bluuebunny/crossref_metadata_2025 huggingface dataset:
Global glaciation in the Neoproterozoic: Reconciling previous modelling results
Authors: Lewis Jeffrey P. , Eby Michael , Weaver Andrew J. , Johnston Stephen T. , Jacob Robert L.
Published: April 2004

Recent Neoproterozoic climate modelling experiments using different sea ice components have yielded opposing results. Here we have attempted to reconcile these differences through the implementation of various representations of sea ice in the University of Victoria Earth System Climate Model. In particular, using a sea ice model similar to that of the Fast Ocean Atmosphere Model version 1.4, global glaciation is not achievable, whereas it occurs with an energy‐conserving version of a more physically complete thermodynamic model. We argue that using a physically incomplete representation of sea ice may be a major factor in the inability of some previous coupled models to simulate global glaciations.
gurke and pasticcino3 mutants affected in embryo development are impaired in acetyl‐CoA carboxylase
Authors: Baud Sébastien , Bellec Yannick , Miquel Martine , Bellini Catherine , Caboche Michel , Lepiniec Loïc , Faure Jean‐Denis , Rochat Christine
Published: April 2004

Normal embryo development is required for correct seedling formation. The Arabidopsis gurke and pasticcino3 mutants were isolated from different developmental screens and the corresponding embryos exhibit severe defects in their apical region, affecting bilateral symmetry. We have recently identified lethal acc1 mutants affected in acetyl‐CoA carboxylase 1 (ACCase 1) that display a similar embryo phenotype. A series of crosses showed that gk and pas3 are allelic to acc1 mutants, and direct sequencing of the ACC1 gene revealed point mutations in these new alleles. The isolation of leaky acc1 alleles demonstrated that ACCase 1 is essential for correct plant development and that mutations in ACCase affect cellular division in plants, as is the case in yeast. Interestingly, significant metabolic complementation of the mutant phenotype was obtained by exogenous supply of malonate, suggesting that the lack of cytosolic malonyl‐CoA is likely to be the initial factor leading to abnormal development in the acc1 mutants.
Follicle separation during Drosophila oogenesis requires the activity of the Kinesin II‐associated polypeptide Kap in germline cells
Authors: Pflanz Ralf , Peter Annette , Schäfer Ulrich , Jäckle Herbert
Published: April 2004

Cellular localization of organelles, protein complexes and single mRNAs depends on the directed transport along microtubule tracks, a process mediated by ATP‐driven molecular motor proteins of the dynein and kinesin superfamilies. Kinesin II is a heterotrimeric protein complex composed of two motor subunits and a unique nonmotor Kinesin‐associated protein (Kap). Kap was shown to transport both particulate cargo, as axoneme components in rafts, and membrane‐bounded organelles such as melanosomes. Drosophila Kinesin II was shown to be essential for the axonal transport of choline acetyltransferase in a specific set of neurons. We have generated Kap mutants and show that gene activity is not only required for neuronal function but also for separation of follicles during early oogenesis. The data suggest that Kap participates in the transport of signalling components required for instructive interactions between germline and soma cells.
Slow Ca2+ dynamics in pharyngeal muscles in Caenorhabditis elegans during fast pumping
Authors: Shimozono Satoshi , Fukano Takashi , Kimura Koutarou D , Mori Ikue , Kirino Yutaka , Miyawaki Atsushi
Published: April 2004

The pharyngeal muscles of Caenorhabditis elegans are composed of the corpus, isthmus and terminal bulb from anterior to posterior. These components are excited in a coordinated fashion to facilitate proper feeding through pumping and peristalsis. We analysed the spatiotemporal pattern of intracellular calcium dynamics in the pharyngeal muscles during feeding. We used a new ratiometric fluorescent calcium indicator and a new optical system that allows simultaneous illumination and detection at any two wavelengths. Pumping was observed with fast, repetitive and synchronous spikes in calcium concentrations in the corpus and terminal bulb, indicative of electrical coupling throughout the muscles. The posterior isthmus, however, responded to only one out of several pumping spikes to produce broad calcium transients, leading to peristalsis, the slow and gradual motion needed for efficient swallows. The excitation–calcium coupling may be uniquely modulated in this region at the level of calcium channels on the plasma membrane.
Two new types of quantum states generated via higher powers of Bogoliubov’s transformation
Authors: Wu Wei , Wu Ling-An
Published: April 2004

By applying higher powers of Bogoliubov’s transformation operator b†=ν*a+μ*a† to the even and odd coherent states we construct mathematically two new types of quantum states. Various special functions and mathematical formulations are used to obtain the matrix elements for the states in the coherent state representation. The nonclassical nature of these states is found to be related to their quantum coherence in phase space. The interference effects can also be regarded as a consequence of the oscillatory behavior of the special functions in the structure of the states.
Geodesic distances on density matrices
Authors: Jenčová Anna
Published: April 2004

We find an upper bound for geodesic distances associated to monotone Riemannian metrics on positive definite matrices and density matrices.
Interior structural bifurcation and separation of 2D incompressible flows
Authors: Ma Tian , Wang Shouhong
Published: April 2004

