bluuebunny/crossref_metadata_2025 huggingface dataset:
The Notch ligand Delta-like 4 negatively regulates endothelial tip cell formation and vessel branching
Authors: Suchting Steven , Freitas Catarina , le Noble Ferdinand , Benedito Rui , Bréant Christiane , Duarte Antonio , Eichmann Anne
Published: February 2007

Delta-like 4 (Dll4) is a transmembrane ligand for Notch receptors that is expressed in arterial blood vessels and sprouting endothelial cells. Here we show that Dll4 regulates vessel branching during development by inhibiting endothelial tip cell formation. Heterozygous deletion of
dll4
or pharmacological inhibition of Notch signaling using γ-secretase inhibitor revealed a striking vascular phenotype, with greatly increased numbers of filopodia-extending endothelial tip cells and increased expression of tip cell marker genes compared with controls. Filopodia extension in
dll4
+/−
retinal vessels required the vascular growth factor VEGF and was inhibited when VEGF signaling was blocked. Although VEGF expression was not significantly altered in
dll4
+/−
retinas,
dll4
+/−
vessels showed increased expression of VEGF receptor 2 and decreased expression of VEGF receptor 1 compared with wild-type, suggesting they could be more responsive to VEGF stimulation. In addition, expression of
dll4
in wild-type tip cells was itself decreased when VEGF signaling was blocked, indicating that
dll4
may act downstream of VEGF as a “brake” on VEGF-mediated angiogenic sprouting. Taken together, these data reveal Dll4 as a negative regulator of vascular sprouting and vessel branching that is required for normal vascular network formation during development.
Spatial memory and the human hippocampus
Authors: Shrager Yael , Bayley Peter J. , Bontempi Bruno , Hopkins Ramona O. , Squire Larry R.
Published: February 2007

The hippocampus and adjacent medial temporal lobe structures are known to support declarative memory, but there is not consensus about what memory functions the hippocampus might support that are distinct from the functions of the adjacent cortex. One idea is that the hippocampus is specifically important for allocentric spatial memory, e.g., the hippocampus is especially needed to remember object locations when there is a shift in viewpoint between study and test. We tested this proposal in two experiments. Patients with damage limited to the hippocampus were given memory tests for object locations in a virtual environment. In the first experiment, participants studied locations of a variable number of images (one to five) and tried to remember the image locations from either the same viewpoint as during study (shift of 0°) or a different viewpoint (shift of 55°, 85°, or 140°). In each viewpoint condition (shifts of 0°, 55°, 85°, and 140°), patients performed normally when remembering one or two image locations. Further, performance declined to a similar degree in each viewpoint condition as patients tried to remember increasing numbers of image locations. In the second experiment, participants tried to remember four images after viewpoint shifts of 0°, 55°, 85°, or 140°. Patients were mildly impaired at all conditions (shifts of 0°, 55°, 85°, and 140°), and the impairment was no greater when viewpoint shifted. We conclude that damage to the hippocampus does not selectively impair viewpoint-independent spatial memory. Rather, hippocampal damage impairs memory as the memory load increases.
The catalytic subunit of DNA–protein kinase (DNA-PKcs) is not required for Ig class-switch recombination
Authors: Kiefer Kerstin , Oshinsky Jennifer , Kim Jiyoon , Nakajima Pamela B. , Bosma Gayle C. , Bosma Melvin J.
Published: February 2007

The joining of DNA ends during Ig class-switch recombination (CSR) is thought to involve the same nonhomologous end-joining pathway as used in V(D)J recombination. However, we reported earlier that CSR can readily occur in Ig transgenic SCID mice lacking DNA-dependent protein kinase (DNA-PK) activity, a critical enzymatic activity for V(D)J recombination. We were thus led to question whether the catalytic subunit of DNA-PK (DNA-PKcs) is essential for CSR. To address this issue, we asked whether class switching to different Ig isotypes could occur in a line of Ig transgenic mice lacking detectable DNA-PKcs protein. The answer was affirmative. We conclude that joining of DNA ends during CSR does not require DNA-PKcs and can occur by an alternative repair pathway to that used for V(D)J recombination.
An obligatory requirement for the heterotrimeric G protein G
i3
in the antiautophagic action of insulin in the liver
Authors: Gohla Antje , Klement Karinna , Piekorz Roland P. , Pexa Katja , vom Dahl Stephan , Spicher Karsten , Dreval Vladyslav , Häussinger Dieter , Birnbaumer Lutz , Nürnberg Bernd
Published: February 2007

Heterotrimeric G proteins of the G
i
class have been implicated in signaling pathways regulating growth and metabolism under physiological and pathophysiological conditions. Knockout mice carrying inactivating mutations in both of the widely expressed Gα
i
class genes, Gα
i2
and Gα
i3
, demonstrate shared as well as gene-specific functions. The presence of a single active allele of Gα
i3
is sufficient for embryonic development, whereas at least one allele of Gα
i2
is required for extrauterine life. Mice lacking both Gα
i2
and Gα
i3
are massively growth-retarded and die
in utero
. We have used biochemical and cell biological methods together with
in situ
liver perfusion experiments to study Gα
i
isoform-specific functions in Gα
i2
- and Gα
i3
-deficient mice. The subcellular localization of Gα
i3
in isolated mouse hepatocytes depends on the cellular metabolic status. Gα
i3
localizes to autophagosomes upon starvation-induced autophagy and distributes to the plasma membrane upon insulin stimulation. Analysis of autophagic proteolysis in perfused mouse livers showed that mice lacking Gα
i3
are deficient in the inhibitory action of insulin. These data indicate that Gα
i3
is crucial for the antiautophagic action of insulin and suggest an as-yet-unrecognized function for Gα
i3
on autophagosomal membranes.
Expression of the transcription factor cKrox in peripheral CD8 T cells reveals substantial postthymic plasticity in CD4-CD8 lineage differentiation
Authors: Jenkinson S. Rhiannon , Intlekofer Andrew M. , Sun Guangping , Feigenbaum Lionel , Reiner Steven L. , Bosselut Rémy
Published: February 2007

