bluuebunny/crossref_metadata_2025 huggingface dataset:
Spherical Aluminum Nitride Fillers for Heat‐Conducting Plastic Packages
Authors: Ohashi Masayoshi , Kawakami Shoji , Yokogawa Yoshiyuki , Lai Gao‐Chao
Published: August 2005

It is necessary for encapsulants to have not only a suitable coefficient of thermal expansion (CTE) compatible to IC devices and a low dielectric constant to reduce the device propagation delay, but also a high thermal conductivity to dissipate large amounts of heat from power‐hungry, high‐speed IC and high‐density packages. Fillers such as silica have been mixed with polymers to improve their properties. Aluminum nitride (AlN) is considered as an alternative one, because it has a higher theoretical thermal conductivity of ∼320 W/mK1, a compatible CTE with silicon chips and a low dielectric constant. Commercial AlN fillers are angular in shape, because they are prepared via grinding coarse AlN powders synthesized by direct nitridation of aluminum metal and classification. The angular AlN are not expected to have high fluidity when mixed with polymers and hence low packing density. Recently, we successfully obtained single‐crystalline spherical AlN fillers. Furthermore, polymer composites filled with the spherical AlN showed excellent thermal conductivity (>8 W/mK) as encapsulants for dissipating the heat generated in electronic devices.
Influence of Grain Size and Humidity on the Nanotribological Properties of Wear‐Resistant Nanostructured ZrO2 Coatings: An Atomic Force Microscopy Study
Authors: Tocha Ewa , Schönherr Holger , Julius Vancso G. , Siebelt Natasha
Published: August 2005

The nanotribological properties of nanostructured thin films of tetragonal ZrO2 on oxidized Si (100) were studied as a function of grain size and relative humidity (RH) by atomic force microscopy. The nanostructured ZrO2 showed a 50% decrease in friction coefficient μ compared with oxidized Si (100) in dry nitrogen atmosphere and 40% RH. A maximum of μ was observed at ca. 40% RH for both samples, while there were insignificant differences in μ for ZrO2 samples with grain sizes between 12 and 30 nm. The good tribological properties open the possibility for nanostructured zirconia to be applied as wear‐resistant, low friction coatings on various materials.
In SituGrowth of β‐SiC Nanowires in Porous SiC Ceramics
Authors: Zhu Sumin , Xi Hong‐An , Li Qin , Wang Ruoding
Published: August 2005

Polycarbosilane (PCS) was used as a precursor to prepare porous silicon carbide (SiC) ceramics within situgrowth of β‐SiC nanowires. The pore size of the as‐prepared porous ceramics was 1.37 μm in average, and had a narrow distribution. The nanowires with diameters ranging from ∼10 to 50 nm existed in the channels of the porous body. Their morphology, microstructure, and composition were characterized by field emission scanning electron microscopy, transmission electron microscopy, and energy‐dispersive X‐ray spectroscopy, which confirmed that the nanowires had a single‐crystal β‐SiC structure with the 〈111〉 growth direction. A vapor–liquid–solid process was discussed as a possible growth mechanism of the β‐SiC nanowires.
Creep Behavior of Soda‐Lime Glass in the 100–500 K Temperature Range by Indentation Creep Test
Authors: Shang Haixia , Rouxel Tanguy
Published: August 2005

The loading time and temperature dependences viscoelastic behavior of a soda‐lime‐silicate glass (SLS) were studied by indentation creep experiments. Experiments were conducted in air, water and silicone oil with 15–10 000 s loading times, and temperatures ranging between 100 and 500 K. The indentation size was found to depend much on the loading time and temperature. Hardness was found to decrease significantly with increasing loading time, even at 173 K, and to decrease rapidly with rising temperature, even well below the glass transition temperature (Tg). Water on the surface of glasses appeared to reduce the hardness and indentation viscosity of the glass.
Durability Improvement of Ancient Bricks by Cementation of Porous Media
Authors: Lopez‐Arce Paula , Benavente David , Garcia‐Guinea Javier
Published: August 2005

The physicomechanical properties of historic bricks in Toledo (Spain) that have undergone a time‐dependent self‐healing by natural weathering processes have been improved by porous infill with gypsum, ettringite, and, mainly, calcite. Both these bricks and their experimental replica bricks, made from the original calcareous clays fired at the appropriate historical temperatures (700°–900°C), have been analyzed by X‐ray diffraction, optical and scanning electron microscopy, mercury intrusion porosimetry, and ultrasound velocities to compare pore structure and strength evolution by mineral cementation. The resultant microstructure and mineral fillings depend on the brick calcareous composition and firing temperature, the brick location environment, burial, indoor or outdoor walls, the lime‐based joint mortars and coat plasters, and infiltration waters.
Influence of Short‐Chain Carboxylic Acids on the Mechanical Properties and Structure of Coagulated Alumina Suspensions
Authors: Tervoort Elena , Tervoort Theo A. , Gonzenbach Urs , Perednis Dainius , Gauckler Ludwig J.
Published: August 2005

Three different short‐chained carboxylic acids, formic, acetic, and propionic acid, were compared as additives to increase the green strength of wet particle networks produced with the direct coagulation casting process, which allows the internal coagulation of a suspension. Small acid additions do not alter the favorable low viscosity of the stabilized slurry, and yet increase the compressive strength of wet coagulated bodies. The strengthening effect increases with increasing chain length of the carboxylic acid. The maximum effect was observed upon addition of propionic acid (0.3 wt% to alumina), which resulted in a sixfold increase in compressive strength of wet coagulated bodies compared with that without propionic acid.
Phase Constitution During Sintering of Red Mud and Red Mud–Fly Ash Mixtures
Authors: Srikanth Srinivasan , Ray Ajay Kumar , Bandopadhyay Amitava , Ravikumar Bandari , Jha Animesh
Published: August 2005

