bluuebunny/crossref_metadata_2025 huggingface dataset:
Implicit Representations of Space after Bilateral Parietal Lobe Damage
Authors: Kim Min-Shik , Robertson Lynn C.
Published: July 2002

There is substantial evidence that the primate cortex is grossly divided into two functional streams, an occipital-parietal-frontal pathway that processes “where” and an occipital-temporal-frontal pathway that processes “what” (Ungerleider and Mishkin, 1982). In humans, bilateral occipital-parietal damage results in severe spatial deficits and a neuropsychological disorder known as Balint's syndrome in which a single object can be perceived (simultanagnosia) but its location is unknown (Balint, 1995). The data reported here demonstrate that spatial information for visual features that cannot be explicitly located is represented normally below the level of spatial awareness even with large occipital-parietal lesions. They also demonstrate that parietal damage does not affect preattentive spatial coding of feature locations or complex spatial relationships between parts of a stimulus despite explicit spatial deficits and simultanagnosia.
Interactive Processing of Sensory Input and Motor Output in the Human Hippocampus
Authors: Tesche C. D. , Karhu J.
Published: July 2002

Recent studies of visuomotor integration suggest that the motor system may be intimately involved in the detection of salient features of the sensory scene. The final stages of sensory processing occur in hippocampal structures. We measured human neuromagnetic responses during motor reaction to an auditory cue embedded in high-speed multimodal stimulation. Our results demonstrate that large-scale cognitive networks may recruit additional resources from the hippocampus during sensorimotor integration. Hippocampal activity from 300 msec before to 200 msec after cued movements was enhanced significantly over that observed during self-paced movements. The dominant hippocampal activity appeared equally synchronized to both sensory input and motor output, consistent with timing by an intrinsic mechanism, possibly provided by ongoing theta oscillations.
Tilt Aftereffects in a Self-Organizing Model of the Primary Visual Cortex
Authors: Bednar James A. , Miikkulainen Risto
Published: July 2002

RF-LISSOM, a self-organizing model of laterally connected orientation maps in the primary visual cortex, was used to study the psychological phenomenon known as the tilt aftereffect. The same self-organizing processes that are responsible for the long-term development of the map are shown to result in tilt aftereffects over short timescales in the adult. The model permits simultaneous observation of large numbers of neurons and connections, making it possible to relate high-level phenomena to low-level events, which is difficult to do experimentally. The results give detailed computational support for the long-standing conjecture that the direct tilt aftereffect arises from adaptive lateral interactions between feature detectors. They also make a new prediction that the indirect effect results from the normalization of synaptic efficacies during this process. The model thus provides a unified computational explanation of self-organization and both the direct and indirect tilt aftereffect in the primary visual cortex.
Self-Organization of Symmetry Networks: Transformation Invariance from the Spontaneous Symmetry-Breaking Mechanism
Authors: Webber Chris J. S.
Published: July 2002

Symmetry networks use permutation symmetries among synaptic weights to achieve transformation-invariant response. This article proposes a generic mechanism by which such symmetries can develop during unsupervised adaptation: it is shown analytically that spontaneous symmetry breaking can result in the discovery of unknown invariances of the data's probability distribution. It is proposed that a role of sparse coding is to facilitate the discovery of statistical invariances by this mechanism. It is demonstrated that the statistical dependences that exist between simple-cell-like threshold feature detectors, when exposed to temporally uncorrelated natural image data, can drive the development of complex-cell-like invariances, via single-cell Hebbian adaptation. A single learning rule can generate both simple-cell-like and complex-cell-like receptive fields.
Modeling Synaptic Plasticity in Conjunction with the Timing of Pre- and Postsynaptic Action Potentials
Authors: Kistler Werner M. , Hemmen J. Leo van
Published: July 2002

We present a spiking neuron model that allows for an analytic calculation of the correlations between pre- and postsynaptic spikes. The neuron model is a generalization of the integrate-and-fire model and equipped with a probabilistic spike-triggering mechanism. We show that under certain biologically plausible conditions, pre- and postsynaptic spike trains can be described simultaneously as an inhomogeneous Poisson process.

Inspired by experimental findings, we develop a model for synaptic long-term plasticity that relies on the relative timing of pre- and post-synaptic action potentials. Being given an input statistics, we compute the stationary synaptic weights that result from the temporal correlations between the pre- and postsynaptic spikes. By means of both analytic calculations and computer simulations, we show that such a mechanism of synaptic plasticity is able to strengthen those input synapses that convey precisely timed spikes at the expense of synapses that deliver spikes with a broad temporal distribution. This may be of vital importance for any kind of information processing based on spiking neurons and temporal coding.
Stochastic Trapping in a Solvable Model of On-Line Independent Component Analysis
Authors: Rattray Magnus
Published: July 2002

Previous analytical studies of on-line independent component analysis (ICA) learning rules have focused on asymptotic stability and efficiency. In practice, the transient stages of learning are often more significant in determining the success of an algorithm. This is demonstrated here with an analysis of a Hebbian ICA algorithm, which can find a small number of nongaussian components given data composed of a linear mixture of independent source signals. An idealized data model is considered in which the sources comprise a number of nongaussian and gaussian sources, and a solution to the dynamics is obtained in the limit where the number of gaussian sources is infinite. Previous stability results are confirmed by expanding around optimal fixed points, where a closed-form solution to the learning dynamics is obtained. However, stochastic effects are shown to stabilize otherwise unstable suboptimal fixed points. Conditions required to destabilize one such fixed point are obtained for the case of a single nongaussian component, indicating that the initial learning rate η required to escape successfully is very low (η = O (N−2) where N is the datadimension), resulting in very slow learning typically requiring O (N3) iterations. Simulations confirm that this picture holds for a finite system.
Encounters
Authors: Sen Ong Keng
Published: July 2002

