bluuebunny/crossref_metadata_2025 huggingface dataset:
Oxygen hypothesis of polar gigantism not supported by performance of Antarctic pycnogonids in hypoxia
Authors: Woods H. Arthur , Moran Amy L , Arango Claudia P , Mullen Lindy , Shields Chris
Published: January 2009

Compared to temperate and tropical relatives, some high-latitude marine species are large-bodied, a phenomenon known as polar gigantism. A leading hypothesis on the physiological basis of gigantism posits that, in polar water, high oxygen availability coupled to low metabolic rates relieves constraints on oxygen transport and allows the evolution of large body size. Here, we test the oxygen hypothesis using Antarctic pycnogonids, which have been evolving in very cold conditions (−1.8–0°C) for several million years and contain spectacular examples of gigantism. Pycnogonids from 12 species, spanning three orders of magnitude in body mass, were collected from McMurdo Sound, Antarctica. Individual sea spiders were forced into activity and their performance was measured at different experimental levels of dissolved oxygen (DO). The oxygen hypothesis predicts that, all else being equal, large pycnogonids should perform disproportionately poorly in hypoxia, an outcome that would appear as a statistically significant interaction between body size and oxygen level. In fact, although we found large effects of DO on performance, and substantial interspecific variability in oxygen sensitivity, there was no evidence for size×DO interactions. These data do not support the oxygen hypothesis of Antarctic pycnogonid gigantism and suggest that explanations must be sought in other ecological or evolutionary processes.
Effects of influenza A virus infection on migrating mallard ducks
Authors: Latorre-Margalef Neus , Gunnarsson Gunnar , Munster Vincent J , Fouchier Ron A.M , Osterhaus Albert D.M.E , Elmberg Johan , Olsen Björn , Wallensten Anders , Haemig Paul D , Fransson Thord , Brudin Lars , Waldenström Jonas
Published: January 2009

The natural reservoir of influenza A virus is waterfowl, particularly dabbling ducks (genusAnas). Although it has long been assumed that waterfowl are asymptomatic carriers of the virus, a recent study found that low-pathogenic avian influenza (LPAI) infection in Bewick's swans (Cygnus columbianus bewickii) negatively affected stopover time, body mass and feeding behaviour. In the present study, we investigated whether LPAI infection incurred ecological or physiological costs to migratory mallards (Anas platyrhynchos) in terms of body mass loss and staging time, and whether such costs could influence the likelihood for long-distance dispersal of the avian influenza virus by individual ducks. During the autumn migrations of 2002–2007, we collected faecal samples (n=10 918) and biometric data from mallards captured and banded at Ottenby, a major staging site in a flyway connecting breeding and wintering areas of European waterfowl. Body mass was significantly lower in infected ducks than in uninfected ducks (mean difference almost 20 g over all groups), and the amount of virus shed by infected juveniles was negatively correlated with body mass. There was no general effect of infection on staging time, except for juveniles in September, in which birds that shed fewer viruses stayed shorter than birds that shed more viruses. LPAI infection did not affect speed or distance of subsequent migration. The data from recaptured individuals showed that the maximum duration of infection was on average 8.3 days (s.e. 0.5), with a mean minimum duration of virus shedding of only 3.1 days (s.e. 0.1). Shedding time decreased during the season, suggesting that mallards acquire transient immunity for LPAI infection. In conclusion, deteriorated body mass following infection was detected, but it remains to be seen whether this has more long-term fitness effects. The short virus shedding time suggests that individual mallards are less likely to spread the virus at continental or intercontinental scales.
Echolocating bats emit a highly directional sonar sound beam in the field
Authors: Surlykke Annemarie , Boel Pedersen Simon , Jakobsen Lasse
Published: January 2009

Bats use echolocation or biosonar to navigate and find prey at night. They emit short ultrasonic calls and listen for reflected echoes. The beam width of the calls is central to the function of the sonar, but directionality of echolocation calls has never been measured from bats flying in the wild. We used a microphone array to record sounds and determine horizontal directionality for echolocation calls of the trawling Daubenton's bat,Myotis daubentonii, flying over a pond in its natural habitat.Myotis daubentoniiemitted highly directional calls in the field. Directionality increased with frequency. At 40 kHz half-amplitude angle was 25°, decreasing to 14° at 75 kHz. In the laboratory,M. daubentoniiemitted less intense and less directional calls. At 55 kHz half-amplitude angle was 40° in the laboratory versus 20° in the field. The relationship between frequency and directionality can be explained by the simple piston model. The model also suggests that the increase in the emitted intensity in the field is caused by the increased directionality, focusing sound energy in the forward direction. The bat may increase directionality by opening the mouth wider to emit a louder, narrower beam in the wild.
Earthworm genomes, genes and proteins: the (re)discovery of Darwin's worms
Authors: Stürzenbaum S.R , Andre J , Kille P , Morgan A.J
Published: January 2009

