bluuebunny/crossref_metadata_2025 huggingface dataset:
Room temperature ultraviolet emission at 357nm from polysilane based organic light emitting diode
Authors: Sharma Asha , Katiyar Monica , Deepak  , Seki Shu , Tagawa Seiichi
Published: April 2006

We have fabricated an organic light emitting diode using poly(n-butylphenylsilane) which has an emission in deep ultraviolet at 357nm at room temperature. The device structure used is glass/indium tin oxide/poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate)/polysilane (emitting material)/calcium/aluminum. These devices emit ultraviolet light with a turn-on voltage of 8V. The electroluminescence spectrum of the device in the ultraviolet range is identical to the photoluminescence spectrum of the polysilane thin film. From these devices, we also observe an additional emission in the visible region, which is not present in the photoluminescence spectrum of the material. The visible emission has a color coordinate of (0.36,0.35), which can be modulated to a required white light coordinate by down converting the ultraviolet emission.
Surface-enhanced Raman scattering efficiency of truncated tetrahedral Ag nanoparticle arrays mediated by electromagnetic couplings
Authors: Baia Monica , Baia Lucian , Astilean Simion , Popp Juergen
Published: April 2006

Surface-enhanced Raman scattering (SERS) efficiency assessment of truncated tetrahedral Ag nanoparticle arrays with different vertical dimensions prepared by nanosphere lithography provides the experimental evidence of the electromagnetic (EM) coupling sensitivity to the nanoparticle heights. It is demonstrated that the EM couplings between the localized plasmon resonance of each particle and photonic modes of the particles array are solely accountable for the SERS enhancement of the rhodamine 6G molecules adsorbed on these substrates. Similar nanoparticle height dependent SERS enhancement trend is observed for the resonant excitation of the probe molecule.
Rectifying NdNiO3∕Nb:SrTiO3 junctions as a probe of the surface electronic structure of NdNiO3
Authors: Kozuka Y. , Susaki T. , Hwang H. Y.
Published: April 2006

We have studied the electronic properties of junctions formed between Nb-doped SrTiO3 substrates, an n-type semiconductor, and NdNiO3 films, which exhibit a strong first-order phase transition from a high temperature paramagnetic metal to a low temperature antiferromagnetic insulator. Although the junctions are rectifying at all temperatures, the current-voltage and capacitance characteristics show no indication of the metal-insulator transition clearly observed in the films. This suggests that the surface electronic structure of NdNiO3 is distinct from the interior of the film and does not undergo the bulk transition.
Hydrogen self-trapping near silicon atoms in Ge-rich SiGe alloys
Authors: Pereira R. N. , Bech Nielsen B. , Coutinho J. , Torres V. J. B. , Briddon P. R.
Published: April 2006

Infrared absorption spectroscopy and ab initio density functional modeling are used to investigate hydrogen defects that are stable at and above room temperature in proton-implanted Ge-rich SiGe alloys. We find that Si atoms are effective nucleation sites for hydrogen, leading to the formation of a dominant defect closely related to the H2* dimer in pure Si and Ge. The minority Si species in the alloys stabilizes the new complex, and strongly reduces the trapping efficiency of hydrogen by vacancies and self-interstitials.
Electro-optic switch in ferroelectric thin films mediated by surface plasmons
Authors: Liu S. W. , Xiao Min
Published: April 2006

We propose an optical switch in simple waveguide geometry with a metal thin film sandwiched between two layers of electro-optic materials. Its mechanism is based on the distinct responsive behaviors of two surface plasmon modes in the metal film to the cladding films. By exploiting the specific distribution of surface plasmon fields in metals, an effective optical switch with a very low crosstalk −27dB and a switching bias of 59kV∕cm is achieved for Ba0.5Sr0.5TiO3 ferroelectric films. The dependences of the optical switch’s crosstalk and switching bias on the geometric parameters of the structure are also analyzed.
Temperature-controlled neutron reflectometry sample cell suitable for study of photoactive thin films
Authors: Yager Kevin G. , Tanchak Oleh M. , Barrett Christopher J. , Watson Mike J. , Fritzsche Helmut
Published: April 2006

We describe a novel cell design intended for the study of photoactive materials using neutron reflectometry. The cell can maintain sample temperature and control of ambient atmospheric environment. Critically, the cell is built with an optical port, enabling light irradiation or light probing of the sample, simultaneous with neutron reflectivity measurements. The ability to measure neutron reflectivity with simultaneous temperature ramping and/or light illumination presents unique opportunities for measuring photoactive materials. To validate the cell design, we present preliminary results measuring the photoexpansion of thin films of azobenzene polymer.
Electroluminescence at 375nm from a ZnO∕GaN:Mg∕c-Al2O3 heterojunction light emitting diode
Authors: Rogers D. J. , Hosseini Teherani F. , Yasan A. , Minder K. , Kung P. , Razeghi M.
Published: April 2006

