bluuebunny/crossref_metadata_2025 huggingface dataset:
Signal‐to‐noise ratio and spectral linewidth improvements between 1.5 and 7 Tesla in proton echo‐planar spectroscopic imaging
Authors: Otazo Ricardo , Mueller Bryon , Ugurbil Kamil , Wald Lawrence , Posse Stefan
Published: November 2006

This study characterizes gains in sensitivity and spectral resolution of proton echo‐planar spectroscopic imaging (PEPSI) with increasing magnetic field strength (B0). Signal‐to‐noise ratio (SNR) per unit volume and unit time, and intrinsic linewidth (LW) of N‐acetyl‐aspartate (NAA), creatine (Cr), and choline (Cho) were measured with PEPSI at 1.5, 3, 4, and 7 Tesla on scanners that shared a similar software and hardware platform, using circularly polarized (CP) and eight‐channel phased‐array (PA) head coils. Data were corrected for relaxation effects and processed with a time‐domain matched filter (MF) adapted to each B0. The SNR and LW measured with PEPSI were very similar to those measured with conventional point‐resolved spectroscopy (PRESS) SI. Measurements with the CP coil demonstrated a nearly linear SNR gain with respect to B0 in central brain regions. For the PA coil, the SNR–B0 relationship was less than linear, but there was a substantial SNR increase in comparison to the CP coil. The LW in units of ppm decreased with B0, resulting in improved spectral resolution. These studies using PEPSI demonstrated linear gains in SNR with respect to B0, consistent with theoretical expectations, and a decrease in ppm LW with increasing B0. Magn Reson Med, 2006. © 2006 Wiley‐Liss, Inc.
Quantified sensory abnormalities in early genetically verified transthyretin amyloid polyneuropathy
Authors: Heldestad Victoria , Nordh Erik
Published: November 2006

Transthyretin amyloid neuropathy of type 1 (Swedish–Portuguese type) is an autosomally inherited progressive disease with a Val30Met mutation, causing generalized sensory‐motor polyneuropathy. Quantitative sensory testing (QST) quantifies thermal threshold changes in patients with manifest general polyneuropathy, but its applicability at an early clinical stage of a strict biochemically defined disease has not yet been shown. Thermal QST was performed in 23 patients having a positive Val30Met marker and clinical symptoms of peripheral small‐fiber neuropathy but normal electrophysiological findings and compared to a reference group of 43 healthy volunteers, both subdivided into age groups ≤45 and >45 years. Significant differences between patients and controls were found at all test sites in both age groups, except for warm thresholds at the medial lower leg in those >45 years. QST thus demonstrated elevated thermal thresholds before the development of electrophysiological abnormalities, which indicate large‐fiber involvement. These findings confirm that QST is a useful method for documentation of developing polyneuropathy. Muscle Nerve, 2006
Safety of nerve conduction studies in patients with implanted cardiac devices
Authors: Schoeck Andreas P. , Mellion Michelle L. , Gilchrist James M. , Christian Fredric V.
Published: November 2006

Patients with implanted cardiac devices and their physicians may defer important electrodiagnostic testing because of anxiety about potential negative effects on the device. To determine the safety of routine nerve conduction studies (NCS) in this population, 10 patients with permanent dual‐chamber pacemakers of various types and five patients with implanted cardiac defibrillators (ICD) underwent nerve stimulation at sites commonly used during NCS. The implanted cardiac device was interrogated before and after the study and there was continuous monitoring of the surface electrocardiogram (ECG) and atrial and ventricular electrograms. Electrical impulses generated during routine NCS were never detected by the sensing amplifier and did not affect the programmed settings of the implanted cardiac device. We conclude that routine NCS is safe in patients with implanted cardiac pacemakers with bipolar sensing configurations and defibrillators. Muscle Nerve, 2006
Effects of hyperbaric exposure with high oxygen concentration on glucose and insulin levels and skeletal muscle‐fiber properties in diabetic rats
Authors: Yasuda Koichiro , Adachi Tetsuya , Gu Ning , Matsumoto Akiko , Matsunaga Tetsuro , Tsujimoto Gozoh , Tsuda Kinsuke , Ishihara Akihiko
Published: November 2006

The effects of hyperbaric exposure with high oxygen concentration on glucose and insulin levels and skeletal muscle‐fiber properties were investigated in type 2 diabetic Goto‐Kakizaki rats. Five‐week‐old rats were exposed to a hyperbaric environment (1.25 atmospheric pressure) with a high oxygen concentration (36%) for 6 h daily. Glucose and insulin levels and properties including fiber‐type distribution, cross‐sectional area, and oxidative enzyme activity in the soleus muscle were examined after hyperbaric exposure for 4 weeks. The growth‐related increase in glucose level was inhibited by hyperbaric exposure, and insulin also showed lower levels compared with control rats. The percentage of low‐oxidative type I fibers in the muscle decreased and high‐oxidative type IIA and type IIC fibers, which were not detected in the muscle of control rats, were observed after hyperbaric exposure. The oxidative enzyme activity of type I fibers in the muscle increased after hyperbaric exposure. Hyperbaric exposure with high oxygen concentration might therefore provide a new approach to improve the glucose tolerance, insulin resistance, and altered skeletal muscle metabolism that are caused by diabetes mellitus. Muscle Nerve, 2006
Investigation of melt manipulation phenomena during injection molding via in situ birefringence observation
Authors: Angstadt David C. , Coulter John P.
Published: November 2006

