bluuebunny/crossref_metadata_2025 huggingface dataset:
Pollinator aggregative and functional responses to flower density: does pollinator response to patches of plants accelerate at low‐densities?
Authors: S. Feldman Tracy
Published: May 2006

Plant reproduction is often reduced at low densities, due to reduced pollinator visitation rates. Recent theory suggests that a disproportionate increase in pollinator visits to patches of plants as heterospecific plant density increases (i.e. if visitation is a sigmoid function of patch density) can rescue sparse populations of a focal plant species from reduced reproductive success or population decline. A field experiment was performed to determine the shape of the pollinator visitation response to patches of differing density of the common weed Brassica rapa. Both the aggregative and functional response for the entire pollinator community were saturating rather than sigmoid, indicating that pollinator response does not accelerate when density increases. The results for the entire pollinator community were consistent among temporal and spatial replicates. Aggregative response curves for specific pollinator taxa were either linear (bombyliid flies) or saturating (syrphid flies, solitary bees, and Lepidoptera). Functional responses for these taxa were saturating (syrphid flies and solitary bees) or flat (bombyliid flies and Lepidoptera). Individual pollinators visited more plants during foraging bouts in high‐density patches, but visits per plant decreased. Seeds per fruit and seeds per flower increased with increasing density. There is no evidence that pollinators disproportionately visit denser patches, or that the conditions for this mechanism of pollination facilitation are likely to be met in this generalist pollinator system.
Disturbance and habitat use: is edge more important than area?
Authors: E. Moenting Alissa , W. Morris Douglas
Published: May 2006

In their efforts to maximize fitness while reducing the probability of dying, animals must decide which patches to forage in, when to forage, and how long to forage in each patch. Each decision will be modified by habitat and habitat disturbance. We evaluate the effects of habitat disturbance on foraging behaviour by imagining an initially homogeneous environment that is altered to create patches of different sizes. Disturbance increases predation risk, or otherwise alters patch profitability. Foragers can respond by changing their pattern of foraging, or by reducing their activity. We develop predictions for each scenario. We then test the predictions with data on the abundance and foraging activity of meadow voles (Microtus pennsylvanicus) in and around four sizes of circular disturbed patches. We created the patches by mowing vegetation in an abandoned hay field in northern Ontario, Canada. The treatments had no effect on vole density, and there was no consistent relationship between vole activity and distance from the edge of disturbed patches. Incidental predation of sunflower seeds, our measure of vole foraging behaviour, declined linearly with increasing patch circumference (edge). Seed consumption by meadow voles, and predation by voles on lower food levels, correlates with the length of edge habitat rather than with the area disturbed. Adaptive behaviour can thereby explain edge effects that, under current priorities emphasizing area, would appear at odds with conservation ecology.
Life history strategies affect climate based spatial synchrony in population dynamics of West African freshwater fishes
Authors: Tedesco Pablo , Hugueny Bernard
Published: May 2006

Spatial synchrony in species abundance is a general phenomenon that has been found in populations representing virtually all major taxa. Dispersal among populations and synchronous stochastic effects (the so called “Moran effect”) are the mechanisms most likely to explain such synchrony patterns. Very few studies have related the degree of spatial synchrony to the biological characteristics of species. Here we present a case where specific predictions can be made to relate river fish species characteristics and synchrony determined exclusively by a Moran effect through the expected sensitivity of species to the regional component of environmental stochasticity. By analyzing 23‐year time series of abundance estimates in two isolated localities we show that species associated with synchronized reproduction during the wet season, high fecundity, small egg size and high gonado‐somatic index (the so called “periodic” strategy) have a higher degree of spatial synchrony in population dynamics than species associated with the opposite traits (the so called “equilibrium” strategy). This is supported by significant relationships (P values <0.01) between species traits and the levels of synchrony after removing taxonomical relatedness. Spatial synchrony computed from summed annual total catches by groups of species, separated into strategy types also showed a significantly higher degree of synchrony for the periodic (r=0.83) than the equilibrium (r=0.46) group. Regional hydrological variability is likely to be partly responsible for the observed synchrony pattern and a regional discharge index showed better relationships with the periodic group, supporting the expected differential effect of regional environmental correlation on population dynamics.
Current food web models cannot explain the overall topological structure of observed food webs
Authors: W. Fox Jeremy
Published: May 2006