We study transitions in the topological structure of a family of divergence-free vector fields u(⋅,t) near an interior point. It is shown that structural bifurcation occurs at t0 if u(⋅,t0) has an isolated degenerate singular point x0∈M̊ with zero index and nonzero Jacobian at x0, and with nonzero acceleration in the direction normal to the (unique) eigenspace of the Jacobian. This result is carried out by analyzing the orbit structure of u near such an isolated degenerate interior singular point of u(⋅,t0). Applications to typical interior separation phenomena in two-dimensional fluid flows are addressed as well.
Group-cohomology refinement to classify G-symplectic manifolds
Authors: Guerrero J. , Jaramillo J. L. , Aldaya V.
Published: April 2004

“Pseudo-cohomology,” as a refinement of Lie group cohomology, is soundly studied aiming at classifying the symplectic manifolds associated with Lie groups. In this study, the framework of symplectic cohomology provides fundamental new insight, which enriches the analysis previously developed in the setting of Cartan–Eilenberg H2(G,U(1)) cohomology.
Generating Gowdy cosmological models
Authors: Sánchez Alberto , Macı́as Alfredo , Quevedo Hernando
Published: April 2004

Using the analogy with stationary axisymmetric solutions, we present a method to generate new analytic cosmological solutions of Einstein’s equation belonging to the class of T3 Gowdy cosmological models. We show that the solutions can be generated from their data at the initial singularity and present the formal general solution for arbitrary initial data. We exemplify the method by constructing the Kantowski–Sachs cosmological model and a generalization of it that corresponds to an unpolarized T3 Gowdy model.
Fluorobenzene–argon ground-state intermolecular potential energy surface
Authors: Fajı́n José Luis Cagide , López Cacheiro Javier , Fernández Berta , Makarewicz Jan
Published: April 2004

The ground-state intermolecular potential energy surface for the fluorobenzene—argon van der Waals complex is evaluated using the coupled-cluster singles and doubles including connected triple excitations model, with the augmented correlation consistent polarized valence double-zeta basis set extended with a set of 3s3p2d1f1g midbond functions. In the surface minima the Ar atom is located above and below the fluorobenzene plane at a distance of 3.562 Å from the fluorobenzene center of mass and at an angle of 6.33° with respect to the axis perpendicular to the fluorobenzene plane. The corresponding binding energy is 391.1 cm−1. Both these results and the eigenvalues obtained from the potential compare well with the experimental data available.
The role of the irreducible representations of the Poincaré group in solving Maxwell’s equations
Authors: Moses Harry E.
Published: April 2004

Maxwell’s equations are universally solved when the charge and current densities are given, without reference to the transformation properties of the fields or charge density–current density four vector. However these transformation properties are generally held to be essential physical properties of the fields and the charge density–current density four-vector. They are required if the consequences of relativity are to hold. The way the fields and four-vectors transform constitutes a representation of the Poincaré group which can be reduced to the irreducible representations of that group first given by Wigner. The use of the irreducible representations corresponds to the expansion of the fields and currents into modes which have the simplest possible transformation properties. These modes can be identified as wave functions of particles of spin 1 and mass m   (0⩽m<∞). We compare the solutions of Maxwell’s equations utilizing the “usual” time-dependent Green’s function and the method introduced in this paper. The solutions are identical, if we assume that the fields created by the time-dependent sources have the same initial values for the fields. Among the new results, we demonstrate the mechanism by which one can transform transverse fields for which the charge density is zero to fields that are partially longitudinal and for which the charge density source is not zero under Poincaré transformations of the space–time coordinates. We give a concrete example of a transverse current density source and one for a longitudinal current density source and show that sources lead to a mass spectrum of the photons. Longitudinal current densities always lead to noncausal (as noncausal is commonly understood) solutions for the fields.
Functional classification of proteins and protein variants
Authors: Lau Albert Y. , Chasman Daniel I.
Published: April 2004

To help characterize the diversity in biological function of proteins emerging from the analysis of whole genomes, we present an operational definition of biological function that provides an explicit link between the functional classification of proteins and the effects of genetic variation or mutation on protein function. Using phylogenetic information, we establish definite criteria for functional relatedness among proteins and a companion procedure for predicting deleterious alleles or mutations. Applied to the functional classification of sequences similar to 13 human tumor suppressor proteins, our methods predict there are functional properties unique to mammals for three of them, BRCA1, BRCA2, and WT1. We examine protein variants caused by nonsynonymous single-nucleotide polymorphisms in a set of clinically important genes and estimate the magnitude of a disproportionate propensity for disruption of function among the nonsynomous single-nucleotide polymorphisms that are maintained at low frequency in the human population.
Cells have distinct mechanisms to maintain protection against different reactive oxygen species: Oxidative-stress-response genes
Authors: Thorpe Geoffrey W. , Fong Chii S. , Alic Nazif , Higgins Vincent J. , Dawes Ian W.
Published: April 2004