This study investigates the effects of melt manipulation on the development of molecular orientation during injection molding processing. Vibration‐assisted injection molding (VAIM), a particular method of melt manipulation, is a variation of conventional injection molding in which oscillatory energy is imparted to the polymer melt by vibrating the injection screw axially during the injection and packing stages of the molding cycle. Previous studies have shown that this process positively affects the tensile strength of polystyrene parts, but that the magnitude of the increase is dependent upon the processing parameters. Observation of birefringence patterns in VAIM processed samples show a significant impact on molecular orientation. A specially designed mold and associated image capture system has been developed and is used in this study to record the birefringence patterns of the polymer melt within the cavity during processing. Observation of birefringence shows that orientation develops primarily during post‐vibration packing of the part and not during the vibration phase as previously thought. The observed effects of process parameters such as melt temperature, packing pressure, and vibration duration are discussed. POLYM. ENG. SCI. 46:1691–1697, 2006. © 2006 Society of Plastics Engineers
Radical mediated graft modification of polyolefins: Vinyltriethoxysilane addition dynamics and yields
Authors: Parent J. Scott , Parodi Renzo , Wu Wei
Published: November 2006

The dynamics and yields of peroxide‐initiated grafting of vinyltriethoxysilane (VTEOS) to tetradecane and linear low density polyethylene (LLDPE) are described. VTEOS grafting kinetics at 160°C abide by the basic tenets of radical‐mediated additions in terms of the influence of initiator loading and homolysis rate. However, reaction yields recorded for both the model and polymer systems are surprisingly insensitive to temperature, in apparent conflict with conventional models of free radical addition chemistry. These experimental observations are used to identify the predominant reactions within a general kinetic scheme, and to support the assumptions required to develop a rate expression that captures the effect of reagent concentrations on the dynamics of graft‐modification. POLYM. ENG. SCI. 46:1754–1761, 2006. © 2006 Society of Plastics Engineers.
Interfacial characteristics of film insert molded polycarbonate film/polycarbonate‐acrylonitrile‐butadiene‐styrene substrate, part 1: Influence of substrate molecular weight and film thickness
Authors: Leong Y.W. , Ishiaku U.S. , Kotaki M. , Hamada H. , Yamaguchi S.
Published: November 2006

Adhesion properties between a polycarbonate (PC)/acrylonitrile‐butadiene‐styrene blend substrate and PC films of various thicknesses, bonded through film insert molding, were investigated. The use of various molecular weights of PC and incorporation of PC‐oligomer in the blend substrate has been found to severely affect the adhesion strength and alter the delamination characteristics at the film–substrate interface. Thicker films were able to increase film–substrate adhesion, apart from providing added impact resistance to a brittle substrate. Polym. Eng. Sci. 46:1674–1683, 2006. © 2006 Society of Plastics Engineers
Comparison of the effect of epoxy microspheres on the thermomechanical and rheological properties of an epoxy resin system
Authors: Ambrogi Veronica , Cosco Simona , Carfagna Cosimo , Cicala Gianluca , Oliveri Ludovica , Recca Antonio
Published: November 2006

The rheological and thermomechanical behaviors of toughened epoxy resins filled with thermosetting microsized spherical particles were investigated. Two epoxy systems were used to prepare microspheres: a Bisphenol A‐type resin (EPON825) cured with 2,4‐diaminotoluene and a Bisphenol F‐based epoxy resin (PY306) crosslinked with diethyltoluenediamine. Both systems of microspheres were synthesized through dispersion polymerization and differed to each other in size, as evidenced by morphological analysis. These microparticles were blended, in different weight percents (10 and 20 wt%), with a matrix consisting of diglycidyl ether of Bisphenol A (EPON828) and 3,3′‐diaminodiphenylsulphone (3,3′DDS). Rheological behavior of the prepared blends was preliminarily studied. After cure, the dynamic‐mechanical properties of the composites were also investigated. Results indicated that the reactivity of the uncured blends, as well as the viscoelastic properties of crosslinked systems, are influenced not only by the nature and the amount of the microparticles introduced, but also, in a significant way, by their size. POLYM. ENG. SCI. 46:1739–1747, 2006. © 2006 Society of Plastics Engineers.
Poly(glycoamidoamine)s: Cationic glycopolymers for DNA delivery
Authors: Reineke Theresa M.
Published: November 2006

