bluuebunny/crossref_metadata_2025 huggingface dataset:
Reduplication with Fixed Segmentism
Authors: Alderete John , Beckman Jill , Benua Laura , Gnanadesikan Amalia , McCarthy John , Urbanczyk Suzanne
Published: July 2002

Fixed segmentism is the phenomenon whereby a reduplicative morpheme contains segments that are invariant rather than copied. We investigate it within Optimality Theory, arguing that it falls into two distinct types, phonological and morphological. Phonological fixed segmentism is analyzed under the OT rubric of emergence of the unmarked. It therefore has significant connections to markedness theory, sharing properties with other domains where markedness is relevant and showing context-dependence. In contrast, morphological fixed segmentism is a kind of affixation, and so it resembles affixing morphology generally. The two types are contrasted, and claims about impossible patterns of fixed segmentism are developed.
A Twin MRI Study of Size Variations in the Human Brain
Authors: Pennington Bruce F. , Filipek Pauline A. , Lefly Dianne , Chhabildas Nomita , Kennedy David N. , Simon Jack H. , Filley Christopher M. , Galaburda Albert , DeFries John C.
Published: July 2002

Although it is well known that there is considerable variation among individuals in the size of the human brain, the etiology of less extreme individual differences in brain size is largely unknown. We present here data from the first large twin sample (N=132 individuals) in which the size of brain structures has been measured. As part of an ongoing project examining the brain correlates of reading disability (RD), whole brain morphometric analyses of structural magnetic response image (MRI) scans were performed on a sample of adolescent twins. Specifically, there were 25 monozygotic (MZ) and 23 dizygotic (DZ) pairs in which at least one member of each pair had RD and 9 MZ and 9 DZ pairs in which neither member had RD. We first factor-analyzed volume data for 13 individual brain structures, comprising all of the neocortex and most of the subcortex. This analysis yielded two factors (“cortical” and “subcortical”) that accounted for 64% of the variance. We next tested whether genetic and environmental influences on brain size variations varied for these two factors or by hemisphere. We computed intraclass correlations within MZ and DZ pairs in each sample for the cortical and subcortical factor scores, for left and right neocortex, and for the total cerebral volume. All five MZ correlations were substantial (r's=.78 to .98) and significant in both samples, as well as being larger than the corresponding DZ correlations, (r's=0.32 to 0.65) in both samples. The MZ-DZ difference was significant for 3 variables in the RD sample and for one variable in the smaller control sample. These results indicate significant genetic influences on these variables. The magnitude of genetic influence did not vary markedly either for the 2 factors or the 2 hemispheres. There was also a positive correlation between brain size and full-scale IQ, consistent with the results of earlier studies. The total cerebral volume was moderately correlated (r=.42, p<.01, two-tailed) with full-scale IQ in the RD sample; there was a similar trend in the smaller control sample (r=.31, p<.07, two-tailed). Corrections of similar magnitude were found between the subcortical factor and full-scale IQ, whereas the results for the cortical factor (r=.16 and .13) were smaller and not significant. In sum, these results provide evidence for the heritability of individual differences in brain size which do not vary markedly by hemisphere or for neocortex relative to subcortex. Since there are also correlations between brain size and full-scale IQ in this sample, it is possible that genetic influences on brain size partly contribute to individual differences in IQ.
IV. Neuroanatomy of Williams Syndrome: A High-Resolution MRI Study
Authors: Reiss Allan L. , Eliez Stephan , Schmitt J. Eric , Straus Erica , Lai Zona , Jones Wendy , Bellugi Ursula
Published: July 2002

Williams syndrome (WMS), a genetic condition resulting from a contiguous deletion on the long arm of chromosome 7, is associated with a relatively consistent profile of neurocognitive and neurobehavioral features. The distinctiveness and regularity of the profile of learning and behavioral characteristics in this genetic condition suggests that underlying neurobiological correlates may be identifiable. In this initial study, we report findings derived from a high-resolution neuroimaging study of 14 young adult subjects with WMS and an individually matched normal control group. Compared to controls, subjects with WMS were noted to have decreased overall brain and cerebral volumes, relative preservation of cerebellar and superior temporal gyrus (STG) volumes, and disproportionate volume reduction of the brainstem. Analyses also suggested that the pattern of cerebral lobe proportions in WMS may be altered compared to normal controls with a greater ratio of frontal to posterior (parietal+occipital) tissue. Assessment of tissue composition indicated that, relative to controls, individuals with WMS have relative preservation of cerebral gray matter volume and disproportionate reduction in cerebral white matter volume. However, within the cerebral gray matter tissue compartment, the right occipital lobe was noted to have excess volume loss. Combined with our growing knowledge of the function of genes in the commonly deleted region for WMS, more detailed information regarding the structure and function of the WMS brain will provide a unique opportunity for elucidating meaningful correlations amongst genetic, neurobiological, and neurobehavioral factors in humans.
The Fusiform “Face Area” is Part of a Network that Processes Faces at the Individual Level
Authors: Gauthier Isabel , Tarr Michael J. , Moylan Jill , Skudlarski Pawel , Gore John C. , Anderson Adam W.
Published: July 2002