Topological food webs illustrating “who eats whom” in different systems exhibit similar, non‐random, structures suggesting that general rules govern food web structure. Current food web models correctly predict many measures of food web topology from knowledge of species richness and connectance (fraction of possible predator–prey links that actually occur), together with assumptions about the ecological rules governing “who eats whom”. However, current measures are relatively insensitive to small changes in topology. Improvement of, and discrimination among, current models requires development of new measures of food web structure. Here I examine whether current food web models (cascade, niche, and nested hierarchy models, plus a random null model) can predict a new measure of food web structure, structural stability. Structural stability complements other measures of food web topology because it is sensitive to changes in topology that other measures often miss. The cascade and null models respectively over‐ and underpredict structural stability for a set of 17 high‐quality food webs. While the niche and nested hierarchy models provide unbiased predictions on average, their 95% confidence intervals frequently fail to include the observed data. Observed structural stabilities for all models are overdispersed compared to model predictions, and predicted and observed structural stabilities are uncorrelated, indicating that important sources of variation in structural stability are not captured by the models. Crucially, poor model performance arises because observed variation in structural stability is unrelated to variation in species richness and connectance. In contrast, almost all other measures of food web topology vary with species richness and connectance in natural webs. No model that takes species richness and connectance as the only input parameters can reproduce observed variation in structural stability. Further progress in predicting and explaining food web topology will require fundamentally new models based on different input parameters.
The structure and stability of model ecosystems assembled in a variable environment
Authors: Lehmann‐Ziebarth Nicolas , R. Ives Anthony
Published: May 2006

To explore how environmental variability may create non‐random community structure, we simulated the assembly of model communities under varying levels of environmental variability. We assembled communities by creating a large pool of randomly constructed species, and then added species from this pool sequentially, allowing extinctions of invading and resident species to occur until the community became saturated. Because much current research on community structure focuses on single trophic levels, we constructed species pools consisting only of competitors. To compare with more realistic communities, we also created species pools with multiple trophic levels. For both types of communities, following assembly we calculated a variety of metrics of community structure, and five measures of community stability.

Communities assembled under high environmental variability had fewer species, fewer and weaker interactions among species, and greater evenness in abundance of persisting species. For single trophic‐level communities, community size was dictated primarily by competitive exclusion. In contrast, for multiple trophic‐level communities, community size was increasingly limited by dynamical instabilities as environmental variability increased.

Differences in community structure resulting from assembly under high environmental variability led to differences in community stability. According to two measures of stability related to population variability – the characteristic return rate to equilibrium and the coefficient of variation in individual species densities – stability increased for communities assembled under high environmental variability. In contrast, three additional measures of stability that are not directly related to population variability showed a variety of patterns, either increasing, decreasing, or remaining constant. Thus, communities assembled in highly variable environments are not necessarily generically more stable.

Our results demonstrate that environmental variability can structure communities and affect their stability properties in non‐trivial ways. Thus, when making predictions about the response of communities to future extinctions or environmental degradation, account should be given to the forces responsible for community structure.
Mobile scavengers create hotspots of freshwater productivity
Authors: X. Payne Laura , W. Moore Jonathan
Published: May 2006

Adjacent communities and ecosystems often differ in underlying productivity but are connected by flows of nutrients, energy, and matter. Pacific salmon (Oncorhynchus spp.) transport substantial quantities of nutrients from marine ecosystems to coastal freshwater habitats when they return to spawn and die. Nutrients from their carcasses are initially concentrated in spawning streams and lakes, but are subsequently dispersed by abiotic (floods, hyporheic flow) and biotic processes (predators and scavengers). In southwest Alaska, mobile avian scavengers (gulls; Larus spp.) breed on small islands within salmon nursery lakes and consume large quantities of spawning salmon during the chick‐rearing period. However the role of birds as vectors of salmon‐derived nutrients remains unknown. We examined how gulls – by transporting salmon tissues to their chicks – create hotspots of biological productivity in the aquatic habitats surrounding their nesting colonies. We found that algal production was ∼10× higher at islands with high gull densities compared to islands without nesting gulls, but was concentrated within 40 m of island shorelines. Carbon stable isotopes (δ13C) confirmed that gulls enhance primary production in local benthic communities and demonstrated that this production was transferred up the food web to grazers (snails) and carnivores (blackfish). Nitrogen stable isotopes (δ15N) confirmed that salmon dominated the diet of gulls and that nutrients from gull guano were incorporated into algae and passed up the food web. By relocating and concentrating salmon‐derived nutrients into new and distant locations, gulls alter and magnify production in local aquatic communities. We offer the first evidence that the avian community can move salmon‐derived nutrients great distances, enriching otherwise isolated habitats.
Evolution of local adaptations in dispersal strategies
Authors: Gros Andreas , Joachim Poethke Hans , Hovestadt Thomas
Published: May 2006

