bluuebunny/crossref_metadata_2025 huggingface dataset:
Prostaglandins in the kidney: developments since Y2K
Authors: Nasrallah Rania , Clark Jordan , Hébert Richard L.
Published: November 2007

There are five major PGs (prostaglandins/prostanoids) produced from arachidonic acid via the COX (cyclo-oxygenase) pathway: PGE2, PGI2 (prostacyclin), PGD2, PGF2α and TXA2 (thromboxane A2). They exert many biological effects through specific G-protein-coupled membrane receptors, namely EP (PGE2 receptor), IP (PGI2 receptor), DP (PGD2 receptor), FP (PGF2α receptor) and TP (TXA2 receptor) respectively. PGs are implicated in physiological and pathological processes in all major organ systems, including cardiovascular function, gastrointestinal responses, reproductive processes, renal effects etc. This review highlights recent insights into the role of each prostanoid in regulating various aspects of renal function, including haemodynamics, renin secretion, growth responses, tubular transport processes and cell fate. A thorough review of the literature since Y2K (year 2000) is provided, with a general overview of PGs and their synthesis enzymes, and then specific considerations of each PG/prostanoid receptor system in the kidney.
Single magnetic particle dynamics in a microchannel
Authors: Sinha Ashok , Ganguly Ranjan , De Anindya K. , Puri Ishwar K.
Published: November 2007

Functionalized magnetic particles are used in micrototal analysis systems since they act as magnetically steered mobile substrates in microfluidic channels, and can be collected for bioanalytical processing. Here, we examine the motion of magnetic microbeads in a microfluidic flow under the influence of a nonuniform external magnetic field and characterize their collection in terms of the magnetic field strength, particle size, magnetic susceptibility, host fluid velocity and viscosity, and the characteristic length scale. We show that the collection efficiency of a magnetic collector depends upon two dimensionless numbers that compare the magnetic and particle drag forces.
Quantum mechanical correlation functions, maximum entropy analytic continuation, and ring polymer molecular dynamics
Authors: Habershon Scott , Braams Bastiaan J. , Manolopoulos David E.
Published: November 2007

The maximum entropy analytic continuation (MEAC) and ring polymer molecular dynamics (RPMD) methods provide complementary approaches to the calculation of real time quantum correlation functions. RPMD becomes exact in the high temperature limit, where the thermal time βℏ tends to zero and the ring polymer collapses to a single classical bead. MEAC becomes most reliable at low temperatures, where βℏ exceeds the correlation time of interest and the numerical imaginary time correlation function contains essentially all of the information that is needed to recover the real time dynamics. We show here that this situation can be exploited by combining the two methods to give an improved approximation that is better than either of its parts. In particular, the MEAC method provides an ideal way to impose exact moment (or sum rule) constraints on a prior RPMD spectrum. The resulting scheme is shown to provide a practical solution to the “nonlinear operator problem” of RPMD, and to give good agreement with recent exact results for the short-time velocity autocorrelation function of liquid parahydrogen. Moreover these improvements are obtained with little extra effort, because the imaginary time correlation function that is used in the MEAC procedure can be computed at the same time as the RPMD approximation to the real time correlation function. However, there are still some problems involving long-time dynamics for which the RPMD+MEAC combination is inadequate, as we illustrate with an example application to the collective density fluctuations in liquid orthodeuterium.
Analysis of the flow pattern modifications in a bubbly Couette-Taylor flow
Authors: Mehel A. , Gabillet C. , Djeridi H.
Published: November 2007

The aim of this Brief Communication is to discuss the bubble effect on the Couette-Taylor flow patterns in the transition from laminar to turbulent flow, especially in the weakly turbulent regime. It is shown that bubble location and local void fractions both in the vortices cores and in the near wall regions directly influence the axial wavelength. Bubbles trapped in the vortices tend to increase the vorticity and reduce the axial diffusivity. Bubbles near the wall contribute to “shear induced” turbulence depending on the void fraction gradient near the wall and the bubble size.
Fast-ion Dα measurements and simulations in quiet plasmas
Authors: Luo Y. , Heidbrink W. W. , Burrell K. H. , Ruskov E. , Solomon W. M.
Published: November 2007

The Dα light emitted by neutralized deuterium fast ions is measured in magnetohydrodynamics (MHD)-quiescent, magnetically confined plasmas during neutral beam injection. A weighted Monte Carlo simulation code models the fast-ion Dα spectra based on the fast-ion distribution function calculated classically by TRANSP [R. V. Budny, Nucl. Fusion 34, 1247 (1994)]. The spectral shape is in excellent agreement and the magnitude also has reasonable agreement. The fast-ion Dα signal has the expected dependencies on various parameters including injection energy, injection angle, viewing angle, beam power, electron temperature, and electron density. The neutral particle diagnostic and measured neutron rate corroborate the fast-ion Dα measurements. The relative spatial profile agrees with TRANSP and is corroborated by the fast-ion pressure profile inferred from the equilibrium.
Geometric π Josephson junction in d-wave superconducting thin films
Authors: Gumann A. , Iniotakis C. , Schopohl N.
Published: November 2007

