bluuebunny/crossref_metadata_2025_split huggingface dataset:
Fatigue crack propagation from a precrack under combined torsional and axial loading
Authors: TANAKA K. , AKINIWA Y. , KATO T. , MIKURIYA T. 
Published: January 2005

ABSTRACTFatigue tests of crack propagation from a precrack in thin‐walled tubular specimens made of a medium‐carbon steel were performed under cyclic torsion with and without superposed static or cyclic axial loading. The stress ratio of cyclic loading was −1. The fatigue crack‐propagation path from a precrack was compared with the predictions based on the maximum tangential stress criterion. The direction of fatigue crack propagation follows the direction of the maximum of the range of the tangential stress, Δσ*θ max, near the crack tip determined from the stress intensity factor (SIF) which was calculated by considering the contacts of crack faces at the minimum load. The SIF calculated from the actual crack path by using the body force method (BFM) showed that the mode II SIF range quickly approached zero after a small amount of crack extension. The crack‐propagation rate decreased first and then increased with crack extension. The initial dip of the crack‐propagation rate was caused by the development of crack closure with crack extension. As cracks extended a long distance, the propagation rate was faster than the uniaxial data. This acceleration of crack propagation was caused by excessive plasticity near the crack tip.
Computational simulation and experimental findings of three‐dimensional fatigue crack growth in a single‐edge notched specimen under torsion loading
Authors: BUCHHOLZ F.‐G. , JUST V. , RICHARD H. A. 
Published: January 2005

ABSTRACTIn this paper, the rather complex three‐dimensional (3D) fatigue crack growth behaviour in a single‐edge notched (SEN) specimen with an inclined plane of the initial crack under torsion loading is investigated with the aid of ADAPCRACK3D programme and by application of a recently developed 3D fracture criterion. It will be shown that the computationally simulated results for fatigue crack growth in the FE model of the specimen are in good agreement with experimental findings for the development of spatially twisted and warped crack faces in the real laboratory test specimen. Consequently, also for this case with a rather complex 3D crack growth behaviour, the functionality of the ADAPCRACK3D programme and the validity of the proposed 3D fracture criterion can be stated.
Doublecortin expression levels in adult brain reflect neurogenesis
Authors: Couillard‐Despres Sebastien , Winner Beate , Schaubeck Susanne , Aigner Robert , Vroemen Maurice , Weidner Norbert , Bogdahn Ulrich , Winkler Jürgen , Kuhn Hans‐Georg , Aigner Ludwig 
Published: January 2005

AbstractProgress in the field of neurogenesis is currently limited by the lack of tools enabling fast and quantitative analysis of neurogenesis in the adult brain. Doublecortin (DCX) has recently been used as a marker for neurogenesis. However, it was not clear whether DCX could be used to assess modulations occurring in the rate of neurogenesis in the adult mammalian central nervous system following lesioning or stimulatory factors. Using two paradigms increasing neurogenesis levels (physical activity and epileptic seizures), we demonstrate that quantification of DCX‐expressing cells allows for an accurate measurement of modulations in the rate of adult neurogenesis. Importantly, we excluded induction of DCX expression during physiological or reactive gliogenesis and excluded also DCX re‐expression during regenerative axonal growth. Our data validate DCX as a reliable and specific marker that reflects levels of adult neurogenesis and its modulation. We demonstrate that DCX is a valuable alternative to techniques currently used to measure the levels of neurogenesis. Importantly, in contrast to conventional techniques, analysis of neurogenesis through the detection of DCX does not require in vivo labelling of proliferating cells, thereby opening new avenues for the study of human neurogenesis under normal and pathological conditions.
Hierarchical processing of sound location and motion in the human brainstem and planum temporale
Authors: Krumbholz Katrin , Schönwiesner Marc , Rübsamen Rudolf , Zilles Karl , Fink Gereon R. , Von Cramon D. Yves 
Published: January 2005