According to modular models of cortical organization, many areas of the extrastriate cortex are dedicated to object categories. These models often assume an early processing stage for the detection of category membership. Can functional imaging isolate areas responsible for detection of members of a category, such as faces or letters? We consider whether responses in three different areas (two selective for faces and one selective for letters) support category detection. Activity in these areas habituates to the repeated presentation of one exemplar more than to the presentation of different exemplars of the same category, but only for the category for which the area is selective. Thus, these areas appear to play computational roles more complex than detection, processing stimuli at the individual level. Drawing from prior work, we suggest that face-selective areas may be involved in the perception of faces at the individual level, whereas letter-selective regions may be tuning themselves to font information in order to recognize letters more efficiently.
A Limit to the Speed of Processing in Ultra-Rapid Visual Categorization of Novel Natural Scenes
Authors: Fabre-Thorpe Michèle , Delorme Arnaud , Marlot Catherine , Thorpe Simon
Published: July 2002

The processing required to decide whether a briefly flashed natural scene contains an animal can be achieved in 150 msec (Thorpe, Fize, & Marlot, 1996). Here we report that extensive training with a subset of photographs over a 3-week period failed to increase the speed of the processing underlying such Rapid Visual Categorizations: Completely novel scenes could be categorized just as fast as highly familiar ones. Such data imply that the visual system processes new stimuli at a speed and with a number of stages that cannot be compressed. This rapid processing mode was seen with a wide range of visual complex images, challenging the idea that short reaction times can only be seen with simple visual stimuli and implying that highly automatic feed-forward mechanisms underlie a far greater proportion of the sophisticated image analysis needed for everyday vision than is generally assumed.
Cerebellar Contributions to Motor Timing: A PET Study of Auditory and Visual Rhythm Reproduction
Authors: Penhune V. B. , Zatorre R. J. , Evans A. C.
Published: July 2002

The perception and production of temporal patterns, or rhythms, is important for both music and speech. However, the way in which the human brain achieves accurate timing of perceptual input and motor output is as yet little understood. Central control of both motor timing and perceptual timing across modalities has been linked to both the cerebellum and the basal ganglia (BG). The present study was designed to test the hypothesized central control of temporal processing and to examine the roles of the cerebellum, BG, and sensory association areas. In this positron emission tomography (PET) activation paradigm, subjects reproduced rhythms of increasing temporal complexity that were presented separately in the auditory and visual modalities. The results provide support for a supramodal contribution of the lateral cerebellar cortex and cerebellar vermis to the production of a timed motor response, particularly when it is complex and/or novel. The results also give partial support to the involvement of BG structures in motor timing, although this may be more directly related to implementation of the motor response than to timing per se. Finally, sensory association areas and the ventrolateral frontal cortex were found to be involved in modality-specific encoding and retrieval of the temporal stimuli. Taken together, these results point to the participation of a number of neural structures in the production of a timed motor response from an external stimulus. The role of the cerebellum in timing is conceptualized not as a clock or counter but simply as the structure that provides the necessary circuitry for the sensory system to extract temporal information and for the motor system to learn to produce a precisely timed response.
On “Natural” Learning and Pruning in Multilayered Perceptrons
Authors: Heskes Tom
Published: July 2002

Several studies have shown that natural gradient descent for on-line learning is much more efficient than standard gradient descent. In this article, we derive natural gradients in a slightly different manner and discuss implications for batch-mode learning and pruning, linking them to existing algorithms such as Levenberg-Marquardt optimization and optimal brain surgeon.

The Fisher matrix plays an important role in all these algorithms. The second half of the article discusses a layered approximation of the Fisher matrix specific to multilayered perceptrons. Using this approximation rather than the exact Fisher matrix, we arrive at much faster “natural” learning algorithms and more robust pruning procedures.
Geometric Analysis of Population Rhythms in Synaptically Coupled Neuronal Networks
Authors: Rubin J. , Terman D.
Published: July 2002

We develop geometric dynamical systems methods to determine how various components contribute to a neuronal network's emergent population behaviors. The results clarify the multiple roles inhibition can play in producing different rhythms. Which rhythms arise depends on how inhibition interacts with intrinsic properties of the neurons; the nature of these interactions depends on the underlying architecture of the network. Our analysis demonstrates that fast inhibitory coupling may lead to synchronized rhythms if either the cells within the network or the architecture of the network is sufficiently complicated. This cannot occur in mutually coupled networks with basic cells; the geometric approach helps explain how additional network complexity allows for synchronized rhythms in the presence of fast inhibitory coupling. The networks and issues considered are motivated by recent models for thalamic oscillations. The analysis helps clarify the roles of various biophysical features, such as fast and slow inhibition, cortical inputs, and ionic conductances, in producing network behavior associated with the spindle sleep rhythm and with paroxysmal discharge rhythms. Transitions between these rhythms are also discussed.
Correctness of Belief Propagation in Gaussian Graphical Models of Arbitrary Topology
Authors: Weiss Yair , Freeman William T.
Published: July 2002

Graphical models, such as Bayesian networks and Markov random fields, represent statistical dependencies of variables by a graph. Local “belief propagation” rules of the sort proposed by Pearl (1988) are guaranteed to converge to the correct posterior probabilities in singly connected graphs. Recently, good performance has been obtained by using these same rules on graphs with loops, a method we refer to as loopy belief propagation. Perhaps the most dramatic instance is the near Shannon-limit performance of “Turbo codes,” whose decoding algorithm is equivalent to loopy propagation.

