bluuebunny/crossref_metadata_2025 huggingface dataset:
Extended Kalman Filter–Based Pruning Method for Recurrent Neural Networks
Authors: Sum John , Chan Lai-wan , Leung Chi-sing , Young Gilbert H.
Published: July 2002

Pruning is one of the effective techniques for improving the generalization error of neural networks. Existing pruning techniques are derived mainly from the viewpoint of energy minimization, which is commonly used in gradient-based learning methods. In recurrent networks, extended Kalman filter (EKF)–based training has been shown to be superior to gradient-based learning methods in terms of speed. This article explains a pruning procedure for recurrent neural networks using EKF training. The sensitivity of a posterior probability is used as a measure of the importance of a weight instead of error sensitivity since posterior probability density is readily obtained from this training method. The pruning procedure is tested using three problems: (1) the prediction of a simple linear time series, (2) the identification of a nonlinear system, and (3) the prediction of an exchange-rate time series. Simulation results demonstrate that the proposed pruning method is able to reduce the number of parameters and improve the generalization ability of a recurrent network.
State-Dependent Weights for Neural Associative Memories
Authors: Kothari Ravi , Lotlikar Rohit , Cahay Marc
Published: July 2002

In this article we study the effect of dynamically modifying the weight matrix on the performance of a neural associative memory. The dynamic modification is implemented by adding, at each step, the outer product of the current state, scaled by a suitable constant η, to the correlation weight matrix. For single-shot synchronous dynamics, we analytically obtain the optimal value of η. Although knowledge of the noise percentage is required for calculating the optimal value of η, a fairly good choice of η can be made even when the amount of noise is not known. Experimental results are provided in support of the analysis. The efficacy of the proposed modification is also experimentally verified for the case of asynchronous updating with transient length > 1.
The Ornstein-Uhlenbeck Process Does Not Reproduce Spiking Statistics of Neurons in Prefrontal Cortex
Authors: Shinomoto Shigeru , Sakai Yutaka , Funahashi Shintaro
Published: July 2002

Cortical neurons of behaving animals generate irregular spike sequences. Recently, there has been a heated discussion about the origin of this irregularity. Softky and Koch (1993) pointed out the inability of standard single-neuron models to reproduce the irregularity of the observed spike sequences when the model parameters are chosen within a certain range that they consider to be plausible. Shadlen and Newsome (1994), on the other hand, demonstrated that a standard leaky integrate-and-fire model can reproduce the irregularity if the inhibition is balanced with the excitation. Motivated by this discussion, we attempted to determine whether the Ornstein-Uhlenbeck process, which is naturally derived from the leaky integration assumption, can in fact reproduce higher-order statistics of biological data. For this purpose, we consider actual neuronal spike sequences recorded from the monkey prefrontal cortex to calculate the higher-order statistics of the interspike intervals. Consistency of the data with the model is examined on the basis of the coefficient of variation and the skewness coefficient, which are, respectively, a measure of the spiking irregularity and a measure of the asymmetry of the interval distribution. It is found that the biological data are not consistent with the model if the model time constant assumes a value within a certain range believed to cover all reasonable values. This fact suggests that the leaky integrate-and-fire model with the assumption of uncorrelated inputs is not adequate to account for the spiking in at least some cortical neurons.
Parameter Convergence and Learning Curves for Neural Networks
Authors: Fine Terrence L. , Mukherjee Sayandev
Published: July 2002

We revisit the oft-studied asymptotic (in sample size) behavior of the parameter or weight estimate returned by any member of a large family of neural network training algorithms. By properly accounting for the characteristic property of neural networks that their empirical and generalization errors possess multiple minima, we rigorously establish conditions under which the parameter estimate converges strongly into the set of minima of the generalization error. Convergence of the parameter estimate to a particular value cannot be guaranteed under our assumptions. We then evaluate the asymptotic distribution of the distance between the parameter estimate and its nearest neighbor among the set of minima of the generalization error. Results on this question have appeared numerous times and generally assert asymptotic normality, the conclusion expected from familiar statistical arguments concerned with maximum likelihood estimators. These conclusions are usually reached on the basis of somewhat informal calculations, although we shall see that the situation is somewhat delicate. The preceding results then provide a derivation of learning curves for generalization and empirical errors that leads to bounds on rates of convergence.
Neuronal Tuning: To Sharpen or Broaden?
Authors: Zhang Kechen , Sejnowski Terrence J.
Published: July 2002

Sensory and motor variables are typically represented by a population of broadly tuned neurons. A coarser representation with broader tuning can often improve coding accuracy, but sometimes the accuracy may also improve with sharper tuning. The theoretical analysis here shows that the relationship between tuning width and accuracy depends crucially on the dimension of the encoded variable. A general rule is derived for how the Fisher information scales with the tuning width, regardless of the exact shape of the tuning function, the probability distribution of spikes, and allowing some correlated noise between neurons. These results demonstrate a universal dimensionality effect in neural population coding.
JPEG Quality Transcoding Using Neural Networks Trained with a Perceptual Error Measure
Authors: Lazzaro John , Wawrzynek John
Published: July 2002