Polymer science is playing an exciting role in inspiring and advancing novel discoveries in the area of genetic drug delivery. Polymeric materials can be synthesized and chemically tailored to bind and compact nucleic acids into viral‐like nanoparticles termed polyplexes that can deliver genetic materials into cells. This article highlights our work in this area to synthesize and study a novel class of cationic glycopolymers that we have termed poly(glycoamidoamine)s (PGAAs). The design of these materials has been inspired by many previous works in the literature. Carbohydrate comonomers have been incorporated into these structures to lower the toxicity of the delivery vehicle, and oligoamine moieties have been added to yield a cationic backbone that facilitates strong DNA binding, compaction, cellular uptake, and delivery of genetic material. PGAAs have been designed to vary in the carbohydrate size, the hydroxyl number and stereochemistry, the amine number, and the presence or absence of heterocyclic groups. Through structure–bioactivity studies, we have discovered that these materials are highly biocompatible, and each specific feature plays a large role in the observed delivery efficacy. Such structure–property studies are important for increasing our understanding of how the polymer chemistry affects the biological activity for the clinical development of polymer‐based therapeutics. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6895–6908, 2006
Melting of solvents nanoconfined by polymers and networks
Authors: Qin Qian , McKenna Gregory B.
Published: November 2006

Thermoporosimetry is becoming increasingly used to study nanoscale heterogeneity and structure in polymer networks. The starting point for thermoporosimetry is the Gibbs‐Thomson (GT) relation between melting point and inverse crystal size. In the case of polymers, the Flory‐Huggins (FH) model also predicts that there is a depression of the melting point because of the mixing of the polymer and the solvent molecules, and this needs to be taken into account. The first step in analysis of size heterogeneity using thermoporosimetry and the GT equation requires that there be quantitative agreement between the FH theory and the melting points of the diluent in the uncrosslinked rubber. We find that both benzene and hexadecane exhibit excessive melting point depressions in uncrosslinked polyisoprene. This may imply that the uncrosslinked polymer is divided into ‘nanoheterogeneities’. We further find that the heat of fusion decreases as polymer concentration increases for the benzene, but not for the hexadecane. Finally, we compare pore size distributions obtained for a crosslinked polyisoprene as determined from the melting behavior ofn‐hexadecane as a diluent, using different references for how the uncrosslinked polymer behaves. While number average distribution is not very different between the different analyses, the weight average distribution is. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 3475–3486, 2006
A quantum mechanics/molecular mechanics study of the reaction mechanism of the hepatitis C virus NS3 protease with the NS5A/5B substrate
Authors: Oliva Carolina , Rodríguez Alejandro , González Miguel , Yang Wei
Published: November 2006

Combined quantum mechanics and molecular mechanics (QM/MM) calculations were carried out to characterize the reaction mechanism of the NS3 protease with its preferred substrate (NS5A/5B). The main purpose of this study was to locate the barrier states and intermediates along the distinguished coordinate path (DCP) involved in this process. These structures, and in particular the one corresponding to the first barrier state and intermediate (B1 and I1), could be a starting point for the synthesis of inhibitors of this protease, which could be used to treat hepatitis C. The two first steps of the reaction mechanism were studied, i.e., the acylation step and the breaking of the peptide bond. The first step takes place through a tetracoordinated intermediate, as suggested from previous works on other Serine proteases. The importance of the different amino acid residues was also considered (perturbation study where the MM charges of each residue were set to zero independently). The residues of the oxyanion hole were confirmed as the most important for the electrostatic stabilization of the tetracoordinate intermediate. Moreover, the role of other residues, e.g., Arg‐155 and Asp‐79, was also explained. Proteins 2007. © 2006 Wiley‐Liss, Inc.
Ferromagnetism in epitaxial Zn0.95Co0.05O films grown on ZnO and Al2O3
Authors: Nielsen K. , Bauer S. , Lübbe M. , Goennenwein S. T. B. , Opel M. , Simon J. , Mader W. , Gross R.
Published: November 2006

In this article, the possible mechanisms resulting in strong ferromagnetic coupling in transition metal(TM)‐doped ZnO and other diluted magnetic semiconductors (DMS) are reviewed and the prerequisites for the observation of room temperature ferromagnetism in TM‐doped ZnO are defined. In order to study the ferromagnetic behavior we have grown epitaxial Zn0.95Co0.05O films simultaneously on (0001) ZnO and Al2O3substrates by laser molecular beam epitaxy at different deposition temperatures. A systematic study of the structural and magnetic properties has been performed to reveal their interdependence. Room temperature ferromagnetism has been found in Zn0.95Co0.05O films grown on ZnO, whereas for films deposited on sapphire only weak ferromagnetic signals have been detected which could not unambiguously be separated from those of the substrate. The different behavior is explained by different structural properties and defect densities in both films. Our experimental findings are in good agreement with a spin split impurity band model, where strong ferromagnetic exchange in ZnO:Co2+is obtained by a strong hybridization between the magnetic Co2+ion states and the donor states due to a large density of native defects. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Quantum cascade lasers: The semiconductor solution for lasers in the mid‐ and far‐infrared spectral regions
Authors: Sirtori Carlo , Dhillon Sukhdeep , Faugeras Clement , Vasanelli A. , Marcadet Xavier
Published: November 2006