The complete set of viable deletion strains in
Saccharomyces cerevisiae
was screened for sensitivity of mutants to five oxidants to identify cell functions involved in resistance to oxidative stress. This screen identified a unique set of mainly constitutive functions providing the first line of defense against a particular oxidant; these functions are very dependent on the nature of the oxidant. Most of these functions are distinct from those involved in repair and recovery from damage, which are generally induced in response to stress, because there was little correlation between mutant sensitivity and the reported transcriptional response to oxidants of the relevant gene. The screen identified 456 mutants sensitive to at least one of five different types of oxidant, and these were ranked in order of sensitivity. Many genes identified were not previously known to have a role in resistance to reactive oxygen species. These encode functions including protein sorting, ergosterol metabolism, autophagy, and vacuolar acidification. Only two mutants were sensitive to all oxidants examined, only 12 were sensitive to at least four, and different oxidants had very different spectra of deletants that were sensitive. These findings highlight the specificity of cellular responses to different oxidants: No single oxidant is representative of general oxidative stress. Mitochondrial respiratory functions were overrepresented in mutants sensitive to H
2
O
2
, and vacuolar protein-sorting mutants were enriched in mutants sensitive to diamide. Core functions required for a broad range of oxidative-stress resistance include transcription, protein trafficking, and vacuolar function.
Small Maf proteins serve as transcriptional cofactors for keratinocyte differentiation in the Keap1–Nrf2 regulatory pathway
Authors: Motohashi Hozumi , Katsuoka Fumiki , Engel James Douglas , Yamamoto Masayuki
Published: April 2004

The small Maf proteins, MafF, MafG, and MafK, possess a leucine zipper (Zip) domain that is required for homodimer or heterodimer complex formation with other bZip transcription factors. In this study we sought to determine the identity of the specific constituent that collaboratively interacts with Nrf2 to bind to the Maf recognition element
in vivo
. Studies
in vitro
suggested that Nrf2 forms heterodimers with small Maf proteins and then bind to Maf recognition elements, but the bona fide partner molecules supporting Nrf2 activity
in vivo
have not been definitively identified. Nrf2 activity is usually suppressed by a cytoplasmic repressor, Keap1, so disruption of the
keap1
gene causes constitutive activation of Nrf2. Nrf2 hyperactivity results in hyperproliferation of keratinocytes in the esophagus and forestomach leading to perinatal lethality. However, simultaneous disruption of
nrf2
rescued
keap1
-null mice from the lethality. We exploited this system to investigate whether small Mafs are required for Nrf2 function. We generated
keap1
and small
maf
compound mutant mice and examined whether keratinocyte abnormalities persisted in these animals. The data show that loss of
mafG
and
mafF
in the
keap1
-null mice reversed the lethal keratinocyte dysfunction and rescued the
keap1
-null mutant mice from perinatal lethality. This rescue phenotype of
mafG
::
mafF
::
keap1
triple compound mutant mice phenocopies that of the
nrf2
::
keap1
compound mutant mice, indicating that the small Maf proteins MafG and MafF must functionally cooperate with Nrf2
in vivo
.
BofA protein inhibits intramembrane proteolysis of pro-σKin an intercompartmental signaling pathway duringBacillus subtilissporulation
Authors: Zhou Ruanbao , Kroos Lee
Published: April 2004

Bacillus subtilisis a bacterium that undergoes a developmental program of sporulation in response to starvation. At the core of the program are σ factors, whose regulated spatiotemporal activation controls much of the gene expression. Activation of pro-σKin the mother cell compartment involves regulated intramembrane proteolysis (RIP) in response to a signal from the forespore. RIP is a poorly understood process that is conserved in prokaryotes and eukaryotes. Here, we report a powerful system for studying RIP of pro-σK.Escherichia coliwas engineered to coexpress the putative membrane-embedded metalloprotease SpoIVFB with pro-σKand potential inhibitors of RIP. Overproduction of SpoIVFB and pro-σKinE. coliallowed accurate and abundant proteolytic processing of pro-σKwith the characteristics expected for SpoIVFB acting as an intramembrane-cleaving protease (I-Clip). Coexpression of BofA in this system led to formation of a BofA–SpoIVFB complex and marked inhibition of pro-σKprocessing. Mutational analysis identified amino acids in BofA that are necessary for complex formation and inhibition of processing, leading us to propose that BofA inhibits SpoIVFB metalloprotease activity by providing a metal ligand, analogous to the cysteine switch mechanism of matrix metalloprotease regulation. The approach described herein should be applicable to studies of other RIP events and amenable to developingin vitroassays for I-Clips.
Regulation of ultraviolet light-induced gene expression by gene size
Authors: McKay Bruce C. , Stubbert Lawton J. , Fowler Casey C. , Smith Jennifer M. , Cardamore Robin A. , Spronck Jennifer C.
Published: April 2004

