bluuebunny/crossref_metadata_2025 huggingface dataset:
Oscillatory Ca2+ Signaling in the IsolatedCaenorhabditis elegansIntestine
Authors: Espelt Maria V. , Estevez Ana Y. , Yin Xiaoyan , Strange Kevin
Published: September 2005

Defecation in the nematode Caenorhabditis elegans is a readily observable ultradian behavioral rhythm that occurs once every 45–50 s and is mediated in part by posterior body wall muscle contraction (pBoc). pBoc is not regulated by neural input but instead is likely controlled by rhythmic Ca2+ oscillations in the intestinal epithelium. We developed an isolated nematode intestine preparation that allows combined physiological, genetic, and molecular characterization of oscillatory Ca2+ signaling. Isolated intestines loaded with fluo-4 AM exhibit spontaneous rhythmic Ca2+ oscillations with a period of ∼50 s. Oscillations were only detected in the apical cell pole of the intestinal epithelium and occur as a posterior-to-anterior moving intercellular Ca2+ wave. Loss-of-function mutations in the inositol-1,4,5-trisphosphate (IP3) receptor ITR-1 reduce pBoc and Ca2+ oscillation frequency and intercellular Ca2+ wave velocity. In contrast, gain-of-function mutations in the IP3 binding and regulatory domains of ITR-1 have no effect on pBoc or Ca2+ oscillation frequency but dramatically increase the speed of the intercellular Ca2+ wave. Systemic RNA interference (RNAi) screening of the six C. elegans phospholipase C (PLC)–encoding genes demonstrated that pBoc and Ca2+ oscillations require the combined function of PLC-γ and PLC-β homologues. Disruption of PLC-γ and PLC-β activity by mutation or RNAi induced arrhythmia in pBoc and intestinal Ca2+ oscillations. The function of the two enzymes is additive. Epistasis analysis suggests that PLC-γ functions primarily to generate IP3 that controls ITR-1 activity. In contrast, IP3 generated by PLC-β appears to play little or no direct role in ITR-1 regulation. PLC-β may function instead to control PIP2 levels and/or G protein signaling events. Our findings provide new insights into intestinal cell Ca2+ signaling mechanisms and establish C. elegans as a powerful model system for defining the gene networks and molecular mechanisms that underlie the generation and regulation of Ca2+ oscillations and intercellular Ca2+ waves in nonexcitable cells.
Lower bounds for the spectral function and for the remainder in local Weyl’s law on manifolds
Authors: Jakobson Dmitry , Polterovich Iosif
Published: September 2005

We announce asymptotic lower bounds for the spectral function of the Laplacian and for the remainder in the local Weyl’s law on Riemannian manifolds. In the negatively curved case, methods of thermodynamic formalism are applied to improve the estimates. Our results develop and extend the unpublished thesis of A. Karnaukh. We discuss some ideas of the proofs; for complete proofs see our extended paper on the subject.
Frequency-dependent taste-rejection by avian predation may select for defence chemical polymorphisms in aposematic prey
Authors: Skelhorn John , Rowe Candy
Published: September 2005

Chemically defended insects advertise their unpalatability to avian predators using conspicuous aposematic coloration that predators learn to avoid. Insects utilize a wide variety of different compounds in their defences, and intraspecific variation in defence chemistry is common. We propose that polymorphisms in insect defence chemicals may be beneficial to insects by increasing survival from avian predators. Birds learn to avoid a colour signal faster when individual prey possesses one of two unpalatable chemicals rather than all prey having the same defence chemical. However, for chemical polymorphisms to evolve within a species, there must be benefits that allow rare chemical morphs to increase in frequency. Using domestic chicks as predators and coloured crumbs for prey, we provide evidence that birds taste and reject proportionally more of the individuals with rare defence chemicals than those with common defence chemicals. This indicates that the way in which birds attack and reject prey could enhance the survival of rare chemical morphs and select for chemical polymorphism in aposematic species. This is the first experiment to demonstrate that predators can directly influence the form taken by prey's chemical defences.
Neocortex evolution in primates: the ‘social brain’ is for females
Authors: Lindenfors Patrik
Published: September 2005

According to the social intelligence hypothesis, relative neocortex size should be directly related to the degree of social complexity. This hypothesis has found support in a number of comparative studies of group size. The relationship between neocortex and sociality is thought to exist either because relative neocortex size limits group size or because a larger group size selects for a larger neocortex. However, research on primate social evolution has indicated that male and female group sizes evolve in relation to different demands. While females mostly group according to conditions set by the environment, males instead simply go where the females are. Thus, any hypothesis relating to primate social evolution has to analyse its relationship with male and female group sizes separately. Since sex-specific neocortex sizes in primates are unavailable in sufficient quantity, I here instead present results from phylogenetic comparative analyses of unsexed relative neocortex sizes and female and male group sizes. These analyses show that while relative neocortex size is positively correlated with female group size, it is negatively, or not at all correlated with male group size. This indicates that the social intelligence hypothesis only applies to female sociality.
Does respiratory sinus arrhythmia occur in fishes?
Authors: Campbell Hamish A , Taylor Edwin W , Egginton Stuart
Published: September 2005

