bluuebunny/crossref_metadata_2025 huggingface dataset:
Attention Mechanisms in Visual Search—An fMRI Study
Authors: Leonards Ute , Sunaert Stefan , Van Hecke Paul , Orban Guy A.
Published: July 2002

The human visual system is usually confronted with many different objects at a time, with only some of them reaching consciousness. Reaction-time studies have revealed two different strategies by which objects are selected for further processing: an automatic, efficient search process, and a conscious, so-called inefficient search [Treisman, A. (1991). Search, similarity, and integration of features between and within dimensions. Journal of Experimental Psychology: Human Perception and Performance, 17, 652-676; Treisman, A., & Gelade, G. (1980). A feature integration theory of attention. Cognitive Psychology, 12, 97-136; Wolfe, J. M. (1996). Visual search. In H. Pashler (Ed.), Attention. London: University College London Press]. Two different theories have been proposed to account for these search processes. Parallel theories presume that both types of search are treated by a single mechanism that is modulated by attentional and computational demands. Serial theories, in contrast, propose that parallel processing may underlie efficient search, but inefficient searching requires an additional serial mechanism, an attentional “spotlight” (Treisman, A., 1991) that successively shifts attention to different locations in the visual field. Using functional magnetic resonance imaging (fMRI), we show that the cerebral networks involved in efficient and inefficient search overlap almost completely. Only the superior frontal region, known to be involved in working memory [Courtney, S. M., Petit, L., Maisog, J. M., Ungerleider, L. G., & Haxby, J. V. (1998). An area specialized for spatial working memory in human frontal cortex. Science, 279, 1347-1351], and distinct from the frontal eye fields, that control spatial shifts of attention, was specifically involved in inefficient search. Activity modulations correlated with subjects' behavior best in the extrastriate cortical areas, where the amount of activity depended on the number of distracting elements in the display. Such a correlation was not observed in the parietal and frontal regions, usually assumed as being involved in spatial attention processing. These results can be interpreted in two ways: the most likely is that visual search does not require serial processing, otherwise we must assume the existence of a serial searchlight that operates in the extrastriate cortex but differs from the visuospatial shifts of attention involving the parietal and frontal regions.
Supramodal Effects of Covert Spatial Orienting Triggered by Visual or Tactile Events
Authors: Macaluso E. , Frith C. D. , Driver J.
Published: July 2002

Event-related functional magnetic resonance imaging was used to identify brain areas involved in spatial attention and determine whether these operate unimodally or supramodally for vision and touch. On a trial-by-trial basis, a symbolic auditory cue indicated the most likely side for the subsequent target, thus directing covert attention to one side. A subsequent target appeared in vision or touch on the cued or uncued side. Invalidly cued trials (as compared with valid trials) activated the temporo-parietal junction and regions of inferior frontal cortex, regardless of target modality. These brain areas have been associated with multimodal spatial coding in physiological studies of the monkey brain and were linked to a change in the location that must be attended to in the present study. The intraparietal sulcus and superior frontal cortex were also activated in our task, again, regardless of target modality, but did not show any specificity for invalidly cued trials. These results identify a supramodal network for spatial attention and reveal differential activity for inferior circuits involving the temporo-parietal junction and inferior frontal cortex (specific to invalid trials) versus more superior intraparietal-frontal circuits (common to valid and invalid trials).
Dissociation of Habit-Learning in Parkinson's and Cerebellar Disease
Authors: Witt K. , Nuhsman A. , Deuschl G.
Published: July 2002

Damage to the medial-temporal region is known to result in declarative (explicit) memory deficits but nondeclarative (implicit) memory is largely unaffected by such lesions. Earlier studies have shown that some forms of implicit learning depend on cerebellar circuits but remain preserved following affections of the basal ganglia circuits. It is unknown which forms of implicit learning persist in patients with cerebellar pathology but are affected after basal ganglia lesions. Therefore, we determined if a test sensitive for habit-learning (probabilistic classification task) resulted in normal values for patients with cerebellar disease but resulted in affected results in patients with Parkinson's disease (PD). To this end, 23 patients with PD, 16 patients with familial or idiopathic cerebellar degeneration (CD), and 20 controls were tested for habit-learning. There was no impairment of patients with CD for the early learning period but there was abnormal learning in the PD group. For a later learning period, the patients with the PD showed improved performance. We conclude that the probabilistic learning task is an implicit, nonmotor learning task which is sensitive for basal ganglia pathology but remains unaffected in the case of cerebellar pathology. Such a test may be of special interest for the detection and possible neurobehavioral treatment of cognitive and motor deficits.
The Neural Circuitry Involved in the Reading of German Words and Pseudowords: A PET Study
Authors: Hagoort Peter , Indefrey Peter , Brown Colin , Herzog Hans , Steinmetz Helmuth , Seitz Rüdiger J.
Published: July 2002

