bluuebunny/crossref_metadata_2025 huggingface dataset:
Asymptotics for some nonlinear damped wave equation: finite time convergence versus exponential decay results
Authors: Baji B. , Cabot A. , Díaz J.I.
Published: December 2006

Given a bounded open set

\Omega \subset \mathbb{R}^{n}

and a continuous convex function

\Phi \:\text{:}L^{2}(\Omega )\rightarrow \mathbb{R}

, let us consider the following damped wave equation

\tag{S}
u_{tt}−\mathrm{\Delta }u + \partial \Phi (u_{t}) \ni 0,\:(t,x) \in (0, + \infty ) \times \Omega ,

under Dirichlet boundary conditions. The notation

∂Φ

refers to the subdifferential of

Φ

in the sense of convex analysis. The nonlinear term

∂Φ

allows to modelize a large variety of friction problems. Among them, the case

\Phi = | \cdot |_{L^{1}}

corresponds to a Coulomb friction, equal to the opposite of the velocity sign. After we have proved the existence and uniqueness of a solution to (S), our main purpose is to study the asymptotic properties of the dynamical system (S). In two significant situations, we bring to light an interesting phenomenon of dichotomy: either the solution converges in a finite time or the speed of convergence is exponential as

t\rightarrow + \infty

. We also give conditions which ensure the finite time stabilization of (S) toward some stationary solution.

Etant donné un ouvert borné

\Omega \subset \mathbb{R}^{n}

et une fonction convexe continue

\Phi \:\text{:}L^{2}(\Omega )\rightarrow \mathbb{R}

, considérons l'équation des ondes amorties suivante :

\tag{S}
u_{tt}−\mathrm{\Delta }u + \partial \Phi (u_{t}) \ni 0,\:(t,x) \in (0, + \infty ) \times \Omega ,

avec conditions de Dirichlet au bord. La notation

∂Φ

désigne le sous-différentiel de

Φ

au sens de l'analyse convexe. Le terme non-linéaire

∂Φ

permet de modéliser une grande variété de problèmes avec frottement. Le cas

\Phi = | \cdot |_{L^{1}}

correspond au frottement de Coulomb, égal à l'opposé du signe de la vitesse. Après avoir établi l'existence et l'unicité d'une solution de (S), notre principal objectif est d'étudier les propriétés asymptotiques du système dynamique (S). Dans deux situations significatives, on met en évidence un phénomène intéressant de dichotomie : la solution converge en temps fini, ou bien la vitesse de convergence est exponentielle lorsque

t\rightarrow + \infty

. On donne également des conditions qui garantissent la stabilisation en temps fini de (S) vers une solution stationnaire.
Third‐trimester erythrocytapheresis in pregnant patients with sickle cell disease
Authors: Gilli S.C. , De Paula E.V. , Biscaro F.P. , Marques J.F. , Costa F.F. , Saad S.T.
Published: December 2006

Objective: To evaluate the effects of prophylactic transfusion by means of erythrocytapheresis at the beginning of the third trimester of pregnancy in women with sickle cell disease (SCD). Methods: A cohort of 14 pregnant women with SCD who received prophylactic erythrocytapheresis transfusions at the beginning of the third trimester was retrospectively compared with a cohort of 17 pregnant women who received simple prophylactic transfusions for no indication other than SCD severity. Results: Prophylactic erythrocytapheresis transfusions were associated with a lower risk of intrauterine growth restriction (OR, 0.11; 95% confidence interval, 0.01–1.00) and oligohydramnios (OR, 0.65; 95% confidence interval, 0.45–0.92) in pregnant women with SCD. Conclusion: These results suggest that erythrocytapheresis transfusions are beneficial in women with SCD who are in the third trimester of pregnancy. Given the decrease in transfusion risks, this therapy deserves further evaluation in future trials.
The role of APICS in professionalizing operations management
Authors: Lummus Rhonda R.
Published: December 2006

The APICS organization is the professional association most closely affiliated with operations management practitioners. The organization is widely known for their Certified in Production and Inventory Management (CPIM) program that assesses individual knowledge in the field of production and inventory management. APICS and the CPIM certification have played a major role in elevating the professionalism of individuals who work in operations management. This paper will detail a history of APICS and the CPIM certification and describe the role of academics in the development of the certification.
Planning effort as an effective risk management tool
Authors: Zwikael Ofer , Sadeh Arik
Published: December 2006

In project management, high levels of risk are considered to be a significant obstacle for project success. This paper investigates whether improving the project plan can lead to improved success for high‐risk projects. A quality of planning index was designed to explore how the presence of high risk affects the quality of planning and project success. The index includes managerial aspects such as costs, human resources, procurement and quality, as well as organizational support aspects based on organization maturity models. In a field study based on data collected from 202 project managers regarding their most recent projects, it was found that the levels of risk at the beginning of projects has no effect on their final success. Drilling down to find an explanation for this surprising phenomenon, we found that in the presence of high risk, project managers significantly improve their project plans. Hence, in high‐risk projects, better project plans improve all four dimensions of project success: schedule overrun, cost overrun, technical performance and customer satisfaction. However, in low‐risk projects, better project plans did not contribute to reducing schedule or cost overruns. In other words, while endless risk management tools are developed, we found that improving the project plan is a more effective managerial tool in dealing with high‐risk projects. Finally, the paper presents the most common planning tools currently being used in high‐risk projects.
Alternatives to Chromatographic Separations
Authors: Thömmes Jörg , Etzel Mark
Published: December 2006