The quantum cascade laser is a semiconductor light source based on resonant tunnelling and optical transitions between quantised conduction band states. In these devices the principles of operation are not re lated to the physical properties of the constituent materials, but arise from an artificial potential designed using a sequence of very thin layers of different semiconductor materials. The quantum design implemented by highly sophisticated epitaxial growth, allows one to ascribe in semiconductor crystals this artificial potential with the desired electronic energy levels and wavefunctions. In recent years the performance of these devices has improved markedly and this semiconductor technology is now an attractive choice for the fabrication of mid‐far infrared lasers in a very wide spectral range (3.5–160 µm). At present, the best performances are obtained at wavelengths between 5–12 µm, where continuous‐wave room temperature operation is routinely achieved and record average power in the order of 1 W has been demonstrated. The long wavelength region has been only recently explored and lasers operating temperatures do not currently exceed 150 K. Interesting nonlinear mixing of diode lasers with a THz laser has been recently demonstrated. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Oligonucleotide hybridization monitored by surface plasmon enhanced fluorescence spectroscopy with bio‐conjugated core/shell quantum dots. Influence of luminescence blinking
Authors: Robelek R. , Stefani F. D. , Knoll W.
Published: November 2006

The influence of the luminescence blinking of quantum dots on kinetic bio‐sensing measurements is investigated. The hybridization kinetics of labelled DNA sequences with surface‐immobilized DNA probes using surface plasmon enhanced fluorescence spectroscopy is employed to compare the behaviour of quantum‐dot‐ and organic‐chromophore‐labelled DNA targets. The presented experiments show that quantum‐dot labelled targets present apparent complex adsorption kinetics that can lead to inaccurate conclusions. By means of single quantum dot luminescence measurements and Monte‐Carlo simulations, it is demonstrated that the anomalous adsorption kinetics observed with the quantum‐dot labelled targets can be accounted for by the luminescence blinking statistics of the quantum dots. Thus, special attention should be paid when applying quantum dots as fluorescent labels in bio affinity studies in order to avoid wrong interpretations due to the special photo physical behaviour of these semiconducting nanocrystals. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Supported membranes as biofunctional interfaces and smart biosensor platforms
Authors: Tanaka Motomu , Sackmann Erich
Published: November 2006

The design of soft biocompatible and functional interfaces on solids is a challenging interdisciplinary endeavour with great potentials for scientific and biotechnnological applications. By combining modern concepts of genetic engineering and bio‐organic chemistry, novel classes of recombinant proteins enable the immobilization of functional nano‐machineries on solid surfaces, which can even beat functions of native biological systems. Mimetics of tissues can be fabricated by deposition of ultrathin films of biopolymers (such as cellulose or hyaluronic acid), which opens new possibilities for fundamental studies of mechanisms of cell adhesion and tissue growth. Careful adjustment of interfacial potentials using such soft interlayers can also realize the stress‐free immobilization of cells for application as monitors of toxic substances and drugs. Planar models of cell surfaces can be fabricated by self‐assembly of membranes on solid substrates functionalized with soft polymers, which play the generic role of cytoskeleton and glycocalix. Planar geometry enables the application of various surface sensitive techniques to study structures and dynamics of biological membranes. This review presents a survey of recent development in supported membranes, and presents some potential application of this concept in smart biosensors. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Ohmic contacts for GaAs based nanocolumns
Authors: Wensorra J. , Lepsa M. I. , Indlekofer K. M. , Förster A. , Jaschinsky P. , Voigtländer B. , Pirug G. , Lüth H.
Published: November 2006

Nonalloyed ohmic contacts with lateral dimensions in the sub‐100 nm range have been processed and characterized. The contacts are suitable for the fabrication of GaAs/AlGaAs nanocolumns designed in a ‘top down’ approach. They are realized on n‐type GaAs using a thin low‐temperature grown GaAs cap layer and Ti/Au metallization. For the lateral patterning of the nanoscaled ohmic contacts, electron‐beam lithography based on Hydrogen Silsesquioxan (HSQ) negative resist is used, followed by sputtering and plasma etching of the metals. The I –V characteristics show ohmic contact behavior and demonstrate the scaling of the proposed contacts down to 50 nm lateral dimension. The specific contact resistance is situated in the range of 1–2 × 10–5 Ω cm2. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Direct biofunctionalization of semiconductors: A survey
Authors: Stutzmann Martin , Garrido Jose Antonio , Eickhoff Martin , Brandt Martin S.
Published: November 2006

The covalent attachment of small organic molecules and larger functional biomolecules such as DNA, enzymes, or other proteins on semiconductors is a new field of basic research with a pronounced interdisciplinary flavour. The ultimate goal of this endeavour is the creation of novel organic/inorganic heterostructures which can provide a direct link between the complex worlds of biology and digital electronics on a nanometer scale. The purpose of the present survey is to provide an overview over basic physics aspects, preparation methods, as well as possible applications of biofunctionalized semiconductors based on different material systems. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
DNA‐Encoded Chemical Libraries
Authors: Dumelin Christoph E. , Scheuermann Jörg , Melkko Samu , Neri Dario
Published: November 2006