Silent reading and reading aloud of German words and pseudowords were used in a PET study using (15O) butanol to examine the neural correlates of reading and of the phonological conversion of legal letter strings, with or without meaning. The results of 11 healthy, right-handed volunteers in the age range of 25 to 30 years showed activation of the lingual gyri during silent reading in comparison with viewing a fixation cross. Comparisons between the reading of words and pseudo-words suggest the involvement of the middle temporal gyri in retrieving both the phonological and semantic code for words. The reading of pseudowords activates the left inferior frontal gyrus, including the ventral part of Broca's area, to a larger extent than the reading of words. This suggests that this area might be involved in the sublexical conversion of orthographic input strings into phonological output codes. (Pre)motor areas were found to be activated during both silent reading and reading aloud. On the basis of the obtained activation patterns, it is hypothesized that the articulation of high-frequency syllables requires the retrieval of their concomitant articulatory gestures from the SMA and that the articulation of low-frequency syllables recruits the left medial premotor cortex.
Discriminant Pattern Recognition Using Transformation-Invariant Neurons
Authors: Sona Diego , Sperduti Alessandro , Starita Antonina
Published: July 2002

To overcome the problem of invariant pattern recognition, Simard, LeCun, and Denker (1993) proposed a successful nearest-neighbor approach based on tangent distance, attaining state-of-the-art accuracy. Since this approach needs great computational and memory effort, Hastie, Simard, and Säckinger (1995) proposed an algorithm (HSS) based on singular value decomposition (SVD), for the generation of nondiscriminant tangent models. In this article we propose a different approach, based on a gradient-descent constructive algorithm, called TD-Neuron, that develops discriminant models. We present as well comparative results of our constructive algorithm versus HSS and learning vector quantization (LVQ) algorithms. Specifically, we tested the HSS algorithm using both the original version based on the two-sided tangent distance and a new version based on the one-sided tangent distance. Empirical results over the NIST-3 database show that the TD-Neuron is superior to both SVD- and LVQ-based algorithms, since it reaches a better trade-off between error and rejection.
Nonholonomic Orthogonal Learning Algorithms for Blind Source Separation
Authors: Amari Shun-ichi , Chen Tian-Ping , Cichocki Andrzej
Published: July 2002

Independent component analysis or blind source separation extracts independent signals from their linear mixtures without assuming prior knowledge of their mixing coefficients. It is known that the independent signals in the observed mixtures can be successfully extracted except for their order and scales. In order to resolve the indeterminacy of scales, most learning algorithms impose some constraints on the magnitudes of the recovered signals. However, when the source signals are nonstationary and their average magnitudes change rapidly, the constraints force a rapid change in the magnitude of the separating matrix. This is the case with most applications (e.g., speech sounds, electroencephalogram signals). It is known that this causes numerical instability in some cases. In order to resolve this difficulty, this article introduces new nonholonomic constraints in the learning algorithm. This is motivated by the geometrical consideration that the directions of change in the separating matrix should be orthogonal to the equivalence class of separating matrices due to the scaling indeterminacy. These constraints are proved to be nonholonomic, so that the proposed algorithm is able to adapt to rapid or intermittent changes in the magnitudes of the source signals. The proposed algorithm works well even when the number of the sources is overestimated, whereas the existent algorithms do not (assuming the sensor noise is negligibly small), because they amplify the null components not included in the sources. Computer simulations confirm this desirable property.
Intrinsic Stabilization of Output Rates by Spike-Based Hebbian Learning
Authors: Kempter Richard , Gerstner Wulfram , Hemmen J. Leo van
Published: July 2002

We study analytically a model of long-term synaptic plasticity where synaptic changes are triggered by presynaptic spikes, postsynaptic spikes, and the time differences between presynaptic and postsynaptic spikes. The changes due to correlated input and output spikes are quantified by means of a learning window. We show that plasticity can lead to an intrinsic stabilization of the mean firing rate of the postsynaptic neuron. Subtractive normalization of the synaptic weights (summed over all presynaptic inputs converging on a postsynaptic neuron) follows if, in addition, the mean input rates and the mean input correlations are identical at all synapses. If the integral over the learning window is positive, firing-rate stabilization requires a non-Hebbian component, whereas such a component is not needed if the integral of the learning window is negative. A negative integral corresponds to anti-Hebbian learning in a model with slowly varying firing rates. For spike-based learning, a strict distinction between Hebbian and anti-Hebbian rules is questionable since learning is driven by correlations on the timescale of the learning window. The correlations between presynaptic and postsynaptic firing are evaluated for a piecewise-linear Poisson model and for a noisy spiking neuron model with refractoriness. While a negative integral over the learning window leads to intrinsic rate stabilization, the positive part of the learning window picks up spatial and temporal correlations in the input.
The Effects of Spike Frequency Adaptation and Negative Feedback on the Synchronization of Neural Oscillators
Authors: Ermentrout Bard , Pascal Matthew , Gutkin Boris
Published: July 2002

There are several different biophysical mechanisms for spike frequency adaptation observed in recordings from cortical neurons. The two most commonly used in modeling studies are a calcium-dependent potassium current Iahp and a slow voltage-dependent potassium current, Im. We show that both of these have strong effects on the synchronization properties of excitatorily coupled neurons. Furthermore, we show that the reasons for these effects are different. We show through an analysis of some standard models, that the M-current adaptation alters the mechanism for repetitive firing, while the after hyperpolarization adaptation works via shunting the incoming synapses. This latter mechanism applies with a network that has recurrent inhibition. The shunting behavior is captured in a simple two-variable reduced model that arises near certain types of bifurcations. A one-dimensional map is derived from the simplified model.
“God Is a Talking Horse”: Dementia and the Performance of Self
Authors: Basting Anne Davis
Published: July 2002