A JPEG Quality Transcoder (JQT) converts a JPEG image file that was encoded with low image quality to a larger JPEG image file with reduced visual artifacts, without access to the original uncompressed image. In this article, we describe technology for JQT design that takes a pattern recognition approach to the problem, using a database of images to train statistical models of the artifacts introduced through JPEG compression. In the training procedure for these models, we use a model of human visual perception as an error measure. Our current prototype system removes 32.2% of the artifacts introduced by moderate compression, as measured on an independent test database of linearly coded images using a perceptual error metric. This improvement results in an average PSNR reduction of 0.634 dB.
The Aesthetics and Technological Aspects of Virtual Musical Instruments: The Case of the SuperPolm MIDI Violin
Authors: Goto Suguru
Published: July 2002

The author discusses how his critical stance against conformity in computer-based interactive art eventually led him to create his own instrument as a way towards individual artistic sensitivity and thought. He first outlines the development and creation of a virtual musical instrument, the SuperPolm, as well as its technical points. He then addresses the relationship between gesture and music and the variety of human perceptual experiences that may occur during a performance on a virtual musical instrument. Finally the author presents the background of the SuperPolm's development and discusses cultural and technological aspects of interactivity.
Using Behavioral Realism to Estimate Presence: A Study of the Utility of Postural Responses to Motion Stimuli
Authors: Freeman Jonathan , Avons S. E. , Meddis Ray , Pearson Don E. , IJsselsteijn Wijnand
Published: July 2002

We recently reported that direct subjective ratings of the sense of presence are potentially unstable and can be biased by previous judgments of the same stimuli (Freeman et al., 1999). Objective measures of the behavioral realism elicited by a display offer an alternative to subjective ratings. Behavioral measures and presence are linked by the premise that, when observers experience a mediated environment (VE or broadcast) that makes them feel present, they will respond to stimuli within the environment as they would to stimuli in the real world. The experiment presented here measured postural responses to a video sequence filmed from the hood of a car traversing a rally track, using stereoscopic and monoscopic presentation. Results demonstrated a positive effect of stereoscopic presentation on the magnitude of postural responses elicited. Posttest subjective ratings of presence, vection, and involvement were also higher for stereoscopically presented stimuli. The postural and subjective measures were not significantly correlated, indicating that nonproprioceptive postural responses are unlikely to provide accurate estimates of presence. Such postural responses may prove useful for the evaluation of displays for specific applications and in the corroboration of group subjective ratings of presence, but cannot be taken in place of subjective ratings.
Virtual Reality-Induced Symptoms and Effects (VRISE)
Authors: Cobb Sue V. G. , Nichols Sarah , Ramsey Amanda , Wilson John R.
Published: July 2002

An experimental program of research was carried out to assess the potential health and safety effects of participating in virtual environments (VEs) via head-mounted displays (HMDs). This paper presents the results obtained from nine experiments examining the effects experienced during and after participation in a variety of VR systems, VE designs, and task requirements, for a total participant sample of 148 individuals. A combination of methods including self-report scales, performance measures, physiological indicators, observation, interview, and user attitude/opinion questionnaires were used to measure simulator (VE) sickness, postural instability, psychomotor control, perceptual judgment, concentration, stress, and ergonomics effects. Greatest effects across the different systems, VEs, and exposure times were found for sickness symptoms and physiological measures, with some concern over postural instability and physical ergonomics, also. Although many of the effects were relatively minor and short lived, they were serious for five percent of participants and irritating for a considerable percentage more. The aetiology of the effects is sufficiently different to that for simulators or transport systems to justify us using a new term, virtual reality-induced symptoms and effects (VRISE). Implications are drawn for VR system design, VE specification, and the ways in which industrial use of VR/VE should be planned and supported.
Connecting Brains to Robots: An Artificial Body for Studying the Computational Properties of Neural Tissues
Authors: Reger Bernard D. , Fleming Karen M. , Sanguineti Vittorio , Alford Simon , Mussa-Ivaldi Ferdinando A.
Published: July 2002

We have created a hybrid neuro-robotic system that establishes two-way communication between the brain of a lamprey and a small mobile robot. The purpose of this system is to offer a new paradigm for investigating the behavioral, computational, and neurobiological mechanisms of sensory-motor learning in a unified context. The mobile robot acts as an artificial body that delivers sensory information to the neural tissue and receives command signals from it. The sensory information encodes the intensity of light generated by a fixed source. The closed-loop interaction between brain and robot generates autonomous behaviors whose features are strictly related to the structure and operation of the neural preparation. We provide a detailed description of the hybrid system, and we present experimental findings on its performance. In particular, we found (a) that the hybrid system generates stable behaviors, (b) that different preparations display different but systematic responses to the presentation of an optical stimulus, and (c) that alteration of the sensory input leads to short- and long-term adaptive changes in the robot responses. The comparison of the behaviors generated by the lamprey's brain stem with the behaviors generated by network models of the same neural system provides us with a new tool for investigating the computational properties of synaptic plasticity.
Environmental and Health Research: Overlapping Agendas
Authors: Thomas Caroline
Published: July 2002