Conventional libraries of chemical compounds, which are individually screened for binding to pharmaceutical targets, are typically limited by screening costs and logistics to an upper size of few hundred thousand compounds. The use of DNA‐encoded chemical libraries promises to revolutionize the way chemical libraries are screened, allowing the synthesis and selection of libraries of unprecedented size. This article reviews the most recent strategies for the construction and selection of DNA‐encoded chemical libraries.
“Syn&Sort”: A Chip‐based Tool for Combinatorial Synthesis
Authors: Gebinoga Michael , Groß G. Alexander , Albrecht Arne , Lübeck Thomas , Henkel Thomas , Hoffmann Patrick , Klemm Uwe , Schlingloff Gregor , Frank Thomas , Schober Andreas
Published: November 2006

In this paper, we present a new method and process for combinatorial solid phase library synthesis. The new method, we call “Syn&Sort”, combines the advantages of the directed sorting technique with those of miniaturized parallel synthesis. Directed sorting steps were realized by combination of two encoding principles: spatially resolved encoding was used for a carrier chip, bearing 60 solid phase units and an individual barcode‐marker for each carrier. Solid phase supports were made of glass with a magnetic core coated with functionalized polymer support. Sixty synthesis units were arranged on each carrier chip using the magnetic “clip board” principle. No special synthesis equipment is necessary because all carriers can be used in standard laboratory equipment. Syn&Sort was applied for the synthesis of a pentamer‐peptide library. The design and construction of the magnetic synthesis support, carrier chips, and handling device are given. Here, we provide proof of principle of the new Syn&Sort method and introduce it to the scientific and commercial research.
Intramolecular hydrogen bond in the hydroxycyclohexadienyl peroxy radicals
Authors: Huang Mingqiang , Wang Zhenya , Yang Yong , Hao Liqing , Zhao Wenwu , Gao Xiaoming , Fang Li , Zhang Weijun
Published: November 2006

The hydroxycyclohexadienyl peroxy radicals (HOC6H6O2) produced from the reaction of OH‐benzene adduct with O2were studied with density functional theory (DFT) calculations to determine their characteristics. The optimized geometries, vibrational frequencies, and total energies of 2‐hydroxycyclohexadienyl peroxy radical IIsand 4‐hydroxycyclohexadienyl peroxy radical IIIswere calculated at the following theoretical levels, B3LYP/6‐31G(d),B3LYP/6‐311G(d,p),and B3LYP/6‐311+G(d,p).Both were shown to contain a red‐shifted intramolecular hydrogen bond (OH … OH bond). According to atoms‐in‐molecules (AIM) analysis, the intramolecular hydrogen bond in the 2‐hydroxycyclohexadienyl peroxy radical IIsis stronger than that one in 4‐hydroxycyclohexadienyl peroxy radical IIIs, and the former is the most stable conformation among its isomers. Generally speaking, hydrogen bonding in these radicals plays an important role to make them more stable. Based on natural bond orbital (NBO) analysis, the stabilization energy between orbitals is the main factor to produce red‐shifted intramolecular hydrogen bond within these peroxy radicals. The hyperconjugative interactions can promote the transfer of some electron density to the OH antibonding orbital, while the increased electron density in the OH antibonding orbital leads to the elongation of the OH bond and the red shift of the OH stretching frequency. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007
A generalized homogeneous domination approach for global stabilization of inherently nonlinear systems via output feedback
Authors: Polendo Jason , Qian Chunjiang
Published: November 2006

In this paper, we introduce a generalized framework for global output feedback stabilization of a class of uncertain,inherentlynonlinear systems of a particularly complex nature since their linearization around the equilibrium is not guaranteed to be either controllable or observable. Based on a new observer/controller construction and ahomogeneous dominationdesign, this framework not only unifies the existing output feedback stabilization results, but also leads to more general results which have been never achieved before, establishing this methodology as a universal tool for the global output feedback stabilization of inherently nonlinear systems. Copyright © 2006 John Wiley & Sons, Ltd.
Distributed multi‐vehicle coordinated controlvialocal information exchange
Authors: Ren Wei , Atkins Ella
Published: November 2006

This paper describes a distributed coordination scheme with local information exchange for multiple vehicle systems. We introduce second‐order consensus protocols that take into account motions of the information states and their derivatives, extending first‐order protocols from the literature. We also derive necessary and sufficient conditions under which consensus can be reached in the context of unidirectional information exchange topologies. This work takes into account the general case where information flow may be unidirectional due to sensors with limited fields of view or vehicles with directed, power‐constrained communication links. Unlike the first‐order case, we show that having a (directed) spanning tree is a necessary rather than a sufficient condition for consensus seeking with second‐order dynamics. This work focuses on a formal analysis of information exchange topologies that permit second‐order consensus. Given its importance to the stability of the coordinated system, an analysis of the consensus term control gains is also presented, specifically the strength of the information states relative to their derivatives. As an illustrative example, consensus protocols are applied to coordinate the movements of multiple mobile robots. Copyright © 2006 John Wiley & Sons, Ltd.
Repeatability of paired counts
Authors: Alexander Neal , Bethony Jeff , Corrêa‐Oliveira Rodrigo , Rodrigues Laura C. , Hotez Peter , Brooker Simon
Published: November 2006