How can the voices of those with cognitive impairments be heard? The director of a creative storytelling project with people suffering from Alzheimer's and related disorders relates how the undertaking has affected patients, staff, and public audiences.
Reverend Billy: Preaching, Protest, and Postindustrial Flânerie
Authors: Lane Jill
Published: July 2002

Reverend Billy rages against the noxious effects of consumerism, transnational capital, and the privatization of public space and culture. His “Church of Stop Shopping” represents a fascinating departure for new left theatre in the era of global capital.
Virtual Environments and the Enhancement of Spatial Behavior: Towards a Comprehensive Research Agenda
Authors: Durlach Nat , Allen Gary , Darken Rudy , Garnett Rebecca Lee , Loomis Jack , Templeman Jim , Wiegand Thomas E. von
Published: July 2002

There is currently much research activity involving virtual environments (VEs) and spatial behavior (spatial perception, cognition, and performance). After some initial remarks describing and categorizing the different types of research being conducted on VEs and spatial behavior, discussion in this Forum paper focuses on one specific type, namely, research concerned with the use of VE technology for training spatial behavior in the real world. We initially present an overview of issues and problems relevant to conducting research in this area, and then, in the latter portion of the paper, present an overview of the research that we believe needs to be done in this area.

We have written this paper for the forum section of Presence because, despite its length, it is essentially an opinion piece. Our aim here is not to report the results of research in our own laboratory nor to review the literature, as other available papers already serve these goals. Rather, the primary purpose of this paper is to stimulate open discussion about needed future research. In general, we believe that such a discussion can serve the research establishment as much as reports of completed work.
Human Motion Capture Driven by Orientation Measurements
Authors: Molet Tom , Boulic Ronan , Thalmann Daniel
Published: July 2002

Motion-capture techniques are rarely based on orientation measurements for two main reasons: (1) optical motion-capture systems are designed for tracking object position rather than their orientation (which can be deduced from several trackers), (2) known animation techniques, like inverse kinematics or geometric algorithms, require position targets constantly, but orientation inputs only occasionally. We propose a complete human motion-capture technique based essentially on orientation measurements. The position measurement is used only for recovering the global position of the performer. This method allows fast tracking of human gestures for interactive applications as well as high rate recording. Several motion-capture optimizations, including the multijoint technique, improve the posture realism. This work is well suited for magnetic-based systems that rely more on orientation registration (in our environment) than position measurements that necessitate difficult system calibration.
Asymmetry of Configuration Space Induced by Unequal Crossover: Implications for a Mathematical Theory of Evolutionary Innovation
Authors: Shpak Max , Wagner Günter P.
Published: July 2002

Evolution can be regarded as the exploration of genetic or morphological state space by populations. In traditional models of population and quantitative genetics, the state space can be formally represented as a configuration space with clearly defined concepts of neighborhood and distance, defined by the action of variational operators such as mutation and/or recombination. In this paper, we describe a process where no genetic configuration space closure (and hence, no non-arbitrary notion of distance and neighborhood) exists. The process is gene duplication by means of unequal crossover, which we regard as an example of an “innovation” process that changes the state space of the system rather than exploring a closed state space. We assert that such processes are qualitatively distinct from representations of the adaptation process, which occur on regular configuration spaces.
Agent-Based Computational Economics: Growing Economies From the Bottom Up
Authors: Tesfatsion Leigh
Published: July 2002

Agent-based computational economics (ACE) is the computational study of economies modeled as evolving systems of autonomous interacting agents. Thus, ACE is a specialization of economics of the basic complex adaptive systems paradigm. This study outlines the main objectives and defining characteristics of the ACE methodology and discusses similarities and distinctions between ACE and artificial life research. Eight ACE research areas are identified, and a number of publications in each area are highlighted for concrete illustration. Open questions and directions for future ACE research are also considered. The study concludes with a discussion of the potential benefits associated with ACE modeling, as well as some potential difficulties.
The View From Elsewhere: Perspectives on ALife Modeling
Authors: Wheeler Michael , Bullock Seth , Paolo Ezequiel Di , Noble Jason , Bedau Mark , Husbands Philip , Kirby Simon , Seth Anil
Published: July 2002

Many artificial life researchers stress the interdisciplinary character of the field. Against such a backdrop, this report reviews and discusses artificial life, as it is depicted in, and as it interfaces with, adjacent disciplines (in particular, philosophy, biology, and linguistics), and in the light of a specific historical example of interdisciplinary research (namely cybernetics) with which artificial life shares many features. This report grew out of a workshop held at the Sixth European Conference on Artificial Life in Prague and features individual contributions from the workshop's eight speakers, plus a section designed to reflect the debates that took place during the workshop's discussion sessions. The major theme that emerged during these sessions was the identity and status of artificial life as a scientific endeavor.
Evolutionary Body Building: Adaptive Physical Designs for Robots
Authors: Funes Pablo , Pollack Jordan
Published: July 2002

Creating artificial life forms through evolutionary robotics faces a “chicken and egg” problem: Learning to control a complex body is dominated by problems specific to its sensors and effectors, while building a body that is controllable assumes the pre-existence of a brain.