AbstractHorizontal sound localization relies on the extraction of binaural acoustic cues by integration of the signals from the two ears at the level of the brainstem. The present experiment was aimed at detecting the sites of binaural integration in the human brainstem using functional magnetic resonance imaging and a binaural difference paradigm, in which the responses to binaural sounds were compared with the sum of the responses to the corresponding monaural sounds. The experiment also included a moving sound condition, which was contrasted against a spectrally and energetically matched stationary sound condition to assess which of the structures that are involved in general binaural processing are specifically specialized in motion processing. The binaural difference contrast revealed a substantial binaural response suppression in the inferior colliculus in the midbrain, the medial geniculate body in the thalamus and the primary auditory cortex. The effect appears to reflect an actual reduction of the underlying activity, probably brought about by binaural inhibition or refractoriness at the level of the superior olivary complex. Whereas all structures up to and including the primary auditory cortex were activated as strongly by the stationary as by the moving sounds, non‐primary auditory fields in the planum temporale responded selectively to the moving sounds. These results suggest a hierarchical organization of auditory spatial processing in which the general analysis of binaural information begins as early as the brainstem, while the representation of dynamic binaural cues relies on non‐primary auditory fields in the planum temporale.
A unified model of presynaptic release site gating by calcium channel domains
Authors: Gentile Luigi , Stanley Elise F. 
Published: January 2005

AbstractCalcium ions enter through discrete ion channels at presynaptic nerve terminals before binding to and activating transmitter release sites. Opposing models hold that release sites are gated either by calcium domains of single, closely associated channels or by extensive, overlapping domains from many remote channels. At the chick calyx synapse we find a linear relation between transmitter release and the number of open calcium channels, favouring single domain activation. This finding is consistent with results from the squid giant synapse but contrasts with steep power dependences reported in rodent synapses, suggestive of activation by extensive overlapping domains. These different reports were reconciled by plotting ‘per cent domain overlap’ against the external calcium concentration used for each species. This relationship predicts the involvement of local channels in the activation of release sites in all species. Further, it suggests that each release site is activated by calcium ions from its immediately associated channels and not by ions that enter through channels associated with a neighbouring release site.
Sequential activation of p75 and TrkB is involved in dendritic development of subventricular zone‐derived neuronal progenitors in vitro
Authors: Gascon E. , Vutskits L. , Zhang H. , Barral‐Moran M. J. , Kiss P. J. , Mas C. , Kiss J. Z. 
Published: January 2005

AbstractDendritic arbor development of subventricular zone‐derived interneurons is a critical step in their integration into functional circuits of the postnatal olfactory bulb. However, the mechanism and molecular control of this process remain unknown. In this study, we have developed a culture model where dendritic development of purified subventricular zone cells proceeds under serum‐free conditions in the absence of added growth factors and non‐neural cells. We demonstrate that the large majority of these cells in culture express GABA and elaborate dendritic arbors with spine‐like protrusions but they do not possess axons. These neurons expressed receptors for neurotrophins including p75, TrkB and TrkC but not TrkA. Application of exogenous neurotrophins, including brain‐derived neurotrophic factor (BDNF), neurotrophin‐3 (NT3) and nerve growth factor (NGF), to cultures stimulated dendritic growth and led to more complex dendritic arbors during the initial 3 days in culture. Our results suggest that these effects are independent of Trk receptors and mediated by the p75/ceramide signaling pathway. We also show that brain‐derived neurotrophic factor is the only neurotrophin that is able to influence late‐phase dendritic development via TrkB receptor activation. These results suggest that dendritic arbor development of subventricular zone‐derived cells may be regulated by neurotrophins through the activation of p75 and the TrkB receptor signaling pathways in a sequentially defined temporal pattern.
Respiratory responses evoked by blockades of ionotropic glutamate receptors within the Bötzinger complex and the pre‐Bötzinger complex of the rabbit
Authors: Mutolo Donatella , Bongianni Fulvia , Nardone Furio , Pantaleo Tito 
Published: January 2005