Except for the case of graphs with a single loop, there has been little theoretical understanding of loopy propagation. Here we analyze belief propagation in networks with arbitrary topologies when the nodes in the graph describe jointly gaussian random variables. We give an analytical formula relating the true posterior probabilities with those calculated using loopy propagation. We give sufficient conditions for convergence and show that when belief propagation converges, it gives the correct posterior means for all graph topologies, not just networks with a single loop.

These results motivate using the powerful belief propagation algorithm in a broader class of networks and help clarify the empirical performance results.
Spike-Timing-Dependent Hebbian Plasticity as Temporal Difference Learning
Authors: Rao Rajesh P. N. , Sejnowski Terrence J.
Published: July 2002

A spike-timing-dependent Hebbian mechanism governs the plasticity of recurrent excitatory synapses in the neocortex: synapses that are activated a few milliseconds before a postsynaptic spike are potentiated, while those that are activated a few milliseconds after are depressed. We show that such a mechanism can implement a form of temporal difference learning for prediction of input sequences. Using a biophysical model of a cortical neuron, we show that a temporal difference rule used in conjunction with dendritic backpropagating action potentials reproduces the temporally asymmetric window of Hebbian plasticity observed physiologically. Furthermore, the size and shape of the window vary with the distance of the synapse from the soma. Using a simple example, we show how a spike-timing-based temporal difference learning rule can allow a network of neocortical neurons to predict an input a few milliseconds before the input's expected arrival.
Connecting Cortical and Behavioral Dynamics: Bimanual Coordination
Authors: Jirsa V. K. , Fuchs A. , Kelso J. A. S.
Published: July 2002

For the paradigmatic case of bimanual coordination, we review levels of organization of behavioral dynamics and present a description in terms of modes of behavior. We briefly review a recently developed model of spatiotemporal brain activity that is based on short-and long-range connectivity of neural ensembles. This model is specified for the case of motor and sensorimotor units embedded in the neural sheet. Focusing on the cortical left-right symmetry, we derive a bimodal description of the brain activity that is connected to behavioral dynamics. We make predictions of global features of brain dynamics during coordination tasks and test these against experimental magnetoencephalogram (MEG) results. A key feature of our approach is that phenomenological laws at the behavioral level can be connected to a field-theoretical description of cortical dynamics.
Mutual Information, Fisher Information, and Population Coding
Authors: Brunel Nicolas , Nadal Jean-Pierre
Published: July 2002

In the context of parameter estimation and model selection, it is only quite recently that a direct link between the Fisher information and information-theoretic quantities has been exhibited. We give an interpretation of this link within the standard framework of information theory. We show that in the context of population coding, the mutual information between the activity of a large array of neurons and a stimulus to which the neurons are tuned is naturally related to the Fisher information. In the light of this result, we consider the optimization of the tuning curves parameters in the case of neurons responding to a stimulus represented by an angular variable.
Concentration Tuning Mediated by Spare Receptor Capacity in Olfactory Sensory Neurons: A Theoretical Study
Authors: Cleland Thomas A. , Linster Christiane
Published: July 2002

The olfactory system is capable of detecting odorants at very low concentrations. Physiological experiments have demonstrated odorant sensitivities down to the picomolar range in preparations from the sensory epithelium. However, the contemporary model for olfactory signal transduction provides that odorants bind to olfactory receptors with relatively low specificity and consequently low affinity, making this detection of low-concentration odorants theoretically difficult to understand. We employ a computational model to demonstrate how olfactory sensory neuron (OSN) sensitivity can be tuned by modulation of receptor-effector coupling and/or by other mechanisms regulating spare receptor capacity, thus resolving this conundrum.

The EC10–90intensity tuning ranges (ITRs) of whole olfactory glomeruli and postsynaptic mitral cells are considerably broader than the commensurate ITRs of individual OSNs. These data are difficult to reconcile with certain contemporary hypotheses that convergent OSNs in mammals exhibit a homogeneous population of olfactory receptors and identical tuning for odor stimuli. We show that heterogeneity in spare receptor capacities within a convergent OSN population can increase the ITR (EC10–90) of a convergent population of OSNs regardless of the presence or absence of a diversity of receptor expression within the population.