A leader of the intercultural movement considers his experiences bringing together Asian filmmakers, drag queens, visual artists, rock-and-roll computer musicians, disk jockeys, modern dancers, and actors—as well as ritualists and other traditional performers. Ong Keng Sen wants to forge a different relationship to intercultural performance than that which has developed in the West.
Simulation Technology: A Strategy for Implementation in Surgical Education and Certification
Authors: Smith C. Daniel
Published: July 2002

Virtual reality and simulation technology promise to be key technologies in medical education. The flight simulator tech nology that has so effectively replaced live, inflight training of pilots is being reengineered for use in medical and surgi cal education. Despite the considerable enthusiasm for this concept, very little practical work has been performed to integrate simulation technology into surgical education and certification. To achieve the potential offered by medical simulation, developers of these new technologies must join with medical/surgical educators to develop meaningful simu lators and virtual learning tools. This paper reviews the cur rent paradigm in surgical education and suggests a strategy for effecting a paradigm shift that facilitates the adoption of simulation technology in surgical education.
Judging Perceived and Traversed Distance in Virtual Environments
Authors: Witmer Bob G. , Kline Paul B.
Published: July 2002

The ability to accurately estimate distance is an essential component of navigating large-scale spaces. Although the factors that influence distance estimation have been a topic of research in real-world environments for decades and are well known, research on distance estimation in virtual environments (VEs) has only just begun. Initial investigations of distance estimation in VEs suggest that observers are less accurate in estimating distance in VEs than in the real world (Lampton et al., 1995). Factors influencing distance estimates may be divided into those affecting perceived distance (visual cues only) and those affecting traversed distance to include visual, cognitive, and proprioceptive cues. To assess the contribution of the various distance cues in VEs, two experiments were conducted. The first required a static observer to estimate the distance to a cylinder placed at various points along a 130-foot hallway. This experiment examined the effects of floor texture, floor pattern, and object size on distance estimates in a VE. The second experiment required a moving observer to estimate route segment distances and total route distances along four routes, each totaling 1210 feet. This experiment assessed the effects of movement method, movement speed, compensatory cues, and wall texture density. Results indicate that observers underestimate distances both in VEs and in the real world, but the underestimates are more extreme in VEs. Texture did not reliably affect the distance estimates, providing no compensation for the gross underestimates of distance in VE. Traversing a distance improves the ability to estimate that distance, but more natural means of moving via a treadmill do not necessarily improve distance estimates over traditional methods of moving in VE (e.g., using a joystick). The addition of compensatory cues (tone every 10 feet traversed on alternate route segments) improves VE distance estimation to almost perfect performance.
Multiobjective Satisfaction within an Interactive Evolutionary Design Environment
Authors: Parmee Ian C. , Cvetković Dragan , Watson Andrew H. , Bonham Christopher R.
Published: July 2002

The paper introduces the concept of an Interactive Evolutionary Design System (IEDS) that supports the engineering designer during the conceptual/preliminary stages of the design process. Requirement during these early stages relates primarily to design search and exploration across a poorly defined space as the designer's knowledge base concerning the problem area develops. Multiobjective satisfaction plays a major role, and objectives are likely to be ill-defined and their relative importance uncertain. Interactive evolutionary search and exploration provides information to the design team that contributes directly to their overall understanding of the problem domain in terms of relevant objectives, constraints, and variable ranges. This paper describes the development of certain elements within an interactive evolutionary conceptual design environment that allows off-line processing of such information leading to a redefinition of the design space. Such redefinition may refer to the inclusion or removal of objectives, changes concerning their relative importance, or the reduction of variable ranges as a better understanding of objective sensitivity is established. The emphasis, therefore, moves from a multiobjective optimization over a preset number of generations to a relatively continuous interactive evolutionary search that results in the optimal definition of both the variable and objective space relating to the design problem at hand. The paper describes those elements of the IEDS relating to such multiobjective information gathering and subsequent design space redefinition.
Synthesizing Emotional Behavior in a Simple Animated Character
Authors: Hille Katrin
Published: July 2002

A simple computer-generated agent was developed of which four behavioral aspects could be altered. Emotional behavior was defined and simulated in terms of these aspects. Participants matched a list of six emotions to the animated emotional behavior of the agent. Results suggest that it is possible to identify emotions from a set of simulated modulation patterns. The successful simulation of a computer-generated “emotional” agent supports a behavioral theory of emotion. In addition, it reveals an almost overlooked aspect of emotion that may spark further research and shows the fertility of the approach known as “artificial life” for the field of psychology.
A New Structurally Dissolvable Self-Reproducing Loop Evolving in a Simple Cellular Automata Space
Authors: Sayama Hiroki
Published: July 2002