A novel way to realize a π Josephson junction is proposed, based on a weak link in an unconventional d-wave superconductor with appropriately chosen boundary geometry. The critical current of such a junction is calculated from a fully self-consistent solution of microscopic Eilenberger theory of superconductivity. The results clearly show that a transition to a π Josephson junction occurs for both low temperatures and small sizes of the geometry.
Correlation between microstructure and optical properties of ZnO nanoparticles synthesized by ball milling
Authors: Giri P. K. , Bhattacharyya S. , Singh Dilip K. , Kesavamoorthy R. , Panigrahi B. K. , Nair K. G. M.
Published: November 2007

Zinc oxide (ZnO) nanoparticles (NPs) in the size range ∼7–35 nm are synthesized by ball-milling technique, and microstructural and optical properties of the NPs are studied using varieties of techniques. Results from ball-milled NPs are compared with those of the commercially available ZnO nanopowder. X-ray diffraction pattern of the milled NPs indicates lattice strain in the NPs. High-resolution transmission electron microscopy analysis reveal severe lattice distortion and reduction in lattice spacing in some of the NPs. Optical absorption spectra of milled NPs show enhanced absorption peaked at 368 nm, which is blueshifted with reference to starting ZnO powder. Room-temperature photoluminescence spectra show five peaks consisting of ultraviolet and visible bands, and relative intensity of these peaks drastically changes with increasing milling time. Raman spectra of milled powders show redshift and broadening of the Raman modes of ZnO, and a new Raman mode evolve in the milled NPs. A correlation between the microstructure and optical properties of ZnO NPs is made on the basis of these results. Our results clearly demonstrate that commercially available ZnO nanopowders do not exhibit nanosize effects due to relatively large size of the ZnO NPs. Implications of these results are discussed.
Remarks on the decomposition of Dirichlet forms on standard forms of von Neumann algebras
Authors: Ko Chul Ki
Published: November 2007

For a bounded generator G of a weakly*-continuous, completely positive, KMS-symmetric Markovian semigroup on a von Neumann algebra M acting on a separable Hilbert space H, let H be the operator induced by G via the symmetric embedding of M into H. We decompose the Dirichlet form associated with H into a direct integral of forms whose associated generators are divergences of derivations. Moreover, if the derivations are inner, then the Dirichlet form can be written as the form given by Park [Infinite Dimen. Anal. Quantum Probab., Relat. Top. 3, 1 (2000); 8, 179 (2005)].
Growth front nucleation of rubrene thin films for high mobility organic transistors
Authors: Hsu C. H. , Deng J. , Staddon C. R. , Beton P. H.
Published: November 2007

We demonstrate a mode of thin film growth in which amorphous islands crystallize into highly oriented platelets. A cascade of crystallization is observed, in which platelets growing outward from a central nucleation point impinge on neighboring amorphous islands and provide a seed for further nucleation. Through control of growth parameters, it is possible to produce high quality thin films which are well suited to the formation of organic transistors. We demonstrate this through the fabrication of rubrene thin film transistors with high carrier mobility.
Flexible programmable logic gate using organic ferroelectric multilayer
Authors: Horie Satoshi , Noda Kei , Yamada Hirofumi , Matsushige Kazumi , Ishida Kenji , Kuwajima Shuichiro
Published: November 2007

In order to simplify the design and to further improve the integration, programmable, three-dimensional circuits are required alongside the development of fine process technology. We demonstrate the operation of programmable logic gates using organic ferroelectrics. Three-dimensionally stacked organic ferroelectric capacitors were assembled, which form logic elements with two inputs and one output. By controlling the directions of the electric dipoles, we have demonstrated the logical “and” and “or” operations using our device.
Phase effects on the exciton polariton amplifier
Authors: Zhang Yongyou , Jin Guojun , Ma Yu-qiang
Published: November 2007

We study the phase effects on the exciton polariton amplifier excited by the signal, pump, and idler lasers simultaneously. The signal amplification can be largely enhanced or depressed in this arrangement, compared with that where only the signal and pump lasers are applied. Moreover, a signal polariton switch can be achieved by controlling the excitation phases and it has a high on-off ratio under certain excitation intensities. For a typical GaAs–AlGaAs microcavity, the switching time is about 50ps and the operating power is about 50mW.
Flexibility in Action: The Temporary Staffing Industry in the Czech Republic and Poland
Authors: Coe Neil M , Johns Jennifer , Ward Kevin
Published: November 2007