The phase constitution during the sintering of pure red mud and red mud–fly ash mixtures was studied in the temperature range of 900°–1250°C. The phases formed at different sintering temperatures were analyzed by X‐ray powder diffraction. The phases that are likely to form at equilibrium at any isotherm were predicted using the Gibbs free energy minimization technique and the databases provided in the FactSage software. Although the thermodynamic prediction is in reasonable agreement with the experimental results for the major phases, there is some disagreement regarding the minor phases, especially the more complex phases. The major limitation of the thermodynamic approach presently is the non‐availability of thermodynamic data for several complex and multi‐component solution phases.
Mechanically Activated Synthesis and Magnetoresistance of Nanocrystalline Double Perovskite Sr2FeMoO6
Authors: Li Chen , Cailei Yuan , Junmin Xue , Wang John
Published: August 2005

Nanocrystalline Sr2FeMoO6 (SFMO) of double perovskite structure has been successfully synthesized by mechanical activation (MA) in air using SrO, Fe2O3, and MoO2 as the starting materials. Magnetization of the polycrystalline SFMO derived from MA increases with increasing MA time. Similarly, the magnetoresistance (MR) effect also increases with increasing MA time up to 25 h, which is ascribed to the elimination of SrMoO4 impurity phase and the refinement in grain size of the polycrystalline double perovskite phase. Prolonged MA adversely affects the MR effect, where Fe contamination was evidenced.
Polymer–Ceramic Conversion of Liquid Polyaluminasilazanes for SiAlCN Ceramics
Authors: Dhamne Abhijeet , Xu Weixing , Fookes Barry G. , Fan Yi , Zhang Ligong , Burton Sarah , Hu Jianzhi , Ford Joe , An Linan
Published: August 2005

Liquid‐phased polyaluminasilazanes were synthesized by simply reacting a liquid polyureasilazane with aluminum isopropoxide. The reaction was studied by Fourier‐transform infrared spectrometry (FTIR) and mass spectroscopy. The resultant polyaluminasilazanes were then pyrolysized to form amorphous SiAlCN ceramics at 1000°C in flowing N2. The structural evolution during pyrolysis was studied using solid‐state NMR and FTIR. Spectral analysis revealed that the amorphous structures of the ceramics consisted of SiC2N2 and SiCN3 as major building units, small amounts of SiC3N and SiN4 units, and penta‐ or hexa‐coordinated aluminum with nitrogen. Such units were connected with each other through C−C/C=C bonds or by shearing N to form network structures. The results also revealed that the relative amount of these units strongly depended on the Al content.
In Situ Neutron Diffraction Study of a Liquid Nitrogen‐Quenched Mg‐PSZ Under Load: A Microcrack‐Dominated System?
Authors: Ma Yuxiang , Kisi Erich Herold
Published: August 2005

The mechanical response of liquid nitrogen‐quenched 9.4 Mg‐PSZ in which the orthorhombic (o) phase is the major constituent (46 wt%) was investigated using in‐situ neutron diffraction during uniaxial compression. The material remains elastic below 1 GPa with a Young's modulus of∼242 GPa, second highest of all zirconia‐based materials and highest of all zirconia‐based ceramics. Beyond 1 GPa, the material develops small plastic strains in a time‐dependent manner (i.e., by room temperature creep) although the strains were generally much smaller than the unquenched material, which contains no o phase. As for standard Mg‐PSZ, the creep was accompanied by a volume change usually indicative of tetragonal to monoclinic (m) phase transformation; however, the amount of m phase apparent in the neutron diffraction patterns increased only marginally. The magnitude of the volume increase could not be accounted for by the observed increase in the m phase and hence, microcracking is believed to be responsible for most of the volume change. There is some evidence for a small amount of o to m transformation at the detection limit of the phase analysis technique.
Strength Analysis of Self‐Supported Films Produced by Aqueous Electrophoretic Deposition
Authors: González S. , Ferrari B. , Moreno R. , Baudín C.
Published: August 2005

The goal of this work is to study the feasibility of the characterization of the fracture strength of porous alumina/zirconia thin layers by three‐point bending and Weibull analysis. Films have been obtained by electrophoretic deposition on graphite and thermo‐gelation of the deposit with carrageenan. On sintering, graphite is burned out and self‐supported films are obtained. Strength values are well fitted to a simple two‐parameter Weibull distribution. The fracture origins are subcritical growth cracks that originated at the surface irregularities associated with the processing method. A Weibull modulus around 3 is obtained.
Preparation of Sputtered (Bax,Sr1−x)TiO3 Thin Films Directly on Copper
Authors: Laughlin Brian , Ihlefeld Jon , Maria Jon‐Paul
Published: August 2005

(Ba0.6,Sr0.4)TiO3 (BST) films were deposited on copper foils by radio frequency magnetron sputtering. By the use of controlled pO2 high‐temperature anneals, the films were completely crystallized in the absence of substrate oxidation. X‐ray diffraction and transmission electron microscopy (TEM) revealed an abrupt Cu/BST interface. The deposited BST films exhibit a zero bias permittivity and loss tangent values of 600 and 0.018, respectively. An electrical tunability ratio of 3.5:1 is observed on these metal–insulator–metal devices. Devices show leakage currents of 10−8 A/cm2 at ±10 V/μm, and loss tangents as low as 0.003 in fields approaching 40 V/μm.
Chemically Bonded Composite Sol–Gel Alumina Coatings
Authors: Troczynski T. , Yang Q.
Published: August 2005