We constructed a simple evolutionary system, “evoloop,” on a deterministic nine-state five-neighbor cellular automata (CA) space by improving the structurally dissolvable self-reproducing loop we had previously contrived [14] after Langton's self-reproducing loop [7]. The principal role of this improvement is to enhance the adaptability (a degree of the variety of situations in which structures in the CA space can operate regularly) of the self-reproductive mechanism of loops. The experiment with evoloop met with the intriguing result that, though no mechanism was explicitly provided to promote evolution, the loops varied through direct interaction of their phenotypes, smaller individuals were naturally selected thanks to their quicker self-reproductive ability, and the whole population gradually evolved toward the smallest ones. This result gives a unique example of evolution of self-replicators where genotypical variation is caused by precedent phenotypical variation. Such interrelation of genotype and phenotype would be one of the important factors driving the evolutionary process of primitive life forms that might have actually occurred in ancient times.
Life‐Cycle Energy, Costs, and Strategies for Improving a Single‐Family House
Authors: Keoleian Gregory A. , Blanchard Steven , Reppe Peter
Published: July 2002

The life‐cycle energy, greenhouse gas emissions, and costs of a contemporary 2,450 sq ft (228 m3) U.S. residential home (the standard home, or SH) were evaluated to study opportunities for conserving energy throughout pre‐use (materials production and construction), use (including maintenance and improvement), and demolition phases. Home construction and maintenance materials and appliances were inventoried totaling 306 metric tons. The use phase accounted for 91% of the total life‐cycle energy consumption over a 50‐year home life. A functionally equivalent energy‐efficient house (EEH) was modeled that incorporated 11 energy efficiency strategies. These strategies led to a dramatic reduction in the EEH total life‐cycle energy; 6,400 GJ for the EEH compared to 16,000 GJ for the SH. For energy‐efficient homes, embodied energy of materials is important; pre‐use energy accounted for 26% of life‐cycle energy. The discounted (4%) life‐cycle cost, consisting of mortgage, energy, maintenance, and improvement payments varied between 426,700 and 454,300 for a SH using four energy price forecast scenarios. In the case of the EEH, energy cost savings were offset by higher mortgage costs, resulting in total life‐cycle cost between 434,100 and 443,200. Life‐cycle greenhouse gas emissions were 1,010 metric tons CO2 equivalent for an SH and 370 metric tons for an EEH.
Life‐Cycle Assessment and Temporal Distributions of Emissions: Developing a Fleet‐Based Analysis
Authors: Field Frank , Kirchain Randolph , Clark Joel
Published: July 2002

Although the product‐centered focus of life‐cycle assessment has been one of its strengths, this analytical perspective embeds assumptions that may conflict with the realities of environmental problems. This article demonstrates, through a series of mathematical derivations, that all the products in use, rather than a single product, frequently should be the appropriate unit of analysis. Such a “fleet‐centered” approach supplies a richer perspective on the comparative emissions burdens generated by alternative products, and it eliminates certain simplifying assumptions imposed upon the analysis by a product‐centered approach.

A sample numerical case, examining the comparative emissions of steel‐intensive and aluminum‐intensive automobiles, is presented to contrast the results of the two approaches. The fleet‐centered analysis shows that the “crossover time” (i.e., the time required before the fuel economy benefits of the lighter aluminum vehicle offset the energy intensity of the processes used to manufacture the aluminum in the first place) can be dramatically longer than that predicted by a product‐centered life‐cycle assessment.

The fleet‐centered perspective explicitly introduces the notion of time as a critical element of comparative life‐cycle assessments and raises important questions about the role of the analyst in selecting the appropriate time horizon for analysis. Moreover, with the introduction of time as an appropriate dimension to life‐cycle assessment, the influences of effects distributed over time can be more naturally and consistently treated.
JEWISH AND CHRISTIAN ASTROLOGY IN LATE ANTIQUITY - A NEW APPROACH
Authors: von Stuckrad Kocku
Published: July 2002

In late antiquity astrology held a key position among the accepted and well-reputed sciences. As ars mathematica closely connected with astronomy, it made its way into the highest political and philosophical orders of the Roman Empire and became the standard model of interpreting past, present, and future events. Although this is widely acknowledged by modern historians, most scholars assume that the application of astrological theories is limited to the 'pagan mind,' whereas Jewish and Christian theology is characterized by a harsh refutation of astrology's implications. As can easily be shown, this assumption is not the result of careful examination of the documentary evidence but of a preconceived and misleading opinion about the basic ideas of astrology, which led to an astonishing disregard of Jewish and Christian evidence for astrological concerns. This evidence has been either played down - if not neglected entirely - or labeled 'heretic,' thus prolonging the polemics of the 'church fathers' right into modernity. After having reviewed the biases of previous research into monotheistic astrology and its crucial methodological problems, I shall propose a different approach. Astrology has to be seen as a certain way of interpreting reality. In this regard it is the very backbone of esoteric tradition. I shall sketch the different discourses reflected in some late antiquity's Jewish and Christian documents. It will be shown that the astrological worldview of planetary and zodiacal correspondences was common to most of the sources. Examples will be presented for illustrating different adoptions of this attitude, namely the discourse of cult theology, the magical and mystical application of astrological knowledge, the debates concerning volition and determinism, and, finally, the use of astrology for political and religious legitimization.
MEMORY RETENTION IN WILD-TYPE AND TAU MUTANT SYRIAN HAMSTERS
Authors: Oklejewicz Małgorzata , Van Der Zee Eddy , Gerkema Menno , Daan Serge
Published: July 2002