Small incremental biological change, winnowed by natural selection over geological time scales to produce large consequences, was Darwin's singular insight that revolutionized the life sciences. His publications after 1859, including the ‘earthworm book’, were all written to amplify and support the evolutionary theory presented in theOrigin. Darwin was unable to provide a physical basis for the inheritance of favoured traits because of the absence of genetic knowledge that much later led to the ‘modern synthesis’. Mistaken though he was in advocating systemic ‘gemmules’ as agents of inheritance, Darwin was perceptive in seeking to underpin his core vision with concrete factors that both determine the nature of a trait in one generation and convey it to subsequent generations. This brief review evaluates the molecular genetic literature on earthworms published during the last decade, and casts light on the specific aspects of earthworm evolutionary biology that more or less engaged Darwin: (i) biogeography, (ii) species diversity, (iii) local adaptations and (iv) sensitivity. We predict that the current understanding will deepen with the announcement of a draft earthworm genome in Darwin's bicentenary year, 2009. Subsequently, the earthworm may be elevated from the status of a soil sentinel to that elusive entity, an ecologically relevant genetic model organism.
Major histocompatibility complex (MHC) heterozygote superiority to natural multi-parasite infections in the water vole (Arvicola terrestris)
Authors: Oliver M.K , Telfer S , Piertney S.B
Published: January 2009

The fundamental role of the major histocompatibility complex (MHC) in immune recognition has led to a general consensus that the characteristically high levels of functional polymorphism at MHC genes is maintained by balancing selection operating through host–parasite coevolution. However, the actual mechanism by which selection operates is unclear. Two hypotheses have been proposed: overdominance (or heterozygote superiority) and negative frequency-dependent selection. Evidence for these hypotheses was evaluated by examining MHC–parasite relationships in an island population of water voles (Arvicola terrestris). Generalized linear mixed models were used to examine whether individual variation at an MHC class II DRB locus explained variation in the individual burdens of five different parasites. MHC genotype explained a significant amount of variation in the burden of gamasid mites, fleas (Megabothris walkeri) and nymphs of sheep ticks (Ixodes ricinus). Additionally, MHC heterozygotes were simultaneously co-infected by fewer parasite types than homozygotes. In each case where an MHC-dependent effect on parasite burden was resolved, the heterozygote genotype was associated with fewer parasites, and the heterozygote outperformed each homozygote in two of three cases, suggesting an overall superiority against parasitism for MHC heterozygote genotypes. This is the first demonstration of MHC heterozygote superiority against multiple parasites in a natural population, a mechanism that could help maintain high levels of functional MHC genetic diversity in natural populations.
Voice pitch alters mate-choice-relevant perception in hunter–gatherers
Authors: Apicella Coren L , Feinberg David R
Published: January 2009

In humans, voice pitch is thought to be a cue of underlying quality and an important criterion for mate choice, but data from non-Western cultures have not been provided. Here we test attributions to and preferences for voices with raised and lowered pitch in hunter–gatherers. Using a forced-choice playback experiment, we found that both men and women viewed lower pitched voices in the opposite sex as being better at acquiring resources (e.g. hunting and gathering). While men preferred higher pitched women's voices as marriage partners, women showed no overall preference for voice pitch in men. However, women who were currently breastfeeding had stronger preferences for higher pitched male voices whereas women not currently breastfeeding preferred lower pitched voices. As testosterone is considered a costly signal associated with dominance, heritable immunity to infection and low paternal investment, women's preferences potentially reflect a trade-off between securing good genes and paternal investment. Men's preferences for higher pitched female voices are probably due to an evolved preference for markers of fecundity, reflected in voice pitch.
Extreme convergence in stick insect evolution: phylogenetic placement of the Lord Howe Island tree lobster
Authors: Buckley Thomas R , Attanayake Dilini , Bradler Sven
Published: January 2009

The ‘tree lobsters’ are an enigmatic group of robust, ground-dwelling stick insects (order Phasmatodea) from the subfamily Eurycanthinae, distributed in New Guinea, New Caledonia and associated islands. Its most famous member is the Lord Howe Island stick insect
Dryococelus australis
(Montrouzier), which was believed to have become extinct but was rediscovered in 2001 and is considered to be one of the rarest insects in the world. To resolve the evolutionary position of
Dryococelus
, we constructed a phylogeny from approximately 2.4 kb of mitochondrial and nuclear sequence data from representatives of all major phasmatodean lineages. Our data placed
Dryococelus
and the New Caledonian tree lobsters outside the New Guinean Eurycanthinae as members of an unrelated Australasian stick insect clade, the Lanceocercata. These results suggest a convergent origin of the ‘tree lobster’ body form. Our reanalysis of tree lobster characters provides additional support for our hypothesis of convergent evolution. We conclude that the phenotypic traits leading to the traditional classification are convergent adaptations to ground-living behaviour. Our molecular dating analyses indicate an ancient divergence (more than 22 Myr ago) between
Dryococelus
and its Australian relatives. Hence,
Dryococelus
represents a long-standing separate evolutionary lineage within the stick insects and must be regarded as a key taxon to protect with respect to phasmatodean diversity.
Individual experience and evolutionary history of predation affect expression of heritable variation in fish personality and morphology
Authors: Dingemanse Niels J , Van der Plas Fons , Wright Jonathan , Réale Denis , Schrama Maarten , Roff Derek A , Van der Zee Els , Barber Iain
Published: January 2009