Since the 1990s the largest transnational temporary staffing agencies have progressively expanded the geographical extent of their operations. Moving beyond the established Dutch, French, UK, and US markets in which the majority are headquartered, and encouraged by supportive supranational and national reregulation, they have entered a number of countries in Southeast Asia, Southern Europe, and Latin America. Moreover, in the run-up to, and since, the accession often new member states to the EU on 1 May 2004, the leading transnational agencies have turned their attentions to establishing and expanding operations in Central and Eastern Europe. This paper offers an initial assessment of the state of temporary staffing and its regulation in two leading markets in the region, the Czech Republic and Poland. It explores how temporary staffing markets are being forged through the interactions between regulators, transnational agencies, local agencies, trade bodies, and inward investors. Both countries legalized temporary staffing in 2004, having begun the legalization process prior to accession. Rather than these developments heralding the start of a period of sustained growth, however, our research suggests that there are still significant constraints on expansion in markets where the pressure to neoliberalize labour markets intersects with postsocialist expectations, norms, and economic structures.
The Learning Machine: European Integration in the Planning Mirror
Authors: Faludi Andreas
Published: November 2007

EU policies seek to bring the EU territory closer to resembling a ‘level playing field’. The paper first discusses efforts to inject a territorial dimension into EU policies, including the European Spatial Development Perspective. During its preparation, the same issue of national sovereignty has been dominant as in the subsequent debate concerning the European Constitution. Had it been ratified, the Constitution would have given European planning a boost. The paper discusses its rejection and reviews literature that presents views of the EU as an unprecedented, dynamic construct, with transnational learning as the engine. Next, the paper discusses the application of the European Spatial Development Perspective, during which planners have been learning about territory and territorial governance in the context of an integrating Europe. Like with European integration generally, European planning can thus be understood as a learning machine.
The Territorial Governance of the Shadow Economy
Authors: Burroni Luigi , Crouch Colin
Published: November 2007

The findings of studies of local economies can be applied to those concerned with ‘shadow’ and illegal activities. These activities need to be seen not as situations with an absence of governance and markets, but as constituting particular kinds of governance—this often being concerned with ensuring the functioning of markets. A scheme for modelling this type of governance is proposed, and is then used to formulate a critique of most of the prevailing policy approaches to trying to counter the shadow economy and to encourage the ‘emersion’ of firms from it. Some instances of policies that are better grounded in an appreciation of the reality of the shadow economy as a social order are also cited.
Perception of Novel Faces: The Parts Have it!
Authors: Lobmaier Janek S , Mast Fred W
Published: November 2007

It has been suggested that, as a result of expertise, configural information plays a predominant role in face processing. We investigated this idea using novel and learned faces. In experiment 1, sixteen participants matched two subsequently presented blurred or scrambled faces, which could be either upright or inverted, in a sequential same—different matching task. By means of blurring, featural information is hampered, whilst scrambling disrupts configural information. Each face was unfamiliar to the participants and was presented for 1000 ms. An ANOVA on the d' values revealed a significant advantage for scrambled faces. In experiment 2, fourteen participants were tested with the same design, except that the second face was always intact. Again, the ANOVA on the d' values revealed a significant advantage for scrambled faces. In experiment 3 half of the faces were learned in a familiarisation block prior to the experiment. The ANOVA of these d' values revealed a significant interaction of familiarity and condition, showing that blurred stimuli were better recognised when the faces were familiar. These results suggest that recognition of novel faces, compared to learned faces, relies relatively more on the processing of featural information. In the course of familiarisation the importance of configural information increases.
Beauty is in the ‘We’ of the Beholder: Greater Agreement on Facial Attractiveness among Close Relations
Authors: Bronstad P Matthew , Russell Richard
Published: November 2007

Scientific research on facial attractiveness has focused primarily on elucidating universal factors to which all raters respond consistently. However, recent work has shown that there is also substantial disagreement between raters, highlighting the importance of determining how attractiveness preferences vary among different individuals. We conducted a typical attractiveness ratings study, but took the unusual step of recruiting pairs of subjects who were spouses, siblings, or close friends. The agreement between pairs of affiliated friends, siblings, and spouses was significantly greater than between pairs of strangers drawn from the same race and culture, providing evidence that facial-attractiveness preferences are socially organized.
Visual Perception and Corollary Discharge
Authors: Sommer Marc A , Wurtz Robert H
Published: November 2007

Perception depends not only on sensory input but also on the state of the brain receiving that input. A classic example is perception of a stable visual world in spite of the saccadic eye movements that shift the images on the retina. A long-standing hypothesis is that the brain compensates for the disruption of visual input by using advance knowledge of the impending saccade, an internally generated corollary discharge. One possible neuronal mechanism for this compensation has been previously identified in parietal and frontal cortex of monkeys, but the origin of the necessary corollary discharge remained unknown. Here, we consider recent experiments that identified a pathway for a corollary discharge for saccades that extends from the superior colliculus in the midbrain to the frontal eye fields in the cerebral cortex with a relay in the medial dorsal nucleus of the thalamus. We first review the nature of the evidence used to identify a corollary discharge signal in the complexity of the primate brain and show its use for guiding a rapid sequence of eye movements. We then consider two experiments that show this same corollary signal may provide the input to the frontal cortex neurons that alters their activity with saccades in ways that could compensate for the displacements in the visual input produced by saccadic eye movements. The first experiment shows that the corollary discharge signal is spatially and temporally appropriate to produce the alterations in the frontal-cortex neurons. The second shows that this signal is necessary for this alteration because inactivation of the corollary reduces the compensation by frontal-cortex neurons. The identification of this relatively simple circuit specifies the organization of a corollary discharge in the primate brain for the first time and provides a specific example upon which consideration of the roles of corollary activity in other systems and for other functions can be evaluated.
Molecular systematics of Dolichopodidae (Diptera) inferred from COI and 12S rDNA gene sequences based on European exemplars
Authors: Bernasconi Marco Valerio , Pollet Marc , Ward Paul Irvine
Published: November 2007