The Bland and Altman technique is widely used to assess the variation between replicates of a method of clinical measurement. It yields the repeatability, i.e. the value within which 95 per cent of repeat measurements lie. The valid use of the technique requires that the variance is constant over the data range. This is not usually the case for counts of items such as CD4 cells or parasites, nor is the log transformation applicable to zero counts. We investigate the properties of generalized differences based on Box–Cox transformations. For an example, in a data set of hookworm eggs counted by the Kato–Katz method, the square root transformation is found to stabilize the variance. We show how to back‐transform the repeatability on the square root scale to the repeatability of the counts themselves, as an increasing function of the square mean root egg count, i.e. the square of the average of square roots. As well as being more easily interpretable, the back‐transformed results highlight the dependence of the repeatability on the sample volume used. Copyright © 2006 John Wiley & Sons, Ltd.
Relative efficiency of unequal versus equal cluster sizes in cluster randomized and multicentre trials
Authors: van Breukelen Gerard J. P. , Candel Math J. J. M. , Berger Martijn P. F.
Published: November 2006

Cluster randomized and multicentre trials evaluate the effect of a treatment on persons nested within clusters, for instance, patients within clinics or pupils within schools. Optimal sample sizes at the cluster (centre) and person level have been derived under the restrictive assumption of equal sample sizes per cluster. This paper addresses the relative efficiency of unequal versus equal cluster sizes in case of cluster randomization and person randomization within clusters. Starting from maximum likelihood parameter estimation, the relative efficiency is investigated numerically for a range of cluster size distributions. An approximate formula is presented for computing the relative efficiency as a function of the mean and variance of cluster size and the intraclass correlation, which can be used for adjusting the sample size. The accuracy of this formula is checked against the numerical results and found to be quite good. It is concluded that the loss of efficiency due to variation of cluster sizes rarely exceeds 10 per cent and can be compensated by sampling 11 per cent more clusters. Copyright © 2006 John Wiley & Sons, Ltd.
Assessing local influence in principal component analysis with application to haematology study data
Authors: Fung Wing K. , Gu Hong , Xiang Liming , Yau Kelvin K. W.
Published: November 2006

In many medical and health studies, high‐dimensional data are often encountered. Principal component analysis (PCA) is a commonly used technique to reduce such data to a few components that includes most of the information provided by the original data. However, PCA is known to be very sensitive to some abnormal observations. Therefore, it is essential to assess such sensitivity in PCA. In this paper, the assessments of local influence based on generalized influence function are developed under the case‐weights and additive perturbation schemes, along with a discussion of the perturbation scheme and the generalized influence function approach. When perturbing different variables of the data, it is noted that the directions of the largest joint local influence for the eigenvalues are all the same. Moreover, these directions are completely determined by the score values of the observations, to which an approximate cut‐off point is given. The proposed methods are applied to analyse a set of haematology study data for illustration. Results add new insights in finding influential observations in the studied data set. Copyright © 2006 John Wiley & Sons, Ltd.
Wind turbine concept market penetration over 10 years (1995–2004)
Authors: Hansen Anca D. , Hansen Lars H.
Published: November 2006

The aim of this article is to investigate the market penetration and share of different wind turbine concepts during the years 1995–2004, a period that represents the maturational era of the modern wind power industry. A detailed overview is given based on suppliers' market data and concept evaluation for each individual wind turbine type sold by the Top Ten suppliers over the selected decade. The investigation is processing information on approximately 160 wind turbine types from 22 different manufacturers that have featured in the Top Ten list of wind turbine suppliers during 1995–2004. The analysis is based on comprehensive data covering approximately 97% of the cumulative wind power installed worldwide at the end of 2004. The article also provides an overall perspective on contemporary wind turbine concepts, classified with respect to both their speed control ability and power control type. Current and future trends for wind turbine concepts are discussed. Copyright © 2006 John Wiley &Sons, Ltd.
Nonlinear time‐series modeling of vole population fluctuations
Authors: Turchin Peter
Published: November 2006

A central goal of population ecology is to understand and predict fluctuations in population numbers. Until recently, much of the debate focused on the issue of population regulation by density‐dependent factors. In this paper, I describe an approach to nonlinear modeling of time‐series data that is designed to go beyond this question by investigating the possibility of complex population dynamics, characterized by lags in regulation and periodic or chaotic oscillations. The questions motivating this approach are: what are relative contributions of endogenous vs. exogenous components of dynamics? Is the irregular component in fluctuations entirely due to exogenous noise, or do nonlinearities contribute to it, too? I describe the philosophy and the technical details of the nonlinear modeling approach, and then apply it to a collection of time‐series data on vole population fluctuations in northern Europe. The results suggest that population dynamics of European voles undergo a latitudinal shift from stability to chaos. Dynamics in northern Fennoscandia are characterized by positive Lyapunov exponent estimates, and a high degree of short‐term (one year ahead) predictability, suggesting a strong endogenous component. In more southerly populations estimated Lyapunov exponents are negative, and there is no one‐step ahead predictability, suggesting that fluctuations are driven by exogenous factors.
Analyses of spatial patterns and population processes of clonal plants
Authors: Harada Yuko , Iwasa Yoh
Published: November 2006