n - Zn O ∕ p - Ga N : Mg heterojunction light emitting diode (LED) mesas were fabricated on c-Al2O3 substrates using pulsed laser deposition for the ZnO and metal organic chemical vapor deposition for the GaN:Mg. High crystal quality and good surface morphology were confirmed by x-ray diffraction and scanning electron microscopy. Room temperature (RT) photoluminescence (PL) showed an intense main peak at 375nm and a negligibly low green emission indicative of a near band edge excitonic emission from a ZnO layer with low dislocation/defect density. The LEDs showed I-V characteristics confirming a rectifying diode behavior and a RT electroluminescence (EL) peaked at about 375nm. A good correlation between the wavelength maxima for the EL and PL suggests that recombination occurs in the ZnO layer and that it may be excitonic in origin. This also indicates that there is significant hole injection from the GaN:Mg into the ZnO.
Groundwater use by riparian vegetation in the wet - dry tropics of northern Australia
Authors: O'Grady Anthony P. , Eamus Derek , Cook Peter G. , Lamontagne Sebastien
Published: April 2006

Within Australia and globally there is considerable concern about the potential impacts of groundwater extraction on ecosystems dependent on groundwater. In this study we have combined heat pulse and isotopic techniques to assess groundwater use by riparian vegetation along the Daly River in the Northern Territory. The riparian forests of the Daly River exhibited considerable structural and floristic complexity. More than 40 tree species were recorded during vegetation surveys and these exhibited a range of leaf phonologies, implying complex patterns of water resource partitioning within the riparian forests. Water use was a function of species and season, and stand water use varied between 1.8 and 4.1 mm day–1. In general, however, water use tended to be higher in the wet season than during the dry season, reflecting the contribution to stand water use by dry-season deciduous tree species. There was a strong relationship between stand basal area and stand water use in the wet season, but the strength of this relationship was lower in the dry season. The amount of groundwater use, as determined by analysis of deuterium concentrations in xylem sap, was principally a function of position in the landscape. Trees at lower elevations, closer to the river, used more groundwater than trees higher on the levees. By using a combination of techniques we showed that riparian vegetation along the Daly River was highly groundwater dependent and that these water-use requirements need to be considered in regional management plans for groundwater.
Groundwater use by dominant tree species in tropical remnant vegetation communities
Authors: O'Grady A. P. , Cook P. G. , Howe P. , Werren G.
Published: April 2006

Defining groundwater dependence and water-use requirements of terrestrial vegetation represents a significant challenge to water-resources managers. Terrestrial vegetation may exhibit complex spatial and temporal patterns of groundwater dependence. In this study we have assessed the sources of water used by dominant tree species in remnant vegetation of Pioneer Valley, Mackay, in northern Queensland. Water use by tree species was determined by sapflow techniques and the sources of water were investigated by using a combination of isotopic and water-potential measurements. Within the remnant vegetation communities of the Pioneer Valley there were complex patterns of water use and water-resource partitioning. However, all communities within the study showed some degree of groundwater use. Riparian communities that were reliant on groundwater discharge for maintenance of river baseflow exhibited high species diversity and complex forest structure and different species within these communities accessed a range of water sources including shallow soil water, river water and groundwater. In contrast, the woodlands and open forest were principally reliant on soil water. Although, species such as Corymbia clarksoniana appeared to be reliant on groundwater for their dry-season water-use requirements. This study demonstrated use of groundwater by remnant vegetation communities in the Pioneer Valley but determination of groundwater dependence requires a better understanding of the temporal patterns of water use and sources of water used by each species.
Valuation of groundwater-dependent ecosystems: a functional methodology incorporating ecosystem services
Authors: Murray Brad R. , Hose Grant C. , Eamus Derek , Licari Damian
Published: April 2006

Groundwater-dependent ecosystems (GDEs) are ecosystems that must have access to groundwater to maintain their ecological structure and function. Rapidly expanding numbers of humans are placing increased demands on groundwater for consumption, industry and agriculture. These demands alter groundwater regimes of GDEs that have evolved over millennia, resulting in the degradation of ecosystem health. As a consequence, the goods and services (ecosystem services) that GDEs provide for humans, which include food production and water purification, are at serious risk of being lost. Effective management of GDEs and their ecosystem services requires prioritisation of the most valuable ecosystems, given that increasing human demands and limited time and money preclude complete protection of all GDEs. Here, we provide an eight-step method for the valuation and initial prioritisation of GDEs. The proposed methodology improves on previous, primarily subjective methods for the valuation of GDEs by employing both economic valuation of the ecosystem services provided by GDEs, and ecological valuation of significant environmental attributes of GDEs. We apply the eight-step method to a hypothetical case study in order to demonstrate its applicability to a catchment containing a range of GDEs of different sizes, each possessing its own suite of threatened taxa. The major benefit of the valuation methodology presented here is that it can be used at three levels of complexity: (1) a full-desktop study, (2) a semi-desktop study requiring stakeholder consultation, and (3) a full field-based study, according to the time and money available for initial prioritisation efforts.
Tree water sources over shallow, saline groundwater in the lower River Murray, south-eastern Australia: implications for groundwater recharge mechanisms
Authors: Holland K. L. , Tyerman S. D. , Mensforth L. J. , Walker G. R.
Published: April 2006