Rats are known to display a temporary deficit in memory function 6 h after training on a learning task, a phenomenon known as the 'Kamin effect'. Later studies showed that maximal retrieval recurs in 24 h intervals after a single training and implied the role of the circadian clock in the suppression of memory retrieval at non-24 h intervals. This study aimed to investigate this further by analysing retention deficits following passive avoidance training in the Syrian hamster. The availability of hamsters carrying the tau mutation was exploited to address the role of the circadian system in periodic retention deficits. It was expected that tau mutant hamsters with an endogenous circadian period of approximately 20 h would have a high retention score at 20 h after training. Surprisingly, deficits in retention were found at 12, 18, 24, and 36 h after training in wild-type hamsters with best performance at 30 h after training. Tau mutant hamsters had significant deficits in memory retention at 20, 24, and 30 h, and no clear periodicity in retention could be observed. Step-through latency scores for mutant hamsters were low at all times except training-testing intervals of 0.25 and 6 h. These results demonstrate the absence of clear memory deficit oscillations in both wild-type and mutant hamsters, and may suggest in particular a long-term memory deficit in tau mutant hamsters.
GENETIC DETERMINATION OF PATERNITY IN CAPTIVE GREY MOUSE LEMURS: PRE-COPULATORY SEXUAL COMPETITION RATHER THAN SPERM COMPETITION IN A NOCTURNAL PROSIMIAN?
Authors: Andrès Marjorie , Gachot-Neveu Hélène , Perret Martine
Published: July 2002

Among nocturnal Malagasy prosimians, the grey mouse lemur (Microcebus murinus) is considered as a solitary species having a promiscuous mating system. Indirect evidence, such as the lack of sexual dimorphism, the high relative testes size of males and the high synchronism in oestrus occurrence among females, supports the presence of a sperm-based scramble competition. In captive animals, we used genetic determination of paternity to define the relationship between mating success and reproductive success of males kept in a group with several females during the mating period. Within each group, an intense sexual competition arose among males for priority of access to oestrous females. High ranking males, as deduced from the direction of agonistic interactions, displayed a significantly higher frequency of marking behaviours, chemosensory investigations of females, and sexual behaviours. A robust relationship was found between male rank and reproductive success since 16 out of the 17 litters (35 young) produced, have been sired by the highest ranked male of the group. Moreover, the finding that female aggression was related to both male sexual solicitations and to male rank, suggests that females could exert a choice. Under specific captive conditions, grey mouse lemurs, showing all traits of post-copulatory sperm-based scramble competition, exhibit a mating system relying on pre-copulatory aggression-based competition. Olfactory signals rather than morphological traits might be used, in this nocturnal primate, for both sexual co-ordination between sexes and partner choice.
FEMALE PREFERENCES FOR NATURALLY-OCCURRING NOVEL MALE TRAITS
Authors: Schlupp Ingo , Waschulewski Meike , Ryan Michael
Published: July 2002

We report two independent cases of female preferences for novel male traits in two species of poeciliid fish, Poecilia latipinna and Poecilia mexicana. In both cases the preference predates the occurrence of the trait, lending strong support to the pre-existing bias hypotheses. This support is independent of the assumptions associated with phylogenetic inference. Unlike the two sexual species, the unisexual hybrid P. formosa had no detectable preference for the novel male traits.
Efficacy of methyl iodide soil fumigation for control of Meloidogyne incognita, Tylenchulus semipenetrans and Heterodera schachtii
Authors: Hutchinson Chad M. , McGiffen Milton E. , Ohr Howard D. , Sims James J. , Becker J. Ole
Published: July 2002

Sigmoidal dose-response curves were derived for Meloidogyne incognita,
Tylenchulus semipenetrans, and Heterodera schachtii treated with methyl
iodide or methyl bromide under laboratory and field conditions. Laboratory
dose-response experiments were conducted in 1.9 dm3 fumigation jars in three
soil types. Field experiments were conducted in a San Emigdio sandy loam and
a Carsetas loamy sand previously infested with M. incognita. Muslin sample
bags containing either roots or soil infested with T. semipenetrans and H.
schachtii were buried in each field plot. M. incognita was bioassayed on
tomato roots and survival of other nematodes was assayed by Baermann funnel
extraction. A comparison of the methyl bromide: methyl iodide ratios at the
EC(ED)90 rates indicated that, averaged over all treatments, methyl iodide
was 4.67 and 1.77 times more potent than methyl bromide in laboratory and
field experiments, respectively. Efficacite de la fumigation des sols au
iodure de methyle pour le controle de Meloidogyne incognita, Tylenchulus
semipenetrans et Heterodera schachtii - Des courbes sigmoides dose-reponse
ont ete etablies pour Meloidogyne incognita, Tylenchulus semipenetrans et
Heterodera schachtii traites au iodure de methyle ou au bromure de methyle
au laboratoire et au champ. Les experimentations dose-reponse au laboratoire
ont ete faites dans des conteneurs de 1,9 dm3 avec trois types de sol. Les
experimentations au champ ont ete realisees sur limon sableux San Emiglio et
sable limoneux Carsetas prealablement infestes par M. incognita. Des sacs a
echantillon en mousseline contenant ou bien des racines ou bien du sol
infestes par M. incognita, T. semipenetrans et H. schachtii ont ete enterres
dans chaque parcelle. La survie de M. incognita a ete evaluee par un test
biologique sur des racines de tomate et celle des autres nematodes par
extraction au Baerman. Une comparaison des rapports bromure de
methyle/iodure de methyle aux taux EC(ED)90 a montre que, en moyenne sur
tous les traitements, l'iodure de methyle a ete respectivement 4,67 et 1,77
fois plus efficient que le bromure de methyle au laboratoire et au champ,
respectivement.
Morphometric study on twelve populations of Nacobbus aberrans (Thorne, 1935) Thorne & Allen, 1944 (Nematoda: Pratylenchidae) from Mexico and South America
Authors: Manzanilla-Lopez Rosa H. , Harding Simon , Evans Ken
Published: July 2002