Against the discouraging background of the fate of the Kyoto Protocol, this article looks at the more encouraging development of a more integrated understanding of the global social, economic and environmental condition. The focus is the learning that is taking place between health researchers and environmental researchers. The article explores the contribution that those interested in global environmental politics can make to their fellow researchers in the public health community, who are keen to tackle transboundary health problems but who have little experience in multilateral arrangements. Moreover the article suggests that the problems are shared, and a more integrated research agenda will bring us closer to a more holistic understanding of development, and more integrated policy prescriptions.
READING WITH YIN YANG EYES: NEGOTIATING THE IDEOLOGICAL DILEMMA OF A CHINESE AMERICAN BIBLICAL HERMENEUTICS
Authors: Liew Tat-Siong Benny
Published: July 2002

Chinese Americans living in today's "postcolonial" North America are often confronted by various forms of neocolonialism. It is no exception for those working within the field of biblical studies. In order to publish and be recognized within the guild, Chinese Americans are often asked to make the "nonchoice" between forsaking their own culture and engaging in the production of some exotic "biblical tourist literature" for others to visit and "sightsee" in times of leisure. This article attempts to expose the oppressive binarism of—in Cornel West's terms—"faceless universalism" and "ethnic chauvinism," and explore how Chinese American Bible scholars may negotiate this ideological dilemma by reading from a marginal site/sight.
(RE)APPRAISAL OF SOME TECHNICAL TERMS IN HADĪTH SCIENCE
Authors:   Juynboll
Published: July 2002

After an introduction in which I define some newly-coined technical terms developed in recent hadīth analysis, such as "isnād bundle", "common link", "spiders" and "diving", I argue (307) that Schacht's technical term "common link" may have in the term madār an Arabic equivalent—never recognized as such in Islam—and which, like tafarrada, subsequently, never made it into Muslim hadīth handbooks (311). Next I describe various technical terms that rarely occur as such in Muslim handbooks, to wit, mutābi'āt and shawāhid together with the apposite verb tāba'a. These terms illustrate the "diving" phenomenon (315). The terms tawātur and mutawātir, well-known from Muslim handbooks, are re-appraised in connection with a tradition on one of the Prophet's alleged miracles (322). I then distinguish and define the terms tawātur ma'nawī and tawātur lafzī and point out the overall inapplicability of the term (326) with illustrative examples (332) such as the mash 'alā 'l-khuffayn cluster (335). Following a summary and some conclusions (341) the reader will find a list of Mālik b. Anas' most important "followers" (345).
UPSTREAM AND DOWNSTREAM UNIFICATION IN SOUTHEAST ASIA'S FIRST ISLAMIC POLITY: THE CHANGING SENSE OF COMMUNITY IN THE FIFTEENTH CENTURY HIKAYAT RAJA-RAJA PASAI COURT CHRONICLE
Authors: Hall Kenneth
Published: July 2002

This study on the thirteenth and fourteenth century emergence of Southeast Asia's earliest Islamic state examines how the fifteenth century Hikayat Raja-Raja Pasai court chronicle can be used to understand the Samudra-Pasai port-polity and its legitimation. The local pre-Islamic north Sumatra order is first portrayed in the Hikayat, which highlights the sovereign's mythical attributes. Indian Ocean commercial and diplomatic channels then provided access to imported textiles, which became the centerpiece of the monarch's ritualized redistributions, as well as the opportunity to enter membership in the community of Islam. Samudra-Pasai's newly converted sultans successfully linked disparate upstream and downstream population clusters under the leadership of their port-centered court, in ways that were not only consistent with local beliefs, but also appropriate to an Islamic society. Cette étude, sur l'émergence du premier état islamique en Asie du sud-est aux treisième et quatorzième siècles, considère comment la chronique de la cour de Hikayat Raja-Raja Pasai, datant du quinzième siècle, peut être utilisée pour comprendre le port-régime de Samudra-Pasai et sa légitimation. L'ordre local et pré-islamique de Sumatra du nord est représenté dans le Hikayat, un texte qui souligne les attributs mythiques du souverain. En particulier, le réseau commercial et diplomatique, centré sur l'océan indien, a permis l'accès aux textiles importés, qui sont devenus la pièce maîtresse du système monarchique de rédistribution rituelle, et l'occasion d'entrer comme membre dans la communauté d'islam. Les souverains de Samudra-Pasai a relié avec succès les populations disparates en amont and en aval de la rivière sous la direction de la cour, centré sur le port, par les moyens qui conforment non seulement aux croyances locales mais aussi qui conviennent à une société islamique.
ACADEMIC NOMADISM: THE RELATIONSHIP BETWEEN SOCIAL ANTHROPOLOGY AND HISTORY OF RELIGION
Authors: Thorbjørnsrud Berit
Published: July 2002