Predation plays a central role in evolutionary processes, but little is known about how predators affect the expression of heritable variation, restricting our ability to predict evolutionary effects of predation. We reared families of three-spined sticklebackGasterosteus aculeatusfrom two populations—one with a history of fish predation (predator sympatric) and one without (predator naive)—and experimentally manipulated experience of predators during ontogeny. For a suite of ecologically relevant behavioural (‘personality’) and morphological traits, we then estimated two key variance components, additive genetic variance (VA) and residual variance (VR), that jointly shape narrow-sense heritability (h2=VA/(VA+VR)). Both population and treatment differentially affectedVAversusVR, henceh2, but only for certain traits. The predator-naive population generally had lowerVAandh2values than the predator-sympatric population for personality behaviours, but not morphological traits. Values ofVRandh2were increased for some, but decreased for other personality traits in the predator-exposed treatment. For some personality traits,VAandh2values were affected by treatment in the predator-naive population, but not in the predator-sympatric population, implying that the latter harboured less genetic variation for behavioural plasticity.

Replication and experimental manipulation of predation regime are now needed to confirm that these population differences were related to variation in predator-induced selection. Cross-environment genetic correlations (rA) were tight for most traits, suggesting that predator-induced selection can affect the evolution of the same trait expressed in the absence of predators. The treatment effects on variance components imply that predators can affect evolution, not only by acting directly as selective agents, but also by influencing the expression of heritable variation.
Distance from Africa, not climate, explains within-population phenotypic diversity in humans
Authors: Betti Lia , Balloux François , Amos William , Hanihara Tsunehiko , Manica Andrea
Published: January 2009

The relative importance of ancient demography and climate in determining worldwide patterns of human within-population phenotypic diversity is still open to debate. Several morphometric traits have been argued to be under selection by climatic factors, but it is unclear whether climate affects the global decline in morphological diversity with increasing geographical distance from sub-Saharan Africa. Using a large database of male and female skull measurements, we apply an explicit framework to quantify the relative role of climate and distance from Africa. We show that distance from sub-Saharan Africa is the sole determinant of human within-population phenotypic diversity, while climate plays no role. By selecting the most informative set of traits, it was possible to explain over half of the worldwide variation in phenotypic diversity. These results mirror those previously obtained for genetic markers and show that ‘bones and molecules’ are in perfect agreement for humans.
Honest sexual signalling mediated by parasite and testosterone effects on oxidative balance
Authors: Mougeot Francois , Martínez-Padilla Jesuús , Webster Lucy M.I , Blount Jonathan D , Pérez-Rodríguez Lorenzo , Piertney Stuart B
Published: January 2009

Extravagant ornaments evolved to advertise their bearers' quality, the honesty of the signal being ensured by the cost paid to produce or maintain it. The oxidation handicap hypothesis (OHH) proposes that a main cost of testosterone-dependent ornamentation is oxidative stress, a condition whereby the production of reactive oxygen and nitrogen species (ROS/RNS) overwhelms the capacity of antioxidant defences. ROS/RNS are unstable, very reactive by-products of normal metabolic processes that can cause extensive damage to key biomolecules (cellular proteins, lipids and DNA). Oxidative stress has been implicated in the aetiology of many diseases and could link ornamentation and genetic variation in fitness-related traits. We tested the OHH in a free-living bird, the red grouse. We show that elevated testosterone enhanced ornamentation and increased circulating antioxidant levels, but caused oxidative damage. Males with smaller ornaments suffered more oxidative damage than those with larger ornaments when forced to increase testosterone levels, consistent with a handicap mechanism. Parasites depleted antioxidant defences, caused oxidative damage and reduced ornament expression. Oxidative damage extent and the ability of males to increase antioxidant defences also explained the impacts of testosterone and parasites on ornamentation within treatment groups. Because oxidative stress is intimately linked to immune function, parasite resistance and fitness, it provides a reliable currency in the trade-off between individual health and ornamentation. The costs induced by oxidative stress can apply to a wide range of signals, which are testosterone-dependent or coloured by pigments with antioxidant properties.
Food-density-dependent inefficiency in animals with a gut as a stabilizing mechanism in trophic dynamics
Authors: Flynn Kevin J
Published: January 2009

Animals with a gut, when confronted with food supplied ad libitum, can elevate their ingestion rates and inefficiently use the material they ingest. As a consequence, assimilation efficiency (AE) declines, resulting in food-density-dependent inefficiency (f-DDI). A model describing these processes shows that f-DDI can dampen the consequences of oscillations in food abundance that may occur in response to external stochastic (e.g. climatic) forcing both with respect to production and timing. This response is illustrated with a simple planktonic food chain of a phytoplankter and two consumers. The assumption of a fixed gut transit time, consistent with the traditional model descriptions of a fixed AE, produces predator–prey oscillations. By contrast, simulations using a model showing f-DDI (behaving in accordance with the experimental data) cushion not only the impact of such oscillations but also the effects of the removal of intermediate grazers in the food chain. The operation of f-DDI affects other trophic interactions through changes in the nutrient regeneration and the voiding rates. The extent to which f-DDI operates in nature needs valuation, followed by the appropriate construction of consumer-based ecosystem models.
Why are (the best) women so good at chess? Participation rates and gender differences in intellectual domains
Authors: Bilalić Merim , Smallbone Kieran , McLeod Peter , Gobet Fernand
Published: January 2009