UV light induces the expression of a wide variety of genes. At present, it is unclear how cells sense the extent of DNA damage and alter the expression of UV-induced genes appropriately. UV light induces DNA damage that blocks transcription, and the probability that a gene sustains transcription-blocking DNA damage is proportional to locus size and dose of UV light. Using colon carcinoma cells that express a temperature-sensitive variant of p53 and undergo p53-dependent apoptosis after UV irradiation, we found that the number of p53-induced genes identified by oligonucleotide microarray analysis decreased in a UV dose-dependent manner. This was associated with a statistically significant shift in the spectrum of p53-induced genes toward compact genes with fewer and smaller introns. Genes encoding proapoptotic proteins involved in the initiation of the mitochondrial apoptotic cascade were prominent among the compact p53 target genes, whereas genes encoding negative regulators of p53 and the mitochondrial apoptotic pathway were significantly larger. We propose that the shift in spectrum of UV-responsive gene expression caused by passive effects of UV lesions on transcription acts as a molecular dosimeter, ensuring the elimination of cells sustaining irreparable transcription-blocking DNA damage.
Activation of dopamine D
4
receptors by ABT-724 induces penile erection in rats
Authors: Brioni Jorge D. , Moreland Robert B. , Cowart Marlon , Hsieh Gin C. , Stewart Andrew O. , Hedlund Petter , Donnelly-Roberts Diana L. , Nakane Masaki , Lynch James J. , Kolasa Teodozyi , Polakowski James S. , Osinski Mark A. , Marsh Kennan , Andersson Karl-Erik , Sullivan James P.
Published: April 2004

Apomorphine, a nonselective dopamine receptor agonist, facilitates penile erection and is effective in patients suffering from erectile dysfunction. The specific dopamine receptor subtype(s) responsible for its erectogenic effect is not known. Here we report that the dopamine D
4
receptor plays a role in the regulation of penile function. ABT-724 is a selective dopamine D
4
receptor agonist that activates human dopamine D
4
receptors with an EC
50
of 12.4 nM and 61% efficacy, with no effect on dopamine D
1
, D
2
, D
3
, or D
5
receptors. ABT-724 dose-dependently facilitates penile erection when given s.c. to conscious rats, an effect that is blocked by haloperidol and clozapine but not by domperidone. A proerectile effect is observed after intracerebroventricular but not intrathecal administration, suggesting a supraspinal site of action. s.c. injections of ABT-724 increase intracavernosal pressure in awake freely moving rats. In the presence of sildenafil, a potentiation of the proerectile effect of ABT-724 is observed in conscious rats. The ability of ABT-724 to facilitate penile erection together with the favorable side-effect profile indicates that ABT-724 could be useful for the treatment of erectile dysfunction.
Requirement for Arf6 in breast cancer invasive activities
Authors: Hashimoto Shigeru , Onodera Yasuhito , Hashimoto Ari , Tanaka Miwa , Hamaguchi Michinari , Yamada Atsuko , Sabe Hisataka
Published: April 2004

In most human breast cancer cell lines, there is a direct correlation between their
in vivo
invasive phenotypes and
in vitro
invasion activities. Here, we found that ADP-ribosylation factor 6 (Arf6) is localized at the invadopodia of the cultured breast cancer cells MDA-MB-231, and its suppression by a small-interfering RNA duplex effectively blocks the invasive activities of the cells, such as invadopodia formation, localized matrix degradation and Matrigel transmigration but not the cell-adhesion activity. We also found that the GTP hydrolysis-defective mutant Arf6(Q67L) and the GTP-binding defective mutant Arf6(T27N) both blocked these invasive activities but not cell adhesion, suggesting the necessity of continued activation and cycling of the Arf6 GTPase cycle in invasion. Among the different human breast cancer cell lines that we examined, cell lines with high invasive activities expressed higher amounts of Arf6 protein than those in weakly invasive and noninvasive cell lines, although no notable correlation was found between Arf6 mRNA expression levels and invasive activities. Moreover, Matrigel-transmigration activity of all of these invasive cells was blocked effectively by an Arf6 small-interfering RNA duplex. Hence, Arf6 appears to be an integral component of breast cancer invasive activities, and we propose that Arf6 and the intracellular machinery regulating Arf6 during invasion should be considered as therapeutic targets for the prevention of breast cancer invasion.
Acculturation and social support in relation to psychosocial adjustment of adolescent refugees resettled in Australia
Authors: Kovacev Lydia , Shute Rosalyn
Published: April 2004

This study examined how different modes of acculturation and perceived social support are related to adolescent refugee psychosocial adjustment, as measured by global self-worth and peer social acceptance. The 83 participants, aged between 12 and 19 and now resident in Australia, were from the former Republic of Yugoslavia. Those who had the most positive attitudes toward both cultures obtained the highest ratings of self-worth and peer social acceptance. In contrast, those who had negative attitudes toward both cultures had the lowest scores on these measures of psychosocial adjustment. Results were consistent with the proposition that the effects of acculturation on adjustment are mediated by peer social support.
Stability and changes in sleep regulation: A longitudinal study from 3 months to 3 years
Authors: Scher Anat , Epstein Rachel , Tirosh Emmanuel
Published: April 2004