Most T cells belong to either of two lineages defined by the mutually exclusive expression of CD4 and CD8 coreceptors: CD4 T cells are major histocompatibility complex (MHC) II restricted and have helper function, whereas CD8 T cells are MHC I restricted and have cytotoxic function. The divergence between these two lineages occurs during intrathymic selection and is thought to be irreversible in mature T cells. It is, however, unclear whether the CD4-CD8 differentiation of postthymic T cells retains some level of plasticity or is stably maintained by mechanisms distinct from those that set lineage choice in the thymus. To address this issue, we examined if coreceptor or effector gene expression in mature CD8 T cells remains sensitive to the zinc finger transcription factor cKrox, which promotes CD4 and inhibits CD8 differentiation when expressed in thymocytes. We show that cKrox transduction into CD8 T cells inhibits their expression of CD8 and cytotoxic effector genes and impairs their cytotoxic activity, and that it promotes expression of helper-specific genes, although not of CD4 itself. These observations reveal a persistent degree of plasticity in CD4-CD8 differentiation in mature T cells.
Corelease and Differential Exit via the Fusion Pore of GABA, Serotonin, and ATP from LDCV in Rat Pancreatic β Cells
Authors: Braun Matthias , Wendt Anna , Karanauskaite Jovita , Galvanovskis Juris , Clark Anne , MacDonald Patrick E. , Rorsman Patrik
Published: February 2007

The release of γ-aminobutyric acid (GABA) and ATP from rat β cells was monitored using an electrophysiological assay based on overexpression GABAA or P2X2 receptor ion channels. Exocytosis of LDCVs, detected by carbon fiber amperometry of serotonin, correlated strongly (∼80%) with ATP release. The increase in membrane capacitance per ATP release event was 3.4 fF, close to the expected capacitance of an individual LDCV with a diameter of 0.3 μm. ATP and GABA were coreleased with serotonin with the same probability. Immunogold electron microscopy revealed that ∼15% of the LDCVs contain GABA. Prespike “pedestals,” reflecting exit of granule constituents via the fusion pore, were less frequently observed for ATP than for serotonin or GABA and the relative amplitude (amplitude of foot compared to spike) was smaller: in some cases the ATP-dependent pedestal was missing entirely. An inward tonic current, not dependent on glucose and inhibited by the GABAA receptor antagonist SR95531, was observed in β cells in clusters of islet cells. Noise analysis indicated that it was due to the activity of individual channels with a conductance of 30 pS, the same as expected for individual GABAA Cl− channels with the ionic gradients used. We conclude that (a) LDCVs accumulate ATP and serotonin; (b) regulated release of GABA can be accounted for by exocytosis of a subset of insulin-containing LDCVs; (c) the fusion pore of LDCVs exhibits selectivity and compounds are differentially released depending on their chemical properties (including size); and (d) a glucose-independent nonvesicular form of GABA release exists in β cells.
Early learning influences species assortative mating preferences in Lake Victoria cichlid fish
Authors: Verzijden Machteld N , ten Cate Carel
Published: February 2007

The Lake Victoria ‘species flock’ of cichlids is puzzling because reproductive isolation often occurs in the absence of substantial ecological differences among species. Theory predicts that this cannot evolve with most genetic mechanisms for mate choice. We provide the first evidence that learning, in the form of sexual imprinting, helps maintain reproductive isolation among closely related cichlid species. Using a cross-fostering experiment, we show that young females develop a sexual preference for males of their foster mothers' species, even reversing species assortative mating preferences. We suggest that learning creates favourable conditions for reproductive isolation to evolve.
Social common mole-rats enhance outbreeding via extra-pair mating
Authors: Bishop Jacqueline M , O'Ryan Colleen , Jarvis Jennifer U.M
Published: February 2007

Females in many species engage in matings with males that are not their social mates. These matings are predicted to increase offspring heterozygosity and fitness, and thereby prevent the deleterious effects of inbreeding. We tested this hypothesis in a cooperative breeding mammal, the common mole-rat
Cryptomys hottentotus hottentotus
. Laboratory-based studies suggested a system of strict social monogamy, while recent molecular studies indicate extensive extra-pair paternity despite colonies being founded by an outbred pair. Our data show that extra-pair and within-colony breeding males differed significantly in relatedness to breeding females, suggesting that females may gain genetic benefits from breeding with non-resident males. Extra-colony male mating success was not based on heterozygosity criteria at microsatellite loci; however, litters sired by extra-colony males exhibited increased heterozygosity. While we do not have the data that refute a relationship between individual levels of inbreeding (
H
s
) and fitness, we propose that a combination of both male and female factors most likely explain the adaptive significance of extra-pair mating whereby common mole-rats maximize offspring fitness by detecting genetic compatibility with extra-pair mates at other key loci, but it is not known which sex controls these matings.
Evolution of graded refractive index in squid lenses
Authors: Sweeney Alison M , Des Marais David L , Andrew Ban Yih-En , Johnsen Sönke
Published: February 2007