With ~7000 species in ~220 genera, the Dolichopodidae is one of the most speciose families of Diptera. Though the family as such is well defined, knowledge on the internal phylogenetic relationships is generally poor and although authors of successive monographs and catalogues indifferently listed most genera in specific subfamilies, their decisions were rarely based on sound phylogenetic analyses and never on molecular data. In a first attempt to unravel the phylogeny of Dolichopodidae, a combined COI + 12S rDNA dataset (1199 characters) of 119 samples of 101 European species was used in Bayesian (BAY), neighbour joining (NJ) and weighted/unweighted maximum parsimony analyses (MP). At the subfamily level, our study supports the monophyly of Dolichopodinae, Sympycninae, and Hydrophorinae (including Machaerium Haliday, 1832). Ten (Campsicnemus Haliday, 1851, Chrysotus Meigen, 1824, Dolichopus Latreille, 1796, Gymnopternus Loew, 1857, Medetera Fischer von Waldheim, 1819, Poecilobothrus Mik, 1878, Rhaphium Meigen, 1803, Teuchophorus Loew, 1857, Sciapus Zeller, 1842, Syntormon Loew, 1857) of the 14 multispecies genera formed monophyletic assemblages in all analyses and relationships among Argyra Macquart, 1834 species were supported in most analyses. At the subgeneric level, seven of the nine stable species-groups in Dolichopus as established during previous research were supported in most analyses. The validity of the recent transfer of Hercostomus chrysozygos Wiedemann, 1817 to Poecilobothrus was clearly supported in all analyses. Within Argyra and Rhaphium, interspecific relationships reflected previously used subgeneric classifications (Lasiargyra Mik, 1878, Leucostola Loew, 1857 and Argyra s.s. in Argyra; Porphyrops Meigen, 1824, Rhaphium s.s. and Xiphandrium Loew, 1857 in Rhaphium). Further, subclades within Medetera corresponded to species-groups defined by other authors featuring a different morphology and ecology. Anepsiomyia flaviventris (Meigen, 1824) most probably does not belong to Sympycninae but its current position within Peloropeodinae could not be confirmed.
Synergic mechanism and fabrication target for bipedal nanomotors
Authors: Wang Zhisong
Published: November 2007

Inspired by the discovery of dimeric motor proteins capable of undergoing transportation in living cells, significant efforts have been expended recently to the fabrication of track-walking nanomotors possessing two foot-like components that each can bind or detach from an array of anchorage groups on the track in response to local events of reagent consumption. The central problem in fabricating bipedal nanomotors is how the motor as a whole can gain the synergic capacity of directional track-walking, given the fact that each pedal component alone often is incapable of any directional drift. Implemented bipedal motors to date solve this thermodynamically intricate problem by an intuitive strategy that requires a hetero-pedal motor, multiple anchorage species for the track, and multiple reagent species for motor operation. Here we performed realistic molecular mechanics calculations on molecule-scale models to identify a detailed molecular mechanism by which motor-level directionality arises from a homo-pedal motor along a minimally heterogeneous track. Optimally, the operation may be reduced to a random supply of a single species of reagents to allow the motor's autonomous functioning. The mechanism suggests a distinct class of fabrication targets of drastically reduced system requirements. Intriguingly, a defective form of the mechanism falls into the realm of the well known Brownian motor mechanism, yet distinct features emerge from the normal working of the mechanism.
Folding of noncoding RNAs during transcription facilitated by pausing-induced nonnative structures
Authors: Wong Terrence N. , Sosnick Tobin R. , Pan Tao
Published: November 2007

RNA folding in the cell occurs during transcription. Expedient RNA folding must avoid the formation of undesirable structures as the nascent RNA emerges from the RNA polymerase. We show that efficient folding during transcription of three conserved noncoding RNAs from
Escherichia coli
, RNase P RNA, signal-recognition particle RNA, and tmRNA is facilitated by their cognate polymerase pausing at specific locations. These pause sites are located between the upstream and downstream portions of all of the native long-range helices in these noncoding RNAs. In the paused complexes, the nascent RNAs form labile structures that sequester these upstream portions in a manner to possibly guide folding. Both the pause sites and the secondary structure of the nonnative portions of the paused complexes are phylogenetically conserved among γ-proteobacteria. We propose that specific pausing-induced structural formation is a general strategy to facilitate the folding of long-range helices. This polymerase-based mechanism may result in portions of noncoding RNA sequences being evolutionarily conserved for efficient folding during transcription.
Maternal heparin-binding-EGF deficiency limits pregnancy success in mice
Authors: Xie Huirong , Wang Haibin , Tranguch Susanne , Iwamoto Ryo , Mekada Eisuke , DeMayo Francesco J. , Lydon John P. , Das Sanjoy K. , Dey Sudhansu K.
Published: November 2007