The goal of the study was to examine the developmental course of sleep consolidation from infancy to preschool. The sleep of 50 healthy infants aged 3 months was recorded, at home, with actigraphs (computerised activity monitors). Follow-up recordings were carried out at 6, 9, 12, 20, and 42 months (due to attrition and occasional technical failures, complete sleep records were not available for all subjects at all ages). The main findings were that by 12 months, nocturnal sleep is well organised; nevertheless, sleep continues to become less fragmented and more efficient beyond the first year. The child’s level of motor activity during sleep, and the overall sleep efficiency were moderately stable across time. In contrast, sleep duration and the number of nightwaking episodes were unstable from 3 to 42 months of age. Taken together, the continuity and change in the group trajectory of sleep maturation, as well as the stability and the periodic instability in the individuals’ rank across time, may be interpreted to reflect the interplay among constitutional, maturational, and experiential factors.
Buprenorphine for Office‐based Practice: Consensus Conference Overview
Authors: Kosten Thomas R. , Fiellin David A.
Published: April 2004

This overview of the March 2003 conference on the U.S. national buprenorphine implementation program is developed to inform the practitioner about the positive experience that has been accumulated worldwide on the use of buprenorphine for office‐based practice. The first paper delineates the challenges for American psychiatry in moving buprenorphine forward into general practice. Most psychiatrists are unprepared to work with opiate‐dependent patients or to use buprenorphine. The international successes with office‐based buprenorphine from France and Australia are presented in the next papers, followed by presentations on several U.S. studies using buprenorphine in the community for detoxification and office‐based maintenance. These experiences have thus far confirmed buprenorphine's utility and promise for opiate addiction treatment in the U.S. Finally, two national monitoring programs have been implemented to assess the public health impact of this new treatment opportunity. This opportunity has a three‐year window, however, and a critical need will be to attract a sufficient number of physicians into prescribing buprenorphine / naloxone in order to allow our patients increased access to this treatment.
Challenges in Increasing Access to Buprenorphine Treatment for Opiate Addiction
Authors: West Joyce C. , Kosten Thomas R. , Wilk Joshua , Svikis Dace , Triffleman Elise , Rae Donald S. , Narrow William E. , Duffy Farifteh F. , Regier Darrel A.
Published: April 2004

The aims of this study are to assess psychiatrists' comfort using office‐based opiate agonist treatment (OBOT) and to identify psychiatrist characteristics associated with OBOT comfort. A random sample of 2,323 AMA Master‐file of Physicians psychiatrists were surveyed through the 2002 APIRE National Survey of Psychiatric Practice (NSSP). Of the 52% responding (N= 1,203), 80.6% (SE = 1.8%) were not comfortable providing OBOT. Males, addiction‐certified psychiatrists, and those treating substance abuse patients were more comfortable providing OBOT. These findings highlight significant barriers in providing buprenorphine treatment. Increasing the understanding of specific financing and services delivery barriers that clinicians face is needed to inform the development of effective integrated services models and policies to facilitate OBOT implementation.
A web‐based tool for dissertation writing Rosanne Strachan, Rowena Murray and Hilary Grierson
Authors: Strachan Rosanne , Murray Rowena , Grierson Hilary
Published: April 2004

Online web tools are becoming an important and accessible means of supporting learning in higher education. Student writing is central to teaching and learning (Lillis, 2001). This paper describes an online tool designed to support dissertation writing. By combining three types of online space—instructional material, a writing space and planning templates—this tool aimed to provide a holistic approach to writing and writing development. This paper demonstrates how the tool was used in an academic course in order to address certain teaching and learning problems identified by the course tutor. Student feedback suggests that while further development is needed, the tool was still useful. This paper raises awareness of the complex array of issues involved in dissertation writing and provides insights into solutions to writing problems. While we designed what we considered to be a web‐based tool for dissertation writing, we argue that the writing space and planning templates go some way towards creating an environment for the development of learning (Häkkinen, 2002).
Unions without rents: the curious economics of faculty unions
Authors: Hosios Arthur J. , Siow Aloysius
Published: April 2004

Abstract.  We show that Canadian faculty unions have had no effect on university revenues, only a small positive effect on earnings, a negative effect on research output, and lead to earnings redistributions across disciplines and ranks. We argue that faculty unions have a negligible positive (and often negative) effect on average faculty wages, because a union that promotes the median faculty member's welfare negotiates wage redistributions and more onerous teaching conditions, despite the negative impact these changes have on research output. Average wages may rise, but only because non‐unionized universities trade off wages against the non‐pecuniary benefits from research and teaching. JEL classification: I20, J51, J54
Informational spillovers and the coordination of speculative investments
Authors: González Francisco M.
Published: April 2004

Abstract.  The influence of informational spillovers on the entrepreneur's incentive to undertake reversible investment opportunities is considered. It is shown how investment activity can be driven by the influence that the prospect of social learning has on the option value of investment. In this context, episodes of high investment activity result from a speculative motive, and the expected short‐run profitability of new investment opportunities may inadequately reflect the entrepreneurs’ incentive to invest.
An incremental analysis of the value of expanding a wilderness area
Authors: Buttle Jonathan , Rondeau Daniel
Published: April 2004

Abstract. 
 Forsyth (2000) concludes from an option value analysis that when considered together, Killarney Provincial Park and two adjacent parcels of land should be preserved in an expanded park. With a simple discrete difference approach, we assess the incremental value of the adjacent land and decompose the benefits of park expansion. We identify a change in the value of the option to log the current park as a new component of value not previously reported. Applying the method to Killarney suggests that logging may be the most efficient use of the adjacent land. We also provide corrections for some of Forsyth's numerical results. JEL Classification: D81, Q20.
Alternative hypotheses and the volume of trade: the gravity equation and the extent of specialization
Authors: Haveman Jon , Hummels David
Published: April 2004