AbstractThe respiratory role of excitatory amino acid (EAA) receptors within the Bötzinger complex (BötC) and the pre‐Bötzinger complex (pre‐BötC) was investigated in α‐chloralose–urethane anaesthetized, vagotomized, paralysed and artificially ventilated rabbits by using bilateral microinjections (30–50 nL) of EAA receptor antagonists. Blockade of both N‐methyl‐d‐aspartic acid (NMDA) and non‐NMDA receptors by 50 mm kynurenic acid (KYN) within the BötC induced a pattern of breathing characterized by low‐amplitude, high‐frequency irregular oscillations superimposed on tonic phrenic activity and successively the disappearance of respiratory rhythmicity in the presence of intense tonic inspiratory discharges (tonic apnea). KYN microinjections into the pre‐BötC caused similar respiratory responses that, however, never led to tonic apnea. Blockade of NMDA receptors by D(–)‐2‐amino‐5‐phosphonopentanoic acid (D‐AP5; 1, 10 and 20 mm) within the BötC induced increases in respiratory frequency and decreases in peak phrenic amplitude; the highest concentrations caused tonic apnea insensitive to chemical stimuli. Blockade of non‐NMDA receptors by 6‐cyano‐7‐nitroquinoxaline‐2,3‐dione (CNQX; 1, 10 and 20 mm) within the BötC produced only less pronounced increases in respiratory frequency. Responses to D‐AP5 in the pre‐BötC were similar, although less pronounced than those elicited in the BötC and never characterized by tonic apnea. In the same region, CNQX provoked increases in respiratory frequency similar to those elicited in the BötC, associated with slight reductions in peak phrenic activity. The results show that EAA receptors within the investigated medullary subregions mediate a potent control on both the intensity and frequency of inspiratory activity, with a major role played by NMDA receptors.
Development of spontaneous mouth/tongue movement and related neural activity, and their repression in fetal mice lacking glutamate decarboxylase 67
Authors: Tsunekawa Naoko , Arata Akiko , Obata Kunihiko 
Published: January 2005

AbstractSpontaneous body movement starts at early fetal stage, at embryonic day (E) 12–15 in mice. In the present study, the movement of the head region was studied in E13–14 mice by in utero ultrasound imaging, together with the in vitro recording of underlying neural activities in the hypoglossal nerve and the ventral root of the upper cervical cord of an isolated brainstem–spinal cord preparation. The role of γ‐aminobutyric acid (GABA) in the generation of fetal movement was assessed using mice lacking GABA‐synthesizing glutamate decarboxylase 67 (GAD67). At E14, mouth opening and tongue withdrawal were observed independently at frequency of 14/h each. This movement was rarely observed in the GAD67‐deficient mouse. The intraventricular administration of picrotoxin or 3‐mercaptopropionic acid abolished mouth opening in the wild‐type mice. In a brainstem–spinal cord preparation, three types of neural discharge were recorded: mouth/tongue‐moving burst, respiratory burst and irregular activity on the basis of their waveform, regularity in occurrence and concomitant muscle activity. In the GAD67‐deficient mice, the occurrence of mouth/tongue‐moving burst and irregular activity was inhibited to about 15 and 40% of those in the wild‐type mice, respectively. Respiratory burst was slightly inhibited but the difference was not significant. Picrotoxin greatly reduced the frequency of mouth/tongue‐moving burst. These results indicate that GABA is involved in rhythm generation in movement of the head region and support the hypothesis that cleft palate in the GAD67‐deficient mouse is due to the impairment of mouth or tongue movement that assists palate formation.
The structure of global species–range size distributions: raptors & owls
Authors: Gaston Kevin J. , Davies Richard G. , Gascoigne Caroline E. , Williamson Mark 
Published: January 2005