Through a narrative of the author's personal academic nomadism, the concepts of interdisciplinary and multidisciplinary studies are explored. It is argued that while interdisciplinary studies are currently being praised, insufficient attention seems to be directed at the methodological challenges involved. Rather a line of strategic avoidance seems to be adopted. Drawing on insights from migrant studies the author compares the questionable concept of migrants as potentially "falling-between-cultures" with the fear of "falling-between-disciplines" sometimes experienced by scholars attempting to move within various disciplines. While there are important reasons why academic boundaries are retained, their existence may also influence the way scholars approach the field in an undesirable manner. By examples from the study of Islam/Muslims, the author illustrates how the boundary between, for example, social anthropology and history of religion tends to become mixed up with boundaries in the field in such a way that our understanding of the field may become seriously distorted. Exploring what transcending boundaries truely involves, the author discusses the meaning of concepts like strategic avoidance, tacit knowledge and triangulation in action, and reflects on their usefulness in terms of actually establishing interdisciplinary studies and/or scholarship.
DECONSTRUCTIVE ECOFEMINISM: A JAPANESE CRITICAL INTERPRETATION
Authors: Maruyama Masatsugu
Published: July 2002

In this paper, I compare deconstructive ecofeminism and traditional Japanese worldviews, particularly those of Shinto. I identify similarities between the two at crucial points, and suggest that this implies considerable difficulties with deconstructive ecofeminism. Traditional Japanese worldviews, in particular those deriving from Shinto, are not unproblematic from the viewpoint of both ecology and feminism. Although deconstructive ecofeminists are eager to break through nature-women oppression, what they propose will not necessarily lead to what they want to create.
Spreading Non-natural Concepts: The Role of Intuitive Conceptual Structures in Memory and Transmission of Cultural Materials
Authors: Barrett Justin , Nyhof Melanie
Published: July 2002

The four experiments presented support Boyer's theory that counterintuitive concepts have transmission advantages that account for the commonness and ease of communicating many non-natural cultural concepts. In Experiment 1, 48 American college students recalled expectation-violating items from culturally unfamiliar folk stories better than more mundane items in the stories. In Experiment 2, 52 American college students in a modified serial reproduction task transmitted expectation-violating items in a written narrative more successfully than bizarre or common items. In Experiments 3 and 4, these findings were replicated with orally presented and transmitted stimuli, and found to persist even after three months. To sum, concepts with single expectation-violating features were more successfully transmitted than concepts that were entirely congruent with category-level expectations, even if they were highly unusual or bizarre. This transmission advantage for counterintuitive concepts may explain, in part, why such concepts are so prevalent across cultures and so readily spread.
DOES TESTOSTERONE AFFECT THE TRADE-OFF BETWEEN INVESTMENT IN SEXUAL/TERRITORIAL BEHAVIOUR AND PARENTAL CARE IN MALE GREAT TITS?
Authors: Van Duyse Els , Pinxten Rianne , Eens Marcel
Published: July 2002

Breeding testosterone (T) profiles of free-living male birds are hypothesized to reflect a trade-off between investment in competitive behaviour for mates or territories, typically accompanied by high T-levels, and investment in paternal care, typically accompanied by low T-levels. To test this hypothesis we monitored song activity, as a measure of territorial advertisement or mate attraction, and feeding efforts, as a measure of paternal care, in great tit Parus major males that either received T-filled or empty implants in the middle of the feeding phase, a period of high paternal commitment and low T-levels. In support of the trade-off hypothesis, T-implanted males sang significantly more than controls. However, we found no significant effect of the elevated T-levels on male and female feeding behaviour despite the large increase in T following implantation. Also, no short-term effects on male fitness were found. Taken together these results do not support the trade-off hypothesis. We discuss that the low overall responsiveness in our study might be related to a high fitness cost of neglecting offspring in favour of T-enhanced behaviour.
ALARM CALLING IN THREE SPECIES OF MARMOTS
Authors: Blumstein Daniel
Published: July 2002

Many species produce alarm calls that vary according to situation. Theoretically, alarm call structure could covary with predator type and could communicate potentially ''referential information, or calls could covary with the degree of risk a caller experienced when it emitted a call. Using similar methods, I studied the ways in which Olympic (Marmota olympus), hoary (M. caligata), and Vancouver Island marmots (M. vancouverensis) communicated situational variation. I observed both natural alarm calling, and I artificially elicited alarm calls with simulated terrestrial and aerial predators. I used playback experiments to study marmots' responses to different alarm call variants. All three species produced four roughly similar but distinctive loud alarm vocalizations that could be categorized by their relative shape, duration, and whether calls were quickly repeated to create multi-note vocalizations. In addition, the Vancouver Island marmot produced a fifth loud alarm call-the kee-aw. Call micro-structure varied as a function of the distance the caller was from an alarming stimulus and the type of alarming stimulus. Two lines of evidence suggest that all three species had alarm calls associated with the caller's risk (i.e. they were not referential). First, marmots often changed call types within a calling bout: there were no unique stimulus-class specific vocalizations. Second, marmot responses to alarm calls were graded: marmots did not have unique responses to different call types. These three close taxonomic relatives with superficially similar calls, communicated risk differently.
Nematode systematics: past, present and future
Authors: Coomans August
Published: July 2002

