bluuebunny/crossref_metadata_2025 huggingface dataset:
Reduced Delayed-Rectifier K+ Current in the Learning Mutant rutabaga
Authors: Alshuaib Waleed B. , Mathew Mini V.
Published: December 2002

In the Drosophila mutant rutabaga, short-term memory is deficient and intracellular cyclic adenosine monophosphate (cAMP) concentration is reduced. We characterized the delayed-rectifier potassium current (IKDR) in rutabaga as compared with the wild-type. The conventional whole-cell patch-clamp technique was applied to cultured Drosophila neurons derived from embryonic neuroblasts. IKDR was smaller in rutabaga(368 ± 11 pA) than in wild-type (541 ± 14 pA) neurons, measured in a Ca2+-free solution. IKDR was clearly activated at ∼0 mV in the two genotypes. IKDR typically reached its peak within 10–20 msec after the start of the pulse (60 mV). There was no difference in inactivation of IKDR for wild-type (14 ± 3%) and rutabaga (19 ± 3%). After application of 10 mM TEA, in wild-type, IKDR was reduced by 46 ± 5%, whereas in rutabaga, IKDR was reduced by 28 ± 3%. Our results suggest that IKDR is carried by two different types of channels, one which is TEA-sensitive, whereas the other is TEA-insensitive. Apparently, the TEA-sensitive channel is less expressed in rutabaga neurons than in wild-type neurons. Conceivably, altered neuronal excitability in the rutabagamutant could disrupt the processing of neural signals necessary for learning and memory.
How do People Solve the “Weather Prediction” Task?: Individual Variability in Strategies for Probabilistic Category Learning
Authors: Gluck Mark A. , Shohamy Daphna , Myers Catherine
Published: December 2002

Probabilistic category learning is often assumed to be an incrementally learned cognitive skill, dependent on nondeclarative memory systems. One paradigm in particular, the weather prediction task, has been used in over half a dozen neuropsychological and neuroimaging studies to date. Because of the growing interest in using this task and others like it as behavioral tools for studying the cognitive neuroscience of cognitive skill learning, it becomes especially important to understand how subjects solve this kind of task and whether all subjects learn it in the same way. We present here new experimental and theoretical analyses of the weather prediction task that indicate that there are at least three different strategies that describe how subjects learn this task. (1) An optimal multi-cue strategy, in which they respond to each pattern on the basis of associations of all four cues with each outcome; (2) a one-cue strategy, in which they respond on the basis of presence or absence of a single cue, disregarding all other cues; or (3) a singleton strategy, in which they learn only about the four patterns that have only one cue present and all others absent. This variability in how subjects approach this task may have important implications for interpreting how different brain regions are involved in probabilistic category learning.
The Differential Role of Premotor Frontal Cortex and Basal Ganglia in Motor Sequence Learning: Evidence From Focal Basal Ganglia Lesions
Authors: Exner Cornelia , Koschack Janka , Irle Eva
Published: December 2002

There has been a growing interest in the differential role of various neural structures in implicit learning processes. The goal of our study was to clarify how focal lesions restricted to the basal ganglia interfere with different aspects of implicit visuo-motor sequence learning. A version of the Serial Reaction Time Task (SRTT) of Nissen and Bullemer using a 12-trial sequence was administered. A total of 20 subjects with focal basal ganglia lesions caused by ischemic or hemorrhagic infarction and 20 matched control subjects participated in this study. The results indicate that subjects with focal basal ganglia lesions showed unimpaired implicit learning of a 12-item motor sequence. Subjects with basal ganglia lesions, however, had more difficulties improving their general proficiency with the reaction-time task independent of sequence-specific learning. We observed a tendency toward smaller regional volumes in the cerebellum and left pre-supplementary motor area (pre-SMA) of subjects with basal ganglia lesions. Smaller cerebellar and pre-SMA volumes were related to lower implicit learning performance in the lesion group. The size of lesions in the basal ganglia was not related to sequence-specific implicit learning but had a significant influence on subjects' general proficiency for execution of the reaction-time task. We propose that implicit learning is achieved by a distributed network of cortical and subcortical structures. The basal ganglia seem to be responsible for adjusting to the general requirements of a task rather than for learning specific associations between stimuli that might be accomplished by premotor frontal areas and the cerebellum instead.
Habit and Skill Learning in Schizophrenia: Evidence of Normal Striatal Processing With Abnormal Cortical Input
Authors: Weickert Thomas W. , Terrazas Alejandro , Bigelow Llewellyn B. , Malley James D. , Hyde Thomas , Egan Michael F. , Weinberger Daniel R. , Goldberg Terry E.
Published: December 2002