The hypothesis that respiratory modulation of heart rate variability (HRV) or respiratory sinus arrhythmia (RSA) is restricted to mammals was tested on four Antarctic and four sub-Antarctic species of fish, that shared close genotypic or ecotypic similarities but, due to their different environmental temperatures, faced vastly different selection pressures related to oxygen supply. The intrinsic heart rate (fH) for all the fish species studied was ∼25% greater than respiration rate (fV), but vagal activity successively delayed heart beats, producing a restingfHthat was synchronized withfVin a progressive manner. Power spectral statistics showed that these episodes of relative bradycardia occurred in a cyclical manner every 2–4 heart beats in temperate species but at >4 heart beats in Antarctic species, indicating a more relaxed selection pressure for cardio-respiratory coupling. This evidence that vagally mediated control offHoperates around the ventilatory cycle in fish demonstrates that influences similar to those controlling RSA in mammals operate in non-mammalian vertebrates.
Coevolution of vocal communication and sociality in primates
Authors: McComb Karen , Semple Stuart
Published: September 2005

Understanding the rules that link communication and social behaviour is an essential prerequisite for discerning how a communication system as complex as human language might have evolved. The comparative method offers a powerful tool for investigating the nature of these rules, since it provides a means to examine relationships between changes in communication abilities and changes in key aspects of social behaviour over evolutionary time. Here we present empirical evidence from phylogenetically controlled analyses indicating that evolutionary increases in the size of the vocal repertoire among non-human primate species were associated with increases in both group size and time spent grooming (our measure of extent of social bonding).
Trans-generational immune priming in a social insect
Authors: Sadd Ben M , Kleinlogel Yvonne , Schmid-Hempel Regula , Schmid-Hempel Paul
Published: September 2005

Detecting functional homology between invertebrate and vertebrate immunity is of interest in terms of understanding the dynamics and evolution of immune systems. Trans-generational effects on immunity are well known from vertebrates, but their existence in invertebrates remains controversial. Earlier work on invertebrates has interpreted increased offspring resistance to pathogens as trans-generational immune priming. However, interpretation of these earlier studies involves some caveats and thus full evidence for a direct effect of maternal immune experience on offspring immunity is still lacking in invertebrates. Here we show that induced levels of antibacterial activity are higher in the worker offspring of the bumblebee,
Bombus terrestris
L., when their mother queen received a corresponding immune challenge prior to colony founding. This shows trans-generational immune priming in an insect, with ramifications for the evolution of sociality.
Propagule pressure and persistence in experimental populations
Authors: Drake John M , Baggenstos Peter , Lodge David M
Published: September 2005

Average inoculum size and number of introductions are known to have positive effects on population persistence. However, whether these factors affect persistence independently or interact is unknown. We conducted a two-factor experiment in which 112 populations of parthenogeneticDaphnia magnawere maintained for 41 days to study effects of inoculum size and introduction frequency on: (i) population growth, (ii) population persistence and (iii) time-to-extinction. We found that the interaction of inoculum size and introduction frequency—the immigration rate—affected all three dependent variables, while population growth was additionally affected by introduction frequency. We conclude that for this system the most important aspect of propagule pressure is immigration rate, with relatively minor additional effects of introduction frequency and negligible effects of inoculum size.
Extrapair mating between relatives in the barn swallow: a role for kin selection?
Authors: Kleven Oddmund , Jacobsen Frode , Robertson Raleigh J , Lifjeld Jan T
Published: September 2005

Why do females of many species mate with more than one male? One of the main hypotheses suggests that female promiscuity is an insurance mechanism against the potential detrimental effects of inbreeding. Accordingly, females should preferably mate with less related males in multiple or extrapair mating. Here we analyse paternity, relatedness among mating partners, and relatedness between parents and offspring, in the socially monogamous North American barn swallow (
Hirundo rustica erythrogaster
). In contrast to the inbreeding avoidance hypothesis, we found that extrapair mating partners were more related than expected by random choice, and tended to be more related than social partners. Furthermore, extrapair mating resulted in genetic parents being more related to their extrapair young than to their withinpair young. We propose a new hypothesis for extrapair mating based on kin selection theory as a possible explanation to these findings.
High olfactory sensitivity for dimethyl sulphide in harbour seals
Authors: Kowalewsky Sylvia , Dambach Martin , Mauck Björn , Dehnhardt Guido
Published: September 2005