Twelve populations of Nacobbus aberrans from Mexico and South America were
cultured in the glasshouse on tomato plants. Second stage juveniles, males,
young females and mature females were recovered from the cultures and
studied using light microscopy. Morphometric data were analysed using
canonical variate analysis. Many of the characters previously used to
establish species or subspecific ranks were shown to be variable and all
variants occurred in all populations studied, even if at low frequencies.
Etude morphometrique de douze populations de Nacobbus aberrans (Thorne,
1935) Thorne & Allen, 1944 (Nematoda: Pratylenchidae) du Mexique et
d'Amerique du Sud - Douze populations de Nacobbus aberrans du Mexique et
d'Amerique du Sud ont ete elevees en serre sur plants de tomate. Les
juveniles de deuxieme stade, les males, les femelles jeunes et les femelles
matures ont ete recoltes a partir de ces elevages et etudies en microscopie
photonique. Les donnees morphometriques ont ete analysees par analyse
canonique. De nombreux caracteres precedemment utilises aux niveaux
specifique ou subspecifique sont apparus variables, tous les variants etant
presents dans toutes les populations etudiees, a des frequences parfois
faibles mais jamais nulles.
Kinetics of palygorskite hydrolysis in dilute salt solutions
Authors: Neaman A. , Singer A.
Published: July 2002

Five palygorskite samples with different chemical compositions and specific surface areas (SSA) were used for this study. Batch experiments in dilute salt solutions under neutral conditions were conducted to study the kinetics of clay hydrolysis. The rates of release of Mg and Si differ significantly among the palygorskite samples. It was found that differences in release rate of Mg among the palygorskite samples are due to differences in both surface area and chemical composition. The rate of release of Mg was greater in palygorskites with high SSA and high Mg and Fe contents than that in palygorskites with low SSA and high Al content. The rate of release of Si depends on the SSA of the mineral and is not related to chemical composition. The initial amount of Si released increases with SSA, while the Si rate of release decreases with increasing SSA. These data suggest that the decomposition of palygorskite in soils and sediments also takes place under neutral conditions.
Nature of mixed iron and aluminium gels as affected by Fe/Al molar ratio, pH and citrate
Authors: Violante A. , Colombo C. , Cinquegrani G. , Adamo P. , Violante P.
Published: July 2002

The nature and mineralogy of mixed Al and Fe(III) gels (initial Fe/Al molar ratios (Ri) of 1.0 and 2.5) formed at pH values ranging from 4.0 to 10.0, both in the presence and absence of citric acid (citrate/Fe + AI molar ratio (Rcit) of 0.01 and 0.1) and aged for a long period at room temperature and at 50°C have been studied. The complexes showed considerable differences in the mineralogy of the precipitation products. The samples formed at Ri = 1.0 contained ferrihydrite at pH 4.0, ferrihydrite + gibbsite at pH 5.0-7.0, and hematite + Al(OH)3polymorphs + ferrihydrite at pH 9.0-10.0. The samples formed at Ri = 2.5 had greater quantities of poorly crystallized ferrihydrite. Large amounts of Fe+Al (25-82%) were solubilized from the samples aged for 60 days at 50°C by ammonium oxalate. The addition of increasing concentrations of citrate to the gel suspensions containing equimolar amounts of Fe and AI strongly inhibited the formation of Al(OH)3polymorphs both at pH 5.0 or 8.5 by promoting the formation of short-range ordered materials. Citrate added initially to Fe-Al solutions (R*cit = 0.1) completely inhibited formation of crystals even after 135 days at 50°C.
Chemistry of the Ta-Nb-Sn-W oxide minerals from the Yichun rare metal granite (SE China): genetic implications and comparison with Moroccan and French Hercynian examples
Authors: Belkasmi M. , Cuney M. , Pollard P. J. , Bastoul A.
Published: July 2002

In the Yichun granite complex (SE China), columbite group minerals, microlite and cassiterite are the main Nb, Ta, Sn-bearing minerals. They are mainly concentrated in the uppermost albite-lepidolite granite. Rutile is the only Nb, Ta-bearing phase in the geochemically primitive muscovite-zinnwaldite granite. The chemical evolution of the columbite group minerals (the most abundant and commonly zoned Nb, Ta-bearing minerals) indicates a complex crystallization history of the host granites with: (1) fractional crystallization at depth, reflected by a strong increase of Mn/(Mn+Fe) ratios with a moderate increase of Ta/(Ta+Nb) ratios from the muscovite-zinnwaldite granite to the Li-mica granite and then the most fractionated topaz-lepidolite granite; and (2) emplacement of successive magma batches corresponding to the different units of the granite complex with progressive crystallization of each unit, mainly reflected by a strong increase of Ta/(Ta+Nb) ratios with moderate variation of Mn/(Mn+Fe) ratios during the growth of the zoned crystals. The data are compared with those from the RMG of Ezzirari (Morocco), Montebras, Beauvoir and Chèdeville (France).
Zr budgets for metamorphic reactions, and the formation of zircon from garnet breakdown
Authors: Degeling H. , Eggins S. , Ellis D. J.
Published: July 2002