A popular explanation for the small number of women at the top level of intellectually demanding activities from chess to science appeals to biological differences in the intellectual abilities of men and women. An alternative explanation is that the extreme values in a large sample are likely to be greater than those in a small one. Although the performance of the 100 best German male chess players is better than that of the 100 best German women, we show that 96 per cent of the observed difference would be expected given the much greater number of men who play chess. There is little left for biological or cultural explanations to account for. In science, where there are many more male than female participants, this statistical sampling explanation, rather than differences in intellectual ability, may also be the main reason why women are under-represented at the top end.
Cnidarian internal stinging mechanism
Authors: Schlesinger Ami , Zlotkin Eliahu , Kramarsky-Winter Esti , Loya Y
Published: January 2009

Stinging mechanisms generally deliver venomous compounds to external targets. However, nematocysts, the microscopic stinging organelles that are common to all members of the phylum Cnidaria, occur and act in both external and internal tissue structures. This is the first report of such an internal piercing mechanism. This mechanism identifies prey items within the body cavity of the sea anemone and actively injects them with cytolytic venom compounds. Internal tissues isolated from sea anemones caused the degradation of live
Artemia salina
nauplii
in vitro
. When examined, the nauplii were found to be pierced by discharged nematocysts. This phenomenon is suggested to aid digestive phagocytic processes in a predator otherwise lacking the means to masticate its prey.
When does optional participation allow the evolution of cooperation?
Authors: Mathew Sarah , Boyd Robert
Published: January 2009

Altruistic punishment has been shown to invade when rare if individuals are allowed to opt out of cooperative ventures. Individuals that opt out do not contribute to the common enterprise or derive benefits from it. This result is potentially significant because it offers an explanation for the origin of large-scale cooperation in one-shot interactions among unrelated individuals. Here, we show that this result is not a general consequence of optional participation in cooperative activities, but depends on special assumptions about cooperative pay-offs. We extend the pay-off structure of optional participation models to consider the effects of economies and diseconomies of scale in public-goods production, rival and non-rival consumption of goods, and different orderings of the pay-offs of freeriding and opting out. This more general model highlights the kinds of pay-offs for which optional participation favours cooperation, and those in which it does not.
Sperm morphology and sperm velocity in passerine birds
Authors: Lüpold Stefan , Calhim Sara , Immler Simone , Birkhead Tim R
Published: January 2009

Sperm velocity is one of the main determinants of the outcome of sperm competition. Since sperm vary considerably in their morphology between and within species, it seems likely that sperm morphology is associated with sperm velocity. Theory predicts that sperm velocity may be increased by enlarged midpiece (energetic component) or flagellum length (kinetic component), or by particular ratios between sperm components, such as between flagellum length and head size. However, such associations have rarely been found in empirical studies. In a comparative framework in passerine birds, we tested these theoretical predictions both across a wide range of species and within a single family, the New World blackbirds (Icteridae). In both study groups, sperm velocity was influenced by sperm morphology in the predicted direction. Consistent with theoretical models, these results show that selection on sperm morphology and velocity are likely to be concomitant evolutionary forces.
Calling in the gap: competition or cooperation in littermates' begging behaviour?
Authors: Madden Joah R , Kunc Hansjoerg P , English Sinead , Manser Marta B , Clutton-Brock Tim H
Published: January 2009

Offspring are frequently raised alongside their siblings and are provisioned early in life by adults. Adult provisioning is stimulated by offspring begging, but it is unclear how each offspring should beg, given the begging behaviour of their siblings. It has previously been suggested that siblings may compete directly through begging for a fixed level of provisioning, or that siblings may cooperate in their begging in order to jointly elevate the level of provisioning by adults. We studied the begging behaviour of meerkat
Suricata suricatta
pups, explored how it changed as the begging behaviour of their littermates altered, and asked how the adults responded to group-level changes in begging. We found conflicting evidence for classic models of competitive and cooperative begging. Pups reared in larger litters begged at higher rates, yet experimentally increasing begging levels within groups caused individual begging rates to decrease. Pups decreased begging rates when close to other begging pups, and pups spaced further apart were fed more. Adults increased their overall level of provisioning as group levels of begging increased, but per capita provisioning decreased. Adults preferred to provision speakers playing back recordings of two pups begging alternately to recordings of the same two pups begging simultaneously. Therefore, we suggest that meerkat pups avoid some of the costs of direct competition imposed by an escalation of begging as other pups beg, by begging in gaps between the bouts of others or avoiding littermates. Such behaviour is also preferred by provisioning adults, thus providing additional benefits to the pups.
Contact heterogeneity in deer mice: implications for Sin Nombre virus transmission
Authors: Clay Christine A , Lehmer Erin M , Previtali Andrea , St. Jeor Stephen , Dearing M. Denise
Published: January 2009