Productive areas are patchily distributed at sea and represent important feeding grounds for many marine organisms. Although pinnipeds are known to travel on direct routes and return regularly to particular feeding sites, the environmental information seals use to perform this navigation is as yet unknown. As atmospheric dimethyl sulphide (DMS) has been demonstrated to be a reliable indicator for profitable foraging areas, we tested seals for their ability to smell DMS at concentrations typical for the marine environment. Using a go/no-go response paradigm we determined the DMS detection threshold in two harbour seals (Phoca vitulina vitulina). DMS stimuli from 8.05×108to 8 pmol (DMS) m−3(air) were tested against a control stimulus using a custom-made olfactometer. DMS-thresholds determined for both seals (20 and 13 pmol m−3) indicate that seals can detect ambient concentrations associated with high primary productivity, e.g. in the North Atlantic. Thus, seals possess an extraordinarily high olfactory sensitivity for DMS, which could provide a sensory basis for identifying or orienting to profitable foraging grounds.
Caterpillars benefit from thermal ecosystem engineering by wandering albatrosses on sub-Antarctic Marion Island
Authors: Sinclair Brent J , Chown Steven L
Published: September 2005

Wandering albatrosses (Diomedea exulans) nest on Southern Ocean islands, building elevated nests upon which they incubate eggs and raise chicks, and which the chicks occupy through winter. The nests support high invertebrate biomass, including larvae of the flightless mothPringleophaga marioni. Here we argue that high biomass ofP. marioniin the nests is not associated with nutrient loading as previously suspected, but that higher temperatures in the nests increase growth and feeding rate, and decrease deleterious repeated cold exposure, providing fitness advantages forP. marioni.Thus, wandering albatrosses may be serving as thermal engineers, modifying temperature and therefore enabling better resource use byP. marioni.
Doing the twist: a test of Darwin's cross-pollination hypothesis for pollinarium reconfiguration
Authors: Peter Craig I , Johnson Steven D
Published: September 2005

Mating success in plants depends largely on the efficiency of pollen dispersal. For hermaphrodite plants, self-pollination, either within or among flowers, can reduce mating opportunities because of pollen and ovule discounting and inbreeding depression. Self-pollination may be particularly detrimental in plants such as orchids and asclepiads that package each flower's pollen into one or more pollinia which, together with accessory structures, comprise a pollinarium. Darwin proposed that physical reconfiguration of pollinaria serves as a mechanism for reducing the likelihood of self-pollination. To be effective, the time taken for pollinarium reconfiguration would need to exceed that spent by a pollinator on a plant. We investigated pollinarium reconfiguration (including pollinarium bending, pollinium shrinking and anther cap retention) in 19 species and found a strong positive relationship between reconfiguration time and the duration of pollinator visits. Reconfiguration times were also consistently longer than pollinator visit times. These results provide strong support for Darwin's idea that this mechanism promotes cross-pollination.
Larger swordtail females prefer asymmetrical males
Authors: Morris Molly R , Rios-Cardenas Oscar , Scarlett Tudor M
Published: September 2005

Many organisms, including humans, find symmetry more attractive than asymmetry. Is this bias towards symmetry simply a by-product of their detection system? We examined female preference for symmetry of the pigment pattern vertical bars in the swordtail fishes
Xiphophorus cortezi
and
Xiphophorus malinche
. We found a relationship between preference for symmetry and female size, with larger and thus older females spending significantly more time with the asymmetrical video animation as compared to the symmetrical video animation. The preference for asymmetry we report demonstrates that even if females can detect symmetrical males better, this does not preclude subsequent selection on females to prefer symmetrical or asymmetrical males. In addition, because the preference was correlated with female size, past studies may have missed preference for either asymmetry and/or symmetry by not examining the relationship between female preference and size/age or by measuring a limited size/age distribution of females. In both of the species of swordtail fishes examined, a high proportion of males are asymmetrical by more than one bar. We suggest that female preference may be maintaining fluctuating asymmetries in these fishes.
Reconstruction algorithm for single photon emission computed tomography and its numerical implementation
Authors: Fokas A.S , Iserles A , Marinakis V
Published: September 2005

The modern imaging techniques of positron emission tomography and of single photon emission computed tomography are not only two of the most important tools for studying the functional characteristics of the brain, but they now also play a vital role in several areas of clinical medicine, including neurology, oncology and cardiology. The basic mathematical problems associated with these techniques are the construction of the inverse of the Radon transform and of the inverse of the so-called attenuated Radon transform, respectively. An exact formula for the inverse Radon transform is well known, whereas that for the inverse attenuated Radon transform was obtained only recently by R. Novikov. The latter formula was constructed by using a method introduced earlier by R. Novikov and the first author in connection with a novel derivation of the inverse Radon transform. Here, we first show that the appropriate use of that earlier result yields immediately an analytic formula for the inverse attenuated Radon transform. We then present an algorithm for the numerical implementation of this analytic formula, based on approximating the given data in terms of cubic splines. Several numerical tests are presented which suggest that our algorithm is capable of producing accurate reconstruction for realistic phantoms such as the well-known Shepp–Logan phantom.
Similarities and differences between induced organ regeneration in adults and early foetal regeneration
Authors: Yannas Ioannis V
Published: September 2005