The idea of coevolution of bodies and brains is becoming popular, but little work has been done in evolution of physical structure because of the lack of a general framework for doing it. Evolution of creatures in simulation has usually resulted in virtual entities that are not buildable, while embodied evolution in actual robotics is constrained by the slow pace of real time.

The work we present takes a step in addressing the problem of body evolution by applying evolutionary techniques to the design of structures assembled out of elementary components that stick together. Evolution takes place in a simulator that computes forces and stresses and predicts stability of three-dimensional brick structures. The final printout of our program is a schematic assembly, which is then built physically. We demonstrate the functionality of this approach to robot body building with many evolved artifacts.
Inferences and Indices: Evaluating the Effectiveness of International Environmental Regimes
Authors: Young Oran R.
Published: July 2002

Institutionalists commonly assume that the operation of regimes accounts for much of what happens in international society. Realists and neorealists, by contrast, typically regard institutions as epiphenomena that reflect deeper forces in international society and that can be expected to change when the deeper forces change. As is so often the case in debates of this nature, the truth no doubt lies somewhere between these polar perspectives. To identify the signal of the effects of institutions and especially to track variations in the strength of this signal, we need to find ways to draw clearcut inferences about the causal links between institutions and collective outcomes at the international level. Ideally, we should also devise an integrated index of regime effectiveness that would allow us to compare and contrast different regimes or the same regimes over time in terms of their effectiveness. This article offers a critical review of the leading efforts to develop useful inferences and indices with particular reference to international environmental regimes. It concludes that our efforts in this realm to date have yielded only modest—though hardly trivial—results. Yet we are far from exhausting the available analytic resources in this field, and there is much that can be done to improve inferences and indices in this important area of research in the future.
Cultured Killers: Creating and Representing Foxhounds
Authors: Marvin Garry
Published: July 2002

This article concerns the related ideas of "presentation" and "representation" with regard to animals and suggests that the prefix "re" indicates a directing agent with its own concerns about the nature and status of animal presence. It further suggests that the representation of animals is perhaps always an expression of human concerns, desires, and imaginings. As with other domesticated nonhuman animals, foxhounds are not present in the world to fulfill their own purposes but there to fulfill these human desires and imaginings and are celebrated as the realization of a complex engagement of humans with the world of animals. The foxhound is central to English foxhunting and is given cultural meaning because of this context.The article offers a close anthropological interpretation of the production of this animal - a complex, cultural creation based on a canine form.
PRIESTLY DYNAMIC HOLINESS AND DEUTERONOMIC STATIC HOLINESS
Authors: Regev Eyal
Published: July 2002

There are several diverences between the laws of cult and the pre-supposition regarding ritual and impurity in the Priestly Schools and the book of Deuteronomy. Both sources regard the relationship between the priest and the laity and the access to the sacred in diverent ways. The fundamental reason that lies at the base of these diverent cultic systems is distinct perceptions of holiness. The diverence is not in the concept of what is holy and what is profane, but rather in the understanding of what holiness really is. The Priestly Schools view holiness as dynamic, sensitive and dangerous, and maintain that the access to the sacred should be limited. In contrast, in Deuteronomy holiness is static, and the access to the sacred is far less restricted, since it is not dangerous or threatening. In other words, in Deuteronomy holiness is not an active entity but a status. These opposing world-views regarding the holy are actually related to general conceptions about the character of the relationship between humans and nature on the one hand, and between man and God on the other hand.
PROGRESS, PURPOSE AND CONTINGENCY: A RESPONSE TO THOMAS BERRY'S THE GREAT WORK: OUR WAY INTO THE FUTURE
Authors: Goodenough Ursula
Published: July 2002

There is much to applaud in Berry's book The Great Work. However this response questions the framework of purposive, hierarchical progress of the universe which is outlined in Berry's narrative. It suggests that an alternative view is to see cosmic change as non-progressive and contingent - and that this perspective encourages the affirmation of wonder at the universe.
COSMOLOGICAL ETHICS? THE GREAT WORK
Authors: Eaton Heather
Published: July 2002

Are we indeed ethically destitute, as suggests Thomas Berry? We are in an era of a barrage of ethical discourses, and yet Berry claims that are unable to respond to the radically new problematique facing any human communities. This article explores the idea of the macro and micro dimensions of ethics, noting the conventional reference points as well as the change of reference points Berry suggests. The discussion dwells on these two dimensions, and the interplay between them. The article also suggests that the religious/spiritual experiences of awakening, and presently to the cosmos, could also be considered as a source for ethics.
Folkbiology doesn't Come from Folkpsychology: Evidence from Yukatek Maya in Cross-Cultural Perspective
Authors: Atran Scott , Medin Douglas , Lynch Elizabeth , Vapnarsky Valentina , Ucan Ek' Edilberto , Sousa Paulo
Published: July 2002