A lens with a graded refractive index is required for vision in aquatic animals with camera-type eyes. This optical design entails a radial gradient of protein density, with low density in external layers and high density in internal layers. To maintain the optical stability of the eye, different material properties are required for proteins in different regions of the lens. In low-density regions of the lens where slight protein aggregation causes significant light scattering, aggregation must be minimized. Squid lens S-crystallin proteins are evolutionarily derived from the glutathione S-transferase protein family. We used biochemistry, optical modelling and phylogenetics to study the evolution and material properties of S-crystallins. S-crystallins are differentially expressed in a radial gradient, suggesting a role in refractive index. This gradient in S-crystallin expression is correlated with their evolutionary history and biochemistry. S-crystallins have been under positive selection. This selection appears to have resulted in stabilization of derived S-crystallins via mutations in the dimer interface and extended electrostatic fields. These derived S-crystallins probably cause the glassy organization and stability of low refractive index lens layers. Our work elucidates the molecular and evolutionary mechanisms underlying the production and maintenance of camera-like optics in squid lenses.
Is there the potential for an epidemic of variant Creutzfeldt–Jakob disease via blood transfusion in the UK?
Authors: Clarke Paul , Will Robert G , Ghani Azra C
Published: February 2007

The discovery of three individuals suspected to have contracted variant Creutzfeldt–Jakob disease (vCJD) through blood transfusions has heightened concerns that a secondary epidemic via human-to-human transmission could occur in the UK. The Department of Health responded immediately to this threat by banning those who had received blood transfusions since 1980 from donating blood. In this paper, we conduct a sensitivity analysis to explore the potential size of a blood-borne vCJD epidemic and investigate the effectiveness of public health interventions. A mathematical model was developed together with an expression for the basic reproduction number (
R
0
). The sensitivity of model predictions to unknown parameters determining the transmission of vCJD via infected blood was assessed under pessimistic modelling assumptions. We found that the size of the epidemic (up until 2080) was bounded above by 900 cases, with self-sustaining epidemics (
R
0
>1) also possible; but the scenarios under which such epidemics could arise were found to be biologically implausible. Under optimistic assumptions, public health interventions reduced the upper bound to 250 and further still when only biologically plausible scenarios were considered. Our results support the belief that scenarios leading to large or self-sustaining epidemics are possible but unlikely, and that public health interventions were effective.
The puzzling afterglow of GRB 050721: a rebrightening seen in the optical but not in the X-ray
Authors: Antonelli L. Angelo , Testa Vincenzo , Romano Patrizia , Guetta Dafne , Torii Ken'ichi , D' Elia Valerio , Malesani Daniele
Published: February 2007

We present here the analysis of the early and late multiwavelength afterglow emission, as observed by
Swift
a small robotic telescope and very large telescope (VLT). We compare early observations with late afterglow observations obtained with Swift and the VLT and we observe an intense rebrightening in the optical band at about 1 day after the burst, which is not present in the X-ray band. The lack of detection in X-ray of such a strong rebrightening at lower energies may be described with a variable external density profile. In such a scenario, the combined X-ray and optical observations allow us to derive that the matter density located at ∼10
17
 cm from the burst is approximately a factor of 10 higher than in the inner region. This is the first time in which a rebrightening has been observed in the optical afterglow of a gamma-ray burst that is clearly absent in the X-ray afterglow.
Swift-BAT results on the prompt emission of short bursts
Authors: Barthelmy Scott D
Published: February 2007

This is a brief review of short hard bursts (SHBs) from previous missions and from Swift-BAT; in particular, a review of the developing class of gamma-ray bursts which are similar to SHBs in that they have the short hard initial spike (0.1 to a few seconds), but that they also have a long extended phase of soft emission (50–200 s). Further, we suggest that a class of events discovered by Horvath in the T90 versus hardness ratio plane is this SHB with extended emission.
X-ray flares in early GRB afterglows
Authors: Burrows D.N , Falcone A , Chincarini G , Morris D , Romano P , Hill J.E , Godet O , Moretti A , Krimm H , Osborne J.P , Racusin J , Mangano V , Page K , Perri M , Stroh M ,   the Swift XRT Team
Published: February 2007

The Swift X-ray Telescope (XRT) has discovered that flares are quite common in early X-ray afterglows of gamma-ray bursts (GRBs), being observed in roughly 50% of afterglows with prompt follow-up observations. The flares range in fluence from a few per cent to approximately 100% of the fluence of the prompt emission (the GRB). Repetitive flares are seen, with more than four successive flares detected by the XRT in some afterglows. The rise and fall times of the flares are typically considerably smaller than the time since the burst. These characteristics suggest that the flares are related to the prompt emission mechanism, but at lower photon energies. We conclude that the most likely cause of these flares is late-time activity of the GRB central engine.
Probing the circumstellar medium of GRB afterglows through absorption-line observations
Authors: Chen Hsiao-Wen
Published: February 2007

A systematic search of Wolf–Rayet wind signatures, as represented by blue-shifted, high-velocity (|Δ
v
|=1000–5000 km s
−1
) C IV
λλ
1548, 1550 absorption doublet has yielded an estimate of 20% for the incidence of these C IV absorbers near the host galaxies of gamma-ray bursts (GRBs). This is consistent with what is observed near classical damped Ly
α
absorbers that have a comparable neutral hydrogen column density as the GRB host galaxies. A detailed ionization analysis of these absorbers, including the associated low-ionization species, shows that the majority in fact originate in foreground galaxies along the sightline, rather than in the vicinity of the GRB afterglows. Taking into account the enhanced afterglow radiation field, the lack of Wolf–Rayet signatures can be applied to constrain the C/He ratio and the density contrast of the winds in the vicinity of GRB progenitor stars.
The circumstellar environment of rotating Wolf–Rayet Stars and the implications for GRB afterglows
Authors: Eldridge John J
Published: February 2007