A brief overview is given of nematode taxonomy since its beginnings in the second half of the 19th century. Most of the work concerned α-taxonomy, but in the thirties and subsequently from the sixties several classifications have been proposed. Since the eighties phylogenetic systematics was introduced as the underlying theory. Due to the pioneering work of several famous nematode taxonomists in the first half of the 20th century an increased interest for the discipline arose. Very unfortunately, this interest decreased in more recent times to an alarming extent. The difficulty to correctly identify and to describe the rapidly increasing numbers of taxa has discouraged many young scientists and diverted them toward more appealing disciplines. Taxonomy provides nevertheless the basic knowledge for studies on biodiversity as well as for analyses of ecological and phylogenetic relationships. Molecular techniques have made systematics again exciting; when combined with the more traditional morphological approach, they will lead to new insights. Hopefully, these will arouse the interest of young scientists. Even then the future of nematode taxonomy will depend on the funding opportunities provided by national and international authorities. La systématique des nématodes est brièvement revue depuis ses origines dans la seconde moitié du 19ème siècle. La plupart des travaux sont relatifs l’ α-taxinomie, mais dans les années trente et ensuite dans les années soixante, plusieurs classifications ont été proposées. Depuis les années 80, la systématique phylogénétique a été introduite comme la théorie sous-jacente. Grâce au travail de pionnier de plusieurs taxinomistes célèbres dans la première moitié du 20ème siècle, un intérêt accru est apparu pour la discipline. Très malheureusement, cet intérêt a décru récemment jusqu’à un niveau alarmant. La difficulté d’identifier correctement et de décrire un nombre de taxons augmentant rapidement a découragé de nombreux jeunes scientifiques et les a poussé vers des disciplines plus attirantes. La taxinomie cependant apporte la connaissance de base tant pour des études de biodiversité que pour des études de relations écologiques et phylogénétiques. Les techniques moléculaires ont rendu la systématique à nouveau attractive; lorsqu’elles seront combinées avec l’approche morphologique plus traditionnelle, elles conduiront à de nouveaux développements. Heureusement, elles vont réveiller l’intérêt des jeunes chercheurs. Malgré cela, le futur de la taxinomie des nématodes dépendra des opportunités de financement par les autorités nationales et internationales.
Paratylenchinae: redescription of Paratylenchus arculatus Luc & de Guiran, 1962, a new senior synonym of P. nainianus Edward & Misra, 1963 (Nematoda: Tylenchulidae)
Authors: Brzeski Michal , Hanel Ladislav , Nico Andres , Castillo Pablo
Published: July 2002

Several populations of Paratylenchus arculatus from sandy soil and root samples from olive nurseries in southern Spain and from uncultivated clay soil in New South Wales, Australia are described. P. nainianus Edward & Misra, 1963 is considered as a junior subjective synonym of P. arculatus. Paratylenchinae: redescription de Paratylenchus arculatus Luc & de Guiran, 1962, un nouveau synonym majeur de P. nainianus Edward & Misra, 1963 (Nematoda: Tylenchulidae) - Sont decrites plusieurs populations de Paratylenchus arculatus provenant d'echantillons de sol sableux et de racines collectes dans des pepinieres d'olivier du sud de l'Espagne et d'un sol argileux en jachere des Nouvelles Galles du Sud, Australie. P. nainianus Edward & Misra, 1963 est considere comme un synonyme mineur subjectif de P. arculatus.
Precipitation and flocculation of spherical nano-silica in North Sea chalk
Authors: Jakobsen F. , Lindgreen H. , Springer N.
Published: July 2002

In the Maastrichtian-Danian chalk in the North Sea, discrete intervals, appearing as normal white chalk, contain up to 60% α-quartz <2 μm in size. Atomic force microscopy (AFM) reveals that the particles are of nm size, appearing as spherical particles and aggregates. Similar particles consisting of opal-CT were found in surface exposures of chalk in Denmark. Two new abiogenic pathways of silica formation in chalk are proposed. The first model proposes that SiO2 nano-size particles and aggregates precipitated and flocculated in the free-water phase as opal and were diagenetically transformed from opal-CT at low temperature to α-quartz at elevated temperature. In the second model, the dominance of radiolarians in the deep-water environment of the North Sea resulted in low dissolution supply with subsequent precipitation and flocculation of nano-size α-quartz particles. In the shallower water of the shelf environment of the present onshore chalk, the abundance of sponges and their dissolution supplied enough Si to precipitate opal-CT in the free-water phase.
K-Ar dating of varied microtextural illite in Permian gas reservoirs, northern Germany
Authors: Liewig N. , Clauer N.
Published: July 2002

Several types of authigenic illite differing in their distribution and morphology are described in Rotliegend (Permian) gas-bearing sandstones of northern Germany. The microtextural environment seems to control the K-Ar age variations of illite-fractions of different sizes. Thin, uncompacted, and radial coatings are 200 Ma old, whereas uncompacted fibrous laths filling enlarged secondary porosity are 180 Ma old, and compacted or recrystallized tangential particles yield intermediate or even younger ages. Such Liassic ages relate to a thermal event, the effects of which on the clay material have not been erased subsequently, despite present-day burial depth of 4500 m and temperatures of 150°C.
The nature and origin of non-marine 10 Å clay from the Late Eocene and Early Oligocene of the Isle of Wight (Hampshire Basin), UK
Authors: Huggett J. M. , Gale A. S. , Clauer N.
Published: July 2002