Nearly all psychological research on basic cognitive processes of category formation and reasoning uses sample populations associated with large research institutions in technologically-advanced societies. Lopsided attention to a select participant pool risks biasing interpretation, no matter how large the sample or how statistically reliable the results. The experiments in this article address this limitation. Earlier research with urban-USA children suggests that biological concepts are (1) thoroughly enmeshed with their notions of naive psychology, and (2) strikingly human-centered. Thus, if children are to develop a causally appropriate model of biology, in which humans are seen as simply one animal among many, they must undergo fundamental conceptual change. Such change supposedly occurs between 7 and 10 years of age, when the human-centered view is discarded. The experiments reported here with Yukatek Maya speakers challenge the empirical generality and theoretical importance of these claims. Part 1 shows that young Maya children do not anthropocentrically interpret the biological world. The anthropocentric bias of American children appears to owe to a lack of cultural familiarity with non-human biological kinds, not to initial causal understanding of folkbiology as such. Part 2 shows that by age of 4-5 (the earliest age tested in this regard) Yukatek Maya children employ a concept of innate species potential or underlying essence much as urban American children seem to, namely, as an inferential framework for understanding the affiliation of an organism to a biological species, and for projecting known and unknown biological properties to organisms in the face of uncertainty. Together, these experiments indicate that folkpsychology cannot be the initial source of folkbiology. They also underscore the possibility of a species-wide and domain-specific basis for acquiring knowledge about the living world that is constrained and modified but not caused or created by prior non-biological thinking and subsequent cultural experience.
Localization of hydrogen peroxide during the defence response of Arabidopsis thaliana against the plant-parasitic nematode Heterodera glycines
Authors: Waetzig Georg , Sobczak Miroslaw , Grundler Florian
Published: July 2002

Hydrogen peroxide (H2O2) production during the infection of Arabidopsis thaliana by the soybean cyst nematode Heterodera glycines was detected histochemically by the reaction of H2O2 with cerium chloride producing four different patterns of electron-dense precipitates of cerium perhydroxides. As A. thaliana is not a regular host of H. glycines, the defence response is considerable, but does not completely inhibit the development of the nematode. H2O2 was produced not only by cells mechanically damaged during invasion and feeding site induction by the nematode, but also by cells surrounding developing syncytia and cells which were neither in contact with the nematode nor with the syncytium. Die Lokalisation von Peroxid wahrend der Abwehrreaktion von Arabidopsis thaliana gegen den pflanzenparasitaren Nematoden Heterodera glycines - Die Bildung von Wasserstoffperoxid (H2O2) im Rahmen der Infektion von Arabidopsis thaliana durch den Sojabohnen-Zystennematoden Heterodera glycines wurde histochemisch durch die Reaktion von H2O2 mit Cerchlorid nachgewiesen, wobei vier verschiedene Muster elektronendichter Prazipitate von Cerperhydroxiden gebildet wurden. Da A. thaliana kein regularer Wirt von H. glycines ist, kommt es zu einer betrachtlichen Abwehrreaktion, die jedoch die Entwicklung des Nematoden nicht vollstandig verhindert. H2O2 wurde nicht nur von Zellen produziert, die im Laufe des Eindringens und der Induktion des Nahrzellensystems durch den Nematoden mechanisch beschadigt worden waren, sondern auch von Zellen, die sich entwickelnde Syncytien umgaben und von Zellen, die weder mit dem Nematoden noch mit dem Syncytium in Kontakt standen.
FIELDNOTES ON STAGING AND TRANSFORMING HISTORICAL GRIEVANCES: FROM CULTURAL MEMORY TO A RECONSTRUCTABLE FUTURE
Authors: Apprey Maurice
Published: July 2002

A journey from cultural memory through recall to transformation of historical grievances is elucidated with the aid of phenomenological thought. The context for this study is a conflict resolution project undertaken by the Center for the Study of Mind and Human Interaction of the University of Virginia. Russians and Estonians of Klooga participated in a group meeting aimed at resolving ethnonational conflict. This meeting is described, and the potential of phenomenology in an interdisciplinary approach to conflict resolution is explored.
Reservoir quality and its relationship to facies and provenance in Middle to Upper Jurassic sequences, northeastern North Sea
Authors: Ramm M.
Published: July 2002

Close relationships are demonstrated between reservoir quality, lithofacies, provenance and burial history in the Jurassic Brent and Viking Groups in the Norwegian North Sea. Porosity and permeability are strongly and systematically related to the initial texture and composition of the sandstones. Porosity variations are related to the amount of compaction, which is more severe in matrix-rich than in clean facies, and quartz cementation, which is most important in clean facies. Permeability variations are related to porosity and facies-controlled variations in grain size, and abundance and texture of intergranular fines. Illitization of early diagenetic kaolins require K, which is derived mainly from dissolution of K-feldspar. Sediments were sourced from K-feldspar- poor provenances during the maximum progradation of the Brent Group, and sandstones deposited at this time are less exposed to illitization and have better permeability at deep burial than reservoir sandstones that initially contained more K-feldspar.
Sorption of chlormequat on montmorillonite as affected by dissolved copper. Influence of background electrolytes
Authors: Maqueda C. , Morillo E.
Published: July 2002

In this paper, the role of Cu in the adsorption of the cationic pesticide chlormequat (CCC) on montmorillonite is studied. The adsorption of CCC was measured in various media, e.g. water and aqueous solutions of NaCl, CaCl2 and Ca(NO3)2 at the same ionic strength (I= 0.01 mol l–1). The retention of CCC on montmorillonite in aqueous media is due principally to a cationic exchange process with inorganic cations which saturate the interlamellar positions on this mineral. However, the amount of inorganic cations liberated from montmorillonite was ∼15% less than the amount of CCC adsorbed. This indicates that not all the pesticide was adsorbed through cation exchange.