The construction of zirconium (Zr) budgets for metamorphic reactions in high-grade rocks provides new insight into zircon growth during metamorphism. In this study we target reactions involving garnet, as they enable zircon growth to be related to known pressure and temperature conditions. Two reactions involving the breakdown of Zr-bearing garnet from Rogaland, SW Norway have been investigated in detail, showing contrasting behaviour of Zr, with zircon formation being subject to the solubility of Zr in product phases. In the decompression reaction garnet + sillimanite + quartz → cordierite, Zr released during garnet breakdown cannot be incorporated into the cordierite structure, resulting in zircon nucleation and growth. In contrast, for the reaction garnet + biotite + sillimanite + quartz → osumilite + orthopyroxene + spinel + magnetite, no new zircon growth takes place, despite the garnet involved containing more than double the Zr concentration of the former reaction. In the latter case, all the Zr released by garnet breakdown can be detected in the product phases osumilite and orthopyroxene, thereby preventing growth of new metamorphic zircon. This study highlights the potential for high resolution geochronology in metamorphic rocks by relating zircon growth to specific metamorphic reactions.
Crystal structure of macphersonite (Pb4SO4(CO3)2(OH)2): comparison with leadhillite
Authors: Steele Ian M. , Pluth Joseph J. , Livingstone Alec
Published: July 2002

The crystal structure of macphersonite (Pb4SO4(CO3)2(OH)2, Pcab, a = 9.242(2), b = 23.050(5), c = 10.383(2) Å) from Leadhills, Scotland has been determined to an R = 0.053. The structure has many features in common with its polymorph leadhillite including three distinct types of layers. Layer A includes sulphate tetrahedra, Layer B is composed of Pb and OH, while Layer C is composed of Pb and CO3 with topology identical to that in cerussite. In both macphersonite and leadhillite these layers are stacked along [010] as …BABCCBABCC… The double CC layer is almost identical in the two structures and forms a structural backbone and occurs in other structures including hydrocerussite and plumbonacrite. The sulphate layer shows the greatest difference between the two structures and can be described by a pattern of up or down pointing tetrahedra. For macphersonite the sequence along [001] is …UDUDUD… while in leadhillite the sequence along [010] is …UDDUUDDU… This latter sequence effectively doubles b relative to the equivalent direction in macphersonite. Susannite, a third polymorph, may have yet another sequence of sulphates to give trigonal symmetry; by heating leadhillite, displacive movements of sulphate groups may occur with a conversion to susannite.
Kyanite-staurolite ortho-amphibolite from the Chapada Region, Goiás, Central Brazil
Authors: Kuyumjian Raul Minas
Published: July 2002

This study deals with the kyanite-staurolite assemblage from a metabasite (ortho-amphibolite) in the Chapada area of the Neoproterozoic Mara Rosa volcano-sedimentary sequence of Goiás state, Brazil. It is closely associated with hydrothermally altered rocks and contains the assemblage hornblende, epidote, quartz, kyanite, staurolite, plagioclase and rutile. The staurolite from the amphibolite shows lower values of SiO2 and higher values of MgO, MnO, ZnO and Xmg than those in staurolites from the metasediments of the same area. In the Al–Na–Ca–(Fe+Mg) diagram, the amphibolite plots in the aluminous part of the diagram and the phase volume encloses the area of mafic volcanic bulk compositions. Field relations and compositions in both kyanite-staurolite amphibolite and staurolite are consistent with formation of this amphibolite as a result of metamorphism of metasomatised basalts.
Lymphocytic vasculitis in X-linked lymphoproliferative disease
Authors: Dutz Jan P. , Benoit Loralyn , Wang Xiaoxia , Demetrick Douglas J. , Junker Anne , de Sa Derek , Tan Rusung
Published: July 2002

Systemic vasculitis is an uncommon manifestation of X-linked lymphoproliferative disease (XLP), a disorder in which there is a selective immune deficiency to Epstein-Barr virus (EBV). The molecular basis for XLP has recently been ascribed to mutations within SLAM-associated protein (SAP), an SH2 domain–containing protein expressed primarily in T cells. The authors describe a patient who died as a result of chronic systemic vasculitis and fulfilled clinical criteria for the diagnosis of XLP. Sequencing of this patient'sSAP gene uncovered a novel point mutation affecting the SH2 domain. The patient presented with virus-associated hemophagocytic syndrome (VAHS) and later had chorioretinitis, bronchiectasis, and hypogammaglobulinemia develop. He further developed mononeuritis and fatal respiratory failure. Evidence of widespread small and medium vessel vasculitis was noted at autopsy with involvement of retinal, cerebral, and coronary arteries as well as the segmental vessels of the kidneys, testes, and pancreas. Immunohistochemical analysis using antibodies to CD20, CD45RO, and CD8 revealed that the vessel wall infiltrates consisted primarily of CD8+ T cells, implying a cytotoxic T-lymphocyte response to antigen. EBV DNA was detected by polymerase chain reaction (PCR) in arterial wall tissue microdissected from infiltrated vessels further suggesting that the CD8+ T cells were targeting EBV antigens within the endothelium. The authors propose that functional inactivation of the SAP protein can impair the immunologic response to EBV, resulting in systemic vasculitis.
Expression and regulation of chemokine receptors in human natural killer cells
Authors: Inngjerdingen Marit , Damaj Bassam , Maghazachi Azzam A.
Published: July 2002