Variegated palaeosols, which formed from weathering of clays, silts and brackish to freshwater limestones, are present in the Late Eocene–Early Oligocene Solent Group of the Hampshire Basin, southern UK. The composition and origin of the clay in three segments of the lower part of the Solent Group have been investigated by X-ray diffraction, microprobe analysis, inductively coupled plasma-mas spectrometry, K/Ar dating, high resolution scanning electron microscopy, analytical transmission electron microscopy and wet chemistry. The detrital clay mineral suite is dominated by illite and smectite with minor kaolinite and chlorite. Seasonal wetting and drying in gley soils has resulted in replacement of smectite by Fe-rich, or illite-rich illitesmectite. Illite has also formed with gypsum and calcite in ephemeral hypersaline alkaline lakes that periodically dried out. This illite may have precipitated directly from solution. X-ray diffraction data and probe analyses indicate that the neoformed illite is Fe-rich. The K and Fe for the illitization are thought to be derived from weathered glauconite reworked from the underlying Bracklesham Group and Barton Beds.
Use of an air brush to spray dry samples for X-ray powder diffraction
Authors: Hillier S.
Published: July 2002

The construction and operation of a spray drier is described where the spray is produced using an air brush, essentially a miniature spray gun. The spray-dried products consist of spheres 50–60 µm in diameter and typical product recoveries are 80%, a marked improvement over simple two-nozzle systems. The spray-dried samples are easy to load into XRD powder holders and present a smooth surface and relatively constant bulk density to the X-ray beam. Problems of preferred orientation are effectively eliminated and the resulting X-ray powder patterns are completely reproducible by different operators.
Middle Jurassic ultramafic lamprophyre dyke within the Ferrar magmatic province, Pensacola Mountains, Antarctica
Authors: Leat P. T. , Riley T. R. , Storey B. C. , Kelley S. P. , Millar I. L.
Published: July 2002

An ultramafic lamprophyre dyke is described from the otherwise tholeiitic Ferrar magmatic province of Antarctica. We report an Ar-Ar age of 183 ± 2.2 Ma for the dyke, indistinguishable from those of the Ferrar tholeiites. However, the dyke has mineralogical and major and trace element compositions, and radiogenic isotopes ratios, very different from the Ferrar tholeiites. The sample consists of olivine and rare clinopyroxene phenocrysts with perovskite and spinel microphenocrysts in a groundmass of amphibole, nepheline and biotite. Carbonatitic globules contain calcite, dolomite, Fe-rich carbonate, nepheline, biotite, orthoclase, pyrite, clinopyroxene, apatite and silicate glass, and were formed by liquid immiscibility. The rock is mildly potassic and classifies as an ouachitite. It is strongly enriched in both moderately and highly incompatible trace elements and is the first high-Ti rock to be described from the Ferrar magmatic province. The rock has similar initial 143Nd/144Nd to OIB, notably Bouvet, Crozet and Réunion, but significantly higher initial 87Sr/86Sr. The lamprophyre magma is interpreted as having been generated by low-degree partial fusion of metasomatized lithospheric mantle as a result of heat conducted from an underlying Jurassic mantle plume. The same mantle plume was probably also responsible for generating one of the world’s largest layered gabbro bodies, the Dufek-Forrestal intrusions.
P-Tconditions during emplacement, and D2 regional metamorphism, of the Ben Vuirich Granite, Perthshire, Scotland
Authors: Ahmed-Said Y. , Tanner P. W. G.
Published: July 2002

The 590±2 Ma Ben Vuirich Granite was intruded into late Proterozoic Dalradian rocks prior to the Grampian orogeny, during which it was affected by upper amphibolite facies regional metamorphism. Spotted cordierite and andalusite (chiastolite) hornfelses at the granite margin were altered to kyanite-and garnet-bearing assemblages during regional metamorphism. From the inferred mineralogy of the hornfels, together with the normative Qz–Ab–Or values of the granite and the application of a simple cooling model, we conclude that the country rocks immediately adjacent to the granite were hornfelsed atT= ∼600°C andP≤ 2 kbar.

The hornfelsed rocks were subsequently metamorphosed during the regional D2 event to form an equilibrium mineral assemblage of muscovite + biotite + garnet + plagioclase + quartz + kyanite (after chiastolite). Garnet which grew during this event shows unusual reversed chemical zoning, with Ca increasing systematically from core to rim as Fe, Mg and Mn decrease. A study of element partitioning between coexisting phases in equilibrium (including zoned garnets), and use of an internally consistent thermodynamic dataset, suggest that isothermal (T= 577±42°C) compression (fromP= 6.2±1.6 kbar to 9.0±1.9 kbar) occurred during crustal thickening. K-feldspar-plagioclase-quartz veinlets found in the hornfels close the granite contact are demonstrated to be of igneous origin.
A high-temperature hydrothermal origin for black dolomite matrix breccias in the Irish Zn-Pb orefield
Authors: Wilkinson J. J. , Earls G.
Published: July 2002