The decline of riparian vegetation in the lower River Murray, south-eastern Australia, is associated with a reduction in flooding frequency, extent and duration, and increased salt accumulation. The plant water sources of healthy Eucalyptus largiflorens trees growing over highly saline (>40 dS m–1) groundwater were investigated during summer when water deficit is greatest. The study found low-salinity soil water overlying highly saline groundwater at most sites. This deep soil water, rather than the saline groundwater, was identified as the plant water source at most sites. Stable isotopes of water and water potential measurements were used to infer how the deep soil water was recharged. The low-salinity, deep soil water was recharged in the following two ways: (1) vertically through the soil profile or via preferential flow paths by rainfall or flood waters or (2) horizontally by bank recharge from surface water on top of the saline groundwater. Vertical infiltration of rainfall and floodwaters through cracking clays was important for trees growing in small depressions, whereas infiltration of rainfall through sandy soils was important for trees growing at the break of slope. Bank recharge was important for trees growing within ∼50 m of permanent and ephemeral water bodies. The study has provided a better understanding of the spatial patterns of recharge at a scale relevant to riparian vegetation. This understanding is important for the management of floodplain vegetation growing in a saline, semi-arid environment.
Modelling vegetation health from the interaction of saline groundwater and flooding on the Chowilla floodplain, South Australia
Authors: Overton I. C. , Jolly I. D. , Slavich P. G. , Lewis M. M. , Walker G. R.
Published: April 2006

The native riparian vegetation communities on the Chowilla floodplain in the lower River Murray in South Australia are suffering severe declines in health, particularly the Eucalyptus camaldulensis Dehnh. (red gum) and Eucalyptus largiflorens F.Muell. (black box) communities. The primary cause of the decline is salinisation of the floodplain soils caused by increased rates of groundwater discharge and hence increased movement of salt up into the plant root zone. The salinity is driven by a lack of flooding and rising saline groundwater tables. Rises in the naturally saline groundwater levels are due to the effects of river regulation from Lock 6 and high inflows from regional groundwater levels increased by Lake Victoria to the east. River regulation has also led to reduced frequency and duration of the floods that leach salt from the plant root zone and supply fresh water for transpiration. The frequency of medium-sized floods occurring on Chowilla has been reduced by a factor of three since locking and water extractions were commenced in the 1920s to provide reliable water for urban and agricultural use. The soil salinisation on the floodplain was modelled by using a spatial and temporal model of salt accumulation from groundwater depth, groundwater salinity, soil type and flooding frequency. The derived soil water availability index (WINDS) is used to infer vegetation health and was calibrated against current extent of vegetation health as assessed from fieldwork and satellite image analysis. The modelling work has shown that there is a severe risk to the floodplain vegetation from current flow regimes. This paper estimates that 65% (5658 ha) of the 8600 ha of floodplain trees are affected by soil salinisation matching a field survey of vegetation health in 2003 (Department of Environment and Heritage 2005a), compared with 40% in 1993 (Taylor et al. 1996). Model results show that the best management option for Chowilla is lowering the groundwater down to 2 m below current levels, which predicts an improvement in the health of the floodplain tree species from 35 to 42%.
A functional methodology for determining the groundwater regime needed to maintain the health of groundwater-dependent vegetation
Authors: Eamus Derek , Froend Ray , Loomes Robyn , Hose Grant , Murray Brad
Published: April 2006

In the past, the phrase ‘environmental allocations of water’ has most often been taken to mean allocation of water to rivers. However, it is now accepted that groundwater-dependent ecosystems are an important feature of Australian landscapes and require an allocation of water to maintain their persistence in the landscape. However, moving from this theoretical realisation to the provision and implementation of a field-based management regime is extremely difficult. The following four fundamental questions are identified as being central to the effective management of groundwater-dependent ecosystems (GDEs): (1) How do we identify GDEs in the field; put another way, which species or species assemblages or habitats are reliant on a supply of groundwater for their persistence in the landscape; (2) what groundwater regime is required to ensure the persistence of a GDE; (3) how can managers of natural resources (principally water and habitats), with limited time, money and other resources, successfully manage GDEs; and (4) what measures of ecosystem function can be monitored to ensure that management is effective? This paper explicitly addresses these questions and provides a step-by-step theoretical and practical framework for providing answers. In particular, this paper provides an introduction to some of the relevant literature and from this, presents a synthesis, presented in the form of a functional methodology for managing groundwater dependent ecosystems.
Protection and management of groundwater-dependent ecosystems: emerging challenges and potential approaches for policy and management
Authors: MacKay Heather
Published: April 2006

The protection of ecosystems associated with groundwater, and thus potentially vulnerable to groundwater exploitation, is only now being recognised as an important aspect of water management. Although there has been a gradual increase in scientific understanding of the links between groundwater availability and ecosystem health, a significant challenge remains in the development and implementation of policy that adequately addresses the protection of groundwater-dependent ecosystems. There is no single right way to solve the problem of protecting groundwater-dependent ecosystems, while still allowing the use of groundwater to support social and economic development, poverty alleviation and improved food and water security. This paper provides a global perspective in examining the potential impacts of the lack of policy, or poor implementation of policy, related to groundwater-dependent ecosystems, and discusses emerging approaches in this field. The following two important factors are considered in the paper: first, the difficulty of managing typically local- and regional-scale problems associated with groundwater exploitation, by using national-scale policy interventions and regulation; second, the need to shorten the cycle from science to policy and regulation, and thence to management activities on the ground, in order to encourage policy shifts in the short to medium term that better reflect the available scientific knowledge of groundwater-dependent ecosystems.
Rivers as groundwater-dependent ecosystems: a review of degrees of dependency, riverine processes and management implications
Authors: Boulton A. J. , Hancock P. J.
Published: April 2006