The modulation of receptor-effector coupling has been observed in OSNs; other mechanisms for cellular regulation of spare receptor capacity are also highly plausible (e.g., quantitative regulation of the relative expression levels of receptor and effector proteins). We present a model illustrating that these processes can underlie both how OSNs come to exhibit high sensitivity to odorant stimuli without necessitating increased ligand-receptor binding affinities or specificities and how a population of convergent OSNs could exhibit a broader concentration sensitivity than its individual constituent neurons, even given a population expressing identical odorant receptors. The regulation of spare receptor capacity may play an important role in the olfactory system's ability to reliably detect low odor concentrations, discriminate odor intensities, and segregate this intensity information from representations of odor quality.
Cocoliche's Romp: Fun with Nationalism at Argentina's Carnival
Authors: Seigel Micol
Published: July 2002

In the early 1900s, during a period of massive European immigration, amid a rising tide of restrictions against workers, unions, and anarchists, as well as the violent marginalization of indigenous and Afro-Argentines, Carnival was the arena for negotiating still-fluid national identity-boundaries.
Adaptive Behavior in Autonomous Agents
Authors: Ziemke Tom
Published: July 2002

This paper provides an overview of the bottom-up approach to artificial intelligence (AI), commonly referred to as behavior-oriented AI. The behavior-oriented approach, with its focus on the interaction between autonomous agents and their environments, is introduced by contrasting it with the traditional approach of knowledge-based AI. Different notions of autonomy are discussed, and key problems of generating adaptive and complex behavior are identified. A number of techniques for the generation of behavior are introduced and evaluated regarding their potential for realizing different aspects of autonomy as well as adaptivity and complexity of behavior. It is concluded that, in order to realize truly autonomous and intelligent agents, the behavior-oriented approach will have to focus even more on lifelike qualities in both agents and environments.
The Early Post-Stalin Succession Struggle and Upheavals in East-Central Europe: Internal-External Linkages in Soviet Policy Making (Part 1)
Authors: Kramer Mark
Published: July 2002

The death of Josif Stalin was followed by momentous changes in the Soviet bloc. Part 1 of this two-part article considers how and why these changes came about, looking at the interaction between domestic and external events. It explores the nature of Soviet decision making, the impact of events in East-Central Europe, the implementation of Moscow's new policy, and the use of Soviet troops to put down a large-scale uprising in East Germany. Politics, Power, and U.S. Policy in Iran, 1950–1953
Dehierarchization and Sustainable Development in Liberal and Non-liberal Societies
Authors: Wissenburg Marcel
Published: July 2002

Modern societies appear to be going through a phase of dehierarchization, that is, a change in the way of governance of nation states, from direction of, to cooperation with, civil society; and in more general terms political pluralization, the emergence of “polities” other than the nation state. The paper argues that one of the most stressing problems of political pluralization is the co-existence of mutually effacing or contradictory systems of political norms. To tackle this problem of incompossibility, it has been suggested that policy teloi, shared conceptions giving direction to cooperative political ventures, in particular sustainable development, could be helpful. This article investigates whether sustainable development as a policy telos can tackle incompossibility, both in liberal (democratic) and non-liberal (democratic) societies. The paper concludes that its best chances of being temporarily successful lie in understanding it in the broadest sense possible—particularly if one values moral pluralism.
JUDGING WITH GOD'S LAW ON EARTH: JUDICIAL POWERS OF THE QĀDĪ AL-JAMĀ'A OF CORDOBA IN THE FIFTH/ELEVENTH CENTURY
Authors: Müller Christian
Published: July 2002

Court cases from al-Ahkām al-kubrā, a fatwā collection compiled by the Andalusian qādī Ibn Sahl (d. 486/1093), form the basis for this inquiry into the judicial authority of the qādī al-jamā'a. The article, which deals with both institutional and legal aspects of the office, demonstrates that adherence to procedural law during court procedure and consideration of the jurisconsults' legal opinions were required to produce a judgment that was binding but potentially reversible. The possible influence of Mālikī fiqh on the range of qādī jurisdiction in Cordoba is tested on a sample of fifty cases that originated in the period between 456/1064 and 464/1072. These cases are noteworthy for their reliability as source material and because they were handled not only by the qādī al-jamā'a but also by other judicial magistrates.
THE ADMINISTRATION OF THE IRON INDUSTRY IN ELEVENTH-CENTURY CHINA
Authors: Wagner Donald
Published: July 2002

Robert Hartwell's research in the early 1960's into the iron industry of Song China (960-1279) showed, using a variety of evidence, that the applications of iron expanded greatly in the early Song. He then calculated from tax data the annual iron production of China in the 11th century. This article argues that, while Hartwell's qualitative conclusions hold, his specific calculation of annual production is flawed: no reliable calculation is possible based on presently available sources. Les recherches de Robert Hartwell au début des années 1960 sur l'industrie du fer en Chine à l'époque Song (960-1279) ont montré, en exploitant un large éventail de faits évidents, que les demandes en fer ont fort augmenté dans la première période de l'époque Song. Il avait alors calculé, d'après les données tirées des registres d'imposition, la production annuelle de ce minerai en Chine au XIème siècle. Cet article relève que, si les conclusions qualitatives de Hartwell paraissent correctes, son évaluation de la production annuelle s'avère infondée: aucun calcul fiable ne peut être effectué en exploitant les données actuellement disponibles.
BEGINNING OF RELIGION
Authors: Wunn Ina
Published: July 2002