We make the first report of fluid inclusion data from a black dolomite matrix breccia from the Irish orefield which confirm a relatively high-temperature hydrothermal origin. Breccia matrix dolomite formed from NaCl-dominated fluids with temperatures primarily in the range 150–220°C and salinities of 13–20 wt.% NaCl equivalent, comparable with inferred ore-stage fluids at the Silvermines, Tynagh, Lisheen and Navan deposits. The spread in salinity is considered to be due to mixing of a moderate salinity (~12 wt.%), higher temperature fluid, probably derived from the Lower Palaeozoic metasedimentary basement, with a low temperature brine. Non-stoichiometric, black dolomites are therefore considered to be a product of relatively high-temperature hydrothermal processes involving the principal orefluid in Ireland, and thus their occurrence is believed to be a prime exploration indicator.

Earlier, coarse white dolomite, texturally similar to regional dolomite cements commonly observed in the Irish Midlands, precipitated from fluids in the temperature range 140–200°C and salinities of 10.3–13.5 wt.% NaCl equivalent. This is comparable with the higher temperature, moderate salinity end-member inferred for the black dolomite. These data call into question a uniquely low-temperature burial origin for coarse white dolomite cements in Ireland. Paragenetically late low-Mg calcites were formed as a result of an influx of relatively low salinity fluids.
An ab initio study of the relative stabilities and equations of state of FeS polymorphs
Authors: Martin P. , Price G. D. , Vočadlo L.
Published: July 2002

An investigation into the relative stabilities and equations of state of stoichiometric FeS was conducted using first-principles pseudopotential calculations. These calculations were based on density functional theory and performed using ultrasoft Vanderbilt pseudopotentials within the generalized gradient approximation. We have identified four stable polymorphs of FeS along the 0 K isotherm as a function of pressure: troilite, an orthorhombic MnP-type structure, a monoclinic structure, and a CsCl-type structure. The calculated internal energy as a function of volume for each polymorph was fitted to 4th order logarithmic and 3rd order Birch-Murnaghan equations of state, yielding values for the bulk modulus, K, and its first and second derivatives with respect to pressure, K′ and K″. These equations of state may be used to characterize models of planetary cores.
REE fractionation by accessory minerals in epidote-bearing metaluminous granitoids from the Sierras Pampeanas, Argentina
Authors: Dahlquist J. A.
Published: July 2002

A study of the distribution of REE in epidote-bearing metaluminous granitoids from Sierra de Chepes, Sierras Pampeanas, Argentina, reveals that a large proportion of the REE reside in the accessory minerals (allanite, epidote, titanite, apatite and zircon), and therefore these minerals control the behaviour of REE in granitic magmas. Well-developed chemical zonation in titanite indicates that the REE content decreases in the melt during crystallization of this mineral. The textural and chemical characteristics of euhedral epidote suggest a magmatic origin, and in that case it may have played an important role in the fractionation of the REE. The amount of silica and any other geochemical parameter indicative of fractionation progress in the dominant granodioritic-tonalitic facies (gtf) do not correlate with observed variations in the REE patterns. When many accessory minerals are involved, as in the gtf, the differentiated melts (e.g. aplites) are REE poor. Thus, the presence/absence of accessory minerals in granitoids can be indicative of the generation of differentiated melt enriched or poor in REE and other trace elements. This may have an economic significance, as it may allow us to predict the probable geochemistry of the differentiated melts (i.e. those that tend to develop mineralization) from the textural analysis of the ‘regional’ granitic rock.

Finally, the type and abundance of accessory minerals in the granitic suite can also help us to define the geotectonic environment where magmas were generated.
Encouraging the extrusion of deep-crustal rocks in collisional zones
Authors: Hynes A.
Published: July 2002

Most unroofing mechanisms invoked for the exhumation of blueschist-plus-eclogite terranes, including corner-flow and extensional collapse of the orogenic wedge, predict steep unroofing paths for the deeply-buried rocks and are applicable only to unroofing from depths within the crust. Many high-P and ultrahigh-P rocks of continental affinity are derived from greater depths than this. Their lack of warming during unroofing, together with indications that they may rest directly on less deeply buried equivalents, are suggestive of shallow unroofing paths similar to those for the subduction-channel model. They are interpreted to have been emplaced by the upward extrusion of coherent slices of continental crust, bounded below by thrust faults and above by normal faults, with unroofing paths essentially reversing the original burial paths.

Where continental crust has been subducted into the mantle, upward extrusion is probably driven largely by buoyancy forces, although examples of upward extrusion without subduction into the mantle indicate that buoyancy forces may not be essential. Two features in addition to buoyancy may promote upward extrusion. Slab breakoff may reduce the pull from the descending slab, and subduction-zone geometry may change as a continental margin is dragged into the subduction zone. Both features may promote the extrusion of continental crust at precisely the time at which it has been partially subducted.