Using flow cytometric and RNase protection assays, this study examined the expression of chemokine receptors in nonactivated natural killer (NK) cells and compared this expression with NK cells activated with interleukin (IL)-2, which either adhered to plastic flasks (AD) or did not adhere (NA). None of the NK cell subsets expressed CXCR2, CXCR5, or CCR5. The major differences between these cells include increased expression of CXCR1, CCR1, CCR2, CCR4, CCR8, and CX3CR1 in AD when compared to NA or nonactivated NK cells. The chemotactic response to the CXC and CC chemokines correlated with the receptor expression except that all 3 populations responded to GRO-α, despite their lack of CXCR2 expression. Pretreatment of these cells with anti-CXCR2 did not inhibit the chemotactic response to GRO-α. In addition, nonactivated and NA cells responded to fractalkine, although they lack the expression of CX3CR1. This activity was not inhibited by anti-CX3CR1. Viral macrophage inflammatory protein (vMIP)-I, I-309, and TARC competed with the binding of 125I-309 to AD cells with varying affinities. Transforming growth factor (TGF)-β1 but not any other cytokine or chemokine examined including interferon (IFN)-γ, MIP-3β, macrophage-derived chemokine (MDC), thymus and activation-regulated chemokine (TARC) or I-309, up-regulated the expression of CXCR3 and CXCR4 on NK cell surface. This is correlated with increased chemotaxis of NK cells treated with TGF-β1 toward stromal cell–derived factor (SDF)-1α and interferon-inducible protein-10 (IP-10). Messenger RNA for lymphotactin, RANTES, MIP-1α, and MIP-1β, but not IP-10, monocyte chemotactic protein (MCP)-1, IL-8, or I-309 was expressed in all 3 NK cell subsets. Our results may have implications for the dissemination of NK cells at the sites of tumor growth or viral replication.
CTLA-4 blockade of antigen-induced cell death
Authors: da Rocha Dias Silvy , Rudd Christopher E.
Published: July 2002

While cytotoxic T lymphocyte antigen–4 (CTLA-4) negatively regulates T-cell receptor (TCR)–driven interleukin (IL)–2 production and proliferation, little is known regarding whether the coreceptor has the capacity to inhibit other events, such as Fas ligand (FasL) expression and antigen-induced cell death (AICD). In this study, it is shown that CTLA-4 expressed in a T-cell hybridoma can elicit a potent block of FasL expression and AICD. Inhibition occurred independently of CTLA-4 blockage of IL-2 production and was partially reversed by a single mutation in the cytoplasmic YVKM motif. These findings indicate that CTLA-4 can block TCR signaling prior to bifurcation of signals leading to IL-2 production and apoptosis.
Replicative stress after allogeneic bone marrow transplantation: changes in cycling of CD34+CD90+ and CD34+CD90− hematopoietic progenitors
Authors: Thornley Ian , Sutherland D. Robert , Nayar Rakash , Sung Lillian , Freedman Melvin H. , Messner Hans A.
Published: July 2002

To further characterize hematopoietic “replicative stress” induced by bone marrow transplantation (BMT), the cell-cycle status of CD90+/− subsets of marrow CD34+ cells obtained 2 to 6 months after transplantation from 11 fully chimeric recipients was examined. Cycling profiles, derived by flow cytometry after staining with Hoechst 33342 and pyronin Y, were compared with those of 14 healthy marrow donors. Primitive CD34+CD90+cells represented a smaller proportion of CD34+ cells in recipients (10% ± 4% versus 19.6% ± 5.3% in donors;P < .0001) and were more mitotically active, with the proportion of cells in S/G2/M nearly 4-fold higher than in donors (15.6% ± 3% and 4.4% ± 1.6%, respectively;P < .0001). By comparison, there was a modest increase in the proportion of CD34+CD90−progenitors in S/G2/M after BMT (10.9% ± 1% vs 9.6% ± 2% in donors; P = .04). Replicative stress after BMT is borne predominantly by cells in a diminished CD34+CD90+ population.
Expression of tumor-suppressor genes interferon regulatory factor 1 and death-associated protein kinase in primitive acute myelogenous leukemia cells
Authors: Guzman Monica L. , Upchurch Donna , Grimes Barry , Howard Dianna S. , Rizzieri David A. , Luger Selina M. , Phillips Gordon L. , Jordan Craig T.
Published: July 2002