ABSTRACTAims To determine the shape of global species–range size distributions, the influence on these of island species, threatened species and patterns of latitudinal variation in range sizes, and the fit to logit‐normal distributions.Location Global.Methods We take the spatial distributions of the raptors and owls of the world as exemplar data sets, document the shapes of their species–range size distributions, the influence of particular groups of species and of latitudinal variation in range sizes on these shapes, and the fit of these distributions to a variety of models.Results The global species–range size distributions of both raptors and owls are extremely right skewed on untransformed axes. They are not lognormally distributed, as has commonly been stated for species–range size distributions, nor logit‐normally distributed as has been suggested might be the case. For raptors, departures from either a lognormal or a logit‐normal are little mitigated by excluding groups of species that might be thought to distort the observed species–range size distribution, nor by the latitudinal gradient in geographical range size. For owls, the effects of excluding island and threatened species are more marked, with the fit of the species–range size distribution to a lognormal or a logit‐normal becoming much closer.Conclusions A simple general description of the shape of species–range size distributions remains elusive. This constitutes a significant constraint on the development of theory as to how they are determined. Whilst in principle the fit of any given mechanistic model can be tested against one or more empirical data sets, whatever their form, a simple general mathematical description of species–range size distributions would make the process of rapidly testing the appropriateness of mechanistic models more straightforward.
Categorizing Australian landscapes as an aid to assessing the generality of landscape management guidelines
Authors: Hobbs Richard J. , McIntyre S. 
Published: January 2005

ABSTRACTAim  A key question in ecology and ecological management is the extent to which management guidelines developed in one location can be generalized to other areas. Landscapes differ in their biophysical characteristics and the degree of human alteration imposed on them. Our aim was to develop a conceptual framework of Australian landscapes, on the basis of a few simple indicators, that can be used to enhance the communication of information in planning and managing landscapes, particularly for biodiversity conservation.Location  The project considered landscapes across the continent of Australia.Methods  The project was a desktop exercise and the approach was to identify the minimum set of variables, and levels within variables, that are most meaningful from the perspective of Australian landscapes and their management. This involved the identification of the key environmental axes and development of a proposed set of matrices involving various combinations of the axes, which was revised following consultation with stakeholders.Results  We developed a framework based on the primary variables of climate and vegetation. For climate, we used an agro‐climatic classification incorporating a moisture index, growth index and seasonality, with climate classes aligned to existing bioregions. Vegetation was broadly classified on the presence or absence of a tree layer and whether the understorey was grassy or shrub‐dominated. Secondary variables were the degree of landscape alteration and modification. The sensitivity of broad categories to ecosystem dysfunction was assessed, and the relative abundance of different categories across Australia was determined. Not all categories need to be considered since not all combinations of variables occur.Main conclusions  The framework provides a set of broad categories of landscapes with differing characteristics. We can then assess the importance of different types of threat in the different categories. By pulling together the potential threats in a systematic way across categories, we can start to consider what appropriate management responses might be in each case. Further, by providing a convenient way to compare landscapes in different categories, it becomes possible to see where generalizations among different landscapes may be possible and where they are definitely not likely to be helpful.
Does energy availability influence classical patterns of spatial variation in exotic species richness?
Authors: Evans Karl L. , Warren Philip H. , Gaston Kevin J. 
Published: January 2005

ABSTRACTAim At macroecological scales, exotic species richness is frequently positively correlated with human population density. Such patterns are typically thought to arise because high human densities are associated with increased introduction effort and/or habitat modification and disturbance. Exotic and native species richness are also frequently positively correlated, although the causal mechanisms remain unclear. Energy availability frequently explains much of the variation in species richness and we test whether such species–energy relationships may influence the relationships of exotic species richness with human population density and native species richness.Location Great Britain.Methods We first investigate how spatial variation in the distributions of the 10 exotic bird species is related to energy availability. We then model exotic species richness using native avian species richness, human population density and energy availability as predictors. Species richness is modelled using two sets of models: one assumes independent errors and the other takes spatial correlation into account.Results The probability of each exotic species occurring, in a 10‐km quadrat, increases with energy availability. Exotic species richness is positively correlated with energy availability, human population density and native species richness in univariate tests. When taking energy availability into account, exotic species richness is negligibly influenced by human population density, but remains positively associated with native species richness.Main conclusions We provide one of the few demonstrations that energy availability exerts a strong positive influence on exotic species richness. Within our data, the positive relationship between exotic species richness and human population density probably arises because both variables increase with energy availability, and may be independent of the influence of human density on the probability of establishment. Positive correlations between exotic and native species richness remain when controlling for the influence of energy on species richness. The relevance of such a finding to the debate on the relationship between diversity and invasibility is discussed.
Regionalized nitrogen budgets in forest soils for different deposition and forestry scenarios in Sweden
Authors: Akselsson Cecilia , Westling Olle 
Published: January 2005