In the last two decades, the study of Palaeolithic religion has come to be of increasing concern to both scholars of the history of religion and archaeologists. In this paper the appropriateness of some recent views in the interpretation of the archaeological findings is re-evaluated. The conclusion of this study is that neither evidence of early ritual practises nor of belief in an afterlife can be endorsed. All relevant conceptions of that kind are either products of a certain mental climate at the time of the discovery of the fossils, or of ideologies. The results of palaeanthropological research prove that none of the early representatives of the genus Homo was capable of developing a complicated symbol system. Only in the middle Palaeolithic period Homo neanderthalensis had developed advanced intellectual abilities. But neither in connection with his hunting customs nor with his domestic activities can any traces of cult practice be found. Only the rare burials can be interpreted as a first sign of religious feelings. But there are no funeral rituals or funeral gifts. All assumptions that Neanderthal man already believed in an afterlife, are mere speculation. Theories of rituals during the lower and middle Palaeolithic belong to the realm of legend.
How Ordinary Cognition Informs Petitionary Prayer
Authors: Barrett Justin
Published: July 2002

Four studies (two experiments, a journaling study, and a questionnaire) conducted with American Protestant college students explored intuitions concerning petitionary prayer. Since Protestant theology offers little teaching on through which modes of causation God is most likely to act, it was hypothesized that intuitive causal cognition would be used to generate inferences regarding this aspect of petitionary prayer. Participants in these studies favored asking God to act via psychological causation over the biological and mechanistic domains. Further, in fictitious scenarios participants reported being more likely to ask a supercomputer or Superman to solve a problem through mechanistic intervention than God. These results are consistent with two previous findings: that God is often intuitively represented as having a single physical location (and it is not nearby); and psychosocial agents (such as God) are expected to require physical contact to act on non-agents.
EAVESDROPPING AND MATE CHOICE IN FEMALE FIGHTING FISH
Authors: Doutrelant Claire , McGregor Peter
Published: July 2002

Despite the fact that most communication occurs in the context of networks of several individuals, the consequences of considering communication as a network on individuals' capacity for gathering information on congeners has been little investigated. Eavesdropping is the behaviour of a receiver extracting information from an interaction in which it is taking no part. Due to the fact that signals used in aggressive interactions are assumed to be reliable, eavesdropping could be an effective way of evaluating the quality of potential mates. We conducted two experiments designed to discover if female fighting fish (Betta splendens) monitor aggressive interactions between two males and if information gained by eavesdropping is used in the initial stages of subsequent mate choice. We found that females that had seen the interaction visited the winner first more often and spent significantly more time near, looking at and displaying to the winner of the interaction. By contrast females that had not seen the interaction visited the loser first more often and did not behave significantly differently to winner and loser. Overall these results are consistent with the idea that in the initial stages of mate choice females eavesdrop, i.e. use information gathered from male-male displays.
Ultrastructure of the stoma in Heth mauriesi Adamson, 1982 (Rhigonematida: Hethidae)
Authors: Spiridonov Sergei , Yushin Vladimir
Published: July 2002

The structure of the highly modified cephalic end of females of Heth mauriesi (Rhigonematida, Hethidae) was studied under transmission and scanning electron microscopy. The specific muscle cells and cuticular differentiations responsible for regular movements of the Heth female cephalic end are described. An identification of separate regions of Heth mauriesi stoma with cheilostom, gymnostom and stegostom is proposed. Ultrastructure du stoma d 'Heth mauriesi Adamson, 1982 (Rhigonematida: Hethidae) - La structure de l'extrémité céphalique fortement modifiée des femelles de Heth mauriesi (Rhigonematida; Hethidae) est étudiée en microscopie électronique à balayage et de transmission. Les cellules musculaires spécifiques et les différentiations cuticulaires responsables des mouvements réguliers de l'extrémité céphalique des femelles de Heth sont décrites. Une identification des régions du stoma de Heth mauriesi , divisé en cheilostome, gymnostome et stégostome, est proposée.
Modelling water uptake in highly compacted bentonite in environmental sealing barriers
Authors: Gattermann J. , Wittke W. , Erichsen C.
Published: July 2002

Plans to close a German radioactive waste repository in rock salt include as one alternative the construction of a ‘Cross Section Closure (CSC)’ sealing barrier. The proposed material for the sealing barrier is highly compacted bentonite. To investigate the swelling behaviour of a highly compacted bentonite, a large number of laboratory tests were performed. In addition, large scale model tests were carried out to demonstrate the development of a nearly homogeneous and isotropic swelling pressure. The results of the large scale model tests were interpreted numerically based on the models for stress-strain behaviour and water uptake which are implemented in the finite element computer codes FEST03 and HYDOPO. The investigations show good agreement between the results of the model tests and the corresponding analyses and show that the theoretical models are capable of describing the behaviour of sealing structures based on highly compacted bentonite.
The reactivity of bentonites: a review. An application to clay barrier stability for nuclear waste storage
Authors: Meunier A. , Velde B. , Griffault L.
Published: July 2002

The thermal stability of bentonites is of particular interest for containment barriers in nuclear waste storage facilities. The kinetics of smectite reactions have been investigated under laboratory conditions for some time. The variables of time, chemical composition and temperature have been varied in these experiments. The results of such an assessment are that there are about as many kinetic values deduced from experiments as there are experiments.