Many rivers are classified as groundwater-dependent ecosystems (GDEs), owing to the contribution of groundwater to their base flow. However, there has been little explicit recognition of the way groundwater influences riverine biota or processes, how degrees of ecological dependency may vary, and the management implications of this dependency. The permeable beds and banks of these GDEs where surface water and groundwater exchange are termed ‘hyporheic zones’. They are often inhabited by invertebrates, with varying reliance on groundwater, although the ecological roles of these invertebrates are little known. Upwelling hyporheic water can promote surface primary productivity, influence sediment microbial activity, and affect organic matter decomposition. In many intermittent streams, variable groundwater inputs alter the duration of flow or water permanence, and the duration and timing of these largely govern the biota and rates of many ecosystem processes (e.g. leaf decomposition). Not only is the physical presence of water important, thermal and chemical conditions arising from groundwater inputs also have direct and indirect effects on riverine biota and rates or types of in-stream processes. Differing degrees of dependency of rivers on groundwater mediate all these influences, and may change over time and in response to human activities. Alteration of groundwater inputs through extraction from riparian wells or changes in local water table have an impact on these GDEs, and some current management plans aim to restrict groundwater extraction from near permeable river channels. However, these are often ‘blanket’ restrictions and the mechanisms of GDE dependency or timing of groundwater requirements are poorly understood, hampering refinement of this management approach. More effective management of these GDEs into the future can result only from a better understanding of the mechanisms of the dependency, how these vary among river types and what in-stream changes might be predicted from alteration of groundwater inputs.
Phenolic lipid synthesis by type III polyketide synthases is essential for cyst formation in
Azotobacter vinelandii
Authors: Funa Nobutaka , Ozawa Hiroki , Hirata Aiko , Horinouchi Sueharu
Published: April 2006

Cysts of
Azotobacter vinelandii
are resting cells that are surrounded by a protective coat, conferring resistance to various chemical and physical agents. The major chemical components of the cyst coat are alkylresorcinols, which are amphiphilic molecules possessing an aromatic ring with a long aliphatic carbon chain. Although alkylresorcinols are widely distributed in bacteria, fungi, plants, and animals, no enzyme systems for their biosynthesis are known. We report here an
ars
operon in
A. vinelandii
that is responsible for the biosynthesis of the alkylresorcinols in the cysts. The
ars
operon consisted of four genes, two of which encoded a type III polyketide synthase, ArsB and ArsC.
In vitro
experiments revealed that ArsB and ArsC, sharing 71% amino acid sequence identity, were an alkylresorcinol synthase and an alkylpyrone synthase, respectively, indicating that ArsB and ArsC are not isozymes but enzymatically distinct polyketide synthases. In addition, ArsB and ArsC accepted several acyl-CoAs with various lengths of the side chain as a starter substrate and gave corresponding alkylresorcinols and alkylpyrones, respectively, which suggests that the mode of the ring folding is uninfluenced by the structure of the starter substrates. The importance of the alkylresorcinols for encystment was confirmed by gene inactivation experiments; the lack of alkylresorcinols synthesis caused by
ars
mutations resulted in the formation of severely impaired cysts, as observed by electron microscopy.
Switchable electro-optic diffractive lens with high efficiency for ophthalmic applications
Authors: Li Guoqiang , Mathine David L. , Valley Pouria , Äyräs Pekka , Haddock Joshua N. , Giridhar M. S. , Williby Gregory , Schwiegerling Jim , Meredith Gerald R. , Kippelen Bernard , Honkanen Seppo , Peyghambarian Nasser
Published: April 2006

Presbyopia is an age-related loss of accommodation of the human eye that manifests itself as inability to shift focus from distant to near objects. Assuming no refractive error, presbyopes have clear vision of distant objects; they require reading glasses for viewing near objects. Area-divided bifocal lenses are one example of a treatment for this problem. However, the field of view is limited in such eyeglasses, requiring the user to gaze down to accomplish near-vision tasks and in some cases causing dizziness and discomfort. Here, we report on previously undescribed switchable, flat, liquid-crystal diffractive lenses that can adaptively change their focusing power. The operation of these spectacle lenses is based on electrical control of the refractive index of a 5-μm-thick layer of nematic liquid crystal using a circular array of photolithographically defined transparent electrodes. It operates with high transmission, low voltage (<2 V
rms
), fast response (<1 sec), diffraction efficiency > 90%, small aberrations, and a power-failure-safe configuration. These results represent significant advance in state-of-the-art liquid-crystal diffractive lenses for vision care and other applications. They have the potential of revolutionizing the field of presbyopia correction when combined with automatic adjustable focusing power.
Nevanlinna theoretical exceptional sets of rational towers and semigroups
Authors: Okuyama Yûsuke
Published: April 2006