Up to now, the productivity of mammalian cell culture has been perceived as limiting the productivity of the industrial manufacture of therapeutic monoclonal antibodies. Dramatic improvements in cell culture performance have changed this picture, and the throughput of antibody purification processes is gaining increasing attention. Although chromatographic separations currently are the centerpiece of antibody purification, mostly due to their high resolving power, it becomes more and more apparent that there may be limitations at the very large scale. This review will discuss a number of alternatives to chromatographic antibody purification, with a particular emphasis on the ability to increase throughput and overcome traditional drawbacks of column chromatography. Specifically, precipitation, membrane chromatography, high‐resolution ultrafiltration, crystallization, and high‐pressure refolding will be evaluated as potential large scale unit operations for industrial antibody production.
Scattering transform for nonstationary Schrödinger equation with bidimensionally perturbed N-soliton potential
Authors: Boiti M. , Pempinelli F. , Pogrebkov A. K.
Published: December 2006

In the framework of the extended resolvent approach the direct and inverse scattering problems for the nonstationary Schrödinger equation with a potential being a perturbation of the N-soliton potential by means of a generic bidimensional smooth function decaying at large spaces are introduced and investigated. The initial value problem of the Kadomtsev-Petviashvili I equation for a solution describing N wave solitons on a generic smooth decaying background is then linearized, giving the time evolution of the spectral data.
Magnetic flux penetration into twisted multifilamentary coated superconductors subjected to ac transverse magnetic fields
Authors: Amemiya Naoyuki , Sato Susumu , Ito Takeshi
Published: December 2006

ac losses in superconductors are generated by the magnetic flux and current penetration into them. To reveal the magnetic flux and current penetration processes in twisted multifilamentary coated superconductors in which the thin superconductor layer is subdivided into filaments and then twisted as a whole for ac loss reduction, a theoretical model for electromagnetic field analysis was developed based on the power law E-J (electric-field–current-density) characteristic for the superconductor and a thin strip approximation of the conductor. The developed theoretical model was implemented into a numerical code using the finite element method to calculate and visualize the current and magnetic flux distributions. The magnetization losses in twisted multifilamentary coated superconductors exposed to ac transverse magnetic fields were calculated from the temporal evolutions of the current distribution to demonstrate the effect of the twisted multifilamentary architecture on ac loss reduction.
Perturbed block circulant matrices and their application to the wavelet method of chaotic control
Authors: Juang Jonq , Li Chin-Lung , Chang Jing-Wei
Published: December 2006

Controlling chaos via wavelet transform was proposed by Wei et al. [Phys. Rev. Lett. 89, 284103–1284103–4 (2002)]. It was reported there that by modifying a tiny fraction of the wavelet subspace of a coupling matrix, the transverse stability of the synchronous manifold of a coupled chaotic system could be dramatically enhanced. The stability of chaotic synchronization is actually controlled by the second largest eigenvalue λ2(α,β) of the (wavelet) transformed coupling matrix C(α,β) for each α and β. Here β is a mixed boundary constant and α is a scalar factor. In particular, β=1 (0) gives the nearest neighbor coupling with periodic (Neumann) boundary conditions. In this paper, we obtain two main results. First, the reduced eigenvalue problem for C(α,0) is completely solved. Some partial results for the reduced eigenvalue problem of C(α,β) are also obtained. Second, we are then able to understand behavior of λ2(α,0) and λ2(α,1) for any wavelet dimension j∊N and block dimension n∊N. Our results complete and strengthen the work of Shieh et al. [J. Math. Phys. 47, 082701–1082701–10 (2006)] and Juang and Li [J. Math. Phys. 47, 072704–1072704–16 (2006)].
Chemical and structural aspects of CoPt silicide nanostructures grown on Si(100)
Authors: Ouerghi A. , Penuelas J. , Andreazza-Vignolle C. , Andreazza P. , Bouet N. , Estrade-Szwarckopf H.
Published: December 2006

We investigate the growth of CoPt-based nanostructures on thermally oxidized Si(100) substrates by ultrahigh-vacuum coevaporation at 50, 400, and 650°C substrate temperatures. The thermal evolution of the bimetallic deposits has been studied by x-ray photoelectron spectroscopy (XPS) as well as x-ray diffraction (XRD) in grazing incidence. This study reveals a fast migration of the deposited Co and Pt towards the SiO2 underlayer, which promotes silicide formation at substrate temperatures higher than 400°C. The XPS spectra of Pt and Co present shifts characteristic of the metal silicide, from 71to72.6eV and from 778to778.5eV, respectively. Moreover, structural investigations on the sample prepared at a substrate temperature of 650°C by symmetric XRD and by high resolution transmission electron microscopy reveal the growth of mixed CoPt silicide nanostructures via an endotaxial solid-state mechanism. It has been found that the extremely low deposition rate together with the high temperature during the deposition and the presence of SiO2 layer favor the disilicide formation, preserving the initial equiatomic CoPt ratio in the silicide islands.
Spontaneous emission mechanisms of GaInAsN∕GaAs quantum dot systems
Authors: Wei Z. F. , Xu S. J. , Li Q.
Published: December 2006