Abstract.  We examine why the gravity equation works and the implications for its use. First, we demonstrate that the gravity equation as a statistical relationship can be generated from a model with incomplete specialization and trade costs. Second, we analyse the predominance of zero bilateral trade values as a ‘puzzle’ broadly inconsistent with the complete specialization models typically used to derive the gravity equation, but consistent with the alternative hypothesis of incomplete specialization. Third, we demonstrate that the explanation for why the gravity equation works has considerable relevance for how the gravity equation is interpreted and used and how we view bilateral trade.
Effects of island isolation and feral mink removal on bird communities on small islands in the Baltic Sea
Authors: Nordström Mikael , Korpimäki Erkki
Published: April 2004

Predation has been suggested as a major cause affecting survival, reproductive success and behaviour in vertebrate prey populations. The breeding season is a critical phase because the essential difference between selecting the proper nest site may be a question of breeding success and failure.

Islands may serve as refuges for ground‐nesting birds against natural mammalian predators. However, many of the bird species breeding on islands are currently threatened by introduced predators because they may lack mechanisms to confront the threats of the new predator.

We studied the combined effects of an introduced generalist predator, American mink (Mustela vison Schreb.), and island isolation and size on species richness, abundance and equitability of birds breeding on small islands in the outer archipelago of SW Finland, Baltic Sea. The study comprised two mink removal areas (one during 1993–2001 and the other during 1998–2001) and two comparable control areas (during 1994–2001 and 1998–2001), each covering 72–130 km2, of which between 1·07 and 1·27 km2 were land area. The mean island size in all areas was < 2 ha.

In the two control areas, both the species richness and abundance were highest on the most isolated islands, while isolation did not have obvious effects on these variables in mink removal areas. Species equitability was not influenced by mink removal or island isolation.

The distribution of a maritime species, the razorbill (Alca torda L.), has changed dramatically: in the 1973–74, before mink invaded the area, the species was found commonly on less isolated islands than in 1994, after mink invasion.

We suggest that in the presence of mink birds may have changed their breeding site selection and started to breed on the most isolated islands, which are not visited by mink as frequently as less isolated islands. Therefore, our results indicate that increasing island isolation may increase the number of bird species and their numbers, because island isolation slows down mink dispersal.
Strong density dependence in a predatory insect: large‐scale experiments in a stream
Authors: Hildrew Alan G. , Woodward Guy , Winterbottom Julie H. , Orton Stuart
Published: April 2004

Empirical information about the intergenerational dynamics of stream insects is scarce, and most field experiments are conducted at small temporal and spatial scales that are inappropriate for assessing effects upon population dynamics. We performed a large‐scale, intergenerational population manipulation of an abundant, stream‐dwelling predator, the alderflySialis fuliginosa, by altering its recruitment over 3 consecutive years (it has a 2‐year life cycle).

Experimental treatments were assigned to three contiguous 150‐m stretches. Each year at least 92% ofS. fuliginosaeggs, that are laid on the streamside vegetation, were removed from an upstream ‘removal’ stretch and transferred below an adjacent ‘control’ stretch to a downstream ‘addition’ stretch, where recruitment was thus effectively doubled.

Although manipulations were successful initially, the effects were transient. Strong density‐dependent survival stabilized the population at a similar density in all three stretches within the first 4 months of life for the 1997 cohort and somewhat later for the 1998 cohort. Survey data suggested that intraguild predation (including cannibalism) and/or starvation, particularly early in the life cycle, might be regulating theS. fuliginosapopulation.

It is intriguing that this abundant predator, which is linked very richly within the complex Broadstone Stream food web, has a strongly stabilized population, even in the face of such a dramatic perturbation in recruitment.
Long‐distance dispersal and human population density allow the prediction of invasive patterns in the horse chestnut leafminerCameraria ohridella
Authors: Gilbert M. , Grégoire J.‐C. , Freise J. F. , Heitland W.
Published: April 2004

After its initial discovery in Macedonia in 1985, during the last 19 years the leafminer mothCameraria ohridellahas invaded most of Central and Western Europe. The species, which causes aesthetic damage to horse chestnuts, is generally observed first in highly populated locations before colonizing the countryside. This pattern is consistent with a stratified dispersal process combining long‐distance movements and local diffusion.

Using large‐scale spatial data on damage caused byCameraria ohridellain Germany, three stochastic spatial models of spread are compared: a diffusion model, a leptokurtic dispersal model and a stratified dispersal model that assumes a two‐scale dispersal process. In addition, the association between human population and moth invasion is tested in this last model by linking long‐distance infestation probability to human population density. Finally, these spatial models constructed with data from Germany are tested at the European scale and compared to historical records of first occurrence.

The fat‐tailed dispersal kernel models (leptokurtic and stratified dispersal models) allowing for long‐distance dispersal provide better predictions than the diffusion model. Among these models, the stratified dispersal model incorporating the effect of human population density provides the best description of the spread ofCameraria ohridellain Germany in predictive (lowest sum of squared errors) and qualitative (similar fractal dimension) terms.