This communication introduces chemically bonded (CB) composite sol–gel (SG) technology. The composite includes majority (>80 vol%) particulate filler, the balance being SG‐derived bonding phase. Ceramic bond formation in such a composite is induced through chemical reaction rather than through sintering. In the particular variant of the process presented here, the reactivity of the SG‐derived alumina ceramics toward phosphates, such as aluminum phosphate or phosphoric acid, is explored to produce a ceramic (reaction) bond in the system without sintering. This allows attaining structural integrity of the composite at relatively low temperatures of 300°C. Several examples of 40–200 μm thick films of CB alumina on stainless steel, Mg and Al, Ni, and on carbon fiber‐reinforced epoxy are discussed.
Structural Parameters of Mullite Formed During Heating of Diphasic Mullite Gels
Authors: Chakraborty Akshoy Kr.
Published: August 2005

Diphasic gels of four different compositions were synthesized. Lattice parameters, crystallite size, and strain values of mullite formed at different stages of annealing of diphasic gels have been calculated by quantitative standard less analysis using X‐ray diffraction. Results show that all three parameters change on progressive heating. Changes in the microstrain of mullite show a reciprocal relationship with crystallite size. Silica‐rich gel shows that the relative changes in the calculated values of three structural parameters of mullite formed during its formation process are because of an increase in its crystallinity rather than changes in composition. However, gels of composition in the solid solution range show that the relationship between lattice constants and chemical composition of mullite formed at high temperature agrees with Cameron data.
Root canal morphology and its relationship to endodontic procedures
Authors: Vertucci Frank J.
Published: August 2005

The hard tissue repository of the human dental pulp takes on numerous configurations and shapes. A thorough knowledge of tooth morphology, careful interpretation of angled radiographs, proper access preparation and a detailed exploration of the interior of the tooth are essential prerequisites for a successful treatment outcome. Magnification and illumination are aids that must be utilized to achieve this goal. This article describes and illustrates tooth morphology and discusses its relationship to endodontic procedures. A thorough understanding of the complexity of the root canal system is essential for understanding the principles and problems of shaping and cleaning, for determining the apical limits and dimensions of canal preparations, and for performing successful microsurgical procedures.
Reaction of periradicular tissues to root canal treatment: benefits and drawbacks
Authors: Siqueira José F.
Published: August 2005

Tissue injury induced by intra‐canal procedures and substances extruded through the apical foramen may influence the development of post‐operative pain as well as the outcome of root canal treatment. While the development of pain is related to the intensity of tissue damage, treatment outcome is more dependent on the persistence of the source of injury. Procedural errors are the main causative agents of either post‐operative pain or persistent periradicular lesions. However, even when the treatment has followed the highest standards, post‐operative pain can occur and periradicular disease can persist, albeit at a lower incidence when compared to teeth treated to a poor technical standard. This paper critically reviews the effects of intra‐canal procedures on the periradicular tissues, with special emphasis on the occurrence of post‐operative pain and the outcome of the root canal treatment. The possible systemic effects stemming from root canal procedures are also discussed in the light of current knowledge.
Root canal instrumentation with ProFile™ instruments
Authors: Lloyd Adam
Published: August 2005

The history behind the introduction of rotary nickel–titanium instruments of increasing taper is outlined along with a logical sequence of crown‐down canal that can be applied to a variety of cases. Clinically applicable canal instrumentation is explained for small, medium and large canals with actual examples prepared with the same technique.
Enhanced protoplast division by encapsulation in droplets: An advance towards somatic hybridisation in recalcitrant white lupin
Authors: SINHA ANUPAM , CALIGARI PETER D S
Published: August 2005

Lupins are highly nutritious fodder and pulse crops but the greatest challenge in their genetic enhancement is the difficulty in obtaining hybrids through conventional sexual approaches. To bypass this, a procedure for the culture of hitherto recalcitrant lupin protoplasts is now being developed so that the somatic hybrids can be regenerated. This study provides a basis for a regime to culture lupin protoplasts. Cotyledonary protoplasts of white lupin (Lupinus albus) were plated in two diverse media for the evaluation of various plating regimes. The protoplasts divided in agarose as well as in Gelrite™ but embedding in agarose at 6 g L−1 concentration resulted in a higher rate of mitosis. Sodium alginate embedding inhibited protoplast division. Protoplast plating in the form of liquid suspension was significantly inferior to embedding. A filter paper substratum was clearly noxious to protoplast division. Vis‐à‐vis other designs of plating, a 400% improvement in protoplast elongation and division was achieved by plating in the form of 25 μL droplets at the base of 60 mm × 15 mm Nunclon™ dish and overlaying with liquid medium. Better results in terms of protoplast elongation and division were obtained with K8p medium as compared to the AS medium. This report on lupin protoplast culture represents a significant breakthrough in the genus in which morphogenesis has not been described to date.
Disease assessment methods and their use in simulating growth and yield of peanut crops affected by leafspot disease
Authors: ADOMOU M , PRASAD P V V , BOOTE K J , DETONGNON J
Published: August 2005