Different forms of nondeclarative learning involve regionally specific striatal circuits. The motor circuit (involving the putamen) has been associated with motor–skill learning and the dorsolateral prefrontal cortex (DLPFC) circuit (involving the caudate) has been associated with cognitive–habit learning. Efforts to differentiate functional striatal circuits within patient samples have been limited. Previous studies have provided mixed results regarding striatal-dependent nondeclarative learning deficits in patients with schizophrenia. In this study, a cognitive–habit learning task (probabilistic weather prediction) was used to assess the DLPFC circuit and a motor–skill learning task (pursuit rotor) was used to assess the motor circuit in 35 patients with schizophrenia and 35 normal controls. Patients with schizophrenia displayed significant performance differences from controls on both nondeclarative tasks; however, cognitive–habit learning rate in patients did not differ from controls. There were performance and learning-rate differences on the motor–skill learning task between the whole sample of patients and controls, however, analysis of a subset of patients and controls matched on general intellectual level eliminated learning rate differences between groups. The abnormal performance offset between patients with schizophrenia and controls in the absence of learning rate differences suggests that abnormal cortical processing provides altered input to normal striatal circuitry.
Memory for Extinction of Conditioned Fear Is Long-lasting and Persists Following Spontaneous Recovery
Authors: Quirk Gregory J.
Published: December 2002

Conditioned fear responses to a tone paired with footshock rapidly extinguish when the tone is presented in the absence of the shock. Rather than erase conditioning, extinction is thought to involve the formation of new memory. In support of this, extinguished freezing spontaneously recovers with the passage of time. It is not known, however, how long extinction memory lasts or whether extinction interferes with consolidation of conditioning if given on the same day. To address this, we gave rats 7 trials of auditory fear conditioning followed 1 h later by 20 extinction trials, and tested for spontaneous recovery after a delay of 0, 1, 2, 4, 6, 10, or 14 d. Conditioned freezing to the tone gradually recovered with time to reach 100% by day 10. No-extinction controls indicated that the increase in freezing with time was not owing to incubation of conditioning memory. Complete spontaneous recovery indicates that extinction training given 1 h after conditioning does not interfere with the consolidation of conditioning memory. Despite complete recovery of freezing, rats showed savings in their rate of re-extinction, indicating persistence of extinction memory. These data support the idea that conditioning and extinction of fear are learned by independent systems, each able to retain a long-term memory.
Second-Order Olfactory-Mediated Fear-Potentiated Startle
Authors: Paschall Gayla Y. , Davis Michael
Published: December 2002

Recently, we reported that discrete (4-sec) olfactory cues paired with footshock serve as effective conditioned stimuli (CSs) for potentiating the acoustic startle response in rats using the fear-potentiated startle paradigm. Because odors are such salient cues for the rat, and because of the robust olfactory conditioning observed previously, the current studies investigated second-order fear conditioning using olfactory and visual cues. In Experiments 1 and 2, we used a small number of first-order and second-order training trials on separate days to investigate second-order fear-potentiated startle. Significant potentiated startle was observed in animals receiving Paired/Paired training in both studies, but surprisingly, control animals in the Unpaired/Paired group (Exp. 1) also showed significant potentiated startle to a light S2 at testing. These findings are addressed in the Discussion. Overall, the results of both experiments suggest that olfactory cues serve as efficient S1 and S2 stimuli in second-order fear-potentiated startle paradigms when only a small number of first and second-order training trials are presented.
Fimbria-Fornix Lesions Disrupt the Dead Reckoning (Homing) Component of Exploratory Behavior in Mice
Authors: Gorny Joanna H. , Gorny Bogdan , Wallace Douglas G. , Whishaw Ian Q.
Published: December 2002

Exploration is the primary way in which rodents gather information about their spatial surroundings. Thus, spatial theories propose that damage to the hippocampus, a structure thought to play a fundamental role in spatial behavior, should disrupt exploration. Exploration in rats is organized. The animals create home bases that are central to exploratory excursions and returns, and hippocampal formation damage alters the organization of exploration by disrupting returns. Mice do not appear to readily establish home bases in novel environments, thus, for this species, it is more difficult to establish the contribution of the hippocampus to exploration. The purpose of the present study was threefold: develop a task in which mice center their exploration from a home base, determine whether the exploratory behavior is organized, and evaluate the role of fimbria-fornix lesions on exploration. Mice were given a novel exploratory task in which their nesting material was placed on a large circular table. Video records of control and fimbria-fornix mice were made in both light and dark (infrared light) conditions. Exploration patterns (outward trips, stops, and homeward trips) were reconstructed from the video records. Control mice centered their activity on their bedding, from which they made circuitous outward trips marked by many stops, and periodic direct returns. The bedding-centered behavior and outward trips of the fimbria-fornix mice were similar to those of the control mice, but significantly fewer direct return trips occurred. The direct homeward trips observed under light and dark conditions were consistent with a dead-reckoning strategy, in which an animal computes its present position and homeward trajectory from self-movement cues generated on the outward trip. Because the fimbria-fornix lesions disrupted the homeward component of exploratory trips, we conclude that the fimbria-fornix may contribute to dead reckoning in mice. The results also show that the home-bedding methodology facilitates the establishment of a home base by mice, thus providing a useful methodology for studies with mice.
A novel alteration of muscle chloride channel gating in myotonia levior
Authors: Ryan Aisling , Rüdel Reinhardt , Kuchenbecker Maya , Fahlke Christoph
Published: November 2002