Variable-temperature photoluminescence (PL) spectra taken on two different kinds of GaInAsN quantum dots (QDs), having different In and N compositions and thicknesses, have been investigated both experimentally and theoretically. It is found that the temperature dependence of the spontaneous emissions from both samples behaves differently. Adopting a localized-state luminescence model, the quantitative reproduction of the measured variable-temperature PL spectra reveals a dissimilarity in luminescence mechanisms of the two samples. These results enrich the present understanding of the luminescence mechanisms in the GaInAsN QD systems and are important for design and improvement of GaInAsN QDs based light-emitting devices.
Influence of capping layers on the crystallization of doped SbxTe fast-growth phase-change films
Authors: Pandian Ramanathaswamy , Kooi Bart J. , De Hosson Jeff Th. M. , Pauza Andrew
Published: December 2006

Isothermal crystallization of doped SbxTe fast-growth phase-change films, with and without capping layers, was investigated using transmission electron microscopy, which provided direct and quantitative information on nucleation and growth processes separately. Two types of amorphous dielectric layers, ZnS–SiO2 and GeCrN, were used for sandwiching the SbxTe films to form typical trilayer stacks, which are the active part in applications. The nucleation and growth parameters of SbxTe films were found to be influenced by the dielectric capping layers. The crystal growth rate is temperature dependent and it reduces when the film is sandwiched between the dielectric layers. The reduction in growth rate differs with the capping layer type. The capping layer influence on the growth rate is pronounced at lower temperatures ∼160°C, but tends to vanish at higher temperatures ∼200°C. The activation energy for crystal growth is 2.4±0.3eV for an uncapped film and it increases ∼40% when the capping layers, GeCrN or ZnS–SiO2, are added. A temperature and time dependent nucleation rate is found and it is accelerated ∼1.7 times by GeCrN layers, whereas it is retarded ∼5 times by ZnS–SiO2 layers. The activation energy for crystal nucleation is 6.1±0.4eV for an uncapped film and it is not noticeably altered by the capping layers. These variations observed in the crystallization kinetics are attributed to variations in interface energy between the phase-change film and the capping layers or vacuum and the confinement effect by the capping layers on the phase-change film.
Role of the spin-pair correlation in magnetic relaxor ferroelectrics
Authors: Xia Q. S. , Jiang Q.
Published: December 2006

In magnetic relaxor ferroelectrics, for the coupling interaction between the relaxor ferroelectricity and magnetic order, the dielectric susceptibility exhibits a sharp increase around the magnetic phase transition temperature. By adding an appropriate coupling term between the electrical and magnetic subsystems, which is related to the interaction of the Heisenberg spin and the order parameter field, the replica theory based on the spherical random-bond-random-field model and the mean-field theory based on the Heisenberg model are successfully applied to the magnetic relaxor ferroelectrics. We find that the fluctuation of the spin-pair correlation plays an important role in the change of dielectric susceptibility around the magnetic phase transition temperature. The obtained static dielectric susceptibility and the magnetocapacitance are in good agreement with the experimental results.
The dynamics of amplified spontaneous emission in CdSe∕ZnSe quantum dots
Authors: Kundys D. O. , Murzyn P. , Wells J.-P. R. , Tartakovskii A. I. , Skolnick M. S. , Dang Le Si , Lutsenko E. V. , Tarasuk N. P. , Lyublinskaya O. G. , Toropov A. A. , Ivanov S. V.
Published: December 2006

We have used the variable stripe technique and pump-probe spectroscopy to investigate both gain and the dynamics of amplified spontaneous emission from CdSe quantum dot structures. We have found modal gain coefficients of 75 and 32cm−1 for asymmetric and symmetric waveguide structures, respectively. Amplified spontaneous emission decay times of 150 and 300ps and carrier capture times of 15 and 40ps were measured for the structures with high and low material gains respectively. The difference in the capture times are related to the fact that for the symmetric waveguide, carriers diffuse into the active region from the uppermost ZnMgSSe cladding layer, yielding a longer rise time for the pump-probe signals for this sample.
Heat capacity, Raman, and Brillouin scattering studies of M2O–MgO–WO3–P2O5 glasses (M=K,Rb)
Authors: Maczka M. , Hanuza J. , Baran J. , Hushur A. , Kojima S.
Published: December 2006