An intimate discourse between the blastocyst and uterus is essential for successful implantation. However, the molecular basis of this interaction is not clearly understood. Exploiting genomic
Hbegf
mutant mice, we show here that maternal deficiency of heparin-binding EGF-like growth factor (HB-EGF) defers on-time implantation, leading to compromised pregnancy outcome. We also demonstrate that amphiregulin, but not epiregulin, partially compensates for the loss of HB-EGF during implantation. In search of the mechanism of this compensation, we found that reduced preimplantation estrogen secretion from ovarian HB-EGF deficiency is a cause of sustained expression of uterine amphiregulin before the initiation of implantation. To explore the significance specifically of uterine HB-EGF in implantation, we examined this event in mice with conditional deletion of uterine HB-EGF and found that this specific loss of HB-EGF in the uterus still defers on-time implantation without altering preimplantation ovarian estrogen secretion. The observation of normal induction of uterine amphiregulin surrounding the blastocyst at the time of attachment in these conditional mutant mice suggests a compensatory role of amphiregulin for uterine loss of HB-EGF, preventing complete failure of pregnancy. Our study provides genetic evidence that HB-EGF is critical for normal implantation. This finding has high clinical relevance, because HB-EGF signaling is known to be important for human implantation.
Halogen Bonds in Adenine-5-Bromouracil Complexes
Authors: Wang Yan-hua , Li Li , Lu Yun-xiang , Zou Jian-wei
Published: November 2007

Ab initio and density functional calculations were employed to investigate the bonding patterns in the adenine-5-bromouracil (AT+) complexes. It is shown that the Bratom in 5-bromouracil (T+) is involved in bonding both with the hydrogen atom of the amino group of adenine (A) and with N7(A) (or N1(A)). With this motif, the Br atom interacts with a nucleophile (H) in a ``head-on" fashion and an electrophile(N) in a ``side-on" fashion, forming both hydrogen and halogen bonds. Electrostatic attraction between the Br atom in T+ and N7 (or N1) of adeninewas found via the electrostatic potential analysis. The existence of the BrN interactions in the pairs was further confirmed by means of Bader's atoms in molecules theory. A bond criticalpoint is identified for the halogen bonds and the topological parameters at the bond critical point indicate the typical closed-shell interactions in the pairs. Natural bond orbital analysis suggests that thecharge transfer from the lone pair of the nitrogen atom of adenine is mainly directed to the C-Br antibonding orbital. Finally, halogen bonds in the T+AT+A tetrads were alsoexplored.
Numerical Study of Vibrational Energy Relaxation of OH Bending in Liquid H2O
Authors: Tian Guo-cai
Published: November 2007

The relaxation of O-H bending of water molecule H2O in the liquid phase was studied with the molecular dynamics simulation approach. Both rigid and flexible solvents were used to identify the different channels for the vibrational energy relaxation. It was observed that the relaxation time for the O-H bend overtone is 174 fs in the rigid solvent while it is 115 fs in the flexible solvent. The main pathway of the O-H bend overtone is transition to the bend fundamental. The relaxation time of the O-H bend fundamental was calculated as 204 fs which is comparable to the experimental value 170 fs.
Influence of Glycine Adsorption on Segregation of Ni-Cu (110) Surface
Authors: Zhang Hui , Zhang Guo-ying , Wang Rui-dan
Published: November 2007

An atomic group model of the disordered binary alloy NixCu1x (x=0.4) was constructed to investigate surface segregation. According to the model, the electronic structure of the NixCu1x alloy surface was calculated by the Recursion method when glycine atoms are adsorbed on the NixCu1x (110) surface under the condition of 0.33 coverage. The calculation results indicate that Cu is segregated on the surface of the NixCu1x alloy, and the chemisorption of glycine restrains the segregation. In addition, the chemical adsorption of glycine greatly changes the density of states of the alloy surface near the Fermi level, and there is electric charge transfer between the alloy surface and the glycine.
Miscibility and Crystallization in Binary Crystalline Blends of Poly(butylene terephthalate) with Poly(butylene terephthalate--caprolactone)
Authors: Cheng Xiao-min , Shi Chu-li
Published: November 2007