At least three organs (skin, peripheral nerves and the conjunctiva) have been induced to regenerate partially in adults following application of porous, degradable scaffolds with highly specific structure (templates). Templates blocked contraction and scar formation by inducing a reduction in the density of contractile fibroblasts (probably myofibroblasts) and by preventing these cells to organize themselves appropriately in the wound. In contrast, during early foetal healing, myofibroblasts were absent and wounds did not close by contraction but rather by spontaneous regeneration. The adult regenerative process has so far led to imperfect recovery of the physiological anatomy of skin (skin appendages were missing), while early foetal healing has led to apparently complete restoration. Furthermore, the mechanism of the adult regenerative process involves thwarting of myofibroblast function while, during early foetal healing, differentiation of myofibroblasts has not yet occurred. The data suggest that induced organ regeneration in the adult is the result of partial reversion to early foetal healing. If so, the adult may conceal a foetal response that may be subject to activation following application of highly active scaffolds or of other substances or cells.
Optimality of the basic colour categories for classification
Authors: Griffin Lewis D
Published: September 2005

Categorization of colour has been widely studied as a window into human language and cognition, and quite separately has been used pragmatically in image-database retrieval systems. This suggests the hypothesis that the best category system for pragmatic purposes coincides with human categories (i.e. the basic colours). We have tested this hypothesis by assessing the performance of different category systems in a machine-vision task. The task was the identification of the odd-one-out from triples of images obtained using a web-based image-search service. In each triple, two of the images had been retrieved using the same search term, the other a different term. The terms were simple concrete nouns. The results were as follows: (i) the odd-one-out task can be performed better than chance using colour alone; (ii) basic colour categorization performs better than random systems of categories; (iii) a category system that performs better than the basic colours could not be found; and (iv) it is not just the general layout of the basic colours that is important, but also the detail. We conclude that (i) the results support the plausibility of an explanation for the basic colours as a result of a pressure-to-optimality and (ii) the basic colours are good categories for machine vision image-retrieval systems.
A non-invasive method forin situquantification of subpopulation behaviour in mixed cell culture
Authors: MacArthur Ben D , Tare Rahul S , Please Colin P , Prescott Philip , Oreffo Richard O.C
Published: September 2005

Ongoing advances in quantitative molecular- and cellular-biology highlight the need for correspondingly quantitative methods in tissue-biology, in which the presence and activity of specific cell-subpopulations can be assessedin situ. However, many experimental techniques disturb the natural tissue balance, making it difficult to draw realistic conclusions concerningin situcell behaviour. In this study, we present a widely applicable and minimally invasive method which combines fluorescence cell labelling, retrospective image analysis and mathematical data processing to detect the presence and activity of cell subpopulations, using adhesion patterns in STRO-1 immunoselected human mesenchymal populations and the homogeneous osteoblast-like MG63 continuous cell line as an illustration.

Adhesion is considered on tissue culture plastic and fibronectin surfaces, using cell area as a readily obtainable and individual cell specific measure of spreading. The underlying statistical distributions of cell areas are investigated and mappings between distributions are examined using a combination of graphical and non-parametric statistical methods. We show that activity can be quantified in subpopulations as small as 1% by cell number, and outline behaviour of significant subpopulations in both STRO-1+/−fractions. This method has considerable potential to understandin situcell behaviour and thus has wide applicability, for example in developmental biology and tissue engineering.
Diving behaviour of whale sharks in relation to a predictable food pulse
Authors: Graham Rachel T , Roberts Callum M , Smart James C.R
Published: September 2005

We present diving data for four whale sharks in relation to a predictable food pulse (reef fish spawn) and an analysis of the longest continuous fine-resolution diving record for a planktivorous shark. Fine-resolution pressure data from a recovered pop-up archival satellite tag deployed for 206 days on a whale shark were analysed using the fast Fourier Transform method for frequency domain analysis of time-series. The results demonstrated that a free-ranging whale shark displays ultradian, diel and circa-lunar rhythmicity of diving behaviour. Whale sharks dive to over 979.5 m and can tolerate a temperature range of 26.4 °C. The whale sharks made primarily diurnal deep dives and remained in relatively shallow waters at night. Whale shark diving patterns are influenced by a seasonally predictable food source, with shallower dives made during fish spawning periods.
Why William Rowan Hamilton was not an FRS
Authors: Sen Siddhartha
Published: September 2005

Sir William Rowan Hamilton was a highly respected mathematician and scientist with close connections to influential members of the Royal Society, but he was not an FRS. The article explored possible reason for this.
Thermomechanical continuum representation of atomistic deformation at arbitrary size scales
Authors: Zhou Min
Published: September 2005