The adsorption of CCC in aqueous media decreased in the presence of a heavy metal, compared with metal-free treatment. This behaviour indicates competition between the two cations for interlamellar positions. The adsorption of CCC in the presence of Cu also decreased in electrolyte media with the effect being highest in the presence of Ca electrolytes. The maximum CCC diminution was ∼30%. However, the isotherms derived in CaCl2 and Ca(NO3)2 media at different Cu concentrations were close to each other, indicating that Ca from background electrolyte exerts greater competition than Cu for montmorillonite planar positions.
Smectite formation in rhyolitic obsidian as inferred by microscopic (SEM-TEM-AEM) investigation
Authors: Fiore S. , Huertas F. J. , Huertas F. , Linares J.
Published: July 2002

Experimental alteration of a rhyolitic obsidian by solutions containing variable concentrations of Mg was carried out at 100, 150 and 200°C, for 30, 60 and 90 days, to investigate the mechanism of smectite formation. The smectite exhibits two distinct morphologies: (1) small flakes (aggregates of a few crystals); and (2) large flakes (massive groups). The small flakes are the earlier alteration products. Both morphological types have distinct chemical compositions: the smallest laminae are dioctahedral and contain more Fe, whereas the particles from the rose-shaped aggregates contain Mg and are trioctahedral. Intermediate compositions have been observed between the extreme compositions.

It is suggested that the two morphologies are the result of two distinct genetic processes: (1) the small flakes (Fe-rich smectite) form by solid state rearrangements of the hydrated external layer of glass and/or via the formation of domains within the glass; (2) the rose-shaped aggregates (Mg-rich smectite) form by precipitation from solution.
Clay mineralogy of the Tertiary sediments in the Internal Subbetic of Málaga Province, S Spain: implications for geodynamic evolution
Authors: Alcalá-García F. J. , Martín-Martín M. , López-Galindo A.
Published: July 2002

The clay mineralogy of a set of Tertiary marine sediments from the Internal Subbetic of the Betic External Zone was examined. Two types of sedimentary environment were distinguished: a platform environment consisting of limestones, marls, organogenic limestones, conglomerates and silexites distributed heterogeneously in time and space; and deep environments, where the sedimentation consisted of marls, marly limestones, marly clays and silexites, with no sedimentary gap. A third group of sediments studied belongs to the Águila Complex, with mineralogical and stratigraphic characteristics very similar to the platform sediments. This third type of sediment is found in the sediments of the Campo de Gibraltar Complex as large, disperse blocks resulting from tectonic activity. A very similar mineral association was observed in all three domains, consisting of smectite, illite, mixed-layer I-S, kaolinite and lesser amounts of palygorskite and chlorite. Materials mainly derive from the erosion of Mesozoic sediments, and sedimentation was controlled by the compressive tectonics of the region.
Pressure-induced transformations in deep mantle and core minerals
Authors: Hemley R. J. , Mao H. K. , Gramsch S. A.
Published: July 2002

Recent experimental and theoretical studies provide new insight into the variety of high-pressure transformations in minerals that comprise the Earth’s deep mantle and core. Representative examples of reconstructive, displacive, electronic and magnetic transformations studied by new diamond-anvil cell techniques are examined. Despite reports for various transitions in (Mg,Fe)SiO3-perovskite, the stability field of the orthorhombic phase expands relative to magnesiowüstite + SiO2 with increasing pressure and temperature. The partitioning of Fe and Mg between Mg-rich silicate perovskite magnesiowüstite depends strongly on pressure, temperature, bulk Fe/Mg ratio, and ferric iron content. The soft-mode transition in SiO2 from the rutile- to CaCl2-type structure, originally documented by X-ray powder diffraction, Raman scattering, and first-principles theory has been explored in detail by single crystal diffraction, and transitions to higher-pressure forms have been examined. The effect of H on the transformations of various nominally anhydrous phases and transitions in dense hydrous Mg-silicates are also examined. New studies of the phase diagram of FeO include the transition to rhombohedral and higher-pressure NiAs polymorphs, and provide prototypical examples of coupled structural, electronic, and magnetic transitions. High-spin/low-spin transitions in FeO have been examined by high-resolution X-ray emission spectroscopy to 150 GPa, and the results are compared with similar studies of Fe2O3 and FeS. Finally, laser-heating studies to above 150 GPa and 2500K show that (hcp) ε-Fe has a large P-T stability field. Radial XRD measurements carried out at room temperature to 220 GPa have constrained the elasticity, rheology and sound velocities of ε-Fe at core pressures.
Strontian fluoro-magnesiohastingsite in Alban Hills lavas (Central Italy): constraints on crystallization conditions
Authors: Gaeta M. , Freda C.
Published: July 2002