Peanut (Arachis hypogaea) crops in Benin often experience late leafspot (Cercosporidium personatum), which causes severe yield losses associated with leaf defoliation and necrosis. The objective of this research was to determine the best method of disease assessment and to test its utility in the CROPGRO‐peanut model to simulate growth and yield as affected by late leafspot in early and late maturing peanut cultivars grown at different sowing dates under rain‐fed conditions (without irrigation) in northern Benin. Two peanut cultivars TS 32‐1 and 69–101 were sown on three dates between May and August during 1998 and 1999. In both years there was severe occurrence of late leafspot and the progression of disease was earlier and faster with later sowing dates. Overall, the long duration cultivar 69–101 produced greater yield than the short duration cultivar TS 32‐1. The CROPGRO‐peanut model was able to predict and simulate the observed crop and pod dry matter over time when input on percent diseased leaf area and percent defoliation were provided. Of several disease assessments, the best approach was to input measured percent main‐stem defoliation above the fourth node and percent diseased leaf area estimated from visual leafspot score.
Inheritance of hypersensitive resistance to Bean yellow mosaic virus in narrow‐leafed lupin (Lupinus angustifolius)
Authors: JONES R A C , SMITH L J
Published: August 2005

In narrow‐leafed lupin (Lupinus angustifolius), segregation for the necrotic (systemic hypersensitive) response to infection with a necrotic strain of Bean yellow mosaic virus (BYMV‐N) was studied in progeny plants from six crosses. The parents were two cultivars that always developed necrosis when infected (Danja and Merrit) and two genotypes that always responded without necrosis (90L423‐07‐13 and P26697). In the four possible combinations of crosses between the different necrotic and non‐necrotically reacting genotypes, segregation for the necrotic response in F2 progeny plants always fitted a 3:1 ratio (necrotic: non‐necrotic). All F2 progeny plants from the cross between the two non‐cultivar genotypes became infected without necrosis while 99% of the F2 from the cross between the two cultivars developed necrosis. These results indicate that the systemic necrotic response to infection with BYMV‐N is probably controlled by a single dominant hypersensitivity gene for which we propose the name Nbm‐1. However, its expression seemed influenced by independently segregating modifier genes in the genetic background since necrosis developed at widely different rates within affected F2 progeny plants resulting in staggered killing.
Genetic variability of Tomato spotted wilt virus in Australia and validation of real time RT‐PCR for its detection in single and bulked leaf samples
Authors: DIETZGEN R G , TWIN J , TALTY J , SELLADURAI S , CARROLL M L , COUTTS B A , BERRYMAN D I , JONES R A C
Published: August 2005

The potential for large‐scale use of a sensitive real time reverse transcription polymerase chain reaction (RT‐PCR) assay was evaluated for the detection of Tomato spotted wilt virus (TSWV) in single and bulked leaf samples by comparing its sensitivity with that of DAS‐ELISA. Using total RNA extracted with RNeasy® or leaf soak methods, real time RT‐PCR detected TSWV in all infected samples collected from 16 horticultural crop species (including flowers, herbs and vegetables), two arable crop species, and four weed species by both assays. In samples in which DAS‐ELISA had previously detected TSWV, real time RT‐PCR was effective at detecting it in leaf tissues of all 22 plant species tested at a wide range of concentrations. Bulk samples required more robust and extensive extraction methods with real time RT‐PCR, but it generally detected one infected sample in 1000 uninfected ones. By contrast, ELISA was less sensitive when used to test bulked samples, once detecting up to 1 infected in 800 samples with pepper but never detecting more than 1 infected in 200 samples in tomato and lettuce. It was also less reliable than real time RT‐PCR when used to test samples from parts of the leaf where the virus concentration was low. The genetic variability among Australian isolates of TSWV was small. Direct sequencing of a 587 bp region of the nucleoprotein gene (S RNA) of 29 isolates from diverse crops and geographical locations yielded a maximum of only 4.3% nucleotide sequence difference. Phylogenetic analysis revealed no obvious groupings of isolates according to geographic origin or host species. TSWV isolates, that break TSWV resistance genes in tomato or pepper did not differ significantly in the N gene region studied, indicating that a different region of the virus genome is responsible for this trait.
The first near-infrared detection of XTE J1118 + 480 in quiescence
Authors: Mikołajewska Joanna , Rutkowski Artur , Gonçalves Denise R. , Szostek Anna
Published: August 2005

We report the first quiescent detection of KV UMa, the optical counterpart of XTE J1118 + 480, in the near-infrared. The observed magnitudes and colours are consistent with a K7–M0 V star, at the distance of 1.4 ± 0.2 kpc. The light curve shows strong orbital modulation with possible contamination from a superhump detected in the quiescent optical light curves.
Multipole invariants and non-Gaussianity
Authors: Land Kate , Magueijo João
Published: August 2005

We propose a framework for separating the information contained in the cosmic microwave background multipoles, aℓm, into algebraically independent components that cleanly separate information pertaining to the power spectrum, non-Gaussianity and preferred axis effects. The formalism builds upon the recently proposed multipole vectors and we elucidate a few features regarding these vectors, namely their lack of statistical independence for a Gaussian random process. In a few cases we explicitly relate our proposed invariants to components of the n-point correlation function (power spectrum, bispectrum). We find the distributions of the invariants using a mixture of analytical and numerical methods. We also evaluate them for the co-added WMAP first-year map.
Identification of extragalactic sources of the highest energy EGRET photons by correlation analysis
Authors: Gorbunov D. S. , Tinyakov P. G. , Tkachev I. I. , Troitsky S. V.
Published: August 2005