The optimal probability and distance of dispersal largely depend on the risk to end up in unsuitable habitat. This risk is highest close to the habitat's edge and consequently, optimal dispersal probability and distance should decline towards the habitat's border. This selection should lead to the emergence of spatial gradients in dispersal strategies. However, gene flow caused by dispersal itself is counteracting local adaptation. Using an individual based model we investigate the evolution of local adaptations of dispersal probability and distance within a single, circular, habitat patch. We compare evolved dispersal probabilities and distances for six different dispersal kernels (two negative exponential kernels, two skewed kernels, nearest neighbour dispersal and global dispersal) in patches of different size. For all kernels a positive correlation between patch size and dispersal probability emerges. However, a minimum patch size is necessary to allow for local adaptation of dispersal strategies within patches. Beyond this minimum patch area the difference in mean dispersal distance between center and edge increases linearly with patch radius, but the intensity of local adaptation depends on the dispersal kernel. Except for global and nearest neighbour dispersal, the evolved spatial pattern are qualitatively similar for both, mean dispersal probability and distance. We conclude, that inspite of the gene‐flow originating from dispersal local adaptation of dispersal strategies is possible if a habitat is of sufficient size. This presumably holds for any realistic type of dispersal kernel.
Does a lack of mating opportunities explain monandry in the green‐veined white butterfly (Pieris napi)?
Authors: Välimäki Panu , Kaitala Arja
Published: May 2006

In the nuptial gift‐giving butterfly, Pieris napi, multiple mating corresponds to higher lifetime fecundity than monandry does. Yet, female mating frequency, which is genetically determined and heritable, varies from strict monandry to a high degree of polyandry. Polyandrous females are known to suffer from reduced longevity when denied the opportunity to mate according to their intrinsic mating frequency. Here we test if monandry is likely to be maintained due to a lack of mating opportunities in the wild. We also explore longitudinal variation in female mating frequency (i.e. lifetime number of matings) and remating rate (i.e. time interval between successive matings). The latter was explored by comparing the mating patterns of females with varying origins in a laboratory, and the former by comparing the mating frequencies of wild and laboratory females. We were able to reveal spatial variation in female mating frequency, with monandry being a clearly more common mating tactic in the north than in the south. However, we did not find direct evidence that either the maintenance of monandry or spatial variation in female mating frequency is promoted by a lack of mating opportunities. Still, our findings may have profound implications, since decreasing mating frequency towards the north generates spatial variation in the strength of sexual selection.
Growth rate constrain morphological divergence when driven by competition
Authors: Olsson Jens , Svanbäck Richard , Eklöv Peter
Published: May 2006

Resource competition has been hypothesized to be important in driving divergence by natural selection. The effect of competition on morphological divergence and plasticity has however rarely been investigated. Since low growth rates might constrain morphological modulation and individual growth rates usually are negatively related to the intensity of competition, there might be a connection between competition, growth rate and morphological divergence. We performed an aquarium experiment with young‐of‐the‐year Eurasian perch (Perca fluviatilisL.) to investigate how individual growth rate affected morphological plasticity induced by contrasting habitat treatments. Furthermore, in a field study of 10 lakes we also related the degree of morphological differentiation between habitats to the intraspecific competitior biomass. In the aquarium experiment we found that morphological plasticity was growth rate dependent in that morphological differentiation between the habitat treatments was confined to high individual growth rates. In the field study we found that morphological differentiation between habitats decreased with increasing intraspecific competitior biomass. Since plasticity is hypothesized to be important in divergence and intraspecific biomass could serve as a proxy for the level of competition, we suggest that our results indicate that morphological divergence might be constrained during periods of intense intraspecific competition due to low growth rates. A possible scenario is that at low growth rates all energy available is used for metabolic maintenance and no surplus energy is therefore available for morphological modulation.
Movements and mortality of common goldeneyeBucephala clangulabroods in a patchy environment
Authors: Pöysä Hannu , Paasivaara Antti
Published: May 2006

Effects of habitat configuration on movements, space use, and mortality of individuals are crucial for our understanding of the dynamics and persistence of populations in patchy environments. We studied these aspects in a naturally patchy environment using radio‐marked common goldeneye (Bucephala clangula) females with their broods. The landscape consisted of suitable patches (lakes) and definitely inhospitable matrix (all terrestrial habitat surrounding the lakes), many of the patches being connected with corridors of varying usability (semipermanent and permanent ditches). We focused on habitat‐related factors potentially affecting the decision of common goldeneye females and broods to leave the hatching patch, the rate of movement within the landscape, and the first‐week mortality of ducklings when moving within the landscape. The probability to leave the hatching patch was high if the number of neighbouring patches was high, whereas mean distance to neighbouring patches and the presence and usability of corridors did not affect the probability to leave the hatching patch. Different measures of distance moved (i.e. within patches, through corridors, through matrix) were not strongly associated with any of the variables measuring habitat configuration. Corridors were used when available, but the broods also frequently moved through the matrix. There was no significant difference in the daily mortality rate of ducklings between broods that stayed in the hatching patch and broods that left the hatching patch. Among the broods that left the hatching patch, high daily mortality rate was associated with the lack and low usability of corridors. Daily mortality rate of ducklings was not associated with the distance moved through the matrix, nor with the other measures of distance moved or the variables measuring habitat configuration. Our findings suggest that species living in naturally patchy environments may have evolved remarkable skills to successfully cross an inhospitable matrix when changing patches.
Viability selection on overwintering eggs in a field cricket mosaic hybrid zone
Authors: Ross Charles L. , Harrison Richard G.
Published: May 2006