Mutations in the voltage‐dependent skeletal muscle chloride channel, ClC‐1, result in dominant or recessive myotonia congenita. The Q552R mutation causes a variant of dominant myotonia with a milder phenotype, myotonia levior. To characterise the functional properties of this mutation, homodimeric mutant and heterodimeric wild‐type (WT) mutant channels were expressed in tsA201 cells and studied using the whole‐cell recording technique. Q552R ClC‐1 mutants formed functional channels with normal ion conduction but altered gating properties. Mutant channels were activated by membrane depolarisation, with a voltage dependence of activation that was shifted by more than +90 mV compared to WT channels. Q552R channels were also activated by hyperpolarisation, and this process was dependent upon the intracellular chloride concentration ([Cl−]i). Together, these alterations resulted in a substantial reduction in the open probability at −85 mV at a physiological [Cl−]i. Heterodimeric WT‐Q552R channels did not exhibit hyperpolarisation‐activated gating transitions. As was the case for WT channels, activation occurred upon depolarisation, but the activation curve was shifted by 28 mV to more positive potentials. The functional properties of heterodimeric channels suggest a weakly dominant effect, a finding that correlates with the inheritance pattern and symptom profile of myotonia levior.
Conversion of PrP to a Self-Perpetuating PrP
Sc
-like Conformation in the Cytosol
Authors: Ma Jiyan , Lindquist Susan
Published: November 2002

A rare conformation of the prion protein, PrP
Sc
, is found only in mammals with transmissible prion diseases and represents either the infectious agent itself or a major component of it. The mechanism for initiating PrP
Sc
formation is unknown. We report that PrP retrogradely transported out of the endoplasmic reticulum produced both amorphous aggregates and a PrP
Sc
-like conformation in the cytosol. The distribution between these forms correlated with the rate of appearance in the cytosol. Once conversion to the PrP
Sc
-like conformation occurred, it was sustained. Thus, PrP has an inherent capacity to promote its own conformational conversion in mammalian cells. These observations might explain the origin of PrP
Sc
.
Neurotoxicity and Neurodegeneration When PrP Accumulates in the Cytosol
Authors: Ma Jiyan , Wollmann Robert , Lindquist Susan
Published: November 2002

Changes in prion protein (PrP) folding are associated with fatal neurodegenerative disorders, but the neurotoxic species is unknown. Like other proteins that traffic through the endoplasmic reticulum, misfolded PrP is retrograde transported to the cytosol for degradation by proteasomes. Accumulation of even small amounts of cytosolic PrP was strongly neurotoxic in cultured cells and transgenic mice. Mice developed normally but acquired severe ataxia, with cerebellar degeneration and gliosis. This establishes a mechanism for converting wild-type PrP to a highly neurotoxic species that is distinct from the self-propagating PrP
Sc
isoform and suggests a potential common framework for seemingly diverse PrP neurodegenerative disorders.
Essential Role for the SMN Complex in the Specificity of snRNP Assembly
Authors: Pellizzoni Livio , Yong Jeongsik , Dreyfuss Gideon
Published: November 2002

The Survival of Motor Neurons (SMN) protein, the product of the spinal muscular atrophy–determining gene, is part of a large macromolecular complex (SMN complex) that functions in the assembly of spliceosomal small nuclear ribonucleoproteins (snRNPs). Using cell extracts and purified components, we demonstrated that the SMN complex is necessary and sufficient to mediate the ATP-dependent assembly of the core of seven Sm proteins on uridine-rich, small nuclear ribonucleic acids (U snRNAs). In vitro experiments revealed strict requirements for ordered binding of the Sm proteins and the U snRNAs to the SMN complex. Importantly, the SMN complex is necessary to ensure that Sm cores assemble only on correct RNA targets and prevent their otherwise promiscuous association with other RNAs. Thus, the SMN complex functions as a specificity factor essential for the efficient assembly of Sm proteins on U snRNAs and likely protects cells from illicit, and potentially deleterious, nonspecific binding of Sm proteins to RNAs.
Guest-Dependent Spin Crossover in a Nanoporous Molecular Framework Material
Authors: Halder Gregory J. , Kepert Cameron J. , Moubaraki Boujemaa , Murray Keith S. , Cashion John D.
Published: November 2002

The nanoporous metal-organic framework Fe
2
(azpy)
4
(NCS)
4
·(guest) (azpy is
trans
-4,4′-azopyridine) displays reversible uptake and release of guest molecules and contains electronic switching centers that are sensitive to the nature of the sorbed guests. The switching of this material arises from the presence of iron(II) spin crossover centers within the framework lattice, the sorbed phases undergoing “half-spin” crossovers, and the desorbed phase showing no switching property. The interpenetrated framework structure displays a considerable flexibility with guest uptake and release, causing substantial changes in the local geometry of the iron(II) centers. The generation of a host lattice that interacts with exchangeable guest species in a switchable fashion has implications for the generation of previously undeveloped advanced materials with applications in areas such as molecular sensing.
The Spectral-Element Method, Beowulf Computing, and Global Seismology
Authors: Komatitsch Dimitri , Ritsema Jeroen , Tromp Jeroen
Published: November 2002

The propagation of seismic waves through Earth can now be modeled accurately with the recently developed spectral-element method. This method takes into account heterogeneity in Earth models, such as three-dimensional variations of seismic wave velocity, density, and crustal thickness. The method is implemented on relatively inexpensive clusters of personal computers, so-called Beowulf machines. This combination of hardware and software enables us to simulate broadband seismograms without intrinsic restrictions on the level of heterogeneity or the frequency content.
Direct Link Between
mhc
Polymorphism, T Cell Avidity, and Diversity in Immune Defense
Authors: Messaoudi Ilhem , Patiño Jose A. Guevara , Dyall Ruben , LeMaoult Joël , Nikolich-Žugich Janko
Published: November 2002