A magmatic calcic amphibole (M4Ca≥1.50) characterized by large Sr and F contents (SrO>1 wt.%, F>2.5 wt.%) is described. According to the crystal-chemical formula, the amphibole can be classified as a strontian fluoro-magnesiohastingsite and the presence of Sr cations in theAsites is suggested. The amphibole occurs in the groundmass of ultrapotassic lavas from the Alban Hills Volcanic District (Central Italy). This peculiar chemical composition is due to the lavas' groundmass compositional trend occurring under low silica-activity conditions. We suggest that the occurrence of F amphiboles allows us to consider the Alban Hills Volcanic District magmas to be as rich in F as other ultrapotassic magmas.
Pararsenolamprite, a new polymorph of native As, from the Mukuno mine, Oita Prefecture, Japan
Authors: Matsubara S. , Miyawaki R. , Shimizu M. , Yamanaka T.
Published: July 2002

Pararsenolamprite, the third polymorph of native As, is found at the Mukuno mine, Oita Prefecture, Japan. It is orthorhombic, Pmn21 or P21nm, a = 3.633(2), b = 10.196(2), c= 10.314(2)Å, Z = 18. The seven strongest lines in the X-ray powder diffraction pattern are: 5.17 (100) (002), 4.60 (24) (012), 3.259 (58) (013), 2.840 (27) (032), 2.580 (22) (004), 2.299 (23) (024), and 1.794 (26) (105). Electron microprobe analysis gives As 91.89, Sb 7.25, S 0.48, total 99.62 wt.% (mean of 8), and lead to the empirical formula, As0.96Sb0.03S0.01. It is lead grey in colour and opaque with metallic lustre and black streak. It is sectile and brittle with perfect cleavage on [001]. The VHN25 is 66–91 kg/mm2, corresponding to 2–2.5 in Mohs' hardness scale. The measured and calculated densities are 5.88(5) g/cm3 and 6.01 g/cm3, respectively. In reflected plane-polarized light in air, it is white with a slightly greenish blue tint. Anisotoropy is strong, dark brown to dark greenish grey. Bireflectance is distinct; parallel to elongation it is creamy; perpendicular to elongation it is brown, grey and green. Internal reflections are absent. The reflectance spectra are tabulated in the text.

Pararsenolamprite occurs as euhedral crystals in close association with arsenic, stibnite and quartz in a Sb-As-Ag-Au-bearing quartz vein cutting altered Neogene andesite from the Mukuno mine. It forms radial or parallel aggregates of bladed cystals up to 0.8 mm in length.
Exhumation of metamorphic terranes: introduction
Authors: Cuthbert S. J. , Ballévre M.
Published: July 2002

Ever since the landmark paper by England and Richardson (1977) it has been clear that metamorphic rocks are not merely passively advected towards the surface during unroofing, but respond in a dynamic and interactive way to the mechanisms and rates of exhumation. England and Richardson based their modelling upon erosion-driven exhumation dominated by fluvial processes in mid-latitude climates. Since then a variety of mechanisms has been identified, mostly emphasizing tectonic mechanisms including extensional tectonics (e.g. Platt, 1996), tectonic extrusion (Chemenda et al., 1996; Hynes et al., 1996; Thompson et al., 1997) and ‘gravity currents’ (Wernicke and Getty, 1997). It has also become apparent that exhumation itself may be strongly influenced by metamorphic processes. For example, changes in petrophysical properties such as density may dramatically affect the buoyancy of rock masses and hence alter the driving forces for exhumation (Bousquet et al., 1997). The evolution of fluids or melts may create weak zones in the crust and enhance ductile or brittle deformation and shear zone development (e.g. Austrheim, 1998).
Compositions and formation conditions of fluid inclusions in emerald from the Maria deposit (Mozambique)
Authors: Vapnik Ye. , Moroz I.
Published: July 2002

The compositions of fluid inclusions hosted in emerald and quartz (the Maria deposit, Mozambique) were studied using microthermometric and Raman microprobe techniques. The fluid inclusions in the emerald contain fluids within the Na-Ca-Mg-(HCO3)−-(CO3)2−-Cl-H2O system saturated in carbonic acid brines. Nahcolite is a main daughter solid phase within the fluid inclusions. The mean nahcolite and NaCl contents are 25 and 5 wt.%, respectively. Mg-calcite, magnesite, calcite and aragonite are also identified as daughter phases in the fluid inclusions. Many fluid inclusions show necked-down appearance. Groups of nahcolite crystals often make up ∼50 vol.% of necked-down inclusions. It seems that zones of fluid inclusions with numerous birefringent solid phases are distinctive of the Maria emerald deposit. The likely conditions of emerald growth are 400 < T < 500°C and 3 < P < 4 kbar.
Tyrosine kinase inhibitor STI571 potentiates the pharmacologic activity of retinoic acid in acute promyelocytic leukemia cells: effects on the degradation of RARα and PML-RARα
Authors: Gianni' Maurizio , Kalaç Yesim , Ponzanelli Isabella , Rambaldi Alessandro , Terao Mineko , Garattini Enrico
Published: July 2002