Habitat segregation allows recently diverged taxa to minimize competition and maximize fitness. Consequently, the overall distribution of a species in part will be determined by interactions with their close relatives. Two recently diverged but hybridizing field crickets,Gryllus firmusandG. pennsylvanicus, form a mosaic hybrid zone in Connecticut in which each species is associated with a specific soil type:G. firmusis found on sand soils andG. pennsylvanicusis found on loam soils. Both species produce diapausing eggs, which spend the winter in the ground. We investigate how viability selection on overwintering eggs in different soils influences the distributions of the two species, habitat partitioning between them, and the structure of the mosaic hybrid zone. Our results suggest that selection on eggs by soil types is not important in determining the success of crickets on different soils. However, winter climate has a strong effect on egg viability, and variation in egg survivorship over different winter climate regimes likely plays an important role in determining the distribution of these cricket species and the position of the hybrid zone.
The predation cost of being a male: implications for sex‐specific rates of ageing
Authors: Christe P. , Keller L. , Roulin A.
Published: May 2006

Evolutionary theory predicts that the rate of extrinsic (i.e. age‐ and condition‐independent) mortality should affect important life history traits such as the rate of ageing and maximum lifespan. Sex‐specific differences in mortality rates due to predation may therefore result in the evolution of important differences in life history traits between males and females. However, quantifying the role of predators as a factor of extrinsic mortality is notoriously difficult in natural populations. We took advantage of the unusual prey caching behaviour of the barn owl Tyto alba and the tawny owl Strix aluco to estimate the sex ratio of their five most common preys. For all prey species, there was a significant bias in the sex ratio of remains found in nests of both these owls. A survey of literature revealed that sex‐biased predation is a common phenomenon. These results demonstrate that predation, a chief source of extrinsic mortality, was strongly sex‐biased. This may select for alternate life history strategies between males and females, and account for a male life span being frequently lower than female lifespan in many animal species.
On the Stability of Second Order Time Varying Linear Systems
Authors: Tadi M.
Published: May 2006

This note considers the stability of linear time varying second order systems. It studies the case where the stiffness matrix is a function of time. It provides sufficient conditions for stability and asymptotic stability of the system provided that certain conditions on the stiffness matrix are satisfied.
Pre-tensioned Layer Damping as a New Approach for Vibration Control of Elastic Beams
Authors: Abd-Elwahab Mostafa , Sherif Hany A.
Published: May 2006

A new approach for suppression and control of mechanical vibration in elastic beams undergoing cyclic motion is presented. The proposed model is based on the idea of generating axial uniform damping forces on the surface of the vibrating structure. Equation of motion and expression for system damping of the new model are derived, where the effectiveness of this model for reducing lateral vibration of a base excited beam is theoretically determined at different force levels. The analysis included the first five mode shapes, and the performance at different boundary conditions is also discussed. The theoretical model is verified experimentally, and the technique used to generate the superficial forces is explained. A comparison between theoretical and experimental results is shown. It is found that the higher the generated superficial force value, the higher the attenuation percentage. The new model is characterized by its simplicity, which enhances its reliability and reduces its cost, as it provides the desired results with higher reliability and reasonable cost, compared with other approaches of active and intelligent structural designs.
Experimental Investigation Into the Effect of Fluid Viscosity on
Instability of an Over-hung Flexible Rotor Partially Filled With
Fluid
Authors: Changsheng Zhu
Published: May 2006

The effect of fluid viscosity on the developing process of the instability in an over-hung flexible rotor partially filled with fluid, the dynamical behavior of the rotor system while the instability occurs, the unstable region of rotational speeds, and the whirl frequency of the rotor system in the unstable region of rotational speeds, are experimentally investigated in this paper. It is shown that when the rotational speed is just over the reduced first critical speed of the fluid-filled rotor system that is less than the first critical speed of empty rotor system, the unstable motion occurs. The rotor system in the unstable speed region does not whirl at either a constant rotational speed or the first critical speed of the empty rotor system, the whirl frequency of the rotor system in the unstable speed region, dominated by the fluid-filled ratio and weakly depending on the viscosity of fluid, linearly increases with the rotational speed. There exists a hysteresis range of rotational speeds at the upper bound of the unstable speed region, which is not caused by the rotor transient motion when passing through the unstable speed region. As the fluid viscosity increases, both the unstable speed region and the hysteresis region narrow. The influence of the fluid viscosity on the unstable speed region of a rotor filled with a high viscosity fluid must be considered.
Modeling of a High Speed Rotor Test Rig With Active Magnetic Bearings
Authors: Li Guoxin , Lin Zongli , Allaire Paul E. , Luo Jihao
Published: May 2006