The authors report the results of temperature-dependent Brillouin scattering from both transverse and longitudinal acoustic waves, heat capacity studies as well as room temperature Raman scattering studies on M2O–MgO–WO3–P2O5 glasses (M=K,Rb). These results were used to obtain information about structure and various properties of the studied glasses such as fragility, elastic moduli, ratio of photoelastic constants, and elastic anharmonicity. They have found that both glasses have similar properties but replacement of K+ ions by Rb+ ions in the glass network leads to decrease of elastic parameters and P44 photoelastic constant due to increase of fragility. Based on Brillouin spectroscopy they show that a linear correlation between longitudinal and shear elastic moduli holds over a large temperature range. This result supports the literature data that the Cauchy-type relation represents a general rule for amorphous solids. An analysis of the Boson peak revealed that the form of the frequency distribution of the excess density of states is in agreement with the Euclidean random matrix theory. The reason of the observed shift of the maximum frequency of the Boson peak when K+ ions are substituted for Rb+ ions is also briefly discussed.
Comparative study of perturbative methods for computing electron transfer tunneling matrix elements with a nonorthogonal basis set
Authors: Teklos Antonios , Skourtis Spiros S.
Published: December 2006

The authors consider the problem of computing tunneling matrix elements for bridge-mediated electron transfer reactions using the Löwdin [J. Math. Phys. 3, 969 (1962); J. Mol. Spectrosc. 13, 326 (1964)] projection-iteration technique with a nonorthogonal basis set. They compare the convergence properties of two different Löwdin projections, one containing the overlap matrix S and the other containing the inverse S−1 in the projected Hamiltonian. It was suggested in the literature that the projected Hamiltonian with S−1 has better convergence properties compared to the projected Hamiltonian with S. The authors test this proposal using a simple analytical model, and ab initio Hartree-Fock calculations on different molecules with several types of basis sets. Their calculations show that, for Gaussian-type basis sets, the projected Hamiltonian containing S has the best convergence properties, especially for diffuse basis sets and in the strong coupling limit. The limit of diffuse basis sets is relevant to tunneling matrix element calculations involving excited states and anionic electron transfer.
Current rectification by asymmetric molecules: An ab initio study
Authors: Zhou Yan-hong , Zheng Xiao-hong , Xu Ying , Zeng Zhao Yang
Published: December 2006

Current rectification effect in an asymmetric molecule HCOO–C6H4–(CH2)n sandwiched between two aluminum electrodes has been studied using an ab initio nonequilibrium Green’s function method. The conductance of the system decreases exponentially with the increasing number n of CH2. The phenomenon of current rectification is observed such that a very small current appears at negative bias and a sharp negative differential resistance at a critical positive bias when n⩾2. The rectification effect arises from the asymmetric structure of the molecule and the molecule-electrode couplings. A significant rectification ratio of ∼38 can be achieved when n=5.
Nonlinear effects on solvation dynamics in simple mixtures
Authors: Murata Shuhei , Yoshimori Akira
Published: December 2006

The authors applied the time dependent density functional method (TDDFM) and a linear model to solvation dynamics in simple binary solvents. Changing the solute-solvent interactions at t=0, the authors calculated the time evolution of density fields for solvent particles after the change (t>0) by the TDDFM and linear model. First, the authors changed the interaction of only one component of solvents. In this case, the TDDFM showed that the solvation time decreased monotonically with a mole fraction of the solvent strongly interacting with the solute. The monotonical decreases agreed with experimental results, while the linear model did not reproduce these results. The authors also calculated the solvation time by changing the interaction of both components. The calculation showed that the mole fraction dependence had the peak. The TDDFM presented a much higher peak than the linear model. The difference between the TDDFM and the linear model was caused by a nonlinear effect on an exchange process of solvent particles.
Excess-entropy-based anomalies for a waterlike fluid
Authors: Errington Jeffrey R. , Truskett Thomas M. , Mittal Jeetain
Published: December 2006

Many thermodynamic and dynamic properties of water display unusual behavior at low enough temperatures. In a recent study, Yan et al. [Phys. Rev. Lett. 95, 130604 (2005)] identified a spherically symmetric two-scale potential that displays many of the same anomalous properties as water. More specifically, for select parametrizations of the potential, one finds that the regions where isothermal compression anomalously (i) decreases the fluid’s structural order, (ii) increases its translational self-diffusivity, and (iii) increases its entropy form nested domes in the temperature-density plane. These property relationships are similar to those found for more realistic models of water. In this work, the authors provide evidence that suggests that the anomalous regions specified above can all be linked through knowledge of the excess entropy. Specifically, the authors show how entropy scaling relationships developed by Rosenfeld [Phys. Rev. A 15, 2545 (1977)] can be used to describe the region of diffusivity anomalies and to predict the state conditions for which anomalous viscosity and thermal conductivity behavior might be found.
Microinversions in mammalian evolution
Authors: Chaisson M. J. , Raphael B. J. , Pevzner P. A.
Published: December 2006