For a rational tower, i.e., a composition sequence of rational maps, in addition to the algebraic and dynamical exceptional sets, various Nevanlinna theoretical exceptional sets are defined, and as we showed previously in the case of iterations, all of them are the same. In this paper, we extend this result to the cases of a rational tower with summable distortions and a finitely generated rational semigroup. We show that all the exceptional sets of a finitely generated rational semigroup are countable, and all of them are empty if and only if the algebraic one is as well (this being the smallest among them). The countability of exceptional sets is fundamental in the Nevanlinna theory, and their emptiness is important in the complex dynamics.
Caenorhabditis elegansKettin, a Large Immunoglobulin-like Repeat Protein, Binds to Filamentous Actin and Provides Mechanical Stability to the Contractile Apparatuses in Body Wall Muscle
Authors: Ono Kanako , Yu Robinson , Mohri Kurato , Ono Shoichiro
Published: April 2006

Kettin is a large actin-binding protein with immunoglobulin-like (Ig) repeats, which is associated with the thin filaments in arthropod muscles. Here, we report identification and functional characterization of kettin in the nematode Caenorhabditis elegans. We found that one of the monoclonal antibodies that were raised against C. elegans muscle proteins specifically reacts with kettin (Ce-kettin). We determined the entire cDNA sequence of Ce-kettin that encodes a protein of 472 kDa with 31 Ig repeats. Arthropod kettins are splice variants of much larger connectin/titin-related proteins. However, the gene for Ce-kettin is independent of other connectin/titin-related genes. Ce-kettin localizes to the thin filaments near the dense bodies in both striated and nonstriated muscles. The C-terminal four Ig repeats and the adjacent non-Ig region synergistically bind to actin filaments in vitro. RNA interference of Ce-kettin caused weak disorganization of the actin filaments in body wall muscle. This phenotype was suppressed by inhibiting muscle contraction by a myosin mutation, but it was enhanced by tetramisole-induced hypercontraction. Furthermore, Ce-kettin was involved in organizing the cytoplasmic portion of the dense bodies in cooperation with α-actinin. These results suggest that kettin is an important regulator of myofibrillar organization and provides mechanical stability to the myofibrils during contraction.
Developing CAM Research Capacity for Complementary Medicine
Authors: Lewith George , Verhoef Marja , Koithan Mary , Zick Suzanna M.
Published: April 2006

This article describes initiatives that have been central to the development of complementary and alternative medicine (CAM) research capacity in the United Kingdom, Canada and the United States over the last decade. While education and service delivery are essential parts of the development of CAM, this article will focus solely on the development of research strategy. The development of CAM research has been championed by both patients and politicians, primarily so that we may better understand the popularity and apparent effectiveness of these therapies and support integration of safe and effective CAM in health care. We hope that the perspective provided by this article will inform future research policy.
Comparison of Anti‐inflammatory Activities of Six Curcuma Rhizomes: A Possible Curcuminoid‐independent Pathway Mediated by Curcuma phaeocaulis Extract
Authors: Tohda Chihiro , Nakayama Natsuki , Hatanaka Fumiyuki , Komatsu Katsuko
Published: April 2006

We aimed to compare the anti‐inflammatory activities of six species of Curcuma drugs using adjuvant arthritis model mice. When orally administered 1 day before the injection of adjuvant, the methanol extract of Curcuma phaeocaulis significantly inhibited paw swelling and the serum haptoglobin concentration in adjuvant arthritis mice. Also when orally administered 1 day after the injection of adjuvant, the methanol extract of Curcuma phaeocaulis significantly inhibited paw swelling. Other Curcuma species (Curcuma longa, Curcuma wenyujin, Curcuma kwangsiensis, Curcuma zedoaria and Curcuma aromatica) had no significant inhibitory effects on adjuvant‐induced paw swelling. Cyclooxygenase (COX)‐2 activity was significantly inhibited by the methanol extract of C. phaeocaulis. Curcuminoids′ (curcumin, bis‐demethoxycurcumin and demethoxycurcumin) were rich in C. longa, but less in C. phaeocaulis and C. aromatica, not in C. wenyujin, C. kwangsiensis and C. zedoaria, suggesting that curcuminoids′ contents do not relate to inhibition of arthritis swelling. Therefore, C. phaeocaulis may be a useful drug among Curcuma species for acute inflammation, and the active constituents of C. phaeocaulis are not curcuminoids.
Oldest coelacanth, from the Early Devonian of Australia
Authors: Johanson Zerina , Long John A , Talent John A , Janvier Philippe , Warren James W
Published: April 2006