This paper reports on the modeling and experimental identification of a high speed rotor-magnetic bearing test rig. An accurate nominal model and an uncertainty representation are developed for robust controller synthesis and analysis. A combination of analytical modeling, model updating, and identification is employed for each system component and for the system as a whole. This approach takes advantage of both the behavior modeling and input/output modeling methods. Analytical models of the rotor and the magnetic bearings are first developed from physical laws and refined by comparison with the experimental data. The substructure model is directly identified from the experimental data by a structured identification approach. Models of the electronic systems, such as the filters, amplifiers, sensors, and digital controller, are developed through experimental identification. These component models are then assembled to obtain the overall system model. Closed-loop tests are conducted to identify parameters in the model. Advanced control techniques based on H∞ control and μ synthesis are developed and successfully implemented on the test rig, which further validates the model.
Behavior of a Self-Sustained Electromechanical Transducer and Routes to Chaos
Authors: Chedjou J. C. , Kyamakya K. , Moussa I. , Kuchenbecker H.-P. , Mathis W.
Published: May 2006

This paper studies the dynamics of a self-sustained electromechanical transducer. The stability of fixed points in the linear response is examined. Their local bifurcations are investigated and different types of bifurcation likely to occur are found. Conditions for the occurrence of Hopf bifurcations are derived. Harmonic oscillatory solutions are obtained in both nonresonant and resonant cases. Their stability is analyzed in the resonant case. Various bifurcation diagrams associated to the largest one-dimensional (1-D) numerical Lyapunov exponent are obtained, and it is found that chaos can appear suddenly, through period doubling, period adding, or torus breakdown. The extreme sensitivity of the electromechanical system to both initial conditions and tiny variations of the coupling coefficients is also outlined. The experimental study of̱the electromechanical system is carried out. An appropriate electronic circuit (analog simulator) is proposed for the investigation of the dynamical behavior of the electromechanical system. Correspondences are established between the coefficients of the electromechanical system model and the components of the electronic circuit. Harmonic oscillatory solutions and phase portraits are obtained experimentally. One of the most important contributions of this work is to provide a set of reliable analytical expressions (formulas) describing the electromechanical system behavior. These formulas are of great importance for design engineers as they can be used to predict the states of the electromechanical systems and respectively to avoid their destruction. The reliability of the analytical formulas is demonstrated by the very good agreement with the results obtained by both the numeric and the experimental analysis.
Modal Analysis to Accommodate Slap in Linear Structures
Authors: Segalman Daniel J. , Roy Anthony M. , Starr Michael J.
Published: May 2006

The generalized momentum balance (GMB) methods, explored chiefly by Shabana and his co-workers, treat slap or collision in linear structures as sequences of impulses, thereby maintaining the linearity of the structures throughout. Further, such linear analysis is facilitated by modal representation of the structures. These methods are discussed here and extended. Simulations on a simple two-rod problem demonstrate how this modal impulse approximation affects the system both directly after each impulse as well as over the entire collision. Furthermore, these simulations illustrate how the GMB results differ from the exact solution and how mitigation of these artifacts is achieved. Another modal method discussed in this paper is the idea of imposing piecewise constant forces over short, yet finite, time intervals during contact. The derivation of this method is substantially different than that of the GMB method, yet the numerical results show similar behavior, adding credence to both models. Finally, a novel method combining these two approaches is introduced. The new method produces physically reasonable results that are numerically very close to the exact solution of the collision of two rods. This approach avoids most of the nonphysical, numerical artifacts of interpenetration or chatter present in the first two methods.
Development of a New Passive-Active Magnetic Damper for Vibration Suppression
Authors: Sodano Henry A. , Inman Daniel J. , Belvin W. Keith
Published: May 2006

Magnetic fields can be used to apply damping to a vibrating structure. Dampers of this type function through the eddy currents that are generated in a conductive material experiencing a time-changing magnetic field. The density of these currents is directly related to the velocity of the change in magnetic field. However, following the generation of these currents, the internal resistance of the conductor causes them to dissipate into heat. Because a portion of the moving conductor’s kinetic energy is used to generate the eddy currents, which are then dissipated, a damping effect occurs. This damping force can be described as a viscous force due to the dependence on the velocity of the conductor. In a previous study, a permanent magnet was fixed in a location such that the poling axis was perpendicular to the beam’s motion and the radial magnetic flux was used to passively suppress the beam’s vibration. Using this passive damping concept and the idea that the damping force is directly related to the velocity of the conductor, a new passive-active damping mechanism will be created. This new damper will function by allowing the position of the magnet to change relative to the beam and thus allow the net velocity between the two to be maximized and thus the damping force significantly increased. Using this concept, a model of both the passive and active portion of the system will be developed, allowing the beams response to be simulated. To verify the accuracy of this model, experiments will be performed that demonstrate both the accuracy of the model and the effectiveness of this passive-active control system for use in suppressing the transverse vibration of a structure.
Rotation Effects on Vibration of Structures Seen From a Rotating Beam Simply Supported off the Rotation Axis
Authors: Kim J.
Published: May 2006