Previous studies indicate that human acute myelogenous leukemia (AML) arises from a rare population of leukemic stem cells. Cells of this nature can initiate and maintain leukemic cell growth in both long-term cultures and nonobese diabetic/severe combined immune-deficient mice. To characterize the biology of primitive AML cells, gene expression screens were performed with 7 primary AML and 3 normal specimens. For each sample, stem cell populations (CD34+/CD38−) were isolated and used to synthesize radiolabeled complementary DNA (cDNA). AML vs normal probes were then hybridized to cDNA arrays containing genes related to cancer and apoptosis. Of approximately 1400 genes analyzed, 2 tumor-suppressor genes were identified that were overexpressed in all 7 of the AML CD34+/CD38−cell populations: death-associated protein kinase and interferon regulatory factor 1. Expression of each gene was confirmed by reverse-transcription polymerase chain reaction and immunoblot analysis. It is proposed that tumor-suppressor proteins play a role in the biology of primitive AML cells.
The combination of chemotherapy and systemic immunotherapy with soluble B7–immunoglobulin G leads to cure of murine leukemia and lymphoma and demonstration of tumor-specific memory responses
Authors: Runyon Kathlene , Lee Kwang , Zuberek Krystyna , Collins Mary , Leonard John P. , Dunussi-Joannopoulos Kyriaki
Published: July 2002

Major mechanisms underlying poor immune responses to autologous tumor-associated antigens are overwhelming tumor kinetics and the absence of effective T-cell costimulation by antigen-presenting cells. To address these issues, leukemia and lymphoma mice were treated with the combination of chemotherapy and systemic immunotherapy with recombinant soluble murine B7–immunoglobulin G (IgG) molecules. In this report, 3 murine models were used, a radiation-induced SJL acute myeloid leukemia, a transplantable spontaneous SJL lymphoma, and the C57BL/6 EL-4 thymic lymphoma. Various treatment modalities were evaluated: single treatments with either B7-IgG or chemotherapy as well as combination therapies. The results demonstrate the following: (1) in all tumor models, the combination of chemotherapy and soluble B7-IgGs is more potent than either therapy alone, leading to cure of tumor-bearing animals; (2) the therapeutic responses are T-cell–dependent, because combined therapy is not efficacious in severe combined immunodeficient mice; (3) the rejection of tumor cells leads to the development of tumor-specific immunity, because cured mice are immune to the rejected tumor but not to a different syngeneic tumor; and (4) 51Cr release assays show that rejection of tumor cells leads to the development of very potent tumor-specific cytotoxic T-lymphocyte activity. On the basis of these results, it is proposed that chemotherapy-mediated tumor reduction, together with consequent augmented tumor-antigen presentation to activated T cells, are primary mechanisms leading to curative responses. The safety profile of the B7-IgG fusion proteins and their synergy with chemotherapy strongly suggest that the combination regimen is a promising strategy in cancer treatment.
Response to hypoxia involves transforming growth factor-β2 and Smad proteins in human endothelial cells
Authors: Akman Hasan O. , Zhang Hong , Siddiqui M. A. Q. , Solomon William , Smith Eric L. P. , Batuman Olcay A.
Published: July 2002

Oxygen deprivation (hypoxia) is a consistent component of ischemia that induces an inflammatory and prothrombotic response in the endothelium. In this report, it is demonstrated that exposure of endothelial cells to hypoxia (1% O2) increases messenger RNA and protein levels of transforming growth factor-β2 (TGF-β2), a cytokine with potent regulatory effects on vascular inflammatory responses. Messenger RNA levels of the TGF-β2 type II membrane receptor, which is a serine threonine kinase, also increased. The stimulatory effect of hypoxia was found to occur at the level of transcription of the TGF-β2 gene and involves Smad proteins, a class of intracellular signaling proteins that mediates the downstream effects of TGF-β receptors. Transient transfection studies showed that the region spanning −77 and −40 base pairs within the TGF-β2 promoter (harboring a Smad-binding “CAGA box”) is activated in hypoxic cells compared with nonhypoxic controls (P < .01). Hypoxia also stimulated transcription from another promoter, 3TP-Lux, a reporter construct responsive to Smads and TGF-β. In addition, specific binding to a Smad-binding oligonucleotide was observed with nuclear extracts from hypoxic endothelial cells but not from nonhypoxic cells. It is concluded that Smad proteins, which can regulate endothelial responses to mechanical and inflammatory stress, also may play an important role in vascular responses to hypoxia and ischemia.
The impaired polymerization of fibrinogen Longmont (Bβ166Arg→Cys) is not improved by removal of disulfide-linked dimers from a mixture of dimers and cysteine-linked monomers
Authors: Lounes Karim C. , Lefkowitz Jerry B. , Henschen-Edman Agnes H. , Coates Andrew I. , Hantgan Roy R. , Lord Susan T.
Published: July 2002

This study identified a new substitution in the Bβ chain of an abnormal fibrinogen, denoted Longmont, where the residue Arg166 was changed to Cys. The variant was discovered in a young woman with an episode of severe hemorrhage at childbirth and a subsequent mild bleeding disorder. The neo-Cys residues were always found to be disulfide-bridged to either an isolated Cys amino acid or to the corresponding Cys residue of another abnormal fibrinogen molecule, forming dimers. Removing the dimeric molecules using gel filtration did not correct the fibrin polymerization defect. Fibrinogen Longmont had normal fibrinopeptide A and B release and a functional polymerization site “a.” Thus, the sites “A” and “a” can interact to form protofibrils, as evidenced by dynamic light-scattering measurements. These protofibrils, however, were unable to associate in the normal manner of lateral aggregation, leading to abnormal clot formation, as shown by an impaired increase in turbidity. Therefore, it is concluded that the substitution of Arg166→Cys-Cys alters fibrinogen Longmont polymerization by disrupting interactions that are critical for normal lateral association of protofibrils.