If Wolf–Rayet stars are the progenitors of gamma-ray bursts (GRBs), they must rotate rapidly to produce the GRB. This rotation may affect their stellar-wind bubbles and possibly explain why so many GRB afterglows occur in a constant density medium.
Observations of short gamma-ray bursts
Authors: Fox Derek B , Roming Peter W.A
Published: February 2007

We review recent observations of short-hard gamma-ray bursts and their afterglows. The launch and successful ongoing operations of the Swift satellite, along with several localizations from theHigh-Energy Transient Explorermission, have provoked a revolution in short-burst studies: first, by quickly providing high-quality positions to observers; and second, via rapid and sustained observations from the Swift satellite itself. We make a complete accounting of Swift-era short-burst localizations and proposed host galaxies, and discuss the implications of these observations for the distances, energetics and environments of short bursts, and the nature of their progenitors. We then review the physical modelling of short-burst afterglows: while the simplest afterglow models are inadequate to explain the observations, there have been several notable successes. Finally, we address the case of an unusual burst that threatens to upset the simple picture in which long bursts are due to the deaths of massive stars, and short bursts to compact-object merger events.
Gravitational wave: gamma-ray burst connections
Authors:   For the LIGO Scientific Collaboration, Hough Jim
Published: February 2007

After 35 years of experimental research, we are rapidly approaching the point at which gravitational waves (GWs) from astrophysical sources may be directly detected by the long-baseline detectors LIGO (USA), GEO 600 (Germany/UK), VIRGO (Italy/France) and TAMA 300 (Japan), which are now in or coming into operation.

A promising source of GWs is the coalescence of compact binary systems, events which are now believed to be the origin of short gamma-ray bursts (GRBs).

In this paper, a brief review of the state of the art in detector development and exploitation will be given, with particular relevance to a search for signals associated with GRBs, and plans for the future will be discussed.
Decay phases of Swift X-ray afterglows and the forward-shock model
Authors: Panaitescu A
Published: February 2007

The X-ray flux of the gamma-ray burst (GRB) afterglows monitored by the Swift satellite from January 2005 to July 2006 displays one to four phases of flux power-law decay. In chronological order, they are: the GRB tail, the ‘hump’, the standard decay and the post-jet-break decay. More than half of the GRB tails can be identified with the large-angle emission produced during the burst (but arriving later at observer). The remaining, slower GRB tails imply that the gamma-ray mechanism continues to radiate after the burst, as also suggested by the frequent occurrence of X-ray flares during the burst tail. The several GRB tails exhibiting a slow unbroken power-law decay until 100 ks must be attributed to the forward shock. In fact, the decay of most GRB tails is also consistent with that of the forward-shock emission from a narrow jet. The X-ray light-curve hump may be due to an increase of the kinetic energy per solid angle of the forward-shock region visible to the observer, caused by either the transfer of energy from ejecta to the forward shock or the emergence of the emission from an outflow seen from a location outside the jet opening. The decay following the X-ray light-curve hump is consistent with the emission from an adiabatic blast wave but, contrary to expectations, the light-curve decay index and spectral slope during this phase are not correlated. The X-ray light curves of two dozens X-ray afterglows that followed for more than a week do not exhibit a jet break, in contrast with the behaviour of pre-Swift optical afterglows, which displayed jet breaks at 0.5–2 days. Nevertheless, the X-ray light curves of several Swift afterglows show a second steepening break at 0.4–3 days that is consistent with the break expected for a jet when its edge becomes visible to the observer.
Gamma-ray bursts prompt emission spectrum: an analysis of a photosphere model
Authors: Pe'er Asaf , Mészáros Peter , Rees Martin J
Published: February 2007

A thermal radiative component is likely to accompany the first stages of the prompt emission of gamma-ray bursts (GRBs) and X-ray flashes. We analyse the effect of such a component on the observable spectrum, assuming that the observable effects are due to a dissipation process occurring below or near the thermal photosphere. For comparable energy densities in the thermal and leptonic components, the dominant emission mechanism is Compton scattering. This leads to a nearly flat energy spectrum (
νF

ν

∝
ν
0
) above the thermal peak at approximately 10–100 keV and below 10–100 MeV, for a wide range of optical depths 0.03≲
τ
≲100, regardless of the details of the dissipation mechanism or the strength of the magnetic field. For higher values of the optical depth, a Wien peak is formed at 100 keV to 1 MeV. In particular, these results are applicable to the internal shock model of GRBs, as well as to slow dissipation models, e.g. as might be expected from reconnection, if the dissipation occurs at a sub-photospheric radii. We conclude that dissipation near the thermal photosphere can naturally explain (i) clustering of the peak energy at sub-MeV energies at early times, (ii) steep slopes observed at low energies, and (iii) a flat spectrum above 10 keV at late times. Our model thus provides an alternative scenario to the optically thin synchrotron–synchrotron self-Compton model.
Observations of GRBs at high redshift
Authors: Tanvir Nial R , Jakobsson Páll
Published: February 2007