Major histocompatibility complex (
mhc
)–encoded molecules govern immune responses by presenting antigenic peptides to T cells. The extensive polymorphism of genes encoding these molecules is believed to enhance immune defense by broadening the array of antigenic peptides available for T cell recognition, but direct evidence supporting the importance of this mechanism in combating pathogens is limited. Here we link
mhc
polymorphism
-
driven diversification of the cytotoxic T lymphocyte (CTL) repertoire to the generation of high-avidity, protective antiviral T cells and to superior antiviral defense. Thus, much of the beneficial effect of the
mhc
polymorphism in immune defense may be due to its critical influence on the properties of the selected CTL repertoire.
The Salinity, Temperature, and δ
18
O of the Glacial Deep Ocean
Authors: Adkins Jess F. , McIntyre Katherine , Schrag Daniel P.
Published: November 2002

We use pore fluid measurements of the chloride concentration and the oxygen isotopic composition from Ocean Drilling Program cores to reconstruct salinity and temperature of the deep ocean during the Last Glacial Maximum (LGM). Our data show that the temperatures of the deep Pacific, Southern, and Atlantic oceans during the LGM were relatively homogeneous and within error of the freezing point of seawater at the ocean's surface. Our chloride data show that the glacial stratification was dominated by salinity variations, in contrast with the modern ocean, for which temperature plays a primary role. During the LGM the Southern Ocean contained the saltiest water in the deep ocean. This reversal of the modern salinity contrast between the North and South Atlantic implies that the freshwater budget at the poles must have been quite different. A strict conversion of mean salinity at the LGM to equivalent sea-level change yields a value in excess of 140 meters. However, the storage of fresh water in ice shelves and/or groundwater reserves implies that glacial salinity is a poor predictor of mean sea level.
Hybrid Speciation in Experimental Populations of Yeast
Authors: Greig Duncan , Louis Edward J. , Borts Rhona H. , Travisano Michael
Published: November 2002

Most models of speciation require gradual change and geographic or ecological isolation for new species to arise. Homoploid hybrid speciation occurred readily between
Saccharomyces cerevisiae
and
Saccharomyces paradoxus
. Hybrids had high self-fertility (about 82%), low fertility when backcrossed to either parental species (about 7.5%), and vigorous growth under different thermal environments that favored one or the other of the parental species. Extensive karyotypic changes (tetrasomy) were observed in the hybrids, although genic incompatibilities accounted for 50% of the variation in self-fertility.
Corepressor-Dependent Silencing of Chromosomal Regions Encoding Neuronal Genes
Authors: Lunyak Victoria V. , Burgess Robert , Prefontaine Gratien G. , Nelson Charles , Sze Sing-Hoi , Chenoweth Josh , Schwartz Phillip , Pevzner Pavel A. , Glass Christopher , Mandel Gail , Rosenfeld Michael G.
Published: November 2002

The molecular mechanisms by which central nervous system–specific genes are expressed only in the nervous system and repressed in other tissues remain a central issue in developmental and regulatory biology. Here, we report that the zinc-finger gene-specific repressor element RE-1 silencing transcription factor/neuronal restricted silencing factor (REST/NRSF) can mediate extraneuronal restriction by imposing either active repression via histone deacetylase recruitment or long-term gene silencing using a distinct functional complex. Silencing of neuronal-specific genes requires the recruitment of an associated corepressor, CoREST, that serves as a functional molecular beacon for the recruitment of molecular machinery that imposes silencing across a chromosomal interval, including transcriptional units that do not themselves contain REST/NRSF response elements.
Truncating Neurotrypsin Mutation in Autosomal Recessive Nonsyndromic Mental Retardation
Authors: Molinari Florence , Rio Marlène , Meskenaite Virginia , Encha-Razavi Férechté , Augé Joelle , Bacq Delphine , Briault Sylvain , Vekemans Michel , Munnich Arnold , Attié-Bitach Tania , Sonderegger Peter , Colleaux Laurence
Published: November 2002

A 4–base pair deletion in the neuronal serine protease neurotrypsin gene was associated with autosomal recessive nonsyndromic mental retardation (MR). In situ hybridization experiments on human fetal brains showed that neurotrypsin was highly expressed in brain structures involved in learning and memory. Immuno-electron microscopy on adult human brain sections revealed that neurotrypsin is located in presynaptic nerve endings, particularly over the presynaptic membrane lining the synaptic cleft. These findings suggest that neurotrypsin-mediated proteolysis is required for normal synaptic function and suggest potential insights into the pathophysiological bases of mental retardation.
Structural Adaptations in a Membrane Enzyme That Terminates Endocannabinoid Signaling
Authors: Bracey Michael H. , Hanson Michael A. , Masuda Kim R. , Stevens Raymond C. , Cravatt Benjamin F.
Published: November 2002