Poly(butylene terephthalate)/poly(butylene terephthalate--caprolactone) is a new A/AxB1x binary crystalline blend with intra-molecular repulsion interaction. Using the mean-field binary interaction model, the value of interaction parameter between the butylene terephthalate and caprolactone structural unit was first reported to be 0.305. This blend exhibited different crystallization behavior from a typical homo-polymer/copolymer blend, which was carefully investigated by differential scanning calorimetry. It was found that poly(butylene terephthalate--caprolactone) copolymers have a great effect on the pure poly(butylene terephthalate) chain mobility and poly(butylene terephthalate) crystalline lattice packing. In the meantime, the crystallization of butylene terephthalate segments in copolymers was restricted by the previously formed poly(butylene terephthalate) crystallites. The two constituents for blending can not form a co-crystal in the range of composition even if they have the same butylene terephthalate unit. It can be concluded that longer segments in a copolymer would be beneficial for the formation of a co-crystal in blends.
Topology bounds energy of knots and links
Authors: Ricca Renzo L
Published: November 2007

In this paper, we determine two quantities, of geometric and topological character, that were left undetermined in two previous results obtained by Arnold (Arnold 1974 In
Proc. Summer School in Diff. Eqs. at Dilizhan
, pp. 229–256.) and Moffatt (Moffatt 1990
Nature
347
, 367–369) on lower bounds for the magnetic energy of knots and links in ideal fluids. For dissipative systems, a lower bound on magnetic helicity in terms of the average crossing number and a new relationship between rates of change of these two quantities are also determined.
Shoal and prey patch choice by co-occurring fishes and prawns: inter-taxa use of socially transmitted cues
Authors: Webster M.M , Ward A.J.W , Hart P.J.B
Published: November 2007

Animals can use socially transmitted information to learn about the distribution and quality of resources without incurring the costs associated with having to search for and sample them first hand. Recently, it has been shown that the use of chemical social information specific to patterns of diet and habitat use is an important mechanism underpinning recognition and social organization in shoaling fishes. In this study we revealed that the use of resource-specific chemical information is not limited to conspecifics, or even members of the same taxon. In a series of laboratory experiments, we showed that threespine sticklebacks (Gasterosteus aculeatus) could recognize similar patterns of habitat use in common prawns (Leander serratus), preferentially orientating towards groups of prawns exposed to the same habitats as themselves, and even selecting foraging patches located close to them. Prawns were seen to use habitat-specific cues generated by conspecifics, but not by sticklebacks, suggesting that the benefits of forming these heterospecific social association patterns may be unequal for prawns and fishes. Our findings suggest that some species might use co-occurring, unrelated species as information centres in order to orient and locate resources within their surroundings.
Avian-like breathing mechanics in maniraptoran dinosaurs
Authors: Codd Jonathan R , Manning Phillip L , Norell Mark A , Perry Steven F
Published: November 2007

In 1868 Thomas Huxley first proposed that dinosaurs were the direct ancestors of birds and subsequent analyses have identified a suite of ‘avian’ characteristics in theropod dinosaurs. Ossified uncinate processes are found in most species of extant birds and also occur in extinct non-avian maniraptoran dinosaurs. Their presence in these dinosaurs represents another morphological character linking them to Aves, and further supports the presence of an avian-like air-sac respiratory system in theropod dinosaurs, prior to the evolution of flight. Here we report a phylogenetic analysis of the presence of uncinate processes in Aves and non-avian maniraptoran dinosaurs indicating that these were homologous structures. Furthermore, recent work on Canada geese has demonstrated that uncinate processes are integral to the mechanics of avian ventilation, facilitating both inspiration and expiration. In extant birds, uncinate processes function to increase the mechanical advantage for movements of the ribs and sternum during respiration. Our study presents a mechanism whereby uncinate processes, in conjunction with lateral and ventral movements of the sternum and gastral basket, affected avian-like breathing mechanics in extinct non-avian maniraptoran dinosaurs.
Spatiotemporal patterns of seed dispersal in a wind‐dispersed Mediterranean tree (Acer opalussubsp.granatense): implications for regeneration
Authors: Gómez‐Aparicio Lorena , M. Gómez Jose , Zamora Regino
Published: November 2007

Seed dispersal can severely limit the quantity of plant recruits and their spatial distribution. However, our understanding of the role of dispersal in regeneration dynamics is limited by the lack of knowledge of seed deposition patterns in space and time. In this paper, we analyse the spatiotemporal variability of seed dispersal patterns in the Mediterranean maple,Acer opalussubsp.granatense, by monitoring seed rain along two years at a broad spatial scale (2 mountain ranges, 2 populations per range, 4 microhabitats per population). We quantified seed limitation and its components (source and dispersal limitation), and explored dispersal limitation in space by analysing dispersal distances, seed aggregation, and microhabitat seed distribution.Acer opalussubsp.granatensewas strongly seed‐limited throughout the gradients explored, being always dispersal limitation much higher than source limitation. The distribution of seeds with distance from adult individuals was leptokurtic and right‐skewed in all populations, being both kurtosis and skewness higher the year of the highest seed production. Dispersal distances were shorter than expected by random in the four populations, which suggests distance‐limited dispersal. Dispersal patterns were highly aggregated and showed a preferential direction around adults. At the microhabitat scale, most seeds accumulated under adult maples. However, there were no more seeds under trees and shrubs other than maple than in open interspaces, implying that established vegetation does not disrupt patterns of seed deposition by physically trapping seeds. When compared with patterns of seedling establishment, limited dispersal ability and inter‐annual spatial concordance in seed rain patterns suggest that several potentially safe sites for recruitment have a very low probability of receiving seeds in most maple populations. These findings are especially relevant for rare species such asAcer opalussubsp.granatense, and illustrate how dispersal studies are not only crucial for our understanding of plant population dynamics but also to provide conservation directions.
The distance decay of similarity in ecological communities
Authors: Soininen Janne , McDonald Robert , Hillebrand Helmut
Published: November 2007