A thermomechanical equivalent continuum (TMEC) theory is developed for the deformation of atomistic particle systems at arbitrary size scales and under fully dynamic conditions. This theory allows continuum interpretation of molecular dynamics (MD) model results and derivation of thermomechanical continuum constitutive properties from MD results under conditions of general macroscopically transient thermomechanical deformations, which are not analysed by statistical mechanics. When specialized to the more specific conditions of non-deforming systems in macroscopic equilibrium, this theory yields certain results that are identical to, or consistent with, the results of statistical mechanics. Coupled thermomechanical continuum equations and constitutive behaviour are derived using MD concepts in a time-resolved manner. This theory is a further advancement from the purely mechanical equivalent continuum (EC) theory developed recently. Within the meaning of classical mechanics, the TMEC theory establishes the ultimate atomic origin of coupled thermomechanical deformation phenomena at the continuum level. The analysis is based on the decomposition of atomic particle velocity into a structural deformation part and a thermal oscillation part. On one hand, balance of momentum at the structural level yields fields of stress, body force, traction, mass density and deformation as they appear to a macroscopic observer. On the other hand, balance of momentum for the thermal motions relative to the macroscopically measured structure yields the fields of heat flux and temperature. These quantities are cast in a manner as to conform to the continuum phenomenological equation for heat conduction and generation, yielding scale-sensitive characterizations of specific heat, thermal conductivity and thermal relaxation time. The structural deformation and the thermal conduction processes are coupled because the equations for structural deformation and for heat conduction are two different forms of the same balance of momentum equation at the fully time-resolved atomic level. This coupling occurs through an inertial force term in each equation induced by the other process. For the structural deformation equation, the inertial force term induced by thermal oscillations of atoms gives rise to the phenomenological dependence of deformation on temperature. For the heat equation, the inertial force term induced by structural deformation takes the phenomenological form of a heat source.
Thermal transport property prediction of a CMC laminate from base materials properties and manufacturing porosities
Authors: Puglia P. Del , Sheikh M.A , Hayhurst D.R
Published: September 2005

This paper reviews two publications of the authors. The first relates to the classification of manufacturing porosity of a ceramic matrix composite material DRL-XT and the second to the quantification of thermal property degradation, due to porosity, at the level of the fibre tow and matrix regions. The paper then shows how these degraded thermal properties can be used in macro unit cell finite element analyses to quantify the effect of manufacturing porosity on bulk composite thermal properties. The dominant porosity type is matrix cracking, which is responsible for a 25% reduction of in-plane bulk thermal conductivity. Key to the success of the approach is an accurate knowledge of thermal properties of the constituent materials. However, in their absence, it is shown how property bounds may be used coupled with: semi-inverse finite element unit cell modelling and experimental values of bulk composite thermal properties.
Diffraction of harmonic flexural waves in a cracked elastic plate carrying electrical current
Authors: Ambur Damodar R , Hasanyan Davresh , Librescu Liviu , Qin Zhanming
Published: September 2005

The scattering effect of harmonic flexural waves at a through crack in an elastic plate carrying electrical current is investigated. In this context, the Kirchhoffean bending plate theory is extended as to include magnetoelastic interactions. An incident wave giving rise to bending moments symmetric about the longitudinal
x
-axis of the crack is applied. Fourier transform technique reduces the problem to dual integral equations, which are then cast to a system of two singular integral equations. Efficient numerical computation is implemented to get the bending moment intensity factor for arbitrary frequency of the incident wave and of arbitrary electrical current intensity. The asymptotic behaviour of the bending moment intensity factor is analysed and parametric studies are conducted.
Examples of nonlinear homogenization involving degenerate energies. I. Plane strain
Authors: Chenchiah Isaac V , Bhattacharya Kaushik
Published: September 2005

The study of polycrystals of shape-memory alloys and rigid-perfectly plastic materials gives rise to problems of nonlinear homogenization involving degenerate energies. This paper presents a characterization of the stress and strain fields in a class of problems in plane strain, and uses it to study examples including checkerboards and hexagonal microstructures. Consequences for shape-memory alloys and rigid-perfectly plastic materials are discussed.
Control of near-grazing dynamics in impact oscillators
Authors: Dankowicz Harry , Jerrelind Jenny
Published: September 2005

A method is presented for controlling the persistence of a local attractor near a grazing periodic trajectory in a piecewise smooth dynamical system in the presence of discontinuous jumps in the state associated with intersections with system discontinuities. In particular, it is shown that a discrete, linear feedback strategy may be employed to retain the existence of an attractor near the grazing trajectory, such that the deviation of the attractor from the grazing trajectory goes to zero as the system parameters approach those corresponding to grazing contact. The implementation relies on a local analysis of the near-grazing dynamics using the concept of discontinuity mappings. Numerical results are presented for a linear and a nonlinear oscillator.
Hydrodynamic construction of the electromagnetic field
Authors: Holland Peter
Published: September 2005