Cellular communication in the nervous system is mediated by chemical messengers that include amino acids, monoamines, peptide hormones, and lipids. An interesting question is how neurons regulate signals that are transmitted by membrane-embedded lipids. Here, we report the 2.8 angstrom crystal structure of the integral membrane protein fatty acid amide hydrolase (FAAH), an enzyme that degrades members of the endocannabinoid class of signaling lipids and terminates their activity. The structure of FAAH complexed with an arachidonyl inhibitor reveals how a set of discrete structural alterations allows this enzyme, in contrast to soluble hydrolases of the same family, to integrate into cell membranes and establish direct access to the bilayer from its active site.
Cosmic Rays, Clouds, and Climate
Authors: Carslaw K. S. , Harrison R. G. , Kirkby J.
Published: November 2002

It has been proposed that Earth's climate could be affected by changes in cloudiness caused by variations in the intensity of galactic cosmic rays in the atmosphere. This proposal stems from an observed correlation between cosmic ray intensity and Earth's average cloud cover over the course of one solar cycle. Some scientists question the reliability of the observations, whereas others, who accept them as reliable, suggest that the correlation may be caused by other physical phenomena with decadal periods or by a response to volcanic activity or El Niño. Nevertheless, the observation has raised the intriguing possibility that a cosmic ray–cloud interaction may help explain how a relatively small change in solar output can produce much larger changes in Earth's climate. Physical mechanisms have been proposed to explain how cosmic rays could affect clouds, but they need to be investigated further if the observation is to become more than just another correlation among geophysical variables.
Molecular Hydrogen as an Energy Source for
Helicobacter pylori
Authors: Olson Jonathan W. , Maier Robert J.
Published: November 2002

The gastric pathogen
Helicobacter pylori
is known to be able to use molecular hydrogen as a respiratory substrate when grown in the laboratory. We found that hydrogen is available in the gastric mucosa of mice and that its use greatly increased the stomach colonization by
H. pylori
. Hydrogenase activity in
H. pylori
is constitutive but increased fivefold upon incubation with hydrogen. Hydrogen concentrations measured in the stomachs of live mice were found to be 10 to 50 times as high as the
H. pylori
affinity for hydrogen. A hydrogenase mutant strain is much less efficient in its colonization of mice. Therefore, hydrogen present in animals as a consequence of normal colonic flora is an energy-yielding substrate that can facilitate the maintenance of a pathogenic bacterium.
In Vivo Imaging of Quantum Dots Encapsulated in Phospholipid Micelles
Authors: Dubertret Benoit , Skourides Paris , Norris David J. , Noireaux Vincent , Brivanlou Ali H. , Libchaber Albert
Published: November 2002

Fluorescent semiconductor nanocrystals (quantum dots) have the potential to revolutionize biological imaging, but their use has been limited by difficulties in obtaining nanocrystals that are biocompatible. To address this problem, we encapsulated individual nanocrystals in phospholipid block–copolymer micelles and demonstrated both in vitro and in vivo imaging. When conjugated to DNA, the nanocrystal-micelles acted as in vitro fluorescent probes to hybridize to specific complementary sequences. Moreover, when injected into
Xenopus
embryos, the nanocrystal-micelles were stable, nontoxic (<5 × 10
9
nanocrystals per cell), cell autonomous, and slow to photobleach. Nanocrystal fluorescence could be followed to the tadpole stage, allowing lineage-tracing experiments in embryogenesis.
Martian Meteorite Launch: High-Speed Ejecta from Small Craters
Authors: Head James N. , Melosh H. Jay , Ivanov Boris A.
Published: November 2002

We performed high-resolution computer simulations of impacts into homogeneous and layered martian terrain analogs to try to account for the ages and characteristics of the martian meteorite collection found on Earth. We found that craters as small as ∼3 kilometers can eject ∼10
7
decimeter-sized fragments from Mars, which is enough to expect those fragments to appear in the terrestrial collection. This minimum crater diameter is at least four times smaller than previous estimates and depends on the physical composition of the target material. Terrain covered by a weak layer such as an impact-generated regolith requires larger, therefore rarer, impacts to eject meteorites. Because older terrain is more likely to be mantled with such material, we estimate that the martian meteorites will be biased toward younger ages, which is consistent with the meteorite collection.
The Emotional Ape
Authors: Whiten Andrew
Published: November 2002

Infant Chimpanzee and Human Child
A Classic 1935 Comparative Study of Ape Emotions and Intelligence. N. N. Ladygina-Kohts. Edited by Frans B. M. de Waal. Oxford University Press, New York, 2002. 468 pp. $65. ISBN 0-19-513565-2. Series in Affective Science.