The roles of short‐distance and long‐distance dispersal inCameraria ohridellainvasion ecology in relation to human population are discussed, together with the models’ scale‐dependence and limitations.
Spatial scale, heterogeneity and functional responses
Authors: Bergström Ulf , Englund Göran
Published: April 2004

In a laboratory experiment, we studied the effect of arena size on the functional response of the mysid shrimp Neomysis integer preying on the cladoceran Polyphemus pediculus. The aim of the study was to examine mechanisms that cause the functional response to be scale‐dependent, by documenting the spatial distribution and the movement behaviour of predator and prey.

The attack rate was significantly higher in large arenas, while the handling time did not differ between arena sizes. The difference in attack rate could be explained by differences in aggregative behaviour of predator and prey and in swimming activity of the predator. It is suggested that distributions of animals are often affected by the walls of the experimental arenas and that this spatial heterogeneity is scale‐dependent, which may have a considerable impact on estimates of ecological process rates.

A method of correcting attack rate estimates for artefacts caused by such spatial heterogeneity is presented.
Spatial abundance structures in an assemblage of gall‐forming sawflies
Authors: McGeoch M. A. , Price P. W.
Published: April 2004

Examination of the fine‐scale internal structure of species geographical ranges, and interspecific variation therein across landscapes, contributes to a more comprehensive understanding of the structure of geographical ranges. Two components of this internal structure that require further examination are the occurrence, extent and position of spatial autocorrelation, and relationships between the spatial abundance structures of closely related, ecologically similar species.

Here we compare the abundance structures of an assemblage of gall‐forming sawflies (Tenthredinidae) across a landscape. We identify the relative roles of spatial and non‐spatial factors in explaining their abundance structures and test the hypothesis that sawfly density is explained by host plant quality, as has been demonstrated repeatedly at finer scales. We use these results to distinguish between alternative sets of mechanisms that may be operating at the landscape scale.

Species densities were mainly multimodal across the landscape and significantly spatially structured, with patch, periodic and trend components. The abundance structures thus mimic those found generally for species across the full extent of their geographical ranges.

Many abundance structure characteristics were unique to species, with differences in their correlogram profiles, distances over which densities were positively autocorrelated, and the absence of significant spatial structure in one species.

In contrast to previous, fine‐scale studies, host plant quality explained little of the variation in sawfly gall density across the landscape, whereas unexplained spatial structure contributed between 30% and 50%. Based on knowledge of the biology of these species and the absence of competitive interactions, species dispersal characteristics and the Moran effect are suggested as probable alternative hypotheses at this scale.

Therefore, a spatial approach has identified the hierarchical nature of mechanisms underlying the population dynamics of this sawfly assemblage for the first time. Furthermore, it has highlighted the importance of spatial processes in explaining the densities of species at the landscape scale, as well as the individualistic nature of their abundance structures.
“The Island has been Handed over to Me”: Ascension Island as a Company Colony, 1922–42
Authors: Royle Stephen A.
Published: April 2004

Ascension Island has spent almost all its years of organised human settlement as a military base. The major exception was between 1922 and 1942 when it was ruled by a civilian company, an unusual form of governance in modern colonial history. Though nominally subject to St Helena, and through that British colony to London, outside interference was largely restricted to rulings on colonial etiquette. The manager of the company was also head of both the government and legal systems. This paper considers the operation of this company colony, the tensions between the company and its workforce/subjects, and the contestation from 1942 for political supremacy between the company, the British state and the American forces that arrived when the island became involved in World War II. Ascension's narrative helps to exemplify some themes in postcolonial discourse and, given the unusual and extreme nature of the island's experiences, informatively broadens understanding of colonialism.
Differential targeting of the L‐type Ca2+ channel α1C (CaV1.2) to synaptic and extrasynaptic compartments in hippocampal neurons
Authors: Obermair Gerald J. , Szabo Zsolt , Bourinet Emmanuel , Flucher Bernhard E.
Published: April 2004

In central nervous system neurons L‐type Ca2+ channels are involved in developmental processes, the integration and conduction of postsynaptic electric activity and synaptic plasticity. However, little is known about the channel isoforms underlying each of these functions or about the exact localization and targeting properties of the major L‐type channel isoform α1C (CaV1.2) in neurons. We addressed these questions using high‐resolution immunofluorescence analysis of the endogenous α1C and epitope‐tagged recombinant channel isoforms expressed in mouse hippocampal neurons. Endogenous α1C and surface‐expressed hemagglutinin (HA)‐tagged α1C‐HA were localized in small clusters distributed between the axon initial segment and the apical branches of the dendritic tree. The average cluster size was estimated to be eight channels per α1C‐HA cluster. Analysis of the subcellular localization of α1C‐HA clusters relative to known synaptic markers suggested the existence of two distinct populations of α1C clusters, extrasynaptic and synaptic, the latter associated with glutamatergic synapses in dendritic spines. Both glutamatergic and GABAergic neurons expressed α1C in the soma and dendrites. In contrast to the N‐type channel GFP‐α1B, GFP‐α1C was excluded from distal axons and nerve terminals of mature neurons. In developing neurons, however, α1C and α1C‐HA were robustly expressed in the growth cone, indicating that specific targeting properties of neuronal compartments change during differentiation. Synaptic and extrasynaptic localizations of α1C correspond to putative roles of L‐type Ca2+ currents in synaptic modulation and in the propagation of dendritic Ca2+ spikes, respectively. The transiently expressed α1C in the growth cone may be involved in neurite extension and axonal pathfinding.
Survival, regeneration and functional recovery of motoneurons in adult rats by reimplantation of ventral root following spinal root avulsion
Authors: Gu Huai‐Yu , Chai Hong , Zhang Jian‐Yi , Yao Zhi‐Bin , Zhou Li‐Hua , Wong Wai‐Man , Bruce Iain , Wu Wu‐Tian
Published: April 2004