Heterogeneities within disease hosts suggest that not all individuals have the same probability of transmitting disease or becoming infected. This heterogeneity is thought to be due to dissimilarity in susceptibility and exposure among hosts. As such, it has been proposed that many host–pathogen systems follow the general pattern whereby a small fraction of the population accounts for a large fraction of the pathogen transmission. This disparity in transmission dynamics is often referred to as ‘20/80 Rule’, i.e. approximately 20 per cent of the hosts are responsible for 80 per cent of pathogen transmission. We investigated the role of heterogeneity in contact rates among potential hosts of a directly transmitted pathogen by examining Sin Nombre virus (SNV) in deer mice (
Peromyscus maniculatus
). Using foraging arenas and powder marking, we documented contacts between wild deer mice in Great Basin Desert, central Utah. Our findings demonstrated heterogeneity among deer mice, both in frequency and in duration of contacts with other deer mice. Contact dynamics appear to follow the general pattern that a minority of the population accounts for a majority of the contacts. We found that 20 per cent of individuals in the population were responsible for roughly 80 per cent of the contacts observed. Larger-bodied individuals appear to be the functional group with the greatest SNV transmission potential. Contrary to our predictions, transmission potential was not influenced by breeding condition or sex.
Fatigue altersin vivofunction within and between limb muscles during locomotion
Authors: Higham Timothy E , Biewener Andrew A
Published: January 2009

Muscle fatigue, a reduction in force as a consequence of exercise, is an important factor for any animal that moves, and can result from both peripheral and/or central mechanisms. Although much is known about whole-limb force generation and activation patterns in fatigued muscles under sustained isometric contractions, little is known about thein vivodynamics of limb muscle function in relation to whole-body fatigue. Here we show that limb kinematics and contractile function in the lateral (LG) and medial (MG) gastrocnemius of helmeted guineafowl (Numida meleagris) are significantly altered following fatiguing exercise at 2 m s−1on an inclined treadmill. The two most significant findings were that the variation in muscle force generation, measured directly from the muscles' tendons, increased significantly with fatigue, and fascicle shortening in the proximal MG, but not the distal MG, decreased significantly with fatigue. We suggest that the former is a potential mechanism for decreased stability associated with fatigue. The region-specific alteration of fascicle behaviour within the MG as a result of fatigue suggests a complex response to fatigue that probably depends on muscle–aponeurosis and tendon architecture not previously explored. These findings highlight the importance of studying the integrativein vivodynamics of muscle function in response to fatigue.
Cell-type selective chromatin remodeling defines the active subset of FOXA1-bound enhancers
Authors: Eeckhoute Jérôme , Lupien Mathieu , Meyer Clifford A. , Verzi Michael P. , Shivdasani Ramesh A. , Liu X. Shirley , Brown Myles
Published: January 2009

Selective activity of a specific set of enhancers defines tissue-specific gene transcription. The pioneer factor FOXA1 has been shown to induce functional enhancer competency through chromatin openings. We have previously found that FOXA1 is recruited to thousands of regions across the genome of a given cell type. Here, we monitored the chromatin structure at FOXA1 binding sites on a chromosome-wide scale using formaldehyde assisted isolation of regulatory elements (FAIRE). Surprisingly, we find that a significant fraction of FOXA1-bound sites have a relatively closed chromatin conformation linked to a shift of the epigenetic signature toward repressive histone marks. Importantly, these sites are not correlated with gene expression in a given cell type suggesting that FOXA1 is required, but not sufficient, for the functional activity of bound enhancers. Interestingly, we find that a significant proportion of the inactive FOXA1-bound regulatory sites in one cell type are actually functional in another cellular context. We found that at least half of the FOXA1 binding sites from a given cell type are shared with another cell lineage. Mechanisms that restrict the activity of shared FOXA1-bound enhancers likely play a significant role in defining the cell-type-specific functions of FOXA1.
Constitutive Repression and Activation of Auxin Signaling in Arabidopsis
Authors: Li Hanbing , Cheng Yan , Murphy Angus , Hagen Gretchen , Guilfoyle Tom J.
Published: January 2009

Aux/IAA proteins are proposed to be transcriptional repressors that play a crucial role in auxin signaling by interacting with auxin response factors and repressing early/primary auxin response gene expression. In assays with transfected protoplasts, this repression was previously shown to occur when auxin concentrations in a cell are low, and derepression/activation was observed when auxin concentrations are elevated. Here we show that a stabilized version of the Arabidopsis (Arabidopsis thaliana) IAA17 repressor, when expressed constitutively or in a specific cell type in Arabidopsis plants, confers phenotypes similar to plants with decreased auxin levels. In contrast, a stabilized version of IAA17 that was converted to a transcriptional activator confers phenotypes similar to plants with increased auxin levels, when expressed under the same conditions in Arabidopsis plants. Free auxin levels were unchanged compared to control (DR5:β-glucuronidase), however, in the seedlings expressing the IAA17 repressor and activator. These results together with our previous results carried out in transfected protoplasts suggest that the hormone auxin can be bypassed to regulate auxin signaling in a cell-autonomous manner in plants.
Synthesis and physical properties of ferrocene derivatives. XXI. Crystal structure of a liquid crystalline ferrocene derivative, 1,1'-bis[3-[4-(4-methoxyphenoxycarbonyl)phenoxy]propyloxycarbonyl]ferrocene
Authors: Okabe Takashi , Nakazaki Keisuke , Igaue Tsuyoshi , Nakamura Naotake , Donnio Bertrand , Guillon Daniel , Gallani Jean-Louis
Published: January 2009