In this work, which originally appeared as a memoir of Moscow's Darwin Museum, the author compares the development of a chimpanzee and her son in terms of inborn tendencies, emotions, play, and habits.
Formation of Giant Planets by Fragmentation of Protoplanetary Disks
Authors: Mayer Lucio , Quinn Thomas , Wadsley James , Stadel Joachim
Published: November 2002

The evolution of gravitationally unstable protoplanetary gaseous disks has been studied with the use of three-dimensional smoothed particle hydrodynamics simulations with unprecedented resolution. We have considered disks with initial masses and temperature profiles consistent with those inferred for the protosolar nebula and for other protoplanetary disks. We show that long-lasting, self-gravitating protoplanets arise after a few disk orbital periods if cooling is efficient enough to maintain the temperature close to 50 K. The resulting bodies have masses and orbital eccentricities similar to those of detected extrasolar planets.
Seismotectonics of Mid-Ocean Ridge Propagation in Hess Deep
Authors: Floyd Jacqueline S. , Tolstoy Maya , Mutter John C. , Scholz Christopher H.
Published: November 2002

Hydroacoustic data from the eastern equatorial Pacific reveal low-magnitude seismicity concentrated at the propagating tip of the Galapagos Rise in Hess Deep. The patterns of seismicity and faulting are similar to those observed in the process zone of laboratory-scale propagating tensile cracks. Because the fracture energy required for propagation scales with crack length and process zone size, it follows that ridges can propagate stably in the brittle crust without exceptional resisting forces as proposed by previous models based on linear elastic fracture mechanics.
Photochemical Smog Hides an Icy World
Authors: Strobel Darrell F.
Published: November 2002

Lifting Titan's Veil
Exploring the Giant Moon of Saturn. Ralph Lorenz and Jacqueline Mitton. Cambridge University Press, Cambridge, 2002. 268 pp. $29, £19.95. ISBN 0-521-79348-3.

As the Cassini-Huygens mission approaches the solar system's second largest satellite, the authors offer a nonspecialist account of Titan, its atmosphere, and our efforts to learn more about both.
N-Linked Glycosylation in
Campylobacter jejuni
and Its Functional Transfer into
E. coli
Authors: Wacker Michael , Linton Dennis , Hitchen Paul G. , Nita-Lazar Mihai , Haslam Stuart M. , North Simon J. , Panico Maria , Morris Howard R. , Dell Anne , Wren Brendan W. , Aebi Markus
Published: November 2002

N-linked protein glycosylation is the most abundant posttranslation modification of secretory proteins in eukaryotes. A wide range of functions are attributed to glycan structures covalently linked to asparagine residues within the asparagine-X-serine/threonine consensus sequence (Asn-Xaa-Ser/Thr). We found an N-linked glycosylation system in the bacterium
Campylobacter jejuni
and demonstrate that a functional N-linked glycosylation pathway could be transferred into
Escherichia coli
. Although the bacterial N-glycan differs structurally from its eukaryotic counterparts, the cloning of a universal N-linked glycosylation cassette in
E. coli
opens up the possibility of engineering permutations of recombinant glycan structures for research and industrial applications.
Creative writing workshops for medical education: learning from a pilot study with hospital staff
Authors: Gull S E , O’Flynn R , Hunter J Y L
Published: December 2002

A course in creative writing was designed as a possible tool in medical education. Twelve volunteers (six doctors and six non-medical staff) participated in seven workshops held weekly. Four aims were identified: to help put thoughts onto paper; to facilitate interpretation of narrative; to encourage expression of emotions related to illness and death, and to encourage creativity. The course was evaluated using participant observational analysis and two questionnaires. This paper discusses the outcomes in relation to these aims, but identifies additional issues raised by the development.

Only six of the 12 participants produced a final piece of written work, with lack of self discipline being cited as the chief reason. There was a strong tendency for self reflection in the group, which needed appropriate support. How creativity can be encouraged remains unclear. The value of multidisciplinary learning in this context was identified.

The value of creative writing for medical education remains difficult to measure, but the participants agreed unanimously that the course would be an enjoyable way of encouraging medical students in its stated aims.
“You keep telling me what has been lost, and I keep telling you something remains.” A personal response to:Scar Tissueby Michael Ignatieff
Authors: Lewis W
Published: December 2002

Michael Ignatieff is well known as a journalist and broadcaster of a distinctly intellectual kind. He has written movingly on the trauma of modern warfare and Europe following the Cold War. His CV also boasts of studies on the Scottish Enlightenment and nineteenth century penal policy. Additionally, his Booker short listed novelScar Tissueis one of the most interesting studies of medicine and the human consequences of disease of the last decade.
Is surgical mystique a myth and double standard the reality?
Authors: Michel L A , Johnson P
Published: December 2002

Clinically relevant attitudes and guidelines issued by a rational evidence based medicine (EBM) approach, integrateindividual clinical expertisewith the bestavailable external clinical evidencefrom systematic research. Many surgeons, however, while considering the ultraliberal world they are practising in, and fearing that the primary goal of managed care in a market environment is reducing cost in order to make profit or decrease spending, remain suspicious of this kind of tentative protocol driven medicine when applied to surgical practice. If surgeons want to develop a health policy agenda that emphasises patient care issues above providers’ or payers’ interests, they should also enhance education programmes, improve continuing objective assessment of the way surgery is performed, face moral issues raised by innovation, and assume an increased leadership role in sound critical evaluation ofnon-validatednew techniques. They should no longer consider EBM as a weapon turned against the surgical profession, but rather see it as a tool that may provide some answers to chronically unresolved questions in the evolving art of surgery.
Art, science, and the existential focus of clinical medicine
Authors: Warsop A
Published: December 2002