We present an alternative Eulerian hydrodynamic model for the electromagnetic field in which the discrete vector indices in Maxwell's equations are replaced by continuous angular freedoms, and develop the corresponding Lagrangian picture in which the fluid particles have rotational and translational freedoms. This enables us to extend to the electromagnetic field the exact method of state construction proposed previously for spin 0 systems, in which the time-dependent wavefunction is computed from a single-valued continuum of deterministic trajectories where two spacetime points are linked by at most a single orbit. The deduction of Maxwell's equations from continuum mechanics is achieved by generalizing the spin 0 theory to a general Riemannian manifold from which the electromagnetic construction is extracted as a special case. In particular, the flat-space Maxwell equations are represented as a curved-space Schrödinger equation for a massive system. The Lorentz covariance of the Eulerian field theory is obtained from the non-covariant Lagrangian-coordinate model as a kind of collective effect. The method makes manifest the electromagnetic analogue of the quantum potential that is tacit in Maxwell's equations. This implies a novel definition of the ‘classical limit’ of Maxwell's equations that differs from geometrical optics. It is shown that Maxwell's equations may be obtained by canonical quantization of the classical model. Using the classical trajectories a novel expression is derived for the propagator of the electromagnetic field in the Eulerian picture. The trajectory and propagator methods of solution are illustrated for the case of a light wave.
Two-dimensional leaps in near-critical flow over isolated orography
Authors: Johnson E.R , Vilenski G.G
Published: September 2005

This paper describes steady two-dimensional disturbances forced on the interface of a two-layer fluid by flow over an isolated obstacle. The oncoming flow speed is close to the linear longwave speed and the layer densities, layer depths and obstacle height are chosen so that the equations of motion reduce to the forced two-dimensional Korteweg–de Vries equation with cubic nonlinearity, i.e. the forced extended Kadomtsev–Petviashvili equation. The distinctive feature noted here is the appearance in the far lee-wave wake behind obstacles in subcritical flow of a ‘table-top’ wave extending almost one-dimensionally for many obstacles widths across the flow. Numerical integrations show that the most important parameter determining whether this wave appears is the departure from criticality, with the wave appearing in slightly subcritical flows but being destroyed by two-dimensional effects behind even quite long ridges in even moderately subcritical flow. The wave appears after the flow has passed through a transition from subcritical to supercritical over the obstacle and its leading and trailing edges resemble dissipationless leaps standing in supercritical flow. Two-dimensional steady supercritical flows are related to one-dimensional unsteady flows with time in the unsteady flow associated with a slow cross-stream variable in the two-dimensional flows. Thus the wide cross-stream extent of the table-top wave appears to derive from the combination of its occurrence in a supercritical region embedded in the subcritical flow and the propagation without change of form of table-top waves in one-dimensional unsteady flow. The table-top wave here is associated with a resonant steepening of the transition above the obstacle and a consequent twelve-fold increase in drag. Remarkably, the table-top wave is generated equally strongly and extends laterally equally as far behind an axisymmetric obstacle as behind a ridge and so leads to subcritical flows differing significantly from linear predictions.
An adaptive polynomial based forward prediction algorithm for multi-actuator real-time dynamic substructuring
Authors: Wallace M.I , Wagg D.J , Neild S.A
Published: September 2005

Real-time dynamic substructuring is a novel experimental technique used to test the dynamic behaviour of complex structures. The technique involves creating a hybrid model of the entire structure by combining an experimental test piece—the substructure—with a set of numerical models. In this paper we describe a multi-actuator substructured system of a coupled three mass–spring–damper system and use this to demonstrate the nature of delay errors which can first lead to a loss of accuracy and then to instability of the substructuring algorithm.

Synchronization theory and delay compensation are used to show how the delay errors, present in the transfer systems, can be minimized by online forward prediction. This new algorithm uses a more generic approach than the single step algorithms applied to substructuring thus far, giving considerable advantages in terms of flexibility and accuracy. The basic algorithm is then extended by closing the control loop resulting in an error driven adaptive feedback controller which can operate with no prior knowledge of the plant dynamics. The adaptive algorithm is then used to perform a real substructuring test using experimentally measured forces to deliver a stable substructuring algorithm.
The electric field of synchrotron radiation
Authors: Hannay J.H , Jeffrey M.R
Published: September 2005