In rotating beams, the Coriolis force acts through the mass and rotary inertias of the beam. A rotating beam simply supported off the axis of rotation is used as an example to study effects of this Coriolis force on vibration of structures. By adopting such a simple model, mass- and rotary inertia-induced terms in the free vibration responses can be obtained in separate, closed forms. The effect of each of these terms on vibration characteristics of the rotating beam is discussed in relation to parameters such as nonrotating natural frequencies, the rotation speed, and the slenderness ratio. Practical implications of these results in analyses of rotating structures of other types are discussed, for example estimating the significance of rotary inertias in relation to the slenderness ratio and the rotation speed.
Modeling and Testing of After-Treatment Devices
Authors: Allam Sabry , Åbom Mats
Published: May 2006

Driven by emission regulations in the US and the EU exhaust systems on new diesel engines are equipped with both a catalytic converter (CC) and a diesel particulate filter (DPF). The CC and DPF are normally placed after each other in an expansion chamber, to create a complete after-treatment device (ATD) to reduce the exhaust pollutants. The ATD unit can also affect the acoustical performance of an exhaust system. In this paper, an acoustic model of a complete ATD for a passenger car is presented. The model is made up of four basic elements: (i) straight pipes; (ii) conical inlet/outlet; (iii) CC unit, and (iv) DPF unit. For each of these elements, a two-port model is used and, with the exception of the DPF unit, known models from the literature are available. For the DPF unit, a new model suggested by the authors has been used. Using the models, the complete acoustic two-port model for the investigated ATD unit has been calculated and used to predict the sound transmission loss. The predictions have been compared to experimental data taken at cold conditions for various flow speeds and show a good agreement.
Transient Vibration Analysis of Open Circular Cylindrical Shells
Authors: Kandasamy Selvakumar , Singh Anand V.
Published: May 2006

A numerical method based on the Rayleigh-Ritz method has been presented for the forced vibration of open cylindrical shells. The equations are derived from the three-dimensional strain-displacement relations in the cylindrical coordinate system. The middle surface of the shell represents the geometry, which is defined by an angle that subtends the curved edges, the length, and the thickness. The displacement fields are generated with a predefined set of grid points on the middle surface using considerably high-order polynomials. Each grid point has five degrees of freedom, viz., three translational components along the cylindrical coordinates and two rotational components of the normal to the middle surface. Then the strain and kinetic energy expressions are obtained in terms of these displacement fields. The differential equation governing the vibration characteristics of the shell is expressed in terms of the mass, stiffness, and the load consistent with the prescribed displacement fields. The transient response of the shell with and without damping is sought by transforming the equation of motion to the state-space model and then the state-space differential equations are solved using the Runge-Kutta algorithm.
A Linearized Theory on Ground-Based Vibration Response of Rotating Asymmetric Flexible Structures
Authors: Shen I. Y. , Kim Hyunchul
Published: May 2006

This paper is to develop a unified algorithm to predict vibration of spinning asymmetric rotors with arbitrary geometry and complexity. Specifically, the algorithm is to predict vibration response of spinning rotors from a ground-based observer. As a first approximation, the effects of housings and bearings are not included in this analysis. The unified algorithm consists of three steps. The first step is to conduct a finite element analysis on the corresponding stationary rotor to extract natural frequencies and mode shapes. The second step is to represent the vibration of the spinning rotor in terms of the mode shapes and their modal response in a coordinate system that is rotating with the spinning rotor. The equation of motion governing the modal response is derived through use of the Lagrange equation. To construct the equation of motion, explicitly, the results from the finite element analysis will be used to calculate the gyroscopic matrix, centrifugal stiffening (or softening) matrix, and generalized modal excitation vector. The third step is to solve the equation of motion to obtain the modal response, which, in turn, will lead to physical response of the rotor for a rotor-based observer or for a ground-based observer through a coordinate transformation. Results of the algorithm indicate that Campbell diagrams of spinning asymmetric rotors will not only have traditional forward and backward primary resonances as in axisymmetric rotors, but also have secondary resonances caused by higher harmonics resulting from the mode shapes. Finally, the algorithm is validated through a calibrated experiment using rotating disks with evenly spaced radial slots. Qualitatively, all measured vibration spectra show significant forward and backward primary resonances as well as secondary resonances as predicted in the theoretical analysis. Quantitatively, measured primary and secondary resonance frequencies agree extremely well with those predicted from the algorithm with mostly <3.5% difference.
Dynamic Actuation and Quadratic Magnetoelastic Coupling of Thin Magnetostrictive Shells
Authors: Tzou H. S. , Chai W. K. , Hanson M.
Published: May 2006