The continuing debate over the status of medicine as an art or a science remains far from resolved. The aim of this paper is to clarify what is meant by the art of medicine. In the following interpretation I contrast two current perspectives of the medical art. I argue that the art of medicine is best understood in terms of the Aristotelian notion oftechne. It consists of listening skills directed to the lived experience of the patient in such a way that knowledge (principally scientific knowledge) can be applied in a therapeutic way. This constitutes what I call medicine’s existential focus. The art of medicine is prior to and independent of medical science which plays an important but subordinate role.
Anticipating deep autumn: a widening lens
Authors: Nixon L Lacivita , Roscoe L A
Published: December 2002

Medicine has become one of the most powerful influences of the twentieth century, and currently dominates how we approach and think about another powerful phenomenon: the aging of the world’s population. Our reliance on the medical model, with its focus on pathology, physiology, and biomedical interventions, makes it difficult for aging men and women and those in the health care field who care for them to seek alternative ways to attach meaning to the process of growing old. This article explores the role of the humanities as an alternative to the biomedical model which can enlarge our abilities to see the multidimensional aspects of aging. Age related writings and visual images by Kenyon, Neel, Olds, Valadon, and Hemingway are discussed to illustrate how fictive representations can and do serve as a moral impetus or stimulus for meaningful reflection about life stages that have not yet been experienced.
A three-dimensional model to simulate joint networks in layered rocks
Authors: Josnin Jean-Yves , Jourde Hervé , Fénart Pascal , Bidaux Pascal
Published: November 2002

Modelling the discontinuity network of fractured reservoirs may be addressed (1) by purely stochastic means, (2) with a fractal approach, or (3) using mechanical parameters describing the spatial organisation of fracture systems. Our paper presents an approach where the geometrical properties of the fracture networks are incorporated in the form of both statistical and mechanical rules. This type of approach is particularly suitable to model stratified fractured rock masses comprising two orthogonal families of joints and a family of sedimentary discontinuities. Their geometrical arrangement is governed by two kinds of rules based on (1) statistical parameters such as the mean, standard deviation of joint length and of bed thickness, both determined by field observations, and (2) geometrical parameters that result from genetic processes inferred from field observations and analogue experiments on the nucleation and propagation mechanisms of joints. Using these parameters, we generate realistic networks in terms of the relative position of joints that control the overall network connectivity: the model enables all combinations of joint spacing and vertical persistence for orthogonal patterns ranging from ladder type to grid type patterns. It also integrates the concept of mechanical "saturation" of a bed, thereby permitting the generation of both "saturated" and "unsaturated" networks.
Stratigraphy, depositional setting, and diagenetic history of the Saint-Jules Formation (Upper Devonian or Mississippian), a newly identified post-Acadian red clastic unit in the southern Gaspé Peninsula, Quebec
Authors: Jutras Pierre , Prichonnet Gilbert
Published: November 2002

The Saint-Jules Formation, a post-Acadian continental clastic unit previously mapped as part of the Bonaventure Formation (pre-Namurian unit), was recently identified in the southern Gaspé Peninsula of Quebec. The Saint-Jules Formation in the study area is confined to a small post-sedimentary graben. The unit is characterized by fault-controlled, oxidized, and poorly sorted detritus that underwent short transportation by fluvial processes. The Saint-Jules Formation is locally overlain by a massive groundwater calcrete several metres in thickness, which is tentatively correlated with the calcretization event that has affected the base of the La Coulée Formation grey clastics (pre-Namurian unit). The calcrete has developed within the karstified upper beds of the Saint-Jules Formation, which brings new insights into the potential hosts of such calcretes and on the potential stratigraphic confusion that such diagenetic overprints can create. Partial erosion of both the La Coulée and Saint-Jules clastic rocks, as well as the massive groundwater calcretes, occurred prior to deposition of the Bonaventure Formation. Like the La Coulée and Bonaventure formations, the Saint-Jules is undated, but unconformably overlies Acadian structures (Middle Devonian) and predates Mabou Group units (Namurian).
An Early Devonian (Emsian) acanthodian from the Bear Rock Formation, Anderson River, Northwest Territories, Canada
Authors: Cumbaa Stephen L , Schultze Hans-Peter
Published: November 2002

A new genus and species of an Early Devonian (Emsian) mesacanthid acanthodiform from outcrops of the Bear Rock Formation along the Anderson River, Northwest Territories, Canada, is described. The new taxon is distinct from other mesacanthid genera and (or) species in having mesiolaterally expanded skull roof plates and paired nasal bones. Mesacanthids have fin-spines that are similar in size, number, position, and proportions. This new genus is the fourth in the family Mesacanthidae. The wider distribution and apparent taxonomic diversity represented by the discovery of the new genus are indications that the latest-surviving and arguably most advanced acanthodian group, the Acanthodiformes, was already well established in the Early Devonian.
Litho- and chronostratigraphic relationships of the SantonianCampanian Milk River Formation in southern Alberta and Eagle Formation in Montana utilising stratigraphy, UPb geochronology, and palynology
Authors: Payenberg Tobias HD , Braman Dennis R , Davis Donald W , Miall Andrew D
Published: November 2002