We propose an approach for identifying microinversions across different species and show that microinversions provide a source of low-homoplasy evolutionary characters. These characters may be used as “certificates” to verify different branches in a phylogenetic tree, turning the challenging problem of phylogeny reconstruction into a relatively simple algorithmic problem. We estimate that there exist hundreds of thousands of microinversions in genomes of mammals from comparative sequencing projects, an untapped source of new phylogenetic characters.
Rotational Analysis of the D2Σ-X2Σ Transition of CaCl
Authors: L-E Berg  , L Klynning  , H Martin  , A Pereira  , P Royen
Published: December 2006

The absorption spectrum of gaseous CaCl in the wavelength region 2990-3300 Å has been studied using a King furnace. Ten bands belonging to theD2Σ-X2Σ transition have been analyzed and both vibrational and rotational constants have been evaluated. The following molecular constants have been determined (cm-1):

X2ΣD2ΣTe0.031 110.934(5)ωe370.201423.254(7)ωexe1.37321.581(3)ωeye9.3 × 10-31.6(4) × 10-3ωeze-4.8 × 10-4-2.9(2) × 10-4Be0.152 2330.162 975 4(8)αe7.92 × 10-47.968(2) × 10-4De1.068 × 10-71.0090(3) × 10-7γe1.38 × 10-31.2 × 10-3

The figures in parentheses stand for one standard deviation in the last digit for the computed quantity.
Eat now, pay later? Evidence of deferred food-processing costs in diving seals
Authors: Sparling Carol E , Fedak Mike A , Thompson Dave
Published: December 2006

Seals may delay costly physiological processes (e.g. digestion) that are incompatible with the physiological adjustments to diving until after periods of active foraging. We present unusual profiles of metabolic rate (MR) in grey seals measured during long-term simulation of foraging trips (4–5 days) that provide evidence for this. We measured extremely high MRs (up to almost seven times the baseline levels) and high heart rates during extended surface intervals, where the seals were motionless at the surface. These occurred most often during the night and occurred frequently many hours after the end of feeding bouts. The duration and amount of oxygen consumed above baseline levels during these events was correlated with the amount of food eaten, confirming that these metabolic peaks were related to the processing of food eaten during foraging periods earlier in the day. We suggest that these periods of high MR represent a payback of costs deferred during foraging.
Changes in body temperature influence the scaling of and aerobic scope in mammals
Authors: Gillooly James F , Allen Andrew P
Published: December 2006

Debate on the mechanism(s) responsible for the scaling of metabolic rate with body size in mammals has focused on why the maximum metabolic rate () appears to scale more steeply with body size than the basal metabolic rate (BMR). Consequently, metabolic scope, defined as/BMR, systematically increases with body size. These observations have led some to suggest thatand BMR are controlled by fundamentally different processes, and to discount the generality of models that predict a single power-law scaling exponent for the size dependence of the metabolic rate. We present a model that predicts a steeper size dependence forthan BMR based on the observation that changes in muscle temperature from rest to maximal activity are greater in larger mammals. Empirical data support the model's prediction. This model thus provides a potential theoretical and mechanistic link between BMR and.
A two-headed reptile from the Cretaceous of China
Authors: Buffetaut Eric , Li Jianjun , Tong Haiyan , Zhang He
Published: December 2006

A malformed embryonic or neonate choristoderan reptile from the Lower Cretaceous Yixian Formation of northeastern China is described. The tiny skeleton exhibits two heads and two necks, with bifurcation at the level of the pectoral girdle. In a fossil, this is the first occurrence of the malformation known as axial bifurcation, which is well known in living reptiles.
The origin of mitochondria in light of a fluid prokaryotic chromosome model
Authors: Esser Christian , Martin William , Dagan Tal
Published: December 2006

Biologists agree that the ancestor of mitochondria was an α-proteobacterium. But there is no consensus as to what constitutes an α-proteobacterial gene. Is it a gene found in all or several α-proteobacteria, or in only one? Here, we examine the proportion of α-proteobacterial genes in α-proteobacterial genomes by means of sequence comparisons. We find that each α-proteobacterium harbours a particular collection of genes and that, depending upon the lineage examined, between 97 and 33% are α-proteobacterial by the nearest-neighbour criterion. Our findings bear upon attempts to reconstruct the mitochondrial ancestor and upon inferences concerning the collection of genes that the mitochondrial ancestor possessed at the time that it became an endosymbiont.
Differential influence ofPomphorhynchus laevis(Acanthocephala) on brain serotonergic activity in two congeneric host species
Authors: Tain Luke , Perrot-Minnot Marie-Jeanne , Cézilly Frank
Published: December 2006

The physiological mechanisms by which parasites with complex life cycles manipulate the behaviour of their intermediate hosts are still poorly understood. In Burgundy, eastern France, the acanthocephalan parasitePomphorhynchus laevisinverses reaction to light in its amphipod hostGammarus pulex, but not inGammarus roeseli, a recent invasive species. Here, we show that this difference in manipulation actually reflects a difference in the ability of the parasite to alter brain serotonergic (5-HT) activity of the two host species. Injection of 5-HT in uninfected individuals of both host species was sufficient to inverse reaction to light. However, a difference in brain 5-HT immunocytochemical staining levels between infected and uninfected individuals was observed only inG. pulex. Local adaptation of the parasite to the local host species might explain its inability to manipulate the behaviour and nervous system of the invasive species.
Bioinspired self-healing of advanced composite structures using hollow glass fibres
Authors: Trask R.S , Williams G.J , Bond I.P
Published: December 2006