The crystal structure of the title 1,1′-disubstituted ferrocene derivative was determined by X-ray diffraction using a single crystal. This compound exhibits a nematic phase only. The X-ray structure analysis revealed that the two substituents lie in the same direction (`U' shape) and the flexible spacer adopts agaucheconformation. These conformations are strongly related to the formation of a rod-like shape, which favors liquid crystalline behavior. In the crystal structure, C—H...π, π–π and T-stacking interactions were observed. It is considered that these interactions play a major role in stabilizing the molecular packing arrangement and the mesomorphism.
Indexation and misorientation analysis of low-quality Laue diffraction patterns
Authors: Gupta Vipul K. , Agnew Sean R.
Published: January 2009

A Laue X-ray diffraction pattern indexing scheme, similar to a method previously proposed for convergent beam and backscattered electron diffraction patterns, was implemented. Experimental diffraction patterns are compared with simulated templates corresponding to crystals of prescribed orientations. The orientation of a diffracting volume is determined by maximizing a normalized cross correlation index between experimental and theoretical patterns. The advantages of template matching include (i) elimination of the requirement for extensive peak search/fitting analysis; (ii) the ability to index overlapped diffraction patterns obtained from neighboring grains or second phase particles; and (iii) the ability to confidently index patterns of low quality. A best fit orientation can then be determined by a least-squares fitting approach based on singular value decomposition. The misorientation within a diffracting volume is calculated from `smeared' and/or `split' Laue patterns. The methodologies developed are illustrated using micro-Laue diffraction data obtained from the wake of a fatigue crack.
Hydrothermal Synthesis of Nanosized Titania Powders: Influence of Peptization and Peptizing Agents on the Crystalline Phases and Phase Transitions
Authors: Yang Juan , Mei Sen , Ferreira José M. F.
Published: January 2009

Nanocrystalline TiO2 particles were prepared by hydrothermally treating three different titanium alkoxide species, which were derived from (i) the hydrolysis of Ti(OPr)4 and Ti(OBu)4 (PT and BT, respectively) in the presence of HNO3, tetraethylammonium hydroxide (TENOH), or NH3·H2O; (ii) water‐washed precipitates; or (iii) sols that were obtained from the precipitates by peptizing with HNO3 or TENOH. X‐ray diffractometry, Brunauer–Emmitt–Teller (BET) surface area analysis, differential thermal analysis, Fourier transform infrared spectroscopy, and scanning electron microscopy were used to characterize the powders. The results showed that peptization of the precipitate favored formation of the rutile phase and highly crystalline anatase under hydrothermal treatment. Particles of 100% rutile phase with high specific surface areas were obtained at a relatively low temperatures: room temperature, for HNO3‐peptized ([H+]/[Ti] = 4) PT sample (BET surface area of 96 m2/g); 200°C, for the HNO3‐peptized ([H+]/[Ti] = 1) PT sample (BET surface area of 49 m2/g); and 240°C for the HNO3‐peptized ([H+]/[Ti] = 1) BT sample (BET surface area of 42 m2/g). Particles that contained highly crystalline anatase, together with a small portion of rutile, were formed in both TENOH‐peptized samples. However, rutile was difficult to form, both in the water‐washed precipitates and in the species that was hydrolyzed in the presence of HNO3, TENOH, and NH3·H2O. The peptization effect of the H+ ion mainly lies in the breakage of oxolation by attacking the electrophilic O atoms among Ti atoms, thus creating conditions for the formation of rutile or anatase nuclei, after structural rearrangement.
Formation Mechanism of Hydrous‐Zirconia Particles Produced by Hydrolysis of ZrOCl2 Solutions: II
Authors: Matsui Koji , Ohgai Michiharu
Published: January 2009

The primary and secondary particle sizes of monoclinic hydrous‐ZrO2 particles produced by the hydrolysis of various ZrOCl2 solutions, with and without the addition of NaCl, CaCl2, or AlCl3, were measured using X‐ray diffraction and transmission electron microscopy in order to clarify the formation mechanisms of primary and secondary particles. The primary particle size of hydrous ZrO2, under a constant ZrOCl2 concentration, decreased monotonously with increasing Cl−‐ion concentration. On the contrary, the secondary particle size increased monotonously with increasing Cl−‐ion concentration. The present experimental results revealed that the primary and secondary particle sizes of hydrous ZrO2 are controlled primarily by the concentrations of H+ and Cl− ions produced during hydrolysis, and are independent of the type of added metal ions. The formation mechanisms of the primary and secondary particles of hydrous ZrO2 were determined on the basis of the present experimental results.
Effects of Calcination Temperature and A/B Ratio on the Dielectric Properties of (Ba,Ca)(Ti,Zr,Mn)O3 for Multilayer Ceramic Capacitors with Nickel Electrodes
Authors: Lee Wen‐Hsi , Tseng T. Y. , Hennings Detlev F. K.
Published: January 2009

The electrical performance of multilayer ceramic capacitors (MLCCs) with Ni inner electrodes, made from (Ba,Ca)(Ti,Zr,Mn)O3 (BCTZM), is closely related to the calcination temperature and the A/B ratio of the powder. For materials showing A/B = 1.000, the lifetime, the breakdown voltage, and the RC increase with higher calcination temperatures. No significant effect of the calcination temperature on RC and lifetime was found for materials showing A/B = 0.991. The isoelectric point of BCTZM is shifted toward higher pH values when the calcination temperature is decreased. The above results are attributed to the colloidal stability of aqueous BCTZM suspensions and the resulting green density of powder compacts.
Lead Zirconate Titanate Particle Dispersion in Thick‐Film Ink Formulations
Authors: Thiele Erik S. , Setter Nava
Published: January 2009