We have found significant correlations between the arrival directions of the highest energy photons (Eγ > 10 GeV) observed by EGRET and the positions of the BL Lac type objects (BL Lacs). The observed correlations imply that not less than 3 per cent of extragalactic photons at these energies originate from BL Lacs. Some of the BL Lacs that are correlated with the highest energy photons have no counterparts in the EGRET source catalogue, i.e. do not coincide with strong emitters of gamma-rays at lower energy. A study of correlating BL Lacs suggests that they may form a subset which is statistically different from the total BL Lac catalogue; we argue that they are prominent candidates for TeV gamma-ray sources. Our results demonstrate that the analysis of positional correlations is a powerful approach, indispensable in cases when low-number statistics limit or even prohibit the standard case-by-case identification.
Modeling of Ground‐Water Contamination Caused by Organic Solvent Vapors
Authors: Mendoza Carl A. , McAlary Todd A.
Published: August 2005

Mathematical models are used to evaluate the potential for ground‐water contamination resulting from vapor transport of volatile organic solvents in the unsaturated zone. A two‐dimensional numerical model for density‐driven flow and transport of vapors shows that trichloroethylene (TCE) vapors can be expected to spread rapidly from a residual source above an unconfined aquifer in an unsaturated, sandy deposit. Sensitivity analyses show that the shape of the vapor plume is particularly sensitive to the ground surface boundary condition and the material permeability. The shape of the vapor plume is insensitive to the mass flux by diffusion through the capillary fringe, although the flux may be significant in terms of ground‐water quality because the drinking‐water standard is very low. The vapor plume simulations and a plug‐flow infiltration model are used to calculate a source function for a ground‐water transport model in order to estimate the potential for ground‐water contamination. Ground‐water simulations show that an impermeable surface cover could reduce the flux of contaminants to the aquifer by preventing infiltration through the vapor plume. However, for the conditions modeled, significant ground‐water contamination can be expected to occur regardless of whether the ground surface is covered or not. Contaminants can reach the saturated zone from a residual source either by liquid‐phase diffusion through the capillary fringe or by migrating as a vapor beyond the lateral limits of a cover and subsequently dissolving and being flushed to the saturated zone by infiltration.
A General Statistical Procedure for Ground‐Water Detection Monitoring at Waste Disposal Facilities
Authors: Gibbons Robert D.
Published: August 2005

Nonparametric upper prediction limits for ground‐water detection monitoring are developed. The limit is defined as the maximum of a previous background sample of size n (i.e., X(max, n)). The probability that at least one out of the next m measurements (i.e., Y(min, m)) will be less than X(max, n) at each of k monitoring wells is computed. In the context of ground‐water monitoring, m is equal to the initial new measurement in a particular monitoring well plus m –1 resamplings of that well. In this way, values of n and m can be selected to assure a desired confidence level (e.g., γ≥ .95). A series of typical examples are described, and a set of Tables that give these probabilities for values of n = 4 to 100, k = 1 to 100, and m = 1 to 3 are provided. Generalization to multiple variables (i.e., indicator parameters) is also discussed.
Colloidal Hard-Sphere Crystal Growth Frustrated by Large Spherical Impurities
Authors: de Villeneuve Volkert W. A. , Dullens Roel P. A. , Aarts Dirk G. A. L. , Groeneveld Esther , Scherff Johannes H. , Kegel Willem K. , Lekkerkerker Henk N. W.
Published: August 2005

Impurities affect the nucleation, growth, and structure of crystals. Here we report the effect of large, spherical, polymethylmethacrylate impurities on the crystal growth of monodisperse, hard, polymethylmethacrylate colloids in a density- and optically matching apolar solvent mixture. Crystal growth, initiated at the bottom of the sample, was studied by imaging sequences of two-dimensional
xy
slices in the plane of the impurity's center with a laser scanning confocal microscope. Impurities form the center of grain boundaries, and a single fluid particle layer around the impurity persists in all cases. The growth rate sensitively depends on the impurity's size. Crystal growth is inhibited to a greater extent near smaller impurities, pointing to local crystal frustration induced by the curvature of the impurity.
Genome Streamlining in a Cosmopolitan Oceanic Bacterium
Authors: Giovannoni Stephen J. , Tripp H. James , Givan Scott , Podar Mircea , Vergin Kevin L. , Baptista Damon , Bibbs Lisa , Eads Jonathan , Richardson Toby H. , Noordewier Michiel , Rappé Michael S. , Short Jay M. , Carrington James C. , Mathur Eric J.
Published: August 2005

The SAR11 clade consists of very small, heterotrophic marine α-proteobacteria that are found throughout the oceans, where they account for about 25% of all microbial cells.
Pelagibacter ubique
, the first cultured member of this clade, has the smallest genome and encodes the smallest number of predicted open reading frames known for a free-living microorganism. In contrast to parasitic bacteria and archaea with small genomes,
P. ubique
has complete biosynthetic pathways for all 20 amino acids and all but a few cofactors.
P. ubique
has no pseudogenes, introns, transposons, extrachromosomal elements, or inteins; few paralogs; and the shortest intergenic spacers yet observed for any cell.
The Illusion of Invariant Quantities in Life Histories
Authors: Nee Sean , Colegrave Nick , West Stuart A. , Grafen Alan
Published: August 2005