Self-healing is receiving an increasing amount of worldwide interest as a method to autonomously address damage in materials. The incorporation of a self-healing capability within fibre-reinforced polymers has been investigated by a number of workers previously. The use of functional repair components stored inside hollow glass fibres (HGF) is one such bioinspired approach being considered. This paper considers the placement of self-healing HGF plies within both glass fibre/epoxy and carbon fibre/epoxy laminates to mitigate damage occurrence and restore mechanical strength. The study investigates the effect of embedded HGF on the host laminates mechanical properties and also the healing efficiency of the laminates after they were subjected to quasi-static impact damage. The results of flexural testing have shown that a significant fraction of flexural strength can be restored by the self-repairing effect of a healing resin stored within hollow fibres.
The initial response of an idealized granular material
Authors: La Ragione Luigi , Jenkins James T
Published: December 2006

In this paper, we propose a theoretical model to study the elastic response of a granular material idealized as a random aggregate of identical, elastic, frictional spheres that has been isotropically compressed. When we consider that contacting particles move according to the average deformation, the effective shear modulus is over-predicted with respect to numerical simulation, while the effective bulk modulus is almost captured. We improve upon this simple approach by relaxing the aggregate. The kinematics of a pair of contacting particles is then given by the average deformation and fluctuations in both translations and rotations. We determine analytical expressions for these fluctuations by means of force and moment equilibrium applied to each particle of the pair. In order to derive the incremental stress associated with an incremental deformation, we introduce conditional averages of the fluctuations that are functions of the statistical geometry of the packing. This brings the theoretical predictions of the effective moduli close to those measured in numerical simulations. The variability of the average number of particle contacts per particle is seen to play an important role in the statistical description of the aggregate.
Variational linear comparison bounds for nonlinear composites with anisotropic phases. I. General results
Authors: Idiart Martín I , Ponte Castañeda Pedro
Published: December 2006

This work is concerned with the development of bounds for nonlinear composites with anisotropic phases by means of an appropriate generalization of the ‘linear comparison’ variational method, introduced by Ponte Castañeda for composites with isotropic phases. The bounds can be expressed in terms of a convex (concave) optimization problem, requiring the computation of certain ‘error’ functions that, in turn, depend on the solution of a non-concave/non-convex optimization problem. A simple formula is derived for the overall stress–strain relation of the composite associated with the bound, and special, simpler forms are provided for power-law materials, as well as for ideally plastic materials, where the computation of the error functions simplifies dramatically. As will be seen in part II of this work in the specific context of composites with crystalline phases (e.g. polycrystals), the new bounds have the capability of improving on earlier bounds, such as the ones proposed by deBotton and Ponte Castañeda for these specific material systems.
Integration of sensory and motor processing underlying social behaviour in túngara frogs
Authors: Hoke Kim L , Ryan Michael J , Wilczynski Walter
Published: December 2006

Social decision making involves the perception and processing of social stimuli, the subsequent evaluation of that information in the context of the individual's internal and external milieus to produce a decision, and then culminates in behavioural output informed by that decision. We examined brain networks in an anuran communication system that relies on acoustic signals to guide simple, stereotyped motor output. We used
egr-1
mRNA expression to measure neural activation in male túngara frogs,
Physalaemus pustulosus
, following exposure to conspecific and heterospecific calls that evoke competitive or aggressive behaviour. We found that acoustically driven activation in auditory brainstem nuclei is transformed into activation related to sensory–motor interactions in the diencephalon, followed by motor-related activation in the telencephalon. Furthermore, under baseline conditions, brain nuclei typically have correlated
egr-1
mRNA levels within brain divisions. Hearing conspecific advertisement calls increases correlations between anatomically distant brain divisions; no such effect was observed in response to calls that elicit aggressive behaviour. Neural correlates of social decision making thus take multiple forms: (i) a progressive shift from sensory to motor encoding from lower to higher stages of neural processing and (ii) the emergence of correlated activation patterns among sensory and motor regions in response to behaviourally relevant social cues.
Upstream reciprocity and the evolution of gratitude
Authors: Nowak Martin A , Roch Sébastien
Published: December 2006

If someone is nice to you, you feel good and may be inclined to be nice to somebody else. This every day experience is borne out by experimental games: the recipients of an act of kindness are more likely to help in turn, even if the person who benefits from their generosity is somebody else. This behaviour, which has been called ‘upstream reciprocity’, appears to be a misdirected act of gratitude: you help somebody because somebody else has helped you. Does this make any sense from an evolutionary or a game theoretic perspective? In this paper, we show that upstream reciprocity alone does not lead to the evolution of cooperation, but it can evolve and increase the level of cooperation if it is linked to either direct or spatial reciprocity. We calculate the random walks of altruistic acts that are induced by upstream reciprocity. Our analysis shows that gratitude and other positive emotions, which increase the willingness to help others, can evolve in the competitive world of natural selection.
Intraspecific competition drives increased resource use diversity within a natural population
Authors: Svanbäck Richard , Bolnick Daniel I
Published: December 2006