A point charge moving uniformly around a circle produces an electric field pattern which co-rotates with it, constituting, for relativistic motion, synchrotron radiation. Surprisingly perhaps, the wealth of knowledge on synchrotron radiation does not seem to include
explicit
knowledge of the field itself, and of the consequent field lines. As with any relativistic motion, there is an obstruction to writing an explicit formula for the field; evaluation of the retarded time requires solving an implicit equation. However, as the relativistic limit is approached the field grows very strong in a very confined ribbon region shaped like a spiral watch spring. Here, the field
can
be written as an explicit scaling, or universal similarity, formula, which is our main result. From it the field lines can be derived analytically. In terms of scaled coordinates along the directions of the length, width and thickness of the ribbon, they twist in two side-by-side bundles in ‘bipolar’ cylinder surfaces, mirror symmetric about the orbit plane.
On the Camassa–Holm equation and a direct method of solution. II. Soliton solutions
Authors: Parker Allen
Published: September 2005

Previous attempts to find explicit
analytic
multisoliton solutions of the general Camassa–Holm (CH) equation have met with limited success. This study (which falls into two parts, designated II and III) extends the results of the prior work (I) in which a bilinear form of the CH equation was constructed and then solved for the solitary-wave solutions. It is shown that Hirota's bilinear transformation method can be used to derive exact multisoliton solutions of the equation in a systematic way. Here, analytic two-soliton solutions are obtained explicitly and their structure and dynamics are investigated in the different parameter regimes, including the limiting ‘two-peakon’ form. The solutions possess a non-standard representation that is characterized by an additional parameter, and the structure of this key parameter is examined. These results pave the way for constructing the hallmark
N
-soliton solutions of the CH equation in part III.
A power flow mode theory based on a system's damping distribution and power flow design approaches
Authors: Xiong Ye-Ping , Xing J.T , Price W.G
Published: September 2005

A power flow mode theory is developed to describe the natural power flow behaviour of a dynamic system based on its inherent damping distribution. The system's characteristic-damping matrix is constructed and it is shown that the eigenvalues and eigenvectors of this matrix identify natural power flow characteristics. These eigenvectors, or power flow mode vectors, are chosen as a set of base-vectors spanning the power flow space and completely describe the power flow in the system. The generalized coordinate of the velocity vector decomposed in this space defines the power flow response vector. A time-averaged power flow expression and theorems relating to its estimation are presented.

Based on this theory, power flow design approaches are proposed to identify energy flow patterns satisfying vibration control requirements. The mode control factor defines the measure of the correlation between a power flow mode and a natural vibration mode of the system. Power flow design theorems are presented providing guidelines to construct damping distributions maximizing power dissipation or to suppress/retain a particular vibration mode and/or a motion.

The developed damping-based power flow mode theory is compared with a mobility-based power flow model. It is shown that the proposed power flow model provides insight into the power flow dissipation mechanisms in dynamic systems.

Examples are presented to demonstrate the applicability of the power flow mode theory and the power flow design approach. These examples demonstrate the generality of the theory, including non-symmetric damping matrices, and illustrate power flow design applications through modifications of the system's damping distribution using passive and/or active control components.
The coupling of elastic, surface-wave modes by a slow, interfacial inclusion
Authors: Harris John G , Block Gareth
Published: September 2005

A layer of homogeneous, isotropic, elastic material overlays a substrate of similar material. The shear wavespeed within the layer is less than that of the substrate causing waves to be trapped within the layer. At the interface a long inclusion, that grows gradually until it reaches a constant thickness, is introduced. The inclusion is composed of a material whose shear wavespeed is less than that in the layer; it is described as slow. It is imagined that the lowest surface-wave mode of the structure is incident to the growing inclusion. Numerical calculations show that the growth of the slow inclusion brings the wavenumber of this lowest mode into an interval where it is close to that of the second mode, thus exciting it. This process is repeated when the wavenumber of the second mode is brought close to that of the third. Within these intervals, energy is exchanged among the coupling modes. Outside of these localized intervals, the modes propagate independently of one another and their amplitudes vary such that the flux of energy in each mode is conserved; they are said to propagate adiabatically. Reflections are also excited, but are shown to be very small in magnitude.
Interference of non-aligned Airy diffraction patterns in transmission acoustic microscopy images of crystals
Authors: Every A.G , Pluta M , Grill W
Published: September 2005

This paper describes interference effects present in narrow band transmission acoustic microscopy images of crystals that arise from the superposition of pairs of non-aligned but symmetry equivalent Airy diffraction patterns. In the cases we examine, these Airy patterns are associated with folded portions of the slow transverse (ST) sheet of the acoustic wave surface of cubic crystals intersecting in the {110} symmetry planes. Each set of Airy fringes is inclined in the (001) observation plane to its overlapping counterpart, giving rise to curved Moiré-like fringes. Also, because of tilting of the two portions of the wave surface in opposite directions out of the (001) plane, each composite Airy fringe breaks up along its length into a large number of narrow, regularly spaced fringes, in a manner akin to wedge diffraction. We present calculations of these effects in GaAs and Ge, based on the elastodynamic Green's function,, for the infinitely extended anisotropic elastic continuum. A measured time-gated diffraction image is presented for GaAs, which is in good agreement with calculation.
From patterns to processes and back: analysing density-dependent responses to an abiotic stressor by statistical and mechanistic modelling
Authors: Jannicke Moe S , Kristoffersen Anja B , Smith Robert H , Stenseth Nils Chr
Published: September 2005