Life-history theory attempts to provide evolutionary explanations for variations in the ways in which animal species live their lives. Recent analyses have suggested that the dimensionless ratios of several key life-history parameters are the same for different species, even across distant taxa. However, we show here that previous analyses may have given a false picture and created an illusion of invariants, which do not necessarily exist; essentially, this is because life-history variables have been regressed against themselves. The following question arises from our analysis: How do we identify an invariant?
Theoretical Study of Geometric Phase Effects in the Hydrogen-Exchange Reaction
Authors: Juanes-Marcos Juan Carlos , Althorpe Stuart C. , Wrede Eckart
Published: August 2005

The crossing of two electronic potential surfaces (a conical intersection) should result in geometric phase effects even for molecular processes confined to the lower surface. However, recent quantum simulations of the hydrogen exchange reaction (H + H
2
→ H
2
+ H) have predicted a cancellation in such effects when product distributions are integrated over all scattering angles. We used a simple topological argument to extract reaction paths with different senses from a nuclear wave function that encircles a conical intersection. In the hydrogen-exchange reaction, these senses correspond to paths that cross one or two transition states. These two sets of paths scatter their products into different regions of space, which causes the cancellation in geometric phase effects. The analysis should generalize to other direct reactions.
Osmium Isotope Evidence for an
s
-Process Carrier in Primitive Chondrites
Authors: Brandon A. D. , Humayun M. , Puchtel I. S. , Leya I. , Zolensky M.
Published: August 2005

Osmium extracted from unequilibrated bulk chondrites has isotope anomalies consistent with an insoluble
s
-process carrier, termed Os(i) here. Osmium from metamorphosed bulk chondrites does not have isotope anomalies, implying that the Os(i) carrier was destroyed by metamorphism. The isotopic homogeneity of metamorphosed bulk chondrites is consistent with extremely effective mixing of presolar grains from varied sources in the nebula. Osmium in the Os(i) carrier is likely from nucleosynthetic sites with a neutron density about two to four times as high as that of the average solar
s
-process Os.
Strong, Transparent, Multifunctional, Carbon Nanotube Sheets
Authors: Zhang Mei , Fang Shaoli , Zakhidov Anvar A. , Lee Sergey B. , Aliev Ali E. , Williams Christopher D. , Atkinson Ken R. , Baughman Ray H.
Published: August 2005

Individual carbon nanotubes are like minute bits of string, and many trillions of these invisible strings must be assembled to make useful macroscopic articles. We demonstrated such assembly at rates above 7 meters per minute by cooperatively rotating carbon nanotubes in vertically oriented nanotube arrays (forests) and made 5-centimeter-wide, meter-long transparent sheets. These self-supporting nanotube sheets are initially formed as a highly anisotropic electronically conducting aerogel that can be densified into strong sheets that are as thin as 50 nanometers. The measured gravimetric strength of orthogonally oriented sheet arrays exceeds that of sheets of high-strength steel. These nanotube sheets have been used in laboratory demonstrations for the microwave bonding of plastics and for making transparent, highly elastomeric electrodes; planar sources of polarized broad-band radiation; conducting appliqués; and flexible organic light-emitting diodes.
The Protein Phosphatases of
Synechocystis
sp. Strain PCC 6803: Open Reading Frames sll1033 and sll1387 Encode Enzymes That Exhibit both Protein-Serine and Protein-Tyrosine Phosphatase Activity In Vitro
Authors: Li Renhui , Potters M. Ben , Shi Liang , Kennelly Peter J.
Published: August 2005

The open reading frames (ORFs) encoding two potential protein-serine/threonine phosphatases from the cyanobacterium
Synechocystis
sp. strain PCC 6803 were cloned and their protein products expressed in
Escherichia coli
cells. The product of ORF sll1033, SynPPM3, is a homologue of the PPM family of protein-serine/threonine phosphatases found in all eukaryotes as well as many members of the
Bacteria
. Surprisingly, the recombinant protein phosphatase dephosphorylated phosphotyrosine- as well as phosphoserine-containing proteins in vitro. While kinetic analyses indicate that the enzyme was more efficient at dephosphorylating the latter, replacement of Asp
608
by asparagine enhanced activity toward a phosphotyrosine-containing protein fourfold. The product of ORF sll1387, SynPPP1, is the sole homolog of the PPP family of protein phosphatases encoded by the genome of
Synechocystis
sp. strain PCC 6803. Like many other bacterial PPPs, the enzyme dephosphorylated phosphoserine- and phosphotyrosine-containing proteins with comparable efficiencies. However, while previously described PPPs from prokaryotic organisms required the addition of exogenous metal ion cofactors, such as Mg
2+
or Mn
2+
, for activity, recombinantly produced SynPPP1 displayed near-maximal activity in the absence of added metals. Inductively coupled plasma mass spectrometry indicated that recombinant SynPPP1 contained significant quantities, 0.32 to 0.44 mol/mole total, of Mg and Mn. In this respect, the cyanobacterial enzyme resembled eukaryotic members of the PPP family, which are metalloproteins. mRNA encoding SynPPP1 or SynPPM3 could be detected in cells grown under many, but not all, environmental conditions.
A Phylogeny of Bacterial RNA Nucleotidyltransferases:
Bacillus halodurans
Contains Two tRNA Nucleotidyltransferases
Authors: Bralley Patricia , Chang Samantha A. , Jones George H.
Published: August 2005