Experiments using natural bentonite to study the smectite-to-illite conversion have been interpreted as a progressive transformation of montmorillonite to illite. It is highly probable that the initial reaction product is not illite but a high-charge beidellite + saponite + quartz mineral assemblage which gives, then, beidellite-mica interstratified mixed-layer minerals. These experimental reactions are noticeably different from those of diagenesis, being closer to reactions in hydrothermal systems.
Illite-smectites and the influence of burial diagenesis on the geochemical cycling of nitrogen
Authors: Schroeder P. A. , McLain A. A.
Published: July 2002

Fixed nitrogen in illite-smectites (I-S) has been measured for Miocene shales from a Gulf of Mexico oil well. Fixed N values for the <0.2 µm fraction increase with depth from 150 ppm (1000 m) to a maximum of 360 ppm (3841 m). This increase is coincident with illitization from 41% I in I-S to 75% I in I-S. Below 3841 m, fixed N values decrease to 190 ppm (4116 m) while I-S is maintained with a slight increase from 77 to 82%. The changes in fixed N with increasing illitization are consistent with the notion that illitization proceeds via both transformation and dissolution/ precipitation reaction mechanisms. The trend of decreasing fixed N in illitic I-S is compatible with surface-controlled crystal growth and Ostwald ripening mechanisms for illitization. The trend may also be linked to the timing of maximum NH] release from kerogen maturation during oil generation. The changing rate of NH+4 liberation from organic matter and multiple illitization reaction mechanisms can result in complex N geochemical cycling pathways throughout early diagenesis to metamorphism.
Low-temperature diagenetic illite-smectite in Lower Cambrian clays in North Estonia
Authors: Kirsimäe K. , Jøgensen P. , Kalm V.
Published: July 2002

Early Cambrian sediments on the East European platform in North Estonia, represented mostly by clays and silty clays, were deposited under normal marine conditions. The sediments were never affected by significant tectonic or thermal events after sedimentation 530 Ma ago, and the clays still have high water contents. The clay fraction, divided into four sub-fractions, was studied using X-ray methods and Rb/Sr dating. Decomposition of the XRD curves was used to quantify the amounts of illitic minerals in the sub-fractions. Dating by Rb/Sr showed that the finest fraction (<0.06 µm) was formed 50–150 Ma after sedimentation. The coarser fractions also contain considerable amounts of diagenetically formed minerals. This shows that neoformation of illitic minerals in marine sediments with high water/sediment ratios is a very important process even at temperatures <35°C.
Computational methods for the study of energies of cation distributions: applications to cation-ordering phase transitions and solid solutions
Authors: Bosenick A. , Dove M. T. , Myers E. R. , Palin E. J. , Sainz-Diaz C. I. , Guiton B. S. , Warren M. C. , Craig M. S. , Redfern S. A. T.
Published: July 2002

The structural and thermodynamic properties of minerals are strongly affected by cation site-ordering processes. We describe methods to determine the main interatomic interactions that drive the ordering process, which are based on parameterizing model Hamiltonians using empirical interatomic potentials and/or ab initio quantum mechanics methods. The methods are illustrated by a number of case study examples, including Al/Si ordering in aluminosilicates, Mg/Ca ordering in garnets, simultaneous Al/Si and Mg/Al ordering in pyroxenes, micas and amphiboles, and Mg/Al non-convergent ordering in spinel using only quantum mechanical methods.
Rare-earth element determination in minerals by electron-probe microanalysis: application of spectrum synthesis
Authors: Reed S. J. B. , Buckley A.
Published: July 2002

Electron-probe microanalysis (EPMA) is applicable to rare-earth elements (REE) in minerals with relatively high REE concentrations (e.g. hundreds of parts per million). However, given that each of the 14 REE has at least 12 X-ray lines in the L spectrum, finding peak-free regions for background measurement can be problematical. Also, measured peak intensities are liable to require correction for interferences. Hitherto, little attention has been paid to the optimisation of background offsets and the implications of the wide variation in REE distribution patterns in different minerals. The ‘Virtual WDS’ program, which enables complex multi-element spectra to be synthesised, has been used to refine the conditions used for different REE distributions. Choices include whether to use the Lβ1 rather than the Lα1 line, background offsets, and counting times for comparable relative precision. Correction factors for interferences affecting peak and background measurements have also been derived.
Zoning of chloritoid from kyanite-facies metapsammites, Alpi Apuane,
Italy
Authors: Franceschelli M. , Memmi I.
Published: July 2002

Chloritoid with significant Mg-Fe zoning occurs as lath-shaped porphyroblasts
and as clusters of subradiating crystals in the Triassic Verrucano metapsammite
(quartz + muscovite + chlorite + chloritoid ± kyanite) of the Massa Unit, Alpi
Apuane. Two main types of chloritoid zoning profiles were found. The first type is
characterised by gradual increase in Mg from core to rim of the porphyroblasts. In
the second type the Mg content is constant from the core to the inner rim, but
sharply decreases in the outer rim. Both types of zoning have been interpreted as
the result of prograde growth during the Alpine metamorphism. The temperature,
estimated using the chlorite-chloritoid thermometer, ranges from 467 to
560°C.
Induction of monocyte tissue factor expression by antibodies to heparin–platelet factor 4 complexes developed in heparin-induced thrombocytopenia
Authors: Pouplard Claire , Iochmann Sophie , Renard Benoit , Herault Olivier , Colombat Philippe , Amiral Jean , Gruel Yves
Published: July 2002