Diverse device applications for lead zirconate titanate (PZT) ceramics in thick‐film form are currently in active development. In the present study, the particle dispersion properties of thick‐film ink formulations containing PZT powder have been determined using rheological measurements. Although all of the eight commercially available dispersants tested are more effective than the terpineol solvent alone in decreasing attractive interparticle forces in suspensions, the best dispersant identified for hard and soft PZT powders is a phosphate ester oligomer. This dispersant is extremely efficient, and its use in thick‐film ink formulations results in viscosity decreases of 50% at low shear rates (10 s−1) and 30% at high shear rates (100 s−1) compared with current ink formulations containing no dispersant. The effects upon rheology of the order of addition of components in the processing of inks have been studied, with the most effective processing route using a fugitive solvent that probably facilitates uniform coverage of the particle surfaces by the dispersant molecules. Modeling of the rheological profiles of inks indicates that the use of a dispersant decreases the depth of the primary minimum in the interparticle potential by a factor of 3. Demonstrated advantages of the use of a dispersant in PZT thick‐film inks include improved microstructural homogeneity in the green body and the ability to formulate printable inks with higher solids loadings. No adverse effects of the dispersant upon the dielectric and piezoelectric properties of bulk PZT samples are found following burnout and sintering.
High‐Voltage Screening of Unidirectionally Surface‐Ground Titania Ceramics
Authors: Kishimoto Akira , Tanaka Tomohiro
Published: January 2009

The effects of high‐voltage screening were examined for perpendicularly and parallelly surface‐ground titania rectangular bars. A screening field at or below which 30% of titania samples break electrically was applied to each group samples. After high‐voltage screening, the surviving samples were subjected to mechanical strength measurement and the resultant strength distribution was compared with the original distribution. After screening, Weibull plots of perpendicularly ground samples bent to become convex curves while plots in the high‐strength region remained almost the same, indicating that low‐strength samples were selectively eliminated by the high‐voltage screening. On the other hand, the screening effect on parallelly surface‐ground samples was very small.
Intermediate‐Temperature Stress Rupture of a Woven Hi‐Nicalon, BN‐Interphase, SiC‐Matrix Composite in Air
Authors: Morscher Gregory N. , Hurst Janet , Brewer David
Published: January 2009

Woven Hi‐Nicalon™‐reinforced melt‐infiltrated SiC‐matrix composites were tested under tensile stress‐rupture conditions in air at intermediate temperatures. A comprehensive examination of the damage state and the fiber properties at failure was performed. Modal acoustic emission analysis was used to monitor damage during the experiment. Extensive microscopy of the composite fracture surfaces and the individual fiber fracture surfaces was used to determine the mechanisms leading to ultimate failure. The rupture properties of these composites were significantly worse than expected compared with the fiber properties under similar conditions. This was due to the oxidation of the BN interphase. Oxidation occurred through the matrix cracks that intersected the surface or edge of a tensile bar. These oxidation reactions resulted in strong bonding of the fibers to one another at regions of near fiber‐to‐fiber contact. It was found that two regimes for rupture exist for this material: a high‐stress regime where rupture occurs at a fast rate and a low‐stress regime where rupture occurs at a slower rate. For the high‐stress regime, the matrix damage state consisted of through‐thickness cracks. The average fracture strength of fibers that were pulled out (the final fibers to break before ultimate failure) was controlled by the slow‐crack‐growth rupture criterion in the literature for individual Hi‐Nicalon fibers. For the low‐stress regime, the matrix damage state consisted of microcracks which grew during the rupture test. The average fracture strength of fibers that were pulled out in this regime was the same as the average fracture strength of individual fibers pulled out in as‐produced composites tested at room temperature.
Energy Conversion during Microwave Sintering of a Multiphase Ceramic Surrounded by a Susceptor
Authors: Lasri Jacob , Ramesh Peelamedu D. , Schächter Levi
Published: January 2009

A quasi‐analytic model has been developed to examine energy conversion during the microwave sintering of a ceramic that is surrounded by a susceptor. Low‐loss ceramics, such as ZrO2, couple poorly with microwave radiation at low temperatures; however, because the dielectric loss usually increases rapidly as temperature increases, coupling improves dramatically at high temperatures. To improve heat transfer at low temperatures, susceptors are used. Three processes of energy flow are considered: microwave absorption due to dielectric losses, blackbody radiation, and heat convection. As expected, the susceptor (SiC) heats rapidly, relative to the ceramic (ZrO2), at low temperatures; however, the ceramic attains higher temperatures after a prolonged period of microwave exposure. Below a critical temperature (800°C), the primary heat‐transfer mechanism to the ZrO2 is blackbody radiation from the susceptor. Above this temperature, microwave radiation is the main source that contributes to the temperature increase of the ceramic. The results of the simulation are in reasonable agreement with recent experimental data.
Stabilization and Memory of the Domain Structures in Barium Titanate Ceramics: Microstructural Observation
Authors: Kim Sang‐Beom , Kim Doh‐Yeon
Published: January 2009