We have analyzed the distribution of RNA nucleotidyltransferases from the family that includes poly(A) polymerases (PAP) and tRNA nucleotidyltransferases (TNT) in 43 bacterial species. Genes of several bacterial species encode only one member of the nucleotidyltransferase superfamily (NTSF), and if that protein functions as a TNT, those organisms may not contain a poly(A) polymerase I like that of
Escherichia coli
. The genomes of several of the species examined encode more than one member of the nucleotidyltransferase superfamily. The function of some of those proteins is known, but in most cases no biochemical activity has been assigned to the NTSF. The NTSF protein sequences were used to construct an unrooted phylogenetic tree. To learn more about the function of the NTSFs in species whose genomes encode more than one, we have examined
Bacillus halodurans
. We have demonstrated that
B. halodurans
adds poly(A) tails to the 3′ ends of RNAs in vivo. We have shown that the genes for both of the NTSFs encoded by the
B. halodurans
genome are transcribed in vivo. We have cloned, overexpressed, and purified the two NTSFs and have shown that neither functions as poly(A) polymerase in vitro. Rather, the two proteins function as tRNA nucleotidyltransferases, and our data suggest that, like some of the deep branching bacterial species previously studied by others,
B. halodurans
possesses separate CC- and A-adding tRNA nucleotidyltransferases. These observations raise the interesting question of the identity of the enzyme responsible for RNA polyadenylation in
Bacillus
.
Proteomic Analysis Reveals the Participation of Energy- and Stress-Related Proteins in the Response of
Pseudomonas putida
DOT-T1E to Toluene
Authors: Segura Ana , Godoy Patricia , van Dillewijn Pieter , Hurtado Ana , Arroyo Nuria , Santacruz Simon , Ramos Juan-Luis
Published: August 2005

Pseudomonas putida
DOT-T1E is tolerant to toluene and other toxic hydrocarbons through extrusion of the toxic compounds from the cell by means of three efflux pumps, TtgABC, TtgDEF, and TtgGHI. To identify other cellular factors that allow the growth of
P. putida
DOT-T1E in the presence of high concentrations of toluene, we performed two-dimensional gel analyses of proteins extracted from cultures grown on glucose in the presence and in the absence of the organic solvent. From a total of 531 spots, 134 proteins were observed to be toluene specific. In the absence of toluene, 525 spots were clearly separated and 117 proteins were only present in this condition. Moreover, 35 proteins were induced by at least twofold in the presence of toluene whereas 26 were repressed by at least twofold under these conditions. We reasoned that proteins that were highly induced could play a role in toluene tolerance. These proteins, identified by matrix-assisted laser desorption ionization-time of flight mass spectrometry, were classified into four categories: 1, proteins involved in the catabolism of toluene; 2, proteins involved in the channeling of metabolic intermediates to the Krebs cycle and activation of purine biosynthesis; 3, proteins involved in sugar transport; 4, stress-related proteins. The set of proteins in groups 2 and 3 suggests that the high energy demand required for solvent tolerance is achieved via activation of cell metabolism. The role of chaperones that facilitate the proper folding of newly synthesized proteins under toluene stress conditions was analyzed in further detail. Knockout mutants revealed that CspA, XenA, and Tuf-1 play a role in solvent tolerance in
Pseudomonas
, although this role is probably not specific to toluene, as indicated by the fact that all mutants grew more slowly than the wild type without toluene.
Transcriptional Termination Control of a Novel ABC Transporter Gene Involved in Antibiotic Resistance in
Bacillus subtilis
Authors: Ohki Reiko , Tateno Kozue , Takizawa Teruaki , Aiso Toshiko , Murata Makiko
Published: August 2005

In members of one of the subfamilies of the bacterial ATP binding cassette (ABC) transporters, the two nucleotide binding domains are fused as a single peptide and the proteins have no membrane-spanning domain partners. Most of the ABC efflux transporters of this subfamily have been characterized in actinomycetes, producing macrolide, lincosamide, and streptogramin antibiotics. Among 40 ABC efflux transporters of
Bacillus subtilis
, five proteins belong to this subfamily. None of these proteins has been functionally characterized. We examined macrolide, lincosamide, and streptogramin antibiotic resistance in insertional disruptants of the genes that encode these proteins. It was found that only a disruptant of
vmlR
(formerly named
expZ
) showed hypersensitivity to virginiamycin M and lincomycin. Expression of the
vmlR
gene was induced by the addition of these antibiotics in growth medium. Primer extension analysis revealed that transcription of the
vmlR
gene initiates at an adenosine residue located 225 bp upstream of the initiation codon. From the analysis of the
vmlR
and
lacZ
fusion genes, a 52-bp deletion from +159 to +211 resulted in constitutive expression of the
vmlR
gene. In this region, a typical ρ-independent transcriptional terminator was found. It was suggested that the majority of transcription ends at this termination signal in the absence of antibiotics, whereas under induced conditions, RNA polymerase reads through the terminator, and transcription continues to the downstream
vmlR
coding region, resulting in an increase in
vmlR
expression. No stabilization of
vmlR
mRNA occurred under the induced conditions.
The Heat Shock Genes
dnaK
,
dnaJ
, and
grpE
Are Involved in Regulation of Putisolvin Biosynthesis in
Pseudomonas putida
PCL1445
Authors: Dubern Jean-Frédéric , Lagendijk Ellen L. , Lugtenberg Ben J. J. , Bloemberg Guido V.
Published: August 2005