Resource competition is thought to play a major role in driving evolutionary diversification. For instance, in ecological character displacement, coexisting species evolve to use different resources, reducing the effects of interspecific competition. It is thought that a similar diversifying effect might occur in response to competition among members of a single species. Individuals may mitigate the effects of intraspecific competition by switching to use alternative resources not used by conspecific competitors. This diversification is the driving force in some models of sympatric speciation, but has not been demonstrated in natural populations. Here, we present experimental evidence confirming that competition drives ecological diversification within natural populations. We manipulated population density of three-spine sticklebacks (
Gasterosteus aculeatus
) in enclosures in a natural lake. Increased population density led to reduced prey availability, causing individuals to add alternative prey types to their diet. Since phenotypically different individuals added different alternative prey, diet variation among individuals increased relative to low-density control enclosures. Competition also increased the diet–morphology correlations, so that the frequency-dependent interactions were stronger in high competition. These results not only confirm that resource competition promotes niche variation within populations, but also show that this increased diversity can arise via behavioural plasticity alone, without the evolutionary changes commonly assumed by theory.
Can artificially selected phenotypes influence a component of field fitness? Thermal selection and fly performance under thermal extremes
Authors: Kristensen Torsten Nygaard , Loeschcke Volker , Hoffmann Ary A
Published: December 2006

Artificially selected lines are widely used to investigate the genetic basis of quantitative traits and make inferences about evolutionary trajectories. Yet, the relevance of selected traits to field fitness is rarely tested. Here, we assess the relevance of thermal stress resistance artificially selected in the laboratory to one component of field fitness by investigating the likelihood of adultDrosophila melanogasterreaching food bait under different temperatures. Lines resistant to heat reached the bait more often than controls under hot and cold conditions, but less often at intermediate temperatures, suggesting a fitness cost of increased heat resistance but not at temperature extremes. Cold-resistant lines were more common at baits than controls under cold as well as hot field conditions, and there was no cost at intermediate temperatures. One of the replicate heat-resistant lines was caught less often than the others under hot conditions. Direct and correlated patterns of responses in laboratory tests did not fully predict the low performance of the heat selected lines at intermediate temperatures, nor the high performance of the cold selected lines under hot conditions. Therefore, lines selected artificially not only behaved partly as expected based on laboratory assays but also evolved patterns only evident in the field releases.
Stability of genetic polymorphism in host–parasite interactions
Authors: Tellier Aurélien , Brown James K.M
Published: December 2006

Allelic diversity is common at host loci involved in parasite recognition, such as the major histocompatibility complex in vertebrates or gene-for-gene relationships in plants, and in corresponding loci encoding antigenic molecules in parasites. Diverse factors have been proposed in models to account for genetic polymorphism in host–parasite recognition. Here, a simple but general theory of host–parasite coevolution is developed. Coevolution implies the existence of indirect frequency-dependent selection (FDS), because natural selection on the host depends on the frequency of a parasite gene, andvice versa. It is shown that polymorphism can be maintained in both organisms only if there is negative, direct FDS, such that the strength of natural selection for the host resistance allele, the parasite virulence allele or both declines with increasing frequency of that allele itself. This condition may be fulfilled if the parasite has more than one generation in the same host individual, a feature which is common to most diseases. It is argued that the general theory encompasses almost all factors previously proposed to account for polymorphism at corresponding host and parasite loci, including those controlling gene-for-gene interactions.
Biodiversity hotspots through time: an introduction
Authors: Willis Katherine J , Gillson Lindsey , Knapp Sandra
Published: December 2006

International targets set for reducing the rate of biodiversity loss—the 2010 target—and ensuring environmental stability (Millennium Development Goals) have helped to focus the efforts of the scientific community on providing the data necessary for their implementation. The urgency of these goals, coupled with the increased rate of habitat alteration worldwide, has meant that actions have largely not taken into account the increasing body of data about the biodiversity change in the past. We know a lot about how our planet has been altered and recovered in the past, both in deep time and through prehistory. Linking this knowledge to conservation action has not been widely practised, by either the palaeoecology or the conservation communities. Long-term data, however, have much to offer current conservation practice, and in the papers for this volume we have tried to bring together a variety of different perspectives as to how this might happen in the most effective way. We also identify areas for productive collaboration and some key synergies for work in the near future to enable our knowledge of the past to be used for conservation action in the here and now. Lateral thinking, across knowledge systems and with open-mindness about bridging data gaps, will be necessary for our accumulating knowledge about our planet's past to be brought to bear on our attempts to conserve it in the future.
Prehistorically modified soils of central Amazonia: a model for sustainable agriculture in the twenty-first century
Authors: Glaser Bruno
Published: December 2006