A close spatial relationship between a lateral ramp and a lobate zone of extruded high-P rocks in the Mesoproterozoic Grenvillian orogen indicates that lateral ramps may be important in localizing extrusion. Lateral ramps disturb the two-dimensional flow, with channelling of material into the region of the lateral ramp as it is extruded. Many exhumed ultrahigh-P terrains are associated with jogs in the trends of orogenic fronts that may reflect the presence of lateral ramps at depth. Ultrahigh-P rocks may be expected to be concentrated at such jogs, and may record the channelling in their deformation history.
Rates of erosion and their implications for exhumation
Authors: Burbank D. W.
Published: July 2002

At time-scales of 102to 105years, erosion by rivers, landslides and glaciers can exceed 5 mm/y. Sustained denudation at these rates is sufficient to account for many of the rapid rates of unloading or cooling that are revealed by geobarometric or thermochronologic studies. Because feedbacks exist among many surface processes, determinations of erosion rates on a few geomorphic processes can be adequate to estimate mean rates across an entire landscape. Rates of fluvial and glacial incision exert a dominant control on landscape lowering, because these rates set the local base level and modulate the flux from adjacent hillslopes. When rates of deformation are sufficiently rapid and sustained, a collisional orogen approaches a dynamic equilibrium or topographic steady state. Due to variations in erosion rates as a function of Late Cenozoic climate changes, such a steady state should be defined at time-scales longer than one climate cycle. During dynamic equilibrium, the geomorphic system displays a predictable configuration of interacting rivers, hillslopes and glaciated process zones. A dynamic equilibrium appears to prevail near Nanga Parbat, Pakistan, and the Southern Alps of New Zealand, where spatial variations in geomorphic erosion rates mimic variations in bedrock cooling rates at time-scales of 106y.
The correlation between lithium and magnesium in trioctahedral micas: Improved
equations for Li2O estimation from MgO data
Authors: Tischendorf G. , Förster H.-J. , Gottesmann B.
Published: July 2002

A major disadvantage of the electron microprobe is its inability to determine
Li, which may make up an essential component in micaceous minerals. Correct
classification of micas and proper calculation of their formulae require
alternative methods. One of these is the indirect estimation of the lithium
concentration by empirical approaches based on element correlations. Relationships
between Li2O and SiO2 have long been
used for this purpose; however, they are valid only for a limited range of mica
compositions (i.e. Li-rich, Mg-poor varieties).

In this paper we report the results from a renewed study of the correlation
between Li2O and MgO contents in trioctahedral micas. It is
demonstrated that the relations between both oxides are strongly dependent upon
the geological environment in which the mica was formed. It is necessary to
distinguish a ‘normal group’, which comprises micas from ‘common’ S- and I-type
magmatic rocks and most metamorphic rocks , a ‘low Li-Mg group’, to which belong
Fe-rich micas from non-alkaline rocks of A-type affinity, and a ‘high Li-Mg group’
which includes micas from either peraluminous or peralkaline igneous rocks and
Mg-enriched wall-rocks. These wall rocks supplied additional magnesium to the
mica-forming environment. We offer empirical expressions relating
Li2O and MgO contents for these three types which, in many
cases, allow a sufficiently good estimation of the lithium content in
trioctahedral micas of widely varying compositions.
Mimicry between neurokinin-1 and fibronectin may explain the transport and stability of increased substance P immunoreactivity in patients with bone marrow fibrosis
Authors: Rameshwar Pranela , Joshi Deval D. , Yadav Prem , Qian Jing , Gascon Pedro , Chang Victor T. , Anjaria Devashish , Harrison Jonathan S. , Song Xiaosong
Published: July 2002

Bone marrow (BM) fibrosis may occur in myeloproliferative diseases, lymphoma, myelodysplastic syndrome, myeloma, and infectious diseases. In this study, the role of substance P (SP), a peptide with pleiotropic functions, was examined. Some of its functions—angiogenesis, fibroblast proliferation, and stimulation of BM progenitors—are amenable to inducing BM fibrosis. Indeed, a significant increase was found in SP-immunoreactivity (SP-IR) in the sera of patients with BM fibrosis (n = 44) compared with the sera of patients with hematologic disorders and no histologic evidence of fibrosis (n = 46) (140 ±12 vs 18 ±3; P < .01). Immunoprecipitation of sera SP indicated that this peptide exists in the form of a complex with other molecule(s). It was, therefore, hypothesized that SP might be complexed with NK-1, its natural receptor, or with a molecule homologous to NK-1. To address this, 3 cDNA libraries were screened that were constructed from pooled BM stroma or mononuclear cells with an NK-1 cDNA probe. A partial clone (clone 1) was retrieved that was 97% homologous to the ED-A region of fibronectin (FN). Furthermore, sequence analyses indicated that clone 1 shared significant homology with exon 5 of NK-1. Immunoprecipitation and Western blot analysis indicated co-migration of SP and FN in 27 of 31 patients with BM fibrosis. Computer-assisted molecular modeling suggested that similar secondary structural features between FN and NK-1 and the relative electrostatic charge might explain a complex formed between FN (negative) and SP (positive). This study suggests that SP may be implicated in the pathophysiology of myelofibrosis, though its role would have to be substantiated in future research.