The nonrandom spatial structure of terrestrial plants is formed by ecological interactions and reproduction with a limited dispersal range, and in turn this may strongly affect population dynamics and population genetics. The traditional method of modelling in population ecology is either to neglect spatial pattern (e.g. in transition matrix models) or to do straightforward computer simulation. We review here three analytical mothods to deal with plant populations in a lattice‐structured habitat, which propagate both by seeds that scatter over the whole habitat and by vegetative reproduction (producing runners, rhizomes, etc.) to neighboring vacant sites. [1]Dynamics of global and local densities: Dynamical equations of population density considering nearest‐neighbor correlation (spatial clumping) are developed as the joint dynamics of global average density and local density (comparable to mean crowding) based onpair approximation. If there is a linear trade‐off between seed production and vegetative reproduction, the equilibrium abundance of the population may be maximized by engaging both means of reproduction. This result is accurately predicted by the pair approximation method, but not by mean‐field approximation (neglect of spatial structure). [2]Cluster size distributions: Using global and local densities obtained by pair approximation, we predicted cluster size distribution, i.e. the number of clusters of occupied sites of various sizes. [3]Clonal identity probability decreasing with distance: Multi‐locus measurement of allozymes or other neutral molecular markers tells us whether or not a given pair of individuals belong to the same clone. From the pattern of clonal identity probability decreasing with the distance between ramets, we can estimate the relative importance of two modes of reproduction: vegetative propagation and sexual seed production.
Bacteria—A link among ecosystem constituents
Authors: Kato K.
Published: November 2006

Microbial ecology has undergone a revolution over the past two decades due to the numerous innovations in techniques, allowing bacteria to be detected more accurately by direct means. Thus, bacterial life can be distinguished in situ by direct counting under epifluorescence microscopy; automatically counting and sizing by image analyzer equipped with epifluorescence microscopy or by use of flow cytometry; specific radioisotope techniques; and molecular techniques to detect specific taxa. All of these approaches do not require cultivation, which provides a biased view of bacterial communities in nature. Bacteria are abundant in aquatic environments and play important roles as links between dissolved nutrients and the grazers in the food web. The new techniques allow an evaluation of bacterial population dynamics and function in relation to other organisms of higher trophic levels. This mini review aims to show briefly the state‐of‐the‐art in microbial ecology for ecologists concerned with organisms other than microbes, in order to develop further intensive study together with microbial ecologists.
Populations and infectious diseases: Dynamics and evolution
Authors: Kakehashi Masayuki
Published: November 2006

The host‐parasite or host‐pathogen system was analyzed from dynamical and evolutionary viewpoints using simple mathematical models incorporating vertical transmission, immunity and its loss. We first analyzed a model without density regulation of host population. In the analysis on dynamics, the condition for the pathogen to work as a density regulating factor was obtained. In the analysis on evolution, criteria for the evolution of host and pathogen were proposed. These criteria implies that the evolution of hosts should result in an increase in infected host density, whereas the evolution of pathogens a decrease in susceptible host density. The direction of evolution at some parameters of host and that of pathogen were examined when the parameters were independently and freely changeable. Among the parameters, only reduction in additional mortality due to infection was the evolutionary trend common to both host and pathogen. In all the other parameters examined, trend of evolution predicted in host is reversed in pathogen. We then analyzed whether the obtained criteria still hold in models with density regulation of hosts. Using randomly generated parameter sets, we obtained the result that the criteria should hold very likely though they do not always hold. We discussed evolution of virulence when there is a constraint between the traits.
Evolution of mutualistic symbiosis: A differential equation model
Authors: Yamamura Norio
Published: November 2006

In geological history, rapid speciation, called adaptive radiation, has occurred repeatedly. The origins of such newly developing taxa often evolved from the symbiosis of different species. Mutualistic symbioses are generally considered to evolve from parasitic relationships. As well as the previous model of host population with discrete generations, a differential equation model of host population with overlapping generations shows that vertical transmission, defined as the direct transfer of infection from a parent host to its progeny, is an important factor which can stimulate reduction of parasite virulence. Evolution of the vertical transmission rate from both points of view, the parasite and the host, is analyzed. There is a critical level of the rate, below which an evolutionary conflict arises (the parasite would want an increase in the rate while the host would not), and above which both species would correspond to increase the rate. Therefore, once the parasite dominates the evolutionary race so as to overcome this critical level, one‐way evolution begins toward a highly mutualistic relationship with a high vertical transmission rate, possibly creating a new organism through symbiosis with perfect vertical transmission. Changes in other parameters may decrease the critical level, initiating one‐way evolution. However, changes in traits, probably developed through a long interrelationship in parasitism, do not necessarily induce the evolution of mutualism. Establishment of the ability to make use of metabolic and digestive wastes from the partner certainly facilitates the evolution of mutualism, while improvements in reproductive efficiency of parasites and reduction of negative effects from exploitation in hosts on the contrary disturb mutualism.
Spatial variation in female fertility related to interactions with flower consumers and pathogens in a forest metapopulation of Primula sieboldii
Authors: Washitani Izumi , Okayama Yasushi , Sato Keiko , Takahashi Hitomi , Ohgushi Takayuki
Published: November 2006