The pathogenesis of thrombosis in heparin-induced thrombocytopenia (HIT) was studied by investigating whether antibodies to heparin-platelet factor 4 (H-PF4) induced tissue factor (TF) synthesis by monocytes. Plasma from 5 patients with HIT containing IgG to H-PF4 was incubated with peripheral blood mononuclear cells without or with purified PF4 and heparin. Significant TF-dependent procoagulant activity (PCA) expressed by monocytes, measured with a factor Xa-based chromogenic assay, was induced after incubation of each HIT plasma sample. This monocyte PCA required the presence of PF4 and was inhibited by high concentrations of heparin. Furthermore, purified HIT IgG added to whole blood with PF4 and heparin also provoked significant synthesis of TF mRNA by monocytes, demonstrated by RT-PCR, and this effect was not observed with normal IgG. These findings strongly support the hypothesis that antibodies to PF4 developed in HIT trigger the production of tissue factor by monocytes, and this effect could account in vivo for hypercoagulability and thrombotic complications in affected patients.
Specific down-regulation of interleukin-12 signaling through induction of phospho-STAT4 protein degradation
Authors: Wang Kathy S. , Zorn Emmanuel , Ritz Jerome
Published: July 2002

Interleukin-12 (IL-12) plays a critical role in modulating the function of T lymphocytes and natural killer cells. IL-12 has potent antitumor effects in animal models, mediated primarily by its ability to enhance cytolytic activity and secretion of interferon-γ (IFN-γ). Unfortunately, the antitumor effect of IL-12 has not been demonstrated in clinical trials. Repeated administration of IL-12 in humans results in decreasing levels of IFN-γ secretion. To understand the mechanism underlying this loss of responsiveness, the effect of IL-12 on its own signaling in activated human T cells was examined. These experiments demonstrate that the level of the signal transducer and activator of transcription 4 (STAT4) protein, a critical IL-12 signaling component, is dramatically decreased 24 hours after IL-12 stimulation, whereas levels of STAT4 messenger RNA are not affected. The decrease of STAT4 protein appears to be due to specific degradation of phospho-STAT4, possibly through the proteasome degradation pathway. Decreased levels of STAT4 protein lead to decreased STAT4 DNA-binding activity and reduced proliferation and secretion of IFN-γ. This down-regulation of STAT4 is specific for IL-12 signaling, presumably owing to the prolonged activation of STAT4 induced by IL-12. IFN-α stimulation, which leads to transient phosphorylation of STAT4, does not reduce the level of STAT4 protein. These findings provide new insights into the regulation of IL-12 signaling in human T cells, where IL-12 promotes TH1 responses, but persistent IL-12 stimulation may also limit this response. The cellular depletion of STAT4 following prolonged IL-12 stimulation may also explain the loss of responsiveness following the repeated administration of IL-12 in clinical trials.
Cell surface receptors Ly-9 and CD84 recruit the X-linked lymphoproliferative disease gene product SAP
Authors: Sayós Joan , Martı́n Margarita , Chen Alice , Simarro Marı́a , Howie Duncan , Morra Massimo , Engel Pablo , Terhorst Cox
Published: July 2002

X-linked lymphoproliferative disease (XLP) is a rare immune disorder commonly triggered by infection with Epstein-Barr virus. Major disease manifestations include fatal acute infectious mononucleosis, B-cell lymphoma, and progressive dys-gammaglobulinemia. SAP/SH2D1A, the product of the gene mutated in XLP, is a small protein that comprises a single SH2 domain and a short tail of 26 amino acids. SAP binds to a specific motif in the cytoplasmic tails of the cell surface receptors SLAM and 2B4, where it blocks recruitment of the phosphatase SHP-2. Here it is reported that Ly-9 and CD84, 2 related glycoproteins differentially expressed on hematopoietic cells, also recruit SAP. Interactions between SAP and Ly-9 or CD84 were analyzed using a novel yeast 2-hybrid system, by COS cell transfections and in lymphoid cells. Recruitment of SAP is most efficient when the specific tyrosine residues in the cytoplasmic tails of Ly-9 or CD84 are phosphorylated. It is concluded that in activated T cells, the SAP protein binds to and regulates signal transduction events initiated through the engagement of SLAM, 2B4, CD84, and Ly-9. This suggests that combinations of dysfunctional signaling pathways initiated by these 4 cell surface receptors may cause the complex phenotypes of XLP.
Acquired activated protein C resistance is associated with lupus anticoagulants and thrombotic events in pediatric patients with systemic lupus erythematosus
Authors: Male Christoph , Mitchell Lesley , Julian James , Vegh Patricia , Joshua Penny , Adams Margaret , David Michelle , Andrew Maureen E.
Published: July 2002