Smart adaptive structures and structronic systems have been increasingly investigated and developed in the last two decades. Although smart structures made of piezoelectrics, shape-memory materials, electrostrictive materials, and electro-/magnetorheological fluids have been evaluated extensively, studies of magnetostrictive continua, especially generic mathematical model(s), are still relatively scarce. This study is to develop a generic mathematical model for adaptive and controllable magnetostrictive thin shells. Starting with fundamental constitutive magnetostrictive relations, both elastic and magnetostrictive stresses, forces, and moments of a generic double-curvature magnetostrictive shell continuum subject to small and moderate magnetic fields are defined. Dynamic magnetomechanical system equations and permissible boundary conditions are defined using Hamilton's principle, elasticity theory, Kirchhoff-Love thin shell theory and the Gibb's free energy function. Magnetomechanical behavior and dynamic characteristics of magnetostrictive shells are evaluated. Simplifications of magnetostrictive shell theory to other common geometries are demonstrated and magnetostrictive/dynamic coupling and actuation characteristics are discussed.
Comment on "The Brain of LB1,
Homo floresiensis
"
Authors: Martin R. D. , MacLarnon A. M. , Phillips J. L. , Dussubieux L. , Williams P. R. , Dobyns W. B.
Published: May 2006

Endocast analysis of the brain
Homo floresiensis
by Falk
et al
. (Reports, 8 April 2005, p. 242) implies that the hominid is an insular dwarf derived from
H. erectus
, but its tiny cranial capacity cannot result from normal dwarfing. Consideration of more appropriate microcephalic syndromes and specimens supports the hypothesis of modern human microcephaly.
Genomics and the Irreducible Nature of Eukaryote Cells
Authors: Kurland C. G. , Collins L. J. , Penny D.
Published: May 2006

Large-scale comparative genomics in harness with proteomics has substantiated fundamental features of eukaryote cellular evolution. The evolutionary trajectory of modern eukaryotes is distinct from that of prokaryotes. Data from many sources give no direct evidence that eukaryotes evolved by genome fusion between archaea and bacteria. Comparative genomics shows that, under certain ecological settings, sequence loss and cellular simplification are common modes of evolution. Subcellular architecture of eukaryote cells is in part a physical-chemical consequence of molecular crowding; subcellular compartmentation with specialized proteomes is required for the efficient functioning of proteins.
A Systems Approach to Mapping DNA Damage Response Pathways
Authors: Workman Christopher T. , Mak H. Craig , McCuine Scott , Tagne Jean-Bosco , Agarwal Maya , Ozier Owen , Begley Thomas J. , Samson Leona D. , Ideker Trey
Published: May 2006

Failure of cells to respond to DNA damage is a primary event associated with mutagenesis and environmental toxicity. To map the transcriptional network controlling the damage response, we measured genomewide binding locations for 30 damage-related transcription factors (TFs) after exposure of yeast to methyl-methanesulfonate (MMS). The resulting 5272 TF-target interactions revealed extensive changes in the pattern of promoter binding and identified damage-specific binding motifs. As systematic functional validation, we identified interactions for which the target changed expression in wild-type cells in response to MMS but was nonresponsive in cells lacking the TF. Validated interactions were assembled into causal pathway models that provide global hypotheses of how signaling, transcription, and phenotype are integrated after damage.
Biogeographic Evolution of Madagascar's Microendemic Biota
Authors: Wilmé Lucienne , Goodman Steven M. , Ganzhorn Jörg U.
Published: May 2006

The endemic species richness on Madagascar, relative to landmass area, is unparalleled in the world. Many organisms on the island have restricted geographical ranges. A comprehensive hypothesis explaining the evolution of this microendemism has yet to be developed. Using an analysis of watersheds in the context of Quaternary climatic shifts, we provide a new mechanistic model to explain the process of explosive speciation on the island. River catchments with sources at relatively low elevations were zones of isolation and hence led to the speciation of locally endemic taxa, whereas those at higher elevations were zones of retreat and dispersion and hence contain proportionately lower levels of microendemism. These results provide a framework for biogeographic and phylogeographic studies, as well as a basis for prioritizing conservation actions of the remaining natural forest habitats on the island.
Desorption of H from Si(111) by Resonant Excitation of the Si-H Vibrational Stretch Mode
Authors: Liu Zhiheng , Feldman L. C. , Tolk N. H. , Zhang Zhenyu , Cohen P. I.
Published: May 2006

Past efforts to achieve selective bond scission by vibrational excitation have been thwarted by energy thermalization. Here we report resonant photodesorption of hydrogen from a Si(111) surface using tunable infrared radiation. The wavelength dependence of the desorption yield peaks at 0.26 electron volt: the energy of the Si-H vibrational stretch mode. The desorption yield is quadratic in the infrared intensity. A strong H/D isotope effect rules out thermal desorption mechanisms, and electronic effects are not applicable in this low-energy regime. A molecular mechanism accounting for the desorption event remains elusive.
Preparation of Poly(diiododiacetylene), an Ordered Conjugated Polymer of Carbon and Iodine
Authors: Sun Aiwu , Lauher Joseph W. , Goroff Nancy S.
Published: May 2006