The extreme luminosity of gamma-ray bursts and their afterglows means they are detectable, in principle, to very high redshifts. Although the redshift distribution of gamma-ray bursts (GRBs) is difficult to determine, due to incompleteness of present samples, we argue that for Swift-detected bursts, the median redshift is between 2.5 and 3, with a few per cent probably at
z
>6. Thus, GRBs are potentially powerful probes of the era of reionization and the sources responsible for it. Moreover, it seems probable that they can provide constraints on the star-formation history of the Universe and may also help in the determination of the cosmological parameters.
Neutrino astronomy and gamma-ray bursts
Authors: Waxman Eli
Published: February 2007

The construction of large-volume detectors of high energy, greater than 1 TeV, neutrinos is mainly driven by the search for extragalactic neutrino sources. The existence of such sources is implied by the observations of ultra-high-energy, greater than or equal to 10
19
 eV, cosmic rays, the origin of which is a mystery. In this lecture, I briefly discuss the expected extragalactic neutrino signal and the current state of the experimental efforts. Neutrino emission from gamma-ray bursts (GRBs), which are probably sources of both high-energy protons and neutrinos, is discussed in some detail. The detection of the predicted GRB neutrino signal, which may become possible in the coming few years, will allow one to identify the sources of ultra-high-energy cosmic rays and to resolve open questions related to the underlying physics of GRB models. Moreover, detection of GRB neutrinos will allow one to test for neutrino properties (e.g. flavour oscillations and coupling to gravity) with an accuracy many orders of magnitude better than is currently possible.
Giant flares in soft
γ
-ray repeaters and short GRBs
Authors: Zane S
Published: February 2007

Soft gamma-ray repeaters (SGRs) are a peculiar family of bursting neutron stars that, occasionally, have been observed to emit extremely energetic giant flares (GFs), with energy release up to approximately 10
47
 erg s
−1
. These are exceptional and rare events. It has been recently proposed that GFs, if emitted by extragalactic SGRs, may appear at Earth as short gamma-ray bursts. Here, I will discuss the properties of the GFs observed in SGRs, with particular emphasis on the spectacular event registered from SGR 1806-20 in December 2004. I will review the current scenario for the production of the flare, within the magnetar model, and the observational implications.
Messages from GRB 060218
Authors: Zhang Bing , Liang Enwei , Gupta Nayantara , Zhang Bin-Bin , Virgili Francisco , Dai Z.G
Published: February 2007

GRB 060218 is a watershed event. Statistically, its detection suggests that there is likely a distinct low-luminosity (LL) population of gamma-ray bursts (GRBs) whose event rate is much higher than that of conventional high-luminosity GRBs. This LL population may give significant contribution to the diffuse neutrino background flux at energies higher than 10
16
 eV. The spectral lag of this burst is very long, and roughly follows the luminosity–lag relation of normal GRBs. This, along with the fact that it follows the
E
p
–
E
iso
relation as well, suggests that X-ray flashes (XRFs) are natural extension of GRBs in the softer regime and that GRBs and XRFs share the same radiation physics. We discuss how the broadband data pose strong constraints on possible models of the prompt emission of this GRB.
Introduction: recent developments in the study of gamma-ray bursts
Authors: Wells Alan , Wijers Ralph A.M.J , Rees Martin J
Published: February 2007

Gamma-ray bursts (GRBs) are immensely powerful explosions, originating at cosmological distances, whose outbursts persist for durations ranging from milliseconds to tens of seconds or more. In these brief moments, the explosions radiate more energy than the Sun will release in its entire 10 Gyr lifetime. Current theories attribute these phenomena to the final collapse of a massive star, or the coalescence of a binary system induced by gravity wave emission.

New results from Swift and related programmes offer fresh understanding of the physics of GRBs, and of the local environments and host galaxies of burst progenitors. Bursts found at very high red shifts are new tools for exploring the intergalactic medium, the first stars and the earliest stages of galaxy formation.

This Royal Society Discussion Meeting has brought together leading figures in the field, together with young researchers and students, to discuss and review the latest results from NASA's Swift Gamma-ray Burst Observatory and elsewhere, and to examine their impact on current understanding of the observed phenomena.
Social intelligence in the spotted hyena (Crocuta crocuta)
Authors: Holekamp Kay E , Sakai Sharleen T , Lundrigan Barbara L
Published: February 2007

If the large brains and great intelligence characteristic of primates were favoured by selection pressures associated with life in complex societies, then cognitive abilities and nervous systems with primate-like attributes should have evolved convergently in non-primate mammals living in large, elaborate societies in which social dexterity enhances individual fitness. The societies of spotted hyenas are remarkably like those of cercopithecine primates with respect to size, structure and patterns of competition and cooperation. These similarities set an ideal stage for comparative analysis of social intelligence and nervous system organization. As in cercopithecine primates, spotted hyenas use multiple sensory modalities to recognize their kin and other conspecifics as individuals, they recognize third-party kin and rank relationships among their clan mates, and they use this knowledge adaptively during social decision making. However, hyenas appear to rely more intensively than primates on social facilitation and simple rules of thumb in social decision making. No evidence to date suggests that hyenas are capable of true imitation. Finally, it appears that the gross anatomy of the brain in spotted hyenas might resemble that in primates with respect to expansion of frontal cortex, presumed to be involved in the mediation of social behaviour.
Dolphin social intelligence: complex alliance relationships in bottlenose dolphins and a consideration of selective environments for extreme brain size evolution in mammals
Authors: Connor Richard C
Published: February 2007