Coelacanths are well-known sarcopterygian (lobe-finned) fishes, which together with lungfishes are the closest extant relatives of land vertebrates (tetrapods). Coelacanths have both living representatives and a rich fossil record, but lack fossils older than the late Middle Devonian (385–390 Myr ago), conflicting with current phylogenies implying coelacanths diverged from other sarcopterygians in the earliest Devonian (410–415 Myr ago). Here, we report the discovery of a new coelacanth from the Early Devonian of Australia (407–409 Myr ago), which fills in the approximately 20 Myr ‘ghost range’ between previous coelacanth records and the predicted origin of the group. This taxon is based on a single lower jaw bone, the dentary, which is deep and short in form and possesses a dentary sensory pore, otherwise seen in Carboniferous and younger taxa.
Simple models for containment of a pandemic
Authors: Arino Julien , Brauer Fred , van den Driessche P , Watmough James , Wu Jianhong
Published: April 2006

Stochastic simulations of network models have become the standard approach to studying epidemics. We show that many of the predictions of these models can also be obtained from simple classical deterministic compartmental models. We suggest that simple models may be a better way to plan for a threatening pandemic with location and parameters as yet unknown, reserving more detailed network models for disease outbreaks already underway in localities where the social networks are well identified.

We formulate compartmental models to describe outbreaks of influenza and attempt to manage a disease outbreak by vaccination or antiviral treatment. The models give an important prediction that may not have been noticed in other models, namely that the number of doses of antiviral treatment required is extremely sensitive to the number of initial infectives. This suggests that the actual number of doses needed cannot be estimated with any degree of reliability. The model is applicable to pre-epidemic vaccination, such as annual vaccination programs in anticipation of an ‘ordinary’ influenza outbreak with limited drift, and as a combination of treatment both before and during an epidemic.
On the consequences of T-stress in elastic brittle fracture
Authors: Smith D.J , Ayatollahi M.R , Pavier M.J
Published: April 2006

By using a generalized maximum tensile stress (MTS) criterion to predict onset of brittle fracture, it is shown that the presence of T-stress can have a significant effect on mode I and mode II toughness. The most prominent influence of T-stress on toughness occurs for mode II conditions. However, earlier tests concentrated on near mode I and results were masked by scatter. New experiments, using combinations of mode II loading and T-stress, support conclusively the generalized MTS criterion. This criterion is shown to be very robust and applicable to predicting probability of brittle failure. The criterion is also relevant to other experimental results where combinations of mode II loading with high values of T-stress can lead to values of mode II toughness that are greater than mode I toughness.
Non-uniqueness of evapotranspiration due to spatial heterogeneity of plant species
Authors: Nordbotten Jan Martin , Rodriguez-Iturbe Ignacio , Celia Michael A
Published: April 2006

Spatially averaged soil moisture dynamics are studied under seasonally fixed conditions. We consider rainfall as a marked Poisson process, uniformly covering a spatial domain consisting of multiple plant types. Each plant type is considered to have different characteristics in terms of evapotranspiration functions, root-zone depth and rainfall interception. Equations for the evolution of joint probability density functions for individual soil moistures associated with different plant types are developed, and the non-uniqueness of the spatially averaged evapotranspiration function as a function of the average soil moisture is demonstrated and quantified in an example.
Three-dimensional elasticity problems for the prismatic bar
Authors: Barber J.R
Published: April 2006

A general solution is given to the three-dimensional linear elastic problem of a prismatic bar subjected to arbitrary tractions on its lateral surfaces, subject only to the restriction that they can be expanded as finite power series in the axial coordinate
z
. The solution is obtained by repeated differentiation of the tractions with respect to
z
, establishing a set of sub-problems

. A recursive procedure is then developed for generating the solution to

from that for

. This procedure involves three steps: integration of the stress and displacement fields

with respect to
z
, using an appropriate Papkovich–Neuber (P–N) representation; solution of two-dimensional in-plane and antiplane corrective problems for the tractions in

that are independent of
z
; and expression of these corrective solutions in P–N form. The method is illustrated by an example.
Species richness changes lag behind climate change
Authors: Menéndez Rosa , Megías Adela González , Hill Jane K , Braschler Brigitte , Willis Stephen G , Collingham Yvonne , Fox Richard , Roy David B , Thomas Chris D
Published: April 2006

Species-energy theory indicates that recent climate warming should have driven increases in species richness in cool and species-poor parts of the Northern Hemisphere. We confirm that the average species richness of British butterflies has increased since 1970–82, but much more slowly than predicted from changes of climate: on average, only one-third of the predicted increase has taken place. The resultant species assemblages are increasingly dominated by generalist species that were able to respond quickly. The time lag is confirmed by the successful introduction of many species to climatically suitable areas beyond their ranges. Our results imply that it may be decades or centuries before the species richness and composition of biological communities adjusts to the current climate.
Asymptotic properties of mathematical models of excitability
Authors: Biktasheva I.V , Simitev R.D , Suckley R , Biktashev V.N
Published: April 2006