Pseudomonas putida
PCL1445 produces two cyclic lipopeptides, putisolvins I and II, which possess surfactant activity and play an important role in biofilm formation and degradation. In order to identify genes and traits that are involved in the regulation of putisolvin production of PCL1445, a Tn
5luxAB
library was generated and mutants were selected for the lack of biosurfactant production using a drop-collapsing assay. Sequence analysis of the Tn5
luxAB
flanking region of one biosurfactant mutant, strain PCL1627, showed that the transposon had inserted in a
dnaK
homologue which is located downstream of
grpE
and upstream of
dnaJ
. Analysis of putisolvin production and expression studies indicate that
dnaK
, together with the
dnaJ
and
grpE
heat shock genes, takes part in the positive regulation (directly or indirectly) of putisolvin biosynthesis at the transcriptional level. Growth of PCL1445 at low temperature resulted in an increased level of putisolvins, and mutant analyses showed that this requires
dnaK
and
dnaJ
but not
grpE
. In addition, putisolvin biosynthesis of PCL1445 was found to be dependent on the GacA/GacS two-component signaling system. Expression analysis indicated that
dnaK
is positively regulated by GacA/GacS.
Species and Incompatibility Determination within the P1parFamily of Plasmid Partition Elements
Authors: Dabrazhynetskaya Alena , Sergueev Kirill , Austin Stuart
Published: August 2005

The P1parfamily of active plasmid partition systems consists of at least six members, broadly distributed in a variety of plasmid types and bacterial genera. Each encodes two Par proteins and contains acis-actingparSsite. Individualparsystems can show distinct species specificities; the proteins from one type cannot function with theparSsite of another. P1par-versus-P7parspecificity resides within two hexamer BoxB repeats encoded byparSthat contact the ParB protein near the carboxy terminus. Here, we examine the species specificity differences betweenYersinia pestispMT1parSandEscherichia coliP1 and P7parS. pMT1parSsite specificity could be altered to that of either P1 or P7 by point mutation changes in the BoxB repeats. Just one base change in a single BoxB repeat sometimes sufficed. The BoxB sequence appears to be able to adopt a number of forms that define exclusive interactions with different ParB species. The loopedparSstructure may facilitate this repertoire of interaction specificities. Different P1parfamily members have different partition-mediated incompatibility specificities. This property defines whether two related plasmids can coexist in the same cell and is important in promoting the evolution of new plasmid species. BoxB sequence changes that switch species specificity between P1, P7, and pMT1 species switched partition-mediated plasmid incompatibility in concert. Thus, there is a direct mechanistic link between species specificity and partition-mediated incompatibility, and the BoxB-ParB interaction can be regarded as a special mechanism for facilitating plasmid evolution.
Induction of Manganese-Containing Superoxide Dismutase Is Required for Acid Tolerance inVibrio vulnificus
Authors: Kim Ju-Sim , Sung Moon-Hee , Kho Dhong-Hyo , Lee Jeong K.
Published: August 2005

The manganese-containing superoxide dismutase (MnSOD) ofVibrio vulnificus, normally detected after the onset of the stationary phase, is expressed during the lag that immediately follows the transfer of cells grown exponentially to a fresh medium acidified to pH 5.0, whereas Fe-containing SOD is constitutively expressed. The signal triggering the growth lag and MnSOD induction therein is not low pH but intracellular superoxide accumulated under these conditions, since addition of a superoxide scavenger not only shortened the lag but also abrogated the MnSOD induction. If the lysine decarboxylase reaction proceeds in the presence of sufficient lysine, the broth is rapidly neutralized to abolish the generation of oxidative stress. Accordingly, the acid tolerance response was examined without the addition of lysine. SoxR regulates MnSOD induction. Lack of MnSOD caused by mutations insoxRorsodAresulted in low tolerance to low pH. Thefurmutant derepressing MnSOD showed better tolerance than the wild type. Thus, an increase in total cytosolic SOD activity through MnSOD induction is essential for the cell to withstand the acid challenge. The contribution of cuprozinc-containing SOD to acid tolerance is not significant compared with those of cytosolic SODs.
Cytochrome
c
Maturation and the Physiological Role of
c
-Type Cytochromes in
Vibrio cholerae
Authors: Braun Martin , Thöny-Meyer Linda
Published: August 2005

Vibrio cholerae
lives in different habitats, varying from aquatic ecosystems to the human intestinal tract. The organism has acquired a set of electron transport pathways for aerobic and anaerobic respiration that enable adaptation to the various environmental conditions. We have inactivated the
V. cholerae ccmE
gene, which is required for cytochrome
c
biogenesis. The resulting strain is deficient of all
c
-type cytochromes and allows us to characterize the physiological role of these proteins. Under aerobic conditions in rich medium,
V. cholerae
produces at least six
c
-type cytochromes, none of which is required for growth. Wild-type
V. cholerae
produces active fumarate reductase, trimethylamine
N
-oxide reductase,
cbb
3
oxidase, and nitrate reductase, of which only the fumarate reductase does not require maturation of
c
-type cytochromes. The reduction of nitrate in the medium resulted in the accumulation of nitrite, which is toxic for the cells. This suggests that
V. cholerae
is able to scavenge nitrate from the environment only in the presence of other nitrite-reducing organisms. The phenotypes of cytochrome
c
-deficient
V. cholerae
were used in a transposon mutagenesis screening to search for additional genes required for cytochrome
c
maturation. Over 55,000 mutants were analyzed for nitrate reductase and
cbb
3
oxidase activity. No transposon insertions other than those within the
ccm
genes for cytochrome
c
maturation and the
dsbD
gene, which encodes a disulphide bond reductase, were found. In addition, the role of a novel CcdA-like protein in
cbb
3
oxidase assembly is discussed.