We investigated the functional recovery of motoneurons after reimplanting an avulsed ventral root in a rat model of traction injury. The eighth cervical root (C8) was avulsed by controlled traction and immediately reimplanted to the spinal cord. Spinal nerves from neighbouring segments (C5, C6, C7 and T1) were ligated and cut. After 12 or 20 weeks, the survival, regeneration and functional recovery of spinal motoneurons were evaluated by Nissl staining, retrograde labelling of motoneurons, NOS histochemistry, histological examination of muscle and nerve–muscle junction, electromyography and behavioural observation. In the control animals, about 14% or 11% of spinal motoneurons survived 12 or 20 weeks postinjury, respectively. By contrast, in animals with ventral root reimplantation, 62% and 55% of motoneurons survived at 12 or 20 weeks postinjury, respectively. Retrograde labelling and histological examination indicated that about 90% of the surviving motoneurons in the C8 segment regenerated axons into the reimplanted ventral root. Staining the muscles with silver and cholinesterase revealed new motor endplates in the reinnervated muscle. Functionally significant electromyographic responses in flexor digitorum superficialis and flexor carpi radialis were observed in experimental animals; however, the average latency of the motor action potentials was greater than normal control. The grasping test showed functional recovery of finger flexors and median nerve. In conclusion, our results indicate that spinal motoneurons can regenerate axons through reimplanted roots and reinnervate muscles to recover partial function.
Projections from the auditory cortex to the superior olivary complex in guinea pigs
Authors: Coomes Diana L. , Schofield Brett R.
Published: April 2004

We used anterograde tracing techniques to characterize projections from auditory cortex to the superior olivary complex (SOC) in guinea pigs. Large injections of fluorescent or biotinylated dextrans into the temporal cortex labeled many axons in the SOC. Labeled boutons were most numerous in the ventral nucleus of the trapezoid body, with additional boutons in all other olivary nuclei. The distribution of boutons was similar in the ipsilateral and contralateral SOC; however, the contralateral SOC had markedly fewer axons and boutons. Similar patterns of labeling were also observed following injections confined to primary auditory cortex or the dorsocaudal auditory field. Cortical axons in many of the SOC nuclei share numerous morphological features, suggesting that individual axons may innervate multiple nuclei and have widespread effects. In addition, some nuclei contain axons with branching or termination patterns unique to that nucleus; these axons may represent focused projections with effects limited to individual SOC nuclei. Given the many projections of SOC nuclei, cortico‐olivary projections are in a position to modify the activity of many brainstem auditory circuits.
Orexin‐A regulates growth hormone‐releasing hormone mRNA content in a nucleus‐specific manner and somatostatin mRNA content in a growth hormone‐dependent fashion in the rat hypothalamus
Authors: López Miguel , Seoane Luisa María , Tovar Sulay , Nogueiras Rubén , Diéguez Carlos , Señarís Rosa
Published: April 2004

The orexins or hypocretins are two neuropeptides involved in the regulation of diverse biological processes such as feeding, sleep and neuroendocrine function. Recent findings suggest a possible functional interaction between orexins, somatostatin and growth hormone‐releasing hormone (GHRH) in the rat hypothalamus. In order to understand the possible functional linkage between orexins and these neuropeptides, we determined the effects of intracerebroventricular orexin‐A administration on hypothalamic somatostatin and GHRH mRNA levels. Furthermore, we examined whether growth hormone (GH) mediates these interactions by using two animal models that showed GH deficiency: hypophysectomized rats and dwarf Lewis rats. Using in situ hybridization, our data showed that GHRH mRNA levels in the paraventricular nucleus of the hypothalamus are decreased after orexin‐A treatment, without changes in the arcuate nucleus of the hypothalamus. On the other hand, orexin‐A treatment induces a GH‐dependent stimulatory effect on somatostatin mRNA content in the periventricular nucleus of the hypothalamus. Finally, we demonstrated, for the first time, that hypophysectomized rats and dwarf Lewis rats, two classical models of GH deficiency with alterations in sleep patterns, showed a marked reduction in the GHRH mRNA levels in the paraventricular nucleus of the hypothalamus. These data improve our understanding of the interactions among the different systems involved in the control and pathophysiology of food intake, sleep and GH secretion.