Bottlenose dolphins in Shark Bay, Australia, live in a large, unbounded society with a fission–fusion grouping pattern. Potential cognitive demands include the need to develop social strategies involving the recognition of a large number of individuals and their relationships with others. Patterns of alliance affiliation among males may be more complex than are currently known for any non-human, with individuals participating in 2–3 levels of shifting alliances. Males mediate alliance relationships with gentle contact behaviours such as petting, but synchrony also plays an important role in affiliative interactions. In general, selection for social intelligence in the context of shifting alliances will depend on the extent to which there are strategic options and risk. Extreme brain size evolution may have occurred more than once in the toothed whales, reaching peaks in the dolphin family and the sperm whale. All three ‘peaks’ of large brain size evolution in mammals (odontocetes, humans and elephants) shared a common selective environment: extreme mutual dependence based on external threats from predators or conspecific groups. In this context, social competition, and consequently selection for greater cognitive abilities and large brain size, was intense.
Fatigue and Static Crack Propagation in Yttria‐Stabilized Tetragonal Zirconia Polycrystals: Crack Growth Micromechanisms and Precracking Effects
Authors: Alcalá Jorge , Anglada Marc
Published: February 2007

The influence of precracking techniques in the crack growth behavior of yttria‐stabilized tetragonal zirconia polycrystals (Y‐TZP) is investigated. Load‐bridge and cyclic‐compression precracking enhance subsequent tensile crack growth rates, in comparison to results that are found with precracks that are extended under four‐point bending prior to testing. The actual influence of these precracking techniques in the near‐threshold crack growth regime is remarkably different. Although load‐bridge precracking produces a pattern of crack growth fluctuations for stress intensity factors, K, lower than the effective crack‐growth threshold of the material, compression‐fatigue precracks start to propagate under far‐field tensile loads at very fast growth rates and for K values that are slightly higher than the effective threshold. Crack‐tip shielding by tetragonal‐to‐monoclinic transformation develops gradually, influencing the crack growth behavior in Y‐TZP. Proposed fatigue crack growth micromechanisms involve damage accumulation at the crack‐tip region. For Kmax > 3 MPa·m1/2, fatigue crack growth rates are strongly affected by environmental interactions at the crack tip, and postulated fatigue micromechanisms include the cyclic degradation of crack‐tip shielding.
Interlamellar Residual Stresses in Single Grains of NiO–ZrO2(cubic) Directionally Solidified Eutectics
Authors: Dickey Elizabeth C. , Dravid Vinayak P. , Hubbard Camden R.
Published: February 2007

Phase‐to‐phase residual stresses due to thermal expansion mismatch were measured in lamellar NiO‐ZrO2(cubic) directionally solidified eutectics (DSEs). The triaxial strain tensors for both phases were measured using single‐crystal X‐ray diffractometry techniques on isolated grains of the DSE. From the strain tensors, the stress tensors were calculated, taking into account the full elastic anisotropy of the phases. The resulting stress tensors indicated that very large compressive stresses accumulated in ZrO2 whereas large tensile stresses were amassed in NiO parallel to the lamellae during the solidification process. The large magnitudes of the stresses indicated that the interfaces between the lamellae were very well bonded and did not facilitate slip or other stress‐relieving processes.
Effects of Copper Coating on the Crystalline Structure of Fine Barium Titanate Particles
Authors: Liu Xinghua , Shih Wan Y. , Shih Wei‐Heng
Published: February 2007

We have investigated the effect of a metal coating—copper—on the tetragonal structure of fine barium titanate (BaTiO3) particles. The BaTiO3 particles were synthesized by a sol‐gel method and heat treated at temperatures >900°C for various amounts of time before coating. The copper coating was achieved by an electroless coating technique. The transmission electron microscopy micrographs revealed that the coated powder contained fine BaTiO3 particles that were embedded in copper patches. The X‐ray diffractometry patterns showed that the copper coating increased the c/a ratio of the fine BaTiO3 particles. For powders that were heat treated at 900°C for 10 h and were initially cubic, the copper coating changed the c/a ratio, from 1 to 1.0034. For powders that were calcined at 900°C for 20 h and were initially tetragonal, the copper coating further enhanced the c/a ratio, from 1.0028 to 1.0043. When the copper‐coated BaTiO3 particles were oxidized, the c/a ratio was reduced to a value that was approximately equal to or below that of the uncoated powders. A conductive coating can eliminate the depolarization energy of an insulating polar particle. The fact that the copper coating promoted the polar tetragonal phase but the nonconductive copper‐oxide coating did not was consistent with the interpretation that the presence of the cubic phase (nonpolar) in small BaTiO3 particles was caused by the depolarization effect.
Sea Salt Hot Corrosion and Strength of an Yttria‐Containing Silicon Nitride
Authors: Fox Dennis S. , Cuy Michael D. , Strangman Thomas E.
Published: February 2007

A commercially available, hot isostatically pressed Si3N4 containing 4 wt% yttria was exposed to 982°C for up to 75 h in a burner rig pressurized to 500 kPa. Synthetic sea salt added to the flame (5 ppm) resulted in formation of a sodium magnesium silicate corrosion product. A 33% reduction in room‐temperature strength occurred after 5 h exposure. This is thought to be due to modification of the near‐surface grain boundary phase and relief of surface compressive stresses. Exposures to longer times resulted in continued strength reduction, up to 46 at 75 h. Strength also decreased when salt concentration was increased, as shown by exposures using 2 and 10 ppm sea salt. In tests at 100 and 300 kPa with other variables held constant, postcorrosion strengths were similar to those after 500 kPa exposure.
Hydroxyapatite/Hydroxyapatite‐Whisker Composites without Sintering Additives: Mechanical Properties and Microstructural Evolution
Authors: Suchanek Wojciech , Yashima Masatomo , Kakihana Masato , Yoshimura Masahiro
Published: February 2007