We analyse small parameters in selected models of biological excitability, including Hodgkin–Huxley (Hodgkin & Huxley 1952
J. Physiol.
117
, 500–544) model of nerve axon, Noble (Noble 1962
J. Physiol.
160
, 317–352) model of heart Purkinje fibres and Courtemanche
et al
. (Courtemanche
et al
. 1998
Am. J. Physiol.
275
, H301–H321) model of human atrial cells. Some of the small parameters are responsible for differences in the characteristic time-scales of dynamic variables, as in the traditional singular perturbation approaches. Others appear in a way which makes the standard approaches inapplicable. We apply this analysis to study the behaviour of fronts of excitation waves in spatially extended cardiac models. Suppressing the excitability of the tissue leads to a decrease in the propagation speed, but only to a certain limit; further suppression blocks active propagation and leads to a passive diffusive spread of voltage. Such a dissipation may happen if a front propagates into a tissue recovering after a previous wave, e.g. re-entry. A dissipated front does not recover even when the excitability restores. This has no analogy in FitzHugh–Nagumo model and its variants, where fronts can stop and then start again. In two spatial dimensions, dissipation accounts for breakups and self-termination of re-entrant waves in excitable media with Courtemanche
et al
. kinetics.
Ovulation, pregnancy, placentation and husbandry in the African elephant (
Loxodonta africana
)
Authors: Allen W.R
Published: April 2006

The African elephant reproduces so efficiently in the wild that overpopulation is now a serious problem in some game parks in Zimbabwe, Botswana and South Africa. The female reaches puberty between 10 and 12 years of age in the wild and, when in captivity, shows oestrous cycles of 14–15 weeks duration. She readily conceives a singleton in the wild yet her uterus has the capacity for twins. She shows a gestation length of 22 months and, in the wild, shows a population density and feed dependent intercalving interval of 4–8 years. The trophoblast erodes the lumenal epithelium of the endometrium and stimulates upgrowths of blood vessel-containing stromal villi, which develop eventually into the broad, tightly folded lamellae of the zonary, endotheliochorial placenta. Significant quantities of leaked maternal erythrocytes and ferric iron are phagocytosed by specialized trophoblast cells in the haemophagous zones at the lateral edges of the placental band. Although the placenta itself is endocrinologically inert, the foetal gonads, which enlarge greatly during the second half of pregnancy can synthesize 5α-dihydryoprogesterone and other 5α pregnane derivatives from cholesterol and pregnenolone. These products may synergize with progestagens secreted by the 2–8 large corpora lutea which are always present in the maternal ovaries throughout gestation to maintain the pregnancy state.
A KSR/CNK complex mediated by HYP, a novel SAM domain-containing protein, regulates RAS-dependent RAF activation in Drosophila
Authors: Douziech Mélanie , Sahmi Malha , Laberge Gino , Therrien Marc
Published: April 2006

RAF is a critical effector of the small GTPase RAS in normal and malignant cells. Despite intense scrutiny, the mechanism regulating RAF activation remains partially understood. Here, we show that the scaffold KSR (kinase suppressor of RAS), a RAF homolog known to assemble RAF/MEK/ERK complexes, induces RAF activation in Drosophila by a mechanism mediated by its kinase-like domain, but which is independent of its scaffolding property or putative kinase activity. Interestingly, we found that KSR is recruited to RAF prior to signal activation by the RAF-binding protein CNK (connector enhancer of KSR) in association with a novel SAM (sterile α motif) domain-containing protein, named Hyphen (HYP). Moreover, our data suggest that the interaction of KSR to CNK/HYP stimulates the RAS-dependent RAF-activating property of KSR. Together, these findings identify a novel protein complex that controls RAF activation and suggest that KSR does not only act as a scaffold for the MAPK (mitogen-activated protein kinase) module, but may also function as a RAF activator. By analogy to catalytically impaired, but conformationally active B-RAF oncogenic mutants, we discuss the possibility that KSR represents a natural allosteric inducer of RAF catalytic function.
The novel SAM domain protein Aveugle is required for Raf activation in the Drosophila EGF receptor signaling pathway
Authors: Roignant Jean-Yves , Hamel Sophie , Janody Florence , Treisman Jessica E.
Published: April 2006

Activation of the Raf kinase by GTP-bound Ras is a poorly understood step in receptor tyrosine kinase signaling pathways. One such pathway, the epidermal growth factor receptor (EGFR) pathway, is critical for cell differentiation, survival, and cell cycle regulation in many systems, including the Drosophila eye. We have identified a mutation in a novel gene, aveugle, based on its requirement for normal photoreceptor differentiation. The phenotypes of aveugle mutant cells in the eye and wing imaginal discs resemble those caused by reduction of EGFR pathway function. We show that aveugle is required between ras and raf for EGFR signaling in the eye and for mitogen-activated protein kinase phosphorylation in cell culture. aveugle encodes a small protein with a sterile α motif (SAM) domain that can physically interact with the scaffold protein connector enhancer of Ksr (Cnk). We propose that Aveugle acts together with Cnk to promote Raf activation, perhaps by recruiting an activating kinase.
Histone sumoylation is a negative regulator in Saccharomyces cerevisiae and shows dynamic interplay with positive-acting histone modifications
Authors: Nathan Dafna , Ingvarsdottir Kristin , Sterner David E. , Bylebyl Gwendolyn R. , Dokmanovic Milos , Dorsey Jean A. , Whelan Kelly A. , Krsmanovic Mihajlo , Lane William S. , Meluh Pamela B. , Johnson Erica S. , Berger Shelley L.
Published: April 2006