Terra Preta soils of central Amazonia exhibit approximately three times more soil organic matter, nitrogen and phosphorus and 70 times more charcoal compared to adjacent infertile soils. The Terra Preta soils were generated by pre-Columbian native populations by chance or intentionally adding large amounts of charred residues (charcoal), organic wastes, excrements and bones. In this paper, it is argued that generating new Terra Preta sites (‘Terra Preta nova’) could be the basis for sustainable agriculture in the twenty-first century to produce food for billions of people, and could lead to attaining three Millennium Development Goals: (i) to combat desertification, (ii) to sequester atmospheric CO2in the long term, and (iii) to maintain biodiversity hotspots such as tropical rainforests. Therefore, large-scale generation and utilization of Terra Preta soils would decrease the pressure on primary forests that are being extensively cleared for agricultural use with only limited fertility and sustainability and, hence, only providing a limited time for cropping. This would maintain biodiversity while mitigating both land degradation and climate change. However, it should not be overlooked that the infertility of most tropical soils (and associated low population density) is what could have prevented tropical forests undergoing large-scale clearance for agriculture. Increased fertility may increase the populations supported by shifting cultivation, thereby maintaining and increasing pressure on forests.
Biocomplexity and conservation of biodiversity hotspots: three case studies from the Americas
Authors: Baird Callicott J , Rozzi Ricardo , Delgado Luz , Monticino Michael , Acevedo Miguel , Harcombe Paul
Published: December 2006

The perspective of ‘biocomplexity’ in the form of ‘coupled natural and human systems’ represents a resource for the future conservation of biodiversity hotspots in three direct ways: (i) modelling the impact on biodiversity of private land-use decisions and public land-use policies, (ii) indicating how the biocultural history of a biodiversity hotspot may be a resource for its future conservation, and (iii) identifying and deploying the nodes of both the material and psycho-spiritual connectivity between human and natural systems in service to conservation goals. Three biocomplexity case studies of areas notable for their biodiversity, selected for their variability along a latitudinal climate gradient and a human-impact gradient, are developed: the Big Thicket in southeast Texas, the Upper Botanamo River Basin in eastern Venezuela, and the Cape Horn Archipelago at the austral tip of Chile. More deeply, the biocomplexity perspective reveals alternative ways of understanding biodiversity itself, because it directs attention to the human concepts through which biodiversity is perceived and understood. The very meaning of biodiversity is contestable and varies according to the cognitive lenses through which it is perceived.
Rates of change in tree communities of secondary Neotropical forests following major disturbances
Authors: Chazdon Robin L , Letcher Susan G , van Breugel Michiel , Martínez-Ramos Miguel , Bongers Frans , Finegan Bryan
Published: December 2006

Rates of change in tree communities following major disturbances are determined by a complex set of interactions between local site factors, landscape history and structure, regional species pools and species life histories. Our analysis focuses on vegetation change following abandonment of agricultural fields or pastures, as this is the most extensive form of major disturbance in Neotropical forests. We consider five tree community attributes: stem density, basal area, species density, species richness and species composition. We describe two case studies, in northeastern Costa Rica and Chiapas, Mexico, where both chronosequence and annual tree dynamics studies are being applied. These case studies show that the rates of change in tree communities often deviate from chronosequence trends. With respect to tree species composition, sites of different ages differ more than a single site followed over time through the same age range. Dynamic changes in basal area within stands, on the other hand, generally followed chronosequence trends. Basal area accumulation was more linked with tree growth rates than with net changes in tree density due to recruitment and mortality. Stem turnover rates were poor predictors of species turnover rates, particularly at longer time-intervals. Effects of the surrounding landscape on tree community dynamics within individual plots are poorly understood, but are likely to be important determinants of species accumulation rates and relative abundance patterns.
Improving gene annotation using peptide mass spectrometry
Authors: Tanner Stephen , Shen Zhouxin , Ng Julio , Florea Liliana , Guigó Roderic , Briggs Steven P. , Bafna Vineet
Published: December 2006

Annotation of protein-coding genes is a key goal of genome sequencing projects. In spite of tremendous recent advances in computational gene finding, comprehensive annotation remains a challenge. Peptide mass spectrometry is a powerful tool for researching the dynamic proteome and suggests an attractive approach to discover and validate protein-coding genes. We present algorithms to construct and efficiently search spectra against a genomic database, with no prior knowledge of encoded proteins. By searching a corpus of 18.5 million tandem mass spectra (MS/MS) from human proteomic samples, we validate 39,000 exons and 11,000 introns at the level of translation. We present translation-level evidence for novel or extended exons in 16 genes, confirm translation of 224 hypothetical proteins, and discover or confirm over 40 alternative splicing events. Polymorphisms are efficiently encoded in our database, allowing us to observe variant alleles for 308 coding SNPs. Finally, we demonstrate the use of mass spectrometry to improve automated gene prediction, adding 800 correct exons to our predictions using a simple rescoring strategy. Our results demonstrate that proteomic profiling should play a role in any genome sequencing project.