ABSTRACTAim  The aim of this work was to estimate on a regional scale the effects of nitrogen (N) deposition and harvest intensity on N‐budgets in forest soils as a basis for strategies of emission reduction and sustainable forest management methods.Location  The calculations were applied to Sweden, a country with a managed forest area of 23 × 106 ha.Methods  Mass balance calculations, including N‐deposition, N‐fixation, N‐loss through harvest, and N‐leaching, were performed on a GIS platform using 5 × 5 km grids. Modelled deposition data together with spatial data obtained from the National Forest Inventory served as the basis for the calculations. Four different scenarios were run: a ‘base scenario’ involving present deposition and conventional forestry (stem harvest only); a ‘whole‐tree harvesting scenario’ with present deposition and the harvesting of stems, branches and needles; a ‘decreased deposition scenario’; and a ‘whole‐tree harvesting and decreased deposition scenario’.Results  There was a sharp N‐accumulation gradient with an increase in accumulation in the direction of the south‐western part of Sweden. In the ‘base scenario’, N‐accumulation appeared in the country as a whole, apart from certain small areas in the northern part. Whole‐tree harvesting led to net losses in extensive areas located mainly in northern and central Sweden. In most parts of the country, whole‐tree harvesting combined with decreased deposition was found to result in net losses.Main conclusions  The intensity of the forestry has a strong impact on the N‐budget. Conventional forestry in combination with the present deposition level results in a high net accumulation of N in the south‐western parts of Sweden and accordingly, in a risk of unwanted environmental effects such as increased N‐leaching. With whole‐tree harvesting, the N‐balance is negative in parts of Sweden, mainly in the northern and central parts. N‐fertilization may become necessary there if the present level of forest production is to be maintained.
Local infiltration of high‐ and low‐molecular‐weight RNA from silenced sunflower (Helianthus annuus L.) plants triggers post‐transcriptional gene silencing in non‐silenced plants
Authors: Hewezi Tarek , Alibert Gilbert , Kallerhoff Jean 
Published: January 2005

SummaryUsing grafting procedures, we have characterized post‐transcriptional gene silencing (PTGS) in transgenic sunflower expressing β‐glucuronidase (GUS) activity. Silencing was observed as early as 2 weeks after grafting of non‐silenced scions on to silenced rootstock. Transmission of the systemic signal occurs solely from stock to scion, is independent of the physiological age of the rootstock and is not heritable. Furthermore, we report, for the first time in plants, an easy and low‐cost method of activating RNA silencing by infiltration of purified RNA from silenced plants. Local application of total RNA derived from silenced sunflower plants to leaves of non‐silenced plants induces PTGS in newly developed leaves above the point of infiltration, as shown by reduced GUS activity and mRNA levels. Silenced plants contain 21–23‐nucleotide RNAs hybridizing to transgene target sequences, in contrast with leaves of non‐silenced plants. However, de novo production of GUS‐specific short RNA in non‐silenced plants can be activated by leaf infiltration of low‐molecular‐weight RNAs isolated from leaves of silenced plants. Significant levels were detected as early as 2 weeks after infiltration, peaked at 3 weeks and declined 5 weeks after infiltration. Our results provide evidence that RNA infiltration in sunflower induces transient silencing and is not transmitted to offspring. This approach could be of major use in dissecting the mechanisms involved in PTGS.