From microstructural observations, we have shown that the domain structures of BaTiO3 ceramics are stabilized by aging. Once stabilized, the original domain structures reappear even when the stress conditions during phase transformation are changed. The pinning of the domain band walls as a result of a space charge is suggested to cause the stabilization of domain structures.
Environmental Scanning Electron Microscopy (ESEM) Investigation of the Reaction Mechanism in Praseodymium‐Doped Zircon
Authors: Bondioli Federica , Corradi Anna Bonamartini , Ferrari Anna Maria , Manfredini Tiziano , Baldi Giovanni
Published: January 2009

The formation mechanism of praseodymium‐doped zircon stain was studied, using environment scanning electron microscopy (ESEM) primarily. The significance of ESEM as a processing tool for studying chemical and morphologic dynamic changes under controlled temperature conditions was evaluated, with respect to the traditional investigation methods.
Porous Titania Ceramic Prepared by Mimicking Silicified Wood
Authors: Ota Toshitaka , Imaeda Masaki , Takase Haruyuki , Kobayashi Mikihiro , Kinoshita Noboru , Hirashita Tunehisa , Miyazaki Hidetoshi , Hikichi Yasuo
Published: January 2009

A porous titania ceramic with a woodlike microstructure that was analogous to silicified wood was prepared. The production of “titanified wood” was performed using the following process: (i) introduction of titanium tetraisopropoxide into wood materials via vacuum infiltration, (ii) hydrolysis of the titanium tetraisopropoxide in the cell structure to form a titania gel, and (iii) firing at a temperature of 600°–1400°C in air. The resulting titania ceramic had the same external and internal forms of the original wood.
Al2O3/TiC Based Metal Cutting Tools by Microwave Sintering Followed by Hot Isostatic Pressing
Authors: Goldstein Adrian , Singurindi Ania
Published: January 2009

The feasibility of producing Al2O3/TiC metal cutting tools by fast microwave sintering followed by hot isostatic pressing was examined. Microwave heating profiles able to ensure near‐full densification of Al2O3/TiC ceramic components were determined. Simple‐shape specimens could be sintered to a bulk density of 97% theoretical density (TD) while in the case of tool‐shaped ones maximal densification levels attained were somewhat lower, i.e., ∼95% TD. Temperature uniformization—within the heating chamber—by using a particulate SiC susceptor noticeably reduced tool cracking propensity. Densification levels in the range acceptable for commercial tool manufacturing (≥98% TD) were achieved by hot isostatic pressing of the microwave‐sintered parts. The isostatically pressed parts exhibited a Vickers hardness Hv≅ 2000 kg/mm2 and a fracture toughness KIC∼ 4.3 MPa·m1/2.
Cardanol: A New Dispersant for Alumina in Toluene
Authors: Prabhakaran Kuttan , Pavithran Chorappan
Published: January 2009

Cardanol, which is a naturally occurring C15 unsaturated aliphatic chain‐substituted phenol derived from cashew nut shell liquid, was used as a dispersant for alumina in toluene. Adsorption data, along with the results of sedimentation studies, green density, and slurry viscosity (as a function of dispersant concentration), suggest that cardanol adsorption initially proceeded through surface coverage by a phenolic group that lies flat on the surface and that the best powder dispersion occurred at surface saturation by more closely packed end‐on adsorbed cardanol molecules. The alkyl‐chain unsaturation significantly contributed to dispersion, such that the saturation by hydrogenation led to an increase in the slurry viscosity by a factor of ∼2.5. Concentrated slurries generally showed shear‐thinning flow behavior, and the measured viscosity of a highly concentrated (53 vol%) slurry was <1 Pa·s at a shear rate of 93 s−1.
Direct Amorphous‐to‐Cubic Perovskite Phase Transformation for Lead Titanate
Authors: Leite E. R. , Paris E. C. , Longo E. , Varela J. A
Published: January 2009

The phase evolution of lead titanate processed by the polymeric precursor method was investigated by thermal analysis, X‐ray diffraction, and high‐resolution transmission electron microscopy. The results showed that the cubic perovskite PbTiO3 (PT) phase is formed from an inorganic amorphous precursor at a temperature of 444°C. A gradual transition from cubic to tetragonal perovskite PT was observed with the increase of calcination time at this temperature. HRTEM results showed that the cubic PT particles have a size of around 5 nm. The identification of cubic PT as an intermediate phase supports the hypothesis that the chemical homogeneity was kept at the molecular level during the synthesis process, with no cation segregation.
Role of Microstructure in Dynamic Fatigue of Glass‐Ceramics after Contact with Spheres
Authors: Yeo Jeong‐Gu , Lee Kee Sung , Lawn Brian R.
Published: January 2009

Dynamic fatigue data are reported for fine‐ and coarse‐grained micaceous glass‐ceramics after contact damage with spheres. The strengths of indented specimens are measured at stressing rates from ∼10−2 to 104 MPa·s−1 in water. The strength degradation is substantially faster in the coarse‐grained structure, and is accelerated further by multicycle contact loading. Failures originate from contact sites in all cases but undergo a progressive transition from classical cone cracks to quasi‐plastic microcrack zones with increases in the grain size and the number of contact cycles. The results highlight the particularly deleterious effect of quasi‐plastic damage accumulation on lifetime.