Covalent histone post-translational modifications such as acetylation, methylation, phosphorylation, and ubiquitylation play pivotal roles in regulating many cellular processes, including transcription, response to DNA damage, and epigenetic control. Although positive-acting post-translational modifications have been studied in Saccharomyces cerevisiae, histone modifications that are associated with transcriptional repression have not been shown to occur in this yeast. Here, we provide evidence that histone sumoylation negatively regulates transcription in S. cerevisiae. We show that all four core histones are sumoylated and identify specific sites of sumoylation in histones H2A, H2B, and H4. We demonstrate that histone sumoylation sites are involved directly in transcriptional repression. Further, while histone sumoylation occurs at all loci tested throughout the genome, slightly higher levels occur proximal to telomeres. We observe a dynamic interplay between histone sumoylation and either acetylation or ubiquitylation, where sumoylation serves as a potential block to these activating modifications. These results indicate that sumoylation is the first negative histone modification to be identified in S. cerevisiae and further suggest that sumoylation may serve as a general dynamic mark to oppose transcription.
Phosphorylation of NtMAP65-1 by a MAP kinase down-regulates its activity of microtubule bundling and stimulates progression of cytokinesis of tobacco cells
Authors: Sasabe Michiko , Soyano Takashi , Takahashi Yuji , Sonobe Seiji , Igarashi Hisako , Itoh Tomohiko J. , Hidaka Mikiko , Machida Yasunori
Published: April 2006

The tobacco mitogen-activated protein kinase (MAPK) cascade, which includes MAPK NRK1/NTF6, positively regulates expansion of the cytokinetic machinery known as the phragmoplast, which is followed by the synthesis of cell plates for completion of cell division. However, molecular events lying between the MAPK and phragmoplast expansion were not known. Here, we show that NRK1/NTF6 phosphorylates the threonine residue at position 579 in NtMAP65-1a, a microtubule-associated (MT-associated) protein. Levels of phosphorylated NtMAP65-1 increase during late M phase of the cell cycle, when NRK1/NTF6 is activated. Phosphorylated NtMAP65-1 is concentrated at the equator of phragmoplast, as is NRK1/NTF6. Overexpression of mutant forms of NtMAP65-1a that cannot be phosphorylated by NRK1 delays progression of the M phase and phragmoplast expansion, also rendering phragmoplast structures resistant to an MT-depolymerizing drug. Phosphorylation of NtMAP65-1 by NRK1/NTF6 down-regulates its MT-bundling activity in vitro. These results suggest that phosphorylation of NtMAP65-1 by NRK1/NTF6 also reduces its MT-bundling activity in vivo, which enhances destabilization and turnover of MTs at the phragmoplast equator, perhaps facilitating phragmoplast expansion.
The transcription factor FLC confers a flowering response to vernalization by repressing meristem competence and systemic signaling inArabidopsis
Authors: Searle Iain , He Yuehui , Turck Franziska , Vincent Coral , Fornara Fabio , Kröber Sandra , Amasino Richard A. , Coupland George
Published: April 2006

Floral development at theArabidopsisshoot apical meristem occurs in response to environmental cues that are perceived in different tissues. Photoperiod is detected in the vascular tissue of the leaf (phloem) and promotes production of a systemic signal that induces flowering at the meristem. Vernalization, the response to winter temperatures, overcomes a block on photoperiodic floral induction. InArabidopsis, this block is caused by inhibitors of flowering that comprise several related MADS-box transcription factors, the most prominent of which is FLC. We show that FLC delays flowering by repressing production in the leaf of at least two systemic signals, one of which is controlled by the RAF kinase inhibitor-like protein FT. Reducing expression of these signals indirectly represses expression of genes involved in floral induction at the meristem. In addition,FLCexpression in the meristem impairs response to the FT signal by directly repressing expression of the SOC1 MADS-box transcription factor and preventing up-regulation of the bZIP transcription factor FD. Repression of genes acting at multiple levels in this hierarchy is required for the extreme delay in flowering caused by FLC. An FLC:HA fusion protein binds directly in vivo to the promoter regions ofFDandSOC1and to the first intron ofFT. Thus vernalization relieves transcriptional repression of key regulatory genes in both the leaf and meristem, allowing production of systemic signals in the leaves and conferring competence on the meristem to respond to these signals.
Solution structure of the antifreeze‐like domain of human sialic acid synthase
Authors: Hamada Toshiyuki , Ito Yoko , Abe Takamasa , Hayashi Fumiaki , Güntert Peter , Inoue Makoto , Kigawa Takanori , Terada Takaho , Shirouzu Mikako , Yoshida Mayumi , Tanaka Akiko , Sugano Sumio , Yokoyama Shigeyuki , Hirota Hiroshi
Published: April 2006

The structure of the C‐terminal antifreeze‐like (AFL) domain of human sialic acid synthase was determined by NMR spectroscopy. The structure comprises one α‐ and two single‐turn 310‐helices and two β‐strands, and is similar to those of the type III antifreeze proteins. Evolutionary trace analyses of the type III antifreeze protein family suggested that the class‐specific residues in the human and bacterial AFL domains are important for their substrate binding, while the class‐specific residues of the fish antifreeze proteins are gathered on the ice‐binding surface.