Biological similartiy typically decreases with geographical distance. Despite the recent attention to the distance decay relationship, there is no consensus on how the relationship varies across organism groups, geographic gradients and environments. We first conducted a quantitative meta‐analysis of 401 distance decay relationships across a wide range of organisms, ecosystems and geographical gradients, and then united the effects of categorical and continuous variables on the rate of distance decay using a general linear model (GLM). As effect sizes we used the similarity at one km distance (initial similarity) and the distance that halves the similarity from its value at one km distance (halving distance). Both the initial similarity and halving distance were significantly affected by variables characterizing the spatial scale, organism properties, study region and ecosystem concerned. The patterns appear robust as the results of meta‐analysis and GLM only differed in marginal details. According to GLM with Akaike's information criterion, the most parsimonious models explained 55.3 and 37.6% of variance in initial similarity and halving distance, respectively. Across large scales, similarity was decreasing slightly faster at high latitudes than at low latitudes, while small‐scale turnover was higher at low latitudes. We also found significant differences in initial similarity among the realms, with terrestrial systems showing higher small‐scale beta diversity. The decrease in community similarity at large scales was higher among organisms that are actively mobile than among passively dispersed organisms. We conclude that regression of similarity against distance unites several ecological phenomena such as dispersal propensity and environmental structuring, and provides an effective approach for gauging the spatial turnover across sites. We also found that the patterns in beta‐diversity are highly scale‐dependent.
Structural risk minimization: a robust method for density‐dependence detection and model selection
Authors: Corani Giorgio , Gatto Marino
Published: November 2007

Statistically distinguishing density‐dependent from density‐independent populations and selecting the best demographic model for a given population are problems of primary importance. Traditional approaches are PBLR (parametric bootstrapping of likelihood ratios) and Information criteria (IC), such as the Schwarz information criterion (SIC), the Akaike information criterion (AIC) or the Final prediction error (FPE). While PBLR is suitable for choosing from a couple of models, ICs select the best model from among a set of candidates. In this paper, we use the Structural risk minimization (SRM) approach. SRM is the model selection criterion developed within the Statistical learning theory (SLT), a theory of great generality for modelling and learning with finite samples. SRM is almost unknown in the ecological literature and has never been used to analyze time series.

First, we compare SRM with PBLR in terms of their ability to discriminate between the Malthusian and the density‐dependent Ricker model. We rigorously repeat the experiments described in a previous study and find out that SRM is equally powerful in detecting density‐independence and much more powerful in detecting density‐dependence.

Then, we compare SRM against ICs in terms of their ability to select one of several candidate models; we generate, via stochastic simulation, a huge amount of artificial time series both density‐independent and dependent, with and without exogenous covariates, using different dataset sizes, noise levels and parameter values. Our findings show that SRM outperforms traditional ICs, because generally a) it recognizes the model underlying the data with higher frequency, and b) it leads to lower errors in out‐of‐samples predictions. SRM superiority is specially apparent with short time series.

We finally apply SRM to the population records of Alpine ibex Capra ibex living in the Gran Paradiso National Park (Italy), already investigated by other authors via traditional statistical methods; we both analyze their models and introduce some novel ones. We show that models that are best according to SRM show also the lowest leave‐one‐out cross‐validation error.
Ecological filters and variability in stream macroinvertebrate communities: do taxonomic and functional structure follow the same path?
Authors: Heino Jani , Mykrä Heikki , Kotanen Juho , Muotka Timo
Published: November 2007

We examined the community‐environment relationships of lotic macroinvertebrates in near‐pristine headwater streams, and the correlation between patterns in taxonomic and functional structure at two regional extents. The across‐ecoregion scale comprised five ecoregions spanning all of Finland, while the within‐ecoregion scale comprised of north boreal and middle boreal ecoregions. We expected that taxonomic structure should exhibit stronger relationships than functional structure to spatial gradients, while the reverse should be true for local environmental factors. We found some support for this notion, because spatial variables were marginally more important for taxonomic than functional structure. Furthermore, within the two ecoregions, local environmental variables were slightly more important for functional than taxonomic structure. Geographical location (i.e. spatial variables) was more influential at the across‐ecoregions extent than within the two ecoregions. Largely the same local environmental variables accounted for variation in both taxonomic and functional structure, including water pH, nutrients, colour, and stream size. Similar responses to local environmental features likely contributed to the significant correlation between patterns in taxonomic and functional structure. It has been suggested that functional traits may be rather insensitive to natural variation, yet our functional categorization showed distinct variation along local environmental, catchment, and spatial gradients across near‐pristine streams. Thus, natural ecological filters should be accounted for prior to the examination of the effects of anthropogenic filters on stream macroinvertebrate community structure.
Estimating the growth of a newly established moose population using reproductive value
Authors: Sæther Bernt‐Erik , Engen Steinar , J. Solberg Erling , Heim Morten
Published: November 2007