The 2-phenylaminopyrimidine derivative STI571 is a selective inhibitor of c-Abl, c-kit, and platelet-derived growth factor–receptor tyrosine kinases and is presently in phase II-III clinical studies. Here, this study reports on a novel pharmacologic activity of the compound, ie, enhancement of the cyto-differentiating, growth-inhibitory, and apoptogenic actions of all-trans-retinoic acid (ATRA). Whereas STI571 is not a cytodifferentiating agent by itself, the compound interacts with ATRA and enhances the myeloid maturation program set in motion by the retinoid in the PML-RARα+ acute promyelocytic leukemia NB4 and the PML-RARα− myeloblastic HL60 and U937 cell lines. In addition, STI571 relieves the cyto-differentiation block observed in the ATRA-resistant cell lines, NB4.R1, NB4.306, and NB4.007. In NB4 promyelocytes, a RARα agonist, but not an RXR agonist, can substitute for ATRA and interact with STI571. By contrast, STI571 is unique among c-Abl–specific tyrosine kinase inhibitors in modulating the pharmacologic activity of ATRA. In NB4 cells, enhanced cyto-differentiation results in increased up-regulation of the expression of a number of genes coding for myeloid differentiation markers, including CD11b, CD11c, and some of the components of the nicotinamide adenine dinucleotide phosphate–oxidase enzymatic complex. All this is accompanied by inhibition of c-Abl tyrosine phosphorylation and retardation of the retinoid-dependent degradation of PML-RARα and RARα. Stabilization of the 2 retinoic acid receptors is likely to be the result of augmented and accelerated inhibition of the proteasome-dependent proteolytic activity observed on ATRA treatment.
Induction of mitochondrial changes in myeloma cells by imexon
Authors: Dvorakova Katerina , Waltmire Caroline N. , Payne Claire M. , Tome Margaret E. , Briehl Margaret M. , Dorr Robert T.
Published: July 2002

Imexon is a cyanoaziridine derivative that has antitumor activity in multiple myeloma. Previous studies have shown that imexon induces oxidative stress and apoptosis in the RPMI 8226 myeloma cell line. This study reports that imexon has cytotoxic activity in other malignant cell lines including NCI-H929 myeloma cells and NB-4 acute promyelocytic leukemia cells, whereas normal lymphocytes and U266 myeloma cells are substantially less sensitive. Flow cytometric experiments have shown that imexon treatment is associated with the formation of reactive oxygen species (ROS) and the loss of mitochondrial membrane potential (Δψm) in imexon-sensitive myeloma cell lines and NB-4 cells. In contrast, reduction of Δψm and increased levels of ROS were not observed in imexon-resistant U266 cells. Treatment of imexon-sensitive RPMI 8226 cells with the antioxidant N-acetyl-l-cysteine (NAC) protects cells against these effects of imexon. Mitochondrial swelling was observed by electron microscopy in RPMI 8226 myeloma cells treated with 180 μM imexon as early as 4 hours. Damage to mitochondrial DNA was detected by a semiquantitative polymerase chain reaction assay in imexon-treated RPMI 8226 cells; however, nuclear DNA was not affected. Finally, partial protection of RPMI 8226 cells against the imexon effects was achieved by treatment with theonyltrifluoroacetone, an inhibitor of superoxide production at mitochondrial complex II. These changes are consistent with mitochondrial oxidation and apoptotic signaling as mediators of the growth inhibitory effects of imexon. Interestingly, oxidative damage and decrease of Δψm induced by imexon highly correlates with sensitivity to imexon in several myeloma cell lines and an acute promyelocytic leukemia cell line.
FLT3, RAS, and TP53 mutations in elderly patients with acute myeloid leukemia
Authors: Stirewalt Derek L. , Kopecky Kenneth J. , Meshinchi Soheil , Appelbaum Frederick R. , Slovak Marilyn L. , Willman Cheryl L. , Radich Jerald P.
Published: July 2002

The prevalence and significance of genetic abnormalities in older patients with acute myeloid leukemia (AML) are unknown. Polymerase chain reactions and single-stranded conformational polymorphism analyses were used to examine 140 elderly AML patients enrolled in the Southwest Oncology Group study 9031 for FLT3, RAS, and TP53 mutations, which were found in 34%, 19%, and 9% of patients, respectively. All but one of the FLT3 (46 of 47) mutations were internal tandem duplications (ITDs) within exons 11 and 12. In the remaining case, a novel internal tandem triplication was found in exon 11. FLT3 ITDs were associated with higher white blood cell counts, higher peripheral blast percentages, normal cytogenetics, and less disease resistance. All RAS mutations (28 of 28) were missense point mutations in codons 12, 13, or 61. RASmutations were associated with lower peripheral blast and bone marrow blast percentages. Only 2 of 47 patients with FLT3 ITDs also had a RAS mutation, indicating a significant negative association between FLT3 and RAS mutations (P = .0013). Most TP53 mutations (11 of 12) were missense point mutations in exons 5 to 8 and were associated with abnormal cytogenetics, especially abnormalities in both chromosomes 5 and 7. FLT3 and RAS mutations were not associated with inferior clinical outcomes, but TP53mutations were associated with a worse overall survival (median 1 versus 8 months, P = .0007). These results indicate that mutations in FLT3, RAS, or TP53 are common in older patients with AML and are associated with specific AML phenotypes as defined by laboratory values, cytogenetics, and clinical outcomes.