.029, 40, (01); 2.883, 80, (310); 2.693, 40, (13); 2.263, 40, (113), (03); 2.188, 50, (23). Chemical analysis by electron microprobe and crystal-structure solution and refinement gave CuO 70.46, Cl 12.71, H2O 19.19, O≡Cl –2.87, sum 99.49 wt.%, where the amount of H2O was determined by crystal-structure analysis. The resulting empirical formula on the basis of 12 anions (including 8 (OH) and 2H2O) is Cu4.99Cl2.02O10H12. The crystal structure was solved by direct methods and refined to an R index of 2.6% for 638 observed reflections measured with X-rays on a single crystal. Three distinct (Cuϕ6) (ϕ = unspecified anion) octahedra share edges to form a framework that is related to the structures of paratacamite and the Cu2(OH)3Cl polymorphs, atacamite and clinoatacamite. The mineral is named for Robert King, formerly of the Department of Geology, Leicester University, prominent mineral collector and founding member of the Russell Society. The mineral and its name have been approved by the Commission on New Minerals and Mineral Names of the International Mineralogical Association.
Barysilite from Garpenberg Norra, Dalarna, Sweden: occurrence and crystal structure refinement
Authors: Kolitsch U. , Holtstam D.
Published: July 2002

A new occurrence of barysilite, Pb8Mn(Si2O7)3, at the polymetallic Garpenberg Norra Zn-Pb deposit, Hedemora, Dalarna, Sweden, is described. The mineral, which forms colourless, transparent grains, is characterized by X-ray diffraction and electron-microprobe analyses. The assemblage includes tephroite, zincian jacobsite, manganoan diopside and others. The crystal structure of a barysilite crystal from Garpenberg Norra was redetermined using single-crystal X-ray diffraction data (Mo-Kα, CCD area detector) and has been refined in space groupRcwitha= 9.804(1),c= 38.416(8)Å,V= 3197.8(8)Å3, toR1 = 2.32% for 1025 ‘observed’ reflections withFo>4σ(Fo). A previous, low-precision structure determination (Lajzérowicz, 1965;R= 20%) is confirmed but improved considerably. The structure contains one distorted MnO6polyhedron with six equivalent Mn–O bonds (2.224 Å), one Si2O7disilicate unit with an Si–O–Si angle of 120.9°, and two non-equivalent Pb sites. The Pb1 site has a highly irregular, one-sided coordination with six O ligands, indicating a stereoactive 6s2lone-electron pair on the Pb2+ion, whereas the [6+3]-coordinated Pb2 site is fairly regular, with Pb–O distances of 2.540 (3×), 2.674 (3×) and 3.098 (3×) Å. The Pb2 site contains ~10% of Ca (+Ba) replacing Pb, corresponding to the structural formula Pb16(Pb,Ca)22Mn(Si2O7)3. This is the first direct proof that not only theMsite in barysilite-type Pb8M(Si2O7)3compounds can be replaced by divalent cations.