UPb geochronology, palynology, and lithostratigraphy were employed on the Late Cretaceous rocks in southern Alberta and Montana to solve litho- and chronostratigraphic correlation problems. In the outcrop area around Writing-On-Stone Provincial Park, southern Alberta, the Milk River Formation has a Santonian to possibly very earliest Campanian age and was deposited between ~84.5 Ma and 83.5 Ma. In southern Montana, the Eagle Formation was deposited from ~83.5 Ma to 81.2 Ma, and contains different lithologies and depositional environments as opposed to southern Alberta. In north-central Montana, the Telegraph Creek Formation and Virgelle and Deadhorse Coulee members are equivalent in depositional environments and time to those of the Milk River Formation in southern Alberta. The upper Eagle member, however, has no time- or facies-equivalent rocks around Writing-On-Stone Provincial Park, but is time equivalent to the Alderson Member of the Lea Park Formation in southeastern Alberta. A hiatus of ~2.5 Ma is present between the top of the Milk River Formation in the outcrop area and the basal beds of the Pakowki Formation. The Pakowki transgression occurred at around 81.0 Ma based on a UPb zircon age of 80.7 ± 0.2 Ma from bentonite beds just above the bottom of the Pakowki Formation in southern Alberta. This age agrees with previous ages of 80.7 ± 0.6 Ma for the Ardmore Bentonite Beds and ~81.0 Ma for the Claggett transgression in southern Montana.
Communities and paleoecology of Eifelian (mid-Devonian) brachiopods from the Bird Fiord Formation of Arctic Canada
Authors: Li Rong-yu , Jones Brian
Published: November 2002

The carbonatesiliciclastic strata in the Bird Fiord Formation of Arctic Canada contain a diverse brachiopod-dominated biota. A collection of 46 381 brachiopods from 126 sites at 35 localities on Ellesmere Island, North Kent Island, Grinnell Peninsula (Devon Island), and Bathurst Island includes 22 species assigned to 21 genera. Many of these taxa are endemic to Arctic Canada. Each collection of brachiopods is typically dominated by only one or two taxa. Cluster analysis, based on binary data, shows that the brachiopods can be divided into an AtrypaElythyna community group and a SpinatrypinaDesquamatia community group. The former encompasses the AtrypaElythyna and AtrypaElythynaPerryspirifer communities, and the latter includes the SpinatrypinaDesquamatia and SpinatrypinaDesquamatiaCranaena communities. The distribution of these communities was primarily related to water depth. Thus, the AtrypaElythyna community group, which belongs to benthic assemblage 3, lived in a shallow, proximal-shelf environment. The SpinatrypinaDesquamatia community group, which belongs to benthic assemblage 4, lived in a deeper, distal-shelf environment.
Sensitive high resolution ion microprobe (SHRIMP) detrital zircon geochronology provides new evidence for a hidden Neoproterozoic foreland basin to the Grenville Orogen in the eastern Midwest, U.S.A.
Authors: Schneider Santos João Orestes , Hartmann Léo Afraneo , McNaughton Neal Jesse , Easton Robert M , Rea Ron G , Potter Paul E
Published: November 2002

A sensitive high resolution ion microprobe (SHRIMP) was used in combination with backscattered electron (BSE) and cathodoluminescence (CL) images to determine the age of detrital zircons from sandstones in the Neoproterozoic Middle Run Formation of the eastern Midwest, United States. Eleven samples from seven drill cores of the upper part of the Middle Run Formation contain detrital zircons ranging in age from 1030 to 1982 Ma (84 analyses), with six distinctive modes at 1.96, 1.63, 1.47, 1.34, 1.15, and 1.08 Ga. This indicates that most, but not all, of the zircon at the top of the Middle Run Formation was derived from the Grenville Orogen. The youngest concordant detrital zircon yields a maximum age of 1048 ± 22 Ma for the Middle Run Formation, indicating that the formation is younger than ca. 1026 Ma minus the added extra time needed for later uplift, denudation, thrusting, erosion, and transport to southwestern Ohio. Thus, as judged by proximity, composition, thickness, and geochronology, it is a North American equivalent to other Neoproterozoic Grenvillian-derived basins, such as the Torridon Group of Scotland and the Palmeiral Formation of South America. An alternate possibility, although much less likely in our opinion, is that it could be much younger, any time between 1048 ± 22 Ma and the deposition of the Middle Cambrian Mount Simon Sandstone at about 510 Ma, and still virtually almost all derived from rocks of the Grenville Orogen.
Three-dimensional velocity images beneath the KangDian Tethyan tectonic zone of China
Authors: Liu Yike , Chang Xu , Liu Futian , Zheng Ye
Published: November 2002

Three-dimensional velocity images of the crust and upper mantle beneath the KangDian Tethyan tectonic zone in China are constructed using P-wave travel-time residuals of earthquakes. The KangDian Tethyan tectonic zone is a transitional zone in tectonic structures and an important topographic border line. It is also a zone of concentration of shallow-focus earthquakes. The imaging results indicate that there is a significant lateral heterogeneity in the crust and upper mantle beneath the KangDian Tethyan tectonic zone in China. The velocity images of the upper crust show features closely related to the tectonic features on the surface. A low-velocity layer exists in a very wide range of the mid-crust. Almost all of the major earthquakes took place in the transition strips between high- and low-velocity zones in the crust above 20 km depth. From the velocity images at 20+0 and 50+0 km depth, respectively, we find that the epicenters of strong earthquakes with magnitude larger than 6.0 are almost entirely distributed in the low-velocity zones or on their boundaries.