Antagonistic biological interactions with flower consumers and pathogens may influence reproductive success of flowering plants, affecting population dynamics and natural selection for floral traits. However, ecological and evolutionary consequences of the interactions may depend on both spatial and temporal patterns of the interactions. In a forest metapopulation of Primula sieboldii E. Morren, an endangered clonal plant species, we measured between‐subpopulation patterns of seed sets and interactions with an influential flower consumer, a rove beetle, Eusphalerum bosatsu Watanabe, and a specific smut fungal pathogen, Urocystis tranzschelina (Lavrov) Zundel (Ustilaginales), for three years. Mean female fertility (seed set per flower) for individual subpopulations fluctuated moderately among years but was highly variable within each year among the five subpopulations studied. In two subpopulations, the impact of Eusphalerum beetle, was sufficiently large to result in almost complete failure in seed production over eight years including the three study and five previous preliminary observation years. In the two other subpopulations, seed set failure was caused by infection by the smut fungus. Infected capsules which constitute 10–30% of the capsules produced in the subpopulations were filled with ustilospores instead of seeds. In the subpopulation that escaped flower damage by Eusphalerum beetles and smut fungal infection, seed sets of both pin and thrum flowers were much higher than in the other subpopulations. The spatial restriction of individual antagonistic agents to a part of subpopulations suggest that dispersal of the agents, as well as the mode of spatial subdivision of the plant population would be important for determining the overall effects of antagonistic interactions on plant performances at the metapopulation level.
The effects of wild cruciferous host plants on morphology, reproductive performance and flight activity in the diamondback moth, Plutella xylostella (Lepidoptera: Yponomeutidae)
Authors: Begum Shefali , Tsukuda Ritsuko , Fujisaki Kenji , Nakasuji Fusao
Published: November 2006

The wild crucifers, Rorippa indica and Lepidium virginicum, are known to serve as host plants for the diamondback moth (DBM),Plutella xylostella, but they are less suitable than the preferred cultivated cruciferous plant, cabbage, in terms of adult body size and fecundity. The life history traits and flight activity of DBM adults grown on various host plants were investigated. The adults thus reared on each host plant were divided into three size groups (small, medium and large). In general, female adults grown on the wild crucifers were less fecund and lived longer than those reared on cabbage. Flight activity was higher in adults grown on wild crucifers than in those reared on cabbage. Male adults flew longer than females. Fecundity, longevity, flight activity and morphometrical characters of adults were positively correlated with pupal weight in individuals reared on the same host plant. A negative relationship was found between fecundity and flight activity in females of the same size group, but a positive one was observed in females reared on the same host plant.
Vertical foodweb structure of freshwater zooplankton assemblages estimated by stable nitrogen isotopes
Authors: France R. , Westcott K. , del Giorgio P. , Klein G. , Kalff J.
Published: November 2006

Although theoretical foodweb models predict the presence of only three to four trophic categories, estimation of “potential” vertical foodweb structure from species lists and inferred feeding interactions suggest that as many as 7 trophic categories can occur in the pelagic foodwebs of North American glaciated lakes. A compilation of data on the nitrogen isotopic composition of zooplankton from 46 Canadian Shield lakes suggested the average existence of one “realized” trophic category in addition to that of filter‐feeding, herbivorous cladocerans. When phytoplankton, planktivorous invertebrates, and plantivorous and piscivorous fish are included, the vertical foodweb structure in the pelagic zones of these lakes are greater than those hypothesized from some theoretical models.
Dynamics of buried seed population and seedling cohorts of two dominant weeds in a hill agroecosystem of the humid subtropics of India
Authors: Misra J. , Pandey H. N. , Tripathi R. S. , Sahoo U. K.
Published: November 2006

Dynamics of the buried seeds and plant population of two dominant weeds, viz.,Emilia sonchifolia (Linn.) DC. and Richardsonia pilosa HBK were studied in the crop fields of Meghalaya, north‐east India during radish and maize cropping and intervening fallow periods. The total buried seed population of R. pilosa was always larger than that of E. sonchifolia, but the germinable fraction was invariably greater in the latter. A major portion (39–41%) of the viable (germinable+dormant) seed population in both weeds was confined to the surface soil layer (0–5 cm). The viable seed population of E. sonchifolia peaked during April, while that of R. pilosa showed two peaks (during August and December). The survival pattern and half‐lives of seedling cohorts showed, some differences in the two weed species, but both being summer annuals, their populations behaved in a similar manner by showing higher seedling recruitment (K) and survivorship (p) rates in the summer crop (maize) than in the winter crop (radish). However, the density of plants that could attain adulthood was significantly higher in E. sonchifolia than R. pilosa which might have resulted in greater seed input of the former to the soil leading to its greater abundance in the crop fields.