Acquired activated protein C resistance (APCR) has been hypothesized as a possible mechanism by which antiphospholipid antibodies (APLAs) cause thrombotic events (TEs). However, available evidence for an association of acquired APCR with APLAs is limited. More importantly, an association of acquired APCR with TEs has not been demonstrated. The objective of the study was to determine, in pediatric patients with systemic lupus erythematosus (SLE), whether (1) acquired APCR is associated with the presence of APLAs, (2) APCR is associated with TEs, and (3) there is an interaction between APCR and APLAs in association with TEs. A cross-sectional cohort study of 59 consecutive, nonselected children with SLE was conducted. Primary clinical outcomes were symptomatic TEs, confirmed by objective radiographic tests. Laboratory testing included lupus anticoagulants (LAs), anticardiolipin antibodies (ACLAs), APC ratio, protein S, protein C, and factor V Leiden. The results revealed that TEs occurred in 10 (17%) of 59 patients. Acquired APCR was present in 18 (31%) of 58 patients. Acquired APCR was significantly associated with the presence of LAs but not ACLAs. Acquired APCR was also significantly associated with TEs. There was significant interaction between APCR and LAs in the association with TEs. Presence of both APCR and LAs was associated with the highest risk of a TE. Protein S and protein C concentrations were not associated with the presence of APLAs, APCR, or TEs. Presence of acquired APCR is a marker identifying LA-positive patients at high risk of TEs. Acquired APCR may reflect interference of LAs with the protein C pathway that may represent a mechanism of LA-associated TEs.
Direct visualization of cytomegalovirus-specific T-cell reconstitution after allogeneic stem cell transplantation
Authors: Cwynarski Kate , Ainsworth Jenni , Cobbold Mark , Wagner Simon , Mahendra Prem , Apperley Jane , Goldman John , Craddock Charles , Moss Paul A. H.
Published: July 2002

Cytomegalovirus (CMV) remains an important cause of morbidity and mortality after allogeneic stem cell transplantation (SCT), but cytotoxic T lymphocytes (CTL) may play a critical role in controlling CMV reactivation. Fluorescent HLA-peptide tetramers containing immunodominant peptides from CMV were used to prospectively monitor the recovery of CMV CTL in recipients of allogeneic transplants from siblings (n = 13) or unrelated donors (n = 11). In patients given allografts from a sibling when both the patient and donor were seropositive for CMV before SCT, recovery of CMV-specific CTL was rapid and reached up to 21% of all CD8+ T cells. Early reconstitution of CMV-specific immunity was not observed if either the donor or recipient was seronegative for CMV. In recipients of transplants from volunteer unrelated donors, recovery of CMV-specific CTL was delayed in comparison to that in recipients of transplants from siblings and no CTL were observed within the first 100 days after SCT. CTL numbers were increased after episodes of CMV reactivation but were suppressed by prednisolone therapy. Recovery of CMV-specific CTL to levels greater than 10 × 106/L was associated with protection from CMV disease. It was concluded that use of HLA-peptide tetramers to quantify CMV CTL is valuable for studying T-cell responses after allogeneic SCT. It should allow prediction of CMV reactivation in individual patients and assist in the development of adoptive T-cell immunotherapy.
Factors affecting thymic function after allogeneic hematopoietic stem cell transplantation
Authors: Weinberg Kenneth , Blazar Bruce R. , Wagner John E. , Agura Edward , Hill Brenna J. , Smogorzewska Monika , Koup Richard A. , Betts Michael R. , Collins Robert H. , Douek Daniel C.
Published: July 2002

Hematopoietic stem cell transplantation (HSCT) is followed by profound immunodeficiency. Thymic function is necessary for de novo generation of T cells after HSCT. Circulating CD45RA+ naive T-cell levels are predictive of antigen-specific T-cell responses in the absence of graft-versus-host disease (GVHD). These T cells may not represent recent thymic emigrants, since naive T cells may maintain this phenotype if not antigen-activated. To accurately measure thymic output after HSCT and determine the factors that influence thymic function, T-cell receptor excision circles (TRECs) were examined in CD4+ and CD8+ cells from a cross-section of patients following HSCT. TREC levels rose weeks after HSCT and could be detected in patients 6 years after HSCT. TREC levels correlated with the frequency of phenotypically naive T cells, indicating that such cells were not expanded progeny of naive T cells present in the donor graft. Chronic GVHD was the most important factor that predicted low TREC levels even years after HSCT. Patients with a history of resolved GVHD had decreased numbers of TREC, compared with those with no GVHD. Because few adults had no history of GVHD, it was not possible to determine whether age alone inversely correlated with TREC levels. Recipients of cord blood grafts had no evidence of decreased TREC induced by immunosuppressive prophylaxis drugs. Compared with unrelated donor grafts, recipients of matched sibling grafts had higher TREC levels. Collectively, these data suggest that thymopoiesis is inhibited by GVHD. Larger studies will be needed to determine the independent contributions of age and preparative regimen to post-transplant thymopoietic capacity.