Hydroxyapatite/0%‐30% hydroxyapatite‐whisker (HAp/0%‐30%HAp(w)) composites have been fabricated by pressureless sintering, hot pressing, and hot isostatic pressing (HIP). Composites that were HIPed at 1000°‐1100°C (2 h, 190 MPa) exhibited the best properties: relative densities of 97.0‐99.5%, fracture toughness of 1.4‐2.0 MPa·m1/2 (as compared with 1.0 MPam1/2 for the nonreinforced HAp matrix). Compressive pre‐stressing and crack deflection contributed mostly to the increase of fracture toughness. Depending on processing conditions, grain growth in the HAp matrix and/or Rayleigh instability of the HAp whiskers were probably responsible for microstructural changes in the composites. The HAp/HAp(w) composites exhibited improved toughness, attaining the lower fracture‐toughness limit of bone without a decrease of bioactivity and biocompatibility.
Monolayer‐Mediated Deposition of Tantalum(V) Oxide Thin Film Structures from Solution Precursors
Authors: Clem Paul G. , Jeon Noo‐Li , Nuzzo Ralph G. , Payne David A.
Published: February 2007

Integration of oxide thin films with semiconductor substrates is a critical technology for a variety of microelectronic memory and circuit applications. Patterned oxide thin film devices are typically formed by uniform deposition followed by postdeposition ion‐beam or chemical etching in a controlled environment. This paper reports details of an ambient atmosphere technique which allows selective deposition of dielectric oxide thin layers without postdeposition etching. In this method, substrate surfaces are selectively functionalized with hydrophobic self‐assembled monolayers of octadecyltrichlorosilane by microcontact printing (μ‐CP). Sol‐gel deposition of ceramic oxides on these functionalized substrates, followed by mild, nonabrasive polishing, yields high‐quality, patterned oxide thin layers only on the unfunctionalized regions. A variety of micrometer‐scale dielectric oxide devices have been fabricated by this process, with lateral resolutions as fine as 4 μm. In this paper, we describe the solution chemistry, evolution of microstructure, and electrical properties of Ta2O5 thin films, as well as the stress‐related mechanism which enables selective de‐adhesion and resultant patterning. Selectively deposited, 80‐120 nm thick Ta2O5 thin film capacitors were crystallized on platinized silicon at 700‐800°C, and had dielectric constants of 18‐25 depending upon the processing conditions, with 1 V leakage current densities as low as 2 × 10−8 A/cm2. The ability to selectively deposit Ta2O5 and other electrical ceramics (such as LiNbO3 and PbTiO3) on a variety of technologically important substrate materials suggests broad potential for integrated circuit and hybrid microelectronics applications.
Properties and Microstructure of Molybdenum Disilicide–β′;‐SiAlON Particulate Ceramic Composites
Authors: Huang Chao M. , Yuh Chao Y. , Farooque Mohammad , Zhu Dong , Xu Youren , Kriven Waltraud M.
Published: February 2007

Particulate ceramic composites that were composed of a combustion‐synthesized β′;‐SiAlON matrix and dispersed MoSi2 particles were hot pressed at 1600°C in a nitrogen atmosphere. The physical and mechanical properties of the composites that contained 15, 30, and 45 vol% MoSi2 were evaluated. The average four‐point bend strength, fracture toughness, and Vickers hardness of the composites were in the ranges of 500‐600 MPa, 3‐4 MP·am1/2, and 11‐13 GPa, respectively. The measured mechanical strength and hardness were very similar to the values that were predicted from the rule of mixtures. The fracture toughness of the combustion‐synthesized β′;‐SiAlON (2.5 MPa·m1/2) was apparently enhanced by the MoSi2 particles that were added. The increase in the fracture toughness was predominately attributed to the residual thermal stress that was induced by the thermal expansion mismatch between the MoSi2 particles and the β′;‐SiAlON matrix. The composites showed improved electrical conductivity and oxidation resistance over monolithic β′;‐SiAlON. High‐resolution transmission electron microscopy examination of the composites indicated that the MoSi2 was chemically well compatible with the β′;‐SiAlON.
Mechanism and Kinetics of the Carbothermal Nitridation Synthesis of α‐Silicon Nitride
Authors: Weimer Alan W. , Eisman Glenn A. , Susnitzky David W. , Beaman Donald R. , McCoy Jeffrey W.
Published: February 2007

The carbothermal nitridation synthesis of α‐Si3 N4is studied using electron microscopy techniques(FEG/SEM and TEM) and chemical composition analysis to characterize the reaction at various degrees of conversion. The reaction follows a nucleation‐growth mechanism. Without “seed”α‐Si3N4in the precursor, the reaction rate is controlled by the formation of nuclei which are associated with a Si‐O‐C intermediate phase. In the presence of “seed,” the limiting step is growth of α‐Si3N4 onto the “seed” nuclei. Growth appears to follow a gas‐phase route and is characterized by an irregular porous layer which grows onto the “seed.” The porous structure is the result of reaction around car‐bon particles which are consumed during the process. The presence of admixed “seed” Si3N4in the precursor formu‐lation increases the reaction rate since the nucleation step is eliminated. An activation energy of E = 457 ± 55 kJ/mol for the overall reaction closely approximates that previously reported for the formation of SiO. This result, along with the finding that residual crystalline SiO2 is present at all stages of the reaction, indicates that the overall reactionrate is controlled by the reduction of SiO2. Since reaction at the carbon and SiO2 contact points is fast, the rate‐limiting step is most likely the gas‐phase carbon reduction of SiO2with CO.
Phase Separation of Alkoxy‐derived (Ti,Sn)O2 Oriented Thin Films
Authors: Arakawa Shuichi , Mogi Kenji , Kikuta Ko‐ichi , Yogo Toshinobu , Hirano Shin‐ichi , Seki Yoji , Kawamoto Mitsutoshi
Published: February 2007