Conjugated organic polymers generally must include large substituents for stability, either contained within or appended to the polymer chain. In polydiacetylenes, the substituents fulfill another important role: During topochemical polymerization, they control the spacing between the diyne monomers to produce an ordered polymer. By using a co-crystal scaffolding, we have prepared poly(diiododiacetylene), or PIDA, a nearly unadorned carbon chain substituted with only single-atom iodine side groups. The monomer, diiodobutadiyne, forms co-crystals with bis(nitrile) oxalamides, aligned by hydrogen bonds between oxalamide groups and weak Lewis acid-base interactions between nitriles and iodoalkynes. In co-crystals with one oxalamide host, the diyne undergoes spontaneous topochemical polymerization to form PIDA. The structure of the dark blue crystals, which look copper-colored under reflected light, has been confirmed by single-crystal x-ray diffraction, ultraviolet-visible absorption spectroscopy, and scanning electron microscopy.
Response to Comment on "The Brain of LB1,
Homo floresiensis
"
Authors: Falk Dean , Hildebolt Charles , Smith Kirk , Morwood M. J. , Sutikna Thomas , Jatmiko  , Saptomo E. Wayhu , Brunsden Barry , Prior Fred
Published: May 2006

Martin
et al
. claim that they have two endocasts from microcephalics that appear similar to that of LB1,
Homo floresiensis
. However, the line drawings they present as evidence lack details about the transverse sinuses, cerebellum, and cerebral poles. Comparative measurements, actual photographs, and sketches that identify key features are needed to draw meaningful conclusions about Martin
et al
.'s assertions.
Oligonucleotide-Modified Gold Nanoparticles for Intracellular Gene Regulation
Authors: Rosi Nathaniel L. , Giljohann David A. , Thaxton C. Shad , Lytton-Jean Abigail K. R. , Han Min Su , Mirkin Chad A.
Published: May 2006

We describe the use of gold nanoparticle-oligonucleotide complexes as intracellular gene regulation agents for the control of protein expression in cells. These oligonucleotide-modified nanoparticles have affinity constants for complementary nucleic acids that are higher than their unmodified oligonucleotide counterparts, are less susceptible to degradation by nuclease activity, exhibit greater than 99% cellular uptake, can introduce oligonucleotides at a higher effective concentration than conventional transfection agents, and are nontoxic to the cells under the conditions studied. By chemically tailoring the density of DNA bound to the surface of gold nanoparticles, we demonstrated a tunable gene knockdown.
Predicting Asbestos's Fallout
Authors: Samet Jonathan M.
Published: May 2006

Forecasting Product Liability Claims
. Epidemiology and Modeling in the Manville Asbestos Case.
By Eric Stallard, Kenneth G. Manton, and Joel E. Cohen
. Springer, Berlin, 2005. 424 pp. $84.95, £69, €89.95. ISBN 0-387-94987-9. Statistics for Biology and Health.

The authors describe the quantitative forecasting they developed to provide the groundwork for resolving the long Johns-Mansville asbestos litigation.
Weather Effects
Authors: Goudie Andrew
Published: May 2006

The Winds of Change
. Climate, Weather, and the Destruction of Civilizations.
By Eugene Linden
. Simon and Schuster, New York, 2006. 314 pp. $26, C$36. ISBN 0-684-86352-9.

The author weaves together findings from paleoclimatology, oceanography, and history to explore the possibility that climate change has been the causal agent in the downfall of human communities throughout our past.
The risk for multiple sclerosis in female nurse anaesthetists: a register based study: Table 1
Authors: Landtblom A-M , Tondel M , Hjalmarsson P , Flodin U , Axelson O
Published: May 2006

Background:Previous studies have suggested that exposure to organic solvents, including volatile anaesthetic agents, may be a risk factor for multiple sclerosis (MS), possibly in combination with genetic and other environmental factors.

Aims:To further investigate the role of volatile anaesthetic agents having similar acute toxic effects to other organic solvents.

Methods:Female nurse anaesthetists, other female nurses, and female teachers from middle and upper compulsory school levels were identified and retrieved from the 1985 census, Statistics Sweden. By means of the unique personal identity number in Sweden, these individuals were linked with the disability pension registers at The National Social Insurance Board and also with data on hospital care 1985–2000 at The National Board of Health and Welfare.

Results:The cumulative incidence rate ratio of MS was found to be increased in female nurse anaesthetists in relation to other nurses (statistically not significant) and teachers (statistically significant), respectively.

Conclusions:These findings give some support to previous findings of an increased risk for MS in nurse anaesthetists. This is interesting in the context of previous observations of organic solvents in general as a potential risk factor in MS.