Our knowledge about population-level effects of abiotic stressors is limited, largely due to lack of appropriate time-series data. To analyse interactions between an abiotic stressor and density-dependent processes, we used experimental time-series data for stage-structured populations (the blowfly
Lucilia sericata
) exposed to the toxicant cadmium through 20 generations. Resource limitation results in competition both in the larval and the adult stages. The toxicant has only negative effects at the organism level, but nevertheless, there were positive population-level effects. These are necessarily indirect, and indicate overcompensatory density-dependent responses. A non-parametric model (generalized additive model) was used to investigate the density-dependent structures of the demographic rates, without making assumptions about the functional forms. The estimated structures were used to develop a parametric model, with which we analysed effects of the toxicant on density-dependent and density-independent components of the stage-specific demographic rates. The parameter estimates identified both synergistic and antagonistic density–toxicant interactions. It is noteworthy that the synergistic interaction occurred together with a net positive effect of the toxicant. Hence, the effects of such interactions should be considered together with the capacity for compensatory responses. The combination of the two modelling approaches provided new insight into mechanisms for compensatory responses to abiotic stressors.
Global versus local adaptation in fly motion-sensitive neurons
Authors: Neri Peter , Laughlin Simon B
Published: September 2005

Flies, like humans, experience a well-known consequence of adaptation to visual motion, the waterfall illusion. Direction-selective neurons in the fly lobula plate permit a detailed analysis of the mechanisms responsible for motion adaptation and their function. Most of these neurons are spatially non-opponent, they sum responses to motion in the preferred direction across their entire receptive field, and adaptation depresses responses by subtraction and by reducing contrast gain. When we adapted a small area of the receptive field to motion in its anti-preferred direction, we discovered that directional gain at unadapted regions was enhanced. This novel phenomenon shows that neuronal responses to the direction of stimulation in one area of the receptive field are dynamically adjusted to the history of stimulation both within and outside that area.
Adaptive sex differences in growth of pre-ovulation oocytes in a passerine bird
Authors: Badyaev Alexander V , Schwabl Hubert , Young Rebecca L , Duckworth Renée A , Navara Kristen J , Parlow A.F
Published: September 2005

Maternal modification of offspring sex in birds has strong fitness consequences, however the mechanisms by which female birds can bias sex of their progeny in close concordance with the environment of breeding are not known. In recently established populations of house finches (
Carpodacus mexicanus
), breeding females lay a sex-biased sequence of eggs when ambient temperature causes early onset of incubation. We studied the mechanisms behind close association of incubation and sex-determination strategies in this species and discovered that pre-ovulation oocytes that produce males and females differed strongly in the temporal patterns of proliferation and growth. In turn, sex-specific exposure of oocytes to maternal secretion of prolactin and androgens produced distinct accumulation of maternal steroids in oocyte yolks in relation to oocyte proliferation order. These findings suggest that sex difference in oocyte growth and egg-laying sequence is an adaptive outcome of hormonal constraints imposed by the overlap of early incubation and oogenesis in this population, and that the close integration of maternal incubation, oocytes' sex-determination and growth might be under control of the same hormonal mechanism. We further document that population establishment and the evolution of these maternal strategies is facilitated by their strong effects on female and offspring fitness in a recently established part of the species range.
Caste evolution and ecology: a special worker for novel prey
Authors: Powell Scott , Franks Nigel R
Published: September 2005

Individual specialization underpins the division of labour within ant societies, but only in a small minority do morphological specialists, or physical castes, exist in the workforce. The genetic conditions that allow such castes to evolve are well understood, but the ecological pressures that select for them are not. We provide compelling evidence that the task of transporting novel prey selected for an exaggerated transport caste, or ‘submajor’, in the army ant
Eciton burchellii
. This species is the only
Eciton
that preys upon large arthropods as well as ants, the ancestral prey type, and by comparing load-transport among
Eciton
species and within
E. burchellii
, we show that this mixed diet significantly constrains transport efficiency. Crucially, however, we also show that
E. burchellii
submajors are highly specialized on transporting non-ant prey, and we demonstrate experientially that it is specifically this prey type that constrains prey-transport efficiency. Our study also suggests that phylogenetic constraints associated with the
Eciton
lifestyle intensified selection for the exaggerated submajor of
E. burchellii
. Thus, we propose that a novel task may only select for a special caste when phylogenetic constraints preclude the evolution of alternative solutions. This identifies a new and potentially general scenario for the evolution of physical castes.