Estimating the population growth rate and environmental stochasticity of long‐lived species is difficult because annual variation in population size is influenced by temporal autocorrelations caused by fluctuations in the age‐structure. Here we use the dynamics of the reproductive value to estimate the long‐term growth rate s and the environmental variance of a moose population that recently colonized the island of Vega in northern Norway. We show that the population growth rate was high (ŝ=0.26). The major stochastic influences on the population dynamics were due to demographic stochasticity, whereas the environmental variance was not significantly different from 0. This supports the suggestion that population growth rates of polytocous ungulates are high, and that demographic stochasticity must be assessed when estimating the growth of small ungulate populations.
Variation in the abundance of fungal endophytes in fescue grasses along altitudinal and grazing gradients
Authors: Granath Gustaf , Vicari Mark , Bazely Dawn R. , Ball John P. , Puentes Adriana , Rakocevic Tomo
Published: November 2007

Epichloë festucae, a common fungal symbiont of the genus Festuca (family Poaceae), can provide its host plant with protection against herbivores. However, infection might also be associated with a cost to its host plant. We examined the distribution of Epichloë festucae infection in natural populations of three fescue grasses, Festuca rubra, F. ovina and F. vivipara, on mountains in northern Sweden to determine whether infection frequency varied with reindeer Rangifertarandus grazing pressure and altitude. Two differently‐scaled approaches were used: 1) infection frequency was measured at a local scale along ten elevational transects within a ca 400 km2 area and 2) infection frequency was measured on a regional scale along elevational transects on 17 mountains classified as having a history of high or low reindeer grazing pressure. Mean infection frequencies in F. rubra were 10% (vegetative tillers at a local scale), and 23% (flowering culms at a regional scale), and in F. ovina they were 13% (local scale) and 15% (regional scale). Endophyte infection frequency in F. vivipara, was, on average, 12% (local scale) and 37% (regional scale). In F. rubra, infection decreased significantly with increasing altitude at both the local and regional scale, and was positively correlated with grazing pressure. In F. ovina, an opposite trend was found at the regional scale: infection frequency increased significantly with increasing altitude, while no discernible distribution pattern was observed at the local scale. No elevational trends were observed in infection of F. vivipara. These patterns in the distribution of endophyte‐infected grasses in non‐agricultural ecosystems may be explained by both biotic (grazing) and abiotic factors (altitude). Differences in ecology and life history of the studied grass species may also be of importance for the different results observed among species.
Red herrings revisited: spatial autocorrelation and parameter estimation in geographical ecology
Authors: Hawkins Bradford A. , Diniz‐Filho José Alexandre F. , Mauricio Bini Luis , De Marco Paulo , Blackburn Tim M.
Published: November 2007

There have been numerous claims in the ecological literature that spatial autocorrelation in the residuals of ordinary least squares (OLS) regression models results in shifts in the partial coefficients, which bias the interpretation of factors influencing geographical patterns. We evaluate the validity of these claims using gridded species richness data for the birds of North America, South America, Europe, Africa, the ex‐USSR, and Australia. We used richness in 110×110 km cells and environmental predictor variables to generate OLS and simultaneous autoregressive (SAR) multiple regression models for each region. Spatial correlograms of the residuals from each OLS model were then used to identify the minimum distance between cells necessary to avoid short‐distance residual spatial autocorrelation in each data set. This distance was used to subsample cells to generate spatially independent data. The partial OLS coefficients estimated with the full dataset were then compared to the distributions of coefficients created with the subsamples. We found that OLS coefficients generated from data containing residual spatial autocorrelation were statistically indistinguishable from coefficients generated from the same data sets in which short‐distance spatial autocorrelation was not present in all 22 coefficients tested. Consistent with the statistical literature on this subject, we conclude that coefficients estimated from OLS regression are not seriously affected by the presence of spatial autocorrelation in gridded geographical data. Further, shifts in coefficients that occurred when using SAR tended to be correlated with levels of uncertainty in the OLS coefficients. Thus, shifts in the relative importance of the predictors between OLS and SAR models are expected when small‐scale patterns for these predictors create weaker and more unstable broad‐scale coefficients. Our results indicate both that OLS regression is unbiased and that differences between spatial and nonspatial regression models should be interpreted with an explicit awareness of spatial scale.