Oriented (Ti,Sn)O2 thin films with modulated microstructure were successfully synthesized on sapphire substrates by using sol–gel processing combined with spinodal decomposition. The degree of orientation of (Ti0.5Sn0.5)O2 thin films increased in the following order: sapphire (0001), (110), and (012). (Ti0.5Sn0.5)O2 thin films underwent spinodal decomposition at 900°C by annealing. The variation of the 2theta value of the 202 reflection of (Ti0.5Sn0.5)O2 films showed the typical behavior of spinodal decomposition. The rate of spinodal decomposition of the (Ti0.5Sn0.5)O2 films on sapphire (110) was faster than that on sapphire (012) substrates. The characteristic modulated microstructure was observed for the spinodally decomposed (Ti0.5Sn0.5)O2 films on sapphire (012) substrates by transmission electron microscopy. (Ti0.3Sn0.7)O2 films on sapphire (012) substrates were binodally decomposed during annealing at 1300°C.
Effect of La/K A‐site Substitutions on the Ordering of Ba(Zn1/3Ta2/3)O3
Authors: Lee Cheng‐Chang , Chou Chen‐Chia , Tsai Dah‐Shyang
Published: February 2007

The 1/3 <111>‐type ordering of Ba(Zn1/3Ta2/3)O3 (BZT) can be transformed to 1/2 <111>–type ordering by substituting the La3+ cation into the A site. The 1/3 <111> ordering in BZT is shown to be reduced, discontinued, and then replaced by 1/2 <111> ordering, using X–ray diffraction, electron microscopy, and Raman spectroscopy. On the other hand, potassium–substituted BZT only displays a reduction in the degree of ordering.
Initial Coarsening and Microstructural Evolution of Fast‐Fired and MgO‐Doped Al2O3
Authors: Lin Frank J. T. , de Jonghe Lutgard C. , Rahaman Mohamed N.
Published: February 2007

The effect of an initial coarsening step (50‐200 h at 800°C) on the subsequent densification and microstructural evolution of high–quality compacts of undoped and MgO–doped Al2O3 has been investigated during fast–firing (5 min at 1750°C) and during constant–heating–rate sintering (4°C/min to 1450°C). In constant–heating–rate sintering of both the undoped and MgO–doped Al2O3, a refinement of the microstructure has been achieved for the compact subjected to the coarsening step. A combination of the coarsening step and MgO doping produces the most significant refinement of the microstructure. In fast–firing of the MgO–doped Al2O3, the coarsening step produces a measurable increase in the density and a small refinement of the grain size, when compared with similar compacts fast–fired conventionally (i.e., without the coarsening step). This result indicates that the accepted view of the deleterious role of coarsening in the sintering of real powder compacts must be reexamined. Although extensive coarsening after the onset of densification must be reduced for the achievement of high density, limited coarsening prior to densification is beneficial for subsequent sintering.
Mechanical Properties of Oxidation‐Resistant SiC/C Compositionally Graded Graphite Materials
Authors: Nakano Junichi , Fujii Kimio , Yamada Reiji
Published: February 2007

Mechanical properties of oxidation‐resistant SiC/C compositionally graded graphite materials composed of a CVD SiC coating layer, a SiC/C graded layer, and a graphite substrate were studied by bending, compressive, and hardness tests at room temperature. CVD SiC coated graphite and graphite with a SiC/C graded layer alone were also examined. The bending strengths of oxidation–resistant SiC/C compositionally graded graphite materials as well as CVD SiC coated graphite were about twice as much as that of graphite. The bending and compressive strengths of graphite with the SiC/C graded layer alone were almost the same as those of graphite. The higher strengths of graphite with the CVD SiC layer can be mainly due to the CVD SiC strength itself, and partly due to the smooth CVD surface. No effect of the SiC/C layer on the strengths was discussed in terms of porosity, surface morphology, and the strength of SiC.
Structure and Nonlinear Optical Properties of Lanthanide Borate Glasses
Authors: Terashima Kentaro , Tamura Suguru , Kim Sea‐Hoon , Yoko Toshinobu
Published: February 2007

The third–order nonlinear optical susceptibility, χ(3), of lanthanide (lanthanum, praseodymium, neodymium, and samarium) borate glasses has been measured by the third harmonic generation method. The structure of the present glass system has been studied by infrared and Raman spectroscopic methods. The network structures of the present Ln2O3–B2O3 glasses have been confirmed to be basically similar to each other. Praseodymium, neodymium, and samarium borate glasses exhibit χ(3) values that are larger than lanthanum borate glasses, because of the optical resonance effect, in accordance with the f–f transition. Especially, the χ(3) value for 30Pr2O3·70B2O3 glass is 1.8 × 10−12 esu, which is a factor of ∼60 larger than that of SiO2 glass. This striking enhancement of χ(3) is mainly attributed to the large transition moment to the first excitation state.